American cinematographer (Jan-Dec 1938)

January, 1938 • American Cinematographer 41 HERE^S THE ANSWER Lighting in ''Garden of Allah" IN your issue of January, 1937, there is an article on "How to Shoot Kodachrome Light Effects," by Harold Rosson, A.S.C. In one paragraph it is stated one of the most effective scenes in "The Garden of Allah" was one where Charles Boyer admits to his wife he is a renegade monk. In this scene his face is strongly illuminated, against a sky lighted by a setting sun. Will you please tell me if it was the sun or artificial lighting that caused the illuminaticn on the face ? I. L. M., Taft, Calif. We discussed this same matter with Mr. Rosson at the time the article to which you refer was written. The scene in question was done on the studio stage, by artificial light. The background was a painted drop, painted very carefully to match actual Technicolor scenes made on the desert location near Yuma, Arizona. The lighting was effected by the arc lighting equipment specially developed by Mole-Richardson for Technicolor lighting. These lamps give an absolutely colorless white light of high intensity, absolutely identical with the spectral distribution of normal daylight, which makes it possible to shoot color interiors and exteriors without any change in cameras, film or processing. In sub-standard filming with Kodachrome, this is of course impractical, so the Type A Kodachrome film was devised. This has a specially modified color sensitivity to offset the light of Photoflood lamps, which, to the color film, is much redder than natural daylight. Effects similar to the one you mention can be made indoors with Photoflood lighting and Type A Kodachrome film. Meters and Speeds I am planning to purchase an exposure meter soon, but before doing so I would like to have the following questions answered: 1. What is the definition of "film speed ?" 2. What is the definition of correct exposure ? 3. How can I determine the film speed of any film at home ? 4. If the speed of a film is 20 and the film is hypersensitized to double its speed, will the film speed then be 40? 5. What is the difference between the Weston and Scheiner ratings? 6. How can I change from Weston to Scheiner ratings and vice versa? 7. What are the different types of exposure meters and their advantages? 8. I understand there is a campaign under way to request the film manuiacturers to place the film speed on the box in which the film is sold. I would like to say I am in favor of such a plan. C. P., Long Island City. Without going into unnecessarily tschnical detail, "film speed" can be simply defined as a quantative measure of that film's overall sensitivity to light. There are many other factors to be considered, however, in addition to overrll sensitivity. The film's sensitivity to light of various colors is equally important in reaching a usable final figure, and so, too, is the color of the light used to make an exposure. That, for example, is why the Weston engineers establish one speed rating for daylight, which is a uniform mixture of light rays of all colors, and another for incandescent (Mazda) light, which is deficient in blue and ultra-violet, and strong in yellow, orange and red. The processing or developing is yet another variable which affects film speed. This can be proved by making a correct, metered exposure on a given film, then cutting the film into three pieces, each of which is developed with a different developer. Film Sensitivity and Meter If, for instance, Eastman's D-72 formula is considered the normal agent for developing that film, the section developed in it would give a normal expofure result; a section developed in a fine-grain solution like most of the paraphenylene-diamine formulae would give an apparently underexposed result; while a section developed in a third solution might well give an overexposed result. Another factor, perhaps the most vitally important in the practical work of the average camerist, is the relation of the film's sensitivity to that of the meter. The familiar Weston speeds, for example, are calculated with direct reference to the color sensitivity and the overall sensitivity of the Weston photronic cell used in that meter. If it were possible to replace the Weston cell with a different type of photoelectric eye, any given Weston film speed rating might very probably be very considerably inaccurate due simply to the meter's changed color-sensitivity. Correct Exposure Correct exposure may most easily be defined as that exposure which places the extremes of highlight and shadow within the characteristic exposure limits of the film; in other words, which places the highlights at such an exposure point that they are not "blocked" or overexposed, and the extreme shadows exposed so they will retain ample detail rather than being merely areas of no exposure. ■The extent to which exposure can be varied up and down while still keeping the exposure extremes within these limits is known as latitude. In the average modern film this may allow very considerable leeway; often an exposure range between shadow and highlight extremes of 1:128 is possible, while the brightness range of these extremes in average pictures is seldom as great. As has been mentioned, correct exposure is relative, depending to a great extent upon the developing or processing of the film. Determining Film Speeds There are many scientific methods of determining film speeds, but the practical camera user is of course most interested in obtaining a speed-value workably related to the meter he uses. For this, the simple method of trial and error is probably the most practical. Make an exposure using a value you think should be approximately correct; then make several more exposures under identical conditions, using values higher and lower than this. Give the exposures identical processing. The results will show you what speed is right. In using sub-standard reversal cine film it is a good idea to ask the laboratory not to make any attempt to equalize your exposures in their processing. However, speaking generally, there is very little real need to make such experiments yourself, since the Weston company each year — sometimes oftener — issues a folder listing the Weston speeds of all available materials. The current one lists more than 187 different types of films and plates for cine miniature camera and still photography, including 37 types of reversal and negative-positive 16mm. and 8mm. cine film and 8 types of natural color processes. Speeds and Hypersensitizing Granting that the method of hypersensitization you use does not alter the film's color balance, your assumption would hold true. If, as is generally the case, hypersensitization does upset this color sensitivity balance, the hypersensitized film speed would not necessarily be the numerical double of the original value. Hypersensitizing almost invariably increases red sensitivity more than that to any other color, so if you hypersensitized an emulsion originally sensitive only to blue, you would merely make it more nearly panchromatic, and the overall speed increase would be very small. If, on the other hand, you first panchromatized the film, and then hyper