History of photography

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History of photography
Abbe James
Allen Albert
Bailey David

Beaton Cecil
Cunningham Imogen
Carroll Lewis
Drtikol Frantisek
Duhrkoop Rudolf
Eisenstaedt Alfred
Feininger  Andreas
Halsman Philippe
Heartfield John
Horst P. Horst
Kasebier Gertrude
Kirkland Douglas
Lartigue Jacques Henri
Laughlin Clarence John


Maar Dora
Man Ray

Miller Lee
Munkacsi Martin


Outerbridge Paul


Rodchenko Alexander
Skoglund Sandy
Smith William Eugene
Smith Rodney
Tabard Maurice
  Watson Albert

Before Photography

In China in the 5th century B.C., Mo Ti recorded his observation that the reflected light rays of an illuminated object passing through a pinhole into a darkened enclo¬sure resulted in an inverted but otherwise exact image of the object. In the following century in die West, Aristode described seeing, during a solar eclipse, a crescent-shaped image of the sun on the ground beneath a tree, which was projected by rays of light passing through the interstices of foliage onto a darkened surface. In the 10th century, the Arabian scholar Abu 'Ali al-Hasan ibn al-Haytham (Alhazen) added the observation that an image thus formed was sharply defined when the aperture through which it was projected was small and became diffuse as the hole was enlarged to admit more light. Similar optical phenomena were noted by Roger Bacon in the 13th century and Rcinerius Gemma-Frisius in the 16th.

During the Renaissance, efforts to control and direct this phenomenon resulted in the concept of a camera obscura—literally, a dark room—that enabled light to enter through a hole in a wall facing another wall or plane on which the projected image appeared in natural colors. Sixteenth -century descriptions by Leonardo da Vinci, Vitruvius, and Girolamo Cardano in Italy and by Erasmus Reinhold and Gemma-Frisius in Northern Europe make it difficult to assign exact dates or authorship to the construction of the first camera obscura, but references to Giovanni Batrista della Porta's Magiae naturalis of 1558 indicate that by then the device had become familiar to scientists, magicians, and artists. By die 17th century, the camera obscura had emerged as a necessary tool for the working out of new concepts of pictorial representation, in which artists and draftsmen depicted objects and space as if seen from one position and one point in time.

STEFANO DELLA BELLA. Camera Obscum with View of Florence, n.d. Ink drawing.
Library of Congress, Washington, D.C.; Lessing J. Rosenwald Collection.

From the 17th to the 19th century, the camera obscura underwent continual improvement. Better lenses sharpened the image, and mirrors corrected the inversion and projected the picture onto a more convenient surface for drawing. Portable models were popular among European geographers as well as artists, including a tentlike collapsible version by Athanasius Kircher illustrated in his 1646 treatise on light as a suitable instrument for drawing the landscape. That scientists and artists regarded it as a device both for aiding graphic representation and for ascertaining basic truths about nature is apparent from the Dutch philosopher Constantijn Huygens's description of die camera obscura image as "life itself, something so refined that words can't say," while others of the 17th century remarked on its ability to produce a "picture of inexpressible force and brightness ... of a vivacity and richness nothing can execll."

ATHANASIUS KIRCHER. Large Portable Camera Obscura, 1646. Engraving.
Gernsheim Collection, Humanities Research Center, University of Texas, Austin

During the 18th century, fantastic literary and graphic explanations about phenomena caused by light rays appeared, among them an allusion in Tiphaigne de la Roche's fictional work Giphantie to a canvas as a mirror that retains images that light transmits, and a visual representation of this concept is seen in an anonymous engraving, The Miraculous Mirror. Actual camera obscurae, used by artists to improve the accuracy of their depictions, were shown on occasion in portrait paintings, as though suggesting that the portrait was a truthful image of the pictured individual. Interest in faithfully transcribing the visible world from the point of view of the individual led to the invention of other devices besides the camera obscura. For example, the camera lucida, invented by William Hyde Wollaston in 1807, is an arrangement of a prism and lens on a stand that enables the draftsman to see a distant object superimposed on the drawing paper, theoretically making transcription easier.

The chemical components necessary for photography were not recognized until some 200 years after the camera obscura was first conceived. From antiquity to the Renaissance, the mystery surrounding organic and mineral substances and their reactions to light and heat made chemical experimentation an inexact exercise practiced mainly by alchemists. In the 17th century, more accurate observation led to the identification of silver nitrate, silver chloride, and ferrous salts, the first chemical substances used in the experiments that led to photography. The accidental discovery in 1725 by Johann Hcinrich Schulze, Professor of Medicine at the University of Altdorf, that silver nitrate darkened when exposed to sunlight and that this change was the result of exposure to light and not heat was crucial to photography. The light sensitivity of silver chloride was the subject of experiments by Swedish Chemist Carl Wilhelm Scheelc who published his results in 1777, un-aware that at mid-century an Italian, Giacomo Battista Beccaria, had discovered the same phenomenon. Scheele also established that the violet end of the solar spectrum was actinically more active in producing this effect and that the darkened material consisted of particles of metallic silver that could be precipitated by ammonia. Silver chloride was one of the many elements tested in 1782 by Jean Senebier, the Chief Librarian of Geneva, in order to determine the time required for various degrees of light to darken the chemical salts. He also studied the reaction of the chloride to different portions of the spectrum, foreshadowing later experiments that demonstrated that the spectrum reproduced itself in natural colors on the chloride surface.

Two 18th-century English scientists, Dr. William Lewis and Joseph Priestley, formed the link between these early chemical experiments and later efforts to find a way to retain an image produced by the darkening of silver halides by light. The notebooks of Dr. Lewis, who had repeated Schulze's experiments by painting designs in silver nitrate on white bone that he exposed to sunlight, were acquired by Josiah Wedgwood, the British commercial potter, who may have become interested in finding a photochemical process when he was commissioned by Catherine the Great of Russia to provide a table service with 1,282 views of country mansions and gardens, many of which were made with the aid of the camera obscura. As a member of Wedgwood's Lunar Society discussion group, Priestley imparted information about the photochemical properties of silver halides that he gathered from his association with prominent figures in the European scientific community". In 1802, young Thomas Wedgwood attempted to transfer paintings on glass to white leather and paper moistened with a solution of nitrate of silver, describing the resulting negative image as follows: "where the light is unaltered, the color of the nitrate is deepest." Neither Wedgwood nor his associate in the experiments, chemist Humphry Davy, were able to find a way to arrest the action of light on the silver salts; unless kept in the dark the picture eventually was completely obliterated. Their early experiments demonstrated, however, that it was possible to chemically transfer by means of light not only pictures but objects in profile such as leaves and fabrics.

UNKNOWN. The Miraculous Mirror, 18th century. Engraving.
International Museum of Photograph}' at George Eastman House, Rochester, NY.

CHARLES AMEDEE PHILIPPE VAN LOO. The Magic Lantern, 18th century.
Oil on canvas, National Gallery of Art, Washington, D.C.

First Successful Experiments

Interest in the practical uses of new scientific discoveries developed among both the enlightened British and French bourgeoisie during the early years of the 19th century and led the brothers Joseph Nicephore Niepce and Claude Niepce. who returned to the family estates at Chalon-sur-Saone after the Napoleonic Wars, to become involved with a series of inventions, including a motor-driven rivercraft (the pyreolophore), a method of making indigo dye, a device for printing lithographs, and a process for obtaining images by the action of light. In 1816, Nicephore and Claude produced an image in the camera obscura using paper sensitized with silver chloride, but because the tones were inverted and efforts to make positive prints were unsuccessful, Nicephore eventually turned to using bitumen, an ingredient in resist varnish that hardens and becomes insoluble when exposed to light. Between 1822 and 1827, while his brother was abroad, Nicephore produced transfers of engravings, first on glass and then on pewter, by coating the plates with bitumen, placing them against engravings made translucent by oiling or varnishing, and exposing the sandwich to sunlight. The bitumen hardened on the portions not covered by the lines of the print and remained soluble on the rest of the plate; after washing, an image appeared with the bare pewter forming the lines. It was Niepce's plan to etch these plates, thus creating an intaglio matrix from which inked prints might be pulled. Heliography, as he called this process, was the forerunner of photomechanical printing processes.

In the summer of 1827, Niepce exposed a pewter plate coated with bitumen in the camera obscura, achieving after some eight hours an image of a dovecote on his estate at Le Gras. Although he changed from pewter to silver and silver-coated copper plates, and introduced iodine to increase the sensitivity of the silver surface to light, he was unable to decrease substantially the exposure time needed to obtain an image. In his search for improved optical elements for his work, Niepce had contacted the Parisian optical-instrument maker Vincent Chevalier, who in turn acquainted scenic designer and Diorama owner Jacques Louis Mande Daguerre with the nature of the experimentation at Le Gras. Daguerre's parallel interest in obtaining a permanent image in the camera obscura led to contacts with Niepce and resulted in a meeting in 1827 and the signing of a deed of partnership in 1829 to pursue the process together.

Following Niepce's death in 1833, activity shifted to Paris as Daguerre continued to work with iodized silver plates, discarding bitumen altogether. However, he, too, was not notably successful in reducing the time needed for the image to appear until 1835, when he hit upon a phenomenon known as latent development, which means that the photographer does not have to wait to see the image appear on the plate during exposure, but can bring it out by chemical development—in this case, mercury vapor— making possible a radical reduction in exposure time. A problem that remained unsolved was how to stop the continued action of light on the silver halides, which caused the image to darken until it was no longer visible, but in 1837 Daguerre found a way to arrest the action of light with a bath of sodium chloride (common table salt), a method he used until March, 1839, when he learned about the property' of hypo (hyposulphite of soda now called sodium thiosulphite) to wash away uncxposcd silver salts indirectly from its discoverer, the English scientist John Herschel. The daguerreotype, as he called his product, was delicate—easily damaged by fingerprints and atmospheric conditions—and therefore needed the protection of being enclosed in a case under glass.

