Re: [ATM] Lerch's Robo Foucault VS. Interferometry, revisited

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

At 14:31 1/31/05, James Lerch wrote:

>If you'd be so kind as to have a look, and let me know what you think, I'd 
>appreciate it.

James:

A couple quick suggestions:

Doesn't your Foucault analysis algorithm look at a fairly narrow band of 
pixels along the horizontal axis? If so the comparison you want to make is 
to a cross section along the same diameter (first graph), rather than one 
constructed from radial Zernikes only.

Why not reflect the surface error line from Foucault onto the left side of 
the cross section graph so you can compare the whole diameter. Simulations 
that Jim Burrows and I have done suggest that if the mirror isn't 
symmetrical (and they never are exactly) Foucault results should more or 
less split the difference between the left and right halves. That appears 
to be pretty much the case in most of your examples.

I've been thinking a little bit about how to give summary quantitative 
measures of how good the correspondence is between Foucault and 
interferometry, and so far have the following ideas:

a) The (area weighted) rms difference between surface error profiles.

b) The rate of "false positives" and "false negatives". Let's assume for 
now that interferometry is perfectly accurate (we know it isn't, but never 
mind that). If Foucault says a mirror is good enough by some criterion and 
Interferometry says it isn't call that a "false positive." On the other 
hand if Foucault says it's not good enough by the same criterion and 
Interferometry says it is call that a "false negative." The sum of those 
two is the total error rate.

Overall it looks as though you're getting more consistent results these 
days. Good work.

Mike Peck


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

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