Electric-flash sources produce infrared as well as visible and ultraviolet light. Using only the infrared portion, the guide number for infrared film is equal to or higher than the guide number for Kodachrome using the visible portion from the same source. Factors affecting the infrared output are discussed. Described is a small airplane instrument panel photographic recorder using an infrared filter over the flashtube to avoid distraction of the pilot. The short-duration infrared flash gives very readable records on 16-mm film at one-second intervals.
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F. E. Barstow (1950) studied this question.
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