A measure of the quality of an optical system. It is the ratio of the amount of light actually delivered by an optical system into the Airy disk compared with the theoretical maximum. Perfect optics have a Strehl ratio of 1.0. Optics that meet the Rayleigh criterion have a Strehl ratio of 0.82. The ratio is named after the German physicist Karl Wilhelm Andreas Strehl (1864–1940).
Subjects: Astronomy and Astrophysics.