American cinematographer (Jan-Oct 1925)

April, 1925 AMERICAN CINEMATOGRAPHER Tuenty-one is fundamentally a red-green, two color process, the two main images are formed side by side on a double width film on a silver ruled glass grating, that part of the image falling on the silver strips being reflected and that part of the image falling on the unsilvered strips being transmitted. The single lens takes therefore two simultaneous pictures thus eleminating parauax and color fringes. The pictures are projected at normal speed from double width positives. A recent exhibition in England'8 of twocolor films made by the C. Friese-Greene process showed in rapid motion scenes with figures, slight confusion of picture, but the color renderings of draperies were successful and essentially true. In open air views the faulty rendering of blues of nature was reported quite noticeable. Greens and reds were excellent. Fringing effects were undetected. For the exposure, panchromatic negative stock is required costing 1 1-2 cents per foot extra but ordinary positive stock may be used for printing; an additional operation being necessary at a cost of less than one cent per foot. The camera requires a rotating disc attachment which may be fitted into most cameras. An exposure aperture of f.8 in bright sunlight is sufficient at a speed of 22-24 pictures per second. Artificial lighting requires 15 per cent more light than is needed for monochrome work. Development is best accomplished in darkness and printing is done on the ordinary machine, the extra processes adding a 10-15 per cent increase in the time required for finishing. Condensing Lenses Of especial interest in connection with improvement in condensing lenses, as well as for other use, is the announcement'9 of the commercial development of clear fused quartz. The very low temperature-expansion coefficient permits this material to be subjected to quick temperature changes without cracking; quartz condensing lenses used with the high intensity arc lamps show no breakage even after several months use. The low light absorption of quartz (about 1-5 that of glass), the low expansion and contraction (1-16 that of platinum), and its ability to pass utraviolet light, are its important characteristics. Educational Complete and detailed studies in the prois Brhi-h Journal of Photography Colored Supplement, Apr. 4, 1924, p. 16. l'J Light, Inly 1924, p. (>. Motion Picture News, May 24, 1924, p. 2528. Carl Zeiss, Jena, have perfected a new lens — a Tessar, with a working aperture of f .2.1. Combining the well known Carl Zeiss quality with the greatly increased light gathering power of f :2.7 means an objective for motion picture photography that is revolutionary — a lens that will produce results under the most adverse conditions. Following are the focal lengths and prices : Foots Standard mount Focussing mount \H inches ....$40.00 $47.00 1916 inches 40.00 47.00 2 inches 43.00 50.00 lyk inches .... 51.00 58.00 4 inches .... 64.00 71.00 4-14 inches .... 72.50 82.50 fzazcld 07T. ften/wff U.S. Qganf OZew ybrk A NEW LENS ''That has made good" Large aperture F:2.3. To a large extent responsible for the Bas-relief, or solid appearance of the subject on the screen. Good definition over the entire field, yet not harsh or wiry. A portrait lens in short focal lengths 40mm, 50mm, 75mm, with full closing diaphragm. Price is reasonable 40 mm $50.00 50 mm 50.00 75 mm 55.00 A trial will be satisfying ASTRO-GESELLSCHAFT, mbh., Berlin For sale by Mitchell Camera Corporation 6025 SANTA MONICA BOULEVARD LOS ANGELES. CAL.