Abstract: A zoom lens unit comprises a first and fourth lens groups with positive refractive power, a second and third lens groups with negative refractive power. The first and the fourth lens groups are fixed, the second lens group moves toward an image side and the fourth lens group moves when changing a magnification ratio from a wide-angle end to a telephoto end. The fourth lens group includes a negative resin lens and at least one positive lens. At least one of said positive lenses fulfills following conditions: 1.40<nd<1.65 65.0<?d<100.0 0.015<Pg, F?(?0.001802×?d+0.6483)<0.060 where nd, ?d, and Pg, F, each represents a refractive index, an Abbe number, a partial dispersion ratio of the positive lens. Pg, F is (ng?nF)/(nF?nC), where ng, nF, and nC represent refractive indexes at g-line, F-line, and C-line of the positive lens.

Abstract: A zoom lens includes, in order from an object side to an image side, first, second, third, and fourth lens groups with positive, negative, negative, and positive refractive powers, respectively. When varying magnification from a short focal length end to a long focal length end, the second lens group is moved to the image side, the third lens group is moved, and the first and fourth lens groups are fixed. The fourth lens group is constituted of a lens group on the object side and a lens group on the image side with a largest distance in the fourth lens group between them. Each of a refractive index, Abbe number, a partial dispersion ratio, and the like of each of at least one positive lens of the lens group on the object side and two positive lenses of the first lens group is regulated to be in a predetermined range.

Abstract: A zoom lens includes, in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power. During change of magnification from a short focal end to a long focal end, the first lens group is fixed, the second lens group is moved to an image side, the third lens group is moved, and the fourth lens group is fixed. The first lens group and the fourth lens group include diffraction surfaces and satisfy the Condition Expressions 50<f1doe/f1<200 (1) and 100<f4doe/f4<300 (2).

Abstract: A zoom lens includes, in order from an object side toward an image side: a first lens unit having a positive refractive power and provided with a positive lens; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power and provided with a diffraction plane of a diffraction optical element; a fourth lens unit having a positive refractive power to perform focusing; and an aperture stop between the second lens unit and the third lens unit. According to a change of magnification from a short focal end to a long focal end, the first lens unit is stationary, the second lens unit is moved to the image side, the third lens unit is moved to the object side, and the fourth lens unit is moved, and the positive lens satisfies the following condition formulas: 1.45<nd<1.65;??[1] 60.0<?d<95.0; and??[2] 0.005<Pg,F?(?0.001802×?d+0.6483)<0.

Abstract: An image forming lens is formed by sequentially arranging, from an object side to an image side, a first lens group having positive refractive power, an aperture stop, a second lens group having positive refractive power, and a third lens group having positive or negative refractive power. When focusing is performed from a long distance to a short distance, the third lens group is fixed relative to an image surface, and the first lens group, the aperture stop, and the second lens group are moved integrally to the object side. In the image forming lens, the third lens group is formed by sequentially arranging, from the object side to the image side, two lenses in order of a negative lens and a positive lens, and a conditional expression is satisfied: 0.20<D/L3F-I<0.60, where D is an air space between the negative lens and the positive lens which form the third lens group, and L3F-I is a distance from an object-side surface of the negative lens of the third lens group to the image surface.

Abstract: An image forming lens is formed by sequentially arranging, from an object side to an image side, a first lens group having positive power, an aperture stop, a second lens group having positive power, and a third lens group having positive power. The image forming lens satisfies following conditional expressions: 0.95<f12/f<1.2, 0.0<f/f3<0.2, ?0.5<(R142+R211)/(R142?R211)<?0.2, where f is a focal length of an entire system, f12 is a composite focal length of the first lens group and the second lens group, f3 is a focal length of the third lens group, R142 is a curvature radius of an image-side surface of the negative lens closest to the image side in the first lens group, and R211 is a curvature radius of object-side surface of the negative lens closest to the object side in the second lens group.

