Hi Kevin. Thanks for your kind comments.
In answer to your questions - I always use darks, bias and flats. I did a comparison with some 45min HA subs last weekend of the difference between dark,bias and flat calibrated, dark, super bias and flat calibrated, bias and flat calibrated, super bias and flat calibrated and flat only calibrated…and the difference was very marginal indeed. It came down to a qualitative visual judgement and I went for dark, bias and flats as the “slightly smoothest”. Incidentally each of these combinations used identical dithered frames, the same preprocessing script and the same image registration and integration settings in Pixinsight.
The only reasons I’ve decided to use darks is that, when you get up to 20 odd 45 minute subs; anything you do is, in my opinion, going to offer marginal benefits …and so long it doesn’t make matters worse - why not use darks? The other thing that I found interesting was that the real difference was in the PI pixel rejection maps in Image Integration - the non dark version clearly showed the differed hot pixels and were more of a snow storm when stretched. To me, this shows that the Winsorised Sigma Clipping and darks both work well with 20 frames!
Sky limited - I don’t know is the honest answer - I just make a judgement of the risk of wasting a huge amount of time if a sub goes astray against the benefit of going deep. So long as only the centre of large stars saturate - I’m happy.
I’ll read up on what Sky Limited really means, but I think it relates to Camera Gain and A-D conversion stuff??
Hope this makes sense and thanks again for your nice comments.