Re: [ATM] Foucault and diffraction

["Mel Bartels" <mbartels@bbastrodesigns.com>]

>>>
Main implication is that the accuracy of zonal radii measurement is limited 
by the
diffractive form of the focal zone. Most so for the outermost zones, usually 
regarded as
those most reliable measurement-wise. For the above mirror, the "blank" 
section of the
KE travel within which there is little or no change in the uniformity of 
zonal darkening
might be up to a few mm for the outermost zone. If so, it would likely be 
more precise
to determine points at which each of the two zones noticeably darkens first, 
and take
the mid-value as that of the zonal r.o.c. than to try to pinpoint it 
directly. A 1mm difference
here can change a lot in the extracted wavefront profile.
<<<

So how would one of the 'spot' tests then be interpreted with respect to 
sensitivity to 'stig?

Mel Bartels 

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