Zoom lens system
AssigneeOlympus Optical Co., Ltd.
InventorHironori Shibata
Life of this patent
Estimating the term…
Abstract
A zoom lens system having a field angle of about 44.degree. to 47.degree. at the wide angle end, a zoom ratio of about 2.6 to 3 and an F-number on the order of 2.8, which is reduced in value while making sure of a back focus and which is improved in terms of its capability to form images. The zoom lens system includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power and a fourth lens group consisting of three lens elements and having a positive refractive power as a whole, the second and third lens groups being movable for zooming.
Claims22
A zoom lens system consisting of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power and a fourth lens group consisting of three lens elements and having a positive refractive power as a whole, said second and third lens groups being moved in zooming, thereby effecting variable power and said zoom lens system satisfying the following condition (1):
- 0.1<(r.sub.4IF +r.sub.4IR)/(r.sub.4IF -r.sub.4IR)<3.0 (1)
- wherein r.sub.4IF is the radius of curvature of a front surface of the lens in the fourth lens group that is proximate to the object side and r.sub.4IR is the radius of curvature of a rear surface of the lens in the fourth lens group that is proximate to the object side;
- wherein said first lens group is fixed for zooming.
A zoom lens system consisting of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power and a fourth lens group consisting of three lens elements and having a positive refractive power as a whole, said second and third lens groups being moved in zooming, thereby effecting variable power and a zoom lens system satisfying the following condition (2):
- 0.5<f.sub.IV /f.sub.W <1.2 (2)
- wherein f.sub.IV is the focal length of the fourth lens group and f.sub.W is the focal length of the total system at the wide angle end;
- wherein the first lens group remains fixed for zooming.
A zoom lens system consisting of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power and a fourth lens group consisting of three lens elements and having a positive refractive power as a whole, said second and third lens groups being moved in zooming, thereby effecting variable power and said zoom lens system satisfying the following condition (3):
- 0.4<.SIGMA.d.sub.IV /f.sub.W <1.12 (3)
- wherein .SIGMA.d.sub.IV is the total thickness of the fourth lens group from a first surface thereof to a final surface thereof, and f.sub.W is the focal length of the total system at the wide angle end;
- wherein said first lens group remains fixed for zooming.
Dependencies are inferred from the claim text.