Did Christiaan Huygens need glasses? A study of Huygens' telescope equations and tables

Abstract

In the later stages of his life, Christiaan Huygens semi-empirically derived a set of relations between the objective focus and diameter, the eyepiece focus, and the magnification that resulted from combining the two lenses. These relations were used by him and his brother to build what he believed were optimized telescopes. When comparing these equations to the ones derived from modern optical principles, Huygens' telescopes were in fact far from optimal. While there are several potential reasons for this discrepancy, one possible reason, explored in this work, is that Huygens might have suffered from a mild case of myopia (or near-sightedness) and that he compensated for this condition by building telescopes that overmagnified by a factor of 3.5. Based on this hypothesis, Huygens' visual acuity is estimated to be around 20/70, which on average corresponds to an optical prescription of -1.5 diopters