Patent ID: 6157493
Filing Date: 2000-12-05
Classification: G02B

Abstract:
A zoom lens comprising:arranged sequentially from an object side to an image surface side, a first lens group having a positive refracting power;a second lens group having a negative refracting power and movable in position along the direction of the optical axis thereby primarily to change a magnification;a third lens group having a positive refracting power;a fourth lens group having a positive refracting power and movable in position along the direction of the optical axis thereby to correct a variation of an image position due to a magnification change and also to focus an image; anda fifth lens group having a substantially zero refracting power;wherein said third lens group is configured of a joint lens of a convex lens and a concave lens, and said fifth lens group is configured of a joint lens of a concave lens and a convex lens; andwherein the following conditions-0.018<1/.upsilon.3<0.01810<.vertline..upsilon.5.1-.upsilon.5.2.vertline.1<.vertline.r5.2/fw.multidot.tan .omega.W.vertline.<3are satisfied, where .upsilon.3 is an equivalent Abbe's number of the third lens group, .upsilon.5.1 is an Abbe's number of the lens of the fifth lens group nearer to the object side, .upsilon.5.2 is an Abbe's number of the lens of the fifth lens group nearer to the image surface, r5.2 is a radius of curvature of the lens joint surface of the fifth lens group, fW is a focal length of the whole lens system at a wide angle edge, and .omega.W is a half field angle at the wide angle edge.