The international photographer (Jan-Dec 1930)

the negative stage. In section 4 the black metallic silver has been bleached out and the film has been exposed to light. In mathematical proportion to the lack of brilliance of any area of the subject there is silver halide left on the film undisturbed by the bleaching. As soon as they have been developed out (Section 5) these remaining grains will determine the density of this area of film and its consequent function in causing shading on the amateur movie screen. Removing Grain Altogether apart from economy, the reversal process has several marked advantages. Most notable, it compensates for improper length of exposure to a striking degree and it practically eliminates graininess. The larger grains, or clumps of grains, which cause this graininess, are, because they are more sensitive to light, exposed in the camera most readily and developed and bleached out in the reversal process as shown in the diagrams. The final image is, therefore, made up of the smaller, less sensitive grains, which do not cause graininess; except that in the areas representing the very dark parts of the subject the original exposure does not affect even the largest grains, and they are left for the second exposure. But that Red Green does not permit graininess, for it occurs only on the light parts of the screen picture. The cause of graininess is removed from the light areas where it is necessary. Too, the second exposure of the film, controlled in accordance with the transparency of the film after it has been bleached, is responsible for the latitude which makes evenly lighted pictures on the screen even though the exposures have been uneven. If the original exposure was too great and overmuch of the silver halide was exposed and developed and bleached away, then the film is abnormally transparent and the second exposure is increased and brings out more of the remaining silver halide grains so that the final image shall be of normal density. Conversely, if under-exposure followed by bleaching removed too little of the original silver halide the s^'-^Tid exposure is decreased so that too many of the remaining grains will not be developed and left to make an over-dense positive image. Enter Panchromatic After the second development fixing removes the silver halide which still has not been exposed. Otherwise it would make the film opaque in the wrong places. Early in 1928 the Eastman Kodak Fig. 1 Film base Film be.mng picture of red object Projection lens and filters Company announced 16mm. panchromatic safety film. Briefly, Cine-Kodak panchromatic film, being sensitive to light of all colors, reproduces these colors in monochrome on the screen more nearly in their accurate tone relationship one to the other. Ordinarily films, on the other hand, are sensitive chiefly to blue and violet light, while to the eye green and red are brighter colors. So it naturally follows that with this material there is a greater difference between the brightness of colors as reproduced on the screen and as seen by the eye. Panchromatic film, however, has no such handicap, and its sensitiveness to all colors assures you of results hitherto impossible. That thing called quality — hard to define but easy to discern — stands out as soon as the picture is snapped on. You don't have to study the screen to see it. It's instantly evident. Almost before the public realized the significance and capabilities of "Pan," a second announcement, almost unbelievable at the time, was made. On Monday, July 30, 1928, a representative gathering of scientists, photographers and motion picture engineers were introduced to Kodacolor — home movies in full natural color. The only equipment necessary beyond that used for regular black and white movies is a lens of f.1.9 speed or better, a Kodacolor filter and sunlight. Kodacolor Follows The Kodacolor filter is composed of three bands of dyed gelatin, red, green and blue — cemented between disks of optical glass. Kodacolor Film is similar to regular CineKodak Film, except for two necessary differences. The first is that Kodacolor film is panchromatic — or sensitive to light of all colors. The second is that the uncoated side of the transparent film base is embossed with minute cylindrical lenses which join one another and extend the entire length of the film. There are about 220 of these lens elements in the width of the picture area, causing the peculiar satin-like appearance characteristic of Kodacolor Film. The film is so wound that when it is loaded into the camera and exposed in the usual way the picture is taken through the film base. Each embossed lens forms an image of the color filter on the sensitive surface of the film. By this means, when white light falls upon the filter, it is broken up into its principal components, which are red, green and blue. (See Figure 1.) When Shooting Red Let us suppose that we are taking a picture of a red object. Only red light is reflected by such an object and some of these rays fall upon the Kodacolor filter in the camera lens. Both the green and blue portions of the filter absorb red light, but the red portion allows the rays to pass through. The camera lens focuses these red rays upon the proper portion of the (Continued on Page 36) Thirty-four