Detail of the turret section of a tent-type camera obscura made by Charles Chevalier, Paris during the second quarter of the 19th century. It consists of a turret with an adjustable right-angle glas prism with lens held in a bras cylinder that rotates aloft a tent-like structure. Within the darkened confines of the contrivance, the artist is able to outline in pencil the view projected onto their paper by the instrument's optics. Camera obscuras were known to the ancient Greeks, Chinese and were used by Arab astronomers in the 10th century to observe the Sun. During the Renaisance period artists used camera obscuras to help them to draw more accurately.
© Science Museum / Science & Society Picture Library