Cutaway view of Camera Obscura from a 1646 engraving


Leonardo Da Vinci in his notebooks, wrote of the principles of optics:

"Experience which shows that the objects transmit their images or likenesses intersected within the eye in the ablugineous humour shows (what happens) when the images of the illuminated objects penetrate through some small round hole into a very dark habitation. You will then receive these images on a sheet of white paper placed inside this habitation somewhat near to this small hole, and you will see all the aforesaid objects on this paper with their true shapes and colours, but they will be less, and they will be upside down because of the said intersection."
Da Vinci was describing the Camera Obscura, (literally translated as dark room) which basically allows rays of light to pass through a small hole and form an image on the wall of a darkened room. Renaissance artists used this principle to trace the outlines of the projected images onto paper placed on the wall.