IMAGE-FORMING OPTICAL SYSTEM AND VIEWING OPTICAL SYSTEM

A viewing optical system and an image-forming optical system, in which an intermediate image is formed once and two decentered prisms, i.e. first and second prisms, are arranged to correct each other's decentration aberrations, thereby attaining a wide viewing field angle and a short focal length. The second prism is placed closer to the image side than the first prism and has four optical surfaces, of which a first surface is an entrance surface, second and third surfaces are reflecting surfaces, and a fourth surface is an exit surface. In the second prism, an optical path crosses itself. At least one of the second and third surfaces has a rotationally asymmetric surface configuration that gives a power to a light beam and corrects aberrations due to decentration. The first prism has a reflecting surface, an entrance surface, and an exit surface. The reflecting surface has a rotationally asymmetric surface configuration that gives a power to a light beam and corrects aberrations due to decentration. An intermediate image surface is formed between the first surface of the first prism and the exit surface of the second prism.