Object contrast and lighting contrast.
We do not intend to scare amateurs or unnecessarily complicate the subject of color photography. However, if someone thought so, he can skip everything without much loss and possibly come back to it later. However, a serious amateur or professional will not want to leave out the topics presented below.
We mentioned, that all reversible films have a small useful exposure range, consequently they cannot reproduce a wide scale of brightness. Experience shows always, that many reversible film images are worthless or at least unsatisfactory, because they use incorrect exposure or incorrect lighting. Therefore, we want to discuss this issue more comprehensively, although in later chapters we will refer to it in various places.
If we consider a gray wedge made by applying colored layers, for example, produced in various types by the company O RWO from Wolfen, we will get the brightest on it, reproducible baryta white and a range of degrees of gray to the deepest black. Reflected radiation, if we express them in the commonly used logarithmic values of optical densities, covers the range from D = 0,15 do ok. 1,5 or if we use velvet as the darkest level - up to approx. 1,8. Expressed in ordinal numbers, the brightness range includes values from 1 : 30 do 1 : 60. As we reported on p. 14, the photographic properties of colored reversible films allow for a ratio of approx. 1 :25. It means, that we can recreate this kind of gray plate, which is a scale of brightness, in a photograph, if we expose them correctly. We also get the same results, if instead of scale we take pictures of objects with the same exposure.
In the case of illuminating the gray scale with half or double the amount of light, the scale reproduced on reversible films will be shortened. With less than half the light, the darkest degree of the scale will practically not differ much from the next gray degree. With double illumination, the same phenomenon will occur for the brightest degree of the gray board.
However, such a variety of lighting occurs on a regular basis, if we are shooting in a large room. Only when it is cloudy will all objects be illuminated evenly from all sides. The sun's rays, on the other hand, will illuminate only some objects, the others in the shadows will be more or less illuminated by reflected and diffused light. We are lucky on earth anyway; if we were taking pictures on the moon, what may happen in a few years during a business trip or on vacation, we would not get any shadows in the picture. Not only in the photo, but also in the original, because there is no atmosphere containing vapors and gases, so no clear sky. The latter is black as night, and so are the shadows; they will not be illuminated by light reflected from nearby surfaces. And how bright are the shadows on the ground compared to the direct illumination of the sun's rays? It depends on the brightness of the sky and on that, how much light can fall from it. In the south, with a dark blue sky, the contrast is very high. In some cases, even in the light of the midday sun, it is almost impossible to take a picture, because shadows predominate, which come out pitch black. In the north, the sky is also brighter on clear days, i.e. more hazy; during normal cloud cover, the contrast is finally Approx. 1 :2.
To wrong tonal values, i.e. not reproduced in accordance with the original, we are used to black and white photography and generally do not require perfect consistency in this area. Some emphasis or oversaturation of tonal values feels rather painterly. In color photography, however, these relations are completely different. Maybe, that by being closer to nature we also expect fidelity in reproducing brightness. In addition, the colors of the motifs in poorly lit places are not very nice, gray shades. Thanks to the eye's ability to adapt, when we get used to the conditions of the shaded place, we see red almost in the same shade, as we see it in the light. Color films cannot do this.