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Al - I suspected when you were throwing the figure of 1/20 and 1/100 wave around that you weren't talking RMS
I'm not sure what you meant about reflected beam being half that .
Those figures would be final focus wavefront error.
There is nothing particularly unusual about a 1/10 PV - 1/40 RMS surface for what I would consider a diffraction limited optic , but on a large RC with highly aspheric surfaces thats a very good result. I think Star Instruments surfaces were typically 1/4 PV wavfront .
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