Bauhaus-Universität Weimar

Optic Projection: Principles, Installation and Use of the Magic Lantern, Projection Microscope, Reflecting Lantern, Moving Picture Machine
Gage, Henry Simon and Henry Phelps Gage
In the above case, with a moving picture objective of 13.3 cm. 
focus, the focus of the magic lantern objective to use with the 
moving picture objective is, for the same: 
42.1cm. i6>£in. 
53.1 cm. 21 in. 
48.5 cm. 19 in. 
Width of picture 
Height of picture 
Diagonal of picture 
3. The same arc lamp, condenser, etc., are to be used inter¬ 
changeably for either films or slides by simply pushing the appara¬ 
tus sidewise. Usually the slide-carrier is mounted permanently 
with the condenser so that the opening is not a circle of the diame¬ 
ter of the condenser but a rectangle 7.5 cm. x 10 cm. (3 in. x 4 in.). 
4. Even illumination of the screen.—If the light is not quite 
uniform it is better to have the center the brighter rather than the 
§ 824. Ideal case, moving pictures.—The ideal case of projec¬ 
tion (shown in fig. 328 a and b) is where the light is a point source 
and the condenser has no spherical aberration. This is the case 
which is usually figured, but it is not the best in practice if an 
extended source is used. 
When changing over to moving picture films the lamp and 
condenser are moved to the position b. The objective O, is still 
45 cm. (18 in.) from the condenser face where the rays will cross 
in the diaphragm plane, and the film is placed 13.3 cm. (5>4 in.) 
from the objective so that it will be in focus on the screen. 
§ 825. Illumination of moving pictures, practical method.— 
The method which has been found most successful in lighting 
moving pictures is to focus the image of the crater not on the objec¬ 
tive but on the aperture plate. This is because a moving picture 
objective usually has a diameter greater than the diagonal of the 
film (40 mm. to 65 mm. against 28.5 mm. diagonal ; 1 J^in. to 2^ in. 
against 1 in. diagonal), hence the important point is to get the 
light through the film ; the large objective will take in all the light 
which can get through the film. 
Figures 333-335 show the effects of different methods of lighting. 
In practice all three are used together, that is, the film is illum¬ 
inated by the area of the condenser which is not covered by the


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