From: rrllff@yahoo.com   
      
   On Thursday, January 16, 2014 11:19:18 AM UTC-5, haitic...@gmail.com wrote:   
   >   
   > The whole thing is a thought experiment, at least to me, to just see what is   
   the minimum required for quantitative measurements in narrow bandwidth   
   filters. Depositing directly onto a Si surface another way to go.   
   >   
   > JB   
      
   I still don't understand how this can work.  A   
   narrow band filter will change its center   
   wavelength with angle.  if you are collecting a   
   reasonable cone of light the filter will only be   
   at the correct angle for a small percentage of   
   the light cone.   
      
   Collecting from an annulus or putting the filter   
   on a curved surface can help.   
      
   http://www.richardfisher.com   
      
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