History TOPIC ID 52
1727 Johann H. Schulze, a German physicist, discovers that silver salts turn dark when exposed to light.
1780s Carl Scheele, a Swedish chemist, shows that the changes in the color of the silver salts could be made permanent through the use of chemicals
1826 A French inventor, Nicephore Niepce, produces a permanent image by coating a metal plate with a light-sensitive chemical and exposing the plate to light for about eight hours.
1830s Louis Daguerre, a French inventor, develops the first practical method of photography by placing a sheet of silver-coated copper treated with crystals of iodine inside a camera and exposing it to an image for 5 to 40 minutes. Vapors from heated mercury developed the image and sodium thiosulfate made the image permanent.
1839 A British inventor, William H. Fox Talbot, an English classical archaeologist, made paper sensitive to light by bathing it in a solution of salt and silver nitrate. The silver turned dark when exposed to light and created a negative, which could be used to print positives on other sheets of light sensitive paper.
1840s Josef M. Petzval, a Hungarian mathematician, develops lenses for portrait and landscape photographs, which produce sharper images and admit more light, thus reducing exposure time.
1851 The British photographer Frederick S. Archer develops a photographic process using a glass plate coated with a mixture of silver salts and an emulsion made of collodion. Because the collodion had to remain moist during exposure and developing, photographers had to process the pictures immediately.
1871 Richard L. Maddox, a British physician, invents the "dry-plate" process, using an emulsion of gelatin, so that photographers did not have to process the pictures immediately. By the late 1870s, exposure time had been reduced to 1/25th of a second. Gelatin emulsion made it possible to produce prints that were larger than the original negatives, allowing manufacturers to reduce the size of cameras.
1888 George Eastman introduces the lightweight, inexpensive Kodak camera, using film wound on rollers.