Interesting posts. Makes sense it would have to represent the surface as a whole.
Ideally under various wavelengths as well as that is what you want from an APO - no false colour.
Not sure how a turned down edge applies to a triplet in a lens cell there the lens looks to go into the cell at least 5mm.
I had an RCOS 12.5mm and it had a slight turned down edge and I simply made a mask for the outer edge. I can't say it made a huge difference but every bit counts. So there must be worse turned down edges than others.
Greg.
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