Camera obscura (from Latin, meaning “darkened room”) is a device in a shape of a box or a room that lets the light through a small opening on one side and projects it on the other. In this simple variant, image that is outside of the box is projected upside-down. More complex cameras can use mirrors to project image upwards and right-side up and they can also have lenses. Camera obscura is used as an aid for drawing and entertainment.
Camera obscura is a very old device. Oldest mention of its effect is by Mozi, Chinese philosopher and the founder of Mohism, during the 5th century BC. He noticed that an image from camera obscura is flipped upside down and from left to right as a result of light’s moving in straight line. The Greek philosopher Aristotle noticed in 4th century that light from a sun eclipse that passes through holes between the leaves, projects an image of an eclipsed sun on the ground. Passing of light in the straight line also noticed Euclid 4th century BC and Theon of Alexandria in 4th century AD. Anthemius of Tralles, which designed the Hagia Sophia, used a type of camera obscura in his experiments in 6th century. Al-Kindi, Arab philosopher, mathematician, physician, and musician, performed experiments with light and a pinhole in 9th century and proved again behavior of light.
All these scientists experimented with a small hole and light but none of them suggested that a screen is used so an image from one side of a hole in surface could be projected at the screen on the other. First one to do so was Alhazen (also known as Ibn al-Haytham) in 11th century. He was a scientist, mathematician, astronomer and philosopher, he wrote the Book of Optics and, among other things, he invented camera obscura and pinhole camera. At about the same time, Chinese scientist Shen Kuo experimented with a camera obscura. He described it geometrically and even used it explain some effects that were mentioned couple centuries ago but were attributed to the geographic characteristics of the area. As described by Roger Bacon, English philosopher, camera obscura was used in 13th century for safe observation of sun eclipse. Arnaldus de Villa Nova, an alchemist, astrologer and physician, used camera obscura at the same time as a projector for entertainment. Artists started using camera obscura in 15th century. Leonardo da Vinci talks about camera obscura in his “Codex Atlanticus”, a twelve-volume bound set of his drawings and writings where he also talked about flying machines, weaponry and musical instruments. Giambattista della Porta, Italian scholar, improved camera obscura by adding it a lens at the place where light enters the box. He also used camera obscura to explain how human eye works. German astronomer Johannes Kepler uses term “camera obscura” for the first time in history in 1604. Johann Zahn, writer of "Oculus Artificialis Teledioptricus Sive Telescopium”, writes in his book in 17th century about camera obscura and magic lantern among other optical instruments. In 18th century Conte Francesco Algarotti writes his book “Saggio sopra Pittura” and dedicates a whole chapter to the use of camera obcura (or how he calls it “camera ottica” ("optic chamber")) in painting.
Early models were large and consisted of a literal room or a tent (Johannes Kepler used a tent one.) Later more portable variants were invented. They were wooden boxes that had a lens instead of pinhole which can be moved to provide a focus. They also had a mirror that rotated image and a screen onto which an image was projected. These cameras were basis for early photographic cameras.