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Internal reflections ?
Bright stars cause an out of focus donut shaped image to appear in my images.
I am using a Celestron CPC925 with f6.3 field flatener and ZWO ASI 1600mm camera.
The artifact occurs even if the bright star is not directly in the camera frame.
It appears to be out of focus which to me indicates a different optical path.
I would appreciate any advice on the cause how to eliminate this problem
Ken
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