Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Imaging with an ADC

  • Please log in to reply
50 replies to this topic

#1 GeorgeInDallas

GeorgeInDallas

    Viking 1

  • -----
  • topic starter
  • Posts: 547
  • Joined: 15 Apr 2012
  • Loc: Dallas, Texas USA

Posted 13 January 2018 - 12:17 PM

In anticipation of the coming planetary imaging opportunities I have modified my imaging configuration to include a ZWO EFW mini filter wheel (I previously utilized a manual filer wheel) and a ZWO ADC. I have read all of the post and web pages that I could find on the subject of the ADC to help me with the configuration and utilization of the ADC in particular. In response to Darryl's recent post on ADC vs. Barlow placement I have arrived at the configuration in the image below. Does this appear to be a correct and reasonable configuration to start with? I will be imaging from Dallas, Texas where Jupiter will reach an elevation of 40 deg. I will use this configuration with a C14, Optec focuser and ZWO ASI174MM camera. The filter wheel contains Chroma Technology LRGB filters and also an Astronomik 742 nm IR pass filter.

 

I have been struggling with how to adjust the ADC with this configuration (in particular using a mono camera).

 

To level the ADC with the horizon I hope to used an App on my iPhone (ProCam) that produces a horizontal level superimposed on the live camera image. Using my phone camera to look at the ADC orientation compared to the App indicated level, I hope to be able to correctly orient the ADC. 

 

To adjust the ADC dispersion correction I hope to utilize the Metaguide integrated, magnified star image to adjust the ADC until I get the best (least distorted) star image. If this approach is unreliable I plan to utilize an approach illustrated on Andre Paquette's web page (  http://paquettefamil...tro/star_study/ ) that shows how using a UHC filter with Metaguide can show separate star images when there is uncorrected dispersion. 

 

I would appreciate any comments and suggestions on this configuration and plan.

Thanks,

George

 

 

Attached Thumbnails

  • Optical_Train.jpg


#2 RedLionNJ

RedLionNJ

    Vanguard

  • -----
  • Posts: 2443
  • Joined: 29 Dec 2009
  • Loc: Red Lion, NJ, USA

Posted 13 January 2018 - 01:24 PM

Hi George,

 

First, this looks like about as close as you can get with your equipment to about the right focal ratio at the sensor. Only actual experimentation and measuring will tell for sure, as the native focal ratio of the C14 is going to vary a bit, particularly with the first piece of focusing/tele-extending glass (the barlow) being so very far back from the C14's rear cell.  In practice, you might end up with a focal ratio anywhere from f/20 to around f/32. It's going to be whatever it's going to be. I would question the Meade T-Adapter present in the diagram, but I know from personal experience you need to do what you need to do in order to physically connect all the pieces.

 

What I am not totally clear on is how you're going to tune the ADC and what piece you intend to turn to keep the white screw parallel with the horizon. I know you referred to a couple methods for the former, but both from a theoretical and a practical perspective, I can't picture #1 working with this gear.  From a theoretical point of view, you're going to try to find lever positions which minimize the distortion of a star. Well, if that's your goal, you can go out and do that any clear, steady night. Then record the lever positions vs the elevation above the horizon. E.g. "30 degrees, 2 notches". This table you're creating will change a minimal amount from night to night, based on differences in atmospheric density. For all intents and purposes, it may never change by enough to render your initial table obsolete.

 

However, there's one problem with the theory - the ADC also *introduces* distortions as it throws the image off-axis. It might be very difficult indeed to tell where the distortion is minimized.

 

I strongly recommend reading (and re-reading) these two pages from Martin Lewis:

 

http://www.skyinspec...-corrector--adc

http://www.skyinspec...o.uk/adcs-part2

 

There is no doubt the ADC can make a significant difference to even RGB results at low elevation, if 100% properly-used.  I've been using an ASH model for several years with great success (when seeing cooperates) at low elevations.

 

Don't be expecting to get the most out of it on your first excursion - it may take a few nights. Now is the time to practice, before the bright planets are easily accessible.

 

Good luck! 



