JP2008052198A - Image reading lens and image reading apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading lens that is small in size, has a high aperture efficiency (95% or more), and has a wide field angle (half field angle of 25 ° or more) in which various aberrations including field curvature are sufficiently corrected. To obtain an image reading apparatus.
An image reading lens for reading image information on a document surface illuminated by light from a light source unit on a reading unit surface, the image reading lens having a biconcave shape in order from the document surface side. A negative first lens, an aperture stop, a biconvex positive second lens, a reading-side convex convex meniscus negative third lens, the third lens and the focal length of the entire system are f3, When f and i are the order when counted from the document surface, and the i-th and i + 1-th lens thicknesses and the air gap are di from the document surface side, 0.1 ≦ f / | f3 | ≦ 2. 0, (d1 + d2 + d3 + d4) /d5≦1.0.
[Selection] Figure 1

Description

  The present invention relates to an image reading lens and an image reading apparatus using the same. In particular, a digital image such as an image scanner or a digital copying machine, in which image information of an original is reduced and projected onto a line sensor (CCD) surface which is a reading element (reading unit) and the image information is read by the line sensor. It is suitable for equipment.

  An image reading lens used in an image reading apparatus such as an image scanner, a digital copying machine, a facsimile or the like reduces and projects image information of a document on a CCD surface as a reading element to form an image. This image reading lens is required to have, for example, an aperture efficiency of 95% or more, and various aberrations including spherical aberration are sufficiently corrected.

  Further, in order to reduce the size of the apparatus main body, it is desired that the image reading lens has a wide angle of view and a short distance between object images. It is also desired that the number of lenses be as small as possible in order to simplify and reduce the weight of the entire optical system. Furthermore, an image reading lens used in an image reading apparatus such as a color scanner is required to have particularly good correction of chromatic aberration.

  Normally, when the image reading lens has a wide angle of view, the curvature of field, astigmatism, distortion, and lateral chromatic aberration increase according to the angle of view, making it difficult to obtain sufficient contrast at all angles of view. .

  2. Description of the Related Art Conventionally, as an image reading lens suitable for use in such a wide angle of view, an image reading lens using a Tesser type, a telephoto type, or the like is known (see Patent Documents 1 and 2).

  Although the Tesser type image reading lens is compact and can correct various aberrations well, the upper limit of the half angle of view is about 18 °, and it is extremely difficult to correct astigmatism at a wider angle of view.

  In Patent Documents 1 and 2, a telephoto type is proposed for a wider angle of view from about 20 °. However, there is a problem that it is difficult to correct axial chromatic aberration and lateral chromatic aberration.

  Further, as a common problem of the two types of image reading lenses described above, the number of constituent lenses is four, which may be disadvantageous for reduction in size and weight.

For this reason, various types of triplet-type image reading lenses have been proposed in the past (see Patent Documents 3 and 4), which have a smaller number of lenses than the Tesser type and the telephoto type.
Japanese Patent Publication No. 61-9607 Japanese Patent Application Laid-Open No. 9-101452 JP-A 63-135911 Japanese Patent No. 3086261

  The image reading lens of Patent Document 3 is composed only of a spherical lens. For this reason, there is a problem that it is difficult to correct curvature of field, lateral chromatic aberration, peripheral coma, and the like.

  In Patent Document 4, Fno (F number) is bright and aspherical lenses are used in place. However, since the reduction magnification is as small as 0.09, for example, when the reduction magnification is 0.18 or more, there is a problem in that the amount of aberration increases.

  Further, since the first lens is a positive lens, there is a tendency to have a large power (refractive power) when a wide angle of view is obtained. Therefore, there is a problem that the curvature of the lens surface becomes small and lens processing becomes difficult.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading lens having a wide field angle in which a small size, high aperture efficiency, and various aberrations such as field curvature are sufficiently corrected, and an image reading apparatus having the same.

The image reading lens of the invention of claim 1
An image reading lens for reading image information by forming image information on a reading surface illuminated by light from a light source means on a reading means surface,
In order from the document surface side, a biconcave negative first lens, an aperture stop, a biconvex positive second lens, and a reading means side having a convex meniscus negative third lens,
The focal lengths of the third lens and the entire system are respectively the order of counting f3, f, and i from the document surface, and the i-th and i + 1-th lens thicknesses and air intervals are sequentially set from the document surface side. When di
0.1 ≦ f / | f3 | ≦ 2.0
(D1 + d2 + d3 + d4) /d5≦1.0
It is characterized by satisfying the following conditions.

