camera lucida

camera lucida (Latin: ‘light chamber’).
An apparatus used as an aid in drawing and copying, patented in 1807 by William Hyde Wollaston (1766–1828), a well-known man of science. It received its misleading name—for it is not a ‘chamber’ at all—because it performed the same function as the camera obscura, but in full daylight. It consists essentially of a prism mounted on a metal arm above a drawing board. The draughtsman sets the prism between his eye and the paper in such a way that he can see an image of the object he wishes to draw apparently lying on the paper and can trace its outline. Various refinements were added to the basic format, including a lens to aid focusing. David Hockney, who is fascinated by the history of artists' techniques, began experimenting with a camera lucida in 1999, using it to draw portraits.