الحبيبات .. كتاب أسس التصوير الضوئي

GRAINS

What is meant is metallic silver granules deposited in gelatin, resulting from the reduction of photosensitive silver salt. These granules are not seen with the naked eye, and the eye does not feel them in the small picture. Rather, they appear in the case of high magnification (Fig. 68), which leads to a lack of artistic value in the picture.

Factors affecting granules:

(1) The effect of the speed of sensitivity on the size of the grains: The greater the enthusiasm of the film or the sensitive board, the larger the size of the grains, and accordingly, in exchange for what we gain from the speed of sensitivity, we lose a measure of artistic quality (Fig. 69).

(2) The effect of the duration of the display process on the size of the particles:
Increasing or decreasing the time required for the process of revealing has a significant effect on the size of the grains. If we examine a sensitive layer with a microscope without the silver salt being reduced in it, we see the silver salt in the form of small crystals. When the process of revealing begins, the process of reducing these crystals begins at a point where the reduction becomes possible until It includes the whole crystal, and it turns into particles of metallic silver. The united particles formed a large one, and the latter merged into other large ones, and so on (Fig. 70).

If we look at another fact, which is that by increasing the exposure time, the penetration of the developer solution into the sensitive gelatin layer increases, so it performs the same process in the lower layers of it (Fig. In some cases, we find a significant increase in the general density of the negative image, in addition to the enlargement of the grains that appear clearly in the image when enlarged, but also lead to the unsharpness of the image. Reduction, and this results in an increase in the general density in the negative image, and vice versa, as we mentioned, meaning that if the sensitive layer does not receive sufficient time to complete the reduction, we find that the grains are small, and the image in this case is deficient in contrast, and the materials included in the composition of the appearing solution also have a significant impact on the size of the image. granules Therefore, the research is always conducted to reach the surfactants that reduce the size of the granules as much as possible, Figure (72).

Fine Grain Developers

Ultra Fine Grain Developers

Super Fine Grain Developers

The revealing solutions that lead to a fine granule are in fact superficial in the sensitive layer, as their effect does not penetrate into the lower layers of the sensitive layer unless the time of revealing exceeds the specified time, and then it loses some of its advantage in giving us a fine grain.

(3) The effect of increasing the exposure to light during imaging on the grains:
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Size If we put a thin metal plate on a sensitive film and pierce this plate in the middle of it, then pass a beam of light through this hole to the sensitive layer as shown

In (Fig. 73), the viewer is the following:

There is no doubt that the passage of the light beam to the sensitive layer affects the point opposite the hole, but is the effect of the light beam limited to this point only, or does it extend beyond it to what is underneath it?

To answer that, we must know that this layer of gelatin is an opaque layer (and what is meant by opacity is that it is not opaque). It can be Turbid Medium or a turbid liquid, and the liquid here is like gelatin. As for the turbidity, it is the silver bromide granules scattered in the gelatin. One of the characteristics of a cloudy or opaque medium is that it facilitates the diffusion of light through it, unlike a transparent medium, where light passes through it without much diffusion, and therefore the passage of the light ray to the sensitive surface of gelatin affects it.