| US 7,333,275 B2 | ||
| Zoom lens system and image pickup apparatus including the same | ||
| Makoto Sekita, Yokohama (Japan) | ||
| Assigned to Canon Kabushiki Kaisha, Tokyo (Japan) | ||
| Filed on May 16, 2005, as Appl. No. 11/129,821. | ||
| Claims priority of application No. 2004-148893 (JP), filed on May 19, 2004. | ||
| Prior Publication US 2005/0259334 A1, Nov. 24, 2005 | ||
| Int. Cl. G02B 15/14 (2006.01) | ||
| U.S. Cl. 359—689 [359/738] | 15 Claims |
| 1. A zoom lens system having an optical axis and object and image sides, comprising:
a first lens unit of negative optical power;
a second lens unit of positive optical power, the second lens unit being disposed on the image side of the first lens unit,
wherein the second lens unit includes a lens element disposed closest to the object side, the lens element including:
a rim;
a surface on the object side and having a vertex; and
an intersection point defined by an intersection between the surface and the rim;
a third lens unit of positive optical power, the third lens unit being disposed on the image side of the second lens unit;
and
an aperture stop determining an effective aperture diameter of the lens system, the position of the aperture stop along the
optical axis being between the vertex and the intersection point and being a negative distance with respect to the vertex,
indicating that the position of the aperture stop is on the image side of the vertex,
wherein the first to third lens units are provided in order from the object side to the image side such that there is no lens
unit between the second lens unit and the third lens unit,
wherein spaces between the first, second and third lens units vary during zooming, and
wherein a focal length of the first lens unit (f1), and a focal length at the wide-angle end of the entire zoom lens system (fw) satisfy the following condition:
−2.6<f1/fw<−1.6.
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