Patent ID: 7023623
Filing Date: 2006-04-04
Classification: G02B

Abstract:
1. A zoom lens comprising a first lens group with a negative power, a second lens group with a positive power to whose object side an aperture stop has been fixed, and a third lens group with a positive power, arranged in that order from an object side to an image plane side; wherein said first lens group comprises a first lens that is a negative meniscus lens whose surface with strong curvature is facing the image plane side, and a second lens that is a positive lens whose surface with strong curvature is facing the object side, arranged in that order from the object side; wherein said second lens group comprises a third lens that is a positive lens whose surface with strong curvature is facing the object side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens, arranged in that order from the object side; wherein said third lens group comprises a seventh lens that is a positive lens; wherein the image plane side surface of said first lens and the object side surface of said third lens are aspherical surfaces whose local radius of curvature is monotonically increased as distance from the center increases; wherein one of the surfaces of said seventh lens is an aspherical surface; wherein when zooming from a wide-angle end to a tele end when an object distance is ∞, said first lens group retreats to the image plane side and then moves toward the object side and said second lens group moves monotonically toward the object side; and wherein when L are satisfied, a zoom ratio is ×2.5 to ×3.2 if the object distance is ∞, and a field angle at the wide-angle end is 60° to 70°.