The invention of claim 2 is the invention of claim 1,
The surface on the light source means side of the third lens has an aspherical shape, the surface on the light source means side has a paraxial radius of curvature of R3a, and the effective radius of the surface on the light source means side is 5 from the optical axis. When the sag amount of the aspherical surface at the height of the split, 70%, 90% is S3a _0.5 , S3a _0.7 , S3a _0.9 ,
-0.15 <S3a _0.5 /R3a<0.00
-0.70 <S3a _0.7 /R3a<-0.01
S3a _0.9 /R3a<-0.015
It is characterized by satisfying the following conditions.

The invention of claim 3 is the invention of claim 1 or 2, wherein
The surface on the reading means side of the third lens has an aspherical shape, the surface on the reading means side has a paraxial radius of curvature of R3b, and the effective radius of the surface on the reading means side is 5 from the optical axis. When the sag amount of the aspherical surface at the height of the split, 70%, 90% is S3b _0.5 , S3b _0.7 , S3b _0.9 ,
-0.15 <S3b _0.5 /R3b<-0.01
-0.60 <S3b _0.7 /R3b<-0.03
-2.50 <S3b _0.9 /R3b<-0.05
It is characterized by satisfying the following conditions.

The invention of claim 4 is the invention of claim 1, 2 or 3,
When the refractive indexes of the materials of the first lens and the third lens are N1 and N3, respectively 1.5 <(N1 + N3) / 2 <1.6
It is characterized by satisfying the following conditions.

The invention of claim 5 is the invention of any one of claims 1 to 4,
When the Abbe numbers of the materials of the first lens and the second lens are ν1 and ν2, respectively 29 <ν1 <33
50 <ν2 <60
It is characterized by satisfying the following conditions.

The invention of claim 6 is the invention of any one of claims 1 to 5,
The aperture stop is set so that the aperture efficiency of a light beam incident on the image reading lens is 95% or more at all angles of view.

An image reading apparatus according to a seventh aspect of the present invention provides:
The image reading lens according to any one of claims 1 to 6 is used to form image information on a document surface on a reading unit surface.

  According to the present invention, it is possible to achieve a small and lightweight image reading lens having a small number of constituent lenses and an image reading apparatus having the same.

  Embodiments of the present invention will be described below with reference to the drawings and tables.

  1 to 5 are cross-sectional views of the first to fifth embodiments of the image reading lens according to the present invention, and FIGS. 6 to 10 are first to third embodiments of the image reading lens according to the present invention. FIG. 5 is a diagram showing various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration).

  In the lens cross-sectional view, in the drawing, the left side is the enlargement side (the one with the long conjugate point) and the document surface P side (the side where the read image is provided), and the right side is the reduction side (the one with the short conjugate point). Q side (for example, a side where a CCD as a photoelectric conversion element is provided).

  LG is an image reading lens, and P is a document surface (object surface), on which image information for reading is formed. Q is an image plane on which reading means (reading element) such as a CCD is placed.

  The image reading lens LG reduces and forms image information on the document surface P illuminated with light from the light source means on the reading means (image surface) Q, and the reading means Q reads the image information.

  The image reading lens LG in FIGS. 1 to 5 includes, in order from the document surface P side, a biconcave negative first lens L1, an aperture stop SP, a biconvex positive second lens L2, and a reading means Q side. It has a convex meniscus negative third lens L3.

  In this embodiment, one or more lenses may be added to the light source means side of the first lens L1 and / or the reading means side of the third lens L3 to constitute four or more lenses.

  The aperture stop SP in the present embodiment is set so that the aperture efficiency of the light beam incident on the image reading lens LG is 95% or more at all angles of view.

In the present embodiment, the focal lengths of the third lens L3 and the entire system are in the order when the f3, f, and i are counted from the document surface P, respectively, and the i-th and i + 1-th in order from the document surface P side. When the lens thickness and air interval of
0.1 ≦ f / | f3 | ≦ 2.0 (1)
(D1 + d2 + d3 + d4) /d5≦1.0 (2)
Is set to satisfy the following conditions.

  The lower limit value of conditional expression (2) is preferably 0.3.

In this embodiment, when the refractive indexes of the materials of the first lens L1 and the third lens L3 are N1 and N3, respectively, 1.5 <(N1 + N3) / 2 <1.6 (3)
Is set to satisfy the following conditions.

