Janko
Don't know about your camera but AFAIK most cameras you push the button part
way down until if focuses then hold until actually taking the picture by
pushing all the way down. Should also hold exposure. Focus and Depth of
Field are not the same thing. Only the aperture changes the Depth of Field.
Changing the aperture will require a change in shutter speed to maintain
correct exposure.
http://en.wikipedia.org/wiki/Depth_of_Field
A camera without manual override should probably only be use by someone who
shouldn't be taking pictures.:)