Quote:
Originally Posted by niko
thanks Paul and everyone for the comments. Yes, I agree focus appears a bit off and perhaps polar alignment also not spot on contributing to the fuzziness.
Paul - differential flexure? You mean of the whole steup on the mount? How could you tell from the image? Useful for me to know to check images in future
thanks
again
Niko
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Niko differential flexure is where the guide camera is moving slightly from the main camera. Typically it will occur with a guide scope mounted on rings which is bolted to the main scope. The fittings and slop in parts can be ever so slight but that is enough to produce elongated stars across the field of view. It can sometimes happen with an OAG if it is not installed correctly.
An indicator of differential flexure is elongated stars across the entire field in the same direction. However, as you point out it could also be PA if that is really bad. PA that is close will show field rotation where the outer stars are elongated in a circular look when you are guiding.
To properly test for differential flexure take an image for 30 seconds, then one for 5 minutes and then one for 10 minutes. The 30 second image should have round stars. The 5 minute shot has slight elongation across the field in the same direction and the 10 minute shot will have much longer elongation across the field with star pointing in the same direction. Remembering of course that you must be guiding on a star for each image.
How far out is your PA?