Projection lens
AssigneeNikon Corporation
InventorMasaya Nakajima
Life of this patent
Estimating the term…
Abstract
A projecting lens for projecting the image of an object onto a screen comprising, in the order from the screen side, a first lens group of a positive refractive power; a cemented second lens group of a positive refractive power; a third lens group of a negative refractive power; and a fourth lens group of a positive refractive power with a concave surface at the screen side; wherein each of the first and third lens group has at least an aspherical face, and the focal length f of the projecting lens, the focal length f1 of the first lens group and the focal length f3 of the third lens group satisfy conditions: 0<f/f1<0.25 and -0.1<f/f3<0.
Claims16
A projection lens for projecting the image of an object onto a screen, comprising in the order from the screen side:
- a first lens group of a positive refractive power;
- a cemented second lens group of a positive refractive power;
- a third lens group of a negative refractive power;
- and
- a fourth lens group of a negative refractive power with a concave face at the screen side;
- wherein each of the first and third lens groups has at least an aspherical face, and the focal length f of the entire lens system, the focal length f1 of said first lens group and the focal length f3 of said third lens group satisfy following conditions:
- 0<f/f1<0.25
- -0.1<f/f3<0.
A projection lens for projecting the image of an object onto a screen, comprising in the order from the screen side:
- a first lens group of a positive refractive power;
- a second lens group of a positive refractive power;
- a third lens group of a positive refractive power;
- and
- a fourth lens group of a negative refractive power;
- wherein said first lens group includes, in the order from the screen side, a positive meniscus-shaped first lens component convex to the screen, a negative meniscus-shaped second lens component convex to the screen, and a meniscus-shaped aspherical plastic third lens component convex to the screen, and said projection lens satisfies following conditions:
- 0<f/f1<0.25
- 0<f/f3<0.3
- 5<(RB+RA)/(RB-RA)<12
- -7<(RD+RC)/(RD-RC)<-5.1
- where f is the focal length of the entire lens system;
- f1 is the focal length of said first lens group;
- f3 is focal length of said third lens group;
- RA and RB are radii of curvature respectively of a face closest to the screen and a face closest to the object of said first lens component in said first lens group;
- and RC and RD are those respectively of a face closest to the screen and a face closest to the object of said second lens component.
A projection lens according to claim 12, satisfying a condition:
- 0.9<D.sub.12 /D.sub.24 <1.5
- wherein D.sub.12 is the axial distance from the top point of a lens face closest to the screen in said first lens group to the top point of a lens face closest to the screen in said second lens group, and D.sub.24 is the axial distance from the top point of a lens face closest to the object in the second lens group to the top point of a lens face closest to the screen in the fourth lens group.
A projection lens for projecting the image of an object onto a screen, comprising in the order from the screen side:
- a first lens group of a positive refractive power including, in the order from the screen side, a positive meniscus-shaped first lens component convex to the screen, a negative meniscus-shaped second lens component convex to the screen, and a meniscus-shaped aspherical plastic third lens component convex to the screen;
- a cemented second lens group of a positive refractive power including a biconvex-shaped positive lens component and a meniscus-shaped negative lens component;
- a third lens group of a negative refractive power, being composed of a single lens;
- and
- a fourth lens group of a negative refractive power, having a concave face at the screen side;
- wherein each of said first and third lens groups has at least one aspherical face.
Dependencies are inferred from the claim text.