Photograph

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Photograph

The term"photography"comes from theGreek words photos (light)and graphia(writing). Earlyphotographersthought ofphotography aswriting with light.

A photograph is an image made by light on a photosensitive (sensitive to light) material and then reproduced permanently on paper (the print) by a subsequent exposure to light. Photography is possible because light that is reflected back from the subject reacts with the silver halide crystals (silver compounds) on the film to form an image of the subject.

Waiting to be invented

Although early scientists knew that light can change silver compounds into silver metal (one of the basic ingredients for making photographs), photography was not invented until the early nineteenth century. As early as 1500, the first crude camera called the camera obscura was used by artists as a tracing tool. The camera obscura, or dark chamber, was a dark room in which light that was reflected off an external object passed through a small hole in the room and was projected as an upside-down image on the opposite wall. The camera obscura was later converted to a portable closet and then to a small box. In 1685, German monk Johann Zahn (1641–1707) outfitted the camera obscura with lenses, constructing a model of today's camera. Even then, no one thought to combine the two ingredients to produce photographs.

In 1727, Johann Schulze (1684–1744), a German professor of anatomy, discovered that silver salts turned dark when exposed to sunlight. He made images on silver salts but could not keep the images permanent. In 1777, Swedish chemist Carl Scheele (1742–1786) found that an image resulting from silver salts that had been exposed to light could be made permanent by washing away the unexposed salt with ammonia. However, no one put these two discoveries to use. Around 1800, English botanist Thomas Wedgwood (1771–1805) came close to inventing photography. To record specimens he had collected outdoors, such as leaves, he put them against leather that had been coated with silver salts and then exposed them to sunlight. The areas surrounding the object turned dark, leaving an outline of the object. Although Wedgwood is considered the first photographer, he could not keep his "sun pictures" from eventually darkening. Unfortunately, he had not heard of Scheele's discovery.

First photographs

It took more than twenty years for the first modern photographs to finally be produced. The first known permanent photograph was made by Joseph Nicéphore Niépce (1765–1833) in 1826. The French chemist coated a pewter plate with bitumen of Judea, a substance used in printmaking. He then put the plate in a camera obscura that was set on an upstairs windowsill in his home and exposed the plate for eight hours. (See sidebar.)

During the 1830s, French inventor Louis Jacques Mandé Daguerre (1787–1851) experimented with several photographic processes, some done in collaboration with Niépce. After the latter died in 1833, Daguerre went on to invent what became known as daguerreotype. He coated a copper plate with silver and exposed it to iodine vapor to form silver iodide. He developed the image with mercury vapor, and then made it permanent using a table salt bath. Daguerre's invention needed camera exposures of thirty minutes. In 1839, the French government bought the rights to the daguerreotype and shared the new invention with the world.

At around the same time in England, William Henry Fox Talbot (1800–1877) was developing a paper negative called calotype, from which any number of positive prints could be made. The calotype was light-sensitized with silver chloride. Unlike daguerreotype, the calotype had an exposure time of about one minute or less. In 1844, Talbot produced the first book in the world illustrated with photographs, calling it The Pencil of Nature. To "fix" (make permanent) his photographs, Talbot used the discovery of another Englishman, John Herschel (1792–1871), an astronomer and a chemist. About twenty years earlier in 1819, Herschel had found that hyposulfate could be used as a fixing agent to dissolve the unexposed silver salts. Like Talbot, he had used light-sensitive paper to produce photographs. In fact, Herschel was responsible for coining the terms "negative" and "positive." Although German astronomer Johann von Maedler (1794–1874) first used the the term "photography," from the Greek words photos (light) and graphia (writing) in 1839, Herschel is usually credited with coining the term because he first used it at a public lecture.

Wet plate, dry plate

In early 1851, British sculptor Frederick Archer (1813–1857) introduced the collodion negative, also called the wet plate. A polished sheet of glass was coated with collodion, or nitrated cotton, that had been dissolved in a solution of ether and alcohol. The glass was then immersed in silver compounds. The plate had to be used while still wet, although exposure took just two to three seconds, and the resulting prints were rich in details. Since the wet-plate negative required immediate development, photographers took portable dark-rooms with them. Interestingly, despite this troublesome method of taking pictures, photographers everywhere in the world used the collodion process for more than twenty years, recording places never seen before, as well as such important events as the American Civil War (1861–65).

The introduction of the dry plate in 1871 not only freed photographers from having to take their darkrooms on location but also from having to use a tripod for cameras because the exposure time was as short as one-twenty-fifth of a second. English physician Richard Maddox (1816–1902) started using gelatin to bind silver salts on sheets of glass. Once the plates dried, they could be used any time and did not require immediate processing. During processing, the gelatin expanded to let the developing and fixing chemicals act on the negative silver salts without dislodging them from the film. Gelatin emulsion could also be used to coat print papers. In the past, negatives had to be the same size as the final print. With the new type of papers, the dry-plate negatives could be made smaller, and the desired print sizes were made using an enlarger with an artificial light source. Maddox's dry-plate photography is the ancestor of today's photography.

