JP2005010197A - Lens for reading image and image scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens for reading an image which is constituted to excellently correct various types of aberrations including chromatic aberration and obtain optical performance suitable for reading an image while realizing size reduction, and to provide an image scanner. <P>SOLUTION: The lens for reading an image is constituted by disposing: a 1st lens group G1 including a doublet consisting of a lens L1 turning its convex surface to an object side and a lens L2 turning its concave surface to an image side; a 2nd lens group G2 including a lens L3 turning its convex surface to the object side; a diaphragm K; a 3rd lens group G3 including a lens L4 turning its convex surface to the image side; and a 4th lens group G4 including a doublet consisting of a lens L5 turning its concave surface to the object side and a lens L6 turning its convex surface to the image side and having negative refractive power as a whole in this order from the object side. The lens is further constituted to satisfy a specified conditional expression (1) (not shown) or a conditional expression (7) (not shown). Thus, the optical performance suitable for reading the image is obtained while realizing the size reduction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading device such as an image scanner and an image reading lens mounted thereon.
[0002]
[Prior art]
Conventionally, an image of a color original such as a negative film or a positive film is imaged on a solid-state image sensor such as a CCD (Charge Coupled Device) via a reading optical system to read the image information. An image reading apparatus is used. Examples of the image reading lens used as the optical system of such an image reading apparatus include those described in Patent Documents 1 to 5 below.
[0003]
In recent years, an image reading lens (hereinafter, simply referred to as a reading lens) used in the optical system of such an image reading device is required to have a higher resolving power as the density of light receiving elements increases. It is like that. In particular, for a reading lens used in an image reading apparatus that reads a color image with only one CCD, for example, each color of red (Red = R), green (Green = G), and blue (Blue = B) Each color needs to be satisfactorily achromatic so that the image formation position of the image matches on the light receiving surface of the CCD, and the resolving power of each color is kept at the same level on the device. Is desirable. More specifically, in the reading lens, axial chromatic aberration and lateral chromatic aberration of each RGB color are reduced, and an image from the center to the periphery of the document is aligned substantially on a plane perpendicular to the optical axis. Imaging performance capable of image formation is required. When the reading lens satisfies such imaging performance, a high-contrast image can be obtained for each of the RGB colors.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 3-121409
[Patent Document 2]
JP-A-5-53052
[Patent Document 3]
JP-A-6-109971
[Patent Document 4]
JP-A-8-286107
[Patent Document 5]
JP-A-11-271612
[0005]
[Problems to be solved by the invention]
However, if the amount of correction of axial chromatic aberration in the reading lens is insufficient, the image points of the respective colors will be shifted. For this reason, even if each color of RGB obtains a high-contrast image alone, there arises a problem that a difference appears in the contrast for each RGB depending on the imaging position. In addition to high resolution, the reading lens is also required to be more compact. In order to reduce the size, it is necessary to reduce the focal length and the conjugate length (conjugate distance) in addition to reducing the size of the reading lens itself.
[0006]
However, the reading lenses described in Patent Document 1 and Patent Document 2 cannot be said to have sufficiently corrected chromatic aberration, and are not sufficiently compact. The reading lenses described in Patent Documents 3 to 5 are corrected for chromatic aberration, but are insufficient for compactness.
[0007]
SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and its object is to obtain an optical performance suitable for reading an image with various aberrations including chromatic aberration being corrected well while achieving compactness. An object of the present invention is to provide an image reading lens and an image reading apparatus which can be used.
[0008]
[Means for Solving the Problems]
The image reading lens of the present invention includes, in order from the object side, a first lens group including a cemented lens including a positive meniscus lens having a convex surface facing the object side and a negative meniscus lens having a concave surface facing the image side. A second lens group including a positive meniscus lens having a convex surface facing the object side, a stop, a third lens group including a positive meniscus lens having a convex surface facing the image side, and a negative lens having a concave surface facing the object side. And a fourth lens group including a cemented lens having a negative refractive power as a whole, and a meniscus lens having a convex surface facing the image side.
