If you use one of the consumer cameras, from the EOS 50D down, you may well have come across the A-DEP mode. But what does it do and how does it work?

 A-DEP stands for Auto Depth [of field] and it aims to give you enough depth of field in your image for the subjects you want to capture. It's most used for landscapes as this is where you most commonly want lots of depth of field. 

In A-DEP mode, the camera evaluates the scene and uses the focus points to determine the nearest and farthest subjects. One thing you need to be aware of is that it only picks up subjects under the focusing points - it won't find a subject not covered by them.

By calculating the distance from the nearest to farthest points, the camera can calculate a point to focus on and an aperture to use to give you enough depth of field to ensure they are all in focus. With this done it works out a shutter speed to use to give the correct exposure and you're ready to shoot. 

It's not a widley used mode really and for many, it is seen as a shortcut for those that don't yet understand the relationship between aperture, subject distance and depth of field, but if you're shooting a landscape it's worth experimenting with, even in conjunction with your normal method of shooting, just to see ther results.