A lens assembly includes a first lens group, a second lens group, and a third lens group, all of which are arranged in order from a first side to a second side along an optical axis. The first lens group is with positive refractive power. The second lens group is with positive refractive power. The third lens group is with positive refractive power. The first lens group is fixed, the second lens group can move along the optical axis, and the third lens group can move along the optical axis, so that the lens assembly is zoomed from a wide-angle end to a telephoto end to change an effective focal length.

A zoom lens includes a plurality of lens units, which consist of, in order from an object side to an image side, a first lens unit having positive refractive power, an intermediate group including a plurality of lens units, and a rear lens unit. A distance between adjacent lens units changes during zooming from a wide-angle end to a telephoto end. The first lens unit is fixed relative to an image plane for zooming from the wide-angle end to the telephoto end. The first lens unit consists of a plurality of subunits in which a distance between adjacent subunits changes during focusing, and the plurality of subunits include, in order from the object side to the image side, a first subunit that does not move for focusing, a second subunit having positive refractive power that moves for focusing, and a third subunit having negative refractive power. A predetermined inequality is satisfied.