camera(redirected from camera posterior bulbi)
Also found in: Dictionary, Thesaurus, Medical, Legal.
camera,lightproof box or container, usually fitted with a lens, which gathers incoming light and concentrates it so that it can be directed toward the film (in an optical camera) or the imaging device (in a digital camera) contained within. Today there are many different types of camera in use, all of them more or less sophisticated versions of the camera obscura, which dates back to antiquity. Nearly all of them are made up of the same basic parts: a body (the lightproof box), a lens and a shutter to control the amount of light reaching the light-sensitive surface, a viewfinder to frame the scene, and a focusing mechanism.
Focusing and Composing the Scene
Except for pinhole cameras, which focus the image on film or viewing surface through a tiny hole, all other cameras use a lens for focusing. The focal length of a lens, i.e., the distance between the rear of the lens (when focused on infinity) and the film or imaging sensor, determines the angle of view and the size of objects as they appear on the imaging surface. The image is focused on that surface (the focal plane) by adjusting the distance between the lens and the surface. In most 35-mm cameras (among the most widely used of modern optical, or film, cameras) and digital cameras this is done by rotating the lens to move it closer to or farther from the focal plane. With twin-lens reflex and larger view cameras, the whole lens and the panel to which it is attached are moved toward or away from the focal plane.
To view the subject for composing (and, usually, to help bring it into focus) nearly every camera has some kind of viewfinder. One of the simplest types, employed in most view cameras, is a screen that is placed on the back of the camera and replaced by the film in making the exposure. This time-consuming procedure is avoided in the modern single-lens (and other) reflex cameras by placing the screen in a special housing on top of the camera. Inside the camera, in front of the film or imaging sensor, there is a movable mirror that bounces the image from the lens to the screen for viewing and focusing, and then flips out of the way when the shutter is tripped, so that the image hits the film or imaging sensor instead of the mirror. The mirror returns automatically to place after the exposure has been made. In rangefinder cameras the subject is generally viewed by means of two separate windows, one of which views the scene directly and the other of which contains an adjustable optical mirror device. When this device is adjusted by rotating the lens, the image entering through the lens can be brought into register, at the eyepiece, with the image from the direct view, thereby focusing the subject on the film or imaging device. Digital cameras typically have a liquid crystal display (LCD) screen and may have an electronic or optical viewfinder as well; some digital cameras have a viewfinder only. The LCD screen allows the photographer to see the image's content before the picture is taken and after, facilitating the deletion of unwanted pictures. An electronic viewfinder effectively reproduces in miniature the image displayed on the LCD screen; the image can be augmented by the camera software in various ways to aid the photographer.
Controlling the Light Entering the Camera
The speed of a lens is indicated by reference to its maximum opening, or aperture, through which light enters the camera. This aperture, or f-stop, is controlled by an iris diaphragm (a series of overlapping metal blades that form a circle with a hole in the center whose diameter can be increased or decreased as desired) inside the lens. The higher the f-stop number, the smaller the aperture, and vice versa.
A shutter controls the time during which light is permitted to enter the camera. There are two basic types of mechanical shutter, leaf-type and focal-plane. The leaf-type shutter employs a ring of overlapping metal blades similar to those of the iris diaphragm, which may be closed or opened to the desired degree. It is normally located between the lens elements but occasionally is placed behind or in front of the lens. The focal-plane shutter is located just in front of the film or imaging sensor and has one or two cloth or metal curtains that travel vertically or horizontally across the film frame. Digital cameras may use a mechanical shutter (normally a focal-plane shutter) or an electronic shutter, or a combination of the two; the digital camera in a smartphone uses an electronic shutter. There are two types of electronic shutters. One, known as a global shutter, transfers the data being recorded by the imaging sensor all at once; the other, a rolling shutter, transfers the data line by line. By adjusting the shutter speed in conjunction with the width of aperture, the proper amount of light (determined by using a light meter and influenced by the relative sensitivity of the film or imaging sensor being used) for a good exposure can be obtained.
