JP2002244033A - Image reader having image reading lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compact image reader provided with an image reading lens of high resolution with which various kinds of aberrations are corrected in a well-balanced state while maintaining high numerical aperture to the peripheral viewing angle of an ultra wide viewing angle although the lens has a large Fno in spite of the simple constitution of five groups and five lenses. SOLUTION: This image reader possesses a means to illuminate the image information of an original placed on an original platen, the image reading lens to form the image of the image information of the original illuminated by the illuminating means, and a means to read the image information obtained by the image formation by the image reading lens by converting the image information into electronic information. The image reading lens possesses a first lens being positive, a second being negative, a third lens being positive, a fourth lens being negative and a fifth lens being negative, in this order from an original side. A least one face out of several lens faces is made as a rotationally asymmetric face having different refracting power in an orthogonal direction, and the rotationally asymmetric face satisfies a conditional expression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus having an image reading lens, and more particularly to a field curvature of an image reading lens when reading image information of a document by a line sequential reading method using an image pickup device such as a CCD. Good correction of astigmatism, etc.
It is suitable for, for example, image scanners, digital copiers, facsimile machines, etc., which can read images with high accuracy.

[0002]

2. Description of the Related Art FIG. 12 is a schematic view of a main part when a conventional image reading lens for image reading is used in a flatbed image scanner.

[0003] In FIG. 1, a light beam emitted from an illumination light source 220 is directly or through a reflector 229.
And illuminates the reflected light flux from the original 228 with first, second,
Third and fourth reflection mirrors 223a, 223b, 223c,
The optical path of the light beam is bent inside the carriage 226 via the 223d, and the image reading lens (imaging lens) 224 is used to charge the CCD (Charge Coupled Device).
e) Linear image sensor 225 (hereinafter referred to as “CCD”)
Called. ) An image is formed on the surface. And carriage 2
Reference numeral 26 denotes an arrow A shown in FIG.
Document 228 by moving the original 228 in the direction (sub-scanning direction).
Is reading the image information. CCD 22 in FIG.
Reference numeral 5 denotes a configuration in which a plurality of light receiving elements are arranged in a one-dimensional direction (main scanning direction).

In order to reduce the size of the image scanner in the above configuration, it is necessary to reduce the size of the carriage 226.
In order to reduce the size of the carriage 226, for example, there is a method of increasing the number of reflecting mirrors, or securing the optical path length by reflecting a plurality of times with one reflecting mirror.

[0005]

However, these methods have a problem that since the structure inside the carriage 226 is complicated, the assembling accuracy is severe and the cost is greatly increased. Further, there is also a problem that the imaging performance is deteriorated in proportion to the surface accuracy of the reflection mirror and the number of reflections, which also affects the read image.

On the other hand, it is conceivable that the image reading lens (imaging system) 224 is widened to reduce the distance between object images. Various types of wide-angle image reading lenses realized with a realistic number of lenses and a spherical shape have hitherto been proposed. However, the upper limit of each of them is about 25 degrees at a half angle of view, and if the angle of view is wider than that, the field curvature and astigmatism increase, and sufficient optical performance cannot be exhibited. was there.

FIG. 13 is a sectional view of a conventional image reading lens, and FIG. 14 is a diagram showing various aberrations of the image reading lens shown in FIG. The image reading lens in FIG. 13 includes a positive first lens 91 and a negative second lens 9 in order from the object (original) side.
2. aperture, positive third lens 93, negative fourth lens 94,
And it is constituted by a telephoto type having five lenses of a negative fifth lens 95. The image reading lens shown in FIG. 14 is set to be used at a half angle of view of 30 degrees, but as shown in the aberration diagram of FIG. Has increased astigmatism. It is difficult to further reduce astigmatism while suppressing other aberrations.

Many image reading lenses have been proposed to further widen the angle of view by introducing a generally rotationally symmetric aspherical surface into the above-mentioned types and correcting the wavefront aberration. As for astigmatism and the like, the fundamental solution has not been made, and it has been difficult to realize a sufficiently wide angle of view.

