Nikon D700 User Manual page 106

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 (II) 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, use manual focus (pg. 81 ) or use focus lock (pg. 78) 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: s ubject is the same color as the background.
The focus pointcon rains objects atdifferent
distances f rom thecamera
Example: subject is inside a cage.
I
The subject is dominated by regular geometric
patterns
Example: a row of windows in a skyscraper.
The focus pointcontains areasofsharply
contrasting b rightness
Example: subject is half in the shade.
Background objects appear larger than thesubject
Example: a buildinc is in the frame behind the subject.
The subject contains many fine details
Example:a field of flowers or other subjects that are
small or lack variation in brightness.
8O