Journal of the Society of Motion Picture Engineers (1930-1949)

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Infrared Photography With Electric-Flash BY FREDERICK E. RARSTOW EDGERTON, GERMESHAUSEN & GRIER, INC., ROSTON, MASS. SUMMARY: 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. THE EXISTENCE of the infrared portion of the spectrum has been known since the early part of the last century, and infrared photographic records have been produced for over sixty years. However, it was not until 1931, when advances in sensitive materials were made, that the application of infrared photography became practical.1 Photography using wavelengths longer than 13,000 A (Angstrom units) is still difficult. Present-day applications depend on: (1) the ability of infrared radiation to penetrate haze; (2) differential absorption and reflectance of these long wavelengths by different materials; and (3) the inability of the human eye to respond to infrared light. These properties have led to the use of infrared in aerial photography, camouflage detection, crime detection, medicine, botany, and many other fields. For some subjects the source of infrared radiation is the subject itself, but in all other cases some external source must be used. Common infrared sources are sunlight, incandescent light, arc lights and photoflash lamps. Less common, although not new, is the use of electric-flash (stroboscopic or high-speed lights) which makes possible the practice of infrared photography using very short exposures. It is this type of infrared light source and its application with which this paper is concerned. Twelve or fifteen years ago electric-flash techniques were little known, but today their use is commonplace.2 Several papers on this subject have been published in this Journal.3-4 However, it is less generally known that an electric-flash source emits a great deal of infrared radiation. Figure 1, a typical spectral distribution curve of PRESENTED: April 26, 1950, at the SMPTE Convention in Chicago. NOVEMBER 1950 JOURNAL OF THE SMPTE VOLUME 55 485