Photography is the art and science of fixing images using light. For most of its history, this has usually meant using silver compounds that darken when exposed to light. With the growth of computers, photography is now often done using electronics that take millions of measurements of light colors and intensities over a focused image in order to make a record of that image.

Photography has affected many areas of science and culture. Photography is not only a ubiquitous aspect of personal life but is an integral part of the modern printing, publishing, and advertising industries, and is used extensively for scientific purposes. Motion pictures consist of a series of photographs, taken at the rate of 24 per second.

The origins of photography

Photography has been called the art of fixing a shadow. The ancient Greeks knew that a clear (though upside down) image of the outside world will be projected if one makes a tiny hole in the wall of a dark room. But no one knew how to make this image permanent. Called a camera obscura, such rooms were chiefly used as aids to drawing, and understanding perspective. After the Renaissance, when perspective became important, camera obscuras become smaller and more sophisticated. By the late eighteenth century, devices had been created that used a series of telescoping boxes and a lens to focus an image. Some even used a mirror to reflect the image upwards onto a piece of glass, making tracing images easier. Gentlemen brought small, portable camera obscuras with them when they traveled, tracing the images onto a piece of paper as a way to record their journeys. In today’s terms, by 1800 the camera had long since been invented, but no one had created film for it.

Many people were thinking about this problem, however. Some chemists had noticed that sunlight cased certain mixtures of silver nitrates to darken. By the early nineteenth century, inventors were trying to combine the camera with these chemical discoveries. The main problems included exposure times as long as eight hours, and how to make photographic images permanent. If light created photographic images, how could they be kept from further darkening once they were finished? This problem was eventually solved by using hyposulfite of soda (now called sodium thiosulfite) to remove the undarkened silver particles.

Early photographic processes

During the 1830s two different photographic processes were invented. The daguerreotype became more popular at first. It was created by Louis Jacques Mande Daguerre, who created illusions for French theater, with help from Joseph Niepce, an inventor. Their process created images on copper plates coated with a mixture of photosensitive silver compounds and iodine. Daguerre realized he could significantly shorten the exposure time by using mercury vapor to intensify, or develop, the image after a relatively short exposure. This made the process more practical, but also dangerous to the photographer since mercury is poisonous. Also, no copies could be make of daguerreotypes, making it virtually useless for purposes of reproduction.

A rival process was created in England by Fox Talbot, a scientist and mathematician. He created images on paper sensitized with alternate layers of salt and silver nitrate. Talbot also used development to bring out his image, resulting in exposure times of 30 seconds on a bright sunny day. Talbot’s process produced negative images, where light areas appear as dark, and dark areas as light. By waxing these negatives to make them clear, and putting another sheet of photographic paper under them, Talbot could make an unlimited number of positive images. This process was called a Calotype.

The daguerreotype produced a positive image with extremely fine detail and was initially more popular. The Industrial Revolution had helped create a growing middle class with money to spend, and an interest in new and better ways of doing things. Soon the area around Paris filled on weekends with families out to take portraits and landscapes. These early processes were so slow, however, that views of cities turned into ghost towns since anything moving became blurred or invisible. Portraits were ordeals for the sitter, who had sit rigidly still, often aided by armatures behind them.

Other photography processes followed quickly. Some were quite different than the previous two methods. One method, invented by French civil servant Hippoyte Bayard in 1839, used light as a bleach that lightened a piece of paper darkened with silver chloride and potassium iodide. Papers employing carbon and iron rather than silver were also used. Platinum chloride, though expensive, proved popular with serious or wealthy photographers because it rendered a fuller range of gray tones than any other process.

Because Calotype negatives were pieces of paper, prints made from them picked up the texture of the paper fibers, making the image less clear. As a result, many artists and inventors experimented with making negatives on pieces of glass. A popular method bound silver compounds in collodion, a derivative of gun cotton that became transparent and sticky when dissolved in alcohol. Negatives made using this process required a shorter exposure than many previous methods, but had to be developed while still wet. As a result, landscape photographers had to bring portable darkrooms around them. These wet collodion negatives were usually printed on a paper treated with albumen. This produced a paper with a smooth surface that could be used in large quantities and reproduced rich photographic detail.

