A zoom lens includes a negative first lens group, a positive second lens group, and a subsequent lens group in order from an object side. A focusing lens group closer to an image side than the first lens group moves during focusing. The first lens group consists of a first-a lens group and a first-b lens group in order from the object side. Assuming that an average of refractive indices of the negative lenses of the first-a lens group is Nd1ave, a focal length of the focusing lens group is ff, and a focal length of the first lens group is f1, Conditional Expression (1) of 1.73<Nd1ave<1.95 and Conditional Expression (2) of 1<|ff/f1|<3 are satisfied.

A zoom lens includes a negative first lens group, a positive second lens group, and a subsequent lens group in order from an object side. A focusing lens group closer to an image side than the first lens group moves during focusing. The first lens group consists of a first-a lens group and a first-b lens group in order from the object side. Assuming that an average of refractive indices of the negative lenses of the first-a lens group is Nd1ave, a focal length of the focusing lens group is ff, and a focal length of the first lens group is f1, Conditional Expression (1) of 1.73<Nd1ave<1.95 and Conditional Expression (2) of 1<|ff/f1|<3 are satisfied.

A zoom lens includes a first lens group and a second lens group. A relative movement between the first lens group and the second lens group is allowed, whereby the zoom lens zooms between a wide-angle end and a telephoto end. While the zoom lens is switched from the wide-angle end toward an intermediate state, the first lens group is moved toward the image side. While the zoom lens is switched from the intermediate state toward the telephoto end, the first lens group is moved toward the object side.

A dome camera includes a camera body rotatable and including a lens system and an imaging device, a correction optical system having a curved shape, and a dome cover covering the camera body and the correction optical system. The correction optical system performs at least any one of tilt, decenter, and rotation in accordance with a rotation angle of the camera body.

A zoom lens includes a first lens group and a second lens group. The first lens group has a negative refractive power and includes a first lens, a second lens, and a third lens arranged in sequence from a magnified side to a minified side, refractive powers of which are negative, negative, and positive, respectively. The second lens group has a positive refractive power and is disposed between the first lens group and the minified side. The second lens group includes a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged in sequence from the magnified side to the minified side, refractive powers of which are positive, negative, positive, negative, positive, negative, and positive, respectively. The first lens and the tenth lens are aspheric lenses, and the second lens to the ninth lens are spherical lenses.

The zoom lens consists of a first optical system including a lens at a position closest to the magnification side and a second optical system forming an intermediate image in order from the magnification side. The first optical system reforms the intermediate image on a magnification side imaging plane. The second optical system includes a lens group including an aperture stop, having a negative refractive power, and moving during zooming. The zoom lens satisfies a conditional expression: 0.1<f2w/fAp<2.1, where fAp is a focal length of the lens group having the aperture stop and f2w is a focal length of the second optical system at a wide angle end.

The zoom lens consists of a first optical system including a lens at a position closest to the magnification side and a second optical system forming an intermediate image in order from the magnification side. The first optical system reforms the intermediate image on a magnification side imaging plane. The second optical system includes a lens group including an aperture stop, having a negative refractive power, and moving during zooming. The zoom lens satisfies a conditional expression: 0.1<f2w/fAp<2.1, where fAp is a focal length of the lens group having the aperture stop and f2w is a focal length of the second optical system at a wide angle end.

A variable magnification optical system consists of a first lens-group having negative refractive-power, a stop and a second lens-group having positive refractive-power in this order from an object-side. The first lens-group includes an L11 negative meniscus lens, an L12 negative lens and a C11 cemented lens, in which a biconcave lens and a positive lens are cemented together in this order from the object-side, in this order from the object-side. The second lens-group includes an L21 positive lens that is arranged closest to the object-side and includes at least one aspheric surface, and an object-side surface of which is convex, and only two cemented lenses toward an image-side of the L21 positive lens, and each of which consists of a negative lens and a positive lens cemented together in this order from the object-side. The following conditional expressions (1) and (2) are satisfied:
−1.0<Rf11/Rf12<0.7  (1); and
55.0<νdave1  (2).

An optical zoom in a small form factor suitable for use in mobile devices such as cell phones, security cameras, and other small-scale imaging systems. One or more Alvarez lens pairs are provided, and moved transversely to the optical axis. The combination of one or more Alvarez lens pairs and the actuator permits a zoom power of at least 3× with a lateral displacement distance of the optical components of approximately five millimeters or less.

A wide angle zoom lens includes sequentially from the object side, a first lens group having a negative refractive power overall and three lenses, including first to third lenses, having a negative refractive power and disposed farthest on the object side; a second lens group having a positive refractive power overall and one or more sets of cemented lenses; and a third lens group having a negative refractive power. This ultra wide angle zoom lens varies intervals between the first lens group, the second lens group, and the third lens group on the optical axis to zoom from the wide angle end to the telephoto end and satisfies given conditions to thereby enable a high zoom ratio, large diameter, and high resolution.