CHAPTER V 



SHUTTERS 



By Alan A. Cook 



In the early days of photography shutters were seldom necessary. Photosensitive 

 materials were slow and long exposures were required. Dry plates appeared in 1880, 

 roll film in 1884, and the first Kodak in 1888. For successful amateur photography 

 there was then a need for an exposing device to uncover the camera lens for a definite 

 short period of time and then to close it again. 



There were earlier shutters, many of them homemade. Some were built like a 

 guillotine with a simple slide and a slit in it and a rubber band set of springs to snap 

 the slide opening across the front of the lens — an 

 early conception of the focal-plane shutter. 

 Another type consisted of two blades sliding 

 like double doors at right angles to the lens axis 

 or pivoted above to swing out at the start of the 

 exposure and back into an overlapping position 

 at the center when the exposure ended. Such 

 blades were of light thin material and could be 

 located between the lens elements. The casing 

 could serve as a holder for the lens mounts. 



Interlens Shutters. — The principles of this 

 early design were naturally carried into the 

 development of the interlens shutter. This term 

 will be used to describe shutters that open 

 centrally and are located between or near the 

 lens elements, as distinguished from focal-plane 

 shutters which are located near the plane of the 

 film or plate. 



Single-blade Shutters. — The interlens shutter 

 in its simplest form is an exposure mechanism 

 with a single moving blade. Inexpensive box 

 cameras are usually equipped with a device of 

 this kind and Fig. 1 shows the details of construction of such a shutter from 

 an Eastman camera. A is the release lever, and B is the release-lever spring, 

 which has a double action according to the position of the double-action link C. 

 The main spring D connects C with the shutter blade E. For alternate exposures this 

 blade oscillates between the position shown in solid lines in Fig. 1 and the dotted-line 

 position. At each pressure on the release lever the opening in the blade G revolves 

 over the lens opening H to give an exposure of about J^5 sec. The lug F stops the 

 rotation of the blade at the proper place after exposure. Note that both the link C 

 and the main spring D have a double action for alternate exposures and that the 

 actuating force on the blade is not the direct pressure of the release lever but the effect 

 of the tension produced in the main spring D. / is a lug which holds the blade until 

 the pressure on the D spring has developed maximum tension. 



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Fig. 1. — Construction details of 

 Eastman single-blade automatic 

 shutter (Julius Springer). 



