Patent ID: 7123420

Claim:
An image optical system in which a plurality of light beams emerging from an image forming devive on a conjugate plane A and having a divergence angle of 10° or greater is made obliquely incident upon a conjugate plane B to form on the conjugate plane B an enlarged image approximately similar to an image formed by the image-forming device, said image optical system comprising: a first optical system and a second optical system each having an optical axis, a plane mirror provided between the first and second optical system, the first optical system converging the light beams emerging from the image-forming device on both of a first light beam cross section parallel to principal rays and a second light beam cross section interesting the first light beam cross section, the plane mirror folding the light beams emerging from the first optical system, and folded light beams are inputted into the second optical system, the second optical system converging light beams that are reflected by the plane mirror on the conjugate plane B, the image optical system satisfying the following relationships: S 1 ≦L 11 ≦S 1 +S 2 (i) S 1 ≦L 21 ≦S 1 +S 2 (ii) L 11 /L 1 n< 0.25 (iii) 0 <L 21 /L 2 n< 1.5 (iv) wherein S 1 is the distance from the point of emergence on the first optical system to the point of incidence on the second optical system along the optical axis of the first optical system; wherein S 2 is the distance from the point of emergence on the second optical system to the conjugate plane B along the optical axis of the second optical system; wherein the maximum and minimum of the distance between a point of convergence in the first and second light beam cross sections of a light beam emerging from the first optical system at a point nearest to the optical axis of the first optical system and the point of emergence on the first optical system are L 11 and L 21 , respectively; wherein the maximum and minimum of the distance between the point of convergence in the first and second light beam cross sections of a light beam emerging from the first optical system at a point remotest from the optical axis of the first optical system and the point of emergence on the first optical system are LIn and L 2 n.