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glass and upon the angle of incidence under which a ray strikes the surface. It increases, therefore, towards the margin of the condenser because the angles of incidence are greater there than nearer the center of the lens.
The following two tables show for 4 different zones of an ordinary M.P. condenser, the path lengths and the mean losses by absorption and refraction in these zones for the absorption coefficients 1.3% and 3.9% per cm., which are about the limit values for glasses available for this purpose. Figure 12 illustrates approximately the paths of the rays representing the middle of the zones through the condenser.
SPHERICAL DOUBLE CONDENSER
Absorption Coefficient 1.3% per cm.
Distanceof
Loss in % by ab 1
Sum
Loss
center of
Loss
in % by reflection
sorption and
of
zone from
on surface
length of path in
losses
J" /o
opt. axis
lens in (mm)
0/ /o
m zone
I
2
3
4
I
(22.5)
II
(19.4)
5
4-4
4-1
3.9
3.6
2.7 (21.7)
2. 1 (18.0)
20.8
1-3
15
4-4
4-1
3-9
3-6
2.6 (18.4)
1-9
(15-0)
20.5
3-9
25
4-4
4-2
4.0
3-7
2-3
(14.9)
1.6
( 9-7)
20.2
6.3
35
4.8
4.5
4-2
4.0
1-9
I . I
20.5
9.0
Total Loss 20.5%
Absorption Coefficient 3.9% per cm.
Distanceof center of
zone from opt. axis
Loss in % by ab ! Sum Loss in % by reflection sorption and of
on surface
length of path in lens in (mm)
losses
%
Loss in zone
I
2
3
4
I
(22.5)
II
(19.4)
5
4-2
3.8
3-7
3-3
8.2 (21.0)
5-9
(18.0)
29.3
1.8
15
4-4
3-8
3-7
3-3
7-7 (18.4)
5-5 (15.0)
28.4
5-3
25
4-4
3-9
3-8
3-5
6.9 (14.9)
4-7 ( 9.7)
27.2
8.5
35
4.8
4-3
4-1
3-7
5-5
3-2
25.6
II .2
Total Loss 26.
The same is done in the next two tables for a Fresnel lens, which is spherically corrected, has only 2 reflecting surfaces, less glass path, but higher angles of incidence in the outer zones. The average glass path is here the same for all zones and equals 10 mm.
55