Nikon D40 - Manual (Page 39)

Reference: More on Photography (All Modes)/Focus 27
Getting Good Results with Autofocus
Autofocus does not perform well under the conditions listed below. If the camera is unable to focus
using autofocus, use manual focus ( 28) or use focus lock ( 26) 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 (e.g., the subject is
the same color as the back-
ground). The focus area contains
objects at different distances
from the camera (e.g., the sub-
ject is inside a cage).
The subject is dominated by
regular geometric patterns
(e.g., a row of windows in a
skyscraper). The focus area contains areas
of sharply contrasting bright-
ness (e.g., the subject is half in
the shade).
The subject appears smaller
than the focus area (e.g., focus
area contains both fore-
ground subject and distant
buildings). The subject contains many
fine details (e.g., a field of flow-
ers or other subjects that are
small or lack variation in
brightness).