Abstract: The imaging optical system consists of, in order from a magnification side: a catoptric system; and a dioptric system that includes a plurality of lenses. The dioptric system forms a first intermediate image between the dioptric system and the catoptric system on an optical path and at a position conjugate to a reduction side imaging surface, and the catoptric system re-forms the first intermediate image on a magnification side imaging surface. The catoptric system consists of a first reflective surface, a second reflective surface, and a third reflective surface in order along the optical path from the magnification side. The first reflective surface and the third reflective surface are formed on one member and have the same surface shapes.

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system for forming an image displayed by image display elements as an intermediate image, and a second optical system for forming the intermediate image on a magnification side conjugate plane. The second optical system is constituted by, in order from the reduction side, a first lens group having a positive refractive power, a first optical path bending means that bends an optical path with a reflective surface, a second lens group having a positive refractive power, a second optical path bending means that bends an optical path with a reflective surface, and a third lens group having a negative refractive power. Conditional Formulae (1) and (2) below are satisfied. 0.05<|f23|/D223<0.50??(1) 5.0<D212/|f|<20.0??(2).

Abstract: A zoom lens forms an intermediate image at a position conjugate to a reduction side imaging plane and forms the intermediate image again on a magnification side imaging plane. The zoom lens includes a plurality of lens groups including at least two movable lens groups, which move by changing spacings between the groups adjacent to each other in a direction of an optical axis during zooming, at a position closer to the reduction side than the intermediate image. Among the plurality of lens groups, a final lens group closest to the reduction side has a positive refractive power, and remains stationary with respect to the reduction side imaging plane during zooming. The zoom lens satisfies predetermined conditional expressions (1) and (2) about the focal lengths of the movable lens groups.

Abstract: The imaging optical system consists of, in order from a magnification side: a catoptric system; and a dioptric system that includes a plurality of lenses. The dioptric system forms a first intermediate image between the dioptric system and the catoptric system on an optical path and at a position conjugate to a reduction side imaging surface, and the catoptric system re-forms the first intermediate image on a magnification side imaging surface. The catoptric system consists of, in order from the magnification side along the optical path, a first reflective surface having a positive power, a second reflective surface having a curved surface shape, and a third reflective surface having a positive power.

Abstract: A zoom lens forms an intermediate image at a position conjugate to a reduction side imaging plane and forms the intermediate image again on a magnification side imaging plane. The zoom lens includes a plurality of lens groups including at least two movable lens groups, which move by changing spacings between the groups adjacent to each other in a direction of an optical axis during zooming, at a position closer to the reduction side than the intermediate image. Among the plurality of lens groups, a final lens group closest to the reduction side has a positive refractive power, and remains stationary with respect to the reduction side imaging plane during zooming. The zoom lens satisfies predetermined conditional expressions (1) and (2) about the focal lengths of the movable lens groups.

Abstract: A projection optical system consists of, in order from the magnification side, a first optical system, which consists of one convex mirror and a plurality of lenses disposed on the reduction side of the convex mirror, and a second optical system. The lens closest to the magnification side in the first optical system is a negative lens. Assuming that a paraxial radius of curvature of the convex mirror is Mr and a focal length of the negative lens closest to the magnification side in the first optical system is fL1, Conditional Expression is satisfied: 0<Mr/fL1<4.5.

Abstract: A projection optical system forms an intermediate image at a position conjugate to a reduction side imaging surface, and forms a final image conjugate to the intermediate image on a magnification side imaging surface. The projection optical system includes a convex mirror disposed to be closer to the magnification side than the intermediate image and at least one lens that has a positive or negative refractive power and is disposed in an optical path so as to be closer to the magnification side than the convex mirror.

Abstract: An imaging optical system consists of, in order from a magnification side: a first optical system that forms an intermediate image on a position conjugate to a magnification side imaging surface; and a second optical system that re-forms the intermediate image on a reduction side imaging surface. The first optical system includes at least two focusing lens groups that move with different loci during focusing. The imaging optical system satisfies predetermined conditional expressions relating to the focusing lens groups.

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system constituted by a plurality of lenses for forming an image displayed by image display elements as an intermediate image, and a second optical system constituted by a plurality of lenses for forming the intermediate image on a magnification side conjugate plane. Conditional Formula (1), being that 0.020<enP/TL2<0.160, is satisfied, wherein enP is the distance along the optical axis from the surface most toward the magnification side in the second optical system to the position of an entrance pupil in the case that the magnification side is a light entry side, and TL2 is the distance along the optical axis from the surface most toward the reduction side in the second optical system to the surface most toward the magnification side in the second optical system.

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system constituted by a plurality of lenses for forming an image displayed by image display elements as an intermediate image, and a second optical system constituted by a plurality of lenses for forming the intermediate image on a magnification side conjugate plane. Conditional Formula (1) below is satisfied. 1.50<f2/|f|<2.80??(1).

