Camera
From Encyclopædia
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[edit] CAMERA DEVELOPMENT
Centuries before the invention of the first practical photographic process, artists had been using a device called camera obscura, literally a dark chamber, as an aid in rendering proper perspective or tracing a scene. Originally, in fact, it was a dark room, with a small opening in an outside wall. An image of an illuminated object outside the room passed through the hole and was reproduced, upside Down and in small scale, on an opposite wall. Later, a light-tight box replaced the room, and a simple lens was inserted in the hole. In 1839 the Pioneer inventor Louis J. M. Daguerre developed the light-sensitive DAGUERREOTYPE, a photographic plate on which a camera obscura image could be held and fixed permanently. That same year, a French firm began production of the world's first commercial camera. In basic design, this instrument was remarkably like a camera obscura. The surface on which an artist sketched the projected image became a removable piece of ground glass, onto which the image could be brought into focus. After the photographer focused the image, the ground glass was replaced by a special wooden frame, which held the light-sensitive plate. Moving a simple, manually operated slide, or simply removing the lens cap for a time, made the exposure. Even after the early processes were speeded up sufficiently to make portraiture possible, exposures of 10 to 15 seconds were not uncommon. The absence of a film-exposure mechanism continued throughout the entire wet-plate era (see photography, HISTORY AND ART OF). The development of the gelatine dry plate in the 1870s began a revolution in camera design that was accelerated by the invention of flexible film. The dry, sensitized new materials allowed designers to make very compact instruments that were much more convenient to operate.The introduction of the Kodak camera in 1888 brought about massive, permanent changes in the world of photography. The Kodak was preloaded at the factory with sufficient film for 100 exposures. When the roll was finished, the entire camera was returned to the factory in Rochester, N.Y., where the film was developed and printed and the camera reloaded. In a single stroke, George EASTMAN had created the class of amateur photographers, those who wanted to take pictures but were unwilling to deal with the darkroom machines of the photographic process. The sales motto "You press the button, we do the rest" accurately summed up the new system. In 1900 the marketing of Eastman's Kodak Brownie #1 popularized photography even further. At a cost of $1.00 for the camera and 10 cents per roll of film, the Brownie put a basic photographic system within reach of virtually everyone.The continuing improvements of sensitized film products were paralleled by the development of more sophisticated cameras. The first optical rangefinder became available in 1916, and a very high-speed lens, the Ernostar, which had an effective aperture of f/20, appeared on a compact camera in 1924, marking the beginning of the era of natural-light candid photography.With the introduction in 1938 of the Super Kodak 620, complete automation of camera exposure systems moved a step closer to realization. A very costly snapshot camera, the Kodak 620 was the first to incorporate a completely automated method of exposure Control. Only a few of these cameras were made before world War II stopped production, but the Super Kodak 620 indicated what was possible. After the war, miniaturized electronic components made automatic exposure systems commonplace on even the most inexpensive cameras. The process of automating most camera functions was completed in the late 1970s, when the first of what have come to be known as "point and shoot" cameras appeared on the market. These cameras, so simple to use that even beginners can take satisfactory pictures, now dominate the amateur market.The evolution of camera design in the professional market tends to be a more gradual process. Professional models are available with automatic exposure-Control systems, and several advanced professional cameras offer automatic focusing.
[edit] THE PARTS OF THE CAMERA
[edit] Lens
The lens is the image-forming device on a camera. It may be composed of from one to as many as 10 or 12 elements. The first cameras were fitted with a single-element meniscus lens (a lens with one concave and one convex surface). In addition to its very low speed, this type of lens suffered from a number of inherent optical defects and it was soon replaced with greatly improved, more complicated designs. The single-element lens remained in use on inexpensive cameras, however, and within limits was capable of producing very acceptable results.The three basic types of lenses are normal, wide angle, and telephoto. The lens's focal length--the point at which light rays converge, or focus, through the lens--determines the size of the image that will be produced on the film. With a normal lens, the viewing field is approximately 50 degrees. The objects photographed appear normal in size and shape, relative to the picture's background. A camera that uses a 35-mm film will usually have a 50-mm lens for normal coverage; on a medium-format 6 x 6-cm camera, the same coverage is obtained with an 80-mm lens.In a wide-angle lens, the field of view is much wider: about 90 degrees. These lenses are used where the distance between camera and subject is limited, as in interior photography. The wide-angle lens is also to make smaller objects look larger (to give a spacious impression of a small room, for instance), or to photograph large objects from close up. Telephoto, or long-focus lenses, have a smaller field of view than a normal lens, and show an enlarged detail of the image over the same film area. Interchangeable-lens cameras offer the photographer the opportunity to select a focal length that is optimum for any given situation. In recent years, variable-focal-length, or "zoom,? lenses, have become very popular. A single lens of this type can replace many individual lenses, and offers a great convenience to the photographer.The speed, or light-gathering power, of a lens is indicated by the f number, called the aperture. The lower the f number, the faster the lens--that is, the more light it lets through. A fast lens has an aperture of at least f/2.0. As the speed increases, the cost of the lens tends to increase, since it is more costly to maintain high standards of optical correction at very high apertures.Diaphragmone of the two factors that determines correct film exposure is the amount of light allowed to pass through the lens. Mechanically reducing the aperture improves optical performance, particularly toward the edge of the picture, and increases the DEPTH OF FIELD, which is the zone of good focus. Most cameras use an iris-type diaphragm, which consists of a number of very thin metal blades. They are so mounted that by rotating a ring or moving a lever, the size of the lens opening can be varied. On automatic cameras the diaphragm is adjusted by a built-in mechanism to produce the optimum exposure over a wide range of lighting conditions.The various openings of the diaphragm--called f-stops--are stamped on the lens mounting. Each change of diaphragm opening changes the amount of light passing through the lens by a factor of 2. For example, the amount of light allowed through the lens at a setting of 2 is twice the amount allowed through the lens at a setting of 2.8. The standard diaphragm settings found on most lenses are 2, 2.8, 4, 5.6, 8, 11, 16, 22, and so on. The smallest lens opening on a lens whose f-stops end in 22 is, in fact, 22.
[edit] Shutter
The second exposure Control factor is the shutter, a mechanical device that acts as a gate, controlling the duration of time that light is allowed to pass through the lens and fall on the film. Two types of shutters are in general use. The leaf type, like the diaphragm, is made up of a number of thin metal blades that are opened and closed either by a spring-driven clockwork mechanism, or--in many recent models--by an electromechanical device. Shutters of this type usually have a maximum speed of 1/500th of a second.