JPH03121409A - Reading lens for scanner - Google Patents

Abstract

PURPOSE:To obtain the reading lens for scanners which is wide in visual angle and high in resolving power and is bright by providing a diaphragm between the 2nd and 3rd groups of the lenses consisting of seven elements in five groups and determining the focal length corresponding to the refracting power of the 1st group so as to satisfy equation I with respect to the combined focal length corresponding to the refracting power of the entire system. CONSTITUTION:The 1st group to the 5th groups are successively arranged and the diaphragm 15 is provided between the 2nd and 3rd groups. The 1st group is constituted of the 1st lens 10 of a positive lens and the 2nd lens 12 of a negative lens joined to the image side thereof. The 2nd group is the 3rd lens 14 of a menicus lens, the convex face of which is directed to an object side and the 3rd group is the 4th lens 16 of the menicus lens, the convex face of which is directed to the image side. The 4th group is constituted of the 5th lens 18 of a biconvex lens and the 6th lens 20 of a biconvex lens joined to the image side thereof. The 5th group is constituted of a 7th lens 22 of parallel plane glass. The equation I is satisfied when the focal length of the entire system is designated as f and the focal length of the 1st group is designated as f12. The reading lens for scanners which is wide in angle and high in resolving power and is bright is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reading lens for a scanner used for reading originals in facsimiles, digital copying machines, and the like.

[Prior Art] Scanning a document and reading it using a solid-state image pickup device such as a COD is well known in connection with facsimiles, digital copying machines, and the like. A scanner reading lens is a lens that forms a reduced image of a document on a solid-state image sensor for this purpose.

In recent years, the size of one pixel in solid-state imaging devices has become smaller, and as a result, scanner reading lenses are required to have higher resolving power.

For example, when reading a document using a COD with a pixel size of 7 μm, there are 71.4 lines/m on the CCD light receiving surface.
A resolution of m is required, and sufficient contrast is required for the above-mentioned spatial frequency up to the most peripheral part of the image plane. Furthermore, making the document reading device more compact and increasing the speed of document reading is a constant improvement goal in the document reading device, and for this purpose, a reading lens for a scanner is required to have a short object-image distance, a wide angle, and a bright lens. That is, in order to meet the demands for compact document reading devices, high speed document reading, and high resolution, scanner reading lenses need to have a wide angle of view, high resolution, and brightness.

Conventionally, as a reading lens for a scanner configured with seven lenses in five groups, those disclosed in Japanese Patent Laid-Open No. 63-75721 and Japanese Patent Laid-Open No. 64-23215 are known.

[Problems to be Solved by the Invention] However, these conventional scanner reading lenses with 7 elements in 5 groups have an FNO of about 4.0, and are not necessarily bright enough to achieve high-speed reading. .

The present invention was made in view of the above-mentioned circumstances, and
The aim is to provide a wide angle of view, high resolution, and F.
The objective is to provide a reading lens for scanners that has a bright NO of about 3.5.

[Means to solve the problem] The present invention will be explained below.

As shown in FIG. 1, the scanner reading lens of the present invention has the first group 1 to the fifth group 5 arranged sequentially from the object side (left side in FIG. 1) to the image side (right side in the same figure). Tenaru, 2nd group 2
A diaphragm 15 is provided between the lens and the third group 3.

The first group 1 is composed of a first lens 10 and a second lens 12 cemented to the image side of the first lens 10.

The first lens 10 is a positive lens, and the second lens 12 is a negative lens.

The second group 2 is a third lens 14 which is a meniscus lens with a convex surface facing the object side.

The third group 3 is a fourth lens 16 which is a meniscus lens with a convex surface facing the image side.

The fourth group 4 is composed of a fifth lens 18 and a sixth lens 20 cemented to the image side of the fifth lens 18.

The fifth lens 18 is a biconcave lens, and the sixth lens 20 is a biconvex lens.

In the fifth group 5, the seventh lens 22 is made of parallel plane glass. This seventh lens 22 includes a solid-state image sensor (
CCD) cover glass.

Thus, the reading lens for a scanner according to the present invention has a structure of 7 lenses in 5 groups.

The combined focal length of the entire system is f, and the focal length of the first group 1 is f12.
Then, these f, f,, are (I) 1.01
<f/f, □<1.15 are satisfied.

[Function] In order to achieve a wide angle of view and a large aperture with a lens constructed of 7 elements in 5 groups as described above, the refractive power of the first group must be appropriately large. Even if the refractive power of the first group is too strong or too weak,
Unable to achieve wide angle of view and large aperture. That is, if the refractive power of the first group is too strong, the angle of view will become narrow, and if it is too weak, the performance in the middle part of the image height will deteriorate. Therefore, if the refractive index of the first group is too strong or too weak, high performance cannot be maintained up to the outermost periphery of the image plane.

