JPH04253016A - Original reading lens - Google Patents

Abstract

PURPOSE:To offer an original reading lens which has high F/No=3 brightness, a wide 30 deg. half-view angle, nearly 100% numerical aperture up to the peripheral part, and a high contrast. CONSTITUTION:A retrofocus type is constituted by arraying a 1st lens 1, a 2nd lens 2, a 3rd lens 3, a 4th lens 4, and a 5th lens 5 in order from the object side to the image side. Two lens surfaces including a 1st lens surface is made aspherical so as to compensate the aberration of divergency generated by the 1st lens.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens for reading originals. The present invention can be used in facsimiles, image scanners, digital copying machines, etc.

0002

2. Description of the Related Art Scanning a document and reading document information using an image sensor such as a CCD is widely used in connection with facsimiles, image scanners, digital copying machines, and the like. A document reading lens is a lens for forming an image of a document on an image sensor, and conventionally known types include Gauss type, topogon type, Tessar type, and triplet type.

[0003] In general, the performance of a document reading lens is that it can form an image with high contrast for spatial frequencies of up to 4 lines/mm on the document surface, and that its aperture efficiency is approximately 100% up to the periphery. is requested.

[0004] In addition, in order to realize miniaturization of the document reading device, it is desirable that the device has a wide angle of view in which the distance between the document image formed by the document reading lens and the document is small.
Furthermore, in order to achieve high-speed document reading, it is desirable to have a large aperture and brightness. However, the above-mentioned various document reading lenses do not fully meet the requirements for wide angle of view and large aperture.

That is, the Gaussian type is suitable for increasing the aperture, but is not suitable for widening the angle of view, and the Tessar type and triplet type have a dark brightness of F/No = 4.5 to 5.6, and are half-sized. The angle of view is also narrow, around 20 degrees or less. Although the topogon type has a relatively wide angle of view, the maximum angle of view of the conventionally known types is about 23 degrees.

[0006]

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances. Approximately 100
% and is capable of forming a high-contrast image.

[0007]

[Means for Solving the Problems] The document reading lens of the present invention has the same lens configuration as the lenses of claims 1 to 5, and the first to fifth groups are sequentially arranged from the object side to the image side. It becomes.

As shown in FIG. 1, the first group disposed closest to the object side is the first lens 1, which is a negative meniscus lens with a convex surface facing the object side, and the second group following this is a positive lens. The second lens 2 and the third lens 3 are biconcave lenses.
, the fourth group is a fourth lens 4 which is a positive lens, and the fifth group disposed closest to the image side is a fifth lens 5 which is a positive meniscus lens with a convex surface facing the object side. Therefore, the total is 5
It consists of 5 elements in a group. Further, the document reading lenses of each claim are also common in that two lens surfaces are aspherical.

In the document reading lens according to the first aspect, the first and third lens surfaces counted from the object side are aspherical surfaces, and the conic constants K1 and K3 of these aspherical surfaces are (1-
I) -0.16<K1<0.03, (1-II)
The condition -0.2 <K3<-0.05 is satisfied.

In the document reading lens according to the second aspect, the first and fourth lens surfaces counted from the object side are aspherical surfaces, and the conic constants K1 and K4 of these aspherical surfaces are (2-
I) -0.54<K1<0, (2-I
I) Satisfies the condition -1100<K4<-1.1.

In the document reading lens according to the third aspect, the first and second lens surfaces counted from the object side are aspherical surfaces, and the conic constants K1 and K2 of these aspherical surfaces are (3-
I) −0.7 <K1< 0 , (3-I
I) Satisfies the condition -0.2 <K2< 0.

In the document reading lens according to the fourth aspect, the first and fifth lens surfaces counted from the object side are aspherical surfaces, and the conic constants K1 and K5 of these aspherical surfaces are (4-
I) -0.47<K1<-0.03, (4-I
I) Satisfies the following condition: 0.8 <K5 < 6.9.

In the document reading lens according to the fifth aspect, the first and sixth lens surfaces counted from the object side are aspherical surfaces, and the conic constants K1 and K6 of these aspherical surfaces are (5-
I) -0.57<K1<-0.045, (5-I
I) Satisfies the condition 0.5 <K6 < 1.2. As described above, the document reading lenses according to claims 1 to 5 also have in common that the first lens surface counted from the object side is an aspherical surface.

