JP2000111794A - Lens for reading and image reader using the lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens whose effective f-number is 3.5 and whose maximum half viewing angle is about 16 deg. and which has high optical performance over an entire image plane by making it satisfy a specified conditional expression. SOLUTION: This lens is composed of a 1st group G1 consisting of a positive 1st lens 1 being a meniscus whose convex surface faces to an object side, a 2nd group G2 consisting of a 1st combined lens obtained by sticking a positive 2nd lens 2 and a negative 3rd lens 3, a diaphragm SP, a 3rd group G3 consisting of a 2nd combined lens obtained by sticking a negative 4th lens 4 and a positive 5th lens 5, and a 4th group G4 consisting of a positive 6th lens 6 being a meniscus whose surface on an image surface side is convex in order from the object side. It is assumed that the focal distances of the 1st and the 6th lenses are f1 and f6, the focal distances of the 2nd and the 3rd groups are f23 and f45, the distances between the 2nd group and the diaphragm and between the diaphragm and the 3rd group are d5 and d6, and the refractive index and the Abbe number of the material of an i-th lens are (ni) and νi. In the case of defining the focal distance of the entire system as (f) and normalizing f=1, the conditions of the expressions I and II are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reading lens and an image reading apparatus using the same. For example, the present invention relates to an effective F-number which is suitable for reading image information on a document surface by forming an image on a line sensor surface. 5. It is suitable for a digital copier, an image scanner, or the like having a maximum half angle of view of about 16 ° and high optical performance over the entire screen and including a lens having a total of four groups and six elements.

[0002]

2. Description of the Related Art Conventionally, an apparatus for reading image information by forming image information on a document surface on a row surface of a solid-state image sensor (line sensor) at a predetermined reduction magnification by a reading lens, for example, Various devices such as digital copiers and image scanners have been proposed. The characteristics required for the reading lens used in such a device are that it has a large aperture in order to increase the reading speed, that it has a large angle of view in order to reduce the size of the reading device, and that it has a high quality digital image. Various aberrations have been sufficiently removed to obtain information, and chromatic aberration has also been sufficiently removed so as to be applicable to color image reading.

Conventionally, various types of lenses having a Gauss type selected as a reading lens have been proposed in, for example, Japanese Patent Application Laid-Open Nos. 6-109971 and 8-146292.

Japanese Patent Application Laid-Open No. 6-109971 discloses a meniscus positive first lens having a convex surface facing the object side in order from the object side, a meniscus positive second lens having a convex surface facing the object side, and an object. Meniscus-shaped negative third lens having a convex surface facing the side, a meniscus-shaped negative fourth lens having a concave surface facing the object side across the aperture, and a meniscus-shaped positive fourth lens having a concave surface facing the object side A Gaussian type lens having a configuration in which five lenses and a sixth lens whose both lens surfaces are convex are arranged, and a second lens and a third lens, and a fourth lens and a fifth lens, each of which is bonded in four groups and six, are arranged. A reading lens is proposed.

In Japanese Patent Application Laid-Open No. 8-146292, first to fourth groups are sequentially arranged from the object side to the image side, and the first group is a meniscus positive positive lens having a convex surface facing the object side. The second group includes a positive second lens disposed on the object side and a negative third lens cemented on the image side of the second lens, and the third group includes a negative third lens. The fourth group proposes a reading lens composed of four lenses and a fifth positive lens cemented to the image side of the fourth lens, and the fourth group is composed of a positive sixth lens.

[0006] However, all of the above-described reading lenses require further improvement in any of the characteristics required for the above-described reading lenses.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a finite F-number of 3.5 and a large aperture can be obtained by appropriately setting the lens configuration of each lens group of a reading lens comprising a Gaussian tie having four groups and six elements. An object of the present invention is to provide a reading lens which can sufficiently perform aberration correction including chromatic aberration sufficiently up to a maximum half angle of view of about 16 ° and an image reading apparatus using the same.