As a method of correcting astigmatism, for example, there is an image reading apparatus proposed in Japanese Patent Application Laid-Open No. H5-14602. In this publication, astigmatism is satisfactorily corrected by providing an optical member having a rotationally asymmetric refractive power in a direction perpendicular to the optical axis in an optical path between an imaging system and image reading means. Although this method is effective in correcting astigmatism, a new optical member must be arranged in the optical path, and thus there is a problem that the entire apparatus becomes large and the number of adjustment items at the time of assembly increases.

By generating vignetting at the peripheral angle of view, a high resolution can be provided at all angles of view. However, in an image reading apparatus requiring a sufficient amount of light up to the peripheral angle of view, the aperture efficiency is 100%. Therefore, the above purpose cannot be attained.

In recent years, sensor elements such as image sensors have been miniaturized, and a brighter Fno (F number) image reading lens has been required to obtain a sufficient amount of light for a sensor element having a small area. Therefore, it is not desirable to reduce the light flux.

When maintaining an aperture efficiency of 100% and obtaining a good image at all angles of view,
By forming a certain surface constituting the image reading lens so as to have a refractive power that is rotationally asymmetric with respect to the optical axis, aberration and the like are corrected.

However, in the conventional correction method, Fn
When o is about 5 and the super-wide angle of view angle is about 30 degrees with a brighter Fno, even if a rotationally asymmetric surface is used, the luminous flux area on that surface is large. In addition to the correction using a lens that is rotationally asymmetric with respect to the correction, the influence of power distribution to other constituent lenses also increases. Therefore, it is necessary to set a strict tolerance in order to suppress the performance deterioration due to the processing error, which has been a factor that makes the manufacturing difficult. In order to establish a bright and super-wide-angle image reading lens with excellent optical performance, it is necessary to improve the above-mentioned problems.

The present invention further improves the previously proposed image reading apparatus, and corrects various aberrations in a well-balanced manner while maintaining a high aperture ratio up to a peripheral angle of view of a super wide angle of view even with a simple Fno. It is an object of the present invention to provide a compact image reading device having an image reading lens having a high resolving power that can be used.

[0015]

According to a first aspect of the present invention, there is provided an image reading apparatus having an image reading lens, which illuminates image information of a document placed on a document loading table, and which is illuminated by the lighting means. An image reading lens having an image reading lens for forming image information of the original document, and reading means for converting the image information formed by the image reading lens into electronic information and reading the electronic information. A meniscus first lens having a positive refractive power with the convex surface facing the document side in order, a second lens having both concave lens surfaces having a negative refractive power, and both lens surfaces having a positive refractive power having a convex surface. A third lens, a fourth lens having a negative refractive power, and a fifth meniscus lens having a negative refractive power with a convex surface facing the reading unit, at least one of the plurality of lens surfaces being orthogonal to each other One In the refractive power differs rotationally asymmetric surface, said rotationally asymmetric surface,

[0016]

(Equation 2)

R (ymax): radius of curvature in the direction along the generatrix direction at the height ymax of the principal ray of the passing light beam at the maximum angle of view on the rotationally asymmetric surface r (ymax): on the rotationally asymmetric surface And the radius of curvature fd in the direction along the sagittal direction at the height ymax of the principal ray of the passing light beam at the maximum angle of view fd: focal length on the d-line of the entire system of the image reading lens Nd: forming a rotationally asymmetric surface It is characterized by satisfying the condition of the refractive index of the lens material.

According to a second aspect of the present invention, when the refractive powers of the fourth and fifth lenses are φ4 and φ5, respectively, the condition of 0.0055 ≦ φ4−φ5 ≦ 0.015 is satisfied. It is characterized by doing.

According to a third aspect of the present invention, in the first or second aspect, an aperture is provided between the second lens and the third lens.

According to a fourth aspect of the present invention, in the first or second aspect, the lens including the rotationally asymmetric surface is a molded glass lens.

According to a fifth aspect of the present invention, in the first aspect, the lens surface of the fifth lens on the reading means side is a rotationally asymmetric surface.

According to a sixth aspect of the present invention, in the first aspect, the illuminating means includes a xenon lamp.

