Patent ID: 7639430

Claim:
A zoom lens comprising in order from the object side to the image side: a first lens unit of negative refractive power; and a second lens unit of positive refractive power, wherein at least the first lens unit and the second lens unit move on the optical axis so that the distance between the first lens unit and the second lens unit decreases during zooming from a wide-angle end to a telephoto end, wherein the first lens unit includes, in order from the object side to the image side, three negative lenses and a positive lens, at least one of the surfaces of the lenses being aspherical, wherein the first lens unit has, in order from the object side to the image side, two negative meniscus lenses concave toward the image side and one negative biconcave lens, and wherein when a spherical surface whose center of curvature is on the optical axis and that includes a point of the intersection of a lens surface and the optical axis and a point on the lens surface determined by an effective aperture is referred to as reference spherical surface of the lens surface, the following condition is satisfied: −2.8<( r 12+ r 21)/( r 12− r 21)<−1.0 where r 12 is the radius of curvature of the image-side reference spherical surface of the most object-side negative lens in the first lens unit, and r 21 is the radius of curvature of the object-side reference spherical surface of the second most object-side negative lens in the first lens unit.