Choose whether the shutter-release button can be used to focus (Shutter/AF-ON) or if focus can only be adjusted using the AF-ON button or other controls to which AF-ON has been assigned (AF-ON only).

A Custom Settings: Fine-Tuning Camera Settings

a: Autofocus

b: Metering/exposure

c: Timers/AE lock

d: Shooting/display

e: Bracketing/flash

f: Controls

g: Movie