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
rU C
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