Islamic scholars continued to study Aristotelian physics during the Islamic Golden Age. One main contribution was to observational astronomy. Some, like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna, worked on optics and vision. In "The Book of Optics", Ibn al-Haytham rejected previous Greek ideas concerning vision and proposed a new theory. He studied how light enters the eye, and developed the camera obscura. European scientists later built eyeglasses, magnifying glasses, telescopes, and cameras from this book.