A variable magnification optical system consists of, in order from an object side to an image side, a first lens group, a second lens group, and a subsequent lens group. The variable magnification optical system satisfies a predetermined conditional expression for a partial dispersion ratio related to F line, C line, and a wavelength of 1970.09 nm, a d-line back focus of the variable magnification optical system at a telephoto end, a back focus in any one wavelength from a wavelength of 1300 nm to a wavelength of 2325.42 nm at the telephoto end, and a d-line focal length of the variable magnification optical system at the telephoto end.

A zoom lens includes a first lens group, a second lens group, a third lens group, a fourth lens group and an aperture. The first lens group, the second lens group, the third lens group and the fourth lens group are sequentially arranged in a direction. The aperture is located between the second lens group and the third lens group. When the zoom lens performs a zoom operation, the first lens group and the third lens group are fixed and the second lens group and the fourth lens group are moved, and a moving distance of the fourth lens group on an optical axis of the zoom lens is less than 5 mm.

There are provided a variable magnification optical system and a control method thereof which are capable of relatively accurately adjusting a positional relationship between a variable magnification optical device and an imaging surface of an imaging device according to a zoom amount. A zoom lens included in the variable magnification optical device is positioned at a telephoto end and a wide angle end, and shift amounts S1 and S2, tilt angles 1 and 2, rotation angles 1 and 2, and focusing adjustment amounts 1 and 2 of the variable magnification optical device are set by a user and are stored. In a case where a zoom amount of the zoom lens is set to a desired value by the user, a shift amount corresponding to the set zoom amount is calculated by using the stored shift amounts S1 and S2. The positional relationship between the variable magnification optical device and the imaging surface of the imaging device is adjusted so as to have the calculated shift amount.

An image lens assembly includes, in order from an object side to an image side along an optical path, a first lens group, a second lens group, a third lens group and a fourth lens group. A total number of lens elements in the image lens assembly is seven. The first lens group includes a first lens element with positive refractive power and a second lens element with negative refractive power. Each of the second lens group and the third lens group includes at least one lens element. The fourth lens group includes a seventh lens element. When the image lens assembly is focusing or zooming, a relative position between the first lens group and an image surface is fixed, a relative position between the fourth lens group and the image surface is fixed, and the second lens group and the third lens group move along the optical axis.

There is provided an optical imaging system including a prism, a first fixed lens group, a first movable lens group, a second movable lens group, and a second fixed lens group. The prism is configured to refract light reflected from an object side toward an imaging plane and a reflecting member. The prism is disposed on the first fixed lens group and the first movable lens group is configured to change a position of the imaging plane so that an overall focal length is changed. The second movable lens group is configured to adjust a position of the imaging plane so that a focal length for an object is adjusted. The imaging plane is disposed on the second fixed lens group.

There is provided an optical imaging system including a prism, a first fixed lens group, a first movable lens group, a second movable lens group, and a second fixed lens group. The prism is configured to refract light reflected from an object side toward an imaging plane and a reflecting member. The prism is disposed on the first fixed lens group and the first movable lens group is configured to change a position of the imaging plane so that an overall focal length is changed. The second movable lens group is configured to adjust a position of the imaging plane so that a focal length for an object is adjusted. The imaging plane is disposed on the second fixed lens group.

A method is provided for adjusting a loupe including an eyepiece and a tube framework having a first optical system adjacent to an object and a second optical system adjacent to the eyepiece. At least two zoom lenses in the first optical system shift along an optical axis between a first and a second position to change magnification. The method includes shifting at least one lens in the first optical system such that a distance at which the object is focused when the zoom lenses are shifted to the first position is substantially equal to a distance at which the object is focused when the zoom lenses are shifted to the second position; and then shifting at least one lens in the second optical system along the optical axis such that the object is focused when the zoom lenses are shifted to the first position or the second position.

There is provided an optical imaging system including a prism, a first fixed lens group, a first movable lens group, a second movable lens group, and a second fixed lens group. The prism is configured to refract light reflected from an object side toward an imaging plane and a reflecting member. The prism is disposed on the first fixed lens group and the first movable lens group is configured to change a position of the imaging plane so that an overall focal length is changed. The second movable lens group is configured to adjust a position of the imaging plane so that a focal length for an object is adjusted. The imaging plane is disposed on the second fixed lens group.

The present disclosure discloses a zoom lens assembly. The zoom lens assembly comprises, sequentially along an optical axis from an object side to an image side, a first lens group comprising a first lens and a second lens; a second lens group having a positive refractive power and comprising a third lens, a fourth lens and a fifth lens; a third lens group having a negative refractive power and comprising a sixth lens; and a fourth lens group having a positive refractive power and comprising a seventh lens and an eighth lens. At least one of the first lens to the eighth lens is an aspheric lens. By changing positions of at least two lens groups in the second lens group, the third lens group and the fourth lens group on the optical axis, the zoom lens assembly switches between a wide-angle state and a telephoto state, and a focal length of the zoom lens assembly changes linearly when the zoom lens assembly switches from the wide-angle state to the telephoto state.

The imaging lens consists of, in order from an object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, a stop, a third lens group having a negative refractive power, and a fourth lens group. The first lens group has, in order from the object side, a positive single lens, and two or more cemented lenses. The second lens group consists of a positive lens and a negative lens. During image blur correction, only the third lens group moves. A conditional expression relating to the back focal length Bf and the lens system total length TTL is satisfied: 2<TTL/Bf<3.6.