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+- 1 arc second Periodic Error G11 mount and TDM

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#1 D_talley

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Posted 22 May 2011 - 11:58 AM

That is correct, my G11 mount has plus or minus 1 arc second Periodic Error after I added the Telescope Drive master to the mount. Here is my experience with the product that has been available in Europe for a few years and now is available in the U.S. through Explorer Scientific. I purchased my G11 mount a little over 5 years ago. It was a non GoTo mount. I used it as a push-to mount for three years. I then upgraded to a Gemini Goto system and have loved it since. I installed Pempro to see how my Periodic Error was with this mount that I have never tweaked or adjusted other than changing out the motors for goto. As it was, the mount gave a +- 7.3 arc second periodic error. (14 arc second peak to peak). The RMS error was 3.65 RMS.

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I wanted to improve my mount's periodic error to aid with astro-photography that I take with my TEC 140 scope. The scope has a 980 mm focal length at F7. I use a SBIG STV guider with the scope and normally get round stars. I still wanted better. There were several worm upgrade kits on the market but looking at the feedback, they still required tweaking and adjusting, sometimes with feeler gages, so it was not what I wanted. Last October I was able to purchase the Telescope Drive Master V2 and added to the mount. At the time it was only available in Europe. Not many people here knew anything about it. I was able to go to the developer's site, TDM Developer's site , to see that this scope works on several makes of mounts. The Meade Lx200, Celestron CGE and AST, the Synta Eq6 and Vixen GPDX mounts are supported. Go to this page to see if your mount is listed: Suported Mounts .

The install was simple and took very little time. One of the drawbacks is you will loose the polar align scope. Not a problem with me since I can use the polar align function in Pempro to align the mount in a few minutes. First you install the main shaft where the polar scope was.

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Then you install the Frame onto your mount:

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Another view.

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Then install the encoder hardware to the frame.

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Final install is the cover over the encoder:

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The TDM brains are in a small case that I attached to the side of my mount:

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The entire setup looks like this:

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There were no other hardware adjustments that I needed to make. Now for the testing. As stated above my Periodic Error was +- 7.3 arc seconds with the TEC 140 scope on the G11 mount that was polar aligned to within 0.4 arc seconds of the pole.

With the TDM turned on, my Periodic Error dropped down to +- 1 arc second or (2 arc seconds peak to peak). The RMS error went from 3.65 to 0.46 RMS. Not bad for not needing to adjust anything else. I am not running PEC during this run. Don't need to with such low error.

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This is better than the seeing in my area. I was able to make 5 minute subs with this setup without a guide scope. I could have gone longer but the sky glow prevented that.

As you can see there is still some error in the graph. I can reduce that by adjusting some of the corrections settings in the G11 hand controller but did not have the time. I would have some photos to show you but my laptop was taken from my hotel by someone who wanted it more than me. Backup your photos!!!

I am glad I have the TDM and don't go to the field without it. Check on the Explorer Scientific site for info and pricing.


I am not associated with either the maker of the TDM or any site selling the device. I am just a normal user of the TDM.

#2 mclewis1

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Posted 22 May 2011 - 03:54 PM

Ok, it's a relatively expensive ($1800 + "mount specific adapter") high performance autoguider that get's it's control input from a very precise optical encoder. Unlike an optical autoguider it doesn't do anything for corrections in DEC so the polar alignment has to be spot on. But then again it doesn't need a guide star and provides great RA tracking accuracy all over the sky (nice benefit).

Dwight, You mentioned that with your previous (pre TDM) setup you were getting "round stars", so aside from the cool graph, more good subs (which should mean less time on a subject), and I assume shorter setup time, can you describe the difference in your images with the TDM?

#3 ZRX-Steve

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Posted 22 May 2011 - 04:03 PM

Wow, that's tremendous results. I'm very impressed!!!!

If I had a mount with no modifications, TDM would be a definite consideration. As it is, I've already got a lot of money invested in High Precision Worms, McClennan gearbox upgrades, autoguiders, PEMPro, and PEC to get similar (though not that good) results. So for for my G11 it wouldn't make sense, but if I were starting from scratch it would be another ballgame.

Great report, and great results! Congrats.

Steve

#4 David Pavlich

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Posted 22 May 2011 - 05:01 PM

Good stuff, Dwight! One of the really cool things about our hobby is the great gizmos people come up with. :ubetcha:

David

#5 D_talley

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Posted 22 May 2011 - 06:53 PM

....

Dwight, You mentioned that with your previous (pre TDM) setup you were getting "round stars", so aside from the cool graph, more good subs (which should mean less time on a subject), and I assume shorter setup time, can you describe the difference in your images with the TDM?


The photos I did take, and then lost had pin point stars. Not as much bloat, which I guess is caused by the PE and seeing. Autoguiding did not remove all of it as I now see. Also getting a guide star took time. Now I just turn on the TDM and go after my image.

I saw another post where someone had upgraded their mount and showed before and after photos. Their photos clearly showed that a well behaved mount will provide better photos.

The cost is relative. I spent $1400 to get Go-to for my mount which I could have just used my push-to setup. Others purchase top of the line mounts for $10,000 and up. I can get similar tracking for much less. Astro Physics state that their 1200 mount's PE is +- 2.4 arc seconds. This TDM system gave me what I needed for a mount I already have.

#6 gdd

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Posted 22 May 2011 - 08:11 PM

Hi Dwight,

You mentioned you did not try PEC with the TDM. Is that even possible?

Also, would you say the best candidate for TDM is a solid mount with minimal axis-orthonality and flexure issues, and not so much whether it has low PE?


