US 6,982,834 B2
Wide-angle zoom lens including at least one aspheric lens surface
Kenichi Sato, Ageo (Japan)
Assigned to Fujinon Corporation, Saitama (Japan)
Filed on Sep. 09, 2004, as Appl. No. 10/936,750.
Claims priority of application No. 2003-320120 (JP), filed on Sep. 11, 2003.
Prior Publication US 2005/0057816 A1, Mar. 17, 2005
Int. Cl. G02B 15/14 (2006.01)
U.S. Cl. 359—682 20 Claims
OG exemplary drawing
 
1. A zoom lens comprising, arranged on an optical axis in order from the object side as follows:
a first lens group of negative refractive power;
a second lens group of positive refractive power and that includes a stop for controlling the amount of light that passes through the zoom lens; and
a third lens group of positive refractive power; wherein
the first and the second lens groups are moved so that the first and second lens groups become closer together during zooming from the wide-angle end to the telephoto end;
the second and third lens groups are moved relatively so that the second and third lens groups become farther apart during zooming from the wide-angle end to the telephoto end;
the third lens group is moved toward the object side during focusing from infinity to a close focus;
the first lens group includes, arranged on the optical axis in order from the object side, a first lens element of negative refractive power and a second lens element of positive refractive power, and at least one of said first lens element and said second lens element includes at least one aspheric lens surface;
the shape of said at least one aspheric lens surface is given by an aspheric lens equation that includes at least one non-zero coefficient of an even power of Y, and at least one non-zero coefficient of an odd power of Y, where Y is the distance of a point on the aspheric lens surface from the optical axis;
and the following conditions are satisfied:
36.0<θw<41.0
νd1−νd2>20.5
where
θw is the half-field angle of the zoom lens at the wide-angle end,
νd1 is the Abbe number at the d-line of said first lens element, and
νd2 is the Abbe number at the d-line of said second lens element.