Nikon D3 - Manual (Page 126)

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Focusing with Contrast-Detect Autofocus
Contrast-detect autofocus will take longer than normal (phase-detection)
autofocus. In the following situations, the camera may be unable to focus
using contrast-detect autofocus:
• The camera is not mounted on a tripod
• The subject contains lines parallel to the long edges of the frame
• The subject lacks contrast
• The subject in the focus point contains areas of sharply contrasting
brightness, or the subject is lit by spot lighting or by a neon sign or other
light source that changes in brightness
• A cross (star) filter or other special filter is used
• The subject appears smaller than the focus point
• The subject is dominated by regular geometric patterns (e.g., windows
in a skyscraper)
• The subject is moving
Note that the focus point may sometimes be displayed in green when the
camera is unable to focus.
Use an AF-S lens. The desired results may not be achieved with other
lenses or teleconverters.