Appendix K Flash guide numbers apertures and distance

Use Table K.1 as a quick reference for the relationship between guide number, aperture, ISO and subject-to-camera distance.

Table K.1 Flash guide numbers, apertures and distance

Guide number of flash

Aperture

f2.8

f4.0

f5.6

f8.0

f11

f16

Distances from camera to subject for good exposure (m)

10

3.50

2.5

1.78

1.25

0.90

0.62

20

7.10

5.0

3.57

2.50

1.81

1.25

30

10.71

7.5

5.37

3.75

2.72

1.87

40

14.28

10.00

7.14

5.00

3.63

2.50

50

17.85

12.50

8.92

6.25

4.54

3.12

60

21.42

15.00

10.71

7.50

5.45

3.75

NB: This table assumes you are using an ISO of 100, that you are not bouncing, diffusing or zooming the flash, and that the distance measurement is in meters.

NB: This table assumes you are using an ISO of 100, that you are not bouncing, diffusing or zooming the flash, and that the distance measurement is in meters.

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