Guide Number, Aperture And Flash-To-Subject Distance - Nikon SB-5000 Reference Manual

Guide Number, Aperture and Flash-
to-subject Distance
The guide number (GN) indicates the amount of light generated by a flash
unit. As the number increases, the flash output becomes greater and the
light extends further.
There is a relation represented by an equation, guide number (ISO 100, m/
ft) = flash-to-subject distance (m or ft) × aperture f-number. The SB-5000's
guide number is 34.5/113 (ISO 100, m/ft, zoom head position: 35 mm, FX
format, illumination pattern: standard, temperature: 23 °C/73.4 °F). When
ISO sensitivity is 100 and aperture f-number is f/8, the illumination of the
SB-5000 reaches 4.31 m (14 ft), which is determined by the equation, flash-
to-subject distance (4.31 m or 14 ft) ≈ guide number (34.5/113) / aperture
f-number (8).
• For ISO sensitivities other than 100, multiply the guide number by the
factors (ISO sensitivity factors) shown in the table below.
ISO 25
Factor
0.5
• See "Specifications" for more details (0H-25).
t
Determining aperture and flash-to-subject distance for
correct exposure
Aperture f-number
= guide number (GN for ISO 100; m or ft)
× ISO sensitivity factor / flash-to-subject distance (m or ft)
Flash-to-subject distance (m or ft)
= guide number (GN for ISO 100; m or ft)
× ISO sensitivity factor / aperture f-number
50 100 200
0.71 1 1.4
400 800 1600 3200 6400
2 2.8 4 5.6 8
H
H-6