photography

The word photography comes from two ancient Greek words: photo, for “light,” and graph, for “drawing.” “Drawing with light” is a way of describing photography. When a photograph is made, light or some other form of radiant energy, such as X rays, is used to record a picture of an object or scene on a light-sensitive surface. Early photographs were called sun pictures, because sunlight itself was used to create the image.

Humans have been creating images at least since the cave paintings of some 20,000 years ago. With the invention of photography, a realistic image that would have taken a skilled artist hours or even days to draw could be recorded in exact detail within a fraction of a second. Today, photography has become a powerful means of communication and a mode of visual expression that touches human life in many ways. For example, photography has become popular as a means of crystallizing memories.

Most of the billions of photographs taken today are snapshots—casual records to document personal events such as vacations, birthdays, and weddings. Photographs are used extensively by newspapers, magazines, books, and television to convey information and advertise products and services.

Practical applications of photography are found in nearly every human endeavor from astronomy to medical diagnosis to industrial quality control. Photography extends human vision into the realm of objects that are invisible because they are too small or too distant, or events that occur too rapidly for the naked eye to detect. A camera can be used in locations too dangerous for humans. Photographs can also be objects of art that explore the human condition and provide aesthetic pleasure. For millions of people, photography is a satisfying hobby or a rewarding career.

Photography in Communication

Since its invention in 1839, photography's unique powers of visual description have been used to record, report, and inform. People prefer to see things with their own eyes, but when this is impossible the camera can often serve the same purpose almost as well. It is not true that photographs never lie—they can be falsified and manipulated. Nevertheless, a photograph can carry a strong measure of authenticity and conviction. As a nonverbal means of communication, photography can surmount the barriers of language and communicate through universal visual symbols.

Photographs are well suited for use in the mass media. Today they are reproduced by the billions, and they can be found everywhere: in the pages of newspapers, magazines, books, catalogs, and brochures; on display in billboards, shop windows, and posters; broadcast over television; and organized into slide shows and film strips.

In photography's early days some of its most eagerly sought images were those brought back by explorers and travelers. These would satisfy people's curiosity about distant places like China, Egypt, and the American West. That same kind of curiosity exists today. People are fascinated with photographs of the surface of the moon, the landscape of Mars, and the appearance of other planets in the solar system.

Photographs in the mass-communication media have made the faces of political leaders, popular entertainers, and other celebrities familiar to the public. When a newsworthy event occurs photojournalists are there to record it. Photojournalists sometimes spend months covering a story. The result of such labor is often a powerful, revealing picture essay that probes far beneath the surface of events.

Photography is also essential to the advertising industry. In efforts to sell a product, attractive photographs of the item are used. Photography is also widely used in education and training within the academic world, industry, and the armed services.

Photographs are also often used in attempts to sway public opinion. Governments, political parties, and special-interest groups have long used the graphic representation and emotional impact of photographs to further their causes. Such use may result in destructive propaganda, such as that of the Nazis during the Third Reich. Photography can also help to bring about desirable changes. Photographs of the Yellowstone region were instrumental in Congress's decision to establish that area as a national park, and photographs of child laborers helped to bring about legislation protecting children from exploitation.

Photography in Science and Technology

• The camera helps astronauts share experiences with the world. This spectacular view of the cloudy …

Photography has many practical applications in industry, medicine, astronomy, archaeology, scientific research, the graphic arts, law enforcement, and many aspects of contemporary life. Aerial photography, for example, is used to make maps and contour charts, to study the Earth and its oceans, and to help forecast the weather. Cameras aboard satellites and space vehicles have photographed the Earth, as well as the moon, the sun, and the other planets. Astronomers use photography to study galaxies in deep space and to analyze the composition of stars through spectroscopy. New photographic applications are constantly being developed.

Industrial and scientific researchers rely heavily on photography. For example, objects too small to be seen with the naked eye can be clearly recorded in photomicrographs—photographic images made through optical or electron microscopes. (See also microscope.) Ultrahigh-speed electronic-flash photography can record events that happen too fast to be seen by the unaided eye. With exposures as brief as one-millionth of a second, an electronic-flash photograph can “freeze” a bullet traveling at 15,000 miles per hour (24,000 kilometers per hour).

Photography is used extensively in medicine and dentistry for research, teaching, and as a day-to-day diagnostic tool. Especially important are films made with X-rays, which reveal the body's inner structure (see X rays).

Another major consumer of photographic materials is the graphic arts industry, which employs photography in several steps of the printing process. Most type used today is composed photographically, and photography is also essential to offset printing, the most commonly used method of reproducing words and pictures in books, magazines, and newspapers. This printed page was created by the use of photography. (See also printing.)

The world of miniaturized electronic equipment would not be possible without photography. A photographic etching process called photoresist is used to produce the extremely small but precisely printed microelectronic chips that are the “brains” of modern electronic hardware (see microprocessor).

Photography by ultraviolet light has a number of applications, including the detection of forged or altered documents, the identification of chemical compounds, and the examination of bacterial colonies. Infrared photography can, in effect, “see in the dark.” It can record invisible infrared illumination. It has significant military and surveillance uses and is also employed in medical and astronomical photography. (See also light; radiation.)

Photography as Art

Today photography is widely recognized as a fine art. Photographs are displayed in art museums, prized by collectors, discussed by critics, and studied in art history courses. Because of the special nature of photography, however, this was not always the case. In the early days of photography some people considered the medium something of a poor relation to the older, established visual arts, such as drawing and painting.

The arguments stemmed from the fact that a camera is a mechanical instrument. Because the mechanical procedure of taking a picture is automatic, detractors claimed that photography required no coordination of hand and eye and none of the manual skills essential to drawing and painting. They also argued that photography required no creativity or imagination because the photographic subject was “ready-made” and did not require manipulation or control by the photographer.

A camera, no matter how many automatic features it may have, is a lifeless piece of equipment until a person uses it. It then becomes a uniquely responsive tool—an extension of the photographer's eye and mind. A photographer creates a picture by a process of selection. Photographers looking through the camera's viewfinder must decide what to include and what to exclude from the scene. They select the distance from which to take the picture and the precise angle that best suits their purpose. They select the instant in which to trip the shutter. This decision may require hours of patient waiting until the light is exactly right or it may be a split-second decision, but the photographer's sense of timing is always crucial.

Photographers can expand or flatten perspective by the use of certain lenses. They can freeze motion or record it as a blur, depending on their choice of shutter speed. They can create an infinite number of lighting effects with flashes or floodlights. They can alter the tonal values or colors in a picture by their choice of film and filters. These are only a few of the controls available to a photographer when taking a picture. Later, in the darkroom, many additional choices are available.

One of the best ways to view artistic photographs is to visit museums. Today most art museums include photography exhibitions, and many have a photography department and a permanent collection of photographic prints. This is a relatively recent development. The first international exhibition of artistic photography took place in Vienna, Austria, in 1891, and in 1910 the Albright Gallery in Buffalo, N.Y., held a large exhibition of work by contemporary photographers. This exhibit was sponsored by a group of photographers, including Alfred Stieglitz and Edward Steichen, known as the Photo-Secession group. It was not until 1940, however, that a museum—the Museum of Modern Art in New York City—established a separate department of photography.

