Photojournalism

In today's society photography plays important roles as information medium, as a tool in science and technology, and as an art form, and it is also a popular hobby. It is essential at every level of business and industry, being used in advertising, documentation, photojournalism, and many other ways. Scientific research, ranging from the study of outer space to the study of the world of subatomic particles, relies heavily on photography as a tool. In the 19th century photography was the domain of a few professionals because it required large cameras and glass photographic plates; during the first decades of the 20th century, however, with the introduction of roll film and the box camera, it came within the reach of the public as a whole. Today the industry offers amateur and professional photographers a large variety of cameras and accessories.

The Development of Cameras

Modern cameras operate on the basic principle of the camera obscur. Light passing through a tiny hole or aperture into an otherwise light-tight box casts an image on the surface opposite the aperture. The addition of a lens sharpens the image, and film makes possible a fixed, reproducible image. The camera is the mechanism by which film can be exposed in a controlled manner. Although they differ in structural details, modern cameras consist of four basic components: body, shutter, diaphragm, and lens. Located in the body is a light-tight chamber in which film is held and exposed. Also in the body, located opposite the film and behind the lens, are the diaphragm and shutter.

The lens, which is affixed to the front of the body, is actually a grouping of optical glass lenses. Housed in a metal ring or cylinder, it allows the photographer to focus an image on the film. The lens may be fixed in place or set in a movable mount. Objects located at various distances from the camera can be brought into sharp focus by adjusting the distance between the lens and the film.

Brief definitions of terms and their significance

The diaphragm, a circular aperture behind the lens, operates in conjunction with the shutter to admit light into the light-tight chamber. This opening may be fixed, as in many amateur cameras, or it may be adjustable. Adjustable diaphragms are composed of overlapping strips of metal or plastic that, when spread apart, form an opening of the same diameter as the lens; when meshed together, they form a small opening behind the center of the lens. The aperture openings correspond to numerical settings, called f-stops, on the camera or the lens.

Shutter speed affected the evolution of policial photography

The shutter, a spring-activated mechanical device, keeps light from entering the camera except during the interval of exposure. Most modern cameras have focal-plane or leaf shutters. Some older amateur cameras use a drop-blade shutter, consisting of a hinged piece that, when released, pulls across the diaphragm opening and exposes the film for about 1/30th of a second.

Anyone can be photographed in a public space where there is no expectation ...