JP2011242526A - Image reading device using image reading lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an image reading device capable of reducing an image surface curvature and a magnification deviation in a secondary scanning direction even when using a high-resolution line sensor.SOLUTION: The image reading device includes: an image reading lens for imaging image information of a document; and reading means disposed in the imaging position of the image information and having a plurality of line sensors in which pixels are arranged in a primary scanning direction. The image reader reads image information by moving the reading means in a secondary scanning direction. The reading means satisfies W/L≤0.015 (where W is the width of each line sensor on the shorter side, and L is the interval between the centers of adjoining line sensors). The image reading lens has an anamorphic lens including an anamorphic face in which at least one face is rotationally asymmetric with respect to an optical axis. Where the cross-sectional form of the anamorphic face within a main scanning cross-section including the optical axis and the main scanning direction is a generatrix, at least one face of the anamorphic lens is such that a sagittal curvature continuously changes in the direction of the generatrix from the optical axis and satisfies a conditional expression. Here, the sagittal curvature is defined within a plane that is perpendicular to the main scanning cross-section and includes a normal line at an arbitrary position in the generatrix direction.

Description

  The present invention relates to an image reading apparatus using an image reading lens. In particular, the image reading lens having an anamorphic lens is suitable for an image reading apparatus such as an image scanner, a copying machine, and a facsimile machine that can perform high-precision image reading by sufficiently exhibiting optical performance.

FIG. 14 is a schematic diagram of a main part showing the configuration of a conventional image reading apparatus.
In the image reading apparatus shown in FIG. 14, the document 101 is placed on the surface of the document table glass 102. The carriage 107 integrally houses an illumination system 103, which will be described later, a plurality of reflecting mirrors 104a, 104b, 104c, and 104d, an imaging optical system (image reading lens) 106, a reading unit 105, and the like. The carriage 107 is moved in the sub-scanning direction indicated by an arrow in FIG. 14 by a sub-scanning mechanism 108 such as a motor, and reads the image information of the document 101. The read image information is sent to an external device such as a personal computer through an interface (not shown).

  The illumination system 103 includes a xenon tube, a halogen lamp, an LED array, and the like. The illumination system 103 may be used in combination with a reflector such as an aluminum vapor deposition plate. Reflecting mirrors 104 a, 104 b, 104 c, and 104 d bend the light beam from the document 101 inside the carriage 107. The imaging optical system 106 images light from the original 101 on the surface of the reading unit 105. The reading unit 105 includes a line sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), and has a configuration in which a plurality of light receiving elements are arranged in a main scanning direction that is perpendicular to the paper surface. .

  In the above configuration, the carriage 107 needs to be downsized to reduce the size of the image scanner. In order to reduce the size of the carriage 107, for example, there are methods of increasing the number of reflecting mirrors or reflecting a plurality of times by one reflecting mirror to ensure the optical path length. By introducing an anamorphic lens having at least one surface that is rotationally asymmetric with respect to the optical axis, the imaging optical system (imaging system) 106 is widened to reduce the distance between object images, and the optical path length itself is shortened. A method has been proposed.

  If the anamorphic lens is used in this way, the field curvature can be effectively reduced, and an image with good contrast can be obtained. However, there is a problem that the imaging magnification, particularly the imaging magnification in the sub-scanning direction (sub-scanning magnification) changes from the optical axis to the periphery. Then, for example, in the case of reading with a line color sensor corresponding to three colors of red, green, and blue (RGB), the image forming position is shifted in each color, and thus color misalignment in the sub-scanning direction occurs. was there.

