Abstract: In a projection optical system that projects an image displayed on an image display device arranged on a reduction-side conjugate plane onto a magnification-side conjugate plane, as a magnified image, the projection optical system includes a refractive optical system and a reflective optical system having negative refractive power in this order from a reduction side. Further, the following conditional formula (1) is satisfied: ?0.0015?(1/tan(?max)?0.16)×(?L/?M?0.27) ??(1).

Abstract: In a projection optical system that projects an image displayed on an image display device arranged on a reduction-side conjugate plane onto a magnification-side conjugate plane, as a magnified image, the projection optical system includes a refractive optical system and a reflective optical system having negative refractive power in this order from a reduction side. Further, the following conditional formula (1) is satisfied: (ZL+ZD)×Ymin/Ymax2?3.2??(1).

Abstract: In a projection optical system that projects an image displayed on an image display device arranged on a reduction-side conjugate plane onto a magnification-side conjugate plane, as a magnified image, the projection optical system includes a refractive optical system and a reflective optical system having negative refractive power in this order from a reduction side. Further, the following conditional formula (1) is satisfied: L/D+2?min/?max?1.01??(1).

Abstract: A variable magnification projection optical system substantially consisting of two lens groups of a first lens group having a positive refractive power and is moved during magnification change, and a second lens group having a positive refractive power and is moved during magnification change, in which the variable magnification projection optical system is configured such that the reduction side is telecentric.

Abstract: A projection optical system substantially consists of a first optical system composed of a plurality of lenses and a second optical system composed of one reflection mirror having a convex aspherical surface arranged in this order from the reduction side and is configured, when an air space between the first optical system and the second optical system is taken as T12 and a displacement in a direction of the optical axial from a position of maximum effective height on the magnification side lens surface of the lens disposed on the most magnification side in the first optical system to the vertex of the lens surface is taken as Zf, to satisfy a conditional expression (1): 0.1<Zf/T12<1.0, in which an image formed on a conjugate plane on the reduction side is magnified and projected onto a conjugate plane on the magnification side.

Abstract: A zoom lens for projection substantially consists of a first lens-group having negative refractive power, and a second lens-group through a fifth lens-group having positive refractive power, arranged in this order from a magnification side. The zoom lens is configured to be telecentric on a reduction side. The first lens-group and the fifth lens-group are fixed while the second lens-group through the fourth lens-group move during magnification change. The fourth lens-group includes at least three positive lenses, and a most-magnification-side lens in the fourth lens-group has a convex surface facing the magnification side. Further, when a focal length of an entire system at a wide angle end is fw, and a focal length of the fourth lens-group is f4, and a full angle of view at a wide angle end is 2?, conditional formulas (1) and (7) are satisfied: 7.5<f4/fw<14.5??(1); and 70°?2???(7).

Abstract: A projection zoom lens in which a magnification change operation is performed by moving three to four lens groups as moving groups, wherein a first lens group, which is a lens group on the most-magnification side, substantially consists of a moving group having a negative refractive power; a lens group on the most-reduction side is composed of a moving group having a positive refractive power; and the first lens group which is the lens group the most-magnification side substantially consists of two lenses. In this case, conditional formula (1) below is satisfied, where fw is the focal length of the entire system at the wide angle end and fm is the focal length of the lens group on the most-magnification side: ?3.5<fm/fw<?1.0??(1). This achieves miniaturization and cost reduction, and corrects various aberrations satisfactorily.

Abstract: A positive first lens group that is fixed during magnification change, a negative second lens group that is movable during magnification change, a positive third lens group that is movable during magnification change, a positive fourth lens group that is movable during magnification change, and a positive fifth lens group that is fixed during magnification change are arranged in this order from the enlargement side. The system is telecentric at the reduction side. Conditional expression (1) is satisfied: L/Im?<15.0??(1), where L is a distance along the optical axis from the most enlargement-side lens surface to the most reduction-side lens surface when the projection distance is infinity, and Im? is a maximum effective image circle diameter at the reduction side.

Abstract: A projection zoom lens has a negative first lens group which is fixed when changing magnification, second through fifth lens groups that move when changing magnification, and a positive sixth lens group which is fixed when changing magnification, in this order from a magnification side. The reduction side is telecentric. When changing magnification from a wide angle end to a telephoto end, the second lens group moves toward the magnification side. The first and second lenses from the reduction side of the fifth lens group are a positive lens and a negative lens, respectively. The sixth lens group is constituted by a single positive lens. The projection zoom lens satisfies a predetermined Conditional Formula.

Abstract: A negative first lens group, a positive second lens group, a negative third lens group, a positive fourth lens group, a negative fifth lens group, and a positive sixth lens group are disposed in this order from the magnification side. The reduction side is made telecentric. While changing magnification, the second lens group through the fifth lens group are moved, and the first lens group and the sixth lens group are fixed. Predetermined conditional expressions are satisfied.

Abstract: The projection zoom lens substantially consists of a first lens group having negative refractive power, a second lens groups through a fourth lens group all having positive refractive power, a fifth lens group having positive or negative refractive power, and a sixth lens group having positive refractive power, arranged in this order from the magnification side; wherein the reduction side is telecentric. Further, the first lens group and the sixth lens group are fixed and the second lens group through the fifth lens group move along the optical axis while changing magnification. The fourth lens group substantially consists of only one positive meniscus lens with a concave surface toward the reduction side. The projection zoom lens satisfies conditional expression (1) below: 1.2<f3/f4<10.0??(1), where f3 is the focal length of the third lens group, and f4 is the focal length of the fourth lens group.

