I've been perfecting my sky flat approach to shooting the daylight Moon and have it just about sorted out. In conjunction with this I have been mulling over using said sky flats as "sky darks" instead, in an attempt to subtract off out the blue sky. Well, that doesn't work. But surprisingly it produces a result that is very similar to using them as flats. Only better. Vignetting is removed seemingly just as well, as are dust shadows on the sensor. More importantly, the result is to produce a subtly higher contrast Moon, especially as you approach the terminator. I have no idea what the mathematics of this is, but it works. I flipped back and forth between the flat version and the dark version of the stack and the dark version definitely looks significantly better, although it is difficult to see from the individual images.
In any event, this was shot yesterday. Poor seeing. 100% stack of 111 frames, 40 "sky darks", reduced by 50%. Sony a6000 in F/4.8 10" Dobsonian.
Link to full size image on astrobin (still reduced 50%, but no crop): https://astrob.in/dgaiey/0/
Edited by Borodog, 23 February 2021 - 06:15 PM.