From: "cosmicrock2001" <ursamajor_1@mac.com>

Date: May 9, 2011 11:48:36 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: Dob on a GEM

Nice job Jim.  If you can, rotate the tube assembly in your fork so the focuser with camera is on the inside and parallel to the Dec axis.  That will reduce some need for counterweight and the whole scope will be more in radial balance while you're imaging.     I built a similar 12 inch partial truss tube thats mounted on GEM to cut weight of full fiberglass tube.  

Ron

--- In Astro_IIDC@yahoogroups.com, "jimchung2338" <jim_chung@...> wrote:

Most of you will know that I've been doing my planetary imaging with a 12" Skywatcher collapsible dob using Meade Autostar and motors to drive the alt/az dob base.  The problem is that it takes constant corrections to keep the image centered as you can't rely on Autostar in alt/az mode at high focal lengths.

Since CSC was predicting very good seeing last night, I wanted to be able to monitor the seeing over two hours and capture data when the seeing peaked.  Doing this with the dob mount would have been exhausting so I designed a simple oak fork mounting system to place the dob onto my EQ6 mount.  Definitely a two man job lifting and maneuvering the 60lb OTA into the dovetail saddle.  I needed over 55 lbs of counterweights to balance necessitating a quick visit to Sears just before closing time to get an additional 20lb free weight.  

It worked well and I was able to track Saturn from 11pm to 1AM with only very minor corrections every 10-15 minutes.  Unfortunately the seeing was never that good so the imaging was a bust.

http://dl.dropbox.com/u/4852049/DOBonGEM.jpg

Jim