As a solution to this problem, there has been proposed a color image reading apparatus that appropriately sets the specification (shape) of the line sensor and the distortion component in the sub-scanning direction of the lens to obtain a good color image. (See Patent Document 1)
There has also been proposed a color image reading apparatus that obtains a good color image by appropriately setting the shape of a lens having two anamorphic surfaces. (See Patent Document 2)

JP 2000-307800 A JP 2008-065234 A

However, Patent Documents 1 and 2 have the following problems.
The color image reading device of Patent Document 1 is mainly used for image reading at a sensor resolution of about 600 dpi, and the length of one side of a line sensor is about 7 to 8 μm, and the RGB line interval is about 63 to 73 μm. there were.
The color image reading apparatus disclosed in Patent Document 2 is mainly used for image reading at a sensor resolution of about 2400 dpi. The length of one side of each pixel is about 2 μm, which is smaller than that of the line sensor disclosed in Patent Document 1, and the image is read in the main scanning direction. In order to increase the resolution, sensors of the same color are arranged in a staggered pattern. For this reason, the RGB line interval in the sub-scanning direction is about 63 to 96 μm.

  However, recent image reading apparatuses are required to read at a higher resolution. For example, the length of one side of one pixel is about 2 μm which is equivalent to 2400 dpi at a resolution of 9600 dpi. In order to increase the resolving power, line sensors of the same color are further arranged in a staggered manner. For this reason, the line spacing of different colors further increases, and the RGB line spacing is required to be about 160 μm. That is, since the size in the sub-scanning direction is about 3 to 5 times that of Patent Documents 1 and 2, the imaging accuracy in the sub-scanning direction is required to be about 3 to 5 times.

Further, in addition to higher resolution, there is a demand for downsizing and higher image quality of the entire apparatus, and an image reading lens is required to have a wide angle of view while reducing field curvature. As a result, it is necessary to use a lens with stronger anamorphic characteristics, and the required imaging accuracy in the sub-scanning direction is 10 times or more that of the conventional art.
In view of these situations, it is necessary to completely correct the change in the vertical magnification, that is, the sub-scanning magnification, at each position of the bus on the anamorphic surface.

However, in Patent Documents 1 and 2, it has not been possible to reduce the magnification shift in the sub-scanning direction accompanying the increase in the line interval.
An object of the present invention is to provide an image reading apparatus using an image reading lens that can reduce both field curvature and magnification deviation in the sub-scanning direction even when a high-resolution line sensor is used.

Ｎ：該アナモフィックレンズの材料の屈折率
ｒ₁：該アナモフィックレンズの原稿側の面の主光線通過位置における子線曲率半径
ｒ₂：該アナモフィックレンズの像面側の面の主光線通過位置における子線曲率半径
ｄ：アナモフィックレンズの原稿側の面と像面側の面の間の主光線が通過する位置での距離
と定義し、軸上光束主光線に対するＡの値をA₀、主走査全画角における光束主光線に対するＡの値の最大値をA_max、とするとき、-0.1≦1-(A_max/A₀)≦0.1を満たすことを特徴とする。 In order to achieve the above object, an image reading apparatus according to the present invention provides:
An image reading lens for imaging image information on the document surface, and a plurality of line sensors arranged in parallel at the image information imaging position of the image reading lens, each pixel of the line sensor being Reading means having a plurality of line sensors arranged in the main scanning direction,
An image reading apparatus for reading image information on a document surface by moving the reading means in the sub-scanning direction,
When the width of the light receiving surface of each line sensor in the lateral direction is W and the distance between the centers of adjacent line sensors is L,
Satisfies W / L ≦ 0.015,
The image reading lens includes an anamorphic lens including at least one anamorphic surface having a rotationally asymmetric shape with respect to the optical axis, and at least one surface of the anamorphic lens includes a main scanning section including an optical axis and a main scanning direction. When the cross-sectional shape of the anamorphic surface is a generating line, the anamorphic surface is perpendicular to the main scanning section and has a sub-curvature curvature defined in a plane including the normal line of the anamorphic surface at a position in an arbitrary generating line direction. , Continuously changing from the optical axis along the generatrix direction,

N: Refractive index of the material of the anamorphic lens r ₁ : Radius of curvature of the principal ray at the principal ray passing position of the original side surface of the anamorphic lens r ₂ : Child at the principal ray passing position of the image side surface of the anamorphic lens Radius of curvature d: Defined as the distance at which the principal ray passes between the document side surface and the image side surface of the anamorphic lens. The value of A with respect to the axial principal ray is A ₀ , the main scanning all When the maximum value of A with respect to the principal ray of light flux at the angle of view is A _max , −0.1 ≦ 1- (A _max / A ₀ ) ≦ 0.1 is satisfied.

