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 according to the present invention includes a plurality of lens units consisting of front and rear groups having negative and positive refractive powers at a wide angle end (WAE), respectively. An interval between front and rear groups on an optical axis is longest among all intervals between adjacent ones of plurality of lens units at WAE. The rear group is disposed at an image side of front group and includes a plurality of lens units including a negative lens unit LN (LULN) disposed closest to image side. The LULN includes negative and positive lenses disposed closest to object and image sides in LULN, respectively. A focal length of LULN, a focal length of zoom lens at WAE, a distance on optical axis between a lens surface closest to object side and that closest to image side in LULN, and a back focus at WAE are appropriately set.

A zoom lens system includes, in order from the object side to the image side, a first lens group having negative power and a second lens group having positive power. The first lens group includes at least two negative lenses. When zooming, one of the first lens group and the second lens group is fixed relative to the imaging surface, and the other moves along an optical axis to change an angle of view.

A variable power optical system for an endoscope comprising a first lens group having a negative power, a second lens group having a positive power and a third lens group, and wherein the first lens group includes at least a negative lens having a concave surface pointing to an image side and a positive meniscus lens having a concave surface pointing to an object side, the second lens group includes at least a meniscus lens having a convex surface pointing to the object side and a cemented lens formed by cementing together a negative lens and a positive lens, and the third lens group includes at least a positive lens having a convex surface pointing to the object side, and wherein the variable power optical system for an endoscope is configured to satisfy a predetermined condition.

An optical imaging system includes a first lens group, a second lens group, and a third lens group, sequentially arranged from an object side, wherein the first lens group includes two lenses having negative and positive refractive power, the second lens group includes a plurality of lenses, and the third lens group includes two lenses having negative and positive refractive power.

In an image pickup apparatus including an optical system and an image pickup element, the optical system includes, in order from an object side to an image side, lens(es), an aperture stop, and lens(es). The lens arranged at the most image side in the optical system is a negative lens, and an infrared cut film is formed on at least one lens surface in the optical system. An optical axial distance from the exit pupil of the optical system to the image plane when focusing on an infinite object, an optical axial distance from the lens surface provided with the infrared cut film to the image plane when focusing on the infinite distance object, the curvature radius of the lens surface provided with the infrared cut film, and a radius of a circle circumscribed about an effective imaging area of the image pickup element are appropriately set.

A variable magnification optical system includes, in order from the object side: a positive first lens group, which is fixed when changing magnification; a negative second lens group that moves from the object side to the image side when changing magnification from the wide angle end to the telephoto end; and a rearward lens group having a positive refractive power throughout the entire variable magnification range that includes at least one lens group that moves when changing magnification. The first lens group includes, in order from the object side, a positive first lens group front group, a positive first lens group middle group, and a first lens group rear group constituted by a negative lens. The first lens group front group and first lens group middle group include cemented lenses formed by cementing a negative lens and a positive lens, provided in this order from the object side, together.

A zoom lens includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and an image plane in an order from object-side to image-side. The first lens group includes a first lens having a positive refractive power and a second lens having a negative refractive power in the order from object-side to image-side. The second lens group includes a third lens having a positive refractive power, a fourth lens having a negative refractive power, and a fifth lens having a positive refractive power in the order from object-side to image-side. The third lens group includes at least one sixth lens.

A variable power optical system for an endoscope comprising a first lens group having a negative power, a second lens group having a positive power and a third lens group, and wherein the first lens group includes at least a negative lens having a concave surface pointing to an image side and a positive meniscus lens having a concave surface pointing to an object side, the second lens group includes at least a meniscus lens having a convex surface pointing to the object side and a cemented lens formed by cementing together a negative lens and a positive lens, and the third lens group includes at least a positive lens having a convex surface pointing to the object side, and wherein the variable power optical system for an endoscope is configured to satisfy a predetermined condition.

A zoom lens (10), a camera module (100) and an electronic device (1000). The zoom lens (10) comprises a first lens group (11) with negative focal power, a second lens group (12) with positive focal power, and a third lens group (13) with negative focal power, wherein both the second lens group (12) and the third lens group (13) can move relative to the first lens group (11); the following relations are met: 2.5<FI/F2<1.5, and 2<F3/F2<1.