In this embodiment, when the Abbe numbers of the materials of the first lens L1 and the second lens L2 are ν1 and ν2, respectively 29 <ν1 <33 (4)
50 <ν2 <60 (5)
Is set to satisfy the following conditions.

  Next, technical meanings of the conditional expressions (1) to (5) will be described.

  Conditional expression (1) is a condition for satisfactorily correcting distortion and coma. If the lower limit value of conditional expression (1) is exceeded, it will be difficult to correct distortion, which is not good. If the upper limit of conditional expression (1) is exceeded, it is not good because it is difficult to correct coma. Conditional expression (1) also serves as a condition that, when the third lens L3 is formed of a resin material, changes in the image plane position due to temperature changes can be minimized.

  Conditional expression (2) is a condition for appropriately setting the position of the third lens L3 having an aspherical surface in the optical axis direction and favorably correcting astigmatism and field curvature at a wide angle of view. . If the conditional expression (2) is not satisfied, it is difficult to correct astigmatism and curvature of field, which is not good.

  Conditional expression (3) is a condition for defining the ranges of the refractive indexes of the glass material and resin of the first lens L1 and the third lens L3. If the conditional expression (3) is not satisfied, it is difficult to correct various aberrations.

  Conditional expressions (4) and (5) are conditions for defining ranges of glass materials and resin materials that can be used for forming the first and second lenses L1 and L2, respectively. If any one of the conditional expressions (4) and (5) is not satisfied, there is no appropriate glass material and resin, or good correction of chromatic aberration becomes difficult, which is not good.

  Furthermore, in the present invention, the conditional expressions (1) to (5) are preferably set as follows.

0.4 ≦ f / | f3 | ≦ 1.4 (1a)
0.4 ≦ (d1 + d2 + d3 + d4) /d5≦0.8 (2a)
1.52 <(N1 + N3) / 2 <1.58 (3a)
30 <ν1 <31 (4a)
51 <ν2 <58 (5a)
In Examples 1 to 5 described later, both surfaces of the first, second, and third lenses L1, L2, and L3 are aspherical surfaces. Thereby, in each embodiment, various aberrations such as spherical aberration are corrected satisfactorily.

  In Examples 1 to 5, two lenses of the first and third lenses L1 and L3 are formed of resin. Thereby, weight reduction is achieved in the present embodiment.

  The resin materials of the first and third lenses L1 and L3 used in Examples 1 to 5 are polycarbonate (PC) for the first lens L1 and brand name ZEONEX (Nippon Zeon Corporation) for the third lens L3. Etc. are used.

The surface on the light source means (original surface P) side of the third lens L3 has an aspherical shape as described above, and the surface on the light source means side has a paraxial radius of curvature of R3a and the effective radius of the surface on the light source means side. Then, when the sag amount of the aspherical surface at the height of 50%, 70%, 90% from the optical axis is S3a _0.5 , S3a _0.7 , S3a _0.9 ,
-0.15 <S3a _0.5 /R3a<0.00 (6a)
-0.70 <S3a _0.7 /R3a<-0.01 (6b)
S3a _0.9 /R3a<-0.015 (6c)
Is set to satisfy the following conditions.

  Conditional expressions (6a), (6b), and (6c) are aspherical surfaces at the height of 50%, 70%, and 90% from the optical axis, respectively, in the aspherical shape of the surface of the third lens L3 on the light source means side. This relates to the ratio between the sag amount of the shape and the paraxial radius of curvature. For reading images with a wide field angle (half field angle of 25 ° or more) in which various aberrations including field curvature are sufficiently corrected if any one of conditional expressions (6a), (6b), and (6c) is deviated It ’s not good because you ca n’t get a lens.

Further, the surface on the reading means Q side of the third lens L3 is aspherical as described above. The surface on the reading means Q side has a paraxial radius of curvature of R3b, and the effective radius of the surface on the reading means Q side. When the sag amount of the aspherical surface at the height of 50%, 70%, 90% from the optical axis is S3b _0.5 , S3b _0.7 , S3b _0.9 ,
-0.15 <S3b _0.5 /R3b<-0.01 (7a)
-0.60 <S3b _0.7 /R3b<-0.03 (7b)
-2.50 <S3b _0.9 /R3b<-0.05 (7c)
Is set to satisfy the following conditions.

