The Cine Technician (1943 - 1945)

.March— April, 1943 T HE CINE-TECHNICIAN 43 ties and signal to noise relationships of all the finegrain emulsions. In order to incorporate the activities of the various experimenters a Committee was formed in 1940 on which sat representatives of ERPI, the Western Electric licensees, and the major film suppliers. Interest in fine-grain was stimulated by the possibility of reducing background noise and the intermodulation of sound and signal. While much progress has been made in the use of noise reduction circuits to enhance the signal to noise ratio on standard stocks, a reduction in film noise itself was considered essential to accommodate fully the volume range available in modern sound recording systems. Further, while the use of noise reduction devices has brought about an increase in signal to noise ratio on standard stocks, the quality of the sound tended to be impaired when noise in excess of IOdb was applied, for beyond this point the breathing of background noise tended to offset the quietness of silent passages. It was long felt that less grain in the negative would reduce background noise, and enhance the signal to noise ratio. Until 1937 no suitable film was available. Eastman's 1360, which, when exposed to white light, was a fair substitute for ultra violet exposure standard stock, was introduced. Dupont also brought in their 216 for the same purpose. Both were intended for variable area work, and with their high contrasts were not ideal for variable density, low gamma development. In 1939 Dupont introduced 222 for variable density and re-recording print use. One of the problems confronting the use of any type of fine-grain emulsion for recording, is the relatively slow speed of the emulsions. Standard sound emulsions call for the maximum exposure from a tungsten lamp in recording. Fine-grain being offered at a speed of about one-fifth that of standard film, either a new light source or drastic improvement in old light sources and optical systems was imperative. Fortunately, the development of the high pressure mercury arc offered a possible solution. The problem of sufficient exposure involved the print as well as the negative. The high pressure mercury arc has, since then, been greatly improved, and is more suitable to-day than it was at the outset. Forced air cooling of the arc makes possible a great increase in illumination by operation at a higher wattage than was designed. A great range of exposure is now possible. Recent improvements at Paramount and Metro's Labs show that with improved recording optics, combined with ultra-violet printing, it is now feasible to substitute completely the use of a standard tungsten filament source for exposure of low gamma fine grain negatives. Experiments, backed up by studio recordings, reveal a marked improvement in signal to noise ratio of at least IOdb on a fine-grain print made from a fine-grain negative. The actual improvement to the ear seems more of the order of 18 to 20 db, because of the almost complete freedom from breathing in the background noise. Laboratory research shows that with a fine-grain stock, signal to noise ratio of 45db may be obtained. These sound improvements are not, however, the end of the story. Improved image definition is achieved, dueto the reduced flare in the emulsion. There is a great increase in the higher frequencies. A very low distortion is indicated when measured by intermodulation or harmonic analysis on fine-grain prints made from a fine-grain negative, especially if ultra violet light is used in exposing the film stock. This is responsible for the pleasing quality of fine grain recording. Tests at a number of Hollywood studios in 1939, on experimental and existent fine-grain emulsions, led to the development of fine-grain stock. Since tests on this particular slock suggested that it fulfilled all the requirements laid out by the experimental committees, and in a special syllabus drawn up by Paramount, further experiments were launched, to work out all phases of operation necessary for its application to release printing. The slowness of the emulsion and the greater susceptibility to abrasion, and to picking up dirt, are problems involved. The greatest care was necessary to keep the negative clean since reduced background noise made noise printed through dirt, even more obvious. There are various technical aspects of fine-grain printing, which are worthy of record. Printing. The increased light calfed for because of the slowness of fine-grain film was greatly assisted by Paramount adopting an optical system for printing with tungsten lamps. The necessary control to obtain Hie desired mean exposure was obtained by adjusting the ground glass and filters. While Model E release printers require a still higher intensity light source, it is now practicable to equip them with improved printing (Continued on page 45J THE CROWN THEATRE PROVIDES STUDIO PROJECTION SERVICE AT ANY TIME TO SUIT YOUR CONVENIENCE Two Double-Heads. Full Range Sound. Mixing Panels for Tracks. Seating for 1C0 Persons. 86 WARDOUR STREET, LONDON, W. 1 Telephone Gerrard 5223