In 1833, at about the same time as Daguerre's early experiments, English scientist and mathematician William Henry Fox Talbot conceived of making a permanent image of what could be seen in the camera obscura:, within two years he had succeeded in obtaining pictures by the action of light on paper treated with alternate washes of sodium chloride and silver nitrate. His first pictures were of flat objects, made by placing leaves, lace, or translucent engravings against the sensitized paper and exposing both to sunlight to produce a tonally and spatially inverted image in monochrome on the paper. Also in 1835, Talbot carried this discovery a step forward when he produced a one-inch-square negative image of his ancestral home, Lacock Abbey, made by inserting sensitized paper in a very small camera with a short focal length (the distance between lens and film) for about ten minutes in bright sunshine. To stabilize these early images, Talbot employed either potassium iodide or table salt, but early in 1839 he changed to hypo on Herschels advice. Calling these images "photogenic drawings," Talbot proposed to correct their tonal and spatial inversions by placing another sheet of silver-sensitized paper against the paper negative image (waxed to make it translucent) and exposing both to Eight, but it is doubtful that he actually made such positive prints at this time.

Apart from the profoundly ingenious concept of a negative from which multiple positives could be made, Talbot's most significant invention was latent development, which he arrived at independently in 1840. He sensitized paper by swabbing it with a combination of silver nitrate and gallic acid solutions that he called gallonitrate of silver, exposed it in die camera, removed the seemingly blank paper after a time, and then bathed it in the same chemical solutions until the image gradually appeared. Having reduced exposure time by chemical development to as little as 30 seconds on a bright day, Talbot took out his first patent in February, 1841, for a negative/positive process he called the calotype.

Other Experiments

Widespread interest during the early 19th century in light-related phenomena led to similar experiments by others. Among them was Hercules Florence, a French-born artist who had joined a Russian expedition to the interior of Brazil in 1828. He began to work with paper sensitized with silver salts (the exact composition of which is unknown) in an effort to produce images of drawings by a process he actually called photography (from the Greek phos—light—and graphos—writing)—apparently die first recorded use of the word, which came into general usage in Europe in 1839. Florence and his work were forgotten until 1973, when his journals and examples of his work came to light in Brazil. Also in 1839, Friederike Wilhelmine von Wunsch, a German painter living in Paris, claimed to have come up with a photographic process that produced both miniature and life-size portraits.

In May, 1839, Hippolyte Bayard, a French civil servant, announced a direct positive process for obtaining photographic images on paper, which he achieved by darkening a sheet of paper with silver chloride and potassium iodide, upon which light acted as a bleach when the plate was exposed in the camera. Bayard's contribution was largely ignored at the time, owing to France's official support for the daguerreotype, but since some French photographers evinced strong interest in a paper process in preference to the daguerreotype, experimentation along this line continued.

By 1847, Louis Desire Blanquart-Evrard, a leading figure in the improvement of the calotype in France, had developed a method of bathing the paper in solutions of potassium iodide and silver nitrate rather than brushing these chemical baths on the surface, as Talbot had done. Exposed in a damp state (as Talbot's had been), the resulting negative showed improved tonal range because the paper fibers were more evenly saturated.

Further improvements in definition followed when the French painter Gustave Le Gray developed the waxed-paper process—a method of using white wax on the paper negative before it was sensitized. After being immersed in a solution of rice water, sugar of milk, potassium or ammonium iodide, and potassium bromide, and being sensitized in silver nitrate and acetic acid, the paper was ready to use in either damp or dry state. Le Gray's attentiveness to the aesthetics of photography led him to experiment with the timing of various chemical baths in an effort to produce different colorations in his prints.

In 1839 Herschel had suggested glass as a support for negatives, but it was not until 1847 that a procedure evolved for making albumen negatives on glass plates. Claude Felix Abel Niepce de Saint-Victor (a relative of the Niepce brothers) proposed a mixture of eggwhite with potassium iodide and sodium chloride to form a transparent coating on glass, which then was immersed in silver nitrate solution and, after exposure, developed in gallic and pyrogallic acid. A similar process, called Crystalotype, was perfected by the American John Adams Whipple; both processes were slow but produced excellent glass lantern slides.

Those working with glass then turned to collodion—a derivative of guncotton, which became liquid, transparent, and sticky when dissolved alcohol and ether. Experiments with collodion were undertaken by Le Gray and Robert Bingham in France in 1850, but the first practicable directions for using it as a binder for light-sensitive silver salts appeared in 1850 and 1851 in a two-part article in The Chemist written by Frederick Scott Archer, an English sculptor. The viscous collodion, which contained potassium iodide (potassium bromide was later added), was poured evenly onto a glass plate, which was then immersed in a silver nitrate bath to form silver iodide. The exposure time was shortened considerably, but only if the plate was used immediately in its wet state. Because it had to be developed—-usually in ferrous sulphate—while still moist, the "wet plate," as it came to be called, made portable darkrooms for outdoor work a necessity.

Before the collodion process became used exclusively for negatives, it enjoyed a period of popularity in the form of the glass positive, or Ambrotype—as its American version, patented in 1854 by James Ambrose Cutting of Boston, was called. By adding chemicals to the developer and backing the glass negative either with black cloth or black varnish, the image was reversed visually from a negative into a one-of-a-kind positive (pi. no. 53) that usually was presented to the client encased in the same type of frame as a daguerreotype. Sensitized collodion also figured in the production of direct positive images on sheet iron. Known generally as tintype, but also called ferrotype and Melainotype, the process was discovered in 1853 in France and in 1856 in both England and the United States; a dry tintype process was introduced in 1891. Since tintypes were quickly made (requiring just over a minute from start to finish), inexpensive to produce, and easy to send through the mails, they were popular with soldiers during the American Civil War; they continued to be made of and for working-class people into the 20th century.

The same albumen or eggwhite suggested by Niepce de Saint-Victor as a binder for glass negatives was also used to close the pores of photographic printing papers, to prevent silver salts from penetrating the irregular fiber structures or affecting the chemical sizings used in paper manufacture. The first practicable process for making albumen paper, announced in 1850 by Blanquart-Evrard, required coating the paper with a mixture of eggwhite and either table salt or ammonium chloride, after which it was dried and kept until needed. Before exposure, the paper was sensitized by floating it albumen-side down in a strong solution of silver nitrate. After drying, it was exposed in contact with a negative for as long as was needed to achieve a visible image—that is, no chemical developer was used. Blanquart-Evrard also contrived a paper that was chemically developed in gallic acid after exposure with the negative—a procedure that enabled his printing plant in Lille, France, to turn out from 300 to 400 prints a day from a single negative. Fine prints resulted when, after exposure of both negative and sensitized paper in a to paper surface under pressure and necessitating, after the hardening of the gelatin in an alum bath, the trimming of its botders to remove the colored ink that had overrun the edges of the image. A photomechanical, rather than a strictly photochemical procedure, Woodburytype (confusingly called photoglyptie in France) produced rich-looking prints without grain structure of any kind.

Early Equipment

The earliest cameras used by Niepce, Daguerre, and Talbot were modeled on camera obscurae in use since the 17th century. Those of Niepce and Daguerre consisted of two rectangular boxes, one sliding into the other, with an aperture to receive the lens and a place to position the plate. Talbot's first small instruments, referred to as "mousetraps", were crude wooden boxes; later British and French makers provided him with better-crafted instruments that incorporated besides the lens a hole fitted with a cork or brass cover through which one could check focus and exposure. The first commercial photographic camera was designed by Daguerre and was manufactured by Alphonse Giroux (a relative by marriage) from 1839 on.

Talbot's Mousetrap Camera. In 1839 Talbot made cameras with removable paper-holders (A) . The image produced by the lens (B) on the thin, sensitive paper could be inspected from behind through a hole, which normally was covered by a pivoted brass plate (c).
Daguerre-Giroux Camera. Giroux's camera of 1839, based on Daguerre's patent, was the first camera to be sold in any numbers to the public. The lens was fitted with a pivoted cover plate (A), which acted as a shutter. A plaque (B) bore Daguerre's signature and Giroux's seal.

A unique design was made by Alexander S. Wolcott, an American who in 1840 substituted for the lens a concave mirror that produced a brighter image by concentrating the light rays and reflecting them onto the surface of the daguerreotype plate. Conical and metal cameras appeared in Austria and Germany in 1841, the same year that a cylindrical instrument enclosed in a wooden box was manufactured in Paris, but these did not catch on. A bellows focusing system for a camera was first suggested in 1839, but did not come into use until 1851 when it was incorporated into a rectangular camera made by the firm of W. and W. H. Lewis in New York. A number of folding cameras, on view first at the Great Exhibition in 1851, with either rectangular or tapered bellows, were manufactured during the 1850s mainly by British firms. By the 1860s many bellows cameras included rising fronts, and swing fronts and backs.
The first arc-pivoted camera, devised in 1844 by Friederich von Martens, was capable of taking a panoramic view of about 150 degrees on a curved daguerreotype plate-measuring approximately 41/2 by 15 inches. Curved glass plates were required for the similar apparatus in use during the collodion era. A Pantascope camera, patented in England in 1862 by John R. Johnson and John A. Harrison, rotated on a circular base, as a holder containing a wet collodion plate was moved by a string and pulley arrangement past an exposing slot.

Photographic accessories such as buffing tools and sensitizing boxes had been necessary for dagucrrcotyping; during the collodion or wet plate era, photographers in the field were required to earn' even greater amounts of additional equipment besides camera and tripod. Portable handcarts and perambulator tents were devised to stow chemicals and apparatus and to allow the photographer to erect a light-tight tent virtually anywhere in order to sensitize plates before exposure and to develop them immediately afterward. The most popular design in England, that of Ernest Edwards, was a type of suitcase mounted on a wheelbarrow or tripod that opened to form a darkroom within a cloth tent.

  Wolcott Camera. In Wolcott's camera, as patented in 1840, a large, concave mirror (A) was placed at the back of an oblong box. A small, sensitized daguerreotype plate (B) was fitted into a wire frame and was held in place by a spring clip. A surviving example of the camera has, however, a more elaborate holder. The frame could be moved backward and forward on a track (c) to focus the image on the sensitive surface of the plate, which faced the mirror.

