Photography Is A Technique Of Producing Permanent Images On Sensitized Surfaces By Means Of The Photochemical Action Of Light

Photography is a technique of producing permanent images on sensitized surfaces by means of the photochemical action of light or other forms of radiant energy. In today’s society, photography plays important roles as an information medium, as a tool in science and technology, and as an art form, and it is also a popular hobby. It is essential at every level of business and industry, being used in advertising, documentation, photojournalism, and many other ways. Scientific research, ranging from the study of outer space to the study of the world of subatomic particles, relies heavily on photography as a tool. In the 19th century, photography was the domain of a few professionals because it required large cameras and glass photographic plates.

During the first decades of the 20th century, however, with the introduction of roll film and the box camera, it came within the reach of the public as a whole. Today the industry offers amateur and professional photographers a large variety of cameras and accessories. See also Motion Picture. The Camera and Its Accessories Modern cameras operate on the basic principle of the camera obscura (see Historical Development, below). Light passing through a tiny hole, or aperture, into an otherwise lightproof box casts an image on the surface opposite the aperture. The addition of a lens sharpens the image, and film makes possible a fixed, reproducible image.

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The camera is the mechanism by which film can be exposed in a controlled manner. Although they differ in structural details, modern cameras consist of four basic components: body, shutter, diaphragm, and lens. Located in the body is a lightproof chamber in which film is held and exposed. Also in the body, located opposite the film and behind the lens, are the diaphragm and shutter. The lens, which is affixed to the front of the body, is actually a 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 may be fixed in place or set in a movable mount. Objects located at various distances from the camera can be brought into sharp focus by adjusting the distance between the lens and the film. The diaphragm, a circular aperture behind the lens, operates in conjunction with the shutter to admit light into the lighttight chamber. This opening may be fixed, as in many amateur cameras, or it may be adjustable. Adjustable diaphragms are composed of overlapping strips of metal or plastic that, when spread apart, form an opening of the same diameter as the lens; when meshed together, they form a small opening behind the center of the lens.

The aperture openings correspond to numerical settings, called f-stops, on the camera or the lens. The shutter, a spring-activated mechanical device, keeps light from entering the camera except during the interval of exposure. Most modern cameras have focal-plane or leaf shutters. Some older amateur cameras use a drop-blade shutter, consisting of a hinged piece that, when released, pulls across the diaphragm opening and exposes the film for about 1/30th of a second. In the leaf shutter, at the moment of exposure, a cluster of meshed blades springs apart to uncover the full lens aperture and then springs shut. The focal-plane shutter consists of a black shade with a variable-size slit across its width. When released, the shade moves quickly across the film, exposing it progressively as the slit moves. Most modern cameras also have some sort of viewing system or viewfinder to enable the photographer to see, through the lens of the camera, the scene being photographed.

Single-lens reflex cameras all incorporate this design feature, and almost all general-use cameras have some form of focusing system as well as a film-advance mechanism. Camera Designs Cameras come in a variety of configurations and sizes. The first cameras, pinhole cameras, had no lens. The flow of light was controlled simply by blocking the pinhole. The first camera in general use, the box camera, consists of a wooden or plastic box with a simple lens and a drop-blade shutter at one end and a holder for roll film at the other.

The box camera is equipped with a simple viewfinder that 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 by professionals, is the camera closest in design to early cameras that is still in widespread use. Despite the unique capability of the view camera, however, other camera types, because of their greater versatility, are more commonly used by both amateurs and professionals. Chief among these are the single- lens reflex (SLR), twin-lens reflex (TLR), and rangefinder. Most SLR and rangefinder cameras use the 35-millimeter film format, while most TLR as well as some SLR and rangefinder cameras use medium-format filmthat is, size 120 or 220. View Cameras View cameras are generally larger and heavier than medium- and small-format cameras and are most often used for studio, landscape, and architectural photography.

These cameras use large-format films that produce either negatives or transparencies with far greater detail and sharpness than smaller format film. View cameras have a metal or wood base with a geared track on which two metal standards ride, one in front and one in back, connected by a bellows. The front standard contains the lens and shutter; the rear holds a framed ground-glass panel, in front of which the film holder is inserted. The body configuration of the 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 Cameras Rangefinder cameras have a viewfinder through which the photographer sees and frames the subject or scene.

The viewfinder does not, however, show the scene through the lens but instead closely approximates what the lens would record. This situation, in which the point of view of the lens does not 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 photographer to frame a scene or subject with certainty. Reflex Cameras Reflex cameras, both the SLR and the TLR types, are equipped with mirrors that reflect in the viewfinder the scene to be photographed. The twin-lens reflex is box-shaped, with a viewfinder consisting of a horizontal ground-glass screen located at the top of the camera.

Mounted vertically on the front panel of the camera are two lenses, one for taking photographs and the other for viewing. The lenses are coupled, so that focusing one automatically focuses the other. The image formed by the upper, or viewing, lens is reflected to the viewing screen by a fixed mirror mounted at a 45-degree angle. The photographer focuses the camera and adjusts the composition while looking at the screen. The image formed by the lower lens is focused on the film at the back of the camera. Like rangefinder cameras, TLRs are subject to parallax.

In the SLR type of reflex camera, a single lens is used for both viewing the scene and taking the photograph. A hinged mirror situated between the lens and the film reflects the image formed by the lens through a five-sided prism and onto a ground-glass screen on top of the camera. At the moment the shutter is opened, a spring automatically pulls the mirror out of the path between lens and film. Because of the prism, the image recorded on the film is almost exactly that which the camera lens sees, without any parallax effects. Most SLRs are precision instruments equipped with focal-plane shutters. Many have automatic exposure-control features and built-in light meters.