Dry plates using silver bromide in a gelatin ground appeared in 1878. They proved popular because they were easier than wet plates, and were soon produced by companies throughout the United States and Europe. In 1883, manufacturers began putting this emulsion on celluloid, a transparent mixture of plant fibers and plastic. Because celluloid was durable and flexible, its use led to the commercial development of negative film on long rolls that could be loaded into cameras. By 1895, such film came with a paper backing so that it could be loaded outside of a darkroom. It was also far more sensitive to light than early photographic processes. These developments made photography more accessible to the average person, and lead to the widespread popularity photography has today.

Roll film also proved important to the motion picture industry because it allowed a series of photographs to be recorded sequentially on the same strip of film.

The evolution of cameras

A commercial camera based on Daguerre’s patent, came out in France in 1839. New camera designs followed, mirroring the changing uses for and technologies used in photography. Large portrait cameras, small, foldable cameras for portable use, and twin-lensed cameras for stereoscope photos came out soon after the invention of photography. Bellows cameras allowed photographers to precisely control the focus and perspective of images by moving the front and back ends of a camera, and thus the focal planes.

The single lens reflex camera, which allowed for great control over focus and a fast exposure time, was an important advance that lead toward today’s cameras. This camera used a mirror, usually set at a 45 degree angle to the lens, to allow photographers to look directly through the lens and see what the film would “see.” When the shutter opened, the mirror moved out of the way, causing the image to reach the film rather than the photographers eye. Single lens reflex cameras were in use by the 1860s, and used roll film by the 1890s. Because they were easy to use and allowed for a great degree of spontaneity, this type of camera proved popular with photojournalists, naturalists, and portrait photographers.

In early photography, exposures were made by simply taking off and replacing the lens cap. With the introduction of dry plates and film that were more sensitive to light, photographers required a more precise way of making fast exposures, and shutters became necessary. By 1900, shutters were sophisticated enough to control the aperture size and shutter speeds, which generally went from one second to 1/ 100th of a second. Lenses were improved to allow larger apertures without a loss of focus resolution. With exposure times becoming more precise, methods of precisely measuring light intensity became important. Initially, a strip of light-sensitive paper was used, then pieces of specially treated glass. The most accurate method used selenium, a light-sensitive element. Photoelectric meters based on selenium were introduced in 1932. They became smaller and less expensive, until by the 1940s, many cameras came with builtin light meters.

Cameras continued to become lighter and smaller throughout the twentieth century. The 35 millimeter roll film camera so widely used today had it’s origins in a 1913 Leitz camera designed to use leftover movie film. In 1925 Leitz introduced the Leica 35mm camera, the first to combine speed, versatility, and high image quality with lightness and ease of use. It revolutionized professional and artistic photography, while later models following its basic design did the same for amateur photography. In the years that followed, motor drives that automatically advanced film, and flashes that provided enough light in dark situations were perfected. The flash started in the mid-19th century as a device that burned a puff of magnesium powder. By 1925 it had become the flashbulb, using a magnesium wire. In the 1950s, the invention of the transistor and dry-cell batteries lead to smaller, lighter flashes, and smaller, lighter cameras as well. In all but the simplest cameras, photographic exposures are controlled by two factors: how long the shutter stays open, and the size of the hole in the lens is that admits light into the camera. This hole, called the aperture, is usually measured as a proportion of the distance from the aperture to the film divided by the actual diameter of the aperture.

