camera
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.
Still Cameras
Focusing and Composing the Scene
Except for pinhole cameras, which focus the image on the film 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 device), determines the angle of view and the size of objects as they appear on the imaging surface. The image is focused on that surface by adjusting the distance between the lens and the surface. In most 35-mm cameras (among the most widely used of modern optical cameras) and digital cameras this is done by rotating the lens, thus moving it closer to or farther from the film or imaging device. 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 film.
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 35-mm 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 plane, 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 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. Digital cameras have an optical viewfinder, a liquid crystal display (LCD) screen, or both. Optical viewfinders are common in point-and-shoot cameras. An LCD screen allows the user see the photograph's content before the picture is taken and after, allowing the deletion of unwanted pictures.
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 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 plane and has one or two cloth or metal curtains that travel vertically or horizontally across the film frame. 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 being used) for a good exposure can be obtained.
Features of Modern Cameras
Most of today's 35-mm cameras, both rangefinder and reflex 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 correct for deficiencies in film sensitivity; flash bulbs and flash mechanisms for supplying light; and monopods and tripods, for steady support.
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. Also very popular are compact 35-mm rangefinder cameras; 126 cartridge cameras; and the subminiature cameras, including the 110 "pocket" variation of the Instamatic type and the Minox, which uses 9.5-mm film. Other categories in use include roll- and sheet-film single-lens reflex (SLR) cameras that use 120 and larger size films; self-processing Polaroid cameras (see Land, Edwin H. ); 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.) Digital cameras are essentially no different in operation but capture the image electronically rather than via a photographic emulsion.
The smaller, pocket-sized, automatic cameras of the Advanced Photo System (APS), introduced in 1996, are unique in that they are part of an integrated system. Using magnetic strips on the film to communicate with the photofinishing equipment, the camera can communicate shutter speed, aperture setting, and lighting conditions for each frame to the computerized photofinishing equipment, which can then compensate to avoid over- or underexposed photographic prints. Basic features of the APS cameras are 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 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 seven megapixels. With more megapixels, more picture detail is captured, resulting in sharper, larger prints. 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 magnetic cards, sticks, or disks. These images can be transferred to a computer for viewing and editing or may be viewed on the camera's liquid crystal display. Digital cameras typically also have the ability to record video, but have less storage capacity and fewer video features than camcorders.
The marriage of microelectronics and digital technology has led to the development of the camera phone, a cellular telephone that also has picture- (and video-) taking capability. Some camera phones can immediately send the picture to another camera phone or computer via the Internet or through the telephone network, 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 camera phone is available for impromptu or unanticipated photographic opportunities.
See also photography, still .
Motion Picture Cameras
The motion picture camera comes in a variety of sizes, from 8 mm to 35 mm and 75 mm. Motion picture film comes in spools or cartridges. The spool type, employed mostly in 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—available for the 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 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.
Lenses for movie cameras also come in "normal," wide-angle, and long 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. Many super-8 cameras come with 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 f -stop 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. For viewing purposes, a super-8 uses 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. Other cameras have a mirror-shutter system that transmits all the light, at intervals, alternately to film and viewfinder. Many of the super-8 cameras also contain some kind of rangefinder, built into the focusing screen, for precise focusing.
See also motion picture photography .
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 Niepce 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 Edison 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. Since then they have gradually superseded many film-based cameras, both for consumers and professionals, leading many manufacturers to eliminate or reduce the number of the film cameras they produce.
Bibliography
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).
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