||Photography (Greek, â€˜writing with lightâ€™), is the process or art of creating optical images on photosensitive surfaces.
The principles on which photography is based were known to the Greek philosopher and scientist Archimedes who knew that if a small pinhole is made in the wall of a darkened space, then images appear upside down and back to front on the opposing wall. This discovery was not utilized until the early 1800s when, in 1826 or 1827, Joseph NicÃ©phore NiÃ¨pce managed to fix an image upon pewter plates. The picture was formed by the reaction of a thin layer of silver iodide to the light falling on it. In the brightest parts of the picture the silver iodide is decomposed and a thin deposit of silver is laid down. When the excess silver iodide was removed, using mercury vapour, a reverse picture or negative was formed by the silver which in fine powder form appeared to be black. Thus the brighter the image at a particular spot the more black-appearing silver was deposited. When the light was darker then less silver was deposited and the image appeared brighter. Thus the whole picture was formed. He called the process heliography from the Greek helio â€˜the sunâ€™. In 1827, NiÃ¨pce met Louis Jacques MandÃ© Daguerre who was working on a similar project. It was Daguerre and not NiÃ¨pce who took the credit for the first practical process of photography, when the AcadÃ©mie des Sciences in Paris in 1839 claimed that Daguerre had discovered a method of permanently recording an image produced by the pinhole camera. His invention, called a daguerreotype, was soon making its impact throughout the world.
Although the daguerreotype was a major breakthrough, it was obsolete within twenty years as other developments superseded it, particularly the introduction by William Henry Fox Talbot of transparent photographic plates which formed the negative image. These could be used to produce negatives of themselves, that is, a positive image. Photography was still unwieldy and awkward as the subject had to remain stationary for minutes on end in order to expose the plates to the right amount of light, since the emulsions used then were not very sensitive.
The introduction in 1871 of â€˜dryâ€™ plates, instead of the wet plates which had been used up until then, transformed photography. Dry plates were made of celluloid or gelatine which provided a transparent, flexible backing for the recording of images. Photography was, by now, a big business as it recorded images of the Victorian age.
The next step was trying to invent a process which could make these images move in synchronization. The first photographs of moving objects were taken in 1877 when Eadweard Muybridge managed to record how a horse gallops by the use of multiple cameras each taking a single image as the horse passed. He invented a â€˜zoopraxiscopeâ€™ which animated his pictures giving the impression of movement. This inspired the LumiÃ¨re brothers in Paris to devise a combined camera and projector. This invention managed to film an event and then have it ready for projection within 48 hours. This was the start of the cinema which first opened in Paris in 1895.
Other innovations such as colour photography and the mass-production of the Kodak camera by George Eastman have made photography one of the biggest businesses in the world. It will remain so as long as people are still influenced by seductive advertisements, the medical profession requires stills of internal scans or the amateur captures moments for his or her own posterity.
Other forms of photography are well known. Most x-rays of the human body are recorded on photographic film. A less well-known type of photography uses film which is only sensitive to infrared light and the camera uses filters to keep normal visible light from the lens. Pictures produced in this way show the surface temperature of the target. In medicine this can be used to detect regions of below normal temperature, for example due to blood circulation restrictions or more frequently to show high skin temperatures which may correspond to the start of â€˜pressure zonesâ€™ in the disabled who spend their life sitting or lying in bed for long periods. After an injury by burning this kind of picture can direct the kind of treatment required by identifying whether the burn is second degree or third degree of severity. Industrially, such pictures of factories can show regions of high temperature where heat is being lost to the atmosphere and form a guide to the area where energy is being lost. AA
Further reading E. Stenger, A History of Photography: its Relation to Civilisation and Practice (1939).