Early uses of photography

Many artists were threatened by the invention of photography. Immediately after photography was first displayed to the public, the painter Paul Delaroche said, “From today, painting is dead.” In fact, many portrait painters realized that photography would steal their livelihood, and began to learn it. Ironically, many early photographic portraits are overly stiff and formal. With exposure times that could easily be half a minute, subjects had to be in poses in which they could remain motionless. As the chemistry of photography improved, exposure times shortened. The public appetite for photographs grew quickly. By the 1860s, portraits on cards presented when visiting someone, and stereographic photos, which used two photographs to create an illusion of three-dimensional space, were churned out by machines in large batches.

As with the camera obscura, one of the biggest initial uses of photography was to record travel and exotic scenery. Photographers lugged the cumbersome equipment used for wet collodion prints through Egypt, India, and the American West. At the time, Europeans were increasingly interested in exotic places (and were colonizing some of them), while most Americans got their first glimpses of a wilderness they would never see through photography. With more people living in cities and working in industrial settings, views of unspoiled nature were in demand.

England’s Francis Frith became famous for his photographs of the Middle East in the 1850s. After the end of the Civil War in 1865, photographers like Edward Muybridge and Timothy O’Sullivan did the same in the American West, often emphasizing its desolate grandeur. (Muybridge’s photographic studies of motion later helped lead to motion pictures.) The West was still an unexplored frontier, and often these photographers traveled as part of mapping expeditions. The pictures they took of geysers in 1871 and 1872 played an important role in the decision to create Yellowstone National Park, America’s first national park. Some of these photographs sold thousands of copies and became part of how Americans saw their country.

Photography as an art form

For much of its early history, people argued about whether photography should be considered art. Some, including many artists (many of whom used photographs as guides for their own work), considered photography a purely mechanical process, produced by chemicals rather than human sensibility. Others said that photography was similar to other printmaking processes like etching and lithography, and no one argued that they were not art. Still, at large expositions, curators usually hung the photographs in the science and industry sections rather than with the paintings.

An 1893 showing of photographs in Hamburg, Germany’s art museum still provoked controversy. But that was about to change. In 1902, American photographer Alfred Stieglitz formed the PhotoSecession in New York City. The group’s shows and publications firmly advocated the view that photography was art. Their magazine, Camera Works, which used high-quality engravings to reproduce photographs, proved extremely influential, showing that photography could be used for artistic purpose.

Artistic photography reflected many of the same trends as other branches of art. By the end of World War I in 1918, leading-edge photography had moved away from the soft-focus pictorialism of the nineteenth century. It became more geometric and abstract. Photographers began concentrating on choosing details that evoked situations and people. Lighter, more versatile cameras enabled photographers to take scenes of urban streets. Photography proved important in documenting the Great Depression. Many photographers concentrated on stark depictions of the downtrodden.

At the other end of the spectrum, this interest in spare but elegant depictions of everyday objects worked well with advertising, and many art photographers had careers in advertising or taking glamorous photographs for picture magazines.

Landscape photography also flourished. The best known twentieth century landscape photographer, Ansel Adams, created a system for precisely controlling the exposure and development of film to manipulate the amount of contrast in negatives.

These developments helped give photography a separate and unique identity. The Museum of Modern Art in New York formed a department of photography in 1940, showing that the medium had been accepted as an art form. Since then, art photography has thrived, with many artists making important contributions in areas ranging from landscape to street photography to surrealist photomontage.

Reproducing photographs using ink

The history of photography is intimately linked to that of mass production. Publishing was growing quickly even as photography did, fueled by the growth of cities and newspapers and increased literacy. Before photography, newspapers, magazines, and illustrated books used wood engravings to illustrate their articles. These engravings could be printed in the same presses, using the same methods and papers as the movable type used to print text. The images and type could therefore be printed on the same piece of paper at the same time. For photography to become practical for publishing, a way of cheaply reproducing photos in large editions had to be found. Some were skeptical that photography would ever prove important as an illustrative method. Most illustrations for newspaper articles were created by artists who had not seen the events they were rendering. If the imagination was so important in illustration, what need was there for the immediacy and “truthfulness” of a photograph?

