The disclosure discloses a zoom lens group. The zoom lens group sequentially includes from an object side to an image side along an optical axis: a first lens group having a negative refractive power, the first lens group including a first lens and a second lens which are sequentially arranged along the optical axis; a second lens group having a positive refractive power, the second lens group including a third lens, a fourth lens and a fifth lens which are sequentially arranged along the optical axis; and a third lens group having a positive refractive power, a separation distance between the first lens group and the second lens group on the optical axis and a separation distance between the second lens group and the third lens group on the optical axis are adjusted, so as to switch the zoom lens group from a wide-angle state to a long-focus state.

A lens assembly includes a first lens group, a second lens group, a third lens group, a fourth lens group, and a fifth lens group, all of which are arranged in order from a first side to a second side along an axis. The first lens group is with negative refractive power. The second lens group is with positive refractive power. The third lens group is with refractive power. The fourth lens group is with refractive power. The fifth lens group is with refractive power. The lens assembly further includes a first reflective element disposed between the first lens group and the fifth lens group, wherein the first reflective element includes a first reflective surface.

Provided is a zoom lens including, in order from an object side to an image side: a first lens unit having a negative refractive power and configured not to move for zooming; a second lens unit having a positive refractive power and configured to move to an object side for zooming from a wide angle end to a telephoto end; and a rear lens unit arranged closest to the image side, wherein the rear lens unit includes an optical element having a positive refractive power and cemented with a lens made of a glass material, and wherein the optical element satisfies the following conditions:

2.10010.sup.3dm+0.693<gFm; and

0.555<gFm<0.900,

where dm and gFm are expressed by the following expressions:

dm=(Nd1)/(NFNC); and

gFm=(NgNF)/(NFNC),

where Ng, NF, Nd and NC respectively represent refractive indices with respect to a g-line, an F-line, a d-line, and C-line.

A projection zoom lens includes: a first lens group having a negative refractive power provided most toward the magnification side, which is fixed when changing magnification; and at least two movable lens groups that move to change the relative distance therebetween in the direction of an optical axis when changing magnification. The first lens group is constituted by, in order from the magnification side to the reduction side, a front group having a negative refractive power and a rear group having a negative refractive power. The front group is fixed and only the rear group moves in the direction of the optical axis during focusing operations. Conditional Formula (1) related to the focal length f1a of the front group and the focal length f1b of the rear group is satisfied:
f1b/f1a<0.8(1).

A projection zoom lens includes: a first lens group having a negative refractive power provided most toward the magnification side, which is fixed when changing magnification; and at least two movable lens groups that move to change the relative distance therebetween in the direction of an optical axis when changing magnification. The first lens group is constituted by, in order from the magnification side to the reduction side, a front group which is fixed during focusing operations and a rear group having a negative refractive power that moves in the direction of the optical axis during focusing operations. The front group moves in the direction of the optical axis to correct field curvature. Conditional Formula (1) related to the focal length fw of the entire lens system at the wide angle end and the focal length fla of the front group is satisfied.
|fw/fla|<0.2(1).

A variable magnification optical system including, 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, and a subsequent lens group including a plurality of lens groups is configured so that at varying magnification, the first and third lens groups are fixed with respect to an image plane, and the spacings between adjacent lens groups are varied, and that the following conditional expression is satisfied:

0.24<(TL/f1)/(ft/fw)<0.55

where TL is the distance from a lens surface closest to the object side to the image plane, f1 is the focal length of the first lens group, ft is the focal length of the variable magnification optical system in a telephoto end state, and fw is the focal length of the variable magnification optical system in a wide-angle end state.