An endoscope magnification optical system includes, in order from an object side, a first lens group having a negative power, a second lens group having a positive power and a third lens group having a meniscus lens with a convex surface facing the object side. A distance from a lens surface of the first lens group that is nearest to the object side to an image surface is kept constant while the second lens group is moved in an optical axis direction with respect to the first lens group and the third lens group, which are fixed lens groups, and thereby an optical image is magnified.

An endoscope magnification optical system includes, in order from an object side, a first lens group having a negative power, a second lens group having a positive power and a third lens group having a meniscus lens with a convex surface facing the object side. A distance from a lens surface of the first lens group that is nearest to the object side to an image surface is kept constant while the second lens group is moved in an optical axis direction with respect to the first lens group and the third lens group, which are fixed lens groups, and thereby an optical image is magnified.

The zoom lens consists of, in order from an object side: a first lens group that has a positive refractive power; a second lens group that has a positive refractive power; a third lens group that has a negative refractive power; a fourth lens group that has a positive refractive power; and a fifth lens group that has a positive refractive power. The first lens group and the fifth lens group remain stationary with respect to an image plane during zooming. The second lens group, the third lens group, and the fourth lens group are moved by changing distances between the lens groups and adjacent groups in a direction of an optical axis during zooming, and are positioned to be closer to the image side at a telephoto end than at a wide-angle end. A stop is provided between the fourth lens group and the fifth lens group. In addition, Conditional Expression (1) is satisfied.
0.1<fw/f4<0.5(1)

The zoom lens consists of, in order from an object side: a first lens group that has a positive refractive power; a second lens group that has a positive refractive power; a third lens group that has a negative refractive power; a fourth lens group that has a positive refractive power; and a fifth lens group that has a positive refractive power. The first lens group and the fifth lens group remain stationary with respect to an image plane during zooming. The second lens group, the third lens group, and the fourth lens group are moved by changing distances between the lens groups and adjacent groups in a direction of an optical axis during zooming, and are positioned to be closer to the image side at a telephoto end than at a wide-angle end. A stop is provided between the fourth lens group and the fifth lens group. In addition, Conditional Expression (1) is satisfied.
0.1<fw/f4<0.5(1)

Provided is a zoom lens, including, in order from object side: a positive first unit; a negative second unit; a third unit having a positive or positive refractive power; and a rear group including at least one unit, in which: the first unit is not moved for zooming, and intervals between adjacent units are changed during zooming; the first unit includes three lenses, and the second unit includes three lenses; at least two lens surfaces, among lens surfaces of lenses included in the second unit except for a lens arranged closest to the object side, have aspherical shapes; and focal lengths of the zoom lens at a wide angle end and at a telephoto end, movement amounts of the second and third units during zooming from the wide angle end to the telephoto end are appropriately set.

Provided is a zoom lens, including, in order from object side: a positive first unit; a negative second unit; a third unit having a positive or positive refractive power; and a rear group including at least one unit, in which: the first unit is not moved for zooming, and intervals between adjacent units are changed during zooming; the first unit includes three lenses, and the second unit includes three lenses; at least two lens surfaces, among lens surfaces of lenses included in the second unit except for a lens arranged closest to the object side, have aspherical shapes; and focal lengths of the zoom lens at a wide angle end and at a telephoto end, movement amounts of the second and third units during zooming from the wide angle end to the telephoto end are appropriately set.

The optical system disclosed in the embodiment of the invention includes first to fourth lens groups arranged along an optical axis from an object side toward a sensor side and including each including at least one lens, wherein the first lens group has a refractive power opposite to that of the fourth lens group, the second lens group has a refractive power opposite to that of the third lens group, the first and fourth lens groups are fixed, the second and third lens groups are moved in a direction of the optical axis, each of the first and fourth lens groups includes at least one lens of a non-circular shape, the non-circular lens has a non-circular ratio (CH/CA) greater than 0.7, the non-circular ratio is a ratio of a minimum clear aperture (CH: clear height) and maximum clear aperture (CA) of a lens surface with a large clear aperture among an object-side surface and a sensor-side surface of the non-circular lens, and the non-circular ratio of at least one lens included in the first lens group may be greater than the non-circular ratio of at least one lens included in the fourth lens group.

The optical system disclosed in the embodiment of the invention includes first to fourth lens groups arranged along an optical axis from an object side toward a sensor side and including each including at least one lens, wherein the first lens group has a refractive power opposite to that of the fourth lens group, the second lens group has a refractive power opposite to that of the third lens group, the first and fourth lens groups are fixed, the second and third lens groups are moved in a direction of the optical axis, each of the first and fourth lens groups includes at least one lens of a non-circular shape, the non-circular lens has a non-circular ratio (CH/CA) greater than 0.7, the non-circular ratio is a ratio of a minimum clear aperture (CH: clear height) and maximum clear aperture (CA) of a lens surface with a large clear aperture among an object-side surface and a sensor-side surface of the non-circular lens, and the non-circular ratio of at least one lens included in the first lens group may be greater than the non-circular ratio of at least one lens included in the fourth lens group.

The optical system according to the embodiment includes a first lens group, a second lens group, and a third lens group sequentially arranged along an optical axis from an object side to an image side and wherein each of the first to third lens groups including at least one lens; wherein a refractive power sign of the first lens group and a refractive power sign of the second lens group are opposite to each other, and wherein the first lens group, the second lens group, and the third lens group satisfy Equation 1 below.

[00001]$\begin{array}{cc}0.6<.Math.\mathrm{f\_}1/\mathrm{f\_}23.Math.<1.4& \left[\mathrm{Equation}1\right]\end{array}$

(In Equation 1, f_1 is a focal length of the first lens group, f_23 is a combined focal length of the second lens group and the third lens group.)

The optical system disclosed in the embodiment of the invention includes first to fourth lens groups disposed along an optical axis in a direction from an object side to a sensor side and including at least one lens, respectively, wherein the first lens group and the fourth lens group have opposite refractive powers, the second lens group and the third lens group have opposite refractive powers, positions of the first and fourth lens groups are fixed, and a position of each of the second and third lens groups is movable in a direction of the optical axis, wherein the optical system having the first to fourth lens groups is operated with magnifications according to changes in at least three modes according to a movement of each of the second lens group and the third lens group, and the following equation may satisfy: TTL/EPD_Tele<2.72, wherein TTL is a distance from the optical axis to a surface of an image sensor and a lens surface closest to the object side among lenses of the first lens group, and EPD_Tele is a size of an entrance pupil diameter (EPD) of the optical system when operating at the highest magnification in an operation mode.