Nikon D3X User Manual page 363

Portrait (Tall-Orientation) Photographs
To use the command dials to select the focus point when framing
shots in portrait ("tall") orientation:
1
Choose [Focus point-selection].
Select [Focus point-selection] for
Custom Setting f4 ([Assign FUNC.
button]) > [FUNC. button+dials].
2
Unlock the shutter-release
button for vertical
shooting.
Vertical shutter-release button
lock
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