For the aspherical surface, the radius of curvature on the optical axis is R, the height from the optical axis is H, the amount of deviation from the reference spherical surface is X, and K is the conic constant, 4th, 6th, 8th, 10th When the following aspheric coefficients are A, B, C, and D, respectively, X=[(1/R)H2/{1+√[Y]}]+A・
H4+B・H6+C・H8+D・H10, Y=1−(1
+K)(1/R)2H2 It is a curved surface expressed by the formula. The symbol √［ in this formula
Y] represents the square root of Y.

[0015]

[Operation] The document reading lens of the present invention uses a retrofocus type to achieve a wide angle of view and approximately 100% aperture efficiency up to the periphery. This type of lens can obtain a wide angle of view and approximately 100% aperture efficiency due to the preceding negative lens (first group), but on the other hand, it has a large aperture due to the divergent aberration caused by the negative lens. is not necessarily easy.

Generally, as the aperture increases, coma flare increases and contrast deteriorates. To suppress coma flare, it is best to correct the extremely refracted surfaces at each entrance and exit surface. However, with a spherical surface, only the same correction can be made on any of the entrance and exit surfaces, so it is insufficient for correcting coma flare. Therefore, an aspheric surface is used as a means to continuously change the refractive power from the axis toward the periphery, thereby minimizing the coma flare that occurs when the diameter of a retrofocus lens is increased.

When the first and third lens surfaces counted from the object side are aspherical as in the lens of claim 1, the first lens surface satisfies the condition (1-I). The spherical shape is "an ellipsoidal surface that is rotationally symmetrical about the major axis or the minor axis," and the aspherical shape of the third lens surface that satisfies condition (1-II) is "an ellipsoidal surface that is rotationally symmetrical about the major axis." By satisfying these conditions, optimal comatic aberration can be achieved.

In the case where the first and fourth lens surfaces counted from the object side are aspherical as in the lens of claim 2, the first lens surface satisfies condition (2-I). The spherical shape is an ellipsoid with rotational symmetry about the long axis, and the condition (2-I
The aspherical shape of the fourth lens surface that satisfies I) is a "hyperboloid", and by satisfying these conditions, optimal comatic aberration can be achieved.

When the first and second lens surfaces counted from the object side are aspherical as in the lens of claim 3, the first lens surface satisfies condition (3-I). The spherical shape is "ellipsoidal surface rotationally symmetrical about the long axis", condition (3-I
The aspherical shape of the second lens surface that satisfies I) is "an elliptical surface that is rotationally symmetrical about the long axis," and by satisfying these conditions, optimal comatic aberration can be achieved.

When the first and fifth lens surfaces counted from the object side are aspherical as in the lens of claim 4, the first lens surface satisfies condition (4-I). The spherical shape is "ellipsoidal surface rotationally symmetrical about the major axis", condition (4-I
The aspherical shape of the fifth lens surface that satisfies I) is "an elliptical surface that is rotationally symmetrical about the short axis," and by satisfying these conditions, optimal comatic aberration can be achieved.

When the first and sixth lens surfaces counted from the object side are aspherical as in the lens of claim 5, the first lens surface satisfies condition (5-I). The spherical shape is an "ellipsoidal surface rotationally symmetrical about the major axis" and the condition (5-I
The aspherical shape of the sixth lens surface that satisfies I) is "an ellipsoidal surface that is rotationally symmetrical about the short axis," and by satisfying these conditions, optimal comatic aberration can be achieved.

[0022]

[Examples] Three specific examples will be given below for each lens in each claim. In each example, as shown in FIG. 1, the i-th surface (numeral 6 in FIG.
The cover of the image sensor CCD shown in (including the lath surface) is
The suffix is Ri, the distance between the i-th surface and the i+1-th surface on the optical axis is Di, and the refractive index and Abbe number of the material of the j-th lens and cover glass are respectively counted from the object side. , Nj with j as the suffix,
Represented by νj. Further, f represents the composite focal length of the entire system, F/No represents brightness, m represents magnification, and ω represents a half angle of view. Further, for an aspherical surface, the shape is specified by giving a conic constant K and higher-order aspherical coefficients A, B, C, and D. Note that the [E-number] in the display of higher-order aspherical coefficients represents a power. For example, [E-10
] means [1/1010], and this number is multiplied by the number before it.

