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FOR MANAGERS AND OPERATORS
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This, so far as I am able to determine, is the principal practical effect of spherical aberration. It amounts to a discoloration of the light, and hence a diminution of its brilliancy, though it may or may not be sufficient to be perceptible to the eye in individual cases.
Also spherical aberration, if excessive, will cause the spot at the aperture to consist of a series of circles of light instead of an evenly illuminated field, and as this plane is refocused at the screen, there will, if there is an absence of rays at the center, be a dark spot or "ghost," or if more of the rays are reaching the center of the spot than its edges, high lights will result. This is usually the result of the film cutting the beam of light too far from the actual mean focus of the crater, but there are, nevertheless, other conditions which result in high lights and shadows on the screen, and spherical aberration may result only in uneven illumination. There is practically no bad effect from spherical aberration through the stereopticon because the rays reach the slide before they are displaced, but chromatic aberration will show if the rays from the outer edges/ of the condenser pass through the slide.
Chromatic Aberration of the Condenser Beam. — In Plate 11, a crater is constructed by cutting an aperture in a piece of cardboard and placing a | ^CARDBOARD
piece of ground glass K I/MNHOU
behind it. Back of this is placed a 100 C. P. incandescent lamp. The nLAMENT crater and screen are placed at conjugate foci of the condensers. The screen corresponds to the aperture plate of the Plate 11, Figure 52.
machine. A piece of cardboard pierced with a pinhole is placed as shown in Plate 11.
The results as observed upon the screen, Plate 11, are: the crater is focused in full definition on the screen, but it is colored with the shades of the spectrum in the manner shown. Now it has been demonstrated by the Kinemacolor process that all the colors of the spectrum can be reduced to approximately two shades, viz: a reddish-orange and blueishgreen, which for the sake of clearness we will call orange and green.
In Plate 11 A are shown the same conditions described in connection with Fig. 1, except that the colors of the spectrum