The history of three-color photography (1925)

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Prismatic Dispersion and Allied Processes 667 a photograph of that which was before it on its own minute portion of sensitive film. Thousands of stereoscopic images would thus be formed side by side, each, slightly varying from the other. When, therefore, the film was examined by transmitted light, a series of juxtaposed images would be seen. The eye would see only a point of each image, but the sum of the points would be a complete image, as seen by the eye, owing to the extraordinary accommodation powers of the latter. The position of each point seen would vary naturally with the movement of the eye, and thus by gently shifting the plate a wonderful panoramic effect would be obtained. Given a structure as here outlined it is comparatively easy to imagine the coating of the rear surface with a panchromatic emulsion, and the splitting up of the image into the necessary minute pictures, so that the whole should form a complete color picture when viewed at a distance. R. Berthon29 patented the use of a lens diaphragm with three apertures, covered respectively with red, green and blue-violet filters, and a sensitive surface on a support, the other side of which was impressed with hemi-spherical, transparent, refractive protuberances, which acted like microscopic lenses. There would thus be formed on the sensitive surface images of the three-field diaphragm. Or the colored filters of the diaphragm might be apportioned into a series of microscopical parallel transparent portions, then the lenticular forms might take the shape of semicylindrical ridges. The opaque striations of the diaphragm must be inversely proportional to the lengths of the fundamental wave of each colored filter ; thus their number must be such that their linear projection on the sensitive film gives at least sixteen lines per millimeter in the red, nineteen in the yellow-green and twenty in the blue-violet. A positive might be made from the negative thus obtained, or the latter might be reversed and the positive viewed through the lens, an image in colors would then be seen or it might be projected. The essential feature of Berthon's patent was that the tri-color filter should be placed at such a distance in the cone of rays, that three elements were included from any point on the sensitive surface, which was supported on celluloid, and that side presented to the lens being impressed with semi-cylindrical lenses. It was pointed out that the tri-color screen could be replaced by a grating or juxtaposed prismatic elements. Fig. 195 shows the various methods suggested, from which it will be seen that not only circular but hexagonal forms were proposed, these latter having the advantage of giving no interspaces. Later30 the curving of the lenticular surfaces into cylindrical or hemi-spherical lenses was claimed and also31 prismatic surfaces. A. Keller-Dorian32 patented a method of making the lenticular supports by passing celluloid between a smooth-surfaced cylinder and an engraved one, or a plate could be used. Three forms of film are shown with refractive elements or objectives of square pyramidal form, of hemi