Example 1 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
33.421 2.398 1
1.48749 70.2 2
11.592 10.180

3 16.220 10.000
2 1.83400 37.2 4
-47.763 0.050

5 -51.406
5.377 3 1.92286 20.
9 6 16.098 1
．． 511
7 107
．． 812 3.536 4 1.786
50 50.0 8 -17.69
6 0.050
9
15.653 6.195 5
1.81600 46.6 10
14.672 15.020

11 ∞
0.700 6 1.51633 64.1
12 ∞

Aspheric first surface K = 0.073050, A = -4.54381E-
7, B=-8.55888E-9, C=-6.9945
1E-11, D=-4.50639E-14 3rd surface K=-0.183285, A=-1.00805E-5
, B=1.78295E-9, C=-4.76141E
-10, D=2.17784E-12

Example 2 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
22.535 0.800 1
1.49700 81.6 2
12.081 16.368

3 13.011 8.60
8 2 1.69500 42.2 4
-53.797 0.405

5 -19.777
0.800 3 1.75084 27
．． 7 6 14.583
1.258
7-201
．． 892 2.477 4 1.651
00 56.2 8 -12.14
8 0.050
9
16.574 8.562 5
1.65100 56.2 10
19.401 15.390

11 ∞
0.700 6 1.51633 64.1
12 ∞

Aspheric first surface K = 0.028395, A = 1.41033E
-6, B=1.18919E-8, C=-1.1591
8E-10, D=3.84470E-13 3rd surface K=-0.060346, A=-7.02415E-6
,B=-1.01647E-7,C=4.0135
4E-9, D=-3.56689E-11

Example 3 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
23.648 4.490 1
1.49700 81.602
9.728 6.693

3 16.898 10.00
0 2 1.88767 36.584
-24.943 0.050

5 -23.441
3.112 3 1.86721 22.
016 17.043 1.
105
7 -255.4
77 4.640 4 1.69674
55.518 -13.183
0.050
9
16.828 6.444 5 1
．． 88300 40.8010 16
．． 139 14.659
11
∞ 0.70
0 6 1.51633 64.1 12
∞

Aspheric first surface K=-0.145310, A=-2.93478E-6
,B=-1.65722E-8,C=6.2766
8E-12, D=-5.34699E-13 3rd surface K=-0.113426, A=-5.38014E-6
, B=-3.50261E-9, C=-3.19693
E-11, D= 3.73658E-12

The first to third embodiments described above are examples of the document reading lens according to claim 1.

Example 4 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
29.584 4.367 1
1.48749 70.2 2
10.844 10.000

3 15.315 9.54
6 2 1.83400 37.2 4
-41.147 0.038

5 -41.274
3.580 3 1.92286 20
．． 9 6 17.306
2.225
7-9
8.184 1.334 4 1.78
650 50.0 8 -14.8
23 0.050
9
16.089 6.604
5 1.81600 46.6 10
15.930 14.832

11 ∞
0.700 6 1.51633 64.
1 12 ∞

Aspheric first surface K=-0.496804, A=-5.63482E-6
,B=-1.05443E-8,C=5.8773
8E-12, D=-5.34172E-14 4th surface K=-19.322497, A= 1.18935E
-5,B=-1.08761E-7,C=-1.177
85E-9, D=9.23411E-11

Example 5 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
19.501 2.137 1
1.49700 81.6 2
10.999 15.287

3 12.092 7.14
2 2 1.69500 42.2 4
-186.067 0.486

5 -21.318
0.800 3 1.75084 27.
7 6 14.857 1
．． 289
7-117.
820 1.857 4 1.6510
0 56.2 8 -11.279
0.050
9
17.033 8.475 5
1.65100 56.2 10
21.588 15.202
1
1 ∞ 0
．． 700 6 1.51633 64.1
12 ∞

Aspheric first surface K=-0.00078, A=1.56366E
-6,B=6.97597E-9,C=-7.0064
6E-12, D=2.43427E-13 4th surface K=-965.65770, A=2.45391E
-5,B=6.31461E-8,C=-2.08
515E-8, D= 1.24916E-9

Example 6 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
22.705 3.825 1
1.52500 78.042
9.512 5.607

