“I shall describe the means of vision, which no one at all to my knowledge has yet examined and understood in such detail. I therefore beg the mathematicians to consider these carefully, so that thereby at last there might exist in philosophy something certain concerning this most noble function.” It is with these words in his Optical Part of Astronomy (1604) that the German mathematician Johannes Kepler credits himself with inaugurating a new chapter in the history of vision. Kepler does indeed fulfill his promise by advancing knowledge about the eye, vision and the use of lenses in the correction of vision. His conclusions, however, bring anything but certainty on a philosophical level, especially with regard to the relationship between an object and its image. Reading Kepler in dialogue with a selection of nonscientific texts, this presentation experiments with the affinities between Kepler’s scientific findings and literature as a form of knowledge and representation in the 17th century.