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Old 23-11-2013, 09:40 AM
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alpal
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Quote:
Originally Posted by Satchmo View Post
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 .
It's not clear that they mean -

"final focus wave front error"

If you have a 1/20 wave mirror then it reflects at 1/10 wave accuracy.
If it then hits a 1/20th wave secondary then the final wave front is 1/5th accuracy.
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