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 L0 consists of a first lens unit L1 having negative refractive power, a middle group Lm including one or more lens units, and a last lens unit having positive refractive power. The first lens unit L1 includes a first negative lens, a second negative lens, and a third negative lens that are arranged sequentially in an order from an object side to an image side. The number of negative lenses included in the first lens unit L1 is four or less. The middle group Lm includes a plurality of cemented lenses each having a cemented surface that is convex toward the object side, and includes a lens element Ln that is disposed closest to the image side among lens elements having negative refractive power included in the middle group Lm. The zoom lens L0 satisfies a predetermined inequality.

A variable magnification optical system includes, in order from an object: a first lens group (G1) having a negative refractive power; a second lens group (G2); a third lens group (G3); a fourth lens group (G4) having a negative refractive power; and a fifth lens group (G5) having a positive refractive power, the system performing varying magnification by changing the distance between the first and second lens groups, the distance between the second and third lens groups, the distance between the third and fourth lens groups, and the distance between the fourth and fifth lens groups, and the fourth lens group including a 42nd lens group (G42) configured to be movable so as to have a component in a direction orthogonal to an optical axis and a 41st lens group (G41) disposed at an object-side of the 42nd lens group.

A zoom projection lens with eleven lens elements is provided. The zoom projection lens sequentially includes a first lens group, a second lens group, a third lens group, an aperture stop, a fourth lens group and a fifth lens group along an optical axis from a screen side to an image source side. The first lens group has a negative refractive power and includes three lens elements. The second lens group has a positive refractive power and includes one lens element. The third lens group has a positive refractive power and includes one lens element. The fourth lens group has a negative refractive power and includes four lens elements. The fifth lens group has a positive refractive power and includes two lens elements. A first lens element in the first lens group is an aspheric lens made of plastic.

A zoom optical system consists of a first lens group having negative refractive power, a second lens group having positive refractive power, and a rear lens group which are disposed in order from an object. The rear lens group comprises a last lens group and an F lens group in order from a side closest to an image. Lens groups forming the first lens group, the second lens group, and the rear lens group are configured in such a manner that, upon zooming, the respective lens groups move and a distance between the lens groups adjacent to each other changes. At least a part of the F lens group is configured to move upon focusing. Further, the following conditional expression is satisfied.
−0.220<f1/fE<0.280
where f1: a focal length of the first lens group, and fE: a focal length of the last lens group

An optical system comprising a plurality of lens groups arranged on an optical axis and comprising a leading lens group, a first focal lens group, and a second focal lens group. The leading lens group is arranged further on the object side than the first focal lens group and the second focal lens group is arranged further on the image side than the first focal lens group. The first focal lens group has positive refractive power and moves along the optical axis to the image side when focusing from an infinite object to a short-distance object. The second focal lens group: has a negative refractive power; travels along the optical axis to the object side when focusing from an infinite object to a short-distance object; and has, between the first focal lens group and the second focal lens group, an intermediate lens group that includes at least one lens.

A zoom lens includes a first lens unit having negative refractive power, a second lens unit having positive refractive power, an intermediate unit including one or more lens units, and a final lens unit having positive refractive power disposed closest to the image side. The first lens unit includes negative lenses G1, G2 and G3 disposed in this order from an object side to an image side. The final lens unit includes at least one negative lens and a positive lens disposed closest to the image side. The zoom lens satisfies predetermined inequalities.

A zoom optical system consists of a first lens group having negative refractive power, a second lens group having positive refractive power, and a rear lens group which are disposed in order from an object. The rear lens group comprises a last lens group and an F lens group in order from a side closest to an image. Lens groups forming the first lens group, the second lens group, and the rear lens group are configured in such a manner that, upon zooming, the respective lens groups move and a distance between the lens groups adjacent to each other changes. At least a part of the F lens group is configured to move upon focusing. Further, the following conditional expression is satisfied.

−0.220<f1/fE<0.280

where f1: a focal length of the first lens group, and fE: a focal length of the last lens group

An optical system (LS) has an aperture stop (S), and a positive lens (L4) disposed closer to the object side than the aperture stop (S). The positive lens (L4) satisfies the following conditional expressions.

−0.010<ndP1−(2.015−0.0068×νdP1)

50.00<νdP1<65.00

0.545<θgFP1

−0.010<θgFP1−(0.6418−0.00168×νdP1)

where ndP1 is the refractive index to the d line of the positive lens, νdP1 is the Abbe number with respect to the d line of the positive lens, and θgFP1 is the partial dispersion ratio of the positive lens.

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.