Abstract: An imaging lens consists of: a first lens group having positive power, the first lens group including a positive lens closest to an object within the first lens group; an aperture stop; and a second lens group having positive power. The first lens group, the aperture stop, and the second lens group are disposed in that order from an object side toward an image side. Only two negative air lenses of a first biconvex air lens and a second biconvex air lens are provided within the imaging lens. The first lens group includes the first biconvex air lens, and the second lens group includes a second biconvex air lens.

Abstract: An imaging lens includes sequentially a first lens group, a second lens group having a positive refractive power, an aperture stop, a third lens group having a positive refractive power, and a fourth lens group. The first lens group includes, sequentially from the object side to the image side, a positive lens having a convex surface facing the object side, and a negative lens having a concave surface facing the image side. The second lens group includes a negative lens disposed closest to the object side and having a concave surface facing the object side, and a positive lens disposed closer than the negative lens to the image side and having a convex surface facing the object side. The third lens group includes a positive lens having a convex surface facing the image side, and a negative lens. The fourth lens group includes a negative lens having a concave surface.

Abstract: An imaging lens includes a front lens group, an aperture stop, and a rear lens group arranged in that order from an object side to an image side. An object-side lens closest to an object within the front lens group and an image-side lens closest to an image within the rear lens group are configured to form only three air lenses therebetween. The air lens is an air gap between an image-side surface of an object-side lens and an object-side surface of an image-side lens. The object-side lens and the image-side lens is adjacent to each other in an optical axis of the imaging lens. The three air lenses include an object-side air lens, an image-side air lens, and an intermediate air lens. The object-side air lens and the image-side air lens is biconvex, and the intermediate air lens is biconcave.

Abstract: An imaging optical system includes a first lens having a concave image side surface and a negative refractive power; a second lens having a convex object side surface and a positive refractive index; a third lens having a concave object side surface and a negative refractive power; a fourth lens having a convex image side surface and a positive refractive power; and a fifth lens having a convex object side surface and a positive refractive power in the order from the object side to the image side, optionally includes a lens on the image side of the fifth lens. The imaging optical system satisfies conditional expressions [1] 1.94<n2<2.20 and [2] 15.0<?2<20.0, where ?2 and n2 represents an Abbe number and a refractive index of a lens material of the second lens L2 at d-line, respectively.

Abstract: An imaging optical system including a first lens having negative refractive power; a second lens having negative refractive power; a third lens having positive refractive power; an aperture stop; a fourth lens having positive refractive power; a fifth lens having negative refractive power; and a six lens arranged in that order from an object side. The first lens is a negative lens with a concave surface facing the image side. The second lens is a negative lens with a concave surface facing the object side. The second lens and the third lens are joined together to form a cemented lens have positive refractive power.

Abstract: An image-forming lens includes, from an object side to an image side in order: a first lens group; an aperture; and a second lens group with a positive refractive power, the first lens group including, from the object side in order: a first F lens group with a negative refractive power; and a first R lens group with a positive refractive power, the first F lens group including, from the object side in order: a first negative lens; and a second negative lens, and the first R lens group including: any one of a positive lens and a cemented lens with a positive refractive power as a whole, wherein a distance from a surface on a most object side of the first lens group to an image plane in a state of focusing on an object at infinity: L, and a maximum image height: Y? satisfy Conditional expression 1: 2.8<L/Y?<4.3.

Abstract: An imaging optical system includes a first lens having a concave image side surface and a negative refractive power; a second lens having a convex object side surface and a positive refractive index; a third lens having a concave object side surface and a negative refractive power; a fourth lens having a convex image side surface and a positive refractive power; and a fifth lens having a convex object side surface and a positive refractive power in the order from the object side to the image side, optionally includes a lens on the image side of the fifth lens. The imaging optical system satisfies conditional expressions [1] 1.94<n2<2.20 and [2] 15.0<?2<20.0, where ?2 and n2 represents an Abbe number and a refractive index of a lens material of the second lens L2 at d-line, respectively.

Abstract: An imaging lens includes a front lens group, an aperture stop, and a rear lens group arranged in that order from an object side to an image side. An object-side lens closest to an object within the front lens group and an image-side lens closest to an image within the rear lens group are configured to form only three air lenses therebetween. The air lens is an air gap between an image-side surface of an object-side lens and an object-side surface of an image-side lens. The object-side lens and the image-side lens is adjacent to each other in an optical axis of the imaging lens. The three air lenses include an object-side air lens, an image-side air lens, and an intermediate air lens. The object-side air lens and the image-side air lens is biconvex, and the intermediate air lens is biconcave.

Abstract: An imaging optical system including a first lens having negative refractive power; a second lens having negative refractive power; a third lens having positive refractive power; an aperture stop; a fourth lens having positive refractive power; a fifth lens having negative refractive power; and a six lens arranged in that order from an object side. The first lens is a negative lens with a concave surface facing the image side. The second lens is a negative lens with a concave surface facing the object side. The second lens and the third lens are joined together to form a cemented lens have positive refractive power.

