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

["James Lerch" <jlerch1@tampabay.rr.com>]

----- Original Message ----- 
From: "Michael Peck" <mpeck1@ix.netcom.com>

> James:
>
> A couple quick suggestions:
>
> Doesn't your Foucault analysis algorithm look at a fairly narrow band of
> pixels along the horizontal axis?

Indeed it does, 11 pixels where each 'Couder mask' hole should be.  The 11 
pixels are arranged in an arc following the zone radius, and centered along the 
horizontal diameter.

>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.

Agreed, but I included both plots as I thought I heard / read somewhere that 
Foucault tests only reveal spherical Zernike terms.  Keep in mind that 
Interferometery and Zernike Terms are just "Tools" to me, similar to my Miller 
Tig Welder.  While I don't know 'Exactly' how my Tig welder works, I know what I 
need to do to make it weld Aluminum Vs. Steel, etc..  I have about the same 
understanding on how to go from Fringe image tracings via least squares fit to 
Zernike Terms as what happens between the 220v outlet and the Tungsten elctrode 
on my Tig welder... :)

>
> 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.

Dale's software wouldn't do that, and at the time Dale's software wouldn't 
export a profile for importation into a spread sheet.  Dale has since fixed the 
export problem, but I've had other fish to fry (like getting the Bino powder 
coated and ready for the WSP next week!)

> 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.

I think I know what you mean, but I don't know how to implement it...  Let me 
see if I can get all 13 optical profiles exported into a spread sheet, perhaps 
that might be a start..

> 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.

Perhaps we could use the good old 0.8 Strehl (or < 20nm rms surface) criterion?

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

Thank you,  the thing that gives me the most pleasure is the fact that same Robo 
hardware and software that started all this fuss, is the same Robo hardware and 
software that's still being used to date!

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
                                                           Calvin Coolidge 

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