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e^OA£<i GAMMJ& 11//?
"NO!" replies a Kodak technician, reporting their research
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
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 Facts 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 efficientlv." — The Editors.