International photographer (Jan-Dec 1935)

Fourteen The INTERNATIONAL PHOTOGRAPHER August, 193.S Super Speed Motion Pictures By Horatio W. Lamson* No. 1 No. 2 No. 3 LOW-MOTION movies of some famous pole vaulter floating leisurely and gracefully over a slender bar high above the ground, or of the 2 to 1 favorite horse crawling -with tantalizing lassitude down the home stretch are always interesting to theater audiences who are mystified by the trick photography employed in producing such results. The method of obtaining these intriguing pictures, which is, of course, familiar to all cinematographers, consists merely of running the ordinary motion picture camera at higher than normal speeds. Such a technigue reguires, naturally, either a more intense illumination of the object or the use of a faster lens than is necessary for normal speed operation. If the 200 frames which may be taken during an interval of one second by means of a superspeed intermittent-action camera, designed by A. S. Howell" are subsequently projected at a rate of say, 16 frames Cinematographic Annual, 1920. per second, an event which occurred in one second will, of course, take 12 V2 seconds to show on the screen so that the observed speed of motion will then be slowed down 1 2 V2 : 1 . When one attempts to increase this reduction ratio by a more rapid driving of an intermittent-motion picture camera, three serious obstacles arise. First, the very rapid starting and stopping of the film as the frames are advanced, one at a time, between successive exposures, places tremendous accelerations and consequent strains upon the film which becomes in great danger of tearing or of igniting by friction. Secondly, as the operating speed of the oscilllating members of the intermittent mechanism is increased, it becomes more difficult to make them engage and otherwise function with the necessary precision to insure accurate and reliable framing. In the third place, increased operating speed means, of course, reduced exposure time, which reaches its final practical limitations in the speed of available lenses, the permissible grain coarseness of high-speed emulsions, and the available lighting facilities. The first and second of these difficulties have, to a certain extent, been overcome in various forms of high-speed movie cameras in which the film no longer advances intermittently a frame at a time, but travels at a constant, high rate of speed. Furthermore, the design of these cameras is such that all oscillatory motions are eliminated and only simple rotary motion, at constant speed, remains. Successive pictures are obtained by systems of rotary lens or prism members. Thereafter the question of obtaining sufficient exposure becomes the deciding factor in limiting the speed obtainable. Noteworthy examples of this technique are to be found in the lenkins camera2 and a camera recently developed by the Bell Telephone Laboratories. This problem of superspeed motion pictures has been under taken in a radically different manner by Professor Harold Edgerton and his associates at the Massachusetts Institute of Technology. The fundamental principle of their procedure was similar to that employed by Abraham and Bloch.4 In collaboration with the author's company, a form of camera has been developed through -which it is possible to run ordinary 35-millimeter perforated film at essentially constant speeds as high as 75 feet per second, approaching a mile a minute and to take superspeed movies at the rate of 1200 full frames per second. This General Radio camera uses a single photographic lens of standard make with speeds varying between f/1.5 and f/2.5. The camera has no shutter and contains no moving parts except the film driving sprocket, and the magazine and take-up reels. The guestion naturally arises in the mind of the reader: "How can a series of pictures be taken with such a camera?" The answer is that the shutter, or equivalent optical mechanism heretofore used with a continuously illuminated object is replaced by a special form of flashing light known as a stroboscope. While ordinary daylight illumination of the object cannot leave any photographic impression upon the film moving at such high speed back of the wide-open lens, each flash of the stroboscopic light makes one normal exposure or frame on the film. The form of stroboscope lamp employed for this purpose and capable of producing the desired results is a special type of mercury-vapor electric arc, likewise first developed by Professor Edgerton and commercialized by the General Radio Company. This new arc possesses three important attributes. In the first place, the duration of each flash, that is, the actual exposure time, is only five microseconds (0.000005 second). The conception of such a short interval of time is difficult for one unaccustomed to think of such magnitudes, but it may, perhaps, help to recall that an automobile racing down the highway at 50 miles per hour can only advance a distance of 1 /200th 1 Research Engineer, General Radio Company, Cambridge, Mass. 2 "Evolution of the Professional Camera," by loseph A. DuBray, 3 "The lenkins Chronoteine Camera for High Speed Motion Studies," by C. Francis Jenkins, Transactions of the Society of Motion Picture Engineers No. 25. * "Ultra-Rapid Kinematograph," by H. Abraham and L. Bloch, Comptes Rendus, December 1, 1919, No. 169. Phone CLadstone 4151 HOLLYWOOD STATE BANK The only Bank in the Industrial District of Hollywood under State Supervision Santa Monica Boulevard at Highland Avenue Please mention The International Photographer when corresponding with advertisers.