How was photography invented?

Photography was not invented in a single moment. It joined two older ideas: the camera obscura, which projects an image of a scene, and chemicals that change when exposed to light. In the 1820s the French inventor Joseph Nicéphore Niépce used a bitumen-coated plate in a camera obscura to make the earliest surviving camera photograph. After his death, Louis-Jacques-Mandé Daguerre built on his work and introduced the daguerreotype in 1839. [1] [2]

Since ancient times people had noticed that light passing through a small hole into a dark room projects an upside-down image on the opposite wall. By the 17th century this had become a portable drawing aid, the camera obscura, a box with a lens that let an artist trace the projected image. What it could not do was keep the image. [2]

The chemical side developed through the 18th century. In the 1720s Johann Heinrich Schulze showed that light, not heat, darkened silver salts. In the 1770s Carl Wilhelm Scheele found that the darkening was a reduction to metallic silver and that ammonia stabilized darkened silver chloride. Around 1802 Humphry Davy published Thomas Wedgwood's experiments with silver nitrate. Their camera images were too faint, and their contact prints of paintings and silhouettes darkened all over because they could not stop the reaction. [2]

Niépce was an amateur scientist and inventor from an old aristocratic family. Around 1816 he began experimenting with printmaking techniques and produced fleeting camera pictures. He settled on bitumen of Judea, a resinous substance that hardens when exposed to light, and called his process heliography, or sun writing. [2] [1]

For his famous image, he coated a polished pewter plate with bitumen dissolved in lavender oil and put it in a camera obscura at an upstairs window. After an exposure of anywhere from eight hours to several days, he washed the plate with lavender oil and white petroleum, which dissolved the bitumen that light had not hardened. The result, View from the Window at Le Gras, shows his family's buildings and a pear tree. It is grainy and lacks detail. [3]

The sources disagree on the date. The Harry Ransom Center gives 1827, the Science History Institute gives 1826, and the Niépce museum site dates his first fixed landscape to 1824. The Oxford History of Science Museum says 1826 or 1827. Niépce himself called the result "the first uncertain step in a completely new direction." [1] [2] [4] [5]

Daguerre, who ran the Diorama in Paris, wrote to Niépce, and in 1829 the two formed a partnership. They met only once but corresponded often. Niépce died of a stroke in July 1833. Daguerre continued the work. In 1835 he found that mercury vapor brought out a latent image on a silver-coated copper plate, and about two years later he fixed such images permanently with a salt solution. [2]

The daguerreotype needed minutes of exposure rather than hours or days, and it was remarkably sharp. It was also fragile, lacked color, and was hard to see except at certain angles. The invention was announced in 1839, and the Harry Ransom Center notes that photography was announced in both France and England that year. [2] [1] [6]