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Jerry Hubbell
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Reged: 02/16/09

Loc: Locust Grove, VA, USA
Telescope Drive Master - The Truth of the Matter
      #4885225 - 10/28/11 12:55 PM

For those of you doubting the capabilities of a lower end mount (EQ6 Pro) coupled with the TDM, please take a look at my full size image of NEO Minor Planet 2001 LO7 taken on 02 July 2011.

http://www.pbase.com/jerry_hubbell/image/136454649/original

You can see a closup negative of 2001 LO7 here

http://www.pbase.com/jerry_hubbell/image/136454702

These images are 10 x 180 sec unguided images with my ES 127 APO ED Carbon Fiber on my EQ6 Pro with the TDM active.

Based on my experience, and what I have seen posted from higher end mounts, I would find it interesting for anyone to say that my results do not match or even exceed the performance of higher end mounts unguided. I understand that there are those that would like to see everyone upgrade their cheap astrophotography mounts to the higher end $5000-$10000 mounts, but that isn't going to happen 9 times out of 10. So what is the alternative? I think I have found it with the TDM. I have attached below my response to a previous thread, because since it is at the bottom of a long thread nobody would probably bother reading it there.

Here is a link to a paper I wrote about my experience with the TDM

http://www.mda-telescoop.com/images/stories/downloads/tdm_control_investigation.pdf


I hope this helps the conversation.

Jerry Hubbell
Lake of the Woods Observatory

Hello Tassilo, members,

I just now ran across this thread. I have read through these comments with a lot of interest, and indeed there is a lot of misunderstanding about how the TDM works, and how it is useful to the average amateur with the good but inexpensive mount i.e., EQ6 Pro, Orion Atlas, etc. I was fortunate enough to work with Dennis DiCicco on his review of the TDM (he mentioned me in the article) and I have also been working with Attila Madai, and Istvan Papp of MDA-Telescoop to get my TDM working as best I can. I have also been working with Attila to improve the TDM. From my point of view, the TDM works exactly as advertised. I have had nothing but positive results using the TDM in my observing program. You can see the initial results of my testing and intitial observations here:

http://www.mda-telescoop.com/images/stories/downloads/tdm_control_investigation.pdf

You have to realize that, for me, the biggest goal I have for my observing program is the amount of time I spend imaging. I have (as we all do) weather issues, available time to observe, etc. I want to maximize my time and efficiency while imaging.

I found that over the past 2 years, although I have mastered using my guide camera and PHD for guiding, it still took time away from my imaging to manage it. Also, since I have a portable system, not a permanent observatory, the time spent setting up and taking down the equipment can be significant (2 hours total). So anything I could do to minimize the time and effort, yet still get high quality images, was going to be worth the expenditure. Also, the only other alternative to the TDM is to purchase a mount in the $5000 to $8000 range. This was not going to happen.

The total cost of the TDM with the Orion Atlas, or Sky-Watcher NEQ6 Pro mount is about $3500. I dare anyone to find a mount and drive corrector system that matches the performance for the price. I have found that the only real reason to purchase a more expensive mount is for the load capacity. The EQ6 provides a very capable load capacity of 40 lbs., 30 lbs. for astrophotography purposes.

Another thing to think about is, how practical is 20 minute subs to those who live with marginal to good sky brightness. I have found that although I can manage 10 minute exposures, for most of the time, the sky starts to fog the image. I would prefer to stick to 3-5 minute subs for deep sky work.

My main work is in Minor Planet astrometry and photometry, so being able to setup my single scope with the TDM EQ6 combo with only my main camera to manage, really goes a long way towards simplifying my setup, and making the most of my imaging time. In this configuration I am very happy with 1-3 minute subs.

The only other complaint about having perfect tracking but still having to use a guide camera, is the fact that polar alignment takes a long time with the standard drift method. This has always been the fallback argument against the TDM. I have found that, just like anything else in astrophotography, you have to work a little to get results. To make things easier, I have found that Alignmaster ( http://www.alignmaster.de/ ) is probably the fastest, most consistent way to get an excellent polar alignment in the least amount of time.

So bottom line, I have a system that with the help of TDM and Alignmaster allows me to set it up in 30-40 minutes, start my imaging within 10 minutes of completing my calibration frames and polar alignment, and for the remainder of the session, worry free tracking and imaging. After proper syncing, I find I can select my objects with ease with every one falling in the field of view of the camera.

That to me is the bottom line. I have done this with the most cost effective equipment I have found available thus far.

I hope that helps those understand my reasons for purchasing the TDM.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA

Edited by Jerry Hubbell (10/29/11 07:18 PM)


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Gord
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Re: Telescope Drive Master new [Re: Jerry Hubbell]
      #4885251 - 10/28/11 01:09 PM

Hi Jerry,

Excellent images and details! Thanks for posting this. I have an interest in doing similar work to what you are doing and can see the benefit to the simplified setup (on less thing to do or worry about). Especially in the case of visiting many objects on a single night.

I'm not experienced in this type of imaging, but I would expect there to be some time fiddling with getting the guiding setup with every new target. Nice to be able to just center and go.

BTW, your first image link isn't coming up for me, but the second one is. How faint is that NEO?

Clear skies,


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CounterWeight
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Re: Telescope Drive Master new [Re: Jerry Hubbell]
      #4885278 - 10/28/11 01:20 PM

Jerry,
That is a great and very informative write up (the linked one) and a great post. I think the images speak volumes. Thanks very much for putting this more in the spotlight. I am a huge fan of real world examples with some amplifying text. Great job and thank you for posting in on this.


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Jerry Hubbell
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Reged: 02/16/09

Loc: Locust Grove, VA, USA
Re: Telescope Drive Master new [Re: CounterWeight]
      #4885329 - 10/28/11 01:47 PM

Hey Gord, CounterWeight (that can't be your real name LOL) I appreciate the comments. The original size image is very large of 2001 LO7, so that may be causing you some issues Gord. 2001 LO7 at the time of imaging was at magnitude 15.1 the faintest stars you can see in that image are around magnitude 19. This is a V-band image.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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Alph
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Re: Telescope Drive Master new [Re: Jerry Hubbell]
      #4885499 - 10/28/11 03:03 PM

Quote:

Hey Gord, CounterWeight (that can't be your real name LOL)



I think he is looking for a counter weight shaft. Oops!

Thanks for the feedback. I do have a problem with the price though, $2200 with a mount adapter.


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Jerry Hubbell
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Loc: Locust Grove, VA, USA
Re: Telescope Drive Master new [Re: Alph]
      #4885519 - 10/28/11 03:15 PM

Hey Alph, I understand the issue people have with the price, but you have to put it in context with what the alternative is, and what the results will be. For my observing program, I think spending a total of around $3500 for the EQ6 Pro/ Atlas plus the TDM is not out of line at all based on the resulting performance.

The alternative would be to spend anywhere from $5000 or more to get the same unguided performance.

If you read my post, and the linked paper, you will understand that my main goal was to obtain high quality images with the minimum amount of setup and fuss. That eats into the available imaging time, which to me is worth quite a bit of money.

Having said all that, I fully understand your position. It all depends on your goals with your imaging program.

I appreciate your comments

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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Alph
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Re: Telescope Drive Master new [Re: Jerry Hubbell]
      #4885559 - 10/28/11 03:38 PM

Quote:

my main goal was to obtain high quality images with the minimum amount of setup and fuss.



I tried to use PemPro for polar alignment. It just takes too long.


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Jerry Hubbell
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Re: Telescope Drive Master new [Re: Alph]
      #4885607 - 10/28/11 03:57 PM

Yes Alph, I found the polar alignment was the biggest issue with being able to minimize the amount of setup time and equipment. There is no doubt about it, using a guide scope and camera can minimize the time you spend setting up the mount. All you have to do is make sure it is pointing somewhat close to North and then rely on your guiding to make up for that and your inexpensive mount's PE. It is very attractive. Having said that, you still have to deal with the continuous maintenance of the guide scope during your imaging session.

What I found though after trying to increase the quality of my images, was that if you start with a weak foundation (poor polar alignment, poor tracking/PE) then no matter how good your guiding, you still had to deal with pointing accuracty, field rotation, etc. plus you can only get up to a certain quality in your imaging.

If you are really after the highest quality images, you need to start with solid performance in polar alignment, an d tracking. This enables very accurate pointing which minimizes your tiime going from one target to the next (which is what I need). Once you sync your mount control software, with a very well aligned mount, then you are good to go all night long. I find this preferable than having to recalibrating my guider and having to resync my mount for every target I want to image. This goes a long way towards minimizing the frustration level, and allows you to concentrate on the other issues with the very highest quality imaging, i.e. focusing and pointing accuracy to place your object in the center of the field. This is very important when imaging a moving object such as minor planets.

To answer your question directly, I have found that AlignMaster (http://www.alignmaster.de/) has been the best method I have found to do a quick polar alignment. I believe that this uses a similar method that Celestron has built into their hand controller. I believe I have read that somewhere.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA

Edited by Jerry Hubbell (10/28/11 03:59 PM)


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Ray Gralak
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4885734 - 10/28/11 04:50 PM

Hi Jerry,

Quote:



These images are 10 x 180 sec unguided images with my ES 127 APO ED Carbon Fiber on my EQ6 Pro with the TDM active.

Based on my experience, and what I have seen posted from higher end mounts, I would find it interesting for anyone to say that my results do not match or even exceed the performance of higher end mounts unguided.
I hope this helps the conversation.

Jerry Hubbell





Here is an image created from six images in a row, 30 minutes each (that's 1800 seconds each, 10x as long as your images), unguided, similar image scale, AP1200GTO, UltraTrack Software:

http://www.gralak.com/Astro/NGC7380-UltraTrack-6x30m-AP105-ST10XE.jpg

There are lots of other long exposure unguided images out there, some at long focal lengths. 180 second unguided images in my opinion is not even close to the level that a high end mount can obtain.

-Ray Gralak


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Jerry Hubbell
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Loc: Locust Grove, VA, USA
Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4885767 - 10/28/11 05:15 PM

Hey Ray, thanks for the image, that is impressive. I would expect nothing less from a $10,000 mount that is probably mounted permanently with a very accurate polar alignment and located at a good dark sky site.

I have done subs up to 10 minutes but my sky is too bright to handle that amount of time, In order to get there I made sure my polar alignment was spot on. The stars in those images were basically the same as in the image I posted a link to previously. I believe I could accomplish similar results if I were at a pretty dark site that did not fog up the image. I hope to be able to image sometime at such a site. This would be a good challenge that I am willing to tackle. If I am not mistaken, the AP105 has a focal length of 610mm versus my scope with a 950mm focal length. The camera differences do make the field of view very similar.

I don't believe this should be a competition between a high end mount and a cheaper mount. For me it seems the primary need for higher priced mounts comes down to load capacity while maintaining accurate tracking. It should be easier to maintain accurate tracking with lower capacity mounts than with higher capacity mounts.

With that said, I think that for those folks that cannot afford the higher end mounts just to get the unguided tracking capability necessary to maximize their imaging time at the scope, the TDM is a cost effective solution.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA

Edited by Jerry Hubbell (10/28/11 05:45 PM)


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Ray Gralak
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4885813 - 10/28/11 05:47 PM

Hi Jerry,
Quote:

Hey Ray, thanks for the image, that is impressive. I would expect nothing less from a $10,000 mount that is probably mounted permanently with a very accurate polar alignment and located at a good dark sky site.

I believe I could accomplish similar results if I were at a pretty dark site that did not fog up the image. I hope to be able to image sometime at such a site. This would be a good challenge that I am willing to tackle. If I am not mistaken, the AP105 has a focal length of 610mm versus my scope with a 950mm focal length. The camera differences do make the field of view very similar.

I don't believe this should be a competition between a high end mount and a cheaper mount. For me it seems the primary need for higher priced mounts comes down to load capacity while maintaining accurate tracking. It should be easier to maintain accurate tracking with lower capacity mounts than with higher capacity mounts.

With that said, I think that for those folks that cannot afford the higher end mounts just to get the unguided tracking capability necessary to maximize their imaging time at the scope, the TDM is a cost effective solution.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA



Actually, I would be very surprised if you could do the kind of exposure lengths without software tracking rate correction for refraction, polar alignment errors, flexure, etc. The *real* truth is having a perfect tracking rate is not good enough in most areas of the sky for long duration unguided exposures because the *required* tracking rate to follow an object will vary as the scope tracks across the sky.

The AP1200/AP105 was setup in my back yard on a pier and not particularly well aligned. I had to use an HAlpha filter to prevent sky glow from overwhelming the image.

Here's another couple 5-minute images at a longer focal length that show what software tracking rate correction can do. These images are of M33's core at 0.55 arc-sec/pixel, which was obtained with my old ST10XE CCD camera at 2449mm focal length (AP155 refractor with a barlow). As you can tell the scope is not perfectly polar aligned yet PEC+tracking rate correction fixes this.

Without tracking rate correction (PE, flexure, alignment errors show):
http://www.gralak.com/Astro/UnguidedTests/AP155-2449mm-5min-NoUT.jpg

With tracking rate correction:
http://www.gralak.com/Astro/UnguidedTests/AP155-2449mm-5min-UT.jpg

Is there any tracking rate correction software for the TDM?

-Ray Gralak


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Jerry Hubbell
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Reged: 02/16/09

Loc: Locust Grove, VA, USA
Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4885827 - 10/28/11 05:56 PM

Hi Ray,

Thanks again for the images. I am not sure what you mean by Software Tracking Rate Correction. The TDM is designed to correct the RA rate either to absolute Sidereal Rate, or to the King Rate that is optimized to a median altitude of around 45 degrees. This is what I use. This will correct for atmospheric refraction around those altitudes. I ensure my scope and mount are very tightly bound to minimize any flexure, I seem to have managed that okay. The only real error that is introduced that is left is polar alignment which of course you know causes field rotation and declination drift. I have used the standard drift alignment method over the past couple of years. That takes too long for me so I have started using AlignMaster to minimize the time I use to polar align. Once I have done these things, and done a good 2 star sync with EQMOD, then I have a very accurate and stable platform for imaging.

I am curious to learn how this software tracking rate correction works.

Thanks

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4885862 - 10/28/11 06:19 PM

Hi Jerry,
Quote:

Hi Ray,

Thanks again for the images. I am not sure what you mean by Software Tracking Rate Correction. The TDM is designed to correct the RA rate either to absolute Sidereal Rate, or to the King Rate that is optimized to a median altitude of around 45 degrees. This is what I use. This will correct for atmospheric refraction around those altitudes. I ensure my scope and mount are very tightly bound to minimize any flexure, I seem to have managed that okay. The only real error that is introduced that is left is polar alignment which of course you know causes field rotation and declination drift. I have used the standard drift alignment method over the past couple of years. That takes too long for me so I have started using AlignMaster to minimize the time I use to polar align. Once I have done these things, and done a good 2 star sync with EQMOD, then I have a very accurate and stable platform for imaging.

I am curious to learn how this software tracking rate correction works.

Thanks

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA



In addition to polar alignment errors and refraction (which varies by temperature and pressure), there are other errors from flexure that cause effective tracking rate errors (and pointing errors as well). If you are using alignment software that counts on centering stars it probably does not account for flexure which can be significant. If your mount has significant uncorrected periodic error that will also lead to positioning errors when centering stars, thus limiting polar alignment accuracy again.

BTW, flexure comes not only from the OTA but from the mount, tripod/pier, and camera/OTA connections. No matter how solid you think your setup is flexure exists at some level (unless you are in space where there is no gravity!).

Tracking rate correction software measures errors in the pertinent parts of the sky and then continuously adjusts the scope's RA and Dec tracking rates to match the apparent rate the sky is moving through the telescope. It requires that the mount be capable of setting RA and Dec tracking rates to a high level of precision. The result is near perfect unguided tracking despite alignment errors, refraction, flexure, etc.

-Ray

Edited by Ray Gralak (10/28/11 06:20 PM)


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Jerry Hubbell
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Reged: 02/16/09

Loc: Locust Grove, VA, USA
Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4885875 - 10/28/11 06:29 PM

Here is an image I took on the second night of testing. This image was taken with my AT8RC and QHY9m.

http://www.pbase.com/jerry_hubbell/image/139217447/original

This is a 600 second image (see fits header below)with the TDM tracking enabled. Unfortunately, I took it with the cooler turned off, just prior to that image, I had restarted MaximDL and neglected to make sure the cooling was set at -20c which is my nominal setpoint during the summer. You can imagine my surprise when I saw all the "snow" in the image, and realized what the problem was. Well after that fiasco, I decided to go on to some real imaging with smaller exposure times.

Anyway, if you look at the image, you can still see how the stars are nice and round, although my focus was a little off.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA

SIMPLE = T
BITPIX = 32 /8 unsigned int, 16 & 32 int, -32 & -64 real
NAXIS = 2 /number of axes
NAXIS1 = 1674 /fastest changing axis
NAXIS2 = 1248 /next to fastest changing axis
BSCALE = 1.0000000000000000 /physical = BZERO + BSCALE*array_value
BZERO = 2147483648.0000000 /physical = BZERO + BSCALE*array_value
DATE-OBS= '2011-06-28T04:43:08' /YYYY-MM-DDThh:mm:ss observation start, UT
EXPTIME = 600.00000000000000 /Exposure time in seconds
EXPOSURE= 600.00000000000000 /Exposure time in seconds
CCD-TEMP= 24.724226079875109 /CCD temperature at start of exposure in C
XPIXSZ = 10.800000000000001 /Pixel Width in microns (after binning)
YPIXSZ = 10.800000000000001 /Pixel Height in microns (after binning)
XBINNING= 2 /Binning factor in width
YBINNING= 2 /Binning factor in height
XORGSUBF= 0 /Subframe X position in binned pixels
YORGSUBF= 0 /Subframe Y position in binned pixels
FILTER = 'None ' / Filter used when taking image
IMAGETYP= 'Light Frame' / Type of image
FOCUSPOS= 1362 /Focuser position in steps
FOCUSTEM= 30.000000000000000 /Focuser temperature in deg C
OBJCTRA = '18 30 20' / Nominal Right Ascension of center of image
OBJCTDEC= '+26 11 34' / Nominal Declination of center of image
OBJCTALT= ' 81.2165' / Nominal altitude of center of image
OBJCTAZ = '142.5231' / Nominal azimuth of center of image
OBJCTHA = ' -0.4157' / Nominal hour angle of center of image
PIERSIDE= 'WEST ' / Side of pier telescope is on
SITELAT = '38 20 35' / Latitude of the imaging location
SITELONG= '-77 46 10' / Longitude of the imaging location
JD = 2455740.6966203703 /Julian Date at start of exposure
JD-HELIO= 2455740.7035019537 /Heliocentric Julian Date at exposure midpoint
AIRMASS = 1.0157437575451260 /Relative optical path length through atmosphere
FOCALLEN= 1610.0000000000000 /Focal length of telescope in mm
APTDIA = 203.50000000000000 /Aperture diameter of telescope in mm
APTAREA = 27321.089037689566 /Aperture area of telescope in mm^2
EGAIN = 1.0000000000000000 /Electronic gain in e-/ADU
SWCREATE= 'MaxIm DL Version 5.15' /Name of software that created the image
SBSTDVER= 'SBFITSEXT Version 1.0' /Version of SBFITSEXT standard in effect
OBJECT = ' '
TELESCOP= ' ' / telescope used to acquire this image
INSTRUME= 'ASCOM QHY9 Driver'
OBSERVER= 'Gerald R Hubbell'
NOTES = ' '
FLIPSTAT= ' '
CBLACK = 21087 /Initial display black level in ADUs
CWHITE = 17875 /Initial display white level in ADUs
PEDESTAL= -100 /Correction to add for zero-based ADU
SWOWNER = 'Gerald R Hubbell' / Licensed owner of software
INPUTFMT= 'FITS ' / Format of file from which image was read
SWMODIFY= 'MaxIm DL Version 5.15' /Name of software that modified the image
HISTORY Flat Field (Flat None 2, None, 1674 x 1248, Bin2 x 2, Temp -20C,
HISTORY Exp Time 2s)
CALSTAT = 'F '
END
----------------------
History added since image was opened...
Original image: E:\Astrophotos\27June2011\600sec_TDM_test.fit
Flat Field (Flat None 2, None, 1674 x 1248, Bin2 x 2, Temp -20C,
Exp Time 2s)

Edited by Jerry Hubbell (10/28/11 06:38 PM)


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Ray Gralak
Vendor (PEMPro)


Reged: 04/19/08

Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4885887 - 10/28/11 06:40 PM

Hi Jerry,

Quote:

Here is an image I took on the second night of testing. This image was taken with my AT8RC and QHY9m.

http://www.pbase.com/jerry_hubbell/image/139217447/original

This is a 600 second image (see fits header below)with the TDM tracking enabled.

SIMPLE = T
BITPIX = 32 /8 unsigned int, 16 & 32 int, -32 & -64 real
NAXIS = 2 /number of axes
NAXIS1 = 1674 /fastest changing axis
NAXIS2 = 1248 /next to fastest changing axis





Is that image binned 2? It looks like it could be from the NAXIS1 and NAXIS2 values (assuming the CCD is a Kodak 8300??).

-Ray


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Jerry Hubbell
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Reged: 02/16/09

Loc: Locust Grove, VA, USA
Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4885900 - 10/28/11 06:48 PM

Yes, Binned 2x The nominal pixel scale for my camera with the AT8RC of 1610mm FL is about 0.69 arcsec. So with a bin 2x it would be 1.38 arcsec. The QHY9m has a Kodak 8300 chip with a nominal size of 3348 x 2496 pixels.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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tomo
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886090 - 10/28/11 09:18 PM

Hi Jerry,

How good does your polar alignment get with Alignmaster? Does it quantify the error?

Cheers,

Tommy


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gdd
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886098 - 10/28/11 09:30 PM

Will the modest mount still be limited in what it can achieve compared to a very precise and rigid mount if you are willing to combine technologies: PEC + TDM + autoguiding + adaptive optics? Is it easy to add TDM to the mix and still get an incremental improvement?

Gale


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: gdd]
      #4886146 - 10/28/11 10:01 PM

Hey Tommy, Gale,

The AlignMaster Program does give you the pointing error from the North Pole in degrees, minutes, and seconds. In this way you can iterate on the adjustment to get as close as you like. I have only used it in the field a couple of times, and have been generally satisfied when I get to withn a few arc minutes of the pole. You can spend a lot of time with it to get within 30 arcseconds, but that is generally not necessary for the exposure times I am using.

To answer your question Gale, you can generally layer on correction systems, but you have to understand how they work to understand what the interactions might be. It is good to understand the time constants or frequencies each technology is designed to correct errors in. For example, The TDM is correcting errors in the range of 0.2 to 1 second time interval, the PEC is only designed to correct long term worm error in the 480 second range. When you incorporate autoguiding into the picture, I would set it to correct for errors (mainly DEC drift due to innaccurate polar alignment) in the 10-60 second range. Finally, Adaptive optics will correct for errors in the <0.2 second range down to how fast you can get your camera to make exposures.

Based on these requirements, I would consider TDM a replacement for PEC, and use a guide camera only for correcting DEC drift set to 10 second exposures. Adaptive optics would correct for seeing, and scintillation at a frequency of from 5-20 hz.

I hope this answers your questions

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA

Edited by Jerry Hubbell (10/28/11 10:11 PM)


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Ray Gralak
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886272 - 10/28/11 11:50 PM

Quote:

Yes, Binned 2x The nominal pixel scale for my camera with the AT8RC of 1610mm FL is about 0.69 arcsec. So with a bin 2x it would be 1.38 arcsec. The QHY9m has a Kodak 8300 chip with a nominal size of 3348 x 2496 pixels.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA



OK, my 30-min AP105 unbinned is about 2.0 arc-sec/pixel, and my 5-min AP155 barlowed is about 0.55 arc-sec/pixel. I think that in both cases the software corrected tracking has better (rounder) stars when you account for image duration and image scale. Would you not agree?

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886275 - 10/28/11 11:52 PM

Hi Jerry,

A couple additions to this...
Quote:


To answer your question Gale, you can generally layer on correction systems, but you have to understand how they work to understand what the interactions might be. It is good to understand the time constants or frequencies each technology is designed to correct errors in. For example, The TDM is correcting errors in the range of 0.2 to 1 second time interval, the PEC is only designed to correct long term worm error in the 480 second range. When you incorporate autoguiding into the picture, I would set it to correct for errors (mainly DEC drift due to innaccurate polar alignment) in the 10-60 second range. Finally, Adaptive optics will correct for errors in the <0.2 second range down to how fast you can get your camera to make exposures.




By the Nyquist theorem you can only correct to 1/2 the frequency. So if sampling is occurring at 5 Hz, the maximum frequency that can be corrected is 2.5Hz.

Also, some PEC systems have corrections that occur 3-5 times a second, so they are capable of correcting frequencies in the same frequency range. But despite what PEC is capable of correcting you are correct that the purpose is to correct the slower worm error and possibly gear errors.

-Ray


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gdd
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4886304 - 10/29/11 12:26 AM

Quote:

To answer your question Gale, you can generally layer on correction systems, but you have to understand how they work to understand what the interactions might be. It is good to understand the time constants or frequencies each technology is designed to correct errors in. For example, The TDM is correcting errors in the range of 0.2 to 1 second time interval, the PEC is only designed to correct long term worm error in the 480 second range.





PEC is the only one of the correction methods able to predict an error and begin the correction in time to prevent it. As Ray points out it can correct errors much shorter than the 480 second range, for example gear box errors that are harmonic with the worm period. The problem is most modest mounts have non-harmonic errors. So PEC can take the already small error of a precision mount and reduce it by a larger percentage than the less precise mount.

The TDM corrects at a much higher frequency, so maybe the lack of a predicting capability does not matter. Perhaps the biggest advantage of the encoder technology is that it will improve over time and become cheaper because it can be adapted to many other products in addition to astronmical tracking mounts.

So given the interactions with the mount, if TDM is installed on both a precision mount and lower tier mount of the same weight class, will both track equally well unguided? Will both guide equally well? I would think the precision mount would have an edge - but how much I don't know.

Gale

Edited by gdd (10/29/11 12:37 AM)


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4886312 - 10/29/11 12:31 AM

Quote:


OK, my 30-min AP105 unbinned is about 2.0 arc-sec/pixel, and my 5-min AP155 barlowed is about 0.55 arc-sec/pixel. I think that in both cases the software corrected tracking has better (rounder) stars when you account for image duration and image scale. Would you not agree?

-Ray




Hi Ray,
I have not measured the FWHM and elongation of the stars in my 600 sec image, or in your images, so it is hard for me to agree that your stars would be rounder without looking closer at the images, although you may be correct. Also, based on your description of the software tracking correction you are either modeling the correction for flexure and refraction based on previously acquired imaging, or it is being done in real time. Either way it sounds an awfully lot alike to using a guide camera to adjust the pointing of the scope to stay locked on the stars. The point of the TDM (for me) is to not have to rely on feedback from the stars in order to minimize the amount of extra equipment used to make excellent images. What is your software tracking correction using as a reference to correct to?