The Metropolitan Museum of Art, also in New York City, has long considered photography a branch of the field of graphic arts. The International Museum of Photography at George Eastman House in Rochester, N.Y., has one of the world's greatest historical collections. In Washington, D.C., the Library of Congress, the National Archives, and the Smithsonian Institution also house extensive photographic collections.

Today photography collections exist in art museums throughout the world and in some colleges and universities. There has also been a growth of photographic galleries and art galleries that maintain a photographic department. Major events for collectors, gallery owners, and art dealers are the auctions held periodically by major art dealers. Here, rare or sought-after photographs may command thousands of dollars.

The Hobby of Photography

Taking photographs is a popular activity. In the United States more than 90 percent of all families own one or more cameras, and the nation's amateur photographers take more than 12 billion pictures annually. The sale of photographic equipment, supplies, and photofinishing services to this segment of the population amounts to about 9 billion dollars per year.

Many amateur photographers are snapshooters who use the camera to satisfy the universal desire to have a personal pictorial record of friends, family, and events. However, some 4 ¹/₂ million persons are seriously interested in photography as a hobby. They usually own more advanced cameras and additional photographic equipment such as extra lenses, tripods, electronic flash units, and filters. Often they have some interest in doing their own darkroom work.

With today's automated cameras, fast films, and simplified processing methods, photography has become a rewarding hobby that offers many levels of satisfaction. As a visual activity it stimulates the photographer to see things in a new way. A successful photographer learns to see in a clear, sensitive, and perceptive manner.

Photography is an active hobby that can be enjoyed in connection with such interests and activities as nature study, gardening, or travel. Camera clubs can be found in many communities, schools, and colleges. Members often exchange information, share and discuss their work, and listen to guest lecturers. Workshops and short courses on photography are also available.

Photography as a Career

Few vocations offer a greater variety of opportunities than does photography. Some professional photographers work as full-time employees, some run their own businesses, and some free-lance.

Commercial photographers who work for advertising agencies photograph products for advertising promotions, brochures, catalogs, and other purposes. Their work can range from simple, straightforward shots to elaborate studio setups. Some commercial photographers may specialize in certain product areas, such as fashion, food, or hardware.

Portrait photographers take pictures of people, singly or in groups, for display in homes and offices. Wedding photographers take formal portraits of the bride, groom, and wedding party and also provide a candid coverage of the ceremony.

Industry uses photographers to photograph plants, manufacturing processes, products, workers, and executives. Photographers who work on annual reports must produce pictures that are visually interesting and that show the corporation in a favorable light.

Photojournalists are reporters with a camera, photographing current events and people for newspapers, magazines, and the electronic media. This physically demanding, and sometimes dangerous, work requires both journalistic and photographic skills. Today most successful photojournalists are graduates of a journalism school that has a photojournalism department or offers photojournalism courses. Many photographers enter the field professionally after gaining experience as amateurs. They may spend time as assistants or apprentices before striking out on their own.

There are a variety of opportunities for specialists and technicians in photography. For example, operators are needed to run the processing equipment for the giant photofinishing industry, and highly skilled darkroom technicians are needed by custom labs that cater to professionals.

The Camera and Its Parts

Every camera, reduced to its most basic components, is simply a lightproof box with an opening at one end where light can be admitted and a device at the other end to hold film. The shape of the body and the operating features, however, vary with different types of cameras.

Except for pinhole cameras, all modern cameras have a lens mounted over the light-admitting hole, making it possible to take sharper pictures with less light. A mechanical device called a shutter controls the amount of time that light is admitted into the camera. Some shutters are spring-operated; others are electronically regulated. The shutter release is a push button or lever that activates the shutter.

• Camera viewing systems let the photographer know how the subject will look on the film after the …

All cameras have some kind of viewing system: a way for the photographer to see the field of view framed by the lens. There are three principal types of viewing systems: the viewfinder, the single-lens reflex, and the twin-lens reflex. The simplest and easiest to operate are viewfinder and small single-lens reflex cameras. The viewfinder is usually a simple lens system; light from the object passes through a viewfinder to the eye and through a different lens to the film. Single-lens reflex cameras have separate viewing and picture-taking systems. During viewing, a mirror reflects the light entering the camera upward through a prism that turns the image right-side-up. When a picture is taken, the mirror flips up to allow the light to strike the film. Twin-lens reflex cameras have fixed mirrors and two lenses, one for the viewing and another for creating the image on the film. The lenses are coupled mechanically so that they are in focus simultaneously.

The purpose of the film advance is to unroll the film, pull it across the back of the camera, and wind it up on a take-up spool. Each individual picture area is called a frame. Depending on the camera, film may be advanced by hand, by a power winder, or by the camera automatically after each exposure.

Camera Lenses

The purpose of a camera lens is to transmit rays of light into the camera and focus them to form a sharp image on the film. With the simplest cameras no manual focusing adjustment is required. All objects, from a few feet in front of the camera to a great distance away, will be recorded in a reasonably sharp image. More advanced cameras, however, have a focusing control that adjusts the lens so that objects at a selected distance from the camera will be in focus on the film.

With some cameras the photographer focuses on the subject simply by estimating the distance to the subject and setting a focusing scale on the camera marked in numbers or distance symbols. With rangefinder cameras the photographer lines up two out-of-register images of the subject. With reflex cameras and those with a ground-glass back, the lens is adjusted until the image on the viewing screen appears in focus.

Some cameras are equipped with a microchip system that focuses by the use of optical, infrared, or ultrasonic signals. The photographer activates the system by placing a focusing spot, visible in the viewfinder, over the subject and depressing the shutter release partway. The system then measures the camera-to-subject distance and automatically adjusts the lens accordingly.

Types and properties of lenses

The simplest type of lens is the meniscus, a single, curved piece of optical glass or molded plastic. All lenses suffer somewhat from aberrations, or imperfections. These can be corrected to some extent, and image sharpness and quality considerably improved, by mounting two or more separate lens elements as a unit. The more expensive, complex lenses may have a dozen or more such elements. In most lenses of good quality these elements are coated with a thin layer of magnesium fluoride or some other substance to reduce internal reflections.

• Each kind of lens is named for its focal length, the distance from the optical center of the lens …

• A 50-millimeter lens reproduces the photographer's view.

• A wide-angle 35-millimeter lens provides a wide field of view and smaller images of the subject.

Lenses have fixed focal lengths. The focal length of a lens is the distance from the optical center of the lens to the plane (in this case, the film) behind it where the sharpest image is formed when the lens is focused on a distant object. The distant object is said to be at infinity. The focal length of a lens is sometimes given in inches, but more commonly it is given in millimeters (mm) or centimeters (cm). (See also optics.)

For ordinary photographic work, cameras are equipped with a lens of “standard” or “normal” focal length. This length is approximately equal to the diagonal of the film frame. Normal lenses do not usually match the film diagonal exactly. For example, the diagonal of a standard 35-mm negative frame is 43.2 mm, but lenses with a focal length of anywhere from 38 mm to 58 mm are normal for this format.

