Exposure Meters and Tables

(Russian, eksponometry), instruments, attachments, and printed tables used to determine the values of exposure parameters (exposure time, or shutter speed, and diaphragm aperture) in making still photographs and motion pictures, in photographic reprography and photographic printing, in film copying, and in other types of photographic operations. Exposure tables, extinction meters, and photoelectric exposure meters differ in their principle of operation.

The simplest devices for determining proper exposure values are exposure tables, which take into consideration the nature and location of the photographic process, the time of year and the time of day, the weather, the illuminance of the object being photographed, the light-sensitivity of the photographic material, the filter factor, and other factors. Disk-type exposure calculators are one type of exposure table. The determination of exposure parameters by this means is fairly subjective and approximate in nature.

Extinction meters are more complicated. Their operation is based on a visual evaluation of the brightness of the object being photographed, for example, by means of an optical wedge (seePHOTOMETER WEDGE). In one common design, the luminous flux from the object being photographed passes through an optical wedge that has numbers inscribed on various sections; the numbers correspond to the optical density of the sections. The brightness of the object is evaluated according to the lowest visible number. The measuring accuracy of such devices is a function of the properties of the human eye (especially the capacity for physiological adaptation). Extinction meters are now seldom used.

Photoelectric exposure meters are the most advanced type of device for determining exposure and the most commonly used. They use an optical detector to measure the brightness of the object being photographed. Many modern still and motion-picture cameras have built-in photoelectric exposure meters or other devices of similar function.