Thanks,

Gale

#7 jmiele

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Posted 22 May 2011 - 08:26 PM

Question... Does the device use the autoguide port? If so, could you autoguide if you wanted to?

Looks interesting indeed... Joe

#8 drksky

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Posted 22 May 2011 - 08:29 PM

The V1 device plugs into the autoguide port and as such does not allow the use of an autoguider. It looks like, however, that there's a V2 that you can plug an autoguider into and allows you to autoguide as well.

#9 D_talley

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Posted 22 May 2011 - 09:08 PM

Question... Does the device use the autoguide port? If so, could you autoguide if you wanted to?

Looks interesting indeed... Joe


The version I have does allow you to use the autoguider port. I tried it with my STV and it worked fine. It is for those days where you are in a rush and have not polar aligned as close as you should.

#10 D_talley

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Posted 22 May 2011 - 09:15 PM

Hi Dwight,

You mentioned you did not try PEC with the TDM. Is that even possible?

Also, would you say the best candidate for TDM is a solid mount with minimal axis-orthonality and flexure issues, and not so much whether it has low PE?


Thanks,

Gale


That is a good question. I have never tried to use PEC with the TDM and I have not looked at the instructions to see if that would work. I think it would be a problem with the mount trying to make corrections and the TDM also making corrections. The developer may pop in and give an answer.

The best mount would be one that has problems with its PE. The TDM only addresses that problem. It will not affect the issues with flexure, which occurs between two scopes or the mounts orthonality.

#11 jmiele

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Posted 22 May 2011 - 11:00 PM

So if you give up the polar scope a 3k mount is a 10k mount :)

Well, 3k+2K for the TDM... Joe

#12 jrcrilly

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Posted 22 May 2011 - 11:45 PM

So if you give up the polar scope a 3k mount is a 10k mount :)

Well, 3k+2K for the TDM... Joe


...only if the capacity increases to 140 pounds...

A more realistic target would be to consider a TDM-equipped G-11 as an alternative to a Mach1 which costs about $1000 more.

#13 jmiele

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Posted 23 May 2011 - 01:01 AM

Good point John.

That kind of changes the target market group a bit. If looking for a new mount why not a Mach1 - if available. Also, a Mach1 is an à la carte deal. There are still several additional things to purchase. It also doesn't include a tripod. It starts adding up quickly. :)

However, if someone has a mount giving them astrophotography wows, this upgrade could be a welcome one.

Joe

#14 Tapio

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Posted 23 May 2011 - 02:09 AM

Not many user reviews of these so good to see this.

#15 orlyandico

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Posted 23 May 2011 - 03:44 AM

my understanding is you need to budget another $2000 on top of the naked Mach1 for parts which are mandatory..

#16 wasyoungonce

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Posted 23 May 2011 - 03:46 AM

Outstanding Dwight.

Thanks for all info.

Just one question...what worm do you have fitted...the older, newer high precision or the new adjustable or the Ovision?

#17 tomo

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Posted 23 May 2011 - 06:12 AM

Thanks for sharing Dwight. I'm thinking about one of these for my CGE.

I noticed you said you got 0.4 arc sec for your polar alignment. This is absolutely AMAZING! How did you do that?

Cheers,
Tommy

#18 D_talley

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Posted 23 May 2011 - 07:14 AM

Thanks for sharing Dwight. I'm thinking about one of these for my CGE.

I noticed you said you got 0.4 arc sec for your polar alignment. This is absolutely AMAZING! How did you do that?

Cheers,
Tommy


My mistake. I wanted to say 0.4 arc minutes.
PEMPro has a polar align system that get me to 0.4 arc minutes of the pole in about 30 minutes. Very slick process.

#19 D_talley

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Posted 23 May 2011 - 07:20 AM

Outstanding Dwight.

Thanks for all info.

Just one question...what worm do you have fitted...the older, newer high precision or the new adjustable or the Ovision?


Thanks!

I have the standard worm that came with the mount 5 years ago. No upgrades or adjustments to it.

#20 Benach

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Posted 23 May 2011 - 07:21 AM

Looks good. However, Losmandy seems to come out with a high precision encoder system for their mounts. Anyone know the specs of that one already?

#21 gdd

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Posted 23 May 2011 - 08:27 AM

I have the standard worm that came with the mount 5 years ago. No upgrades or adjustments to it.



If you were to upgrade to the high precision worm, or even the OPWB, and improve your PE from 14 arcsec p-p to 7 arcsec p-p, is it likely your PE with TDM may improve to 1 arcsec?

Gale

#22 D_talley

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Posted 23 May 2011 - 08:30 AM

I have the standard worm that came with the mount 5 years ago. No upgrades or adjustments to it.



If you were to upgrade to the high precision worm, or even the OPWB, and improve your PE from 14 arcsec p-p to 7 arcsec p-p, is it likely your PE with TDM may improve to 1 arcsec?

Gale


Yes, I bet it would get below 1 arc sec. But you would not gain much with that because of seeing.

#23 tomo

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Posted 23 May 2011 - 08:45 AM

Phew Dwight! You saved me from hours of fine tuning to try an match 0.4 arcsec. :jump:

#24 dawziecat

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Posted 23 May 2011 - 08:52 AM

I am perplexed at this thread.

There is no such thing as perfect alignment, nor perfect "orthogonality" for that matter.

So the mount still has to be guided in dec at least.

The mount is still as susceptible to bad tracking due imperfect alignment and cone error as it ever was.

The guider will have to work less in RA correction but there will still be the other errors.

What has really been gained? :confused:

#25 Tapio

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Posted 23 May 2011 - 09:03 AM

I've done polar alignment with WCS and it's so accurate that I can take 4-5 min subs with only RA guiding.






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