From: "Jerry" 
To: "'ATM shore'" 
Reply-To: "Jerry" 


>However after several sessions of figuring with a 1/4 Amplitude TOT stroke
>to bring the surface back to a paraboloid, I ended up with a mild TUE
>(which I plan to correct) and the central hole is fairly reduced. The
>overall figure shows a 1/5 wave PV and 0.93 Strehl according to figure
>XP.(this time I am sure the readings are accurate :) ). But putting the
>same data into Foucault test analysis which works on the maths of Jim
>Burrows shows a 1/3.9 PV and 1/17.5 RMS Surface.


>Don't know what causes the discrepancy, from what I've heard; I feel
>figxp should be trusted more,

>What are your thoughts on this ?

I doubt that you could ever heard anything like this. Or you misinterpreted
something.  And finally it can't be matter of trust. It is math. That is my
thought.

Please have my best regards.
Vladimir.


Possible reasons for the discrepancy which is not really very large. The
difference between a 1/4 and 1/5 wave is about 1/20 wave or 1 millionth
inch.

1-    Is the center of mask openings calculated the same; Center of the zone
or a weighted center?

2-    Does one program allow the area covered by the diagonal mirror to be
disregarded in the output.

3-    Rounding in data input/conversion/calculating.

The discrepancy is large enough that assuming correct data entry #3 is not
likely the reason. So it is most likely number 1 or 2. I would think that
you would know if you told the program to ignore the glass hidden by the
diagonal. So that leaves number reason #1.

Jerry

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