[0008]

According to the present invention, there is provided a reading lens comprising: (1) a first group of a meniscus-shaped positive first lens in which a lens surface on the object side faces the object side in order from the object side. ,
A second unit composed of a first cemented lens in which a positive second lens and a negative third lens are cemented, an aperture, and a second cemented lens in which a negative fourth lens and a positive fifth lens are cemented. A reading lens comprising a third group, and a fourth group consisting of a meniscus-shaped positive sixth lens whose lens surface on the image surface side faces the convex surface on the image surface side, wherein The focal lengths of the lenses are respectively f1 and f6, the focal lengths of the second and third groups are f23 and f45, respectively, the air gap between the second group and the aperture, and the air gap between the aperture and the third group are each in order. d5, d
6. The refractive index and Abbe number of the material of the ith lens are ni and
νi, the focal length of the whole system is f, and when normalized to f = 1,

[0009]

(Equation 4) 1.11 · f ≦ f1 / n1 + f6 / n6 ≦ 1.56 · f (2) −12.5 ≦ f23 / f1 ≦ 11.1 (3) 1.14 ≦ 3 × (n6-1) /((N1+n2+n5)-3)≦1.4‥‥(4)

[0010]

(Equation 5) It is characterized by satisfying certain conditions.

In particular, (1-1) when the aperture is counted as one surface of the reading lens, the radius of curvature of the i-th lens surface is ri, and the i-th axial thickness or air space is di. 1.20 ≦ (r5-r7) / (d5 + d6) ≦ 1.57 (6)

[0012]

(Equation 6) It is characterized by satisfying certain conditions.

(2) An image reading apparatus according to the present invention, wherein an image is formed on an imaging means surface using the reading lens described in any one of the above (1) to (1-1). Features.

[0014]

1A and 1B are sectional views of a reading lens according to a first embodiment of the present invention, which will be described later, and FIG. 1A is a meridional sectional view and FIG. (B) is a sagittal sectional view. 2 to 7 show various aberration diagrams (spherical aberration,
Curvature of field, distortion, chromatic aberration of magnification). In the spherical aberration diagram, the solid line, the two-dot chain line, and the one-dot chain line are respectively 546 nm (d line), 460 nm (g line), and 630 nm.
It shows the characteristics at the wavelength of (c line). A broken line, a solid line, a two-dot chain line, and a one-dot chain line in the field curvature aberration diagram indicate 546 in order.
meridional field curvature at nm (d-line), sagittal field curvature, meridional field curvature at 460 nm (g-line),
Represents characteristics in sagittal field curvature. In the chromatic aberration of magnification diagram, the two-dot chain line and the one-dot chain line are respectively 460 nm (g).
Line) and 630 nm (c line).

As shown in FIG. 1, the reading lens in the present embodiment includes a first meniscus positive first lens 1 having a lens surface on the object side convex toward the object side in order from the object side. The second group G2 composed of the first cemented lens in which the positive second lens 2 and the negative third lens 3 are bonded, the aperture SP, the negative fourth lens 4 and the positive fifth lens 5 are bonded. A fourth group G4 including a third group G3 including a second cemented lens and a fourth group G4 including a meniscus-shaped positive sixth lens 6 whose lens surface on the image surface side is convex toward the image surface side. Consists of a Gaussian tie of composition. FIG.
In the figure, 7 is a platen glass, and 8 is a cover glass such as a CCD.

In this embodiment, the reading lens is constituted by a Gaussian type having four groups and six elements as shown in FIG. 1, and the refracting power and the lens interval of each lens are defined by conditional expressions (1) to (5).
2. Effective F-number by setting as in (7).
5, maximum half angle of view about 16 °, imaging magnification β is β = -0.1
In 6535, a reading lens having excellent optical performance is obtained.

Also, as in the present embodiment, the first lens is a meniscus lens having a convex surface facing the object side.
The fact that the lens is a meniscus lens having a convex surface facing the image plane is a useful condition for reducing the size of the reading lens.

