What is the history of medieval optics really about?

INCE ITS PUBLICATION IN 1975, David Lindberg’s Theories of Vision from Al-Kind to Kepler 2 has become the canonical ı̄ source for our understanding of medieval optics and its place in the development of modern optics. Lindberg’s ulterior purpose in writing this book was to show that, contrary to prevailing opinion, Johan Kepler’s account of sight, which is based on the casting of point-bypoint images through the lens at the front of the eye onto the retina at the back, represented a continuation of, rather than a break with, the medieval optical tradition, whose foundations were laid by the Arab Ibn al-Haytham, or Alhacen as he came to be known in the Latin West. 3 To be sure, Lindberg concluded, “Kepler attacked the problem of vision with greater skill than had theretofore been applied to it, but he did so without departing from the basic aims and criteria of visual theory established by Alhazen in the eleventh century.” 4 So, even if we credit Kepler with opening the way toward the development of modern optics, neither the opening itself nor what came out of it during the seventeenth century marked a fundamental departure from the past. The transition from medieval to modern optics was evolutionary, not revolutionary.