SHUTTERS at., Obturatewrs ; Ger., Ver schliisse) Mechanical devices for exposing the plate. Their use is necessitated by the fact that expos ures shorter than one-quarter of a second, cannot be given by hand, nor even that without risk of shaking the camera. There are many kinds of shutters, a convenient classification being that which groups them into those working before the lens, between the lens combinations, and behind the lens, though this division is not rigid since many before-the-lens shutters can be used equally well behind. The earlier shutters, such as the flap, drop, and combined drop and flap shutters, belonged to the first class, and are practically obsolete, excepting the first-named, which is still found useful in studio work. The drop shutter has been completely superseded by the roller-blind shutter A, in which a spring blind with a central aperture is caused to pass before the lens. The speed is varied by altering the tension of the spring by means of a winding knob, a given number of turns corresponding to a given speed.
The focal plane shutter (which see) is also a roller-blind shutter, but is placed close to the plate. In this, not only can the spring tension be altered, but provision is made for varying the width of the slit or opening, thus giving a greater range of speed. This shutter has d.
higher efficiency, and is capable of greater rapidity than any other type ; but is liable in some cases to cause distortion of moving objects, since the plate is exposed a portion at a time.
In the second class of shutters are included those known as diaphragm shutters, which work between the combinations of the lens usually by the opening and closing of thin metal or vulcanite plates. The speed is varied either by adjusting the tension of a spring, by a pneumatic brake, or by altering the size of the aperture. Such shutters form part of the lens, as at B.
The rotary shutter, C, which may work either between or in front of the lens, consists of a circular disc with an opening towards the side. This is made to revolve by means of a spring, the opening passing across the lens during the revolution.
The behind-lens bellows studio shutter con sists of two semi-circular bellows, which open silently from the centre when the pneumatic ball is pressed, closing again as the latter is released. A clip prevents the return of the air when it is desired to keep the shutter open. (See also " Pneumatic Release," and other headings.)