Abstract: A variable magnification projection optical system includes, in order from an enlargement side: a first lens group having negative refractive power; a second lens group having negative refractive power; and a third lens group having positive refractive power. During zooming, the first lens group is fixed, and the second lens group and the third lens group move. The second lens group includes a plurality of lenses each having positive refractive power. All lenses each having positive refractive power in the first lens group and the second lens group are made of a glass material having a transmittance greater than 0.98 per thickness of 10 mm with respect to light having a wavelength of 440 nm.

Abstract: A projection optical system includes: a first optical system and a second optical system disposed in that order from an enlargement side. The second optical system forms an intermediate image of the image, and the first optical system enlarges and projects the intermediate image. The first optical system includes: a first lens group, a first reflecting optical element, and a part of a second lens group, disposed in that order from the enlargement side. The second optical system includes: a remainder of the second lens group, a second reflecting optical element, and a third lens group, disposed in that order from the enlargement side. The second reflecting optical element reflects light output from the third lens group toward the second lens group. The first reflecting optical element reflects light output from the second lens group toward the first lens group.

Abstract: A projection optical system that enlarges and projects an image displayed on an image display includes: a first optical system; and a second optical system. The projection optical system is a monofocal lens or a zoom lens. The first optical system and the second optical system are arranged, in order starting with the first optical system, from an enlargement side of the projection optical system. The second optical system forms an intermediate image of the image between the first optical system and the second optical system. The first optical system enlarges and projects the intermediate image. The first optical system includes: a first-A optical system and a first-B optical system in order from the enlargement side; and a reflecting optical element that bends a light path between the first-A optical system and the first-B optical system.

Abstract: A projection optical system that projects, while enlarging, an image displayed on an image display surface includes in order from an enlargement side: a first negative refractive power lens group; a second negative refractive power lens group; at least one positive or negative refractive power lens group; a stop; and a first positive refractive power lens group. The projection optical system causes magnification variation by varying distances between lens groups. The at least one positive or negative refractive power lens groups disposed between the second negative refractive power lens group and the stop is movable during the magnification variation. The first positive refractive power lens group is an only lens group that is positioned closer to a reduction side than the stop and is also movable during the magnification variation.

Abstract: A projection optical system that projects, while enlarging, an image displayed on an image display surface includes in order from an enlargement side: a first negative refractive power lens group; a second negative refractive power lens group; at least one positive or negative refractive power lens group; a stop; and a first positive refractive power lens group. The projection optical system causes magnification variation by varying distances between lens groups. The at least one positive or negative refractive power lens groups disposed between the second negative refractive power lens group and the stop is movable during the magnification variation. The first positive refractive power lens group is an only lens group that is positioned closer to a reduction side than the stop and is also movable during the magnification variation.

Abstract: A projection optical system that enlarges an image to be displayed on an image display surface to an angle of view of 70 degrees or more, projects the enlarged image, and includes: a fixed focal length lens that has, in order from an enlargement side, a first optical system and a second optical system on a same optical axis, wherein the second optical system forms an intermediate image of the image, the first optical system enlarges and projects the intermediate image, the projection optical system comprises positive lenses that are positioned on both of the enlargement side and a reduction side of the intermediate image and are adjacent to each other, and following conditional expressions are satisfied: 0.4<Tm1/Tw<0.7 and T12w/Tw<0.2 (2).

Abstract: A projection optical system that enlarges and projects an image displayed on an image display includes: a first optical system; and a second optical system. The projection optical system is a monofocal lens or a zoom lens. The first optical system and the second optical system are arranged, in order starting with the first optical system, from an enlargement side of the projection optical system. The second optical system forms an intermediate image of the image between the first optical system and the second optical system. The first optical system enlarges and projects the intermediate image. The first optical system includes: a first-A optical system and a first-B optical system in order from the enlargement side; and a reflecting optical element that bends a light path between the first-A optical system and the first-B optical system.