Finding a method for mechanically reproducing photographs in large numbers proved difficult. By the late nineteenth century, several methods had been perfected that created beautiful reproductions. But these methods were not compatible with type or with mass production. This limited their usefulness for editions larger than a couple of hundred copies. An early method that was compatible with type, developed by Frenchman Charles Gillot around 1875, produced metal relief plates that could reproduce only lines and areas of solid tone.

The method that finally worked, called photoengraving, broke the continuous tones of a photograph down into patterns of black dots that were small enough to look like varying shades of gray when seen from a slight distance. Such dot patterns, called screens, can easily be seen in a newspaper photograph, but a photograph in the finest magazine or art book uses essentially the same method, although it may require a magnifying glass to see the dots. Although Fox Talbot had conceived of using a screen to reproduce photographs as early as 1853, a practical screening method was first patented in 1881 by Frederick E. Ives.

A photoengraving is made by coating a printing plate with light-sensitive emulsion. A negative is then printed on the plate through a grid, called a screen, which breaks the image into dots. The dots are made acid resistant, and then the plate is put into a bath of acid. This removes areas around the dots, making the dots raised. The dots can then be inked with a roller, and printed on paper using a printing press.

By the 1890s these halftones (so called because they were composed of areas that were either black or white), were appearing in magazines and books, and some newspapers. With the edition of photographs, publications evolved, changing their layouts to emphasize the powerful realism of the new medium. Magazines began sending photographers to the scenes of wars and revolutions. The resulting photographs often did not appear until days or weeks later, but the images they brought back from conflicts like the Spanish-American war and World War I fascinated the public to a degree it is hard to imagine now that wars are broadcast live on television.

The mass production of photographic images affected more than publications. Original photographs were costly. But such images became affordable when printed by a printing press. We think nothing of getting a postcard with a photograph on it, but until the invention of photoengraving, such postcards were far more expensive. Nor did an image have to be a photograph to benefit from photoengraving. A drawing or painting, whether for an art book or an advertisement, could be photographed, then printed through a screen to create a mass-reproducible image.

Halftone reproductions quickly increased in quality, partly under pressure from magazine advertisers, who wanted their products to look good. By the time World War I began in 1914, magazine reproductions were sometimes as good as less expensive modern reproductions.

These developments expanded and changed the audience for photography. To appear in a mass-circulation magazine, a photograph had to have mass appeal. Many photographers had earned a living selling photographs and postcards of local sights. This became difficult to do once photographs of the most famous international sights and monuments became widely available.

Reproductions were not the only way large audiences could see photographs, however. Many photos were shown in the nineteenth century equivalent of the slide projector. Called the magic lantern, it was often used to illustrate lectures. Early documentary photography was often shot to accompany lectures on subjects like the condition of the poor in urban slums.

Color photography

From the invention of photography, most people considered its inability to render color to be an important defect. Many early photographs had color painted on by hand in an attempt to compensate. Those attempting to solve the problem of creating color photographs took their cues from researchers into human vision, who theorized that all colors in nature are made from combinations of red, green, and blue. Thus early attempts to create color photographs centered on making three layers of transparent images, one in each of these colors, and sandwiching them together. Each layer was photographed using filters to block out other colors of light. This resulted in photographs that were foggy with poor color.

In 1904, the first practical method of creating color images, called the autochrome, was invented by the Lumiere brothers of Lyon, France. Autochromes used a layer of potato starch particles, dyed red, green, and blue, attached to a layer of silver bromide photographic emulsion, all on a plate of glass. They were expensive and required long exposures, but autochromes had significantly better color and were easier to process than previous methods. By 1916, two other color methods competed with the autochrome. All were considered imperfect, however, because they were grainy, and their color was inaccurate and changed over time. Therefore, with the publishing industry and the public hungry for color photographs, attention turned to subtractive color methods.