  The above conditional expressions (7a), (7b), and (7c) are respectively non-spherical at the height of 50%, 70%, and 90% from the optical axis in the aspherical shape of the surface on the reading means Q side of the third lens L3. This relates to the ratio between the sag amount of the spherical shape and the paraxial radius of curvature. For reading images with a wide field angle (half field angle of 25 ° or more) in which various aberrations including field curvature are sufficiently corrected if any one of conditional expressions (7a), (7b), and (7c) is deviated It ’s not good because you ca n’t get a lens.

Here, in FIG. 11, the sag amount (Sag) of the aspherical shape is the surface position Rah in the optical axis direction at the height h from the optical axis of the reference spherical surface, and the optical axis direction in the height h from the optical axis of the aspherical surface. When the surface position is Rash,
Sag = Rah-Rash
It is. However, the coordinates of the surface position are positive in the light traveling direction. The relationship between the shape of the reference spherical surface, the sign of the sag amount Sag, and the aspherical shape is as shown in Table A below.

(Table-A)
Reference spherical surface Sag amount Sag Aspheric shape Light source means side is concave positive Positive negative refractive power is strong Light source means side is concave negative Negative refractive power is weak Read means side is concave positive Negative refractive power is weak Read means side is concave negative Negative The refractive power of the light source means is convex convex on the light source side.The positive refractive power is weak. In addition, in Example 1, in Example 1,
The aspherical shape of the surface on the light source means side of the first lens L1 is a shape in which the negative refractive power increases from the lens center to the lens peripheral part.

  The aspherical shape of the surface on the reading means side of the first lens L1 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the second lens L2 is a shape in which the positive refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the second lens L2 is such that the positive refractive power increases from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the third lens L3 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the third lens L3 is such that the positive refractive power increases from the lens center to the lens periphery.

In Example 2,
The aspherical shape of the surface on the light source means side of the first lens L1 is a shape in which the negative refractive power increases from the lens center to the lens peripheral part.

  The aspherical shape of the surface on the reading means side of the first lens L1 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the second lens L2 is a shape in which the positive refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the second lens L2 is such that the positive refractive power increases from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the third lens L3 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the third lens L3 is such that the positive refractive power increases from the lens center to the lens periphery.

In Example 3,
The aspherical shape of the surface on the light source means side of the first lens L1 is a shape in which the negative refractive power increases from the lens center to the lens peripheral part.

  The aspherical shape of the surface on the reading means side of the first lens L1 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the second lens L2 is a shape in which the positive refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the second lens L2 is such that the positive refractive power increases from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the third lens L3 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the third lens L3 is such that the positive refractive power increases from the lens center to the lens periphery.

In Example 4,
The aspherical shape of the surface on the light source means side of the first lens L1 is a shape in which the negative refractive power increases from the lens center to the lens peripheral part.

  The aspherical shape of the surface on the reading means side of the first lens L1 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the second lens L2 is a shape in which the positive refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the second lens L2 is such that the positive refractive power increases from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the third lens L3 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the third lens L3 is such that the positive refractive power increases from the lens center to the lens periphery.

In Example 5,
The aspherical shape of the surface on the light source means side of the first lens L1 is a shape in which the negative refractive power increases from the lens center to the lens peripheral part.

  The aspherical shape of the surface on the reading means side of the first lens L1 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the second lens L2 is a shape in which the positive refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the second lens L2 is such that the positive refractive power increases from the lens center to the lens periphery.

  The aspherical shape of the surface on the light source means side of the third lens L3 is a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  The aspherical shape of the surface on the reading means side of the third lens L3 is such that the positive refractive power increases from the lens center to the lens periphery.

  Next, numerical examples 1 to 5 corresponding to the first to fifth embodiments of the present invention will be shown.

  In each numerical example, the i column in the table is a surface number counted from the document surface. r is the radius of curvature of the surface, d is the lens thickness and air spacing, and n and ν are the refractive index and Abbe number of the material at the d-line, respectively. Note that the description of the air gap between the document surface and the first lens and the air gap between the third lens and the CCD is omitted. f is the focal length of the entire system at line e, Fno is the F number when the document surface distance is infinite, Y is the object height on the document side, m is the imaging magnification (document reading magnification), and ω / 2 is the half angle of view. ing.

  The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, k is the eccentricity, and B, C, D, and E are not When using spherical coefficient

It is expressed by the following formula.

