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HANDBOOK OF PHOTOGRAPHY 



variations in different commercial designs. The question of blade action in relation 

 to shutter efficiency will be discussed in a later paragraph. 



There is one design of blade mechanism which is worth noting although shutters 

 made to that pattern are no longer on the market. This design is characterized by- 

 blades revolving in one continuous motion from closed position through open position 

 to closed again. The principle itself is interesting because blades that open and close 

 in one motion are theoretically capable of higher speeds than the design actually used 

 at present in which the blades open, come to rest, and then close again. 



Cab/e re/ease 

 bushin.-: 



Seffing 

 Jever ^Self-iimer 



rjiiiose caich 



'effing lever 



Release 

 lever J 



Relea::^ 

 lever 



Cable release 



Fig. 15. — Photograph of modern Compur Fig. 16. — Illustration of Kodamatic shut- 

 shutter, ter. 



Fig. 17. — Mechanism of Wollensak Betax shutter. 



Retarding Devices. — In the timing-control mechanism of a shutter there have been 

 tried a number of different mechanical principles. Among the first were adjustable 

 spring tension on the main lever of the shutter (the one which operates the blades) 

 and the application of a leather brake to a coil spring to slow down its action. The 

 air pump as a retarding device was mentioned in an American patent in 1885 and has 