3 15.761 10.00
0 2 1.88627 37.744
-24.795 0.050

5 -23.611
2.787 3 1.87379 21.
876 17.363 1.
109
7-81.
017 4.191 4 1.7274
7 53.718 -12.892
0.050
9
16.663 6.124 5
1.88300 40.8010 1
6.429 14.597
11
∞ 0.7
00 6 1.51633 64.1 1
2 ∞

Aspheric first surface K=-0.354787, A=-7.11359E-6
, B=-2.28794E-8, C=-1.42448
E-11, D=-5.45912E-13 4th surface K=-1.118743, A= 6.22703E-
6, B=-1.65508E-7, C=-5.5755
6E-9, D=1.51216E-10

The fourth to sixth embodiments described above are examples of the document reading lens according to claim 2.

Example 7 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
22.630 2.782 1
1.48749 70.2 2
9.687 6.946

3 15.590 10.0
00 2 1.83400 37.2 4
-44.522 0.054

5 -39.721
4.462 3 1.92286 2
0.9 6 16.751
1.411
7
93.320 3.950 4 1.
78650 50.0 8 -16
．． 254 0.050
9
15.909 6.623
5 1.81600 46.6 10
14.524 13.849

11 ∞
0.700 6 1.51633 6
4.1 12 ∞

Aspheric first surface K=-0.665470, A=-6.12417E-6
, B=-1.14435E-7, C=-2.46058
E-10, D = 1.46981E-12 2nd surface K = -0.144584, A = 1.26080E-
5,B=-2.15648E-7,C=7.167
40E-10, D=-2.16116E-11

Example 8 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
18.180 0.800 1
1.49700 81.6 2
10.628 16.651

3 15.200 9.97
2 2 1.69500 42.2 4
-39.185 0.370

5 -18.819
0.800 3 1.75084 27
．． 7 6 15.691
1.266
7 11
4.146 2.598 4 1.65
100 56.2 8 -12.7
16 0.050
9
14.331 6.792
5 1.65100 56.2 10
14.276 16.746

11 ∞
0.700 6 1.51633 64.
1 12 ∞

Aspheric first surface K=-0.167672, A=3.26764E-
6, B=-1.61535E-7, C=-6.8703
8E-10, D = 3.61541E-12 2nd surface K = -0.189111, A = 1.89698E-
5,B=-3.62870E-7C=1.9969
7E-9, D=-2.92771E-11

Example 9 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
20.466 1.034 1
1.51983 74.292
8.856 4.379

3 15.366 9.9
87 2 1.88805 36.274
-32.303 0.074

5 -27.059
3.190 3 1.92014 20
．． 956 18.529 0
．． 659
7 -55
．． 193 4.889 4 1.710
65 54.668 -11.518
0.050
9
17.288 6.309 5
1.88300 40.8010
17.681 15.701
11
∞ 0.
700 6 1.51633 64.1
12 ∞

Aspheric first surface K=-0.052913, A=-1.02937E-6
, B=-8.69246E-9, C=-8.27213
E-11, D=-6.35650E-13 2nd surface K=-0.000609, A= 1.94554E-
6, B=-7.84633E-9, C=-8.0400
5E-11, D=-3.95610E-12

The seventh to ninth embodiments described above are examples of the document reading lens according to claim 3.

Example 10 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
27.666 4.403 1
1.48749 70.2 2
10.396 8.904

3 15.457 9.5
64 2 1.83400 37.2 4
-46.151 0.075

5 -39.452
3.662 3 1.92286 2
0.9 6 18.175
2.025
7-10
5.563 1.627 4 1.78
650 50.0 8 -14.2
30 0.050
9
16.536 6.884
5 1.81600 46.6 10
16.485 14.716

11 ∞
0.700 6 1.51633 64.
1 12 ∞

Aspheric first surface K=-0.416166, A=-5.00990E-6
,B=-1.05091E-8,C=1.3584
5E-11, D=-1.60432E-13 5th surface K= 6.250172, A=-1.96936E-
5, B=1.76003E-7, C=6.1922
6E-9, D=-2.05305E-10

Example 11 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
21.286 1.215 1
1.49700 81.6 2
11.973 16.738

