American cinematographer (Jan-Dec 1948)

tremely bright subject for best photo¬ graphic results. The camera has been widely and successfully used in the study of high explosives. The Bowen RC-3 camera is similar to the RC-4; using the principle of the ro¬ tating mirror, but containing no shutter. It consists of a field lens, horizontal nar¬ row slit, condensing lens, rotating mirror and film four inches wide by 42 inches long. The field lens focuses the object under study on or along the slit of the camera. Tire condensing lens behind the Shock waves created by a travelling bullet pene¬ trating a one fourth inch sheet of plywood are graphically shown above. Note the echo shock wave receding on left of each photo. slit directs that slice of the object on the slit to the mirror, from which it is re¬ flected onto the film placed in an arc above the mirror. The film and the slit are conjugate so that the object focused on the slit is also focused in a narrow line across the film. The usefulness of the RC-3 camera lies in its ability to show one-dimensional motion continuously as a function of time. Microtime Photography Explanation of synchronized microtime photography is briefly described in re¬ lease by the Navy, which first explains the shutter operation as follows: "Ordinary light consists of a random mixture of electro magnetic vibrations of no directional preference. When the vi¬ brations exist in only one direction, the light is said to be plane polarized. Polar¬ izers are materials which transmit light, the vibrations of which are in one direc¬ tion only — all other vibrations are sup¬ pressed. . "Elliptically polarized light is the most general type of polarized light. Plane po¬ larized and circular polarized light are special cases of elliptically polarized light. The state of polarization of light may be altered in several ways; in the Kerr cell, electrically induced optical activity is used to alter at will the state of polarization of light passing through it. "The two polarizers are set for mini¬ mum transmission and at 45° to the elec¬ trode axis with no voltage applied to the electrodes, the plane polarized light from the first polarizer is completely extin¬ guished by the second polarizer and no light passes through the shutter arrange¬ ment. The application of voltage to the Kerr cell electrodes A A’ causes alterna¬ tion in the state of polarization of the transmitted light; consequently the light transmitted by the second polarizer de¬ pends upon the voltage applied to the electrodes. The effective open time of the shutter is therefore limited to the rapidity with which the voltage can be applied to and removed from the cell electrodes.” Kerr Cell and Camera A simple combination of a Kerr cell shutter and a conventional still camera may be used to obtain photographs with effective exposure times as short as thou¬ sandths of a millionth of a second, the Navy discloses. The effective exposure times obtainable with such a camera are determined by the voltage forming sys¬ tem, and are readily adjustable by means of plug-in type networks. Accuracy of timing pulses is monitored or checked by a special high speed oscillograph — which is capable of indicating time differences of two or three billionths of a second. RENTALS SALES SERVICE : Mitchell— Bell & Howell ► (USED) (USED) ► Standard, Silenced, N.C., Hi-Speed, Process, £ and Eyemo Cameras. ► Fearless Blimps and Panoram Dollys — ► Synchronizers — Moviolas t. 35mm Double System Recording Equipment — r Cutting Room Equipment t WE SPECIALIZE in REPAIR WORK on MITCHELL and BELL & HOWELL CAMERAS C*Ue ClflEQUIP framh c. sucker c , e soso u flnKRB cQuipmenT Co. Cifil* 0 5080 ^ 1600 BROROUIRV ntUJMRKClT* IMPROVED SAFETY FILM ANNOUNCED BY KODAK A new type of film base, adopted by Eastman Kodak Company for manufac¬ ture of much of its "safety” motion-pic¬ ture film, was described last month before the national convention of the Society of Motion Picture Engineers in Santa Moni¬ ca, California. Charles R. Fordyce, superintendent of Manufacturing Experiments at Kodak Park, the company’s sensitized-product plant in Rochester, N. Y., told the So¬ ciety’s meeting that since early in 1946 Kodak has replaced acetate propionate safety film support with a new, improved "high acetyl” acetate type. He pointed out that Kodak has con¬ ducted research on safety film since the early 1920’s and developed the first good safety film for its introduction of "home movies” in 1923. . The company’s continued research brought a major improvement in safety film quality in 1937 when a change was made to cellulose acetate propionate base. Development of the present improved "high acetyl” formula is the result of ex¬ tensive research since that time. Essentially, the new film is made by retaining chemical "acetyl groups” which in the earlier process were washed away. Fordyce said that considerable experi¬ mental work has been done on the new film to test it as a possible substitute for cellulose nitrate film, which is widely used for professional motion-pictures. "In addition to experimental tests,” he said, "the new film has been carefully watched through limited commercial trade use. Special prints of several feature pic¬ tures were circulated through film ex¬ changes in different parts of the country. "In these tests, for which alternate reels of safety and nitrate film were used in each print, satisfactory quality was ob¬ tained in every respect.” Safety film generally is slow-burning, -in contrast with nitrate film which burns rapidly. Commenting on the extensive labora'tory test, Fordyce said that results with the new safety film show that: Low shrinkage of the new safety base will keep the film free from "buckle” and the resulting in-and-out of focus images on the motion-picture screen. The tensile strength, rigidity, and flexi¬ bility of the "high acetyl” films are more like nitrate film than earlier safety films. Greater resistance to effects of moisture and humidity means less processing trou¬ ble as well as less film distortion. Projection quality, which is better than earlier safety films, is equal to nitrate film in screen steadiness and appearance. New cements, manufactured especially for use with the new film, will also make satisfactory splices with the older types of safety film and with nitrate film. 208 June, 1948 American Cinematographer