Features of Cameras
Most modern 35 mm film cameras, both reflex and rangefinder models, incorporate a rapid film-transport mechanism, lens interchangeability (whereby lenses of many focal lengths, such as wide-angle and telephoto, may be used with the same camera body), and a built-in light meter. Many also have an automatic exposure device whereby either the shutter speed or the aperture is regulated automatically (by means of a very sophisticated solid-state electronics system) to produce the "correct" exposure. Accessories include filters, which can be used to produce special affects and compensate for difficult lighting conditions (more important in film photography in some instances); flash mechanisms for supplying light; and monopods and tripods, for steady support. Digitial versions of reflex and rangefinder models (the former of which is much more common) also have similar features.
Simple box cameras, including cameras of the Eastman Kodak Instamatic type, are fixed-focus cameras with limited or no control over exposure. Twin-lens reflex cameras use one lens solely for viewing, while the other focuses the image on the film. Formerly very popular were compact 35-mm rangefinder cameras; 126 cartridge cameras; and the subminiature cameras, including the 110 "pocket" variation of the Instamatic type and the 9.5-mm Minox. Other types of film cameras include roll- and sheet-film single-lens reflex (SLR) cameras that use 120 and larger size films; self-processing Polaroid cameras (see Land, Edwin HerbertLand, Edwin Herbert,
1909–91, American inventor and photographic pioneer. While at Harvard, Land became interested in the properties and manipulation of polarized light.
..... Click the link for more information. ); press cameras and view cameras that use 2 1-4 × 3 1-4 in., 4 × 5 in., 5 × 7 in., 8 × 10 in., and 11 × 14 in. film sizes; stereo cameras, the double slides from which require a special viewer; and various special types such as the super wide-angle and the panoramic cameras. (The numbers 110, 120, and 126 are film-size designations from the manufacturer and do not refer to actual measurements.)
The smaller, pocket-sized, automatic cameras of the Advanced Photo System (APS), introduced in 1996 and now obsolete, were unique in that they were part of an integrated system. Using magnetic strips on the film to communicate with the photofinishing equipment, the camera could report shutter speed, aperture setting, and lighting conditions for each frame to the computerized photofinishing equipment, which could then compensate to avoid over- or underexposed photographic prints. Basic features of the APS cameras were drop-in loading, three print formats (classic, or 4 by 6 in.; hi vision, or 4 by 7 in.; and panoramic, or 4 by 11.5 in.) at the flick of a switch, and auto-focus, auto-exposure, "point-and-shoot" operation.
Digital cameras are similar in many respects to film cameras but capture the image electronically by means of a semiconductor-based imaging device rather than via a photographic emulsion. The imaging device uses either a complementary metal-oxide semiconductor (CMOS) image sensor or a charge-coupled device (CCD). Generally CMOS image sensors are cheaper and faster than those based on CCDs, but CCDs typically produce higher quality images. Because good quality digital cameras are now incorporated in cellphones, especially smartphones, the camera phone has superseded previously popular consumer cameras such as the "pocket" cameras. High-end digital single-lens reflex cameras and point-and-shoot digital cameras have also supplanted 35 mm cameras for most professionals and nearly all consumers.
Digital cameras have several unique features. Resolution is made up of building blocks called pixels, one million of which are called a megapixel. Digital cameras have resolutions ranging from less than one megapixel to greater than 24 megapixels. With more megapixels, more picture detail may be captured, resulting in sharper, larger images, but picture quality also benefits from the use of a larger imaging sensor with larger pixels, which will have more light-gathering capacity, so a digital camera with somewhat fewer but larger pixels may produce better images than one with more but smaller pixels. Focus is a function of "zoom." Most digital cameras have an optical zoom, a digital zoom, or both. An optical zoom lens actually moves outward toward the subject to take sharp close-up photographs; this is the same kind of zoom lens found in traditional cameras. Digital zoom is a function of software inside the camera that crops the edges from a photograph and electronically enlarges the center portion of the image to fill the frame, resulting in a photograph with less detail. Some models also have a macro lens for close-ups of small, nearby objects. Storage of digital photographs may be in the camera's internal memory or in removable solid-state flash memory devices. The images can be transferred to a computer for viewing and editing or may be viewed on the camera's LCD screen. Digital cameras typically also have the ability to record video, but have less storage capacity and fewer video features than camcorders.
