Nikon Df - Manual (Page 271)

251
U
If On is selected, exposure will lock when the shutter-release
button is pressed halfway.
Choose how long the camera continues to
meter exposure when no operations are
performed. The shutter-speed and aperture
displays in the control panel and viewfinder
turn off automatically when the timer expires.
Choose a shorter standby timer delay for longer battery life.
c: Timers/AE Lock
c1: Shutter-Release Button AE-L
G
button ➜ A Custom Settings menu
c2: Standby timer
G
button ➜ A Custom Settings menu