Thanks

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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orlyandico
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886325 - 10/29/11 12:41 AM

as an aside.. the notion of using a high-precision encoder on the RA axis for corrections is not unique to the TDM (it is a $5000 option on the El Capitan).

so.. i tried looking for such encoders, the idea being "hmm.. maybe i can roll my own." only Gurley and Renishaw seem to make encoders of the required precision (>1 million pulses per revolution). maybe Johannes Heidenhain does as well but all their docs are in German.

the usual encoder makers (BEI, US Robotics, HP, Allen-Bradley..) don't make million-count encoders, they top out at around 200K PPR. and, the million-count encoders cost at least $500 (used).

so I don't really see how the TDM price can go much lower. Maybe (just maybe) it can hit $1000, but ultra-high count metrology encoders aren't exactly a mass-market item, they've been around for decades, and the astronomy market isn't really a mass market.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886330 - 10/29/11 12:50 AM

Hi Jerry,

Quote:

Quote:


OK, my 30-min AP105 unbinned is about 2.0 arc-sec/pixel, and my 5-min AP155 barlowed is about 0.55 arc-sec/pixel. I think that in both cases the software corrected tracking has better (rounder) stars when you account for image duration and image scale. Would you not agree?

-Ray




Hi Ray,
I have not measured the FWHM and elongation of the stars in my 600 sec image, or in your images, so it is hard for me to agree that your stars would be rounder without looking closer at the images, although you may be correct. Also, based on your description of the software tracking correction you are either modeling the correction for flexure and refraction based on previously acquired imaging, or it is being done in real time. Either way it sounds an awfully lot alike to using a guide camera to adjust the pointing of the scope to stay locked on the stars. The point of the TDM (for me) is to not have to rely on feedback from the stars in order to minimize the amount of extra equipment used to make excellent images. What is your software tracking correction using as a reference to correct to?

Thanks

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA



The reference is plate-solved images precessed to JNow coordinates. The rate corrections are made by offseting the tracking rate in RA and Dec slightly from sidereal... enough to compensate for refraction, polar alignment errors, flexure, etc.

Although you could try FWHM it is probably not a good comparison because our sites are completely different and you said your image was a little out of focus.

Instead, please take a look at the stars in the AP155's 5-minute image at 0.55 arc-sec/pixel, which would be equivalent to a 10-minute image at 1.10 arc-sec/pixel. Then compare them to the stars in your 10-minute image (at 1.38 arc-sec/pixel). As I mentioned before I think I can see a slight bit of trailing in stars in your image (from upper left to lower right). It's slight, but it's there. I don't think there is any trace of trailing of stars in my AP155 image.

Now I realize that is just one image so if you have better images then my conclusion might be different.

-Ray


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gdd
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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4886341 - 10/29/11 01:03 AM

Quote:

so I don't really see how the TDM price can go much lower. Maybe (just maybe) it can hit $1000, but ultra-high count metrology encoders aren't exactly a mass-market item, they've been around for decades, and the astronomy market isn't really a mass market.





My thought was true the astronomy market is not a mass market, but there exist other markets which may be much larger. Also the encoders do not appear to require much modification other than a shaft adapter to re-purpose them from one industry to another. They must have come down in price over the decades or they would have been applied to telescope mounts years ago.

Gale


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orlyandico
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Re: Telescope Drive Master - The Truth of the Matter new [Re: gdd]
      #4886381 - 10/29/11 02:12 AM

they have been applied to telescope mounts for years.. just not at the $1500 level.

it's the same case with harmonic drives, they're used everywhere in industry (probably to a much greater extent than million-count encoders). but there aren't any mass-market mounts with harmonic drives.

the bottom-line is, the 200K PPR encoders are probably good enough for the vast majority of applications out there. Note that the 10K PPR encoders cost $20 - and are used everywhere.

somehow i don't see million-count encoders for $20... or even $200.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4886398 - 10/29/11 02:50 AM

Heres another point: most mass market scopes lose sync if you move the mount manually. The cgem and atlasas well as most of the vixens definitely fall in this group.

But what would it take to ensure that the mount never loses sync? A couple of lousy $20 encoders, one on each axis. I believe these encoders are options on the G11, and standard on the Taks. $20! And yet the mass market cant be bothered to add these.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4886483 - 10/29/11 06:26 AM

Quote:

But what would it take to ensure that the mount never loses sync? A couple of lousy $20 encoders, one on each axis. I believe these encoders are options on the G11, and standard on the Taks. $20! And yet the mass market cant be bothered to add these.




The inexpensive encoders on mounts are able to be high precision because they are in front of the gearbox and aren't directly reading the axis angle as the TDM encoders do. But this also means they can't "see" periodic error and gearbox errors. In order to have high precision to move the 'scope by hand, you would need much more expensive encoders on the axes - unless all you want is an approximate sky location.

I'm not sure how inexpensively these encoders can be made, but I do expect them to appear more - but maybe not for the low to mid-range mounts - at least for a while.

Frank


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886494 - 10/29/11 06:41 AM

Quote:

I have read through these comments with a lot of interest, and indeed there is a lot of misunderstanding about how the TDM works, and how it is useful to the average amateur with the good but inexpensive mount i.e., EQ6 Pro, Orion Atlas, etc.




Hi Jerry-

I think if you look at the comments I made in the other thread, you'll see that I agree with parts of your assessment, but not all. I think you have demonstrated unique performance at a low cost for the specific goal of short, unguided images for photometric and astrometric work - but I don't think you have demonstrated a cost-effective solution for long exposure deep sky imaging - either with or without autoguiding. As I said, I have yet to see an FWHM value for a long exposure image with this system - and that's the main thing I go by.

You allude to having tried to autoguide your mount, but I don't think you explored the full space of software and techniques for optimal results. In my view, if you use OAG and low latency guiding with video, and rapid corrections (a la MetaGuide, which I wrote, and which is free), you can achieve much better results than by more conventional methods. This involves no costly hardware add-ons. I work with cge and cge-pro mounts and achieve 2" fwhm and below from unexceptional skies in the northeast U.S., and I believe others have done well with more inexpensive mounts via EQMod and similar methodology.

You also allude to the lack of need for 10-20m exposures given typical light pollution - but that ignores narrow band work at f/5 to f/10 - which is growing in popularity. You need long exposures for that.

I think high-res encoders have the potential to smooth out RA errors due to gearbox and bearings - and that is a key limitation to obtaining good results with a non high-end mount. But you will still need to autoguide to make corrections in RA and Dec to achieve optimal fwhm in long exposures - and the end result may not be much different from tight autoguiding at high frequency and low latency with no special encoders involved.

So - I expect high-res encoders to make guiding easier and more casual with cheaper mounts, and they will smooth out errors at arbitrary frequencies that are unreachable by PEC at any update rate, but they will still require tight guiding with a good centroid to obtain optimal fwhm.

Frank


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4886573 - 10/29/11 08:18 AM

Quote:

Hi Jerry,

The reference is plate-solved images precessed to JNow coordinates. The rate corrections are made by offseting the tracking rate in RA and Dec slightly from sidereal... enough to compensate for refraction, polar alignment errors, flexure, etc.


Now I realize that is just one image so if you have better images then my conclusion might be different.

-Ray




Hi Ray,

So your system DOES use a guide camera to acquire images for correcting PE. The only difference between using PHD and your software guide correction is that yours uses multiple stars to calculate a plate center as opposed to using an individual star to adjust the drive rate.

Well, isn't this cheating a little on our discussion here? The premise I presented was that the EQ6 coupled with the TDM performed as well as an expensive mount WITHOUT GUIDING on STARS. That was the basis for comparison. Further my contention is that with an excellent polar alignment and the TDM the results are comparable to mounts in the $5000-$10000 range for the type of imaging I am doing, UNGUIDED. I don't believe we can have an honest conversation until we see the results under the same requirements.

Let me ask an interesting question, Don't take this wrong, I am honestly curious about why this is:

If Guiding is absolutely necessary, why don't the manufacturers make large mounts (load capacities in the 20-50Kg range) that have mediocre (30-40 arcsec p-p) PE. It seems they could make mounts cheaper if they didn't have to worry about trying to achieve unguided PE <5 arcsec p-p. I understand that everything needs to be beefier but I am sure a lot of time and effort is put in to make sure the PE is low on these mounts resulting in the higher cost and price for the buyer. If external guiding with a guidescope is necessary anyway, why not create a mount that has an equipment capacity of 50Kg and offer it for say $2500?

I think I know the answer, When customers pay >$5000 for a mount the expectation that not only the capacity increases, but that all the performance parameters improve including PE. That's reasonable.

But to expect the performance improvements when paying a large sum of money, and then come back and then say it doesn't matter that PE has improved on the expensive mounts, we have to use guide cameras anyway, is a bit disengenuous.

Jerry

Edited by Jerry Hubbell (10/29/11 08:51 AM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4886594 - 10/29/11 08:38 AM

Quote:

Quote:

I have read through these comments with a lot of interest, and indeed there is a lot of misunderstanding about how the TDM works, and how it is useful to the average amateur with the good but inexpensive mount i.e., EQ6 Pro, Orion Atlas, etc.




Hi Jerry-

I think if you look at the comments I made in the other thread, you'll see that I agree with parts of your assessment, but not all. I think you have demonstrated unique performance at a low cost for the specific goal of short, unguided images for photometric and astrometric work - but I don't think you have demonstrated a cost-effective solution for long exposure deep sky imaging - either with or without autoguiding. As I said, I have yet to see an FWHM value for a long exposure image with this system - and that's the main thing I go by.

You allude to having tried to autoguide your mount, but I don't think you explored the full space of software and techniques for optimal results. In my view, if you use OAG and low latency guiding with video, and rapid corrections (a la MetaGuide, which I wrote, and which is free), you can achieve much better results than by more conventional methods. This involves no costly hardware add-ons. I work with cge and cge-pro mounts and achieve 2" fwhm and below from unexceptional skies in the northeast U.S., and I believe others have done well with more inexpensive mounts via EQMod and similar methodology.

You also allude to the lack of need for 10-20m exposures given typical light pollution - but that ignores narrow band work at f/5 to f/10 - which is growing in popularity. You need long exposures for that.

I think high-res encoders have the potential to smooth out RA errors due to gearbox and bearings - and that is a key limitation to obtaining good results with a non high-end mount. But you will still need to autoguide to make corrections in RA and Dec to achieve optimal fwhm in long exposures - and the end result may not be much different from tight autoguiding at high frequency and low latency with no special encoders involved.

So - I expect high-res encoders to make guiding easier and more casual with cheaper mounts, and they will smooth out errors at arbitrary frequencies that are unreachable by PEC at any update rate, but they will still require tight guiding with a good centroid to obtain optimal fwhm.

Frank




Thanks Frank for your thoughtful discussion. I agree, for the absolute highest quality deep sky (long exposure)work with the lower cost mounts, there is no substitute for using a guide camera. And the system that Ray has talked about in this thread (using multiple stars to do plate solves) is probably the best way to do it. But trying to use a guide camera for high frequency (<0.5 hz) gets a little dicey depending on the field you are imaging.

Finding a bright enough guide star is always problematic. Plus the trend is towards lower focal length, smaller guidescopes. This creates a problem in that the plate scale for the guiding image does not have enough resolution to correct to sub arcsecond movements, especially when the seeing is not that poor. So the answer of course is to use guidescope similar to the old days with long focal lengths and smaller fields of view which only aggravates the issue of finding a bright enough guide star.

There is absolutely no doubt that for narrow band imaging, long exposures (20-60 minutes, if anyone goes that high) are necessary to beat down the noise and not be overwhelmed with readout noise because of the number of frames necessary with shorter exposures, that external guiding systems are necessary. I agree with you 100%.

I have used PHD with an OAG and with external guide scopes, and for me it's not a matter of tweaking my equipment and refining my skills, and finding the best software available... It's about how much time do I want to spend messing with all that. That's all, that's the bottom line for me.

I think the recent development of Adaptive Optics for amateur level systems is a response to the need for very fast corrections due to bad seeing and scintillation, and may take the place of guide scopes also. These system's cost are the same, or more than the TDM, and I do not see the same level of discussion, but I have not been looking for it either.

I understand fully that the TDM is not for every amateur, just like refractors are not for everyone, or DOBS or RC's, Every tool has it's strengths, and for me and my observing program, the TDM saves me time and effort at a reasonable cost.

I appreciate the discussion, I think it is valuable.

Jerry Hubbell
Lake of the Woods Observatory
Locust Grove, VA

Edited by Jerry Hubbell (10/29/11 09:21 AM)


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gdd
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886618 - 10/29/11 09:13 AM

I have wondered why someone does not put a mid-precision encoder on the output of the gearbox so PEC will have a cleaner worm error to deal with. That should be a lot cheaper than a high precision encoder on the RA. There would still be uncorrected noise from the worm and RA bearings, but there should still be an overall improvement.

Gale


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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4886628 - 10/29/11 09:17 AM

Frank,

The encoders on say the CGEM or LXD75 are on the motor shaft. These are used solely for counting pulses (to determine position) and for determining motor speed. These usually are only hundreds of PPR (pulses per revolution), perhaps even dozens - the Meade motor boards have these 24-odd tooth encoders on the motor shaft before the gearbox.

The encoders on the Tak mounts (the later ones, e.g. EM200) are indeed on the RA and DEC axis. They don't have to be million-tick like the TDM, since they don't need to measure periodic error, they are solely for pointing. A 10000-tick encoder is probably plenty for this application (and costs $20 in bulk) -- all DSC's out there use either 2000-, 4000- or 10000-tick encoders on the RA and DEC axes. Even 50000- to 100000-tick encoders aren't crazy expensive like the Gurleys and Renishaws. Of course you won't get sub-arcsecond pointing but for GoTo that is probably not needed.

The FS2 Goto system can also take encoder inputs from RA and DEC to lock the controller's pointing to the axes.

My point is - putting 10000-tick encoders on the RA and DEC of a mount is an "obvious" feature, but none of the entry- to midrange mounts have it (you have to go to a G11 or Tak EM-200 to get it).

Hence - I really don't see TDM-style million-tick encoders migrating to the mass market anytime soon, if 10K-tick encoders aren't even there. I assume TDM-style technology would appear on the $5K class mounts first (CGE-Pro, etc.) in fact doesn't the iEQ-75 come with such an encoder?


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886631 - 10/29/11 09:22 AM

Hey Jerry,

One of the things that you pointed out that I think is important to re-iterate is the simplicity involved with the TDM solution. This was described in the S&T article, and to me at least, it's a big factor.

You install it (bolt it on), plug it in, and turn it on. Instant result. No software, no configuration, no playing around, no extra steps. It just works. Yes there is a cost, but in the grand scheme of things, there is a cost to everything in one way or another ($$, time, effort, frustration, etc.).

Clear skies,


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886663 - 10/29/11 09:52 AM

Quote:

Quote:

Hi Jerry,

The reference is plate-solved images precessed to JNow coordinates. The rate corrections are made by offseting the tracking rate in RA and Dec slightly from sidereal... enough to compensate for refraction, polar alignment errors, flexure, etc.


Now I realize that is just one image so if you have better images then my conclusion might be different.

-Ray




Hi Ray,

So your system DOES use a guide camera to acquire images for correcting PE. The only difference between using PHD and your software guide correction is that yours uses multiple stars to calculate a plate center as opposed to using an individual star to adjust the drive rate.

Well, isn't this cheating a little on our discussion here? The premise I presented was that the EQ6 coupled with the TDM performed as well as an expensive mount WITHOUT GUIDING on STARS. That was the basis for comparison. Further my contention is that with an excellent polar alignment and the TDM the results are comparable to mounts in the $5000-$10000 range for the type of imaging I am doing, UNGUIDED. I don't believe we can have an honest conversation until we see the results under the same requirements.

Let me ask an interesting question, Don't take this wrong, I am honestly curious about why this is:

If Guiding is absolutely necessary, why don't the manufacturers make large mounts (load capacities in the 20-50Kg range) that have mediocre (30-40 arcsec p-p) PE. It seems they could make mounts cheaper if they didn't have to worry about trying to achieve unguided PE <5 arcsec p-p. I understand that everything needs to be beefier but I am sure a lot of time and effort is put in to make sure the PE is low on these mounts resulting in the higher cost and price for the buyer. If external guiding with a guidescope is necessary anyway, why not create a mount that has an equipment capacity of 50Kg and offer it for say $2500?

I think I know the answer, When customers pay >$5000 for a mount the expectation that not only the capacity increases, but that all the performance parameters improve including PE. That's reasonable.

But to expect the performance improvements when paying a large sum of money, and then come back and then say it doesn't matter that PE has improved on the expensive mounts, we have to use guide cameras anyway, is a bit disengenuous.

Jerry




Um... I never said there was a guide camera. In fact, let me state this now... there was NO guide camera. NO autoguiding was done!!!

What was done was pre-measurement of pointing errors across the sky. Have you heard of TPoint or MaxPoint? They collect the positional errors of the mount by doing plate solves. The process can take anywhere from 10 minutes for a small model to several hours for a 500+ point model. Once the modeling is done the positional and tracking rate errors can be calculated from the data. The key to making this work is the quality of the data model and the precision of the mount. The mount has to be able to repeatably slew accurately and have the ability to precisely change the rate slightly from sidereal to match the required (modeled) RA and Dec tracking rates. The technique is not new. It's been used in production Paramount ME's for perhaps 10 years (it's called ProTrack if you want to Google it). Also, major observatories have used this method for even longer.

So, as I clearly said before, using an encoder is not good enough to do long exposure unguided images at longer focal lengths. You would also need software tracking correction and a precision mount.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Gord]
      #4886672 - 10/29/11 10:01 AM Attachment (26 downloads)

Quote:

Hey Jerry,

You install it (bolt it on), plug it in, and turn it on. Instant result. No software, no configuration, no playing around, no extra steps. It just works...




Yes Gord, I have stated that more than once in this discussion. That is a big part of it, again for me.

For those who have not read the paper I posted, here is my initial chart of my measured Tracking Error (TE) as measured by the TDM encoder, and then the results when I turn on the TDM, first at 1 Hz/ 1 arcsec control band, and then at 5 Hz / 0.5 arcsec control band. You be the judge. What I have measured and reported in my paper is that with my TDM mounted on my EQ6 Pro, I get a TE value < +/-0.7 arcseconds 95% of the time. That is the starting point, or my foundation for my imaging system performance.

You be the judge, is it worth $2200 to get this type of improvement for your imaging program with practically zero setup time or ongoing maintenance during your imaging session? That's up to you.

Jerry Hubbell
Lake of the Woods Observatory
Locust Grove, VA

Edited by Jerry Hubbell (10/29/11 01:57 PM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4886694 - 10/29/11 10:16 AM

Quote:


Um... I never said there was a guide camera. In fact, let me state this now... there was NO guide camera. NO autoguiding was done!!!

What was done was pre-measurement of pointing errors across the sky. Have you heard of TPoint or MaxPoint? They collect the positional errors of the mount by doing plate solves. The process can take anywhere from 10 minutes for a small model to several hours for a 500+ point model. Once the modeling is done the positional and tracking rate errors can be calculated from the data. The key to making this work is the quality of the data model and the precision of the mount. The mount has to be able to repeatably slew accurately and have the ability to precisely change the rate slightly from sidereal to match the required (modeled) RA and Dec tracking rates. The technique is not new. It's been used in production Paramount ME's for perhaps 10 years (it's called ProTrack if you want to Google it). Also, major observatories have used this method for even longer.

So, as I clearly said before, using an encoder is not good enough to do long exposure unguided images at longer focal lengths. You would also need software tracking correction and a precision mount.

-Ray




Okay, I give you that, but if you recall, I did originally state that either you were doing some kind of static modeling using a camera OR using a guide camera realtime. I am familiar with T-point, but did not realize it had the resolution and capacity to correct for small errors or non-periodic errors in the mount, only for correcting pointing errors. I understood it was only for the correction of possibly refraction, and flexure pointing errors. I knew you were having to put some work (a lot of work) into it at somepoint, LOL

This method is even more onerous for the less expensive mounts because of the inconsistent performance of the mount. This is very similar to creating a PEC curve for your mount. I have found that for my EQ6 mount. The PEC curve is bounded by the range of positions you were pointing at when acquiring the data, and only corrected 60-70%, at the best, of the PE. So for a typical EQ6 class mount you may be able to bring the PE down from 40 arcsec p-p to 10-15 arcsec p-p. I suspect if I used T-Point on my EQ6 I would manage >5 arcsec p-p but not much better.

I guess the only other question is how much is that software, and what is the cost of upkeep?

Thanks for the insights into what it takes to get the performance you are getting.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA

Edited by Jerry Hubbell (10/29/11 10:41 AM)


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886739 - 10/29/11 10:51 AM Attachment (15 downloads)

Just as another piece of data to examine, here is an image from the TDM developer site:

http://www.mda-telescoop.com/index.php?option=com_content&task=view&id=55&Itemid=85

This image shows the tracking performance using a star image not the output from the encoder when the TDM is on and controlling the mount (an EQ6). It looks to me that over the 300 seconds of data shown, the star image only exhibits scintillation on the order of +/- 2-3 arcseconds; there are no other defects in this image using a correctly tuned, polar aligned mount. I am sure over a 30 minute period you would not see much difference than what you are seeing here. There are other images on the linked page above that show the various defects that may be present in your mount that would need to be corrected to expect the nominal kind of performance that Ray and I are talking about.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA

Edited by Jerry Hubbell (10/29/11 10:59 AM)


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Ray Gralak
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Reged: 04/19/08

Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886779 - 10/29/11 11:20 AM

Hi Jerry,

Quote:

Quote:


Um... I never said there was a guide camera. In fact, let me state this now... there was NO guide camera. NO autoguiding was done!!!

What was done was pre-measurement of pointing errors across the sky. Have you heard of TPoint or MaxPoint? They collect the positional errors of the mount by doing plate solves. The process can take anywhere from 10 minutes for a small model to several hours for a 500+ point model. Once the modeling is done the positional and tracking rate errors can be calculated from the data. The key to making this work is the quality of the data model and the precision of the mount. The mount has to be able to repeatably slew accurately and have the ability to precisely change the rate slightly from sidereal to match the required (modeled) RA and Dec tracking rates. The technique is not new. It's been used in production Paramount ME's for perhaps 10 years (it's called ProTrack if you want to Google it). Also, major observatories have used this method for even longer.

So, as I clearly said before, using an encoder is not good enough to do long exposure unguided images at longer focal lengths. You would also need software tracking correction and a precision mount.

-Ray




Okay, I give you that, but if you recall, I did state that either you were doing some kind of static modeling using a camera OR using a guide camera realtime. I am familiar with T-point, but did not realize it had the resolution and capacity to correct for small errors or non-periodic errors in the mount. I understood it was only for the correction of possibly refraction, and flexure. I knew you were having to put some work (a lot of work) into it at somepoint, LOL





Actually, TPoint cannot correct for periodic error. That is still done with PEC. But some higher end mounts, like Astro-Physics mounts, ship with PEC already recorded so, without installing anything extra you get a mount with typically less than 1 arc-sec PE. In fact the other night I programmed my Ap1200 and the resulting PE was +/-0.2 arc-secs. So right there this mount probably tracks better than any cheaper mount plus encoder.

BTW, there are other advantages to having low inherent periodic error. As I alluded to (and I think you acknowledged) pointing errors will be lower with lower PE mounts. That's because when you slew to the same RA/Dec at different times it will be at different positions in the worm so positioning accuracy is affected by the amount of periodic error. When doing plate solves have a precision mount (low PE, great pointing accuracy) can make a big difference in calculating an accurate model from which precise tracking rates can be calculated. That's not saying it can't be done with a less accurate mount. It just won't be as precise.

And, once you go non-sidereal, for instance if you are tracking a fast-moving earth satellite, high PE might clearly show as a wobbling motion because I don't think the encoder solutions available work at rates significantly faster than sidereal, correct?

Quote:


This method is even more onerous for the less expensive mounts because of the inconsistent performance of the mount. This is very similar to creating a PEC curve for your mount. I have found that for my EQ6 mount. The PEC curve is bounded by the range of positions you were pointing at when acquiring the data, and only corrected 60-70%, at the best, of the PE. So for a typical EQ6 class mount you may be able to bring the PE down from 40 arcsec p-p to 10-15 arcsec p-p. I suspect if I used T-Point on my EQ6 I would manage >5 arcsec p-p but not much better.





Oh, I agree that software tracking rate correction probably will not work as well for less accurate mounts. But that was the big debate this whole discussion, wasn't it? To show if there is a difference in potential performance between a less precise mount and encoder versus what you can accomplish with a higher precision mount. I do acknowledge the value of the setup you are using but I think that I have shown that there is improvement that could be had in unguided tracking with a precision mount and tracking rate correction software.

Quote:


I guess the only other question is how much is that software, and what is the cost of upkeep?




Interesting that you should mention cost! In general I think higher end gear holds its value more and generally looks and works better and longer than cheaper gear. For instance my AP1200 still looks great after 5-6 years of use while a couple cheap mounts I own have corroding bolts already. The value of the cheap mounts probably has gone down more than my expensive mounts. In general I think most higher-end mounts are designed to last longer while cheaper mounts have had "corners cut" to make them as cheap as possible and probably not last as long. I think you know what I'm talking about, I hope?

If one is really interested in this hobby they will likely progress from less expensive mounts up to more expensive mounts. If they just save and purchase a good expensive mount first then in the long run I think they may save money. It might cost a lot more initially but over the long term they won't lose money every time they upgrade. If they started with a higher-end mount it would retain value better, last longer, and they will probably be a lot happier with the imaging results they get.

-Ray


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freestar8n
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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4886806 - 10/29/11 11:40 AM

Quote:

The encoders on the Tak mounts (the later ones, e.g. EM200) are indeed on the RA and DEC axis. They don't have to be million-tick like the TDM, since they don't need to measure periodic error, they are solely for pointing. A 10000-tick encoder is probably plenty for this application (and costs $20 in bulk) -- all DSC's out there use either 2000-, 4000- or 10000-tick encoders on the RA and DEC axes. Even 50000- to 100000-tick encoders aren't crazy expensive like the Gurleys and Renishaws. Of course you won't get sub-arcsecond pointing but for GoTo that is probably not needed.




I agree it would be nice to have absolute encoders on the axes, and when I first used a computerized mount I felt hindered by not being able to move it by hand. But I got used to it, and I don't think there is a big demand for it expressed very much in these forums for example, while there is a constant demand to keep prices down. So - to answer your question as to why they don't include them - I don't think there is a big demand, and they are trying to keep cost down.

I don't think I would pay extra for 100000 tick encoders, but I would one day like a high end mount with sub arc-second absolute encoders - which I think may start to be common. The question is - will they penetrate the mid-range market much.

Frank


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4886820 - 10/29/11 11:45 AM

Quote:

Hi Jerry,

Interesting that you should mention cost! In general I think higher end gear holds its value more and generally looks and works better and longer than cheaper gear. For instance my AP1200 still looks great after 5-6 years of use while a couple cheap mounts I own have corroding bolts already. The value of the cheap mounts probably has gone down more than my expensive mounts. In general I think most higher-end mounts are designed to last longer while cheaper mounts have had "corners cut" to make them as cheap as possible and probably not last as long. I think you know what I'm talking about, I hope?

If one is really interested in this hobby they will likely progress from less expensive mounts up to more expensive mounts. If they just save and purchase a good expensive mount first then in the long run I think they may save money. It might cost a lot more initially but over the long term they won't lose money every time they upgrade. If they started with a higher-end mount it would retain value better, last longer, and they will probably be a lot happier with the imaging results they get.

-Ray




Hi Ray,

thanks for the thoughtful response. I understand what you are saying about the value of the more expensive high quality mounts. Consider this though, as you well know, this hobby for the last 10-15 years has been driven by the baby boomers who have the disposable income to invest in the new technologies, and have made it somewhat of a golden age for amateur astronomy.

