A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, the first lens group being moved along the optical axis, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expressions being satisfied, thereby the focusing lens group(s) being reduced in weight.

A zoom lens includes, in order from the object side to the image side, a first lens unit having negative refractive power, a second lens unit having positive refractive power. A distance between adjacent lens units changes during zooming from a wide-angle end to a telephoto end. During zooming from the wide-angle end to the telephoto end, the first lens unit moves to the image side and then to the object side. The first lens unit includes four lenses or more, the four lenses or more including, in order from the object side to the image side, a first negative meniscus lens with a convex surface facing the object side and a second negative meniscus lens with a convex surface facing the object side. A predetermined condition is satisfied.

A plurality of lens units of a zoom lens according to an aspect of the embodiments includes a first lens unit having a negative refractive power, and a rear lens group which includes one or more lens units and has a positive refractive power as a whole. The first lens unit consists of a first negative lens, a second negative lens, and a positive lens which are disposed in order from an object side to an image side. A specific gravity of the first negative lens, a focal length of the second negative lens, and a focal length of the first lens unit are appropriately determined.

An optical system (LS) includes lenses (L22,L23) satisfying the following conditional expressions,
ndLZ+(0.01425??dLZ)<2.12, and
?dLZ<35.0,
where ndLZ: a refractive index of the lens with reference to d-line, and ?dLZ: Abbe number of the lens with reference to d-line.

A variable magnification optical system comprises, in order from an object side, a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group. Upon varying a magnification, a distance between the first lens group and the second lens group, a distance between the second lens group and the third lens group, and a distance between the third lens group and the fourth lens group are varied. The first lens group consists of, in order from the object side, a negative lens and a positive lens. The second lens group consists of, in order from the object side, a positive 2a lens group, a positive 2b lens group, and a negative 2c lens group. A downsized system having high optical performance is provided.

The zoom lens consists of, in order from an object side to an image side, a first lens group having a negative refractive power, a middle group, and a final group. During zooming, a spacing between the first lens group and the middle group changes, and a spacing between the middle group and the final group changes. During focusing, at least a part of the middle group moves, and the first lens group and the final group remain stationary with respect to an image plane. The zoom lens satisfies predetermined conditional expressions about a back focal length, a focal length, and a maximum half angle of view.

Providing a zoom lens system having excellent optical performance with a high zoom ratio, an imaging apparatus, and a method for zooming the zoom lens system. The system including, in order from an object, a first group G1 having negative refractive power, a second group G2 having positive refractive power, a third group G3 having negative refractive power, and a fourth group G4 having positive refractive power. An aperture stop S is disposed between the second group G2 and the fourth group G4. Upon zooming from a wide-angle end state to a telephoto end state, each group is moved such that a distance between the second group G2 and the third group G3 increases, a distance between the third group G3 and the fourth group G4 decreases, and the aperture stop S is moved together with the third group G3. Given conditions are satisfied.

A zoom image pickup apparatus includes a mount portion, a zoom lens which forms an image of light incident from the mount portion, and an image pickup element which is disposed at an image forming position. The zoom lens includes a plurality of lens unit, and a focusing lens unit, and the following conditional expressions (1) and (2) are satisfied:
1.5<f.sub.Lt/f.sub.Lw(1), and
|(y.sub.w7dy.sub.w7d)/y.sub.w7d100<0.66(2).

An optical system according to the present invention is an optical system consisting of a front lens group having a positive or negative refractive power, an aperture stop, and a rear lens group having a positive or negative refractive power that are placed in order from an object side to an image side. In the optical system, relationships between a distance on an optical axis between a negative lens having the strongest refractive power in the rear lens group and a positive lens placed on the image side of the negative lens, an opening angle of the positive lens, a back focus of the optical system, and a focal length of the optical system are appropriately determined.

A zoom lens includes a plurality of lens units that consist of, in order from an object side to an image side, a first lens unit having negative refractive power, a second lens unit having positive refractive power, a third lens unit having negative refractive power, and a fourth lens unit having positive refractive power. A distance between adjacent lens units changes during zooming from a wide-angle end to a telephoto end. During zooming from a wide-angle end to a telephoto end, the first lens unit and the fourth lens unit are fixed relative to an image plane, and the third lens unit moves to the object side. During focusing from infinity to a shortest distance, the first lens unit is fixed relative to the image plane. The second lens unit consists of four or more spherical lenses. A predetermined inequality is satisfied.