Guide number – Nikon Autofocus Speedlight SB-24 User Manual

Page 110

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GUIDE NUMBER

In manual flash and Repeating-Flash modes, apart from checking the shooting

distance in the LCD panel, you can also determine the correct f/stop using the
following equation.

f/stop =

guide number

flash-to-subject-distance

See table for the guide numbers at various film speeds.

Guide number at various film speeds

meters (feet) at ISO 100

setting

Light output''^.^

24mm

28 mm

35 mm

50mm

70mm

85 mm

1/1

30 (98)

32(105)

36(118)

42(138)

47(154)

50(164)

1/2

21 (69)

22 (72)

25 (82)

30 (98)

33(108)

36(118)

1/4

15(49)

16 (52)

18(59)

21 (69)

23(75)

25 (82)

1/8

10.5(34)

11 (36)

12.5 (41)

15(49)

16.5 (54)

18(59)

1/16

7.5 (25)

8(26)

9(29)

10.5(34)

11.5 (38)

12.5 (41)

For film other than ISO 100, multiply the above figures by the following magnifications:

ISO 25

50
200
400
800

1600

xO.5
xO.71
x1.4
x2
x2.8
x4

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