Depth-Of-Field Preview Button - Nikon F 4 Instruction Manual

DEPTH-OF-FIELD PREVIEW BUTTON

When a lens with an automatic diaphragm is used, the view-
finder image is viewed with the lens at maximum aperture. By
depressing the depth-of-field preview button, you stop the lens
down to the aperture set, enabling you to examine depth of
field before shooting. The viewfinder image normally darkens
as the aperture gets smaller. Portions of the picture that appear
n focus when the button is pressed are in the zone of sharpest
focus.
•Depth of field can only be previewed in the Aperture-Priority
Auto (A) or Manual (M) exposure modes.
•During preview, autofocus and Electronic Rangefinder opera-
tion are not possible.
•During preview with lenses with meter coupler, attaining
correct exposure is not possible, because exposure must be
determined by full-aperture metering.