0.93 <n1 / n2 <1.08 (1)
14.0 <ν1-ν2 (2)
1.05 <R1 / R3 <1.33 (3)
0.70 <(D35) / (D68) <1.11 (4)
-20.0 <f4 / f <-1.5 (5)
0.008 <(R5 / R7) · M / (Fe) ² <0.025 (6)
2.1 <R7 / R9 <2.7 (7)
Are configured to satisfy the conditional expressions (1) to (7). However, the refractive index and Abbe number for the d-line of the positive meniscus lens in the first lens group are n1, ν1, the refractive index and Abbe number for the d-line of the negative meniscus lens in the first lens group are n2, ν1, first. The radius of curvature on the object side of the positive meniscus lens in the lens group is R1, the radius of curvature on the image side of the negative meniscus lens in the first lens group is R3, and the surface distance from the surface closest to the image side to the stop in the first lens group. D35, the surface distance from the stop to the most object side surface in the fourth lens group is D68, the focal length of the fourth lens group is f4, the focal length of the entire system is f, and the positive meniscus lens in the second lens group The radius of curvature on the image side is R5, the radius of curvature of the positive meniscus lens in the third lens group is R7, the magnification is M, the effective F number is Fe, and the fourth lens group is Let R9 be the radius of curvature of the negative meniscus lens on the object side.
[0009]
An image reading apparatus according to the present invention includes the above-described image reading lens.
[0010]
Here, the image reading lens or the image reading device of the present invention further includes at least one of anomalous dispersion of the negative meniscus lens of the first lens group and an anomalous dispersion of the negative meniscus lens of the fourth lens group. One side
−0.0100 <δθ _{g, F} <0.0040 (8)
It is desirable to satisfy the conditional expression (8) expressed by However, δθ _{g, F} Is anomalous dispersibility.
[0011]
In the image reading lens or the image reading device of the present invention, at least one of the positive meniscus lens in the first lens group and the positive meniscus lens in the fourth lens group is further provided.
−0.002 <δθ _{g, F} <0.015 (9)
It is desirable to satisfy the conditional expression (9) expressed by However, δθ _{g, F} Is anomalous dispersibility. This anomalous dispersion δθ _{g, F} Are the refractive indices for g-line, F-line and C-line, respectively, ng, nF, nC,
θ _{g, F} = (Ng-nF) / (nF-nC)
Partial dispersion ratio θ of g-line and F-line defined by _{g, F} Represents a deviation from the reference line, and is a value specific to the material. Here, the reference line is, for example, a partial dispersion ratio θ in a reference material such as two glass materials K7 and F2 manufactured by Schott. _{g, F} Is a straight line obtained by connecting the coordinate points of two glass materials K7 and F2 on a graph with the vertical axis representing the Abbe number νd.
[0012]
With the image reading lens according to the present invention, the above-described configuration can provide performance suitable for image reading. That is, by configuring the first and second lens groups to have a focusing action while the third and fourth lens groups have a diverging action, the Petzval value of the entire system is corrected to an appropriate value, and Since appropriate values are given to the radius of curvature, refractive index, focal length, and surface interval of each component, various aberrations are corrected in a well-balanced manner, and the size can be reduced as compared with the prior art. In the image reading apparatus of the present invention, a high-quality image obtained through such an image reading lens is read.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
An image reading apparatus 10 according to an embodiment of the present invention shown in FIG. 1 is a transparent original type image reading apparatus, for example, an original placing table 3 on which an original 2 such as a negative film or a positive film is placed. , A light source 7 that emits illumination light toward the document table 3, an image sensor 4 that captures an image of the document 2, and a reading lens for image reading that forms an image of the document 2 on the imaging surface of the image sensor 4. 1 is provided. The image sensor 4 is composed of a CCD, for example. In the image reading apparatus 10, an optical element 5 such as a document pressing glass or a filter for pressing the document 2 against the document placing table 3 is disposed between the document 2 and the reading lens 1 as necessary. The Further, in the image reading apparatus 10, an optical element 6 such as a cover glass for protecting the image sensor 4 is disposed between the reading lens 1 and the image sensor 4 as necessary. In the image reading apparatus 10, illumination light is irradiated from the light source 7 toward the document 2. The light transmitted through the document 2 is imaged on the image sensor 4 by the reading lens 1. A transmission image of the document 2 obtained through the reading lens 1 is picked up and read by the image pickup device 4.
