تباين الإضاءة ونسبة الانعكاسات من أجزاء الموضوع الجارى تصويره .

The contrast of lighting and the percentage of reflections from parts of the subject being photographed and the effect of these two factors when! Photography .

We will first begin by explaining these conventions in the following points: (a) The reflection ratio of the subject being photographed, i.e. the brightness range:

Assuming that the subject being photographed is a brown man wearing a white shawl and a black robe (Fig. 49), and supposing that we have measured the amount of rays reflected from the three parts of the photographed subject, it is possible that we will find it as follows:

Rays reflected from the white shawl = 80% of the rays falling on it

Rays reflected from the bronze face = 20 20% of the rays falling on it

Rays reflected from the black robe = 10% of the rays falling on it.

Thus, we conclude that the ratio of . The rays reflected from the white shawl over the rays reflected from the face = 4: 1

Also the ratio. The rays reflected from the white shawl over the rays reflected from the black cloak = 8: 1

In the first case, it is said that the ratio of reflections = 1:4
In the second case, it is said that the ratio of reflections = 1:8

(B) Lighting Ratio on the subject being photographed

In the previous example, we assumed that the light falling on the object being photographed was completely equal and distributed justly to all its parts, but what would happen if we used two sources of focused light (Spot Lights), one of which emits an amount of light equal to twice what the second emits, and so that both are far from each other. Both sides of the photographed subject at exactly the same distance?

There is no doubt that if the ratio of reflections from the subject being photographed is Reflectence Ratio = 1: 1, then the amount of light reflected from the side illuminated by the strong source will be double that reflected from the side illuminated by the weaker source.

The contrast is in Lighting Contrast in this case. 1:Y= However, the ratio of the reflections was not 1:1, but rather it was 4:1, as we mentioned in the first case in item (a), so if we make the stronger focused light source illuminate the side that by nature reflects a larger amount of rays, the Subject Contrast is equal to the product multiplied by the first factor x The second factor. From, here is a variation of the topic
We summarize that as follows:

Reflections ratio = 4:1
Contrast in lighting. = 2 : 1
Subject contrast = 4:1 x 2:1 = 8:1

And it is possible that the subject contrast range would be close if we reversed the position of the two light sources so that the stronger source illuminates the side of the body from which the lesser amount of light is reflected, and the weaker source illuminates the side that reflects the greater amount of it.
= 4 : 1 x 1 : 2 = 4 : 2 = 2 : 1
It is also possible that the brightness of the subject may also be affected by the distance or proximity of the light source to the object being photographed, and then the law of squareness, previously mentioned on p. 25 in this book, is applied.

Fundamentals of calculating subject contrast If a strong artificial light source is used, it illuminates both shadows and light regions equally.

Supposing that we were in the process of photographing an exterior side of a house in the daylight, and the sun was shining, and by measuring the rays falling on the intense parts of the illumination, we found them to be 35,000 lux, while those falling on the shadow areas were 1,000 lux. This means that the contrast ratio = 35:1

Now it is assumed that we have seen an approximation of the previous ratio, that we use an auxiliary light source to illuminate the shadow areas. Fill in light faces both the highly illuminated areas and the shadow areas and emits 10,000 lux. Although the function of this mainly is to illuminate the shadows areas only, the reality is that it will shed light on the very bright areas, the source is the hight light as well.

The relationship between subject contrast and color film emulsion latitude (1)
It will not harm in (black and white) photography that the contrast range of the subject reaches 1:10 or more than that, because these films are characterized by a wide latitude, so in the same case they are able to show details of both shadows and high-light areas despite the increase in “contrast”. Subject.” As for color films, they are not characterized at all by this degree of tolerance, rather the contrast of the subject should not exceed 3:1 on the worst hypothesis, in order for colors to be transmitted faithfully without fear of decreasing their saturation or fear of losing the details of shadow areas or the details of intense areas. Illumination (also known as areas of high light), and it is always better that the contrast of the subject does not exceed 3: 1. As we concluded from the foregoing that color films are not characterized by a wide tolerance, therefore we find that it is necessary to reduce the contrast of the subject to the maximum extent The contrast in a color image depends to a large extent on the contrast of the colors themselves and not on the contrast of lighting or the percentage of reflections It is not permissible to photograph with colored film against a source of light, the Silhouette, unless the photographer intends to do so for a purpose in himself, just as it is not permissible to photograph color film in the light of the bright sun at noon. In the summer, for example, when the intensity of illumination increases greatly in the areas of high light and is relatively transmitted in the areas of shadows.

What is the amount of brightness contrast resulting from the difference in the reflectence ratio in the usual subjects?

The Reflectence Ratio, or in other words, the degrees of variation in the brightness of subjects vary greatly according to the nature of these subjects and the lighting conditions. In the following table (1) are examples to give us an idea of ​​the extent of the variation in the brightness of some of the usual topics.