Nikon D800 - Manual (Page 144)

En_03
120
Z
g: Aperture-Priority Auto
In aperture-priority auto, you choose the aperture while the camera
automatically selects the shutter speed that will produce the
optimal exposure. Large apertures (low f-numbers) increase flash
range (
0 187) and reduce depth of field, blurring objects behind
and in front of the main subject. Small apertures (high f-numbers)
increase depth of field, bringing out details in the background and
foreground. Short field depths are generally used in portraits to
blur background details, long field depths in landscape
photographs to bring the foreground and background into focus.
To choose an aperture
between the minimum
and maximum values
for the lens, rotate the
sub-command dial
while the exposure
meters are on. Aperture
can be locked at the selected setting (
0 126).
Small aperture (f/36) Large aperture (f/2.8)
Sub-command dial