In general, in a reading lens for forming an image on the surface of a one-dimensional solid-state imaging device, the width of an effective area for transmitting a light beam without passing through a meridional section and a sagittal section is often different. That is, the effective area width in the sagittal section is smaller than the effective area width of the lens in the meridional section. Therefore, in order to make the reading lens thinner as can be understood by comparing FIG. 1A and FIG. 1B, in the present embodiment, the first group (first
The ends of the lens 1) G1 and the fourth group (sixth lens 6) G4 are cut off.

Next, the technical meaning of each of the conditional expressions (1) to (5) will be described.

Conditional expression (1) is a condition for determining the power distribution of the lens units before and after the stop. If the value deviates from the range of conditional expression (1), it becomes difficult to mainly correct distortion, which is not good.

Conditional expression (2) is a condition for determining the sharing of refractive power between the first group of positive refractive power and the fourth group of positive refractive power. It is not good because mainly it becomes difficult to correct spherical aberration and field curvature aberration.

Conditional expression (3) is a condition for determining the contribution of power to the entire system of the second lens unit. If the value deviates from the range of conditional expression (3), it becomes difficult to mainly correct coma aberration, which is not good.

Conditional expression (4) is a condition for determining the selection of the refractive index of the material of each lens. If the value deviates from the range of conditional expression (4), it becomes difficult to correct mainly astigmatism.

Conditional expression (5) is a condition for determining the selection of the Abbe number of the material of each lens, and if it is out of the range of conditional expression (5), it becomes difficult to correct chromatic aberration.
Conditional expression (5) is also a condition to be considered together with conditional expression (4).

This reading lens functions sufficiently by satisfying the above conditions, but it is preferable to satisfy the above-mentioned conditional expressions (6) and (7) in order to further improve the performance.

Next, the technical meaning of the conditional expressions (6) and (7) will be described.

Conditional expression (6) is an effective condition mainly for correction of spherical aberration and removal of coma aberration in consideration of conditional expressions (2) and (3), and deviates from the range of conditional expression (6). Then, the resolving power is remarkably deteriorated, which is not good.

Conditional expression (7) is a condition mainly for correcting the field curvature aberration while reducing the size of the reading lens.
If the value deviates from the range of the conditional expression (7), the effect is reduced, which is not good.

FIG. 8 is a schematic view of a main part when the reading lens of the present invention is applied to an image reading apparatus such as a digital copying machine.

In FIG. 1, reference numeral 18 denotes a document, which is placed on a platen glass 17. 21 is a lighting means,
For example, it comprises a light source 11 composed of a halogen lamp, a fluorescent lamp or the like, a reflector 12 and the like. Reference numeral 13 denotes an aperture (slit), which has an opening that is long in the direction (main scanning direction) perpendicular to the paper surface, which is the direction in which pixels of a CCD (line sensor) 16 serving as reading means, which will be described later, are arranged. Regulates the luminous flux from Reference numerals 14a, 14b, and 14c denote first, second, and third scanning mirrors for scanning, respectively.
Are guided to a reading lens 15 described later. Reference numeral 15 denotes a reading lens (imaging lens) according to the present invention.
The light flux based on the image information on the original 18 is imaged on the CCD 16. Reference numeral 16 denotes a reading means (imaging means), which comprises a CCD (line sensor) in which a plurality of pixels are arranged in the main scanning direction.

In this embodiment, the original 18 placed on the original platen glass 17 reflects the direct light from the light source 11 and the reflection shade 1.
2 illuminates from both sides. Then, the light beam from the original 18 passes through the opening of the stop 13, and the first, second, and third scanning mirrors 14a, 14b, and 14 for scanning are provided.
The image is formed on the surface of the CCD 16 by the reading lens 15 via the line c, and is converted into an electric signal in accordance with the density of the document 18, and one line of image information in the main scanning direction is read. The image reading in the sub-scanning direction (the direction of arrow Y in FIG. 8) is performed on a document 18 by a first mirror base including a light source 11, a reflection shade 12, a stop 13, and a first scanning mirror (full-speed scanning mirror) 14a. Is moved in the sub-scanning direction, and second and third scanning mirrors (half-speed scanning mirrors) 14b, 14
(c) in the same direction at half the speed of the first mirror table (moving speed ratio: 2: 1), thereby keeping the optical path length from the original 18 to the CCD 16 constant. The image information of the document 18 is read.

