Abstract: The refractive power(s) of a lens which may possess cylindrical power are determined by retro-reflecting a particular target image through an optical system and varying the axial positioning of one or more elements in the system to bring the reflected image to one or two clear and unambiguous foci at a target plane. By employing a small, intense diffraction image as the target image and further detecting only reflected light passing through a pinhole area on the optical axis at the target plane, a single significant light energy peak is observed at system focus for a lens possessing sphere power only and two significant light energy peaks appear at the respective foci of the principal meridians if the lens also has cylinder power. Means are provided for recognizing the existence, number, and/or relative size of light energy peaks and for correlating their occurrence with the position of the movable element in the optical system to determine respective refractive powers of the test lens.