We are getting older and I think the goal should be to get as many younger people involved as we can. In that regard, having high performance lower cost equipment available on the market really makes a difference in attracting the younger folks to this hobby. Both you and I know that even if it is the best policy to buy the higher quality equipment, 90% of the buyers just don't have the income.

For me, I was out of astronomy for several years, and in the late 80's and 90's I was strictly visual, I had tried some astrophotography but it was very frustrating. Three years ago, I decided to see how the technology progressed and found that it was to the point where I could really get into it with both feet. My main goal in purchasing the level of equipment I bought was to train myself in the use of the latest technologies, and see how much I could do for the least amount of money. I wanted to get 80% of the bang for 30% of the cost. I think I am just about there, and I have also taught myself what is important and what isn't so that when I invest 30-50k into a system when I retire, I will know what I am doing. That is what the lower cost equipment has done for me.

It can get very frustrating for beginners to visit star parties and see and touch the latest state-of-the-art amateur equipment and realize that it is practically impossible to invest < $3000 total and expect to get anywhere near the performance, even with spending 2-3 years of continuous study and practice, of what we are talking about. So in my mind, anything that brings the performance up in equipment available to the beginner goes a long way to maintaining the vitality and ongoing sustainability of our hobby. Sure, it may not meet 100% of the requirements that high end users expect, but if we can get 80% there for 30% of the cost, why not. It will always cost a lot to get that extra 20% and we are lucky to have people like you willing to invest in that technology.

Thanks again for the discussion, I think it has been valuable.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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Ray Gralak
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886849 - 10/29/11 11:58 AM

Hi Jerry,

Quote:

Quote:

Hi Jerry,

Interesting that you should mention cost! In general I think higher end gear holds its value more and generally looks and works better and longer than cheaper gear. For instance my AP1200 still looks great after 5-6 years of use while a couple cheap mounts I own have corroding bolts already. The value of the cheap mounts probably has gone down more than my expensive mounts. In general I think most higher-end mounts are designed to last longer while cheaper mounts have had "corners cut" to make them as cheap as possible and probably not last as long. I think you know what I'm talking about, I hope?

If one is really interested in this hobby they will likely progress from less expensive mounts up to more expensive mounts. If they just save and purchase a good expensive mount first then in the long run I think they may save money. It might cost a lot more initially but over the long term they won't lose money every time they upgrade. If they started with a higher-end mount it would retain value better, last longer, and they will probably be a lot happier with the imaging results they get.

-Ray




Hi Ray,

thanks for the thoughtful response. I understand what you are saying about the value of the more expensive high quality mounts. Consider this though, as you well know, this hobby for the last 10-15 years has been driven by the baby boomers who have the disposable income to invest in the new technologies, and have made it somewhat of a golden age for amateur astronomy.

We are getting older and I think the goal should be to get as many younger people involved as we can. In that regard, having high performance lower cost equipment available on the market really makes a difference in attracting the younger folks to this hobby. Both you and I know that even if it is the best policy to buy the higher quality equipment, 90% of the buyers just don't have the income.

For me, I was out of astronomy for several years, and in the late 80's and 90's I was strictly visual, I had tried some astrophotography but it was very frustrating. Three years ago, I decided to see how the technology progressed and found that it was to the point where I could really get into it with both feet. My main goal in purchasing the level of equipment I bought was to train myself in the use of the latest technologies, and see how much I could do for the least amount of money. I wanted to get 80% of the bang for 30% of the cost. I think I am just about there, and I have also taught myself what is important and what isn't so that when I invest 30-50k into a system when I retire, I will know what I am doing. That is what the lower cost equipment has done for me.

It can get very frustrating for beginners to visit star parties and see and touch the latest state-of-the-art amateur equipment and realize that it is practically impossible to invest < $3000 total and expect to get anywhere near the performance, even with spending 2-3 years of continuous study and practice, of what we are talking about. So in my mind, anything that brings the performance up in equipment available to the beginner goes a long way to maintaining the vitality and ongoing sustainability of our hobby. Sure, it may not meet 100% of the requirements that high end users expect, but if we can get 80% there for 30% of the cost, why not. It will always cost a lot to get that extra 20% and we are lucky to have people like you willing to invest in that technology.

Thanks again for the discussion, I think it has been valuable.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA



You make many good points! I do agree with the issue of money is an important one, and that everyone has their own limit on how much they can spend. I strongly believe there is good value in many lower end and mid range mounts, especially coupled with a TDM. My main point was only that there is extra performance to be had on higher end mounts. it might only be an extra 20%, or 10%, or 5%, but it's there. It kind of is similar to the audiophile equipment marketplace. That last 10% costs you a lot of $$!!

In any case. this has been an enjoyable discussion, Jerry. I wish you the best luck with your equipment. I'll keep an eye out for new images from you!

Take care,

-Ray


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freestar8n
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4886860 - 10/29/11 12:03 PM

Quote:

Finding a bright enough guide star is always problematic. Plus the trend is towards lower focal length, smaller guidescopes. This creates a problem in that the plate scale for the guiding image does not have enough resolution to correct to sub arcsecond movements, especially when the seeing is not that poor. So the answer of course is to use guidescope similar to the old days with long focal lengths and smaller fields of view which only aggravates the issue of finding a bright enough guide star.




For tight guiding with mirror optics at long focal length, I would only consider off-axis guiding, or dual-chip - i.e. common optical path. I'm not interested in trying to get optimal results with a guidescope, and I'm not interested in multiple star guiding because of the longer exposures required, and corresponding latency. Instead I use centroid analysis of multiple video frames of a single star. Finding a guide star with OAG is not so bad if you use a planetarium FOVI and dial it in ahead of time - but either way I consider OAG or dual-chip to be essential for optimal results when guiding mirror optics.

As for difficulty tuning - again I think that can be a limitation of software. In my case I strictly show plots and so forth in arc-second scale as the relevant fundamental unit - so that if you change the guide focal length or something, the scale that determine the error correction is unchanged. Furthermore, I show live error plots that update every 0.5 seconds - providing a good "feel" for the error as you change things like aggressiveness - and this update rate is independent of the effective exposure time because it is video-based. Overall this makes it easy to dial in good parameters, and those parameters change little except due to seeing conditions.

Guided imaging does not require a critical polar alignment, unlike non-guided imaging with no dec. corrections, though I recommend getting it as close as possible. With a celestron mount you can have it setup and polar aligned adequately in a matter of minutes, in bright twilight, using the AllStar polar alignment routine. All of this greatly reduces setup time and doesn't rely on extra hardware or software. Tracking and guide error plots don't tell the whole story of what is really happening at the image plane.

My main point in all this is that you are comparing your experience and results of your current setup with a previous setup - but it is not a comprehensive conclusion because I don't think you explored all the options that are available with freely available software and no additional hardware. And the best way to show deep sky guiding results is to show non-binned long exposures at long focal length with corresponding fwhm's of the stars.

But you do have what appears to be a concrete result of a low-cost setup that works well for unguided 1-3m exposures. I don't know anything that beats it in that price range, and it shows at least one clear win of the tdm with an inexpensive mount.

Frank


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psandelle
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Reged: 06/18/08

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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4886877 - 10/29/11 12:14 PM

Really great discussion - I'm enjoying it, and scratching my head and having to go research some of the points myself (and on a Saturday!).

I will be curious when Explore Scientific's new mount comes out. It has a TDM build in (along with the nifty right-angled polar scope) I believe, and supposedly in the 5 to 7 grand range (if I'm not mistaken). That would be one and a half to two times Jerry's price range...but still, if it were the whole kit AND the kaboodle, I think that might fit the bill.

Paul

Edited by psandelle (10/29/11 12:15 PM)


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4886893 - 10/29/11 12:27 PM

Quote:

Hi Jerry,

You make many good points! I do agree with the issue of money is an important one, and that everyone has their own limit on how much they can spend. I strongly believe there is good value in many lower end and mid range mounts, especially coupled with a TDM. My main point was only that there is extra performance to be had on higher end mounts. it might only be an extra 20%, or 10%, or 5%, but it's there. It kind of is similar to the audiophile equipment marketplace. That last 10% costs you a lot of $$!!

In any case. this has been an enjoyable discussion, Jerry. I wish you the best luck with your equipment. I'll keep an eye out for new images from you!

Take care,

-Ray




Thanks Ray, I have enjoyed this discusson very much also. I always like to flex my debating muscles every now and again, this is the first one for me on Cloudy Nights. You have given me a lot of good information on the differences on higher end and lower end mounts, and the value that each brings to the table. I appreciate your interest in my work, you may be able to count me as a PEMPRO customer in the future if the need arises.

Clear Skies!

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4886905 - 10/29/11 12:36 PM

Quote:

Quote:

Finding a bright enough guide star is always problematic. Plus the trend is towards lower focal length, smaller guidescopes. This creates a problem in that the plate scale for the guiding image does not have enough resolution to correct to sub arcsecond movements, especially when the seeing is not that poor. So the answer of course is to use guidescope similar to the old days with long focal lengths and smaller fields of view which only aggravates the issue of finding a bright enough guide star.




For tight guiding with mirror optics at long focal length, I would only consider off-axis guiding, or dual-chip - i.e. common optical path. I'm not interested in trying to get optimal results with a guidescope, and I'm not interested in multiple star guiding because of the longer exposures required, and corresponding latency. Instead I use centroid analysis of multiple video frames of a single star. Finding a guide star with OAG is not so bad if you use a planetarium FOVI and dial it in ahead of time - but either way I consider OAG or dual-chip to be essential for optimal results when guiding mirror optics.

As for difficulty tuning - again I think that can be a limitation of software. In my case I strictly show plots and so forth in arc-second scale as the relevant fundamental unit - so that if you change the guide focal length or something, the scale that determine the error correction is unchanged. Furthermore, I show live error plots that update every 0.5 seconds - providing a good "feel" for the error as you change things like aggressiveness - and this update rate is independent of the effective exposure time because it is video-based. Overall this makes it easy to dial in good parameters, and those parameters change little except due to seeing conditions.

Guided imaging does not require a critical polar alignment, unlike non-guided imaging with no dec. corrections, though I recommend getting it as close as possible. With a celestron mount you can have it setup and polar aligned adequately in a matter of minutes, in bright twilight, using the AllStar polar alignment routine. All of this greatly reduces setup time and doesn't rely on extra hardware or software. Tracking and guide error plots don't tell the whole story of what is really happening at the image plane.

My main point in all this is that you are comparing your experience and results of your current setup with a previous setup - but it is not a comprehensive conclusion because I don't think you explored all the options that are available with freely available software and no additional hardware. And the best way to show deep sky guiding results is to show non-binned long exposures at long focal length with corresponding fwhm's of the stars.

But you do have what appears to be a concrete result of a low-cost setup that works well for unguided 1-3m exposures. I don't know anything that beats it in that price range, and it shows at least one clear win of the tdm with an inexpensive mount.

Frank




Thanks Frank, I understand your point about comparing my old setup with the new one, and maybe not exploring the full extent of what is available. I appreciate your thoughts on the matter, and will re-evaluate my needs in that area. I can foresee that even with the TDM, for long focal length, Long (20-60 minute) exposures guiding will be very necessary with my setup. I am just not into that at the present, but I need to get into that in order to round out my skill set. The TDM does make provisions for using a guidng camera, and it is seemlessly integrated into the system.

As far as using the OAG for guiding, that is all well and good for normal non-filtered, or photometric filtered work, but it does not work for narrow band imaging, as others have said, and I have read. In order to do narrow band imaging effectively through an OAG setup, you need either a very high end mount with low PE or on a lower cost mount with the TDM driver corrector. I do have an OAG setup that I have used with my AT8RC that I can conceivably do effective narrow band imaging with coupled with the EQ6 and TDM.

Thanks again for your thoughtful discussion.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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Alph
Carpal Tunnel


Reged: 11/23/06

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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4886916 - 10/29/11 12:43 PM

Quote:

I don't really see how the TDM price can go much lower. Maybe (just maybe) it can hit $1000




The price could be cut significantly if the electronics box was removed from the equation. The electronics box alone costs $1800 while the custom mount adapter that includes the encoder costs just $400. I don’t see any reason why a mount could not be driven from your laptop. So here is a challenge for someone with skills and plenty of time to make that electronic box obsolete. Are there any plans to do just that?


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orlyandico
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4886927 - 10/29/11 12:54 PM

The adapter + encoder only costs $400?

I thought the encoder + box was $1800 and the adapter was extra. I tried (and failed) to find a Gurley million-tick encoder for under $500. They were about $900.


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4886957 - 10/29/11 01:11 PM

Your are correct, Alph you misunderstood, the Encoder + the microcontroller is $1800. The mount adapter can cost from $330 to $400. See
http://store.explorescientific.com/tdmtelescopedrivemasterver2encoderandelectronicssetrequiresmountadapter.aspx

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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jmiele
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4886969 - 10/29/11 01:16 PM

"Actually, TPoint cannot correct for periodic error. That is still done with PEC. But some higher end mounts, like Astro-Physics mounts, ship with PEC already recorded so, without installing anything extra you get a mount with typically less than 1 arc-sec PE."

Ray, Just a note. While AP does record a PE track before shipping it's by no means a to the level required for astrophotography. It may be, just not a sure thing. You statement makes it seem like AP is one of the only ways to get this. I'm sure that wasn't your intent.

So, let clear several things up. I've purchased a 1200, 900 and Mach I this year. None of which came with anything below 4 arc second PE - with the AP training. I've purchased both a Paramount ME and Paramount MX this year as well. The ME has PE at .8 arc seconds P2P untrained. The MX 4 arc second also - untrained.

IME mount accuracy for pointing with the supplied software goes like this:

Bisque
Celestron
AP is somewhere down the line. sorry that's a fact as of today
Tak

For PE it's like this:
Bisque
Tak
AP
The rest...

When the new software comes along then we will see. Believe me however, I go with whatever is best and should AP take the crown I will be the first to say so. I think discrediting T-Point is inappropriate. T-Point is integral to the Bisque products and works with the Paramounts and ProTrack to do things you are only now "trying to do". When you do them, let me know... I'd love to see them....even buy them. Until the we should focus more on what available today and the OP's thread intend.

You know I'm a fan Ray, but as the AP Software release has progressed I've seen a trend in the way it's being discussed. If you want to compare apples and apples you'll have to have an OPEN beta. Otherwise, we'll wait and see what we see when ALL have access. In several posts we are getting teasers and things leading people to believe things. I don't find it appropriate. I will be looking for such in all these posts.

Bisque mounts go with ALL the Bisque software suite. When they are considered they should be considered as a package. Comparing them without would be like asking what an AP mount can do without it's hand control. That answer is clear - nothing.

These comment reference several posts concerning AP software and comparisons currently being made with other products..


Joe

Edited by jmiele (10/29/11 02:17 PM)


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CounterWeight
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Re: Telescope Drive Master new [Re: Jerry Hubbell]
      #4886974 - 10/29/11 01:18 PM

Jerry, Ray, all-

Really interesting discussion and great points made (Jerry - no my real name 'Jim' is in my sigline). IMO this TDM aftermarket 'mod' adds a great alternative to the community. I think the marketing is a fair representation and the relative straightforward plug-and-play are great There are a great many threads here where mount owners have gone to far greater time and effort (watever the cost, wait times, availability of parts and etc) to improve a lower range mount with far less discrenable results. That this is quick, immediate, and IMO very simple - huge plusses. Priced IMO very fair. Most important is that it does what it says, quickly, simply, that was one of the main take aways from the reviews / write ups.

Again my thanks to all the great contributions in the thread.


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harry page 1
sage


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Re: Telescope Drive Master new [Re: CounterWeight]
      #4887020 - 10/29/11 01:40 PM

Hi

I have just recently purchased the TDM kit and have fitted it to my rather One off scope

My scope uncorrected was about 20 -30 arc sec peak to peak and with the aid of pempro got this down to about 6 arc sec peak to peak but My scope suffers from some small bumps etc which could not be removed with training .
I must admit I did not expect perfection with the TDM on my mount as I had to do some rustic additions
But with little effort I got the promised 1 sec tracking the plug and play is very easy indeed and personally think its well worth the money and think it will aid my hunt for a decent image greatly
A small write up on my web page Harrysastroshed
Regards Harry


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freestar8n
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4887039 - 10/29/11 01:51 PM

Quote:

As far as using the OAG for guiding, that is all well and good for normal non-filtered, or photometric filtered work, but it does not work for narrow band imaging, as others have said, and I have read.




I'm afraid that's a common misconception. Narrow-band is where OAG shines - because the filters are after the pickoff mirror. So - the guide camera sees unfiltered light - unlike the other main mode of common-path guiding, which is dual chip. I don't know anyone with OAG who puts the filters in front of the pickoff mirror - there is no reason to.

I have lots of examples with my C11 and cge, and later a cge-pro, on the MetaGuide site. When I bought the c11 and cge as a unit years ago, together they were $3999. The OAG I mainly use is a taurus-mini that cost a few hundred dollars and weighs less than a typical guidescope. The guide camera I use is a Lumenera, which is relatively expensive but doubles for planetary work and many other uses - as opposed to a simple guide ccd that is mainly for guiding. The associated software I uses is MetaGuide (free) and I do PEC training with the free PECTool from Celestron. This keeps all the costs down and achieves very tight stars in long, narrow band exposures.

Video guiding with MetaGuide and OAG is very different from normal guiding with a guidescope - and requires some effort to make the change. But that's also true of switching to hardware encoders. So - for people doing deep sky work - I'm hoping there will be more such examples when combining tdm with a mid-range mount so we can have a more direct comparison.

Thanks - and have fun with your new setup.

Frank


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Jerry Hubbell
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Re: Telescope Drive Master new [Re: CounterWeight]
      #4887042 - 10/29/11 01:53 PM

Quote:

Jerry, Ray, all-

Really interesting discussion and great points made (Jerry - no my real name 'Jim' is in my sigline).




Hey Jim, sorry about that I just now located your name in your signature. I very much appreciate your thoughts and glad you enjoyed the discussion. I think it is a very honest assessment of the TDM and the things we must consider when purchasing such a device. I would put the recent availabilty of Active Optics Guiders such as this one from Orion in the same catagory:

http://www.telescope.com/Astrophotography/Autoguiding-Solutions/Orion-SteadyStar-Adaptive-Optics-Guider-with-Rotator/pc/-1/c/4/sc/60/p/53077.uts?sortByColumnName=SortByPriceDescending

I consider this as a complement to TDM and maybe a replacement for an off-axis guider. The impact of this technology is interesting in the way people will react to it, and put it to use.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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orlyandico
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Re: Telescope Drive Master new [Re: harry page 1]
      #4887043 - 10/29/11 01:54 PM

harry, that's an amazing mount! if there's any pudding to prove the TDM "does what its advertised to" then harry's photo should be it.

what gear are you using on it?


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harry page 1
sage


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Re: Telescope Drive Master new [Re: orlyandico]
      #4887060 - 10/29/11 02:04 PM

Hi

Well there is the 14" newt on which I am using a sx H35 camera , The advantage of this mount is I can just bolt anything on it I even sat on it once to see if it could take the weight

Harry


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4887070 - 10/29/11 02:12 PM

Quote:

Quote:

As far as using the OAG for guiding, that is all well and good for normal non-filtered, or photometric filtered work, but it does not work for narrow band imaging, as others have said, and I have read.




I'm afraid that's a common misconception. Narrow-band is where OAG shines - because the filters are after the pickoff mirror. So - the guide camera sees unfiltered light - unlike the other main mode of common-path guiding, which is dual chip. I don't know anyone with OAG who puts the filters in front of the pickoff mirror - there is no reason to.

Thanks - and have fun with your new setup.

Frank




Hey Frank, I do apologize, I was thinking about the SBIG dual chip cameras that put the guiding chip adjacent to the imaging chip. Those are the type of cameras and OAG I had in my mind. Sorry for that. You are very much correct about the filtering being after the pick-up mirror. That would work very well indeed. The Active Optics Guider would have similar performance I believe.

Sorry about the confusion (on my part! )

Thanks

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA


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Alph
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4887074 - 10/29/11 02:15 PM

Quote:

Your are correct, Alph you misunderstood, the Encoder + the microcontroller is $1800. The mount adapter can cost from $330 to $400. See
http://store.explorescientific.com/tdmtelescopedrivemasterver2encoderandelectronicssetrequiresmountadapter.aspx

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, VA



Thanks for the clarification. Nonetheless I still think that the electronics box is a significant cost factor.


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Ray Gralak
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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: jmiele]
      #4887204 - 10/29/11 03:41 PM

Post deleted by David Pavlich

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Alph
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Re: Telescope Drive Master - The Truth of the Matter new [Re: jmiele]
      #4887331 - 10/29/11 05:22 PM

Quote:

I've purchased a 1200, 900 and Mach I this year. None of which came with anything below 4 arc second PE - with the AP training. I've purchased both a Paramount ME and Paramount MX this year as well.



I am curious as to what you do with all those mounts?


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jmiele
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4887374 - 10/29/11 05:48 PM

" I think I've seen many more PE curves than you have and for sure the AP and Bisque mounts average about the same 2.1-2.5 arc-secs uncorrected. I've seen some exceptional curves for both Paramounts and APs. I've seen some bad curves for BOTH mounts too."

I'll have to concede this point to you with regard to the number of viewed curves. I also, don't disagree there are bad and good from all things. My point was that you eluded to the AP's and no other mounts. As you are currently contracted to work with them developing AP product, I think you should consider the ToS that's all. I've been a support of yours Ray and I'm not looking to:

Have an issues between us
Have folks get un unbalanced view of things

I hope we can do both of those things.


" I'm sorry if this maybe throws a wrench into your list but my Paramount ME does not point very well with the supplied software. But I don't think it is the Paramount. I think the supplied software has a bug in it. If you would like to log onto my New Mexico Skies system with me and see on the next clear night maybe you can fix it for me! :-)))"

As you stated and I agreed, there are good and bad in all things. As a software developer in this field, and given the ToS, I just don't find (once again) your commenting on other (competing) software, and your thinking they have a bug, appropriate - at all. As to assisting with the problem, I'd be glad to. Given your "all be it written" tone and smiley, I believe you meant that facetiously. It implies you don't need my help and are above me and my ability. I on the other hand don't believe I'm better than anyone and am always looking to learn or assist. So, I would still be willing to assist. As the IT Crisis Manager of a fortune 50 company over 25 years I may well be able to help. My background in software development and Sigma 6 software quality assurance certification most certainly say so.

"LOL! Are you kidding me!? Does the Paramount ME come with a PC in it's package? If not then it's dead in the water! (Not so with an AP! )"

The point was - with it's supplied software. The Paramount ME and MX are supplied with advanced pointing/modeling and navigation software. As to them coming with a PC, I think you know the answer, however the technology within these mounts is certainly more advanced than many PC's.

"Have a nice day, Joe. I need to get back to work!"

Same to you Ray, and yes you do, or my AP mounts will never point straight.

Apologies to the thread for the distraction. I won't pursue this further here.

Joe


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jmiele
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4887377 - 10/29/11 05:50 PM

Quote:

Quote:

I've purchased a 1200, 900 and Mach I this year. None of which came with anything below 4 arc second PE - with the AP training. I've purchased both a Paramount ME and Paramount MX this year as well.



I am curious as to what you do with all those mounts?





I'm in search of intelligent life on Melmac. So far, no dice.

Joe


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Alph
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Re: Telescope Drive Master - The Truth of the Matter new [Re: jmiele]
      #4887427 - 10/29/11 06:20 PM

Quote:

Quote:

Quote:

I've purchased a 1200, 900 and Mach I this year. None of which came with anything below 4 arc second PE - with the AP training. I've purchased both a Paramount ME and Paramount MX this year as well.



I am curious as to what you do with all those mounts?





I'm in search of intelligent life on Melmac. So far, no dice.

Joe



Well, every intelligent person on Earth knows that Melmac was destroyed.


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jmiele
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4887432 - 10/29/11 06:23 PM

LOL..


Joe


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MeadeEurope
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4887968 - 10/30/11 01:06 AM

Dear Ray,

this is not true. Sampling frequency with 1/8" resolution is of course 8*15"/sec=120Hz. So 5Hz correction is very well within limits.

Clear skies

Tassilo


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MeadeEurope
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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Ray Gralak]
      #4887977 - 10/30/11 01:19 AM

Post deleted by David Pavlich

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MeadeEurope
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4887988 - 10/30/11 01:30 AM

Dear Ray,

sorry, but I do doubt very much that with your setup you are able to measure +-0,2" with any reliability. Just apply the Nyquist theorems to your image scale and add the seeing.
You are right that high end gear does not go down in price in time with the same percentage as cheap gear. But it starts with a much higher price, so the loss in total usually can be very well in the same size.
Donīt get me wrong - I like high end stuff. But always remember that % donīt feed you - itīs $ that are important.

Clear skies

Tassilo


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Re: Telescope Drive Master - The Truth of the Matter new [Re: MeadeEurope]
      #4887994 - 10/30/11 01:38 AM

So much passion in this topic

Lets agree to disagree.

Each product has it's benefits and optimal use scenario. Each has it's positive and negative sides. So instead of slugging it out like a boxing match, maybe we could try and see each product works best?

This is beginning to look like a PC vs. Mac discussion.


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Ray Gralak
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Re: Telescope Drive Master - The Truth of the Matter new [Re: MeadeEurope]
      #4888318 - 10/30/11 10:23 AM

Quote:

Dear Ray,

if you doubt the roundness of the stars for longer exposures with the TDM, take a look at the 10min shot Dennis di Cicco did in the Sky and Telescope review with 4000mm focal length. We do also have pictures like this from other 16"LX200 owners with 15min.
You know the picture from Dennis, so where is your point?

Clear skies

Tassilo



Sorry, I'm not familiar with those images. Could you please provide me a link(s)? Thanks!

-Ray


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Ray Gralak
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Re: Telescope Drive Master - The Truth of the Matter new [Re: MeadeEurope]
      #4888319 - 10/30/11 10:24 AM

Dear Tassilo,
Quote:

Dear Ray,

this is not true. Sampling frequency with 1/8" resolution is of course 8*15"/sec=120Hz. So 5Hz correction is very well within limits.

Clear skies

Tassilo



Respectfully, you are incorrect. It doesn't matter how fast you *internally* sample (e.g. 120 Hz). You cannot correct frequencies faster than 2.5 Hz with 5 Hz *physical* corrections.

-Ray


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Ray Gralak
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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: MeadeEurope]
      #4888323 - 10/30/11 10:26 AM

Post deleted by David Pavlich

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Alph
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Hilmi]
      #4888512 - 10/30/11 12:30 PM

Quote:

This is beginning to look like a PC vs. Mac discussion.



Many owners of very expensive equipment feel compelled to defend their purchasing decisions. They don’t like to be reminded that you can achieve same results with modest equipment.


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psandelle
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4888543 - 10/30/11 12:50 PM

I think part of the problem is there's no clear-cut definitive answer. I know Alph likes the possibilities of the new Meade; we have some strong votes for the TDM; obviously AP & Bisque have solutions. Me, I like Taks because their polar scopes are so good (and are nicely made, but no PEC) - so it's quick in the field.

There's no "easy" end-all, be-all solution. You go Bisque, it's dang complicated and somewhat lengthy when you go out in the field (not so much with a Tak). The TDM is a one-step solution to a real problem, but it is pricey in some regards. AP - great fit and finish, waiting on the new software.

Sigh - I really wish there were one mount that had a Tak polar scope, the TDM on the RA and the fit and finish of the high ends, was as automatic as the Meade might be, but wasn't up over 20 grand.

