Re: [ATM] webcam and foucault test?

[Jeff Rowe <jroweapp@swbell.net>]

Bob;
I have often wondered but not tested, the improvement that might occur 
if a high quality, flat field lens was used in these tests, such as a 
Nikkor or Rodenstock enlarger lens, or an APO process lens.  I have read 
the great debates on this list and others concerning the use of webcams 
and the like for foucault testing. To me it seems like the really weak 
link in this approach is the imaging lens. Could the cheesy lenses that 
come with webcams or the non flat field mini scopes that are added to 
testers be the source of  less than desirable results?  Is this the 
Achilles heel, of all these tests? We use great eyepieces and mirrrors 
in our scopes, are less than prime imaging lens the source of errors in 
our test equipment?  James Lerch, have you ever tried a premium flat 
field lens on your Robo Tester? Mike Lockwood any further thoughts?
Regards
Jeff Rowe

Bob May wrote:

>You might want to look at my article on cameras at the KE.
>It really doesn't matter too much what camera you use as you are
>replacing your eye with a camera and all cameras basically do
>that job, some better than others.  The lens you put on the
>camera will be more important as it will allow the filling of the
>image field with the mirror under test.  Polaris is a good
>supplier of lenses as they have one at 25mm which will provide a
>good FOV for a typical focal length range of mirrors.
>Bob May
>
>
>  
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