[0015]
FIG. 2 schematically shows a lens configuration of the reading lens 1 according to the present embodiment, and shows a cross-sectional structure of each lens element in a cross section including the optical axis Z1. In FIG. 2, the side indicated by the symbol Zobj is the object side, that is, the side on which the document 2 is placed and the image for reading is provided. In FIG. 2, the side indicated by the symbol Zimg is the image forming side, that is, the side on which the object side image is formed. On the imaging surface Simg of the reading lens 1, the imaging surface of the imaging device 4 is arranged. In FIG. 2, the symbol P indicates the center imaging position of the reading lens 1. Symbol Ri indicates the radius of curvature of the i-th lens surface Si from the object side, and symbol Di indicates the surface distance on the optical axis between the i-th lens surface and the (i + 1) -th lens surface from the object side. . However, in FIG. 2, the part denoted by reference numeral S6 (R6) represents the diaphragm K of the lens system.
[0016]
The reading lens 1 includes, in order from the object side, a positive meniscus lens L1 (hereinafter simply referred to as a lens L1) having a convex surface directed toward the object side, and a negative meniscus lens L2 (hereinafter simply referred to as a lens L1) facing the image side. And a second lens group G2 including a positive meniscus lens L3 having a convex surface facing the object side (hereinafter simply referred to as a lens L3). A third lens group G3 including a stop K, a positive meniscus lens L4 having a convex surface facing the image side (hereinafter simply referred to as a lens L4), and a negative meniscus lens L5 having a concave surface facing the object side (hereinafter referred to as a lens L4). And a fourth lens group including a cemented lens having a negative refractive power as a whole, and a positive meniscus lens L6 having a convex surface directed to the image side (hereinafter simply referred to as a lens L6). G4 is It has been constructed by set. Here, the first lens group G1 and the second lens group G2 on the object side with respect to the stop K are collectively referred to as a front group G12, and the third lens group G3 and the fourth lens group on the image side with respect to one stop K are combined. G4 is collectively referred to as a rear group G34.
[0017]
The reading lens 1 has the following conditional expression (1) when the refractive index and Abbe number for the d-line of the lens L1 are n1 and ν1, respectively, and the refractive index and Abbe number for the d-line of the lens L2 are n2 and ν2, respectively. ) And (2) are satisfied.
[0018]
0.93 <n1 / n2 <1.08 (1)
14.0 <ν1-ν2 (2)
[0019]
Here, the effect brought about by the conditional expressions (1) and (2) will be described. Conditional expressions (1) and (2) ensure the degree of freedom of the radius of curvature R2 on the surface S2 that is the joint surface while correcting chromatic aberration well. That is, by satisfying the above conditional expressions (1) and (2), it is possible to satisfactorily correct various aberrations (particularly chromatic aberration) even when the radius of curvature R2 is freely changed. . If the numerical value range of the conditional expression (1) or (2) is not satisfied, the aberration is not sufficiently corrected.
[0020]
Furthermore, the reading lens 1 satisfies the following conditional expression (3) when the radius of curvature of the lens L1 on the object side is R1, and the radius of curvature of the lens L2 on the image side is R3.
[0021]
1.05 <R1 / R3 <1.33 (3)
[0022]
Conditional expression (3) indicates a condition for keeping the Petzval sum of the entire system at an appropriate value by suppressing the Petzval value of the first lens group G1 from becoming a large negative value. When the value is smaller than the lower limit of the conditional expression (3), the convergence property of the front group G12 becomes too strong, and the beam diameter of the on-axis homogenous ray incident on the rear group G34 becomes too small. For this reason, in order to maintain the Petzval sum of the entire system at an appropriate value, it is necessary to increase the divergence in the rear group G34. To that end, the radius of curvature of the concave surface in the rear group G34 must be excessively reduced. As a result, it becomes difficult to correct off-axis coma. On the other hand, when the value is larger than the upper limit of the conditional expression (3), the focusing property of the front group G12 becomes too weak, and the beam diameter of the on-axis homogenous ray incident on the rear group G34 becomes too large. For this reason, in order to keep the Petzval sum of the entire system at an appropriate value, it is necessary to weaken the divergence in the rear group G34. To that end, the radius of curvature of the concave surface in the rear group G34 must be excessively increased. In other words, it becomes difficult to correct off-axis coma.
