Patent ID: 6925253
Filing Date: 2005-08-02
Classification: G02B

Abstract:
1. A zoom lens comprising a first lens group with a negative power, an aperture stop, a second lens group with a positive power, and a third lens group with a positive power, arranged in that order from an object side to an image plane side, wherein the first lens group comprises a first lens that is a negative meniscus lens whose surface with strong curvature is facing the image plane, a second lens that is a negative meniscus lens whose surface with strong curvature is facing the image plane, and a third lens that is a positive lens, arranged in that order from the object side; wherein the second lens group comprises a fourth lens that is a positive lens, a fifth lens that is a positive lens, a sixth lens that is a negative lens, and a seventh lens that is a positive lens, arranged in that order from the object side; wherein the third lens group comprises a single positive lens, and can be moved in the optical axis direction for focus adjustment; wherein the image plane-side surface of the first lens or the second lens is an aspherical surface whose local radius of curvature is monotonically increased as distance from the center increases; wherein the object-side surface of the fourth lens is an aspherical surface whose local radius of curvature is monotonically increased as distance from the center increases; wherein the object-side surface of the seventh lens is an aspherical surface whose local radius of curvature is monotonically increased as distance from the center increases, or the image plane-side surface of the seventh lens is an aspherical surface whose local radius of curvature is monotonically decreased as distance from the center increases; wherein when zooming from a wide-angle end to a telescope end, an air gap between the first lens group and the second lens group is reduced and an air gap from the second lens to the third lens group is increased; wherein a zoom ratio is ×2.5 to ×3.2 if the shooting distance is ∞, wherein the angle of view at the wide-angle end is approximately 60°; and wherein when the shooting distance is ∞, f are satisfied.