Paul


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Alph
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Re: Telescope Drive Master - The Truth of the Matter new [Re: psandelle]
      #4888562 - 10/30/11 01:05 PM

Quote:

The TDM is a one-step solution to a real problem, but it is pricey in some regards.




Tassilo,
Can you hear the voice of people? Lower the price by replacing the electronics box with a laptop. At least this should be an option.


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BlueGrass
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4888592 - 10/30/11 01:28 PM

Frankly, I would NOT spend another $2k on 'upgrading' my CGEM with this add-on. It is still a CGEM with all of its possible motor, PCB and HC failures. These reoccurring failures are posted here regularly.

The justification you refer to can be given in two words: Quality and Reliability.


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Stew57
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Re: Telescope Drive Master - The Truth of the Matter new [Re: BlueGrass]
      #4888644 - 10/30/11 02:13 PM

And poor support with 6 week minimum wait times!

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gdd
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4888692 - 10/30/11 02:35 PM

Quote:



Quote:
--------------------------------------------------------------------------------

The TDM is a one-step solution to a real problem, but it is pricey in some regards.


--------------------------------------------------------------------------------



Tassilo,
Can you hear the voice of people? Lower the price by replacing the electronics box with a laptop. At least this should be an option.





Hi Alph,

While I am sure that using a mass produced laptop that you probably already have is cheaper than the the electronic box, the real problem is the return on investment Tasillo must be able to make on a niche product to make it worth his time. Otherwise he would need to make his money elsewhere and treat the TDM as a hobby.

Gale


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dawziecat
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4888747 - 10/30/11 03:06 PM

At $2220 (incl an adapter for a G11), this is not going to be flying out the door.
I don't think the market will bear it. Without drastic price reduction, this thing will be a failure in the marketplace.

My opinion.


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harry page 1
sage


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Re: Telescope Drive Master - The Truth of the Matter new [Re: dawziecat]
      #4888801 - 10/30/11 03:27 PM

Hi
This hobby is not cheap and if you add up what a lot of us spend on cameras , mounts ,scopes . filters and software etc it is not beyond a lot of peoples budget.
Of course you can move the TDM from scope to scope so IMO it will do well

Regards Harry


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Phil Cowell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Stew57]
      #4888873 - 10/30/11 04:24 PM

Quote:

And poor support with 6 week minimum wait times!



Think yourself luck you didn't get a Gemini Goto. It was non-existent.


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gdd
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Re: Telescope Drive Master - The Truth of the Matter new [Re: harry page 1]
      #4888885 - 10/30/11 04:30 PM

For those who do not already have a big investment in autoguiding setups you can subtract the cost of all that from the $2200, especially if you plan on imaging only at moderate focal lengths. If you subtract the weight of autoguiding setups you can go with a larger OTA on the same mount and simplify balancing. The TDM should be accurate enough to work with adaptive optics for extremely high focal lengths.

Gale


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: BlueGrass]
      #4888891 - 10/30/11 04:33 PM

Quote:

Frankly, I would NOT spend another $2k on 'upgrading' my CGEM with this add-on. It is still a CGEM with all of its possible motor, PCB and HC failures. These reoccurring failures are posted here regularly.

The justification you refer to can be given in two words: Quality and Reliability.




That's why I went with the EQ6, that and EQMOD makes a tough to beat, reliable platform. Coupled with the TDM does it for me!

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: dawziecat]
      #4888961 - 10/30/11 05:05 PM

Quote:

At $2220 (incl an adapter for a G11), this is not going to be flying out the door.
I don't think the market will bear it. Without drastic price reduction, this thing will be a failure in the marketplace.

My opinion.




Are the AP 1200's and Paramount ME's flying out the doors? Are these mounts considered failures? How many years went by for these products before they were considered a success? Are they a success?

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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orlyandico
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4889162 - 10/30/11 07:23 PM

I in fact wonder if a single product like the AP1200 or PME actually make money..

Of coutse the difference is if you buy an AP1200 or PME (or AP3600..) you know what you're getting. It's like the difference between buying a Mercedes and a Ssangyong (unknown Korean car) with a licensed-from-Mercedes engine (and yes.. this car brand does exist.. and they do use Mercedes engine designs.. and they never sell anything).

OTOH, Ovision has all those pictures of AP mounts in Antarctica, so maybe they sell a lot of these to academic and research institutions.

w.r.t. TDM pricing, like I said I can't find the million-tick encoder for much below $900. So if the TDM is being sold at $1800.. I feel that the margin is perilously low already as it is.

One option is to sell just the control box for $500 (or, port it to a laptop and sell the software for $200) and then let the end-user look for their own Gurley or Renishaw. Then we'd all see how much less that would cost..


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David PavlichAdministrator
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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4889394 - 10/30/11 09:51 PM

Following this thread, I've come up with a thought. In my case, I have an MI250 that is controlled with a SiTech system. As it is, Pempro will not read the PE unless I install some sort of sensor on the worm and that isn't going to happen. So....

Is there some sort of software that will improve an already good mount as far as tracking goes? SiTech has the ability to create a pointing model with as many stars as I like. I'm assuming that this model is nothing more than a very accurate pointing model and not one that improves tracking. So...anything for me to consider?

David


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4889478 - 10/30/11 10:40 PM

Quote:

I in fact wonder if a single product like the AP1200 or PME actually make money..

Of coutse the difference is if you buy an AP1200 or PME (or AP3600..) you know what you're getting. It's like the difference between buying a Mercedes and a Ssangyong (unknown Korean car) with a licensed-from-Mercedes engine (and yes.. this car brand does exist.. and they do use Mercedes engine designs.. and they never sell anything).

OTOH, Ovision has all those pictures of AP mounts in Antarctica, so maybe they sell a lot of these to academic and research institutions.

w.r.t. TDM pricing, like I said I can't find the million-tick encoder for much below $900. So if the TDM is being sold at $1800.. I feel that the margin is perilously low already as it is.

One option is to sell just the control box for $500 (or, port it to a laptop and sell the software for $200) and then let the end-user look for their own Gurley or Renishaw. Then we'd all see how much less that would cost..




Just to let you in on some details, the encoder used for the TDM is a heidenhain rate encoder (not an absoute encoder) which is a 5000 cycle encoder. What this means is that the encoder does not only put out a digital signal, it also puts out sine/cosine signals which are analog. The way you boost an analog sine cosine signal from 5000 cycles per rev to 10,000,000 counts per rev is through a 14 bit a/d converter on each signal. This is why you can't just hook the encoder up to a laptop. You need a micro controller to read the sine/cosine signals convert it to digital and then do some calculatIons on the signals to calculate the rate of change of the signal. Then you scale that and figure out your rate error compared to a standard rate provided by a high accuracy digital clock (hardware). This is straight forward, but very hardware dependent, so you would never be able to put it on a laptop by itself.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va

Edited by Jerry Hubbell (10/30/11 10:43 PM)


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orlyandico
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4889502 - 10/30/11 10:54 PM

Jerry - interesting point.

As I noted in one of my prior posts, the only companies I know of which make million-tick encoders are Gurley, Renishaw, and (Dr. Johannes) Heidenhain. And yes, these high-tick encoders require an external decoder box to get the full resolution..

I didn't think a laptop (alone) could do it. But an external box with a quartz oven crystal timebase and an ADC could surely be manufactured for $200-$300.. besides which Arduino microcontrollers are dirt-cheap ($30).


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4889528 - 10/30/11 11:04 PM

Quote:

Jerry - interesting point.

As I noted in one of my prior posts, the only companies I know of which make million-tick encoders are Gurley, Renishaw, and (Dr. Johannes) Heidenhain. And yes, these high-tick encoders require an external decoder box to get the full resolution..

I didn't think a laptop (alone) could do it. But an external box with a quartz oven crystal timebase and an ADC could surely be manufactured for $200-$300.. besides which Arduino microcontrollers are dirt-cheap ($30).




I have done some work with PIC microcontrollers, and the Propeller chip from Parallax. They have some really cool tools and tons of documentation. I have thought about building my own encoder microcontroller system (similar to TDM) that would interface directly into EQMOD directly and provide a substitute signal for the stepper motor ring counter on the RA axis. That way it could be used with the pulse guide mode of correction which is more accurate than the ST4 interface. Maybe someday when I have the courage to start interfacing directly with my expensive encoder. I may have to buy an encoder to test on.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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orlyandico
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4889548 - 10/30/11 11:21 PM

Jerry.. the 48000 tick Gurleys can be had for $20

http://www.ebay.com/itm/New-Gurley-Precision-8125S-04096P-5P01-A18TQ-Encoder-/370341076692?pt=LH_DefaultDomain_0&hash=item563a0c5ed4#ht_2839wt_952


http://www.gurley.com/Encoders/PDF/825pdf/825pdf.pdf


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CounterWeight
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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4889808 - 10/31/11 06:36 AM

I've been looking at this as a possibility in my next GEM purchase (and have been stewing alternatives for a goof while now...) that's why I'm thankful for the review and positive posts from those who have actually used it.

I am glad it is 'as is'(yes, with the electronics box and encoders - about as 'kit level' as I care for) and not after being diluted by some marketing dept. person who decides - "ok now make 1/5 as good at 1/10 the cost"... I like that it is a pretty much self contained hardware solution.

This arrangement may be beneficial to the average user (the two that have actually used did not complain), simpler to support and warranty. More important though is it might make metrology errors less likely by being simple.

But sticking to what the unit is and does do-

Some intelligent discussion about tradeoffs in other existing products and performance.

As far as I understand the vendor TOS is that they can discuss their own products-

-direct quote from the CN TOS-
"In addition, vendors/manufacturers are to refrain from commenting on their competitor’s equipment (directly or indirectly). Please restrain your comments to products you manufacture or resell."


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harry page 1
sage


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Re: Telescope Drive Master - The Truth of the Matter new [Re: CounterWeight]
      #4890522 - 10/31/11 03:19 PM Attachment (43 downloads)

Hi

One of the great boons to me also for the TDM is simplicity of use , no hrs training or retraing your scope just switch it on and it just works .
I have just finished my first image with unguided 10 min subs Iris high res--- the seeing was a bit soft but I am enjoying the help TDM is giving me in aquiring my images
KInd Regards Harry

Edited by harry page 1 (10/31/11 03:20 PM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: harry page 1]
      #4890717 - 10/31/11 05:48 PM

Yepp! Congratulation, Harry!

One picture tells much more then one thousand words...

Attila


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Alph]
      #4890764 - 10/31/11 06:30 PM

Post deleted by David Pavlich

Edited by TDM (10/31/11 06:59 PM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4890798 - 10/31/11 06:53 PM

Hi Jerry,
Please excuse my ignorance.
I can't quite follow this thread.

Are you using PHD guiding with a guide camera at
the same time as you're using Telescope Drive Master? -

or is Telescope Drive Master a stand alone system of
software & encoder hardware using a guide camera
or not using a guide camera?


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: alpal]
      #4890845 - 10/31/11 07:35 PM

Quote:

Hi Jerry,
Please excuse my ignorance.
I can't quite follow this thread.

Are you using PHD guiding with a guide camera at
the same time as you're using Telescope Drive Master? -

or is Telescope Drive Master a stand alone system of
software & encoder hardware using a guide camera
or not using a guide camera?




Hello Alpal, no need to apologize. Our conversation does take place with some unstated assumptions and knowledge, it can be hard to follow sometimes. The TDM is more correctly a drive (Right Ascension axis) rate corrector.

It uses the ST4 Guide port to effect change in the nominal RA tracking rate of the mount to counter any PE in the mount, plus most, if not all, of the non-PE components of the mount's drive system. It uses a very high resolution encoder to measure the actual rate of the RA axis, and compares this to a very accurate hardware clock to control the drive rate to as close to Sidereal rate (or average King rate) as possible.

This system is integrated into the operation of the normal mount controller and does not use any camera system to provide feedback from the sky (star images). The fact that it uses the ST4 guide input may confuse some because the TDM makes an innovative use of this standard input that most mounts provide. The ST4 standard is an open interface to any rate correction system be it camera (sky feedback) based or internal standard based as the TDM is. To make it clear, I do not use any camera based autoguiding system (SSAG + PHD for example) to obtain the performance I am demonstrating here.

I hope this explains it for you.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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frolinmod
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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Ray Gralak]
      #4890989 - 10/31/11 09:05 PM

Post deleted by David Pavlich

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frolinmod
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4891012 - 10/31/11 09:22 PM

Quote:

....you can achieve same results with modest equipment.



Of course you can, particularly if you're highly experienced and highly skilled or very persistent and not easily frustrated.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4891044 - 10/31/11 09:48 PM

Quote:

The TDM is more correctly a drive (Right Ascension axis) rate corrector.




But guiding is necessary in dec anyway, no? Others may have perfect alignment and need no correction in dec but I never expect to achieve that myself.

So, TDM or no TDM, there has to be a guider in the system too.

So, I don't really see the advantage of this thing. It tracks perfectly in RA but you still need a guider for dec. What has been gained?


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Re: Telescope Drive Master - The Truth of the Matter new [Re: dawziecat]
      #4891053 - 10/31/11 09:54 PM

Quote:

So, I don't really see the advantage of this thing. It tracks perfectly in RA but you still need a guider for dec. What has been gained?





Doesn't it depend on the FL and length of exposure? If you stay within the capabilities of the TDM you gain simplicity and less equipment weight.

Gale

Edited by gdd (10/31/11 09:57 PM)


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: dawziecat]
      #4891168 - 10/31/11 10:53 PM

Quote:

Quote:

The TDM is more correctly a drive (Right Ascension axis) rate corrector.




But guiding is necessary in dec anyway, no? Others may have perfect alignment and need no correction in dec but I never expect to achieve that myself.

So, TDM or no TDM, there has to be a guider in the system too.

So, I don't really see the advantage of this thing. It tracks perfectly in RA but you still need a guider for dec. What has been gained?




I think you sell yourself short dawziecat, polar alignment is a skill like any other skill in astrophotography. There are excellent tools to help you achieve excellent polar alignment like AlignMaster as I have mentioned previously. I guess you haven't read my reasons for using the TDM. The key concept is SIMPLIFY.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4891192 - 10/31/11 11:08 PM

Quote:

Quote:

Hi Jerry,
Please excuse my ignorance.
I can't quite follow this thread.

Are you using PHD guiding with a guide camera at
the same time as you're using Telescope Drive Master? -

or is Telescope Drive Master a stand alone system of
software & encoder hardware using a guide camera
or not using a guide camera?




Hello Alpal, no need to apologize. Our conversation does take place with some unstated assumptions and knowledge, it can be hard to follow sometimes. The TDM is more correctly a drive (Right Ascension axis) rate corrector.

It uses the ST4 Guide port to effect change in the nominal RA tracking rate of the mount to counter any PE in the mount, plus most, if not all, of the non-PE components of the mount's drive system. It uses a very high resolution encoder to measure the actual rate of the RA axis, and compares this to a very accurate hardware clock to control the drive rate to as close to Sidereal rate (or average King rate) as possible.

This system is integrated into the operation of the normal mount controller and does not use any camera system to provide feedback from the sky (star images). The fact that it uses the ST4 guide input may confuse some because the TDM makes an innovative use of this standard input that most mounts provide. The ST4 standard is an open interface to any rate correction system be it camera (sky feedback) based or internal standard based as the TDM is. To make it clear, I do not use any camera based autoguiding system (SSAG + PHD for example) to obtain the performance I am demonstrating here.

I hope this explains it for you.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va




Thanks Jerry,
O.K. - now I understand -
I work with industrial closed loop control systems as a major part of my job.
I have never seen a system like Telescope Drive Master
except as part of what we call a nested loop.

In the case of a nested loop I would have expected the Telescope Drive Master system to be working inside
a PHD guiding loop so that it would further enhance the accuracy of the whole system.

I am surprised that it works so well as is.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: frolinmod]
      #4891215 - 10/31/11 11:21 PM

Quote:

Quote:

But, I'm sorry if this maybe throws a wrench into your list but my Paramount ME does not point very well with the supplied software. But I don't think it is the Paramount. I think the supplied software has a bug in it. If you would like to log onto my New Mexico Skies system with me and see on the next clear night maybe you can fix it for me! :-)))



If you're still running the original software that was supplied with your Paramount ME, then you're likely running some very old software.



I've been using TPoint for over 10 years. Actually, the older versions worked. That's about all I can say because of the ToS. I do not have SkyX/Tpoint supermodel plugin, but I shouldn't need it. Doesn't matter though, The software I use plate solves and corrects the position anyway.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: harry page 1]
      #4891232 - 10/31/11 11:33 PM

Quote:

Hi

One of the great boons to me also for the TDM is simplicity of use , no hrs training or retraing your scope just switch it on and it just works .
I have just finished my first image with unguided 10 min subs Iris high res--- the seeing was a bit soft but I am enjoying the help TDM is giving me in aquiring my images
KInd Regards Harry



Relatively good tracking Harry. About how much did the telescope mount cost for that 14" Newt?

-Ray


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Ray Gralak]
      #4891317 - 11/01/11 12:43 AM

Post deleted by David Pavlich

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Re: Telescope Drive Master - The Truth of the Matter new [Re: frolinmod]
      #4891341 - 11/01/11 01:42 AM

Terry,

I managed last week to "accidentally" get my polar alignment spot on, a task I doubt I will be able to repeat again any time soon.

It is doable with enough persistence. I found that PoleAlign max was a nice way to do it. I only had to do a couple of minutes of drift align to finally nail it spot on.

Remember my post about my guiding being in one axis only? I was getting corrections in the other axis, but they were minimal, you really had to zoom in on the scale to be able to see them clearly.

I wonder how well TDM will handle backlash.

Edited by Hilmi (11/01/11 02:03 AM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4891410 - 11/01/11 03:26 AM

Quote:

Quote:

Hi

One of the great boons to me also for the TDM is simplicity of use , no hrs training or retraing your scope just switch it on and it just works .
I have just finished my first image with unguided 10 min subs Iris high res--- the seeing was a bit soft but I am enjoying the help TDM is giving me in aquiring my images
KInd Regards Harry



Relatively good tracking Harry. About how much did the telescope mount cost for that 14" Newt?

-Ray




Relatively??? Compared to what? Would you be so kind to expound it in details?

Btw: AIP4Win can measure the elongation of the stars, so it is very easy to check the numbers.


Attila


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4891553 - 11/01/11 08:27 AM

Quote:

Quote:

Quote:

Hi

One of the great boons to me also for the TDM is simplicity of use , no hrs training or retraing your scope just switch it on and it just works .
I have just finished my first image with unguided 10 min subs Iris high res--- the seeing was a bit soft but I am enjoying the help TDM is giving me in aquiring my images
KInd Regards Harry



Relatively good tracking Harry. About how much did the telescope mount cost for that 14" Newt?

-Ray




Relatively??? Compared to what? Would you be so kind to expound it in details?

Btw: AIP4Win can measure the elongation of the stars, so it is very easy to check the numbers.


Attila




Hello Attila, just to add 2 cents here, in the image I provided a link to in my original message that started this thread, the elongation ranged from 0.022 to 0.048. More telling (for me) is that the astrometry performed on that image of Minor Planet 2001 LO7 (1800 sec total exposure) had a residual of only 0.06 arcsec (60 milli-arcseconds!).

This is based on over 400 stars used for the measurement using the UCAC3 database. This to me demonstrates how well the star images were formed using the TDM and the polar alignment I was able to obtain, regardless of the elongation values. Also, I did have a slight amount of tilt in my camera in that image.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: frolinmod]
      #4891586 - 11/01/11 08:50 AM

Post deleted by David Pavlich

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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4891607 - 11/01/11 09:06 AM

Quote:

Quote:

Quote:

Hi

One of the great boons to me also for the TDM is simplicity of use , no hrs training or retraing your scope just switch it on and it just works .
I have just finished my first image with unguided 10 min subs Iris high res--- the seeing was a bit soft but I am enjoying the help TDM is giving me in aquiring my images
KInd Regards Harry



Relatively good tracking Harry. About how much did the telescope mount cost for that 14" Newt?

-Ray




Relatively??? Compared to what? Would you be so kind to expound it in details?

Btw: AIP4Win can measure the elongation of the stars, so it is very easy to check the numbers.


Attila



Hi Attila,

The mount looks like it costs more than your average EQ6 so I was hoping to find out how about much was spent on the mount so I know which mount to compare it against. That said, I recall seeing 10-minute unguided images with a 20" RC (far greater focal length) on some mounts with round stars.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4891847 - 11/01/11 12:00 PM

Hi Attila,

For the lower tier mounts the TDM outperforms PEC and eliminates the need for guiding up to about a 2 arcsec image scale provided good PA. For a higher tier mount PEC alone will also allow you to image at the 2 arcsec image scale. Both lower tier and higher tier mounts will image at better than the 2 arcsec image scale with autoguiding and/or adaptive optics without TDM. Will TDM enhance the use of these other technologies? What is the best mix of TDM, PEC, autoguiding, and adaptive optics for lower and higher tier mounts for those seeking the best possible performance rather than simplicity?

Thanks,

Gale

Edited by gdd (11/01/11 12:02 PM)


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Ray Gralak]
      #4891968 - 11/01/11 01:12 PM

Post deleted by David Pavlich

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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4892116 - 11/01/11 02:36 PM

I have just been spending money renting on GRAS. I understand that all the GRAS scopes in New Mexico are on Paramount ME's. But in spite of that, even for 10-minute exposures they use guiding by default...

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harry page 1
sage


Reged: 07/25/09

Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4892389 - 11/01/11 04:51 PM

Hi Ray

The stepper kit cost me about Ģ1000 and the rest of the beast about Ģ2000 not the cheapest mount but not 10K either
The tracking I am getting now is better than I would ever dreamed of
Kind Regards Harry


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4892466 - 11/01/11 05:54 PM

Quote:


Hi Attila,

The mount looks like it costs more than your average EQ6 so I was hoping to find out how about much was spent on the mount so I know which mount to compare it against. That said, I recall seeing 10-minute unguided images with a 20" RC (far greater focal length) on some mounts with round stars.

-Ray




Ray,

you can find several unguided reference shots in my website taken by different mounts, different OTA and different focal length. One of them shows round stars with cca. 4m FL: 16" LX200ACF on Hungarian Fornax mount (not Paramount ME).

Attila


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Re: Telescope Drive Master - The Truth of the Matter new [Re: frolinmod]
      #4892672 - 11/01/11 07:55 PM

Quote:

Quote:

Because if so, I probably could break some of my software for you to "entice" you to upgrade!!



Ray, I thought all of your old software was broken and full of bugs. You've been fixing bugs and making enhancements for many years now. I seem to recall quite a few. I always run your latest and greatest and keep it up-to-date, not act like a stick in the mud.




OK, I think I found out who you are. So, I don't see you as a PEMPro user in my database but maybe I'm mistaken? So which software of mine are you talking about?

-Ray Gralak

Edited by David Pavlich (11/02/11 10:25 PM)


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MeadeEurope
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4893227 - 11/02/11 05:06 AM

Dear Ray,

the picture from Dennis di Cicco is in the october issue of Sky & Telescope.

Clear skies

Tassilo


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MeadeEurope
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4893230 - 11/02/11 05:09 AM

Dear Ray,

sorry, but thatīs not true. 5Hz is absolutely no problem.

Clear skies

Tassilo


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MeadeEurope
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4893233 - 11/02/11 05:16 AM

Dear Ray,

sorry, my statement was unprecise. I do not doubt your ability to extract a number from your readings. I doubt that this number has any meaning. However, comparing your extracted value to the number Jerry has posted does make no sense: you are only referring to the periodic part of the error, Jerry reports the complete error including the non-periodic terms, that you donīt have any data about.

Clear skies

Tassilo


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MeadeEurope
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Hilmi]
      #4893236 - 11/02/11 05:20 AM

Dear Hilmi,

isnīt passion what makes life worth living? I have never been much of a Zen type of guy...

Clear skies

Tassilo


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MeadeEurope
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4893242 - 11/02/11 05:30 AM

Dear Alph,

we do hear the voice - however the core of the system is a expensive part. Sacrificing accuracy is not in the german mind set, so we have to wait until the encoder gets cheaper. The box is not a big cost factor. There is also a BIG argument against the laptop (additional to the signal processing circurity that you have to have anyway): It consumes energy. I am a mobile guy - Munich is the most expensive part in germany. Nobody could afford a observatory within 70 miles. I do setup and polar align with the help of my laptop, using itīs internal batteries. Then I attach the DSLR, and my small 17Wh battery is dealing with mount, DSLR, TDM (160mA). Thatīs it, even in the coldes winter nights. I reload the battery on my trip home without any need to ever carry around big heavy batteries.

Clear skies

Tassilo


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Re: Telescope Drive Master - The Truth of the Matter new [Re: MeadeEurope]
      #4893379 - 11/02/11 08:52 AM

Quote:

Dear Ray,

the picture from Dennis di Cicco is in the october issue of Sky & Telescope.

Clear skies

Tassilo



OK, but do you have a link online somewhere with image details? It's hard to see star details in a magazine print.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: MeadeEurope]
      #4893401 - 11/02/11 09:15 AM

Dear Tassilo,
Quote:

Dear Ray,

sorry, my statement was unprecise. I do not doubt your ability to extract a number from your readings. I doubt that this number has any meaning. However, comparing your extracted value to the number Jerry has posted does make no sense: you are only referring to the periodic part of the error, Jerry reports the complete error including the non-periodic terms, that you donīt have any data about.

Clear skies

Tassilo



The method works because each position of the worm is sampled 8 times thus averaging the effects of seeing at each point in the worm. And, importantly, the number comes from over-sampling the worm cycle 8 times (8 worm cycles) against an actual star.

The RMS error calculated was about 0.3 arc-secs which represents the total accumulated error *including* seeing across 2500 samples. The RMS error includes all tracking errors after subtracting the best-fit periodic error curve.

BTW, does the TDM measure tracking rate internally, or against a star? If it is internal, then how can you be sure of its accuracy? Any slight timing variation would not show up in the tracking data. For instance could dropping temperature during the night cause the actual tracking rate to change slightly? It would be an interesting experiment if I could get one. By the way, I tried emailing Explore Scientific about obtaining one of these units, but no one replied.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: MeadeEurope]
      #4893411 - 11/02/11 09:23 AM

Quote:

Dear Ray,

sorry, but thatīs not true. 5Hz is absolutely no problem.

Clear skies

Tassilo



Tassilo, I don't want to argue with you but I think you are misapplying the Nyquist theorem if you think that. If movements can happen up to 5 times per second (5 Hz) then maximum corrected frequency is 1/2 that, or 2.5 Hz. I'm not saying this is a bad thing. It's actually quite good.

And, by the way, even Atilla quoted 2.5Hz in another post in this thread:

http://www.cloudynights.com/ubbthreads/showthreaded.php?Cat=0&Board=lxd55&Number=4892439

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4893580 - 11/02/11 10:52 AM

Dear Ray,

as I said, I understand how you did it. But by using more than one cycle you loose the nonperiodic errors.
We know that TDM readings are corresponding to star movements because of several people who did verify this with a webcam. Your question is of course very valid, since we didnīt mention that here, but this is no problem. I donīt know if Jerry did this, and my other sources are in german (including the test report in the german magazine Sterne und Weltraum), so I cannot post them here. But it has been done with positive results.

Clear skies

Tassilo


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Re: Telescope Drive Master - The Truth of the Matter new [Re: MeadeEurope]
      #4893659 - 11/02/11 11:42 AM

Quote:

Dear Ray,

as I said, I understand how you did it. But by using more than one cycle you loose the nonperiodic errors.
We know that TDM readings are corresponding to star movements because of several people who did verify this with a webcam. Your question is of course very valid, since we didnīt mention that here, but this is no problem. I donīt know if Jerry did this, and my other sources are in german (including the test report in the german magazine Sterne und Weltraum), so I cannot post them here. But it has been done with positive results.

