Color shades.
During the process of chemical treatment of reversible materials, we cannot influence the quality of the image colors. The latter is dependent on abnormal deviations of color shades and more so, than we can imagine. For example, the color of the glass has a completely noticeable effect, from which photographic lenses are made. Changing lenses to different ones, at other focal lengths, we can see the picture change, np. from bluish to yellowish, and this change of colors we can not explain at first. The blue-violet tint of enhanced lenses with anti-reflection layers has no direct effect on this, and the difference in the color of the lenses can also be distinguished with the naked eye. In the past, no attention was paid to the change in the color of the light in different seasons. in summer, at noon, sunlight is bluer than in the afternoon or evening. Also in late autumn or winter the sun shines* noticeably more yellow. The problem of changing the shades of colors caused by photosensitive materials to a more yellowish or more bluish will be dealt with in detail later in connection with the reasons, that cause them.
The occurrence of color shades can be caused by many reasons and have different saturation. For example, reversible materials that have been stored in improper conditions or have expired show a marked tendency to color haze in various shades. However, we can get photos with intense colors on them, for example flowers, completely correct, while other images are closer to gray or have lighter shades, larger areas will show quite clear distortions of the correct color shades. First of all, it should be emphasized, that slight color haze becomes noticeable only when the viewed objects are illuminated with daylight. But during the projection, for which the colored material is primarily intended, the changes are almost invisible, because the eye then reacts completely differently than in a bright environment and cannot compare the transparency with other natural colors.
The human eye is incapable of isolating itself from the dominant colors of the light that enters it, and, for example, sees a sheet of paper as white both in daylight, as well as incandescent lighting. Only then, when both types of light are observed simultaneously, we can see big differences between them. Therefore, when taking pictures on reversible material, if the lighting conditions are not precisely defined, there is a danger of using the wrong filter. However, the average amateur should not be afraid of getting colors with shades slightly more than normal. A more serious photographer, if, for example, he wants to use his photos as illustrations for a lecture or a paper, wishing to obtain the same shades of colors as possible, can run into serious trouble in a series of photos. A light color temperature meter can be of great help in this case.
At the beginning we do not want to delve too much into the subject of color shades due to the small scope of information and we will come back to this, after having seen further data needed to better understand it.