Most modern SLRs have electronically triggered shutters. Apertures, too, may be electronically actuated or they may be adjusted manually. Increasingly, camera manufacturers produce SLRs with automatic focusing, an innovation originally reserved for amateur cameras. Minolta’s Maxxum series, Canon’s EOS series, and Nikon’s advanced professional camera, the F-4, all have autofocus capability and are completely electronic. Central processing units (CPUs) control the electronic functions in these cameras (see Microprocessor).

Minolta’s Maxxum 7000i has software cards that, when inserted in a slot on the side of the camera, expand the camera’s capabilities (see Computer). Autofocus cameras use electronics and a CPU to sample automatically the distance between camera and subject and to determine the optimum exposure level. Most autofocus cameras bounce either an infrared light beam or ultrasonic (sonar) waves off the subject to determine distance and set the focus. Some cameras, including Canon’s EOS and Nikon’s SLRs, use passive autofocus systems. Instead of emitting waves or beams, these cameras automatically adjust the focus of the lens until sensors detect the area of maximum contrast in a rectangular target at the center of the focusing screen. Design Comparisons Of the three most widely used designs, the SLR is the most popular among both professionals and amateurs.

Its greatest advantage is that the image seen through the viewfinder is virtually identical with that on which the lens is focused. In addition, the SLR is generally easy and fast to operate and comes with a greater variety of interchangeable lenses and accessories than the other two camera types. The rangefinder camera, previously used by photojournalists because of its compact size and ease of operation (compared with the big, slow 4-by-5 inch press cameras used by an earlier generation) has largely been replaced by the SLR. Rangefinder cameras, however, have a simpler optical system with fewer moving parts and are thus inherently more sturdy than SLRs, in addition to being quieter and weighing less. For these reasons, some photographers, mainly professionals, continue to use them. Compared with the other two designs, TLRs have a relatively slow focusing system.

As with rangefinder cameras, fewer interchangeable lenses are available, yet the TLR remains popular. The camera produces larger negatives than most SLRs and rangefinders, an advantage when fine detail must be rendered in the final image. In recognition of this, some manufacturersincluding Hasselblad, Mamiya, Bronica, and Rolleihave combined the convenience of the SLR with the medium-film format, further reducing the market for the TLR. Some cameras are designed primarily for amateurs: They are simple to operate, and they produce photographs acceptable to the average snapshot photographer. Many point-and-shoot amateur cameras now employ sophisticated technology, with features such as autofocus and exposure-control systems that simplify the process of taking pictures and almost guarantee good-quality photos. Camera Lenses The lens is as important a part of a camera as the body.

Lenses are referred to in generic terms as wide-angle, normal, and telephoto. The three terms refer to the focal length of the lens, which is customarily measured in millimeters. Focal length is defined as the distance from the center of the lens to the image it forms when the lens is set at infinity. In practice, focal length affects the field of view, magnification, and depth of field of a lens. Cameras used by professional photographers and serious amateurs are designed to accept all three lens types interchangeably.

In 35-millimeter photography, lenses with focal lengths from 20 to 35 millimeters are considered wide-angle lenses. They provide greater depth of field and encompass a larger field (or angle) of view but provide relatively low magnification. Extreme wide-angle, or fish-eye, lenses provide fields of view of 180 degrees or more. A 6-millimeter fish-eye lens made by Nikon has a 220-degree field of view that produces a circular image on film, rather than the normal rectangular or square image. Lenses with focal lengths from 45 to 55 millimeters are referred to as normal lenses because they produce an image that approximates the field of view of the human eye. Lenses with longer focal lengths, called telephoto lenses, constrict the field of view and decrease the depth of field while greatly magnifying the image.

For a 35-millimeter camera, lenses with focal lengths of 85 millimeters or more are considered telephoto. A fourth generic lens type, the zoom lens, is designed to have a variable focal length, which can be adjusted continuously between two fixed limits. Zoom lenses are especially useful in conjunction with single-lens reflex cameras, for which they allow continuous control of image scale. Developing and Printing The latent image on film becomes visible through the process called developingthe application of certain chemical solutions to transform the film into a negative. The process in which this negative is used to create a positive image is called printing, and the image is called a print. Film is developed by treating it with a weak reducing alkaline chemical called the developing solution, or developer.

This solution reactivates the process begun by the action of light when the film was exposed. The effect is to reduce further the silver-halide crystals in which metallic silver had already formed, so that large grains of silver form around the minute particles that make up the latent image. As large particles of silver begin forming, a visible image becomes apparent on the film. The thickness and density of silver deposited in each area depend on the amount of light received by the area during exposure. In order to arrest the action of the developer, the film is then bathed in a weakly acidic solution, which neutralizes the alkaline developer.

After rinsing, the negative image is fixed: Residual silver-halide crystals are removed, and remaining metallic silver particles are stabilized. The chemical solution used for fixing, commonly referred to as hypo, or fixer, is usually sodium thiosulfate, although potassium or ammonium thiosulfate may also be used. Fixer remover, or hypo clearing agent, is then used to rinse any remaining fixer from the film. Film must be rinsed thoroughly in water, as residual fixer tends to destroy negatives with time. Finally, bathing the processed film in a washing aid promotes uniform drying and prevents formation of water spots and streaks.

Printing is done by either of two methods: contact or projection. The contact method is used when prints of exactly the same size as the negative are desired. They are made by placing the emulsion side of the negative in contact with the printing material and exposing the two together under a source of light. In projection printing, the negative is fir …

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