According to a seventh aspect of the present invention, in the first aspect of the present invention, the illuminating means has an LED.

According to an eighth aspect of the present invention, in the first aspect of the present invention, the illuminating means has a metal reflecting member for converting a traveling direction of a light beam.

A ninth aspect of the present invention is characterized in that, in the first aspect of the present invention, the illuminating means has a resin reflecting member for converting a traveling direction of a light beam.

According to a tenth aspect of the present invention, in the first aspect of the present invention, the illuminating means has a resin light guiding member.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Image Reading Apparatus] FIG. 1 is a schematic view of a main part of an image reading apparatus according to a first embodiment of the present invention having an image reading lens of one of Numerical Examples 1 to 3 to be described later.

In FIG. 1, reference numeral 2 denotes an original mounting table (original table glass) on which an original 1 is placed. Reference numeral 11 denotes a carriage, which integrally accommodates an illumination unit 21, a plurality of reflection mirrors 5, 6, 7, 8, an image reading lens 9, and a reading unit 10, and is driven by a driving device such as a sub-scanning motor 17. Scanning is performed in the sub-scanning direction (the direction of arrow A in FIG. 1), and image information of the original 1 is read.

The illuminating means 21 has an illuminating light source 3 and a reflecting member (reflecting shade) 4, and illuminates the image information of the original 1 efficiently. The illumination light source 3 is, for example, a xenon lamp or L
It is made up of ED etc. The reflecting member 4 can be made of a metal that converts the traveling direction of a light beam or a plastic (resin) having a vapor-deposited film on its surface, and reflects the light beam from the illumination light source 3 to efficiently convert the image information of the document 1. Lighting. The illuminating means 21 may illuminate the document 1 using a light guide member made of resin using total internal reflection.

Reference numerals 5, 6, 7 and 8 denote first, second, third and fourth reflection mirrors, respectively, which bend the optical path of the light beam from the original 1 inside the carriage 11. Reference numeral 9 denotes an image reading lens (imaging lens) of one of Numerical Examples 1 to 3 described later, which forms a light beam based on image information of the document 1 on the surface of the reading unit 10. Reference numeral 10 denotes a photoelectric conversion element (CCD) as reading means, which reads image information of the original 1 after converting the image information into electronic information. 12 is a main body.

In FIG. 1, a light beam emitted from an illumination light source 3 illuminates the original 1 directly or via a reflecting member 4.
The light beam of the light beam reflected from the original 1 is bent inside the carriage 11 via the first, second, third, and fourth reflection mirrors 5, 6, 7, and 8, and the image reading lens 9 applies the CC light.
An image is formed on the D10 plane. The image information of the original 1 is read by moving the carriage 11 in the direction of arrow A (sub-scanning direction) by the sub-scanning motor 17.

In FIG. 1, the present invention is applied to an image reading apparatus such as a digital copying machine. However, the present invention is not limited to this, and may be applied to an image reading apparatus such as an image scanner.

Until now, the distance from the original surface to the photoelectric conversion element in a copying machine or the like has been 500 to 600 mm in a 2: 1 mirror scanning system.
Although there is usually some degree, in this embodiment, it is within about 300 mm, and a more compact configuration is possible. Further, all of the above elements shown in FIG. 1 are housed inside the carriage, and the optical adjustment can be performed with the carriage alone before being incorporated into the main body.

Further, in the 2: 1 mirror scanning method, when scanning in the sub-scanning direction, a fine adjustment operation is required so that the magnification and the focus position match at the scanning start position and the scanning end position due to assembly tolerance. In this embodiment, since it is only necessary to perform positioning when the carriage is incorporated into the main body, the integral operation can omit the operation, and the adjustment time can be greatly reduced.

When the carriage is instructed to start scanning by an input operation unit (not shown), the carriage is scanned by the motor and guide (not shown) together with the carriage in the sub-scanning direction indicated by arrow A in the figure. At this time, during scanning, the distance between the document and the image reading lens and the photoelectric conversion element is always immovable and constant.
Unlike the mirror scanning method, there is no need to move the mirror base with a 2: 1 speed ratio, which contributes to simplification of the structure.