3 12.385 7.07
9 2 1.69500 42.2 4
-152.228 0.625

5 -20.948
0.800 3 1.75084 27.
7 6 14.948 1
．． 396
7 -200.
587 1.917 4 1.6510
0 56.2 8 -11.478
0.050
9
15.741 7.092 5
1.65100 56.2 10
17.803 16.347
1
1 ∞ 0
．． 700 6 1.51633 64.1
12 ∞

Aspheric first surface K=-0.035870, A=9.80424E-
7, B=-3.16059E-9, C=-1.9920
4E-11, D = 3.76642E-13 5th surface K = 1.549514, A = -2.83247E-
5,B=5.70758E-7,C=2.2769
4E-8, D=-1.02164E-9

Example 12 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
22.611 3.870 1
1.52528 74.982
9.479 5.552

3 15.767 10.00
0 2 1.88642 37.614
-25.067 0.050

5 -23.838
2.793 3 1.87797 21.
786 17.535 1.
086
7-76.
183 4.241 4 1.7291
8 53.618 -12.800
0.050
9
16.728 6.156 5
1.88300 40.8010 1
6.525 14.608
11
∞ 0.7
00 6 1.51633 64.1 1
2 ∞

Aspheric first surface K=-0.338509, A=-6.80826E-6
, B=-2.17990E-8, C=-1.54578
E-11, D=-5.37688E-13 5th surface K= 0.915934, A=-7.83282E-
6,B=1.88396E-7,C=6.4869
0E-9, D=-1.77964E-10

The tenth to twelfth embodiments described above are examples of the document reading lens according to claim 4.

Example 13 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
27.109 4.015 1
1.48749 70.2 2
10.224 8.895

3 14.835 9.4
04 2 1.83400 37.2 4
-38.137 0.062

5 -35.642
3.334 3 1.92286 2
0.9 6 18.191
2.155
7-
88.191 1.616 4 1.7
8650 50.0 8 -14.
802 0.050
9
16.420 6.794
5 1.81600 46.6 10
16.429 14.557

11 ∞
0.700 6 1.51633 64
．． 1 12 ∞

Aspheric first surface K=-0.515221, A=-6.00847E-6
,B=-1.42554E-8,C=2.7757
3E-11, D=-3.32998E-13 6th surface K= 1.108477, A= 2.03919E
-5,B=7.17742E-8,C=8.667
62E-10, D=1.95329E-12

Example 14 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
20.917 1.158 1
1.49700 81.6 2
11.873 16.772

3 11.965 6.70
1 2 1.69500 42.2 4
-78.666 0.633

5 -20.325
0.800 3 1.75084 27
．． 7 6 14.513
1.634
7-7
1.885 1.453 4 1.65
100 56.2 8 -11.4
46 0.050
9
16.393 8.092
5 1.65100 56.2 10
19.853 15.505

11 ∞
0.700 6 1.51633 64.
1 12 ∞

Aspheric first surface K=-0.050498, A=2.04164E-
7, B=-1.40397E-10, C=-5.591
18E-11, D = 3.78996E-13 6th surface K = 0.550763, A = 2.66565E
-5,B=-2.98731E-7,C=-3.045
68E-8, D=1.02188E-9

Example 15 f=21.4mm, F/No=3, m=0.088
, ω=30 degrees i Ri
Di j
Nj νj 1
23.616 4.383 1
1.53225 73.612
9.677 6.616

3 15.320 10.00
0 2 1.88545 38.464
-27.394 0.050

5 -26.320
2.527 3 1.88412 21.
656 17.729 1.
164
7-70.
846 4.110 4 1.7264
2 53.768 -13.299
0.050
9
16.738 6.010 5
1.88300 40.8010 1
6.624 14.708
11
∞ 0.7
00 6 1.51633 64.1 1
2 ∞

Aspheric first surface K=-0.286810, A=-5.72629E-6
,B=-2.00071E-8,C=6.4496
5E-11, D=-7.07989E-13 6th surface K= 0.882203, A= 1.90772E
-5,B=-1.94099E-7,C=1.20
954E-8, D=-2.46912E-10

Embodiments 13 to 15 are examples of the document reading lens according to claim 5.

Aberration diagrams for Examples 1 to 15 are shown in FIGS. 2 to 16 in sequence. In each aberration diagram, the solid line in the spherical aberration diagram shows spherical aberration, the broken line shows the sine condition, and the solid line in the astigmatism diagram shows radial, and the broken line shows tangential. Also, ■■■ indicates that they relate to the d, c, and F lines, respectively.