#3 moonwatching ferret

moonwatching ferret

    Vanguard

  • *****
  • Posts: 2021
  • Joined: 26 Jun 2016
  • Loc: sebastian fl

Posted 13 January 2018 - 01:28 PM

all i can say is the adc should be level with the horizon in the focus tube, as for the barlow location if you place it in front of the adcitl just increase the fl. im no pro at adc corectors and have been loosing interest due to bad weather. it was suposed to be mostly sunny today but its cloudy cold and windy.


  • GeorgeInDallas likes this

#4 GeorgeInDallas

GeorgeInDallas

    Viking 1

  • -----
  • topic starter
  • Posts: 547
  • Joined: 15 Apr 2012
  • Loc: Dallas, Texas USA

Posted 13 January 2018 - 02:38 PM

Thanks for your reply. 

 

The Meade T-Adapter is to provide a space between the filter wheel and the ADC so that the adjustment screws easier to reach (not so close to the filter wheel). 

 

My assumption is that rotating the slip ring that the white screw screws into is what is changed to make the white screw level with the horizon. Once the correct horizon position is identified, then the two prisms are adjusted to be centered either side of the horizon position with the same separation that they had prior to the adjustment (assuming that the dispersion adjustments were correct prior to changing the horizon level adjustment). Hopefully, that can be done without having to rotate anything else in the optical path.I have never successfully done any of this, so these are only my current understandings from reading. 

 

I am encouraged and surprised to see your comment about the table. Are the ADC prism adjustment so coarse as to be 1 notch, 2 notches or 3 notches? 

 

I will take you suggestion an re-read Martin Lewis web pages. 

 

I expect to have to spend several nights of trial and error to find a way to utilize the ADC.

 

Thanks for your help,

George

 

Hi George,

 

First, this looks like about as close as you can get with your equipment to about the right focal ratio at the sensor. Only actual experimentation and measuring will tell for sure, as the native focal ratio of the C14 is going to vary a bit, particularly with the first piece of focusing/tele-extending glass (the barlow) being so very far back from the C14's rear cell.  In practice, you might end up with a focal ratio anywhere from f/20 to around f/32. It's going to be whatever it's going to be. I would question the Meade T-Adapter present in the diagram, but I know from personal experience you need to do what you need to do in order to physically connect all the pieces.

 

What I am not totally clear on is how you're going to tune the ADC and what piece you intend to turn to keep the white screw parallel with the horizon. I know you referred to a couple methods for the former, but both from a theoretical and a practical perspective, I can't picture #1 working with this gear.  From a theoretical point of view, you're going to try to find lever positions which minimize the distortion of a star. Well, if that's your goal, you can go out and do that any clear, steady night. Then record the lever positions vs the elevation above the horizon. E.g. "30 degrees, 2 notches". This table you're creating will change a minimal amount from night to night, based on differences in atmospheric density. For all intents and purposes, it may never change by enough to render your initial table obsolete.

 

However, there's one problem with the theory - the ADC also *introduces* distortions as it throws the image off-axis. It might be very difficult indeed to tell where the distortion is minimized.

 

I strongly recommend reading (and re-reading) these two pages from Martin Lewis:

 

http://www.skyinspec...-corrector--adc

http://www.skyinspec...o.uk/adcs-part2

 

There is no doubt the ADC can make a significant difference to even RGB results at low elevation, if 100% properly-used.  I've been using an ASH model for several years with great success (when seeing cooperates) at low elevations.

 

Don't be expecting to get the most out of it on your first excursion - it may take a few nights. Now is the time to practice, before the bright planets are easily accessible.

 

Good luck! 



#5 Kokatha man

Kokatha man

    Voyager 1

  • *****
  • Posts: 11041
  • Joined: 13 Sep 2009
  • Loc: "cooker-ta man" downunda...

Posted 13 January 2018 - 08:08 PM

George, John gave one approach to tuning your ADC on a star with this (don't know what link it came from)

 

<"...After you become familiar with it's operation there are a couple of ways to adjust the degree of correction for a monochrome camera. The one I tend to use is visually adjusting the ADC with an eyepiece set to be parfocal with the camera--- the amount of corrective dispersion an ADC produces increases with projection distance from the ADC so that's why the eyepiece needs to be at least closely parfocal. Another way is use of a W47 or similar filter that has 2 widely separated bandwidths, each at opposite ends of the imaging spectrum. The W47 has an intended deep blue bandpass but also has a near-IR leak, so when used with a camera with atmospheric dispersion present it will show a star split into two on your monitor---">

