RE: [ATM] Astigmatism in round robin mirror C with Foucault.

[Michael Peck <mpeck1@ix.netcom.com>]

At 14:06 1/13/05, Koehler, Steve wrote:

>Finally, I was involved in some discussions on the Zambuto group regarding
>detection of astigmatism with the knife test.  My position was the same as 
>what
>Scott Milligan just recently posted, i.e., that PRIMARY astigmatism is not
>detectable by measuring two diameters.  Carl says that he IS able to detect
>astigmatism by seeing different surface profiles on two different 
>diameters, but
>I contend that these are higher-order effects, and not primary astigmatism.
>Carl's final word on this was that pure primary astigmatism probably does not
>show up on real mirrors, because of they way they are figured.  I don't 
>believe
>this is the case, because any actual astigmatism can be considered a 
>mixture of
>different asymmetric modes, and the lower order ones (e.g., PA) are likely 
>to be
>the largest ones.
>

Mirror C provides a good counterexample. The only significant aberration 
was primary astigmatism, with higher order aberrations too small to show up 
in Foucault testing. None of the MRR testers who used zonal tests picked up 
on the astigmatism.

Mike Peck


------
Michael Peck
mpeck1@ix.netcom.com

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