Optical: systems and elements – Lens – Multiple component lenses
Reexamination Certificate
2000-02-22
2001-09-11
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
Multiple component lenses
C359S715000
Reexamination Certificate
active
06288850
ABSTRACT:
RELATED APPLICATIONS
This application claims the priority of Japanese Patent Application No. 11-054035 filed on Mar. 2, 1999, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image readout apparatus such as a facsimile machine, image scanner, or the like; and an image readout lens employed as an optical system thereof. In particular, the present invention relates to an image readout lens for reducing or enlarging images, and an image readout apparatus using the same.
2. Description of the Prior Art
Imaging lenses for reading out images employed in facsimile machines, image scanners, and the like of a type in which a reduced or enlarged image of an original is formed onto an imaging device such as CCD are basically required to have a high resolution at the imaging magnification in use, a large amount of marginal illumination, and a low distortion. In addition, along with recent demands for making the whole optical apparatus more compact and less expensive, these lenses are required to have a compact size and to be made at a lower cost.
As an imaging lens which can fulfill these requirements, one having a four-element configuration disclosed in Japanese Unexamined Patent Publication No. 9-101452 has been known.
Though the four-element imaging lens disclosed in the above-mentioned publication can yield a favorable quality of readout images over a wide angle, brighter image readout lenses have been desired for use in line sensors for copiers and the like in view of demands for higher readout speed.
SUMMARY OF THE INVENTION
In view of such circumstances, it is an object of the present invention to provide an inexpensive, bright image readout lens, composed of four lens elements, which is capable of yielding a wider angle of view and a favorable quality of readout images.
It is another object of the present invention to provide an image readout apparatus using such an image readout lens.
The image readout lens in accordance with the present invention comprises, successively from an object side, a first lens made of a positive meniscus lens having a convex surface directed onto the object side, a second lens made of a biconcave lens, a third lens made of a biconvex lens, and a fourth lens made of a negative meniscus lens having a convex surface directed onto an imaging surface side, wherein at least one surface in at least one of the first and third lenses is an aspheric surface, and wherein a stop is disposed between the second and third lenses.
Preferably, the image readout lens in accordance with the present invention is configured so as to satisfy the following conditions:
1.38
<f
(1
/R
9
−1
/R
8
)<2.38 (1)
0.28
<R
1
/f<
0.58 (2)
0.23
<D
7
/f<
0.46 (3)
0.71
<|D
4
×f
2
|/f<
1.98 (4)
1.14
<|N
4
×f
4
|/f<
1.90 (5)
where
f is the composite focal length of the whole lens system;
f
2
is the focal length of the second lens;
f
4
is the focal length of the fourth lens;
R
i
is the radius of curvature of the i-th surface;
D
i
is the distance between the i-th surface and the (i+1)-th surface; and
N
4
is the refractive index of the fourth lens at e-line.
The image readout apparatus in accordance with the present invention uses the above-mentioned image readout apparatus.
While the image readout lens in accordance with the present invention can be used as an image reducing lens when the first to fourth lenses are successively disposed from the object side as mentioned above, it can also be used as an image enlarging lens when the direction of the whole lens system is reversed as it is so that the first to fourth lenses are successively disposed from the imaging surface side.
REFERENCES:
patent: 4606607 (1986-08-01), Kurihara
patent: 4695134 (1987-09-01), Nakayama et al.
patent: 5499142 (1996-03-01), Ohshita
patent: 5936783 (1999-08-01), Nakai et al.
patent: 6147811 (2000-11-01), Fujibayashi
patent: 5926715-A (1984-02-01), None
Japanese Patent Office, Patent Abstracts of Japan, Publication No.: 09101452 A, Date of Publication: Apr. 15,1997.
Fuji Photo Optical Co., Ltd.
Schwartz Jordan M.
Snider Ronald R.
Snider & Associates
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