[0044]

As described above, according to the present invention, a novel document reading lens can be provided. Since this lens is constructed as described above, it can achieve a half angle of view of 30 degrees, an aperture efficiency of approximately 100% up to the periphery, F/No=3, and high contrast.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a lens configuration of a document reading lens according to the present invention.

FIG. 2 is an aberration diagram regarding Example 1.

FIG. 3 is an aberration diagram regarding Example 2.

FIG. 4 is an aberration diagram regarding Example 3.

FIG. 5 is an aberration diagram regarding Example 4.

FIG. 6 is an aberration diagram regarding Example 5.

FIG. 7 is an aberration diagram regarding Example 6.

FIG. 8 is an aberration diagram regarding Example 7.

FIG. 9 is an aberration diagram regarding Example 8.

FIG. 10 is an aberration diagram regarding Example 9.

FIG. 11 is an aberration diagram regarding Example 10.

FIG. 12 is an aberration diagram regarding Example 11.

FIG. 13 is an aberration diagram regarding Example 12.

FIG. 14 is an aberration diagram regarding Example 13.

FIG. 15 is an aberration diagram regarding Example 14.

FIG. 16 is an aberration diagram regarding Example 15.

[Explanation of symbols]

1 First lens 2 Second lens 3 Third lens 4 4th lens 5 5th lens

Claims (5)

[Claims] Claim 1: From the object side to the image side, the first to fifth
The first group is a negative meniscus lens with a convex surface facing the object side, the second group is a positive lens, and the third group is a third biconcave lens. The lens is composed of 5 elements in 5 groups, with the 4th group being a positive lens and the 5th group being a positive meniscus lens with a convex surface facing the object side. The first and third lens surfaces are aspherical surfaces, and the conic constants K1 and K3 of these aspherical surfaces are (1-I) -0.16<K1<0.03, (1-I
I) A document reading lens that satisfies the condition -0.2<K3<-0.05. Claim 2: From the object side to the image side, the first to fifth
The first group is a negative meniscus lens with a convex surface facing the object side, the second group is a positive lens, and the third group is a third biconcave lens. The lens is composed of 5 elements in 5 groups, with the 4th group being a positive lens and the 5th group being a positive meniscus lens with a convex surface facing the object side. The first and fourth lens surfaces are aspherical surfaces, and the conic constants K1 and K4 of these aspherical surfaces are (2-I) -0.54<K1<0, (
2-II) A document reading lens that satisfies the following condition: -1100<K4<-1.1. Claim 3: From the object side to the image side, the first to fifth
The first group is a negative meniscus lens with a convex surface facing the object side, the second group is a positive lens, and the third group is a third biconcave lens. The lens is composed of 5 elements in 5 groups, with the 4th group being a positive lens and the 5th group being a positive meniscus lens with a convex surface facing the object side. The first and second lens surfaces are aspherical surfaces, and the conic constants K1 and K2 of these aspherical surfaces are (3-I) −0.7 <K1< 0 , (
3-II) A document reading lens that satisfies the following condition: -0.2<K2<0. Claim 4: From the object side to the image side, the first to fifth
The first group is a negative meniscus lens with a convex surface facing the object side, the second group is a positive lens, and the third group is a third biconcave lens. The lens is composed of 5 elements in 5 groups, with the 4th group being a positive lens and the 5th group being a positive meniscus lens with a convex surface facing the object side. The first and fifth lens surfaces are aspherical, and the conic constants K1 and K5 of these aspherical surfaces are (4-I) -0.47<K1<-0.03, (
4-II) A document reading lens that satisfies the following condition: 0.8<K5<6.9. Claim 5: From the object side to the image side, the first to fifth
The first group is a negative meniscus lens with a convex surface facing the object side, the second group is a positive lens, and the third group is a third biconcave lens. The lens is composed of 5 elements in 5 groups, with the 4th group being a positive lens and the 5th group being a positive meniscus lens with a convex surface facing the object side. The first and sixth lens surfaces are aspherical surfaces, and the conic constants K1 and K6 of these aspherical surfaces are (5-I) -0.57<K1<-0.045, (
5-II) A document reading lens that satisfies the following condition: 0.5<K6<1.2.