Re: Pay Attention to Those Declination Top Plate Locking Knobs

Roland Christen

Off-axis guider is preferred method for guiding a long refractor. Next best would be to mount a Baader Guide scope using our special bracket right on the tube itself. Worst method is to mount a guide scope on top of the rings.


-----Original Message-----
From: M Hambrick <mhambrick563@...>
Sent: Tue, Feb 23, 2021 10:09 pm
Subject: Re: [ap-gto] Pay Attention to Those Declination Top Plate Locking Knobs

George & Shailesh

Good point about the holding screws. For some reason I seem to recall reading in the mount assembly instructions that they did not need to be installed if the user was planning to remove the declination top plate. Anyway, for whatever reason I never installed them. It was not long after I got the mount that I got a DOVELM162 which eliminated the need to ever remove the declination top plate. As soon as I finish this post I am going to install them.

As for the 180 EDT on the 1100 GTO mount, I have had no issues with balancing. As far as loads go, I have the scope with a pretty large and heavy SBIG STXL16200 camera and filter wheel. For guiding I use a Tele-Vue Pronto with a SBIG ST2000-XM camera piggybacked on top of the 180 EDT rings. I also have a ST-i guiding camera, but I really like the wide field of view with the ST2000. It is much easier to find guide stars. For balancing you can see my counterweight arrangement in the attached sketch. If I had a couple more 18 lb counterweights I would move more of the weight up to the top of the counterweight shaft to minimize the moment arm.

My guiding is decent enough, but I think I could do better. With an image scale of 1.1 arc-seconds per pixel, the 180 EDT really shows poor guiding. Roland has stated on many occasions that it is a bad idea to use a piggyback guide scope due to flexure. I use an A-P portable pier, and I set up and take the mount down every night, I only use the RAPAS for polar alignment, but this seems to be pretty accurate. I have not updated the PEC since I bought the mount. 

I use MaxIm DL for guiding, running separate sessions for imaging and guiding. Lately I have been working on my guiding parameters (guide exposure time, exposure delay, etc) to see if I can get better guiding, and based on Roland's comments in another post, I am going to try multi-star guiding as well. I may try to invest in one of the A-P guide scopes that mounts directly on the main OTA to eliminate the piggyback guiding, but the 250 mm focal length of the A-P guide scope seems rather short for the 180.


Roland Christen

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