Patent ID: 6519094
Filing Date: 2003-02-11
Classification: G02B

Abstract:
A zoom lens comprising, a first lens group having a positive refracting power that is fixed, a second lens group having a negative refracting power and varying power by moving along an optical axis, a third lens group having a positive refracting power that is fixed, and a fourth lens group having a positive refracting power and moving along the optical axis so that it keeps an image plane following up the movement of the second lens group and an object at a constant position with respect to a standard plane, the first, second, third and fourth lens groups being disposed from a side near the object to a side far away from the object in this order;wherein the first lens group comprises a negative lens, a positive lens, and a positive lens having a convex surface facing the object side, disposed from the object side in this order; the second lens group comprises a negative lens and a cemented lens of a negative lens and a positive lens in which the negative lens is located at the object side being disposed from the object side in this order, wherein at least one surface of the lenses is an aspherical surface; the third lens group comprises a positive lens and a negative meniscus lens having a convex surface facing the object side, disposed from the object side in this order, wherein at least one surface of the lenses is an aspherical surface, and the fourth lens group comprises a cemented lens of a negative lens and a positive lens in which the negative lens is located at the object side, wherein at least one surface of the lens has an aspherical surface; and the following relationships are satisfied: 9.01/fw<10.5 1.22/fw|<1.6 4.53/fw<6.0 4.04/fw<5.5 where f1 is a composed focal length of the first lens group, f2 is a composed focal length of the second lens group, f3 is a composed focal length of the third lens group, f4 is a composed focal length of the fourth lens group, and fw is a composed focal length of the entire system at a wide-angle end.