Some cameras, including most 35-mm single-lens reflex cameras (SLRs), allow the photographer to change lenses. Although a lens of normal focal length may be satisfactory much of the time, there are occasions when a lens of shorter or longer focal length may be desirable.

A lens that has a focal length substantially shorter than that of a normal lens is called a wide-angle lens. It provides a smaller image of the subject but covers a wider field of view. It is often used when the photographer wants to include more of the original scene in the picture but is unable to move farther back, as, for example, when taking a picture in a small room. A wide-angle lens can also give a picture an effect of exaggerated perspective and great depth. For 35-mm cameras, wide-angle lenses are available with focal lengths ranging from 35 mm to an ultrawide 15 mm.

Lenses with a focal length that is substantially longer than normal are called long-focus lenses or telephoto lenses. Technically these are not identical. Long-focus lenses are bulky; telephoto lenses are constructed to be more compact. In practice, however, long-focus lenses of all types are indiscriminately called telephoto. Such lenses provide a larger image of the subject but cover a narrower field of view than do lenses of shorter focal length. Because telephoto lenses can be used to magnify a distant subject, they are frequently used in wildlife photography. In portraiture, an intermediate telephoto lens can minimize perspective distortion, and in landscape photography a telephoto lens can flatten a scene to achieve a more two-dimensional effect.

With a conventional lens the focal length is fixed, but a zoom lens provides the photographer with a continuous range of focal lengths. There are wide-angle zooms, telephoto zooms, and versatile zooms that go from wide-angle through normal focal lengths into the telephoto range.

Macro and micro lenses are specially designed for extreme close-up photography. Fish-eye lenses are special ultrawide-angle lenses that give a distorted “fishbowl” image of a scene.

Lens aperture

• Depth of field, the distance in front of and behind a sharply focused subject in which other things …

Adjustable cameras are equipped with an iris diaphragm, a device located in or near the lens and consisting of thin overlapping leaves that fold together to create a hole of continuously variable size. In this way the aperture, or lens opening, can be adjusted to admit more or less light as required. The diaphragm is usually marked with a series of settings called stops, which are designated by f-numbers, such as f/5.6 or f/8. The f-number expresses the ratio of focal length to aperture. The larger the number, the smaller the aperture.

To “stop down” or “close down one stop” is to set the diaphragm control at the next smaller marked stop, for instance from f/4 to f/5.6, or from f/8 to f/11. This reduces the amount of light admitted by one half.

To “open up one stop” means to set the diaphragm control at the next wider aperture: f/11 to f/8, or f/8 to f/5.6, for example. This doubles the amount of light admitted.

Depth of field

• In a scene of great depth the use of an aperture of f2 allows either foreground subjects or …

The lens aperture not only controls the amount of light entering the camera, it also affects another fundamental aspect of the photograph—depth of field. Depth of field is the range in front of and behind a sharply focused subject in which details also look sharp in the final photographic image. It depends on lens aperture, the focused distance, and the focal length of the lens. A small lens aperture, great camera-to-subject distance, and short focal length result in greater depth of field.

• In a scene of great depth, if the aperture is decreased to f16, both the foreground and background …

Sometimes photographers may want as much depth of field as possible in order to record objects sharply from nearby to infinity. In that case they would stop down to the smallest aperture practical. In other circumstances they might prefer a shallow depth of field to make a focused subject stand out clearly against a soft, blurred background. In this case they would use a wide lens aperture.

The Shutter

The purpose of the shutter is to regulate the length of time that light is admitted to the camera during an exposure. Shutters come in various kinds.

Types of shutters

One basic type of shutter that is found on many simple and compact 35-mm cameras is composed of overlapping leaves and is located between the front and rear elements of the lens. The leaves open and close to admit light. This is called a leaf or between-lens shutter. A second type, found on 35-mm interchangeable-lens cameras, is the focal-plane shutter, located in the back of the camera just in front of the film. With this type of shutter, two opaque blinds, or curtains, sweep in front of the film. The curtains are adjusted to create slits of various widths.

Most cameras provide a method of adjusting shutter speed, either by mechanical or electronic means. The shutter speeds may range from a full second to as little as ¹/_4,000 of a second. A typical range of marked shutter speeds for an average 35-mm SLR camera might be as follows: 1, ¹/₂, ¹/₄, ¹/₈, ¹/₁₅, ¹/₃₀, ¹/₆₀, ¹/₁₂₅, ¹/₅₀₀, ¹/_1,000. Note that each marked setting is approximately twice as fast as the preceding one and half as fast as the following one.

Many cameras also have either a T (for time) or B (for bulb or brief) setting, which allows the photographer to make longer exposures than those provided by the marked shutter-speed settings. This feature is useful for taking photographs after dark and for creating special effects. Many cameras are also equipped with a self-timer. Photographers can place the camera on a tripod or other support, activate the self-timer, and be allowed several seconds to put themselves in the picture before the shutter is tripped.

Shutter speed and motion

• The aperture and shutter-speed combinations shown below allow the same amount of light to enter the …

Shutter speed determines how effectively a moving object can be “stopped”—that is, how sharply it can be reproduced without blurring or streaking in the final image. With a fast shutter speed, the shutter is opened only briefly and the moving object has little time to change its position before the exposure is completed. With a slow shutter speed, on the other hand, the shutter remains open for a relatively long time. Thus the faster the shutter speed, the sharper a moving object will appear on the final image, and the slower the shutter speed, the more blurred the object will appear.

This principle also holds true for camera motion. The faster the shutter speed, the less noticeable any shaking of the camera will be in the final photograph. This is particularly relevant when holding a camera while taking a picture with a telephoto lens. The lens magnifies the effect of camera motion, so that if the camera is moved even slightly when the picture is taken, the final image will appear blurred. To avoid this, many photographers select a shutter speed of no slower than ¹/₁₂₅ of a second for hand-held shooting, though some photographers are successful with a speed of ¹/₆₀ or even ¹/₃₀ of a second.

The camera shutter must stop the subject's apparent speed or the speed at which its image moves across the film, regardless of the subject's actual motion through space. Factors such as distance, direction of motion, and focal length of the lens must all be taken into consideration. Generally, the closer the moving subject is to the camera, the greater its apparent motion will be. Thus, if they wish to get a sharp image, most photographers avoid extreme close-ups of moving subjects.

In action pictures, the focal length also plays a role in the final image. A lens with a long focal length will magnify the image and its apparent motion. Apparent motion is greatest when the subject is moving at right angles across the line of sight, and it is least when the subject is moving directly toward or away from the camera. Much of the time photographers wish to stop all motion for a sharp, clear image. Sometimes, however, they use slower shutter speeds to produce expressive blurs of motion.

Films and Filters

Film is the basic material of photography. It consists of a light-sensitive emulsion—microscopic crystals of silver halide suspended in gelatin—that is coated onto a flexible support of plastic. Color film also includes various dyes, couplers, and other chemical ingredients.

