| CPC G02B 13/16 (2013.01) [G03B 17/17 (2013.01); G03B 21/28 (2013.01)] | 20 Claims |
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1. An optical system having a reduction conjugation point on a reduction side and a magnification conjugation point on a magnification side and internally having an intermediate imaging position that is conjugated to both the reduction conjugation point and the magnification conjugation point,
wherein the reduction conjugate point has an image-forming relationship in a rectangular region having a longitudinal direction and a lateral direction,
wherein the optical system includes a first sub-optical system including an aperture stop defining a range in which a light flux can pass through the optical system and a second sub-optical system disposed on the magnification side of the first sub-optical system and including a prism made of a transparent medium,
wherein the prism has a first transmission surface located on the reduction side, a second transmission surface located on the magnification side, and at least one reflection surface located on an optical path between the first transmission surface and the second transmission surface,
wherein the aperture stop is positioned between the reduction conjugate point and the intermediate imaging position,
wherein a first reflection surface closest to the first transmission surface on the optical path in the prism has a shape with a concave surface facing a direction into which a light ray incident on the first reflection surface is reflected,
wherein the second transmission surface has a shape with a convex surface facing the magnification side,
wherein the intermediate imaging position is positioned away from the first reflection surface only toward the reduction side of the first reflection surface,
wherein a portion or whole of intermediate images formed at the intermediate imaging position are positioned inside the medium of the prism,
wherein in case an X-direction, a Y-direction, and a Z-direction are a longitudinal direction, a lateral direction, and a normal direction, respectively, of the rectangular region of the reduction conjugate point, when a Y cross-section is a plane including a position where a principal ray passing through the center in the X-direction is reflected by the first reflection surface, and an X cross-section is a cross-section perpendicular to the Y cross-section, a curvature shape of the first reflection surface is set such that some of multiple principal rays passing through the reduction conjugate point intersect on the optical path between the first reflection surface and the second transmission surface as viewed in a direction perpendicular to the Y cross-section while some of multiple principal rays passing through the reduction conjugate point intersect on the optical path between the first reflection surface and the second transmission surface as viewed in a direction perpendicular to the X cross-section, and
wherein the light flux passing through the first sub-optical system forms both the intermediate image in the Y-direction parallel to the Y cross-section and the intermediate image in the X-direction parallel to the X cross-section at positions different to each other, the intermediate image in the Y-direction being defined as the light flux passing through the first sub-optical system being focused only in the Y-direction and not focused in the X-direction, the intermediate image in the Y-direction being defined as the light flux passing through the first sub-optical system being focused only in the X-direction and not focused in the Y-direction.
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