Book excerpt: From its inception in Greek antiquity, the science of optics was aimed primarily at explaining sight and accounting for why things look as they do. By the end of the seventeenth century, however, the analytic focus of optics had shifted to light: its fundamental properties and such physical behaviors as reflection, refraction, and diffraction. This dramatic shift—which A. Mark Smith characterizes as the “Keplerian turn”—lies at the heart of this fascinating and pioneering study. Breaking from previous scholarship that sees Johannes Kepler as the culmination of a long-evolving optical tradition that traced back to Greek antiquity via the Muslim Middle Ages, Smith presents Kepler instead as marking a rupture with this tradition, arguing that his theory of retinal imaging, which was published in 1604, was instrumental in prompting the turn from sight to light. Kepler’s new theory of sight, Smith reveals, thus takes on true historical significance: by treating the eye as a mere light-focusing device rather than an image-producing instrument—as traditionally understood—Kepler’s account of retinal imaging helped spur the shift in analytic focus that eventually led to modern optics. A sweeping survey, From Sight to Light is poised to become the standard reference for historians of optics as well as those interested more broadly in the history of science, the history of art, and cultural and intellectual history.