Clear skies

Tassilo




Tassilo, Ray, I have not (as yet) compared the star PE with the encoder base TE that the TDM provides. To satisfy those who doubt Attila's fine work demonstrated in the image linked below, I will try and obtain some data the next time I am out observing (perhaps tonight) to compare to Attila's data as shown in this previous message.

http://www.cloudynights.com/ubbthreads/showthreaded.php?Cat=0&Board=lxd55&Number=4886739

I will setup my guidescope and camera and set the camera to acquire star image data as fast as I can. I will try and do this for a bright star of course. I use PHD with my guide camera so if I can acquire data at a 5 Hz rate from my camera I will use that data to compare directly with the TDM encoder data. My version of the firmware and custom software allows me to acquire TDM data at a faster rate of 12.5 Hz. I can statistically compare the TDM data to the star data and hopefully separate the seeing from the actual tracking performance in the star data.

Ray, you quote performance as an RMS value (0.3 arcsec, I believe), where I quote performance statistically at a 2 sigma level (95% of the samples within the range calculated) of +/- 0.7 arcsec for my mount. In my paper I equate this to an RMS value of 0.12 measured with an EQMOD utility PEC Prep. If we scale your RMS value to a 95% 2 sigma equivalent value, that would make your measurement equal to +/- 1.75 arcsec or 3.5 arcsec peak to peak. This seems reasonable to me based on what your seeing may have been at the time.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4893714 - 11/02/11 12:08 PM

Quote:

Quote:

Dear Ray,

as I said, I understand how you did it. But by using more than one cycle you loose the nonperiodic errors.
We know that TDM readings are corresponding to star movements because of several people who did verify this with a webcam. Your question is of course very valid, since we didnīt mention that here, but this is no problem. I donīt know if Jerry did this, and my other sources are in german (including the test report in the german magazine Sterne und Weltraum), so I cannot post them here. But it has been done with positive results.

Clear skies

Tassilo




Tassilo, Ray, I have not (as yet) compared the star PE with the encoder base TE that the TDM provides. To satisfy those who doubt Attila's fine work demonstrated in the image linked below, I will try and obtain some data the next time I am out observing (perhaps tonight) to compare to Attila's data as shown in this previous message.

http://www.cloudynights.com/ubbthreads/showthreaded.php?Cat=0&Board=lxd55&Number=4886739

I will setup my guidescope and camera and set the camera to acquire star image data as fast as I can. I will try and do this for a bright star of course. I use PHD with my guide camera so if I can acquire data at a 5 Hz rate from my camera I will use that data to compare directly with the TDM encoder data. My version of the firmware and custom software allows me to acquire TDM data at a faster rate of 12.5 Hz. I can statistically compare the TDM data to the star data and hopefully separate the seeing from the actual tracking performance in the star data.

Ray, you quote performance as an RMS value (0.3 arcsec, I believe), where I quote performance statistically at a 2 sigma level (95% of the samples within the range calculated) of +/- 0.7 arcsec for my mount. In my paper I equate this to an RMS value of 0.12 measured with an EQMOD utility PEC Prep. If we scale your RMS value to a 95% 2 sigma equivalent value, that would make your measurement equal to +/- 1.75 arcsec or 3.5 arcsec peak to peak. This seems reasonable to me based on what your seeing may have been at the time.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va



Jerry, sorry but I think that's completely wrong (your conclusion of 3.5 arcsec peak to peak). The RMS value I quoted is the measurement of the random error *after* PE is subtracted, not a measurement of the error of the PE or tracking itself. Because the nature of periodic error is known (I.e. sine wave) the fitted PE curve was calculated with 2500 points over 8 worm cycles. This results in extremely good accuracy of periodic error, probably less than 10% error on +/- 0.2 arc-secs. The RMS error accounts for excursions in seeing, which could be completely different at your site than mine, so that in itself doesn't mean anything. What it does mean something is that my mount has negligible PE and excellent tracking without having to add an encoder!

Also, I don't think I would believe the values quoted from the freeware app, PEC Prep, because I believe it includes all frequencies, including non-existant fundamentals which then calculates an RMS value after subtracting those. I could use PEMPro to fit an arbitrary number of frequencies and get a super low RMS number too. If you recorded with PEMPro an unchecked all fundamental frequencies that would be sort of an apples to apples comparison (except for different site conditions and equipment). Still it's a very hard comparison to make, that's why I centered my answer on the excellent tracking that a higher end mount can provide without resorting to an encoder.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: MeadeEurope]
      #4893730 - 11/02/11 12:16 PM

Quote:

Dear Ray,

as I said, I understand how you did it. But by using more than one cycle you loose the nonperiodic errors.
We know that TDM readings are corresponding to star movements because of several people who did verify this with a webcam. Your question is of course very valid, since we didnīt mention that here, but this is no problem. I donīt know if Jerry did this, and my other sources are in german (including the test report in the german magazine Sterne und Weltraum), so I cannot post them here. But it has been done with positive results.

Clear skies

Tassilo



No, I did not lose non-periodic errors. They are entirely contained 2500 centroid points capture and calculated to be RMS 0.3 arc-sec (residual value) after subtracting periodic error. The RMS includes all tracking errors from non-periodic terms and seeing.

Just so you understand how small this error is, one pixel of my CCD is about 2 arc-secs! Tracking is perfect enough that it cannot be seen visually. Only when measured over hundreds (or thousands) of short exposures can it be calculated.

-Ray

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4893800 - 11/02/11 12:44 PM

Quote:

Jerry, sorry but I think that's completely wrong (your conclusion of 3.5 arcsec peak to peak). The RMS value I quoted is the measurement of the random error *after* PE is subtracted, not a measurement of the error of the PE or tracking itself. Because the nature of periodic error is known (I.e. sine wave) the fitted PE curve was calculated with 2500 points over 8 worm cycles. This results in extremely good accuracy of periodic error, probably less than 10% error on +/- 0.2 arc-secs. The RMS error accounts for excursions in seeing, which could be completely different at your site than mine, so that in itself doesn't mean anything. What it does mean something is that my mount has negligible PE and excellent tracking without having to add an encoder!

Also, I don't think I would believe the values quoted from the freeware app, PEC Prep, because I believe it includes all frequencies, including non-existant fundamentals which then calculates an RMS value after subtracting those. I could use PEMPro to fit an arbitrary number of frequencies and get a super low RMS number too. If you recorded with PEMPro an unchecked all fundamental frequencies that would be sort of an apples to apples comparison (except for different site conditions and equipment). Still it's a very hard comparison to make, that's why I centered my answer on the excellent tracking that a higher end mount can provide without resorting to an encoder.

-Ray




Hi Ray,
I disagree, I guess this is one of those unstated assumptions in our discussion. I *did* consider your number, 0.3 arcsec RMS, as a residual *After* the PE was removed. Just as the number I am quoting for my mount is the residual TE after being corrected by the TDM. I have no reason to believe the RMS calculation in PEC Prep is in error. I am not trying to set you up to violate your agreement to not comment on other vendor's products since I believe PEC Prep is open source. .

Normally the RMS value of a noise signal is equal to basically 1 sigma of the noise. In my case, RMS = 0.35 arcsec.

but in the PEC Prep, and in other things I have read, the RMS is quoted as something like this:


RMS is roughly equal to the absolute value of the 1 sigma value for noise measured in a raw signal divided by 2 x sqrt(2).
So for example, I quoted +/- 0.7 arcsec for my 2 sigma value. The 1 sigma value would be +/- 0.35 arcsec. So,

RMS = abs(+/- 0.35 arcsec) / 2.828
RMS = 0.124 arcsec

So, that is why I suggested the peak to peak value for your RMS value of 0.3 arcsec.

I guess if you can provide a value for your 2 sigma peak to peak value that is equivalent to the 0.3 arcsec RMS value you are quoting then we can compare apples to apples.

Of course there will be issues with differences in seeing at different sites, times, etc. but there is not a lot we can do to get around that.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va

Edited by Jerry Hubbell (11/02/11 12:59 PM)


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Jerry Hubbell]
      #4893825 - 11/02/11 12:58 PM

Post deleted by David Pavlich

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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4893836 - 11/02/11 01:03 PM

Hey Ray, I added some text to the message you responded to. I wanted to make it clear that the strict calculation for RMS in a noise signal is equal to the 1 sigma of the noise.

This is NOT what PEC Prep or PHD uses (I don't believe) and this may be related to the impact the noise actually has on the image, and it is equivalent to an RMS value that PEC Prep or PHD provides.

When I get the PHD data, I can email it to you if you like

Jerry Hubbell


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4893862 - 11/02/11 01:17 PM

Quote:


I guess if you can provide a value for your 2 sigma peak to peak value that is equivalent to the 0.3 arcsec RMS value you are quoting then we can compare apples to apples.

Of course there will be issues with differences in seeing at different sites, times, etc. but there is not a lot we can do to get around that.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va



Just one more point about this... the RMS value for both cases includes seeing and non-periodic tracking errors. There is no way to separate non-periodic tracking errors from seeing because they are both random.

But, let's not forget that it is totally irrelevant anyway because it is well known that perfect sidereal tracking does NOT match the apparent tracking rate in almost every case. There is almost always dec drift and non-sidereal drift from refraction, polar alignment errors, and flexure. Without a doubt to obtain the best possible unguided performance you need to be able to track at non-sidereal rate in RA and non-zero rate in declination. And a Right Ascension King's rate only addresses the RA axis approximately. Note that refraction causes an apparent non-zero dec rate as well.

So, what I'm saying, is that perfect RA tracking will not always give you perfect unguided images. Expose long enough at any reasonably long focal length and you'll see trailing. This doesn't mean there is anything wrong with an encoder solution. It just isn't the complete solution, just like PEC only addresses periodic error and not RA/Dec drift from other sources, so does an RA encoder only address RA tracking issues relative to sidereal.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4893863 - 11/02/11 01:17 PM

Quote:

Hey Ray, I added some text to the message you responded to. I wanted to make it clear that the strict calculation for RMS in a noise signal is equal to the 1 sigma of the noise.

This is NOT what PEC Prep or PHD uses (I don't believe) and this may be related to the impact the noise actually has on the image, and it is equivalent to an RMS value that PEC Prep or PHD provides.

When I get the PHD data, I can email it to you if you like

Jerry Hubbell




After thinking about this for a few minutes, the impact that the TE/PE has on an image must not be considered in only one dimension, it really applies to 2 dimensions, so when you apply the random changes measured in one dimension (RA Axis) and apply it to two dimensions, you probably have to calculate the equivalent RMS in a 2 dimensional space to make sense of it as it applies to a 2 dimensional image. This may be why there is a difference.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Reged: 06/18/08

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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4893887 - 11/02/11 01:27 PM

That's it! I say we build a cage, get the two of youse inside with some mounts and scopes and GET READY TO RUMBLE!

Actually, this is all great stuff for me - learning a lot (or at least thinking a lot, not sure how much is being absorbed into what's left of my little grey cells after copious amounts of vodka over the years.

It's very obvious that I need someone to make a mount that DOES IT ALL because if I have to think too much about what y'all are talkin' about for too long, my head explodes.

Thanks everyone for good info and a civil discussion I can follow.

Paul


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4893935 - 11/02/11 01:58 PM

Quote:

Quote:


I guess if you can provide a value for your 2 sigma peak to peak value that is equivalent to the 0.3 arcsec RMS value you are quoting then we can compare apples to apples.

Of course there will be issues with differences in seeing at different sites, times, etc. but there is not a lot we can do to get around that.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va



Just one more point about this... the RMS value for both cases includes seeing and non-periodic tracking errors. There is no way to separate non-periodic tracking errors from seeing because they are both random.

But, let's not forget that it is totally irrelevant anyway because it is well known that perfect sidereal tracking does NOT match the apparent tracking rate in almost every case. There is almost always dec drift and non-sidereal drift from refraction, polar alignment errors, and flexure. Without a doubt to obtain the best possible unguided performance you need to be able to track at non-sidereal rate in RA and non-zero rate in declination. And a Right Ascension King's rate only addresses the RA axis approximately. Note that refraction causes an apparent non-zero dec rate as well.

So, what I'm saying, is that perfect RA tracking will not always give you perfect unguided images. Expose long enough at any reasonably long focal length and you'll see trailing. This doesn't mean there is anything wrong with an encoder solution. It just isn't the complete solution, just like PEC only addresses periodic error and not RA/Dec drift from other sources, so does an RA encoder only address RA tracking issues relative to sidereal.

-Ray




Hey Ray,
You raise some interesting points. I am thinking that these effects can be analyzed in different ways: effects can be lumped together depending on their source, effects can be separated by time constant (frequency). I have in mind the following model for analyzing this problem. The main premise for my model is this:

Sidereal rate is based on the Earth's revolution rate and is therefore a fixed value. This is the fundamental rate that the internal tracking for a mount should rely on. Every other effect (mount periodic and non-periodic errors, flexure, seeing, atmospheric refraction, polar alignment DEC drift, temperature effects on focus, etc.) adds layers of complexity to this fundamental. I like the TDM because it is based on this model, and makes logical sense to me.

Now, these effects can be considered either random, i.e. seeing and flexure, or a bias, i.e. DEC drift, Temperature effects. I choose to start with the fundamental that a fixed rate as provided by a high quality crystal oscillator is the best reference you can have, regardless of any small temperature effect. Flexure and Seeing are random effects that are generally in the (relatively) high frequency range of 5-20 Hz. This is not the realm of the TDM. TDM is designed to solve 2 of these issues, First, it provides a very precise reference that matches the fundamental requirement of the model, Sidereal Rate Tracking. Then it uses the encoder to measure the periodic and non-periodic errors in the mount with the sidereal rate as a reference.

Once this is done, then we have to deal with seeing, flexure, and refractive errors. Seeing and flexure are similar in that they are random and high frequency. Flexure is also intermittant. These are not handled by TDM, and is not handled by a guide camera either.

That leaves refractive errors. This is a long term effect that on the TDM is handled through the use of the average King Rate vs using the Sidereal Rate. Guide cameras correct for this real-time via the fact that the camera is tracking a star.

As an aside, PEC is designed to correct only for periodic error and some fundamentals of gear frequencies also. Any non-periodic error is not handled.

DEC drift is a bias error, and is not handled by the TDM, it is considered a characteristic of the mount in this model called Polar Alignment. This is why DEC drift when using the TDM can only be corrected by an accurate polar alignment.

Finally we have temperature effects. I have yet to analyze this error, and up to this point have considered it as being a very small issue. One reason I consider it to be very small is because it is a very slow effect that does not impact your images unless you are making exposures > 20 minutes in my estimation.

I hope this gives you and the members some insight into my thinking and why I think the TDM is a better route to higher quality imaging.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4893959 - 11/02/11 02:17 PM

Quote:


Hey Ray,
You raise some interesting points. I am thinking that these effects can be analyzed in different ways: effects can be lumped together depending on their source, effects can be separated by time constant (frequency). I have in mind the following model for analyzing this problem. The main premise for my model is this:

Sidereal rate is based on the Earth's revolution rate and is therefore a fixed value. This is the fundamental rate that the internal tracking for a mount should rely on. Every other effect (mount periodic and non-periodic errors, flexure, seeing, atmospheric refraction, polar alignment DEC drift, temperature effects on focus, etc.) adds layers of complexity to this fundamental. I like the TDM because it is based on this model, and makes logical sense to me.

Now, these effects can be considered either random, i.e. seeing and flexure, or a bias, i.e. DEC drift, Temperature effects. I choose to start with the fundamental that a fixed rate as provided by a high quality crystal oscillator is the best reference you can have, regardless of any small temperature effect. Flexure and Seeing are random effects that are generally in the (relatively) high frequency range of 5-20 Hz. This is not the realm of the TDM. TDM is designed to solve 2 of these issues, First, it provides a very precise reference that matches the fundamental requirement of the model, Sidereal Rate Tracking. Then it uses the encoder to measure the periodic and non-periodic errors in the mount with the sidereal rate as a reference.

Once this is done, then we have to deal with seeing, flexure, and refractive errors. Seeing and flexure are similar in that they are random and high frequency. Flexure is also intermittant. These are not handled by TDM, and is not handled by a guide camera either.

That leaves refractive errors. This is a long term effect that on the TDM is handled through the use of the average King Rate vs using the Sidereal Rate. Guide cameras correct for this real-time via the fact that the camera is tracking a star.

As an aside, PEC is designed to correct only for periodic error and some fundamentals of gear frequencies also. Any non-periodic error is not handled.

DEC drift is a bias error, and is not handled by the TDM, it is considered a characteristic of the mount in this model called Polar Alignment. This is why DEC drift when using the TDM can only be corrected by an accurate polar alignment.

Finally we have temperature effects. I have yet to analyze this error, and up to this point have considered it as being a very small issue. One reason I consider it to be very small is because it is a very slow effect that does not impact your images unless you are making exposures > 20 minutes in my estimation.

I hope this gives you and the members some insight into my thinking and why I think the TDM is a better route to higher quality imaging.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va




Jerry, most flexure is not random. Maybe you are thinking of vibration?

Mechanical flexure is caused by gravity. It can change the telescope pointing position subtly based on the 3-dimensional position of the telescope. Because the amount of mechanical flexure changes as the telecope tracks this imparts an apparent RA/Dec drift as seen by a perfectly tracking telescope. Flexure usually can be accurately modeled, which allows pointing correction programs to subtract it out.

Sources of flexure are things like the OTA drooping, the camera drooping, and pier/tripod/mount mechanical flexure. But again, the important thing to us is that it changes as the telescope position changes. When magnified by the incredible image scale of the telescope it causes subtle apparent drift relative to perfect sidereal tracking.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4893975 - 11/02/11 02:27 PM

Quote:

Quote:


Hey Ray,
You raise some interesting points. I am thinking that these effects can be analyzed in different ways: effects can be lumped together depending on their source, effects can be separated by time constant (frequency). I have in mind the following model for analyzing this problem. The main premise for my model is this:

Sidereal rate is based on the Earth's revolution rate and is therefore a fixed value. This is the fundamental rate that the internal tracking for a mount should rely on. Every other effect (mount periodic and non-periodic errors, flexure, seeing, atmospheric refraction, polar alignment DEC drift, temperature effects on focus, etc.) adds layers of complexity to this fundamental. I like the TDM because it is based on this model, and makes logical sense to me.

Now, these effects can be considered either random, i.e. seeing and flexure, or a bias, i.e. DEC drift, Temperature effects. I choose to start with the fundamental that a fixed rate as provided by a high quality crystal oscillator is the best reference you can have, regardless of any small temperature effect. Flexure and Seeing are random effects that are generally in the (relatively) high frequency range of 5-20 Hz. This is not the realm of the TDM. TDM is designed to solve 2 of these issues, First, it provides a very precise reference that matches the fundamental requirement of the model, Sidereal Rate Tracking. Then it uses the encoder to measure the periodic and non-periodic errors in the mount with the sidereal rate as a reference.

Once this is done, then we have to deal with seeing, flexure, and refractive errors. Seeing and flexure are similar in that they are random and high frequency. Flexure is also intermittant. These are not handled by TDM, and is not handled by a guide camera either.

That leaves refractive errors. This is a long term effect that on the TDM is handled through the use of the average King Rate vs using the Sidereal Rate. Guide cameras correct for this real-time via the fact that the camera is tracking a star.

As an aside, PEC is designed to correct only for periodic error and some fundamentals of gear frequencies also. Any non-periodic error is not handled.

DEC drift is a bias error, and is not handled by the TDM, it is considered a characteristic of the mount in this model called Polar Alignment. This is why DEC drift when using the TDM can only be corrected by an accurate polar alignment.

Finally we have temperature effects. I have yet to analyze this error, and up to this point have considered it as being a very small issue. One reason I consider it to be very small is because it is a very slow effect that does not impact your images unless you are making exposures > 20 minutes in my estimation.

I hope this gives you and the members some insight into my thinking and why I think the TDM is a better route to higher quality imaging.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va




Jerry, most flexure is not random. Maybe you are thinking of vibration?

Mechanical flexure is caused by gravity. It can change the telescope pointing position subtly based on the 3-dimensional position of the telescope. Because the amount of mechanical flexure changes as the telecope tracks this imparts an apparent RA/Dec drift as seen by a perfectly tracking telescope. Flexure usually can be accurately modeled, which allows pointing correction programs to subtract it out.

Sources of flexure are things like the OTA drooping, the camera drooping, and pier/tripod/mount mechanical flexure. But again, the important thing to us is that it changes as the telescope position changes. When magnified by the incredible image scale of the telescope it causes subtle apparent drift relative to perfect sidereal tracking.

-Ray




Thanks Ray, I just learned something from you. I always considered flexure as a random event in terms of being non-repeatable and intermittant in time. If it is correlated with telescope position then this is a good thing. I am curious though on how repeatable it is with the lower end mounts where if you have flexure it *seems* to be very random because of the lesser quality materials/construction. This is okay because it is *easier* (in my mind) to correct for flexure in smaller systems, then modeling does not provide the value that it would on larger/heavier mounts. I can very much understand that large systems (50-200 kg) can very much benefit from flexure modeling, but if we are talking about small systems where the loads are < 15 Kg then it is much more practical to just use higher quality mounting hardware and tighten/support everything as much as possible. Getting rid of the guide scope goes a long way to getting rid of flexure

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va

Edited by Jerry Hubbell (11/02/11 03:36 PM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4894025 - 11/02/11 03:01 PM

From http://www.astro-physics.com/products/mounts/3600gto/precision-encoder-complete.pdf

"The 3600 PE is specified to be equal to or less than 5 arc seconds. One can use PEM to correct for this small error, but this does not fully guarantee that you can have long term sub-arc second tracking on every worm cycle. This is where the auxiliary precision encoder comes in. Since it is attached to the output worm wheel itself, the pulses from this encoder can be used to gauge the speed exactly. At the sidereal rate, there are approximately 170 pulses per second coming from this large encoder ring, so it is able to resolve sub-arc second speed errors to a high degree of accuracy."

"Basically, the encoder is simply a finely divided ring of 9" diameter with a pickup consisting of laser and pin diode receiver. The pickup has a resolution of 0.09 arc seconds and the encoder ring itself has a guaranteed accuracy of +/- 0.97 arc seconds for the entire 24 hour period."

170 pulses/second * 86400 = 1.5 Million tick encoder

This is the $6000+ option! (base AP3600 = 19900, with precision encoder = 26700)

The document linked does talk about where the encoder would be useful, even with a sophisticated pointing model.

So there must be something to this RA encoder thing.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4894047 - 11/02/11 03:09 PM

Quote:

From http://www.astro-physics.com/products/mounts/3600gto/precision-encoder-complete.pdf

"The 3600 PE is specified to be equal to or less than 5 arc seconds. One can use PEM to correct for this small error, but this does not fully guarantee that you can have long term sub-arc second tracking on every worm cycle. This is where the auxiliary precision encoder comes in. Since it is attached to the output worm wheel itself, the pulses from this encoder can be used to gauge the speed exactly. At the sidereal rate, there are approximately 170 pulses per second coming from this large encoder ring, so it is able to resolve sub-arc second speed errors to a high degree of accuracy."

"Basically, the encoder is simply a finely divided ring of 9" diameter with a pickup consisting of laser and pin diode receiver. The pickup has a resolution of 0.09 arc seconds and the encoder ring itself has a guaranteed accuracy of +/- 0.97 arc seconds for the entire 24 hour period."

170 pulses/second * 86400 = 1.5 Million tick encoder

This is the $6000+ option! (base AP3600 = 19900, with precision encoder = 26700)

The document linked does talk about where the encoder would be useful, even with a sophisticated pointing model.

So there must be something to this RA encoder thing.





Dang! you got to the punchline already!

If it's useful at 3 times the cost, just think how useful it would be at 1/3rd the cost

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4894073 - 11/02/11 03:25 PM

As far as temperature effects on the reference Sidereal rate clock on the TDM, this is from the wikipedia article on crystal oscillators:

Temperature effects: crystal's frequency characteristic depends on the shape or 'cut' of the crystal. A tuning fork crystal is usually cut such that its frequency over temperature is a parabolic curve centered around 25 °C. This means that a tuning fork crystal oscillator will resonate close to its target frequency at room temperature, but will slow down when the temperature either increases or decreases from room temperature. A common parabolic coefficient for a 32 kHz tuning fork crystal is &#8722;0.04 ppm/°Cē.

http://en.wikipedia.org/wiki/Crystal_oscillator#Temperature_effects

I don't think that at .04 ppm/degC we have to worry about the reference being off by very much, LOL. I didn't realize they were that precise.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4894102 - 11/02/11 03:40 PM

Quote:

Thanks Ray, I just learned something from you. I always considered flexure as a random event in terms of being non-repeatable and intermittant in time. If it is correlated with telescope position then this is a good thing. I am curious though on how repeatable it is with the lower end mounts where if you have flexure it *seems* to be very random because of the lesser quality materials/construction. This is okay because it is *easier* (in my mind) to correct for flexure in smaller systems, then modeling does not provide the value that it would on larger/heavier mounts. I can very much understand that large systems (100-500 kg) can very much benefit from flexure modeling, but if we are talking about small systems where the loads are < 30 Kg then it is much more practical to just use higher quality mounting hardware and tighten/support everything as much as possible. Getting rid of the guide scope goes a long way to getting rid of flexure






A number of mounts have modeling software independent of PEC to handle flexure of the mount and the imaging setup in a particular configuration. Shouldn't this software work in the same manner with TDM? Modeling with TDM installed may be even more accurate because the mounts movements are already smoothed out.

Gale


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4894114 - 11/02/11 03:45 PM Attachment (59 downloads)

Hi

I leave all the techy stuff to people who understand it I.e not Me

For Rest of the people watching this is a trace image from AA5 that I took from my autoguider fixed up of axis wise and at 1350 FL. This is a 10 min sub and of course the scope was not being guided I just used it to gather the DATA
Image scale is 1.33 arc sec per pixel

KInd Regards Harry


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Re: Telescope Drive Master - The Truth of the Matter new [Re: harry page 1]
      #4894122 - 11/02/11 03:48 PM

Quote:

Hi

I leave all the techy stuff to people who understand it I.e not Me

For Rest of the people watching this is a trace image from AA5 that I took from my autoguider fixed up of axis wise and at 1350 FL. This is a 10 min sub and of course the scope was not being guided I just used it to gather the DATA
Image scale is 1.33 arc sec per pixel

KInd Regards Harry




That's Cool Harry! I like that display. This is a good indication of what we are discussing.

Thanks

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4894221 - 11/02/11 04:44 PM

Quote:

Dang! you got to the punchline already!

If it's useful at 3 times the cost, just think how useful it would be at 1/3rd the cost



I think it is closer to 10 times the cost of Atlas, CGEM and alike.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: harry page 1]
      #4894223 - 11/02/11 04:47 PM

Quote:


For Rest of the people watching this is a trace image from AA5



Are you referring to this one
http://en.wikipedia.org/wiki/Grumman_American_AA-5


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4894291 - 11/02/11 05:34 PM

Quote:

Quote:


For Rest of the people watching this is a trace image from AA5



Are you referring to this one
http://en.wikipedia.org/wiki/Grumman_American_AA-5





Not really I think...
This one seems to be a better approach:
Astro Art v5

(Maxim DL competitor)

Attila

Edited by TDM (11/02/11 05:37 PM)


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Alph]
      #4894411 - 11/02/11 06:33 PM

Post deleted by Jerry Hubbell

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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4894624 - 11/02/11 08:33 PM

Re: 1/3rd the cost: I think Jerry is referring to the fact that the encoder option on the El Capitan costs $6000+ (so the TDM is 1/3rd the cost).