[0023]
Further, the reading lens 1 has a surface distance from the most image-side surface S3 to the stop K in the first lens group G1, that is, the sum of the surface distances D3 to D5, D35, and from the stop K to the most object side in the fourth lens group G4. When the distance between the surfaces up to the surface S9, that is, the sum of the surface distances D6 to D8 is D68, the following conditional expression (4) is satisfied.
[0024]
0.70 <(D35) / (D68) <1.11 (4)
[0025]
Conditional expression (4) defines the symmetry between the front group G12 and the rear group G34 in the reading lens 1. That is, the conditions for the front group G12 and the rear group G34 to have opposite effects on the light flux and to correct various aberrations in a balanced manner are shown. If the numerical value range of conditional expression (4) is not met, the symmetry between the front group G12 and the rear group G34 will be lost, and the effect of canceling out aberrations will be reduced, making it difficult to correct aberrations satisfactorily.
[0026]
Further, the reading lens 1 satisfies the following conditional expression (5), where f4 is the focal length of the fourth lens group G4 and f is the focal length of the entire system.
[0027]
-20.0 <f4 / f <-1.5 (5)
[0028]
By satisfying this conditional expression (5), the aberration generated when the incident light beam from the object is converged in the front group G12 is appropriately corrected by appropriately diverging in the rear group G34. If the upper limit is exceeded, the correction by the rear group G34 becomes excessive, and a large positive spherical aberration occurs, and the field curvature increases positively. On the other hand, below the lower limit, the correction by the rear group G34 is insufficient, and the aberration caused by the front group G12 is not sufficiently corrected.
[0029]
Further, the reading lens 1 has the following conditional expression (6) when the radius of curvature of the image side of the lens L3 is R5, the radius of curvature of the object side of the lens L4 is R7, the magnification is M, and the effective F number is Fe. Satisfied.
[0030]
0.008 <(R5 / R7) · M / (Fe) ² <0.025 (6)
[0031]
Conditional expression (6) represents a condition for maintaining the Petzval sum of the entire system at an appropriate value and favorably correcting off-axis coma. The radius of curvature R5 of the surface S5, which is the final surface of the front group G12, is conveniently increased in order to maintain the convergence of the front group G12, and the radius of curvature R7 of the surface S7 facing this is the rear group G34. In order to give divergence, it is shown that it is convenient to make it moderately small. Further, the height of the light beam passing through the surface S5 or the surface S7 varies depending on the magnification M of image formation and the effective F number Fe. Therefore, it is desirable to determine the curvature radii R5 and R7 in consideration of the change in the height of the passing light. For example, in the case of a relatively bright lens, if the radius of curvature R5 is too large, the flare of the lower frame of the off-axis light beam becomes large. If the radius of curvature R7 is reduced to correct this, it is difficult to correct the upper coma aberration. By satisfying conditional expression (6), it is possible to correct field curvature and coma with a good balance. If the numerical value range of the conditional expression (6) is not met, the Petzval value will not be an appropriate value, and the correction of the field curvature will be insufficient. Further, when the value exceeds the upper limit, the radius of curvature R5 becomes too large, or the radius of curvature of the concave surface of the rear group G34 becomes too small, so that higher-order coma aberration is likely to occur.
[0032]
Furthermore, the reading lens 1 satisfies the following conditional expression (7) when the radius of curvature of the object side of the lens L5 is R9.
