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THE LIGHT SOURCE
AOr
Figure 99F
and (cl) the distance of the aperture from the condensing and the projection lenses.
Examination of the curve in Fig. 99G shows that in a typical incandescent lamp optical system the screen illumination increases with the increase in the area of light source up to one-half inch square. ( \()2 ) A Tore than that merely adds illumination to the cooling plate without raising the screen illumination to any appreciable degree. Therefore the light source area cannot be increased beyond the limits of one-half inch square for the 35 mm projector optical system with any beneficial effect. The newer lamps produce additional screen illumination only because more filament has been included within the usable one-half inch area.
M error Reflector
Mazda lamps of course emit an equal amount of light in a direction opposite to that of the condenser. It is desirable to make use of as much of this light as is possible. (193) This has been accomplished by locating a spherical glass reflector pictured in Fig 99F behind the lamp. This mirror reflects from 80 to 85 percent of the light incident upon its surface and the greater part of the light is brought to a focus in the plane (or planes) of the filament, in the form of an inverted and reversed image of the filament. (194) In the case of the monoplane filament the mirror is positioned so that the image of the filament dovetails with the filament coils, as shown in Fig. 991. With the mirror adjusted in this way, most of the reflected light flux merges with the beam from the filament coils and passes on to the collector lens.
(195; Two important advantages result. First, the