Nikon D700 - Manual (Page 313)

287
U
a4: Focus Tracking with Lock-On
This option controls how autofocus adjusts to sudden large
changes in the distance to the subject.
a5: AF Activation
This option controls whether both the shutter-release button and
the B button can be used to initiate autofocus, or whether
autofocus is only initiated when the B button is pressed.
Option Description
C
Long
When the distance to the subject changes abruptly, the
camera waits for the specified period (long, normal, or
short) before adjusting the distance to the subject. This
prevents the camera from refocusing when the subject is
briefly obscured by objects passing through the frame.
D Normal
(default)
E
Short
Off
The camera immediately adjusts focus when the distance
to the subject changes. Use when photographing a series
of subjects at varying distances in quick succession.
Option Description
Shutter/
AF-ON
(default)
Autofocus can be performed with the B button or by
pressing the shutter-release button halfway.
AF-ON only Autofocus can only be performed using the B button.