I’m new to Siril, and pretty new to stacking in general. I’m trying to process my images from a session this weekend of M31 and 12P/Pons–Brooks. After stacking and a first-run at background removal, I have some concentric circular artifacts, as seen here:
After digging around for a while trying to find the source, I noticed that my dark master has what look like the matching rings:
And for reference, here’s the master bias:
(The master flat, by contrast, is much smoother, without any obvious circular artifacts).
My darks are 15 frames at the same shutter speed, aperture, and focus as the lights, but with the lens cap on and inside a bag to ensure complete darkness.
The bias frames (15 of them) were taken a 1/8000, f1.8, lens cap on.
This is all with a Sony A7r IV, shot on a Sony 85mm f1.8 prime. Shooting raw.
If anyone has any pointers on where I should start looking to try to improve this, or a guess at what I’m doing wrong, I’d really appreciate it!