aperture priority

Aperture priority, often abbreviated Av or A on a camera dial, is a setting on some cameras that allows the user to choose an aperture while the camera selects a shutter speed to match. The camera will ensure proper exposure. This is different from manual mode, where the user must decide both values, shutter priority where the user picks a shutter speed with the camera selecting the aperture to match, or program mode where the camera selects both.
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