The exposure was made by opening a door on the camera front. Other doors gave access to the mirror and the plate frame and allowed the focus to be checked. The camera took plates measuring about 2 x 2.5 inches (51 x 64 mm).


The stereoscope, conceived by Charles Wheatstone in 1832 before the invention of photography, originally was a device that permitted a view by means of mirrors of a pair of superimposed pictures that had been drawn as if seen by each eye individually, but appeared to the viewer to be a single three-dimensional image. In 1849, Scottish scientist David Brewster adapted the stereoscopic principle to lenticular viewing, devising a viewer with two lenses placed about 2 1/2 inches apart laterally for viewing the stereograph —an image consisting of two views appearing side by side either on a daguerreotype plate, a glass plate, or on paper mounted on cardboard. Stereographic calotypes were made for viewing by Talbot, Henry Collen, and Thomas Malone after photography was invented. Stereographs and stereoscopes manufactured by the French optical firm of Duboscq and shown at the Great Exposition in 1851 became exceedingly popular and were produced for all tastes and pocketbooks. The viewers ranged from the simple devices invented by Antoine Claudet and Oliver Wendell Holmes to elaborately decorated models for the very wealthy to large stationary floor viewers that housed hundreds of cards that could be rotated past the eyepieces.

Claudet Stereoscope. The top opened up to form the back, into which the stereoscopic daguerreotypes (A) were fitted; the lenses (B) were set in telescoping mounts.
Holmes-Bates Stereoscope. Joseph Bates manufactured an inexpensive viewer invented in 1861 by Oliver Wendell Holmes; it was sold in this improved form from die mid-i86os until 1939. The stereograph was held on the cross-piece (A), which could be slid up and down the central strip for focusing. A folding handle (B) and a curved eyeshade (c) were fitted.

Stereographic views could be made by moving a single camera laterally, a few inches, but care was needed to make sure that the two images were properly correlated. In 1853, a means of moving the camera laterally along a track was devised. Another method, first described by John A. Spencer in England in 1854, involved moving a plateholder in a stationary camera equipped with an internal septum so that the images did not overlap. During the 1850s, a binocular camera with two lenses was patented in France by Achille Quinet, and a twin-lens stereoscopic camera de-signed by John Benjamin Dancer was offered for general sale in 1856. A number of other designs appeared during the 1860s, including a folding bellows binocular camera made by George Hare and a stereoscopic sliding box camera divided into an upper and lower compartment, each with a pair of lenses, designed by Andre Eugene Disderi .

In 1857, David A. Woodward, an American artist, patented a device he called a "solar microscope or magic lantern" for the enlargement of photographic negatives. A mirror fixed at a 45-degree angle to receive the rays of the sun reflected them onto a condensing lens inside a box into which a negative on paper or glass could be fitted, throwing an enlargement of the image onto a sensitized support placed at a suitable distance away. Woodward actively promoted this device in the United States and Europe. Along with a similar apparatus developed by the Belgian scientist Desire von Monckhoven, this forerunner of the enlarger proved to be a significant tool in graphic as well as photographic portraiture.

Dancer Camera. Dancer's stereoscopic camera of 1856 had two lenses, which were fitted with a pivoted shutter (A) and with aperture wheels (B). In addition, some models had a lens shade (c) in the form of a pivoted flap. Dry plates could be drawn up, one by one, by means of a screwed rod (D), from a plate-changing box (E). The number on the exposed plate could be read through a window (F).
Disderi Camera. Andre Adoiphe Eugene Disderi's stereoscopic camera of c. 1864: the upper compartment was equipped with a pair of lenses (A), which were matched to the taking lenses (B) and were focused on a ground-glass screen (c), fitted in the back of the compartment in the same plane as the plate-holder below. A vertical, sliding shutter (D) was opened by pulling a string (E).

The unwieldy nature of wet collodion on glass led to continued efforts to find other supports of chemical sub-stances for negatives during the third quarter of the 19th century. Collodion dry plates, invented by French scientist Dr. J. M. Taupenot and manufactured in England in i860, were too slow in action to replace the wet plate. In the late 1870s, experiments by English physician Dr. Richard Leach Maddox to substitute a gelatin bromide plate for collodion and refinements made in 1873 by John Burgess and Richard Kennett, and in 1878 by Charles Harper Bennet, led to a practicable dry plate. These appeared on the market in 1878 and were soon being manufactured by firms in Europe and the United States, ushering in a new era in photography. Consisting initially of a glass support coated with a silver bromide emulsion on a specially prepared gelatin ground (produced either by "ripening" or "digestion"), the fragile glass was replaced by celluloid in 1883, after it had become possible to manufacture this material in standardized sheets of about .01 inch thickness.

A paper roll film (first conceived by British inventor Arthur James Melhuish in 1854—see below) was commercially produced by the Eastman Company in Rochester, New York, in 1888. At first, the gelatin emulsion had to be removed or "stripped" from the paper backing, transferred to glass, and then developed and printed, but with the substitution of transparent celluloid roll film in 1889, and the addition in 1895 of a paper backing that enabled the film to be loaded in daylight, roll film as it is known today came into being.

The improvement of the color sensitivity of black-and-white film began during the collodion era when the re-nowned German photochemist Hermann Wilhelm Vogel added dyes to silver bromide emulsions. This process, called optical sensitizing, in 1873 produced the first ortho-chromatic plates (sensitive to all but red and oversensitive to blue light) and it was applied to gelatin dry plates when they supplanted collodion. Experiments, notably by Adolphe Miethe of the German Agfa works in 1903, resulted in the development of panchromatic film sensitive to all colors but still requiring a yellow filter to cut down the sensitivity to all blue light.
Permanence and long tonal scale in printing papers were difficult problems to solve satisfactorily because of the many variables (such as atmospheric conditions, water quality, amount and thoroughness of washing) that characterized photographic printing procedures. In spite of its uneven performance, albumen paper continued to be manufactured until the end of the 19th century, but new papers were being developed to respond to the need for sharper definition and speed created by the increased use of camera images for records, documentation, and reproduction in newspapers and magazines. Two types of printing papers were produced: printing-out paper and developing-out paper. Gelatin-silver-chloride emulsion papers (marketed in the United States under the names Aristotype and Solio). which required no chemical development, became available in 1890, while developing-out papers coated with silver bromide emulsions became popular in the late 1880s even though this product had been introduced as early as 1873. Gelatin-silver-chloride paper for printing by gas light (known as Velox) also appeared around 1890. At the same time that these materials were manufactured to serve commercial needs, platinum paper, based on John Herschcl's discovery of the light sensitivity of chloride of platinum, was produced in England under the trade name Platino-type. This expensive material appealed to well-to-do amateurs and serious photographers who required a printing paper of permanence with a long tonal scale.

The standardization of papers went hand-in-hand with the automation of large-scale photographic printing. Improving on the steam-driven machines that had made it possible to expose, print, and fix carte-de-visite portraits and stereographs during the 1860s, the new machinery installed by large photographic firms such as Automatic Photographs of New York and Loescher and Petsch in Berlin was capable, for example, of exposing 245 cabinet-size pictures a minute and turning out 147,000 prints daily on the new fast-acting bromide paper.

During the first 30 years of photography, camera design was subject to continual experimentation. Instruments were made in large and small formats to accommodate plate sizes that ranged from mammoth to tiny postage size, while multiple lenses and septums were added to boxes to make cartes de visite and stereographs. By the 1880s, camera design needed to expand further to accommodate new negative materials—the dry plate and celluloid film. The folding-bed view cameras, introduced in England in 1882 by camera designer George Hare became the prototype for similar instruments manufactured in other parts of Europe and the United States. Variations of the basic instrument incorporated the capacity to advance the rear element, change from horizontal to vertical format, and fold the front element down into the base. Some models were given sliding racks that enabled the bellows to be greatly extended. As improved by British designer Frederick H. Sanderson in 1895, the view camera became an instrument of great sensitivity and precision, provided the subject was immobile.

Hare Camera. On George Hare's camera of 1882, screwed rods (A) were used to secure the front panel (B), which could be moved toward die rear panel (c). When the lens was removed, the hinged baseboard (D) could be folded up.
Sanderson Camera. Frederick Sanderson used two slotted stays on either
side of the lens panel in his 1895 camera.
This allowed a considerable degree of vertical, horizontal, and swing movement
to be applied to the lens panel.

A serious effort to make possible fast exposure, control over focus, and large image size resulted in the development of the single-lens reflex camera. Based on the use of a mirror to redirect the light rays to a horizontal ground-glass focusing surface, an early model of this type was patented in 1861 by Thomas Sutton. The most influential design was that of the Graflex, introduced by Folmer and Schwing in 1898; it assumed its inimitable shape of cubic box with bellows extension and four-sided hood on top around 1900. A mirror, usually inserted at a 45 degree angle to the axis of the lens focused the image onto a screen within the hood and dropped out of the way when the exposure was made. In the hand or on the tripod, reflex cameras (which came in a variety of sizes and shapes) were flexible enough to accommodate naturalists in the field, news and portrait photographers, and individuals looking for street subjects.

Graflex Camera. The No. IA Graflex camera of 1910
was a single-lens reflex camera for roll-films.
It was fitted with the Graflex multispeed focal plane shutter.

Reputable equipment with which one could almost simultaneously view the scene, make the exposure, and advance the film in ordinary daylight did not become generallv available until the 1920s, but long before then it was possible to capture some street action using small cameras with a single short-focus lens. Other than the 1886 Gray-Stirn Vest Camera, an instrument designed to be worn under a waistcoat and that took 1 3/4 inch diameter negatives, these instruments, made to look like books, binoculars, revolvers, and walking sticks, were little more than novelties. The dry-plate hand cameras that began to appear in the early 1880s were a different story; they became known as detective cameras because, though larger than the concealed cameras, they too were inconspicuous to operate and could capture spontaneous activity under certain conditions. An early, widely sold model was the Patent Detective Camera, invented by the American William Schmid in 1883, but the Kodak (pi. no. 568), announced in 1888 by The Eastman Company, was both easier to operate and revolutionan' in that it created a completely new system and a different constituency for photography.

