An optical system (ZL(1)) comprises a plurality of lens groups including a first focusing lens group (G2) and a second focusing lens group (G4) that are disposed side by side on an optical axis, and the second focusing lens group (G4) is disposed at a position closer to an image surface than the first focusing lens group (G2). The first focusing lens group (G2) has positive refractive power, and moves toward an object along the optical axis from focusing on an infinite-distance object to focusing on a short-distance object. The second focusing lens group (G4) moves toward the image surface along the optical axis from focusing on the infinite-distance object to focusing on the short-distance object. The optical system (ZL(1)) satisfies the following conditional expression. −020<βF1/βF2<0.50 where βF1 is the lateral magnification of the first focusing lens group at the time of focusing on the infinite-distance object, and βF2 is the lateral magnification of the second focusing lens group at the time of focusing on the infinite-distance object.

A zoom lens includes a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and two or more additional lens units. In zooming, the first lens unit moves, and an interval between adjacent lens units changes. The refractive index of a negative lens A disposed on a most object side of negative lenses included in the first lens unit is higher than or equal to 1.89, and the negative lens A and a lens B disposed adjacent to an image side of the negative lens A satisfy a predetermined relationship.

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<Iff/f1I<3 are satisfied.

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 optical system (ZL) includes: a first lens group (G1) having negative refractive power; a second lens group (G2) having positive refractive power, the second lens group (G2) being disposed further toward an image than the first lens group (G1); and a succeeding lens group (GL) having a vibration-isolating group (GVRb) that moves so as to have a displacement component in a direction orthogonal to an optical axis, the succeeding lens group (GL) being disposed further toward the image than the second lens group (G2), a distance between the first lens group (G1) and the second lens group (G2) changing and a distance between the second lens group (G2) and the succeeding lens group (GL) changing upon zooming, and the following conditional expression being satisfied:
4.899≤|f1VRaw/fw|<1000.000
where f1VRaw is a composite focal length in a wide-angle end state of a lens disposed further toward the object than the vibration-isolating group, and fw is a focal length of the whole system in the wide-angle end state.

An optical system (ZL(1)) comprises a plurality of lens groups including a first focusing lens group (G2) and a second focusing lens group (G4) that are disposed side by side on an optical axis, and the second focusing lens group (G4) is disposed at a position closer to an image surface than the first focusing lens group (G2). The first focusing lens group (G2) has positive refractive power, and moves toward an object along the optical axis from focusing on an infinite-distance object to focusing on a short-distance object. The second focusing lens group (G4) moves toward the image surface along the optical axis from focusing on the infinite-distance object to focusing on the short-distance object. The optical system (ZL(1)) satisfies the following conditional expression. −020<βF1/βF2<0.50 where βF1 is the lateral magnification of the first focusing lens group at the time of focusing on the infinite-distance object, and βF2 is the lateral magnification of the second focusing lens group at the time of focusing on the infinite-distance object.

A zoom lens includes: a first lens group having negative refractive power on a most object side; and a positive lens group Pa having positive refractive power, a negative lens group N having negative refractive power, and a positive lens group Pb having positive refractive power that are arranged in this order from the object side and provided on an image side with respect to the first lens group.

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

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 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.