EXPOSURE METER

also called Light Meter, photographic auxiliary device that measures the intensity of light and indicates proper exposure (i.e., the combination of aperture and shutter speed) for film of a specific sensitivity. Modern instruments are of two basic types: the self-generating, or photovoltaic, and the variable resistance, or photoconductive. The photovoltaic type, usually with a selenium element, converts the incoming light directly into an electric current. A microammeter measures this current and is calibrated to indicate the intensity of the light. Exposure is then set by adjusting dials to control aperture opening and shutter speed, taking into consideration the specific sensitivity of the film. In the photoconductive type, the element, a cadmium sulfide cell or silicon photodiodes, is connected to a battery-powered circuit and changes its resistance with variations in the light intensity. The change in current is measured by a milliammeter calibrated to read light intensity. The exposure meter is incorporated into the camera mechanism of most modern hand cameras. The operator of a semiautomatic camera model sets the correct exposure by adjusting the exposure controls to align two pointers in the viewfinder; in fully automatic cameras, the exposure is adjusted by the camera mechanism itself.