Abstract: A zoom lens for projection substantially consists of a first lens-group having negative refractive-power, and which is arranged on a most magnification-side, and which is fixed during magnification change, a second lens-group having negative refractive-power, and which is arranged on a reduction-side of the first lens-group, and which is fixed during magnification change, a last lens-group having positive refractive-power, and which is arranged on a most reduction-side, and which is fixed during magnification change, and three lens-groups arranged between the last lens-group and the second lens-group, and which move during magnification change. The zoom lens is configured to be telecentric on a reduction-side, and focusing is performed by moving only the second lens-group.

Abstract: A projection optical system substantially consists of a first optical system composed of a plurality of lens groups and a second optical system composed of one reflection mirror having a convex aspherical surface arranged in this order from the reduction side, in which all optical surfaces constituting the first and second optical systems are formed so as to have rotationally symmetrical shapes around one common axis, the projection optical system is configured such that focus adjustment is performed by individually moving two lens groups in the first optical system along the common axis, and the lens disposed on the most magnification side in the reduction side lens group of the two lens groups is a lens having a convex surface on the magnification side, thereby magnifying and projecting an image formed on a conjugate plane on the reduction side to a conjugate plane on the magnification side.

Abstract: A zoom lens for projection substantially consists of a first lens-group having negative refractive power, and a second lens-group through a fifth lens-group having positive refractive power, arranged in this order from a magnification side. The zoom lens is configured to be telecentric on a reduction side. The first lens-group and the fifth lens-group are fixed while the second lens-group through the fourth lens-group move during magnification change. The fourth lens-group includes at least three positive lenses, and a most-magnification-side lens in the fourth lens-group has a convex surface facing the magnification side. Further, when a focal length of an entire system at a wide angle end is fw, and a focal length of the fourth lens-group is f4, and a full angle of view at a wide angle end is 2?, conditional formulas (1) and (7) are satisfied: 7.5<f4/fw<14.5 ??(1); and 70°?2???(7).

Abstract: A projection zoom lens has a negative first lens group which is fixed when changing magnification, second through fifth lens groups that move when changing magnification, and a positive sixth lens group which is fixed when changing magnification, in this order from a magnification side. The reduction side is telecentric. When changing magnification from a wide angle end to a telephoto end, the second lens group moves toward the magnification side. The first and second lenses from the reduction side of the fifth lens group are a positive lens and a negative lens, respectively. The sixth lens group is constituted by a single positive lens. The projection zoom lens satisfies a predetermined Conditional Formula.

Abstract: A negative first lens group, a positive second lens group, a negative third lens group, a positive fourth lens group, a negative fifth lens group, and a positive sixth lens group are disposed in this order from the magnification side. The reduction side is made telecentric. While changing magnification, the second lens group through the fifth lens group are moved, and the first lens group and the sixth lens group are fixed. Predetermined conditional expressions are satisfied.

Abstract: A projection zoom lens having broad angle of view, high zoom ratio, and large back focus while aberrations are corrected satisfactorily, including a negative first lens group, a positive second lens group, a positive third lens group, a negative fourth lens group, a positive fifth lens group, and a positive sixth lens group from the magnification side and is telecentric on the reduction side. When zooming, the first and sixth lens groups are fixed while the second to fifth lens groups are moved and the fourth lens group is composed of one negative lens whose magnification side surface has a greater curvature in absolute value than that of the reduction side surface, and the zoom lens satisfies conditional expression (1): ?12.0<f4/fw<?5.0, where f4 is focal length of the fourth lens group, and fw is focal length of the entire lens system at the wide angle end.

Abstract: A positive first lens group that is fixed during magnification change, a negative second lens group that is movable during magnification change, a positive third lens group that is movable during magnification change, a positive fourth lens group that is movable during magnification change, and a positive fifth lens group that is fixed during magnification change are arranged in this order from the enlargement side. The system is telecentric at the reduction side. Conditional expression (1) is satisfied: L/Im?<15.0??(1), where L is a distance along the optical axis from the most enlargement-side lens surface to the most reduction-side lens surface when the projection distance is infinity, and Im? is a maximum effective image circle diameter at the reduction side.

Abstract: A projection optical system substantially consists of a first optical system composed of a plurality of lenses and a second optical system composed of one reflection mirror having a convex aspherical surface arranged in this order from the reduction side and is configured, when an air space between the first optical system and the second optical system is taken as T12 and a displacement in a direction of the optical axial from a position of maximum effective height on the magnification side lens surface of the lens disposed on the most magnification side in the first optical system to the vertex of the lens surface is taken as Zf, to satisfy a conditional expression (1):0.1<Zf/T12<1.0, in which an image formed on a conjugate plane on the reduction side is magnified and projected onto a conjugate plane on the magnification side.

Abstract: A projection optical system substantially consists of a first optical system composed of a plurality of lens groups and a second optical system composed of one reflection mirror having a convex aspherical surface arranged in this order from the reduction side, in which all optical surfaces constituting the first and second optical systems are formed so as to have rotationally symmetrical shapes around one common axis, the projection optical system is configured such that focus adjustment is performed by individually moving two lens groups in the first optical system along the common axis, and the lens disposed on the most magnification side in the reduction side lens group of the two lens groups is a lens having a convex surface on the magnification side, thereby magnifying and projecting an image formed on a conjugate plane on the reduction side to a conjugate plane on the magnification side.