6.12. Av (aperture priority) mode

In this mode, the photographer chooses a lens aperture value by rotating the main dial. The Canon abbreviation is thus "Av" for "aperture value," though it's often called "A" mode by other brands. The camera then chooses a shutter speed ranging from 30 seconds to the camera's X-sync speed, in order to expose the background correctly. Flash output is automatically determined by the flash metering system.