Camera phones have become the ubiquitous progeny of the marriage of microelectronics and digital technology, common in relatively simple cellular telephonescellular telephone
or cellular radio,
telecommunications system in which a portable or mobile radio transmitter and receiver, or "cellphone," is linked via microwave radio frequencies to base transmitter and receiver stations that connect the user to a conventional
..... Click the link for more information. and a defining and essential feature of smartphones, which really are small computers masquerading as cellphones. Like digital cameras, they can record both still images and video, and though they are limited by fixed apertures, relatively small image sensors, digital zoom, and reliance on an LCD screen as a viewfinder, CMOS-based smartphone cameras produce good quality images. The phone can be used to view the image or immediately send the picture to another camera phone or computer via the Internet, the telephone network, and the like, offering the opportunity to take and share pictures in real time. Unlike the traditional camera, and to some extent the equivalent digital camera, which are used primarily for scheduled events or special occasions, the omnipresent camera phone is available for impromptu or unanticipated photographic opportunities, including the always essential "selfie."
See also photography, stillphotography, still,
science and art of making permanent images on light-sensitive materials.
See also photographic processing; motion picture photography; motion pictures.
..... Click the link for more information. .
Motion Picture Cameras
Standardized motion picture film cameras have utilized a variety of film sizes, from 8 mm to 35 mm and 75 mm, but the smaller and nonprofessional film cameras have been superseded by digital video cameras, and most commercial motion pictures are now also photographed using digital cameras.
Motion picture film comes in spools or cartridges. The spool type, employed mostly by 16- and 35-mm camera systems, must be threaded through the camera and attached to the take-up spool by hand, whereas a film cartridge—such as was used by super-8-mm systems—avoids this procedure. In all modern movie cameras the film is driven by a tiny electric motor that is powered by batteries.
Motion picture film cameras all operate on the same basic principles. Exposures are usually made at a rate of 18 or 24 frames per second (fps), which means that as the film goes through the camera it stops for a very brief moment to expose each frame. This is accomplished in nearly all movie cameras by a device called a rotary shutter—basically a half-circle of metal that spins, alternately opening and closing an aperture, behind which is located the film. To make the film travel along its path and hold still for the exposure of each frame, a device called a claw is required. This is another small piece of metal that alternately pops into the sprocket holes or perforations in the film, pulls the film down, retracts to release the film while the frame is being exposed, and finally returns to the top of the channel in which it moves to grasp the next frame. The movement of the shutter and claw are synchronized, so that the shutter is closed while the claw is pulling the frame downward and open for the instant that the frame is motionless in its own channel or gate.
Digital video cameras for commercial motion picture production are similar to in operation to both digital photography cameras and television cameras, but they use larger formats, either 2K or 4K, which are defined by the number of horizontal pixels, 2048 or 4096 respectively; the number of vertical pixels determines the aspect ratio. Digital movie cameras typically record images at the rate of 24 or, less commonly, 48 frames a second; higher frame rates have also been used. The resulting images are most commonly recorded as files on optical discs or hard or solid-state drives; videotape also has been used for recording.