 

Most definitely his suggestion to me to place more distance behind the ADC for the dispersion effects to be corrected effectively works - we were imaging at about 40° elevation both times & the difference was very palpable! waytogo.gif

 

As Grant said, you work with what you have (unless you go & spend more money on something extra! lol.gif ) but I'm concerned re your: <"My assumption is that rotating the slip ring that the white screw screws into is what is changed to make the white screw level with the horizon.">

 

It's not rotating the slip ring that orientates the ADC for use, it is rotating the ADC body itself, & that ADC body's slot overlap mid-point is what needs to be referenced to the horizon. This is marked in the 1st image below. First you simply loosen the white nylon screw on the ADC which allows you to turn both the white nylon screw & the slip ring until they correspond to that slot overlap mid-point & then lock the white screw & slip ring in that position.

 

After doing that & moving both levers to this mid-point also, you place or position it into the filter wheel using whatever connector you have with that white screw etc pointing either left or right & horizontal/level to the horizon in an SCT, also depending upon whether you have a "lefty" or "righty" ADC.

 

SCT's are easy in that all you need to do is every now & then check to see that the white screw is maintaining a level position as the mount & scope moves over time, correcting the entire ADC unit's position when necessary by rotating the entire ADC body so that the white nylon screw stays level with the horizon - it is NOT the screw or slip ring that gets moved, it merely serves as a reference point for the entire ADC body after your initial fixing of them at the slots' mid-point overlap. You of course alter the position of each lever to compensate for dispersion appropriately.

 

ZWO_ADC.png

 

It can be deduced from the preceding that you really need to rotate the ADC wherever it is situated in your train independently of any other aspect of the imaging train: in the pikky above I have 2 of the top elements (one at each end of the ADC, that's the right hand fitting in next pikky) & my EFW has a fitting like the left-hand fitting in this 2nd pikky: I can then insert the nosepiece of the ADC into that 2nd "T2(male) -1.25" (female) holder" which then screws on to the EFW.

 

By loosening the additional "T2(male) -1.25" (female) holder" clamps I can rotate the the ADC with it's nosepiece in said holder to keep the white nylon reference screw horizontal & then by loosening the clamps at the other "holder"  on the opposite end of the ADC I can compensate the camera's orientation for my re-orienting of the ADC - this is necessary if you want your planet to continue any of its' X & Y corrections on an even keel! wink.gif

 

Hope this is clear lol.gif but don't hesitate to ask for any further clarification! smile.gif

 

ZWO-fittings.png

 

 

 

 

 

 

 

 

 


  • John Miele, GeorgeInDallas and Lacaille like this

#6 Lacaille

Lacaille

    Mariner 2

  • -----
  • Posts: 275
  • Joined: 27 Nov 2015
  • Loc: Canberra and Strasbourg

Posted 13 January 2018 - 08:41 PM

Hi George,

 

RedLionNJ posted links to two useful articles, in the first of which there is mention of tuning the ADC using Firecapture. I think that this article pre-dates the ADC-tuning function now available in Firecapture.  With this, you focus on the target planet and click a button, giving saturated colours (as seen in the article), but you also get two 'live' discs representing the two prisms -as you move the levers, the discs start to converge, and you then aim to get the two discs overlying one another - when they do the ADC is tuned (apologies if you were aware of this but I couldn't see this specifically mentioned above).

 

I have been using an ADC with an 8SE for a year or so.  I have just modified it as suggested elsewhere in CN by Kokatha Man, to attach a bubble vial to get the white screw close to horizontal (I can't see the horizon from my backyard!).  I am also going to try shifting the order of the ADC, Barlow and camera as discussed above - currently I have the ADC next to the camera.

 

Mark


  • GeorgeInDallas likes this

#7 RedLionNJ

RedLionNJ

    Vanguard

  • -----
  • Posts: 2443
  • Joined: 29 Dec 2009
  • Loc: Red Lion, NJ, USA

Posted 13 January 2018 - 09:28 PM

Darryl's bubble-level idea is a great one, particularly if you are not 100% sure you're parallel with the horizon. I bought a little ten-pack of one-inch bubble levels from Amazon for next-to-nothing. They have square, plastic ends which I found easy enough to carve/grind a curve into, making for a nice surface to cement onto my ADC barrel.