Next, numerical examples of the present invention will be described. In the numerical examples, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air space from the object side, and ni and νi are the i-th lens surfaces in order from the object side. These are the refractive index (d-line) and Abbe number (d-line) of glass. a1 and a2 each represent the surface of the platen glass;
Reference numerals 1 and 2 denote the surface of the cover glass of the CCD, respectively.

In the numerical example, the focal length f of the entire system is normalized to f = 1. The finite F number is 3.5, the maximum half angle of view is about 16 °, and the imaging magnification β is −0.16535.

Tables 1 and 2 show the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. [Numerical Example 1] Surface number rdn ν a1 ∞ 0.05183 1.51633 64.15 a2 ∞ 1 0.60248 0.05222 1.62041 60.29 2 2.15828 0.00311 3 0.28281 0.08383 1.63854 55.38 4 0.68537 0.04133 1.64769 33.79 5 0.21844 0.11052 6 (Aperture) 0.19163 7 -0.21939 33.05 1. -1.99223 0.07839 1.63854 55.38 9 -0.31565 0.00130 10 -3.13138 0.05779 1.80610 40.92 11 -0.55578 b1 ∞ 0.01296 1.51633 64.15 b2 ∞ [Numerical Example 2] Surface number rdn ν a1 ∞ 0.05173 1.51633 64.15 a2 ∞ 1 0.84054 0.04621 4.02041 60.29 2 3 0.28856 0.07108 1.63854 55.38 4 0.64287 0.05590 1.64769 33.79 5 0.23085 0.11696 6 (Aperture) 0.17392 7 -0.20439 0.02218 1.66680 33.05 8 -2.14639 0.07494 1.63854 55.38 9 -0.28491 0.00042 10 -2.56606 0.05692 1.80610 40.92 11 -0.51 443 b1 64- [Numerical Example 3] Surface number rdn ν a1 ∞ 0.05233 1.51633 64.15 a2 ∞ 1 0.48405 0.06254 1.62041 60.29 2 1.52686 0.00254 3 0.26399 0.07663 1.63854 55.38 4 0.56535 0.02770 1.64769 33.79 5 0.2015 7 0.13229 6 (aperture) 0.17391 7 -0.22853 0.03110 1.66680 33.05 8 -2.73747 0.09117 1.63854 55.38 9 -0.33626 0.00440 10 -4.66889 0.05613 1.80610 40.92 11 -0.61739 b1 ∞ 0.01308 1.51633 64.15 b2 ∞ [Numerical example 4] Face number rdn νa1 ∞ 0.05171 1.51633 64.15 a2 ∞ 1 0.53637 0.05650 1.53996 59.46 2 2.24048 0.00200 3 0.27821 0.08141 1.63854 55.38 4 0.65491 0.03947 1.64769 33.79 5 0.21415 0.11222 6 (Aperture) 0.18858 7 -0.21121 0.02661 1.66680 33.05 8 -1.88880 0.07905 90.355 55 2.68182 0.05805 1.80610 40.92 11 -0.53526 b1 ∞ 0.01293 1.51633 64.15 b2 ∞ [Numerical Example 5] Face number rdn ν a1 ∞ 0.05229 1.51633 64.15 a2 ∞ 1 0.60961 0.05662 1.62041 60.29 2 2.04716 0.00961 3 0.27701 0.08324 1.67790 55.29 40.500 0.22787 0.12939 6 (aperture) 0.19928 7 -0.18999 0.02600 1.72151 29.23 8 -0.46783 0.06731 1.71300 53.87 9 -0.25943 0.02960 10 -5.93381 0.05816 1.80610 40.92 11 -0.68494 b1 ∞ 0.01307 1.51633 64.15 b2 ∞ [Numerical Example 6] Surface number rdn ν a1 ∞ 0.05196 1.51633 64.15 a2 ∞ 1 0.71451 0.04723 1.62041 60.29 2 2.71317 0.00248 3 0.29087 0.06717 1.67790 55.34 4 0.62636 0.06028 1.68893 31.07 5 0.24837 0.11869 6 (aperture) 0.20876 7 -0.18546 0.02597 -0.44390 0.06690 1.71300 53.87 9 -0.25524 0.03041 10 -8.66698 0.05702 1.80610 40.92 11 -0.71451 b1 ∞ 0.01296 1.51633 64.15 b2 ∞

