Nikon D6 Reference Manual page 708

3
Turn the flash unit on and choose a flash control
mode of monitor pre-flash q A or A.
•
If you are using an SB-5000, SB-500, SB-400, or SB-300
mounted on the camera accessory shoe, choose [TTL] or
[Auto external flash] for [Flash control] > [Flash control
mode].
•
For information on other flash units, see the
documentation provided with the unit.
4
Focus.
Position the subject in the center of the frame and press the
shutter-release button halfway to focus.
656
FV Lock