Nikon Autofocus: Dynamic Area AF

Dynamic Area AF
The Dynamic Area AF is separated into two different functions, depending on the AF Drive (AF-S and AF-C only) set on the camera.

In AF-S Drive, the camera will focus in only one AF point selected by the user.
In AF-C Drive, the camera will focus on only one AF point and its surroundings selected by the user.

Again, in AF-C Drive, once a subject is moving away from the main AF point (central), the surrounding AF points, that lies around the main AF point, sends the distance information to make quick focus adjustment to the main AF point to get the off-center subject, which is located within the surrounding AF points, in focus.
In higher end digital and film SLR's, it allows the user to choose total amount of AF points:
9 Points

• Ideal for photographing any subjects that will move predictable, such as football, basketball, weddings, rock concerts, wildlife, and some portraits

21 Points

• any subjects that will move unpredictable, such as runners (not large group) or skateboarders.

39/51 Points and

• for very isolated subjects that moves very quick and difficult to frame within the viewfinder's AF area, such as running cheetahs, military jets, or flying birds.

39/51 Points with 3D tracking

• In AF-C Drive and Dynamic Area AF, the camera will use all AF points within the AF area to track a moving subject.  The user is required to get the primary subject in focus, while holding the shutter release button halfway down, the camera will start tracking the moving subject, keeping the subject in focus.  The 3D tracking with Focus Tracking with Lock-On (in the Autofocus menus) set to Off is highly recommended for fast action.

How do I decide which AF Area to use for the current shooting scenario?
It depends on the size of the subject, unpredictable or predictable, and how isolated the subject appears in the frame (depending on the lens' focal length).

Excellent tip for accurate continuous focusing and tracking

• the subject's majority color must be different apart from the background's majority color.
• Reminder: If the user plans to do a lot of sports using AF-C Drive + Dynamic Area AF + Focus Tracking with Lock-On set to Off, the user must carry spare batteries and high speed autofocus lenses with AF-S [AF-SWM (Silent Wave Motor)] engine because with these combinations, it uses up more power from the batteries.