Further, for example, the display of “e-Z” means “10 ^−Z ”. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.
[Numerical Example 1]
f = 32.38mm Fno = 6.5 m = -0.18898 Y = 108.0 ω / 2 = 31.1 °
i r d n ν
1 -101.73 2.37 1.5831 30.2
2 11.21 0.49
3 Aperture 0.12
4 17.60 3.08 1.6884 52.6
5 -11.52 12.02
6 -7.89 1.39 1.5247 56.2
7 -14.62

Aspheric coefficient
R1 k = -2.18159e + 02 B = -1.27311e-03 C = 1.73771e-05 D = 1.77550e-07 E = -6.99612e-09
R2 k = -6.76798e + 00 B = -1.07373e-03 C = 2.28480e-05 D = 9.66990e-07 E = 3.80441e-08
R3 k = -2.49188e + 00 B = -4.88146e-04 C = -6.39907e-06 D = 8.72221e-07 E = 2.77242e-08
R4 k = -3.30849e-01 B = -1.53105e-04 C = -3.40564e-06 D = -3.16843e-07 E = 1.87024e-08
R5 k = -1.54979e-01 B = 2.23659e-05 C = -7.35209e-07 D = -7.73028e-09 E = -1.27356e-10
R6 k = -5.03607e-01 B = 4.79811e-05 C = -5.63846e-07 D = 2.50057e-09 E = 1.51867e-12

[Numerical Example 2]
f = 28.42mm Fno = 6.5 m = -0.18898 Y = 108.0 ω / 2 = 34.5 °
i r d n ν
1-160.14 3.11 1.5831 30.2
2 9.94 0.50
3 Aperture 0.10
4 14.50 2.09 1.6884 52.6
5 -11.94 13.64
6 -5.29 1.15 1.5247 56.2
7 -7.67

Aspheric coefficient
R1 k = -1.77629e + 03 B = -1.03085e-03 C = 1.03402e-05 D = 1.23098e-07 E = -4.32727e-09
R2 k = -1.13948e + 00 B = -1.17412e-03 C = 3.05292e-05 D = 4.95063e-07 E = 7.35780e-08
R3 k = -1.14651e + 00 B = -4.68684e-04 C = 1.19534e-07 D = -1.76260e-07 E = 7.39693e-08
R4 k = 2.23425e-02 B = -1.76702e-04 C = -7.68893e-06 D = -3.56861e-07 E = 2.11532e-08
R5 k = -5.13608e-01 B = 2.20334e-04 C = 2.45868e-08 D = -1.09124e-10 E = 1.37266e-10
R6 k = -7.84789e-01 B = 1.56453e-04 C = -7.93378e-07 D = 3.27773e-09 E = 1.25196e-11

[Numerical Example 3]
f = 32.38mm Fno = 6.5 m = -0.18898 Y = 108.0 ω / 2 = 31.6 °
i r d n ν
1 -98.45 2.28 1.5831 30.2
2 13.12 0.86
3 Aperture 0.13
4 17.50 2.26 1.6779 54.9
5 -12.98 12.69
6 -8.05 1.79 1.5300 55.8
7 -15.02

Aspheric coefficient
R1 k = 1.11447e + 02 B = -1.29948e-03 C = 1.80696e-05 D = 4.99136e-08
R2 k = -9.12738e + 00 B = -1.04319e-03 C = 2.63278e-05 D = 7.02897e-07
R3 k = 5.53422e-01 B = -2.32387e-04 C = 2.86113e-08 D = 1.15704e-06
R4 k = -6.87387e-01 B = -1.15429e-05 C = 3.15966e-06 D = -2.12330e-07 E = 4.22310e-08
R5 k = -1.14994e-01 B = 1.77308e-05 C = -1.21438e-06 D = -8.04801e-09 E = -4.47290e-11
R6 k = -5.06792e-01 B = 3.64800e-05 C = -7.28039e-07 D = 3.52594e-09 E = 6.94803e-12

[Numerical Example 4]
f = 35.93mm Fno = 6.5 m = -0.22028 Y = 108.0 ω / 2 = 31.0 °
i r d n ν
1 -156.98 2.29 1.5831 30.2
2 11.60 0.48
3 Aperture 0.09
4 18.11 3.23 1.6884 52.6
5 -12.32 11.62
6 -7.61 2.01 1.5247 56.2
7 -13.56

