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I agreeHere is a picture of my autoguiding problem. You can see two stacked images without alignment two hours apart (first and last picture of a session).
I learned from the helpful guys at the PHD-Forums (thanks!) that my guiding problem is known as differential flexure. Over the time the two views of the two cameras are slightly drifiting apart due to slightest changes in the differential positions to each other. The good news is that i now know what's the problem and where to start solving.
I will use this picture to inform about my steps to a solution. Maybe i am not the only one with this problem and someday someone will read this and rejoice that he is not alone with this problem.
2018/02/16: Bruce Waddington edited my RC8-image to show where potential problems for differential flexure could be. A lot to work through...
2018/02/20: Next try. Removed the guide scope rings and replaced them by clam shell style rings. If there is a chance to get at least one hour of clear sky tonight, i will check if this helps. I am a bit skeptical because the rings are each connected to the mainscope via one screw only. I fear this can't be stabil.
2018/02/20: Surprisingly the drift has reduced a lot. Picture D was taken with the modificated scope shown under C. Like the original picture it is the same object (star near NGC 2392) after about 2 hours of autoguiding (exposure is greater than in the original), stacking only the first and the last picture without aligning them. Scale of Original and D should be the same.
2018/02/20: Second test with C. Well, it is better but far from perfect... Picture shows the core of M81, by the way...
2018/02/22: Okay, i gave up earlier than i thought. This is now the replacement for the StarTravel 80/400 guiding scope. A Orion Off-Axis-Guider (OAG). I will check this setup tonight and hope, that the differential-flexure-problem is solved with this solution.
2018/02/23: That's it. The problem is solved using an OAG. You guys were right. G) is a picture combined of two subs two hours apart without aligning them. I can see no drift at all. It was a bit tricky to setup the OAG, but once everything was fine it worked like hell. I assume it will be easier with some practice. This topic is closed. Yeah!
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