[0033]
2.1 <R7 / R9 <2.7 (7)
[0034]
By satisfying conditional expression (7), various aberrations generated in the front group G12 can be corrected in a balanced manner in the rear group G34. That is, the large positive Petzval value generated in the front group G12 can be corrected to an appropriate value, and the coma aberration generated in the front group G12 is corrected to cancel out the off-axis ray, and the coma in the rear group G34 is corrected. It becomes possible to suppress the occurrence of aberration. When the numerical value range of the conditional expression (7) is not satisfied, particularly high-order coma aberration is generated, so that good performance cannot be obtained.
[0035]
The reading lens 1 is preferably configured so that at least one of the anomalous dispersion of the lens L2 and the anomalous dispersion of the lens L5 satisfies the following conditional expression (8). However, δθ _{g, F} Is anomalous dispersion, and the refractive indexes for g-line, F-line and C-line are ng, nF and nC,
θ _{g, F} = (Ng-nF) / (nF-nC)
Partial dispersion ratio θ of g-line and F-line defined by _{g, F} Represents the deviation from the baseline. Here, the reference line is, for example, a partial dispersion ratio θ in a reference material such as two glass materials K7 and F2 manufactured by Schott. _{g, F} Is a straight line obtained by connecting the coordinate points of two glass materials K7 and F2 on a graph with the vertical axis representing the Abbe number νd. The wavelengths of g-line, F-line, and C-line are about 435.8 nm, 486.1 nm, and 656.3 nm, respectively.
[0036]
−0.0100 <δθ _{g, F} <0.0040 (8)
[0037]
Furthermore, it is desirable that the reading lens 1 is configured such that at least one of the anomalous dispersion in the lens L1 and the anomalous dispersion in the lens L6 satisfies the following conditional expression (9).
[0038]
−0.002 <δθ _{g, F} <0.015 (9)
[0039]
Here, the anomalous dispersibility will be described in more detail before describing the effects brought about by the conditional expressions (8) and (9). In general, for example, when a graph of ν vs. θ is drawn with the Abbe number ν on the horizontal axis and the partial dispersion ratio θ on the vertical axis, many glass materials have characteristics that are distributed along a predetermined reference line on the graph. It is known. And the glass material distributed in the position away from the predetermined reference line is considered to have anomalous dispersion.
[0040]
Specifically, for example, two glass materials K7 and F2 manufactured by Schott are selected as normal optical glasses, and νd (Abbe number with respect to d-line) vs. θ. _{g, F} A reference line L is defined by connecting the coordinate points of the two glass materials K7 and F2 on the graph of (partial dispersion ratio with respect to g-F line). Partial dispersion ratio θ corresponding to Abbe number νd on this reference line L _L , The partial dispersion ratio θ of any glass material _{g, F} Is a deviation of the partial dispersion ratio, that is, a value δθ indicating anomalous dispersion in any of the above glass materials _{g, F} It is said.
[0041]
Anomalous dispersion δθ _{g, F} Is a numerical value described in a catalog or the like of each glass material manufacturer, and is a unique value in each glass material.
[0042]
Next, the conditional expressions (8) and (9) will be described. Conditional expressions (8) and (9) are conditional expressions for particularly favorably correcting chromatic aberration. That is, a glass material having anomalous dispersion in the range shown in the conditional expression (8) is used for at least one of the negative lenses L2 and L5 in the cemented lenses constituting the front group G12 and the rear group G34. As a result, an appropriate refractive power can be given, so that chromatic aberration can be corrected well. On the other hand, at least one of the positive lenses L1 and L6 in the cemented lenses constituting the front group G12 and the rear group G34 is made of a glass material having anomalous dispersion in the numerical range indicated by the conditional expression (9). As a result, an appropriate refractive power can be given, so that chromatic aberration can be corrected well. In particular, the negative lenses L2 and L5 have a smaller value of anomalous dispersion in the negative numerical range of the numerical range shown in the conditional expression (8), so that the correction of the secondary spectrum of chromatic aberration is good. One of the positive lenses L1 and L6 has a larger value of anomalous dispersion in the positive numerical value range of the numerical value range shown in the conditional expression (9). The spectrum can be corrected well, and the reading lens 1 with higher resolution can be obtained. These are particularly effective in the imaging magnification region where the reduction ratio is small.
