Table 1
Reflection/Transmission Values
for Various Beamsplitter Ratios
|
Normal Ratio
R/T
|
Actual Ratio
R/T
|
% Projected Light Passed to Camera
|
% Foreground Light Passed to Camera
|
50/50
45/55
40/60
35/65
30/70
25/75
20/80
15/85
10/90
5/95a
|
48/48
43/53
38/58
33/63b
28/68
23/73c
18/78
13/83d
8/88
3/93e
|
23.04
22.79
22.04
20.79f
19.04
16.79g
14.04
10.79
7.04
2.79
|
48
53
58
63
68
73
78
83
88
93
|
a Plain glass, one side AR-coated.
e Three-stop reduction.
b One-quarter stop reduction.
f One-quarter stop reduction.
c Half-stop reduction.
g One-half stop increase.
d One-stop reduction.
The expense of foreground lighting in front projection
can be reduced, where lamphouse power is available, by the
use of off-ratio beamsplitters. At a ratio of 30/70, for example,
a loss of 4% of projected light yields a saving of 20% of
foreground lighting.
|