The Origins of Photography

Photography is a method for producing lasting images by means of a chemical reaction that occurs when light hits a specially prepared surface. It was invented during the first three decades of the 19th century as a direct consequence of advances in chemistry and optics (the science of the behavior of light). The word photography comes from two Greek words that mean "writing with light."

Although the technology is fairly recent, the origins of photography lie in an artistic technique known as single-point or linear perspective, which was developed in the early 1400s. Pioneered in Italy by architect Filippo Brunelleschi and others, the system of single-point perspective provided painters with a method for depicting three-dimensional space on a flat surface. It is based on the notion of a single observation point and results in lines that appear to recede into the distance by converging on a fixed point on the horizon, called the vanishing point.

In the 16th century many artists employed a boxlike device known as a camera obscura (Latin meaning "dark room") as an aid to depicting space with single-point perspective. This consisted of a box with a pinhole on one side and a glass screen on the other. Light coming through this pinhole projected an image onto the glass screen, where the artist could easily trace it by hand. Artists soon discovered that they could obtain an even sharper image by using a small lens in place of the pinhole. The camera obscura was used by Renaissance artists such as Michelangelo and Leonardo da Vinci.

Also essential to the invention of photography was knowledge of the light sensitivity of certain materials. More than 2000 years before the invention of the camera obscura, the ancient Phoenicians knew that a certain snail, the purpura, left a yellow slime in its wake that turned purple in sunlight. In the 18th century a German anatomy professor, Johann Heinrich Schulze, observed that silver salts darkened when exposed to light. But the idea of making pictures using this phenomenon did not occur to him. That innovation required the talents of a later generation of scientists.

By 1800 a young English chemist, Thomas Wedgwood, had succeeded in producing images of leaves on leather that he had treated with silver salts. However, he could find no way to halt the darkening action of light and his leaf images eventually faded into blackness. His attempts to capture the image displayed by a camera obscura also proved unsuccessful. For the birth of photography two key discoveries were still needed: a way to combine a light-sensitive material with the camera obscura, and a way to fix, or make permanent, the resulting image.