Between the rails (BTR).
Placing filters between the camera film rails.
Roll film cameras have metal or plastic film rails which support the film as it runs between the shutter opening and pressure plate. Some photographers like to cut gel filters to the precise size which fits into this space and tape them in place. This allows the photographer to use any lens and retain the same filter effect.
This trick is most commonly used for photographing scenes with infrared film using infrared filters which are opaque to light but which pass infrared energy. If you were to put such a filter in front of the lens you wouldnt be able to see anything through the viewfinder, since such filters block almost all visible light from entering. By positioning the filter between the film rails you can see and focus through the viewfinder but only infrared energy will hit the film.
There are two drawbacks to this approach. First, you will need to meter using an external lightmeter since the cameras internal lightmeter will be reading whatever light is coming into the lens, not whatevers actually making it to the film surface. Second, you must keep the gel filter scrupulously clean. The closer the filter is to the film surface the more apparent dust specks and fingerprints become.
cf. film rails, filter, gel, infrared, infrared film, opaque, transparent.
Entry last updated 2002-04-27. Term 120 of 1487.
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