 

It really does make the initial alignment a breeze, as well as subsequent "phase 1" adjustments.

 

Thanks for the idea, Darryl!


  • kbev, GeorgeInDallas and Lacaille like this

#8 Kokatha man

Kokatha man

    Voyager 1

  • *****
  • Posts: 11041
  • Joined: 13 Sep 2009
  • Loc: "cooker-ta man" downunda...

Posted 13 January 2018 - 10:33 PM

Hi again - George has a mono camera Mark, so ADC tuning via FC isn't an option...

George (& anyone else) there are 2 good reasons for being able to rotate/orientate the ADC independently of the camera...you of course need to adjust its own orientation to keep that white reference screw* parallel to the horizon (ie, horizontal) as the scope & mount move across the sky (in practice this is something you can do every 10 minutes or so, less often if you're not so fussy) but if you don't then re-orientate the came after re-orientating the ADC then the planet will not move in good X-Y planes on your sensor & screen & this also means if you rely on FC's auto-guide you can run into problems. wink.gif

*Remember, you initially set that white screw in the mid-point of the ADC's 2 slots where they overlap to make it the reference point so that the orientation & subsequent re-orientations of the ADC as a whole can be kept at the correct orientation - the white screw is just the reference for once you've set it initially in that mid-point & is not touched again! smile.gif

 

And of course you will be tweaking the 2 ADC levers for best dispersion over time... wink.gif


  • GeorgeInDallas, Lacaille and kevinbreen like this

#9 Lacaille

Lacaille

    Mariner 2

  • -----
  • Posts: 275
  • Joined: 27 Nov 2015
  • Loc: Canberra and Strasbourg

Posted 13 January 2018 - 11:39 PM

Hi again - George has a mono camera Mark, so ADC tuning via FC isn't an option...
 

Oops! Must develop better reading habits!



#10 kbev

kbev

    Viking 1

  • -----
  • Posts: 777
  • Joined: 29 Dec 2010
  • Loc: Far, far east Mesa

Posted 14 January 2018 - 08:04 AM

I've used a W47 filter as referenced above to tune my mono cameras and it works quite well.  You just need to make sure you have the exposure set so you can see both UV and IR images of the target star, then you adjust the prisms to bring the two to the same point.  Note that one of the star images will be out of focus given the different wavelengths; I usually set focus to the dimmer IR image and while the UV image is out of focus it should be bright enough that you can see the Poisson point in the center, then bring it in line with the IR image.

 

As for rotating the ADC and camera, I will set the ADC level and then rotate the camera in the adapter on the back of the ADC to get its orientation correct (since I do use the FC autoguide feature).  Currently my configuration is:

 

2.5x powermate with T-thread adapter screwed into the front of the ZWO filter wheel

ADC screwed into T-threads on the back of the filter wheel (via a T2/T2 adapter similar to what Darryl has pictured)

Camera slipped into a T2/1.25" holder (again as Darryl shows above)

 

This gets me roughly f/23-25.  I may go ahead and try swapping the powermate and ADC around to see what I get, it won't take long and if it gets me better results then I'll be happy.

 

 


  • GeorgeInDallas and Lacaille like this

#11 GeorgeInDallas

GeorgeInDallas

    Viking 1

  • -----
  • topic starter
  • Posts: 547
  • Joined: 15 Apr 2012
  • Loc: Dallas, Texas USA

Posted 14 January 2018 - 12:42 PM

Ferret, Kokatha man, RedLionNJ, Lacaille and Kbev

 

Thanks for your reply/suggestions and insight. This is just the kind of feed-back that I was needing. 

 

Sounds like the best strategy for keeping the prisms oriented with respect to the horizon is to rotate the body of the ADC. I will attempt to attach a small level, the way that Darryl and RedLionNJ have to assist with the periodic level adjustments. 

 

I utilize FC for auto guiding so I will definitely have to assure that the camera is correctly oriented following each level adjustment to make that work properly. 

