An optical system (OL) comprises a first lens group (G1) having positive refractive power, an aperture stop (S), and a rear group (GR) that are arranged in order from the object side along an optical axis, the rear group (GR) comprising a first focusing lens group (GF1) that moves along the optical axis during focusing, and a second focusing lens group (GF2) that is disposed closer to the image side than the first focusing lens group (GF1) and moves along the optical axis during focusing, and the optical system satisfies the following conditional expression. 0.03<D1/TL<0.25 where D1 is a distance on the optical axis from a lens surface closest to the object side to a lens surface closest to the image side in the first lens group (G1), and TL is the entire length of the optical system (OL).

The disclosure provides a zoom lens assembly, which sequentially includes from an object side to an image side along an optical axis: a first lens group; a second lens group with a positive refractive power, spaced from the first lens group by a first air space and movable on the optical axis; a third lens group with a positive refractive power, spaced from the second lens group by a second air space and movable on the optical axis; and a fourth lens group, spaced from the third lens group by a third air space; wherein a Total Track Length (TTL) of the zoom lens assembly and a difference Δf between an effective focal length of the zoom lens assembly at a wide end and an effective focal length of the zoom lens assembly at a tele end satisfy 2.5<TTL/|Δf|<4.0.

A composite optical element includes a glass lens and a resin lens that are joined together. The resin lens has an aspheric shape. When Nd is a refractive index of the resin lens, ?d is an Abbe number of the resin lens, and ?gF is a partial dispersion ratio of the resin lens, Nd, ?d, and ?gF are appropriately set.

A variable-magnification optical system (ZL) comprises: a first lens group (G1) having a positive refractive power; and a rear group (GR) including a plurality of lens groups. When changing the magnification, the gap between each adjacent pair of lens groups changes. The plurality of lens groups in the rear group (GR) include a second lens group (G2) having a positive refractive power and disposed nearest to the object side in the rear group (GR). The variable-magnification optical system (ZL) satisfies the following conditional expression: 0.15<f2/f1<0.80, where f1 is the focal length of the first lens group (G1), and f2 is the focal length of the second lens group (G2).

An optical system (OL) comprises a front group (GA), an intermediate group (GM), and a rear group (GR). The intermediate group (GM) comprises a first focusing lens group (GF1) and a second focusing lens group (GF2). During focusing, the first focusing lens group (GF1) and the second focusing lens group (GF2) move along the optical axis on different trajectories from each other. The front group (GA) and the rear group (GR) are fixed in relation to an image plane (I). The rear group (GR) has a negative lens disposed closest to the image plane. The following conditional formula is satisfied.

[00001]$0.01<\mathrm{fF}2/\mathrm{fF}1<10.;$$0.5<Y/\mathrm{Bf}<5..$

where, fF1: the focal length of the first focusing lens group (GF1), fF2: the focal length of the second focusing lens group (GF2), Y: the image height of the optical system (OL), Bf: the back focus of the optical system (OL).