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Chapter 11:
Shutters and Flash
A shutter is an automatic mechanical device to open the light path through a camera for a predetermined and usually brief time, for the purpose of making a photographic exposure. Most shutters also include a device to set the lens in the open position, either locking it open (“T” for time) or allowing it to remain open for as long as pressure is applied to the release lever (“B” for bulb, or nowadays, brief). In addition, all shutters provide for a very short “instantaneous” exposure, which may be of a fixed duration, say 1∕25 or 1∕40 second as in box cameras (Fig. 11.1), or varied at will from 2 seconds down to 1∕1000 second or less in the more complex shutters (Fig. 11.2) or in focal-plane shutters. An incredible amount of ingenuity has been applied to the mechanical design of shutters, from the simple flip-flop rotary shutters common in the earliest box cameras, through the more complex shutters equipped with flash synchronization that appeared after World War II, to the extremely accurate and reliable shutters made today. The timing of modern shutters is often electronically controlled. We shall not consider here the mechanical construction of shutters, but only those aspects that are of a purely optical character.
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