In the 19th century, photographywas the domain of a few professionals because it required large camerasand glass photographic plates. During the first decades of the 20th century,however, with the introduction of roll film and the box camera, it camewithin the reach of the public as a whole. Today the industry offers amateurand professional photographers a large variety of cameras and accessories. See also Motion Picture. The Camera and Its AccessoriesModern cameras operate on the basicprinciple of the camera obscura (see Historical Development, below).
Lightpassing through a tiny hole, or aperture, into an otherwise lightproofbox casts an image on the surface opposite the aperture. The addition ofa lens sharpens the image, and film makes possible a fixed, reproducibleimage. The camera is the mechanism by which film can be exposed in a controlledmanner. Although they differ in structural details, modern cameras consistof four basic components: body, shutter, diaphragm, and lens.
Located inthe body is a lightproof chamber in which film is held and exposed. Alsoin the body, located opposite the film and behind the lens, are the diaphragmand shutter. The lens, which is affixed to the front of the body, is actuallya 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 maybe fixed in place or set in a movable mount. Objects located at variousdistances from the camera can be brought into sharp focus by adjustingthe distance between the lens and the film.
The diaphragm, a circular aperturebehind the lens, operates in conjunction with the shutter to admit lightinto the lighttight chamber. This opening may be fixed, as in many amateurcameras, or it may be adjustable. Adjustable diaphragms are composed ofoverlapping strips of metal or plastic that, when spread apart, form anopening of the same diameter as the lens; when meshed together, they forma small opening behind the center of the lens. The aperture openings correspondto numerical settings, called f-stops, on the camera or the lens. The shutter, a spring-activated mechanicaldevice, keeps light from entering the camera except during the intervalof exposure. Most modern cameras have focal-plane or leaf shutters.
Someolder amateur cameras use a drop-blade shutter, consisting of a hingedpiece that, when released, pulls across the diaphragm opening and exposesthe film for about 1/30th of a second. In the leaf shutter, at the momentof exposure, a cluster of meshed blades springs apart to uncover the fulllens aperture and then springs shut. The focal-plane shutter consists ofa black shade with a variable-size slit across its width. When released,the shade moves quickly across the film, exposing it progressively as theslit moves. Most modern cameras also have somesort of viewing system or viewfinder to enable the photographer to see,through the lens of the camera, the scene being photographed. Single-lensreflex cameras all incorporate this design feature, and almost all general-usecameras have some form of focusing system as well as a film-advance mechanism.
Camera DesignsCameras come in a variety of configurationsand sizes. The first cameras, “pinhole” cameras, had no lens. The flowof light was controlled simply by blocking the pinhole. The first camerain general use, the box camera, consists of a wooden or plastic box witha simple lens and a drop-blade shutter at one end and a holder for rollfilm at the other. The box camera is equipped with a simple viewfinderthat shows the extent of the picture area.
Some models have, in addition,one or two diaphragm apertures and a simple focusing device. The view camera, used primarily byprofessionals, is the camera closest in design to early cameras that isstill in widespread use. Despite the unique capability of the view camera,however, other camera types, because of their greater versatility, aremore commonly used by both amateurs and professionals. Chief among theseare the single- lens reflex (SLR), twin-lens reflex (TLR), and rangefinder. Most SLR and rangefinder cameras use the 35-millimeter film format, whilemost TLR as well as some SLR and rangefinder cameras use medium-formatfilm?that is, size 120 or 220. View CamerasView cameras are generally largerand heavier than medium- and small-format cameras and are most often usedfor studio, landscape, and architectural photography.
These cameras uselarge-format films that produce either negatives or transparencies withfar greater detail and sharpness than smaller format film. View camerashave a metal or wood base with a geared track on which two metal standardsride, one in front and one in back, connected by a bellows. The front standardcontains the lens and shutter; the rear holds a framed ground-glass panel,in front of which the film holder is inserted. The body configuration ofthe view camera, unlike that of most general-purpose cameras, is adjustable.
The front and rear standards can be shifted, tilted, raised, or swung,allowing the photographer excellent control of perspective and focus. Rangefinder CamerasRangefinder cameras have a viewfinder through which the photographer seesand frames the subject or scene. The viewfinder does not, however, showthe scene through the lens but instead closely approximates what the lenswould record. This situation, in which the point of view of the lens doesnot match that of the viewfinder, results in what is known as parallax. At longer distances, the effects of parallax are negligible.
At short distances,however, they become more pronounced, making it difficult for the photographerto frame a scene or subject with certainty.Reflex Cameras