This has been a fun thread!
Mark Sutching has quite correctly pointed out the possible shortcomings of interferometric testing, and I'd put Peter Ceravolo (my optical testing mentor), has also stated provided you are aware of the pitfalls Mark mentions, quantitative testing can be equally valid. (i.e numbers!!)
The only way you are going to know a mirror has a Strehl of 0.99 is if someone actually took the time to apply some sort of quantitative test...ie
measure the bugger!
I am not saying, nor have ever said, an excellent optic can not be made without said test.
But now after the measurements have been taken you have a few possibilities....
1) They are falsifying the data
2) They are incompetent
3) The optic is indeed excellent
Assuming 1) and 2) are unlikely with reputable optical artisans (hey, you know the names) then it's reasonable to also assume the optic is indeed excellent.
Quote:
Originally Posted by wavelandscott
Can you have a bad mirror with a .99 strehl (or .95 or .96 etc. etc.)?
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