From: pcdhobbs@gmail.com   
      
   Tip it a bit so it effectively isn't a full wave plate anymore, put it between   
   crossed polarizers, and turn to get a dark fringe. To find out whether you've   
   found the fast or slow axis is a little more involved, but you can do it by   
   putting your two QWPs    
   nearly orthogonal, so as to make an almost-zero wave plate, and adjust to   
   cancel out the retardation of the tipped FWP.    
      
   You'll want to use Jones matrices or the equivalent to sort it out and double   
   check.      
      
   Cheers   
      
   Phil Hobbs   
      
   --- SoupGate-Win32 v1.05   
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