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Darin E. Fields' Astrophotography Pages
 

The Gemini GOTO System for the G11

Gemini GOTO System
I purchased the Gemini Retrofit kit for the G11. Installation was very easy. The stepper motors and gears were replaced by servo motors and new gears. The Gemini unit uses a larger control box and a new hand controller. It offers PPEC, PC control availability, remote operation, and many other features.

Thoughts and Pointers:
A few important issues must be taken into consideration when using this unit:

1. You need to make sure your mount is well maintained and that the worm gears turn freely (by finger) when tightly clamped.

2. Scope balance is very important since it affects more than guiding, but slewing and pointing as well. If the scope is poorly balanced it can require too much torque to move the OTA assembly; thus, the motors will stall.

3. It's a good idea to lower the slewing rate slightly. I had several motor stalls when the slewing was set too high (1200), but after lowering it (800), the stalls ceased and pointing accuracy and reliability greatly improved. After about five "additional alignments" I had achieved enough accuracy to be able to slew from M82 in Ursa Major to NGC 3115 (The Spindle Galaxy) in Sextans and have the object appear in the FOV of the ST-237 on the C11 @ f/6.5--which is a FOV of approximately 7 arcminutes by 9 arcminutes.

4. Highly recommended is a reliable 3 amp (at least) power supply. It is the consensus of Gemini users that batteries are inadequate for operating this unit. That pretty much confines its use to an observatory situation--or at least to a field use with AC power availability.

5. Cold can be an issue. I have had trouble getting the unit to initialize when the unit is very cold. By very cold, I mean -20 to -25 Celsius. I found that if I warmed the hand controller and the control box with a hair dryer for a few minutes, all worked fine. Then I usually warm my hands in the same fashion and quickly retreat to the warm-room!

6. Replace the Lithium battery every six months or so.