What optical device did Leonardo da Vinci use to study how images form?

Leonardo da Vinci used a camera obscura to study how images form.

A camera obscura is a dark chamber or box with a small opening that projects an image of the outside scene onto an interior surface. Leonardo described the principle in his notebooks and compared the projected image with the way the eye receives light.

The image appears upside down because light travels in straight lines through the opening and rays from the top and bottom of the scene cross. Leonardo was especially interested in this optical effect as part of his investigations of vision, perspective, and painting.

A camera obscura is not a lens-based telescope or microscope. It is an optical projection device and a conceptual ancestor of the photographic camera. Leonardo’s notes did not turn the apparatus into a modern camera, but they provide important Renaissance discussion of its operation.