We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
266
HANDBOOK OF PROJECTION FOR
cording to their relative merits. The highest average reflecting power within the required angle from the normal will necessitate the least energy expenditure in the projecting system to produce a given screen brightness.
Assuming cases in which the maximum angles of observation are 20 degrees, 30 degrees, 40 degrees, and 50 degrees the values of the ratio of the reflecting power at normal observation to that at these various angles were computed for all screens and likewise values of mean reflecting power for the same limiting angles. These values are tabulated for the Class A screens in Table 15, those for the Class B screens in Table 16, and those for the Class C screens in Table 17.
TABLE 16 CLASS B
20°
. 30°
40"
50°
No.
Ro
Ro
R.
Ro
R.
R.
R.
R.
Rao
Rso
R40
Rso
12
1.55
179
2 45
155
3.91
135
6.30
117
19
1.55
161
2.34
141
3.88
129
5.95
109
13
1.45
156
2.06
139
3.34
121
5.37
106
33
1.43
123
1.93
111
2.87
99
3 97
88
26
1.96
151
2.67
131
3.30
115
3 70
104
29
1.39
111
1.83
100
2.68
90
3.68
79
25
1.59
130
2.05
115
2.75
104
2 91
94
32
1.78
112
2.30
99
2.56
89
2.76
82
27
1.52
120
1.86
108
2.23
98
2.56
91
7
1.26
60.3
1.42
56.7
1.65
53.5
1.84
50.4
Now it seems reasonable to demand that the ratio of the brightness on the axis to that at the extreme angle of observation sholl not be greater than 4.0. This value is decided upon after consideration not only of the variation in brightness as observed from various points in the auditorium, but also from a consideration of the fact that from a given point of observation the screen may appear of unequal brightness over its area. The danger of this inequality being serious increases rapidly as the value of the above mentioned ratio in reflecting powers increases. Assuming now that we adopt the value of 4 as the limiting value of the reflecting power ratio, it is possible from the figures in Tables 15, 16 and 17 to choose the best screen for any one of the cases considered. For instance, assuming that the maximum angle of observation is 20 degrees, it will be noted that all