In other words the AP3600 encoder costs as much as a Mach1! (which costs 4X as much as an Atlas)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4894960 - 11/02/11 11:52 PM

Quote:

Quote:

Quote:


Hey Ray,
You raise some interesting points. I am thinking that these effects can be analyzed in different ways: effects can be lumped together depending on their source, effects can be separated by time constant (frequency). I have in mind the following model for analyzing this problem. The main premise for my model is this:

Sidereal rate is based on the Earth's revolution rate and is therefore a fixed value. This is the fundamental rate that the internal tracking for a mount should rely on. Every other effect (mount periodic and non-periodic errors, flexure, seeing, atmospheric refraction, polar alignment DEC drift, temperature effects on focus, etc.) adds layers of complexity to this fundamental. I like the TDM because it is based on this model, and makes logical sense to me.

Now, these effects can be considered either random, i.e. seeing and flexure, or a bias, i.e. DEC drift, Temperature effects. I choose to start with the fundamental that a fixed rate as provided by a high quality crystal oscillator is the best reference you can have, regardless of any small temperature effect. Flexure and Seeing are random effects that are generally in the (relatively) high frequency range of 5-20 Hz. This is not the realm of the TDM. TDM is designed to solve 2 of these issues, First, it provides a very precise reference that matches the fundamental requirement of the model, Sidereal Rate Tracking. Then it uses the encoder to measure the periodic and non-periodic errors in the mount with the sidereal rate as a reference.

Once this is done, then we have to deal with seeing, flexure, and refractive errors. Seeing and flexure are similar in that they are random and high frequency. Flexure is also intermittant. These are not handled by TDM, and is not handled by a guide camera either.

That leaves refractive errors. This is a long term effect that on the TDM is handled through the use of the average King Rate vs using the Sidereal Rate. Guide cameras correct for this real-time via the fact that the camera is tracking a star.

As an aside, PEC is designed to correct only for periodic error and some fundamentals of gear frequencies also. Any non-periodic error is not handled.

DEC drift is a bias error, and is not handled by the TDM, it is considered a characteristic of the mount in this model called Polar Alignment. This is why DEC drift when using the TDM can only be corrected by an accurate polar alignment.

Finally we have temperature effects. I have yet to analyze this error, and up to this point have considered it as being a very small issue. One reason I consider it to be very small is because it is a very slow effect that does not impact your images unless you are making exposures > 20 minutes in my estimation.

I hope this gives you and the members some insight into my thinking and why I think the TDM is a better route to higher quality imaging.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va




Jerry, most flexure is not random. Maybe you are thinking of vibration?

Mechanical flexure is caused by gravity. It can change the telescope pointing position subtly based on the 3-dimensional position of the telescope. Because the amount of mechanical flexure changes as the telecope tracks this imparts an apparent RA/Dec drift as seen by a perfectly tracking telescope. Flexure usually can be accurately modeled, which allows pointing correction programs to subtract it out.

Sources of flexure are things like the OTA drooping, the camera drooping, and pier/tripod/mount mechanical flexure. But again, the important thing to us is that it changes as the telescope position changes. When magnified by the incredible image scale of the telescope it causes subtle apparent drift relative to perfect sidereal tracking.

-Ray




Thanks Ray, I just learned something from you. I always considered flexure as a random event in terms of being non-repeatable and intermittant in time. If it is correlated with telescope position then this is a good thing. I am curious though on how repeatable it is with the lower end mounts where if you have flexure it *seems* to be very random because of the lesser quality materials/construction. This is okay because it is *easier* (in my mind) to correct for flexure in smaller systems, then modeling does not provide the value that it would on larger/heavier mounts. I can very much understand that large systems (50-200 kg) can very much benefit from flexure modeling, but if we are talking about small systems where the loads are < 15 Kg then it is much more practical to just use higher quality mounting hardware and tighten/support everything as much as possible. Getting rid of the guide scope goes a long way to getting rid of flexure

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va



Hi Jerry,

I have not done a comparison of repeatability of higher end and lower end mounts, so I cannot say for sure if flexure is more or less reliable. This is in fact a capability I would like to add to PEMPro some day.

I can say with some certainty that a stiffer, more massive mount probably flexes less, which may leave most of the remaining flexure to that in the OTA, focuser, and camera/OTA connections.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4894975 - 11/03/11 12:07 AM

Quote:

From http://www.astro-physics.com/products/mounts/3600gto/precision-encoder-complete.pdf

"The 3600 PE is specified to be equal to or less than 5 arc seconds. One can use PEM to correct for this small error, but this does not fully guarantee that you can have long term sub-arc second tracking on every worm cycle. This is where the auxiliary precision encoder comes in. Since it is attached to the output worm wheel itself, the pulses from this encoder can be used to gauge the speed exactly. At the sidereal rate, there are approximately 170 pulses per second coming from this large encoder ring, so it is able to resolve sub-arc second speed errors to a high degree of accuracy."

"Basically, the encoder is simply a finely divided ring of 9" diameter with a pickup consisting of laser and pin diode receiver. The pickup has a resolution of 0.09 arc seconds and the encoder ring itself has a guaranteed accuracy of +/- 0.97 arc seconds for the entire 24 hour period."

170 pulses/second * 86400 = 1.5 Million tick encoder

This is the $6000+ option! (base AP3600 = 19900, with precision encoder = 26700)

The document linked does talk about where the encoder would be useful, even with a sophisticated pointing model.

So there must be something to this RA encoder thing.




I think this is an example of the ultimate in encoder technology, for those that must have the highest possible precision. This is a system truly capable of exceeding the accuracy of PEC as it's done now. The encoder used is much more accurate than what is used in cheaper products. In fact I heard that just the encoder costs more than the entire unit about which this thread originated.

Also this unit is capable of doing non-sidereal tracking rates, which is the holy grail of tracking and is mandatory for accurate tracking of celestial objects including stars, comets, planets, the moon, and asteroids. I think it's definitely worth the price for those that need this level of accuracy for research.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: gdd]
      #4894986 - 11/03/11 12:13 AM

Quote:


A number of mounts have modeling software independent of PEC to handle flexure of the mount and the imaging setup in a particular configuration. Shouldn't this software work in the same manner with TDM? Modeling with TDM installed may be even more accurate because the mounts movements are already smoothed out.

Gale




Hi Gale,

A lot of mounts do have modeling, but mostly for pointing correction, not tracking rate correction. That said, you would probably have to ask Atilla whether or not it is possible to set a non-sidereal rate in the TDM. Also, I think a declination axis tracking rate also has to be included in some way.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4894999 - 11/03/11 12:20 AM

Ray - based on my calculation, the AP3600 encoder is 1468000 ticks per revolution. The document mentions that it has a 9" diameter ring.

My wild guess is, it is a Renishaw REXT/REXM 229mm encoder

http://www.renishaw.com/media/pdf/en/80e8826d693a4e50abe35972ddbbe4b3.pdf

The TDM uses a Johannes Heidenhain unit. Whether it is inferior to the Renishaw or not, I would not know - but both Renishaw and Heidenhain make ultra-high end encoders that are competitive with each other.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4895015 - 11/03/11 12:33 AM

Quote:

Ray - based on my calculation, the AP3600 encoder is 1468000 ticks per revolution. The document mentions that it has a 9" diameter ring.

My wild-*BLEEP* guess is, it is a Renishaw REXT/REXM 229mm encoder

http://www.renishaw.com/media/pdf/en/80e8826d693a4e50abe35972ddbbe4b3.pdf

The TDM uses a Johannes Heidenhain unit. Whether it is inferior to the Renishaw or not, I would not know - but both Renishaw and Heidenhain make ultra-high end encoders that are competitive with each other.



Because of optical physics there is a limit to the smallest size that can be used for markings in an encoder. So, one way to increase accuracy is to increase the diameter of the encoder so more markings can be placed. I wonder what size the Heidenhain unit is in the TDM? Less than 9 inches diameter?

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4895060 - 11/03/11 01:24 AM

regardless, you are saying that a properly-done implementation of the RA encoder is a sound concept..

so in the same way that there are low-end and high-end mounts, there ought to be room for low- (or mid-range) and high-end encoder implementations.

the way I see it is, if the TDM can get a $1500 - $2500 mount to sub-arc second (or even +1/-1 arc-second) periodic error for an additional $2000, this is not a bad bargain.

I do not believe there are any mounts in the $3500 - $4000 range that can give +/- 1 arc-second periodic error (even after PEC) unless you buy used.

Surely then the TDM fills a particular niche...


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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4895353 - 11/03/11 09:37 AM

Quote:

regardless, you are saying that a properly-done implementation of the RA encoder is a sound concept..

so in the same way that there are low-end and high-end mounts, there ought to be room for low- (or mid-range) and high-end encoder implementations.

the way I see it is, if the TDM can get a $1500 - $2500 mount to sub-arc second (or even +1/-1 arc-second) periodic error for an additional $2000, this is not a bad bargain.

I do not believe there are any mounts in the $3500 - $4000 range that can give +/- 1 arc-second periodic error (even after PEC) unless you buy used.

Surely then the TDM fills a particular niche...



I never said using encoders was not a sound concept! The point I was trying to get across was that using an encoder to track at precisely sidereal rate will not allow a scope to go unguided for an unlimited amount of time! That's because refraction, polar alignment, flexures, etc. cause the apparent tracking rate to be different from sidereal. This essentially limits the maximum duration that you can image *unguided* at any given image scale. However, coupled with autoguiding using an encoder can provide a good solution.

Using an encoder can tame most of the PE and tracking roughness in lower end/mid range mounts. Although it corrects errors after they are seen this is usually much better than most PEC mechanisms in a telescope can do and also it corrects some slower tracking errors from (relatively) poorly cut worm wheels.

A high-end precision mount usually uses much more precise and expensive gears so tracking is inherently smoother to begin with and the errors that an encoder needs to correct are much smaller and less frequent. I believe that is why a more expensive encoder is required for a mount like the AP3600GTO. A lesser encoder might not be able to correct very subtle tracking errors when they are present. I think that most of the time a 3600+PEC will track very precisely without an encoder.

So, about its value, that's really up to the individual whether it's worth the cost. I think that the technology might not get much cheaper because of the expensive price of the encoders. However, as more features are introduced, like non-sidereal tracking, that may affect the resale value of current products. But that may present a buying opportunity to buy one cheaply used!!

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4895458 - 11/03/11 10:54 AM

hi ray -

thanks for the summary, your point kind of got lost with all the technical discussion. i didn't think that one could get away without guiding no matter how good the mechanics or encoder - i simply think that an encoder is an effective (though not cheap) way to overcome the mechanical deficiencies of certain classes of mounts..

edit: ok i'll admit it - instead of buying the $1800 TDM and bolting it on my CGEM, i bought that AP600 on the other site. will it perform as well as a CGEM+TDM? (probably not, actually)


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Ray Gralak]
      #4895485 - 11/03/11 11:11 AM

Post deleted by David Pavlich

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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4895493 - 11/03/11 11:17 AM

Attila, at the risk of stirring the pot some more -

If one is willing to sacrifice accuracy (say, a +/- 1 arc-second periodic error is enough) is it possible to use a less expensive encoder?

I noticed from my research that the 100K-tick encoders cost MUCH less than the >1M-tick encoders. There might actually be a bigger market for a modestly-priced "TDM Junior" if a lesser encoder could be used.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4895500 - 11/03/11 11:22 AM

Quote:

hi ray -

thanks for the summary, your point kind of got lost with all the technical discussion. i didn't think that one could get away without guiding no matter how good the mechanics or encoder - i simply think that an encoder is an effective (though not cheap) way to overcome the mechanical deficiencies of certain classes of mounts..

edit: ok i'll admit it - instead of buying the $1800 TDM and bolting it on my CGEM, i bought that AP600 on the other site. will it perform as well as a CGEM+TDM? (probably not, actually)




Hi Orlando, I think you missed the point of the conversation. It's not that you can't get away without guiding, because clearly you can... in some circumstances.

The point is that there are different levels and different requiremenst for gathering data via astrophotography. For the purpose of minor planet observing (astrometry and photometry) the TDM very easily allows one to take unguided images that more than meet the requirement for highly accurate astrometry. I demonstrated that I can plate solve my images with a residual of 0.06 arcseconds. This is excellent mount performance with an accurate polar alignment. I am comfortable that the TDM will provide the performance I need to take exposures up to 10 minutes if needed. Even though the high dollar mounts may be able (with some work) to provide 30-60 minute subs, I think only a small percentage of astrophotographers need that kind of performance. For the rest of us, the TDM very ably meets the requirements.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4895544 - 11/03/11 11:50 AM

Quote:

I am comfortable that the TDM will provide the performance I need to take exposures up to 10 minutes if needed. Even though the high dollar mounts may be able (with some work) to provide 30-60 minute subs, I think only a small percentage of astrophotographers need that kind of performance. For the rest of us, the TDM very ably meets the requirements.




I think you have found a system that does what you need, but you appear to misjudge the proportion of folks doing only astrometry. Your first sample image shows obvious trailing in 3 minute exposures with under 1000mm focal length. That is apparently fine for what you are doing, but it won't do for imaging. The vast majority of users are capturing images for aesthetic reasons and do need tighter tracking - especially given that we frequently use longer focal lengths and longer exposures. Guiding will usually be required to achieve the required performance. A few are getting there with mount modeling but that's a complicated process.

Most of the market for this product will be folks who have not-very-guidable mounts (EQ-6?) and want to modify them to be more easily guided rather than investing in higher-end, more guidable mounts. That makes perfect sense to me. Some will want to shoot short exposures at modest focal lengths (as in 500mm and 3 minutes) without guiding. Premium mounts do this with ease. Again, the TDM should bring some lower-end mounts up to that level so it will be useful.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4895582 - 11/03/11 12:13 PM

Quote:

Quote:

... The point I was trying to get across was that using an encoder to track at precisely sidereal rate will not allow a scope to go unguided for an unlimited amount of time! ...

-Ray




Ray,

where did you read this about TDM??? (I mean precise tracking for an unlimited amount of time.)

Attila




Hi Attila,

I didn't read it anyplace but the impression that I got from some of the posts was that some people think that you wouldn't ever need to autoguide (and thus think they would not need to purchase autoguiding equipment). And if they have to purchase autoguiding equipment then maybe an encoder is now competing against a cheaper AO device or using (free) Metaguide with fast updates. There is a limit for the unguided duration that is strongly dependent on the equipment that is used.

A perfect example of this was comparing my AP105 and AP155 unguided images (with software tracking rate correction). There seemed to be disbelief that perfect sidereal tracking would not produce as good a result! Harry even showed a AA5 autoguider snapshot, which sure it can happen, but surely not with every setup and in every part of the sky. You are just not going to be able to get perfect tracking with just an encoder because objects virtually never track at exactly sidereal rate. And if the encoder cannot adjust RA and Dec tracking rates to match the non-sidereal rates then it will not be able to achieve the unguided results you can get with a high-end mount without an encoder (but with tracking rate correction).

BTW, the above is not intended to diminish the usefulness of an encoder. I think it can be an excellent tool to correct some tracking issues if you cannot get alternative solutions to work.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4895665 - 11/03/11 01:14 PM

Quote:

or using (free) Metaguide with fast updates



Wow! What a turnabout! The TDM did change your mind about guiding mid-range mounts.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4895693 - 11/03/11 01:36 PM

Quote:

Quote:

or using (free) Metaguide with fast updates



Wow! What a turnabout! The TDM did change your mind about guiding mid-range mounts.



I'm not sure how you got that conclusion! I just think that Metaguide in particular does a very similar function (fast updates), but using a star so the RA/Dec tracking rate isn't an issue. It's still a compromise because you have to go through the trouble of framing the image to find a bright enough star to use. The question becomes (to a user) is it worth the trouble to do this, pay $2K for an encoder solution, or choose something intermediate. I would probably make a decision based on the particular tracking characteristics of the mount I wanted to use (i,e, analyze first, then pick the appropriate solution).

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: jrcrilly]
      #4895697 - 11/03/11 01:41 PM

Quote:

I think you have found a system that does what you need, but you appear to misjudge the proportion of folks doing only astrometry.



Not really. I have seen high quality unguided 8 min subs taken with the CGE at 2000mm focal length. I am sure that much longer unguided exposures are possible with the TDM. The TDM should definitely remove any need for guiding when shooting narrowband with the 14” Hyperstar on the CGE.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4895710 - 11/03/11 01:49 PM

Quote:

I'm not sure how you got that conclusion! I just think that Metaguide in particular does a very similar function (fast updates), but using a star so the RA/Dec tracking rate isn't an issue



As I recall you were always skeptical if a mid-range mount can respond to corrections every 1 second. The TDM proved that it is actually possible to correct a mid-range mount 5 times a second.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4895728 - 11/03/11 02:06 PM

Alph, is it really correcting 5X a second? or is it issuing pulse guide commands 5X a second but the mount is not necessarily responding at the same rate? there's a lot of backlash in 'em gears..

Maybe I'm just unlucky but PHD is having big troubles even with 2000ms guide pulses moving my CGEM.. (or it could be my ultra-short finder guide scope)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: orlyandico]
      #4895733 - 11/03/11 02:11 PM

Quote:

Alph, is it really correcting 5X a second? or is it issuing pulse guide commands 5X a second but the mount is not necessarily responding at the same rate? there's a lot of backlash in 'em gears..

Maybe I'm just unlucky but PHD is having big troubles even with 2000ms guide pulses moving my CGEM.. (or it could be my ultra-short finder guide scope)



The CGEM is not a mid-range mount. I doubt if there is any cure for the CGEM.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4895734 - 11/03/11 02:12 PM

Hi
There are 2 rates available with the TDM sideral and avg King

Harry


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Re: Telescope Drive Master - The Truth of the Matter new [Re: harry page 1]
      #4895756 - 11/03/11 02:28 PM

Alph - that's a good one a bit exaggerated but I have to laugh, there's a good bit of truth there.

But Jerry the OP is using an EQ6/Atlas - which is more or less the same thing.


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: orlyandico]
      #4895837 - 11/03/11 03:14 PM

Post deleted by David Pavlich

Edited by TDM (11/03/11 03:39 PM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4895854 - 11/03/11 03:24 PM

Quote:

... I didn't read it anyplace but the impression that I got from some of the posts was that some people think that you wouldn't ever need to autoguide (and thus think they would not need to purchase autoguiding equipment). ...





Ray,

Dennis di Cicco has already answered this question in the October issue of S&T Magazine and I fully agree his evaluation.

Attila


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: orlyandico]
      #4895875 - 11/03/11 03:34 PM

Post deleted by David Pavlich

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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4895879 - 11/03/11 03:37 PM

Check this out: http://www.renishaw.com/en/tonic-incremental-encoders-have-star-potential-for-astrosysteme-austria--15935

Btw, I love the debate. I'm think TDM and Ray should team up and give us a great combined solution.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: harry page 1]
      #4895900 - 11/03/11 03:52 PM

Quote:

Hi
There are 2 rates available with the TDM sideral and avg King

Harry




Hi Harry,

Two rates are not enough! In virtually every mount the apparent tracking rate is continuously changing in both RA and Dec.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4895922 - 11/03/11 04:12 PM

Quote:

If your mount is rigid and calm (e.g. friction drive) then TDM will need to interact in every fifth second. But if you have a low gear rate servo drive with tooth gears and relatively high guide speed (1x sidereal or higher), TDM will correct the drive two or three times per second.




That's a good info. So it is up to 5x per second. The corrections are NOT fixed to 5x or 1x per second. Are you passing data through the Kalman filter?


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4895927 - 11/03/11 04:13 PM

Quote:

Quote:

... I didn't read it anyplace but the impression that I got from some of the posts was that some people think that you wouldn't ever need to autoguide (and thus think they would not need to purchase autoguiding equipment). ...





Ray,

Dennis di Cicco has already answered this question in the October issue of S&T Magazine and I fully agree his evaluation.

Attila



And what was his answer?

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4895933 - 11/03/11 04:16 PM

Quote:

... In virtually every mount the apparent tracking rate is continuously changing in both RA and Dec.

-Ray




Ray,

have you calculated these position slips?
I have done it (I have made an Excel sheet especially for this). The result is that is not relevant in 5-10 min time frames and on photographic altitudes. Seeing washes it completely. This is rough indeed and has to be corrected close to the horizon only.

Again: look at the reference shots, please.
Calculations are very important of course but do not lose the contact with practice!!!

Attila


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4895937 - 11/03/11 04:17 PM

Quote:

Quote:

Hi
There are 2 rates available with the TDM sideral and avg King

Harry




Hi Harry,

Two rates are not enough! In virtually every mount the apparent tracking rate is continuously changing in both RA and Dec.

-Ray




Hey Ray,

Not enough, don't you mean not enough for your purposes, I think every user should decide that for himself, and that is the crux of this whole discussion. I think we are starting to iterate on our debating points!

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4896052 - 11/03/11 05:23 PM

Quote:

Quote:

... In virtually every mount the apparent tracking rate is continuously changing in both RA and Dec.

-Ray




Ray,

have you calculated these position slips?
I have done it (I have made an Excel sheet especially for this). The result is that is not relevant in 5-10 min time frames and on photographic altitudes. Seeing washes it completely. This is rough indeed and has to be corrected close to the horizon only.

Again: look at the reference shots, please.
Calculations are very important of course but do not lose the contact with practice!!!

Attila




Are you kidding?! Every type of mount and scope is different. What type of scope did you do your calculations and tell me how you did it? Anything can change the amount of flexure including where the balance point is set for the OTA and counterweights.

Let's consider what would happen if what you said were true. If in a 10-minute exposure the star moved less than 1 arc-sec. That would mean 6 arc-sec for an hour and over 3 hours only 18 arc-secs, or just over a quarter of an arc-minute. If that where true then apps like TPoint and Maxpoint wouldn't be needed because you would only be off by 1/4 arc-minute at most in the sweet spot area of the sky (assuming perfect polar alignment). I tell you that doesn't happen often!

Attila, even a the drop in temperate causes a measurable change in refraction and thus position and tracking rate. I experimented with this by automating a scope taking plate solves along a path near 0=dec. I did this 5 times over a period of hours while temperature dropped maybe 10C. The effects of temperature dropping on refraction where easily measurable.

-Ray


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: Ray Gralak]
      #4896121 - 11/03/11 06:13 PM

Post deleted by David Pavlich

Edited by TDM (11/03/11 06:17 PM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4896155 - 11/03/11 06:38 PM

Let me see if I have a grasp on this:

For a few 5-10 minute images, the no guide TDM with a good polar alignment and a reasonably rigid setup will yield nice pictures.

However, if you are taking, say, 25X10 minute exposures, there is going to be some sort of star distortion due to the subtle tracking changes due to several factors; flexure, refraction, slight changes in Sidereal speed according to placement in the sky.

In the end, it sounds to me like a good polar alignment, a TDM or some such ecoder addition and a decent guiding program will produce some exceptional results. And, if I may, add in PEC if your mount supports it and yikes!

So...do I have it right, or am I missing something?

David


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4896168 - 11/03/11 06:47 PM

Quote:

Ray,
E.g. you systematically mixes pointing error with tracking error. Who cares what happens with an object 3 hours later if I want to expose just 5 minutes now... Flexure is practically zero during a five-minute exposure (except a few OTAs or mounts from far-east... )
Good luck,
Attila



OK, I assumed that you knew (from one of my previous posts) that the differential change in pointing error can be used to calculate the necessary tracking rate to keep an object centered. It is just simple calculus. Does that make things clearer?

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: David Pavlich]
      #4896173 - 11/03/11 06:51 PM

Hi David,

Quote:

Let me see if I have a grasp on this:

For a few 5-10 minute images, the no guide TDM with a good polar alignment and a reasonably rigid setup will yield nice pictures.

However, if you are taking, say, 25X10 minute exposures, there is going to be some sort of star distortion due to the subtle tracking changes due to several factors; flexure, refraction, slight changes in Sidereal speed according to placement in the sky.

In the end, it sounds to me like a good polar alignment, a TDM or some such ecoder addition and a decent guiding program will produce some exceptional results. And, if I may, add in PEC if your mount supports it and yikes!

So...do I have it right, or am I missing something?

David



Yes, except that you don't need PEC at all with the TDM!

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: David Pavlich]
      #4896174 - 11/03/11 06:52 PM

Quote:

Let me see if I have a grasp on this:

For a few 5-10 minute images, the no guide TDM with a good polar alignment and a reasonably rigid setup will yield nice pictures.




Hi, David!

I'm sure that is true for some range of image scales (many mounts can manage it for some range of image scales without the TDM). What we don't know is the scale at which the device is claimed to deliver this performance. "Normal exposures" and no mention of scale is either not informative or deliberately misleading.

If I had your mount, I'd give thought to adding an RA encoder, as your controller has built-in support for that so it would be relatively inexpensive to add. A buddy of mine uses a SiTech with RA encoder and is quite pleased with it. Of course, he still guides.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4896182 - 11/03/11 06:55 PM

Quote:

Ray,

sorry for this question but you use telescopes or you are just speaking about telescopes?

I feel you do not want to hear or understand other's voice.

E.g. you systematically mixes pointing error with tracking error. Who cares what happens with an object 3 hours later if I want to expose just 5 minutes now... Flexure is practically zero during a five-minute exposure (except a few OTAs or mounts from far-east... )

TDM does nothing with pointing error, flexure, etc. You have nice software to correct these problems. TDM is for nice pictures as soon as you open the CCD shutter.

Sorry, I need to apologize; I do not have time for long theoretical argues about practically non-existing problems.

Again and at last: please look at the several wonderful test shots.

Good luck,
Attila




Hello Atilla,
I wouldn't apologise for trying to point out that the "proof is in the pudding" Do you know this saying in Hungary? I feel your frustration also. It's hard to discuss these topics without everyone being able to try it out for themselves.

I feel that with only a few sessions under my belt I still have not obtained all the performance my system is capable of. Maybe after a few more months of tuning my skills I will be able to demonstrate a level of quality in my images that others will appreciate. Having said that, I think that for my minor planet work, I was able to quickly demonstrate the practical use of the TDM in obtaining very accurate images for astrometry and photometry purposes.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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harry page 1
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Re: Telescope Drive Master - The Truth of the Matter new [Re: David Pavlich]
      #4896190 - 11/03/11 06:59 PM

Hi

You can take as many 10 min subs as you like , its the lenth of the sub that might cause a problem
I can not do 15 min unguided subs , probabley more due to my bendy newt
Harry


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4896196 - 11/03/11 07:06 PM

Quote:

Quote:

Quote:

Hi
There are 2 rates available with the TDM sideral and avg King

Harry




Hi Harry,

Two rates are not enough! In virtually every mount the apparent tracking rate is continuously changing in both RA and Dec.

-Ray




Hey Ray,

Not enough, don't you mean not enough for your purposes, I think every user should decide that for himself, and that is the crux of this whole discussion. I think we are starting to iterate on our debating points!

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va




Hi Jerry,

Look at the thread context above. I posted to Gale that you would have to ask Atilla if non-sidereal rates were possible. Harry answered that there were two. I said that is not enough (i.e, to match the almost infinite number of possible apparent tracking rates).

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: jrcrilly]
      #4896241 - 11/03/11 07:24 PM

Quote:

What we don't know is the scale at which the device is claimed to deliver this performance.



