Nikon D5100 Reference Manual page 49

The Nikon Creative Lighting System (CLS)
Nikon's advanced Creative Lighting System (CLS) offers improved communication
between the camera and compatible flash units for improved flash photography.
II CLS-Compatible F lashUnits
The camera can be used with the following CLS-compatible flash units:
° TheSB-900,SB-800,SB-700,SB-600,SB-400,andSB-R200:
I Ifa color filter is attached to the SB-900 when AUTOor _ (flash) is selected for white balance, the
camera will automatically detect the filter and adjust white balance appropriately.
2 Controlled remotely using optional SB-900, SB-800, SB-700 flash unit or SU-800 wireless Speedlight
commander.
3 m/ft., 20 °C (68 °F), SB-900, SB-800, SB-700, and SB-600 at 35 mm zoom head position; SB-900 and
SB-700 with standard illumination.
TheSU-800wireless speedlight commander: W hen mounted on a CLS-compatible
camera, the SU-800 can be used as a commander for remote SB-900, SB-800,
SB-700, SB-600, or SB-R200 flash units in up to three groups. The SU-800 itself is
not equipped with a flash.
[] Guide Number
To calculate the range of the flash at full power, divide the Guide Number by the aperture.
For example, at ISO I00 the SB-800 has a Guide Number of 38 m or 125 ft. (35 mm zoom head
position); its range at an aperture of f/5.6 is 38+5.6 or about 6.8 meters (or in feet,
125+5.6=approximately 23 ft. 7 in.). For each twofold increase in ISO sensitivity, multiply
the Guide Number by the square root of two (approximately 1.4).
2O3