 

As for setting the prism dispersion correction position, since I am using a mono camera, it sounds like using a W47 or similar filter is an approach that provides good visual feedback to assist in the adjustments. I notice that the image near the bottom of Andre Paquette's web page labeled "Denebola, 38d, UHC Lumenera + MetaGuide" was made with a Baader UHC-S filter. That image shows clear dispersion at an altitude (38 deg) similar to the position of Jupiter from my location. I have found an Astronomik CLS-CCD with virtually identical band pass characteristics at Opt (See graph below). I am considering buying the Astronomik CLS-CCD filter and replacing the IR filter in my new filter wheel (I should have bought a 7 position filter wheel!!). 

 

http://paquettefamil...tro/star_study/

 

Again, thanks to everyone for your excellent responses,

George Hall

 

 

Attached Thumbnails

  • astronomik_cls-ccd_trans.png


#12 kbev

kbev

    Viking 1

  • -----
  • Posts: 777
  • Joined: 29 Dec 2010
  • Loc: Far, far east Mesa

Posted 14 January 2018 - 07:53 PM

George, if this is the filter you're considering buying:

https://optcorp.com/...er-ccd-1-25inch

 

I would hold off unless you also have plans to use it as a light pollution filter for imaging.  A much cheaper alternative (the one I use) is this #47 filter by TPO (also sold at Opt): 

https://optcorp.com/...filter-case-f47

 

Hope this helps.


  • GeorgeInDallas likes this

#13 GeorgeInDallas

GeorgeInDallas

    Viking 1

  • -----
  • topic starter
  • Posts: 547
  • Joined: 15 Apr 2012
  • Loc: Dallas, Texas USA

Posted 14 January 2018 - 09:08 PM

Kevin,

 

Thanks for the info. Do you know where I can see a graph of the band pass for this filter?

 

George

 

George, if this is the filter you're considering buying:

https://optcorp.com/...er-ccd-1-25inch

 

I would hold off unless you also have plans to use it as a light pollution filter for imaging.  A much cheaper alternative (the one I use) is this #47 filter by TPO (also sold at Opt): 

https://optcorp.com/...filter-case-f47

 

Hope this helps.



#14 kbev

kbev

    Viking 1

  • -----
  • Posts: 777
  • Joined: 29 Dec 2010
  • Loc: Far, far east Mesa

Posted 14 January 2018 - 10:04 PM

 

Kevin,

 

Thanks for the info. Do you know where I can see a graph of the band pass for this filter?

 

George

 

I found this chart on the Kodak site for the Wratten 47:

https://www.kodak.co...lters/W2-47.pdf



#15 kbev

kbev

    Viking 1

  • -----
  • Posts: 777
  • Joined: 29 Dec 2010
  • Loc: Far, far east Mesa

Posted 15 January 2018 - 09:32 AM

I was able to get out this morning and try tuning the new setup (ADC - Filter wheel - Powermate - Camera) and was able to do a couple of captures to illustrate tuning with a Wratten 47 type of filter.  Here are the processed images:

 

Star - ADC not tuned

star_untuned.png

 

Star - ADC tuned

star_tuned.png

 

The seeing was pretty atrocious and I was imaging thru a thin layer of high clouds but I think it still get the idea across.  Interestingly my ADC seemed to be tuned when the levers were centered and almost overlapped; I think I may need to do some more experimenting because I know the last time I used it (situated behind the powermate instead of in front) I had decent separation between the levers.  But there's plenty of time until Jupiter and Mars reach opposition.

 


  • GeorgeInDallas likes this

#16 GeorgeInDallas

GeorgeInDallas

    Viking 1

  • -----
  • topic starter
  • Posts: 547
  • Joined: 15 Apr 2012
  • Loc: Dallas, Texas USA

Posted 15 January 2018 - 11:42 AM

Kevin,

 

Thanks for the demonstration images. Based on your previous post, I ordered the W 47 filter that you recommended from Opt. (TPO #47 Violet Color Filter & Case - 1.25")

 

These images are very encouraging. Even the IR star image seems to be noticeably less elongated in the corrected image. From what I have read in Darryl's post your results seem to be in line with the expectation of less dispersion correction required with the ADC before the Powermate in the optical path. 

 

Now, on to getting a level attached to my ADCsmile.gif

 

Thanks,

George



#17 RedLionNJ

RedLionNJ

    Vanguard

  • -----
  • Posts: 2443
  • Joined: 29 Dec 2009
  • Loc: Red Lion, NJ, USA

Posted 15 January 2018 - 12:06 PM

Kevin - that's a great pair of images to demonstrate the difference between poorly-tuned and well-tuned using the UV/IR method. Nice job.