In order to achieve a wide angle of view and large aperture, it is necessary that f1□, which corresponds to the refractive power of the first group, satisfies the above condition (I) with respect to f, which corresponds to the refractive power of the entire system. is necessary.

[Example] Nine specific examples are shown below.

In each example, F/No means brightness, f means the combined focal length of the entire system with respect to the d-line, m means magnification, and ω means half angle of view (degrees).

Radius of curvature r of each surface, (i・1~13), distance between surfaces d; (i
・1 to 12), refractive index n4 (j・1 to 7), Atsube number ν
(j=1 to 7) are taken from the object side to the image side as shown in FIG. The refractive index relates to the d-line, and the Abbe number relates to the d-line.

Example 1: F/No=3.5, f=43.0. m
knee 0.112, ω: 19.4, f/f, 2=1.
027.

lrid, j n, ν41
17.947 5.625 1 1.73500
49.762 206.096 3 36.687 4 14.236 5 9.765 6 ω (Aperture) 7 -7.957 8 -10.471 9 -84.131 10 223.766 11 -17.810 12 00 13 (1) Example 2: F/No=3.5, fir. =1.037.

1 ri 1 18.544 2 83.604 3 33.186 4 12.824 5 9.517 1.467 0,500 3,240 3,386 6,788 2, 196 0,500 1.000 4,590 29.421 0,700 d.

6,858 1,777 0,500 2.174 4,115 1.75520 27,51 1.75520 27,51 1.75520 27,51 1.84666 23.89 1.73500 49.76 1.51633 64. 15, f=43.0. m=-0,112, ω=19.4
n, ν.

1.81600 46.62 1.84666 23.89 1.84666 23, 89 6 (X) (Aperture) 7 -8.477 8 -10.491 9 -67.051 10 322.136 11 -19.524 12 (X) 13 0) Example 3: F/No=3.5, f=43.0. m
=-0,112, f/L□=1.052.

l　　　　　r 1 18.114 2 80.068 3 31.795 4 12.438 5 9.375 6 ω (aperture) 7 -8.315 8 -10.423 9 -67.589 1.84686 1.84666 5 1.84668 23.89 6 1.81600 46.62 1.51633 J　　　　　ν4 1 1.81600 46.62 2 1.84666 23.89 1.84866 1.84666 6,032 1,494 0,500 2,419 5,741 28.003 0,700 1 6,904 1,810 o, so.

1.978 3,988 6, 168 1.58'? o, so.

2, 394 23, 89 64, 15, ω2 19.4 23, 89 23, 89 23, 89 10 317.465 5.79411 -19
．． 657 27.70812 (X)
0.70013 ω Example 4: F/No=3.5, f=43.0. m
=-0,112, (,)=19.4, fir, □=1.
063.

1 ri 1 17.768 2 74.088 3 30.672 4 12.338 5 9.418 600 (aperture) 7 -8. IJ4 8 -10.303 9 -66.608 10 338.658 11 -19.649 2o3 13　　　o) ,1 46, 62 23, 89 23, 89 64, 15 84.15 1.51633 1.81600 n, ν.

1.81600 46.62 1.84666 23.89 1.84666 1.84666 1.84668 23.89 1.81600 46.62 1.51833 6,893 1.804 0,500 1.785 3,897 6.347 1.693 o, so.

2, 191 5.676 27.811 0,700 Example 5: F/No=3.5 , f/L□=1.074.

l　　　　ri 1 16.940 2 -450.421 3 32.750 4 13.584 5 9, 554 6　■　(Aperture) 7 -7.931 8 -10.252 9 -54.387 10 59.696 11 -17.302 12 (1) 13 a) Example 8: F/No=3.5 , fir, □=1.086.

l　　　　ri 1 16.899 dB　　　j　　　n,i　　　　ν.

5.520 1 1.74400 44.79d
.

5,970 1,168 0,500 2,568 3,139 6,711 1.711 0,500 1,000 5,081 29.478 0,700 , f=43.0. m=-0,112, ω=19.4 J　　　nj　　　　　C 1 1.74400 44.79 2 1.75520 27.51 1.75520 1.75520 27, 51 27, 51 5 1.72825 28.46 6 1.74400 44.79 1.51633 , f=43.0. m=-0,11264,15 ,ω=20.4 2 -1045.152 3 33.466 4 13.884 5 9.520 (3co (aperture) 7 -7.818 8 -10.299 9 -67.420 10 146.913 11 -16.922 12 ω 13 G.

