Nikon D6 Reference Manual page 741

6
C / f : Compose the shot and arrange the flash
units.
•
See the documentation provided with the flash units for
more information.
•
Test-fire the units and confirm that they are functioning
normally. To test-fire the units, press the test button on the
master flash or press the i button in the flash info display
and select [ N Test flash] ( 0 697).
7
C / f : Take the photograph after confirming that
the flash-ready lights for all flash units are lit.
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Optical AWL