Photo Restoration & Training

Photography

Photography is the method of picture making developed in the early 19th century, based on principles of light, optics, and chemistry. The word photography comes from Greek words and means “drawing with light.”

This article discusses how photographs are produced using film, cameras, and lenses. It also outlines techniques of modern photography, such as filtration and electronic flash, and surveys how photographic technologies have evolved since the medium's invention.

Light is the most essential ingredient in photography. Nearly all forms of photography are based on the fact that certain chemicals change in some way when exposed to light. These chemicals are "photosensitive."

For the purpose of producing a photograph, silver salts are distributed in gelatin to make a mixture called an emulsion, which is applied to film or another supporting material in a thin layer. When the emulsion is exposed to light, the silver halide crystals undergo chemical changes and, after further processing, an image becomes visible. The stronger the light that strikes the crystals, the denser or more opaque that part of the film becomes. Most types of film produce a negative image, from which a positive final copy can be printed on sensitized paper. The dense (or dark) areas of the negative translate into light areas on the final photograph. Almost all modern photography relies on this negative-to-positive process.

In most cases, the camera and its lens determine the appearance of the photographic image. Cameras work on the basic principle of the camera obscura, a device that artists once used to project a temporary image of something they wanted to draw. In both the camera obscura and the modern camera, light passes through a lens fitted into an otherwise light-proof box. Light passing through the lens casts an image of the camera’s subject—the object, person, or scene in front of the camera—onto the inside of the box which, in a modern camera, contains film. The camera and lens control how much light strikes the film--the exposure.

The lens refracts (bends) light reflected from the subject so that these rays cross and reappear upside-down on the other side of the lens. The area where they re-form an image inside the camera is called the plane of focus. You, the photographer--or an automatic mechanism--must focus the image; that is, the distance between the lens and the film must be adjusted so that the plane of focus falls precisely on the film.

Various types of lenses admit different amounts of light and permit different angles of view. Lenses that take in a wide angle of view make the subject seem farther away; lenses that take in a narrow angle make the subject seem closer.

The amount of light that a lens allows to fall on the film is controlled by a lens diaphragm, a mechanism consisting of overlapping metal blades. The diaphragm controls the size of the opening (called the aperture) of the lens. A shutter controls how long light is allowed to strike the film; the shutter speed can range from a small fraction of a second (1/1000 or less) to minutes or even hours.

The film type, camera size, focus, view angle, lens aperture, and shutter speed all influence the appearance of the photograph as much as the choice of subject and the time of day.