Abstract: A projection optical system includes: a first optical system and a second optical system disposed in that order from an enlargement side. The second optical system forms an intermediate image of the image, and the first optical system enlarges and projects the intermediate image. The first optical system includes: a first lens group, a first reflecting optical element, and a part of a second lens group, disposed in that order from the enlargement side. The second optical system includes: a remainder of the second lens group, a second reflecting optical element, and a third lens group, disposed in that order from the enlargement side. The second reflecting optical element reflects light output from the third lens group toward the second lens group. The first reflecting optical element reflects light output from the second lens group toward the first lens group.

Abstract: A projection optical system that enlarges and projects an image displayed on an image display includes: a first optical system; and a second optical system. The projection optical system is a monofocal lens or a zoom lens. The first optical system and the second optical system are arranged, in order starting with the first optical system, from an enlargement side of the projection optical system. The second optical system forms an intermediate image of the image between the first optical system and the second optical system. The first optical system enlarges and projects the intermediate image. The first optical system includes: a first-A optical system and a first-B optical system in order from the enlargement side; and a reflecting optical element that bends a light path between the first-A optical system and the first-B optical system.

Abstract: A projection optical system capable of performing magnification projection of an image displayed on an image display surface, with a 40° half angle of view, or more includes, in an order from a magnification side: a first optical system; and a second optical system, wherein the second optical system forms an intermediate image of the image, the first optical system performs magnification projection of the intermediate image, and the following conditional expressions (1) and (2) are satisfied: 1<Ff/|Fw|<2 . . . (1), 0.4<Lf/Lw<0.6 . . . (2), where, Ff: a focal length of the first optical system, Fw: a focal length of an entire system, Lf: a distance on optical axis, from a most-magnification-side surface vertex to the intermediate image, in the first optical system, Lw: an entire length of a lens.

Abstract: A projection optical system that enlarges and projects an image displayed on an image display includes: a first optical system; and a second optical system. The projection optical system is a monofocal lens or a zoom lens. The first optical system and the second optical system are arranged, in order starting with the first optical system, from an enlargement side of the projection optical system. The second optical system forms an intermediate image of the image between the first optical system and the second optical system. The first optical system enlarges and projects the intermediate image. The first optical system includes: a first-A optical system and a first-B optical system in order from the enlargement side; and a reflecting optical element that bends a light path between the first-A optical system and the first-B optical system.

Abstract: Provided is a projection optical system that is a monofocal lens or a zoom lens that includes a first and a second optical system. The second optical system forms an intermediate image and the first optical system enlarges and projects the intermediate image. The first optical system includes a first-A optical system and a first-B optical system and includes a reflecting optical element. In response to the monofocal lens or the zoom lens, conditional formulas (1) and (2) are satisfied in an infinity in-focus state, 0.18<Ta/Tw<0.4 . . . (1), 1<fa/|fw|<15 . . . (2). In the conditional formulas (1) and (2), Ta is an on-axis distance in the first-A optical system, Tw is an on-axis distance in the projection optical system, fa is a focal length of the first-A optical system, and fw is a focal length of an entirety of the projection optical system.

Abstract: A projection optical system that enlarges an image to be displayed on an image display surface to an angle of view of 70 degrees or more, projects the enlarged image, and includes: a fixed focal length lens that has, in order from an enlargement side, a first optical system and a second optical system on a same optical axis, wherein the second optical system forms an intermediate image of the image, the first optical system enlarges and projects the intermediate image, the projection optical system comprises positive lenses that are positioned on both of the enlargement side and a reduction side of the intermediate image and are adjacent to each other, and following conditional expressions are satisfied: 0.4<Tm1/Tw<0.7 and T12w/Tw<0.2 (2).

Abstract: A projection optical system projects, while enlarging, an image displayed on an image display surface and performs zooming by moving a plurality of lens groups arranged along a same optical axis. The projection optical system includes, from an enlargement side: a first lens group having a negative refractive power; a second lens group having a negative refractive power and movable during zooming; a third lens group having a positive refractive power and movable during zooming; and a lens group disposed at a most reduction-side position. The first lens group includes, from the enlargement side: a front group having a negative refractive power; and a rear group having a positive refractive power and including, from the enlargement side, a negative lens element and a positive lens element. For zooming from a wide-angle end to a telephoto end, the third lens group moves toward the enlargement side monotonically.

