Nikon D7200 - Guide Number; The AS-15 Sync Terminal Adapter

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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, SB-500, 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 AS-15 Sync Terminal Adapter
When the AS-15 sync terminal adapter (available separately) is
mounted on the camera accessory shoe, flash accessories can be
connected via a sync terminal.