This simple box, incorporating spools to hold roll film, a winding key to advance the film, and a string to open the shutter for the exposure, was an immediate success and prompted other manufacturers to design similar apparatus that would make use of the Kodak roll film. Actually, roll film attachments for plate cameras had been invented in 1854 by Mclhuish and Joseph Blakelcy Spencer, and in the following years Humbert de Molard and Camillc Silvy also designed such devices. In 1875 Leon Warnerke, a Russian emigre in London, patented a practicable holder that accommodated stripping film in 100 exposure lengths, but the film itself was not sensitive enough for the camera's capabilities. This was followed by a similar holder invented in 1884 by George Eastman and William H. Walker, which also had to be attached to a plate camera. Undoubtedly it was the simplicity of a camera with integral roll-film holder, the case of operation, and the freedom from the necessity of processing that attracted amateurs to the "smallest, lightest and simplest of all Detective cameras"—the Kodak. The Eastman Company, which from the start had been involved with both the manufacture and the processing, soon gave up the processing aspects. Like Lumiere, its counterpart in France, Eastman employed many women workers as it continued to provide photo-graphic supplies and develop new processes and equipment for a growing market.

Photo-Revolver de Poche. E. Enjalbert's Photo-Revolver de Poche of 1882 carried small plates (A) in a compartment (B) in the chamber (c). When a catch (D) was slid, a plate moved into the exposing position (E). When the chamber was rotated through 1800, the exposed plate was transferred to a second compartment (F). The chamber was turned again to its original position for the next exposure. This movement also set the rotary shutter (G), which was released by the trigger (H). The lens (1) was mounted in the barrel. The hammer (j) held and located the plate chamber (c).
Stim Secret Camera. The Carl P. and Rudolph Stirn Secret or Waistcoat camera
of 1886 was worn under a waistcoat, the lens (A) poking through a buttonhole.
The circular plate was turned and the shutter set when the pointer (B) was rotated.
Exposures were made by pulling on a string (c).


Walking-Stick Camera. Emile Kronke's walking-stick camera of 1902 took
spools of roll-film (A), carried in the handle. Storage space (B) for three
spare spools was provided.
A shutter release knob (c) was placed underneath the front of the handle,
(D) Lens panel, (E) Winding-on key.

Schmid Camera. In 1883, the first popular hand-held dry plate camera
was designed by William Schmid.
Eastman's Kodak Camera of 1888. (1) Sectional view, (2) roll-holder as seen from above,
(3) cutaway view, (4} external view. The camera had an integral roll-holder (A), in which George
Eastman's American Film (B) was first fed over a metering roller (c), the end of which carried
3 disc with an index mark visible through a window (D) on the top of the camera.
The film was then fed past the circular exposing aperture (E) and onto the take-up roller F),
which was turned by a key (G). The cylindrical shutter (H) was set by pulling a string (1).
The lens (j) was fitted within the shutter. (5) A new model, designated die No. 1 Kodak camera,
was introduced in 1889. It differed from the 1888 version in having a sector shutter (K);
the positions of the shutter release (L) and setting string (M) were also altered.
Both models had lens plugs (N) for protection; the plugs also permitted time exposures to be made.


In the early years of photography, exposure usually was effected by removing and replacing the lens cap manually or by moving a simple plate that pivoted over the lens. Although shuttets had at times been used earlier, with the coming of the more sensitive gelatin dry films they became a necessity. They could be purchased separately to be affixed in front of the camera lens. Commonly of the flap, drop, or sliding plate construction, they were activated either by a string or a pneumatic cylinder attached to a rubber bulb. In the late 1880s, sets of metal blades called diaphragm shutters were sometimes mounted within the lens barrel, usually with settings of 1/100 to a full second. In about 1904, the compound shutter, designed for the Zeiss Company by Friedrich Deckel, introduced sets of blades totally enclosed within the camera that controlled both the size of the aperture and the length of time it remained open; after improvements it became standard on all better hand cameras. The focal plane shutter, positioned in the camera behind the lens but in front of the plate or film, was derived from earlier roller-blind shutters that operated on the principle of a window shade. Various designs for this type were made during the 1870s and '80s, but the most famous, patented in 1888 by the German photographer Ottomar Anschutz for his instantaneous animal studies, made possible exposures at 1/1000 of a second.

Improvements in glass manufacture in Jena, Germany, after 1880 made possible new designs in lenses. Besides the all-purpose rapid rectilinear lenses with which hand and view cameras initially were fitted, the German firms of Carl Zeiss and Carl Goerz began in the early 1890s to manufacture anastigmats—lenses that resolved distortion in both vertical and horizontal planes and made possible apertures up to f/4.5. The Dallmeyer firm in England and Bausch & Lomb in the United States also contributed new designs, but between 1890 and 1904 the German firms preempted the field by introducing the Zeiss Protar and Tessar and the Goerz Dagor lenses. While the wide-angle Globe lens, designed by the American Charles C. Harrison, had been used since 1860, the first telephoto lens was patented in 1891 by Thomas Rudolf Dallmeyer.

Lens Cap. Until the advent of the gelatin dry plate in the 1870s, most exposures were made by removing the lens cap and replacing it after a suitable interval of seconds—or minutes.
Sliding cap shutter. Some early lenses were fitted with sliding cap shutters.
This example was made by N. P. Lerebours and is a close copy of the shutter on the Daguerre-Giroux camera of 1839.

Guerry's Flap Shutter. C. I. Guerry's flap shutter of 1883 had two pivoted flaps,
which were connected by a string-and-pulley system (A), set on the side.
As a pneumatic release (B) was pressed, the two flaps were raised to uncover
and cover the lens in turn. A screw-adjusted device (C), bearing on the string,
was used to van' the period of opening by altering the relationship between the two flaps.
Goerz Sector Shutter. In the improved Goerz sector shutter of 1904, designed by
Carl Paul Goerz, the functions of an iris diaphragm and a shutter were combined.
The apertures and speeds were set on dials (A). The shutter was cocked by a lever (B)
and released by a pneumatic cylinder (c). Slow speeds were provided by
a pneumatic delay cylinder (D).

Deckel's Compound Shutter, Fredrich Deckel's improved compound shutter
of 1911 had slow speeds provided by a pneumatic delay cylinder (A).
Speeds were set on a dial (B). This model had a cable release socket (c);
earlier models were pneumatically released. Deckel's Compur Shutter.
Deckel's compur shutter of 1912 was based on the Ilex design; (1) exterior view,
(2) sectional view. Slow speeds were provided by a train of gears (A),
controlled by a rocking pallet (B). A lever (c) was used to cock the shutter;
the speeds were set on a dial (D). The shutter was released by another lever (E).
Anschutz Focal Plane Shutter. Ottomar Anschiitz's focal plane shutter of 1888
was adjusted from the back of the camera. A catch (A) could be set in one of
several notches (B) on the lower edge of the upper blind (c). A cord linkage,
which was attached to the catch, adjusted the position of the lower blind (D),
setting die width of the gap and, thus, affecting the exposure time.

During the collodion era, exposure meters had not been necessary because wet plates were sensitized differently by different photographers, who determined the correct exposure time on the basis of experience. With the manufacture of standardized silver bromide plates in the late 1870s, methods of measuring the light reflected from an object and relating it to the sensitivity of the negative material became important. The first device to effectively measure and establish this relationship was a slide-rule -type exposure calculator designed and patented in 1888 by Charles Driffield and Ferdinand Hurter. Working in England as an engineer and a physical chemist respectively, in 1890 the two jointly published a significant work on sensitomctry, having devised the mathematical equations on which to base a table of exposures. Evidence of a consistent relationship between image brightness, exposure, and emulsion sensitivity was welcomed by most photographers even though this development prompted Peter Henry-Emerson to briefly reconsider his ideas about the potential of photography for artistic expression.

Measuring the light reflected from objects was done both with chemical meters—actinometers—that employed a strip of light-sensitive paper that darkened when exposed, and optical or visual devices. The latter, first made in France around 1887, consisted of numbered gradations seen through an eyepiece in which the last number visible gave the exposure time. Design changes on this kind of meter continued to be made until 1940, but none produced a reading as accurate as that produced by a photoelectric cell meter. Making use of the light-sensitive characteristics of selenium, discovered in the 1870s, the photoelectric meter was first marketed in 1932, but until the 1940s it was too expensive to be widely used. In 1938, cameras themselves began to be manufactured with built-in light meters.

Hurter and Driffield Actinograph. The Actinograph,
patented in 1888 by Ferdinand Hurter and Vero Charles Driffield,
was a slide-rule form of exposure calculator.
A rotary cylinder (A) was calibrated for a range of times of day
and year; thirteen versions were available for different latitudes.
Weston Exposure Meter. In the Weston Universal 617 meter of 1932,
the electric potential developed by two photoelectric cells was used
to deflect the needle of a meter placed between them.


Developments in Color

From the earliest days of photography, the absence of color was almost universally deplored, with the result that daguerreotypes were tinted with dry pigments and calotypes were painted with watercolors. In the wake of a patent taken out by Richard Beard in 1842 for a coloring method, instructional manuals and specialized materials appeared on the market and remained popular throughout the collodion era. However, soon after the invention of the medium, efforts by scientists to determine the sensitivity of silver salts to the colors of the spectrum had engendered the hope that photography in color would soon be possible. In these experiments, by Herschel in 1840, by Edmond Becquerel in 1848, by Nicpec de Saint-Victor in the 1850s and Alphonse Poitevin in 1865, various chemicals were added to the silver compounds without conclusive results.
In 1851 a method of making daguerreotypes in color, supposedly achieved by American Levi L. Hill, also was found to be inconclusive although it is possible that Hill had stumbled upon a result that he was unable to duplicate. Positive images in color on glass were produced in 1891 by German physicist Gabriel Lippmann on the basis of the interference theory of light waves—the phenomenon one sees in oil slicks and soap bubbles—but while the results were said to be "an admirable reproduction of the colors of nature," the long exposures and difficulties in viewing the images prevented commercial exploitation.