Abstract: Provided is a projection optical system that is a monofocal lens or a zoom lens that includes a first and a second optical system. The second optical system forms an intermediate image and the first optical system enlarges and projects the intermediate image. The first optical system includes a first-A optical system and a first-B optical system and includes a reflecting optical element. In response to the monofocal lens or the zoom lens, conditional formulas (1) and (2) are satisfied in an infinity in-focus state, 0.18<Ta/Tw<0.4 . . . (1), 1<fa/|fw|<15 . . . (2). In the conditional formulas (1) and (2), Ta is an on-axis distance in the first-A optical system, Tw is an on-axis distance in the projection optical system, fa is a focal length of the first-A optical system, and fw is a focal length of an entirety of the projection optical system.

Abstract: A projection optical system projects, while enlarging, an image displayed on an image display surface and performs zooming by moving a plurality of lens groups arranged along a same optical axis. The projection optical system includes, from an enlargement side: a first lens group having a negative refractive power; a second lens group having a negative refractive power and movable during zooming; a third lens group having a positive refractive power and movable during zooming; and a lens group disposed at a most reduction-side position. The first lens group includes, from the enlargement side: a front group having a negative refractive power; and a rear group having a positive refractive power and including, from the enlargement side, a negative lens element and a positive lens element. For zooming from a wide-angle end to a telephoto end, the third lens group moves toward the enlargement side monotonically.

Abstract: A projection optical system capable of performing magnification projection of an image displayed on an image display surface, with a 40° half angle of view, or more includes, in an order from a magnification side: a first optical system; and a second optical system, wherein the second optical system forms an intermediate image of the image, the first optical system performs magnification projection of the intermediate image, and the following conditional expressions (1) and (2) are satisfied: 1<Ff/|Fw|<2 . . . (1), 0.4<Lf/Lw<0.6 . . . (2), where, Ff: a focal length of the first optical system, Fw: a focal length of an entire system, Lf: a distance on optical axis, from a most-magnification-side surface vertex to the intermediate image, in the first optical system, Lw: an entire length of a lens.

Abstract: A projection lens system is constructed as a zoom lens system which is for use with a laser light source and performs magnification variation by moving at least a lens group along the optical axis, and the projection lens system fulfills the following conditional formula: (|AC(B2?G)|+|AC(R2?G)|)/(|AC(B1?G)|+|AC(R1?G)|)<0.8, where AC(B2?G) represents longitudinal chromatic aberration between the wavelengths ?B2 and ?G; AC(R2?G) represents longitudinal chromatic aberration between the wavelengths ?R2 and ?G; AC(B1?G) represents longitudinal chromatic aberration between the wavelengths ?B1 and ?G; and AC(R1?G) represents longitudinal chromatic aberration between the wavelengths ?R1 and ?G.

Abstract: In a zoom lens, at least a first group of negative optical power and a second group of positive optical power are included from an object side, when zooming is performed from a wide-angle end to a telephoto end, a distance between the first and the second groups is reduced and an aperture is moved together with the second group. The first group is formed with a front group composed of only negative lenses and a rear group which is composed of two lenses, a positive and a negative from the object side and which has a positive optical power as a whole and the zoom lens satisfies a conditional formula: 0.06<T1/Lmax<0.11 (T1 is a distance on an optical axis between the front and rear groups, and Lmax is the maximum total length of the zoom lens in zooming).

Abstract: In a zoom lens, at least a first group of negative optical power and a second group of positive optical power are included from an object side, when zooming is performed from a wide-angle end to a telephoto end, a distance between the first and the second groups is reduced and an aperture is moved together with the second group. The first group is formed with a front group composed of only negative lenses and a rear group which is composed of two lenses, a positive and a negative from the object side and which has a positive optical power as a whole and the zoom lens satisfies a conditional formula: 0.06<T1/Lmax<0.11 (T1 is a distance on an optical axis between the front and rear groups, and Lmax is the maximum total length of the zoom lens in zooming).