US 4,792,219 AGranted

Large aperture long focus macro lens system

AssigneeOlympus Optical Co., Ltd.

InventorShin-ichi Mihara

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Abstract

A large aperture long focus macro lens system comprising a first lens group having positive refractive power, a stop, a second lens group having positive refractive power, and a third lens group in the order from the object side, the large aperture long focus marco lens system being arranged to be focused on an object at a short distance by advancing the lens system as a whole in the state that the first lens group, the stop and the second lens group are advanced integrally by varying the relative airspace in respect to the third lens group, the large aperture long focus macro lens system being arranged that aberrations are corrected favorably and the variation of aberrations at the time of focusing is small and that the working distance does not become short and the advancing amount of the lens system does not become large when focused on the object at a very short distance.

Claims7

Dependent claims

A large aperture long focus-macro lens system comprising, in the order form the object side, a first lens group having positive refractive power as a whole, a stop, a second lens group having positive refractive power as a whole, and a third lens group, consisting of a negative lens unit and one biconvex lens, said large aperture long focus macro lens system being arranged to advance the lens system as a whole, when focusing on an object at a short distance, in the state that said first lens group, said stop and said second lens group are advanced integrally at the same time as varying the airspace in respect to said third lens group, said large aperture long focus macro lens system being further arranged to fulfill the conditions (1) through (5) shown below:

(1) -0.4.phi.<.phi..sub.III <0.4.phi.
(2) 0.33<(.DELTA..sub.12 -.DELTA..sub.3)/.DELTA..sub.12 <0.85(.DELTA..sub.3 >0)
(3) 0.7.phi.<.DELTA..sub.A <1.8.phi.
(4) 0.6.DELTA.<-.phi..sub.A <1.7.phi.
(5) n.sub.A >n.sub.B
where, reference symbol .phi. represents the refractive power of the lens system as a whole, reference symbol .phi..sub.III represents the refractive power of the third lens group, reference symbol .DELTA..sub.12 represents the advancing amount of the first lens group, the stop and the second lens group, reference symbol .DELTA..sub.3 represents the advancing amount of the third lens group, reference symbol .phi..sub.A represents the refractive power of a positive lens in the third lens group, reference symbol .phi..sub.B represents the refractive power of a negative lens on the object side in the third lens group;
reference symbol n.sub.A represents the refractive index of the positive lens in the third lens group, and references symbol n.sub.B represents the refractive index of the negative lens on the object side in the third lens group.

4 more elements

Dependencies are inferred from the claim text.