Abstract: An optical system includes a first negative lens element disposed nearest a front side and a first positive lens element whose front surface resides within a distance 0.4 L from the surface nearest the front side toward a rear side of the optical system having a total lens length L. By appropriately determining the materials for the two lens elements, the optical system realizes a wide angle of view while correcting lateral chromatic aberration well.

Abstract: An optical system used for an image pickup apparatus including an image pickup element is provided. The optical system includes a negative lens disposed furthest away on the enlargement conjugation side and satisfies the following condition: 80 degrees<2?, where 2? (degrees) denotes an angle of view of the optical system. In addition, the following parameters of the optical system are optimally determined: a lens open angle ? of a surface of the negative lens on the reduction conjugation side, an index of refraction Ndn and an Abbe number vdn of a material of the negative lens for a d-line, and a relative partial dispersion ?gFn of the material of the negative lens for a g-line and an F-line.

Abstract: An optical system includes a first negative lens element disposed nearest a front side and a first positive lens element whose front surface resides within a distance 0.4 L from the surface nearest the front side toward a rear side of the optical system having a total lens length L. By appropriately determining the materials for the two lens elements, the optical system realizes a wide angle of view while correcting lateral chromatic aberration well.

Abstract: An image projection optical system introduces light from an image-forming element by a zoom lens via an optical element. The optical element satisfies ?(Di×Ndi)/fw>4.0. The zoom lens includes, in order from a magnification side, first and second lens units, and lens units disposed closer to a reduction side than the second lens unit. The first lens unit is a negative lens unit. The lens units disposed closer to the reduction side than the second lens unit satisfy |dn/dt|<1.0×10?5. Magnification-side positive lens elements disposed closer to the magnification side than a negative lens element whose effective diameter is smallest in the lens units disposed closer to the reduction side than the second lens unit satisfy {9.0×?(1/fpA)+5.0×?(1/fpB)+0.5×?(1/fpC)}/?(1/fp)<1. Reduction-side positive lens elements disposed closer to the reduction side than the negative lens element whose effective diameter is smallest satisfy {9.0×?(1/fpA)+0.3×?(1/fpB)+2.0×?(1/fpC)}/?(1/fp)<1.

Abstract: At least one exemplary embodiment is directed to a projection optical system which includes at least one prism and at least one positive lens. In a projection lens included in the projection optical system, the dispersion properties of the prism and the positive lens are set such that chromatic aberration occurring in the at least one prism can be appropriately corrected and/or reduced by using the at least one positive lens.

Abstract: A zoom lens telecentric on a reduction side includes a first negative lens, a second negative lens and a first positive lens arranged from the enlargement side to the reduction side. At least one of the first and second negative lenses has an aspherical surface. The zoom lens satisfies ?f12/fw<1.4, ?f12/(Hwpn?f12)<0.6 and |dn/dt|<1.0×10?5, where f12 is the focal length of the combined optical system composed of the first and second negative lenses, Hwpn is the distance from the rear principal point of the combined optical system composed of the first and second negative lenses to the front principal point of the first positive lens, dn/dt is a change in the refractive index of the material of which said one negative lens is made relative to a change in its temperature from 25° C., and fw is the focal length of the entire lens system at the wide angle end.

Abstract: An image projection optical system introduces light from an image-forming element by a zoom lens via an optical element. The optical element satisfies ?(Di×Ndi)/fw>4.0. The zoom lens includes, in order from a magnification side, first and second lens units, and lens units disposed closer to a reduction side than the second lens unit. The first lens unit is a negative lens unit. The lens units disposed closer to the reduction side than the second lens unit satisfy |dn/dt|<1.0×10?5. Magnification-side positive lens elements disposed closer to the magnification side than a negative lens element whose effective diameter is smallest in the lens units disposed closer to the reduction side than the second lens unit satisfy {9.0×?(1/fpA)+5.0×?(1/fpB)+0.5×?(1/fpC)}/?(1/fp)<1. Reduction-side positive lens elements disposed closer to the reduction side than the negative lens element whose effective diameter is smallest satisfy {9.0×?(1/fpA)+0.3×?(1/fpB)+2.0×?(1/fpC)}/?(1/fp)<1.

