A zoom lens includes, in order from an object side to an image 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, a fourth lens unit having a positive refractive power, and a fifth lens unit having a negative refractive power. During zooming, each distance between adjacent lens units changes. During zooming from a wide-angle end to a telephoto end, the first lens unit moves toward the object side, a distance between the third lens unit and the fourth lens unit decreases, and a distance between the fourth lens unit and the fifth lens unit decreases. The number of optical elements each having a refractive power in the first lens unit is two or less. Predetermined conditions are satisfied.

A zoom optical system comprises, in order from an object side: a first lens group having positive refractive power; a front-side lens group; an intermediate lens group having positive refractive power; and a rear-side lens group. The front-side lens group is composed of one or more lens groups and has a negative lens group. At least part of the intermediate lens group is a focusing lens group. The rear-side lens group is composed of one or more lens groups. Upon zooming, distances between the first lens group and the front-side lens group, between the front-side lens group and the intermediate lens group, and between the intermediate lens group and the rear-side lens group change. The following conditional expressions are satisfied:
−10.000<fF/fRF<10.000
0.010<|fF/fXR|<10.000
where fF denotes a focal length of the focusing lens group, fRF denotes a focal length of a lens group closest to the object side in the rear-side lens group, and fXR denotes a focal length of a lens group closet to an image surface in the front-side lens group.

A zoom optical system comprises, in order from an object side: a first lens group having positive refractive power; a front-side lens group; an intermediate lens group having positive refractive power; and a rear-side lens group. The front-side lens group is composed of one or more lens groups and has a negative lens group. At least part of the intermediate lens group is a focusing lens group. The rear-side lens group is composed of one or more lens groups. Upon zooming, distances between the first lens group and the front-side lens group, between the front-side lens group and the intermediate lens group, and between the intermediate lens group and the rear-side lens group change. At least one of the following conditional expressions is satisfied:
0.010<fF/fXR<10.000
2.250<TLW/ZD1<10.000
where fF denotes a focal length of the focusing lens group, fXR denotes a focal length of a lens group closet to the image surface in the front-side lens group, TLW denotes an entire length of the optical system in a wide angle end state, and ZD1 denotes a movement amount of the first lens group upon zooming from the wide angle end state to a telephoto end state.

A zoom optical system (ZL) comprises, in order from an object: a first lens group (G1) having a positive refractive power; and a second lens group (G2) having a negative refractive power, wherein upon zooming, a distance between the adjacent lens groups changes. The zoom optical system further comprises an aperture stop (S) disposed closer to an image than the second lens group (G2, and satisfies the following conditional expression:

0.10<Df/Dr<0.90 where Df: a distance to the aperture stop from a lens surface of the zoom optical system closest to an object in a wide angle end state, and Dr: a distance from the aperture stop to a lens surface of the zoom optical system closest to the image in the wide angle end state.

A variable magnification optical system capable of realizing a high-resolution observation image display system that can arbitrarily change an observation field of view without changing a working distance of an observation optical system while keeping the observation optical system small in size and an imaging apparatus including the variable magnification optical system.

A zoom lens includes, in order from an object side to an image side, first, second and third lens units having positive, negative and positive refractive powers. The first lens unit moves during zooming. During zooming from a wide-angle end to a telephoto end, a distance between the first and second lens units widens, and a distance between the second and third lens units narrows. The first lens unit consists of three or less lenses. The second lens unit consists of, in order from the object side to the image side, a first single lens as a spherical lens having a negative refractive power, a cemented lens in which a lens having a negative refractive power and a lens having a positive refractive power are cemented, and a second single lens as a spherical lens having a negative refractive power. A predetermined condition is satisfied.

Comprising, in order from an object side: a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having positive refractive power, and a fifth lens group having negative refractive power; upon varying a magnification, the first lens group being fixed with respect to the image plane, and each distance between the neighboring lens groups being varied; upon focusing, at least a portion of the fourth lens group being moved; and predetermined conditional expression(s) being satisfied, thereby variations in various aberrations upon varying magnification being superbly suppressed.

A rear attachment lens according to the aspect of the embodiments is configured to vary a focal length of a system by being attached to an image side of a master lens. The rear attachment lens includes a positive lens arranged closest to the image side in which a lens surface on the image side of the positive lens has a shape convex toward the image side. A focal length of the rear attachment lens, a magnification of the rear attachment lens when attached to the master lens, and a distance from the lens surface on the image side of the positive lens to a rear principal point position of the rear attachment lens when attached to the master lens are appropriately set.

A zoom lens including, in order from object side to image side, first to fourth lens units respectively having positive, negative, positive, and positive refractive powers. During zooming from a wide-angle end to a telephoto end, the first lens unit is arranged to move, the distance between the first lens unit and the second lens unit increases, the distance between the second lens unit and the third lens unit decreases, and the distance between the third lens unit and the fourth lens unit decreases. The second lens unit consists of a first lens having a negative refractive power and a second lens having a positive refractive power, the second lens being disposed on the image side of the first lens. A predetermined condition is satisfied.

In an optical system according to each exemplary embodiment, an interval between adjacent lens units changes in focusing from an infinite-distance object to a close-distance object, and a first in-focus state in which β=−1.2 is obtained can be caused, where β is a lateral magnification of an entire system. The optical system according to each exemplary embodiment includes a plurality of focus lens units, and out of a focus lens unit having a largest absolute value of a focus sensitivity and a focus lens unit having a second largest absolute value of a focus sensitivity in a state in which focus is put on an infinite-distance object, a focus lens unit disposed on an object side is a lens unit LA, and a focus lens unit disposed on an image side is a lens unit LB. A partial optical system LC including all lenses disposed on the image side of the lens unit LB has negative refractive power. The partial optical system LC satisfies a predetermined conditional expression.