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Determining the aperture, flash output level and shooting distance
In Distance-priority, Manual and Repeating flash modes, use the guide number
table and the following equation to calculate the aperture, flash output level, and
shooting distance to obtain the correct exposure.
•
The guide number (GN at ISO 100; m/ft) indicates the amount of light generated
by the flash.
•
The larger the number, the greater the flash output.
ISO sensitivity factors
For sensitivities, multiply the guide number by the factors shown in the table below.
ISO
25
Factors
0.5
Guide number (GN at ISO 100; m/ft)
D
The table below shows the guide numbers while using the standard illumination
pattern when the SB-900 is mounted on a Nikon FX format camera.
•
For others, see "Specifications" (kF-18).
Flash
14mm
output
WP +
level
BA
BA
13/
16/
1/1
42.7
52.5
9.1/
11.3/
1/2
29.9
37
6.5/
8/
1/4
21.3
26.2
4.5/
5.6/
1/8
14.8
18.4
3.2/
4/
1/16
10.5
13.1
2.2/
2.8/
1/32
7.2
9.2
1.6/
2/
1/64
5.2
6.6
1.1/
1.4/
1/128
3.6
4.6
•
BA: With the Nikon Diffusion Dome attached
•
WP: With the wide-flash adapter in place
D–22
50
100
0.71
1
17
18
20
24
WP
17/
22/
23/
24/
27/
55.8
72.2
75.5
78.7
88.6
12/
15.5/
16.2/
16.9/
19/
39.3
50.9
53.1
55.4
62.3
8.5/
11/
11.5/
12/
13.5/
27.9
36.1
37.7
39.3
44.3
6/
7.7/
8.1/
8.4/
9.5/
19.7
25.3
26.6
27.6
31.2
4.2/
5.5/
5.7/
6/
6.7/
13.8
18
18.7
19.7
21.9
3/
3.8/
4/
4.2/
4.7/
9.8
12.5
13.1
13.8
15.4
2.1/
2.7/
2.8/
3/
3.3/
6.9
8.9
9.2
9.8
10.8
1.5/
1.9/
2/
2.1/
2.3/
4.9
6.2
6.6
6.9
7.5
200
400
800
1.4
2
2.8
Zoom position (mm)
28
35
50
70
30/
34/
40/
44/
98.4
111.5
131.2
144.1
21.2/
24/
28.2/
31.1/
69.6
78.7
92.5
102
15/
17/
20/
22/
49.2
55.8
65.6
72.2
10.6/
12/
14.1/
15.5/
34.8
39.3
46.3
50.9
7.5/
8.5/
10/
11/
24.6
27.9
32.8
36.1
5.3/
6/
7/
7.7/
17.4
19.7
23
25.3
3.7/
4.2/
5/
5.5/
12.1
13.8
16.4
18
2.6/
3/
3.5/
3.8/
8.5
9.8
11.5
12.5
1600
3200
4
5.6
85
105 120 135 180 200
47/
49.5/
51/
51.5/
154.2
162.4
167.3
169
117.2
33.2/
35/
36/
36.4/
38.1/
108.9
114.8
118.1
119.4
125
23.5/
24.7/
25.5/
25.7/
77.1
81
83.7
84.3
88.6
16.6/
17.5/
18/
18.2/
54.5
57.4
59
59.7
62.3
11.7/
12.3/
12.7/
12.8/
13.5/
38.4
40.4
41.7
42
44.3
8.3/
8.7/
9/
9.1/
9.5/
27.2
28.5
29.5
29.9
31.2
5.8/
6.1/
6.3/
6.4/
6.7/
19
20
20.7
21
21.9
4.1/
4.3/
4.5/
4.5/
4.7/
13.5
14.1
14.8
14.8
15.4
6400
8
54/
56/
183.7
39.5/
129.6
27/
28/
91.9
19/
19.7/
64.6
14/
45.9
9.8/
32.2
7/
23
4.9/
16.1
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