Wide-angle zoom lens
First Claim
1. A wide-angle zoom lens comprising, in order from the object side:
- a first lens group of negative refractive power and which includes at least one negative lens element having different radii of curvature on its opposite surfaces, with the smaller radius of curvature surface being concave and on the image side;
a second lens group of positive refractive power and which includes at least one biconvex lens element;
a third lens group of positive refractive power and which consists only of a single positive lens element; and
a fourth lens group of positive refractive power;
wherein, in zooming, said first lens group and said fourth lens group remain at a fixed position on the optical axis and said second lens group and said third lens group are moved on the optical axis, thereby changing the focal length of the wide-angle zoom lens while maintaining the image at a fixed position; and
the following conditions are satisfied,
space="preserve" listing-type="equation">-2.5<
f.sub.1 /f.sub.w <
-1.5
space="preserve" listing-type="equation">2.0<
f.sub.2 /f.sub.w <
4.0.where f1 is the focal distance of the first lens group, fw is the focal distance of wide-angle zoom lens at the wide angle end, and f2 is the focal distance of the second lens group.
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Accused Products
Abstract
A wide-angle zoom lens is disclosed having four lens groups of negative, positive, positive, and positive refractive power, in order from the object side. By satisfying prescribed conditions, the overall length as well as the outer diameter of the wide-angle zoom lens can be kept small, the number of lens elements required can be minimized so as to keep manufacturing costs low, yet a high-quality image is provided over the entire range of zoom. During zooming, the first and fourth lens groups remain in a fixed position while the second and third lens groups are moved along the optical axis. The first lens group G1 includes at least one negative lens element with a concave surface of strong curvature on the image side. The second lens group G2 has at least one biconvex lens. The third lens group G3 may consist of a single positive lens. The following conditions are satisfied:
-2.5<f.sub.1 /f.sub.w <-1.5
2.0<f.sub.2 /f.sub.w <4.0
where
f1 of the focal distance of the first lens group G1,
fw is the focal distance of the zoom lens at the wide-angle end, and
f2 is the focal distance of the second lens group G2.
Further, a diaphragm which serves as an aperture stop may be positioned between the first lens group and the second lens group to vary the brightness in the image plane as well as to control certain aberrations, and to ensure the outer diameter of the first lens group is small
47 Citations
9 Claims
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1. A wide-angle zoom lens comprising, in order from the object side:
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a first lens group of negative refractive power and which includes at least one negative lens element having different radii of curvature on its opposite surfaces, with the smaller radius of curvature surface being concave and on the image side; a second lens group of positive refractive power and which includes at least one biconvex lens element; a third lens group of positive refractive power and which consists only of a single positive lens element; and a fourth lens group of positive refractive power; wherein, in zooming, said first lens group and said fourth lens group remain at a fixed position on the optical axis and said second lens group and said third lens group are moved on the optical axis, thereby changing the focal length of the wide-angle zoom lens while maintaining the image at a fixed position; and
the following conditions are satisfied,
space="preserve" listing-type="equation">-2.5<
f.sub.1 /f.sub.w <
-1.5
space="preserve" listing-type="equation">2.0<
f.sub.2 /f.sub.w <
4.0.where f1 is the focal distance of the first lens group, fw is the focal distance of wide-angle zoom lens at the wide angle end, and f2 is the focal distance of the second lens group. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification