Nikon SB 700, SB-700 user manual Guide Number, Aperture and Flash-to-subject Distance

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 (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)

tDetermining 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

Tips on Speedlight Care and Reference Information

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