 

I think you find the exact appearance of the alignment varies as you wander around the chip, though. Since the ADC throws the light off-axis a bit to achieve the required dispersion cancellation, I would think you'd want to place the image just a tiny bit off to one side of the axis to make most use out of this compensation. [Don't ask me which side, I'd have to try, firsthand].

 

I would also be hoping ("expecting" is likely too strong a word, for I can rarely get my own FC red/blue to overlap perfectly) the two star images would be on top of one another. It's hard to estimate image scale, but the difference in position between UV and IR peaks looks to be an appreciable fraction of an arcsec (if not bigger) in your lower image. I'm assuming you picked one of the better ('frozen") frames when seeing wasn't at its utter worst?

 

All in all, though - great demonstration of the UV/IR method.

 

Personally, I take the easier (but more $$$) route - I either use a color cam for imaging (hence have the FC tool right there) or I have a mono cam which is parfocal with a color cam, and can use the FC tool with my color cam, then replace (Baader Quiklock is great, here) it with the mono cam.



#18 GeorgeInDallas

GeorgeInDallas

    Viking 1

  • -----
  • topic starter
  • Posts: 547
  • Joined: 15 Apr 2012
  • Loc: Dallas, Texas USA

Posted 15 January 2018 - 12:22 PM

Kevin,

 

I also wonder about the separation in the corrected image that RedLionNJ has pointed out. It seems to be off-axis from the Dispersion correction. Is it possibly a mis-alignment with respect to the horizon?

 

Also, a couple of more questions have come to mind. Do you recall the elevation of the star in the images? What size scope did you use to make the images? Your post says the images were processed. What kind of processing was done (stacking?) Were these images from Metaguide? 

 

Thanks,

George



#19 kbev

kbev

    Viking 1

  • -----
  • Posts: 777
  • Joined: 29 Dec 2010
  • Loc: Far, far east Mesa

Posted 16 January 2018 - 02:14 PM

George, to answer your questions:

 

The dispersion could be from misalignment, I did have the unit as level as I could get it (within a degree or two I'd guess).  I had a thought last night at work that I may have had the levers on the wrong side (righty vs. lefty) and that might have contributed to the displacement; it could also explain why the ADC seemed tuned at the null point.  I'm going to install it tonight with the levers on the right and see what that gets me.

 

The star I used was Spica and at the time it was about 35 degrees altitude, similar to what Jupiter was going to be when I was planning on imaging it.  The images were made with my normal setup - 10" Meade SCT, ASI290MM and a 2.5x powermate.  As far as processing, I captured 1000 frames in FC and stacked them in AS!3, then did a very mild wavelet adjustment in Reg6 to help bring out detail.  I don't currently have Metaguide installed on my laptop so did not use it.  Here is a side by side of Zubenelgenubi when I was checking my collimation - raw stack on the left, processed on the right.  This would be the same amount of processing I did to the images I posted above.

 

collimation_check.jpg



#20 John Boudreau

John Boudreau

    Surveyor 1

  • *****
  • Posts: 1567
  • Joined: 06 Apr 2008
  • Loc: Boston Area, MA

Posted 16 January 2018 - 03:38 PM

George, to answer your questions:

 

The dispersion could be from misalignment, I did have the unit as level as I could get it (within a degree or two I'd guess).  I had a thought last night at work that I may have had the levers on the wrong side (righty vs. lefty) and that might have contributed to the displacement; it could also explain why the ADC seemed tuned at the null point.  I'm going to install it tonight with the levers on the right and see what that gets me.

 

The star I used was Spica and at the time it was about 35 degrees altitude, similar to what Jupiter was going to be when I was planning on imaging it.  The images were made with my normal setup - 10" Meade SCT, ASI290MM and a 2.5x powermate.  As far as processing, I captured 1000 frames in FC and stacked them in AS!3, then did a very mild wavelet adjustment in Reg6 to help bring out detail.  I don't currently have Metaguide installed on my laptop so did not use it.  Here is a side by side of Zubenelgenubi when I was checking my collimation - raw stack on the left, processed on the right.  This would be the same amount of processing I did to the images I posted above.

