JP2000266911A - Manufacture of image formation lens and image reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a cost required in machining and assembling of a lens, by absorbing dispersion of the central thickness of each lens composing a junction lens by adjusting the thickness of an adhesive, in an image formation lens having the junction lenses. SOLUTION: When an image formation lens having one or more pairs of junction lenses is manufactured, manufacturing errors of the thickness on an optical axis of each lens (L1 and L2, L5 and L6) are absorbed, by adjusting the thickness of adhesive layers (D2, D9) for bonding each lens (L1 and L2, L5 and L6) composing the junction lenses, so that the thickness on the optical axis of the whole junction lenses (D1+D2+D3, D9+D10+D11) is in a prescribed range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an image forming lens and an image reading apparatus such as a facsimile or an image scanner using the image forming lens, and more particularly to manufacturing of an image forming lens having one or more sets of cemented lenses. The present invention relates to a method and an image reading apparatus using the imaging lens.

[0002]

2. Description of the Related Art There are various types of imaging lenses. For example, there is an imaging lens for reading an image having one or more sets of cemented lenses.

[0003] For example, an imaging lens for image reading of a three-group, four-element construction includes, in order from the object side, a first positive lens, a second negative lens, a third negative lens, and a fourth positive lens. In some cases, the third lens and the fourth lens are joined to each other.

[0004] Further, as an imaging lens for image reading of, for example, a four-group, six-element configuration, a positive first lens,
It consists of a positive second lens, a negative third lens, a negative fourth lens, a positive fifth lens, and a positive sixth lens, wherein the second lens and the third lens, and the fourth lens and the fifth lens are each other. What has been joined, and in order from the object side,
The first lens includes a first positive lens, a second negative lens, a third positive lens, a fourth positive lens, a fifth negative lens, and a sixth positive lens, and includes a first lens, a second lens, and a fifth lens. There is a configuration in which the sixth lens is bonded to each other.

Similarly, a five-group or five-group or five-group or seven- or eight-lens configuration is obtained by adding one or more lenses to such various lenses, and a cemented lens is partially formed. What is provided is known as an imaging lens for image reading.

[0006]

By the way, in an imaging lens for image reading, it is necessary to satisfactorily correct various aberrations in order to obtain a good image. However, if the thickness on the optical axis (center thickness) of the entire cemented lens constituting the imaging lens fluctuates, spherical aberration, curvature of field and coma become worse, and a good image cannot be obtained. .

For this reason, in the above-mentioned conventional imaging lens, the center thickness of each lens constituting the cemented lens is processed with high precision, so that variation in the center thickness can be suppressed or the central thickness of the entire cemented lens can be reduced. By selecting a lens having a combination of center thicknesses that falls within a predetermined range, the center thickness of the entire cemented lens must be maintained within a predetermined range.

[0008] Accordingly, the cost for processing and assembling the lens increases, and the yield is reduced.

The present invention has been made in view of such circumstances, and in an imaging lens having one or more cemented lenses, it is possible to compensate for variations in the center thickness of each lens constituting the cemented lens. It is an object of the present invention to provide a method of manufacturing an imaging lens that can reduce costs for processing and assembling the lens, and an image reading apparatus using the imaging lens.

[0010]

According to the present invention, there is provided a method of manufacturing an imaging lens having one or more sets of cemented lenses, wherein the thickness of the entire cemented lens on the optical axis is within a predetermined range. The thickness of the adhesive layer for adhering each lens constituting the cemented lens is adjusted so as to be within, and the manufacturing error of the thickness on the optical axis of each lens is absorbed. And

Further, an image reading apparatus according to the present invention is characterized in that the image forming lens is used.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for manufacturing an imaging lens and an image reading apparatus according to the present invention will be described with reference to the drawings. FIG. 2 is a perspective view showing a schematic configuration of an image reading apparatus using an imaging lens manufactured by the manufacturing method of the present invention.

As shown in FIG. 2, an imaging lens 1 manufactured by the manufacturing method of the present invention is used for an optical system of an image reading device 2 such as a facsimile or an image scanner. The image reading apparatus 2 has an imaging lens 1 disposed between a glass plate 4 on which a document 3 is placed and a cover glass 6 of a linear CCD 5, and an illuminating device 7 is provided on the glass plate 4 on the imaging lens side. Is arranged.

In the image reading device 2, when light is irradiated from the illumination device 7 toward the document 3, the light beam reflected by the document 3 is imaged by the image forming lens 1 to form a linear CCD.
5 is read.

FIG. 1 shows a basic lens configuration according to an embodiment of an imaging lens manufactured by the manufacturing method of the present invention.

As shown in FIG. 1, the imaging lens (for example, an image reading lens) according to these embodiments is of an ortho meta type constituted by _six lenses L _{1 to} L ₆ . the first lens L ₁ and second lens L _2, and the fifth lens L ₅ consists sixth lens L ₆ is a lens system of bonded 4-group 6-lens configuration, respectively, a diaphragm 8 is the third lens L ₃ 4 It is disposed between the lens L _4, the optical axis X from the object side
The light flux incident along is formed at an image forming position P on the image forming surface 9.

