Abstract

The Strehl ratio is widely used as a theoretical measure of lens quality. It is well correlated with other traditional figures of merit, such as mean-square wavefront aberration, modulation transfer function, and Linfoot’s mean-square image-object correlation. A common misconception is that the Strehi ratio of an optical system cannot be measured directly because the unaberrated image of the system under test is unavailable. The Strehl-ratio can be determined from measurements of the peak irradiance and total power in the image of a subresolution pinhole. A map of the Strehl ratio over field is a useful and concise summary of the imaging capability of a well-corrected lens. A lens bench which measures the Strehl ratio is described. The experimental parameters are the dimension of the pinhole, the illumination coherence, and the dynamic range of the image detector. Measurement accuracy is analyzed in terms of these parameters and the wavefront aberrations present in the lens.

© 1988 Optical Society of America