Nikon D300 User Manual page 268

But, this "sluggishness" is really a feature designed to keep
you from losing your subject's tracked focus. Once the
camera locks on to a subject's area of focus, it tries its best to
stay with that subject even if it briefly loses the subject. This
keeps the lens from racking in and out and searching for a
new subject as soon as the previous subject is no longer under
an AF point.
It also causes the camera to ignore other higher-contrast or
closer subjects while it follows your original subject. You will
have to judge the usefulness of this technology for yourself. I
suggest that you go to some event, or down to the lake, and
track moving objects with and without lock-on enabled. Your
style of photography has a strong bearing on how you'll
use—or whether you'll
Focus tracking with lock-on
camera focuses. Instead, it is concerned with what it is
focused on. Here are some good reasons to leave
tracking with lock-on
If Focus tracking with lock-on
and Auto-area AF
between your subject and the camera. When you enable
tracking with
briefly gets between you and your subject. If you turn it off,
your camera will happily switch focus to a closer subject even
if it only appears in the frame for a moment. A good example
of this is when you are tracking a moving subject and just as
you are about to snap the picture, a closer or brighter object
enters the edge of the frame and is picked up by an outside
sensor. The camera may instantly switch focus to the
intruding subject.
use—Focus tracking with
has little to do with how well the
enabled in your camera.
will instantly react to something coming
lock-on, the camera will ignore anything that
is set to Off,
268
lock-on.
Focus
Dynamic-area AF
Focus