Photography made easy

American George Eastman (1854–1932) learned about Maddox's dry-plate process and experimented with his own gelatin emulsions. By 1881, he was mass-producing dry plates for amateur photographers. In 1885, Eastman introduced a roll film wound around a spool with enough film for taking several pictures. Eastman's Kodak portable box camera, introduced in 1888, made photography quite practical. The camera contained a roll film for one hundred pictures. After all the film was exposed, the user mailed the camera to Eastman's company, which developed the film, made prints, and returned the camera reloaded with a fresh roll of film. The following year Eastman improved on his film by putting his gelatin-silver halide crystal emulsion onto celluloid, a transparent mixture of plant fibers and plastic. Both film processing and camera equipment have improved since Eastman's inventions, but the basic principles of photography have remained the same.

Raw Materials

Film

Modern film is made by coating light-sensitive ingredients onto a transparent (see-through) material, such as acetate. Film manufacture is a complicated process because a typical roll of film may contain twenty or more different layers that make up a thickness of less than one-thousandth of an inch.

REVISING HISTORY: THE OLDEST PHOTOGRAPH

Joseph Nicéphore Niépce is credited with taking what is considered the world's first photograph. The 1826 photograph has been on display at the University of Texas in Austin since 1964. The fuzzy picture, which can be seen only from certain angles, shows part of a rooftop and a portion of Niépce's home in France. In the 1990s, the National Library of France acquired what is said to be a photograph, also done by Niépce, that predates that picture: An 1825 photograph of a boy leading a horse.

The first step in the process is to grow silver halide crystals, the light-sensitive ingredients mainly responsible for capturing an image exposed to light. These crystals are grown in solution from silver nitrate and halide ions (bromide, chloride, and iodide). After the crystals have reached the desired sizes and shapes, they are mixed in a gelatin base to form an emulsion.

In their original form, the silver halide crystals are sensitive only to blue light, and, therefore, need some improvements. The silver halide crystals and gelatin emulsion is melted and the crystals are coated with chemical agents to enhance their sensitivity to other colors. The melted emulsion is then applied on a transparent film.

The film may be coated with the emulsion of silver halide crystals and gelatin using different methods. One method involves dipping the film in a tray containing the melted emulsion. Excess liquid is removed by a knife edge or air jets. Another method involves passing the film under a funnel-shaped container called a hopper, which spreads the emulsion on the film. After coating, the emulsion is spread evenly on the film with rollers and transported to a cooling chamber where the emulsion assumes a semisolid state. The film is then sent through a heated chamber, which dries and hardens the emulsion.

The film can be coated with several layers of emulsion using these methods.

Certain coatings can also be added to control how the light is reflected on or absorbed by the film. For this purpose, dyes, carbon particles, or colloidal silver may be added. Finally, the film is painted with a gelatin overcoat to hold the inner layers in place and to seal the film. Generally, the thicker the layers of emulsion and the larger the size of the silver halide crystals, the more light-sensitive the film.

The final step involves winding the film onto spools, which are packaged in lightproof containers. When the consumer opens the container, he or she has to make sure the film is loaded into the camera immediately without exposing it to light.

Materials for film development and printing

In order to produce a negative from a photographic film, chemicals called developer solutions are used. The developer solutions consist of a reducing agent, a restrainer, and a preservative. The reducing agent (also called the developing agent) is designed to turn the silver halide crystals into metallic silver large enough to be seen by the naked eye. Some of the reducing agents used are hydroquinone and phenidone. The restrainer, such as potassium bromide, serves to protect the unexposed (not acted on by light) crystals from developing. The preservative is added to prevent premature reaction of the developing agent with oxygen in the air. Sodium sulfite is the preservative commonly used.

The paper used to print the final image from a negative is a high-quality paper made just for this purpose. Both sides of the paper have waterproof plastic layers. The face side is coated with light-sensitive silver halide crystals. As with the photographic film, gelatin is used to hold together the silver halide crystals and dyes in multiple layers. The paper is available in different grades, which vary in smoothness and shine.

Printing also requires an enlarger, or a projector, to increase the size of the image. Developing and toning solutions are also needed to control the intensity and color of the image. Other equipment needed for both developing and printing includes a developing tank, a developing spool (a cylinder for winding), trays, measuring glassware, thermometers, drying screens, timers, paper cutters, and mixing pails and stirring paddles.

The Manufacturing Process

Three steps are involved in making a photograph—exposing the film to light (commonly referred to as taking a picture), developing the image, and making a printing of the image. The following steps discuss the general process of developing a 35-millimeter film into photographic prints.

Exposure

1 A film is ready for picture-taking once it is loaded inside the camera. When a camera takes a picture, the light reflected on the person or object passes through the lens, which focuses that light on the emulsion crystals of the film to reproduce the image of the person or object. The reaction between the emulsion and the light forms a latent (not yet seen) image on the film. The camera controls the light through a combination of the size of the aperture (opening in the lens) and the length of time the aperture stays open (the shutter speed). The photographer determines the appearance of the final photograph print by, among other things, varying these two factors.

Development

2 When all the film has been used, it can be developed. Development refers to the process by which the latent image on the film is treated with chemicals to produce the negative from which the final paper print will be made.

