Filter placed between film rails

[mturner@xxxxxxxxxxxxxxx (Marc Turner)]

     Putting an opaque IR filter between the film rails seems like a great 
     idea.  One thing that bothers me though is how near the film plane 
     this is.  It seems like any dust specs on the filter are going to cast 
     shadows on the film, resulting in dark spots on your print.  Has 
     anyone ever seen any problems with this?
     
     It also seems like there might be some automatic TTL camera meters 
     that would be confused by this technique.  For example, the OM-4 cloth 
     shutter curtain has a speckled pattern on the lens side that simulates 
     the reflectance of film.  Before the picture is taken, the meter uses 
     light reflected from this pattern to estimate shutter speed.  Once the 
     picture is being taken, it takes the "real time" reading directly off 
     the film surface and holds the shutter open until it "sees" enough 
     reflected light.  If you had a dark polyester filter between the film 
     rails, it would see that instead of the film.  Maybe its reflectivity 
     is about the same as IR film and there wouldn't be a difference.  Just 
     curious if anyone's thought about it before.  I guess it's generally 
     best to shoot IR on manual anyway.
     
     -- Marc
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