The pinhole camera or camera obscura is one of the oldest optical devices. Pinhole photography is lensless photography, ligth passes through the hole and an image is formed. Legend has it that pinhole was discovered by an Arab who saw, on his awakening, a marvelous vision on the wall of his tent. Then he realized that the "vision" was an image produced by a little hole in the tent. This legend may or may not be true. Certainly the Chinese and the Greeks knew the principle of the pinhole camera and used it for observation of solar eclipses. The Arabian physicist and mathematician Alhazen (about 1000 A.D.) explained why the image is upside down. Leonardo da Vinci cited the device in Codex Atlanticus, while the first detailed widely known description of the pinhole camera was given by Giambattista della Porta (about 1560) in his Magiae Naturalis. A fair account of pinhole story and other useful information can be found in Pinhole Photography by Jon Grepstad. Pinhole cameras have some remarkable features: no distortion, great depth of focus, reasonable degree of resolution, and a major shorcoming: they are very slow (about f/100 or more). A pinhole "lens" can be easily designed considering the pinhole as a particular case of a Fresnel zone plate. A Fresnel zone plate consists of a series of concentric circles whose radii are proportional to the square root of whole numbers. The zones corresponding to odd or even numbers are blackened. Using the relation for zone plate under plane wave illumination, a design equation can be found. A very practical pinhole camera can be easily realized mounting the pinhole "lens" on a low-cost Leica copy. This pinhole camera has great flexibility. As the pinhole is just a "lens", you can always replace it and take a "normal" photo. A pinhole "lens" can also be mounted on a TV camera, thus realizing an electronic camera obscura. We enjoyed a lot using our pinhole cameras.
