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Exposure (photography)

In photography, exposure is the total amount of light allowed to fall on the film during the process of taking a photograph. Exposure is measured in ev, with higher values denoting more light.

The correct exposure for a photograph is determined by the sensitivity of the film used. Film sensitivity is referred to as 'speed' and is measured as an ISO rating. Faster film requires less exposure and has a higher ISO rating. Exposure is controlled in a camera by shutter speed and lens aperture. Slower shutter speeds and greater lens apertures produce greater exposures.

An approximately correct exposure will be obtained on a sunny day using ISO 125 film, an aperture of f/16 and a shutter speed of 1/125th of a second. This is called the sunny f/16 rule.

The Zone System is another method of determining exposure.

Today, most cameras automatically determine the correct exposure at the time of taking a photograph by using a built-in light meter.

See also: exposure value, light value