Patent ID: 6028716
Filing Date: 2000-02-22
Classification: G02B

Abstract:
A zoom lens comprising, from front to rear, a first lens group of negative refractive power, a second lens group of positive refractive power, said second lens group including, from front to rear, a lens unit of positive refractive power, a lens unit of negative refractive power and a lens unit of positive refractive power, and a third lens group of negative refractive power, zooming being performed by varying a separation between each adjacent two of said lens groups, wherein for an object at infinity, letting heights of incidence for a wide-angle end and a telephoto end of an on-axial ray of light on the i-th lens surface, when counted from the object side, be denoted by Hiw (Hiw>0) and Hit (Hit>0), respectively, and letting heights of incidence for the wide-angle end and the telephoto end of an off-axial principal ray of light from the maximum angle of field on the i-th lens surface, when counted from the object side, be denoted by Hbiw and Hbit, respectively, an aspheric surface of such shape that a negative refractive power gets progressively stronger as going from a lens center to a lens margin is applied to a lens surface Ra located on the object side, which lens surface is of negative refractive power and which lens surface is concave toward the object side and which lens surface satisfies the following conditions:Hiw>.vertline.Hbiw.vertline.Hit>.vertline.Hbit.vertline.,and wherein said zoom lens satisfies the following conditions:0.7.ltoreq..vertline.Fw/f3.vertline..ltoreq.2.50.2.ltoreq..vertline.Fw/f1.vertline..ltoreq.1.01.0.ltoreq.Fw/f2.ltoreq.2.5where Fw is the shortest focal length of the entire system, f3 is the focal length of said third lens group and f1 and f2 are the focal lengths for the wide-angle end of said first lens group and said second lens group, respectively.