Popular Science Monthly
��227
��reflected by the silver; the other passes through the transparent openings.
The film which is made by this process when it is projected is not a succession of blue and green pic- tures. The pictures are black and white. They represent, how- ever, the red and blue color qualities of the original object photo- graphed. Why, then, do they appear in colors on the screen?
Study the accom- panying picture of the projector and the answer is plain. The projector required is fitted with two lenses spaced two pictures apart. The upper lens is provided with a green-blue screen through which the images representing the red shades on the film are projected; the lower lens is pro- \'ided vinth a \dolet-red screen which supplies the blue sensation. These two colors appear at the same time on the screen, one over the other. The two colors are accurate- ly registered on the screen chiefly by ob-
��servation of the general effect produced. However, it is not necessary for the operator to rely entirely on his judgment
��Registering ielescope
���Double lens projecioc
The operator of the projector is looking through a microscope in order to make the two sets of exposures register accurately on the screen
��Silvered sectiorr
��Light s|iliUin9 device
��Course of direct ray \
��Lighf raY striking clear class passes directly through
��Green-blut colof screen
���Scene with violet- red sKades
��Projection lei
��The double lens systen" co-oper- ates with the doubly exposed film to secure natural effects
��to secure registration. In one corner of each red film is a minute circle, and in the corresponding corner of each blue film is a very small solid circu- lar spot. The opera- tor shifts the pictures so that the solid spot on one film is cen- tered within the cir- cle of the correspond- ing film. These regis- tration marks are so small that they can- not be detected on the screen. They are located by means of a microscope perma- nently attached to the projection machine. The images are shifted by an additional lens to avoid the distortion resulting when the entire main line system is shifted.
The two pictures which were taken at the same time by the camera are projected simultane- ously, so that colors are actually mixed on the screen, but by a process akin to that which is used in mak- ing the colored covers on the Popular Sci- ence Monthly and other magazines.
It is true that double the film length used in ordinary motion pic- ture work is required. On the other hand, the rate of speed is that ordinarily adopted. The pictures are ad- vanced, two at each shift, and sixteen two- color pictures are dis- played every second on the screen, which is the average speed of all ordinary motion pic- ture projections.
��Cleai- glass
section
��The light-splitting device consists of a glass plate part of which is silvered and part of which is transparent, producing a checkerboard effect. Some of the rays are reflected by the silvered portions and others pass through the transparent portions. The reflected rays strike cer- tain parts of the film to produce one set of ex- posures, and also the transmitted rays strike other parts to produce the second set of exposures
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