[ATM] testing an f/2.6 mirror?

[Nils Olof Carlin]

Jim and others,


I would agree that the LWT is a very handy test - though it has been 
a 
while since I tried it. But I'd suggest you stay slightly closer to 
the 
mirror than the paraxial ROC - i.e. the line will appear widest at 
the 
center.  Or is that what you mean, Jim?

But based on my limited experience, I'd say the test is a bit 
sensitive - trying a hand-cranked (geared-down) tester has never 
given 
useful results for me, no doubt due to disturbing the setup by the 
odd 
few microns, while turning the dial. With a remote, computer 
controlled 
stepping-motor setup however, this has not been a problem for me, 
even 
with a set-up that is far from rock-steady.

I've only tried to evaluate the LWT with SIXTESTS.

IMHO, the "classic" wire test is difficult to impossible to read near 
the center. But as always, before actually testing, it is a good idea 
to run a simulation or two with DIFFRACT to see what the (finished) 
mirror should look like under the different tests. 

Nils Olof
--------------
At 2007-12-16 05:33 -0800, Guy Brandenburg wrote:

>Somebody wants me to test test an f/2.6 mirror, (8 inch diameter)? 
>Sounds to me like something one would need a wire test to do, and 
>I've never done that before. Any thoughts?

The lateral wire test (LWT) is much better than Foucault at that f/, 
and better than Ronchi because you get measurements rather than 
guesses.  Essentially you mount a "pinstick" on the mirror rather 
than a mask, and run the source and wire beyond the mirror's 
ROC.  Sixtests has a few words about reducing the test data:

         http://home.earthlink.net/~burrjaw/public/win6.zip 
(Win32, 2007-03-17, 372 k)

Let's see, Diffract has some simulations of what you see in a wire 
test:

         http://home.earthlink.net/~burrjaw/public/diffract.zip 
(Win32, 2004-04-12, 375 k)

It's cute - the wire shadow has a bright line in the center - helps 
measuring.

Some of the other test routines (FigureXP?) may have something, too.

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

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