DEPTH OF FIELD
Depth of field refers to the zone of acceptable focus ex- tending in front of, and behind, the plane of sharpest focus. Within this zone, image blur is negligible and everything may be considered as being in sharp focus. Three factors greatly influence the depth of field : the focal length of the lens in use, the camera-to-subject distance, and the taking aperture. The smaller the aper- ture and the shorter the focal length of the lens, the greater the depth of field. Also, the closer the subject, the shallower the depth of field. These three factors can operate independently or in conjunction with one an- other, with anyone factor capable of partially cancel ing the effects of the other. Thus, by careful selection and use, the photographer can exercise wide creative control over the final picture.
Depth-of-Field Preview Button
As most Nikkor lenses are operated at full aperture for ease of focusing, visualization of the depth of field at the shooting aperture may be difficult. Thus, the camera's depth-of-field preview button often can come in handy. The depth-of-field preview button lets you check (or "preview") the zone of sharpness at any time before (or after) shooting. Simply by depressing the button, the lens is stopped down to the preselected aperture to allow you to see how much background and foreground is in or out of focus.