If you go into a room darkened by a heavy shade on a sunny day and prick the shade with a pin, you will see the image of the outside world on the opposite wall, in color but upside down. This dark room, or camera obscura in Latin, illustrates the physics and origin of the modern photographic camera.

This phenomenon was observed as early as the 5th century BCE in China and was studied by Aristotle, the Arabian scholar Alhazen of Basra, and Leonardo da Vinci among others, particularly as a technique for viewing solar eclipses.

The complexity of the camera obscura remained at the level of a pin prick in a darkened tent until the 16th century when lenses and mirrors were introduced. In the early 17th century, the German astronomer Johannes Kepler was the first to use the term camera obscura.

San Francisco's Camera Obscura, located above the Pacific behind the Cliff House, was built by Floyd Jennings in 1946 as an attraction for nearby Playland-at-the-Beach. About ten years later, Mr. Jennings modified the building to look like a camera carelessly left behind by a giant tourist enraptured by the view of the Pacific.

The simple mechanism consists of a ten-inch rotating mirror which projects a flowing image of the outside world through focusing lenses onto a horizontal viewing surface.