Re: [ATM] getting the foucault test right

[Jim Burrows <burrjaw@earthlink.net>]

At 2004-10-28 13:28 -0400, David  Williams wrote:

>I have the foucault tester and the 20", 1" thick mirror, uncoated, and I 
>think that it is hyperbolic.  And right now I'm wondering how to take 
>pictures of the shadowgram so that I can show you guys what it looks like 
>so that I can get your advice on what to do next.

Probably best to take some readings and post those.  Even though a picture 
is worth a thousand words, good hard data is worth a thousand pictures <for 
ATMs, anyway>.

>I have a Bronica S2 medium format camera and that would have good 
>resolution because of the finer grain, but the ground glass makes it 
>harder to focus the image.  Then I have a Pentax K1000 camera (that is 
>35mm).  Then there is a camcorder that takes not only video, but still 
>pictures.  The problem with all of these is that the foucault test is so 
>sensitive that I barely move and the image is off.  And I have the camera 
>mounted on a tripod, but that doesn't help either.

Just like your eye, the camera lens must be very close to the KE.  To set 
up the camera, turn on the lights, put the camera right where it'll be 
behind the KE, move the KE away, and focus on the mask.

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

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