Most cameras allow us to shoot using different exposure modes – Aperture priority (A), Shutter priority (S), Program (P) and Manual (M). On Canon cameras, Aperture priority is known as Aperture value (Av) and Shutter priority is known as Time value (Tv). Some cameras also offer Scene modes but in this write-up, we shall not be discussing them. Let’s see how the A, S, P and M modes work and when should we use them.
An exposure is basically a product of ISO sensitivity, aperture and shutter speed. You first set the ISO sensitivity depending on the brightness of the available light.
Aperture priority mode (A or Av)
Apertures control the quantity of light entering the lens. They also control the depth of field (the zone of acceptable sharpness in the picture). When using Aperture priority, you select the aperture of your choice depending on the depth of field that you desire and the camera will automatically select the appropriate shutter speed.