JPH04338907A - Lens for document read - Google Patents

Abstract

PURPOSE:To obtain the small-sized, inexpensive lens with a wide visual angle by arranging a stop between a 1st and a 2nd group, forming the 2nd and 3rd groups of resin materials, and making at least one surface of the 3rd group aspherical. CONSTITUTION:The 1st-3rd groups 1-3 are arranged in order from an object side to an image side and the stop 6 is provided between the 1st and 2nd groups 1 and 2. The 1st group 1 is a positive lens which has a large-curvature convex surface on the object side, the 2nd group 2 is a negative lens which has a large- curvature concave surface on the image side, and the 3rd group 3 is a positive lens which has a large-curvature convex surface on the image side; and the 2nd and 3rd groups are formed of the resin materials and at least one surface of the 3rd group 3 is aspherical. Then inequalities I hold, where nuj is the Abbe number of the material of the lens of a j-th group (j=1-3) to the (d) line including (j) as a suffix, Di (i=1-6) including (i) as a suffix the surface interval on the optical axis between an (i)th surface (including the stop surface) counted from the object side and an (i+1)th surface, f2 the focal length of the 2nd group 2, and (f) the composite focal length of the whole system.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading lens.

0002

[Prior Art] In recent years, facsimile machines, digital copying machines, etc. have been made smaller, faster, and cheaper, and along with this, there has been a demand for document reading lenses used in these devices to be smaller, cheaper, and brighter. ing.

[0003] A triplet type document reading lens has been known for a long time as a lens with a small number of lens components and easy to reduce size and cost (Japanese Patent Application Laid-Open No. 61-134).
No. 780, No. 64-21411, No. 63-1
35911).

[0004] Among these conventional original reading lenses, the ones described in Japanese Patent Application Laid-open No. 61-134780 and Japanese Patent Application Laid-open No. 64-21411 all have problems in terms of brightness with F/No = 5.6. Yes, it is not suitable for high-speed scanning of originals, and is not suitable for high-speed scanning of originals, and is not suitable for high-speed scanning of originals, and is not suitable for high-speed scanning of originals, and is not suitable for high-speed scanning of originals.
It is also difficult to adapt to D lighting.

Furthermore, the lens described in Japanese Patent Application Laid-Open No. 135911/1983 has a bright F/No of 4.0, but the half angle of view is 18
The degree and angle of view are narrow, and with a reduction ratio of about 1/10, the maximum document that can be read is as small as No. 6 in row B, which is not practical.

[0006]

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a novel document reading lens that is small, inexpensive, bright, and has a wide angle of view. There is.

[0007]

[Means for Solving the Problems] The document reading lens of the present invention is of a triplet type as shown in FIG.
It has an aperture 6 between the first group 1 and the second group 2.

The first group 1 is a positive lens with a strongly convex surface facing the object side, and the second group 2 is a negative lens with a strongly concave surface facing the image side. Further, the third group 3 is a positive lens with a strongly convex surface facing the image side. Therefore, the overall configuration is three groups and three elements.

Among these first to third groups of lenses,
The second group 2 and the third group 3 are formed of resin material. Further, at least one surface of the third group 3 is an aspherical surface.

[0010] d of the material of the lens of the jth group (J=1 to 3)
The Abbe number for the line is νj with j as the suffix, the i-th surface (including the aperture surface) and the i+th surface counting from the object side.
When the distance between the first surfaces on the optical axis is Di (i = 1 to 6), where i is the suffix, the focal length of the second group is f2, and the combined focal length of the entire system is f, (1) 29 <ν2<33 (2) 55<ν3<62 (3) 0.13<(D2+D3)/D5<0.22
(4) The condition 0.36<|f2|/f<0.41 is satisfied.

The document reading lens according to the second aspect of the present invention has the following features in addition to the above configuration. That is, the radius of curvature of the i-th surface (including the aperture surface) counting from the object side is i
When Ri (i=1 to 7) is used as a suffix,
(5) 1.6<|R7|/(D3+D4+D5+D
6)<2.4(6) 3.9<|R4|/R5<5.
0 (R4<0) is satisfied.