 

attachicon.gifcollimation_check.jpg

My W47 filter (from OPT) was supplied with a plastic screw-in retainer that barely engaged with the cell's threads --- it would loosen so that the filter would flop around in the cell and I'd see similar slanted results as yours. Luckily I had a metal retainer that solved the problem. You may want to check yours. 


  • kbev likes this

#21 GeorgeInDallas

GeorgeInDallas

    Viking 1

  • -----
  • topic starter
  • Posts: 547
  • Joined: 15 Apr 2012
  • Loc: Dallas, Texas USA

Posted 16 January 2018 - 05:14 PM

Kevin,

 

Thanks for taking the time to respond to my questions. Those are pretty nice results for your collimation. Good to know the details of the prior images.

 

Thanks again,

Good Luck,

George

 

John,

 

I expect my W47 from Opt. to arrive in the next couple of days. I will check for the problems you encountered. Thanks for the heads up.

 

George



#22 kbev

kbev

    Viking 1

  • -----
  • Posts: 777
  • Joined: 29 Dec 2010
  • Loc: Far, far east Mesa

Posted 16 January 2018 - 07:02 PM

 

My W47 filter (from OPT) was supplied with a plastic screw-in retainer that barely engaged with the cell's threads --- it would loosen so that the filter would flop around in the cell and I'd see similar slanted results as yours. Luckily I had a metal retainer that solved the problem. You may want to check yours. 

 

 

I will do that, although when I installed it in the filter wheel the other night it didn't seem to rattle.  Looks like I'll have time since it appears we're going to have another typical January night here in the valley of the clouds.



#23 GeorgeInDallas

GeorgeInDallas

    Viking 1

  • -----
  • topic starter
  • Posts: 547
  • Joined: 15 Apr 2012
  • Loc: Dallas, Texas USA

Posted 17 January 2018 - 08:35 AM

Below is a graph of a Meade W47 filter which might be similar to the TPO W47 filter.

 

Here is a link to a web page with measured transmission graphs for various filters, the Meade W47 filter is about midway down the page.

 

http://www.astrosurf.../filtres-en.php

 

George

 

 

Kevin,

 

Thanks for the info. Do you know where I can see a graph of the band pass for this filter?

 

George

 

George, if this is the filter you're considering buying:

https://optcorp.com/...er-ccd-1-25inch

 

I would hold off unless you also have plans to use it as a light pollution filter for imaging.  A much cheaper alternative (the one I use) is this #47 filter by TPO (also sold at Opt): 

https://optcorp.com/...filter-case-f47

 

Hope this helps.

 

Attached Thumbnails

  • W47_BandPassGraph.jpg

Edited by GeorgeInDallas, 17 January 2018 - 09:06 AM.


#24 SteveInNZ

SteveInNZ

    Messenger

  • -----
  • Posts: 471
  • Joined: 07 Oct 2007
  • Loc: Auckland, New Zealand

Posted 17 January 2018 - 02:21 PM

If anyone has an ADC, a CLS-CCD and a bit of curiosity, I'd be interested to know how well that filter works with this technique.

While the W47 is much cheaper, a CLS-CCD has other uses and has much more than 3% transmission. I'm not sure if that would be a pro or a con for this application. I'm curious but not $$$ curious.

 

Steve.



#25 John Boudreau

John Boudreau

    Surveyor 1

  • *****
  • Posts: 1567
  • Joined: 06 Apr 2008
  • Loc: Boston Area, MA

Posted 17 January 2018 - 04:08 PM

If anyone has an ADC, a CLS-CCD and a bit of curiosity, I'd be interested to know how well that filter works with this technique.

While the W47 is much cheaper, a CLS-CCD has other uses and has much more than 3% transmission. I'm not sure if that would be a pro or a con for this application. I'm curious but not $$$ curious.

 

Steve.

I've tried ADC adjustment with an Optolong CLS-CCD filter, which has similar bandpasses to the Astronomik CLS-CCD. It worked OK and if that's what you've got it'll be worth trying out.  However the W47 and a BG-3 filter I also own have bandpasses separated by over 200nm, while the CLS-CCD filters have bandpasses separated by only a bit over 100nm. The greater the bandpass separation, the more sensitive the filter is for ADC adjustment as the twin images of the target star will show greater separation until the ADC is properly adjusted. 


  • happylimpet likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics