Movie Makers (Jan-Dec 1949)

gkwM fC&daxhxme ie "YES!" claims a reader, citing his experience WILLIAM H. KROUSE, ACL W|\SI.O\\ RANDALL'S article, Tourist Tips on Mexico (October, 1948), was both interesting and enlightening. However, near the end of his discussion he says, "Remember, though, no color exposure smaller than / 1 1, no matter what your meter says. No doubt he is (as an man) other movie makers) a blind follower of the following statement which appears in a manual (page 17. Kodachrome and Kodacoloi Films, tth eel. I'M!! Ed. I published b) the Eastman Kodak Company: . Meter readings on outdoor subjects in lull sunlight that indicate lens openings smaller than j 1 1 for an amateur motion picture camera, or exposures of less than 1/50 of a second at j/H with a 35mm. or Bantam still camera, should be disregarded, because underexposure is almost certain to result." STATEMENT QUESTIONED I. too, followed (hot advice at one time (much to my sorrow) and the result was a lot of overexposed, washedout looking film. Finally, after losing a great many feet of film due to overexposure by following the above statemenl. I decided there must be other factors which determine the Bize of the diaphragm opening. Later, I had the opportunity of talking with one of Eastman's top color n, ami [challenged their statement as being misleading. lie was surprised that the statement appeared in that form in their manual and replied that that was not what was meant, lie said, further, that he would discuss the statement with the company and have it changed; but I notice in the Inst edition, tin cited above, that no changes have been made. FACTORS INVOLVED \\ hen using black and white film no such advice is given. There, it the meter reading calls for a stop of / 16 or / 22. it is used and ihe results certainly justify such use. However, in the ease of color film, there are several factors to be considered that limit the size of the diaphragm opening: 1. Co],,] film is much thicker than black and white film. 'This is due to its three layers ol emulsion, each separated b) a layer of gelatin, whereas lire black and white film has but one layer of emulsion. 2. Regardless of advances in optic-, there are still many movie lenses in use which arc not color corrected or which are of such inferior qualit) I due to cheapness of production) that they cannot be fully color corrected. Thus, each color does not focus at the same plane. This is the reason why box cameras often produce very sharp black and while negatives but yield unsatisfactory results when color film is used. . 3 The diaphragm of a movie lens, especially that of Ihe 1 ' inch on 8mm. cameras, approaches a pin hole in size "hen stopped down smaller than f/ll. ft thus utilizes practically none of the color correction ability available „;il, the use of a larger diaphragm opening. EFFECT OF SMALL OPENINGS There is no doubt that, in most instances, if the meter reading calls for stops of f/16 or //22 or smaller, the results will be unsharp, not underexposed. As I have said before, this phenomenon is much more noticeable on 8mm. than on 16mm. color film. Therefore, the reason for not stopping down below //ll is not one of underexposure, but one of degraded definition. OTHER CONTROLS What, then, should be done in order to secure the correct exposure and yet not stop down smaller than //ll? There are several possibilities. A polaroid filter can be used, reducing the effective exposure by approximately two full stops. If the scene contains little or no movement, a shutter speed of 32 frames per second (equal to one stop less exposure) or 64 frames (two stops less exposure) can be used. For those having a Cine-Kodak Special, the variable shutter adjustment can be used to cut down the amount of light reaching the film without decreasing the aperture. In other words, one-half open is equal to one stop smaller and one-quarter open equal to two stops smaller. I have exposed color film over most of the United States, in Mexico, Canada and Alaska, and I have frequently had Weston meter readings of 800 foot candles or more — especially at the Valley of 10,000 Smokes in Alaska and at White Sands National Monument in New Mexico. Had I (and I have) used an opening no smaller than //ll at 16 frames per second, the film would have been perfectly clear, so overexposed that not even a trace of an image could be seen. It is my hope that those who read these comments will be saved the loss of never-to-be-replaced scenes so often caused by the misinformation prevalent in this //ll rule. In other words, if the meter calls for an opening smaller than //ll, and if you have no way (other than reduced diaphragm) to cut down on the amount of effective light — don't waste your film! If you do use a smaller // stop, you can be fairly sure of unsharp results. But at least you will not have underexposed film. exp&ded adioixe ll//? 'NO!'" replies a Kodak techni IN THE last year or so we have had a few people claim the same experience as Mr. Krouse. During the same period we have had a much greater number of people complain because the minimum exposure suggestion was not given more prominence in our literature. EXPERIENCE CONFIRMS The latter are all people who have permitted themselves to be led into underexposure by high meter readings obtained from light-colored subjects in bright sunlight. The experience of the great majority of our customers, and of our own photographers, confirms the fact that subjects are very rarely so light in color and so brilliantly illuminated as to require less than //ll in the exposure of Kodachrome movies. In my own movie making, with cameras checked for speed and accuracy, I have photographed many lightcolored subjects in various parts of the country. Old Faithful in bright sunlight was right at //ll, too dark at //16. Other geysers, hot springs, and the paint pots at Yellowstone were also right at //ll. The same has been true of pictures taken on the white sands at Miami Beach and of white boats with white sails on the ocean. SUNLIGHT THE SAME Light measurements made all over the world show that the intensity of sunlight at noon on a clear day is substantially the same throughout the temperate and torrid zones. It varies only between 8500 and 9000 foot candles. This is why our general exposure recommendations do apply so well over most of the world. CAMERAS SHOULD BE CHECKED We have been able to check a few of the reports of exposures less than //ll and have found that the cameras being used were not functioning normally. If the driving spring of a movie camera is worn out, it may run at only 10 to 12 frames per second. If this condition is combined with diaphragm scales that are not perfectly calibrated, there can easily be a difference of a full stop in exposures required. It might be worthwhile for Mr. Krouse to have the speed and diaphragm scale of his camera checked. Despite this defense of our general recommendations, please don't think that we wish to change the picturetaking habits of anyone who is getting good results with his own equipment. Movie making is by no means an exact science. There are variations in equipment, in the picture-taking habits of photographers, and in their judgment of what constitutes a good picture. The successful photographer is one who has learned to make pictures he cian, reporting their research HARRIS B. TUTTLE, ACL likes with his own equipment regardless of how far he has to depart from the recommendations of the manufacturer. FILM NOT THICKER Incidentally, it is not true that Kodachrome film is thicker than black-and-white Cine-Kodak films. The Kodachrome emulsion is slightly thicker than a black-and-white emulsion but it is coated on a thinner base. The result is that all our Cine-Kodak films are about equal in total thickness and vary only from 5% to 6 thousandths. The latter part of Mr. Krouse's letter seems to confuse film resolving power with exposure and lens performance. I am not sure what he has in mind. In connection with Mr. Krouse's assertion that stopping down lenses of short focal length beyond //ll tends to degrade the definition of their resultant images. Photographic Fads and Formulas, an outstanding reference work by E. J. Wall and Franklin I. Jordan, makes the following general summation: "Every lens has one approximate aperture at which it theoretically gives the sharpest definition The difference between the sharpness at this and neighboring apertures on a good lens is ... so slight that it can be determined only upon an optical bench in a laboratory. At abnormally small apertures, diffraction (of light rays) causes lack of definition. This is governed by the actual, rather than the relative, size of the aperture; so that the minimum usable aperture ratio varies with the focal length of the lens. The manufacturer usually takes care of this problem by supplying the lens with no smaller stop than can be used efficiently." — The F.dilors.