Lenses for movie cameras also come in "normal," wide-angle, and long (or telephoto) focal lengths. Some older cameras had a turret on which were mounted all three lens types. The desired lens could be fixed into position by simply rotating the turret. Some cameras have—as super-8 cameras did—a single zoom lens, incorporating a number of focal lengths that are controlled by moving a certain group of lens elements toward or away from the film. Most of these cameras have an automatic exposure device that regulates the size of the aperture according to the reading made by a built-in electric eye. Movie camera lenses are focused in the same way as are still camera lenses. Most film movie cameras have a mirror-shutter system similar to that in a reflex camera, transmitting all the light, at intervals, alternately to film and viewfinder. Digital movie cameras may have an optical or electronic viewfinder; optical viewfinders, however, are found only in professionial motion picture cameras. Super-8 cameras used a beam splitter—a partially silvered reflector that diverts a small percentage of the light to a ground-glass viewfinder while allowing most of the light to reach the film. Many super-8 cameras also contained some kind of rangefinder, built into the focusing screen, for precise focusing.
See also motion picture photographymotion picture photography
photographic arts and techniques involved in making motion pictures.
See also photography, still. The Camera
..... Click the link for more information. .
Development of the Camera
The original concept of the camera dates from Grecian times, when Aristotle referred to the principle of the camera obscura [Lat.,=dark chamber] which was literally a dark box—sometimes large enough for the viewer to stand inside—with a small hole, or aperture, in one side. (A lens was not employed for focusing until the Middle Ages.) An inverted image of a scene was formed on an interior screen; it could then be traced by an artist. The first diagram of a camera obscura appeared in a manuscript by Leonardo da Vinci in 1519, but he did not claim its invention. The recording of a negative image on a light-sensitive material was first achieved by the Frenchman Joseph Nicéphore NiépceNiépce, Joseph Nicéphore
, 1765–1833, French chemist who originated a process of photography (see photography, still). In 1826 he produced the first known photograph, which he called a heliograph, using bitumen of Judea (a form of asphalt) on on a pewter
..... Click the link for more information. in 1826; he coated a piece of paper with asphalt and exposed it inside the camera obscura for eight hours.
Although various kinds of devices for making pictures in rapid succession had been employed as early as the 1860s, the first practical motion picture camera—made feasible by the invention of the first flexible (paper base) films—was built in 1887 by E. J. Marey, a Frenchman. Two years later Thomas EdisonEdison, Thomas Alva,
1847–1931, American inventor, b. Milan, Ohio. A genius in the practical application of scientific principles, Edison was one of the greatest and most productive inventors of his time.
..... Click the link for more information. invented the first commercially successful camera. However, cinematography was not accessible to amateurs until 1923, when Eastman Kodak produced the first 16-mm reversal safety film, and Bell & Howell introduced cameras and projectors with which to use it. Systems using 8-mm film were introduced in 1923; super-8, with its smaller sprocket holes and larger frame size, appeared in 1965.
A prototype of the the digital camera was developed in 1975 by Eastman Kodak, but digital cameras were not commercialized until the 1990s. They have gradually superseded many film-based cameras, both for consumers and, by the mid-2010s, for professionals as well, leading many manufacturers to eliminate or reduce the number of the film cameras they produce. The digital camera phone, which developed rapidly in the the 21st cent., contributed to the demise of the film camera, and has supplanted the camera for most amateur uses.
The demise of the super-8 film format began with the development of the camcorder, which used videotape cassettes, in the early 1980s; digital recording was introduced in the late 1980s and early 1990s. In the late 1990s and 2000s high-definition digital video recording and tapeless (optical disc, hard drive, and solid-state) recording were introduced. By the 2010s most movies, whether taken by professionals or amateurs, were shot using digital video cameras.
See The Encyclopedia of Photography (1971); The Focal Encyclopedia of Photography (rev. ed. 1972); C. Alesse, Basic 35 mm Photo Guide (1987); M. Freeman, The Medium Format Manual (1989).
(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.
REFERENCESShul’man, M. Ia. Sovremennye fotograficheskie apparaty. Moscow, 1968.
Kulagin, S. V. Proektirovanie foto- i kinopriborov, 2nd ed. Moscow, 1976.
S. V. KULAGIN
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.
|Not Exactly Digital|
|Film cameras like these were used to take millions of pictures in the first half of the 20th century. See film camera.|