A variable magnification optical system comprising, in order from an object side, a first lens group and a plurality of lens groups; upon varying a magnification, a distance between the first lens group and the plurality of lens groups being varied, and distances between respective lens groups in the plurality of lens groups being varied; the plurality of lens groups comprising an object side focusing lens group which is moved upon carrying out focusing and at least one image side focusing lens group disposed in a more image side than the object side focusing lens group and moved with a trajectory differing from that of the object side focusing lens group, upon carrying out the focusing; and the predetermined conditional expressions being satisfied, whereby variations in aberrations upon varying magnification from the wide angle end state to the telephoto end state as well as variations in aberrations upon carrying out focusing from an infinite distance object to a close distance object can be suppressed superbly.

A variable magnification optical system comprising, in order from an object side, a first lens group and a plurality of lens groups; upon varying a magnification, a distance between the first lens group and the plurality of lens groups being varied, and distances between respective lens groups in the plurality of lens groups being varied; the plurality of lens groups comprising an object side focusing lens group which is moved upon carrying out focusing and at least one image side focusing lens group disposed in a more image side than the object side focusing lens group and moved with a trajectory differing from that of the object side focusing lens group, upon carrying out the focusing; and the predetermined conditional expressions being satisfied, whereby variations in aberrations upon varying magnification from the wide angle end state to the telephoto end state as well as variations in aberrations upon carrying out focusing from an infinite distance object to a close distance object can be suppressed superbly.

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.

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

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

A converter lens has negative refractive power, and is disposed on an image side of a master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone. The converter lens includes a first lens element closest to an object and a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element. A focal length of the converter lens, a focal length of an air lens formed by the first lens element and the second lens element, the shape of an image-side lens surface of the first lens element, and the shape of an object-side lens surface of the second lens element are determined as appropriate.

A converter lens has negative refractive power, and is disposed on an image side of a master lens so that a focal length of an entire system becomes greater than a focal length of the master lens alone. The converter lens includes a first lens element closest to an object and a second lens element next to an image side of the first lens element with a space between the first lens element and the second lens element. A focal length of the converter lens, a focal length of an air lens formed by the first lens element and the second lens element, the shape of an image-side lens surface of the first lens element, and the shape of an object-side lens surface of the second lens element are determined as appropriate.

A zoom optical system according to an embodiment of the present invention comprises a first lens group, a second lens group, a third lens group, and a fourth lens group which are successively arranged from an object side to an image side, wherein the first lens group to the fourth lens group each comprise two lenses, wherein the second lens group and the third lens group are movable, and wherein the telephoto effective focal length (EFL) is defined by the mathematical expression below:

[00001]$9.0<\frac{{\mathrm{EFL}}_{\mathrm{tele}}}{H_{\mathrm{imageD}}}<9.5$ where, EFL.sub.tele refers to the effective focal length of the zoom optical system in the telephoto, and H.sub.imageD refers to a value of half a diagonal length of an image sensor pixel area.

A zoom optical system according to an embodiment of the present invention comprises a first lens group, a second lens group, a third lens group, and a fourth lens group which are successively arranged from an object side to an image side, wherein the first lens group to the fourth lens group each comprise two lenses, wherein the second lens group and the third lens group are movable, and wherein the telephoto effective focal length (EFL) is defined by the mathematical expression below:

[00001]$9.0<\frac{{\mathrm{EFL}}_{\mathrm{tele}}}{H_{\mathrm{imageD}}}<9.5$ where, EFL.sub.tele refers to the effective focal length of the zoom optical system in the telephoto, and H.sub.imageD refers to a value of half a diagonal length of an image sensor pixel area.