A zoom lens system includes a first lens group; a second lens group; and a subsequent lens group arranged in that order from the object side. The second lens group consists of a second lens group-a, a second lens group-b, and a second lens group-c arranged in that order from the object side. A distance between the first lens group and the second lens group increases and a distance between the second lens group and the subsequent lens group decreases during a change in magnification from a short focal length end to a long focal length end. During a change in focus from infinity to a short distance, the second lens group-b is movable to the image side, and a distance between the second lens group-a and the second lens group-b and a distance between the second lens group-b and the second lens group-c are changeable.

A finder is a reverse Galileo type finder comprising, in order from the object side to the eye point side: an objective lens group having a negative refractive power; and an eyepiece lens group having a positive refractive power. The distance between the objective lens group and the eyepiece lens group is the longest distance from among distances between lenses, as an air converted length, in an observation optical system from the objective lens group to the eyepiece lens group. The eyepiece lens group consists of, in order from the object side to the eye point side: a first lens having a negative refractive power; a second lens having a positive refractive power; and a third lens having a negative refractive power. The first lens and the third lens are fixed while the second lens moves in the direction of the optical axis during diopter adjustment.

A finder is a reverse Galileo type finder comprising, in order from the object side to the eye point side: an objective lens group having a negative refractive power; and an eyepiece lens group having a positive refractive power. The distance between the objective lens group and the eyepiece lens group is the longest distance from among distances between lenses, as an air converted length, in an observation optical system from the objective lens group to the eyepiece lens group. The eyepiece lens group consists of, in order from the object side to the eye point side: a first lens having a negative refractive power; a second lens having a positive refractive power; and a third lens having a negative refractive power. The first lens and the third lens are fixed while the second lens moves in the direction of the optical axis during diopter adjustment.

An optical system includes: a first lens group having a positive refractive power, a second lens group having a negative refractive power and a third lens group having a negative refractive power, sequentially arranged from an object side, when focusing, the second lens group moves along an optical axis, the first lens group and the third lens group are fixed relative to the imaging plane; when a distance from a face closest to the object side to a face closest to an image side of the second lens group is OAL2, and a distance from a face closest to the object side of the entire optical system to the imaging plane is OAL, it is satisfied that: 0.06OAL2/OAL.

The invention relates to a telescope optics for a telescopic observational instrument having an objective lens, having a prism erecting system and having an eyepiece lens, wherein an image of an object generated by the objective lens is located between the prism erecting system and the eyepiece lens, and wherein the objective lens, in an order starting from the object side, comprises a first lens group G1 with a positive refractive power, a second lens group G2 with a negative refractive power and a third lens group G3, and wherein the second lens group G2 is adjustable in parallel to an optical axis for focusing, and wherein at least one lens with a negative refractive power of the third lens group G3 is adjustable perpendicularly to the optical axis for changing the position of the image, and wherein the third lens group G3 has a negative refractive power.

An object of the present invention is to provide an imaging optical system that is inherently small and lightweight, and suitable for use in a small and lightweight telephoto lens with a small and lightweight focusing unit.

The imaging optical system of the present invention includes, in order from an object side to an image side: a first group G1 with positive power overall; a second group G2 composed of a lens that moves along an optical axis during focusing; and a third group G3 with power. The imaging optical system satisfies a specified conditional expression.

An optical system used in an optical apparatus, such as a camera 1, is configured to include a plurality of lens groups such that at focusing the distances between the lens groups are varied, that a final lens group disposed closest to an image side of the lens groups includes at least one lens surface having a pole, and that all of the following conditional expressions are satisfied:
0.020<Y/f<0.120(1)
0.010<Bf/TL<0.150(2)
where Y is image height, f is the focal length of the optical system, TL is the total optical length of the optical system, and Bf is the back focus of the optical system.

The invention relates to a telescope optics for a telescopic observational instrument having an objective lens, having a prism erecting system and having an eyepiece lens, wherein an image of an object generated by the objective lens is located between the prism erecting system and the eyepiece lens, and wherein the objective lens, in an order starting from the object side, comprises a first lens group G1 with a positive refractive power, a second lens group G2 with a negative refractive power and a third lens group G3, and wherein the second lens group G2 is adjustable in parallel to an optical axis for focusing, and wherein at least one lens with a negative refractive power of the third lens group G3 is adjustable perpendicularly to the optical axis for changing the position of the image, and wherein the third lens group G3 has a negative refractive power.

An optical system includes: a first lens group having a positive refractive power, a second lens group having a negative refractive power and a third lens group having a negative refractive power, sequentially arranged from an object side, when focusing, the second lens group moves along an optical axis, the first lens group and the third lens group are fixed relative to the imaging plane; when a distance from a face closest to the object side to a face closest to an image side of the second lens group is OAL2, and a distance from a face closest to the object side of the entire optical system to the imaging plane is OAL, it is satisfied that: 0.06OAL2/OAL.