Nikon D6 Reference Manual page 106

A
Framing Photos in Portrait ("Tall") Orientation
The camera is equipped with controls for use in
portrait ("tall") orientation, including vertical
shutter-release, Fn, and AF-ON buttons, main
and sub-command dials, and a multi selector.
•
Rotate the vertical shooting
shutter-release button lock to L
to avoid accidentally operating
these controls when the camera
is in landscape ("wide")
orientation.
54
Taking Photographs