From: pcdhSpamMeSenseless@electrooptical.net   
      
   On 2020-08-04 13:08, adamstrange8w7@gmail.com wrote:   
   > I am designing an infrared lens to work at 10 microns.  I have a   
   > detector with a 12 micron pitch and a system maximum aperture of 95   
   > mm.  What would be the optimum focal length for this lens? I realize   
   > that it is best to have two pixels across the Airy disk, which would   
   > mean this system should a focal length of 80 mm.   
      
   At some point the FOV has to come into the equation.  Otherwise you can   
   oversample the image as much as you want.   
      
   >   
   > However, the customer wants the resolution equivalent of a   
   > diffraction-limited system with a focal length of 200 mm, which of   
   > course is not happening with this aperture and this detector pitch.   
      
   Why not?  The FL just determines what the angular subtense of each pixel   
   is. The image-side numerical aperture is what determines the maximum   
   available resolution for a given wavelength.   
      
   > but I was wondering if there is some optimum value for a mismatch   
   > between the lens and a detector?  Some focal length which would allow   
   > the unresolved details of the scene to best be extracted?   
      
   Professional astronomers with relatively deep pockets often use four   
   pixels per cycle at Nyquist.  Amateurs have to trade off the diameter   
   and FOV of the scope (which determine the image NA) vs. the available   
   budget.   
      
   >   
   > The system will be taking several images of the scene, and they   
   > could, theoretically, be combined to increase the level of detail.   
   >   
   > Thanks in advance for your replies.   
   >   
      
   Cheers   
      
   Phil Hobbs   
   --   
   Dr Philip C D Hobbs   
   Principal Consultant   
   ElectroOptical Innovations LLC / Hobbs ElectroOptics   
   Optics, Electro-optics, Photonics, Analog Electronics   
   Briarcliff Manor NY 10510   
      
   http://electrooptical.net   
   http://hobbs-eo.com   
      
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