From: jsavard@ecn.ab.ca   
      
   On Saturday, June 4, 2016 at 9:27:52 PM UTC-6, m...@uga.edu wrote:   
      
   > So... Maybe they're making something like a Fresnel zone plate, except that   
   > instead of being alternately transparent and opaque, the different zones have   
   > phase shifts due to different thicknesses of glass.   
      
   I don't know what Nikon and Canon are doing, but this is certainly possible, as   
   it's a standard technique - as an example, there are diffraction gratings where   
   the whole surface is reflected, but half is set back by a quarter-wavelength.   
      
   John Savard   
      
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