To: atm{at}shore.net
From: Jim Burrows 
Reply-To: Jim Burrows 


At 10:52 2003-03-27 -0800, Bob May wrote:

>Ah, I had assumed that you had made a pair of slits at the light source.  It
>looks like you have the two slits at the mirror mask instead.  Check with
>your setup (if it is still available) to see how accurately you can overlap
>the two images and see if that does anything reasonable.

Be aware that my test might be different than the "double slit test".

The tester has been disassembled for quite a while, the mirror is coated
and installed in an OTA.  The mask holes were 5 mm wide; with just one hole
open on each side, the images were quite wide and hard to match.  When I
opened a pair of holes, each image had a bright narrow central band with
two dim side bands.  Usually it was easy to match the hole-pair images, but
occasionally there was some ambiguity about which was the central fringe. 
What I did was to measure each zone twice, once with hole pairs, once with
a single hole, then average if they were close, take a look again if they
differed by too much.

>I'll also note that the Gaviola test should be quite accurate for the
>shorter FL mirrors as the caustic curve becomes larger and more spread as
>the FL shrinks.

Lateral measurements such as in caustic tests are intrinsically less
accurate than the longitudinal measurements in good ol' Foucault, which is
why it's standard procedure to write down the lateral measurements with
another digit.

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

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