Page:Popular Science Monthly Volume 6.djvu/730

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IN the previous chapters we have become acquainted with the development and the theory and practice of photography, and have mentioned cursorily various of its applications. It is our present purpose to give special attention to one point which is of great import in judging of the value of a photograph.

Most persons have a fancy that the application of photography is always uniform, whatever may be the object to be taken, and, therefore, that a photographer who can take a portrait must be able to take equally well a machine, a landscape, or an oil-painting. This results from the erroneous notion that the picture makes itself when the photographer opens and shuts the lid. But our readers know already that the picture does not make itself, but that it must be first developed, brought out, fixed, and copied. In all these operations there is no precise measure or rule how long the photographer should expose to the light, develop, fortify, copy, and tone the picture. This depends on his option and judgment; and he is able at pleasure to bring out the picture more or less in detail, according to the time of exposure. Again, he can make it more or less brilliant, according to the degree of strengthening; he can make it more or less dark, according to the mode of imprinting; more or less blue, according as he tones it down. But what is it that directs his judgment to determine if the picture is correct or not? It is Nature, and Nature alone! He must know Nature, and compare it with his picture. Nor is this easy. Nature appears positive to him, but in the picture she appears first negative; and, if he compares the two, he must be able in his mind to convert the picture, that is, to change it and represent it as a positive, which it is afterward to become. More comparing and study is required to do this than is generally supposed.

If two printed proofs are presented to a man who is ignorant of the art of printing, one of the sheets in question being well and the other ill printed, if the defects be not too glaring, this person will not be able to detect any difference between the proofs. Far otherwise is it with the practised eye of the printer, who immediately detects that in one proof the type is too thick, or thin, or leaded, or that the letters are faint, or blotched, or uneven. In like manner, a practised eye is needed to judge a photograph—an eye not only able to detect the finest details of the picture, but also the peculiarities of the original. The unprofessional man often uses the expression, “I have no eye for

  1. Abridged from the “Chemistry of Light and Photography,” No. XIV. of the “International Scientific Series.”