International photographer (Feb-Dec 1929)

Tweh The INTERNATIONAL PHOTOGRAPHER July, 1929 Sound and the High Intensity and Plain Carbon Arc BY EUGENE (M. WALTER) SEBRING Press Secretary L. U. No. 40, L. B. E. W. With the inception of Voice Synchronization with the film for a while it was thought that the carbon arc was destined to take it place with the kerosene lamp and other antiques. Through the faithful efforts of various electrical chiefs and cameramen and untiring research work in studios such pictures as "Fox Movietone Follies," "Hearts in Dixie," "The Black Watch" by Fox, incidentally the jubilee scene of "Hearts in Dixie" was shot with the all carbon lamps; 42 sun arcs, 163 twin arcs, 20-80 amp rotaries and 12, 120 amp spots were used. Katrinka carnival shot used 30-24-in. sun arcs, 2-36-in. sun arcs, 15 or 20, 80 amp rotaries tor noises. E. Miller uses a toggle switch to cut out the motor. It is found that by cutting out the motor and feeding the carbons by hand a shot of 25 minutes' duration has been made. This might be continued indefinitely until you had burned up an entire trim. By using a choke coil, Creco scoops are being used with very excellent success for overhead lighting. The only bad feature being the fact that they must be shaken up oftener than for black and white photography. Paramount's "Thunderbolt," "The Woman Trap" and "The Virginian" were shot with 75% carbon arcs. We do not question the fact that Fig. 1 Relative position of earbons 100120 amps. Fig. 2 Relative position of carbons 80100 amps. 700 and 75 or 80 twin arcs. At no time during filming of the above pictures was any difficulty encountered with either ripples or gear noises. At the Paramount studio and R. K. O. through the efforts of Chief E. Miller and William Johnson in their experimenting with choke coils and toggle switches (to cut out the motors during the actual shooting of a scene) many useful things have been discovered. One of the questions uppermost in mind and used as an argument against arc lighting was mo for perfect motion photography one must have noonday sunlight. I should like to present for your consideration a chart of tests compiled by the Kress Engineering Company. A. Visibility of the naked eye in respect to the range of the spectrum. B. Cooper-Hewitt light emissions at various wave lengths. C. Curve shows energy distribution in the spectrum of a vacuum type lamp. D. Curve is a gas filled lamp operation at medium efficiency. E. Curve is of a modern high efficiency high wattage, gas filled lamp used in picture studios. F. Curve is of noon sunlight. G. Curve of north skylight. H. Curve is of a direct current, hard cored carbon arc lamp. The energy radiation from the positive crater at a color temperature of 4000 degrees C. I. Curve of energy distribution in relation to wave length of an high intensity arc. Agreeing that noon sunlight is perfect lighting properly reflected for photography, allow me to call your attention to curve "I." compared to curve "F" and if you must have an increase of red it is presumed you also desire a proportionate increase in the ultra violet. Again permit me to sight curve "E" to be compared to curve "H." In your observation of the above mentioned curves you have found that curve "I" is almost identical with the light you strive for in photography curve "F." Presuming that there is need for more red, after glancing at and comparing curve "E," a studio type incandescent lamp, with curve "H" the plain carbon (twin arc) "H" as you see gives you an increased percentage in the deep red and infra-red over curve "I." It is timely now to discuss and compare other features of the carbon arc and high intensity arc. The following is parts of and additions to an article in the Journal of Electrical Workers and Operators, 1927 and 1928. (Much credit and thanks is due to the National Carbon Company, Incorporated, Mr. Frank Benford, General Electric Engineer, in the twentyfourth number of the Society of Motion Picture Engineers; Mr. Ashcraft, of the Ashcroft Automatic Arc Company of Los Angeles; Mole Richardson and others, for their assistance in compiling the following tests). The High Intensity Arc The H. I. arc as used in studio lighting for photographic purposes, which, although radically different from the plain carbon, both have current passing between spaced electrodes, both have carbon as current carriers, but here the resemblance ends. In the carbon arc the carbon itself is the source of light. In the H. I. arc the carbon is secondary and acts as holder for the real source of light which is a small body of luminous gas. The current density in the carbon arc is 0.33 amps per sq. mm. of crater surface. The H. I. arc is approximately four (4) times greater or 1.2 amps per sq. mm. of crater surface. These differences emphasize the fact that the H. I. arc is radically different and requires its own mechanism and technique for its proper operation. This is not the first arc to use a salt-bearing electrode for the production of luminous gas, but it is the first one to so control these gases