A pinhole camera consists of a darkened box or room with a small hole at one end. Because light travels in straight lines, the hole permits rays from each point of an object to fall only within a small circle on the opposite wall, effectively forming an image. As the pinhole is made smaller the image will become more distinct until the hole is so small that diffraction becomes important.
Although pinhole cameras were probably known to the ancient Greeks, they are still used in preference to lens systems in some situations. Pinholes are obviously useful for imaging x- rays or particle streams, where no lens materials are available, but even for light they offer complete freedom from linear distortion, virtually infinite depth of focus and a very wide angular field. Modest resolution and a very dim image are the disadvantages. Overall, pinhole cameras are worth study because they are useful and also because they illustrate some interesting physics.