6652d137   
   From: boyd@apt0.sao.arizona.edu   
      
   Bret Cahill wrote:>   
   >   
   > It might be more cost effective to just buy a lot of cheap IR LEDs and   
   > use a conventional camera, first testing for an IR cut off filter with   
   > a single cheap IR LED.   
      
   What is cost effective depends on what you're trying to accomplish.   
   Would a $10,000 multi-camera motion sensing alarm system be expensive if   
   it saves your life?  That could  be more effective than hiring 24/7   
   security guards and certainly less expensive.   
      
   With a wide field and short range (maybe 50 yards) system a bunch of   
   LEDs may work well.  For long range (300 yards+) a telephoto lens and a   
   single diode laser focused to the same area as the camera's field of   
   view will work much better for the money spent.   
      
   What do you want to view in the infrared?  (humans, animals, IR emitters   
   (such as other humans using cheap night vision equipment).   
   Do you want to also view in color in the daytime?   
      
   At what maximum distance?   There is little transmission loss through   
   the atmosphere, but all divergent light sources obey the inverse square   
   law.  That applies twice for a light near the camera illuminating a   
   target.  At long range atmospheric backscatter can blind the camera from   
   a nearby illuminator if the outgoing path passes in between the camera   
   and the target.   
      
   In what environment? (indoor, outdoor, bad weather)   
      
   If outdoor, in city night illumination,  moonlight, under clear sky,   
   overcast?   
      
   Do you want to simply view the scene? (monitor, computer)   
      
   Do you want to capture images either as still or video?   
      
   Do you want to do motion sensing with alarm  and/or storage of the images?   
      
   Do you have a computer with USB2.0? A computer with firewire? A computer   
   with an NTSC (or PAL) framegrabber?  Ethernet WiFi?  All of those can   
   carry video images depending on camera selection. Image processing can   
   be done in the camera or in the display computer.   
      
   Do you need to be covert to a viewer with no night vision capability? Do   
   you need to be covert to a viewer with night vision capability?   
      
   What resolution do you need to be able to recognize at what distance,   
   for example,   tell a human from a deer at 500 yards or identify a   
   particular human as friend or foe at 50 yards.   
      
   You have to decide what YOU want or need.  If what you buy won't do the   
   job it's a waste of money no matter how cheap it may be.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)