Abstract: A projection optical system and a projection display device using the same is provided, wherein the projection optical system has a sufficiently small size to be provided in a front-projection-type projector and can effectively correct various aberrations. An original image on an image display surface is enlarged and projected onto a screen by a first optical system that includes a plurality of lenses and a second optical system that includes a reflecting mirror having a concave surface with an aspheric shape. All of the optical surfaces of the first optical system and the second optical system are rotationally symmetric surfaces each having the optical axis common to all of the optical surfaces as its center. A first lens surface, which is a reduction-side surface, and a second lens surface, which is a magnification-side surface, of a lens (fourteenth lens) closest to a magnification side in the first optical system satisfy predetermined conditional expressions.

Abstract: A zoom lens for projection includes a first negative lens group, a second positive lens group, a third positive lens group, a fourth lens group, and a fifth positive lens group, which are sequentially arranged from the magnification side of the zoom lens. The first lens group and the fifth lens group are fixed, and the second lens group, the third lens group and the fourth lens group move along the optical axis of the zoom lens when magnification of the zoom lens is changed. Each of the first lens group and the second lens group is composed of two lenses. Each of the third lens group and the fifth lens group is composed of a positive lens, and the fourth lens group is composed of five lenses. Further, the reduction side of the zoom lens is telecentric.

Abstract: In order from a magnification side of the projection zoom lens system, five lens groups are arranged. The fourth lens group includes, in order from the magnification side, a negative lens having at least one aspheric surface, a positive lens, a negative lens concave toward the magnification side, a positive lens convex toward the reduction side, and a positive lens. The fifth lens group is formed of one lens, and is configured so that a ratio of a focal length of the fifth lens group to a focal length of the whole system at a wide-angle end is within a numerical range of 3 to 8.

Abstract: A variable magnification optical system for projection includes a first-lens-group having negative refractive power, and which is fixed when magnification of the variable magnification optical system is changed, a second-lens-group having negative refractive power, and which is movable when magnification of the variable magnification optical system is changed, a third-lens-group having positive refractive power, and which is movable when magnification of the variable magnification optical system is changed, and a fourth-lens-group having positive refractive power, and which is fixed when magnification of the variable magnification optical system is changed, which are arranged from the magnification side of the variable magnification optical system in the order mentioned above. The reduction side of the variable magnification optical system is telecentric, and formula (11) is satisfied: 1.

Abstract: A zoom lens for projection includes a first negative lens group, a second positive lens group, a third positive lens group, a fourth lens group, and a fifth positive lens group, which are sequentially arranged from the magnification side of the zoom lens. The first lens group and the fifth lens group are fixed, and the second lens group, the third lens group and the fourth lens group move along the optical axis of the zoom lens when magnification of the zoom lens is changed. Each of the first lens group and the second lens group is composed of two lenses. Each of the third lens group and the fifth lens group is composed of a positive lens, and the fourth lens group is composed of five lenses. Further, the reduction side of the zoom lens is telecentric.

Abstract: Disclosed are a projection optical system that has a sufficiently small size to be provided in a front-projection-type projector and can effectively correct various aberrations and a projection display device using the same. An original image on an image display surface is enlarged and projected onto a screen by a first optical system that includes a plurality of lenses and a second optical system that includes a reflecting mirror having a concave surface with an aspheric shape. All of the optical surfaces of the first optical system and the second optical system are rotationally symmetric surfaces each having the optical axis common to all of the optical surfaces as its center. A first lens surface, which is a reduction-side surface, and a second lens surface, which is a magnification-side surface, of a lens (fourteenth lens) closest to a magnification side in the first optical system satisfy predetermined conditional expressions.

Abstract: In order from a magnification side of the projection zoom lens system, five lens groups are arranged. The fourth lens group includes, in order from the magnification side, a negative lens having at least one aspheric surface, a positive lens, a negative lens concave toward the magnification side, a positive lens convex toward the reduction side, and a positive lens. The fifth lens group is formed of one lens, and is configured so that a ratio of a focal length of the fifth lens group to a focal length of the whole system at a wide-angle end is within a numerical range of 3 to 8.

Abstract: A projection zoom lens includes a first lens group having a negative reflecting power and a second to fifth lens groups each having a positive reflecting power are provided in the order from the magnification side. Nine lenses are distributed in a manner that the first lens group has one lens, the second lens group has one lens, the third lens group has two lenses, the fourth lens group has four lenses and the fifth lens group has one lens. Since the second lens group, the third lens group and the fourth lens group are moved at the time of the power-varying operation, various kinds of aberrations may be made despite of simple configuration. The first lens group is an aspherical lens which concave surface is directed to the reduction side.

Abstract: A projection lens includes, in order form a magnification side: a first lens group having negative refractive power; and a second lens group having positive refractive power. An aspheric lens is arranged on the most magnification side of the first lens group. The conditional expressions 3<Bf/f and 0.4<H/L are satisfied, where f denotes a focal length of the projection lens, Bf denotes an air-converted back focal length, H denotes a height of a principal ray at the maximum angle of view on a plane which is orthogonal to an optical axis and which passes through point A, and L denotes a length from the point A to a vertex of a lens surface on the most reduction side on the optical axis. Here, the point A is a vertex of a lens surface on the most magnification side on the optical axis.