Film is supplied in a wide variety of formats, or dimensions, to fit the many types of cameras available. Most 35-mm film has perforated edges and is preloaded into cartridges, but it is also available in bulk for those who prefer to load the film themselves. Roll film is a nonperforated film supplied in strips wound on spools for a number of formats. Film loaded into drop-in cartridges is provided for Instamatic and Pocket Instamatic cameras. A circular disk of film is used in disk cameras. For medium- and large-format professional cameras, individual sheets of film and film packs are available.

A film's speed refers to its sensitivity to light. A fast, or highly light-sensitive, film can produce a satisfactory image with less light than that required by a slower film. Film speed is designated by an exposure index, established by the International Standards Organization (ISO). Films of ISO 100 and less are considered relatively slow, those in the 200 range are medium speed, those around 400 are high speed, and those of 800, 1,000, or higher are ultrahigh speed.

The faster the film, the grainier its image tends to be. Grain—caused by the clumping together of silver particles during film processing—appears as a mottling or pattern of distinct grains. Naturally, the more an image is enlarged, the more evident the grain becomes. Thus, for best image quality, most photographers follow the general rule, “choose a film that is fast enough for your needs but no faster.”

Black-and-white films

Virtually all black-and-white films for general use are panchromatic—equally sensitive (or approximately so) to the light of all colors. The monochromatic tonal values of a subject photographed on panchromatic film will match those of the subject quite closely. Orthochromatic film was once common but is now used mostly for specialized professional applications. It is relatively “blind” to the red and orange end of the light spectrum. Infrared film is sensitive to invisible infrared radiation. When used with an infrared filter it has many applications, including medical and legal photography, photographing in the dark, and creating special visual effects. (See also light.)

Color films

There are two basic types of color film in general use: color reversal and color negative. When processed, a color reversal film produces a positive transparency in which the colors match those of the original subject. It can be viewed by the transmitted light of a hand viewer or light box, or it can be mounted as a color slide for projection.

A color negative film, on the other hand, produces a color negative in which the colors are complementary to those of the subject. This negative is used to make color prints and enlargements for viewing with reflected light.

So-called “white” light can vary considerably from bluish to yellowish. The human eye adapts to these variations easily, and so most persons are unaware of differences in lighting. Color film, however, cannot adjust to such differences. It is balanced, or matched, to provide the most natural-looking colors with the use of one particular light source. For example, a daylight-type color film is designed to be used with daylight, which is bluish, or with an electronic flash, which creates a bluish light. Another film, Type A film, is balanced for the much more yellowish illumination given by a photoflood bulb. Tungsten, or Type B, film is matched to the light of tungsten-halogen bulbs. For the most natural-looking results, photographers use color film with the light source for which it is balanced, or they use the proper conversion filter (see “Filters for Color Film” in this article).

Instant, or self-processing, film is available for taking both color and black-and-white photographs. In this type of film, the chemicals necessary to develop the latent image on the emulsion and produce a finished print are included in the film itself. The chemicals are automatically activated when the film is removed from the camera. Development may take place very rapidly—within a matter of seconds—depending on the particular make of film and the ambient temperature.

Filters for black-and-white film

Filters are transparent colored squares or disks placed in front of the camera lens to modify the light passing to the film. A filter is a kind of screen that allows light of its own color to pass but partially or totally absorbs the light of other colors. Filters are useful accessories for black-and-white photography because they allow the photographer to control the tonal values of a picture. By using the appropriate filter, a photographer can reproduce a certain color or colors in darker or lighter tones, depending on the desired effect.

A red filter, for instance, transmits red light and blocks blue and green. Thus red objects will be relatively dark on the negative. Because of the nature of negatives, however, the red will reproduce as a lighter shade of gray in the print, while the blue and green objects will appear darker.

Generally, photographers select filters according to two basic principles. To render a color lighter, they use a filter of the same color. To render a color darker, they use a filter of a complementary color.

For most black-and-white photography with panchromatic film, no filters are necessary. Sometimes, however, they can be useful in creating certain effects. For example, photographers may wish to darken the tone of the blue sky and emphasize the white clouds. They may use a medium-yellow or light-green filter or, for a more dramatic effect, they may select a red filter.

Photographers sometimes use filters to distinguish colors or to make a certain color stand out. Red blossoms and green foliage, for example, would both be recorded as similar shades of gray when photographed without special filters. The same photograph taken with a red filter, however, would accentuate the blossoms by reproducing them in a lighter shade of gray against a darker background.

Because most filters reduce the amount of light that reaches the film, the exposure time must be increased when using them. The amount of increased exposure time required is expressed as a filter factor. For example, a medium-yellow filter in daylight with panchromatic film has a factor of 2 (usually written as 2X). This means that the length of exposure time must be doubled.

Filters for color film

When taking pictures in color, photographers may choose to use filters for one of two basic reasons. One is to achieve a normal rendition of color by adapting a color film to a light source for which it is not balanced. The second is to modify the colors in a picture in order to achieve a special effect or create a particular mood.

A useful filter for outdoor color photography is the skylight filter. It is tinted a pale pink and has a slightly warming effect. It helps reduce the bluish cast that may be found in color pictures made in open shade under a blue sky or in overcast conditions.

Conversion and light-balancing filters are used to adapt film balanced for one type of light for use with another kind of light. They may be used to save film, for instance, when a photographer has a partly finished roll of daylight film in the camera and must photograph with photoflood or tungsten-halogen illumination.

Color compensating (CC) filters are supplied in a wide range of colors and densities. They are most frequently used to make fine corrections in color during exposure. They may also be used in color printing. Experimental photographers use them to create unusual color effects.

Polarizing filters darken a blue sky in the final image without affecting other colors. They also reduce reflections from shiny nonmetallic surfaces such as glass, water, or varnished wood. They may be used in black-and-white as well as in color photography.

Neutral density filters are colorless filters that are available in various degrees of density. They are used to reduce the amount of light reaching the film without otherwise affecting the colors or values in the picture.

A great variety of special-effects filters are available for photographic experimentation. They produce rainbow color fragmentation, star-burst effects, multiple images, soft-focus renditions, and other effects.

Making a Photograph

There are a number of steps in the photographic process. Once the film has been selected and loaded into the camera, the photographer decides what to photograph and when to trip the shutter. At this moment the film is exposed. Light momentarily enters the dark interior of the camera, causing a chemical reaction in the microscopic particles of light-sensitive silver halide on the film emulsion. The particles react variably to the different intensities of light reflected from different parts of the subject framed in the lens. The darker areas of the subject reflect less light and cause less penetration into the emulsion than the lighter areas do, and so an invisible “latent” image is formed on the film emulsion.

When the exposed film is ready to be developed, it is removed from the camera and processed in a series of chemical baths to form the photographic negative. Finally a print is made from the negative.

Exposing the Film

• Film exposure depends on the duration and intensity of the light and is controlled by the shutter …

• An underexposed negative has few details in the shadow areas.

• An overexposed negative is generally dark and lacks detail in bright areas.

