Nikon SB-700 AF Speedlight Users Manual - English - Page 135

Guide Number, Aperture and Flash-to-subject Distance

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Guide Number, Aperture and Flash-to-subject Distance Tips on Speedlight Care and Reference Information 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 (m or ft; for ISO 100) = flash-to-subject distance (m or ft) × f-number of aperture. The SB-700's guide number is 28 m (92 ft) (for ISO 100, zoom head position: 35 mm, FX format, illumination pattern: standard, temperature: 20 ˚C/68 ˚F). When ISO sensitivity is 100 and f-number of aperture is 8, the illumination of the SB-700 reaches 3.5 m (11 ft), which is determined by the equation, flash-to-subject distance (3.5 m or 11 ft) = guide number (28 m or 92 ft) / f-number of aperture (8). • For ISO sensitivities other than 100, multiply the guide number by the factors (ISO sensitivity factors) shown in the table below. ISO 25 50 100 200 400 800 1600 3200 6400 Factor 0.5 0.71 1 1.4 2 2.8 4 5.6 8 • See "Specifications" for more details. (0H-21) t Determining aperture and flash-to-subject distance for correct exposure f-number of aperture = 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 / f-number of aperture H H-6

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H
–
6
Tips on Speedlight Care and Reference Information
H
Guide Number, Aperture and Flash-to-subject Distance
The guide number (GN) indicates the amount of light generated by a
fl
ash unit. As the number increases, the
fl
ash output becomes greater
and the light extends further.
There is a relation represented by an equation, guide number (m or
ft; for ISO 100) =
fl
ash-to-subject distance (m or ft) × f-number of
aperture. The SB-700’s guide number is 28 m (92 ft) (for ISO 100,
zoom head position: 35 mm, FX format, illumination pattern: standard,
temperature: 20
˚
C/68
˚
F). When ISO sensitivity is 100 and f-number
of aperture is 8, the illumination of the SB-700 reaches 3.5 m (11 ft),
which is determined by the equation,
fl
ash-to-subject distance (3.5 m
or 11 ft) = guide number (28 m or 92 ft) / f-number of aperture (8).
• For ISO sensitivities other than 100, multiply the guide number by
the factors (ISO sensitivity factors) shown in the table below.
ISO
25
50
100
200
400
800
1600
3200
6400
Factor
0.5
0.71
1
1.4
2
2.8
4
5.6
8
• See “Specifications” for more details. (
0
H-21)
t
Determining aperture and
fl
ash-to-subject distance for
correct exposure
f-number of aperture =
guide number (GN for ISO 100; m or ft) ×
ISO sensitivity factor /
fl
ash-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 / f-number of aperture