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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.