Abstract: An optical system in which a maximum value of a height from an optical axis of a paraxial marginal ray closer to an expanded side than a point of intersection between an optical axis and a paraxial chief ray, includes a lens unit Lr including at least one refractive optical element Gn of a negative refractive power. In the optical system, ?d (Gn) as an Abbe number of a material of the refractive optical element Gn, ?gF (Gn) as a partial dispersion ratio regarding g and F-lines, FGn as a focal lengths of the refractive optical element Gn, and Fr as focal lengths of the lens unit Lr are set appropriately.

Abstract: A zoom lens including, in an order from an object side to an image side, a first lens group having a positive refracting power, a second lens group having a negative refracting power, a rear group including at least one lens group, the zooming operation being performed by changing a spacing of the lens groups, wherein the zoom lens has an aperture stop and, when the second lens group is taken as a first focus group and a sub-lens group constituting a portion of one lens group of the rear group is taken as a second focus group, the lens structure and the movement amount of the first and second focus groups are set appropriately.

Abstract: An optical system in which a maximum value of a height from an optical axis of a paraxial marginal ray closer to an expanded side than a point of intersection between an optical axis and a paraxial chief ray, includes a lens unit Lr including at least one refractive optical element Gn of a negative refractive power. In the optical system, ?d (Gn) as an Abbe number of a material of the refractive optical element Gn, ?gF (Gn) as a partial dispersion ratio regarding g and F-lines, FGn as a focal lengths of the refractive optical element Gn, and Fr as focal lengths of the lens unit Lr are set appropriately.

Abstract: At least one exemplary embodiment is directed to a zoom lens including a plurality of lens units, in which an interval between respective adjacent lens units varies during zooming, an aperture stop, and a refractive optical element made of a solid material having an Abbe number (?d) and a relative partial dispersion (?gF) satisfying the following condition: ?gF?(?1.665×10?7·?d3+5.213×10?5·?d2?5.656×10?3·?d+0.755)>0. The refractive optical element is located at a position in which distances (dw, dt) from the aperture stop to the refractive optical element on an optical axis at a wide-angle end and a telephoto end, respectively, satisfy the following condition: dt/dw>1.1.

Abstract: At least one exemplary embodiment is directed to A retro focus optical system that is capable of sufficiently correcting and/or reducing various aberrations including the chromatic aberration. The optical system includes a refractive optical element including a solid material. The Abbe number ?d and the partial dispersion ratio ?gF of the solid material along with a shape of the refractive optical element can reduce various aberrations.

Abstract: At least one exemplary embodiment is directed to a zoom lens including a plurality of lens units, in which an interval between respective adjacent lens units varies during zooming, an aperture stop, and a refractive optical element made of a solid material having an Abbe number (?d) and a relative partial dispersion (?gF) satisfying the following condition: ?gF?(?1.665×10?7·?d3+5.213×10?5·?d2?5.656×10?3·?d+0.755)>0. The refractive optical element is located at a position in which distances (dw, dt) from the aperture stop to the refractive optical element on an optical axis at a wide-angle end and a telephoto end, respectively, satisfy the following condition: dt/dw>1.1.

Abstract: At least one exemplary embodiment is directed to A retro focus optical system that is capable of sufficiently correcting and/or reducing various aberrations including the chromatic aberration. The optical system includes a refractive optical element including a solid material. The Abbe number ?d and the partial dispersion ratio ?gF of the solid material along with a shape of the refractive optical element can reduce various aberrations.