Here, the first lens L ₁ is a positive meniscus lens having a convex surface facing the object side, the second lens L ₂ is a negative meniscus lens having a concave surface facing the image side, and the third lens L ₃ is a object side. A positive meniscus lens with a convex surface facing the lens, the fourth lens L ₄ is a positive meniscus lens with a convex surface facing the image side, the fifth lens L ₅ is a negative meniscus lens with a concave surface facing the object side, and the sixth lens L Reference numeral ₆ denotes a positive meniscus lens having a convex surface facing the image side.

FIG. 3 is a longitudinal sectional view showing a schematic configuration of a jig 10 used for manufacturing a cemented lens in the method of manufacturing an imaging lens according to the present embodiment.

As shown in FIG. 3, a jig 10 used for manufacturing a cemented lens includes a pair of lens holders 11 and 12 which can be divided into upper and lower parts.
The lenses 13 and 14 can be held while being housed in the lenses 1 and 12. Also, each lens holding unit 1
Each of the lenses 1 and 12 has a shape in which the lenses 13 and 14 are held such that the total thickness of the lenses to be joined is within a predetermined range in a state where both are assembled together.

Further, when the two lens holding portions 11 and 12 are assembled together, the adhesive 15 protruding from between the lenses 13 and 14 to be joined is taken into a portion where the two lens holding portions 11 and 12 come into contact. Space 16 is provided.

Using this jig 10, a pair of lenses 13,
In order to join the lenses 14, first, the insides 11 and 12 of each lens holding portion
Hold the lenses 13 and 14 respectively.
An adhesive 15 is applied to the joint surfaces of the lens holders 3 and 14, and the two lens holders 11 and 12 are assembled together. After a predetermined time has passed and the adhesive 15 has been cured, the lens holding unit 1
The cemented lens is taken out by dividing 1 and 12, and the protruding adhesive 15 is removed.

By joining the pair of lenses in this manner, the thickness of the adhesive 15 is adjusted, and the lens thickness of the entire cemented lens can be kept within a predetermined range. As the adhesive 15 for bonding the cemented lens, a plastic adhesive is mainly used, but any kind of adhesive 15 may be used as long as it is transparent and has a uniform refractive index to some extent. Good.

The reference value of the thickness of the adhesive 15 can be selected as appropriate, but it is necessary to avoid the deformation of the adhesive 15 due to the environment such as the temperature and humidity and the influence on the optical performance when the characteristics are changed. Therefore, the thickness is preferably 1000 μm or less.

Further, the jig 10 used for manufacturing the cemented lens is not limited to the above-described one, and the lenses 13 and 14 are adjusted so that the total thickness of the lens to be cemented is within a predetermined range. Any shape may be used as long as it can be held.

Hereinafter, each of Examples 1 and 2 and Comparative Example will be described using specific numerical values.

<Embodiment 1> In Embodiment 1, the radius of curvature R (mm) of each lens surface, the center thickness of each lens, the air gap D (mm) between each lens, and the refractive index N _d of each lens at d-line The Abbe number ν _d and the material name of each lens are shown in the upper part of Table 1 below.

However, in Table 1, each symbol R,
The numbers corresponding to D, N _d and ν _d are sequentially increased from the object side. Each number in the surface numbers 2 and 10 indicates the value of the adhesive layer (the same in Tables 2 and 3). Further, the lower part of Table 1 shows values of the F number, the focal length f, the magnification β and the half angle of view ω of the entire lens system in the first embodiment.

[0028]

[Table 1]

As shown in Table 1, in the first embodiment, the first lens L ₁ and the second lens L ₂ , and the fifth lens L ₅ and the sixth lens L ₆ are bonded by an adhesive, respectively. there a reference value of the thickness D ₁₀ of the adhesive layer as a 200 [mu] m.

Therefore, even if the center thicknesses of the individual lenses constituting the cemented lens vary by about ± 100 μm, the thickness D ₁₀ of the adhesive layer is reduced from around 0 μm to 20 μm.
By adjusting the distance between 0 μm, the center thickness of the entire cemented lens can be made closer to the reference value, so that deterioration of aberration can be prevented.

<Embodiment 2> In Embodiment 2, the radius of curvature R (mm) of each lens surface, the center thickness of each lens and the air gap D (mm) between each lens, and the refractive index N _d of each lens at d-line The Abbe number ν _d and material name of each lens are shown in the upper part of Table 2 below. In addition, the lower part of Table 2 shows Example 2
The values of the F-number, the focal length f, the magnification β of the entire lens system, and the half angle of view ω in FIG.

[0032]

[Table 2]

As shown in Table 2, in Example 2, the center thickness D ₉ of the fifth lens L _{5 and} the center thickness D ₉ of the sixth lens L _6
11 is 90 μm thicker than that of the first embodiment, and is 180 μm thicker in total.

