From: "Charles Rydel" 
To: "Jerry Hudson" , 
Reply-To: "Charles Rydel" 


There is a good thin green plastique filter , the Rosco Supergel filter
nø89 and nø90.  A Fresnel lens is a good idea. It could be more interesting
to put the filter at the fresnel lens level in such a way the light pass
thru it two times. It could like that magnify the fringe contrast. I think
you can buy the filter in a photo shop.

Charles Rydel
----- Original Message -----
From: "Jerry Hudson" 
To: 
Sent: Monday, February 24, 2003 7:52 PM Subject: Re: ATM Question on fringe
testing convex surfaces


>
> Kevin,
>
> I use this jig for testing convex curves:
>
>       near UV
>     o Lamp (Hg) o Eye
>
>                === Green filter
>
>
>
>
>
>
>
>      ================
>          Fresnel magnifier
>
>
>         ---------
>         |       |  Concave master
>         ---------
>         ---------
>         |       |  Convex surface being tested
>         ---------
>
> The mercury lamp is just a bug-catcher lamp
> with the high voltage supply carefully taped off.
> The Fresnel magnifier comes from Office Max (I'm
> sure other companies like Staples have them),
> and is roughly 8 X 10 inches, plastic.  I built a
> jig to hold the lens and lamp at various distances
> off the table.  Adjust until you see nice even
> illumination coming from the interface, and
> use wedges of tissue paper betw. surfs., pressing down
> until you get fringes.  I've used this rig
> on everything from flats to 39 inches convex
> radius.  No limit implied; you could easily
> add another magnifier if needed; they're cheap.
> You could also turn the concave surface upward
> and dispense with the lens, but I think the
> working distance isn't so convenient.  Depends
> on the radius of course.  Texereau describes
> this setup in his book.
>
> A neon lamp will work, too, but it is harder to
> catch the returning rays with your eye from
> such a small source.  (Don't need a filter in
> that case.)  For a filter, I've been using just
> a green piece of plastic.
>
> This rig is called a Fizeau interferometer.
>
> - Jerry Hudson
>
>
>

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