  According to the present invention, even when a high-resolution line sensor is used, it is possible to achieve an image reading apparatus using an image reading lens that can reduce both image field curvature and magnification deviation in the sub-scanning direction. .

FIG. 2 is a schematic diagram of a main part showing a basic configuration of an optical system of an image reading apparatus of the present invention. Lens cross section of Numerical Example 1 of the present invention Various aberration diagrams of Numerical Example 1 of the present invention Amount of color misregistration by sub-scanning magnification according to Numerical Example 1 of the present invention Lens cross section of Numerical Example 2 of the present invention Various aberration diagrams of Numerical Example 2 of the present invention Amount of color misregistration by sub-scanning magnification according to Numerical Example 2 of the present invention Lens cross section of Numerical Example 3 of the present invention Various aberration diagrams of Numerical Example 3 of the present invention Amount of color misregistration by sub-scanning magnification according to Numerical Example 3 of the present invention The principal part perspective view which showed the relationship between a 4th lens and an image surface Schematic diagram of main parts of the image reading apparatus of the present invention. Schematic diagram of main parts of the image reading apparatus of the present invention. Schematic diagram of main parts of a conventional image reading apparatus

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a main part schematic diagram showing a basic configuration of an optical system of an image reading apparatus of the present invention.
FIG. 1 shows reading ranges 1R, 1G, and 1B conjugate to line sensors (CCD or CMOS sensors) 2R, 2G, and 2B, which will be described later, on a document surface (1) on which a color image is formed. The image reading lens 3 includes an anamorphic surface having a rotationally asymmetric shape with respect to the optical axis on at least one surface, and forms a light beam based on image information of the document 1 on the surface of the reading unit 2. That is, a plurality of line sensors are arranged in parallel at the image information imaging position on the document surface by the image reading lens.

  The reading unit 2 includes three line sensors 2R, 2G, and 2B, and is composed of monolithic three line sensors arranged on the same substrate surface so as to be parallel to each other. Non-indicated color filters based on colored light (for example, red, green, blue) are provided. Each of the line sensors 2R, 2G, 2B has a width W in the lateral direction, and is arranged with a line interval therebetween. The three line sensors sequentially read different color information (for example, R, G, B).

The resolution of the reading means 2 is increased by reducing the width W in the short direction of the light receiving surface of each line sensor as much as possible, widening the distance L between the centers of two adjacent line sensors, and staggering them at high density. is doing. In this invention, if it is the range of the following conditional expressions, it will become an application range.
W / L ≦ 0.015 (1)
In this embodiment, a 9600 dpi sensor is used in which the width W in the short direction of the light receiving surface of each line sensor is 2 μm, and the distance L between the centers of two adjacent line sensors is 160 μm, and the W / L is 0.0125. It is the scope of application.

  2, 5, and 8 are sectional views of lenses of numerical embodiments 1, 2, and 3 to be described later of the image reading lens 3 according to the present invention. 3, 6, and 9 are various aberration diagrams (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) of numerical examples 1, 2, and 3 to be described later of the image reading lens 3 according to the present invention. . 4, 7, and 10 are diagrams showing the amount of color misregistration caused by sub-scanning magnification misalignment in numerical embodiments 1, 2, and 3 to be described later of the image reading lens 3 according to the present invention. FIG. 11 is a perspective view of a main part showing the relationship between the fourth lens G4 and the image plane Q constituting one element of the image reading lens according to the present invention.

In the sectional view of the lens, the document surface P, the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the stop SP, the image surface Q, the document table glass C1, the cover glass C2, and the image reading lens. (Image-forming optical system) LG is shown.
In the aberration diagrams, e, g, and c are e-line, g-line, c-line, ΔM, and ΔS are meridional image plane, sagittal image plane, and lateral chromatic aberration are represented by g-line and c-line, respectively.

