Abstract: A zoom lens consists of, in order from an object side to an image side, a first lens unit having negative refractive power, a second lens unit having positive refractive power, and a third lens unit having negative refractive power. The first lens unit and the second lens unit move during zooming to make a distance between the first lens unit and the second lens unit larger at a telephoto end than at a wide-angle end. The third lens unit consists of, in order from the object side to the image side, a first lens subunit having positive refractive power and a second lens subunit having negative refractive power, and the second lens subunit moves toward the image side during focusing from an infinite-distance object to a near-distance object.

Abstract: Provided is a zoom lens in which a variation in aberration with respect to a temperature change is small and excellent optical characteristics can be easily obtained. The zoom lens includes multiple lens units in which a distance between adjacent ones of the multiple lens units changes for zooming. When an average value of a change in refractive index with respect to a temperature change within a temperature range of from 0° C. to 40° C. is ?Nav, at least one lens unit L of the multiple lens units includes multiple optical elements A made of materials satisfying a conditional expression: |?Nav|>5.0×10?5. When an anomalous partial dispersion ratio for a g-line and an F-line is ??gF??, at least one optical element A? of the multiple optical elements A satisfies a conditional expression: |??gF??|>0.0272.

Abstract: An optical sight ensures a more accurate aim at feebly discernible targets in the twilight and in dull weather. The sight includes an objective, a reticule, an erecting system consisting of a first and a second positive component, each of which is cemented of two lenses, and an eyepiece. The sight also includes a beam-splitting cube, the beam-splitting face made as a diagonal face, three mirrors and a third positive component cemented of two lenses, a first plane mirror parallel to the beam-splitting face of the cube on the same axis with the third positive component, a second plane mirror perpendicular to the first mirror in front of a focal plane of the eyepiece, and a third mirror tilted to the optical axis and faced with its reflective surface toward the eyepiece arranged between the eyepiece focal plane and the second component of the erecting system.

Abstract: A zoom lens includes, in order from an object side to an image side, first to fourth lens units having negative, positive, negative, and positive refractive power, respectively. Each lens unit moves during zooming so that a distance between the first lens unit and the second lens unit at the telephoto end is shorter than at the wide-angle end and a distance between the second lens unit and the third lens unit and a distance between the third lens unit and the fourth lens unit at the telephoto end are larger than those at the wide-angle end. A focal length of the third and fourth lens units, a focal length of the entire zoom lens at the wide-angle end, a focal length of the entire zoom lens at the telephoto end, and a sum of axial thicknesses of the first to fourth lens units are appropriately set.