Exposure is a function of the total amount of light that strikes the film when a picture is taken. To make a photograph of good quality, just the right amount of light is required. A film that receives too much light will be overexposed, and the negative will be too dark. Prints made from this type of negative will appear pale and washed out. If the film receives too little light it will be underexposed. The resulting negative will be too light, and prints made from it will appear dark and muddy and will lack detail in areas of shadow. Achieving the correct exposure, therefore, is crucial.

Exposure is generally determined by two factors: the duration of the light, which is controlled by the shutter, and the brightness, or intensity, of the light, which is controlled by the size of the lens opening, or aperture. Different combinations of shutter speeds and apertures can produce identical exposures. A shutter speed of ¹/₁₂₅ of a second at an aperture of f/5.6, for example, results in the same exposure as a shutter speed of ¹/₂₅₀ of a second at f/4. The shutter speed is reduced by half, but the aperture is opened up one stop to double the intensity of the light. If, instead, the shutter speed were changed to ¹/₆₀ of a second, the duration of exposure would be doubled, so that the aperture would have to be closed down by one stop, to f/8, to reduce the brightness by one half.

The selection of the combination of shutter speed and aperture depends on the photographer's needs. Is a fast shutter speed required to stop action or to reduce camera motion when using a telephoto lens? Or is a small aperture needed to give greater depth of field? Sometimes a compromise is satisfactory.

The simplest cameras have a single shutter speed and a lens with a fixed opening designed to give adequate exposure in brightly lit outdoor scenes. More advanced cameras are adjustable, providing a number of shutter-speed and lens-aperture settings. These may be set manually based on experience, following an exposure guide, or more accurately by a light- measuring device called an exposure, or light, meter.

One such meter, the reflected-light exposure meter, measures the intensity of the light reflected from the subject toward the camera. A second type, the incident-light exposure meter, measures the intensity of the light falling on the subject or scene. When used properly both can produce reliable results.

Many cameras are equipped with a built-in reflected-light meter system that automatically provides the correct exposure. The system is set manually to match the ISO number of the film. In DX-compatible cameras the light meter system is set automatically when the camera is loaded with DX-coded film.

Some automatic exposure systems provide aperture priority, a system that allows the photographer to choose the aperture and then automatically sets the shutter speed that will result in the correct exposure. Other cameras have a shutter priority system, which allows the photographer to choose the shutter speed and then automatically selects the aperture.

With a programmed exposure system, the camera selects both lens aperture and shutter speed, compromising between depth of field and the ability to stop motion. In some cameras the photographer may have a choice of programmed modes, including one that favors stop-action ability and another for greater depth of field.

For photographs of the highest technical quality, accurate exposure is crucial. In order to ensure image quality, however, films have a degree of exposure latitude, or a range of exposures that will produce an acceptable image. The degree of exposure latitude varies with the type of film. It is substantial with most color and black-and-white negative films, which may tolerate as much as two or more stops overexposure or underexposure and still yield satisfactory results.

Color transparency film, however, usually has a narrow exposure latitude. It is particularly sensitive to overexposure and requires exact exposure for good results. When using transparency film, photographers sometimes bracket their exposures. In this procedure, a photographer makes one exposure at the estimated best exposure settings, and then makes additional exposures at one or one half f-stop intervals above and below the first aperture setting. The photographer can then select the best result as the final picture.

Lighting

Successful photographers are always aware of the light. Light is both the energy that implants the image on the film and an essential visual component of the photograph. It can dramatize, glamorize, and evoke subtle shades of mood. It can conceal defects or reveal the unvarnished truth. It can be used to draw the eye to some details and downplay others.

In addition to the duration and intensity of the light, which determine the amount of exposure, the creative photographer is also concerned with the quality of the light. Does it create distinct highlights and sharp-edged shadows, as bright sunlight does? Or is it soft and diffuse, with subdued highlights and open shadows, like the light of an overcast day?

• In indoor photography, the direction of the light source affects the final image. Front lighting …

• Front lighting.

• Top lighting causes dark shadows in the eyes.

• Top lighting.

• Bottom lighting is used to give the subject a haunting aura.

• Bottom lighting.

• Side lighting casts illumination on half of the subject, modeling him in three-dimensional form.

• Side lighting.

• For portraits, a reflector is used with side lighting to show detail in the shadows.

• Portrait lighting.

• Backlighting can create a silhouette effect.

• Back lighting.

The direction of the light is equally important. Front light, coming from behind the camera, tends to flatten the subject by providing even illumination with a minimum of defining shadows. Sidelighting creates shadows that sculpt the subject and reveal texture. Backlighting, or lighting that comes from behind the subject, can create silhouette effects.

Photographers have a wide variety of light sources at their disposal. The sun itself remains the most richly varied and versatile source of outdoor lighting. Photographers can work with the blazing light of the noonday sun, the silvery illumination of a foggy day, the soft lighting of an overcast sky, or the dramatic hues and shadows of a sunset.

Using fast film, photographers can take pictures indoors—by normal indoor lighting or by sunlight entering through a door or window—or outdoors at night by the artificial glow of street lights. Sometimes, however, an adjustable or portable artificial light source is required. One such source is the photoflood, which is powered by ordinary house current and provides a continuous source of illumination over its lifetime. At one time flashbulbs were widely used. These disposable bulbs produce a bright momentary flash of light that is synchronized with the opening of the camera's shutter. Today they have been largely supplanted by the electronic flash.

Electronic flash units are available in a range of sizes from miniature versions built into small cameras to large, powerful studio units. These too must be synchronized with the camera's shutter, but they provide many thousands of flashes without the need of replacement. Specialized units having a very brief flash duration are used to stop fast action.

Darkroom Techniques

From minilabs to huge laboratories, a variety of processing services are available to both amateur and professional photographers. Many photographers, however, prefer to develop their film and also make prints and enlargements themselves. They find it a satisfying activity that provides many possibilities for creativity and self-expression.

The first step in mastering darkroom procedures is to develop black-and-white film and make black-and-white prints. Such processing requires a minimum of equipment, and the basic skills are not difficult to acquire. After learning the fundamentals of black-and-white processing, the photographer is better prepared to make the next step to color processing.

Processing Black-and-White Film

To make the latent image formed on an emulsion visible, the exposed film must be processed in a series of chemical solutions. First a solution called the developer changes the exposed particles of silver halide into black, metallic silver. Wherever a great deal of light reached the emulsion when the film was exposed there will be a heavy concentration of metallic silver. Wherever little light reached the emulsion there will be few grains of metallic silver.

Next the film is processed in a stop bath (or short-stop), which halts the action of the developer after development is complete. Another chemical solution, called the fixer, removes the unexposed silver particles from the film so that only the metallic silver remains. Finally, the film is washed in water until it is free of residual chemicals. The result is a permanent negative in which the tonal values of the original subject are reversed: the areas that were dark on the subject are recorded as light or transparent, and areas that were light are recorded as dark.

Darkroom Equipment

Although many amateur photographers prefer a photographic darkroom, it is not necessary for processing black-and-white film. With the so-called time-and-temperature method, a daylight tank can be used. The tank must be loaded with film in total darkness, but once the tank top is in place the remainder of the processing can be completed in ordinary room light. The processing is monitored with the aid of a clock or timer and a thermometer.