The image reading lens LG in FIGS. 2, 5, and 8 has the following structure in order from the document surface P side to the image surface Q side.
A first lens G1 having a meniscus shape having a positive refractive power facing the original surface side, an aperture stop SP, a second lens G2 having a concave shape on both lens surfaces, and a third lens G3 having a convex shape on both lens surfaces. Furthermore, it has a meniscus fourth lens G4 with a convex surface facing the image surface side.

In the fourth lens G4, the light incident surface (first surface, document side surface) and the light emitting surface (second surface, image surface side surface) are anamorphic surfaces.
Here, as shown in FIG. 11, the optical axis La (x direction) determined by the first lens G1 to the third lens G3 having a rotationally symmetric surface and the arrangement direction (main scanning direction) of the pixels on the image plane Q are included. A cross-sectional shape in the main scanning cross section (in the xy cross section) is defined as a bus.

On the optical axis La, the anamorphic surface has the same curvature of the generatrix in the main scanning section and the curvature of the child lines in the direction perpendicular to the main scanning section (sub-scanning direction, z direction, and child line direction).
The anamorphic surface continuously changes as the curvature in the direction perpendicular to the main scanning section moves away from the optical axis La along the generatrix direction (y direction).

In the present embodiment, the curvature of the child line is a curvature defined in a plane that is perpendicular to the main scanning section and includes the normal line of the anamorphic surface at a position in an arbitrary generatrix direction.
In other words, the curvature of the child line is a curvature defined in a plane including a line perpendicular to the main scanning section and perpendicular to the tangent of the bus bar shape at a position in an arbitrary bus bar direction.
The curvature of the bus bar is a curvature at a position in an arbitrary bus bar direction in the main scanning section.

  In the present embodiment, the fourth lens G4 is formed of resin. This is to reduce the cost by molding the fourth lens G4, which is likely to have a large lens diameter among the constituent lenses, with resin.

Next, Numerical Examples 1 to 3 of the present invention will be shown.
Tables 1, 3, and 5 show the lens shapes of Numerical Examples 1, 2, and 3.
In Tables 1, 3, and 5, f is the focal length of the image reading lens LG, Fno is the F number, β is the magnification, Y is the maximum image height, and ω is the half field angle.
In the image reading lens LG shown in Tables 1, 3, and 5, the surface number i indicates the order of the surfaces from the document surface P side, Ri is the radius of curvature of each surface, Di is the i-th surface and the i + 1-th surface. The member thickness or air interval between them, Ndi and νdi respectively indicate the refractive index and Abbe number with respect to the d-line.
The shape of the anamorphic surface is an aspherical shape described below using the coefficients shown in Tables 2, 4, and 6 for each of Numerical Examples 1, 2, and 3.

なる式で表わされる。但し、Ｒは曲率半径、ｋ_y、Ｂ₄、Ｂ₆、Ｂ₈、Ｂ₁₀は非球面係数である。
子線形状Ｓは母線上において母線と垂直な平面を断面とし、

なる式で表わされる。但し、ｒ₀は光軸上の子線の曲率半径で、Ｒ＝ｒ₀、Ｄ_i、Ｍ_{j_k}、Ｅ₂、Ｅ₄、Ｅ₆、Ｅ₈、Ｅ₁₀は非球面係数である。 The aspherical shape having a refractive power that is rotationally asymmetric with respect to the optical axis has the intersection point between the lens surface and the optical axis as the origin, the optical axis direction is the x axis, and the axis orthogonal to the optical axis in the main scanning section is the y axis. When the axis perpendicular to the optical axis in the sub-scan section is the z-axis, the generatrix shape X is

It is expressed by the following formula. Here, R is the radius of _{curvature, k y, B 4, B} 6, B 8, B 10 are aspherical coefficients.
The child wire shape S has a cross section on a plane perpendicular to the bus bar on the bus bar,

It is expressed by the following formula. Here, r ₀ is the radius of curvature of the child line on the optical axis, and R = r ₀ , D _i , M _{j_k} , E ₂ , E ₄ , E ₆ , E ₈ , E ₁₀ are aspherical coefficients.