Abstract: The zoom lens includes: a first lens group that is disposed to be closest to an object side, first moves toward an image side along an optical axis during zooming from a wide-angle end to a telephoto end, and has a positive refractive power; a second lens group that is disposed to be adjacent to the first lens group on the image side of the first lens group, moves during zooming, and has a negative refractive power; a final lens group that is disposed to be closest to the image side, includes an aperture stop, remains stationary during zooming, and has a positive refractive power; and an image side negative lens group that is disposed to be adjacent to the final lens group on the object side of the final lens group, moves during zooming, and has a negative refractive power.

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system constituted by a plurality of lenses for forming an image displayed by image display elements as an intermediate image, and a second optical system constituted by a plurality of lenses for forming the intermediate image on a magnification side conjugate plane. Conditional Formula (1), being that 0.020<enP/TL2<0.160, is satisfied, wherein enP is the distance along the optical axis from the surface most toward the magnification side in the second optical system to the position of an entrance pupil in the case that the magnification side is a light entry side, and TL2 is the distance along the optical axis from the surface most toward the reduction side in the second optical system to the surface most toward the magnification side in the second optical system.

Abstract: A zoom lens forms an intermediate image at a position conjugate to a reduction side imaging plane and forms the intermediate image again on a magnification side imaging plane. The zoom lens includes a plurality of lens groups including at least two movable lens groups, which move by changing spacings between the groups adjacent to each other in a direction of an optical axis during zooming, at a position closer to the reduction side than the intermediate image. Among the plurality of lens groups, a final lens group closest to the reduction side has a positive refractive power, and remains stationary with respect to the reduction side imaging plane during zooming. The zoom lens satisfies predetermined conditional expressions (1) and (2).

Abstract: The imaging optical system consists of, in order from a magnification side: a first imaging optical system that forms an intermediate image on a position conjugate to a magnification side imaging surface; and a second imaging optical system that re-forms the intermediate image on a reduction side imaging surface. The first imaging optical system consists of, in order from the magnification side, a first A lens group, a first optical path deflection unit that deflects an optical path, a first B lens group, and a second optical path deflection unit that deflects the optical path. In addition, the intermediate image is formed between the second optical path deflection unit and the second imaging optical system.

Abstract: An imaging optical system consists of, in order from a magnification side: a first imaging optical system that forms an intermediate image on a position conjugate to a magnification side imaging surface; and a second imaging optical system that re-forms the intermediate image on a reduction side imaging surface. The second imaging optical system consists of a plurality of lens groups including at least two movable lens groups which move during zooming. The imaging optical system satisfies predetermined conditional expressions.

Abstract: The zoom lens includes: a first optical system on a magnification side; and a second optical system on a reduction side in a state where the intermediate image is formed between the magnification side and the reduction side. The first optical system includes, in order from the magnification side, a first-1 lens group which has a positive power, and a first-2 lens group which has a positive power. The second optical system includes, in order from the magnification side, a second-1 lens group which has a positive power, a second-2 lens group which has a positive power, and a second-3 lens group which has a positive power. The first-2 lens group, the second-1 lens group, and the second-2 lens group move during zooming. The first-1 lens group and the second-3 lens group remain stationary during zooming.

Abstract: The zoom lens includes: a first optical system on a magnification side; and a second optical system on a reduction side in a state where the intermediate image is formed between the magnification side and the reduction side. The second optical system includes, in order from the magnification side, a second-1 lens group which has a positive refractive power, a second-2 lens group which has a positive refractive power, and a second-3 lens group which has a positive refractive power. The second-1 lens group and the second-2 lens group move in directions opposite to each other while changing spacings between the groups adjacent to each other in a direction of an optical axis during zooming. The second-3 lens group remains stationary with respect to the reduction side imaging plane during zooming. In addition, the zoom lens satisfies a predetermined conditional expression (1).

Abstract: The imaging lens includes at least one positive lens that satisfies predetermined conditional expressions (1) to (3) indicating conditions in which dispersion is relatively low and refractive index is high while having a negative rate of change of the refractive index. In a case where a lens that satisfies a conditional expression (4) meaning a low dispersion material is included, the lens that satisfies the conditional expression (4) satisfies a predetermined conditional expression (5).

Abstract: A projection optical system consists of, in order from the magnification side, a first optical system, which consists of one convex mirror and a plurality of lenses disposed on the reduction side of the convex mirror, and a second optical system. The lens closest to the magnification side in the first optical system is a negative lens. Assuming that a paraxial radius of curvature of the convex mirror is Mr and a focal length of the negative lens closest to the magnification side in the first optical system is fL1, Conditional Expression is satisfied: 0<Mr/fL1<4.5.

Abstract: The imaging optical system consists of, in order from a magnification side, a first optical system and a second optical system. The first optical system consists of, in order from the magnification side, a first A lens group having a positive refractive power and a first B lens group having a positive refractive power with the maximum air gap interposed between the lens surfaces in the first optical system. The second optical system consists of, in order from the magnification side, a second A lens group having a positive refractive power and a second B lens group having a positive refractive power with the maximum air gap interposed between the lens surfaces in the second optical system.