Depth Of Field.87 - Pentax ZX-5 Operating Manual

(17) DEPTH OF FIELD
Depth of field refers to the range around the optimum
focusing point of the subject in which the elements at
different distances are in focus. The depth of field in¬
creases as the aperture is closed down, the focal length
of the lens becomes shorter, or the subject is positioned
farther away.
The Range Allowed for Focusing
The in-focus range varies depending on the aperture in
use. Zoom lenses do not have a depth-of-fie!d scale for
mechanical considerations.