A-DEP is the notation for Automatic Depth of Field, which is a shooting mode included on some cameras. With A-DEP mode, you tell the camera which parts of your photo need to be in-focus, and the camera picks a corresponding aperture to get the correct amount of DOF.
This is a useful mode for portrait photography when your efforts to create the correct amount of DOF are not working out as you desire. Cameras that have this feature have a method for the user to select the specific points that need to be in focus, and making the correct Aperture setting based on that. The camera will also adjust the exposure with the correct shutter speed.
CONSIDERATIONS:
- ISO: If the image is too dark, or the camera does not fire, you may need to increase ISO to gain exposure
- As this is a feature that is camera specific, and not available on all cameras, please refer to your user manual.