Re: Bad images _Bouncing stars

Mike Shade

Good to see feedback.  Not sure what your mount/imaging system is but a good test might be to see what the mount does unguided for a worm cycle...with PEC on and PEC off (you have a good PEC curve right?).  My 1600 it is a 382" period.  Asking a mount to go unguided for 20 minutes (1200 seconds), unless you have a very low resolution system is asking a lot and you will likely get some RA drift, or other errors (mirror flop, component sag, dragging cables, and optical aberrations caused by seeing variations to name a few) and this is not unexpected.  See what it does for a worm cycle.


Mike J. Shade

Mike J. Shade Photography:


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International Dark Sky Association:


From: [] On Behalf Of John Thompson via
Sent: Friday, May 01, 2020 4:51 PM
Subject: Re: [ap-gto] Bad images _Bouncing stars


This is a follow up to my "Bouncing Stars" post. I imaged the next night (with and without guiding) for 1200 sec exposures. The images were fine (round stars) no zig-zag patterns or elongated stars. I did notice a slight oblong effect in the unguided image. Looking at  PHD2 graphics it appears I have some drift in RA that I must correct. All my RA corrections were on the same side of the graph.I believe that signifies an RA drift ? Looking at my PHD2 log from night one I see a frequent occurrence of "guide star lost" either for low SNR or low Star mass. I assume that losing the guide star for long periods means large sudden corrections and the "bouncing" I described. In any case I am attributing the primary cause of the problem to the guiding software either due to a settings error or poor selection of guide star. I will work on a solution with PHD2. Definitely not a mount problem as proved by last nights test. If anyone has a proven set of PHD2 settings i would appreciate getting them.

Thanks for your responses.   

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