US 5,805,359 A · Wide-angle lens system

Abstract

The invention provides a solution to a problem of allowing a symmetrical wide-angle lens system to have a large aperture ratio, and achieves an optical system which is well improved in terms of sagittal coma and curvature of field, and has a satisfactory vignetting factor as well. The optical system comprises basically a first lens group G1 having a negative refracting power, a second lens group G2 containing an aperture stop and having a positive negative power, and a third lens group having a negative refracting power. The second lens group G2 is divided into front and rear sub-groups G.sub.21 and G.sub.22, each having a positive refracting power, between which the aperture stop is located. The first lens group G1 comprises at least one negative meniscus lens convex on an object side; the front sub-group G.sub.21 of the second lens group comprises at least one set of cemented lens including a positive lens and a negative lens; and the rear sub-group G.sub.22 of the second group comprises at least one set of cemented lens including a positive lens and a negative lens. A third lens group G3 comprises at least one negative meniscus lens convex on an image side. An aspherical surface is used in any one of the lens groups.

Claims25

Dependent claims

A wide-angle lens system comprising, basically in order from an object side;

a first lens group having a negative refracting power;
a second lens group having a positive refracting power and including an aperture stop;
and
a third lens group having a negative refracting power, wherein
said second lens group is divided into front and rear sub-groups G.sub.21, and G.sub.22, each having a positive refracting power, between which said aperture stop is located,
said first lens group comprises at least one negative meniscus lens convex on the object side,
said front sub-group of said second lens group comprising at least one set of cemented lenses containing a positive lens and a negative lens, and
said rear sub-group of said second lens group comprising at least one set of cemented lenses containing a positive lens and a negative lens,
said third lens group comprises at least one negative meniscus lens convex on an image side,
an aspherical surface is used in any one of said lens groups, and
said wide-angle lens system is a fixed focus lens system.

8 more elements

A wide-angle lens system comprising, basically in order from an object side;

a first lens group having a negative refracting power;
a second lens group having a positive refracting power and including an aperture stop;
and
a third lens group having a negative refracting power, wherein
said second lens group is divided into front and rear sub-groups G.sub.21 and G.sub.22, each having a positive refracting power, between which said aperture stop is located,
said first lens group comprises at least one negative meniscus lens convex on the object side,
said front sub-group of said second lens group comprising at least one set of cemented lenses containing a positive lens and a negative lens, and
said rear sub-group of said second lens group comprising at least one set of cemented lenses containing a positive lens and a negative lens,
said third lens group comprises at least one negative meniscus lens convex on an image side, and
said wide-angle lens system is a fixed focus lens system in which focusing from an object at infinity on a finite object is effected by an inner focusing method in which said second lens group is moved from a reference position toward the object side without varying the entire length of said wide-angle lens system while the spacing between said first and second lens groups is decreased with an increase in the spacing between said second and third lens groups.

7 more elements

A wide-angle lens system comprising, basically in order from an object side:

a first lens group having a negative refracting power:
second lens group having a positive refracting power and including an aperture stop, and
a third lens group having a negative refracting power, wherein
said second lens group is divided into front and rear sub-groups G.sub.21 and G.sub.22, each having a positive refracting power, between which said aperture stop is located,
said first lens group comprises at least one negative meniscus lens convex on the object side,
said front sub-group of said second lens group comprising at least one set of cemented lenses containing a positive lens and a negative lens, and
said rear sub-group of said second lens group comprising at least one set of cemented lenses containing a positive lens and a negative lens,
said third lens group comprises at least one negative meniscus lens convex on an image side, and
said wide-angle lens system is a fixed focus lens system in which focusing from an object at infinity on a finite object is effected by moving the entire system toward the object side and, at the same time, varying the spacings between the respective lens groups or an inner space of a given lens group, so that aberration variations can be corrected.

6 more elements

Dependencies are inferred from the claim text.

Wide-angle lens system

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Wide-angle lens system

Life of this patent

Abstract

Claims25