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Carl evaluates his mirrors using zonal focault testing only. Expanding on what Mark said this only evaluates the mirror over a handful of data points and then extrapolates a strehl ratio from this. The selected data points may not be representative of the accuracy of the entire mirror surface. Strehl ratios calculated in this manner will always give an optimistic strehl ratio compared to what would be obtained with interferometric testing of the mirror, which calculates the strehl by sampling hundreds of random data points over the entire surface of the mirror. The foregoing is not a negative in any way, it just means the numbers, as such, are overly optimistic. Any mirror with a true strehl over .90 is going to be very very good and will run to at least 50x per inch of aperture under good seeing.
On the practical side I own a 14"/F4.5 Zambuto mirror and it is exceptional. I have looked through several other ZOC mirrors and they have been exceptional. In summary the numbers are most likely very optimistic, but that doesn't detract from the fact that the mirror will very likely be exceptional.
Cheers
John B
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