I need some help understanding how dark subs are suppose to look. I just bought an ASI1600MM Pro camera and connected it to my computer to take multiple Dark (60) subs at 180sec and 300sec exposures. The camera is NOT mounted on my SCT but just sitting on the table with a cap over the lens in a dark room. When stretched both exposures showed light areas at the corners, which surprised me. My old OSC Canon 60D dark subs seemed to be completely black even when stretched.
When I calibrated the 180sec subs and stretched one of them, the image corners seemed to be even lighter. Is this normal? I'm pretty sure these darks were generated in complete darkness. I'm not that familiar with the ASI1600MM.
Attached is a dark sub and the same dark sub calibrated.
BTW - My Flat subs seem to have the same issue with lighted corners, but probably caused by my SCT optics and F6.3 reducer.
Thanks for any help on this issue.