Next, the image reading lens 9 according to the present invention shown in FIG. 1 will be described.

FIGS. 2, 3 and 4 are lens sectional views of image reading lenses according to Numerical Examples 1, 2, and 3, which will be described later.
6 and 7 show various aberration diagrams (spherical aberration, astigmatism, and distortion) of the image reading lenses of Numerical Examples 1, 2, and 3 described below, respectively. FIGS. 8, 9, and 10 show numerical values described later. Various aberration diagrams (lateral aberration diagrams) of the image reading lenses of Examples 1, 2, and 3;
FIGS. 11A and 11B are diagrams for explaining the rotationally asymmetric surface of the image reading lens. FIG. 11A is a sectional view of the lens, and FIG. 11B is a front view of the fifth lens L5. It is.

In the lens cross-sectional view, the left side is the enlargement side (longer conjugate point) and the document surface P side (side on which the read image is provided), and the right side is the reduction side (short conjugate point).
To the reading means surface Q side (for example, a CCD as a photoelectric conversion element)
Is provided). In the figure, a cover glass G of a CCD is inserted immediately before the reading means surface Q.

Here, Numerical Embodiment 1 shown in FIGS.
Image reading lens 9 in 2 and 3 (9A, 9B, 9C)
Is a first group of a meniscus-shaped first lens L1 having a positive refractive power with the convex surface facing the document side in order from the document surface side;
A second lens L2 having negative refractive power with both lens surfaces concave.
A second group consisting of a third lens L3 having a positive refractive power with both lens surfaces being convex, a fourth group consisting of a fourth lens L4 having a negative refractive power, and a convex surface facing the reading means. And a fifth lens group composed of a fifth lens element L5 having a negative refractive power and a fifth lens unit L5. At least one of the plurality of lens surfaces has a rotationally asymmetric surface having a different refractive power in an orthogonal direction. have.

In each numerical example, the aspherical surface (rotationally symmetric surface) rotationally symmetric with respect to the optical axis on the surface L5a on the original surface P side of the fifth lens L5, and the rotationally asymmetrical surface on the lens surface L5b on the reading means surface Q side. A non-spherical surface (rotationally asymmetric surface) is introduced. The fifth lens L5 is made of a molded glass lens. SP denotes an aperture, which is provided between the second lens L2 and the third lens L3. The aperture SP may be provided other than between the second lens L2 and the third lens L3.

In FIG. 11A, assuming that the point at which the off-axis principal ray at the maximum angle of view passing through the center of the stop SP enters the rotationally asymmetric surface L5b of the fifth lens L5 is Pa, FIG.
(B), the Y-axis direction including the point Pa (X-axis direction)
Is the radius of curvature in the direction along the generatrix direction (satellite direction) at the height of the principal ray of the passing light beam at the maximum angle of view.

As described above, according to the present invention, the image reading lens
The above-mentioned rotationally asymmetric surface is composed of a group of 5

[0043]

(Equation 3)

R (ymax): radius of curvature in the direction along the generatrix direction at the height ymax of the principal ray of the passing light beam at the maximum angle of view on the rotationally asymmetric surface r (ymax): on the rotationally asymmetric surface The radius of curvature fd in the direction along the sagittal direction at the height ymax of the principal ray of the passing light beam at the maximum angle of view fd: focal length of the entire system of the image reading lens Nd: lens forming a rotationally asymmetric surface The material is configured to satisfy the following condition.

Thus, despite having a simple structure of five elements and five elements, a high resolving power capable of correcting various aberrations in a well-balanced manner while maintaining a high aperture ratio up to a peripheral angle of view of an ultra wide angle of view even in a bright Fno. The obtained image reading lens is obtained.

In the present invention, it is desirable to satisfy the following conditional expression (2) in order to correspond to a lens having a higher resolution.

That is, the refractive power of the fourth and fifth lenses is φ
4, when φ5, the condition of 0.0055 ≦ φ4−φ5 ≦ 0.015 (2) is satisfied.

Next, the technical meaning of each of the conditional expressions (1) and (2) will be described.

