Nikon D90 - Manual (Page 102)

82
t
Mode A (Aperture-Priority Auto)
In aperture-priority auto, you choose the aperture to control depth of field (see
below) while the camera automatically selects the shutter speed that will produce
the optimal exposure. To take photographs in aperture-priority auto:
1
Rotate the mode dial to A.
2
Choose an aperture.
Press the shutter-release button
halfway to activate the exposure
meters and rotate the sub-command
dial to choose the desired aperture
from values between the minimum
and maximum for the lens.
3
Frame a photograph, focus, and shoot.
A Depth of Field
“Depth of field” is the distance to which objects behind and in front of the focus point appear
to be in focus. Large apertures (low f-numbers) 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 (note that depth of field is also
influenced by other factors, such as focal length and focus distance). 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 preview depth of field, press and hold the depth-of-field preview
button. The lens will be stopped down to the current aperture value,
allowing depth of field to be previewed in the viewfinder.
Mode dial
Sub command
dial
Depth-of-field preview
button