[0043]
If the conditions of conditional expressions (8) and (9) are not met, it will be particularly difficult to correct chromatic aberration well, and it will be difficult to obtain high resolution performance.
[0044]
According to the reading lens 1 of the present embodiment configured as described above, the front group G12 including the first lens group G1 and the second lens group G2, the third lens group G3, and the fourth lens group G4 are provided. The rear group G34 provided is arranged so as to be substantially symmetric with respect to the aperture K, and the front group G12 has a focusing action while the rear group G34 has a divergence action, so that the Petzval value of the entire system can be obtained. Since it is corrected to an appropriate value, and various aberrations are corrected in a well-balanced manner by giving appropriate values to the radius of curvature and refractive index of each component, or the focal length and surface interval, it is compact. The optical performance suitable for reading the image can be obtained while achieving the above.
[0045]
【Example】
Next, specific numerical examples of the image reading lens according to the above embodiment will be described.
[0046]
<Examples 1-7>
Hereinafter, the first to seventh numerical examples (Examples 1 to 7) will be described together.
[0047]
FIG. 3 illustrates basic lens data related to the image reading lens according to the first embodiment. FIG. 3 shows the curvature radii R1 to R11 of the surfaces S1 to S11, the surface spacings (thicknesses) D1 to D10, the refractive indices nd1 to nd6, and the Abbe number νd1 of the image reading lens according to the first embodiment. The values of νd6 and anomalous dispersion δθj (j = 1 to 6) are shown. Anomalous dispersion δθj is anomalous dispersion δθ in the j-th lens from the object side. _{g, F} Indicates. The unit of numerical values for the radius of curvature and the surface spacing is millimeters (mm). A portion where the values of the curvature radii R1 to R11 are 0 indicates the stop K. Similarly, basic lens data related to the image reading lenses according to Examples 2 to 7 are shown in FIGS. Here, Example 3 corresponds to the cross-sectional configuration shown in FIG. Note that examples other than the third embodiment are substantially the same as the cross-sectional configuration shown in FIG. FIG. 10 shows data relating to the image reading lenses according to Examples 1 to 7 as the focal length f of the entire system, the effective FNo. , Magnification M, focal length f4 of the fourth lens group G4, and conjugate length (conjugate distance) are collectively shown. The unit of the focal length f, the focal length f4, and the conjugate length is millimeter (mm).
[0048]
FIG. 11 shows values corresponding to the conditional expressions (1) to (9) described above for the image reading lenses according to the first to seventh embodiments. Here, the column corresponding to the conditional expression (8) indicates that anomalous dispersion δθ2 and δθ5 of the lenses L2 and L5 satisfy the conditional expression (8). Similarly, the column corresponding to the conditional expression (9) shows the anomalous dispersion δθ1 and δθ6 of the lenses L1 and L6 that satisfy the conditional expression (9). As shown in FIG. 11, the image reading lenses of the respective examples all satisfy the conditional expressions (1) to (7). However, in each of Examples 1 to 4, the anomalous dispersion δθ5 of the lens L5 satisfies the conditional expression (8). In particular, in Example 3, the anomalous dispersion δθ2 of the lens L2 also satisfies the conditional expression (8). Satisfies. In each of Examples 5 to 7, the anomalous dispersion δθ2 and δθ5 satisfy the conditional expression (8), and the anomalous dispersion δθ6 of the lens 6 satisfies the conditional expression (9). In particular, in Examples 5 and 7, the anomalous dispersion δθ1 of the lens 1 also satisfies the conditional expression (9).
[0049]
12 to 18 sequentially show various aberrations for each example, that is, spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration. Spherical aberration is shown for d-line, g-line and C-line, astigmatism and distortion are shown for d-line, and lateral chromatic aberration is shown for g-line and C-line. Further, astigmatism is shown in the sagittal direction and the tangential direction. “Ω” indicates a half angle of view.
