Strehl ratio

The Strehl ratio is a measure of the quality of optical image formation, originally proposed by Karl Strehl (1864-1940) after whom the term is named. Used variously in situations where optical resolution is compromised due to lens aberrations or due to imaging through the turbulent atmosphere, the Strehl ratio has a value between 0 and 1, with an unaberrated optical system attaining the value of unity.