I've shied away from
the A-DEP mode ever since doing a science project on depth-of-field for school.
The basis for measuring depth-of-field is known as the Circle of Confusion
(CoC). In Canon's EF Lens Work II, they state that they used a 0.035mm
CoC for EF lenses. That's fine, until you print larger than 5x7, since they
assume that the average photo will only be enlarged 5x over the size of the
negative/sensor (35mm/full-frame). Thus, I assumed that they used the same math
for A-DEP, so I've left the mode alone, although it will do a fine job with
fairly small prints.



There are some handy depth-of-field calculators online that
allow you to set your own CoC*.


Resources:


www.luminous-landscape.com/tutorials/understanding-series/dof.shtml


*www.bobatkins.com/photography/technical/dofcalc.html


http://en.wikipedial.org/wiki/Depth_of_field


http://www.dpreview.com/learn/?/key=depth+of+field


http://www.dpreview.com/learn/?/key=aperture



http://www.cambrigeincolour.com/tutorials/depth-of-field.htm