modafoto said:
I'd really have to go over the text with you, and I'm not going to do that here. Suffice it to say that Kodak does not recommend variable film development, the cornerstone of the zs. Below is a quote from a Kodak technical publication.
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(From: Negative Making for Professional Photographers, Eastman Kodak, 1956.)
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THE COMMERCIAL NEGATIVE
Commercial photography encompasses almost all subjects not included under the portrait category previously discussed. Commercial negatives would be typified by normal negatives of product illustrations for advertising, display, or catalogue purposes, press shots, and many types of industrial photography.
Whereas in portraiture the photographer is primarily concerned with the reproduction of facial tones, in commercial photography he is interested equally in both highlights and shadows. In other words, the commercial photographer wants to reproduce all important portions of his subject with a minimum of tonal value distortion. In general, this means a slightly more dense negative in order to avoid the tonal distortion of shadows occurring in the toe portion of the characteristic curve. Many commercial photographers feel that these conditions are fulfilled if the average commercial negative receives about one stop more than the average portrait negative. Thus, the recommended technique for making a meter reading by either reflected light or incident light will produce negatives of the desired exposure level.
It has been customary for commercial negatives to be developed somewhat more than portrait negatives. However, there is no photographic reason why an average commercial negative should be developed to a higher gamma than a portrait negative.
As the portrait photographers have their adage, so also do the commercial photographers who say, "Expose for the shadows and develop for the highlights." Is this sound advice? First, let us examine this statement more closely. Admittedly, adequate exposure is desirable to record the important shadow tones. But to "develop for the highlights" implies that the time of development, or in other words, the gamma, should be varied in accordance with the brightness range of the scene. The idea is, of course, to prevent overdevelopment of highlights, so the scale of tones can be kept within that which photographic paper can render. Thus, should a negative of a short scale subject, such as an average building exterior taken on an overcast day, be developed to a higher gamma than a negative of the same scene taken in brilliant sunlight? The answer is generally no; both negatives should be developed alike. This is probably contrary to the practice which some professional photographers advocate. The reasoning for this answer follows: Although photographers speak of "important highlights" and "important shadows," for the most part it is actually the middle tones which are most important of all. Middle tones are, of course, the range of grays between highlights and shadows. Stated differently, middle tones of a negative or print are those densities which are not associated with toe or shoulder areas of the characteristic curve.
It has been found through a series of comprehensive tests that for the great majority of scenes the middle tones should be reproduced at a gradient of 1.0 on a tone reproduction curve. This curve is a plot of densities in the print versus the logarithms of the luminances or "brightnesses" of corresponding areas in the scene. A gradient of 1.0 means that if there is a 10 percent difference between two tones in the scene, then these same tones should be reproduced with a 10 percent difference in the print. Generally speaking, the middle tones should be reproduced with a gradient of 1.0, even if this can be done only at a sacrifice of gradient in the highlights and shadows.
In other words, the majority of people want the middle tones of the print to reproduce most original subjects as closely as possible, regardless of the lighting conditions that prevailed when the pictures were taken. To do this, all negatives should be developed to the same contrast or gamma for the same printing conditions and paper grade.
There are exceptions, of course. The "majority" of outdoor subjects in the tests mentioned previously included about 85 percent of picture-taking situations, such as portraits, landscapes, and architectural pictures taken in sunlight, in shade, and on overcast days. The remaining 15 percent of the scenes had, for the most part, large and very deep shadow areas which comprised an important part of the subject. It was these latter scenes which the majority of observers thought were best printed on a paper one grade softer than normal. Thus, even for subjects with a long scale of brightnesses, it was found satisfactory to develop the negative as though for a normal scene and to let the range of paper grades compensate for the unusual nature of the subject. In other words, the varying lighting conditions may demand the use of a paper grade other than No.2 for best results.
However, unusual subjects in which heavy shadows may either be present or actually predominate the scene are usually treated differently by professional photographers than they are by amateur photographers. The professional uses fill-in flash illumination, whereas the amateur does them without the benefit of supplementary illumination. The flash converts an "unusual" subject into a "normal" subject, and as such requires a normal negative development and will print on a normal grade of paper.
The degree of negative development for some subjects naturally depends on the photographer's "artistic intent." For example, suppose he were to photograph a sailboat at anchor during foggy weather. If it is thought that the fog lends a desirable pictorial effect to the scene, then it can be reproduced as the eye saw it with a normal negative development and a print on No.2 grade paper. If, on the other hand, a clear record picture of the boat was the photographer's object, and the exposure could be made only under a fog condition, then the negative should receive more than normal development to compensate for the contrast-reducing action of the fog particles. In this case, overdevelopment of the negative is desirable only if a print from a normally developed negative on No.4 paper grade would contain insufficient contrast. Accordingly, in view of the desirability of reproducing most scenes with a gradient of 1.0, and because of the wide control over contrast possible with various paper grades, it is highly advisable for the professional photographer to develop the great majority of his negatives to the same gamma.
A sensible approach to planning a standard photographic technique, including the degree of negative development, is to strive for a negative that will print best on a normal grade of paper. Although there is no necessity to confine oneself to anyone gamma if several paper grades are available, it is only logical to aim for No.2 paper. If this is done successfully, the printing problem is simplified by using one grade of paper for most negatives. At the same time, the photographer is protected on both sides of normal by papers with greater or less contrast capacity, should an underdeveloped or overdeveloped negative accidentally result.
Kodak processing recommendations for film are generally based on the use of diffusion-type enlargers, or on contact printing which results in prints of approximately the same contrast, everything else being equal. Obviously, these same processing recommendations should be modified by a reduction of 15 to 20 percent in gamma to suit condenser-type enlargers if prints of the same contrast are to be obtained.
Individual preferences are shown in a survey made of several individual newspapers and the principal news photo services. The results showed that films were developed to gammas ranging from 0.62 to 1.18, with an average of 0.85; that Kodak Developer DK-60a was the most popular of the developers, although a number of others were used; and that developing times ranged all the way from 4 ½ to 8 minutes. The photographers who preferred the lower range of gammas used condenser enlargers. The ones who developed films in the intermediate range used tungsten-source, diffusion enlargers, and those using the highest gammas employed mercury-vapor enlargers. In a similar manner, commercial and, to a lesser extent, portrait photographers also modify the basic development recommendations according to individual conditions.
(From: Negative Making for Professional Photographers, Eastman Kodak, 1956.)