The subtractive color starts with white light, a mixture of all wavelengths of light, and subtracts color from it. The process uses a three-layer emulsion of yellow, cyan (a greenish-blue), and magenta (a cool pink). When subtracted from white, these colors produce their opposites: red, green and blue. Kodak released a subtractive color film for motion pictures in 1935, and in 1938 a sheet film for photography, while the German Agfa Company released its own variation in 1936. Other companies followed. By the 1940s, color negative roll film for use in 35 millimeter cameras was available.

Two methods are currently used for creating color prints. In the chromogenic method the color dyes are created when the print is processed. In the dye-bleach or dye-destruction method, the color dyes are present before processing. The dyes not needed for the image are removed by bleaching.

Snapshots: popular photography

For the first 50 years of its existence, photography was so difficult it usually dissuaded amateurs. In 1888, the first Kodak camera, aimed at the amateur market, sold for $25 (equal to about $513 in 2005 dollars). It used factory-loaded film of 100 exposures, and had to be returned to the factory for film development. In 1900, the first of the very popular Brownie cameras was released. The camera cost $1 ($22 in 2005 dollars), the film was 15 cents a roll ($3.32 in 2005 dollars), and the camera was light and simple to operate. The Brownie, and the cameras that followed it, quickly made photography a part of American family life.

Instant photographs

Instant print film, which was introduced by Polaroid in 1948, delivers finished photographs within minutes. The film consists a packet that includes film and processing chemicals, and, often, photographic paper. After exposure, the packet is pulled from the camera. In the process it gets squeezed between rollers that break open the developing and fixing chemicals, spreading them evenly across the photographic surface. Although popular with amateurs for instant snapshots, instant photographs are often used by professional photographers as well because they can be used to test how lighting and compositions look to a camera before they shoot for later development.

The uses of photography in science

Photography has became an essential component of many areas of science. Ever since the U.S. Surgeon General’s office compiled a six-volume record of Civil War wounds shortly after the war, it has played a crucial role in the study of anatomy. Photographs can provide an objective standard for defining the visual characteristics of a species of animal or a type of rock formation.

But photography can also depict things the human eye cannot see at all. Hours-long exposures taken through telescopes bring out astronomical details otherwise unseeable. Similar principals apply to some photos taken through microscopes. High-speed photography allows us to see a bullet in flight. In 1932, the existence of neutrons was proven using photographs, as was the existence of viruses in 1942. The dwarf planet Pluto was discovered through comparisons of photographic maps taken through telescopes.

X rays taken at hospitals are really photographs taken with x-ray light rather than visible light. Similarly,

KEY TERMS

Aperture— The size of the opening in a camera lens through which light comes.

Camera obscura— A dark room or box with a light-admitting hole that projects an image of the scene outside.

Negative— Images with tonal values reversed, so that objects appear dark. Usually negatives are film from which positive prints are made.

Photoengraving— A process through which the continuous tones of a photograph are converted into black and white dots that can be reproduced on a printing press.

Single lens reflex camera— A camera that uses a single lens and a mirror to admit light for the film and for the photographer to use to focus on.

infrared and ultra-violet photographs, which detect invisible wavelengths of light, can be used for numerous purposes including astronomy and medicine, and the detection of cracks in pipes or heat loss from buildings. In all these cases, evidence and experimental results can be easily exchanged between scientists using photographs.

Photography enters the computer age

Like many other things, photography has been deeply affected by computers. Photographs now can be taken by cameras that do not even use film. Instead they use electronic sensors to measure light intensities and translate them into digital code that can be read by a computer. The computer translates the digital code into a grid of points, each assigned a number that represents a color (or level of gray for black-and-white photos). The process is similar to the way in which music is translated into digital form when it is put on a compact disc.

Once digitized, images can be manipulated by computers in many of the same ways they can be changed while making prints in a darkroom. But because digital images are essentially a series of numbers, they can be manipulated in other ways as well. For publishing purposes, digital images can be converted to halftones by the computer, making the process easier and faster. As a result, many newspapers, magazines and advertising firms have switched to digital photography for increasing amounts of their work.

See also Photocopying; Scanners, digital.