Re: [ATM] holographic null test on round robin mirror C

[Jim Burrows <burrjaw@earthlink.net>]

At 2005-02-04 09:41 -0700, Andy Saulietis wrote:

>Jim Burrows has a functional Hartmann derivative test but it's not
>the classical type..he uses the overlapping spot diagram interference
>pattern to determine slopes. Perhaps he can weigh in on the subject?
>He and I participated in the development of the modified Harmann
>test, and the analysis that just using a CCD to do a classical Hartmann
>test was not practical. Actually, I was hoping that it *would* work
>because of it's inherent simplicity and the potential ability to
>test *any* conic surface.

Within limits it does work.  It seemed to work well on the round robin 
mirrors, except I just tossed them on a standard test stand and had to 
remove the resulting primary astigmatism estimates which were large and of 
the proper sign to be coming from test-stand induced "potato chipping".

As Dale Eason mentioned, it's a pain in the a** to cut out the mask (it 
takes me 4 hours for a typical mask), but one mask would work for several 
mirrors of different D, f/, and, as Andy says, conic constants.  The square 
holes are a lot easier to cut out than the classical Hartmann 
circles.  It's worth it, though, to see the slopes of ~500 patches on my 
hyperbolic 10"f/2.6 RC cass primary being refigured (250 actual holes, 2 
images with mask centered and de-centered).

There's no lenses involved:  you remove the lens from a webcam and capture 
the chip's image.  One of the major advantages over the classical Hartmann 
is that the processing doesn't involve finding spot centroids which, as 
Suiter says, p. 284, requires the spots to be "...identifiable, resolved, 
and not so large that their positions are uncertain."  (Requiring in turn 
glass plates and measuring engines.)  In fact, for the 10"f/2.6, the image 
central parts are a smear of real spots and diffraction spots which the 
algorithm can sort out.

I'll push the download again:

         http://home.earthlink.net/~burrjaw/public/hart2d.zip 
(2004-04-24, Win32, 1.13 M)

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84)  

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