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lester, purely the seeing i would presume. Have you had a night of imaging in 8/10 or better?
There is always a trade off from number of frames for stacking and quality of frames.
In say 5/10 or 6/10 seeing. 10 or 15 or 20 fps will be great as you get more and more frames to try and get rid of the crap. Compression plays very little effect here, as you would never notice it!
BUT in 9/10 seeing, when you can capture 400 frames that are all great in their own right, then you want them to be as uncompressed as possible, hence 5 fps is best. There are no distortions to try and stack out! Each and every image in that avi is the same size
See the attachment, it is a converted jpeg from the avi. I had nearly 400 of these frames to work with. The moon stayed in focus nearly the whole time. So, the only thing i can improve here is making sure it is not compressed. Stacking 200 perfect frames compared to 2000 perfect frame will have very little difference. The only difference is the compression.
Damian Peach captures in barbados due to the seeing, Chris Go captures in the phillipines where he has 7/10 or better nearly every night. Very little processing is needed. Into registax, and a little wavelets and thats it.
So, you are spot on, 20fps works well, except if your seeing is great, then compression effects will come into play. You don't need 2000 frames if the seeing is great, even 100 frames will produce a great image. The DSO guys might take 5, 10 or maybe 20 frames and stack them and produce great results.
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