cb1b6f49   
   From: boyd@apt0.sao.arizona.edu   
      
   It depends on the design of the particular CCD used in the camera.   
   There are several  common types of infrared and/or low light  commercial   
   ccd cameras.   
      
   1 Common B&W ccds  which have no infrared cut filter have peak   
   sensitivity in the red through blue range (.4-.5 micron)  but are still   
   moderately sensitive to  an infrared illuminator  from about .7  to 1.0   
   micron. These are most common for cheap  short range surveillance   
   cameras with 850nm LEDs.   
      
   2. common 3 color cameras.   The red channel of these typically has a   
   "tail" into the infrared similar to common b&w ccds.   These are usually   
   called day/night color cameras.  With an illuminator they display a B&W   
   image with infrared illumination. (the red color information is shut off)   
      
   3.  Enhanced infrared cameras.  These have their highest sensitivity in   
   the red-and infrared.  The Sony ExView cameras are an example.  They   
   have about 3x higher sensitivity in the IR, about like 1 and 2 in the   
   visible.  These work well to a few hundred yard range with a telephoto   
   lenses and partially focused diode IR laser.  ExView CCDs cost more and   
   usually have more defects than "plain" ccds.   
      
   All of the above need a long pass blocking filter to ONLY be sensitive   
   in the visible or a long wave pass filter to only be sensitive in the   
   IR.  Types 1 and 2 often have short pass  filters to  give "normal"   
   images pleasing to the human eye.   
      
   4. For much more sensitive cameras in wavelengths .4 to 1 micron CCD   
   cameras can integrate for longer than normal video frames.   The   
   sensitivity is roughly linear with the integration time. Integration up   
   to about 2 seconds is practical before noise becomes severe.   Cooling   
   the CCD will allow  increased  integration time.   At -40C hour   
   integrations are practical.  The downside is that if objects move during   
   the exposure the images are smeared.   
      
   Lenses make a large difference too as lenses with small f ratios can   
   gather many times more light than the roughly f/3.5 lens of the human   
   eye.  Lenses faster then about F/1.4 start getting expensive.   
      
   For outdoor use the clear night sky (no moon) is several times brighter   
   in the 0.8 to 0.9 micron range because of infrared sky glow.  An   
   integrating ExView CCD camera or a plain ccd with a gen III intensifier   
   work well even without moonlight.   
      
   So... what to use depends on your application and your budget.  Also   
   whether your application allows the use of an IR illuminator.   
      
      
   Bret Cahill wrote:   
   > Are IR cameras more sensitive to IR or just less sensitive to white   
   > light?   
   >   
   > If it's the latter then a filter on a white light camera will do.   
   >   
   >   
   > Bret Cahill   
   >   
   >   
      
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