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High-Speed Silhouette Photography Of Small Biological Subjects

A photographic system of great simplicity is described which appears to have some advantages over conventional microscopic photography. The key element is a small-size light source of short-flash duration and considerable output. Two possible sources are described, (1) a guided air spark with an aperture hole, and (2) a xenon arc of small size. In addition to short exposure, because of the flash source characteristics, the ability of the system to cover a large area with high resolution may be useful. One inherent advantage of the silhouette system is depth-of-field at the subject. Two limitations are treated in this paper, the blur caused by an edge, and the light diffraction around a sharp edge. Theory shows that the definition and diffraction are both improved by a very close subject-to-film distance, as well as a small source size at a large distance from the film. Diffraction effects improve with shorter wave lengths of the exposing light, as is well known. There is some promise that the silhouette photography system may have advantages over the electron microscope since the subject need not be in a vacuum and; therefore, is not dead when studied.