Patent ID: 8248716
Filing Date: 2012-08-21
Classification: G02B

Abstract:
1. An imaging optical system provided, comprising, in order from an object side to an image side thereof, a front lens group having a plurality of lenses including at least one negative lens, an aperture stop, and a rear lens group having positive refracting power, wherein: said rear lens group comprises, in order from the object side, a lens subgroup having positive refracting power and a focus lens group that has positive refracting power and moves upon focusing, and a lens located on the closest to object side in said front lens group always remains fixed in position, with satisfaction of the following conditions (1) and (2): where f is a focal length of the whole imaging optical system, fn is a focal length of a first negative lens on the closest to object side of negative lenses in said front lens group provided that lenses located on the closest to object side are not necessarily of negative power, fb is a back focus of the imaging optical system upon focusing on an object point at infinity provided that the back focus is a length, as calculated on an air basis, from an image-side refractive surface of a lens located on the closest to image side in said rear lens group to an imaging plane, and IHω is a distance from an optical axis of a position where a chief ray from a maximum incident half angle of view upon focusing on an object point at infinity is imaged at the imaging plane.