[0050]
As is clear from the lens data and aberration diagrams described above, in each example, in order from the object side, a cemented lens including the lens L1 and the lens L2, a lens L3, an aperture K, a lens L4, and a lens. Since a cemented lens having a negative refractive power as a whole consisting of L5 and lens L6 is arranged and further configured to satisfy conditional expressions (1) to (7), it is excellent over a wide angle of view. Aberration correction was performed, and it was possible to obtain good performance suitable for reading an image and to achieve further compactness.
[0051]
Although the present invention has been described with reference to the embodiment and some examples, the present invention is not limited to the above embodiment and each example, and various modifications can be made. For example, the values of the radius of curvature, the surface interval, the refractive index, and the Abbe number of each lens component are not limited to the values shown in the above numerical examples, and may take other values.
[0052]
In the above-described embodiments and examples, a description has been given of a transparent original type image reading apparatus that projects light from a light source onto an image original and reads the transmitted image. However, the present invention is not limited to this. Alternatively, for example, a reflection original type image reading apparatus as shown in FIG. 19 may be used. In the image reading apparatus 20 shown in FIG. 19, the reading lens 1 is disposed between the document placing table 3 and the imaging element 4, and the illumination device 7 is disposed between the document placing table 3 and the reading lens 1. Is. As shown in FIG. 19, the light source 7 has, for example, a rod shape, and illuminates the document 2 continuously over the entire surface by moving in parallel on the document table 3. Thereby, the light reflected from the document 2 is imaged on the image sensor 4 by the reading lens 1. A reflection image of the document 2 obtained through the reading lens 1 is picked up and read by the image pickup device 4. Further, the middle of the optical path may be bent by a mirror or the like to make it compact.
[0053]
【The invention's effect】
As described above, according to the image reading lens or the image reading apparatus of the present invention, in order from the object side, a positive meniscus lens having a convex surface facing the object side and a negative meniscus lens having a concave surface facing the image side A first lens group including a cemented lens, a second lens group including a positive meniscus lens having a convex surface facing the object side, a stop, and a third lens including a positive meniscus lens having a convex surface facing the image side. A fourth lens group including a lens unit, a negative meniscus lens having a concave surface facing the object side, and a positive meniscus lens having a convex surface facing the image side, including a cemented lens having a negative refractive power as a whole is disposed. In addition, since it is configured to satisfy the conditional expressions (1) to (7), it is possible to reduce the size of the apparatus while correcting various aberrations in a balanced manner. Therefore, performance suitable for reading an image can be obtained.
[0054]
In particular, when at least one of the anomalous dispersion of the negative meniscus lens in the first lens group and the anomalous dispersion of the negative meniscus lens in the fourth lens group satisfies the conditional expression (8), Alternatively, when at least one of the anomalous dispersion of the positive meniscus lens in the first lens group and the anomalous dispersion of the positive meniscus lens in the fourth lens group satisfies the conditional expression (9). Can correct chromatic aberration better.
[Brief description of the drawings]
FIG. 1 is a configuration diagram schematically illustrating an image reading apparatus according to an embodiment of the present invention.
FIG. 2 is a lens cross-sectional view illustrating a configuration of an image reading lens according to an embodiment of the present invention and corresponding to Example 3;
FIG. 3 is an explanatory diagram illustrating basic data among lens data of the image reading lens according to the first embodiment of the invention.
FIG. 4 is an explanatory diagram showing basic data among lens data of an image reading lens according to Embodiment 2 of the present invention.
FIG. 5 is an explanatory diagram showing basic data among lens data of an image reading lens according to Example 3 of the invention.
FIG. 6 is an explanatory diagram showing basic data among lens data of an image reading lens according to Example 4 of the invention.
FIG. 7 is an explanatory diagram showing basic data among lens data of an image reading lens according to Example 5 of the present invention.
FIG. 8 is an explanatory diagram showing basic data among lens data of an image reading lens according to Example 6 of the present invention.
FIG. 9 is an explanatory diagram showing basic data among lens data of an image reading lens according to Example 7 of the invention.
FIG. 10 is an explanatory diagram showing other basic data among the lens data of the image reading lenses according to the first to seventh embodiments of the present invention.
