JPH04127109A - Lens system for read - Google Patents

Abstract

PURPOSE:To hold sufficient image forming performance, to decrease the F number, and to increase the aperture efficiency and half view angle by constituting the lens system of small-element constitution, i.e. 7 elements in five groups, properly arranging the lenses, and employing aspherical surfaces. CONSTITUTION:The lens system consists of the seven elements L1 - L7 in the five groups, the 2nd surface r2 of th 1st lens L1 and the 1st surface of the 6th lens are formed into aspherical surfaces r9, and inequalities I hold. Here, d1 is the lens thickness or gap distance from an (i)th refracting surface to an (i+1)th refracting surface, n1 the refractive index of an (i)the to a (d) line, upsilon1 the Abbe number of the (i)th lens, and (f) the focal length of the whole lens system. Consequently, the lens system 1 which has the sufficient image forming performance for a line sensor with a 7 - 8 mum picture element pitch is obtained although the system has a large diameter or a 2.4 F number, a 20 deg. half view angle, and nearly 90% aperture efficient.

Description

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

[Conventional technology]

Traditionally, facsimiles, image scanners, etc.
A document reading lens system using a solid-state image sensor (COD) as a light-receiving element is used.
The one described in Publication No. 1 is known. This type of reading lens system consists of a lens used for copying and duplication at a rough object distance, a lens with an aspherical surface, and a lens with five components. ), the F number is 1.8 and the angle of view is ±12.
．． 6°, and judging from the amount of aberration, the reading density is 20°.
The lens system is configured to have a lens system of about 0 dpi.

[Problem to be solved by the invention]

In recent years, image scanners, facsimile machines, etc. have been increasing their reading density in order to obtain clear images, and the lenses used are required to have high resolution.

In addition, the smaller the F number is, the better to increase the reading speed, and the larger the aperture efficiency is, the better so that the light intensity ratio between the center and peripheral parts of the image does not become too large. It is said that a lens with a large angle is desirable.

However, in conventional high-density reading lens systems, while imaging performance is generally prioritized, F-number, aperture efficiency, half-field angle, etc. tend to be kept to low specifications in order to maintain imaging performance. The current situation is that

Therefore, in the present invention, sufficient imaging performance can be maintained, the F number can be reduced, the aperture efficiency can be increased,
The object of the present invention is to provide a reading lens system that can increase the half angle of view.

[Means to solve the problem]

In order to solve the above problems, the reading lens system of the present invention includes a second lens L2 consisting of a positive meniscus lens with a convex surface facing the object side 2, a second lens L2 which is a positive meniscus lens with a convex surface facing the object side 2, A second lens L2 consisting of a positive meniscus lens with a convex surface facing toward the object side 2, a third lens Ls consisting of a negative meniscus lens with a convex surface facing the object side 2, a fourth lens Ls consisting of a negative lens 4, and a fifth lens Ls consisting of a positive lens. , a sixth lens L6. consisting of a positive lens. and a seventh lens consisting of a positive lens, and the first lens L.

The surface ASPI facing the image plane (l!!I3) and the surface ASP2 facing the object side 2 of the sixth lens L are formed into aspherical surfaces, and the second lens L2 and the third lens Ls
, the fourth lens L, and the fifth lens L, each of which is cemented to form seven lenses in five groups, is a reading lens system 1 that satisfies the following conditions.

21<-(ν1 +ν2 +ν5 + white +ν])
s 0.31<...(3) However,
d: Lens thickness or gap distance from the 1st refractive surface to the 1st+1st refractive surface nI: Refractive index of the 1st lens with respect to dm νI: Atsube number f of the 1st lens: All lenses Focal length of the system [Function] According to the reading lens system with such a configuration, although the lens system has a small configuration of 7 elements in 5 groups, by appropriately arranging the lenses and using an aspheric surface, Prevents deterioration of imaging performance due to larger aperture, half angle of view 20°, aperture efficiency 90
%, it is possible to obtain a large-diameter lens system with an F number of 2.4 and sufficient imaging performance for a line sensor with a pixel pitch of 7 to 8 μm.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. 1 to 4 are diagrams showing an embodiment of a reading lens system according to the present invention.

FIG. 1 is a diagram showing a reading lens system 1 according to the present embodiment, in which reference numeral 2 indicates a document placement crow on the object side, and reference numeral 3 indicates a cover of a line sensor (light receiving element) on the image plane side. As shown in the figure, the lens system 1 of this embodiment includes first to seventh lenses L+ and L2 sequentially from the object side 2 to the image plane side 3.

L3. L4, Ls, L6, and L7 are arranged, and the second
The lens L2 and the third lens L3, and the fourth lens L4 and the fifth lens L are each cemented to each other to form a lens system with seven lenses in five groups.

