آلة التصوير الأساسية .. طريقة عمل آلة التصوير .. كتاب التصوير الضوئي

The basic camera .. How the camera works .. The book of photography

The basic camera

All photographic cameras from the simplest to the most complex and the most perfect are based on a similar concept: a sealed box to prevent light from entering from an opening other than the lens. The camera also contains an eye with an adjustable aperture, a shutter and a mechanism for advancing the sensitive film. The machines are also equipped with extensions that allow the image of the subject to be seen and framed. There is an important point regarding the very precise adjustment of the position of the lens in relation to the film surface. The image formed by the lens is recorded on a sensitive surface in the form of a square or rectangle of the film, whether this film is single or in the form of a strip.

A film that is not exposed to light can record a latent image on its light-sensitive layer. The camera can be described as a device that allows the light rays that form the image given by the lens to the film under the control of the eye and shutter. The image is not clear unless the distance between the lens and the film is accurately adjusted.

Because of the high sensitivity of photographic film, a method must be found to monitor the light rays passing through the lens. The pupil changes the amount of light by means of an aperture with a variable or fixed diameter (placed between the glass lenses). Usually, under strong light, this aperture must be made smaller, while if the light is weak, it is necessary to give the pupil its largest aperture. This process increases the overall clarity of the image, thus giving a greater depth to the field to be photographed, i.e. it makes the different surfaces of the subject arranged in depth appear in a clear image according to the calibrated distance. However, the depth of field should not be confused with the depth of focus of the focal point, as this last term indicates the distance that allows maintaining the clarity of the image of a surface perpendicular to the optical axis. The different apertures of the pupil are calibrated with values ​​​​represented by the letter F. These apertures range from 1/F to 64/F, and the latter corresponds to a diameter equal to the diameter of the eye of a needle. As for the shutter, it monitors the duration of the light that penetrates the lens and the pupil. This shutter is often moved by a spring and is passed by a push button or a lever called a release. Shutter speeds, either clockwise or electronically calibrated, usually range from 1 sec to 1/1000 sec (1/500 sec for some machines) and are selected as needed. There is a calibration that allows the shutter to be kept open indefinitely. The simplest machines have only one speed and one aperture (1/40 at F/14, for example). These are suitable for instant cameras when shooting in the sun. The more sophisticated machines, on the contrary, are equipped with many calibrations and additional parts (accessories).

The objective lens is the basic element of every machine. Modern objective lenses consist of several crystalline lenses carefully placed and arranged in a cylindrical case. These lenses give images of extreme purity and clarity and there are several models with specific functions: a wide-angle lens, a close-up lens, a lens for shooting from a distance, etc.

As we have mentioned, the pupil is an integral part of the lens and works in connection with the shutter (which rather belongs to the machine itself) to ensure a correct exposure of the film according to the amount of light that illuminates the subject. For each lighting condition, there is a close relationship between the pupil aperture and the speed given by the shutter.

If the first increases, the second decreases: for example: an aperture of 2/F is suitable for a speed of 60/1 second in low light, while the same aperture, 2/F, requires a speed of
1000/1 second in strong light.

There are two types of shutter: the central shutter, which is located in the lens next to the pupil, and the firing shutter, which operates just next to the film in the manner of a curtain. The nature of the shutter (central or firing) depends on the type of machine. Small-sized machines, i.e. 35 mm, are usually equipped with a firing shutter, which is fed at the same time as the film advance by a lever located on the right side above the case. For large-sized machines and some double-lens reflex machines, the shutter is fed by a feeding lever and the view is taken by pressing the trigger. When the flash is used, an internal contact in the shutter closes the flash circuit and this is what causes the movement simultaneously with the open shutter aperture. This timing depends on the type of flash used: contact (X) for electronic flash, contact (M) or (FP) for flash with burst lamps. In any case, the flash should burst exactly when the shutter is at its maximum aperture. To enable the photographer to form his image, the machines are equipped with a reflex sight that uses the image formed by the lens and transmitted by a mirror and prism.

Large-scale cameras are used for still subjects when the photographer has enough time to compose and frame his image. Small-scale cameras are more flexible and faster to use: they are therefore suitable for moving subjects and reportage. In addition, they are easy to carry and transport even if they are accompanied by a large number of additional parts.

The lens can be adjusted to allow for adjustment of clarity. A - The distance between the lens and the film surface can be adjusted to obtain clarity for different surfaces of the subject.

B - The aperture of the pupil can also be controlled manually or automatically to allow for monitoring the amount of light that passes through the lens and passes to the film surface.

C - The shutter speed determines the amount of exposure to the film.

D - The film surface is the area on which the image is calibrated and recorded. There is a device that allows the film to move forward; the film plates are placed by a chassis manually on the back of the camera.

E - The collimator model allows for framing the subject and composing the image.