0012

[Operation] As described above, in the document reading lens of the present invention, the second and third groups are made of resin material. Furthermore, an aspheric surface is used for at least one surface of the third lens group, which has a large difference in the height of rays between on-axis and off-axis, in order to improve aberrations.

[0013] Also, the second and third groups made of resin material are made of negative
As a combination of positive lenses, focal shift due to changes in temperature and humidity is kept to a minimum.

In order to correct chromatic aberration in a lens with three elements in three groups, a material with low dispersion is used for the positive lens and a material with high dispersion is used for the negative lens. Since the third group is made of a resin material, it is limited by the resin material.

Conditions (1) and (2) are conditions for correcting chromatic aberration within the range of resin materials that can be used to form the second and third groups. Outside these conditions, there may be no suitable resin material, or good chromatic aberration correction may not be possible.

Condition (3) is a condition for satisfactorily correcting distortion and coma. When the lower limit is exceeded, distortion aberration increases in the negative direction, producing introverted coma flare; when the upper limit is exceeded, distortion aberration increases in the positive direction, producing extroverted coma flare, and both of these aberrations are well corrected. I can't.

Condition (4) is a condition for maintaining good spherical aberration and image plane. If the lower limit is exceeded, both the spherical aberration and the image plane will be overcorrected, the astigmatism difference will increase, and if this is attempted to be corrected, the coma aberration at intermediate angles of view will worsen. Also,
If the upper limit is exceeded, both spherical aberration and image plane will be undercorrected, and any attempt to correct this will worsen peripheral coma aberration.

When the lower limit of condition (5) regarding the document reading lens of claim 2 is exceeded, the distortion increases in the negative direction, and when the upper limit is exceeded, the distortion increases in the positive direction, so it is necessary to balance it with other aberrations. It becomes difficult to take and correct.

Condition (6) is a condition for properly correcting coma aberration under condition (4), and if the lower limit is exceeded, inward coma flare will occur and coma at intermediate angles of view will be distorted. Aberrations worsen. Moreover, when the upper limit is exceeded, extroverted coma flare occurs, worsening peripheral coma aberration, and causing deterioration of imaging performance.

[0020]

[Example] Specific examples will be given below. As shown in FIG. 1, the radius of curvature of the i-th surface counted from the object side (including the aperture surface and the surface of the cover glass of the solid-state image sensor CCD indicated by reference numeral 4) is Ri (i=
1 to 9), and the i-th surface and i+th surface counting from the object side are
The distance between the first surfaces on the optical axis is Di (i=1 to 8) with i as the suffix. In addition, the jth group (J=1 to 3
) is the refractive index and Abbe number for the d-line of the lens material j
Let Nj and νj be the suffixes. Furthermore, the refractive index and Abbe number of the cover glass 4 are expressed by the above suffix j=4.
Display as . Further, f represents the composite focal length of the entire system, F/No represents the brightness, m represents the magnification, ω represents the half angle of view (unit: degrees), and Y represents the object height.

As is well known, the aspheric surface is aligned with the optical axis and
The paraxial radius of curvature R is taken with the Y-axis perpendicular to the optical axis.
When the reciprocal of , that is, the curvature on the optical axis is C (=1/R), the conic constant is K, and the 4th, 6th, 8th, and 10th aspheric coefficients are A, B, D, and F, respectively, X=[CY2/{1+√[1+(1+K)C2Y2]}
]+A・Y4+B・Y6+D・Y8+F・Y10 is a curved surface obtained by rotating the curve around the optical axis, and in addition to the paraxial radius of curvature, the conic constant and higher-order aspheric coefficients A, B, D,
Specify the shape by giving F. Symbol √ [ ] in the above formula
means the square root of the quantity in [ ]. Furthermore, in the representation of an aspherical surface, E and the number following it indicate a power. In other words, for example, "E-10" is 1/101.
It means 0, and this number is multiplied by the number before it.

