Abstract: A projection zoom lens is constituted by: a negative first lens group; a positive moving second lens group; a positive moving third lens group; a positive final lens group; at least one lens group positioned between the final lens group and the third lens group; and an aperture stop provided between adjacent moving lens groups. The aperture stop is a variable stop, of which the aperture diameter changes such that the numerical aperture of the zoom lens becomes constant. The zoom lens satisfies Conditional Formulae below: 2.8<Bf/Im???(1?) L/Im?<12??(2) wherein Bf is the back focus of the entire system at the reduction side at the wide angle end, Im? is the maximum effective image circle diameter at the reduction side, and L is the distance from the lens surface most toward the magnification side to the lens surface most toward the reduction side when the projection distance is infinity.

Abstract: In a projection optical system that projects an image displayed on an image display device arranged on a reduction-side conjugate plane onto a magnification-side conjugate plane, as a magnified image, the projection optical system includes a refractive optical system and a reflective optical system having negative refractive power in this order from a reduction side. Further, the following conditional formula (1) is satisfied: L/D+2?min/?max?1.01??(1).

Abstract: In a projection optical system that projects an image displayed on an image display device arranged on a reduction-side conjugate plane onto a magnification-side conjugate plane, as a magnified image, the projection optical system includes a refractive optical system and a reflective optical system having negative refractive power in this order from a reduction side. Further, the following conditional formula (1) is satisfied: ?0.0015?(1/tan(?max)?0.16)×(?L/?M?0.27) ??(1).

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system constituted by a plurality of lenses for forming an image displayed by image display elements as an intermediate image, and a second optical system constituted by a plurality of lenses for forming the intermediate image on a magnification side conjugate plane. Conditional Formula (1) below is satisfied. 8.20<Im?·f2/f2<20.

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system for forming an image displayed by image display elements as an intermediate image, a first optical path bending means that bends an optical path with a reflective surface, and a second optical system for forming the intermediate image on a magnification side conjugate plane. The second optical system is constituted by, in order from the reduction side, a first lens group having a positive refractive power, a second optical path bending means that bends an optical path with a reflective surface, and a second lens group having a positive refractive power. Conditional Formulae (1) and (2) below are satisfied. 10.0<TL1/|f|<50.0??(1) 4.0<TL21/|f|<30.0??(2).

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system constituted by a plurality of lenses for forming an image displayed by image display elements as an intermediate image, and a second optical system constituted by a plurality of lenses for forming the intermediate image on a magnification side conjugate plane. Conditional Formula (1) below is satisfied. 1.50<f2/|f|<2.80??(1).

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system constituted by a plurality of lenses for forming an image displayed by image display elements as an intermediate image, and a second optical system constituted by a plurality of lenses for forming the intermediate image on a magnification side conjugate plane. Conditional Formula (1) below is satisfied. 0.020<enP/TL2<0.

Abstract: A projection optical system is constituted by, in order from the reduction side, a first optical system for forming an image displayed by image display elements as an intermediate image, and a second optical system for forming the intermediate image on a magnification side conjugate plane. The second optical system is constituted by, in order from the reduction side, a first lens group having a positive refractive power, a first optical path bending means that bends an optical path with a reflective surface, a second lens group having a positive refractive power, a second optical path bending means that bends an optical path with a reflective surface, and a third lens group having a negative refractive power. Conditional Formulae (1) and (2) below are satisfied. 0.05<|f23|/D223<0.50??(1) 5.0<D212/|f|<20.0??(2).

Abstract: A projection zoom lens in which a magnification change operation is performed by moving three to four lens groups as moving groups, wherein a first lens group, which is a lens group on the most-magnification side, substantially consists of a moving group having a negative refractive power; a lens group on the most-reduction side is composed of a moving group having a positive refractive power; and the first lens group which is the lens group the most-magnification side substantially consists of two lenses. In this case, conditional formula (1) below is satisfied, where fw is the focal length of the entire system at the wide angle end and fm is the focal length of the lens group on the most-magnification side: ?3.5<fm/fw<?1.0??(1). This achieves miniaturization and cost reduction, and corrects various aberrations satisfactorily.

Abstract: A projection zoom lens essentially consists of a negative first lens group, a positive second lens group through the fourth lens group that move along the optical axis while changing magnification, a fifth lens group that moves while changing magnification, and a positive sixth lens group disposed in this order from the magnification side, wherein the projection zoom lens satisfies conditional formulas (1) and (2) below: 1.9<m4/fw??(1) 0.7<(m3+m4)/(m2+m3+m4+m5)??(2), where, mk (k=2 through 5) is the absolute value of movement of the k-th lens group while changing magnification from the wide angle end to the telephoto end, and fw: the focal length of the entire system at the wide angle end.

Abstract: A variable magnification projection optical system substantially consisting of two lens groups of a first lens group having a positive refractive power and is moved during magnification change, and a second lens group having a positive refractive power and is moved during magnification change, in which the variable magnification projection optical system is configured such that the reduction side is telecentric.

