768 HANDBOOK OF PHOTOGRAPHY 



the camera — a serious limitation to its usefulness. Table I shows the speed of the 

 film in feet per second as a function of the height of the frame and the number of expo- 

 sures per second. 



When film speeds higher than about 150 or 200 ft. per sec. are desired, a short strip 

 of film is usually placed on the periphery of a drum. The length of film that can be 

 used is limited to the circumference of the drum, but very high film velocities can be 

 attained in this way more easily than with a long strip. There are no acceleration 

 problems, since the fUm may be brought up to speed as slowly as desired. Cameras 

 of this type require a shutter that remains open during one revolution only, to prevent 

 multiple exposure of the film. 



Still another method employs a stationary film over which the beam of light is 

 rapidly thrown by means of a rapidly rotating mirror. 



The electric spark in air produced by the discharge of an electrical condenser 

 through an air gap has been extensively used as a source of stroboscopic light. The 

 diu-ation of the flash can be made as short as 1/100,000 sec, or less. A spark gap, 

 however, presents serious problems when it is desired to produce enough light to 

 illuminate an area several feet square 1000 or more times a second, because of the 

 great power required and the difficulty of controlling it. Although a spark is not an 

 efficient source of light, it is sufficient for some purposes, such as silhouette photog- 

 raphy. The light is highly concentrated, having a high intrinsic brilliancy which 

 permits the use of reflectors and condensing lenses. 



The discharge of electrical condensers through gas-filled tubes, such as the argon- 

 filled tube of Fig. 3, provides an efficient source of intermittent light for taking high- 

 speed motion pictures. In service the lamp is connected to a condenser and is made to 

 flash at the desired instant by suddenlj^ charging an external grid to a high potential. 

 Naturally the circuit must be capable of recharging the condenser in time for the next 

 flash, and this becomes increasingly difficult as the frequency of exposure or the power 

 used per flash is increased. Difficulty is sometimes encountered because of the tend- 

 ency of the tube to hold into a steady glow or to fail to deionize, i.e., to trip by itself 

 as the voltage builds up across the condenser. A mercury-control tube of the type 

 shown in Fig. 2 can be used to advantage to overcome these limitations. 



Bibliography 



Periodicals: 



Abraham, H., E. Block, and L. Bloch: Ultra-rapid Kinematograph, Compt. rend., 169, 217 (1919). 



Legg, J. W.: The Polar, Multi-exposure, High Speed Camera, Elec. J., 16, 509-512 (1919). 



CoNNELL, W. H.: The Heape and Crylls Machine for High-speed Photography, /. Sci. I nstruments, 4, 

 82-87 (1926). 



.Jenkins, C. F.: The Chronoteine Camera, /. Soc. Automotive E)igrs., 22, 200-202 (1928); Trans. Soc. 

 Motion Picture Engrs., No. 25, p. 25 (1926). 



SuHARA, T.: New High Speed Kinematographic Camera, Proc. Imp. Acad. (Tokyo), 5, 334-337, 1929. 



Crakz, C, and H. Schardin: Eanematographie auf ruhendem Film und mit extrem hoher Bildfrequenz, 

 Z. Physik, 66, 147 (1929). Contains a short bibliography. 



Suhara, T.: New Ultra-Speed Kinematographic Camera, Aeronaut. Research Inst., Tokyo Imp. Univ. 

 Kept. 60, 187-194 (1930). 



Ende, W.: Theorie des Thunschen Zeitdehners und ihre Anwendung in der Aufnahmepraxis, Z. tech. 

 Physik, 11, 394 (1930); AEG Zeitdehner, AEG Mitt.. November (1933). 



Harvey, E. N., and A. L. Loomis: High Speed Photomicrography of Living Cells Subjected to Super- 

 sonic Vibrations, J. Gen. Physiol., 15, 147-153 (1931). 



RoTHROCK, A. M.: The N.A.C.A. Apparatus for Studying the Formation and Combustion of Fuel 

 Sprays and the Results from Preliminary Tests, Nat. Advisory Comm. Aeronaut. Tech. Rept. 429 

 (1932). 



TtJTTLE, F. E., and C. D. Reed: The Problem of Motion Picture Projection from Continuously- 

 Moving Film, J. Optical Soc. Am., 22, (No. 2), 39 (1932). Also in J. Soc. Motion Picture Engrs., 

 20, 3 (1933). 



TuTTLE, F. E.: A Nonintermittent High-Speed 16-mm Camera, J. Soc. Motion Picture Engrs., 21, 474 

 (1933). 



