Abstract: A lens unit includes a jointed lens having a first optical member, a second optical member disposed on an optical axis of the first optical member, and a jointing member having a light transmissive property and disposed between the first optical member and the second optical member, and a holding mechanism configured to hold the first and second optical members. The holding mechanism holds the first and second optical members so that a distance along an optical axis direction between a first lateral surface at an opposite side to a second optical member side in the first optical member and a second lateral surface at an opposite side to a first optical member side in the second optical member becomes a preset distance. The jointing member adheres to the first optical member and the second optical member so that the distance becomes the preset distance.

Abstract: A projection system includes a first optical system and a second optical system including an optical element and a reflector and disposed at the enlargement side of the first optical system. The optical element has a reflection surface, a first transmissive surface disposed at the enlargement side of the reflection surface, and a second transmissive surface disposed at the enlargement side of the first transmissive surface. The reflector is disposed at the enlargement side of the reflection surface and at the reduction side of the first transmissive surface. The reflector is disposed between the optical element and the first optical system in the direction along a first optical axis of the first optical system.

Abstract: A projection system includes a first optical system, a second optical system including an optical element and disposed on the enlargement side of the first optical system, and a deflector disposed between the first optical system and the second optical system and deflecting the optical path. The optical element has a first transmissive surface, a reflection surface disposed on the enlargement side of the first transmissive surface, and a second transmissive surface disposed on the enlargement side of the reflection surface.

Abstract: A projection system includes a first optical system and a second optical system sequentially arranged from a reduction side toward an enlargement side. The second optical system includes an optical element having a concave reflection surface and a first lens having negative power, the optical element and the first lens sequentially arranged from the reduction side toward the enlargement side. The projection system satisfies Conditional Expressions (1) and (2) below. 3.5 ? LL + MR / imy × TR × 1 / NA ? 6.0 ­­­(1) TR ? 0 .

Abstract: A projection system includes a first lens group having positive power, an aperture stop, and a second lens group having positive power sequentially arranged from the enlargement side toward the reduction side. The portion at the reduction side of a reduction-side lens that forms the second lens group and is located at a position closest to the reduction side is a telecentric portion. The projection system satisfies Conditional Expressions (1) and (2) below, ?>40°??(1) YL1/YIM<6.0 ??(2) where ? represents a maximum half angle of view of the overall projection system, YIM represents the distance from an optical axis to the largest image height of the projection image formed at an image formation device, and YL1 is the distance from the optical axis to a chief beam corresponding to the maximum image height in an imaginary plane.

Abstract: A projection system includes a first lens group, an aperture diaphragm, and a second lens group. A reduction side of the second lens group is telecentric. The first lens group includes a first sub-lens group having negative power and a second sub-lens group having positive power. Between a lens located at the most reduction side of the first sub-lens group and a lens located at the most enlargement side of the second sub-lens group, an air gap wider than air gaps between the other lenses adjacent to each other is provided. A lens located at the most reduction side in the first lens group is a positive lens. A cemented lens of the second lens group includes a first lens having negative power, a second lens having positive power, and a third lens having negative power from an enlargement side toward a reduction side. ?>40.

Abstract: A projection system includes a first lens group having refractive power, an aperture stop, and a second lens group having refractive power sequentially arranged from the enlargement side toward the reduction side. The first lens group includes a first lens disposed at a position closest to the enlargement side, a second lens disposed at the reduction side of the first lens, and a plurality of positive lenses disposed at the reduction side of the second lens and each having positive power. The portion at the reduction side of a reduction-side lens that forms the second lens group and is located at a position closest to the reduction side is a telecentric portion. The projection system satisfies Conditional Expressions (1) and (2) below, Ln?gF?0.

Abstract: An optical system forms an intermediate image between a reduction-side conjugate plane and a enlargement-side conjugate plane. The optical system includes a first optical system and a second optical system including a lens and disposed on the enlargement side of the first optical system. The lens has a first transmission surface, a reflection surface disposed on the enlargement side of the first transmission surface, and a second transmission surface disposed on the enlargement side of the reflection surface. At least one of the reflection surface and the second transmission surface is a free-form surface.

Abstract: A projection system includes a first and second optical system arranged from a reduction side toward an enlargement side. The second optical system includes an optical element having a concave reflection surface and a first lens having negative power, the optical element and first lens arranged from reduction side toward enlargement side. The projection system satisfies the following expressions: TR?0.3 ??(1) 35?(OAL/imy)×(LL/imy)×TR×(1/NA)?60 ??(2) OAL represents an axial inter-surface spacing from an image formation device to the reflection surface, imy represents a first distance from an optical axis to the largest image height at the image formation device, LL represents the largest radius of the first lens, TR represents a throw ratio, and NA represents the numerical aperture of the image formation device.

Abstract: An optical system includes a lens having a first transmission surface, a reflection surface disposed on an enlargement side of the first transmission surface, and a second transmission surface disposed on the enlargement side of the reflection surface. The lens is made of resin. The reflection surface has a concave shape. A conditional expression below is satisfied, 10?q×Fno/f2?2989 where Fno is an F-number of the optical system, f is a focal length of the optical system, and q is an amount of light in an enlargement-side conjugate plane.

