How Was Photography Invented? From the Camera Obscura to the Sensor

The chemical fact was known by 1727, when a German professor, Johann Schulze, noticed that a jar of chalk and silver nitrate darkened where the sun struck it. Thomas Wedgwood, son of the potter, used the effect around 1800 to make silhouettes of leaves on leather soaked in silver salts, but he could not stop the process: the whole sheet went dark once it was brought into the light. The first person to fix an image was Nicephore Niepce, a gentleman inventor in Burgundy, who in 1826 or 1827 coated a pewter plate with bitumen, which hardens where light falls, exposed it in a camera pointed out of his window for a day or more, and washed away the unhardened parts. The view from his window survives, the oldest photograph in the world, and it is almost unreadable.

Niepce died in 1833, and his partner, the Parisian showman and painter Louis Daguerre, went on to a different process: a silver-plated copper sheet made sensitive with iodine vapour, exposed for a few minutes, developed with mercury fumes and fixed with salt. The daguerreotype was a small mirror holding an image of hallucinatory sharpness, and when it was announced in January 1839 and the French government bought the rights and gave them to the world that August, Paris went photography-mad within the month. In England William Henry Fox Talbot, who had been working quietly since 1834, hurried his own method into print: paper soaked in silver salts, which produced a negative from which any number of positive prints could be made. The two methods divided the field:

• •The daguerreotype: exquisitely detailed, a unique object with no negative, reversed left to right, and the dominant form of portrait until the 1850s
• •Talbot's calotype: softer, on paper, reproducible from a negative, and the ancestor of every photographic process that followed
• •The wet collodion process of 1851: glass negatives with the detail of one and the reproducibility of the other, at the cost of coating, exposing and developing the plate within minutes while it was still wet, which is why Victorian photographers travelled with tents
• •The dry gelatin plate of the 1870s, and then roll film in 1888, sold by George Eastman in a box camera under the slogan that the customer pressed the button and Kodak did the rest

The painter Paul Delaroche is supposed to have said, on seeing a daguerreotype, that from that day painting was dead. It was not, but it was released from a job. Portrait miniaturists went out of business within a decade; the recording of faces, places and events passed to the camera, and painting turned towards what the camera could not do, which is one of the roots of impressionism and everything after. Photography also changed what people knew. Roger Fenton's pictures of the Crimean War in 1855 and Mathew Brady's of the American Civil War were the first time the public had seen a battlefield, Eadweard Muybridge's sequences of a galloping horse in 1878 settled the question of whether all four hooves left the ground at once, and the family album, the passport, the mugshot and the X-ray followed within a generation. The question of whether a photograph is art was argued from the beginning, and settled in practice by Julia Margaret Cameron, Alfred Stieglitz and the others who made ones that were.

Colour arrived slowly: the Lumiere brothers' autochrome plates in 1907, made with dyed grains of potato starch, and Kodachrome film in 1935. The next revolution replaced the chemistry altogether. In 1969 two engineers at Bell Labs invented the charge-coupled device, a silicon chip in which light knocks electrons loose in a grid of cells and the charges are read out as numbers, and a Kodak engineer built the first digital camera from one in 1975, a device the size of a toaster that recorded a 100 by 100 pixel image onto a cassette tape in twenty-three seconds. Kodak, which had invented it, did not want to disturb its film business and was bankrupt by 2012. The sensor in a phone today has tens of millions of cells, each smaller than a bacterium, and the phone takes more photographs in a day than were made in the entire nineteenth century. The optics have barely changed since Niepce's window: a lens, a dark box, an image thrown upside down onto a surface that remembers it.

The usual explanation for the stern faces in Victorian portraits is that exposures were too long to hold a smile, and in the earliest years that was true. A daguerreotype portrait could need many seconds to minutes in bright light, and studios used iron head braces hidden behind the sitter to stop them moving. But brighter lenses and more sensitive chemistry soon cut exposure times to a few seconds, and serious faces persisted for decades. Custom mattered as much as chemistry: a portrait was an expensive, formal record, modelled on painted portraits, where a broad grin was associated with drunkenness or foolishness.

Early materials also saw colour differently from the eye, which changes how people and places look in old pictures. Most early plates and films were sensitive mainly to blue and violet light and barely registered red, so red lips looked dark, blue skies came out white and blank, and freckles or ruddy cheeks appeared darker than in life. It is also why photographers could develop their plates by the light of a red lamp without spoiling them. Film sensitive to the full range of visible colours only became common in the twentieth century, gradually giving monochrome photographs their more natural tones.

Daguerre and Talbot were not alone. In Paris, Hippolyte Bayard, a civil servant at the Ministry of Finance, invented his own way of making positive images directly on paper, and in June 1839 he put about thirty of them on show, the first public exhibition of photographs. Officials who were promoting Daguerre's process persuaded him to hold back, and he received far less recognition and money. In 1840 he replied with a picture of himself slumped as if dead, with a note on the back complaining that the neglected inventor had drowned himself. It is often called the first staged photograph.

Further away, in the Brazilian town of Campinas, a French-born artist named Hercules Florence was experimenting with light-sensitive silver compounds in the early 1830s, partly in search of a cheap way to print labels and documents. His notebooks from 1834 use the word photographie, years before it became common in Europe, where the astronomer John Herschel popularised photography in 1839 and soon afterwards the terms negative and positive. Florence worked in isolation and published little, and his achievement was only recognised when a historian studied his papers in the 1970s. Invention, here as so often, was happening in several places at once.

The principle behind nearly all colour photography was demonstrated in 1861, decades before colour film existed. The physicist James Clerk Maxwell, who had studied how the eye builds every colour from three kinds of receptor, arranged for the photographer Thomas Sutton to photograph a tartan ribbon three times, through filters of red, green and blue. Positive images were made from each negative and projected onto a screen through the same three filters, carefully overlapped. A coloured picture of the ribbon appeared, shown at a lecture at the Royal Institution in London, and the idea of rebuilding colour from three separate records was established.

There was a puzzle in the result that went unexplained for a century. The plates of the time were barely sensitive to red light, so the red exposure should have been almost blank. When researchers at Kodak looked into the demonstration in 1961, they concluded that the red parts of the ribbon happened to reflect ultraviolet light, which passed through the red filter and was recorded instead. Maxwell's success owed something to luck, but the method was sound. In the early twentieth century the Russian photographer Sergei Prokudin-Gorsky used it to record the Russian Empire in colour, taking three filtered exposures in quick succession on a single glass plate.

Photography was invented when the centuries-old projected image of the camera obscura was made permanent by chemistry: Niepce fixed the first one with bitumen in the 1820s, Daguerre's silvered plates and Talbot's paper negatives were both announced in 1839, glass plates and then roll film made it fast and reproducible, and the silicon sensor of 1969 replaced silver with numbers. It took portraiture and documentation away from painting and gave the world a new way of remembering and of knowing.