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 21/4 × 31/4 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.
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.
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.
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).
A camera is a device used to capture images, either as still photographs or as sequences of moving images (movies or videos). The term comes from the camera obscura (Latin for "dark chamber"), an early mechanism of projecting images where an entire room functioned as a real-time imaging system; the modern camera evolved from the camera obscura.
Cameras may work with the light of the visible spectrum or with other portions of the electromagnetic spectrum. A camera generally consists of an enclosed hollow with an opening (aperture) at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. A majority of cameras have a lens positioned in front of the camera's opening to gather the incoming light and focus all or part of the image on the recording surface. The diameter of the aperture is often controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture.
The forerunner to the camera was the camera obscura. The camera obscura is an instrument consisting of a darkened chamber or box, into which light is admitted through a convex lens, forming an image of external objects on a surface of paper or glass, etc., placed at the focus of the lens. The camera obscura was first invented by the Iraqi scientist Ibn al-Haytham (Alhazen) as described in his Book of Optics (1015-1021). Irish scientist Robert Boyle and his assistant Robert Hooke later developed a portable camera obscura in the 1660s.
The first camera that was small and portable enough to be practical for photography was built by Johann Zahn in 1685, though it would be almost 150 years before technology caught up to the point where this was practical. Early photographic cameras were essentially similar to Zahn's model, though usually with the addition of sliding boxes for focusing. Before each exposure, a sensitized plate would be inserted in front of the viewing screen to record the image. Jacques Daguerre's popular daguerreotype process utilized copper plates, while the calotype process invented by William Fox Talbot recorded images on paper.
The first permanent photograph was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles and Vincent Chevalier in Paris. Niépce built on a discovery by Johann Heinrich Schultz (1724): a silver and chalk mixture darkens under exposure to light. However, while this was the birth of photography, the camera itself can be traced back much further. Before the invention of photography, there was no way to preserve the images produced by these cameras apart from manually tracing them.
The development of the collodion wet plate process by Frederick Scott Archer in 1850 cut exposure times dramatically, but required photographers to prepare and develop their glass plates on the spot, usually in a mobile darkroom. Despite their complexity, the wet-plate ambrotype and tintype processes were in widespread use in the latter half of the 19th century. Wet plate cameras were little different from previous designs, though there were some models, such as the sophisticated Dubroni of 1864, where the sensitizing and developing of the plates could be carried out inside the camera itself rather than in a separate darkroom. Other cameras were fitted with multiple lenses for making cartes de visite. It was during the wet plate era that the use of bellows for focusing became widespread.
Traditional cameras capture light onto photographic film or photographic plate. Video and digital cameras use electronics, usually a charge coupled device (CCD) or sometimes a CMOS sensor to capture images which can be transferred or stored in tape or computer memory inside the camera for later playback or processing.
Cameras that capture many images in sequence are known as movie cameras or as ciné cameras in Europe; those designed for single images are still cameras. However these categories overlap, as still cameras are often used to capture moving images in special effects work and modern digital cameras are often able to trivially switch between still and motion recording modes. A video camera is a category of movie camera that captures images electronically (either using analogue or digital technology).
Due to the optical properties of photographic lenses, only objects within a limited range of distances from the camera will be reproduced clearly. The process of adjusting this range is known as changing the camera's focus. There are various ways of focusing a camera accurately. The simplest cameras have fixed focus and use a small aperture and wide-angle lens to ensure that everything within a certain range of distance from the lens, usually around 3 metres (10 ft) to infinity, is in reasonable focus. Fixed focus cameras are usually inexpensive types, such as single-use cameras. The camera can also have a limited focusing range or scale-focus that is indicated on the camera body. The user will guess or calculate the distance to the subject and adjust the focus accordingly. On some cameras this is indicated by symbols (head-and-shoulders; two people standing upright; one tree; mountains).
Rangefinder cameras allow the distance to objects to be measured by means of a coupled parallax unit on top of the camera, allowing the focus to be set with accuracy. Single-lens reflex cameras allow the photographer to determine the focus and composition visually using the objective lens and a moving mirror to project the image onto a ground glass or plastic micro-prism screen. Twin-lens reflex cameras use an objective lens and a focusing lens unit (usually identical to the objective lens) in a parallel body for composition and focusing. View cameras use a ground glass screen which is removed and replaced by either a photographic plate or a reusable holder containing sheet film before exposure. Modern cameras often offer autofocus systems to focus the camera automatically by a variety of methods.
The size of the aperture and the brightness of the scene controls the amount of light that enters the camera during a period of time, and the shutter controls the length of time that the light hits the recording surface. Equivalent exposures can be made with a larger aperture and a faster shutter speed or a corresponding smaller aperture and with the shutter speed slowed down.