SHUTTERS 



115 



as possible and in a case of some kind when not in use. Cameras with focal-plane 

 shutters made of cloth should not be left open in the sunlight; the sun's image is hot 

 enough to burn holes in them. In fact, it is unwise to leave a camera open in the 

 sunlight at any time. The reason for this is that the emulsions used on films have 



100 



90 



^ 80 



^70 



u 



0) 



Q- 60 



c 

 - 50 



c 40 



'.^ 30 



t ^ 

 uj 20 



1 3 5 



10 



30 



40 



Fig. 31.- 



15 20 



S=Width of Slit, Mm 



-Efficiency of focal-plane shutter at different distance from the film plane to 

 the shutter curtain, e. Curve e = represents ideal case, impossible in practice; curve 

 c = 3 is plotted for//4.5 lens of 120-mm. focal length, curve e = 10 is plotted for//5.7 lens 

 of 260-mm. focal length; curve e = 23 is plotted for//5.7 lens of 260-rQm. focal length. 



5.28" 

 distance 

 ■'befween 

 ^marks 



Fig. 32. — Automobile tire as a shutter test object. If Pi is the angular velocity of the 

 point 331, and Pz the angular velocity of j)2, then P2/P1 = Pi/ Pi, and the shutter speeds may 

 be determined by photographing the wheel while rotating at a known speed. 



been enormously increased in speed during the past few years. Cameras and shutters 

 have not yet caught up with them, from the point of view of being built to prevent 

 fogging when the outfits are left in bright sunlight for a considerable length of time. 



Bibliography 



Yost, Lloyd: Testing Focal Plane Shutters, Am. Phot., December, 1936, p. 808. 

 Clabk, R. G.: Measuring Shutter Speeds, Am. Phot., July, 1937, p. 498. 

 Holmes, L. S.: On Checking Relative Shutter Speeds, Am. Phot., September, 1937, p. 626. 

 WoLCOTT, F. W.: Camera Shutter Speed Experiments, Camera, January, 1938, p. 17. 

 Greenlaw, D. S.: Accurate Method of Testing Shutter Speeds, Am. Phot. June, 1938, p. 400. 

 Waters, L. A.: Testing Shutter Shutters, Camera, November, 1938, p. 316. 



Hay and Von Rohr: "Handbuch der Wissentshaftlichen und Augewandten Photographie," Vol. 2, 

 in "Die Photogiaphische Kamera und die Zeibehor," by Karl Pritschow, Springer, Berlin. 