Daylight developing tanks are made of plastic or stainless steel and consist of three parts: the cylindrical tank itself, a reel upon which the film is rolled, and a lightproof cover through which solutions can be poured. Other equipment includes a number of graduated flasks for mixing and pouring, a stirring rod, funnel, dip-type darkroom thermometer, timer, fine-textured cellulose photographic sponges for wiping the film, and metal clips for hanging the film to dry.

Packaged processing chemicals are available either in the form of powder or as liquid concentrates called stock solutions. Either kind must be mixed with water to make a working solution. For complete film processing it is necessary to have working solutions of developer, short-stop, and fixer.

Developing the Film

• Three chemical solutions, kept at a constant temperature (a), are used to develop film: a …

• The reel is placed into the developing tank, the tank is filled with developer and agitated (c), …

• The tank agitation process is repeated using the stop bath (e) and fixer (f).

• Water is run over the reel (g) and the developed film is unwound from the reel and hung for drying …

In order to produce a properly developed negative in a daylight tank, the temperature and duration of the process must be carefully regulated. Generally, a temperature of 68° F (20° C) is recommended for black-and-white film developers and other processing solutions. Depending on the film and developer combination, recommended developing times may vary from a few to several minutes. Photographers often use a timer with a bell or buzzer at this stage.

During development the solution is periodically agitated—gently sloshed around—to ensure uniform development and to prevent streaks from forming on the film. Experienced photographers usually agitate the solution for ten seconds every two minutes.

The Stop Bath

After development is complete, the film is rinsed in a stop bath. This halts the chemical action of the developer and prevents contamination of the following solution. Packaged stop baths are available, but many photographers prepare their own using a mixture of acetic acid and water.

The Fixing Bath

The next step in processing is to place the film in a fixing bath. This dissolves any undeveloped particles of silver halide and leaves only the developed grains of black, metallic silver. A commonly used fixer is a solution of hypo mixed with water. (“Hypo” is short for hyposulfite of soda, the obsolete name for sodium thiosulphate.)

Depending on the hypo's freshness, such a fixing bath may take ten minutes or longer to be fully effective. There are a number of rapid or high-speed fixers available, however, that require only a couple of minutes or less.

After fixing, the film is thoroughly washed to remove any residual chemicals and to ensure the permanence of the negative. The excess water is then gently wiped off with photographic sponges and the film is hung from a clip to dry.

Storing Solutions

Some photographic solutions are best prepared in small quantities for one-time use, after which they are discarded. Others can be used a number of times. Still others can be used indefinitely if they are stored under the proper conditions. Generally, solutions are stored in dark, well-capped bottles in a cool place. To avoid cross-contamination of solutions, all equipment is thoroughly washed before and after use.

Making Prints and Enlargements

Printing is both a skill and a highly creative activity. The print is the climax in the long chain of events that began when the photographer first visualized the picture. For many photographers, making a fine print is one of the most challenging and satisfying aspects of their hobby or work.

A print is made by passing light through a negative onto sensitized paper. Because the least light passes through the darkest parts of the negative, those areas are the lightest in the print. Similarly, the most light passes through the transparent areas of the negative, so that they are the darkest areas of the print. Thus the tonal values of the negative are reversed to create a positive image resembling the original subject.

The exposed paper is then developed in chemical solutions in much the same way in which the film was processed. Printmaking can be carried out by the subdued illumination of a darkroom safelight. A yellow-green safelight is generally used for most graded printing and enlarging papers because it does not affect their emulsion; a light-amber safelight is generally used for variable-contrast papers.

• A contact print is made by placing the negative in direct contact with printing paper. The chemical …

• The negatives and paper are then positioned in the frame with their emulsion sides facing one …

• The paper is immersed in the developer for one minute (e) and the stop bath for five to ten seconds …

• The paper then sits in the fixing bath for about ten minutes (g), and the print is rinsed in …

• A test strip is made to determine the desired exposure time for the final print. Sections exposed …

A contact print is one made by placing the negative in direct contact with the printing paper. Contact prints can be made with a printing frame, which resembles a picture frame with glass. The negative is placed on the glass with its emulsion side up, and the paper is placed on the negative with its emulsion side down. Then a spring-held back is locked into place. The print is exposed by a light held several inches above the frame for five to 15 seconds. The length of time required depends on the density of the negative and the type and grade of paper used. If the print is too dark, the exposure time was too long; if the print is too light, the time was too short. One or two test prints are usually made to determine the correct exposure for the final print. Contact printers are also available that contain their own light source.

The exposed print is then processed in the developer solution. Contact paper is usually left in the solution for about one minute. The tray is gently rocked or the print held by a corner and moved back and forth. The print is then placed in a tray containing a stop bath, where it is agitated continuously for five or ten seconds. Next, it is placed in a fixing bath for about ten minutes, then washed in running water at 65° F to 70° F (18° C to 21° C) for an hour. Finally, the print is dried.

Types of Printing Paper

A great many types of printing paper are available. Some are slow and are designed for contact printing; others are considerably faster and are suitable for making enlargements, though they can be used for contact printing as well.

Contrast is a fundamental characteristic of printing papers. It refers to the density range—the difference between the whitest white and the blackest black that the paper can supply—and the number of distinct shades of gray that it can produce between the two extremes. A low-contrast paper can produce a relatively large number of these intermediate tones and can provide the best print from a negative with strong contrasts, or extremely light and extremely dark areas. A high-contrast paper has a shorter scale of intermediate tones and is used to add sparkle to a “flat,” or low-contrast, negative.

Paper contrast is designated by grade from 0 to 5, though not all papers are available in all grades. No. 0 grade paper is the lowest contrast, or softest. No. 5 grade paper is the highest contrast, or hardest. There are also variable-contrast papers whose contrast can be regulated by using special filters. Such filters offer an advantage because they eliminate the need to stock several grades of paper.

Making an Enlargement

• An enlarger is a device that can project a magnified image of the negative onto printing paper.

An enlarger is a device that projects the magnified image of a negative onto a piece of printing paper. Enlargers vary in size, construction, and type of light source, but the basic procedures for using them are similar. The first step in making an enlargement is placing a clean, dust-free negative, emulsion side down, into the enlarger's holder. The safelight is turned on and the room lights are turned off. The enlarger is then turned on and its lens diaphragm fully opened. The enlarger head is raised or lowered until the image corresponds to the desired print size.

Sharp focus is essential in making a good enlargement. A target sheet of blank enlarging paper is often placed in the easel to make focusing easier. An easy-to-see detail is selected and the focusing control is rocked back and forth until the sharpest image is found. As an aid, some photographers use a focusing magnifier, which magnifies a small portion of the projected image. Some enlargers focus automatically to keep the image sharp at all times.

Next the enlarger lens is stopped down to an intermediate aperture setting, such as f/8, and the enlarger is turned off. A sheet of enlarging paper is placed in the easel. The enlarger light is turned on to expose the paper for the desired length of time. The exposed print is then processed in open trays in the same manner as a contact print.

