From: astroelectronic@t-online.de   
      
   Hello,   
      
   I have a question about stress measurement in optical glass with a circular   
   polariscope, as described in (1) and also in french language in (2).   
   The polariscope consists of the following parts:    
   -- White light source   
   -- Polarizer, 0°   
   -- Quarter wave plate, fast axis at +45°   
   -- Test piece   
   -- Quarter wave plate, fast axis at -45°   
   -- Analyzer, 90°   
   This works fine, but it's not very sensitive if the stress is small. In (1)   
   and (2) it's described how a "tint plate" (which is a full wave plate) can be   
   used to enhance contrast. So I did make a full wave plate by cementing 4   
   layers of 1/4 wave foil    
   between two glass plates. Of course all layers have the fast axis in the same   
   direction. Unfortunately after I've mounted it in a rotating filter holder, I   
   don't know where the fast axis is. Is there any way to find it out? I have two   
   polarizers and two    
   1/4 wave plates with known axes.    
      
   Thanks,   
   Michael   
      
   (1) H.W. McKenzie & R.J. Hand: Basic Optical Stress Measurement in Glass, ISBN   
   978-0-900682-72-8   
   (2) http://strock.pi.r2.3.14159.free.fr/Ast/Art/Tension.html   
      
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