Nikon D300 Complete Manual page 393

• Some lenses turn it off! The 80-200mm f/2.8 AF-S lens and
most of the VR lenses disable the function (the 18-200mm
and 24-120mm VR lenses are exceptions, and do not turn
off autofocus assist).
• The range is minimal. Beyond about 10' (3m), the light
isn't strong enough to make a difference.
• The light is annoying to subjects. Do you like having a
strong white light shined in your face just before being
photographed?
• Settings must be correct for it to work. You must be in
Single Servo autofocus mode. You must be using the
central autofocus sensor or have selected Auto Area
autofocus.
• The lamp may turn itself off if it gets hot. The lamp can't
be used continuously. So if you're using the lamp
constantly, it'll eventually shut down until it cools. I can
usually get that to happen within five or six shutter release
presses.
• It uses more power. When the lamp is lit the camera is
using a minimum of another 20mA in power. While that
figure is relatively low, multiple activations will certainly
drain the battery faster, and in low light you may be
activating the light repeatedly.
If you're getting the idea that I don't like the Autofocus Assist
lamp on the D300, you're right. Fortunately, you can turn it
off (see "CSM #A9, Autofocus Assist Light" on page <532>).
If you have an SB-600 or SB-800 mounted on the D300, the
camera will use the Autofocus Assist lamp on the flash (if the
conditions above are met) unless you turn that feature off at
the flash (or are using a lens wider than 16mm). In very low
light conditions, the wide red focus pattern thrown by the
Speedlight SB-600 and SB-800 makes the D300 almost eerily
accurate in focus, but even without it the camera does just
fine in virtually any situation you could handhold.
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 393