Although I have been an amateur astronomer for more than 40 years, I just recently got into imaging. I spent a long time studying the issues of sub exposure times, binning, frame counts, stacking, etc. The conventional wisdom says you really need 16+ subs in each filter to produce a good image and my own experience has usually supported that idea. However, during a recent trip to my observatory (to test new SGP auto focus routines), I decide to take a set of test subs of M51. It is going to be my next target and I wanted to see how it fit my FOV. So, I took one red, one green and one blue sub – 600 seconds, 2x2 binning.
At home looking at the subs, I decided to see just what I could do with three subs by processing them in PixInsight. I was surprised at the result shown below. Clearly there are image artifacts and noise from just having three subs but the image quality is much better than I would have ever expected. Just thought this was interesting.