Patent ID: 6124990
Filing Date: 2000-09-26
Classification: G02B

Abstract:
A close-up photographing lens capable of forming an image of an object and changing focus from an infinite focus state to a most close-up focus state, comprising, objectwise to imagewise along an optical axis:a) a first lens group having positive refractive power;b) a second lens group having positive refractive power and axially separated from said first lens group by an air space D12;c) an aperture stop between said first lens group and said second lens group;d) a relay optical system having positive refractive power, wherein said relay optical system includes a third lens group having negative refractive power and a fourth lens group having positive refractive power, said fourth lens group including at least one positive lens and at least one negative lens, wherein said third and fourth lens groups are axially separated by an air space d.sub.NP and the following condition is satisfied: 0.1<d.sub.NP /Y<5.0, further wherein said fourth lens group has at least one cemented lens comprising a positive single lens and a negative single lens and the following condition is satisfied: .nu..sub.N <30 wherein, .nu..sub.N is a minimum Abbe number for the negative lenses in said fourth lens group;e) wherein the correction lens is designed such that, when changing focus from the infinite focus state to the most close-up focus state, said first lens group and said second lens group move objectwise on different trajectories, and said air space D12 is narrower when in the most close-up focus state than when in the infinite focus state;f) wherein the following conditions are satisfied0.25<.vertline..beta..sub.MOD .vertline.2.0<BF/Y<10.00.02<.DELTA.D12/BF<3.0wherein .beta..sub.MOD is a photographic magnification in the most close-up focus state, BF is a back focus in the infinite focus state, Y is a maximum height of the image, and .DELTA.D12 is a change in said air space D12 when focusing from the infinite focus state to the most close-up focus state; andg) further wherein the following condition is satisfied:1.0<.DELTA.1.multidot..vertline..beta..sub.MOD .vertline./Y<10.0wherein .DELTA.1 is an amount of movement of said first lens group when focusing from the infinite focus state to the most close-up focus state, said amount of movement .DELTA.1 having a positive sign when said first lens group moves objectwise.