Abstract: An image forming lens is formed by sequentially arranging, from an object side to an image side, a first lens group having positive refractive power, an aperture stop, and a second lens group having positive or negative refractive power. The image forming lens satisfies a conditional expression: 0.15<D1a/D1<0.50, where D1a is an air space between the first positive lens and the second positive lens in the first lens group, and D1 is a distance on an optical axis from an object-side lens surface of the first positive lens to an image-side lens surface of the third positive lens in the first lens group.

Abstract: A zoom lens unit comprises a first and fourth lens groups with positive refractive power, a second and third lens groups with negative refractive power. The first and the fourth lens groups are fixed, the second lens group moves toward an image side and the fourth lens group moves when changing a magnification ratio from a wide-angle end to a telephoto end. The fourth lens group includes a positive lens L41 having a convex surface on the object side, a negative lens L42 having a concave surface on an image side, positive lenses L43, L45, and a negative lens L44. A following condition is fulfilled: 0.1<(R411?R422)/(R411+R422)<0.6 where R411 represents a curvature radius of the object-side surface of the positive lens L41, and R422 represents a curvature radius of the image-side surface of the negative lens L42.

Abstract: A zoom lens includes, in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power. During change of magnification from the short focal end to the long focal end, the first lens unit is stationary, the second lens unit is moved to an image side, the third lens unit is moved, and the fourth lens unit is stationary. A positive lens, included in the fourth lens unit or the first lens unit, satisfies the condition formulas: 1.40<nd<1.65; 65.0<?d<100.0; and 0.015<Pg,F?(?0.001802×?d+0.6483)<0.060, and the first lens unit includes a diffraction plane and satisfies the condition formula: 50<fdoe/f1<200.

Abstract: An imaging lens system and an imaging system that includes the imaging lens system are provided. The imaging lens system includes an aperture stop, a first lens group with positive refractive power, and a second lens group with positive refractive power, arranged in that order from an object side to an image side. The first lens group includes a positive lens L11, and a negative meniscus lens L12 that has a convex surface on the object side. The second lens group includes a negative lens L21 that has a concave surface on the object side, a positive lens L22 and a positive lens L23 each of which has a convex surface on the image side, a negative meniscus lens L24 that has a convex surface on the object side, and a positive lens L25 that has a convex surface on the object side.

Abstract: A zoom lens unit comprises a first and fourth lens groups with positive refractive power, a second and third lens groups with negative refractive power. The first and the fourth lens groups are fixed, the second lens group moves toward an image side and the fourth lens group moves when changing a magnification ratio from a wide-angle end to a telephoto end. The fourth lens group includes a positive lens L41 having a convex surface on the object side, a negative lens L42 having a concave surface on an image side, positive lenses L43, L45, and a negative lens L44. A following condition is fulfilled: 0.1<(R411?R422)/(R411+R422)<0.6 where R411 represents a curvature radius of the object-side surface of the positive lens L41, and R422 represents a curvature radius of the image-side surface of the negative lens L42.

Abstract: A zoom lens includes, in order from an object side to an image side, first, second, third, and fourth lens groups with positive, negative, negative, and positive refractive powers, respectively. When varying magnification from a short focal length end to a long focal length end, the second lens group is moved to the image side, the third lens group is moved, and the first and fourth lens groups are fixed. The fourth lens group is constituted of a lens group on the object side and a lens group on the image side with a largest distance in the fourth lens group between them. Each of a refractive index, Abbe number, a partial dispersion ratio, and the like of each of at least one positive lens of the lens group on the object side and two positive lenses of the first lens group is regulated to be in a predetermined range.

Abstract: A zoom lens unit comprises a first and fourth lens groups with positive refractive power, a second and third lens groups with negative refractive power. The first and the fourth lens groups are fixed, the second lens group moves toward an image side and the fourth lens group moves when changing a magnification ratio from a wide-angle end to a telephoto end. The fourth lens group includes a negative resin lens and at least one positive lens. At least one of said positive lenses fulfills following conditions: 1.40<nd<1.65 65.0<vd<100.0 0.015<Pg, F?(?0.001802×vd+0.6483)<0.060 where nd, vd, and Pg, F, each represents a refractive index, an Abbe number, a partial dispersion ratio of the positive lens. Pg, F is (ng-nF)/(nF-nC), where ng, nF, and nC represent refractive indexes at g-line, F-line, and C-line of the positive lens.

