Photography is the recording of visible images by focusing light on light-sensitive materials. English astronomer Sir John Herschel (1792-1871) first used the term photography in 1839. The word comes from the Greek photos, meaning light, and graphos, meaning writing.

There are many forms of photography. Still photography captures individual self-contained images on single sheets of film. Portraits are an example of still photography. Motion photography, also called cinematography, records a series of images illustrating a subject in motion. These photographic images are focused onto a screen using a movie projector. Television, video, even medical x rays are based on the principles of photography.

The predecessor to the modern handheld camera was the camera obscura. This giant, cumbersome device consisted of a dark box or room with a tiny hole in one wall. When peered through the tiny opening, an inverted image could be seen on the opposite wall. Leonardo...