The film is developed in a darkroom illuminated with an orange light bulb called a safelight, which generally does not cause changes to the light-sensitive film. The film is removed from its canister and rolled onto a spool. For most films, this initial step has to be done in a completely dark room. The film is then submerged in a stainless steel or plastic developing tank and the tank lid is closed. Through a small hole in the tank, the developing chemicals are added. The gelatin in the film expands to allow the chemicals to penetrate the exposed areas of the film (the silver halide crystals changed by light during the picture-taking), while at the same time holding the crystals in place.

3 Next, the developing solution is poured off. The development process is stopped by the addition of dilute acetic acid, called the stop bath because it stops the film from overdeveloping. Then, the film is immersed in a fixing bath to make the image permanent. During fixing, the film is also made insensitive to light by dissolving any undeveloped silver halide crystals. Finally, the developed film is washed and rinsed to remove remaining chemicals. The film spool is then removed from the developing tank and hung to dry. The developed film is called a negative because it is the opposite of how it is seen by the eye. Those areas of the image that received the most light during exposure appear dark in the negative, while areas that received no light appear clear.

Printing

4 Printing is the process of producing a final image from a negative. The print made is usually bigger than the negative. The negative is placed in a machine called an enlarger, which uses a lens to focus light through the negative, projecting it onto a light-sensitive paper. In this manner, an enlarged image of the negative is formed on the silver halide crystals of the paper.

5 The print paper with the positive image (image that corresponds to the original subject taken) is then developed by a process similar to that used in developing the film. After the print is dry, it can be mounted on cardboard or other backing material. Reprints (additional prints of the same image) may be produced in a similar manner from the original negative or from a print.

Quality Control

The manufacture of photographic film is an exact process. The emulsion coatings of silver halides must be free of streaks and must be of uniform thickness to yield a quality film. Each stage of production is checked to ensure the finished product is free from defects. During development of both the negative and the print, areas of importance include the correct concentrations of chemicals in the development tank, as well as proper temperature and time of development. If the solutions are not the right concentration, the negative or the print may be overprocessed or underprocessed.

The Future

Although the fundamental principles of photography remain the same, advances continue to be made in the way pictures are taken. Some major developments include the Advanced Photo System (APS) camera and the digital camera. The APS technology is a cartridge-based alternative to 35-millimeter film. Unlike the 35-millimeter film that has to be threaded to a take-up spool in the camera, the APS cartridge has drop-in loading and unloading, which means that the photographer does not have to touch the film. Manufacturers claim this results in a higher proportion of well-developed films. In addition, the system allows photos of different formats from the same film cartridge, such as a standard print, a panoramic view, or a group picture. Recent designs include combining the APS technology with shoot-and-point capabilities using interchangeable zoom lenses.

The ease of sharing photographs instantly through computers has contributed to the increasing popularity of digital photography. Digital cameras do not use films. Instead, they use electronic sensors that convert light into digital code, or number code, which can be read by a computer. New models not only allow the manipulation of images to fit a postcard, but they also let the sender include text and voice messages.

FILM SPEED

Photographic films that have more layers of silver halide–gelatin emulsion and larger-sized silver halide crystals are generally more sensitive to light. The film's sensitivity to light is represented by the ISO (International Standards Organization) number (ASA, or American Standards Association, number for older cameras). The higher the ISO number, the more sensitive the film is to light, which means it has a higher film speed. For example, an ISO 400 film is a faster film than an ISO 200 film and, therefore, needs a shorter exposure to record an image. Hence, a 400-speed film might be a better choice when photographing fast-moving action, such as an athletic event, or a moving object.

In the meantime, chemists and other scientists employed by manufacturers of photographic films and papers continue to research technologies that would produce films and papers that not only yield better pictures but also pictures that last longer.

aperture:: Opening of camera lens.
darkroom:: A room in which photographic films and prints are processed, either in complete darkness or illuminated by a safelight that does not act on light-sensitive materials.
development:: The process by which the latent image on the film is treated with chemicals to produce the negative from which the final paper print is made.
emulsion:: A mixture of silver halide crystals in gelatin, used to coat photographic film.
exposure:: The process of allowing light from a subject being photographed to reach the light-sensitive photographic film in order to form an image.
fixing:: The process of removing from photographic film the undeveloped silver halide crystals, resulting in a negative or print that cannot be affected by the further action of light.
gelatin:: Protein made from animal skins and bones and used to bind light-sensitive silver halide crystals to photographic film.
latent image:: The invisible image produced by light on photographic film before it is processed.
negative:: The developed photographic film in which the dark and light tones of the original image are reversed.
photosensitive:: Sensitive to light.
silver halide:: Compound of silver, such as silver bromide, silver chloride, and silver iodide, used for most photographic films.

For More Information

Books

Bustard, Bruce I. Picturing the Century: One Hundred Years of Photography from the National Archives. Seattle, WA: University of Washington Press, 1999.

Langford, Michael. Story of Photography. 2nd ed. Oxford, England: Reed Educational and Professional Publishing Ltd., 1997.

Sills, Leslie. In Real Life: Six Women Photographers. New York, NY: Holiday House, 2000.