Example 7: F/No=3.5 , f/f, 2=1.090.

l　　　　r□ 1 16.625 2 -956.545 3 32-025 4 13.573 5 9.513 5,849 1,034 0,500 2,514 3,110 1.174 0,500 2,813 3,323 6,719 1,944 o, so.

1.00 (1 4,759 28,077 0,700 1,75520 27, 51 1,75520 27, 51 1,75520 27, 51 1,7282528,46 1,7440044,79 1,51633 64, 15 , f:43.0. m 0.112 ,ω=19.4 nj　　　　　　ν.

1.74400 44.79 1.75520 27.51 1.75520 27, 51 6 co (aperture) 7 -7.807 8 -10.044 9 -50.661 10 63.772 11 -16.985 12 (X ) 13 (X) Example 8: F/No; 3.5, f43. o, m=
-0,112, f/f, □=1.100.

1 rt 1 16.490 2 -9098.763 3 31.841 4 13.643 5 9.540 6 (aperture) 7 -7.788 8 -10.063 9 -50.395 1.75520 1.75520 5 1.72825 28.46 6 1.74400 44.79 1.51633 nl sea 1.74400 44.79 1.75520 27.51 1.75520 d, j 5.783 1 1.000 2 0, 500 2.494 3 3,062 6,723 1.638 4 0,500 1.000 5 1.72825 6.749 1,625 0,500 1.000 5,075 29.781 0.700 27,51 64.15 , ω =19.4 27, 51 27, 51 28, 48 10 67.747 11 -16.928 29.90612 ω 13 00 Example 9: F/No=3.5, f=43.0. m=-
0,112, f/fI2=1. N1.

l　　　　ri 1 16.606 2 58.666 3 27.485 4 11.218 5 8.844 6 Co (aperture) 7 -7.887 8 -10.152 9 -58.509 10 1775.017 11 -19.061 12 ■ 13 (X) 1.84666 5,012 1.74400 1.51633 n, ν.

1.81600 46.62 1.84666 23.89 1.84666 1.84666 1.81600 1.51633 6.786 1,619 0,703 1.282 4,088 5,933 1.875 o, so.

2, 113 5, 442 28.277 0, 700 0, 700 44, 79 64, 15, ω=19.4 23, 89 23, 89 23, 89 46, 62 64.15 Figures 2 to 10 2A and 2B show aberration curve diagrams for Examples 1 to 9, respectively. In these aberration diagrams,
(2), (2), and (2) indicate optical wavelengths as parameters, and represent d, F, and c lines in the above order.

Further, the broken line for spherical aberration represents the sine condition, the solid line for astigmatism relates to sagittal rays, and the broken line relates to meridional rays.

As is clear from each aberration curve diagram, each example has good performance.

[Effects of the Invention] According to the present invention, the number of constituent elements is small, 7 elements in 5 groups, and it has a wide angle and high resolution, and moreover, F.・Bright at about 3.5,
We can provide reading lenses for scanners.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the lens configuration of the present invention, and FIGS.
Figure 0 is an aberration diagram. 110. Group 1, 286. Group 2, 300. Group 3, 4
The land? Figure F/No. 15.5 Y-152.4 Y-4 2.4 Figure F/No. 15.5 Y-152, A Y-1 2.4 No spherical aberration, no aberration Shyness (〆) Comatic aberration diagram F/No D-ri Y-452,4 E1ri24 俤5 Figure spherical aberration astigmatism H! l Plan 1!3 Aberration (%> Coma J15? Difference 2) Comatic aberration 73- "No J Y-NO52.4 -1624 Bee-chamfer base Astigmatism Onset convergence (beginning) Comatic aberration No. Chamfering difference, dust collection, but tlJIKjl observation 2) Comatic aberration, θ Fig. Chamfering difference, dust collection, Aα difference distortion I!

Claims (1)

[Claims] A lens used at a reduction magnification and used to read documents at high speed, wherein the first to fifth groups are arranged sequentially from the object side to the image side, and the first to fifth groups are arranged sequentially from the object side to the image side, and between the second and third groups. The first group includes a first lens that is a positive lens and a second lens that is a negative lens that is cemented to the image side of the first lens, and the second group has a convex surface. The third lens group is a meniscus lens with a convex surface facing the image side, and the fourth group is a fifth lens that is a biconcave lens. and a sixth lens which is a biconvex lens cemented to the image side of this fifth lens, and the fifth group is a seventh lens which is a parallel plane glass, and the focal length of the entire system is f, and the first lens is A reading lens for a scanner, characterized in that when the focal length of the group is f_1_2, these satisfy the condition (I) 1.01<f/f_1_2<1.15.