The Cine Technician (1939)

21)1 T H E C I N E-TECHNICI A N ber ui tiny lenticulations. which ma\ either be along the film o) across it. the result being a series ot verj small cylindrical louses. These lenses throw a microscopically small image of the three-colour filter on the emulsion behind them, and thus form a three-colour separation re cord of each point ol the image on the film. A mono chrome image is formed on development and consists of a series of separation records, pig, 3 shows the path ol the rays during exposure. By reversing the path ol the rays in projection, the film developed by the reversed process direct into a positive results, behind a three-colour filter, in an additive colour pict lire. 5. — The Agfa Lenticulated Bipack Flm [Note. — The Agfa lenticulated bipack (German Pat. 588747) is not yet on the market, since1 the process is still in the experimental stage] The front film of the Agfa lenticulated bipack is only sensitive to blue and green, ami has a lenticulated celluloid base. The hack Him is sensitised for red. Either front or back film may have a re 1 filter layer to prevent the blue and green rays from influencing the red-sensitive back film. The red record is thus prodr ed on the back film, while the front film shows a blue and green record produced h\ a banded filter in front ot the lens, the outer bands being yellow and the inner ones blue-violet. The yellow hands produce the red image on the back film and the green image on the trout film, while the blue-violet bands produce the blue record on the front film only. The two records on the front film may be separated without difficulty in printing by known methods, and separate blue and green negative records are thus produced. The simplest method oi printing is that of subtractive coloured positive by the silver-dye-bleaching process. The Reproduction Process in the Projector Additive Processes All colour reproduction processes can he divided into two main classes, the additive ami the suhir active processes. Independently of the manner in which the separation colour records have been made, ever\ projection process produces the impression of a coloured image on the screen by one of these two basic methods. In the additive method the so-called "optical synthesis" by a filter or Exposure Original subject A March-April. L938 Reproduction Projected image 3| Screen Lens system filter iktsj' g"j' >' f Lenticulorfilm rbg Fig. 2. Arrangement of the optical system and films in the Technicolor Camera Fig. 3. Principles of the Lenticular Process screen is used. Just as in taking, the filters or screens used produce a separation of the picture in the respective colour components, the composition of the picture on the screen is done in an absolutely identical manner. Whereas the light path during exposure is lens-colour screenemulsion, or alternatively banded filter-lens-lenticulated screen-emulsion, the light during projection travels in tindirection emulsion-colour screen-lens-screen, or alternatively emulsion-lenticulated screen-lens-banded filterscreen. The respective composite records thrown as images on the screen fuse together to the eye, and a coloured picture, resembling that seen naturally, is the result. For exposure and reproduction, filters of the three primary colours red, green, and blue are used. All recording processes where separation is effected by beam-splitter and filters, or by a screen process (i.e., those systems noted above under the general heads ol beam-splitting and screen processes), give quite simply a suitable set of images for additive reproduction if the film exposed is reversed to a positive image instead of developed to a negative. The synthesis of the coloured image on the screen is produced by the superimposition of the different rays of coloured light : the single colour hues perceived are, with respect to their nuances and intensities, the sum of the three primary components. White or grey tone results where equal quantities of the three primaries are present simultaneously. This synthesis by mixing coloured lights characteristics all additive colour processes. (Charts II and IV). Additive two and three-colour processes which do not use a screen — optical synthesis through primary filters — have not proved satisfactory in the cinematographic pra fcice on account of the time or spacial parallax which thej introduce. Such films as have been publicly shown a cinemas, made by the Raycol, Bernardi, Chromofilm, Francita and other similar processes, have really hardly passed the experimental stage. Among the additive processes available as reversal L6 mm. to amateurs are Agfacolor and Kodacolor (lenticulated film) and Dufaycolour (regular colour mosaic screen). The American Keller-Dorian Corporation and the Siemens Opticolor Gesellschaff have tried for many years to produce satisfactory copies ot lenticulated film which would be useful in the theatre, but finality has not yet been reached in this matter, and demonstrations ol the present results are hardly convincing in the sense of being a practical proposition.