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What is the practical value of knowing the color temperature of the rays:

Now we wonder about the practical value and benefit that the photographer has gained from his knowledge of the color temperature unit (caffeine) and other units associated with it (such as mercury and deca, which are mentioned, and we will talk about them).

This is what we explain as follows:
As for those prepared for filming with colored films that have artificial light sources (tungsten lamps, for example), the sensitivity of blue rays is greater than its sensitivity to red rays (1), because these light sources emit a lot of red and yellow rays and little blue in their light energy. For the aforementioned reason, the color film maker aims to compensate for this decrease in the amount of blue rays emitted by the source, by increasing the sensitivity of one of the sensitive layers of this film to these rays. Perhaps in that introduction what explains the importance of using a colored film suitable for the color temperature of the radiation source

Daylight white rays consist of approximately equal proportions of each of the red, green and blue rays. Therefore, daylight films are made of color films intended for photography in such a way that they are equally affected by each of the colors of the previous rays.

It is usual for the factory that produces color film to indicate the color temperature of the light source for which the film was prepared. Color films are often balanced for color temperatures that we mention below: 5600 Kelvin for daylight photography.

Daylight films

In artificial light films

3400

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Clear flash bulbs

But does this mean that it is impossible to use colored film for filming in a light that differs in its characteristics from the color of the light for which the film was prepared? For example, is it not used for a film that I prepared to work in the daylight, to photograph in the light of a two-tone lamp, for example? Or vice versa ?

(1) We will come back in the second part to explaining the structure of the sensitive layers in the colored films in an adequate way.

In response, we say that this is also permissible, but on the condition that we change the proportions of the components of the rays that enter the film by means of special optical filters that may be placed in front of the light source or in front of the lens, and absorb some of the rays emitted by the light source and allow the rest to penetrate into the film, so that The characteristics and proportions of the interspersed rays are consistent with the characteristics of the rays for which the film was prepared.

Film intended for photography in daylight

Film prepared for imaging in tungsten light

blue green

blue

red

The colors of the rays of the light source

blue

Color sensitivity of film layers

blue

The final balance (Fig. 20)

The principles that are taken into account in the film industry to maintain a balance between the sensitivity of the color film layers to colors and the colors of the light source rays:

In daylight, the percentage of blue rays is higher than it is in tungsten light. Therefore, in the manufacture of colored films, it is taken into account that the sensitivity of the sensitive layer to blue rays in films prepared for imaging in tungsten light is greater than it is in films prepared for daylight. Therefore, if the photographer assumed and made a mistake and used the film prepared for the light of the nungsten for filming in the daylight, then it is certain that the image will be covered with a severe tinge of blue. We conclude from the figure that if the percentage of a particular color increases in the rays emitted by the light source, then the sensitivity of the colored film to it must decrease, and vice versa. In order to facilitate

Maintaining the final balance in colors. Color Balance.

It must be mentioned about these filters that they do not raise or lower the color temperature to the same extent in both daylight and tungsten light. The color temperature of daylight is several thousand degrees Kelvin (1).

It is very important to realize that raising the color temperature of a light source from 3,000 K to 3,100 K may have a tangible effect in color photography, but it may not be significant to raise the color temperature of a light source from 6,500 K to 6,600 K. (i.e. an increase of 100 kelvins in each of the two previous cases). Filters that are used to adjust the color temperature of the rays are known as “light balancing filters,” or sometimes by another name, “color temperature conversion” filters.

filters

. This is unless there is any change in the color temperature. In order for the light source to match the color temperature for which the color film was prepared, the positive image must appear to be covered with color casts.

The film prepared for shooting in the light of day is covered with a smear. It is reddish cast if it was used for filming in the light of a tungsten lamp, but if the film was prepared for filming in the light of a tungsten lamp and was mistakenly used for filming in daylight, it is certain that the image is covered with a tinge of bluish. For this reason, we may sometimes deliberately use colored film prepared for imaging in tungsten light for imaging in daylight, so that this blue tint appears, and gives the image a nocturnal effect (2). Day for Night effect

(1) American Cinematographer Manual, 1960 edition P. 251 unique in Cairo.

Although the color temperature of the rays must be converted to suit the color temperature for which the colored film was prepared if it is of the reversal type, yet it is very permissible for us to bypass this conversion process if the film is of the negative type, because it is in Fourth Stages Colored negative image To obtain positive images, other arrangements are made to correct the image's colors. As for the color primer film, it is difficult to control its colors after the imaging stage. It is worth mentioning that as a result of scientific progress in photographic research in general, and color visualization in particular - multi-purpose negative color films have been produced in recent years, the use of which does not call for the use of filters to adjust the color temperature when photographing. The inner mask (3) ORWOCOLOR Negative Film Ne 17 Mask, in addition to other excellent properties that characterize this film and were included in its manufacture (and you will talk about them in detail later (1)), it has been prepared to be used without the need for light filters when filming in both light Daytime, tungsten lamps, electronic flash, blue fluorescent lamps, yellow fluorescent lamps, photoflood lamps of all kinds, and regular home lamps. Its sensitivity to rays with a color temperature of 4200 Kelvin has been weighed, i.e. roughly mediating between the color temperatures of the previous light sources. A serious mistake is also to use a color film (whether negative or negative).

River Sal) for filming in conditions or a place that combines different light sources (1) We will go back to explaining what is meant by the internal mask and the advantages to be avoided from it, in the fifth chapter (2) The characteristics of this film will be mentioned in the third part. .
The color temperature of its rays, as if we combined, for example, daylight with the light of an atoungsten lamp. In this case, we will find one side of the color image covered with a tinge that may be red or yellow, and the other side with a blue tinge, according to the type of film. No fix for this error will work yet. Film exposure ends.