Abstract: At least one exemplary embodiment is directed to a zoom lens comprising a plurality of lens units, where the plurality of lens units have at least one negative lens including a first negative lens Gn1 arranged at a position where an effective diameter is minimized among negative lenses of the zoom lens, where when the at least one negative lens is represented by an ith negative lens Gni indicating the ith negative lens from an expansion side toward the reduction side and Xi=?gFni?(0.6438?0.001682×?dni), the following condition is satisfied: (?Xi×fni)/(?fni)<?0.003, where the Abbe number and the partial dispersion ratio of the material of the ith negative lens Gni are ?dni and ?gFni, respectively, and the focal length of the ith negative lens Gni is fni.

Abstract: A zoom lens telecentric on a reduction side includes a first negative lens, a second negative lens and a first positive lens arranged from the enlargement side to the reduction side. At least one of the first and second negative lenses has an aspherical surface. The zoom lens satisfies ?f12/fw<1.4, ?f12/(Hwpn?f12)<0.6 and |dn/dt|<1.0×10?5, where f12 is the focal length of the combined optical system composed of the first and second negative lenses, Hwpn is the distance from the rear principal point of the combined optical system composed of the first and second negative lenses to the front principal point of the first positive lens, dn/dt is a change in the refractive index of the material of which said one negative lens is made relative to a change in its temperature from 25° C., and fw is the focal length of the entire lens system at the wide angle end.

Abstract: Provided is a zoom lens which is telecentric on a reduction side, including a plurality of lens units, in which the zoom lens satisfies the following conditions: ?dp>75 fw/fp<0.6 where ha indicates a height of a paraxial marginal ray passing through the zoom lens, and hb indicates a height of a paraxial chief ray passing through the zoom lens, where, among a plurality of positive lenses in the zoom lens, a positive lens whose hb/ha is the smallest is defined as a smallest positive lens in at least a part of a zoom range from a wide-angle end to a telephoto end, and where ?dp indicates an Abbe constant of a material of the smallest positive lens, fp indicates a focal length of a lens unit including the smallest positive lens, and fw indicates a focal length of an entire system at the wide-angle end.

Abstract: At least one exemplary embodiment is directed to a zoom lens comprising a plurality of lens units, where the plurality of lens units have at least one negative lens including a first negative lens Gn1 arranged at a position where an effective diameter is minimized among negative lenses of the zoom lens, where when the at least one negative lens is represented by an ith negative lens Gni indicating the ith negative lens from an expansion side toward the reduction side and Xi=?gFni?(0.6438?0.001682×?dni), the following condition is satisfied: (?Xi×fni)/(?fni)<?0.003, where the Abbe number and the partial dispersion ratio of the material of the ith negative lens Gni are ?dni and ?gFni, respectively, and the focal length of the ith negative lens Gni is fni.

Abstract: Provided is a zoom lens which is telecentric on a reduction side, including a plurality of lens units, in which the zoom lens satisfies the following conditions: ?dp>75 fw/fp<0.6 where ha indicates a height of a paraxial marginal ray passing through the zoom lens, and hb indicates a height of a paraxial chief ray passing through the zoom lens, where, among a plurality of positive lenses in the zoom lens, a positive lens whose hb/ha is the smallest is defined as a smallest positive lens in at least a part of a zoom range from a wide-angle end to a telephoto end, and where ?dp indicates an Abbe constant of a material of the smallest positive lens, fp indicates a focal length of a lens unit including the smallest positive lens, and fw indicates a focal length of an entire system at the wide-angle end.

Abstract: At least one exemplary embodiment is directed to a projection optical system which includes at least one prism and at least one positive lens. In a projection lens included in the projection optical system, the dispersion properties of the prism and the positive lens are set such that chromatic aberration occurring in the at least one prism can be appropriately corrected and/or reduced by using the at least one positive lens.