What optical device did Leonardo da Vinci study by comparing it with the human eye?

Leonardo da Vinci studied the camera obscura by comparing it with the human eye.

A camera obscura is a dark chamber or box with a small opening through which light enters. The opening projects an upside-down image of the outside scene onto an opposite surface. Leonardo investigated this image formation in notebooks while studying vision and light.

He used the device as an analogy for the eye: light enters through an opening, and an image forms inside. His observations helped connect geometric optics with the anatomy of sight, although Renaissance explanations of vision were not identical to modern neuroscience.

Leonardo did not invent the camera obscura. The basic phenomenon had been discussed by earlier scholars, including Ibn al-Haytham. Leonardo’s importance lies in his detailed experiments, drawings, and use of the device to investigate how images are formed.