Nikon D3body D3 Professional Technical Guide - Page 10

Autofocus Focus Tracking with Lock-On Focus tracking with lock-on controls how the camera responds to abrupt changes in focus distance. It can be used to prevent the camera from immediately refocusing when objects move through the space between the subject and the camera, ensuring that the camera will continue to track the main subject once the obstacle has moved away. Choose the length of time before the camera refocuses from Long, Normal, and Short. Camera will wait before refocusing on objects behind the subject Camera will track and focus on objects the same distance from the camera as the subject Camera will wait before refocusing on objects behind the subject 10