Camera Shutter

the mechanism in a camera that admits light rays to the photosensitive layer of a photographic material for a specific, predetermined period of time. A camera shutter contains blades, blinds, disks, or similar components that are opaque to light and that open and close to allow light to pass through the lens aperture or frame opening; a mechanism for changing exposure times, which is set before the exposure is made; and a drive element, which moves the shutter elements and exposure mechanism components.

Modern cameras use two types of shutters: leaf, or diaphragm, shutters and focal-plane shutters. Leaf shutters consist of thin, metal blades, usually of complex configuration, arranged symmetrically relative to the optical axis of the lens. The blades form a diaphragm that usually opens from the center of the aperture toward the edges and closes in the reverse direction; thus, exposure time is even over the entire frame. Leaf shutters are usually positioned inside the lens near the aperture diaphragm.

A focal-plane shutter consists of one or two metal or fabric blinds, which move across the film plane perpendicular to the optical axis of the lens. The light rays reach the photosensitive material through a slit cut in the blind or formed by two blinds, which moves across the film when the shutter is actuated. Exposure of the photosensitive material occurs section by section as the blind or blinds move across the film plane. Such shutters are positioned near the focal plane of the lens.

Exposure mechanisms may be classified as mechanical (usually with escapement-type retarding mechanisms), pneumatic, or electronic. Electronic exposure mechanisms are the most advanced type. They have a mechanical shutter-closing unit controlled by an electronic relay, which is actuated when a condenser is charged to a specific voltage. The exposure time is regulated by varying the resistance of a resistor, which alters the condenser’s charging time. The following series of exposure values (in seconds) has been established for camera shutters in the USSR: 30, 15, 8, 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1,000,1/2,000, and 1/4,000.

Camera shutters are sometimes equipped with an automatic release, or self-timer, which allows the shutter actuation to be delayed a specific period of time after the release button is pressed, and a synchronizing contact, which ensures synchronized operation of the shutter and a flash lamp. Certain leaf shutters are coupled to exposure meters; when actuated, they open up to a specific diameter and simultaneously function as a diaphragm.