Nikon D90 - Manual (Page 98)

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Shutter Speed and Aperture
P , S, A, and M modes offer different degrees of control over shutter
speed and aperture:
D Lens Aperture Rings
When using a CPU lens equipped with an aperture ring (pg. 228), lock the aperture ring at the minimum
aperture (highest f-number). Type G lenses are not equipped with an aperture ring.
Non-CPU lenses can only be used in exposure mode M, when aperture can be adjusted manually
using the lens aperture ring (in other modes, the shutter-release will be disabled). The camera
exposure meter, auto ISO sensitivity control, and variety of other features can not be used (pg.
165).
A See also
Use the ISO sensitivity auto control option in the shooting menu (pg. 165) to enable auto
ISO sensitivity control in P, S, A, and M modes. Custom Setting b1 (EV steps for exposure cntrl.;
pg. 177) determines the size of the increments used for setting shutter speed and aperture.
Custom Setting f5 (Customize command dials; pg. 201) determines the roles played by the
main and sub-command dials in setting shutter speed and aperture.
Mode Description
P
Programmed auto
(pg. 80)
Camera sets shutter speed and aperture for optimal exposure.
Recommended for snapshots and in other situations in which
there is little time to adjust camera settings.
S
Shutter-priority auto
(pg. 81) User chooses shutter speed; camera selects aperture for best
results. Use to freeze or blur motion.
A
Aperture-priority auto
(pg. 82)
User chooses aperture; camera selects shutter speed for best
results. Use to blur background or bring both foreground and
background into focus.
M Manual (pg. 83)
User controls both shutter speed and aperture. Set shutter speed
to “
A” or “&” for long time-exposures.