Finally, the onion ring discussion we had to have...
I know Mike's convinced that this is due to under-exposure, but I have to confess to being far less sure. Really need a scientific approach trialling a wide range of settings and exposures and under different conditions to get to grips with this. It may be that under-exposure is a contributing factor, but Asi and I both think that undulating planet edge/shape due to poor seeing - when it can't be filtered out with quality (and the quality setting in registax alone can't do it), alignment box placement or culled manually, is certainly contributing.
One thing I do know is that I have Jupiter shots that
Do show onion rings when they were captured with medium gain/gamma and light meter almost at the top of the K3CCD tools scale (e.g. >220), and yet others with much reduced gain/gamma settings so the light meter is reading 170-180 which
Don't show onion rings?
This strongly suggests to me that exposure can only be part of the puzzle.
Anyone with clear skies often enough to run some tests
