Nikon D5000 - Manual (Page 73)

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D
Continuous-servo Autofocus
In AF-C mode or when continuous-servo autofocus is selected in AF-A mode, the camera gives
priority to shutter response and the shutter may be released before the in-focus indicator is
displayed.
A
Getting Good Results with Autofocus
Autofocus does not perform well under the conditions listed below. The shutter release may
be disabled if the camera is unable to focus under these conditions, or the in-focus indicator
(
I) may be displayed and the camera may sound a beep, allowing the shutter to be released
even when the subject is not in focus. In these cases, focus manually (0 60) or use focus lock
(0 58) to focus on another subject at the same distance and then recompose the
photograph.
There is little or no
contrast between the
subject and the
background.
Example : Subject is the
same color as the
background.
The focus point contains
areas of sharply
contrasting brightness.
Example : Subject is half in
the shade.
The focus point contains
objects at different
distances from the
camera.
Example : Subject is inside
a cage.
Background objects
appear larger than the
subject.
Example : a building is in
the frame behind the
subject.
The subject is dominated
by regular geometric
patterns.
Example : A row of
windows in a skyscraper.
The subject contains many
fine details.
Example : A field of flowers
or other subjects that are
small or lack variation in
brightness.
D
The AF-Assist Illuminator
If the subject is poorly lit, the AF-assist illuminator will light
automatically to assist the autofocus operation when the shutter-
release button is pressed halfway. The AF-assist illuminator will not
light during continuous-servo autofocus or manual focus, in
shooting modes in which the AF-assist illuminator can not be used,
or if Off has been selected for Custom Setting a2 (Built-in AF-assist
illuminator; 0 155). The illuminator has a range of about 0.5–3.0
m (1 ft. 8 in.–9 ft. 10 in.); when using the illuminator, use a lens with
a focal length of 18–200 mm and remove the lens hood.
A
The Beep Speaker
Custom Setting d1 (Beep; 0 158) can be used to turn the beep speaker on or off.
AF-assist illuminator