In photography, exposure value (EV) denotes all combinations of a camera's shutter speed and relative aperture that give the same exposure. In an attempt to simplify choosing among combinations of equivalent camera settings, the concept was developed by the German shutter manufacturer Friedrich Deckel (de) in the 1950s (Ray 2000, 318). Exposure value also is used to indicate an interval on the photographic exposure scale, with 1 EV corresponding to a standard power-of-2 exposure step, commonly referred to as a stop.
Exposure value was originally indicated by the quantity symbol ; this symbol continues to be used in ISO standards, but the acronym EV is more common elsewhere.
Although all camera settings with the same exposure value nominally give the same exposure, they do not necessarily give the same picture. The exposure time (“shutter speed”) determines the amount of motion blur, as illustrated by the two images at the right, and the relative aperture determines the depth of field. The light sensitive medium may exhibit reciprocity failure, which is a change of light sensitivity dependent on the intensity.
Read more about Exposure Value: Formal Definition, Camera Settings Vs. Photometric Exposure, EV As An Indicator of Camera Settings, Tabulated Exposure Values, Setting EV On A Camera, Exposure Compensation in EV, Meter Indication in EV, Relationship of EV To Lighting Conditions, EV and APEX, EV As A Measure of Luminance and Illuminance