Example 1 f=20, F/No=4, m=0.088, ω=2
3.6, Y=108i Ri
Di j
Nj νj 1
7.492 1.57
1 1.88300 40.8 2 -
412.194 0.193
∞ (aperture) 0.41 4
-22.724 0.8
2 1.58347 29.3 5
5.435 3.536
57.858 2.26
3 1.49142 57.87 -
11.768 14.178 ∞
0.7
4 1.51633 64.19
∞

[0023] Aspherical surface 6th surface
7th side K=-1
24.673396 K= 0.81
3579 A=-0.130618E-
3 A=-0.173035E-4
B= 0.495613E-5 B=
-0.940665E-5 D=-0.63
1867E-7 D=0.415094
E-6 F=-0.31351E-9
F=-0.101509E-7

[0024] Value of condition value (D2+D3)/D5=0.17, |f2|/f=0.
37, |R7|/(D3+D4+D5+D6)=1.6
8, |R4|/R5=4.18

Example 2 f=20, F/No=4, m=0.088, ω=2
3.7, Y=108i Ri
Di j
Nj νj 1
7.49 1.6
1 1.88300 40.8 2
807.905 0.2 3
∞ (Aperture) 0.4
4 -26.179 0.8
2 1.58347 29.
3 5 5.679 4.
0 6 27.65 2.
1 3 1.49142 57
．． 87 -17.041 13.458
∞ 0.7
4 1.51633 64.
19 ∞

[0026] Aspherical surface Page 7 K = 0.669227 A=　　0.916044E-4 B=-0.16148E-5 D = 0.96959E-8 F=-0.64076E-9

Value of condition value (D2+D3)/D5=0.15, |f2|/f=0.
40, |R7|/(D3+D4+D5+D6)=2.3
3, |R4|/R5=4.61

Example 3 f=20, F/No=4, m=0.088, ω=2
3.7, Y=108i Ri
Di j
Nj νj 1
7.49 1.6
1 1.88300 40.8 2
317.932 0.213
∞ (Aperture) 0.4
4 -26.656 0.8
2 1.58347 29.3
5 5.644 3.6
6 30.778 2.1
3 1.49142 57.8
7 -15.274 13.798
∞ 0.7
4 1.51633 64.19
∞

[0029] Aspherical surface Page 7 K = 0.921238 A = 0.907498E-4 B=-0.235218E-5 D = 0.31859E-7 F=-0.154273E-8

Value of condition value (D2+D3)/D5=0.17, |f2|/f=0.
40, |R7|/(D3+D4+D5+D6)=2.2
1, |R4|/R5=4.72

Example 4 f=20, F/No=4, m=0.088, ω=2
3.7, Y=108i Ri
Di j
Nj νj 1
7.199 1.58
1 1.83481 42.7 2 -
2084.534 0.2 3
∞ (aperture) 0.41 4
-22.718 0.8
2 1.58347 29.3 5
5.507 2.956
34.929 2.08
3 1.49142 57.87 -
12.855 14.438 ∞
0.7
4 1.51633 64.19
∞

[0032] Aspherical surface Page 7 K=-0.196633 A = 0.329226E-4 B=-0.689816E-5 D=　　　0.185097E-6 F=-0.686657E-8

Value of condition value (D2+D3)/D5=0.21, |f2|/f=0.
38, |R7|/(D3+D4+D5+D6)=2.0
6, |R4|/R5=4.13

Example 5 f=20, F/No=4, m=0.088, ω=2
3.7, Y=108i Ri
Di j
Nj νj 1
7.42 1.56
1 1.88300 40.8 2
227.228 0.213
∞ (Aperture) 0.39
4 -27.364 0.8
2 1.58347 29.3
5 5.574 3.446
32.189 2.08
3 1.49142 57.87
-14.74 14.008
∞ 0.7
4 1.51633 64.19
∞

[0035] Aspherical surface Page 7 K=-0.528175 A = 0.479827E-4 B=-0.504844E-5 D = 0.129102E-6 F=-0.365931E-8

Value of condition value (D2+D3)/D5=0.17, |f2|/f=0.
39, |R7|/(D3+D4+D5+D6)=2.2
0, |R4|/R5=4.91

