Photo

    Exposure
    There may be people among the readers who, having faced the difficulties of mastering their first camera, were absorbed in labyrinth of photographic art. I’ll tell for them about the main concepts used in photography in brief.
Photo film has been the main image carrier till recently: very thin layer of photosensitive emulsion applied over a transparent substrate. Emulsion is made of gelatin mixed with microscopical crystals of photobromide. Under the influence of light which comes to the film through the lens opening, these crystals turn into small parts of metallic silver. In such way invisible image appears which is hidden and becomes visible only after a chemical treatment – development. The film is developed by means of dipping it into developer. At that, places, at which light fell in the camera, become dark. Degree of darkening is more at the spots of emulsion which were affected by more light. This means that light objects look as the darkest in the film. On the contrary, the darkest objects appear almost transparent.
 

    4. Negative.
 

    5. Positive.
    This image is inconvenient to view. Perhaps this is the reason why it was named negative, and people contrived positive process for obtaining normal photographs. As a matter of fact, it’s one more shooting. Negative image is projected in the photographic paper by means of magnifying device; the photo paper is covered with photosensitive emulsion. A negative image is formed in it under the influence of light in the same way as it was formed in the film. This negative image of the negative is called positive. This is a usual photograph at which all objects are in their proper position: a white man has white skin and an African has black one.
The more light falls into the film, the darker it becomes after developing. If emulsion is affected by too much light, it becomes so black that no image is left on it. To get a high-quality picture, you must measure out precisely the amount of light that falls on the carrier of “hidden” image. An optimal dose of light necessary for obtaining an image is called exposure. Exposure is equal to product of the time of light effect on the film and lighting.
    Camera allows controlling the amount of light passing to the film by means of altering the time of flare and adjustment of the light flux by changing the camera lens opening.
The time for which the camera shutter is opened to make an image is called an exposure.