Provided is a distortion correction method for an image pickup mode in which an image pickup is performed with an image pickup area, whose diagonal length is Ib, of an image pickup element which receives light from an optical system, an expression, 1.05<Ia/Ib, being satisfied in a case where a distortion correction is not performed, where Ia represents a diagonal length of an effective pixel area of the image pickup element, wherein distortion correction is performed for an image having a positive distortion so that image information positioned at an image height of Ic/2 is positioned at an image height of Ib/2, and so that a conditional expression, 1.0<Ic/Ib, is satisfied.

A lens support mechanism 10 comprises lens group units 23 to 27, a substantially cylindrical rectilinear cylinder 11, and a substantially cylindrical cam cylinder 12. The rectilinear cylinder 11 envelops the lens group units 23 to 27, and has main cam followers 11b protruding outward in the radial direction from the outer peripheral surface, and a sub cam groove 11c. The cam cylinder 12 has main cam grooves 12b and a sub cam follower 12c, and is disposed on the outer peripheral side of the rectilinear cylinder 11. The main cam grooves 12b engage with the main cam followers 11b and are formed substantially parallel to the sub cam groove 11c, and upon rotating relative to the rectilinear cylinder 11, move the lens group units 23 to 27 back and forth in the optical axis direction. The sub cam followers 12c project inward in the radial direction and engage with the sub cam grooves 11c.

A variable magnification optical system comprising a plurality of lens groups which includes a first negative lens group having negative refractive power, a second negative lens group disposed at a more image side than the first negative lens group and having negative refractive power, a third negative lens group disposed at a more image side than the second negative lens group and having negative refractive power; upon varying a magnification, distances between adjacent lens groups being varied; the first negative lens group being movable to include a component in a direction perpendicular to the optical axis as a vibration reduction lens group; the second negative lens group being moved along the optical axis upon carrying out focusing; and the predetermined conditional expression(s) being satisfied. The variable magnification optical system can attain a high optical performance and be made in small in size.

A lens barrel which stably secures strength of a lens barrel without hampering miniaturization thereof. In an inner peripheral portion of a rotary cylinder rotatively driven while being inhibited from moving in a direction of an optical axis on an outer peripheral side of a straight advance cylinder which is movable in the direction of the optical axis while being inhibited from rotating on an outer peripheral side of a cam cylinder and has a through cam groove through which a first projecting portion of the cam cylinder passes, second projecting portions are provided on opposite sides of a straight advance groove of the rotary cylinder, with which the first projecting portion is to be engaged, in a circumferential direction. In an outer peripheral portion of the straight advance cylinder, circumferential grooves with which the second projecting portions are to be engaged are provided in the circumferential direction.

This antireflection film includes a dielectric layer having a surface exposed to air and having a refractive index of 1.35 or more and 1.51 or less, a metal layer having an interface with the dielectric layer, containing silver, and having a thickness of 5 nm or less, and an interlayer having an interface with the metal layer and constituted by a laminate formed by alternately laminating total four layers or more of a layer of high refractive index having a relatively high refractive index and a layer of low refractive index having a relatively low refractive index and is laminated on a substrate having a refractive index of 1.61 or more in the order of the interlayer, the metal layer, and the dielectric layer.

A zoom lens forms an intermediate image at a position conjugate to a reduction side imaging plane and forms the intermediate image again on a magnification side imaging plane. The zoom lens includes a plurality of lens groups including at least two movable lens groups, which move by changing spacings between the groups adjacent to each other in a direction of an optical axis during zooming, at a position closer to the reduction side than the intermediate image. Among the plurality of lens groups, a final lens group closest to the reduction side has a positive refractive power, and remains stationary with respect to the reduction side imaging plane during zooming. The zoom lens satisfies predetermined conditional expressions (1) and (2) about the focal lengths of the movable lens groups.

A zoom lens forms an intermediate image at a position conjugate to a reduction side imaging plane and forms the intermediate image again on a magnification side imaging plane. The zoom lens includes a plurality of lens groups including at least two movable lens groups, which move by changing spacings between the groups adjacent to each other in a direction of an optical axis during zooming, at a position closer to the reduction side than the intermediate image. Among the plurality of lens groups, a final lens group closest to the reduction side has a positive refractive power, and remains stationary with respect to the reduction side imaging plane during zooming. The zoom lens satisfies predetermined conditional expressions (1) and (2).

The zoom lens is a lens system that forms an intermediate image, and consists of, in order from the magnification side: a first lens group that remains stationary during zooming; a plurality of movable lens groups that move during zooming; and a final lens group that has a positive power and remains stationary during zooming. Two or more movable lens groups are positioned to be closer to the reduction side than the intermediate image. The lens system closer to the reduction side than the intermediate image consists of, in order from the magnification side, a front group and a rear group. The zoom lens satisfies predetermined conditional expressions (1) and (2) relating to the rear group.

A zoom lens comprises a first lens group (G1), a second lens group (G2), a third lens group (G3), a fourth lens group (G4), and a fifth lens group (G5) having positive refractive power. Upon zooming, the first lens group (G1), the second lens group (G2), the third lens group (G3), the fourth lens group (G4), and the fifth lens group (G5) are moved along an optical axis to change a distance between the first lens group (G1) and the second lens group (G2), a distance between the second lens group (G2) and the third lens group (G3), a distance between the third lens group (G3) and the fourth lens group (G4), and a distance between the fourth lens group (G4) and the fifth lens group (G5), in such a manner that the following conditional expression is satisfied.

2.30<f5/d4w<3.60

A variable magnification optical system comprising a plurality of lens groups which includes a first negative lens group having negative refractive power, a second negative lens group disposed at a more image side than the first negative lens group and having negative refractive power, a third negative lens group disposed at a more image side than the second negative lens group and having negative refractive power; upon varying a magnification, distances between adjacent lens groups being varied; the first negative lens group being movable to include a component in a direction perpendicular to the optical axis as a vibration reduction lens group; the second negative lens group being moved along the optical axis upon carrying out focusing; and the predetermined conditional expression(s) being satisfied. The variable magnification optical system can attain a high optical performance and be made in small in size.