In article , Bill W
wrote:

What is 3D tracking? My problem at this air show location with all
those focus points is that it will start focusing on the power lines,
trees, mountains, clouds, etc. Does it mean that it tries to track
objects that are at a consistent distance? My Pentax does not have
that option, so it might be moot anyway.

http://www.nikonusa.com/en/Learn-And...i4lx/3d-focus-
tracking.html
An invaluable feature for sports, action and wildlife photography, 3D
focus tracking, available in select Nikon D-SLRs, automatically
shifts the focus point to follow the movement of the subject. With
the shutter release pressed halfway, you'll see in the viewfinder the
lens continuously maintain focus as the subject moves.

However, maintaining focus doesn't guarantee a sharp image, as there
is a short time lag between the release of the shutter and the
capture of the picture. To solve this problem, the focus tracking
system is a predictive system that uses special algorithms to
forecast the position of the subject at the moment the image is
captured. The prediction is based on a measurement of the subject's
movement and speed.