816a731a   
   From: boyd@apt0.sao.arizona.edu   
      
   Brian wrote:   
   > On Mar 25, 10:55 pm, Optic Guy  wrote:   
   > ...   
   >   
   >>Or does it NEED an IR filter to restore proper color performance.   
      
   > The spectrum of light indoors and outdoors is usually not that   
   > different. My guess is the problem is with the colour balancing   
      
   The spectrum of the Sun and and indoor lighting  has relatively little   
   infrared content.   Even moonlight is mostly visible light since it's   
   just reflected sunlight.  But in a moonless night outdoors  skyglow from   
   the upper atmosphere is several times than the sum of all starlight and   
   it's mostly in the infrared longer than 700 nm.   Long exposure color   
   photos with CCD or CMOS cameras will produce very color distorted images   
   without a near IR blocking filter.    There are lots of cheap color   
   cameras made without IR blocking filters usually called Day/Night   
   cameras  but better quality cameras have them. Some cameras have   
   switchable filters.   
   These pictures were taken with the same Sony DSC-F717 camera at about   
   the same time. The first has an internal blocking filter for wavelengths   
     longer than ~650 nm    The second has an external filter blocking   
   wavelengths  shorter than ~ 700 nm.   
   http://i174.photobucket.com/albums/w108/ubvri/NightVision/dsc007   
   0.jpg?t=1241921482   
   http://i174.photobucket.com/albums/w108/ubvri/NightVision/dsc007   
   6.jpg?t=1241921482   
      
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