Nikon Df - Manual (Page 149)

129
l
A
Optional Flash Units
The flash compensation selected with the optional flash unit is added to
the flash compensation selected with the camera.
A
See Also
For information on choosing how flash and exposure compensation
combine, see Custom Setting e4 (Exposure comp. for flash, 0 259).
For information on automatically varying flash level over a series of
shots, see page 136.