Abstract: A zoom lens includes, in order from the object side: a positive first lens group; a negative second lens group; a positive third lens group; a negative fourth lens group; and a positive fifth lens group. The distance between the first and second lens groups constantly increases, the distance between the second and third lens groups constantly decreases, the distance between the third and fourth lens groups constantly changes, and the distance between the fourth and fifth lens groups constantly increases when changing magnification from the wide angle to the telephoto end. The first lens group includes, in order from the object side, a negative lens, a positive lens, and a positive lens. The fourth lens group includes, in order from the object side, a negative lens, a negative lens, and a positive lens, and moves toward the image side when focusing from a far distance to a close distance.

Abstract: A zoom lens consists of, in order from the 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 positive refractive power, a fourth lens group having a negative refractive power, a fifth lens group having a positive refractive power, and a sixth lens group having a positive refractive power, wherein magnification change is effected by changing all distances between adjacent lens groups. The second lens group is moved from the object side toward the image side during magnification change from the wide-angle end to the telephoto end. The position of the third lens group at the telephoto end is nearer to the image side than the position of the third lens group at the wide-angle end.

Abstract: An imaging lens is constituted by six lenses, including, in order from the object side to the image side: a positive first lens having a convex surface toward the object side; a negative second lens; a positive third lens, which is a meniscus lens having a convex surface toward the object side; a positive fourth lens; a negative fifth lens having a concave surface toward the object side; and a negative sixth lens, of which the image toward the image side is of an aspherical shape which is concave in the vicinity of the optical axis and convex at the peripheral portion thereof. Conditional formulae related to the focal length f of the entire lens system, the focal length f1 of the first lens, and the focal length f4 of the fourth lens is satisfied.

Abstract: An objective lens for endoscopes includes, in order from the object side: a front group; an aperture stop; and a positive rear group. The front group includes, in order from the object side, a negative first lens, in which the absolute value of the radius of curvature of the surface toward the image side is less than that of the surface toward the object side, and at least one plane parallel plate. The rear group includes, in order from the object side, a positive second lens, and a cemented lens formed by a positive third lens and a negative fourth lens. The coupling surface of the cemented lens is convex toward the image side. Conditional Formulae (1) through (3) concerning the plane parallel plates within the front group, the focal length of the first lens, the radius of curvature of the coupling surface of the cemented lens, etc., are satisfied.

Abstract: An objective lens for endoscopes is constituted essentially by, in order from the object side: a negative first lens having a concave surface toward the image side; a first cemented lens, formed by cementing a second lens and a third lens having refractive powers with signs opposite each other, provided in this order from the object side, together; a stop; a positive fourth lens having a convex surface toward the image side; and a second cemented lens, formed by cementing a positive fifth lens and a negative sixth lens, provided in this order from the object side, together, in which the coupling surface is convex toward the image side. Focusing from an object at a most distant point to an object at a most proximal point is performed by moving only the second cemented lens. A predetermined conditional formula is satisfied.

Abstract: An imaging lens consists of five lenses, including: a first lens having a positive refractive power and a meniscus shape with a convex surface toward the object side, a second lens having a biconcave shape with the surface having the radius of curvature with the smaller absolute value toward the image side, a third lens having a meniscus shape with a convex surface toward the object side, a fourth lens having a negative refractive power and a meniscus shape with a convex surface toward the image side, and a fifth lens having a negative refractive power and a meniscus shape with a concave surface toward the image side, the image-side surface thereof having at least one inflection point, disposed in this order from the object side.

Abstract: A projection zoom lens is essentially constituted by, in order from the magnification side: a negative first lens group; a positive second lens group; a third lens group; a positive fourth lens group; a fifth lens group; and a positive sixth lens group. The distance between the first and second lens groups is shorter, the distance between the second and third lens groups is longer, the distance between the third and fourth lens groups is shorter, the distance between the fourth and the fifth lens groups is longer, and the distance between the fifth and sixth lens groups is longer at the telephoto end than at the wide angle end. A lens having a negative refractive power in the paraxial region is provided most toward the magnification side in the first lens group. The fifth lens group has a negative lens.

Abstract: A five-group zoom lens including, in order from the object side, positive, negative, negative, positive, and positive groups. The first group includes a negative meniscus lens with the concave surface toward the image side, a positive lens and a positive lens. The second group includes a negative lens with the image-side surface having an absolute value of curvature radius smaller than that of the object side surface, a biconcave lens, and a biconvex lens. The third group includes a negative lens with the object side surface having an absolute value of curvature radius smaller than that of the image-side surface, and is moved during focusing on a closer object. The fifth group includes a positive fifth-A group including a biconvex lens, and a negative fifth-B group including a biconcave lens and a biconvex lens, wherein condition expression (1) is satisfied: ?4<f5/f5B<?0.7??(1).

Abstract: An imaging lens consists of, disposed in order from the object side, a front group, a stop, and a rear group, wherein the front group includes, in order from the most-object side, a positive first lens, a negative second lens, and a negative third lens which are adjacently disposed, the rear group consists of two sets of cemented lenses having positive refractive powers and a positive single lens, the object-side cemented lens is formed by cementing, in order form the object side, a positive lens with a convex surface toward the image side and a negative meniscus lens together, the image-side cemented lens is formed by cementing, in order from the object side, a negative meniscus lens with a concave surface toward the image side and a positive lens together, and the image-side cemented lens is disposed at the most-image side of the rear group.

Abstract: An imaging lens consists of, in order from the object side, a front group, a stop, and a rear group, wherein the front group includes, in order from the most-object side, a positive first lens, a negative second lens, a negative third lens which are adjacently disposed, and further includes a final lens of the front group adjacent to the stop, with the surface toward the stop being convex toward the image side, the rear group includes, in order from the image side, two sets of cemented lenses having positive refractive powers, which are adjacently disposed, the object-side cemented lens of the two sets of cemented lenses is formed by cementing a positive lens and a negative meniscus lens together, and the image-side cemented lens is formed by cementing a negative meniscus lens and a positive lens together.

