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Hi Mike,
I posted this question on another group and got a few interesting replies.
Firstly unlike sound where it is oversampled 2.2X (CDs) and that is acceptable, Stan Moore contends that oversampling with light needs to be 3.3X. Now that is an educated theory but it does seem to work out.
So resolution is limited by your FWHM of stars and thus your seeing but if you assume an average of 2.0 (not sure how real that is) and divide by your 3.3 you get around .6 arc seconds/pixel as the theoretical limit of your resolution for that area.
So the example below was 1.93 arc seconds/pixel so there is potentially 3X worth of resolution left to obtain under good seeing conditions.
This oversampling factor probably is the difference between your image and Martins. As we know that last little bit of difference is what the thousands of dollars pays for. Also your scope is an AP with super high strehl and the ability to cut through seeing more easily than a bigger scope.
So in the end for optimum you would still need a long focal length scope of the same aperture to get best resolution but as you well point out excellent results can be gotten by cropping. Depends on how far you want to take it to get that last bit of detail.
I have seen Rolanf Christen use cropping to great effect from his refractor shots as well.
Greg.
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