sort of a peeve of mine i guess:
dof - depth of field translates to how much of an image is in focus. It's not an effect like flare or motion blur.
if your dof is 8', that means there's a zone in the scene which is 8' deep and in focus.. (this rendering probably has a dof of ~25' which begins near the furthest mat and extends outside)
we're seeing the same thing but in writing it would say something like "there's not enough dof here.. the dof is too shallow.. etc."
con't
Great.
In parallel, for precise usage (that was my original intention), I think it is better to orbit around a selected point then the center of the bounding box (of a component), but it is not difficult to add.
Regards
Marcio