Improving Enlargements

Enlarging allows the photographer to improve the technical quality of the picture and to exercise creative control. Cropping, for example, or printing only part of the total picture area, offers almost unlimited possibilities. Cropping enables the photographer to eliminate unwanted or distracting details, to emphasize the most important area of a picture, to adjust the shape of a print, or to level tilted horizon lines.

Dodging is a method used to hold back light from areas within a picture that would print too dark if given the same exposure as the overall print. An opaque device called a dodging tool is placed between the enlarger lens and the printing paper to cast a shadow over the area and is kept in constant motion to prevent hard edges from forming. The opposite result is obtained by burning in, a method of providing additional exposure to selected areas.

Color in the Darkroom

Many amateur photographers process their own color film and make color prints and enlargements. Although the procedure is somewhat more demanding and requires stricter temperature control, anyone with some skill in black-and-white processing can learn to process color film.

Most reversal color transparency films can be processed by the photographer. Materials are available for making color enlargements directly from these transparencies. Color negative film can also be processed by the photographer, and a variety of color printing papers are available. To achieve natural looking colors in a color print, special color filters must be used during exposure. Thus a basic understanding of light and color is necessary. There are also kits for color processing that contain the necessary chemicals, materials, and complete instructions.

The History of Photography

• Still Life, daguerreotype by Louis-Jacques-Mandé Daguerre, 1837; …

Photography is generally considered to have had its birth in 1839, when the Frenchman Louis-Jacques-Mandé Daguerre first revealed his photographic process to the public. The roots of photography, however, were developed much earlier.

The camera obscura, for example, had been known since ancient times. Meaning literally “darkened room,” it was originally a room completely sealed from light except for a very small hole in one wall. An image of the outside world—houses, trees, and even people—could be projected, upside down and reversed right-to-left, onto a wall or white screen placed opposite the opening.

Later the camera obscura was reduced in size until it became a small portable box. It was equipped with a lens and a mirror at a 45-degree angle, which reflected the image upward and focused it on a viewing screen. This was a great aid to artists in making sketches on location, but there was not yet a way to capture directly and permanently the camera obscura's images.

Scientists had known for some time that certain silver compounds, then called silver salts and now named silver halides, would turn black when exposed to light. In England, Thomas Wedgwood, son of the famous potter, experimented with one of these silver halides, silver nitrate, to produce silhouettes. The pictures, however, were not permanent and turned black unless stored in the dark.

In the early 19th century Joseph-Nicéphore Niépce of France began to experiment with a then novel graphic arts printing method called lithography. His work led him to further experiments using bitumen, a resinous substance, and oil of lavender. Niépce developed a process whereby he could permanently capture the image of a camera obscura. In 1827 he made the world's first surviving photograph from the window of a country home in France. It required an exposure, in bright sunlight, of eight hours.

Meanwhile, Daguerre was experimenting with silver-iodide images. Hearing of Niépce's work, he contacted him, and in 1829 they became partners. During the next few years Daguerre, with Niépce's help, worked out the process that came to be known as daguerreotypy. It was a complicated procedure that demanded considerable skill. A silver-coated sheet of copper was sensitized by treatment with iodine vapor, forming a coating of light-sensitive silver iodide. The daguerreotype plate was exposed in the camera and then developed in mercury fumes at temperatures of about 120° F (50° C). The exposed areas absorbed mercury atoms and highlighted the image. Finally, the image was fixed by washing it in hypo.

The daguerreotype's silver image was capable of rendering exquisitely fine detail. It was a single-image process, however—each exposure produced only one picture, incapable of reproduction. Furthermore, the process required exposures of up to several minutes even in bright sunlight, thus constraining its subjects to absolute motionlessness.

In spite of this, the process immediately became popular, particularly for portraiture. Daguerreotypy rapidly developed into a thriving business in England and the United States. Superb portraits were made by such daguerreotypists as Albert Sands Southworth and Josiah Johnson Hawes in Boston. The French excelled in landscapes and cityscapes.

In 1840 a much faster lens was designed by the Hungarian József Petzval and manufactured by Peter Voigtlander in Austria. At about the same time a method was discovered that increased considerably the light sensitivity of the daguerreotype plate. This method involved a second fuming with chlorine or bromine before exposure.

In England William Henry Fox Talbot had developed his own method of photography at about the same time that Daguerre was inventing the daguerreotype. Talbot impregnated paper with silver nitrate or silver chloride. When exposed in a camera, the sensitized paper turned black where light struck it, creating a negative image of the subject. This was made permanent by fixing with hypo.

To achieve a positive image, a contact print could be made by placing the negative over a second piece of sensitized paper and exposing the combination to bright light. Talbot's “photogenic drawings,” as he called them, lacked the daguerreotype's sharp detail and brilliance but offered the great advantage that from one negative a large number of positive prints could be made. His process, known as the calotype, and later talbotype, process, was at first less popular than the daguerreotype. Most later methods of photography, however, have evolved from Talbot's work. His was the first negative-positive process.

In 1851 F. Scott Archer of England made public his wet-collodion process, in which he used a glass plate coated with collodion as a base for light-sensitive silver halides. His procedure, requiring seven steps, was only slightly less complicated than the daguerreotype process, but it was considerably less expensive. It also produced a negative that was much sharper than that of the calotype method. Soon the wet-collodion process had supplanted both the older techniques as the most widely used process of photography. A major inconvenience of the wet-collodion method was the fact that the plate was light-sensitive only as long as it remained wet; after it dried it lost its sensitivity. Thus plates had to be used almost immediately after preparation. Since these plates could not be prepared and stockpiled in advance, a portable darkroom, in the form of a tent, wagon, or railway car, for instance, had to accompany the camera wherever it went.

Despite this drawback, intrepid photographers made photographs in remote locations and under the most dangerous conditions, creating images that are still considered masterpieces of the medium. Roger Fenton of England became a pioneer in war photography with his camp scenes from the Crimean War. Mathew Brady and his team of associates, including Alexander Gardner, Timothy O'Sullivan, and James Gibson, achieved a magnificent documentation of the American Civil War (see Brady, Mathew). After the war, Gardner, O'Sullivan, and William Henry Jackson photographed the opening of the American West and provided a lasting record of its awesome scenery.

In the mid-1850s the tintype, an inexpensive imitation of the daguerreotype, was patented by the American Hamilton L. Smith. It was, in fact, not made of tin, but of a very thin sheet of iron specially treated and coated with a light-sensitive emulsion. The tintype became very popular for personal portraits.

Stereoscopic photography also became extremely popular during this period. A special stereo camera with two lenses was used to take two simultaneous photographs of the subject from viewpoints separated by about the same distance as a pair of human eyes. When the resulting pictures were viewed through a special viewing device, they merged to create a three-dimensional image. Stereoscopic images of travel pictures, landscapes, important events, and comic pictorial short stories were sold by the millions.

