The D300 offers Dynamic-area AF modes that use information from surrounding focus points to provide precise focus, even if the subject momentarily moves outside the user-selected focus point. Dynamic-area AF allows a choice of three different size areas to match the movement of the subject, using groups of 9, 21 or all 51 focus points. Also available is 51-point Dynamic-area AF with 3D-tracking, which takes full advantage of all 51 AF points as it uses color and light information to accurately track the subject and automatically switch focus points. This is particularly convenient when you want to freely compose shots of sporting events, or any scene in which the subject moves about in random fashion.
9-point mode is particularly useful when specific composition is your priority or your subject moves in predictable fashion that is relatively easy to catch within the focus points, and 21-point mode is the better choice when your subject moves about randomly.
You can also select one point from the 51 focus points and use it individually to match the subject's position or other needs for the shot. Single-point AF mode is convenient when you want to focus on the subject's eye or some other reference point when shooting still subjects. And it can be set to give human subjects, or subjects closer to the camera priority when automatically selecting which individual focus point to use. When using G or D type lenses, you can also use Automatic area AF mode, which increases focus precision by automatically distinguishing the subject from the background and foreground as it selects the appropriate focus point.