Example 6 f=20, F/No=4, m=0.088, ω=2
3.7, Y=108i Ri
Di j
Nj νj 1
7.18 1.6
1 1.83481 42.7 2
-489.517 0.193
∞ (aperture) 0.43
4 -21.871 0.8
2 1.58347 29.3
5 5.505 3.126
30.857 2.16
3 1.49142 57.87
-13.811 14.188
∞ 0.7
4 1.51633 64.19
∞

[0038] Aspherical surface Page 6 K=-7.48108 A=-0.463368E-4 B=　　0.107545E-4 D=-0.362861E-6 F=　　0.712224E-8

Value of condition value (D2+D3)/D5=0.20, |f2|/f=0.
37, |R7|/(D3+D4+D5+D6)=2.1
2, |R4|/R5=3.97

FIGS. 2 and 3 show aberration diagrams regarding Example 1. Further, FIGS. 4 and 5 show aberration diagrams regarding Example 2. Figure 6
, 7 show aberration diagrams regarding Example 3. Aberration diagrams regarding Example 4 are shown in FIGS. 8 and 9. 10 and 11 show aberration diagrams regarding Example 5. 12 and 13 show aberration diagrams regarding Example 6.

[0041] In these aberration diagrams, ■■ are respectively,
This indicates that the wavelengths are 587.56 nm (d-line) and 546.07 nm. Further, in the diagram of astigmatism, S indicates sagittal aberration, and M indicates meridional.

Aberrations are well corrected in each example. Furthermore, in each embodiment, the distance between the first group and the aperture stop is small, so the diameter of the first group (which has a high refractive index and is made of expensive material) can be kept small, and the first group can be manufactured at low cost.

[0043]

As described above, according to the present invention, a novel document reading lens can be provided. This lens can be realized compactly because it has a three-element structure in three groups and has a small number of elements, and can be realized at low cost because up to two of the three lenses are formed of an inexpensive resin material. Moreover, it is bright with F/No = 4.
It has a wide angle of view with a half angle of view of about 24 degrees.

[Brief explanation of drawings]

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 1.

FIG. 4 is an aberration diagram regarding Example 2.

FIG. 5 is an aberration diagram regarding Example 2.

FIG. 6 is an aberration diagram regarding Example 3.

FIG. 7 is an aberration diagram regarding Example 3.

FIG. 8 is an aberration diagram regarding Example 4.

FIG. 9 is an aberration diagram regarding Example 4.

FIG. 10 is an aberration diagram regarding Example 5.

FIG. 11 is an aberration diagram regarding Example 5.

FIG. 12 is an aberration diagram regarding Example 6.

FIG. 13 is an aberration diagram regarding Example 6.

[Explanation of symbols]

1. 1st group positive lens 2 Second group negative lens 3 3rd group positive lens 6 Aperture

Claims (2)

[Claims] 1. A first to third group arranged sequentially from the object side to the image side, with an aperture between the first and second groups,
The first group is a positive lens with a strongly convex surface facing the object side, the second group is a negative lens with a strongly concave surface facing the image side, the third group is a positive lens with a strongly convex surface facing the image side, and the second group is a positive lens with a strongly convex surface facing the image side. , the third group is formed of a resin material, at least one surface of the third group is an aspherical surface, and the Abbe number of the material of the lens of the j-th group (J=1 to 3) with respect to the d-line is expressed as the suffix j. νj, the i-th surface (including the aperture surface) and the i+1-th surface counting from the object side
The surface spacing on the optical axis of the th surface is D with i as the suffix.
i (i=1 to 6), the focal length of the second group is f2, and the combined focal length of the entire system is f, (1) 29<ν2<33 (2) 55<ν3<62 (3) 0 .13<(D2+D3)/D5<0.22
(4) A document reading lens of three groups and three elements, which satisfies the condition: 0.36<|f2|/f<0.41. Claim 2: In claim 1, the i-th object as counted from the object side.
When the radius of curvature of the th surface (including the aperture surface) is Ri (i=1 to 7) with i as the suffix, (5) 1
．． 6<|R7|/(D3+D4+D5+D6)<2.4
(6) 3.9<|R4|/R5<5.0 (
A document reading lens characterized by satisfying the following condition: R4<0).