A variable magnification optical system 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 positive refractive power; and an image-side lens unit. The image-side lens unit includes a lens belonging to a first region and a lens belonging to a second region. At a time of changing magnification, the second lens unit and the third lens unit move.

A four-group or five-group zoom lens consists of, in order from the object side, a positive first group being fixed during magnification change, a negative second group being moved during magnification change, one or two middle groups including a positive mp lens group being moved during magnification change, and a positive rearmost group being fixed during magnification change. Zooming is effected by changing all distances between the adjacent groups. The rearmost group consists of, in order from the object side, a positive front group, a negative middle group, and a positive rear group. Air spaces between the front and middle groups, and between the middle and rear groups are constant during zooming and focusing. The front group includes at least two positive lenses and at least one negative lens. Image stabilization is effected by shifting the middle group perpendicularly to the optical axis. The zoom lens satisfies given condition expressions.

A zoom lens system includes a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group. The second and third lens groups are moved during zooming. The first lens group includes a positive first sub-lens group which does not move during a focusing operation, and a positive second sub-lens group which moves during the focusing operation. The first sub-lens group includes at least one negative lens element, the second sub-lens group is a positive single lens element, and the following conditions (1) and (2) are satisfied:
60<νd1b<75   (1),
and
νd1a<24  (2),
wherein νd1b and νd1a_designates Abbe numbers at the d-line of the positive single lens element of the second sub-lens group and at the d-line of the negative lens element within the first sub-lens group, respectively.

A zoom lens system includes a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group. The second and third lens groups are moved during zooming. The first lens group includes a positive first sub-lens group which does not move during a focusing operation, and a positive second sub-lens group which moves during the focusing operation. The first sub-lens group includes at least one negative lens element, the second sub-lens group is a positive single lens element, and the following conditions (1) and (2) are satisfied:
60<νd1b<75   (1),
and
νd1a<24  (2),
wherein νd1b and νd1a_designates Abbe numbers at the d-line of the positive single lens element of the second sub-lens group and at the d-line of the negative lens element within the first sub-lens group, respectively.

A rear conversion lens, which may include a plurality of lenses may be disposed at a side of master lenses facing an image side for varying a focal length, and may include: a first lens having a positive refractive power; a second lens having a biconcave shape; a third lens having a positive refractive power; a fourth lens having a positive refractive power; and a fifth lens having a negative refractive power. The first to fifth lenses may be sequentially arranged in a direction from an object side to the image side.

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 three lenses. The second lens group includes four lenses. The third lens group includes six lenses and an aperture stop. The fifth lens group includes a single lens component.

A zoom lens is constituted by, 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 end to the telephoto end. The first lens group is constituted by three lenses, which are negative, positive, and positive in order from the object side. The second lens group is constituted by five lenses, which are negative, negative, positive, positive, and negative in order from the object side. The fifth lens group is constituted by a single lens component.

A zoom lens system according to the present disclosure includes, in order from an object side to an image plane side, a first lens group having positive optical power; a second lens group having negative optical power; a third lens group having positive optical power; and a subsequent lens group including a fourth lens group, a fifth lens group, and a sixth lens group. The first lens group comprises, in order from the object side, a first lens element having negative optical power; a second lens element having positive optical power; a third lens element having positive optical power; and a fourth lens element having positive optical power. The fifth lens group in the subsequent lens group has negative optical power. The first lens group is fixed with respect to the image plane in zooming from a wide-end to a tele-end upon image shooting.

A zoom lens system according to the present disclosure includes, in order from an object side to an image plane side, a first lens group having positive optical power; a second lens group having negative optical power; a third lens group having positive optical power; and a subsequent lens group including a fourth lens group, a fifth lens group, and a sixth lens group. The first lens group comprises, in order from the object side, a first lens element having negative optical power; a second lens element having positive optical power; a third lens element having positive optical power; and a fourth lens element having positive optical power. The fifth lens group in the subsequent lens group has negative optical power. The first lens group is fixed with respect to the image plane in zooming from a wide-end to a tele-end upon image shooting.

The zoom lens system includes a first lens group with positive power, a second lens group with negative power, a third lens group with positive power, a fourth lens group with negative power, and a fifth lens group with positive power. An aperture stop is provided between the second and the third lens groups. The third lens group includes lens element L3a and L3b with positive power, lens element L3c with negative power, and lens element L3d with positive power. The lens elements L3c and L3d are cemented. The lens element L3b corrects image blurring. The fourth lens group moves when focusing. When zooming, the first to the fourth lens group move.

Here, condition (1) below is satisfied.

0.24<fL3b/fG3<3.0  (1) Where fL3b is a focal length of the lens element L3b, and fG3 is a focal length of the third lens group.