5f4261c6   
   XPost: sci.physics, sci.physics.electromag   
   From: jos.bergervoet@xs4all.nl   
      
   On 2/10/2012 7:06 PM, Helpful person wrote:   
   > On Feb 10, 3:03 am, "anorton"   
      ...   
   >> (Remove antispam feature before replying)   
   >   
   > It's amazing how many people believe that for an extended object a   
   > larger telescope results in a brighter image.   
      
   And how stupid are those astronomers to believe they   
   need larger telescopes! Has none of them consulted you   
   to save cost, yet?   
      
   > I like to explain the   
   > physics by explaining that the image illuminance is a function of the   
   > square of the numerical aperture.   
      
   Which will go up if the lens diameter is increased   
   while the same focal distance is maintained to the   
   IR-to-visible convertor (whatever you choose for it).   
      
   If you would directly see the light (like in ordinary   
   binoculars) then NA bigger than that of the human eye   
   would not help as the light would be wasted outside the   
   pupil. Perhaps that is what you mean. But even there,   
   as long as you have not reached the human-eye NA, a   
   larger lens will make the image brighter.   
      
   > If they still don't believe, talk   
   > about F/# in a camera.   
      
   And then? If they still don't believe it after that?   
   (This is usenet, you will need extreme methods!)   
      
   --   
   Jos   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)