Yrjo VaisalaYrjö Väisälä (September 6, 1891 - July 21, 1971) was a Finnish astronomer and physicist.
His main contributions were in the field of optics. He developed several methods for measuring the quality of optical elements. This allowed the construction of some of the earliest high-quality Schmidt telescopes. Some historians even claim that Väisälä invented the Schmidt telescope independently, but this has remained an open question. The Schmidt telescopes he built were used at the University of Turku for searches of asteroids and comets. His research group discovered several comets and more than 800 asteroids.