Abstract: A projection zoom lens is constituted essentially by: a plurality of lens groups that include at least two lens groups that move when changing magnification; the distances among all pairs of adjacent lens groups changing when changing magnification; the reduction side being configured to be telecentric; and a negative first lens group, which is fixed when changing magnification, being provided most toward the magnification side. The first lens group is constituted essentially by, in order from the magnification side to the reduction side, a negative first lens, which is a meniscus lens having a convex surface toward the magnification side, a biconcave second lens, and a positive or negative third lens. Conditional Formula (1) related to fw, which is the focal length of the entire projection zoom lens at the wide angle end, and f3, which is the focal length of the third lens, is satisfied: ?0.070<fw/f3<0.070??(1).

Abstract: A projection lens includes a compound aspherical lens in which a resin layer is formed on a surface of a glass lens and a lens surface of the resin layer on the air contacting surface side has an aspherical shape. If the glass transition temperature of the resin layer is taken as Tg and its unit is taken as ° C., Tg of at least one of the resin layers is 150<Tg<280. The projection lens is configured to satisfy a given conditional expression with respect to the at least one of the resin layers.

Abstract: A six group projection zoom lens downsized with broadened angle of view while aberrations are satisfactorily corrected over the entire zoom range, including a negative lens group having a negative power, a second lens group having a positive power, a third lens group having a positive power, a fourth lens group having a negative power, a fifth lens group having a positive power, and a sixth lens group having a positive power in this order from the magnification side and is configured telecentric on the reduction side. The first and sixth lens groups are fixed while the second to fifth lens groups are moved independently of each other at the time of zooming. The fifth lens group includes a plurality of lenses and a biconvex lens is disposed on the most magnification side. The projection zoom lens satisfies conditional expressions (1): (R51a+R51b)/(R51a?R51b)?0 and (2): 25.0<?d51<45.0.

Abstract: The projection zoom lens substantially consists of a first lens group having negative refractive power, a second lens groups through a fourth lens group all having positive refractive power, a fifth lens group having positive or negative refractive power, and a sixth lens group having positive refractive power, arranged in this order from the magnification side; wherein the reduction side is telecentric. Further, the first lens group and the sixth lens group are fixed and the second lens group through the fifth lens group move along the optical axis while changing magnification. The fourth lens group substantially consists of only one positive meniscus lens with a concave surface toward the reduction side. The projection zoom lens satisfies conditional expression (1) below: 1.2<f3/f4<10.0??(1), where f3 is the focal length of the third lens group, and f4 is the focal length of the fourth lens group.

Abstract: A projection zoom lens is constituted by: a negative first lens group; a positive moving second lens group; a positive moving third lens group; a positive final lens group; at least one lens group positioned between the final lens group and the third lens group; and an aperture stop provided between adjacent moving lens groups. The aperture stop is a variable stop, of which the aperture diameter changes such that the numerical aperture of the zoom lens becomes constant. The zoom lens satisfies Conditional Formulae below: 2.8<Bf/Im???(1?) L/Im?<12??(2) wherein Bf is the back focus of the entire system at the reduction side at the wide angle end, Im? is the maximum effective image circle diameter at the reduction side, and L is the distance from the lens surface most toward the magnification side to the lens surface most toward the reduction side when the projection distance is infinity.

Abstract: A projection zoom lens constituted by: a negative first lens group; a positive final lens group; and moving lens groups between the first and the final lens groups that move independently while changing magnification, satisfies the conditional formulae below: 1.00<(Rf2?Rr2)/(Rf2+Rr2)??(1) 0.00?(Rr2?Rf3)/(Rr2+Rf3)<0.15??(2) 2.5<Bf/Im???(9) wherein Rf2 and Rr2 respectively are the radii of curvature of the front and rear surfaces of the second lens from the magnification side within the most reduction side moving lens group, Rf3 is the radius of curvature of the front surface of the third lens from the magnification side within the most reduction side moving lens group, Bf is the back focus of the entire system at the reduction side at the wide angle end as an air converted length, and Im? is the maximum effective image circle diameter at the reduction side.

Abstract: A projection zoom lens essentially consists of a negative first lens group, a positive second lens group through the fourth lens group that move along the optical axis while changing magnification, a fifth lens group that moves while changing magnification, and a positive sixth lens group disposed in this order from the magnification side, wherein the projection zoom lens satisfies conditional formulas (1) and (2) below: 1.9<m4/fw??(1) 0.7<(m3+m4)/(m2+m3+m4+m5)??(2), where, mk (k=2 through 5) is the absolute value of movement of the k-th lens group while changing magnification from the wide angle end to the telephoto end, and fw: the focal length of the entire system at the wide angle end.

Abstract: A zoom lens for projection substantially consists of a first lens-group having negative refractive-power, and which is arranged on a most magnification-side, and which is fixed during magnification change, a second lens-group having negative refractive-power, and which is arranged on a reduction-side of the first lens-group, and which is fixed during magnification change, a last lens-group having positive refractive-power, and which is arranged on a most reduction-side, and which is fixed during magnification change, and three lens-groups arranged between the last lens-group and the second lens-group, and which move during magnification change. The zoom lens is configured to be telecentric on a reduction-side, and focusing is performed by moving only the second lens-group.

Abstract: In a projection optical system that projects an image displayed on an image display device arranged on a reduction-side conjugate plane onto a magnification-side conjugate plane, as a magnified image, the projection optical system includes a refractive optical system and a reflective optical system having negative refractive power in this order from a reduction side. Further, the following conditional formula (1) is satisfied: ?0.0015?(1/tan(?max)?0.16)×(?L/?M?0.27) ??(1).