camera
camera
[′kam·rə]camera
camera
(1) A combination microphone and video capture device that is built into or attaches to a computer monitor (see Webcam).(2) A rear- or front-facing component in a smartphone or tablet that captures digital still and moving images. See rear-facing camera and video calling.
(3) A stand-alone device that records still or moving images as analog scenes on film or as pixels in digital storage. Consumer video cameras (camcorders) also include a microphone for audio capture. See digital camera, point-and-shoot camera, POV camera, DSLR and camcorder.
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| Not Exactly Digital |
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| Film cameras like these were used to take millions of pictures in the first half of the 20th century. See film camera. |
Camera
(still camera), a device combining optical and mechanical elements, designed to produce optical images of objects being photographed on a photosensitive emulsion covering a film, plate, or other photographic material.
Cameras may be designed for amateur, professional, or special use. Amateur and professional cameras are used in making portraits and to photograph groups of people, landscapes, and so on. Specialized cameras are designed for technical photographic work, aerial photography, photomicrography, and other special types of photography. In the USSR, cameras are classified according to the dimensions of the images produced as miniature (13 × 17 mm), half-frame (18 × 24 mm), small-format (28 × 28 and 24 × 36 mm), medium-format (from 45 × 60 to 60 × 90 mm), and large-format (90 × 120 mm or larger).
A camera usually consists of the following basic assemblies: a lightproof body, a lens with a focusing mechanism, a viewfinder, a shutter, and a film holder with a winding mechanism.
The lightproof body is the housing on which all the camera components are mounted. The lens forms a real image of the object being photographed in the plane of the photosensitive emulsion. It is usually attached to the body by means of a screw-thread mounting, but bayonet mountings are also used. Some cameras are designed to use interchangeable lenses having different focal lengths or are equipped with a single lens having a variable focal length. The lens is focused by rotating a focusing ring, which moves the lens assembly or the individual lens components along the optical axis; the plane of the image formed is thus made to coincide with the plane of the photographic material.
The simplest method of focusing is to make a visual estimate of the distance to the object being photographed and then to set the index mark on the lens barrel to the proper point on the distance scale. In order to facilitate focusing, the distance scale is sometimes divided into several sections, or zones, corresponding to a particular type of subject, for example, a portrait, a group of people, or a landscape. Each subject is identified by a symbol inscribed on the distance scale. With this type of zone focusing, the index mark on the lens barrel is set to one of the symbols.
Focusing is often done by means of an image formed on a ground glass or similar screen by the camera lens or an auxiliary lens (seeREFLEX CAMERA). In this case, the focusing ring is rotated until the optical image observed on the surface of the screen reaches maximum sharpness. Since it is desirable to have the lens diaphragm opened to its maximum aperture when focusing on a ground screen, thus providing maximum illumination of the image, some lenses are equipped with diaphragms that remain opened to the maximum aperture when focusing and that automatically shut the aperture down quickly to a previously established setting before the shutter is operated.
Focusing with a monocular range finder is accomplished by rotating the focusing ring until two optical images of the object being photographed merge into a single image. The two images correspond to the two legs of the range finder and are observed through a single eyepiece.
Cameras may be used to photograph ultraviolet or infrared rays, which are invisible to the eye but which can be recorded on a photosensitive emulsion. In these cases, the mirrors or lenses used have components made of materials that are transparent to the corresponding rays: quartz, fluorite, and lithium fluoride for ultraviolet rays, and sodium chloride, silicon, germanium, fluorite, lithium fluoride, and cesium iodide for infrared rays.
Various light filters may be used to obtain an image of an object in a narrow spectral range or to correct the color of an image for improved artistic expression; the filters are made in the form of attachments for the camera lenses. The use of light filters is required to obtain color-separation negatives in color photography.
The camera viewfinder is used to determine the boundaries of the field that is being photographed and to select the desired perspective.
The camera shutter permits light rays to strike the photosensitive emulsion for a prescribed time interval, called the exposure. Shutters have special mechanisms to produce automatic exposures of different durations. Escapements and electronic devices are used extensively in shutter mechanisms.
The film holder is a lightproof housing in which the photosensitive material is carried. Cylindrical cassettes, or cartridges, are used predominantly in half-frame and small-format amateur cameras; they may use a spool, or they may be of the “Rapid” type (without a spool). Film packs are usually used in medium-format cameras, and plate holders with photographic plates are used in large-format cameras.
The winding mechanism for the photographic film is usually coupled with the camera shutter and the frame counter. The mechanism may be operated manually by a cylindrical knob, cocking lever, or push key, or it may use a built-in spring motor or electric motor.
Some cameras are equipped with a built-in automatic shutter release, a synchronizing contact, an exposure meter or exposure measuring device, and other accessories. The automatic shutter release operates the shutter automatically a short time after it is turned on (10–15 seconds). The synchronizing contact is used to operate a flash lamp, usually when the scene being photographed is insufficiently illuminated. The exposure measuring device is designed to provide the necessary diaphragm and exposure settings as a function of the film’s light sensitivity, or speed, and the illumination, or brightness, of the scene being photographed. It consists of a photoelectric exposure meter coupled with the diaphragm and shutter mechanisms. Exposure measuring devices are classified as semiautomatic or automatic, depending on their mode of operation. The exposure values are automatically established in accord with a single program or several programs.
Specialized cameras include camera guns, which are mostly used to photograph wild animals, the Gorizont camera for panoramic photography, the Foton camera for taking pictures without processing the photographic material in a laboratory (by means of the Moment photographic kit), stereoscopic cameras, and other types.
Future improvements in camera design will include automation of the various operations that precede the exposure process—winding the film and cocking the shutter, setting the exposure and the diaphragm, operating the flash lamp, and focusing the lens. Lenses, shutters, and other camera subassemblies will also be improved.
REFERENCES
Shul’man, M. Ia. Sovremennye fotograficheskie apparaty. Moscow, 1968.Kulagin, S. V. Proektirovanie foto- i kinopriborov, 2nd ed. Moscow, 1976.
S. V. KULAGIN