In 1871 a new era in photography began when an amateur English photographer, R.L. Maddox, produced a successful dry plate that retained its light-sensitivity after drying. Other inventors followed his lead, and soon fast, reliable dry plates, much more convenient to use than the earlier wet plates, became available at a reasonable cost.

The dry plate represented a turning point in photography. With the availability of faster emulsions, photographers could make exposures on the order of a fraction of a second, and for the first time the camera was freed from a stand.

A new breed of smaller, more portable cameras proliferated, variously called hand cameras or detective cameras. With fast-dry plates, and later with film, photography could be practiced by amateurs without the need for professional training or equipment.

As shutter speeds became fast enough to stop motion, a fascinating new world of vision unfolded. Especially notable was the work of the Englishman Eadweard Muybridge, who pioneered work in the field of motion-picture projection (see Muybridge, Eadweard). He photographed sequences of human and animal motion that fascinated artists, anatomists, and the general public alike. (See also motion pictures.)

In the 1880s the American George Eastman put flexible roll film on the market, and in 1889 he introduced the first Kodak camera with the slogan, “You push the button and we do the rest.” Thus was launched the era of mass-market photography.

Meanwhile, gifted photographers were exploring the new medium from a creative standpoint, attempting to discover its potential and limitations and define photography as an art form. At first it was only natural that photographers should take their inspiration from painting. Oscar G. Rejlander and Henry Peach Robinson, for example, working in England, used various darkroom techniques, tricks, and manipulations to produce staged photographs that frankly imitated the sentimental, moralistic paintings of the era.

The English amateur Julia Margaret Cameron did not take up photography until she was almost 50. Nevertheless, she imposed her own personal style on the medium and produced a collection of extraordinary portraits that were soft focused but impassioned. Another English amateur, Peter Henry Emerson, developed a strong pictorial style of his own and advanced detailed theories of photographic aesthetics that had a considerable influence on late 19th-century art photographers. The American Alfred Stieglitz, a distinguished photographer in his own right, began to promote photography as a fine art in the pages of his illustrated quarterly Camera Work, in his Photo-Secession group, and later in his 291 gallery (see Stieglitz, Alfred).

A new generation of photographers emerged who were determined to turn away from the pictorial style and its soft-focus, painterly effects to a more direct, unmanipulated, and sharply focused approach. This new form was called “straight” photography, and its practitioners believed it most truly expressed photography's unique vision. One pioneer was Paul Strand, whose photographs reveal a deep awareness of what he called “the spirit of place.” The movement's most famous figures were Edward Weston and his younger associate Ansel Adams (see Adams, Ansel; Strand, Paul; Weston, Edward).

• Young girl operating machinery in a North Carolina textile mill, photograph by Lewis Hine, 1908.

From the late 19th century on, many photographers began to use the medium to document social problems. A Danish immigrant to the United States, Jacob A. Riis, became a crusader with a camera, revealing the plight of the urban poor. To illuminate the interior of slum tenements he often used the recent German invention, flashpowder, a highly explosive mixture that ignited in a blaze of white light. Later, another American, Lewis Hine, took up photography to draw the public's attention to such social ills as the abuses of child labor. During the Great Depression of the 1930s a large-scale program in documentary photography was established in the United States. Organized by Roy Stryker, talented photographers such as Walker Evans, Dorothea Lange, and Ben Shahn compiled an unsurpassed portrait of the nation (see Evans, Walker; Lange, Dorothea; Riis, Jacob; Shahn, Ben).

Technical developments in photographic equipment continued. Shortly before World War I, Oskar Barnack in Germany, working as a technician for the E. Leitz company, invented a miniature camera that used perforated strips of 35-mm film. It was first introduced to the market in 1924 as the Leica. Many dismissed it as a mere toy ill-equipped for serious work, but others were delighted by its compact size and ability to make up to 36 exposures in rapid succession. Continual improvement over the years established the 35-mm camera, especially in its single-lens reflex form, as the dominant camera for both professionals and serious amateurs.

In 1930 the highly dangerous flashpowder was largely supplanted by flashbulbs. At the Massachusetts Institute of Technology, experiments with gas discharge flash tubes led to the development of the electronic flash, which could produce astonishing images made at exposures as brief as ¹/_10,000 second. Although they originally required expensive and cumbersome equipment, electronic flash units became so miniaturized that they could be built into a pocket camera.

Color had been the dream of photographers since the medium of photography was invented. The foundation for color photography had been established in 1859 by James Clerk Maxwell, a Scottish physicist who demonstrated that all colors could be reduced to combinations of three primary colors. Many attempts were made to apply this principle to photography, but it was not until many decades later that inventors were successful.

In 1907 two Frenchmen, the brothers Auguste and Louis Lumière, placed on the market their autochrome glass plates. These plates were coated with starch grains that were dyed red, green, and blue, over which was a second coating of panchromatic emulsion. After 1930 the much sharper “integral tripack” color films were introduced, which used dyes rather than grains. Kodachrome in particular became famed for its sharpness and rich colors. These new films were positive transparency films, but soon color negative films were introduced. Today color negative film constitutes the vast majority of film sold to amateur photographers in the United States.

Instant, or self-processing, photography was invented by the American Edwin H. Land. He introduced the Polaroid Land camera in 1947, and a color version became available in 1963.

• Untitled rayograph of feather, glass pestle, and sheet of glass, silver gelatin print by Man Ray, …

In art photography, a new class of photographers began to conduct experiments in cameraless abstractions, images produced directly on film without the use of a camera. Principal among these photographers were the Hungarian-born László Moholy-Nagy, a teacher in the Bauhaus school in Germany, and the American Man Ray (see Moholy-Nagy, László). In the years before World War II the rise of picture magazines in Europe provided a showcase for such talented photographers as Martin Munkacsi, André Kertész, and Ilse Bing. Other photographers—notably Raoul Hausmann, John Heartfield, and George Grosz—used their cameras to make outspoken political and social protests in the form of photomontages, or collages of powerful, often savage images.

Picture-oriented, mass-market magazines such as Life and Look flourished during the post–World War II decades, bringing the work of many outstanding photographers to the public. Margaret Bourke-White, an innovative photojournalist during the war, and W. Eugene Smith became famous for their powerful picture essays (see Bourke-White, Margaret). Henri Cartier-Bresson exhibited unprecedented precision in his perception and capture of the significant moment, and Richard Avedon and Irving Penn explored new frontiers of fashion photography (see Cartier-Bresson, Henri). The advent of television caused a decline in such picture-oriented magazines, but photography as an art form continues to thrive.

Increasingly, cameras are becoming more automated and electronically controlled. Virtually every step, from film loading to rewinding, has become automatic. In the mid-1990s the technology of photography was combined with computer technology to produce a digital camera, with which it was possible to take a picture that could then be accessed and manipulated through a desktop computer.

In addition to the camera itself, other components of the photographic process changed as well. In the early 1990s a new type of film was introduced. Known as a dry film because it did not require the usual chemical processing, it was coated with a selenium-based compound instead of the usual silver halide and was recyclable.

In spite of the increasing sophistication of the equipment, however, the photographer's eye remains all-important. Photography remains a unique human act.

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