Aspheric coefficient
R1 k = -3.37017e + 02 B = -1.17720e-03 C = 1.57835e-05 D = 2.51992e-07 E = -1.05139e-08
R2 k = -6.22276e + 00 B = -1.04802e-03 C = 2.16482e-05 D = 1.23216e-06 E = 1.44740e-08
R3 k = -2.42590e + 00 B = -4.22922e-04 C = -5.08660e-06 D = 9.52004e-07 E = 1.88072e-08
R4 k = -3.52820e-01 B = -1.46449e-04 C = -2.45358e-06 D = -2.62400e-07 E = 1.56460e-08
R5 k = -1.65241e-01 B = 4.11619e-05 C = -8.45408e-07 D = -4.99554e-09 E = -9.51538e-11
R6 k = -4.28230e-01 B = 5.20067e-05 C = -480204e-07 D = 2.08442e-09 E = 5.69643e-12

[Numerical Example 5]
f = 48.99mm Fno = 6.5 m = -0.22028 Y = 152.0 ω / 2 = 31.7 °
i r d n ν
1 -147.91 3.28 1.5831 30.2
2 17.90 0.83
3 Aperture 0.13
4 23.31 4.10 1.6779 54.9
5 -17.51 14.10
6 -9.04 2.75 1.5300 55.8
7 -15.59

Aspheric coefficient
R1 k = -1.07918e + 01 B = -4.26479e-04 C = 3.71249e-06 D = 2.60927e-10 E = -1.70793e-10
R2 k = -1.13258e + 01 B = -3.34832e-04 C = 5.98846e-06 D = 5.29378e-08 E = 1.30884e-09
R3 k = -2.48280e + 00 B = -1.82681e-04 C = 6.60389e-07 D = 7.27734e-08 E = 2.73057e-10
R4 k = -6.29964e-01 B = -4.44814e-05 C = -4.97389e-07 D = -3.42783e-08 E = 1.00466e-09
R5 k = -2.02667e-01 B = 3.28029e-05 C = -8.85291e-08 D = -2.10157e-09 E = 1.29830e-11
R6 k = -7.96531e-01 B = 2.21592e-05 C = -1.37678e-07 D = 5.75834e-10 E = -1.97864e-13

  FIG. 12 is a schematic view of the essential portions of Embodiment 1 when any of the image reading lenses of Embodiments 1 to 5 of the present invention is applied to an image reading apparatus of a digital color copying machine.

  In the figure, reference numeral 2 denotes an original platen glass on which an original 1 is placed. Reference numeral 4 denotes an illumination light source, which includes, for example, a halogen lamp, a fluorescent lamp, a xenon lamp, or the like. Reference numeral 3 denotes a reflective shade, which reflects a light beam from the illumination light source 4 and efficiently illuminates the document 1. Reference numerals 5, 6, and 7 denote first, second, and third reflecting mirrors, respectively, which bend the optical path of the light beam from the document 1 inside the main body. Reference numeral 8 denotes the image reading lens according to any one of the first to fifth embodiments described above, and forms a light beam based on the image information of the original 1 on the surface of the reading unit 9. Reference numeral 9 denotes a line sensor (CCD) as reading means. Reference numeral 10 denotes a main body, and 11 denotes a pressure plate.

  In this embodiment, the light beam emitted from the illumination light source 4 illuminates the document 1 directly or via the reflective shade 3. Then, the reflected light from the document 1 illuminated by the illumination light source 4 is bent through the first, second, and third reflecting mirrors 5, 6, 7 inside the main body, and the light path of the light beam is bent by the image reading lens 8. The image is formed on the CCD 9 surface. At this time, the image information of the document 1 is read by electrically scanning the main scanning direction while the first, second, and third reflecting mirrors 5, 6, and 7 move in the sub-scanning direction. At this time, the second and third reflection mirrors 6 and 7 are moved by half of the movement amount of the first reflection mirror 5 so that the distance between the document 1 and the CCD 9 is constant.

  In this embodiment, the image reading lens of the present invention is applied to an image reading apparatus having a 1: 2 scanning optical system. However, the present invention is not limited to this, and for example, an integrated (flatbed) image reading shown in FIG. Even when applied to an apparatus, the present invention can be applied in the same manner as in the first embodiment.