The performance was defined in terms of arc-sec. That's all what matters.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: jrcrilly]
      #4896252 - 11/03/11 07:29 PM

Quote:

Quote:

I am comfortable that the TDM will provide the performance I need to take exposures up to 10 minutes if needed. Even though the high dollar mounts may be able (with some work) to provide 30-60 minute subs, I think only a small percentage of astrophotographers need that kind of performance. For the rest of us, the TDM very ably meets the requirements.




I think you have found a system that does what you need, but you appear to misjudge the proportion of folks doing only astrometry. Your first sample image shows obvious trailing in 3 minute exposures with under 1000mm focal length. That is apparently fine for what you are doing, but it won't do for imaging. The vast majority of users are capturing images for aesthetic reasons and do need tighter tracking - especially given that we frequently use longer focal lengths and longer exposures. Guiding will usually be required to achieve the required performance. A few are getting there with mount modeling but that's a complicated process.

Most of the market for this product will be folks who have not-very-guidable mounts (EQ-6?) and want to modify them to be more easily guided rather than investing in higher-end, more guidable mounts. That makes perfect sense to me. Some will want to shoot short exposures at modest focal lengths (as in 500mm and 3 minutes) without guiding. Premium mounts do this with ease. Again, the TDM should bring some lower-end mounts up to that level so it will be useful.




Hi John, thanks for the thoughtful response.

I don't know where you get that the EQ6 is not very guideable. Apparently you do not know what you are talking about in terms of the performance of the EQ6/Atlas mounts.
I think it is funny that you disparage those of us who do not want or need the performance of a $10,000 mount since we can get 80% of the performance for 1/3rd the cost.

I need to understand what kind of imaging you are doing where the purpose is for aesthetic reasons but apparently requires you have *perfect* stars at an image scale of < 0.6 arcsec/pixel.

From most everything I have read about "aesthetic" pictures you want a wide field to be able to capture your whole subject, i.e., on the order of at least 1 square degree. Having a FOV of 20' x 20' of arc that most high focal length scopes provide with the cameras that most amateurs can afford just don't lend themselves to aesthetic imaging.

A typical setup for *most* amateurs would be an 8" SCT with a Kodak 8300 chip camera with 5.4 micron pixels. The image scale for this 2000 mm FL scope with that camera would be on the order of 0.6 arcsec/pixel . This image scale provides 1.2 arcseconds of resolution. Now couple that with a typical seeing of 2-3 arcsecs, or worse, you can see that the typical tracking provided by the TDM of +/- 0.7 arcsec (as I have demonstrated) really doesn't have that big an impact. To demonstrate this fully, If we add these two error terms together using the square root of the sum of the squares method for random errors:

sqrt(Seeing^2 + TDM TE^2) = total error
sqrt(2.5arcsec^2 + 1.4arcsec^2) = 2.86 arcsec

Compare 2.86 arcsec total error to just the seeing of 2.5 arcsec. Based on this, if you would explain to me how having tighter tracking with a total peak to peak error of < 1 arcsec adds any value especially when taking subs of 10 minutes or less.

As Attila said, you can only see any value in tracking any better when you have seeing of < 1.5 arcseconds, as you might have regularly at high altitudes on a mountain, or maybe near a large body of water where temperatures are very stable.

I guess I am trying to say that for 80% of the amateurs who need only 80% of the performance of a high end setup because of their location and environmental conditions, it just does not make any sense to try and achieve that.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4896358 - 11/03/11 08:16 PM

Quote:

I don't know where you get that the EQ6 is not very guideable. Apparently you do not know what you are talking about in terms of the performance of the EQ6/Atlas mounts.




I've owned a couple of EQ-6 mounts (still have one, now that I think of it). Compared to the EM-200 that it copies, it isn't very guidable and not very useful unguided. If a TDM would make it guide like an EM-200 or image unguided at moderate focal lengths like an EM-200 then there would be a net savings and it could be an attractive alternative (though more than the "1/3 the cost" that you mention). I merely suggested that this might be the case.

Quote:

I think it is funny that you disparage those of us who do not want or need the performance of a $10,000 mount since we can get 80% of the performance for 1/3rd the cost.




I don't disparage anyone. It's extremely unlikely that I will ever spend anywhere near $10,000 myself for a hobby mount and I certainly don't care what anyone else spends. I'm talking about hardware. If I were convinced that I could buy a lesser mount than my NJP and add a $2000 device to make it work as well unguided as my current mount works guided at 3900mm with a 70 pound load (the worst case scenario in my observatory) while costing no more than what I can sell the NJP for ($5000?) I'd do it in a flash. If it would still require guiding, or cost more money, it wouldn't be worth the trouble since I can do that just fine as things are.

Quote:

I need to understand what kind of imaging you are doing where the purpose is for aesthetic reasons but apparently requires you have *perfect* stars at an image scale of < 0.6 arcsec/pixel.

From most everything I have read about "aesthetic" pictures you want a wide field to be able to capture your whole subject, i.e., on the order of at least 1 square degree. Having a FOV of 20' x 20' of arc that most high focal length scopes provide with the cameras that most amateurs can afford just don't lend themselves to aesthetic imaging.




If you start doing a lot of DSO imaging you will quickly realize that there are plenty of objects that aren't presented well in a 1 degree or larger field. That's why there are so many popular Cassegrain variant imaging scopes in the 2000mm-4000mm range. We use shorter telescopes for large fields and longer telescopes for the small fields. It's at those longer focal lengths that an enhanced RA tracking rate is only part of the formula.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4896359 - 11/03/11 08:17 PM

Quote:

Quote:

Quote:

Quote:

Hi
There are 2 rates available with the TDM sideral and avg King

Harry




Hi Harry,

Two rates are not enough! In virtually every mount the apparent tracking rate is continuously changing in both RA and Dec.

-Ray




Hey Ray,

Not enough, don't you mean not enough for your purposes, I think every user should decide that for himself, and that is the crux of this whole discussion. I think we are starting to iterate on our debating points!

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va




Hi Jerry,

Look at the thread context above. I posted to Gale that you would have to ask Atilla if non-sidereal rates were possible. Harry answered that there were two. I said that is not enough (i.e, to match the almost infinite number of possible apparent tracking rates).

-Ray




Hi Ray, I really don't mean to quibble, but I did understand the context of your statement. The fact that while using the TDM we can't track at non-Sidereal rates may be a limitation, but really, how many images do you take NOT at the nominal Sidereal rate. It was with this in mind that I made the statement. Now if you had in mind an infinitely variable tracking rate around the nominal Sidereal rate, I am not sure how that would work or even be workable. You still need some kind of reference to set your rate to, whether it be a real-time star image, or a modeled solution such as yours that rely on a lot of imaging to create an accurate model.

I thought I had posted previously the design model I use to separate the different components of the imaging problem, where I explain that the fundamental basis for any tracking is the Earth's rotation rate, and everything else is layered upon that. I think that model is more valid because it allows you to separate the error components cleanly and not muddle everything together without separating the sidereal rate component first.

Once you have a baseline rate to control to, then other error terms can be investigated and corrected. without an accurate baseline for rate, you have nothing to compare to to justify your rate corrections.

I imagine when Attila and Istvan designed the TDM they had to decide what tracking rates to provide to give the most bang for the buck. Of course standard Sidereal rate was first, then they decided on an average King rate which compensates for refractive errors over some of the sky.

This would add some extra performance without overcomplicating the design of their microcontroller. That is also why, I believe, they went ahead in version 2 and provided a way to pass-through the DEC autoguiding signals to your mount from a guide camera or AO guider. It wasn't that expensive to add, and added some extra performance for those who wanted to be able to guide on very faint stars with long guide exposures of >10 seconds, or get by with only a fair polar alignment.

I think that your approach using PEC and mount flexure modeling is valuable but is not based on any first principles as a design basis. It is an empirical approach that will work very well indeed but can only reach a certain performance level. I think that is demonstrated by the fact that it is only workable on expensive mounts that already have an inherent low PE. The low end mounts need something else to enable them to perform at a comparable level due to their real-time inconsistencies in performance. Thus the need for the TDM.

Basically different approaches for different problems. This reminds me of the saying that for the man with a hammer, everything looks like a nail.

Bottomline is for >80% of the imaging that *most* amateurs do, the TDM provides a simple configuration that is quick and easy to setup and has Harry and I have said, it just works.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va

Edited by Jerry Hubbell (11/03/11 08:36 PM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: jrcrilly]
      #4896383 - 11/03/11 08:32 PM

Quote:

Quote:

I don't know where you get that the EQ6 is not very guideable. Apparently you do not know what you are talking about in terms of the performance of the EQ6/Atlas mounts.




I've owned a couple of EQ-6 mounts (still have one, now that I think of it). Compared to the EM-200 that it copies, it isn't very guidable and not very useful unguided. If a TDM would make it guide like an EM-200 or image unguided at moderate focal lengths like an EM-200 then there would be a net savings and it could be an attractive alternative (though more than the "1/3 the cost" that you mention). I merely suggested that this might be the case.

Quote:

I think it is funny that you disparage those of us who do not want or need the performance of a $10,000 mount since we can get 80% of the performance for 1/3rd the cost.




I don't disparage anyone. It's extremely unlikely that I will ever spend anywhere near $10,000 myself for a hobby mount and I certainly don't care what anyone else spends. I'm talking about hardware. If I were convinced that I could buy a lesser mount than my NJP and add a $2000 device to make it work as well unguided as my current mount works guided at 3900mm with a 70 pound load (the worst case scenario in my observatory) while costing no more than what I can sell the NJP for ($5000?) I'd do it in a flash. If it would still require guiding, or cost more money, it wouldn't be worth the trouble since I can do that just fine as things are.

Quote:

I need to understand what kind of imaging you are doing where the purpose is for aesthetic reasons but apparently requires you have *perfect* stars at an image scale of < 0.6 arcsec/pixel.

From most everything I have read about "aesthetic" pictures you want a wide field to be able to capture your whole subject, i.e., on the order of at least 1 square degree. Having a FOV of 20' x 20' of arc that most high focal length scopes provide with the cameras that most amateurs can afford just don't lend themselves to aesthetic imaging.




If you start doing a lot of DSO imaging you will quickly realize that there are plenty of objects that aren't presented well in a 1 degree or larger field. That's why there are so many popular Cassegrain variant imaging scopes in the 2000mm-4000mm range. We use shorter telescopes for large fields and longer telescopes for the small fields. It's at those longer focal lengths that an enhanced RA tracking rate is only part of the formula.




Thanks again John for your thoughtful response. I fully understand your design requirements, and the choices you made make perfect sense. I understand your need for a larger load capacity. I did not realise how popular the smaller objects were to astrophotographers, and the necessity of focal lengths in the 2-4 meter range. That is something I hadn't considered. Of course my design requirements are almost the opposite of yours: I have a portable system, I need to be able to set it up and take it down in minimal time. I need medium size fields with fairly high resolution images capable of astrometry residuals of < 0.1 arcsec if possible. I need to be able to place a target in the field of view of my camera with a minimum of fuss, without relying on mount modeling software and the extra overhead that entails. I won't go on, you get the picture.

I think the TDM is really about having a fundamental piece of gear that when coupled to your mount provides a foundation for all types of imaging. Otherwise, as I have said in previous emails, why bother building big mounts with large capacities that track with PE < 5 arcsec.

It would be easier to build mounts that have PE > 30 arcseconds and then just use guiding to correct the errors in the mount. You are guiding anyway, what difference would that make. Of course I know the answer, as I stated in the previous post, there's no money in cheap mounts, and no one is going to spend upwards of $6000 for a poor performing mount.

Thanks again,

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4896420 - 11/03/11 08:57 PM

Quote:

Of course my design requirements are almost the opposite of yours:




Yes. We both have gear appropriate to our interests. I went through quite a few mounts in the observatory before ending up a few years ago with with what I expect will be the last one. I suspect that my needs (except, perhaps in weight capacity) are more typical than yours. RC, D-K, SCT, MCT, Classical Cass designs (and the resultant focal lengths) are fairly common (I've had them all here at one time or another). All the imagers around here have at least one.

You mention guiding as a solution for 30 arcsecond PE drives. I think those are the best candidate for the kind of hardware being discussed here. 30 arcsecond mounts generally have fairly abrupt variations that are tricky to correct with after-the-fact guiding. PEC is the usual solution, and it helps to bring the variations down to rates that guiding deals with more effectively. An RA encoder could be better yet (especially given that 30 arcsecond mounts tend to have substantial nonperiodic errors as well). An RA encoder completely tamed my friend's fidgety SiTech-controlled homebrew mount (the worm was fidgety, not the controller) a few years ago. He still guides when using the RC, but now it guides beautifully. That's probably the best target market for this.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: jrcrilly]
      #4896444 - 11/03/11 09:18 PM

Quote:

Quote:

Of course my design requirements are almost the opposite of yours:




Yes. We both have gear appropriate to our interests. I went through quite a few mounts in the observatory before ending up a few years ago with with what I expect will be the last one. I suspect that my needs (except, perhaps in weight capacity) are more typical than yours. RC, D-K, SCT, MCT, Classical Cass designs (and the resultant focal lengths) are fairly common (I've had them all here at one time or another). All the imagers around here have at least one.

You mention guiding as a solution for 30 arcsecond PE drives. I think those are the best candidate for the kind of hardware being discussed here. 30 arcsecond mounts generally have fairly abrupt variations that are tricky to correct with after-the-fact guiding. PEC is the usual solution, and it helps to bring the variations down to rates that guiding deals with more effectively. An RA encoder could be better yet (especially given that 30 arcsecond mounts tend to have substantial nonperiodic errors as well). An RA encoder completely tamed my friend's fidgety SiTech-controlled homebrew mount (the worm was fidgety, not the controller) a few years ago. He still guides when using the RC, but now it guides beautifully. That's probably the best target market for this.




Indeed John, I have an old 10" Meade 2120 LX5 SCT, an AT8RC, and a ES 127 ED APO CF. So I understand the issues with long focal length scopes, although I have not conquered them as yet. My AT8RC FL is 1610mm and this is probably the most I would push my mount for long exposure imaging. I am still working on my skills using that scope, but I have found that for general minor planet imaging, my refractor does an excellent job. Coupled with my QHY9m camera, it is almost the perfect match of image scale, and FOV to position my target and get the astrometry results I like to see with my mounts performance.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: jrcrilly]
      #4896465 - 11/03/11 09:38 PM

Hello John, I was just looking at your Cloudy Nights gallery, and saw that you use an AT12RC. That's pretty cool! I saw your image of M13 and the number of stars visible to the core is amazing. Here is a link to an image of M13 I made on the first night I used my TDM, of course unguided on my EQ6. I was pretty happy with it. It is a 10 x 90 second image stack (calibrated and processed in AIP4Win, and Photoshop). I think it speaks for itself.

http://www.pbase.com/jerry_hubbell/image/139381169/original

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4896487 - 11/03/11 09:51 PM

Quote:

Quote:

Quote:

Quote:

Quote:

Hi
There are 2 rates available with the TDM sideral and avg King

Harry




Hi Harry,

Two rates are not enough! In virtually every mount the apparent tracking rate is continuously changing in both RA and Dec.

-Ray




Hey Ray,

Not enough, don't you mean not enough for your purposes, I think every user should decide that for himself, and that is the crux of this whole discussion. I think we are starting to iterate on our debating points!

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va




Hi Jerry,

Look at the thread context above. I posted to Gale that you would have to ask Atilla if non-sidereal rates were possible. Harry answered that there were two. I said that is not enough (i.e, to match the almost infinite number of possible apparent tracking rates).

-Ray




Hi Ray, I really don't mean to quibble, but I did understand the context of your statement. The fact that while using the TDM we can't track at non-Sidereal rates may be a limitation, but really, how many images do you take NOT at the nominal Sidereal rate. It was with this in mind that I made the statement. Now if you had in mind an infinitely variable tracking rate around the nominal Sidereal rate, I am not sure how that would work or even be workable. You still need some kind of reference to set your rate to, whether it be a real-time star image, or a modeled solution such as yours that rely on a lot of imaging to create an accurate model.

I thought I had posted previously the design model I use to separate the different components of the imaging problem, where I explain that the fundamental basis for any tracking is the Earth's rotation rate, and everything else is layered upon that. I think that model is more valid because it allows you to separate the error components cleanly and not muddle everything together without separating the sidereal rate component first.

Once you have a baseline rate to control to, then other error terms can be investigated and corrected. without an accurate baseline for rate, you have nothing to compare to to justify your rate corrections.

I imagine when Attila and Istvan designed the TDM they had to decide what tracking rates to provide to give the most bang for the buck. Of course standard Sidereal rate was first, then they decided on an average King rate which compensates for refractive errors over some of the sky.

This would add some extra performance without overcomplicating the design of their microcontroller. That is also why, I believe, they went ahead in version 2 and provided a way to pass-through the DEC autoguiding signals to your mount from a guide camera or AO guider. It wasn't that expensive to add, and added some extra performance for those who wanted to be able to guide on very faint stars with long guide exposures of >10 seconds, or get by with only a fair polar alignment.

I think that your approach using PEC and mount flexure modeling is valuable but is not based on any first principles as a design basis. It is an empirical approach that will work very well indeed but can only reach a certain performance level. I think that is demonstrated by the fact that it is only workable on expensive mounts that already have an inherent low PE. The low end mounts need something else to enable them to perform at a comparable level due to their real-time inconsistencies in performance. Thus the need for the TDM.

Basically different approaches for different problems. This reminds me of the saying that for the man with a hammer, everything looks like a nail.

Bottomline is for >80% of the imaging that *most* amateurs do, the TDM provides a simple configuration that is quick and easy to setup and has Harry and I have said, it just works.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va




Hi Jerry,

The reason I brought up the non-sidereal tracking rate issue is to demonstrate why, even with an encoder, you will need to use an autoguider for long duration exposures! I think I have proven that point. Besides, others, including yourself, Atilla, and Dennis DiCicco of S&T, all seem to agree.

In practice I don't just use tracking rate modelling. I turn ProTrack on, which does tracking rate modeling, but I also autoguide as a second level of "defense" against drift. Most of my exposures lately are 30-minute exposures so using just an encoder would still require me to autoguide.

In fact a vast number of people image from the city using narrowband filters where 20-30 minute exposers are the norm. Again, these imagers would probably need to autoguide because of the long exposures involved. I think I would have to agree with Mr. Crilly, whom I think said or implied that most people want to do "pretty pictures". Most also don't have access to dark skies. Long exposures (and autoguiding) are often the norm for these individuals. So, even if they are using an encoder they would still have to autoguide.

Anyway, soon I will barely be able to pay attention to this thread as AIC is imminent, so if I don't respond right away it's because I'm busy at AIC. Thanks again for the interesting discussion!

-Ray


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4896496 - 11/03/11 09:57 PM

Ray, thanks for the exchange, I have enjoyed the back and forth. I understand about AIC. I am sure we will be discussing this in the future. I attended NEAIC and NEAF this past April, and thoroughly enjoyed the time there. I am sure you will have a great time at the AIC. I wish I could be there also.

Thanks

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Ray Gralak]
      #4896536 - 11/03/11 10:22 PM

To be honest, Ive skipped parts of this thread (for lack of time, not interest - its fascinating) but from what I've read..

This system would not work for me for photometry, even though I only take 120 sec exposures, because I need precise tracking for hours on end, at all altitudes. It seems that all that is needed is software to control and adjust the tracking rate, to compensate for flexure, refraction etc. Would that be hard to do?


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Re: Telescope Drive Master - The Truth of the Matter new [Re: jrcrilly]
      #4896546 - 11/03/11 10:27 PM

Quote:

Quote:

Let me see if I have a grasp on this:

For a few 5-10 minute images, the no guide TDM with a good polar alignment and a reasonably rigid setup will yield nice pictures.




Hi, David!

I'm sure that is true for some range of image scales (many mounts can manage it for some range of image scales without the TDM). What we don't know is the scale at which the device is claimed to deliver this performance. "Normal exposures" and no mention of scale is either not informative or deliberately misleading.

If I had your mount, I'd give thought to adding an RA encoder, as your controller has built-in support for that so it would be relatively inexpensive to add. A buddy of mine uses a SiTech with RA encoder and is quite pleased with it. Of course, he still guides.




Ayup! Paul Burke has a SiTech controlled MI250 with a Gurley encoder. He posted a 20 minute unguided image, however, he has polar aligned his mount to death. He did say that it doesn't eliminate guiding. He just posted it to show what an encoder can do,

David


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Re: Telescope Drive Master - The Truth of the Matter new [Re: gavinm]
      #4896583 - 11/03/11 10:56 PM

Quote:

To be honest, Ive skipped parts of this thread (for lack of time, not interest - its fascinating) but from what I've read..

This system would not work for me for photometry, even though I only take 120 sec exposures, because I need precise tracking for hours on end, at all altitudes. It seems that all that is needed is software to control and adjust the tracking rate, to compensate for flexure, refraction etc. Would that be hard to do?




Hi Gavin, I am curious about why you think that you cannot get good photometry unless you have precise tracking hours on end. The best technique for obtaining the most accurate photometry requires that you over sample to some degree. Usually that is accomplished with the poor seeing we all get that increases the FWHM of our star images. With 120 second exposures, most mounts will provide fairly good star images, certainly good enough, as long as the star you are measuring is not overexposed. Most programs used for photometry will provide an ellipticle aperture to allow you to use trailed star images. In fact this is necessary when measuring minor planets since they have discernible trails against a field of perfectly round stars. If you saw the first post in this thread, you saw the link to my image of minor planet 2001 LO7. This is a V-band image that I did photometry on the minor planet (mag 15.1) on each of the images individually. Having perfect tracking does nothing for you when doing photometry on a moving object, but it can be done very accurately nonetheless.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va

Edited by Jerry Hubbell (11/03/11 11:20 PM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4896612 - 11/03/11 11:18 PM

I need/want stars on the same pixels all night. Even flat fielding isnt perfect. Autoguiding works fine, but if I lose a guide star, I dont want to muck around re-centering (even automatically using plate-solving etc).

Just wondering - enjoying this thread


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Re: Telescope Drive Master - The Truth of the Matter new [Re: gavinm]
      #4896636 - 11/03/11 11:33 PM

Quote:

I need/want stars on the same pixels all night. Even flat fielding isnt perfect. Autoguiding works fine, but if I lose a guide star, I dont want to muck around re-centering (even automatically using plate-solving etc).

Just wondering - enjoying this thread




Gavin

Not losing a guide star is a big advantage of using the TDM, especially for very long exposures. The longer the exposure, the more risk you run in losing your guide star and ruining the exposure. As long as you have an accurate polar alignment, with the TDM you have a greater chance of successfully imaging in cloudy conditions, if there is a need for that.

Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4896758 - 11/04/11 01:53 AM

I see your point Jerry (and nice analysis BTW). I've used encoders, built ADCs and written software (in MATLAB), so I can appreciate what a great product TDM is, and I'm not concerned by the cost either. Ray also has a great product (which I use). But before I bought TDM it would need two things (for my use). One is variable tracking (for reasons mentioned by Ray) and the other is absolute encoders vs incremental or relative (I know alignment is easy using plate-solves and Maxim etc, but I'm so sick of doing it and surely its unnecessary these days). If it had those, I would easily buy it, even if it cost $10,000. I can already get perfect (or close enough given my gear) tracking using autoguiding.

I guess my question for Attila is, is this possible?

I also agree with someones earlier post - if TDM and Ray worked together, the result would be...... Im waiting for TDM v3


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Re: Telescope Drive Master - The Truth of the Matter new [Re: gavinm]
      #4896803 - 11/04/11 02:57 AM

Quote:

I see your point Jerry (and nice analysis BTW). I've used encoders, built ADCs and written software (in MATLAB), so I can appreciate what a great product TDM is, and I'm not concerned by the cost either. Ray also has a great product (which I use). But before I bought TDM it would need two things (for my use). One is variable tracking (for reasons mentioned by Ray) and the other is absolute encoders vs incremental or relative (I know alignment is easy using plate-solves and Maxim etc, but I'm so sick of doing it and surely its unnecessary these days). If it had those, I would easily buy it, even if it cost $10,000. I can already get perfect (or close enough given my gear) tracking using autoguiding.

I guess my question for Attila is, is this possible?

I also agree with someones earlier post - if TDM and Ray worked together, the result would be...... Im waiting for TDM v3





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Re: Telescope Drive Master - The Truth of the Matter new [Re: jrcrilly]
      #4896831 - 11/04/11 04:34 AM

Dear John,

Dennis di Cicco was using 4000mm focal length in his review, and it worked.

Clear skies

Tassilo


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4896862 - 11/04/11 05:38 AM

In all this talk I still haven't seen the key thing I want to see in assessing guiding quality: an fwhm value, in arc-seconds, in a long fl, long exposure. I'm sorry but when assessing guide results, you can't simply say the results are limited by bad seeing. All you can say is - here is a sub-exposure and X software says the fwhm is Y arc-seconds. If the seeing is truly bad then your result doesn't tell anything about how well the mount would guide under good seeing conditions. If the seeing is good, then the result is not compelling.

There have been a number of images posted and some plots - with statements that they should satisfy skeptics - but without close-ups of sub-exposures and fwhm values, I can't assess anything beyond perhaps 3-4" fwhm - which should be easily achievable by conventional methods. Guide plots and post-PE residuals tell me very little about the star spot that forms on the imaging CCD, which is what matters.

I'm also surprised that people are casually talking about refractor imaging and the use of adaptive optics in tandem with encoders. Refractors can be easily guided well with a small guidescope to achieve the level of results posted here. With regard to AO - it is well known that AO can make a mid-range mount perform like a high end mount - but at added expense and complexity. It's not clear to me if the earlier Newtonian shot was made with AO or not - the lack of detail on these images makes it hard to tell anything.

People have been mentioning MetaGuide, and I want to emphasize that the results I get with MG on a cge and cge-pro involve nothing other than OAG and the mount itself. I am not concerned about PE because the main work is in high frequency terms not addressable by PE. I do use the free PECTool to remove the main harmonics just for the heck of it - I doubt it improves guiding much.

Here is an astrometric fit via TheSkyX for a recent 2m exposure of m13:

******** ASTROMETRIC SOLUTION RESULTS ********
Center RA: 16h 41m 42.3s
Center Dec: +36° 27' 31.4"
Scale: 0.84 arcseconds/pixel
Size (pixels): 1392 x 1040
Angular Size: 0° 19' 25" x 0° 14' 30"
Position Angle: 179° 17' from North
RMS: 0.21 (X: 0.15 Y: 0.15)
Number of Stars Used in Solution: 80 (66%)
FWHM: 2.13 pixels, 1.78 arcseconds
***********************************************

Here is an astrometric fit for the M1 narrow band image shown on the MetaGuide site - here for a 15m Ha exposure:

******** ASTROMETRIC SOLUTION RESULTS ********
Center RA: 05h 34m 19.8s
Center Dec: +22° 01' 26.5"
Scale: 0.78 arcseconds/pixel
Size (pixels): 1392 x 1040
Angular Size: 0° 18' 10" x 0° 13' 34"
Position Angle: 355° 37' from North
RMS: 0.17 (X: 0.15 Y: 0.07)
Number of Stars Used in Solution: 8 (14%)
FWHM: 2.75 pixels, 2.15 arcseconds
***********************************************

Note that the residuals are in pixels and the pixel scale is around 0.8 pixels, so the fit RMS is about 0.15". If you want accurate astrometry on faint objects, I would use tight guiding and long focal length so the stars are well sampled but very small in arc-seconds.

