Greetings Camera: sbig aluma 8300 + FW8S aluma Telescope : skywatcher esprit100ed Reducer : apex 0.65 L version Can you help me to find the back focus because starts not round at corners . Or the reducer will not fit with camera ? Sent from my iPhone using Tapatalk
That isn't a focus problem, it's an off-axis aberration issue. This may be caused by the reducer being at the wrong spacing from the focal plane.
Your Aluma 8300 camera plus filter wheel plus a mounting plate adapter ring (M48 or M42) would require approximately 40.3mm of backfocus. That scope and reducer would produce a focal plane somewhere between 55mm and 58mm if my understanding of that equipment is correct. So you would need between 15 and 18mm of extra space from the back of the reducer to the front of the mounting plate.
Also, you should probably be using the field flatener made by Skywatcher that is matched to it's optics. There is one for that specific telescope.
