I just bought a modded T3i and the first few nights I used it with my 80ED f/7.5 with a Celestron 6.3 FR yielding a f/5.25. All my frames had a darker area at the bottom of the image that ran the full length and had a uniform straight edge like a dark transparent banding. I've included a jpg of a RAW file as an example from the 80mm lights. When I used it with my C8 and the same 6.3 FR with the same spacing, which by the way yielded less focal reduction, I ended up with f7.65, but there wasn't any shadow or banding.
Flats will take care of the banding but I want to make sure that the modding of the camera was properly executed, so if need be I can send it back to have it adjusted if that's what it takes.
Does anyone have any idea what is going on? Are the angle of entry of the optical rays hitting the top of the mirror edge on the 80mm and not the C8?