The first lens L+, the second lens L2 are positive meniscus lenses, the fifth lens Ls, the sixth lens L6 . The seventh lens L7 consists of a positive lens, the third lens L) consists of a negative meniscus lens, and the fourth lens L consists of a negative lens. 1st. Second. Third lens L1. L2,1. s is arranged with its convex surface facing the object side 2.

In addition, the second surface ASP1 which is the image plane side 3 of the first lens L1
The first surface ASP2, which is the object side 3 of the sixth lens L6, is formed into an aspherical surface. The shapes of these aspherical surfaces are expressed in the form of the following equation.

+A4 H' +Ah H' +A* H
'''However, Furthermore, the lens system 1 of this example is expressed by the following formulas (1) to (3).
It is configured to satisfy the following conditions.

(n+ +nz + ns +ni + n? Bow (ν3 +ν4)...(2) However, d: Lens thickness or gap distance from the 1st refractive surface to the i+1th refractive surface nl: The 1st The refractive index of the lens for the d-line ν1: The Abbe number f of the first lens: The focal length of the entire lens system The above condition (1) is a condition for maintaining the curvature of the field appropriately; If the value of exceeds the lower limit, the image plane will be too undersized; on the other hand, if it exceeds the upper limit, the image plane will be too close, making it impossible to obtain a well-balanced image plane.The above condition (2) is due to chromatic aberration. This is a condition for correction, and if this range is exceeded, it becomes difficult to correct chromatic aberration.

The above condition (3) is a condition for correcting coma aberration,
In order to correct the coma flare that occurs with the increase in aperture, the second lens of the third lens L3 is used for the intermediate angle of view.
By controlling the amount of refraction of the light ray at the surface rs and the first surface r6 of the fourth lens L4, the second surface r2 of the first lens L1 and the second surface r2 of the sixth lens L6 can be adjusted from the intermediate angle of view to the peripheral angle of view. The first surface r is corrected by forming the aspheric surfaces ASPI and ASP2, respectively. That is, coma flare occurs most at the second surface rs of the third lens L and the first surface r6 of the fourth lens L4, but the light rays from the intermediate angle of view to the peripheral angle of view are caused by the first lens L1 and the sixth lens L6. , 7th lens L
7, etc., the rays pass relatively outside of each lens, so by using an aspheric surface in these lenses, it is possible to correct the aberrations without adversely affecting other aberrations, but the rays at intermediate angles of view are transmitted through the third lens. It is difficult to correct only the diagonal coma flare that passes relatively inside Lj, the sixth lens La, the seventh lens L7, etc. Therefore, the coma flare at an intermediate angle of view is caused by the second surface of the third lens Lj. It is most effective to reduce the amount of aberration generated at the first surface r6 of the fourth lens L4, and when the above condition 3 is satisfied, it is possible to satisfactorily correct coma aberration.

For example, in this example, as shown in Table 1, the focal length of the entire lens system (NCe line) f = 43.093, the magnification M = 0.1
104. In the case of F number 2.4, by setting the multi-value as shown in the table, condition (1 value is 1.0098, condition (
The value of 2) is 27.06, and the value of condition (3) is 0.3179.
The image plane, chromatic aberration correction, and coma aberration can each be made appropriate. Therefore, it is possible to obtain a large-diameter reading lens system while maintaining sufficient imaging performance. The aberrations of this example are shown in FIGS. 2, 3, and 4, and good results can be obtained.

However, the symbols in Table 1 are as follows.

: Original aIp of H draft device glass 2! Radius of curvature of the surface of I: Radius of curvature r + (i = 1 to 12) of the surface on the lens side of the original holding glass 2: Radius of curvature of the first refractive surface counting from the object side 2 of each lens: Light receiving element Radius of curvature of the lens-side surface of the cover glass 3 of the light-receiving element: Radius of curvature of the light-receiving element-side surface of the cover glass 3 of the light-receiving element: Conic constant of the refractive surface of the second surface counting from the object side 2 2A4: From the object side 2 Coefficient 2A6 of the 4th order term of the second refractive surface counting from the object side 2: Coefficient 2A8 of the 6th order term of the second refractive surface counting from the object side 2: Coefficient 2A8 of the 8th order term of the second refractive surface counting from the object side 2 Coefficient: Circle r of the 9th refractive surface counting from the object side 2.

r.