Abstract: A zoom lens includes, in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power. During change of magnification from a short focal end to a long focal end, the first lens group is fixed, the second lens group is moved to an image side, the third lens group is moved, and the fourth lens group is fixed. The first lens group and the fourth lens group include diffraction surfaces and satisfy the Condition Expressions 50<f1doe/f1<200 (1) and 100<f4doe/f4<300 (2).

Abstract: A zoom lens includes, in order from an object side toward an image side: a first lens unit having a positive refractive power and provided with a positive lens; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power and provided with a diffraction plane of a diffraction optical element; a fourth lens unit having a positive refractive power to perform focusing; and an aperture stop between the second lens unit and the third lens unit. According to a change of magnification from a short focal end to a long focal end, the first lens unit is stationary, the second lens unit is moved to the image side, the third lens unit is moved to the object side, and the fourth lens unit is moved, and the positive lens satisfies the following condition formulas: 1.45<nd<1.65;??[1] 60.0<?d<95.0; and??[2] 0.005<Pg,F?(?0.001802×?d+0.6483)<0.

Abstract: A zoom lens includes, in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power. During change of magnification from the short focal end to the long focal end, the first lens unit is stationary, the second lens unit is moved to an image side, the third lens unit is moved, and the fourth lens unit is stationary. A positive lens, included in the fourth lens unit or the first lens unit, satisfies the condition formulas: 1.40<nd<1.65; 65.0<?d<100.0; and 0.015<Pg,F?(?0.001802×?d+0.6483)<0.060, and the first lens unit includes a diffraction plane and satisfies the condition formula: 50<fdoe/f1<200.

Abstract: An imaging lens system and an imaging system that includes the imaging lens system are provided. The imaging lens system includes an aperture stop, a first lens group with positive refractive power, and a second lens group with positive refractive power, arranged in that order from an object side to an image side. The first lens group includes a positive lens L11, and a negative meniscus lens L12 that has a convex surface on the object side. The second lens group includes a negative lens L21 that has a concave surface on the object side, a positive lens L22 and a positive lens L23 each of which has a convex surface on the image side, a negative meniscus lens L24 that has a convex surface on the object side, and a positive lens L25 that has a convex surface on the object side.

Abstract: A zoom lens includes a first lens group having a positive refractive power, and a second lens group having a negative refractive power, an aperture stop, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power arranged in order from an object side, the third lens group having a first positive lens, a second positive lens, and a negative lens, and a third positive lens in order from the object side. When zooming from short to long focal end, the zoom lens is moved so that the interval between the first and second lens groups increases, that between the second and third lens groups decreases, that between the third and fourth lens groups increases, and the first and third lens groups are positioned closer to the object at the long focal end than the short focal end.

Abstract: A zoom lens includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, which are disposed in order from an object side to an image side and an aperture stop disposed between the second and third lens groups. When changing the magnification of the zoom lens from a short focal end to a long focal end, an interval between the first and second lens groups increases, an interval between the second and third lens groups decreases, and an interval between the third and fourth lens groups increases. The first and third lens groups are moved so as to be positioned at object side positions at the long focal end relative to positions at the short focal end. The third lens group has two positive lenses. Predetermined conditions of the positive lenses of the third lens group are satisfied.

Abstract: A zoom lens includes, in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, the second lens group including, in order from the object side, a first negative lens and a cemented lens including a second negative lens having a convex shape on the object side and a positive lens, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and an aperture stop arranged between the second lens group and the third lens group, wherein when changing a magnification from a short focal end to a telephoto end, an interval between the first lens group and the second lens group is increased, an interval between the second lens group and the third lens group is decreased, an interval between the third lens group and the fourth lens group is increased, and the first lens group and the third lens group are moved to be located closer to the object side at the long focal end than the short fo