[Numerical Example 1]

[Numerical example 2]

[Numeric Example 3]

Next, an image reading apparatus having the image reading lens LG of this embodiment will be described.
The fourth lens G4 of the image reading lens LG is composed of an anamorphic lens.

Ｎ：アナモフィックレンズの材料の屈折率
ｒ₁：アナモフィックレンズの第１面（原稿側の面）の主光線通過位置における子線曲率半径
ｒ₂：アナモフィックレンズの第２面（像面側の面）の主光線通過位置における子線曲率半径
ｄ :アナモフィックレンズの第１面と第２面間の主光線が通過する位置での距離
と定義し、
A₀ ：軸上光束主光線に対するＡの値
A_max：主走査全画角における光束主光線に対するＡの値の最大値
とするとき、第４レンズＧ４は、
-0.1≦1-(A_max/A₀)≦0.1 (２)
なる条件を満足する。 Where A is

N: Refractive index of the material of the anamorphic lens r ₁ : Radius of curvature of the principal ray at the principal ray passing position of the first surface (original side surface) of the anamorphic lens r ₂ : Second surface (image side surface) of the anamorphic lens The radius of curvature of the ray at the principal ray passage position of d: is defined as the distance at which the principal ray passes between the first and second surfaces of the anamorphic lens,
A ₀ : A value for the axial principal ray
A _max : When the maximum value of the value of A with respect to the principal ray of light flux at the main scanning full angle of view is set, the fourth lens G4
-0.1 ≦ 1- (A _max / A ₀ ) ≦ 0.1 (2)
Satisfy the following conditions.

  Conditional expression (2) is a conditional expression for satisfactorily correcting the field curvature at all angles of view and favorably reducing the magnification shift in the sub-scanning direction. If the lower limit or upper limit constraint of the conditional expression (2) is not satisfied, not only the image surface curvature correction becomes excessive, but also the sub-scanning magnification deviation deteriorates.

Also,
A _50% : Value of A with respect to the luminous flux principal ray at _{50% field} angle in the main scanning direction
A _70% : Value of A with respect to the principal ray of light at a _{70% field} angle in the main scanning direction
A _90% : Assuming that the value of A with respect to the principal ray of light at _{90% field} angle in the main scanning direction is
-0.05 ≦ 1- (A _70% / A _50% ) ≦ 0.05 (3)
-0.08 ≦ 1- (A _90% / A _50% ) ≦ 0.08 (4)
Is satisfied.

By satisfying both conditional expressions (3) and (4), it is possible to satisfactorily correct the field curvature from 50% to 90% and to reduce the magnification deviation in the sub-scanning direction. it can.
If the lower limit or upper limit constraint in the conditional expressions (3) and (4) is not satisfied, not only the image field curvature correction becomes excessive from 50% to 90%, but also the sub-scan magnification deviation is deteriorated.

[Numerical Example 1]
The image reading lens LG of Numerical Example 1 has an F number of 6.5 that is necessary and sufficient for an image scanner, and various aberrations from on-axis to off-axis are sufficiently reduced as shown in FIG. Has gained performance.
The line sensor used in combination can be used in any case as long as the magnification is 0.189 times.
Each numerical value of conditional expressions (1) to (4) is shown in Table 7 to be described later.
As described above, even if a 9600 dpi line sensor with a center distance of 160 μm and a width of 2 μm in the short direction of the line sensor is used at this time, a ray tracing study is performed. As a result, as shown in FIG. 4, the color misalignment due to the sub-scanning magnification misalignment is about 0.5 pixel, which is sufficient.

