Motion Picture News (Sept-Oct 1916)

October 21, 1916 ACCESSORY NEWS SECTION 2S85 COLOR PHOTOGRAPHY (Continued from page 2583) natural colors could be produced. Lippman communicated the details of his process to the French Academy of Sciences in that year. Lippman's researches (along the lines suggested by Zenker in 1868) were directed toward the production of photographic results in color by interference, and he called the results " interference heliochromes." While the Lippman process is in no way applicable to cinematography, a description of its underlying principles will prove of value here, because in addition to the fact that " interference " is a physical phenomenon by which many of the colors of Nature are produced, some of the most accurate tests in photographic optical work (the polishing of lenses and the selection and surfacing of glass for light filters) are accomplished by the observation of interference bands or colors. The Lippman process of Interference Heliochromy will be best understood by reference to the diagram, Fig. 10. Making Interference Heliochrome In Fig. 10 P is a glass plate coated with a perfectly transparent bromide emulsion sensitized for all colors and having its silver particles in an extremely fine state of division (much finer than in an ordinary plate). Such a coated and sensitized plate is placed, with the glass side towards the lens, in a special plate holder having a reservoir at the back. This reservoir is next filled with clean dry mercury, the mercury being introduced so that it comes into direct contact with the emulsion side of the plate, forming a reflecting mirror as indicated by M, Fig. 10. In Fig. 10 the thickness of the emulsion between the glass P and the mercury M is shown greatly exaggerated. Light rays from the lens falling upon the glass plate P and traversing the emulsion are reflected back by the mercury M. The path of the incident light waves are shown by the solid wavy lines in Fig. 10, while the reflected light waves are shown by the dotted wavy lines. By a study of Fig. 10 it will now be seen that the reflected waves come together, or interfere, with the incident waves at periodic intervals. Thus stationary or stand'"^ waves are formed within the transparent sensitive emulsion. At the points where the waves come together (or interfere) the light is extinguished, but at intervals of half a wave length (of the incident light) between the points of interference, exposure takes place, iorming a series of fine lines or laminae within the structure (or thickness) of the emulsion. These points at which exposure takes place are indicated by the shaded portions in the center of the loops in Fig. 10. It will furthermore be deduced that these exposed lines must be closer together and more numerous for light of short wave lengths than for light of long wave lengths. We have, therefore, in preparing the diagram, shown sets of waves for red, green and blue light respectively. What a Heliochrome Looks Like B, Fig. 10, serves to show that there is a loss of one-half a wave length of the incident light when reflection takes place at the mercury mirror. The causes for this need not be dwelt upon here. Now as to the actual appearance of a developed fixed and dried interference heliochrome. In order that the readers who have never seen one of these results may be under no misapprehension we will state that the exposed lines or laminae are not side by side upon the surface of the plate but are situated (side by side) in the structure of the transparent emulsion — between its outer surface and the glass plate. When one of these interference photographs (a transparency of course) is looked through, only a brownish color is seen, but when the plate is viewed at an angle (by reflected light), the objects photographed are seen in their true natural colors. When it is considered how infinitesimal a wave-length of light is, and when it is realized that there are within the emulsion film of an interference photograph many exposed lines separated by a distance of only half a wave-length, it will be appreciated that an interference heliochrome is really one of the wonders of science. Equip Your Projection Machines A^OH^-with the mse MARK It's the surest and quickest way to show better pictures ; build a bigger business and make larger profits. Don't be criticised by your patrons because of blurred pictures, slip-ups and delays. Don't put up with the inconvenience, annoyance and expense of Inferior projection equipment. Take a lesson from hundreds of the largest and most prominent picture houses who have been through it all — and now won't have any generator but the Transvert«r in their booths. Economy of Cost and Operation The Transverter is compact, simple and easily installed in any booth : operates on A. 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