Experimentation to achieve viable color materials was based on the researches into human vision carried out in England by Thomas Young in the early 1800s, which were later elaborated by Hermann von Helmholtz in Germany.
These researchers held that all colors in nature are combinations of three primary colors—red, blue, and green. The full range of spectral colors can be duplicated either by adding portions of the primaries together or by subtracting them by using filters of complementary colors. In 1861, the Scottish physicist James Clerk Maxwell produced a color photograph by superimposing three positive lantern slides of a striped tartan ribbon (plate no. 337); both the taking and the projection were effected through liquid filters. At about the same time in France, Louis Ducos du Hauron attempted to perform similar experiments; in 1869, he and Charles Cros, working independently, published proposals for color processes based on the addition of three primary colors to represent the entire spectrum. However, until the invention of panchromatic film in the early 20th century, the plates used in these experiments were not sensitive enough to all spectral hues to make these efforts truly successful.

In his 1869 publication, Les Couleurs en photographic (Photography in Color), Ducos du Hauron had proposed another method by which the additive theory might result in a color image. This comprised a screen ruled with fine lines in primary colors that, when properly blocked off by their complements, would yield all the hues in nature. In other words, the primaries were to be encompassed on one negative instead of three. Ducos tin Hauron did not actually experiment with this idea, but in 1894 John Joly in Dublin produced such a screen by ruling red, green, and blue aniline dyes on a gelatin-coated glass plate. When used in conjunction with an orthochromatic dry plate and a yellow filter, the result was a color image that was limited in accuracy by the lack of sensitivity of the plates then in use. A similar but improved process, patented in 1897 in Chicago, turned out to be too expensive, but Autochrome, a process invented in 1904 by the Lumiere brothers in Lyon, produced the first commercially feasible color material based on this idea.
An Autochrome consisted of a glass plate coated with minute granules of potato starch dyed in each of the three primary colors and dusted with a fine black powder to fill in the interstices that would have allowed light to pass through; the glass was then coated with a layer of silver bromide panchromatic emulsion. The result was a positive transparency whose improved color sensitivity and relative ease of processing were immediately successful in spite of the high cost, long exposures, and the fact that the final result had to be seen in a viewer. Until the 1930s, the only real competition for Autochrome was plates manufactured by the French firm of Louis Dufay from about 1908 and by the German Agfa Company beginning in 1916, for which the dyes were poured and rolled on rather than ruled or dusted. Despite these improvements, researches to find an alternative color process continued, since these materials all produced colors that were thought nor to be natural enough, the aniline dyes were unstable (a problem that continues to bedevil color photography), and the methods of obtaining prints from transparencies were exceedingly complicated.

Dueos du Hauron's theories also proved to be the wellspring of experiments with subtractive color processes, which involved starting with white light (in which all spectral colors are present) and removing or absorbing diose colors not in the subject to be photographed. When three separation negatives taken by orange, green, and violet light are printed as positives on dichromated-gelatin sheets of their complementary colors—cyan (blue green), magenta, yellow—-and placed in register, each color absorbs its own complement; together all three produce a full-color image that Ducos du Hauron called a heliochrome. The advantages of subtraction include the avoidance of filters in the making of exposures, thereby enabling more light to reach the plate (with a consequent shortening of exposure time), and greater convenience in the viewing. Neither lines nor granules are visible in the final result, and all the light is absorbed where the primaries overlap, so that the stock on which the images are printed remains unaffected; white paper stays white. Experiments based on this process required the design of equipment to make three color negatives (either one at a time or with multiple backs on the camera) and improved methods of superimposing the three complementary positives. In this endeavor, the contributions of Frederic E. Ives, who had invented a Kromskop camera and viewer in 1895 and produced a Tripak camera that eventually was marketed in 1914 as the Hicro Universal camera, were significant.

To produce color prints, photographers turned first to the carbon process. Following Ducos du Hauron's early heliochromes on tissues dyed magenta, cyan, and yellow, nearly all color printing revolved around gelatin and carbon materials, with the Pinatype process in France, the Ives-Hicro and carbro processes in the United States, and the Jos-Pe process in Germany the best known. None of these processes survived after the middle of the 20th century, when they were replaced by methods worked out during the 1930s and popularized commercially after the second World War. Ducos du Hauron produced a lithographic reproduction and later announced that his experiments were adaptable to three-color pigment printing on mechanical presses, using red, blue, and yellow ink. Additional impetus came from the discoveries by Hermann W. Vogel regarding increased sensitizing of photographic emulsions to the green and yellow portions of the spectrum.

Experiments with pigmented-ink printing from photographs reflected the great interest in using color images in advertising and periodicals, especially in the United States during the last two decades of the 19th century. Much of the research was carried out by Ives, who by 1885 had exhibited a process for photographing colors and then reproducing them photomechanically, albeit crudely, using a camera that exposed three negatives simultaneously and then line screens to make three relief printing plates, each of which would receive a different color ink relating to the original color of the image. A more accurate process was demonstrated in 1893 by William Kurtz, a commercial photographer in New York City, who had turned his attention to the problems of halftone printing in color. Using techniques similar to Ives's—three single-line halftone blocks—he reproduced a still-life camera image whose color quality was immediately recognized as authentic enough for use in advertising such items as flowers and fruits. Just before the turn of the century, magazines began to print both covers and advertisements using the color-engraving process developed by Kurtz and perfected by others. Whether produced by using three separate halftone color blocks or with black added as a fourth block (as later became common), color images made on glossy paper by the relief printing technique have been creditable since the turn of the century. Intaglio or gravure methods have not been amenable to multiple-plate color printing, in part because of the intrinsic nature of the process and in part due to the amount of handwork required.

Toward the end of the 19th century, photolithography also began to be used for color printing, with collotype producing some of the most delicately colored prints of the era. Throughout the 20th century, as offset printing has replaced relief printing as the preferred technology, it has employed the four-color block method of superimposing magenta, cyan, yellow, and black inks to produce a full-color image. Another discovery in this area involved screenless offset, in which a plate is prepared by graining it with peaks and valleys and random patterning. The tonal range of the print depends on how light exposes the peaks and depressions.

Photomechanical Processes

Photomechanical reproduction developed during the late 19th century in response to the growing demand for photographic reproductions for social documentation and, later, advertising. The possibility of reproducing photographs in printer's ink had occurred to those who had discovered how to make light-generated images. Indeed, as early as the 1820s, Claude and Joseph Nicephore Niepce, inspired in part by the recent invention of lithography, sought to transfer engraved images onto glass and metal plates through the action of light on asphaltum and then to process the plates so that they could be printed in ink on a press.

This aim was deflected by the death of Joseph Nicephore Niepce and by the subsequent discovery of the daguerreotype, but because the unique daguerreotype did not provide a negative image for replication, printing by mechanical means continued to be recognized as a goal. Alfred Donne and Hippolyte Fizeau in Paris and Joseph Berres in Vienna were among those who experimented successfully with methods of etching metal daguerreotype plates after the image had been brought out chemically so that they could be inked and printed on a press. A booklet on the process, issued by Berres in 1840 and illustrated with five such prints, is the first work entirely illustrated by photomechanical reproduction. In 1842, two plates reproduced by Fizeau's process were included in Noel Marie Paymal Lerebours's Excursions daguerriennes. Notwith-standing these successes, the process required considerable handwork, making it slow and costly,  Given that the contemporaneous discovery of photography by William Henry Fox Talbot in England produced a negative from which prints could be made on sensitized paper, the need for a mechanical means of reproducing photographs might have become less urgent. However, during the 1840s, the limited knowledge about the infant process could not prevent instability in light-generated images, while at the same time the making of paper prints proved to be time consuming. As a consequence, Talbot himself sought methods by which the photographic positive image could be transferred onto a metal block, engraved or etched, inked, and printed on a press.

In Talbot's time, the two traditional methods by which prints were made involved breaking areas of continuous tone into patterns of discrete lines or dots. In relief printing, the areas inked were higher than the other surfaces, which did not print. In intaglio printing, the ink was introduced into cuts below the plate surface, which was wiped clean of ink to create nonprinting areas. Those attempting to utilize the photographic image in relief and intaglio printing recognized that the main challenge was to translate the continuous tonalities rendered in the original print by the darkening of the silver salts into printed lines, dots, or other patterns that would fool the eye into reading the tonalities as continuous.
The simple step of sensitizing the surface of the printing block (wood, metal, glass, or stone) so that it received light-generated images directly (without the necessity of an interim transfer) was accomplished in 1839, but solving the more complex problem of transferring photography to steel engraving began in earnest only around 1850. Talbot's experimentation, which centered on the intaglio system, is considered the forerunner of photogravure. His first patent in this area involved using potassium dichromated gelatin (the light sensitivity of which had been demonstrated in 1839) on a steel plate, with platinum dichloride as an etchant. A significant aspect of the process was Talbot's recommendation that either "a piece of black gauze" in several thicknesses with the threads intersecting one another or a glass plate on which fine lines at regular intervals had been drawn or fine particles of powdered material dispersed be used to divide the continuous tonalities into discrete elements that could be etched. These suggestions foreshadowed the eventual use of line screens in the successful gravure and halftone processes perfected toward the end of the century, but in the meantime Talbot's initial techniques required laborious handwork by skilled engravers. A second patent, taken out in 1858, improved on the process—now called photoglyphic engraving—by introducing the use of aquatint resin to break up continuous-tone areas and a different procedure for etching the plate. Both improvements simplified the process so that the intervention of die engraver could be minimized.

Talbot was not alone in experimenting with photo-reproduction techniques during the 1850s. With the need for permanent and inexpensively reproduced photographic images becoming so pressing that prize money was offered for a practicable method of making permanent prints, experimentation increased on the Continent. Working in the same direction as Talbot, Claude Felix Abel Niepce de Saint-Victor achieved relatively good results with the use of light-sensitive asphaltum and aquatint techniques on steel plates. A strong attack on the problem was mounted by Paul Pretsch, a Viennese who undertook a systematic study of methods of applying photography to printing. Eventually settling in London, in 1854 he patented a process called photogalvanography. He used potassium dichromated gelatin to produce a mold of thicker and thinner parts, representing lighter and darker areas, which then could be clectrotyped and inked so that 300 to 400 impressions could be taken.

