Lens system for reading image
AssigneeMahk Co., Ltd.
InventorKazuo Kikutani
Life of this patent
Estimating the term…
Abstract
A lens system used for reading an image, the system being constructed of two lenses and presents sufficient performance for reading an image in an image scanner, a facsimile, etc. The system is constructed of a positive meniscus image-forming lens and a positive meniscus auxiliary lens. The convexes of both lenses face an object. The image-forming lens has at least one aspherical surface or it has an aspherical surface formed by joining an aspherical surface layer formed of a transparent material to the surface of a spherical glass lens. Both surfaces of the auxiliary lens are aspherical.
Claims2
A lens system for reading an image, said system comprising a positive meniscus image-forming lens the convex of which faces an object and a positive meniscus auxiliary lens the convex which faces said object in the order from said object, wherein said image-forming lens has at least one aspherical surface and wherein both surfaces of said auxiliary lens are aspherical, said system satisfying the conditions expressed by the following formulas;
- 0.7<f/f.sub.1 <1 (1)
- 1.7<f.sub.2 /f.sub.1 ( 2)
- where f indicates the focal length of the overall system;
- f.sub.1 shows the focal length of said image-forming lens;
- and f.sub.2 represents the focal length of said auxiliary lens;
- said system also satisfying the conditions expressed by the following formulas;
- .nu..sub.1 >56 (3)
- 0.8<r.sub.1 /r.sub.2 <1.2 (4)
- where .nu..sub.1 indicates the Abbe's number of a material forming said image-forming lens;
- r.sub.1 shows the radius of curvature of the front surface of said image-forming lens on the axis;
- and r.sub.2 represents the radius of curvature of the rear surface of said image-forming lens on the axis.
A lens system for reading an image, said system comprising a positive meniscus image-forming lens the convex of which faces an object and a positive meniscus auxiliary lens the convex which faces said object in the order from said object, wherein said image-forming lens has at least one aspherical surface which is formed by joining an aspherical surface layer formed of a transparent material to the surface of a spherical glass lens, and wherein both surfaces of said auxiliary lens are aspherical, said system satisfying the conditions expressed by the following formulas;
- 0.7<f/f.sub.1 <1 (1)
- 1.7<f.sub.2 /f.sub.1 ( 2)
- where f indicates the focal length of the overall system;
- f.sub.1 shows the focal length of said image-forming lens;
- and f.sub.2 represents the focal length of said auxiliary lens, said system also satisfying the conditions expressed by the following formulas;
- .nu..sub.1 >56 (5)
- 0.8<r.sub.1 /r.sub.2 <1.2 (6)
- where .nu..sub.1 indicates the Abbe's number of a material forming the spherical glass lens portion of said image-forming lens;
- r.sub.1 shows the radius of curvature of the front surface of said image-forming lens on the axis;
- and r.sub.2 represents the radius of curvature of the rear surface of said image-forming lens on the axis.
Dependencies are inferred from the claim text.