Therefore, the fifth lens L ₅ and the sixth lens L ₆
Preparative thick D ₁₀ of the adhesive layer for adhering, by the 20μm and thin as 180μm compared to that of Example 1, and the fifth lens L ₅ which is adhered by the adhesive 6 The overall thickness D ₉ + D ₁₀ + D ₁₁ of the lens L _{6 is} the same as that of the first embodiment.

<Comparative Example> In the comparative example, the radius of curvature R (mm) of each lens surface, the center thickness of each lens, the air gap D (mm) between each lens, the refractive index N _d of each lens at d-line, and each Table 3 below shows the Abbe number ν _d and material name of the lens.
Is shown at the top. Further, the lower part of Table 3 shows the values of the F number, the focal length f, the magnification β of the entire lens system, and the half angle of view ω in this comparative example.

[0036]

[Table 3]

As shown in Table 3, in the comparative example, the fifth lens
Z L_Five Center thickness D₉ And the sixth lens L ₆ Center thickness D₁₁But,
90 μm each in comparison with that of Example 1,
The thickness is increased by 180 μm.

However, the fifth lens L ₅ and the sixth lens L ₆
Since the thickness D ₁₀ of the adhesive layer for adhering the door is set to 200μm in the same manner as in Example 1, the thickness D of the fifth lens L ₅ which is bonded across the sixth lens L ₆ by adhesive
₉ + D ₁₀ + D ₁₁ is 180 μm compared to that of the first embodiment.
m thicker.

FIGS. 4 to 6 show aberration diagrams (spherical aberration, astigmatism, distortion, and lateral aberration) corresponding to Examples 1 and 2 and Comparative Example. It should be noted that each of the spherical aberration diagrams shows e.
Aberrations for the line, g-line, and C-line are shown, and each astigmatism diagram shows aberrations for the sagittal (S) image plane and the tangential (T) image plane.

As apparent from FIGS. 4 and 5, according to the above-described embodiments, all the above-described aberrations can be made favorable. Further, when the first embodiment and the second embodiment are compared, each aberration is almost the same.

On the other hand, as is apparent from FIG. 6, according to the comparative example described above, each aberration changes greatly as compared with the first and second embodiments, and it is impossible to obtain good optical performance.

That is, when the thickness of the entire cemented lens is maintained within a predetermined range by adjusting the thickness of the adhesive layer as in Examples 1 and 2, various aberrations are corrected well. If the thickness of the adhesive layer is not adjusted, various aberrations are not corrected satisfactorily and a good image can be obtained. Can not get.

Various image reading apparatuses such as a facsimile and a color scanner equipped with the imaging lens of the present embodiment are used for reading an image of a document, and the quality of the read image at that time is considered to be good. Become.

[0044]

As described above, according to the method of manufacturing an imaging lens of the present invention, the variation in the center thickness of each lens constituting the cemented lens can be absorbed by adjusting the thickness of the adhesive layer. Thereby, the center thickness of the cemented lens can be maintained within a predetermined range. Therefore, it is not necessary to process the center thickness of each lens constituting the cemented lens with high accuracy, and it is not necessary to consider a combination of lenses, and it is possible to reduce costs for processing and assembling the lenses.

According to the image reading apparatus using the imaging lens manufactured by the manufacturing method of the present invention, it is possible to improve the image quality when reading an image.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a basic configuration of a lens according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a schematic configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 3 is a longitudinal sectional view showing a schematic configuration of a jig used when manufacturing a cemented lens in the method of manufacturing an imaging lens according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating aberrations (spherical aberration,
Astigmatism, distortion, lateral aberration)

FIG. 5 is a diagram illustrating each aberration (spherical aberration,
Astigmatism, distortion, lateral aberration)

FIG. 6 is a diagram illustrating aberrations (spherical aberration, astigmatism, distortion, and lateral aberration) of the lens according to the comparative example.

[Explanation of symbols]

L _{1 to} L ₆ Lenses R _{1 to} R ₁₂ Radius of curvature of lens surfaces D _{1 to} D ₁₁ Lens surface spacing (lens thickness) X Optical axis P Imaging position 1 Imaging lens 2 Image reading device 3 Document 4 Glass plate 5 CCD 6 Cover glass 7 Illumination device 8 Aperture 9 Image plane 10 Jig 11, 12 Lens holding part 13, 14 Lens 15 Adhesive 16 Space

Claims (2)

[Claims] 1. A method for manufacturing an imaging lens having one or more sets of cemented lenses, wherein each lens constituting the cemented lenses is such that the thickness of the entire cemented lens on the optical axis is within a predetermined range. A method of adjusting the thickness of an adhesive layer for adhering the lens to absorb a manufacturing error of the thickness on the optical axis of each lens. 2. An image reading apparatus using the imaging lens according to claim 1.