Guide no. (at iso 100 in meters – Canon 550EX User Manual
Page 121
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Specifications
• Guide No. (At ISO 100 in meters
[Normal Mode]
Flash Coverage (mm)
17
24
28
35
50
70
80
105
Normal (full) Flash Guide No
15
28
30
36
42
46
50
55
Quick Flash
Same as for manual flash from 1/2 to 1/6.
Manual Flash Guide No.
1/1
15
28
30
36
42
46
50
55
1/2
10.6
19.8
21 2
25.5
29.7
32 5
35 4
38 9
1/4
7.5
14
15
18
21
23
25
27 5
1/8
5 3
9.9
10,6
12,7
14.8
163
17.7
19.5
1/16
38
7
7.5
9
10.5
11.5
12.5
13.8
1/32
27
49
5 3
6.4
7,4
8 1
8.8
97
1/64
1.9
35
3.8
4.5
5,3
58
6.3
6.9
1/128
1 4
2 5
2 7
3.2
3.7
4.1
4.4
49
[High-Speed Sync (FP Flash) ]
Shutter Speed
Flash Coveraae (mm)
17
24
28
35
50
70
80
105
1/125
106
19.8
21.2
252
29.7
32.5
35 4
38.9
1/160
9.4
175
18,8
22.5
26.3
28 8
31.3
34.4
1/180
8.8
16.5
17.7
21,2
24.7
27.1
29 5
32,4
1/250
7.5
140
15.0
180
21.0
23.0
25.0
27.5
1/320
6.6
12.4
13.3
15,9
18.6
20.3
22.1
24.3
1/350
6,3
11 8
12.7
15.2
177
194
21.1
23.2
1/400
5.9
11.1
11.9
14.2
16.6
18.2
19.8
21 7
1/500
5 3
99
10.6
12,7
14.8
16.3
177
194
1/640
4,7
8.8
9.4
11.3
13.1
14-4
15.6
17.2
1/750
4.3
8.1
8.7
10.4
12.1
13.3
14.4
15.9
1/800
4.2
7.8
8.4
10.1
11.7
12.9
14,0
15.4
1/1000
3.8
7.0
7.5
9.0
10.5
11.5
125
13.8
1/1250
3.4
6.3
6.7
8.0
9.4
103
11.2
12.3
1/1500
3 1
5.7
6.1
7.3
8.6
94
102
11,2
1/1600
3.0
5,5
5.9
7.1
8.3
9.1
9.9
10.9
1/2000
2.7
4.9
5,3
64
7.4
8.1
8.8
9.7
1/2500
2.4
4.4
4.7
5.7
6.6
7.3
79
8.7
1/3000
22
40
4.3
5.2
6.1
6.6
7.2
7.9
1/3200
2.1
3.9
4.2
5.0
5.9
64
7.0
7.7
1/4000
1.9
3.5
3.8
4.5
5.3
5.8
6.3
6.9
1/5000
1.7
3.1
3.4
4.0
4.7
5.1
56
6.1
1/6000
1.5
2.9
3.1
37
4.3
4,7
5.1
5.6
1/6400
1.5
2.8
3.0
3.6
4,2
4.5
49
5.4
1/8000
1.3
2.5
2.7
3.2
3.7
4 1
44
4.9
(Multiply by 3,3 to convert to feet)
121