Thread: Strehl ratio
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Old 31-08-2019, 11:53 AM
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Peter Ward
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Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
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Your thinking is correct.

I lifted this quote (of a quote) by Roland Christien.

The "Bible" of optical shop testing, Malacara states:

"The P-V error must be regarded with some
skepticism, particularly when it is derived from a large number of
measured data points, as is the case with phase shifting
interferometry. Even relatively large wavefront errors often have
little effect on the optical performance if the error involves only a
very small part of the aperture
.

Because the P-V error is calculated from just two data points out of possibly thousands,
it might make the system under test appear worse than it actually is.
The RMS error is a statistic that is calculated from all of the measured data, and it gives a better indication of the overall system performance


The corollary being, if the PV error is over an extended area, bad things happen. A turned edge would be a case in point. I once sent an RCOS mirror back to the manufacturer for that very reason....most of the mirror had a great figure...but the turned edge proved fatal.
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