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ISO speed coefficient
Photography distance range = Guide number × ISO speed coefficient
÷ Aperture
Ex) 35 mm-format or manual flash, power level: 1/1, focal length: 35 mm, aperture:
F4, ISO: 400
25 (Guide number) × 2 (ISO speed coefficient) ÷ 4 (Aperture) = 12 m
The flash light reaches to 12 m.
When using the HSS flat flash (flash
with HSS)
The flash range becomes shorter than that of normal flash photography when the
high speed sync is used. You can get the correct flash range using the following
guide number table and an ISO speed coefficient.
Guide number
35 mm-format or manual flash (ISO100)
ISO100 ISO200 ISO400 ISO800 ISO1600 ISO3200
11.422.845.7
Shutter speed
Flash Coverage Settings (mm)
16* 24 28 35 50 70 105
1/250 4.7 8.8 9.1 9.5 10.9 13.4 16.4
1/500 3.3 6.2 6.4 6.7 7.7 9.5 11.6
1/1000 2.4 4.4 4.5 4.7 5.5 6.7 8.2
1/2000 1.7 3.1 3.2 3.4 3.9 4.7 5.8
1/4000 1.2 2.2 2.3 2.4 2.7 3.4 4.1
1/8000 0.8 1.6 1.6 1.7 1.9 2.4 2.9
1/12000 0.6 1.1 1.1 1.2 1.4 1.7 2.1
* When the wide panel is attached.