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


At 18:08 2003-04-26 -0400, Dave McCarter wrote:

>Not so. Perkin Elmer did not use any form of Foucault test on the Hubble
>mirror, as
>they were using a much more sensitive interferometric test that gave them
>absolutely
>total confidence in the surface they prepared. Unfortunately they were
>using the same
>set up they had developed for the KH11 Keyhole Spy satellites, which use not
>parabolic mirrors, but slightly elliptical mirrors. After the error was
>discovered by
>star testing, another test most good ATMs use before coating and certainly
>before
>"flying" their scopes, PE put out the story that a small
washer misplaced the
>reference element in their test set up, hence the error. NOT! Don't
>believe it for a
>second!
>
>Had they done a Foucault test they would indeed have noticed the error.
>But they had
>misplaced confidence in their high tech solution. As someone on this list
>is fond of
>saying, always question "conventional wisdom", for therein
lies folly and
>error.

This from Bob Goff:

 >>The Hubble was figured using a botched null test.  A beginning amateur with
 >>a wood Foucault test rig could have seen the spherical aberration if too
 >>many optical experts weren't standing around giggling. 
 >
 >
 >Actually, the opticians working on the Space telescope had noticed that
 >there was a great discrepancy between the test results with the catadioptric
 >null tester and the Offner type null tester and the Foucault device. The
 >offner and Foucault agreedexactly, showing gross undercorrection.
 >Management made an executive decision without having any experience that the
 >Catidioptric null tester was the best that could be had and didn't
 >understand the evidence. The MAN said go with the Perfect one; the Cat.
 >WRONG.
 >Basically, all of the people who were reall qualified and really understood
 >the project had retired due to the various delaying tactics of Congress.
 >The Large Space Telescope was to have been 120" o.d.
 >That's another story.

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

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