Nikon D3X - Manual (Page 338)

312
U
a9: AF-ON Button
Choose the function performed when the
B button is pressed.
Option Description
A
B
(default)
Pressing the B button initiates autofocus.
B AE/AF lock
Focus and exposure lock while the B button is
pressed.
C AE lock only Exposure locks while the B button is pressed.
D
AE lock
(Reset on
release)
Exposure locks when the B button is pressed, and
remains locked until the button is pressed a second
time, the shutter is released, or the exposure meters
turn off.
E
AE lock
(Hold)
Exposure locks when the B button is pressed, and
remains locked until the button is pressed a second
time or the exposure meters turn off.
F AF lock only Focus locks while the B button is pressed.