The photogravure process that became widely used toward the end of the 19th century, and continues in modified use today, is based on the method developed in 1879 by the Viennese printer Karl Klic. A copper plate dusted with resin—to which adhered a gelatin sheet that had been exposed to light in contact with a positive and developed—-was etched in ferric acid. The acid acted more quickly on the metal where the gelatin was thinnest—the dark areas—and more slowly where it was thick, thus producing varying tonalities. Because the resin particles on the plate break up the continuous tonalities into minute grains, this process also is known as grain gravure (not to be confused with sand-grain gravure, a short-lived, complicated technique that produced an image similar in appearance to a mezzotint).
The delicate values it could produce and the soft quality of the overall image made grain gravure the preferred method for photographers who wished to produce artistic images in quantity yet felt that photographic printing was too laborious to be practicable. Starting with Peter Henry Emerson, a number of Pictorialist photographers installed flat-bed printing presses and turned out their own photo-gravures, which they chose to call original prints instead of reproductions. The process called rotogravure had commercial rather than artistic potential. Based on earlier examples of using engraved cylinders to print textile designs, it was an intaglio method and employed a crossline screen as a means of dividing the tonalities and a rotating cylinder rather than a flat plate to print the images.

Lithography (invented in Bavaria toward the end of the 18th century) required working from a flat (piano-graphic) surface and made use of the fact that fatty ink and water repel each other; where the surface had been prepared to receive the ink, it adhered and was transferred to the printing paper. Because lithography involved the creation of continuous tonalities on a flat surface, it became the process in which a great deal of experimentation took place with methods of reproducing the camera image on stone, glass, and more recently on flat metal plates. Basic to both photolithography and collotype is the fact that when light-sensitive gelatin hardens it reticulates into a network of small areas, thus providing the discrete segments in which the tonal areas of the original photographic image could be divided. The two methods differ in that collotype involves direct printing from the gelatin, whereas photolithography involves transfer of the gelatin matrix to stone or a zinc plate; the latter requires thicker gelatin and consequently results in less reticulation and thus coarser reproduction quality.

In the mid-19th century, Louis Charles Barreswil, Louis Alphonse Davanne, the Lemercier firm, Lerebours, John Pouncy, and most important, Alphonse Louis Poitevin experimented with these materials and processes. Poitevin, the most capable of the group, received a patent in 1855 for a process that involved sensitizing a lithographic stone with a solution of albumen and potassium dichromate and exposing this surface in contact with a photographic negative. The albumen turned insoluble and reticulated in the darkest areas where the light had passed through. After the unhardened albumen in the areas untouched by light was washed away, the greasy ink would adhere to the stone only in the dark areas.

In 1868 Joseph Albert, the most notable of a group of experimenters, used gelatin-coated glass plates to produce prints (which he called Albertypcs) with excellent middle tones, in runs of more than 2,000 prints. The introduction of high-speed cylinder presses in 1873 made possible large editions of photolithographs, which in addition to Albertype went by names such as artotype, autogravure, heliotype, Lichtdruck, and phototypie. Because of the irregularity and fineness of the dot structure in collotype (the name used to embrace all these efforts), it became the technology of choice for reproducing drawings and paintings in books and art reproductions. Planographic printing methods remained essentially the same until the 1960s, when new methods of setting type provided the impetus for revising photolithographic procedures.

Walter B. Woodbury, working in England in 1866, perfected a process in which a gelatin relief, produced by exposing a dichromated gelatin sheet against a photographic negative, was imbedded in a lead mold, filled with a mixture of gelatin, and then transferred to paper under pressure. The fine definition and absence of grain made the Woodburytype (calle photoglyptie in France) the most authentic translation of photographic tonalities in reproduction. Though widely used in Europe during the 1870s, the process was difficult to control in large format; and the finished print had to be trimmed and mounted before being inserted into a book or periodical.

However inventive and successful were the processes noted above, none solved the pressing problem of inexpensively reproducing photographs in books and journals simultaneously with the printing of the text, which at the rime involved the use of raised metal type. Initially this problem had been solved by having engravers translate onto a wood or metal block the continuous tonal values of the photograph, using a code of dots or lines that more or less reproduced the information in the photograph. This block—which in order to speed up the process was sometimes sawed into sections to be cut by several crafts-men and then reassembled—could be printed with the type. However, the fact that this way of translating photographic tonalities was both time consuming and inexact, combined with the tendency of engravers to add or omit portions of the camera information, necessitated a continued search for better solutions.
The technology that made possible the perfection of a halftone plate that could be used to print photographic images along with texts emerged in the late 1870s. Known generally as zincography, it grew out of early tentative efforts in the 1850s by Charles Gillot and Charles Negre in France and by a number of printers working in Vienna, Canada, and England to produce photographic etchings in relief (rather than intaglio) on zinc plates. The most significant breakthrough came in 1877, when the Jaffe brothers, owners of a printing establishment in Vienna, turned back to Talbot's use of gauze to break up the solid tones in the photograph. This technique finally became practicable through experimentation by individuals working throughout the industrialized world. Most notable were Stephen Horgan, Frederic E. Ives, George Meisenbach, and Charles Petit, all of whom substituted a screen for the miller's gauze used by the Jaffes. The screen was created by ruling cither intersecting or parallel lines on two glass plates, which then were interposed (at an angle to each other) between the photographic negative and the dichromated gelatin layer, producing a printing matrix in which the tonalities were divided into dots. The closeness of the lines on the screen governed the size of the dots; the smaller they were, the more accurate the translation from photographic print to ink print.

The contributions of Ives, an American inventor, are considered to be among the most significant in perfecting this technology. In 1886, he recommended the use of two parallel-ruled screens, superimposed at right angles to each other, to be used in front of die photographic plate in the camera; the screens were further perfected in 1890 by the American printer Max Levy to give sharp, clear definition. In addition, Ives, using copper plates coated with dichromated glue solution, worked out a method of etching the plate with the halftone image to produce a relief matrix, the surface of which would receive the ink at the same time and in the same manner as the raised surface of the text type.

Not until the appearance in the early 1960s of type generated by photographic methods did relief or letterpress printing (the method just described) give way to offset printing. In this method, both text and illustrations are printed by an updated version of photolithography. The image information is transferred to the plate through a screen similar to that used in relief printing, and the inked matrix (affixed to a cylinder) is offset onto a rubber roller before being transferred to paper. Endeavors to enrich the quality of the offset image led to the perfection of duotone printing, which uses two different plates, each with a different exposure of the same image, with one plate reproducing detail in the light areas and the other, the darks; either identical or different colored inks can be used for the plates.


Cameras and Equipment

In the early years of the 20th century, refinements in camera equipment were made in response to new demands for different kinds of images for advertising, documentation, and photojournalism. Two flexible-plate cameras, incorporating features from earlier cameras, were introduced around 1910—the Linhof (pi. no. 808), designed by Valentin Linhof in Germany, and the Speed Graphic, patented by William Folmer of the Folmer and Schwing Division of the Eastman Kodak Company in Rochester, New York; both remained relatively unchanged in design into the 1950s. The range of up-and-down, in-and-out movement of these cameras, which could be used with or without tripods, became integral to modern view and studio cameras.

Single-lens reflex (SLR) cameras were improved by being made smaller and lighter. Suggestions that such cam-eras be equipped with a pentaprism (a device for correcting the upside-down reversed image seen through the lens) in order to make eye-level viewing possible eventually led to the (East) German Zeiss-Ikon Company's introduction in 1949 of the Contax S—the first camera produced with a pentaprism built in. All single-lens reflex cameras now have either a pentaprism or another method for normalizing the inverted image.

The modern twin-lens reflex camera evolved from an apparatus developed in the 19th century in which the image received in the upper viewing lens was reflected by a mirror onto a ground glass at the top of the camera in order to facilitate focusing. Several different models were introduced from 1889 on, but it was not until the appearance of the Rollcifkx in 1928 that this type of camera achieved wide public acceptance.

A notable 20th-century advance in professional equipment was the invention of a small, lightweight 35mm roll-film camera. The Leica, introduced in 1925 (but based on a 1913 model devised by Oskar Barnack of the Leitz Company to make use of leftover movie film), became the first commercially successful instrument to offer instantaneous exposure, fast film advance, and a high level of image definition under a variety of lighting conditions. The earlier Ermanox, a small-plate camera with an exceptionally fast lens, had performed well in low-light situations, but the Leica was better suited to make repeated exposures without attracting the attention of the subject. This camera and the other 35mm instruments that quickly followed transformed photojournalism. The images they produced were sharp enough to be enlarged, and when reproduced, the multiple shots could be arranged in sequences that paralleled the action they recorded. Eventually, 35mm cameras inspired new aesthetic standards in personal photographic expression, too. later improvements to 35mm equipment included motor drives that automatically advance the film and pre-pare the shutter for the next exposure. Cameras used by professionals now are equipped with both manual and electronic controls for focus, flash, and film advance, and they can read ASA ratings from a barcode on the film. Built-in light meters measure light either from various spots or from the center, or they match the light to logarithms compiled from thousands of test pictures and built into the camera.

Camera equipment designed for amateur use also underwent significant improvement during the 20th century. The fixed-focus Eastman Brownie camera, introduced in 1900 as the cheapest and simplest camera on the market, was revised over the years until by 1963 it had evolved into the Kodak Instamatic—a light-weight eye-level instrument that accepted film cassettes; by 1972 it had become small enough to be called a pocket Instamatic, accepting 16mm film. The most recent equipment for recreational use, known as point-and-shoot (P/S) cameras, makes use of the Advanced Photo System. Developed by a consortium of equipment and film manufacturers, the system features a redesigned camera with a drop-in cassette that does not have to be wound on a spool by the user and that can be removed and reinserted no matter how many exposures have been made. The film, which offers a limited choice of formats, contains a magnetic coating that records the data essential for proper commercial processing.

