From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 




I think the fresnel lens is to collimate the light from the source in
testing flats. This also allows you to use a larger air gap between the
disks, according to M.V.R.K. Murty in "Optical Shop Testing".

In testing curved surfaces, Mr.Murty shows an arrangement that places the
light source at the center of curvature of the surfaces.  I think this was
in a reply previously.

Jerry, I like the basic homebrewed Fizeau setup.  I suspected it was simple
to setup.  The fresnel lens is the trick!

Colin

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of
Charles Rydel
Sent: Monday, February 24, 2003 4:10 PM To: Jerry Hudson; atm{at}shore.net
Subject: Re: ATM Question on fringe testing convex surfaces



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
>
>
>

--- BBBS/NT v4.00 MP