For pictorial purposes, the greatest use of infrared sensitive film for motion-picture photography has been for "day-for-night" effects. Foliage and grass reflect infrared and record as white on B & W film. Painted materials which visually match in color but do not have a high infrared reflectance will appear dark. Skies are rendered almost black, clouds and snow are white, shadows are dark, but often show considerable detail. Faces require special makeup and clothing can only be judged by testing.
A suggested EI for testing prior to production is daylight EI 50, tungsten EI 125 with a Wratten 25,29,70, or 89 filter, or daylight EI 25, tungsten EI 64 with 87 or 88A (visually opaque) filter. Infrared light comes to a focus farther from the lens than does visual light. An average correction for most lenses is 0.25 % of the focal length of the lens ,0125mm (.005 inches) for a 50mm lens.
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