In photography, exposure value (EV) denotes all combinations of camera shutter speed and relative aperture that give the same exposure. The concept was developed in Germany in the 1950s, in an attempt to simplify choosing among combinations of equivalent camera settings. 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 Ev; this symbol continues to be used in ISO standards, but the acronym EV is now 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.
H = Et
H is Photometric Exposure
E is Image Plane illuminance
t is Exposure time
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