Re: [ATM] mobsby null test

[mdholm@telerama.com]

Martin Trittelvitz schrieb:

>The grating that you get from the program from Mark Holm is exactly the 
>same tiny grating. 

Well, it is not exactly the same ;) though it is just as small.  The small size
is fundamental to the test.  Grating size can be changed by changing the Grating
Z Offset in the program.  The default value is the one calculated according to
Mobsby's instructions.

As Martin says, one could get a larger grating by moving the grating position
closer to the mirror, but the test probably becomes less sensitive as one does
so.  This could be partially offset by adding more lines.  The program lets one
do this easily.  I think Malacara and Cornejo's article showed an example with 7
lines whereas Mobsby only used 3.

I say my program's gratings are not quite the same as Willman-Bell's because
mine should be a bit better.  W-B used, so far as I knkow, Mobsby's procedure
for designing the gratings.  That was an empirical and approximate method.  Mine
is ray traced, and should be exact, so far as the ray theory of light will let
one be exact.  Maybe someday I will be smart enough to figure out how to do it
with wave optics, but don't hold your breath.  Malacara and Cornejo wrote that
their version of the Mobsby grating performed well, even though it was also
designed without reference to wave theory.

Mark Holm
mdholm@telerama.com
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