Telescope Reviews: +- 1 arc second Periodic Error G11 mount and TDM

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.

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.

Then you install the Frame onto your mount:

Another view.

Then install the encoder hardware to the frame.

Final install is the cover over the encoder:

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

The entire setup looks like this:

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.

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.