What is A-DEP?

The Basics:

A-DEP, or Automatic Depth (of Field) is a feature on some EOS cameras that automatically determines the best aperture and shutter speed settings based on your desired depth of field, ie how much of the scene you want to be in focus.

A Little More Detail:

The A-DEP feature allows you to pinpoint the closest subject you want in focus, as well as the furthest point. Once you have identified the range of the scene that you want in focus, the camera will then set the correct aperture to ensure the right depth of field, together with the right shutter speed to expose the image correctly. 

This feature can be handy when taking a group photo of people placed at different distances to you. You want all those people in focus, but you don’t want to use an aperture so small that you risk blurring the shot. 

A-DEP was first seen on Canon EOS 35mm film cameras, where you couldn’t get an instant review of the shot. In the digital era, it is therefore less useful to photographers, and has been dropped entirely from most EOS cameras. Additionally, the Depth of Field Preview button is a more user friendly and tactile way of gauging your depth of field before capturing the shot.
OTHER WORDS UNDER A