 Kepler also gave an important place to experience in the field of optics. As a matter of fact, he began his research on optics because of a disagreement between theory and observation, and he made use of scientific instruments he had designed himself (see, for instance, KGW 21.1, p. 244). Recent research on the problem of the camera obscura and the “images in the air” shows, however, the limits of a traditional approach to Kepler’s optics following the main current of the history of physics. Rather, his notion of experimentum needs to be contextualized within the social practices and epistemological commitments of his time (see Dupré 2008).