  In FIG. 13, the light beam emitted from the illumination means 24 illuminates the document 21 directly or via the reflective shade 23. The reflected light beam from the document 21 illuminated by the illumination means 24 is bent in the carriage 31 through the first, second, third, and fourth reflecting mirrors 25, 26, 27, and 28. The bent light beam forms an image on the surface of a linear image sensor 30 (hereinafter referred to as “CCD”) such as a one-dimensional CCD by an image reading lens 29. Then, the image information of the original 21 is read by moving the carriage 31 in the direction of arrow C (sub-scanning direction) shown in the drawing by a sub-scanning motor (not shown). The CCD 30 in the figure has a configuration in which a plurality of light receiving elements are arranged in a one-dimensional direction (main scanning direction).

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

  As described above, according to each embodiment, by introducing an aspherical surface into the image reading lens, the reduction magnification is 0.18 or more, the aperture efficiency is 95% or more, and various aberrations including curvature of field are sufficient. Thus, it is possible to obtain an image reading lens and an image reading apparatus having a half angle of view of 25 ° or more corrected in this way.

Cross-sectional view of a lens according to Example 1 of the present invention Lens sectional drawing of Example 2 of the present invention Lens sectional view of Example 3 of the present invention Lens sectional view of Example 4 of the present invention Lens sectional drawing of Example 5 of the present invention Various aberration diagrams of Example 1 of the present invention Various aberration diagrams of Embodiment 2 of the present invention Various aberration diagrams of Embodiment 3 of the present invention Various aberration diagrams of Embodiment 4 of the present invention Various aberration diagrams of Embodiment 5 of the present invention Explanatory drawing for demonstrating the amount of sag of this invention Schematic diagram of essential parts when the image reading lens of the present invention is applied to an image reading apparatus. Schematic diagram of essential parts when the image reading lens of the present invention is applied to an image reading apparatus.

Explanation of symbols

LG Image Reading Lens L1 First Lens L2 Second Lens L3 Third Lens SP Aperture P Document Surface Q Reading Element 1 Document 2 Document Glass 3 Reflecting Shade 4 Illumination Light Source (Lamp)
5, 6, 7 Reflecting mirror 8 Image reading lens 9 Reading means (CCD)
10 Body 11 Pressure plate

Claims (7)

An image reading lens for reading image information by forming image information on a reading surface illuminated by light from a light source means on a reading means surface,
In order from the document surface side, a biconcave negative first lens, an aperture stop, a biconvex positive second lens, and a reading means side having a convex meniscus negative third lens,
The focal lengths of the third lens and the entire system are respectively the order of counting f3, f, and i from the document surface, and the i-th and i + 1-th lens thicknesses and air intervals are sequentially set from the document surface side. When di
0.1 ≦ f / | f3 | ≦ 2.0
(D1 + d2 + d3 + d4) /d5≦1.0
An image reading lens satisfying the following conditions: The surface on the light source means side of the third lens has an aspherical shape, the surface on the light source means side has a paraxial radius of curvature of R3a, and the effective radius of the surface on the light source means side is 5 from the optical axis. When the sag amount of the aspherical surface at the height of the split, 70%, 90% is S3a _0.5 , S3a _0.7 , S3a _0.9
-0.15 <S3a _0.5 / R3a <0
-0.70 <S3a _0.7 /R3a<-0.01
S3a _0.9 /R3a<-0.015
The image reading lens according to claim 1, wherein the following condition is satisfied. The surface on the reading means side of the third lens has an aspherical shape, the surface on the reading means side has a paraxial radius of curvature of R3b, and the effective radius of the surface on the reading means side is 5 from the optical axis. When the sag amount of the aspherical surface at the height of the split, 70%, 90% is S3b _0.5 , S3b _0.7 , S3b _0.9 ,
-0.15 <S3b _0.5 /R3b<-0.01
-0.60 <S3b _0.7 /R3b<-0.03
-2.50 <S3b _0.9 /R3b<-0.05
The image reading lens according to claim 1, wherein the following condition is satisfied. When the refractive indexes of the materials of the first lens and the third lens are N1 and N3, respectively 1.5 <(N1 + N3) / 2 <1.6
The image reading lens according to claim 1, wherein the following condition is satisfied. When the Abbe numbers of the materials of the first lens and the second lens are ν1 and ν2, respectively 29 <ν1 <33
50 <ν2 <60
The image reading lens according to claim 1, wherein the following condition is satisfied.   6. The aperture stop according to claim 1, wherein the aperture stop is set so that an aperture efficiency of a light beam incident on the image reading lens is 95% or more at all angles of view. The lens for image reading as described.   7. An image reading apparatus, wherein image information on a document surface is formed on a reading means surface using the image reading lens according to claim 1.