Quote:
Originally Posted by Peter Ward
Mark...I am curious...do you actually have a phase shift rig? I spent a good deal of time a few years ago trying to get a questionable optic tested in Australia, and could not find anyone (including the CSIRO) with anything larger than a 4" Zygo.
But I digress. Both Star and AP get the required density by taking many samples over multiple orientations.
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Peter, I used a Wyko 6000 Phase shifting rig at the CSIRO in Lindfield for 10 years. We had an F3 diverger lens that was quite happy testing up to 24" on the anti vibration damping bench.
Was your bum scope a C8 ?. I recall giving a quote of $400 to do the testing on the testing on the Wyko 6000 back in the early to mid 90's?
I don't agree that 1 sample point per cm is enough to characterise an edge defect and it will only diagnose very coarse figure roughness of a scale of 1 cm or more. Rotating and stacking will tend to smooth insufficient data not increase its accuracy, though it is good at removing transient atmospheric effects.
Quote:
Originally Posted by Peter Ward
And the coup de-grace for smoothness would be Ion-Milling offered by RCOS....a process hard to replicate by pushing glass and using a null test  |
Ion beam milling still relies on feedback results from a Null test ( usually autocollimation against a large flat for Cassegrains) and the results showing where glass needed to be polished off would be just as obvious to a skilled optician using a humble knife edge at the Null focus, as placing an interferometer. As Leon Foucault discovered a knife edge is capable of revealing small period defects of less than lambda/100