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Hello Pat,
I use a c9.25 on a CGEM, I've never seen field rotation - and it seems like quite a lot for only 3 minute exposures? I only use the mount bubble level and the all star polar alignment - so I'm sure my polar alignment isn't that good (+/- 5' according to the hand controller).
Sometimes I get good guiding - other times I get drift - possibly due to differential flexure?
I don't know how often you have used the f6.3 reducer but I haven't had much success with mine. I get excessive vignetting (as in yours) and distortion/coma of stars, especially in the corners. I only have a cheap Hirsch brand - maybe the Celestron one is better?
Regards,
Tony.
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