Conditional expression (1) satisfies a wide angle of view and a bright Fn.
In the setting of o, this is for favorably correcting field curvature and astigmatism, etc., and is an important condition mainly for correcting a light beam width having a large area even at a peripheral angle of view. Conditional expression (1)
If the lower limit value is exceeded, astigmatism, image surface curvature, chromatic aberration of magnification, etc. will be insufficiently corrected and deteriorated.
If the value exceeds the upper limit of conditional expression (1), the correction becomes excessive, and
This is not good because the image surface distortion becomes worse in addition to astigmatism.

Conditional expression (2) defines the power distribution between the fourth lens and the fifth lens. By satisfying the conditional expression (2), it is possible to prevent the load of aberration correction on the lens on the document side from becoming excessive from the fourth lens, and to balance the power arrangement so that each lens can share the correction of aberration without difficulty. Can be performed. Deviating from the range of the conditional expression (2) is not preferable because coma aberration becomes worse over the entire image height range and astigmatism of the outer peripheral angle of view becomes worse. Further, since the balance of the power distribution as a whole is lost, other aberrations are also affected, which is not good.

In the present invention, it is possible to efficiently correct the aberration up to the peripheral portion by satisfying the conditional expression (1), and further efficiently correct the aberration up to the peripheral portion by satisfying the conditional expression (2). It is possible to do.

More preferably, in the present invention, the above-mentioned conditional expressions (1) and (2) are set as follows.

[0053]

(Equation 4)

0.0060 ≦ φ4−φ5 ≦ 0.012 (2a) In each numerical example, as described above, the fifth lens L5 is rotated on the original surface P side and rotated on the reading means surface Q side. An asymmetric surface (free-form surface) is introduced. These shapes have the origin at the intersection of the lens surface and the optical axis, the optical axis direction is the Z axis,
An axis parallel to the main scanning direction and perpendicular to the optical axis is defined as a generatrix direction, and Y
When the axis parallel to the sub-scanning direction and orthogonal to the optical axis is defined as the sagittal direction and the X axis, the shape of the rotational symmetry plane

[0055]

(Equation 5)

Here, Z: distance in the Z direction from the intersection at the height y along the Y from the intersection of the optical axis and the surface R: radius of curvature of the vertex of the surface y: along Y from the intersection of the optical axis and the surface distance _{k y, B 4, B 6} , B 8, B 10: represented by aspheric coefficient becomes equation.

The shape of the rotationally asymmetric surface is

[0058]

(Equation 6)

Z: distance from the intersection of the optical axis and the surface in the Z direction at a height y along the Y from the intersection R: radius of curvature of the vertex of the surface y: along Y from the intersection of the optical axis and the surface distance _{k y, B 4, B 6} , B 8, B 10: represented by aspheric coefficient becomes equation.

In the sagittal direction, r ′ = r ₀ (1 + D ₂ y ² + D ₄ y ⁴ + D ₆ y ⁶ + D _{8
^{y 8 + D 10 y 10)}} y: the distance along the intersection of the optical axis with the surface in Y r ': generatrix direction height curvature radius r in a direction along the sagittal direction in the y _0: sagittal curvature on the optical axis It is a radius, and R = ± r ₀ D ₂ , D ₄ , D ₆ , D ₈ , and D ₁₀ are represented by free-form surface coefficients.

Note that the child line is perpendicular to the bus and Z
The shape has a radius of curvature r 'in a plane along the axis. These surfaces can be formed using a glass mold material or an optical resin. By pouring a molten material into a mold whose surface shape is precisely machined and transferring the surface shape of the mold, it can be manufactured without variation in optical performance, and stable quality can be obtained even in mass production.

If the above-described image reading lens is applied to an image reading apparatus such as an image scanner or a digital copying machine, the size of the entire apparatus can be reduced.

