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Re: [OM] Autocollimator tests on filters

Subject: Re: [OM] Autocollimator tests on filters
From: Gary Reese <pcacala@xxxxxxxxxxxxx>
Date: Sat, 04 Mar 2000 22:55:01 -0800
Buddy W. writes:

<< To show my ignorance; what is a Vertical Autocollimator and how does
it test filters. >>

It projects a purple colored multipointed "star" image through a lens
(or even a filter if you prefer). You look into tube of the the
collimator like a telescope (with a side mounted objective) and you see
the star pattern reflected off a shiny surface below the optic (polished
metal in my case). In a perfectly centered lens without aberrations and
with minimal flare, the star image comes right back through the optic
and seems perfectly superimposed with the projected image. It is
centered, sharp and with indistinct ghosts. Upon rotating the lens, the
star remains stationary.  But in a lens with faults, all hell breaks
loose in the image. It might get fussy, or uncentered, or have strong
ghost images, or rotate all over the viewfinder, or become overlapping
multiple images of the same intensity - all combinations of the above. 

To see what these look like, go to the C.R.I.S. site on the WWW.  I
recall they are about US$3,000 and up.

Gary Reese
Las Vegas, NV

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