One outstanding event in the amateur field was the introduction in 1948 of a camera and film that made instant one-step photography possible. The Polaroid camera, designed by Edwin H. Land, was based on an idea virtually as old as photography itself—that of sensitizing and processing the film inside the camera. A number of 19th- and early-20th-century inventions, exemplified by the Dubroni, had incorporated this concept, but the Polaroid was the first instant-print camera, requiring in its original version just one minute after exposure to produce a monochromatic positive print by means of a sealed pod of developer-fixer and a complicated image receiver. Because this system also provided a simple way to make test shots to previsualize the composition, lighting, and decor in advertising and fashion work, Polaroid film was adapted for use in professional studio and field cameras. There now exists a wide range of instant-print professional Polaroid films, including Polacolor, which was introduced in 1962 and ProVivid, introduced in 1995. The apparatus has been continually improved; the sx-70 system, introduced in 1972, was later supplanted by a 600 system that features automatic focus and electronic flash, with the batteries incorporated in the high-speed instant-color film pack.

One innovation in photographic technology was the use of standard color negative film in specially designed 35mm cameras to produce three-dimensional images in color that could be viewed in the hand without a special viewer. Another involved a camera and film system based on a disk (rather than a roll of film) that could be inserted in a camera the size of a cigarette box. Both developments, which were aimed at the mass photography market—where, it has been estimated, amateur photographers have taken over 10 billion pictures a year since 1980—had only limited success.

A development of great service to both amateur and professional photographers was that of eiectric flash illumination. Magnesium, in wire, ribbon, or powder form, had been ignited by several methods from the 1860s on (pi. no. 816), but most became obsolete after the introduction in 1925 of the flashbulb, invented in Germany by Dr. Paul Vierkotter. Encasing the magnesium wire in glass made artificial illumination safer and smoke free, and it produced less contrast. Foil-filled lamps appeared in 1929; like the wire bulbs, they were set off by batteries and eventually could be automatically triggered by the exposure mechanism of the camera. After the second World War, flash synchronization became a built-in feature of virtually all cameras; a modern mini-version is the flash cube. After 1950, the development of dry-cell-battery-powered circuitry and transistors made possible even lighter units. High-speed electric flash (known since Talbot's experiments in 1852), with a flash duration of about 1/100,000 of a second, required laboratory facilities. It was available mainly for special projects such as those carried on by Ernst Mach in Czechoslovakia in 1887 and Harold Edgerton in the United States starting in 1940. Heavy-duty electric flash systems for studio use were introduced by Kodak in the 1940s and were followed by gradually lighter and more portable electronic flash (stroboscopic) equipment; a unit designed in 1959 by Edward Rolke Farber, an American newscameraman, was probably the first.

Linhof Camera. In 1910, the first model of the famous and versatile Linhof press and professional camera appeared. It had a full range of movements and adjustments.
Speed Graphic Camera. A favorite with American press photographers in the 1940s, Speed Graphic is here shown (in a later model) with a flash-gun, which is connected to an electromagnetic release on the between- the-lens shutter. The shutter thus opened as the flash-gun was fired.

Dubroni Camera. The Dubroni camera of 1864 took a collodion-coated plate, which was held firmly against the flat-ground edges (A) of a ceramic or glass container, forming the inside of the camera. The sensitizing silver nitrate solution was introduced through a hole in the top of the camera by means of a pipette (B) and was made to flow over the plate when the camera was tilted onto its back. After exposure had taken place, the sensitizing solution was sucked out of the camera and processing chemicals were introduced into it, again by using the pipette. A yellow glass (c) in the rear door allowed the progress of development to be inspected.
Polaroid Land Camera, The first instant-print camera was the Polaroid Land 95 camera of 1948. A large roll of print paper (A) and a smaller roll of negative paper (B), connected by a leader, fitted into the top and bottom of the camera back. By means of the leader, the negative paper and the print paper were brought together and drawn between a pair of rollers (c), which broke a pod of processing chemicals, carried on the print strip, and spread its contents evenly between the two strips. After one minute, the finished print could be removed from the camera through a flap in the back.

Rolleiflex Camera. The prin-ciple of the twin-lens reflex camera: Light, passing through the upper lens (A), is reflected from a mirror (B) onto a ground-glass focusing screen (c), which is viewed through a hood (D). The film (E) is exposed through the lower lens (F). The Rolleiflex camera of 1928 was the first of the modern twin-lens retlex cameras.
Leica Camera. The Leica camera of 1925: the film winding knob (A) also set the shutter, the six speeds of which were set on a dial (B). A direct-vision, optical viewfinder (c) was fitted near the film rewind knob (D). The noninterchangeable lens was set in a helically focused, telescoping mount.

Contax S Camera. The Contax S camera of 1949 was the first 35mm single-lens reflex camera to be equipped with a built-in pentaprism; it was set in the viewfinder housing. The camera's specification included a delayed-action shutter mechanism and screw-mounted, interchangeable lenses.
Ermanox Camera. The Ernemann Ermanox camera of 1924 carried its f/2 Ernostar lens in a helical focusing mount. A folding, optical frame viewfinder was fitted, and the focal plane shutter gave speeds from 1/20 to 1/1,000 second.

Ceramic Magnesium Lamp. A ceramic magnesium lamp, typical of the powder flash lamps made in the 1890s. A charge of magnesium powder was placed in the funnel (A), which was surrounded by a circular tray (B). When lit, the spirit-soaked cotton wool in this tray gave a circular flame. A rubber bulb (c) was squeezed to inflate a thin-wallcd rubber bag (D), connected to the lamp by a clamped (E) tube. When the clamp was released, the puff of air propelled the magnesium powder through the flame.
Burvin Synchronizer. The Burvin Synchronizer of 1934 was designed for miniature cameras, notably the Leica. It was fitted to the underside of the camera and was coupled to the shutter by means of a cable release. The synchronizer could be precisely adjusted so that the flash was fired when the shutter was fully open.

Eastman's Brownie Camera. The original Brownie camera of 1900 had the shutter release (A) and the film winding key (B) on the top; the film rolls (C) were placed vertically. To help in aiming the camera, V-lines (D) were marked on it. The first Brownie models had a push-on back (F.) with a red window (F), but an improved back, hinged at the bottom and with a sliding catch at the top, was soon introduced.
Kodak Instamatic Camera. The Kodak Instamatic cam-eras were introduced in 1963. They took a drop-in cartridge that greatly simplified the loading of the cameras. Like most of the Instamatic cameras, the model 100 had a built-in, pop-up flash gun, released by a button.


Materials and Processes

Photographic materials have undergone considerable refinement since the invention of the medium, but perhaps the most significant change has been the increase in the light sensitivity of film emulsions. It has been estimated that from the daguerreotype of 1839 to the materials of the late 1970s, the sensitivity of film in full sunlight at f/16 aperture increased 24 million times. Both black and white and color film differ in sensitivity according to the size of the silver halide crystals suspended in the gelatin emulsion. Black and white and color films are rated from slow (ASA/ISO 25) to fast (ASA/ISO IOOO or more), with the larger crystals in the faster film more sensitive to light, thereby enabling faster shutter speeds to be used in making the exposure. In the past, the larger crystals in high-speed film usually resulted in grainier and less tonally defined images (especially in enlargement), but in recent years both black and white and color positive and negative films have been vastly improved in terms of speed and resolution. Manufacturers have recently marketed films in which the final monochromatic image is formed by a different arrangement of silver halide crystals or by crystals to which dyed couplers have been added. Film is now available in a variety of formats, speeds, sensitivities, and contrasts designed to meet the differing needs of amateurs and professionals. For use in scientific documentation and for penetrating haze conditions, infrared film, sensitive to light that is not visible to the human eye, is being used.

For black and white prints, two basic kinds of paper are available: resin coated (RC) and fiber based. Both have a gelatin coating over the light-sensitive emulsion on a paper base, but the RC: papers carry extra plastic layers on the bottom and beneath the emulsion layer. Both come in different grades of contrast.

One very significant development in the 20th century has been the improvement of color. Following the invention of Autochrome palates (see A Short Technical Histoiy. Part II), a variety of color materials appeared (Dufay Dioptichrome, Fenske's Aurora, Szezepanik-Hollborn Veracolor, Whitfield's Paget Colour Plates, Dawson's Leto Colour Plates, and Agfacolor), all of which were based on additive-color principles. From the second decade of this century on, George Eastman and the Kodak Research Laboratory worked on color materials, exploring additive processes that would enable amateurs and snapshooters to obtain color images without mastering complex technicai skills. By 1925, as the demand for color grew, so did the efforts to find a practicable system based on subtractive principles, a search that was further stimulated by competition among commercial firms and the Hollywood film industry, which looked toward color as an inducement to moviegoers during the Great Depression. During the 1930s, this goal became achievable with the discovery of new and more stable sensitizing dyes.

The possibility of adapting subtractive color theory to the production of color film was suggested early in the century by Karl Schinzel of Austria and Rudolph Fischer of Germany. They envisaged the formation of a triple-layer emulsion containing dye-couplers in primary colors that would block out their complements, which was realized some 25 years later in Kodachrome, Invented by the American amateur chemists and musicians Leopold Godowsky and Leopold Marines in collaboration with Kodak Research Laboratory personnel, Kodachrome became the first tripack film to be released—first in 1935, as movie film, then as sheet film in 1938 and as a negative Kodacolor roll film in 1942. The German Agfa Company—which had introduced a color plate that rivaled Autochrome in 1916 and had been experimenting with tripack systems based on subtractive theory—in 1936 announced Agfacolor Neu, a three-layer film in which the dye couplers were incorporated in the layers and released during development; this enabled the film to be processed in individual darkrooms. An almost identical product was marketed in 1939 by Ansco, the American firm affiliated with Agfa. In 1946, Eastman Kodak marketed Ektachrome, a positive transparency film that could be processed in home darkrooms; shortly thereafter, the same firm introduced Ektacolor—a color negative film from which prints could be made. Today's color films are some 32 times faster than the early versions, and processing time has been reduced from hours to minutes.

