A photographer is concerned with reproducing the tone values of his subject as different degrees of light and shade in the print, each tone in the original being represented by a corresponding tone in the finished print, and it is the purpose of this new series of articles, embodying many of the results obtained in the last few years by the Research Laboratory of the Eastman Kodak Company, to trace the various steps in the photographic process and to explain the factors which affect the photographic rendering obtained. The different articles will deal with the lighting of the subject, the translation of the tone of the subject in the making of the negative, including the effect of exposure and development, the scale of printing papers and the translation of the scale of the negative into the scale of the print, and, finally the accuracy of reproduction itself as shown by a direct comparison of the print with the original subject.

1. The Distribution Of Light And Shade In The Subject

When a representation of a natural object is made upon a flat surface, the form must be represented by differences of tone and differences of color. A painter, for instance, uses both differences of tone and color, while a black and white draughtsman confines himself to differences of tone, ignoring color. Except the special branch of color photography, photography deals only with the reproduction of objects in different gradations of light and shade, and in this series of articles we shall not only ignore the question of reproduction in color but we shall also ignore the fact that natural objects have different colors, and shall consider their reproduction as if everything consisted of shades of black and white and gray; that is to say, we shall deal with the different tone gradations of natural objects but shall ignore the fact that they have also differences of color.

The translation of differences of color into monochrome is best dealt with as a separate branch of photography - what is called "orthochromatic" photography or the photography of colored objects - and it is not proposed to take up this subject in the present series of articles.

If we had to make a photograph or a painting of a thing which was all of one tone, we should find it impossible to convey any impression of what tone is unless the photograph included other lighter or darker objects for comparison. A piece of black velvet placed in bright sunlight is brighter than a sheet of white paper in a dark room, so that it is impossible to speak of the brightness of paper or the blackness of velvet unless we have some standard of comparison by which to measure it. We cannot make a photograph of a sheet of plain white paper which will convey anything to the mind. We get a uniform deposit of gray on our plate, and when we print it the result depends on how much exposure we give in printing. If we give a short exposure, we get a print showing only white paper; if we give more, we get a uniform gray tint; and if we give more still, we get a completely black print, but none of them convey anything to our mind as representing any particular object.

Artura Iris Print, From Eastman Portrait Film Negative.

Artura Iris Print, From Eastman Portrait Film Negative.

Middle Atlantic States Convention Demonstration By W. B. Poynter, Cincinnati, Ohio.

Natural objects are visible not because they reflect light but because they reflect light in various amounts. If all objects were of equal brightness they would be invisible. An artist can suggest natural objects by representing them in two tones; that is to say, by a line drawing. In nature, however, there are no outlines and all of its wonderful scenes are shown to us through the medium of an infinite scale of tones, an object only standing out from its background when it differs in tone or color from that of the objects beyond. In order to get a faithful representation of nature, we must get a reproduction, as accurate as possible, of the whole scale of tones occurring in the scene which we are photographing.

In natural objects these different tone gradations can be produced by differences in the reflecting power. Black ink reflects less light than white paper and so with the same light falling on each there is a difference in brightness by which the ink marks are distinguished from the paper. Even if an object has uniform reflecting power, however, different tone gradations can be produced by differences in the illumination of the object. If we light a plaster cast, for instance, from one side, part of the cast will be in shadow and part in full light, and so although the whole cast has the same reflecting power, yet there will be differences of brightness, the part in shadow being less bright than that on which the light falls.

The brightness of a natural object depends therefore upon the illumination falling upon it and also on its reflecting power. If its reflecting power is 20%, its brightness will be 20% of whatever illumination may fall upon it.