ضبط عاملى التعريض حين استخدام الضوء الخاطف كمصدر وحيد للإضاءة ٢-a .. كتاب آلة التصوير

(High lighting) resulting from the main light source. (as if there were no other flickering light source illuminating the shadows), and let's say this estimate was 1/100th of a second with a focal number of 11 f....

2- Based on our previous knowledge of the guide number (for the flashlight device and suitable for the speed of the sensitivity of the film), we can decide the distance that must be available between the light source and the object being photographed, by applying the aforementioned law, which is: the guide number on the distance = the focal number..

If we assume that the guide number is 44 (when measuring in meters), then it is possible to determine the distance between the object to be photographed and the light source.
(Provided that this distance is compatible with the focal number that we estimated, which is 11 f). By applying the law, it becomes 44 divided by cm = 11 f

... x (i.e. the distance between the light source and the object) = 4 metres.

We conclude from the above that in order for the exposure to be correct, the flash light source must be made four meters away from the object to be photographed, and thus the areas of light resulting from the main source have obtained correct exposure, just as the areas of shadows resulting from the first source that were illuminated by the flash light get exposure. also true.

We see from the foregoing that the appropriate focal number for photographing areas of high illumination (or areas of light resulting from the main source) is the one that determines the object and the source of flashing light when it is used as an auxiliary light source for other main lighting, such as the sun, for example.

But what must the photographer do if he wants the distance between the light source and the object to be less than the previous amount? In this case, he must follow any of the following methods:

(a) Reassessment of the exposure factors:

In the previous example, we noticed that the two exposure factors that were estimated to fit the high-light area were 11 f with 1/100 of a second, which prompted us to make the distance between the light source and the object = 4 meters.

If we change the estimation of the two exposure factors and make it 22 f with a speed of 1/25 of a second, it is easy to reduce the distance between the camera and the object, and the new distance is then estimated as follows:

Distance guide number = focal number ... 44 x = 22 f

... x (i.e. the distance between the camera and the body) = 2 meters.

That is, if we make the two exposure factors 22 f with a speed of 1/25 of a second, it is possible that the distance between the object will decrease. And the flash light source made it only 2 meters instead of 4 meters as it was in the first case.

(b) Reducing the amount of light emitted by the source: some electronic flashlight devices are equipped so that the light energy they emit can be reduced.

(c) Helping to distribute the light without concentrating it on a specific area: by placing a tissue, for example, on the light source. As long as we have been able to reduce the amount of light, it is possible to shorten the distance.

Is it for a difference of estimation. Does the shutter speed have any effect on the image when using a flashlight as an auxiliary light source to illuminate shadow areas only?

According to what we have already mentioned regarding the use of electronic flashlight as the main and only source of illumination, we find that the shutter speed is the same. From a second or + a second, as what counts is the speed of the flash, which is the period during which the latent image is formed. Increasing or decreasing the shutter speed has no effect on that, but in the case of flash photography as an auxiliary source, there is a slight difference that we explain as follows:

Suppose we are photographing a person standing in a room with a window shining behind him. The room in general, so this window is considered a main source that illuminates the back of the person who turns his face towards the inside of the room, and some of the side parts of his face are illuminated (these side areas are then considered high lights areas). ), we use flashlight. We suppose that the data related to the circumstances of the shooting were as follows:

Flash speed = 1/3000 of a second

Guide number = 44

The distance between the person and the flashlight = 2 meters

Diaphragm aperture = 22 f

Then let's say the shutter speed we estimated. = 1/400th of a second

Here we wonder, would the result we get in the image differ if the shutter speed we estimated was 1/400, 1/100, or 1/5 second, for example?

In order to answer the previous question, we assume that we will photograph this person four times, in the circumstances described later:

1- If we make the shutter speed 1/100 of a second and the speed of the flash light is 1/3000 of a second, a latent image will be formed, and its formation (from a theoretical point of view) is a result. 1/400 of a second.As for the practical point of view, the image was formed from the amount of light emitted by the flashlight, which is the large light energy that actually affects the sensitive film.To imagine that, we ask, “Was it possible for a latent image to form at a speed of 1/400 of a second is 22 f, and in a room that is illuminated only by one window, if there is no flash light? There is no doubt that the answer is in the negative, as this amount of light is not sufficient to affect the sensitive layer to be a latent image. Therefore, it is not expected that we will find in In the final image, there is no effect of the backlight resulting from the window light, as its effect was very weak to the extent that it is virtually non-existent.

2- If we set the shutter speed to 1/100 of a second in the second case, the effect of the backlight resulting from the window light will increase by four times the effect of the first, and there is no doubt that increasing this amount has a greater effect on increasing the appearance of the backlight effect, while the effect does not change. The amount of light produced by a flash light source.

3- If we set the shutter speed to 1/25 of a second in the third case, the effect of the window light increases, and it begins to appear on the person’s image in the form of a stronger backlight than in the previous case, while the effect of the amount of light resulting from the flash light source does not change.

4- In the fourth case, we will make the shutter speed 1/5 of a second, which is approximately eighty times the amount of window light that we allowed to enter in the first case. The image of the person as side or background light lines, even though there is a flash of light.

By weighing the first case (when the shutter speed was 1/400 of a second) and the fourth case (when we estimated the shutter speed to be 1/5 of a second), we find that the last photo truly and correctly expressed the shooting conditions when we used more than one light source, which is An effect that has artistic value sometimes.

We conclude from the foregoing that if we want to show the effect of the back light in the case of flash photography as an auxiliary source for illuminating the shadows, the shutter must be slow.