110 



HANDBOOK OF PHOTOGRAPHY 



The shutter of the Contax camera uses a metal strip assemblj^ instead of cloth as 

 curtain material with an adjustable width of slit. This Contax shutter is rated at 

 M250 sec. at its fastest speed. 



The advantage in respect to speed that focal-plane shutters have over those of the 

 interlens type is due to the fact that the focal-plane shutter does not expose the whole 

 area of the film at once. The blades of an interlens shutter actually move much 

 faster than a curtain at the focal plane; for example, assume a }i,-va.. slit in a curtain 

 shutter set for 3i^ooo sec. in a miniature camera, the film width being about 1% in. 

 {i.e., '^}-'8 in.), and the slit requires ^^iooo or 0.00909 sec. to complete the exposure. 

 Compare this with an interlens shutter where at maximum speed the blades open and 

 close completely within I500 or 0.002 sec. in the fastest models. 



Aperture 

 indicator 



Curfoln 

 winding key 



Release 

 trigger 



Tension 

 indicator 



Tension 

 winding l<nob 



Fig. 21. — Back of Graflex camera showing focal-plane shutter construction. 



A disadvantage accompanies the high speed of focal-plane shutters. The result 

 is distortion, caused by the fact that a moving object is not completely "stopped" 

 by a focal-plane shutter but changes its position during the time required for the slit 

 to travel across the area of the film. The elliptical wheels of racing cars are a familiar 

 example of this. This distortion makes the focal-plane shutter unsuitable for aerial 

 mapping where complete freedom from distortion is desirable. 



Shutters of Special Types. — There are few other kinds of shutters that need be 

 mentioned. Those for studio use are generally made only in large sizes, to accommo- 

 date portrait lenses, and are limited to a bulb exposure. In these shutters one set of 

 blades often serves for both diaphragm and shutter blades by the introduction of a 

 stop ring which can be adjusted to prevent the blades from opening to their full 

 extent when the release is operated. Exposures of about Y^ sec. are the fastest possible 

 with these outfits, and longer exposures are secured by holding the release for the 

 required length of time. 



In a stereo shutter two separate blade assemblies are mounted at the proper dis- 

 tance in a single casing and connected by a long lever to operate from tlie standard 