Initially, Kodak color products were sent back to the company for processing and were returned to the customers in the form of positive transparencies rather than color prints. In consequence, the use of 35mm color film gave rise to renewed interest among amateurs in slides and slide projection during the late 1940s. Color positive films (transparencies) were preferred to color negative film by many professionals because they had a finer grain and were therefore sharper. The projection of color positives was no longer just an amateur pastime but became of interest to educational institutions and corporations, which found color slides and sophisticated multiple-imaging systems to be successful teaching and sales tools.

Starting with Louis Ducos du Hauron, color prints were made by using a variant of the carbon process that is now called assembly printing. This procedure was transformed into ozo-brome—a monochromatic print—invented in 1905 by Thomas Manley in England, from which carbro (or trichrome carbro) evolved into a full-color print during the early 1920s and remained popular until World War II. The Eastman wash-off relief process, introduced in 1935, was similar to the carbro process except that greater control ensured that there were fewer variations from print to print. In 1946 Eastman introduced a substitute—the Kodak dye-transfer (or dye-imbibition) system—whereby three separation negatives were used to produce three gelatin-relief images that were dyed magenta, cyan, and yellow; eventually the three images were made directly from a tripack negative film by exposing it through filters. For the print, the three dyed reliefs were transferred in exact register to gelatin-coated paper.

At present, color negatives and positives are created by-one of two methods: the chromogenic system, in which dyes are added during the processing, and the dye-destruction (or dye-bleach) system, in which a complete set of dyes is present at the start and the ones not needed to form die image are subsequently removed by bleaching. The latter method, which evolved from experiments undertaken in Hungary in 1930 by Bela Gaspar, is basic to Cibachrome. Within the chromogenic system, two methods can be used: the dye-injection system mentioned above in connection with Kodachrome or the dye-incorporation method. In the latter—used in the manufacture of nearly all well-known color films and color printing papers—the chemicals that will form the dyes are included in each layer of the emulsion and are activated during processing.


As greater numbers of serious photographers began to work in color during the 1970s, questions regarding the stability of the images became more pressing. Central to the problem is the fact that magenta, cyan, and yellow dyes change and fade at differing rates when exposed to regular light and to ultraviolet radiation. Also, color materials arc affected to an even greater degree than monochromatic silver crystals by humidity, heat, and chemicals in the environment. With both color and black and white images being collected by individuals and museums, increasing awareness of the potential problems in the conservation of photographic materials has prompted efforts by manufacturers to produce more stable products. Specialists in conservation have devised strategies to print, store, and display all types of photographs in ways that will minimize their deterioration. At the same time, interest in restoring works that have already deteriorated has grown. These developments reflect the fact that the photograph has become an artistic commodity with market value, but they also offer a promise that diverse images can be preserved, no matter what their original purpose may have been.


An entirely new idea in image-making, holography has been developed only within the last 45 years or so. A hologram (from the Greek holos—whole—and gramma— message) is a three-dimensional image that appears on a film or glass that has been coated with photographic emul-sion and exposed to laser light reflected from an object. In order to produce a hologram, the laser beam must be split into two parts by a beam splitter (partial mirror). A full mirror directs one beam to the object; the other, known as the reference beam, is directed by another mirror to the emulsion surface on which the image will be recorded. In the area where the light from the reference beam and the light from the object meet, they expose a pattern of lines (interference fringes) that will form the image after the emulsion is photographically processed. The hologram becomes visible when it is illuminated from the same direction as the original reference beam. There are two main kinds of holograms: transmission and reflection. Transmission holograms are illuminated from either laser or white light sources located behind or below the emulsion surface; reflection holograms become visible when white light bounces off the surface of the emulsion.

Holography is based on experiments in the reconstruction of optical phenomena conducted by the Hungarian scientist Dennis Gabor in 1947 (for which he was awarded a Nobel Prize in 1971) and on the invention in i960 of a new device for manipulating light known as the laser. In 1962, Emmett Leith and Juris Upatnicks in the United States and Yuri Denisyuk in the Soviet Union independently invented techniques for recording on photographic plates the image of objects illuminated by laser beams. Improvements in holographic techniques have included methods of making frill-color holograms discovered by Stephen Benton and Denisyuk. Holograms have found a practical use in the scanning of earth formations and the locating of buried archaeological remains, in advertising, in scientific and optical measurements, and in the production of three-dimensional models of industrial objects, buildings, and human cells. They are also being investigated as a method of efficient data storage and for the creation of three-dimensional film and television images. In addition, artists in the United States, Eastern Europe, Japan, England, and Australia have experimented with holograms as a means of personal artistic expression.

Digital Image-Making

Electronic imaging is a fairly recent development that has already had significant effects, especially on the reproduction of photographs. Made possible initially by the invention in 1945 of electronic analog computers, the ability to produce and enhance images using this instrument received considerable impetus from the photographic

explorations of space carried out by NASA in the 1960s. At first, computers enhanced photographs taken in space by satellites by eliminating imperfections or by transforming multiple views from varying perspectives into three-dimen¬sional images. Eventually, digital cameras, which convert light rays into electronic signals, were used to picture the most distant reaches of the solar system. Also in the 1960s, electronic imaging made its way into specialized fields such as archaeology, the medical sciences, and military surveil¬lance; light, measured by sensors, can produce images of buried cities, brain cells, DNA structure, or hidden military installations.

Around 1979, computers became digital—that is, equipped to process information about light and shade by dividing the picture plane into a microscopic grid and by designating the tone and color of each tiny cell, or pixel, by a number. Stored in the computer's memory, pixels can be viewed on a screen, altered if desired, and printed or transmitted. Image resolution and detail are determined by the density of pixels—higher resolution and greater detail require a larger number of pixels, which in turn requires more computer memory. The communications industries used computers to size images, to create color separations, and to facilitate the manipulation and combination of photographs. With the introduction of the microchip in the early 1980s, smaller and less expensive personal computers became available to a larger public-— artists and photographers among them. By the mid-1990s, the expansion of color capabilities allowed users a choice of over 16 million colors.

The digitally encoded image is sometimes referred to as "electronic photography" or "still video," but its physical characteristics are different from those of traditional photographic representations or video images. In both of those media, the changes in tonality are continuous—that is, the tones blend together in uninterrupted gradations from black to white.

Enlarging a photographic image captured on a silver-based negative produces more information than can be seen in small format, but the larger the image the fuzzier its forms become. Because their number is finite, enlarging a grid of pixels will not yield more information, but color and tone will remain unchanged (although the grid itselt will become visible and distort the image). Furthermore, quality is lost when traditional photographs are copied (a copy negative, for example, is always less sharp than the original negative), whereas digital copies are indistinguishable from each other.

Digital images can be produced in several ways: by using a digital camera, which has light sensors that record information about outside reality on a magnetic disk or memory card; by a scanner, which digitizes the information from a flat visual field, such as a painting or photograph; or by a software graphics system, which is used in a computer to select and organize pixels into original arrangements of color and form. The digital camera (or a special back designed to be attached to a conventional camera), which was introduced to the public in 1990, is analogous to a conventional camera only in that it records images of external reality. Increasingly, photojournalists use this apparatus to capture their images on disk or memory cards and then transmit them over the telephone wires to an editor with a computer. This process eliminates the need for chemical processing in darkrooms, and specially designed software facilitates once-laborious tasks such as enlarging, dodging, burning in, toning, and retouching. (Digital images can nonetheless simulate the effects of different film emulsions, developers, and toners.)

In the past, photo editors routinely cropped and edited the prints submitted by photographers, usually with their knowledge and acquiescence. Now, however, photojournalists who must file picture stories by transmitting electronic images directly to photo editors for processing and editing in the computer have, by and large, given up individual control over their images used in print. Because there is no "original" hard copy in the traditional sense—that is, no negative—photographers have little recourse when images are manipulated without their con-sent or knowledge. These and other issues raised—both for photojournalists and for viewers—by the increasing use of digitized images in the news media have prompted a number of books on the subject, among the first being Fred Ritchin's In Our Own Image: The Coming Revolution in Photography (1990).

A scanner, which reads images and texts and translates them into pixels, permits the creation of digital archives of artwork, photographs, and documents. Because this mate-rial can be housed on disks and printed out only as needed, space is saved and wear and tear on the original work is reduced. The usefulness of such archives has been enhanced by the emergence of on-iine services, which give subscribers with computers access to a variety of indepth records—among them library catalogs and picture collections. Scanners also enable artists to appropriate images from any printed image as well as from on-line services in order to transform them for their own expressive purposes.

Various software programs, tailored for both the professional and the amateur, facilitate the creation of images in the computer. "Imaging software" refers to programs, which can be used in conjunction with digitally captured or scanned images, that allow the operator to mask out elements, to make color separations, and to produce montages and special effects. There are, in addition, "paint programs" that an operator can use to create entirely new shapes, forms, and colors, as well as combine these elements with scanned images. Three-dimensional images can also be generated, and they can be made to rotate so that all their surfaces are visible. This idea first emerged in the late 1960s; later research into position-sensing techniques has made possible a more sophisticated approach known as "virtual reality. Architects, for example, can now "walk" through the digital representation of the spaces of proposed buildings, and doctors can see a three-dimensional image of any body part as if looking through the skin or skull.

Computer-generated images can also be printed as hard copy. Depending on the kind of printing equipment used (dot matrix, inkjet, laser), the image can be printed either on film for processing as a traditional silver print or on paper, fabric, or other materials. Print quality is directly related to the quality of the printer. As a consequence, printing highly resolved digitized images is usually done by specialized laboratories.

As has been the case with conventional photographic technology throughout its 150 plus years of existence, the equipment and methods of electronic imaging will continue to change—in all probability', with greater rapidity than was true of photography based on silver processes. Whatever these changes entail, there can be little doubt that in the future a great many of the tasks previously undertaken by conventional photography will be effected through the use of a computer.