Abstract: An attachment optical system is detachably attached to a magnification side of a projection optical system provided to a projection display device, and projects projection light emitted from the projection optical system on an imaging plane different from a magnification side imaging plane of the projection optical system. The attachment optical system is provided with an optical element having a second optical axis arranged on an extension of a first optical axis of the projection optical system. The optical element has a plane of incidence arranged on the second optical axis, a first reflecting surface configured to reflect light emitted from the plane of incidence, a second reflecting surface configured to reflect light reflected by the first reflecting surface, and an exit surface configured to transmit light reflected by the second reflecting surface.

Abstract: An attachment optical system is detachably attached to a magnification side of a projection optical system of a projection display device, and projects light emitted from the projection optical system on an imaging plane different from a magnification side imaging plane of the projection optical system. The attachment optical system includes an optical element having a second optical axis as an extension of a first optical axis of the projection optical system. The optical element has a plane of incidence on the second optical axis, a first reflecting surface that reflects light emitted from the plane of incidence, a second reflecting surface that reflects light reflected by the first reflecting surface, and an exit surface that transmits light reflected by the second reflecting surface. The first reflecting surface and the exit surface are continuous in an axial area where light passes the second optical axis and the first optical axis.

Abstract: A projection system includes a first optical system including a first lens, and a second optical system including an optical element and disposed at the enlargement side of the first optical system. The first lens is disposed in a position closest to the enlargement side in the first optical system. The optical element has a first transmissive surface, a first reflection surface, a second reflection surface, and a second transmissive surface. The second reflection surface is disposed between the first reflection surface and a first surface of the first lens that is a surface on the enlargement side in a direction along a first optical axis of the first optical system. The second transmissive surface is disposed at a side opposite a side where the first optical system is located with respect to the second reflection surface in the direction.

Abstract: A projection system includes a first optical system, a second optical system including a first optical element and a second optical element and disposed on the enlargement side of the first optical system, and a placement mechanism configured to selectively place one of the first and second optical elements on a first optical axis of the first optical system. The first optical element has a first light incident surface, a first reflection surface disposed on the enlargement side of the first light incident surface, and a first light exiting surface disposed on the enlargement side of the first reflection surface. The second optical element has a second light incident surface, a second reflection surface disposed on the enlargement side of the second light incident surface, and a second light exiting surface disposed on the enlargement side of the second reflection surface.

Abstract: An optical system forms an intermediate image between a reduction-side conjugate plane and a enlargement-side conjugate plane. The optical system includes a first optical system and a second optical system including a lens and disposed on the enlargement side of the first optical system. The lens has a first transmission surface, a reflection surface disposed on the enlargement side of the first transmission surface, and a second transmission surface disposed on the enlargement side of the reflection surface. At least one of the reflection surface and the second transmission surface is a free-form surface.

Abstract: An optical system includes a lens having a first transmission surface, a reflection surface disposed on an enlargement side of the first transmission surface, and a second transmission surface disposed on the enlargement side of the reflection surface. The lens is made of resin. The reflection surface has a concave shape. A conditional expression below is satisfied, 10?q×Fno/f2?2989 where Fno is an F-number of the optical system, f is a focal length of the optical system, and q is an amount of light in an enlargement-side conjugate plane.

Abstract: The lens unit includes a jointed lens having a first optical member, a second optical member disposed on an optical axis of the first optical member, and a jointing member having a light transmissive property and disposed between the first optical member and the second optical member, and an adjustment mechanism holding the first optical member and the second optical member and adjusting a distance between the first optical member and the second optical member along an optical axis direction. The jointing member adheres to the first optical member and the second optical member in a deformable manner. The adjustment mechanism adjusts the distance to change the thickness of the jointing member along the optical axis direction.

Abstract: A projection system includes a first optical system, a second optical system including a first optical element and a second optical element and disposed on the enlargement side of the first optical system, and a placement mechanism configured to selectively place one of the first and second optical elements on a first optical axis of the first optical system. The first optical element has a first light incident surface, a first reflection surface disposed on the enlargement side of the first light incident surface, and a first light exiting surface disposed on the enlargement side of the first reflection surface. The second optical element has a second light incident surface, a second reflection surface disposed on the enlargement side of the second light incident surface, and a second light exiting surface disposed on the enlargement side of the second reflection surface.

Abstract: A projection system includes a first optical system, a second optical system including an optical element and disposed on the enlargement side of the first optical system, and a deflector disposed between the first optical system and the second optical system and deflecting the optical path. The optical element has a first transmissive surface, a reflection surface disposed on the enlargement side of the first transmissive surface, and a second transmissive surface disposed on the enlargement side of the reflection surface.

Abstract: A projection system includes a first optical system including a first lens, and a second optical system including an optical element and disposed at the enlargement side of the first optical system. The first lens is disposed in a position closest to the enlargement side in the first optical system. The optical element has a first transmissive surface, a first reflection surface, a second reflection surface, and a second transmissive surface. The second reflection surface is disposed between the first reflection surface and a first surface of the first lens that is a surface on the enlargement side in a direction along a first optical axis of the first optical system. The second transmissive surface is disposed at a side opposite a side where the first optical system is located with respect to the second reflection surface in the direction.