Patent ID: 6441968
Filing Date: 2002-08-27
Classification: G02B

Abstract:
A zoom lens comprising, in the order of an increasing distance from an object,a first lens group having a positive refractive power and being fixed with respect to an image plane, a second lens group having a negative refractive power and being in charge of a variable power action by being moved on an optical axis, a third lens group having a positive refractive power and being fixed with respect to the image plane, and a fourth lens group having a positive refractive power and moving on the optical axis so that it keeps the image plane following up the movement of the second lens group and the object at a constant position with respect to a standard plane, wherein said first lens group comprises, in the order of an increasing distance from the object, a lens having a negative refractive power, a lens having a positive refractive power, and a meniscus lens having a positive refractive power and having a convex surface facing the object side; said second lens group comprises, in the order of an increasing distance from the object, a lens having a negative refractive power, a biconcave lens having a negative refractive power, and a lens having a positive refractive power, having a convex surface facing the object side, and being connected to said biconcave lens; said third lens group comprises, in the order of an increasing distance from the object, a biconvex lens having a positive refractive power, a lens having a positive refractive power and having a convex surface facing the object side, and a lens having a negative refractive power, wherein said lens having a negative refractive power of said third lens group is connected to the lens having a positive refractive power and having a convex surface facing the object side of said third lens group, said lens having a negative refractive lens of said third lens group has a concave surface facing the side of the image plane, and said connected lenses as a whole have negative refractive power; said forth lens group comprises one lens; each of said second lens group, the third lens group and the fourth lens group contains at least one aspherical surface; and the following relationships are satisfied: 2.01<2.3, â€ƒ0.24/L<0.35,and0.34<0.4 where CL1 is an effective aperture of the lens positioned closest to the object in said first lens group, L is a distance between the lens positioned closest to the object in said first lens group and the image plane, f4 is a focal distance of said fourth lens group, and fw is a focal distance at a wide-angle end.