[Numerical Example 2]
The image reading lens LG of Numerical Example 2 has an F number 6.5 that is necessary and sufficient for an image scanner, and various aberrations from on-axis to off-axis are sufficiently reduced as shown in FIG. Have gained.
The line sensor used in combination can be used in any case as long as the magnification is 0.189 times.
Each numerical value of conditional expressions (1) to (4) is shown in Table 7 to be described later.
As described above, even if a 9600 dpi line sensor with a center distance of 160 μm and a width of 2 μm in the short direction of the line sensor is used at this time, a ray tracing study is performed. As a result, as shown in FIG. 7, the color misalignment due to the sub-scanning magnification misalignment is about 0.4 pixels, which is sufficient performance.

[Numerical Example 3]
The image reading lens LG of Numerical Example 2 has an F number 6.5 that is necessary and sufficient for an image scanner, and various aberrations from on-axis to off-axis are sufficiently reduced as shown in FIG. Have gained.
The line sensor used in combination can be used in any case as long as the magnification is 0.189 times.
Each numerical value of conditional expressions (1) to (4) is shown in Table 7 to be described later.
As described above, even if a 9600 dpi line sensor with a center distance of 160 μm and a width of 2 μm in the short direction of the line sensor is used at this time, a ray tracing study is performed. As a result, as shown in FIG. 10, the color misalignment due to the sub-scanning magnification misalignment is about 0.4 pixels, which is sufficient performance.

Next, Table 7 shows the relationship between the conditional expressions (1) to (4) described above and various numerical values in the numerical examples 1 to 3.

The image reading lenses of any of the numerical examples have high imaging performance while having an ultra wide angle of view as described above.
The optical path length from the document surface to the line sensor is about 250 mm, which is suitable for use as a small carriage and an image reading device.
As described above, in this embodiment, the fourth Gs G4 is formed of an anamorphic surface as described above, and satisfies the above conditional expression, so that even when a high-resolution line sensor is used, field curvature aberration and magnification in the sub-scanning direction are used. Two of the deviations can be reduced satisfactorily.
In addition, this embodiment can realize an image reading lens having a wide angle of view and high image quality while having a lens configuration as small as four lenses.

[Flatbed image reader]
FIG. 12 is a schematic view of a main part when the image reading lens of any one of Numerical Examples 1, 2, and 3 of the present invention is applied to a carriage-integrated type (flatbed type) image reading apparatus such as a digital copying machine. .

The light beam emitted from the illumination system 53 illuminates the document directly or via a reflective shade.
The light reflected from the illuminated original 51 has its light path bent inside the carriage 57 via the first, second, third, and fourth reflecting mirrors 54a, 54b, 54c, and 54d. The bent light beam forms an image on the surface of the line sensor 55 as reading means by the image reading lens 56 of any one of the numerical examples 1, 2, and 3 described above.

The image information of the original 51 is read by moving the carriage 57 in the arrow H direction (sub-scanning direction) by the sub-scanning mechanism 58.
The read image information is sent to an external device such as a personal computer through an interface (not shown).
The image reading apparatus of the present invention uses the image reading lens 56 of any one of the numerical examples 1, 2, and 3 described above, thereby realizing an ultra-compact and high-quality image reading apparatus.
Note that the present invention is not limited to an integrated (flatbed) image reading apparatus, and may be applied to an image reading apparatus having a 1: 2 scanning optical system shown in FIG. be able to.

As shown in FIG. 13, a document 61 is placed on the surface of a document table (document glass) 62.
The illumination light source 63 is configured by, for example, a halogen lamp, a fluorescent lamp, a xenon lamp, an LED array, or the like.
The reflection shade 64 reflects the light beam from the illumination light source 63 and efficiently illuminates the document.
First, second, and third reflecting mirrors 65, 66, and 67 bend the optical path of the light beam from document 61 inside the main body.
The light beam based on the image information of the original 61 is imaged on the surface of the line sensor (CCD or CMOS sensor) 69 by any one of the image reading lenses 68 of the numerical examples 1 to 3.
70 is a main body, 74 is a pressure plate, 72 is a first mirror base, and 73 is a second mirror base.

