Nikon D810 - Manual (Page 453)

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• SU-800 Wireless Speedlight Commander: When mounted on a CLS-
compatible camera, the SU-800 can be used as a commander
for remote SB-910, 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.
A
Guide Number
To calculate the range of the flash at full power, divide the Guide
Number by the aperture. If, for example, the flash unit has a Guide
Number of 34 m or 111 ft (ISO 100, 20 °C/68 °F); its range at an aperture
of f/5.6 is 34÷5.6 or about 6.1 meters
(or in feet, 111÷5.6=approximately 19 ft 10 in.). For each twofold
increase in ISO sensitivity, multiply the Guide Number by the square
root of two (approximately 1.4).
A
The Sync Terminal
A sync cable can be connected to the sync
terminal as required. Do not connect
another flash unit via a sync cable when
performing rear-curtain sync flash
photography with a flash unit mounted on
the camera accessory shoe.