Beam-splitting optical system

Abstract

An optical system for insertion into projection apparatus to permit viewing an image projected on an image plane without affecting its quality, size or position, including a beam-splitting element disposed in the optical path before the image plane which will transmit the radiation to the image plane and reflect a portion of the radiation reflected from the image plane in a direction which permits viewing, optical elements disposed in the optical path to correct for image displacement and aberrations caused by the beam-splitting element, said optical system being of unit power; according to one aspect of the invention the system is afocal so that it will remain at unit power when it is shifted longitudinally and the image position is insensitive to longitudinal displacement; and according to another aspect of the invention each element of the system is afocal so that the system remains at unit power and insensitive to changes in spacing between the elements.

Dependencies are inferred from the claim text.