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

As described above, according to the present invention, the finite F-number is obtained by appropriately setting the lens configuration of each lens group of the reading lens comprising a Gaussian tie having four groups and six elements and satisfying each conditional expression. Despite having a large aperture of 3.5, the maximum half field angle can be sufficiently corrected up to about 16 °, including chromatic aberration, and aberrations can be satisfactorily corrected. Furthermore, a small-sized reading lens excellent in resolution and an image using the same. A reading device can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a diagram showing various aberrations of Numerical Embodiment 1 of the present invention.

FIG. 3 is a diagram showing various aberrations of Numerical Example 2 of the present invention.

FIG. 4 is a diagram showing various aberrations of Numerical Example 3 of the present invention.

FIG. 5 is a diagram showing various aberrations of Numerical Example 4 of the present invention.

FIG. 6 is a diagram showing various aberrations of Numerical Example 5 of the present invention.

FIG. 7 is a diagram showing various aberrations of Numerical Example 6 of the present invention.

FIG. 8 is a schematic diagram of a main part when the reading lens of the present invention is applied to an image reading apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens 6 6th lens 7 Platen glass 8 Cover glass 11 Light source 12 Reflector shade 13 Aperture 14a, 14b, 14c Scanning mirror 15 Reading lens 16 Reading means (CCD) 17 Platen glass 18 Document 21 Illumination means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA08 KA18 LA06 PA04 PA19 PB06 QA02 QA07 QA12 QA21 QA26 QA32 QA41 QA46 RA32 RA42 9A001 KK16

Claims (3)

[Claims] 1. A first group comprising a meniscus-shaped positive first lens having a lens surface on the object side convex toward the object side in order from the object side, and a positive second lens and a negative third lens are stuck. The second group of the first cemented lens, the stop, the third group of the second cemented lens in which the negative fourth lens and the positive fifth lens are bonded, and the lens surface on the image plane side is the image plane. A fourth lens group comprising a meniscus-shaped positive sixth lens having a convex surface directed to the side, wherein the focal lengths of the first and sixth lenses are respectively f1, f6,
The focal lengths of the second and third lens units are respectively set to f23, f45,
The air spacing between the second group and the stop, the aperture and the third group are d5 and d6, respectively, the refractive index and Abbe number of the material of the ith lens are ni and νi, and the focal length of the entire system is f. And f = 1
When normalized, 1.11 · f ≦ f1 / n1 + f6 / n6 ≦ 1.56 · f −12.5 ≦ f23 / f1 ≦ 11.1 1.14 ≦ 3 × (n6-1) / ((n1 + n2 + n5)
-3) ≦ 1.4 (2) A reading lens satisfying the following conditions. 2. The reading lens according to claim 1, wherein a radius of curvature of an i-th lens surface is ri when the stop is counted as one surface.
Assuming that the i-th axial thickness or air space is di, 1.20 ≦ (r5−r7) / (d5 + d6) ≦ 1.57 2. The reading lens according to claim 1, wherein the following condition is satisfied. 3. An image reading apparatus, wherein an image is formed on an imaging means surface using the reading lens according to claim 1.