Exposure is the total amount of light allowed to fall on the photographic medium (photographic film or image sensor) during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance.

The camera information in this standard conforms to the APEX (Additive System of Photographic Exposure) unit ystem. APEX is a convenient unit for expressing exposure (Ev).