The main conclusion from using MetaGuide and nothing else for these results is that it shows what the mount is truly capable of when guided well. The principles involved would apply to other guide software - mainly to use OAG and rapid corrections with low latency. MG is based on video guiding to achieve the low latency, but I go down to 8 fps with Lumenera and guide directly on 9.5M guidestars in OAG. Fainter stars can be reached by other centroiding methods within MG. For tightest FWHM, you need to use common optical path guiding, and you should choose the brightest available guidestar for shortest exposure and lowest correction latency - regardless of the software. As for computational requirements - guiding has minimal processor demand on my 2 year old laptop.

In summary - I repeat that TDM with low/mid range mount is probably cost-effective for short unguided results - but I have not seen a single compelling deep sky result with quantitative guiding info - including the S&T review.

It may be that TDM ends up being cost-effective to make a mount achieve fwhm's tighter than it could achieve by any other means - but so far I haven't seen any evidence of that.

Frank


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Re: Telescope Drive Master - The Truth of the Matter *DELETED* new [Re: freestar8n]
      #4896914 - 11/04/11 06:49 AM

Post deleted by David Pavlich

Edited by TDM (11/04/11 06:51 AM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: gavinm]
      #4896997 - 11/04/11 08:34 AM

Quote:

I see your point Jerry (and nice analysis BTW). I've used encoders, built ADCs and written software (in MATLAB), so I can appreciate what a great product TDM is, and I'm not concerned by the cost either. Ray also has a great product (which I use). But before I bought TDM it would need two things (for my use). One is variable tracking (for reasons mentioned by Ray) and the other is absolute encoders vs incremental or relative (I know alignment is easy using plate-solves and Maxim etc, but I'm so sick of doing it and surely its unnecessary these days). If it had those, I would easily buy it, even if it cost $10,000. I can already get perfect (or close enough given my gear) tracking using autoguiding.

I guess my question for Attila is, is this possible?

I also agree with someones earlier post - if TDM and Ray worked together, the result would be...... Im waiting for TDM v3




Hi Gavin, I'm glad you enjoyed my writeup on the TDM and appreciate the compliment. I think Attila has given you a good summary of his product in his response to this message. Based on what you have told me, and the experience I have had with my system and the TDM, I can suggest the following:

For variable rate tracking the TDM accommodates the input of an alternate ST4 based guiding system that passes through the DEC control inputs from that system. With the TDM, this alternate system is most efficiently used as a longer time constant correction for slight polar alignment errors and slow changing refractive errrors. These changes will be in the 0.1 Hz to 0.005 Hz range, and only in the DEC axis.

The TDM will handle position changes in the > 0.2 Hz range in the RA axis. These changes are due to imperfections in the inherent mount PE errors, and non-periodic errors.

Additionally, if you can perform a very accurate polar alignment to manage your long term drift, I would suggest an Active Optics Guider similar to this:

http://www.telescope.com/Articles/Current-Articles/Astrophotography/The-SteadyStar-Adaptive-Optics-Guider/pc/9/c/192/sc/198/p/100122.uts

This system will manage fast changes in position, and slow minimal refractive and drift errors with a frequency of from 5-20 Hz, and from 0.1 Hz to 0.001 Hz (or slower).

I think the simplest system that would meet your needs would be the TDM coupled with the AOG on a very well polar aligned mount that has minimal flexure. This solution would probably cost anywhere from $5000-$8000 depending on the mount you chose, and the load capacity required.

I have not used an AOG but I imaging you can get stars with a FWHM down 1.5-2 arcseconds (perhaps), with long term position accuracy immune to intermittent cloud cover.

As far as using absolute position encoders, I think it is important to understand why you would need these, as opposed to the alternative. I have found that when you have an accurate polar alignment, a 2 star or 3 star (if you have cone errors) alignment will easily place an object to within an arcminute of the center of the frame. See my image of minor planet 2001 LO7.

http://www.pbase.com/jerry_hubbell/image/136454649/original

I had no problem placing that object in the center of the frame by only performing an accurate polar alignment and then an accurate 2 star sync using my normal planetarium software and the EQMOD ASCOM mount driver. In my opinion, the expense of a highly accurate absolute encoder is not justified in this application, especially if you have a permanent mount. My system is portable, and I find I have no problems locating and imaging moving objects (minor planets).

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va

Edited by Jerry Hubbell (11/04/11 08:45 AM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4897045 - 11/04/11 09:16 AM

Quote:

In all this talk I still haven't seen the key thing I want to see in assessing guiding quality: an fwhm value, in arc-seconds, in a long fl, long exposure. I'm sorry but when assessing guide results, you can't simply say the results are limited by bad seeing. All you can say is - here is a sub-exposure and X software says the fwhm is Y arc-seconds. If the seeing is truly bad then your result doesn't tell anything about how well the mount would guide under good seeing conditions. If the seeing is good, then the result is not compelling.

There have been a number of images posted and some plots - with statements that they should satisfy skeptics - but without close-ups of sub-exposures and fwhm values, I can't assess anything beyond perhaps 3-4" fwhm - which should be easily achievable by conventional methods. Guide plots and post-PE residuals tell me very little about the star spot that forms on the imaging CCD, which is what matters.

I'm also surprised that people are casually talking about refractor imaging and the use of adaptive optics in tandem with encoders. Refractors can be easily guided well with a small guidescope to achieve the level of results posted here. With regard to AO - it is well known that AO can make a mid-range mount perform like a high end mount - but at added expense and complexity. It's not clear to me if the earlier Newtonian shot was made with AO or not - the lack of detail on these images makes it hard to tell anything.

People have been mentioning MetaGuide, and I want to emphasize that the results I get with MG on a cge and cge-pro involve nothing other than OAG and the mount itself. I am not concerned about PE because the main work is in high frequency terms not addressable by PE. I do use the free PECTool to remove the main harmonics just for the heck of it - I doubt it improves guiding much.

Here is an astrometric fit via TheSkyX for a recent 2m exposure of m13:

******** ASTROMETRIC SOLUTION RESULTS ********
Center RA: 16h 41m 42.3s
Center Dec: +36° 27' 31.4"
Scale: 0.84 arcseconds/pixel
Size (pixels): 1392 x 1040
Angular Size: 0° 19' 25" x 0° 14' 30"
Position Angle: 179° 17' from North
RMS: 0.21 (X: 0.15 Y: 0.15)
Number of Stars Used in Solution: 80 (66%)
FWHM: 2.13 pixels, 1.78 arcseconds
***********************************************

Here is an astrometric fit for the M1 narrow band image shown on the MetaGuide site - here for a 15m Ha exposure:

******** ASTROMETRIC SOLUTION RESULTS ********
Center RA: 05h 34m 19.8s
Center Dec: +22° 01' 26.5"
Scale: 0.78 arcseconds/pixel
Size (pixels): 1392 x 1040
Angular Size: 0° 18' 10" x 0° 13' 34"
Position Angle: 355° 37' from North
RMS: 0.17 (X: 0.15 Y: 0.07)
Number of Stars Used in Solution: 8 (14%)
FWHM: 2.75 pixels, 2.15 arcseconds
***********************************************

Note that the residuals are in pixels and the pixel scale is around 0.8 pixels, so the fit RMS is about 0.15". If you want accurate astrometry on faint objects, I would use tight guiding and long focal length so the stars are well sampled but very small in arc-seconds.

The main conclusion from using MetaGuide and nothing else for these results is that it shows what the mount is truly capable of when guided well. The principles involved would apply to other guide software - mainly to use OAG and rapid corrections with low latency. MG is based on video guiding to achieve the low latency, but I go down to 8 fps with Lumenera and guide directly on 9.5M guidestars in OAG. Fainter stars can be reached by other centroiding methods within MG. For tightest FWHM, you need to use common optical path guiding, and you should choose the brightest available guidestar for shortest exposure and lowest correction latency - regardless of the software. As for computational requirements - guiding has minimal processor demand on my 2 year old laptop.

In summary - I repeat that TDM with low/mid range mount is probably cost-effective for short unguided results - but I have not seen a single compelling deep sky result with quantitative guiding info - including the S&T review.

It may be that TDM ends up being cost-effective to make a mount achieve fwhm's tighter than it could achieve by any other means - but so far I haven't seen any evidence of that.

Frank




Hi Frank,

Although I cannot provide any real long exposure ( > 20 minutes) data for FWHM, I think Attila has a 20 minute exposure on his website; he may be able to provide some FWHM data on that image. Based on my measurements using the TDM, if we only consider the TDM performance at this point I have demonstrated a 95% TE of +/- 0.7 arcsec. Now the relationship between 1 sigma and FWHM (see Wikipedia article: http://en.wikipedia.org/wiki/Full_width_at_half_maximum) is

FWHM = 1 sigma value x 2.35482

So for my measurements the 1 sigma value is 0.35 arcsec, an the calculated FWHM for this is 0.825 arcsec. Now, if we were to have a seeing value of 1.5 arcsec, what would the total FWHM be with the TDM plus the seeing.

We can calculate that by using the square root of the sum of the squares method for adding errors in quadrature.

Total FWHM = sqrt(seeing^2 + TDM^2)
Total FWHM = sqrt(1.5^2 + 0.825^2)
Total FWHM = 1.71 arcsec

As you can see the contribution of the TDM is very small -
1.71 arcsec - 1.5 arcsec = 0.21 arcsec.

In a previous message I posted, I presented an image that Attila provides on his website that shows the actual performance using a star image which had a 1 sigma Total of 0.7 arcsec. This equates to a total FWHM value of about 1.65 arcseconds. This, again shows the dominance of the seeing term in the overall total FWHM value.

This is what everyone needs to understand about the contribution of the TDM error to the total error, seeing vastly overwhelms the impact that the TDM has on the final FWHM value for star images.

This is why using an AOG to handle the higher frequency scintillation (5-20 Hz) is effective in reducing the FWHM of star images.

Harry is using the TDM on a larger, longer focal length telescope, perhaps he can provide some data on FWHM measurements for his images.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va

Edited by Jerry Hubbell (11/04/11 09:25 AM)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4897243 - 11/04/11 11:48 AM

Quote:

Flexure is practically zero during a five-minute exposure (except a few OTAs or mounts from far-east...



Hold on a second. That doesn't match my experience. I think maybe you give too much credit to high end mounts there. Even with a Paramount ME and a rigidly mounted (bolted to the Versaplate) OTA, at ~4M focal length I've seen as much as one arc second per minute of DEC drift caused by flexure. That's five arc-seconds of DEC drift over a five minute period. Enough to ruin a nice pretty picture for sure. Turning on ProTrack corrects that, but if I didn't have ProTrack, I'd need to guide that exposure. And if I wanted to take much longer subs, I'd need to guide anyway no matter what. And this is with a Paramount and an expensive scope, not an OTA and mount from the far East.

(Mind you I have nothing against mounts from the far East. I love my Atlas every bit as much as my Paramount.)


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Re: Telescope Drive Master - The Truth of the Matter new [Re: frolinmod]
      #4897411 - 11/04/11 01:21 PM

Quote:

I've seen as much as one arc second per minute of DEC drift caused by flexure.



How do you know it wasn't caused by polar misalignment? I think I know what your answer will be.


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Re: Telescope Drive Master - The Truth of the Matter new [Re: TDM]
      #4897444 - 11/04/11 01:45 PM

Quote:

Jerry Hubbell has made a quite detailed quantitative test on TDM.
RMS: 0.12
http://www.mda-telescoop.com/images/stories/downloads/tdm_control_investigation.pdf

He can tell you the other data and conclusion of his tests.




I saw that write up a long time ago - and it doesn't actually show empirical measurements of the tracking error. The only empirical result is the error measured in a guidestar centroid - but that is subject to errors of its own.

I'm fine with the possibility that TDM provides compelling unguided results with a low to mid-range mounts in the 1-3m exposure range and perhaps 3-4" fwhm - but when it comes to making claims about the actual tracking error of the mount, and the ability of the encoder to play nice with the mount firmware and actually deliver accurate tracking - I don't see data for that. It's just based on theory assuming everything is working as expected.

As for long exposure deep sky work - I'm still looking for an actual realized result that shows good guiding with a low to mid-range mount in 10-20m exposures and sub-arcsecond pixels.

Note that I am the opposite of elitist when it comes to mid-range mounts. The whole point of my work with MetaGuide is to demonstrate that extremely good results can come with better software and technique - and in fact you don't "need" to have a high-end mount to achieve high end results. So - if you provide a cost-effective way to achieve the same goal - that's great. But you really need to provide long sub exposures and details of the images - and fwhm's in arc-seconds.

Frank


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4897445 - 11/04/11 01:45 PM

Jerry,

In your opening post you stated that nothing comes close to the performance at $3500 to the TDM and EQ6. I'm wondering whether the iOptron iEQ45-GT #8100 advertised as $3888 in Sky&Telescope and Astronomy magazines fits the bill. It uses a Renshaw encoder, has a 45lb. payload and states better than ą1 arcsec PE. Unlike the TDM setup the iEQ45 still maintains a polar scope.


Don


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4897470 - 11/04/11 02:06 PM

Quote:

This is what everyone needs to understand about the contribution of the TDM error to the total error, seeing vastly overwhelms the impact that the TDM has on the final FWHM value for star images.




Hi Jerry-

I'm afraid you are extrapolating from theory and speculation - and you really need to focus instead on actual results because the realities of autoguiding can be full of surprises. The only way to know if you have good guiding in a deep sky image is to demonstrate it with actual results.

The key thing missing in your theory is that somehow you have a perfect centroid reference for the guidestar, and every time you make a guide correction it will happen perfectly. In my view, the dominant error overlooked in your discussion is that of the star centroid itself - not to mention flexure if you are not guiding with OAG. So - if you do guide with OAG, then you have already adopted one of the keys to good guiding with a mid-range mount. If you aren't guiding with OAG and instead are using a short refractor, you will have only a crudely accurate centroid, and flexure on top of that. This means that seeing isn't limiting your results - instead it's the centroid error - and high-res encoders won't help with that if you are autoguiding.

If you do guide with OAG, and you make low latency corrections with an accurate centroid, then you have a chance to achieve the results I post regularly, with no additional hardware. As a reminder, my m13 image had a mean fwhm of 1.78" - no theory involved.

You imply that everyone has bad seeing. Well - I have an ordinary location in the northeast u.s., and I regularly get fwhm's around 2" and sometimes below. If my seeing doesn't let me get below 3" then I do something else that night. And on nights when seeing is good, mainly due to the jet stream, I find that people 1-200 hundred miles away will post similar comments about good seeing. So - I don't think bad seeing is as common as you assume, and I don't think that people around the world would be spending lots on high-end mounts if they were doomed to 3-4" fwhm with expensive equipment.

Frank


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tomo
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Re: Telescope Drive Master - The Truth of the Matter new [Re: DonBoy]
      #4897536 - 11/04/11 03:14 PM

Great point Don. Any info on this would be great.

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harry page 1
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Re: Telescope Drive Master - The Truth of the Matter new [Re: tomo]
      #4897568 - 11/04/11 03:36 PM

HI
I took a 10 min sub into maxim and I seem to have FWHM between 2 and 2.5 sec ( not to good at this tech thing )

I do not think the Plug and play thing can be overstated I love that I switch it on and it works , therefore it will be used everytime a no brainer.
I mean I have a SX AO and very good it is , but problems with setup time back focus ETC means it does not get used , My clear nights in the UK are Few and I need to make the most of them.
Will the TDM be the answer to everything , probably No but it a bazooka in my armory of Tracking Hardware

Kind Regards Harry


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Re: Telescope Drive Master - The Truth of the Matter new [Re: Alph]
      #4897601 - 11/04/11 04:00 PM

Quote:

Quote:

I've seen as much as one arc second per minute of DEC drift caused by flexure.



How do you know it wasn't caused by polar misalignment? I think I know what your answer will be.



Excellent question Alph. Realistically I can't be certain. All I can go by is what flexure terms Tpoint had calculated as being in the system as well as their magnitude plus what Tpoint told me my polar alignment was at the time. But I don't fully trust it, especially I don't trust its polar alignment report! Color me untrusting I guess. And it doesn't matter that ProTrack corrected it. That is not conclusive of anything really. Despite the mathmatical results happening to come out the same and correct things, the identified cause may not have been the actual cause. The final results with Protrack turned on were good to be sure, but as a diagnostic tool if I had wanted to actually identify and fix the true cause, well, I'm not so certain. That was a year ago btw and I've since torn down and reassembled the system several times. Does any of this match your expectations?

Edited by frolinmod (11/04/11 04:25 PM)


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DonBoy
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Re: Telescope Drive Master - The Truth of the Matter new [Re: tomo]
      #4897628 - 11/04/11 04:20 PM

Tomo,

Here is a link http://www.ioptron.com/index.cfm?select=newsdesc&nid=6085d81e-8811-49ca-9223-9a6ef1b8c7d1

In this link look for test results and there will be a pdf of testing iOptron has done.

Don


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Re: Telescope Drive Master - The Truth of the Matter new [Re: frolinmod]
      #4897660 - 11/04/11 04:43 PM

Quote:

Does any of this match your expectations?



Fair enough. Thanks.
I think this thread turned into a great promotion of the TDM, at least for me. I do realize though, from the questions asked, that there are still many people out there that might still be confused about the TDM. It is all clear to me!


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Jerry Hubbell
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Re: Telescope Drive Master - The Truth of the Matter new [Re: DonBoy]
      #4897881 - 11/04/11 06:54 PM

Quote:

Jerry,

In your opening post you stated that nothing comes close to the performance at $3500 to the TDM and EQ6. I'm wondering whether the iOptron iEQ45-GT #8100 advertised as $3888 in Sky&Telescope and Astronomy magazines fits the bill. It uses a Renshaw encoder, has a 45lb. payload and states better than ą1 arcsec PE. Unlike the TDM setup the iEQ45 still maintains a polar scope.


Don




Hi Don, I haven't seen that mount yet. I am very interested. I was aware that the iEQ 75 had the encoder, but I didn't know that they had released a lighter mount with an encoder. Attila has done some work with the iEQ 45 mount and he might want to weigh in on that.

Thanks

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4897897 - 11/04/11 07:12 PM

Quote:

Quote:

This is what everyone needs to understand about the contribution of the TDM error to the total error, seeing vastly overwhelms the impact that the TDM has on the final FWHM value for star images.




Hi Jerry-

I'm afraid you are extrapolating from theory and speculation - and you really need to focus instead on actual results because the realities of autoguiding can be full of surprises. The only way to know if you have good guiding in a deep sky image is to demonstrate it with actual results.

The key thing missing in your theory is that somehow you have a perfect centroid reference for the guidestar, and every time you make a guide correction it will happen perfectly. In my view, the dominant error overlooked in your discussion is that of the star centroid itself - not to mention flexure if you are not guiding with OAG. So - if you do guide with OAG, then you have already adopted one of the keys to good guiding with a mid-range mount. If you aren't guiding with OAG and instead are using a short refractor, you will have only a crudely accurate centroid, and flexure on top of that. This means that seeing isn't limiting your results - instead it's the centroid error - and high-res encoders won't help with that if you are autoguiding.

If you do guide with OAG, and you make low latency corrections with an accurate centroid, then you have a chance to achieve the results I post regularly, with no additional hardware. As a reminder, my m13 image had a mean fwhm of 1.78" - no theory involved.

You imply that everyone has bad seeing. Well - I have an ordinary location in the northeast u.s., and I regularly get fwhm's around 2" and sometimes below. If my seeing doesn't let me get below 3" then I do something else that night. And on nights when seeing is good, mainly due to the jet stream, I find that people 1-200 hundred miles away will post similar comments about good seeing. So - I don't think bad seeing is as common as you assume, and I don't think that people around the world would be spending lots on high-end mounts if they were doomed to 3-4" fwhm with expensive equipment.

Frank




Thanks Frank for your post. I have to consider what you are saying before I respond, but on your question about the star centroid measurement I have a couple of observations. In the picture of minor planet 2001 LO7, the 10 x 180 second integration; that integrated image has an astrometric residual of 0.06 arsec using over 400 stars spread over the bulk of the image. I used the UCAC3 database as my astrometric reference. That to me says that I definitely do not have an issue as you describe. I do not have a centroid issue. Plus I don't have use any guiding. The refractor has a focal length of 950mm so I don't know if you consider that a short focal length. I would consider it a medium focal length instrument (ES 127 ED APO CF).
As far as seeing is concerned, take a look at the clear sky charts and you can see what most people have for seeing.

Jerry Hubbell
Lake of the Woods Observatory (MPC I24)
Locust Grove, Va


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freestar8n
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4897965 - 11/04/11 08:06 PM

Quote:

I used the UCAC3 database as my astrometric reference. That to me says that I definitely do not have an issue as you describe. I do not have a centroid issue. Plus I don't have use any guiding.




Ugh - there are two different things being discussed in this thread - at least:

1) High res encoders make short, unguided imaging possible with low/mid range mounts.

2) High res encoders make it possible for low/mid range mounts to do long exposure deep sky imaging as well as high end mounts.

I am specifically talking about long exposure deep sky imaging - and even with high res encoders, that will require autoguiding - as I thought everyone agreed. And autoguiding requires a centroid - and its associated errors. Best autoguiding requires OAG - so despite encoders you still need OAG, and its associated complexity to get best results with a given mount.

I'm baffled that people are talking about combining high res encoders with PEC or adaptive optics. If you have adaptive optics you don't need encoders, and if you have encoders you don't need PEC. Of course - based on my results, if you have OAG and low latency corrections - you don't need adaptive optics OR encoders OR pec to get sub-2" fwhm.

I think it's fine if you want to focus on 1-2m exposures with medium focal length - unguided. But if you want to talk about deep sky and how well encoders would work, you really need detailed, actual examples of high res, long exposure deep sky work.

As for seeing - I have found that when people move to a high end mount and OAG - suddenly their "seeing" improves, as shown in their subsequent images.

Frank


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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4898143 - 11/04/11 10:39 PM

This thread has been locked for review.

David Pavlich
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Re: Telescope Drive Master - The Truth of the Matter new [Re: Jerry Hubbell]
      #4898813 - 11/05/11 12:39 PM

I've returned the thread, but it's on probation. I've removed a lot of posts that had the smell of product promotion. I've also removed any that are provocative or otherwise unhelpful posts that are not adding to the conversation.

Let's keep it on a factual mission. I appreciate your patience.

David


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BlueGrass
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Re: Telescope Drive Master - The Truth of the Matter new [Re: David Pavlich]
      #4898928 - 11/05/11 01:43 PM

David. This is one of those threads that contains a great deal of fundamental information about tracking and guiding that everyone can study.

Thanks!


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jmiele
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Re: Telescope Drive Master - The Truth of the Matter new [Re: BlueGrass]
      #4898978 - 11/05/11 02:14 PM

I think David has worked hard to ensure as much of the important information as possible is here. I for one appreciate the effort and the difficult position some of us (myself included) put him in..

I'm sorry for any part I played in the distraction and will do my level best to stay on point.

To the topic at hand. I've been asked in PM's if I have a problem with this product. I don't, at all. The concept being utilized by TDM in the unit is a sound method for removing PE noise from a mount. Folks shouldn't read into that, that guiding is unnecessary for many reasons. There are many (as pointed out by others) different factors affecting the gathering of quality imaging data. Flexure as earlier stated is one. As you spend more money on a mount you "generally" get improved (not perfect) bearings, shafts and the like. These add up to a solid imaging platform. Quality mounts by AP and Bisque (along with many others)additionally add a smooth PE (regardless of the number) to the mix. That smoothness makes for less trouble when permanently correcting it and while guiding. Backlash is also, "generally" improved.

None of that means a CGE or other isn't going to be a great mount. A TDM unit on a mid range mount may very well take as good an image as a higher priced mount. Several folks have stated they have a low tolerance for frustration. I count myself among them. I find spending more on the mounting from a given astro budget is a "generally" less frustrating experience - for me.

I should have made this post rather than some of the other I posted earlier in this thread. Hopefully this is a bit more constructive.

Joe


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Re: Telescope Drive Master - The Truth of the Matter new [Re: jmiele]
      #4899070 - 11/05/11 03:14 PM

Joe,
Your posts are typically very constructive and to the point. Enough said.

The whole gist of this thread, adding an encoder to a less capable mount to improve its performance, is an area of great interest to many. Improving mount performance is a never ending quest in this hobby, whether it be an Atlas or an AP1200. I'd like to see this discussion continue ...


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Re: Telescope Drive Master - The Truth of the Matter new [Re: BlueGrass]
      #4899426 - 11/05/11 07:23 PM

Quote:

I'd like to see this discussion continue ...



You don't get it, do you? They delete posts. Who is going to comment?


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Re: Telescope Drive Master - The Truth of the Matter new [Re: freestar8n]
      #4899524 - 11/05/11 08:34 PM

Quote:

Quote:

I used the UCAC3 database as my astrometric reference. That to me says that I definitely do not have an issue as you describe. I do not have a centroid issue. Plus I don't have use any guiding.




Ugh - there are two different things being discussed in this thread - at least:

1) High res encoders make short, unguided imaging possible with low/mid range mounts.

2) High res encoders make it possible for low/mid range mounts to do long exposure deep sky imaging as well as high end mounts.

I am specifically talking about long exposure deep sky imaging - and even with high res encoders, that will require autoguiding - as I thought everyone agreed. And autoguiding requires a centroid - and its associated errors. Best autoguiding requires OAG - so despite encoders you still need OAG, and its associated complexity to get best results with a given mount.

I'm baffled that people are talking about combining high res encoders with PEC or adaptive optics. If you have adaptive optics you don't need encoders, and if you have encoders you don't need PEC. Of course - based on my results, if you have OAG and low latency corrections - you don't need adaptive optics OR encoders OR pec to get sub-2" fwhm.

I think it's fine if you want to focus on 1-2m exposures with medium focal length - unguided. But if you want to talk about deep sky and how well encoders would work, you really need detailed, actual examples of high res, long exposure deep sky work.

As for seeing - I have found that when people move to a high end mount and OAG - suddenly their "seeing" improves, as shown in their subsequent images.

Frank




Hi Frank,

First I want to thank David for allowing this discussion to continue.

Now, I guess I am curious about the difference between single long exposures and shorter exposures integrated via software. Based on my study over the past couple of years, the only difference between a long integrated exposure, and several short exposures integrated via software is that the readout noise gets added into the subs and for 20 x 3 minute exposures you have 20 times the readout noise versus the single 60 minute exposure. This of course is for properly calibrated images (flat frame adjusted, dark, and bias - if necessary).

From what I have read and experienced, once you have integrated properly calibrated sub frames then the result should be really no different for low readout noise cameras taking longer exposures.

On the other hand you will definitely have an issue with a 60 minute exposure where the sky background will definitely be a bigger issue than the readout noise from the sub frames. The readout noise is measurable where sky background varies from night to night so it cannot be properly compensated for.

Now, I understand that astrophotographers use narrow band filters to beat back the sky background, especially in urban areas. This makes perfect sense. Apparently there are a large number of you folks imaging in this environment.

The way I look at the difference between long exposures and shorter sub exposures that are integrated in software in the context of guiding is that instead of relying on a real-time process to adjust the centroid position continuously, I am relying on a post imaging process that does the same thing as far as adjusting and aligning the centroid of the images.

For 30 second sub frames being integrated post imaging, it is equivalent to guiding with a 30 second integration on the guide camera real-time in that you readjust the image based on a star centroid calculated every 30 seconds.

I guess the bottom line question I am asking is other than readout noise, for normal non-narrow band imaging, what is the downsid