Exposure (photography)

In photography, the total amount of light allowed to fall on the film during the process of taking a photograph.

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.

Exposure is measured in 'ev' with higher values denoting more light.

For example, an approximately correct exposure will be obtained on a sunny day using ISO 100 film, an aperture of f11 and a shutter speed of 1/100th of a second.

The Zone System is an excellent method of determining exposure.