التعريض الناجح ( Successful Exposure ) .. كتاب فن التصوير الفوتوغرافي

Successful Exposure

The degree of appropriate exposure (Exposure) is essential to the success of the image. Successful imaging depends on a suitable exposure of the photosensitive film. Therefore, understanding this topic is very important to take a successful photo. Let's see why? Why, for example, is that you cannot simply open the shutter with your camera, and close it whenever you want, and that the exposure period must be precisely determined?

To answer this question, we must remember the photosensitive nature of film.

We mention that the film is a transparent plastic film, one side of which is coated with a thin layer of silver salts powder, especially silver bromide. When light falls on silver salt granules, chemical reactions occur, releasing some of the silver, which remains attached to the transparent plastic membrane. When endorsing the film, an additional amount of silver is released in the place that was exposed to the effect of light. As for the silver salts that were not exposed to light, they fall off and are washed off the film, leaving a transparent spot, while the liberated silver leaves a dark spot in the place that was exposed to the action of light.

Silver salts need a minimum level of light for the reaction to occur in them, and this means that no reaction takes place before the amount of light on the film reaches a certain level of intensity.
In addition, the silver bromide granules are not equally affected by light, that is, some of them need more light to react.
Therefore, the greater the exposure, the more and more granules will interact with the light, leaving a darker spot on the negative crystal, which gives a clearer image.
On the contrary, if the film is not given sufficient exposure, most of the silver bromide is washed off and expelled from the film, leaving a semi-transparent negative crystal that, when printed, gives a dark image as a result of insufficient exposure (Underexposed Print).

But if we continue exposing the film to light for a longer period, an increasing amount of silver bromide interacts with the light, and most of it is fixed on the film in the form of silver granules, which results in an overexposed negative crystal that gives a faded image with low contrast values ​​when printed. tones) so we see the importance of exposing the film to the right amount of light. If the exposure is not enough, we get a dark image in which details cannot be seen, but if the exposure is more than We should get a lifeless picture with low tones of contrast, especially in the lighter parts.