International projectionist (Jan-Dec 1956)

pearing on the three kinescope screens, then a set of three color-separation records will be obtained. This is actually done in the embossed film method of color kinesope recording, but as pointed out earlier, all three separation images are combined, frame by frame, on a single strip of film. Figure 1 shows the arrangement of kinescopes, optical system, and recording camera. All of the kinescope screens are coated with P-16 phosphor, which emits blue and ultraviolet radiation. A blue-sensitive embossed film records the images. The film is loaded into the camera with its base side toward the lens, so that light must travel through the embossed lenses before it can strike the light-sensitive emulsion layer. The lenticules on the film base are greatly enlarged in the diagram to show how they operate. Actually, they are very small cylindrical lenses, each 1/25-mm high, running all the way across the film, perpendicular to the edge. The three color separations are recorded in different areas behind each lenticule by employing special apertures located in front of the camera lens. This lens images the three kinescope pictures in focus and in register on the film, and at the same time each one of the lenticules images the special apertures in focus on the very narrow area of the emulsion which lies directly behind that lenticule. Light from each individual kinescope passes through one of the apertures, and light from the other two kinescopes is excluded from that aperture. Beam-Splitter Used As illustrated in Fig. 1, light from the red-channel kinescope is directed to a silvered glass surface placed in front of the camera lens. This surface acts as the aperture for the red channel, and reflects the light into the camera lens. Light from the green channel Embossed side of film Photomultipliers Flyingspot kinescope Mirrors FIG. 3. Televising embossed film color records by means of a flying-spot scanner. is similarly reflected from an adjacent silvered surface. The useful light from the blue-channel kinescope is divided into two beams which pass above and below the two silvered surfaces. Figure 2 shows the effective apertures as seen from the lenticules. The insert at the bottom right side of Fig. 1 shows how each lenticule images these apertures onto the emulsion. From top to bottom, the four subdivisions of the emulsion area behind the lenticule receive images of the lower half of the blue-channel aperture, the green-channel aperture, the red-channel aperture, and the upper half of the blue-channel aperture. Thus, the picture information on each kinescope is recorded within a specific area of the emulsion, interlaced with the information recorded from the other two kinescopes. Stated in another way, the picture as a whole is divided into about 390 horizontal strips, corresponding to the number of lenticules contained in the height of one 35-mm motion-picture frame, and each of these strips is subdivided into its three color-separation components. Although the developed silver images are Mirror which reflects light / from first kinescope (red channel) \ .Mirror which reflects light r from second kinescope (green channel ) -~-_2_Part aperture which passes ( *\ \N( V/'// light from third kinescope (blue channel) FIG. 2. Effective apertures of the three optical channels of Fig. 1 as seen from the lenticules. colorless, nevertheless they contain the information required by the television system to produce a color picture. This information can be fed .back into the television system by any of the means commonly used to televise motion-picture film. However, special optical systems have to be employed. Figure 3 shows an arrangement utilizing a flying-spot scanner. The scanning spot is focused on the emulsion side of the film, and light transmitted by the various black-and-white color-separation images then passes through the lenticules. They project this light in bands corresponding to the apertures used in recording. A lens and mirror assembly separates the bands of light and directs them to three different photomultiplier tubes which generate, in accordance with the information recorded on the film, the "red," "green", and "blue" video signals. In a threeVidicon system, embossed film can be televised by inserting a banded filter in front of the projection lens to form a colored picture in the field lens commonly employed in that system. The sensitivity and the signal-to-noise ratio of the Vidicon tubes are sufficient to overcome the loss of light by absorption in the filter. In addition to its direct use for time-zone-delayed rebroadcasting, the embossed-film original can also be used in a reduction printer to make ordinary 16-mm color prints. These prints are convenient permanent records which can be projected with any 16-mm projector, and which can be televised at any station having regular 16-mm color-TV projection equipment. 22 INTERNATIONAL PROJECTIONIST • JULY 1956