Patent ID: 9261767
Filing Date: 2016-02-16
CPC Classification: G02B,G03B

Claim Text:
1. A projection optical system comprising: in order from a reduction side to a magnification side, an image forming unit configured to form an image thereon; a refraction optical system including a plurality of lenses; a first reflecting surface and a second reflecting surface, wherein, when an optical axis shared by the largest number of lenses among optical lenses of the refraction optical system is defined as an optical axis of the projection optical system; in arrangement where a distance between an intersection of a magnification-side surface of a lens which is arranged to be closest to the magnification side of the refraction optical system and the optical axis and an intersection of the first reflecting surface and the optical axis has a minimum value, the distance between the intersections is denoted by L, a focal length of the refraction optical system is denoted by f, a direction parallel to the optical axis is defined by a Z axis direction, an arrangement direction of the first reflecting surface and the second reflecting surface is defined by a Y axis direction, a maximum value of a distance between the optical axis and an end portion of the image forming unit in the Y axis direction is denoted by Ymax, in a YZ plane which is a plane parallel to the Y axis direction and the Z axis direction, a maximum value D1 of a distance between an intersection of a light beam path from the image forming unit and the magnification-side surface of the lens which is arranged to be closest to the magnification side of the refraction optical system and the optical axis, a sag amount ds1 which is a sag amount of the magnification-side surface of the lens which is arranged to be closest to the magnification side of the refraction optical system at the D1 and of which positive direction is defined by the direction from the reduction side in the Z axis toward the magnification side, a point H of which distance from the optical axis has a maximum value among the intersections of the light beam path and the first reflecting surface, a point F of which distance from the optical axis has a minimum value among the intersections of the light beam path and the second reflecting surface, an angle θ1 between a line connecting the H and the F and the optical axis satisfies the condition 1: 0<Ymax/f−1/tan θ1; and condition 2: −0.1<(L−D1−ds1)/(L+D1−ds1)−1/tan θ1.