FIG. 11 is an explanatory diagram showing data corresponding to conditional expressions (1) to (8) among the lens data of the image reading lenses according to the first to seventh embodiments of the present invention.
12 is a diagram showing spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration for the image reading lens of Example 1. FIG.
13 is a diagram showing spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration for the image reading lens of Example 2. FIG.
14 is a diagram showing spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration for the image reading lens of Example 3. FIG.
15 is a diagram showing spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration for the image reading lens of Example 4. FIG.
16 is a diagram illustrating spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration for the image reading lens of Example 5. FIG.
17 is a diagram showing spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration for the image reading lens of Example 6. FIG.
18 is a diagram showing spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration for the image reading lens of Example 7. FIG.
FIG. 19 is a configuration diagram illustrating a modified example of the image reading apparatus according to the embodiment of the present invention.
[Explanation of symbols]
D1 to D10: Inter-surface distance, L1 to L6: Lens, K ... Aperture, P ... Center imaging position, R1 to R11 ... Radius of curvature, Simg ... Imaging plane, Z1 ... Optical axis, 1 ... Reading lens, 2 ... Original DESCRIPTION OF SYMBOLS 3 ... Original mounting stand, 4 ... Image pick-up element, 5, 6 ... Optical element, 7 ... Light source, 10, 20 ... Image reading apparatus.

Claims (4)

From the object side,
A first lens group including a cemented lens including a positive meniscus lens having a convex surface facing the object side and a negative meniscus lens having a concave surface facing the image side;
A second lens group including a positive meniscus lens having a convex surface facing the object side;
Aperture,
A third lens group including a positive meniscus lens having a convex surface facing the image side;
A fourth lens group including a negative meniscus lens having a concave surface facing the object side and a positive meniscus lens having a convex surface facing the image side and including a cemented lens having a negative refractive power as a whole; and An image reading lens configured to satisfy the following conditional expressions (1) to (7):
0.93 <n1 / n2 <1.08 (1)
14.0 <ν1-ν2 (2)
1.05 <R1 / R3 <1.33 (3)
0.70 <(D35) / (D68) <1.11 (4)
-20.0 <f4 / f <-1.5 (5)
0.008 <(R5 / R7) · M / (Fe) ² <0.025 (6)
2.1 <R7 / R9 <2.7 (7)
However,
n1: Refractive index for the d-line of the positive meniscus lens in the first lens group n2: Refractive index for the d-line of the negative meniscus lens in the first lens group ν1: Abbe number ν2 of the positive meniscus lens in the first lens group: Abbe number R1 of negative meniscus lens in first lens group R1: Radius of curvature of object side of positive meniscus lens in first lens group R3: Radius of curvature of image side of negative meniscus lens in first lens group D35: First Surface distance from the most image side surface to the stop in the lens group D68: Surface distance from the stop to the most object side surface in the fourth lens group f4: Focal length of the fourth lens group f: Focal length R5 of the entire system: Image-side curvature radius R7 of the positive meniscus lens in the second lens group: Object-side curvature radius M of the positive meniscus lens in the third lens group: Magnification Fe: Effective F-number R9: The radius of curvature on the object side of the negative meniscus lens in the fourth lens group. Further, at least one of the anomalous dispersion of the negative meniscus lens of the first lens group and the anomalous dispersion of the negative meniscus lens of the fourth lens group satisfies the following conditional expression (8). The image reading lens according to claim 1, wherein the image reading lens is configured.
−0.0100 <δθ _{g, F} <0.0040 (8)
However, δθ _{g, F} is anomalous dispersion. Further, at least one of anomalous dispersion in the positive meniscus lens of the first lens group and an anomalous dispersion in the positive meniscus lens of the fourth lens group satisfies the following conditional expression (9). The image reading lens according to claim 1, wherein the image reading lens is configured.
−0.002 <δθ _{g, F} <0.015 (9)
However, δθ _{g, F} is anomalous dispersion. An image reading apparatus comprising the image reading lens according to any one of claims 1 to 3.

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