A Spot Diagram Generator for Lens Testing

Abstract

An instrument is described for measuring the geometrical aberrations of a lens. The instrument operates by scanning the lens pupil with a ‘ray’ of light and measuring the coordinates of the ray intersection points in the image plane using a position-sensitive photocell. The ray intersection points are displayed as a spot diagram on a cathode ray tube. Up to 300 rays are traced through the lens in under 1 sec. Facilities are included for automatically counting the total number of rays traced through the lens as well as the number intersecting the image plane within an area defined by four adjustable boundaries. Two detectors are available for the instrument, one covers the visible spectrum and the other the near infra-red.