Abstract: An imaging lens consists of five lenses consisting of, in order from the object side, a biconvex first lens, a biconcave second lens, a positive third lens having a meniscus shape with the convex surface toward the image side, a positive fourth lens having a meniscus shape with the convex surface toward the image side, and a negative fifth lens having a concave surface toward the image side, and having at least one inflection point on the image-side surface thereof, wherein condition expression (1), 0<f/f3<0.6, relating to the focal length f of the entire system and the focal length f3 of the third lens, and condition expression (2), 0.12<D7/f<0.3, relating to the focal length f of the entire system and the distance D7 between the third lens and the fourth lens along the optical axis are satisfied.

Abstract: An imaging lens consists of a first lens group, a second lens group, an aperture stop and a third lens group that has positive refractive power in this order from an object side. The first lens group consists of an L11 lens having positive refractive power, an L12 lens having negative refractive power, an L13 meniscus lens having negative refractive power with its concave surface facing an image side, an L14 lens having negative refractive power with its concave surface facing the object side and two or three lenses, each having positive refractive power, in this order from the object side. The second lens group consists of an L2p lens having positive refractive power and an L2n lens having negative refractive power.

Abstract: An imaging lens consists of a front group having positive refractive power as a whole and a rear group in this order from an object side. The front group consists of three positive lenses, a negative lens with its concave surface facing an image side, a positive lens with its convex surface facing the object side, a negative lens with its concave surface facing the image side, a stop, a negative lens with its concave surface facing the object side and plural positive lenses in this order from the object side. The rear group has positive refractive power and consists of a positive lens and a negative lens in this order from the object side.

Abstract: An imaging lens consists of three lenses of, in order from an object side, a first lens having a biconcave shape, and an object-side surface of which is aspherical, a second lens having negative refractive power and a third lens having positive refractive power with a convex surface facing an image side. The absolute value of a curvature radius of an image-side surface of the third lens is less than the absolute value of a curvature radius of an object-side surface of the third lens.

Abstract: An imaging lens consists of, in order from the object side, a first lens group fixed during focusing, and a positive second lens group moved toward the object side during focusing from a distant object to a close object. The second lens group consists of, in order from the object side, a first cemented lens consisting of a biconvex lens and a negative lens having a smaller absolute value of curvature radius of the object-side surface than that of the image-side surface, and a second cemented lens as a whole having a positive refractive power and consisting of a negative lens having a smaller absolute value of curvature radius of the image-side surface than that of the object-side surface and a positive lens having a smaller absolute value of curvature radius of the object-side surface than that of the image-side surface. The imaging lens satisfies specific condition expressions.

Abstract: An imaging lens includes, in order from the object side, a first lens group fixed during focusing, a positive second lens group moved toward the object side during focusing from a distant to a close object, and a third lens group fixed during focusing and including one positive lens. The second group includes, in order from the object side, a first cemented lens including a biconvex lens and a negative lens having a smaller absolute value of curvature radius of the object-side surface than of the image-side surface, and a second cemented lens having a positive refractive power and including a negative lens having a smaller absolute value of curvature radius of the image-side surface than of the object-side surface and a positive lens having a smaller absolute value of curvature radius of the object-side surface than of the image-side surface. The imaging lens satisfies specific condition expressions.

Abstract: A zoom lens is constituted by, in order from the object side to the image side: a positive first group which is fixed when changing magnification, a negative second lens group which moves when changing magnification, a negative third lens group which moves when changing magnification, and a positive fourth lens group which is fixed when changing magnification. The first lens group is constituted by a 1a lens of a negative meniscus shape, a positive 1b lens, and a positive 1c lens. The second lens group is constituted by a negative 2a lens, a biconcave 2b lens, a positive 2c lens, and a negative 2d lens. The third lens group is constituted by a negative 3a lens and a positive 3b lens. The fourth lens group includes a 4a lens, an aperture stop, and a positive 4b lens, which are consecutively provided from the most object side thereof.

Abstract: An imaging lens is constituted of five lenses, including, in order from the object side to the image side: a first lens having a positive refractive power, which is of a meniscus shape having a convex surface toward the object side; a second lens having a negative refractive power and a concave surface toward the image side; a third lens having a positive refractive power, which is of a meniscus shape having a convex surface toward the object side; a fourth lens having a negative refractive power; and a fifth lens having a negative refractive power and at least one inflection point on the surface thereof toward the image side. Predetermined conditional formulae are satisfied.

Abstract: A zoom lens includes, in order from the object side, a positive first group, a negative second group, a stop, a positive third group, a negative fourth group, and a positive fifth group. During magnification change from the wide-angle end to the telephoto end, the first to fourth groups are moved to always increase the distance between the first and second groups, always decrease the distance between the second and third groups, and change the distance between the third and fourth groups and the distance between the fourth and fifth groups. The third group includes, in order from the object side, at least a positive lens, a positive lens, a negative lens, and a positive lens, and satisfies condition expression (1) below: 25<?dD??dA<70??(1), where ?dA and ?dD are Abbe numbers at the d-line of the most object-side lens A and the most image-side lens D.

Abstract: An imaging lens is essentially constituted by five lenses, including: a first lens of a biconvex shape; a second lens of a meniscus shape having a concave surface toward the image side; a third lens of a biconcave shape; a fourth lens of a meniscus shape having a convex surface toward the image side; and a fifth lens of a biconcave shape having at least one inflection point on the surface thereof toward the image side, provided in this order from the object side.