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DUPLICATION OF LENTICULAR FILM 271 one-third of the space behind the lenticular element, and the exact portion that the line covers depends upon the angle which the axis of the beam makes with the elementary axes of the miniature lenses. Since the source of illumina- tion is substantially at infinity, the light reaching the film consists of parallel rays. Three such films are made, one each with the angle to correspond to that of a single primary color. If these are printed by contact upon a smooth- based film, registry being maintained by use of the perforations on the side of the film, there will be obtained a line which corresponds to the width of two color densities. The contact prints are called stencils. The master positive or negative is now printed by contact upon a smooth-based film with a stencil lying between the master and the copy film. This will completely block out the densities corresponding to two color primaries, leaving the third one to come through to print upon the copy film. Since there will be the thickness of a base between the master and the copy, no trace of moire will be present if the source of illumination be properly chosen. This was discussed in some detail in the chapter dealing with screen plates. In order to avoid the lateral inversion that takes place when lenticular film is printed, G. Heymer (U.S.P. 1874529; Eng. P. 353121) would print the film with the emulsion sides in contact. If the printing is done by projec- tion the original objective can be used, and the zones occupied by two of the filters are to be blocked out. This is practically identical to the schemes pro- posed by Ives and Kalmus and Ball. P. A. Richard (U.S.P. 1750358) also disclosed a similar scheme. The reverse procedure, printing color separations on to lenticular positive film, has also been disclosed. Several schemes were proposed by V. Hudeley and J. Lagrave (U.S.P. 2030795; Eng. P. 408109, 421582 and 430585). The negatives were made in a special triple-lens camera, which gave three images in a single frame. This created the problem of enlarging and properly register- ing each of the three part-images in a single frame of lenticular film. The I.G. Company (Eng. P. 392987) would print the separations on to the lenticu- lar positive by contact. The color record is placed in contact with the lenticu- lar side of the copy film, and the beam used for exposure is given the proper angle with respect to the elementary lenticular axes so that the image will be formed in the proper zones behind each lenticule. In a subsequent patent, a stencil such as is disclosed in English patent 412021 is placed between the color record and the lenticulated side of the copy film. Here again the angu- larity of the incident light is controlled to deposit the image in the proper zone. Dr. Bela Gaspar (Eng. P. 343369, 406013 and 409270), and the I.G. (Eng. P. 375338, 451175 and 460653) proposed to print lenticular master positives upon other types of monopack film, and process them to color transparencies by means of dye-destruction or dye-coupling methods. In line with the use of lenticular film as a negative process, the I.G. has disclosed its use as the front element of a bipack (U.S.P. 2093655; Eng. P. 395124). The film is coated with an orthochromatic emulsion. In the lens