A projection system that can be incorporated in a projector includes a first lens unit that makes a screen (enlargement-side image formation plane), which is located on the enlargement-side, conjugate with an intermediate image and a second lens unit that makes the intermediate image conjugate with a reduction-side image formation plane, which is located on the reduction side. The first lens unit has positive power, and the second lens unit has negative power. A second-lens-unit intermediate-image-side first lens, which is provided in the second lens unit and closest to the intermediate image, has positive power. The following expression is satisfied:

−0.3≦fU1/fU2<0

where fU1 denotes the focal length of the first lens unit, and fU2 denotes the focal length of the second lens unit.

A zoom lens system according to the present disclosure includes a plurality of lens groups each of which is made up of at least one lens element. The zoom lens system includes, in order from an object side to an image side: a first focusing lens group having a negative power; and a second focusing lens group having a positive power, wherein when zooming is performed from a wide end to a telephoto end, the first focusing lens group and the second focusing lens group move along an optical axis, when focusing is performed from an infinity focusing state to a proximity object focusing state, the first focusing lens group and the second focusing lens group move to perform the focusing, and a predetermined condition is satisfied.

The 1-2nd lens group is divided into three lens groups which move when focusing is performed during the magnification change. Even in a case in which the second optical group is formed of one mirror, it is possible for a primary image to contain appropriate aberration and to hereby reduce aberration of an image which is finally projected onto a screen through the second optical group.

An optical system includes, in order from an object side toward an image side, a first lens unit having positive refractive power, and a second lens unit having negative refractive power. A distance between consecutive ones of the lens units changes when focusing is performed. The first lens unit is stationary during focusing. The second lens unit is moved toward the image side when focus is changed from an object at infinity to an object at a short distance. Lateral magnification β2 of the second lens unit when focusing on the object at infinity, focal length f1 of the first lens unit, and focal length f2 of the second lens unit are set appropriately to satisfy predetermined mathematical conditions.

A zoom lens includes, in order from a magnified side to a minified side, a first lens group, an aperture stop, and a second lens group. The second lens group has at least one aspheric surface. The zoom lens satisfies the conditions: 0.1<Ic/TTLw<0.15 and TTLw/EFLw≦10, where Ic denotes a radius of an image circle, TTLw denotes a total track length of the zoom lens in the wide configuration, and EFLw denotes an effective focal length of the zoom lens in the wide configuration.

A zoom lens system includes a positive first lens group, a negative second lens group, in that order from the object side, and a positive n.sup.th lens group provided closest to the image side. During zooming from the short to long focal length extremities, the first lens group and the n.sup.th lens group remain stationary and the second lens group moves. A positive m.sup.th lens group is provided between the second and n.sup.th lens groups. The following conditions (1) and (2) are satisfied:
1.23<f1/fn<1.50  (1), and
1.20<fn/fm<1.60  (2),
wherein f1, fn and fm designate the focal lengths of the first, n.sup.th and m.sup.th lens groups, respectively, wherein n is a positive integer of 4 or greater, and m is a positive integer of 3 or greater.

A mobile terminal includes a terminal body, and a camera module provided on one side of the terminal body and including a lens assembly exposed outwardly in at least a portion thereof, an iris provided on an inner side of the lens assembly to adjust an amount of incident light, and an actuator moving the lens assembly and the iris, wherein the lens assembly includes a first lens assembly provided on a front side of the iris and exposed to the outside and a second lens assembly provided on a rear side of the iris and determining a magnification together with the first lens assembly, the actuator includes a moving member disposed on a rear side of the second lens assembly, a housing accommodating the moving member, and a driving unit provided between the moving member and the housing.

A zoom lens system includes: a first lens group having a negative refractive power; a second lens group having a positive refractive power; and an aperture between the first and second lens groups, wherein the first lens group and the second lens group are sequentially arranged from an object side to an image side, wherein the zoom lens system performs zooming and focusing by moving the second and first lens groups, respectively, along an optical axis, and satisfies
2.5<(f.sub.w/f.sub.t)×(T.sub.w/Y)<4.5, where f.sub.w denotes an entire focal length at a wide-angle end, f.sub.t denotes an entire focal length at a telephoto end, and Tw denotes a distance between an image plane and an object side lens surface of a lens closest to the object side of the first lens group at the wide-angle end, and Y denotes a radical axis image height.

An imaging apparatus includes: a zoom lens unit that forms image light on an imaging unit; a zoom ring that is provided around the zoom lens to be manually rotated; a rotation detection unit including: a slit member that includes a plurality of blades that are spaced apart from one another in a rotation direction and is rotated by being connected to the zoom ring, and a sensor that detects rotation of the slit member and outputs a detection signal; and a lens control unit that adjusts a zoom ratio by driving the zoom lens unit based on the detection signal of the sensor, wherein a rotation ratio of the slit member to the zoom ring is greater than 1.

A zoom lens includes a first lens group and a second lens group. The first lens group has a negative refractive power and includes a first lens, a second lens, and a third lens arranged in sequence from a magnified side to a minified side, refractive powers of which are negative, negative, and positive, respectively. The second lens group has a positive refractive power and is disposed between the first lens group and the minified side. The second lens group includes a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged in sequence from the magnified side to the minified side, refractive powers of which are positive, negative, positive, negative, positive, negative, and positive, respectively. The first lens and the tenth lens are aspheric lenses, and the second lens to the ninth lens are spherical lenses.