Next, Numerical Examples 1 to 3 of the present invention will be described. In Numerical Examples 1 to 3, column i is the surface number counted from the document surface side, R is the radius of curvature of the lens surface, D is the lens thickness and air gap, and nd and νd are the refractive indices of the lens material at d-line, respectively. Abbe number. The air gap between the document loading table and the first lens and the air gap between the fifth lens and the cover glass of the CCD are omitted. fd is the focal length, Fno is the F-number at the infinite object distance, and m is the imaging magnification.
Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. Note that “ ^Ex ” is represented as “× 10 ^−x ”. [Numerical Example 1] fd = 26.2 Fno = 3.8 m = −0.1110236 × ω / 2 = 29.8 ° i R D nd νd 1 11.091 2.0 1.696678 55.5 2 29.175 2.32 3 -53.164 0.77 1.68893 31.1 4 20.484 0.96 5 Aperture 1.67 6 17.711 1.91 1.77250 49.6 7 -27.179 4.87 8 -13.281 1.12 1.72825 28.5 9 -17.711 2.00 10 * -9.115 5.58 1.68893 31.1 11 * -13.880 * 10,11 The surface is an aspherical surface. 10 aspherical surface coefficients k = 1.2794E-2B4 = -1.366969E-4B6 = 8.62410E-7B8 = 8.312108E-9B10 = 6.669375E-1 Eleven aspherical surface coefficients and free-form surface coefficients k = -1.266647 B4 = -1.05366E-4B6 = 3.97614E-7B8 = 2.267747E-8B10 = -8.999166E-11 D2 = −2.222976E−4 D4 = −1.96910E−6 D6 = 4.31819E−6 D8 = −8.06177E−8 D10 = 7.548332E−10 [Numerical example 2] fd = 26.1 Fno = 3.8 m = −0.1110236 × ω / 2 = 29.8 ° i RD nd νd 1 10.768 2.20 1.69678 55.5 2 27.779 0.67 3 − 51.415 0.73 1.68893 31.1 4 19.719 1.42 5 Aperture 2.31 6 17.372 5.35 1.78800 47.4 7 -25.035 0.83 −14.153 1.63 1.72825 28.5 9 −20.981 5.55 10 * −9.163 1.63 1.68893 31.1 11 * −14.468 * Surfaces 10 and 11 are aspheric. Aspherical surface coefficient of 10 surfaces k = 3.70903E-2B4 = -1.124116E-4B6 = 6.93001E-7B8 = 7.18244E-9B10 = 7.556226E-10 11 aspherical surfaces Coefficient and free-form surface coefficient k = −1.17096 B 4 = −8.262646E−5 B 6 = 3.52022E−7 B 8 = 2.241010−8 B10 = −8.844405E−11 D 2 = −2 .14978E-6D4 = 3.46068E-6D6 = 4.22378E-6D8 = -8.13057E-8 D10 = 8.33189E-10 [numerical value] Example 3] fd = 26.4 Fno = 3.8 m = −0.1110236 × ω / 2 = 29.6 ° i RD nd νd 1 11.053 2.20 1.696678 55.5 226. 675 0.693 3-51.122 1.45 1.68893 31.1 4 21.433 1.18 5 Aperture 2.33 6 17.382 5.28 1.78800 47.4 7-25.601 0. 928-13.775 1.51 1.72825 28.5 9-20.480 5.81 10 * -9.269 1.84 1.68893 31.1 11 * -14.164 * The 10 and 11 surfaces are Aspherical surface Aspherical surface coefficient of 10 surfaces k = 3.9980E-2B4 = -1.36168E-4B6 = 6.887724E-7B8 = 7.11707E-9B10 = 7.171877E-1011 Aspherical surface coefficient and free-form surface coefficient k = -1.333892 B4 = -1.0000E-4B6 = 1.98281E-7B8 = 2.27817E-8B10 = -7.932242E-11D 2 = −3.51311E−4D 4 = −4.991860−6 D 6 = 4.24996E−6D 8 = −8.111730E−8 D10 = 7.71252E−10

[0064]

[Table 1]

Each of Numerical Examples 1 to 3 described above satisfies the conditional expressions (1) and (2).