C C 2 to 9 Conic constant 9A4: Coefficient 9A6 of the 4th order term of the 9th refractive surface counting from the object side 2: Coefficient 9A8 of the 6th order term of the 9th refraction surface counting from the object side 2: Object fl ! Coefficient of the 8th order term of the ninth refractive surface counting from 2: Thickness of the document placement glass 2: Distance d+ (i=1 to 11) from the document placement glass 2 to the third lens Lj: of each lens. Distance from the first refractive surface to the i+1st refractive surface counting from the object side: Distance dC from the second surface of the seventh lens L7 to the cover glass 3: Thickness of the cover glass 3 no: Document placement The refractive index nt(i
= 1 to 7): d of the first lens counting from the object side 2
Refractive index nc for the line: refractive index ν of the cover glass 3 for the d line. : Atsube number ν+(i=l~7) of the document placement glass 2: Atoube number νe of the first lens counted from the object side 2: Atoube number νe of the cover glass 3 Next, the second embodiment will be described.

In this example, f=43.186, M=0.1104,
In the case of F number 2.41, by setting the multivalue as shown in Table 2, condition (1) is 1.0355, condition (2) is 21.41, and condition (3) is 0.3172. Therefore, it is possible to obtain a lens system suitable for the same machine as the above embodiment. Incidentally, each aberration in this example is shown in FIGS. 5, 6, and 7.

Further, a third embodiment will be explained.

In this example, f=43.433, M=0.1104,
In the case of F number 2.42, by setting the multivalue as shown in Table 3, condition (1) is 1.0098, condition (2) is 27.06, and condition (3) is 0.3523. The same effect as the above embodiment can be obtained. Incidentally, each aberration in this example is shown in FIGS. 8, 9, and 10.

〔Effect of the invention〕

As explained above, according to the present invention, the lens system has five groups and seven
The second surface of the first lens and the first surface of the sixth lens are formed into aspherical surfaces, and the F-number is 2.4
It is possible to obtain a lens system that has a large aperture, a half field angle of 20°, and an aperture efficiency of nearly 90%, and yet has sufficient imaging performance even for a line sensor with a pixel pitch of 7 to 8 μm.

(Margin below) No. table No. table No. table

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 to 4 are views showing a first embodiment of a reading lens system according to the present invention, FIG. 1 is a side view thereof, and FIGS. 2(a) and (b). ), (c) are characteristic diagrams showing spherical aberration, astigmatism, and distortion, respectively. Figures 3 (a) to (e) are characteristic diagrams showing meridional comatic aberration, respectively. Figure 4 (a).
) to (e) are characteristic diagrams showing sagittal comatic aberration, respectively.
Figure 5 (a), (b), (c), Figure 6 (a) to (e)
, FIGS. 7(a) to (e) show a second embodiment of the present invention, and characteristic diagrams showing respective aberrations similar to those in the first embodiment, FIGS. 8(a>, (b), (c)) , Figures 9(a) to (e), 1st
FIGS. 0(a) to 0(e) are characteristic diagrams showing a third embodiment of the present invention and showing respective aberrations similar to those in the first embodiment. 1... Lens system 2... Object side 3... Image side L1~L? ...... 1st to 7th lenses r2 (AS
Pl)... Second surface of the first lens (ASP2)
・・・・・・First surface of 6th lens Patent dispatcher Rico Co., Ltd. Figure 3 (e) Meridional coma aberration (mm) Figure 4 (d) Sagittal coma aberration (mm) Figure 6 (e) (d) (b) Meridional coma aberration (mm) (a) Spherical aberration (mm) (b) (DEG) Astigmatism (mm) (c) (DEG) Distortion aberration ('/,) Fig. 7 (d) (c) (b) Sagittal coma aberration (mm) Fig. 9 (e) (d) (a) Meridional coma aberration (mm) Fig. 10 (d) (C) Sagittal coma aberration (mm)

Claims (1)

[Claims] Sequentially from the object side to the image side: a first lens consisting of a positive meniscus lens with a convex surface facing the object side; a second lens consisting of a positive meniscus lens with a convex surface facing the object side; A third lens consisting of a negative meniscus lens with a convex surface facing, a fourth lens consisting of a negative lens, a fifth lens consisting of a positive lens, a sixth lens consisting of a positive lens, and a seventh lens consisting of a positive lens are disposed. , the surface of the first lens facing the image side and the surface of the sixth lens facing the object side are formed into aspherical surfaces, and the second lens, the third lens, and the fourth lens A reading lens system comprising 7 lenses in 5 groups, each of which has a fifth lens cemented to it, and is characterized in that it satisfies the following conditions. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(1) -1/2(ν_3-ν_4)...(2) 0.31<(d_5)/(F)...(3) However, d_1: i-th Lens thickness or gap distance from the refractive surface to the i+1th refractive surface n_1: Refractive index of the i-th lens with respect to the d-line ν_1: Abbe number f of the i-th lens: Focal length of the entire lens system