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Yes, it seems that pretty much all barlows add some over-correction, even if their marketing department says otherwise... probably due in large part to my f/4 mirror being right at the edge of the design criteria and using the barlow for more magnification than intended.
It was very handy to have 3 different mirrors on hand for the testing - all of them gave the same over-corrected images which helped to isolate the problem, but for a while there I wondered if they all had turned edges so I asked Mark to check them out. There is a very slight turned edge on all of them that can be covered by a mask a few mm wide, so now I do that always as a matter of course. Kills off stray reflections too from the edge of the glass.
Bird
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