Abstract: A zoom lens unit includes, in order from an object side to an image side, a first lens group having positive refractive power and a focus function, a second lens group having negative refractive power, which moves when changing a magnification, a third lens group which moves when changing a magnification, and a fourth lens group having positive refractive power, which is fixed when changing a magnification, wherein the following condition (1) is fulfilled: |M2W·M3W·M4W|<0.14 ??(1) where M2W represents an imaging magnification of the second lens group at a wide-angle end, M3W represents an imaging magnification.the third lens group at the wide-angle end, and M4W represents an imaging magnification of the fourth lens group at the wide-angle end.

Abstract: An image-forming lens includes, from an object side to an image side in order: a first lens group; an aperture; and a second lens group with a positive refractive power, the first lens group including, from the object side in order: a first F lens group with a negative refractive power; and a first R lens group with a positive refractive power, the first F lens group including, from the object side in order: a first negative lens; and a second negative lens, and the first R lens group including: any one of a positive lens and a cemented lens with a positive refractive power as a whole, wherein a distance from a surface on a most object side of the first lens group to an image plane in a state of focusing on an object at infinity: L, and a maximum image height: Y? satisfy Conditional expression 1: 2.8<L/Y?<4.3.

Abstract: An image-forming lens includes, from an object side to an image side in order: a first lens group; an aperture; and a second lens group with a positive refractive power, the first lens group including, from the object side in order: a first F lens group with a negative refractive power; and a first R lens group with a positive refractive power, the first F lens group including, from the object side in order: a first negative lens; and a second negative lens, and the first R lens group including: any one of a positive lens and a cemented lens with a positive refractive power as a whole, wherein a distance from a surface on a most object side of the first lens group to an image plane in a state of focusing on an object at infinity: L, and a maximum image height: Y? satisfy Conditional expression 1: 2.8<L/Y?<4.3.

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: A zoom lens unit includes, in order from an object side to an image side, a first lens group having positive refractive power and a focus function, a second lens group having negative refractive power, which moves when changing a magnification, a third lens group which moves when changing a magnification, and a fourth lens group having positive refractive power, which is fixed when changing a magnification, wherein the following condition (1) is fulfilled: |M2W·M3W·M4W|<0.14 ??(1) where M2W represents an imaging magnification of the second lens group at a wide-angle end, M3W represents an imaging magnification.the third lens group at the wide-angle end, and M4W represents an imaging magnification of the fourth lens group at the wide-angle end.

Abstract: A zoom lens unit includes, in order from an object side to an image side, a first lens group having positive refractive power and a focus function, a second lens group having negative refractive power, which moves when changing a magnification, a third lens group which moves when changing a magnification, and a fourth lens group having positive refractive power, which is fixed when changing a magnification, wherein the following condition (1) is fulfilled: |M2W·M3W·M4W|<0.14??(1) where M2W represents an imaging magnification of the second lens group at a wide-angle end, M3W represents an imaging magnification of the third lens group at the wide-angle end, and M4W represents an imaging magnification of the fourth lens group at the wide-angle end.

Abstract: A zoom lens includes, in the order starting from the object side to the side of an image plane, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power. The fourth lens group includes, in the order starting from the side closest to the image plane to the object side, a first positive lens, a first negative lens, a second negative lens and a second positive lens. The fourth lens group G4 has a configuration that satisfies the following conditional expression (1) when ?dP1 represents an Abbe number of the first positive lens L46 and ?dN1 represents an Abbe number of the first negative lens L45: ?40<?dP1??dN1<0??(1).

Abstract: An image forming lens consists of from an object side to an image side in the following order: a first group with a positive refractive power; an aperture stop; and a second group with a positive refractive power, wherein the second group includes, from the object side to the image side in the following order, a biconvex lens, a biconcave lens, a negative meniscus lens a convex surface of which faces the image side, a biconvex lens, and a positive meniscus lens a convex surface of which faces the image side.

Abstract: A zoom lens includes, in order from an object side to an image surface 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, the second lens group and the third lens group are moved such that the second lens group is located on a most object side at a wide-angle end and the third lens group is located on a most image surface side at a telephoto end during zooming.

Abstract: A zoom lens includes a first lens group with a diffraction optical element and having positive refractive power, a second lens group having negative refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power, which are sequentially arranged from an object side to an image side. The second lens group and the third lens group are moved in accordance with zooming between a wide angle end and a telephoto end such that the second lens group is positioned to the object-most side at the wide angle end, and the third lens group is positioned to the image-most side at the telephoto end. At least one of the second lens group and the third lens group includes a negative lens satisfying the conditional expressions: 1.50<nd<1.75; 60.0<?d<75.0; and ?C,A??0.0015×?d<0.2550.

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.