In the figure, the light beam emitted from the illumination light source 63 illuminates the document 61 directly or via the reflective shade 64.
Then, the reflected light from the illuminated original 61 is bent through the first, second and third reflecting mirrors 65, 66, 67 inside the main body 70, and the surface of the line sensor 69 is bent by the image reading lens 68. The image is formed on the top.
At this time, the image information of the document 61 is read by electrically scanning the main scanning direction while the first, second, and third reflecting mirrors 65, 66, and 67 move in the sub-scanning direction.
At this time, the second and third reflection mirrors 66 and 67 move a half of the movement amount of the first reflection mirror 65 to keep the distance between the document 61 and the line sensor 69 constant.

  In this embodiment, the imaging optical system of the present invention is applied to an image reading apparatus of a digital color copying machine. However, the present invention is not limited to this, and can be applied to various color image reading apparatuses such as a color image scanner. it can.

1, 51, 61, 101 Document 2, 55, 69, 105 Reading means (line sensor)
3, 56, 68, 106 Image reading lens 58, 108 Sub-scanning mechanism

Claims (6)

An image reading lens for imaging image information on the document surface, and a plurality of line sensors arranged in parallel at the image information imaging position by the image reading lens, each pixel of the line sensor being Reading means having a plurality of line sensors arranged in the main scanning direction,
An image reading apparatus for reading image information on a document surface by moving the reading means in the sub-scanning direction,
When the width of the light receiving surface of each line sensor in the lateral direction is W and the distance between the centers of adjacent line sensors is L,
W / L ≦ 0.015
The filling,
The image reading lens includes an anamorphic lens having an anamorphic surface having at least one surface having a rotationally asymmetric shape with respect to the optical axis,
When at least one surface of the anamorphic lens has a cross-sectional shape of the anamorphic surface in the main scanning cross section including the optical axis and the main scanning direction as a generatrix, the anamorphic surface is perpendicular to the main scanning cross section and positioned in any generatrix direction The sub-curvature curvature defined in the plane including the normal line of the anamorphic surface at, changes continuously as it moves away from the optical axis along the generatrix direction,
A

N: Refractive index of the material of the anamorphic lens r ₁ : Radius of curvature of the principal ray at the principal ray passing position of the original side surface of the anamorphic lens r ₂ : Child at the principal ray passing position of the image side surface of the anamorphic lens Radius of curvature d: Defined as the distance at which the principal ray passes between the original side surface and the image side surface of the anamorphic lens, and the value of A with respect to the axial principal ray is A ₀ , the main scanning When the maximum value of A with respect to the luminous flux principal ray at all angles of view is A _max ,
-0.1 ≤ 1- (A _max / A ₀ ) ≤ 0.1
An image reading apparatus characterized by satisfying the above. The value of A with respect to the principal ray of light at a _{50% field} angle in the main scanning direction is A _50% .
_70% of the value of A with respect to the principal ray of light at a _{70% field} angle in the main scanning direction,
If the value of A with respect to the luminous flux principal ray at _{90% field} angle in the main scanning direction is A _90% ,
-0.05 ≦ 1- (A _70% / A _50% ) ≦ 0.05,
-0.08 ≦ 1- (A _90% / A _50% ) ≦ 0.08,
The image reading apparatus according to claim 1, wherein:   The image reading apparatus according to claim 1, wherein an incident surface and an output surface of the anamorphic lens are anamorphic surfaces having a rotationally asymmetric shape with respect to an optical axis.   4. The image reading apparatus according to claim 1, wherein the surface of the anamorphic lens has a curvature of a bus line and a curvature of a child line on the optical axis equal to each other. 5. The image reading lens includes, in order from the document surface side, a first lens having a meniscus positive refractive power with a convex surface on the document surface side, a second lens having a concave shape on both lens surfaces, and a first lens having convex surfaces on both lens surfaces. 3 lenses, a fourth meniscus lens with a convex surface facing the image side,
The anamorphic lens is the fourth lens.
The image reading apparatus according to claim 1, wherein the image reading apparatus is an image reading apparatus.   The image reading apparatus according to claim 5, wherein the fourth lens is formed of a resin.

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