Within the past year or so, we've been seeing patterns appear in our darks which I suspect to be a light leak. I thought we'd eliminated it by making sure our dome is absolutely as dark as possible while taking the darks, but the pattern still exists - it's just more subtle. I thought we'd gotten rid of it until Astrometry.net ramped the contrast way up on a stacked image and it was very clearly evident. The flat calibration also didn't work well on those images, but our dome is often lit way up thanks to nearby lights and I think on this night it was lit up by the Moon, too. I'm mostly looking for a sanity-check that I am in fact looking at a light-leak - and if so, whether I can minimize light sources from the camera itself. There's a green LED that's on all the time making light even if I cover the imaging setup with a black bag. Our "normal" readout mode, I think, means we shouldn't have any pre-flash going on internally. I attached examples of the bad darks, taken within about a half hour of each other yet not identical (the 11162023 ones). I also attached one we took when we started eliminating every source of light possible (Darks_02242024 etc) as well as a screenshot of what it looked like when the darks that seemed okay were used to calibrate images and they were stacked (with the contrast turned way way way up). I included that fits file, too. Astrometry.net makes it look far worse than it is when viewed with more reasonable histogram settings, but the background fluctuations will affect photometry too, at least a little bit. (I'm not currently troubleshooting the terrible flat calibration in this data set - it's an issue, but not a camera problem, and in most sets the flat calibration works better than this - attached the previous night's Flame Nebula stack to show an example of calibration that did work well).
Jamie, Can you describe your optical setup? e.g. C14 Edge HD with rotator/focuser/AOX/FW8G-STXL/STXL-6303 ? Any chance you have an AO-X? There were a number of them made that have a Red LED visible on the side, and there's a chance that light source is affecting your images. Bascially putting a tiny piece of black weatherstripping type foam or hockey tape / electrical tape around the backside of the LED holder will prevent stray light from getting into the AO-X optical window and in through filters. This image: Darks_11162023-0001_180s.fit looks like polishing marks are showing up from the sensor, although it could be something else. So possibly a somewhat monochromatic light source - we don't know what filter was in place at the time, e.g. deep red or JC I filter might make the marks appear. This image: Darks_02242024-0001_180s.fit looks like there may be a shutter timing issue or a bit of trailing charge. Does the behaviour change if you swap filters? e.g. shoot a light on Ha or SII then a dark, vs luminance and a dark? Have you looked down the nose of the camera (or through the front of the scope) to see if the shutter is behaving properly? You'd need to set a clear filter in place. It could be the rotating shutter is loose or mispositioned. Side comment: In MaxIm... File... Settings... Site and Optics. Confirm you have complete and correct info for your telescope's aperture area and your location.
