Nikon D330018-55VR User Manual (en)

300 Technical Notes
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. Refer to the documentation provided 
with the flash unit for details.
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).