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Under low light when flash must be used, the following chart gives you the effective flash range f or correct exposures for filmsof various speeds. Note that high-speed film (ISO 400/800) extends your flash range significantly.

Effective flash range

Film speed
Wide angle (38 mm)
Telephoto(140mm)
ISO 100 0.9 – 2.8 m 0.9 – 2.0 m
3.0 – 9.2 ft. 3.0 – 6.6 ft.
ISO 400 0.9 – 5.6 m 0.9 – 4.0 m
3.0 – 18.4 ft. 3.0 – 13.1 ft.
ISO 800 0.9 – 7.9 m 0.9 – 5.6 m
3.0 – 25.9 ft. 3.0 – 18.4 ft.
ISO 1600 0.9 – 11.2 m 0.9 – 8.0 m
3.0 – 36.7 ft. 3.0 – 26.2 ft.
(Using color negative film)