Zoom optical system and camera comprising the same
View Patent ↗The invention relates to a compact two-group zoom optical system which has an angle of view of 70° or greater at the wide-angle end and satisfactory image-formation capability all over the zoom range while maintaining a zoom ratio of 3 or greater. The zoom optical system comprises a first lens group G 1 having positive refracting power and a second lens group G 2 having negative refracting power. For zooming from the wide-angle end to the telephoto end, the respective lens groups move toward the object side while the spacing between the first lens group G 1 and the second lens group G 2 becomes narrow.
1. A zoom lens optical system having a zoom ratio of 3 or greater and comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
said first lens group consists of, in order from an object side thereof, a first lens component (U 1 ) that has negative refracting power and in which a surface located nearest to an object side thereof is concave on the object side, a second lens component (U 2 ) having positive refracting power, a third lens component (U 3 ) having negative or positive refracting power and a fourth lens component (U 4 ) having positive refracting power, wherein the respective lens components in the first lens group consist of a single lens or a doublet and satisfy the following conditions:
0.5 <|f G1 /f 11 |<3 (7)
0.4 <f G1 /f 13 <0.1 (8)
where f G1 is a focal length of the first lens group, f 11 is a focal length of the first lens component, and f 13 is a focal length of the third lens component.
2. The zoom optical system according to claim 1 , wherein at least one surface of the second or fourth lens component in the first lens group is defined by an aspheric surface.
3. A camera which uses a zoom optical system as recited in claim 1 as a phototaking lens and comprises a finder disposed on an optical path different from an optical path for said zoom optical system for observing a phototaking range defined by said phototaking lens.
4. A zoom lens optical system comprising, in order from an object side thereof, a first lens group having positive refracting power and a second lens group having negative refracting power in which, for zooming from a wide-angle end to a telephoto end of the zoom lens optical system, the respective lens groups move toward the object side with a decreasing spacing between the first lens group and the second lens group, wherein:
said first lens group consists of, in order from an object side thereof, a first lens component (U 1 ) that has negative refracting power and in which a surface located nearest to an object side thereof is concave on the object side, a second lens component (U 2 ) that has positive refracting power and is in a meniscus form convex on an object side thereof, a third lens component (U 3 ) that is a doublet consisting of a negative lens and a positive lens in order from an object side thereof and has negative or positive refracting power and a fourth lens component (U 4 ) having positive refracting power.
5. The zoom optical system according to claim 1 or 4 , which has an angle of view of 70° or greater at the wide-angle end.
6. A camera which uses a zoom optical system as recited in claim 4 as a phototaking lens and comprises a finder disposed on an optical path different from an optical path for said zoom optical system for observing a phototaking range defined by said phototaking lens.
7. A zoom optical system, comprising, in order from an object side thereof,
a first lens group having positive refracting power, and
a second lens group having negative refracting power, in which upon zooming from a wide-angle end to a telephoto end of the zoom lens, the first and second lens groups move toward the object side while a spacing therebetween becomes narrow, wherein:
only the first and second lens groups define lens groups having positive or negative refracting power, and
the first lens group consists of, in order from an object side thereof,
a first lens component (U 1 ) having negative refracting power with a surface nearest to an object side thereof being concave on the object side,
a second lens component (U 2 ) that has positive refracting power and is convex on an object side thereof,
a third lens component (U 3 ) composed of a doublet consisting of, in order from an object side thereof, a negative lens element and a positive lens element, and
a fourth lens component (U 4 ) having positive refracting power,
wherein the first lens component (U 1 ) in the first lens group is a single lens element in a meniscus form concave on an object side thereof.
8. The zoom optical system according to claim 7 , wherein the second lens component (U 2 ) in the first lens group is a single lens element in which an absolute value of a radius of curvature of a convex surface on an object side thereof is smaller than an absolute value of curvature of a surface on an image side thereof.
9. The zoom optical system according to claim 7 , wherein the doublet that is the third lens component (U 3 ) in the first lens group is a doublet in which a double-concave negative lens element and a double-convex positive lens element are cemented together.
10. The zoom optical system according to claim 7 , wherein the fourth lens component (U 4 ) in the first lens group is a single lens element in a double-convex form.
11. A camera, in which a zoom optical system as recited in claim 7 is used as a phototaking lens and which comprises a finder located on an optical path different from that for the zoom optical system for visually identifying a phototaking range by the phototaking lens.
12. A zoom optical system, comprising, in order from an object side thereof,
a first lens group having positive refracting power, and
a second lens group having negative refracting power, in which upon zooming from a wide-angle end to a telephoto end of the zoom lens, the first and second lens groups move toward the object side while a spacing therebetween becomes narrow, wherein:
only the first and second lens groups define lens groups having positive or negative refracting power, and
the first lens group consists of, in order from an object side thereof,
a first lens component (U 1 ) having negative refracting power with a surface nearest to an object side thereof being concave on the object side,
a second lens component (U 2 ) that has positive refracting power and is convex on an object side thereof,
a third lens component (U 3 ) composed of a doublet consisting of, in order from an object side thereof, a negative lens element and a positive lens element, and
a fourth lens component (U 4 ) having positive refracting power,
wherein:
the first lens component (U 1 ) in the first lens group is a single lens element in a meniscus form that is concave on an object side thereof,
the second lens component (U 2 ) in the first lens group is a single lens element in which an absolute value of a radius of curvature of a convex surface on an object side thereof is smaller than that of a surface on an image side thereof,
the doublet that is the third lens component (U 3 ) in the first lens group is a doublet in which a double-concave negative lens element and a double-convex positive lens element are cemented together, and
the fourth lens component (U 4 ) in the first lens group is a single lens element in a double-convex form.
13. The zoom optical system according to claim 7 or 12 , wherein a stop is interposed between the first lens group and the second lens group.
14. The zoom optical system according to claim 7 or 12 , wherein the second lens group comprises a positive meniscus lens component convex on an image side thereof and a negative meniscus lens component convex on an image side thereof.
15. The zoom optical system according to claim 7 or 12 , has an angle of view of 70° degrees or greater at the wide-angle end.
16. The zoom optical system according to claim 7 or 12 , wherein the first lens group further comprises a plurality of aspheric surfaces and the second lens group further comprises an aspheric surface.
17. A camera, in which a zoom optical system as recited in claim 12 is used as a phototaking lens and which comprises a finder located on an optical path different from that for the zoom optical system for visually identifying a phototaking range by the phototaking lens.
18. A zoom optical system, comprising, in order from an object side thereof,
a first lens group having positive refracting power, and
a second lens group having negative refracting power, in which upon zooming from a wide-angle end to a telephoto end of the zoom lens, the first and second lens groups move toward the object side while a spacing therebetween becomes narrow, wherein:
only the first and second lens groups define lens groups having positive or negative refracting power, and
the first lens group consists of, in order from an object side thereof,
a first lens component (U 1 ) having negative refracting power with a surface nearest to an object side thereof being concave on the object side,
a second lens component (U 2 ) that has positive refracting power and is convex on an object side thereof,
a third lens component (U 3 ) composed of a doublet consisting of, in order from an object side thereof, a negative lens element and a positive lens element, and
a fourth lens component (U 4 ) having positive refracting power, which has a zoom ratio of 3 or higher.