A zoom optical system includes a first lens group, a position of which with respect to an imaging plane is adjustable, and including first and second lenses. The zoom optical system also includes a second lens group of which a position with respect to the imaging plane is adjustable and includes third to fifth lenses. The zoom optical system further includes a third lens group including a sixth lens. An object-side surface of the first lens is convex.

An imaging lens system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens, sequentially disposed from an object side. A field of view (FOV) of the imaging lens system according to an embodiment is wider than 85 degrees and narrower than 160 degrees. In the imaging lens system according to an embodiment, a distance (TTL) from an object-side surface of the first lens to an imaging plane is greater than 6.0 mm and less than 9.0 mm.

An image capturing lens system includes three lens groups including five lens elements. The three lens groups are, in order from an object side to an image side: first, second and third lens groups. The five lens elements are, in order from the object side to the image side: first, second, third, fourth and fifth lens elements. The first lens element has an object-side surface being convex in a paraxial region thereof. The second lens element has negative refractive power. At least one lens element has an inflection point. A focal length of the image capturing lens system is varied by changing axial distances between the three lens groups in a zooming process. The image capturing lens system has a long-focal-length end and a short-focal-length end. The second lens group is moved relative to the first lens group along an optical axis in the zooming process.

A zoom optical system consists of a first lens group having negative refractive power, a second lens group having positive refractive power, and a rear lens group which are disposed in order from an object. The rear lens group comprises a last lens group and an F lens group in order from a side closest to an image. Lens groups forming the first lens group, the second lens group, and the rear lens group are configured in such a manner that, upon zooming, the respective lens groups move and a distance between the lens groups adjacent to each other changes. At least a part of the F lens group is configured to move upon focusing. Further, the following conditional expression is satisfied.

−0.220<f1/fE<0.280

where f1: a focal length of the first lens group, and fE: a focal length of the last lens group

The variable magnification optical system consists of a front group, a middle group, and a rear group, in order from an object side. The front group consists of two or fewer lens groups and has a negative refractive power. The middle group includes only one lens group that has a positive refractive power as a lens group. The rear group consists of three or less lens groups. An aperture stop is disposed between a lens surface closest to an image side in the front group and a lens surface closest to the object side in the rear group. The front group includes at least three negative lenses and at least one positive lens. A negative meniscus lens convex toward the object side is disposed closest to the object side in the front group. The variable magnification optical system satisfies predetermined conditional expressions.

A zoom optical system includes a first lens group, a position of which with respect to an imaging plane is adjustable, and including first and second lenses. The zoom optical system also includes a second lens group of which a position with respect to the imaging plane is adjustable and includes third to fifth lenses. The zoom optical system further includes a third lens group including a sixth lens. An object-side surface of the first lens is convex.

A zoom lens is provided. The zoom lens includes a first lens group, a second lens group, a third lens group and an aperture stop. The second lens group is disposed between the first lens group and the third lens group. The aperture stop is disposed between the first lens group and the second lens group. When the zoom lens zooms, the aperture stop is fixed without moving and the first lens group correspondingly moves.

An objective lens including a first lens group immovable in changing magnification from a normal observation state to a close-up observation state, a second lens group arranged nearer to the image side than the first lens group and moving along the optical axis in the change of magnification, a third lens group arranged nearer to the image side than the second lens group and immovable in the change of magnification, and an aperture stop arranged between the second lens group and an image plane and immovable in the change of magnification, and the objective lens satisfying the following condition:
1.24<|F.sub.1f/F.sub.n|<1.8
where F.sub.1f denotes the focal length of a lens that is placed nearest to the object side in the first lens group and F.sub.n denotes the focal length of the whole system in the normal observation state.

The wide angle optical system includes in order from a side of an object in front, a first lens group having a negative refractive power, a second lens group having a catadioptric optical element, an aperture stop, and a third lens group having a positive refractive power, and the catadioptric optical element has a first surface, a second surface, and a third surface, and the first surface has a first transmitting surface and a first reflecting surface, the second surface has a second transmitting surface and a second reflecting surface, and the third surface has a third transmitting surface, and the third transmitting surface is a side surface of a circular truncated cone, and the following conditional expressions (1), (2), and (3) are satisfied:

νp<νn  (1),

|φp|<|φn|  (2), and

90°−θk<α/2  (3).

The zoom lens consists of, in order from an object side to an image side, a first lens group having a negative refractive power, a middle group, and a final group. During zooming, a spacing between the first lens group and the middle group changes, and a spacing between the middle group and the final group changes. During focusing, at least a part of the middle group moves, and the first lens group and the final group remain stationary with respect to an image plane. The zoom lens satisfies predetermined conditional expressions about a back focal length, a focal length, and a maximum half angle of view.