Hello all.
I'm pretty new to astrophotography. I noticed some distortions near the edges of images. It also seems like stars on the edges, especially on the bottom, are slightly out of focus while stars in the center are in focus. I have a f/4 200 mm Newtonian reflector and a 1x coma corrector. ASIAIR reports a focal length of 783 mm instead of the expected 800 mm. Is this an issue of back focus, collimation, guiding, something else, all of the above?
Thanks a lot.
Nikhil
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