Abstract: An optical system includes lenses and a prism. The prism includes a first transmissive surface, a first reflective surface, a second reflective surface, and a second transmissive surface. A first rectangular region at a reduction conjugate point: has an imaging relationship in which the first rectangular region is conjugate to a second rectangular region at a magnification conjugate point; and does not intersect with an optical axis. When a space is divided into a first space and a second space, all principal rays passing through the first rectangular region pass through the first rectangular region, the first transmissive surface, and the first reflective surface in the first space, and pass through the second reflective surface and the second transmissive surface in the second space.

Abstract: The present disclosure is directed to an optical system internally having an intermediate imaging position MI that is conjugate with both of a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, the optical system including: a first positive lens group GP1 including a plurality of lens elements and positioned on the magnification side with respect to the intermediate imaging position; a second positive lens group GP2 including a plurality of lens elements and positioned between the first positive lens group GP1 and the intermediate imaging position Ml; and a negative lens group GN including a plurality of lens elements and positioned on the reduction side with respect to the intermediate imaging position MI, wherein, during focusing, the first positive lens group GP1 and the negative lens group GN move in an optical axis direction, and the second positive lens group GP2 is stationary.

Abstract: The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugate with both of a magnification conjugate point on a magnification side and a reduction conjugate point on reduction side, including: a magnification optical system including a plurality of lens elements and positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system including a plurality of lens elements and positioned on the reduction side with respect to the intermediate imaging position, wherein the relay optical system includes a plurality of moving lens groups which are independently movable in an optical axis direction during zooming, and wherein the reduction side-closest moving lens group that is positioned closest to the reduction side among the plurality of moving lens groups has a negative refractive power.

Abstract: The optical system includes a first sub-optical system including an aperture stop and a second sub-optical system including a prism. The prism has a first transmission surface located on a reduction side, a second transmission surface located on a magnification side, and at least one reflection surface between the first transmission surface and the second transmission surface. The first sub-optical system includes a plurality of rotationally symmetric lens elements.

Abstract: The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system comprising: a magnification optical system positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system positioned on the reduction side with respect to the intermediate imaging position; the relay optical system including: a first lens group positioned closest to the magnification side; two lens groups positioned on the reduction side with respect to the first lens group; and a negative lens group interposed between the two lens groups, wherein during zooming the negative lens is fixed, while the two lens groups are displaced.

Abstract: A projection lens system projects an image of a reduction side into a magnification side in an image projection device, a back glass being disposed on the reduction side. In the projection lens system, all of one or more negative lenses that satisfy, in a surface on the reduction side or a surface on the magnification side, condition |h/H|<2.0 defined by height h of a most off-axis principal ray and height H of an axial ray passing through a highest pupil position satisfy conditions Tn?98.5% and Dn/Db?0.05 defined by transmittance Tn, thickness Dn of the negative lens on an optical axis, and total thickness Db of the back glass.

Abstract: A projection lens system that projects an image of a reduction side into a magnification side includes a diaphragm, a plurality of positive lenses, and a plurality of negative lenses. The plurality of positive lenses include a first positive lens closer to the magnification side than the diaphragm is and closest to the diaphragm, a second positive lens second closest to the diaphragm after the first positive lens on the magnification side, a third positive lens closer to the reduction side than the diaphragm is and closest to the diaphragm. The plurality of negative lenses include a first negative lens closer to the magnification side than the diaphragm is and closest to the diaphragm, and a second negative lens closer to the reduction side than the diaphragm is and closest to the diaphragm. The lenses have transmittances larger than threshold values, respectively.

Abstract: The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugate to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including: a magnification optical system having a plurality of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system having a plurality of lens elements, positioned on the reduction side with respect to the intermediate imaging position, wherein a first lens element located closest to the magnification side among the plurality of lens elements in magnification optical system is an aspherical lens having a negative power, the optical system satisfies the conditions (1) to (3).

Abstract: The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugate to magnification and reduction conjugate points, respectively, the optical system including: a magnification optical system having a plurality of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system having a plurality of lens elements, positioned on the reduction side with respect to the intermediate imaging position, wherein there are a plurality of air distances among the lens elements, the magnification optical system includes a magnification optical system front group positioned on the magnification side with respect to the longest air distance in the magnification optical system and a magnification optical system rear group positioned on the reduction side with respect to the longest air distance, and the optical system satisfies the conditions (1) and (2).

Abstract: A lens system includes a plurality of lens elements arranged from an object side to an image plane side, and a diaphragm arranged between the plurality of lens elements. The plurality of lens elements include a plurality of freeform lenses each having a freeform surface that is asymmetrical with respect to a first direction and a second direction which cross with each other. At least one freeform lens is placed on the image plane side of the diaphragm. With a lens thickness T1 in the first direction at a maximum height of an axial ray and a lens thickness T2 in the second direction at the maximum height of the axial ray, at least one freeform lens satisfying 0.3<T1/T2<0.76 is placed on the object side of the diaphragm.

