auto-exposure

Definition: Automatic exposure control: mechanical or opto-electronic means of controlling camera exposure without user having to make individual settings for each exposure reading or change in scene luminance. * Operation may be semi-automatic or fully automatic, assuming film speed is already set: (1) Semi-automatic modes include (a) aperture-priority: user sets the lens f/number, system sets shutter time to give correct exposure with variations in scene luminance (b) shutter-priority: user sets shutter time, system sets lens aperture to give correct exposure with variations in scene luminance (c) variants in which system may over-ride user setting in some circumstances. (2) Fully automatic modes set both lens aperture and shutter time, the combination of settings varying with scene luminance according to a pre-programmed table or user-selectable preferences.

Related Terms: evaluative metering

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