Abstract: A projection optical system includes a first refractive system, a reflective optical system, and a second refractive system, disposed in the stated order in a direction from the reduction side toward the enlargement side, to enlarge and project an image displayed on an image display element, onto a projection surface. A first lens group of the first refractive system forms a first intermediate image with a light beam from the image display element. A second lens group of the first refractive system forms a second intermediate image with a light beam from the first intermediate image. A light beam from the second intermediate image is reflected by the reflective optical system and is then refracted by the second refractive system. A condition (1): 1.5<Bf/f<25 is satisfied, in which f represents a focal length of the entire projection optical system and Bf represents a back focus obtained by air conversion.

Abstract: A projection optical system includes a first refractive system, a reflective optical system, and a second refractive system, disposed in the stated order in a direction from the reduction side toward the enlargement side, to enlarge and project an image displayed on an image display element, onto a projection surface. A first lens group of the first refractive system forms a first intermediate image with a light beam from the image display element. A second lens group of the first refractive system forms a second intermediate image with a light beam from the first intermediate image. A light beam from the second intermediate image is reflected by the reflective optical system and is then refracted by the second refractive system. A condition (1): 1.5<Bf/f<25 is satisfied, in which f represents a focal length of the entire projection optical system and Bf represents a back focus obtained by air conversion.