Abstract: A lens system includes lens elements and a diaphragm. The lens elements include freeform lenses each having a freeform surface asymmetrical with respect to first and second directions. At least one freeform lens is placed on the image plane side of the diaphragm. The lens system satisfies a following conditional expression (1); 0.0075 < ? ? k = 1 N ? { ( SAG ? ? 1 k - SAG ? ? 2 k ) × ? ? ? nd k } Y ? ? 2 × tan ? ? ? ? ? 1 ? ( 1 ) where N: a total number of the freeform surfaces on the object side of the diaphragm, k: a number indicating a freeform surface among the N freeform surfaces, SAG1k, SAG2k: a sag amount at a position where a height of a k-th freeform surface in the first or second direction is 40% of an image height in the first direction, Y2: an image height in the second direction, ?1: a full angle of view in the first direction, and ?ndk: a difference between refractive indexes on the both sides of the k-th freeform surface.

Abstract: The present embodiment discloses an interchangeable lens that can be detachably attached to an apparatus body having an image forming surface on which an image is formed, and the interchangeable lens has a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side. The interchangeable lens includes a focus lens group that can move along an optical axis to adjust a focus at the magnification conjugate point and a flange back distance correction lens group that can move along the optical axis to correct an error in a flange back distance of the interchangeable lens with respect to the image forming surface.

Abstract: The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including: a magnification optical system having A (A is an integer of three or more) pieces of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system having B (B is an integer of two or more) pieces of lens elements, positioned on the reduction side with respect to the intermediate imaging position. A first lens group composed of ? pieces (? is one or more and less than B) of lens elements positioned first from the magnification side in the relay optical system has a negative power.

Abstract: The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including: a magnification optical system having a plurality of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system having a plurality of lens elements, positioned on the reduction side with respect to the intermediate imaging position. The magnification optical system has a first lens element and a second lens element in this order from the magnification side, and the second lens element has a positive power. The optical system satisfies the following condition (1): 23<|f2/fw|<1000 . . . (1), where, f2 is a focal length of the second lens element, and fw is a focal length of the entire optical system at the wide-angle end.

Abstract: A projection lens system is a projection lens system including a plurality of lens groups, the plurality of lens groups each including one or more lenses and moving such that an interval between the lens groups changes during a zooming action, the projection lens system including a first lens group disposed closest to a magnification side, the first lens group having positive power, wherein the first lens group includes one negative lens satisfying 0.0005<?pgfn<0.01 and 32<vdn<45.

Abstract: An imaging optical system includes a plurality of lens groups each moving such that spaces between each one of the plurality of lens groups change during a zooming. The imaging optical system conjugates a conjugate point on a magnification side and an intermediate imaging position, and conjugates a conjugate point on a reduction side and the intermediate imaging position. The imaging optical system includes a first lens group located at a furthest place on the magnification side and a rear group in this order from the magnification side toward the reduction side. The first lens group includes a field curvature correction lens group moving along an optical axis when an amount of a field curvature is changed, and a focusing lens group. The imaging optical system satisfies condition (4) below: |{(1??cw2)×?crw2}/{(1??fw2)×?frw2}|<0.

Abstract: The lens system forms an image conjugately between each of a magnification conjugate point and a reduction conjugate point; and an intermediate image-forming position. The lens system includes a magnification optical system with positive power, the magnification optical system having a plurality of lens elements and positioned closer to the magnification side than the intermediate image-forming position; and a relay optical system with positive power, the relay optical system having a plurality of lens elements and positioned closer to the reduction side than the intermediate image-forming position. The lens system satisfies following conditions (1) and (2). 0.08?fp/fr?0.8??(1) {Ymax?ft·tan(?max)}/{ft·tan(?max)}??0.3??(2) where fr is composite focal length of the relay optical system, fp is composite focal length of the magnification optical system, Ymax is a radius of an effective image diameter, ?max is a maximum half view angle, and ft is the focal length of the lens system.

Abstract: A projection lens system projects an image of a reduction side into a magnification side in an image projection device, a back glass being disposed on the reduction side. In the projection lens system, all of one or more negative lenses that satisfy, in a surface on the reduction side or a surface on the magnification side, condition |h/H|<2.0 defined by height h of a most off-axis principal ray and height H of an axial ray passing through a highest pupil position satisfy conditions Tn?98.5% and Dn/Db?0.05 defined by transmittance Tn, thickness Dn of the negative lens on an optical axis, and total thickness Db of the back glass.

Abstract: A projection lens system that projects an image of a reduction side into a magnification side includes a diaphragm, a plurality of positive lenses, and a plurality of negative lenses. The plurality of positive lenses include a first positive lens closer to the magnification side than the diaphragm is and closest to the diaphragm, a second positive lens second closest to the diaphragm after the first positive lens on the magnification side, a third positive lens closer to the reduction side than the diaphragm is and closest to the diaphragm. The plurality of negative lenses include a first negative lens closer to the magnification side than the diaphragm is and closest to the diaphragm, and a second negative lens closer to the reduction side than the diaphragm is and closest to the diaphragm. The lenses have transmittances larger than the respective lower limit values.

Abstract: An imaging optical system includes a plurality of lens groups each moving such that spaces between each one of the plurality of lens groups change during a zooming. The imaging optical system conjugates a conjugate point on a magnification side and an intermediate imaging position, and conjugates a conjugate point on a reduction side and the intermediate imaging position. The imaging optical system includes a first lens group located at a furthest place on the magnification side and a rear group in this order from the magnification side toward the reduction side. The first lens group includes a field curvature correction lens group moving along an optical axis when an amount of a field curvature is changed, and a focusing lens group. The imaging optical system satisfies condition (4) below: |{(1??cw2)×?crw2}/{(1??fw2)×?frw2}|<0.