Camera obscura

A camera obscura (pl. camerae obscurae or camera obscuras; from Latin camera obscūra 'dark chamber') is the natural phenomenon in which light passing through the small hole of a dark chamber or box will project an image of a scene outside the chamber (box) onto the surface opposite to the hole, resulting in an inverted (upside down) and reversed (left to right) projection of the view outside.

Camera obscura refers to analogous constructions such as a darkened room, box or tent in which an exterior image is projected inside or onto a translucent screen viewed from outside. Camera obscuras with a lens in the opening have been used since the second half of the 16th century and became popular as aids for drawing and painting. The technology was developed further into the photographic camera in the first half of the 19th century, when camera obscura boxes were used to expose light-sensitive materials to the projected image.

The image (or the principle of its projection) of a lensless camera obscura is also referred to as a "pinhole image".

The camera obscura was used to study eclipses without the risk of damaging the eyes by looking directly into the Sun. As a drawing aid, it allowed tracing the projected image to produce a highly accurate representation, and was especially appreciated as an easy way to achieve proper graphical perspective.

Before the term camera obscura was first used in 1604, other terms were used to refer to the devices: cubiculum obscurum, cubiculum tenebricosum, conclave obscurum, and locus obscurus.

A camera obscura without a lens but with a very small hole is sometimes referred to as a "pinhole camera", although this more often refers to simple (homemade) lensless cameras where photographic film or photographic paper is used.

Rays of light travel in straight lines and change when they are reflected and partly absorbed by an object, retaining information about the color and brightness of the surface of that object. Lighted objects reflect rays of light in all directions. A small enough opening in a barrier admits only the rays that travel directly from different points in the scene on the other side, and these rays form an image of that scene where they reach a surface opposite from the opening.

The human eye (and that of many other animals) works much like a camera obscura, with rays of light entering an opening (pupil), getting focused through a convex lens and passing a dark chamber before forming an inverted image on a smooth surface (retina). The analogy appeared early in the 16th century and would in the 17th century find common use to illustrate Western theological ideas about God creating the universe as a machine, with a predetermined purpose (just like humans create machines). This had a huge influence on behavioral science, especially on the study of perception and cognition. In this context, it is noteworthy that the projection of inverted images is actually a physical principle of optics that predates the emergence of life (rather than a biological or technological invention) and is not characteristic of all biological vision.