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Flash modes and functions
Determining the aperture, flash output level and shooting distance
ISO 25 50 100 200 400 800 1600 3200 6400
Factors 0.5 0.71 1 1.4 2 2.8 4 5.6 8
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.
•
•
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).•
BA: With the Nikon Diffusion Dome attached
WP: With the wide-flash adapter in place
•
•
Guide number (GN at ISO 100; m/ft)
ISO sensitivity factors
For sensitivities, multiply the guide number by the factors shown in the table below.
Flash
output
level
Zoom position (mm)
14mm
17 18 20 24 28 35 50 70 85 105 120 135 180 200
WP
+
BA
BA WP
1/1
13/
42.7
16/
52.5
17/
55.8
22/
72.2
23/
75.5
24/
78.7
27/
88.6
30/
98.4
34/
111.5
40/
131.2
44/
144.1
47/
154.2
49.5/
162.4
51/
167.3
51.5/
169.0
54/
117.2
56/
183.7
1/2
9.1/
29.9
11.3/
37
12/
39.3
15.5/
50.9
16.2/
53.1
16.9/
55.4
19/
62.3
21.2/
69.6
24/
78.7
28.2/
92.5
31.1/
102.0
33.2/
108.9
35/
114.8
36/
118.1
36.4/
119.4
38.1/
125.0
39.5/
129.6
1/4
6.5/
21.3
8/
26.2
8.5/
27.9
11/
36.1
11.5/
37.7
12/
39.3
13.5/
44.3
15/
49.2
17/
55.8
20/
65.6
22/
72.2
23.5/
77.1
24.7/
81.0
25.5/
83.7
25.7/
84.3
27/
88.6
28/
91.9
1/8
4.5/
14.8
5.6/
18.8
6/
19.7
7.7/
25.3
8.1/
26.6
8.4/
27.6
9.5/
31.2
10.6/
34.8
12/
39.3
14.1/
46.3
15.5/
50.9
16.6/
54.5
17.5/
57.4
18/
59.0
18.2/
59.7
19/
62.3
19.7/
64.6
1/16
3.2/
10.5
4/
13.1
4.2/
13.8
5.5/
18.0
5.7/
18.7
6/
19.7
6.7/
21.9
7.5/
24.6
8.5/
27.9
10/
32.8
11/
36.1
11.7/
38.4
12.6/
40.4
12.7/
41.7
12.8/
42.0
13.5/
44.3
14/
45.9
1/32
2.2/
7.2
2.8/
9.2
3/
9.8
3.8/
12.5
4/
13.1
4.2/
13.8
4.7/
15.4
5.3/
17.4
6/
19.7
7/
23.0
7.7/
25.3
8.3/
27.2
8.7/
28.5
9/
29.5
9.1/
29.9
9.5/
31.2
9.8/
32.1
1/64
1.6/
5.2
2/
6.6
2.1/
6.9
2.7/
8.9
2.8/
9.2
3/
9.8
3.3/
10.8
3.7/
12.1
4.2/
13.8
5/
16.4
5.5/
18.0
5.8/
19.0
6.1/
20.0
6.3/
20.7
6.4/
21.0
6.7/
21.9
7/
23.0
1/128
1.1/
3.6
1.4/
4.6
1.5/
4.9
1.9/
6.2
2/
6.6
2.1/
6.9
2.3/
7.5
2.6/
8.5
3/
9.8
3.5/
11.5
3.8/
12.5
4.1/
13.5
4.3/
14.1
4.5/
14.8
4.5/
14.8
4.7/
15.4
4.9/
16.1