T.O. 33B-1-1
6-15
Note
To change the SFD from any given distance to any desired distance, locate the
given distance on top of the chart. Then read down the left side of the table to the
desired distance. The original exposure should be multiplied by the number
common to both the given column and the desired row to get the new exposure.
This chart may be used for distance changes providing the kV and mA levels are
not changed.
Table 6-1. Exposure-Time Correction Factors for Different Source Film Distances.
Desired Distance (Feet)
Given Distance (Feet)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1
1
0.25
.11 .06
.04
.03
.02
.01
.01
.01
.01
.01
.01
.01
.01
.01
.01
.01
.01
2
4
1
.44 .25
.16
.11
.08
.06
.05
.04
.03
.03
.02
.02
.02
.02
.01
.01
.01
.
3
9
2.3
1
.56
.36
.25
.18
.14
.11
.09
.07
.06
.05
.05
.04
.04
.03
.03
.02
.02
4
16
4
1.8
1
.64
.44
.33
.25
.20
.16
.13
.11
.09
.08
.07
.06
.06
.05
.04
.04
5
25
6.3
2.8
1.6
1
.69
.57
.4
.31
.25
.21
.17
.15
.13
.11
.10
.09
.08
.07
.06
6
36
9
4
2.3
1.4
1
.73
.56
.44
.36
.30
.25
.21
.18
.16
.14
.12
.11
.10
.09
7
49
12.3
5.4
3.1
2
1.4
1
.77
.60
.49
.40
.34
.29
.25
.22
.19
.17
.15
.14
.12
8
64
16
7.1
4
2.6
1.8
1.3
1
.80
.64
.53
.44
.38
.33
.28
.25
.22
.20
.18
.16
9
81
20.3
9
5.1
3.2
2.2
1.7
1.3
1
.81
.67
.56
.48
.41
.36
.32
.28
.25
.22
.20
10
100
25
11.
1
6.3
4
2.8
2
1.6
1.2
1
.83
.69
.59
.57
.44
.39
.35
.31
.28
.25
11
121
30.2
13.
4
7.6
4.8
3.4
2.5
1.9
1.5
1.2
1
.84
.72
.62
.54
.47
.42
.37
.34
.30
12
144
36
16
9
5.8
4
2.9
2.3
1.8
1.4
1.2
1
.85
.73
.64
.56
.50
.44
.40
.36
13
169
42.2
18.
8
10.
6
6.8
4.7
3.4
2.6
2.1
1.7
1.4
1.2
1
.86
.75
.66
.58
.52
.47
.42
14
196
49
21.
7
12.
3
7.8
5.4
4
3.1
2.5
2
1.6
1.4
1.2
1
.87
.77
.68
.61
.54
.50
15
225
56.2
25
14
9
6.3
4.6
3.5
2.8
2.2
1.9
1.6
1.3
1.1
1
.88
.78
.69
.62
.56
16
256
64
28.
4
16
10.
2
7.1
5.2
4
3.2
2.6
2.1
1.8
1.5
1.3
1.1
1
.89
.79
.71
.64
17
289
72.2
32.
1
18.
1
11.
6
8
5.9
4.5
3.6
2.9
2.4
2
1.7
1.5
1.3
1.1
1
.89
.80
.72
18
324
81
36
20.
2
13
9
6.6
5.1
4
3.2
2.7
2.3
1.9
1.6
1.4
1.3
1.1
1
.89
.81
19
361
90.2
40.
1
22.
6
14.
4
10
7.4
5.6
4.5
3.6
3
2.1
1.8
1.6
1.4
1.2
1.1
1.1
1
.90
20
400
100
44.4
25
16
11.1
8.2
6.3
4.9
4
3.3
2.8
2.4
2
1.8
1.6
1.4
1.2
1.1
1
