[ATM] ATM Digest, Vol 40, Issue 16

[Guy Brandenburg]

I thought it looked very much like some of the phase-contrast photos in Texereau's book.

Curt Diggs <mokiman_210 at yahoo.com> wrote: 
>Message: 2
>Date: Sat, 14 Apr 2007 22:30:46 -0700 (PDT)
>From: Dale Eason 
>Subject: [ATM] Phase Contrast and Foucault image puzzle
>To: atm at atmlist.net
>Message-ID: <674967.82567.qm at web50604.mail.re2.yahoo.com>
>Content-Type: text/plain; charset=iso-8859-1

>http://home.comcast.net/~doeason/phase_and_foucault.jpg

>100k image.

>I just learned how to make a phase contrast image of a
>mirror.  Texerau calls it the Lyot test in his book. 
>The above image has the phase contrast on the left and
>the Foucault image of the same mirror on the right.
>
>The fouculat image presents a puzzle to me.  It has a
>very strange surface.  This mirror was made by a local
>ATM 60 years ago and it has been in storage or on a
>shelf ever since.  I think he was 17 when he made it
>and made and used a machine to make it.  It is
>uncoated Pyrex 10 inch F5.  It has been cored part way
>through.  The surface looks very smooth with no hint
>of what is seen here except for 2 small scratches and
>the finger prints close to the edge.
>
>Has anyone any idea what has caused the groves and
>winding features seen in the Foucault image?  None of
>the features visible on the back show up in Foucault
>image.
>
>Dale Eason
   
  Incredible images, Dale. As someone else suggested, this appears to be some sort of surface contamination to me, possibly from whatever covered the mirror in storage. Probably only a few microns thick. Somewhere I've seen a similar image in the past but for the life of me, I can't find it again. 
   
  If you haven't already you may want to try careful application of common solvents to see if any have a cleaning effect. I would try (with proper precautions) acetone,MEK, 100% isopropanol,  etc. Something may dissolve whatever it is and not harm the glass. 
   
  Good luck with it!
   
  Curt


       
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Guy Brandenburg, Washington, DC
My home page on astronomy, mathematics, education:
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