Abstract: A projection zoom lens includes a first lens group having a negative reflecting power and a second to fifth lens groups each having a positive reflecting power are provided in the order from the magnification side. Nine lenses are distributed in a manner that the first lens group has one lens, the second lens group has one lens, the third lens group has two lenses, the fourth lens group has four lenses and the fifth lens group has one lens. Since the second lens group, the third lens group and the fourth lens group are moved at the time of the power-varying operation, various kinds of aberrations may be made despite of simple configuration. The first lens group is an aspherical lens which concave surface is directed to the reduction side.

Abstract: A projection lens includes, in order form a magnification side: a first lens group having negative refractive power; and a second lens group having positive refractive power. An aspheric lens is arranged on the most magnification side of the first lens group. The conditional expressions 3<Bf/f and 0.4<H/L are satisfied, where f denotes a focal length of the projection lens, Bf denotes an air-converted back focal length, H denotes a height of a principal ray at the maximum angle of view on a plane which is orthogonal to an optical axis and which passes through point A, and L denotes a length from the point A to a vertex of a lens surface on the most reduction side on the optical axis. Here, the point A is a vertex of a lens surface on the most magnification side on the optical axis.

Abstract: A first lens group having a negative refractive power, an aperture diaphragm, and a second lens group having a positive refractive power are arranged in order from an enlargement side. A reduction side of a projection lens is made essentially telecentric. Further, cemented triplet lenses, each of which includes cemented three lenses, are provided in the first lens group and the second lens group, respectively. Further, air spacing which enables placement of a mirror is ensured between the first lens group and the second lens group. Moreover, specific conditional expressions for the lens are satisfied.

Abstract: A first lens group having a negative refractive power, an aperture diaphragm, and a second lens group having a positive refractive power are arranged in order from an enlargement side. A reduction side of a projection lens is made essentially telecentric. Further, cemented triplet lenses, each of which includes cemented three lenses, are provided in the first lens group and the second lens group, respectively. Further, air spacing which enables placement of a mirror is ensured between the first lens group and the second lens group. Moreover, specific conditional expressions for the lens are satisfied.

Abstract: A large numerical aperture objective lens is disclosed having three lens groups. In order from the object side, these lens groups include: a first lens group of positive refractive power that is formed of two positive lens elements and an achromatic set of paired lens elements formed of a lens element of negative refractive power and a lens element of positive refractive power, respectively; a second lens group of negative refractive power; and a third lens group of positive refractive power, with the surface of the third lens group nearest the object side being convex. Specified conditions are satisfied in order to provide a compact, large numerical aperture objective lens having its aberrations favorably corrected as well as to correct for shifts of focus caused by expansion/contraction of the lens barrel with changes in temperature.

Abstract: An optical instrument for observation includes, in order from the object side, an objective lens system having positive refractive power, an erecting optical system, and an ocular lens system having positive refractive power. When an anti-vibration mechanism is used to maintain the erecting prism at an orientation in space that is stabilized so as to prevent image degradation due to vibrations of the optical instrument for observation, the erecting prism is constructed to satisfy specified conditions so that ghost light is not generated and so that the optical instrument for observation may be compact.

Abstract: An ocular zoom lens is formed of three lens groups, of positive, positive, and negative refractive power, in order from the eye-point side. The second and third lens groups are moved along the optical axis in opposite directions during zooming, and the second lens group is formed of, in order from the eye-point side, a biconvex lens and a negative meniscus lens with its concave surface on the eye-point side, with the surfaces of the biconvex lens and the negative meniscus lens that face one another having different radii of curvature and being positioned on-axis with an intervening air space. Various conditions are preferably satisfied in order to ensure sufficient eye relief using a relatively small number of lens elements while providing increased freedom of design and enabling favorable correction of aberrations even for wide image angles.

Abstract: An optical instrument for observation includes, in order from the object side, an objective lens system having positive refractive power, an erecting optical system, and an ocular lens system having positive refractive power. When an anti-vibration mechanism is used to maintain the erecting prism at an orientation in space that is stabilized so as to prevent image degradation due to vibrations of the optical instrument for observation, the erecting prism is constructed to satisfy specified conditions so that ghost light is not generated and so that the optical instrument for observation may be compact.

Abstract: An ocular zoom lens is formed of three lens groups, of positive, positive, and negative refractive power, in order from the eye-point side. The second and third lens groups are moved along the optical axis in opposite directions during zooming, and the second lens group is formed of, in order from the eye-point side, a biconvex lens and a negative meniscus lens with its concave surface on the eye-point side, with the surfaces of the biconvex lens and the negative meniscus lens that face one another having different radii of curvature and being positioned on-axis with an intervening air space. Various conditions are preferably satisfied in order to ensure sufficient eye relief using a relatively small number of lens elements while providing increased freedom of design and enabling favorable correction of aberrations even for wide image angles.

Abstract: A large numerical aperture objective lens is disclosed having three lens groups. In order from the object side, these lens groups include: a first lens group of positive refractive power that is formed of two positive lens elements and an achromatic set of paired lens elements formed of a lens element of negative refractive power and a lens element of positive refractive power, respectively; a second lens group of negative refractive power; and a third lens group of positive refractive power, with the surface of the third lens group nearest the object side being convex. Specified conditions are satisfied in order to provide a compact, large numerical aperture objective lens having its aberrations favorably corrected as well as to correct for shifts of focus caused by expansion/contraction of the lens barrel with changes in temperature.