[0066]

According to the present invention, as described above, at least one of a plurality of lens surfaces constituting an image reading lens is formed of a rotationally asymmetric surface having a different refractive power in a direction perpendicular to the lens, thereby forming a five-group, five-lens structure. A compact image reading device having a high-resolution image reading lens capable of maintaining a high aperture ratio up to a peripheral angle of view of an ultra wide angle of view and correcting various aberrations in a well-balanced manner even with a bright Fno despite its simple configuration. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of an image reading apparatus having an image reading lens according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 4 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 5 is a diagram showing various aberrations of Numerical Example 1 of the present invention.

FIG. 6 is a diagram showing various aberrations of Numerical Example 2 of the present invention.

FIG. 7 is a diagram showing various aberrations of Numerical Example 3 of the present invention.

FIG. 8 is a diagram illustrating various aberrations (lateral aberration diagrams) according to Numerical Example 1 of the present invention.

FIG. 9 is a diagram illustrating various aberrations (lateral aberration diagrams) according to Numerical Example 2 of the present invention.

FIG. 10 is a diagram illustrating various aberrations (lateral aberration diagrams) according to Numerical Example 3 of the present invention.

FIG. 11 is a view for explaining a rotationally asymmetric surface of the image reading lens.

FIG. 12 is a schematic view of a main part of a conventional image reading apparatus.

FIG. 13 is a sectional view of a conventional image reading lens.

FIG. 14 is a diagram showing various aberrations of a conventional image reading lens.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 document 2 document loading table 3 illumination light source 4 reflection member 5, 6, 7, 8 reflection mirror 9 image reading lens 10 reading means (CCD) 11 carriage 12 body 17 sub-scanning motor 21 illumination means L1 first lens L2 second lens L3 Third lens L4 Fourth lens L5 Fifth lens L5a Rotationally symmetric surface L5b Rotationally asymmetric surface SP Aperture

Claims (10)

[Claims] An illumination unit configured to illuminate image information of an original placed on an original mounting table; an image reading lens configured to form an image of the image information of the original illuminated by the illumination unit; A reading means for converting imaged image information into electronic information and reading the electronic information, wherein the image reading lens has a meniscus-shaped first meniscus having a positive refractive power with a convex surface facing the document side in order from the document side. A lens, a second lens having both concave lens surfaces having negative refractive power, a third lens having both convex lens surfaces having positive refractive power, a fourth lens having negative refractive power, and a convex surface facing the reading unit. A fifth meniscus lens having a negative refractive power, and at least one of the plurality of lens surfaces is a rotationally asymmetric surface having a different refractive power in a direction orthogonal to the lens surface. 1) R (ymax): radius of curvature in the direction along the generatrix direction at the height ymax of the principal ray of the passing light beam at the maximum angle of view on the rotationally asymmetric surface r (ymax): maximum on the rotationally asymmetric surface Radius of curvature in the direction along the sagittal direction at the height ymax of the principal ray of the passing light beam at the angle of view fd: Focal length at d-line of the entire system of the image reading lens Nd: Lens forming a rotationally asymmetric surface An image reading apparatus having an image reading lens, which satisfies the following condition. 2. The refractive power of each of the fourth and fifth lenses is φ
2. The image reading apparatus according to claim 1, wherein the condition of 0.0055 ≦ φ4−φ5 ≦ 0.015 is satisfied when 4,5 is satisfied. 3. An image reading apparatus having an image reading lens according to claim 1, further comprising a stop between said second lens and said third lens. 4. The image reading apparatus according to claim 1, wherein the lens including the rotationally asymmetric surface is a molded glass lens. 5. The image reading apparatus according to claim 1, wherein a lens surface of the fifth lens on a reading unit side is a rotationally asymmetric surface. 6. An apparatus according to claim 1, wherein said illuminating means includes a xenon lamp. 7. An image reading apparatus according to claim 1, wherein said illumination means has an LED. 8. An image reading apparatus according to claim 1, wherein said illuminating means has a metal reflecting member for converting a traveling direction of a light beam. 9. An image reading apparatus having an image reading lens according to claim 1, wherein said illuminating means has a resin reflecting member for changing a traveling direction of a light beam. 10. An image reading apparatus according to claim 1, wherein said illuminating means has a resin light guide member.