Many thanks for taking time to read my below question.
Has anyone tried to do DSO long exposure imaging with Celestron C6 SCT and Celestron f6.3 focal reducer field flattener along with a 4/3rd micro chip sensor (e.g. ZWO ASI 294MC/MM or ZWO ASI 1600MM)? If yes then have you experienced any vignetting in your subs? This is because the orange tube body Nexstar 6SE has only 1.25" of visual back (hole diameter at the back of the telescope body). Considering 105mm of back focus distance on Celestron f6.3 focal reducer field flattener this should most probably cause vignetting. Please let me know if you have any such vignetting experience.