The AF-Area Mode is the area which the camera uses to automatically focus is determined by rotating the selector.
AF-Area Mode Options:
Single Point AF (Auto-Focus):
The camera focuses only on this single point. Use for relatively static compositions when the subject doesn’t move faster than you can follow through the viewfinder. You can manually move this point with the multi-selector button.
Dynamic Area AF:
Camera focuses on the subject in user selected area. If the subject moves out of this area, the camera will focus based on information from surrounding points. Use for moving subjects. User can choose how many points are to be used.
Camera automatically detects the subject and focuses on it. Use whenever subject moves so quickly or erratically it’s hard to keep single or dynamic points on it (like flying birds or sports).