تقدير الرقم الدليل المجهول لجهاز الإضاءة الخاطفة .. كتاب آلة التصوير

Estimation of the unknown guide number for the flashlight device

We may get a flashlight device without knowing its guide number. Therefore, some experiments must be conducted to estimate this number correctly, and these tests are usually necessary when purchasing a new electronic flashlight device. The unknown guide number estimates that approximately five images are made for one subject using The flashlight device that is being tested with a sensitive film whose speed is known (for example, 32 shinners) and then determines the distance between the object and the light source accurately. (Let us assume that the distance measured was three meters, for example). Then shooting is done using five consecutive f-numbers such as 22 f - 16 f - 11 f - 6 f . And after the end of photography, the film is shown in the solution, the appearance that we always use. Then we examine the negative images to decide which one is best exposed (and let us suppose that it was the one that was photographed at aperture 16 f), then the index number can be calculated as follows:

Guide number = Diaphragm Fatiha * Distance
= 16 x 3 = 48

48 = 3 x

... The appropriate guide number for the flashlight device we used is 48 when using a 32-shine speed film.

This and other factors other than the foregoing affect the result we get. An example of these factors is the type of solution, the appearance, the degree of its concentration, and the temperature at which the display was made..and the last of these factors that affect negative images. Therefore, it is wise to take into account the effect of these factors when photographing and showing films in the following conditions.

Use clustered flash light sources as the main lighting method

There is a common mistake made by many when using more than one source of flashing light gathered together in one place (in order to increase the amount of light). Similar to the first in strength, that is, they consider the appropriate guide number for the two combined light sources to be 2 x 44 = 88. This is a mistake that results in less exposure than if we used only one source. The power of light is directly proportional to the square root of the index number.

Example 1 - If we use two light sources. The leading number is multiplied by the square root of the number 2, i.e. (1, 4 ×). According to the previous example, the leading number becomes 44 × 1,4) (as 2 = 1,4).

Example 2- If we use three sources of light, the index number for each source is multiplied by the square root of the number 3, i.e. (1,73). (as 3 = 1.73)

Example 3 - If we use four sources of light, the index number for each source is multiplied by the square root of the number 4, i.e. (×2). As 4 = 2) and according to the last example, the index number is doubled only in the case of using four sources of light.

So the guide number = 2 x 44 = 88

Important note:

This rule also applies when using a single flash light source with the film if its sensitivity is increased to double. If the guide number is 44, for example, when using a 32-shine speed film, then it is wrong to double the guide number and consider it 88 if we use a 32-shine speed film, i.e. 35-shine. The correct way is to multiply the guide number X by 2, which means the guide number becomes 44 x 1.4, or approximately 62. And if we use a movie. Its speed is four times the first, i.e. 38 Shiners, so the guide number = 44 x 4 = 44 x 2 = 88

Estimating the index number for two flash light sources, one main and the other auxiliary

Our previous research was concerned with estimating the index number in the case of using more than one flashlight lamp as basic sources gathered at one point in order to increase the amount of light, but circumstances often call for the use of more than one source, making one main and the other auxiliary, in order to distribute lighting on the body or to get rid of Strong shadows that result from using only one source, so we place light sources on different dimensions of the body without collecting them in one place.

Here we wonder: Is the index number for these light sources assessed on the same basis as the previous one? In response to that, we say: When the photographer used only one source, he aimed to illuminate the side directly facing the main searchlight, and that when he used the other auxiliary searchlight, he required lighting the area of ​​shadows produced by the first searchlight, so the second source performs this with the following functions:

(a) To illuminate the area of ​​shadows resulting from the first main searchlight, as it represents a major source for illuminating an area that could not be illuminated with the first source.

(b) The second searchlight sheds light on some areas facing the first main searchlight, thus it represents a secondary source for these areas.

Based on the foregoing, the excess amount of light that we must take into consideration is that resulting from the function shown in b. This quantity may be so small that it can sometimes be overlooked if the auxiliary source is far from the body, but if the two sources are close in distance from it, then what is called the distance must be calculated.
The equation Epuivalent Distance, and what is meant by it is “that distance at which if the source of flashing light was only one and it is far from the body at that equivalent distance, then the intensity of its illumination (when it is illuminated by both sources together) would be equal to the intensity of its illumination when it is illuminated by this one source only.” As an explanation for this, we suppose that the distance The body is three meters away from the main light source, for example, and its distance from the second source is approximately five meters, then the intensity of its illumination resulting from the two sources together becomes equal to (x unit), and here we say that the body’s illumination intensity is equal to (x unit) also if the single source is far from the body By the amount of this equivalent distance (Fig. 215).
If we imagined the previous description, we would find that this equivalent distance must be shorter than the distance between the body and the main source, and the difference between the two distances is simple. According to the previous example, the equivalent distance becomes a little less than two meters (which is the distance between the main source and the object (Fig. 215). Based on an estimate of the equivalent distance, the appropriate focal number can be known by applying the law:

Distance index number = focal number.