Re: [ATM] webcam and foucault test?

["pbunn@matrixei.com" <pbunn@patbunn.com>]

Would be worth a try as a really good enlarger lens can be had for nearly
nothing these days. I have a Nikor 135MM for 4x5 that I couldn't get $25 for
on EBAY - I'd hate to think what it cost new.


----- Original Message ----- 
From: "Jeff Rowe" <jroweapp@swbell.net>
To: "Bob May" <bobmay@nethere.com>
Cc: <atm@atmlist.net>
Sent: Saturday, July 22, 2006 11:37 AM
Subject: Re: [ATM] webcam and foucault test?


> 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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