Re: [ATM] holographic null test on round robin mirror C

[Andy Saulietis <iss@pvtnetworks.net>]

Matt Tudor writes:

>With all the talk about the holoraphic null test, what about a more modern
>version of a Hartman test ? All it takes is a mask in front of a ccd 
>camera <snip>

I suggested this exact test a couple of year ago. The optics gurus
looked at it and concluded that there would be too much uncertainty
in the slope determination to be able to reconstruct the figure
of the mirror using this technique, mostly because the in/out
focus pattern was limited in size by the CCD, resulting in a too
short baseline (in>out distance).

The old style Harmann test using glass photographic plates was useful for 
*large* optics because
the size of the patterns was huge relative to a CCD chip, and
the requirement was not expressed as a fractional wavelength,
but as  a required maximum spot size, usually ~ 1 arc sec dia.

Today's big mirrors don't use the Hartmann test, usually they're
figured by null testing using a custom-made correcting lens
in the test fixture.

   


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