Patent ID: 9494776
Filing Date: 2016-11-15
CPC Classification: G02B

Claim Text:
1. A zoom lens comprising, in order from an object side: a first lens group that has a positive refractive power and is fixed relative to an image plane during magnification change; a moving lens group comprising at least two lens groups that are moved along an optical axis direction to change an air space therebetween during magnification change; a stop; and an end lens group that has a positive refractive power and is fixed relative to the image plane during magnification change, wherein the first lens group comprises, in order from the object side, a first lens-group front group that has a negative refractive power and is fixed relative to the image plane during focusing, a first lens-group middle group that has a positive refractive power and is moved along the optical axis direction during focusing, and a first lens-group rear group that has a positive refractive power and is fixed relative to the image plane during focusing, the first lens group, the moving lens group and the end lens group are the only lens groups with refractive power, the first lens-group middle group includes at least one aspheric lens that satisfies the condition expression (1) below, and at least one aspheric surface of the aspheric lens satisfies the condition expression (2) below: where yf is a height on an object-side surface of the aspheric lens of a principal ray at a maximum image height at a wide-angle end, yr is a height on an image-side surface of the aspheric lens of the principal ray at the maximum image height at the wide-angle end, Xf(yf) is a positional difference in the optical axis direction between the object-side surface of the aspheric lens and a paraxial spherical surface of the object-side surface at the height yf, Xr(yr) is a positional difference in the optical axis direction between the image-side surface of the aspheric lens and a paraxial spherical surface of the image-side surface at the height yr, fw is a focal length of the entire system at the wide-angle end, Das is a distance along the optical axis from the aspheric surface of the aspheric lens to the aperture stop, y is a height on the aspheric surface of the aspheric lens of the principal ray at the maximum image height at the wide-angle end, and IH is the maximum image height, where a negative Xf(yf) indicates that the object-side surface of the aspheric lens at the height yf is on the object side of the paraxial spherical surface of the object-side surface, and a positive Xf(yf) indicates that the object-side surface of the aspheric lens at the height yf is on the image side of the paraxial spherical surface of the object-side surface, and where a negative Xr(yr) indicates that the image-side surface of the aspheric lens at the height yr is on the object side of the paraxial spherical surface of the image-side surface, and a positive Xr(yr) indicates that the image-side surface of the aspheric lens at the height yr is on the image side of the paraxial spherical surface of the image-side surface.