> >>> I have used Hamamatsu before but I think you cannot make money   
   >   
   > >>> by using Hamamatsu.   
   >   
      
   >   
   >   
   > Since you know pretty accurately the direction your light is coming   
   >   
   > from, you ought to be able to do a lot better than 3x.  Making the PD   
   >   
   > smaller will help a _lot_ with the noise at 2 MHz.   
   >   
   >   
   >   
   > Cheers   
   >   
   >   
   >   
   > Phil Hobbs   
   >   
   snip   
      
   Please allow me to pose some questions here, and do some "thumb" figuring   
   on this lens. I'm frankly taking advantage of Phil's expertise, to learn lens   
   sizing.   
      
   OK - suppose you choose a 12mm dia lens with FL = 25mm. Thumb: Since the ray   
   source is relatively far away, figure the PD is near 25mm behind lens. Thumb:   
   use a plastic lens, since this is cost-sensitive. Thumb: use a small area PD,   
   like the Vishay 3mm case with area = .23mm2.   
      
   Then, you can have an "idealistic improvement in SNR based on the ideal   
   geomtry: area lens/ area PD. In this case, the lens dia is 12 mm, so area is   
   100 mm2. So gain = 500X. thumb: cut that in half, to allow for fresnel losses,   
   misalignment, etc.   
   So the gain is 250 from the lens alone.   
   Phil, any feedback on this rough figuring?   
   jb   
      
   PS - I realize PD area seems on small side, creating alignment difficulties...?   
      
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