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I have had this issue with CCDstack many times. I never have had 50 subs though. It would depend on your file size. CCDStack used to be very poor with memory management and large file sizes (like what you get with an 11002 camera on up) would bog it down terribly and you would get memory exception error messages if you tried to stack more than about 10 images.
CCDStack 2 seems to have improved its memory management and is less prone to that.
Even so I tend to stack no more than about 10 x 32mb images into groups.
Again it depends on your camera as well. My Proline 16803 is very clean so stacks of 5 to 10 submasters stacked together later would result in a very clean image anyway. A noisier camera may require larger numbers.
All these stacking routines come from statisical analysis maths. Basically for any of these to work effectively there needs to be a large enough sample so that outliers can be identified and removed by the maths.
In other words 2 images would not give you an outlier. Either one could be correct. But 3 now gives you an idea of what is normal. 6 for sure. 100 would be more reliable. So there would be a dimishing return on the improvement unless conditions were very variable between images.
But if you get a run of images that look much the same as you flick through them then the maths is not going to do much anyway. There is not much variability to detect and reject to get a normal sample.
I haven't used PI to do stacking and it sounds like it gives a nice report so you can see the differences but at the end the above theory is what is occurring no matter which program you are using.
You could work out a progression of more and more discriminating maths formulas. Plain average settles some differences. Median would too (mid points). A standard deviation after several samples starts to further refine what is a normal pixel value. square root of squared differences from a standard deviation is now discriminating more finely. Etc etc.
Greg.
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