Re: [ATM] fringe testing a convex and concave surface together.

[Mark Holm <mdholm@telerama.com>]

Mike Lockwood wrote:

> Collimated light is nice, but it requires extra equipment.
> 
> For the water flat method, the thickness of the water is on the order
> of thousandths of wavelengths, so there is significant error in the test
> results due to perspective/parallax if the light is uncollimated.  I
> have used a Fresnel lens for the water test (testing a flat submerged in
> water) and it works.  Yes, a high F-ratio is necessary.


Where does one get a high f-ratio Fresnel lens of moderately large size
and sufficient quality?  Here is a mildly crazy idea.  Could you use a
fairly fast Fresnel lens with a negative lens to make it a telephoto or
Barlow sort of setup?  No need for achromatism since you will be wanting
monochromatic light anyhow.  Distortion would seem like the main
abberation one would want to avoid.

-- 
Mark Holm
mdholm@telerama.com

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