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Re: [ATM] Calculate Astigmatism
Jim Burrows wrote:
> Anyway, the required accuracy dR in the radii of
> curvature on two diameters to achieve the accuracy dRMS from primary
> astigmatism is 2*sqrt(6)*(R/r)²*dRMS, with r the mirror semi-diameter.
To
> get dRMS to 5 nm (20 nm is a passing mirror) for Texereau's standard
8"f/6,
> dR = 2*sqrt(6)*24²*5E-6 = .014 mm.
I think I follow this. But if I run the numbers from my earlier scenario
(16", 2500 mm f.l.), I get 0.0037 mm, still different than the 0.04mm
quoted earlier. Is that because of different references using different
criteria?
My real question related to how to interpret the sixtests output. On one
diameter, I input R=2500, then the program re-calculates to 2498.6 mm. On
the other diameter, I input the same measured R=2500, and the program
re-calculates this to 2499.0 mm. Does that difference of 0.4mm really
represent physical difference in focal length on the two diameters? And if
so, is that the number that I need to compare to the 0.0037mm calculated
through the tolerance formula? In short, can I use the sixtests calculated
R to evaluate astigmatism?
Yeah, I know it's all the fault of the last guy, but we don't know where he
is now, so we're blaming you anyway...<g>
thanks,
-Doug
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