Patent ID: 7525740

Claim:
A display optical system that introduces light from an original image to an exit pupil, comprising: a first surface, a second surface, and a third surface each having at least a reflection function; and a fourth surface having a reflection function and disposed outside an inside area surrounded by the first, second, and third surfaces, wherein the display optical system is configured such that: the light from the original image passes through the inside area and then is reflected by the fourth surface to return into the inside area; the light that has returned into the inside area is reflected by the first surface and then is reflected by the second surface toward the first surface to impinge again thereon; the light impinging again on the first surface is re-reflected thereby such that a central-viewing-angle principal ray of the light proceeds in a direction opposite to, with respect to a normal to the first surface at its hit point thereon, a direction in which the central-viewing-angle principal ray has previously reflected by the first surface; and the light re-reflected by the first surface is reflected by the third surface to proceed toward the exit pupil.