Nikon Df - Manual (Page 290)

270
U
If On is selected, the main command dial can be used to adjust the
shutter speed selected with the shutter-speed dial by ±
2 /
3
EV in
increments of 1 /
3
EV. If the shutter speed dial is set to 4 (4 s, labelled
in red), the main command dial can be used to select shutter
speeds as slow as 30 s.
f11: Easy Shutter-Speed Shift
G
button ➜ A Custom Settings menu