American cinematographer (Jan 1930)

January, 1930 American Cinamatographer Three "Principles and "Processes <0E "Photography in A^atural (Colors An Interesting and Instructive Discussion of Color in Photography By Glenn E. Matthews r Kodak Research Laboratories, Rochester, N. Y. his article, reprinted from the 1930 edition of the American Annual of Photography, will be printed in two installments. The next will be in the February issue. — Editor's Note. f IlM' ANY hundreds of color processes have been patented and some few placed on the market since May, 1861, when Maxwell demonstrated the first process of color I • photography. Only three of these processes, however, have r> withstood the test of over twenty years of continuous use, namely, three-color lithography, three-color carbon transfer, and I 'the Autochrome screen plate process. On the other hand, during f Ithis same half century ordinary photography has become almost I ■ indispensable as a record- iring medium, is extensively ; used in business adver- I itising, and through the (.-motion pictures consti- ;.,tutes one of our most im- r portant forms of enter- ! Jtainment and instruction. During the years 1928- 1929 a renewed interest •has been developing in ; color photography. It has found considerable use in connection '. with the development of sound motion pictures. A new process I of amateur cinematography was announced during the late sum- , ::mer of 1928 which has been employed extensively in 1929. A K.color roll film and film pack method was exploited in England ■; during the same year and several professional photographers in '. various parts of the world were specializing in commercial color prints. A staff of workers has been in the field making color rtransparencies chiefly with the Autochrome process which are reproduced each month in the National Geographic Magazine iiand other magazines. In view of this increased interest in the .subject this article has been prepared to give a short review of the :principles underlying the processes of color photography and to ’(describe those processes which have found some practical applica- tion. Color and Its Relation to Light In the making of a photograph of any subject, light is needed Right, fig, 2; left, fig. 6. BLUE VIOLET BLUC iSwtEN GREEN ORANGE VELLOW RED 400 TT\^ 600 WAVELENGTH (m/ij Top, &g. /; bottom, fig. 3; middle, fig. 5. for illumination, a light sensitive material and a camera for record- ing and making it permanent. The requirements in color photo- graphy are similar with certain modifications in order that the final record may be in colors. To better understand the problem, let us examine the known facts about color in relation to light. Most everyone is somewhat familiar with the subject of radio whereby sounds are changed from a frequency of vibration and wave-length sensitive to the ear to a much higher frequency suit- able for broadcasting. Similarly, light may be considered to be when a ray of white light (usual- ly sunlight) is passed through a narrow slit and then either through a prism or through an in- terference grating (a glass surface ruled with several thousand fine lines to the inch) , the light is broken up into a multicolored ribbon or brand known as the visible spectrum (Fig. 1). The normal eye sees this band as an almost infinite number of hues, seven of which Newton distinguished as the most prominent; made up of a series of complex waves of varying frequency, violet, indigo, blue, green, yellow, orange, and red. The light rays producing each minute portion of this band have a definite wave-length, and therefore the color which the normal eye sees may be expressed in terms of a wave-length of about 400 mu. (millionth of a mil- limeter or one-twenty-five millionths of an inch) in the violet to about 700 mu. in the red (Fig. 2). Why Natural Objects Appear Colored Consider now, three strips of cardboard colored red, green, and blue respectively. To the normal eye the strips will appear to be red, green, and blue when illuminated with white light because they absorb, respectively, all other colors of the light falling on them and reflect only these three colors. This pro- ULTRA VIOLET 400 500 600 TOO Fig. 4. Wedge spectrum of ordinary Orthochromatic and Panchromatic films showing range of sensitivity.