Nikon D4 User Manual page 160

Aperture (exposure modes g and h): Press the selected control and
rotate the sub-command dial until F icons appear in the
viewfinder and the top control panel.
Fn button
To unlock aperture, press the control and rotate the sub-
command dial until the F icons disappear from the displays.
Z
A
See Also
Use Custom Setting f8 (Shutter spd & aperture lock; 0 334) to keep
shutter speed and/or aperture locked at the selected values.
134
Sub-command dial