JP2012133298A - Image read lens, image reader, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image read lens having large diameter, wide view angle, high aperture efficiency, and satisfactory color aberration.SOLUTION: The image read lens comprises five groups and seven lenses, which are in order from an object side to an image side: the first group of positive refractive power, the second group of negative refractive power as a whole group, the third group of negative refractive power, the fourth group of positive refractive power, and the fifth group of positive refractive power as a whole group. In the image read lens, the first group has the first lens of positive meniscus shape whose convex face is oriented toward the object side, the second group has the second lens and the third lens cemented together, the second lens being biconvex lens shape in which convex faces are oriented toward both the object side and image side, the third lens being biconcave lens shape in which concave faces are orientated toward both the object side and image side. The third group has the fourth lens with a negative meniscus shape whose concave face is oriented toward the object side. The fourth group has the fifth lens of a positive meniscus shape whose concave face is orientated toward the object side, the fifth group has the sixth lens of positive meniscus shape whose concave face is orientated toward the object side, and the seventh lens of a negative meniscus shape whose concave shape is oriented toward the object side. A diaphragm is provided between the second and third groups.

Description

  The present invention relates to an image reading lens, an image reading apparatus, and an image forming apparatus including the same.

  An image reading apparatus of a facsimile or a digital copying machine reduces image information to be read by a reading lens and forms an image on a solid-state image pickup device such as a CCD (Charge Coupled Device) to convert the image information into a signal. In order to read document information in color, for example, a so-called three-line CCD in which light receiving elements having red, green, and blue filters are arranged in three rows on one chip is used, and a document image is connected to the light receiving surface. There is an optical system that separates the three primary colors by image formation and converts color image information into a signal.

  Such a reading lens generally requires a high contrast in a high spatial frequency region on the image plane, and in order to read a color original well, the image forming positions of red, green, and blue colors on the light receiving surface. Must be matched with the optical axis direction. Further, it is necessary to correct the chromatic aberration of each color satisfactorily, and it is required that the aperture efficiency is close to 100% up to the periphery of the angle of view. Here, the aperture efficiency refers to the ratio of the light beam focused on the image point on the optical axis and the light beam focused on the off-axis point. Further, chromatic aberration means that the imaging position of the optical system changes depending on the wavelength of light.

  Furthermore, a reading lens having a large aperture as bright as possible is desired in order to cope with energy saving of the scanner optical system. As a conventional example, a seven-lens lens is disclosed as such a large aperture lens. For example, Patent Document 1 achieves a very large aperture of F value (also referred to as F number) of 1.8, but the half angle of view is as narrow as 12.6 degrees, which increases the size of the scanner optical system. There are drawbacks. Here, the F number (F value) is an index indicating the brightness of the lens, and the larger the value, the darker the light, and the smaller the value, the brighter the light.

  In Patent Document 2, the F value is 2.4, the aperture is large, and the half angle of view is about 20 degrees. However, since two aspheric surfaces are used, there is a disadvantage that the cost is increased. . Furthermore, both Patent Document 3 and Patent Document 4 have a large aperture with an F value of about 3.5, but the absolute aberration amount is large, for example, corresponding to high-density reading such as 600 dpi (Dot Per Inch). I can't.

  Therefore, the present invention has been made in view of the above problems, and in order to cope with the energy saving of the scanner, the F value is 3.5 and a large aperture, and the half angle of view exceeds 18 °. The aperture efficiency is close to 100% up to the periphery, the chromatic aberration is corrected well, the contrast is high in the high spatial frequency range, and full color reading is possible. All lenses are chemically stable and lead. By using optical glass that does not contain harmful substances such as arsenic and arsenic, it is possible to recycle materials, and a compact and low-cost image reading lens that takes into account the global environment free from water pollution caused by waste liquid during processing. It is an object of the present invention to provide a reading device and an image forming apparatus including the reading device.

In order to solve the above problem, the image reading lens according to the first aspect of the present invention has a negative refractive power in the first group having the positive refractive power and the whole group in order from the object side to the image side. In an image reading lens comprising a second group, a third group having a negative refractive power, a fourth group having a positive refractive power, and a fifth group having a positive refractive power as a whole,
The first group includes positive meniscus-shaped first lenses disposed with a convex surface facing the object side, and the second group includes both convex surfaces facing both the object side and the image side. A second lens having a convex lens shape is joined to a third lens having a biconcave lens shape having concave surfaces facing both the object side and the image side, and the third group has a concave surface facing the object side. The fourth lens unit comprises a positive meniscus fifth lens with a concave surface facing the object side, and the fifth group comprises a positive lens with a concave surface facing the object side. A five-group, seven-lens configuration comprising a meniscus sixth lens and a negative-mechanical seventh lens with a concave surface facing the object side, and a diaphragm is formed between the second group and the third group It is characterized by being.

  The image reading lens according to the present invention is the image reading lens according to claim 1, wherein the fourth lens adjacent to the diaphragm has an aspheric surface facing the diaphragm.

Furthermore, the image reading lens according to the present invention is the image reading lens according to claim 1 or 2, wherein f1 is a focal length of the e-line of the first group, and f23 is an e-line of the second group and the third group. F is the total focal length of the e-line of the entire system, n is the average value of the refractive index of the d-line of the positive lens, n is the average value of the refractive index of the d-line of the negative lens, and ν is the convex The following conditional expression is satisfied, where the average value of the Abbe number of the positive lens and the concave ν are the average value of the Abbe number of the negative lens.
(1) 1.1 <f / f1 <1.2
(2) -3.0 <f / f23 <-2.5
(3) -0.055 <n convex-n concave <-0.3
(4) 15.0 <ν convex−ν concave <18.5
It is characterized by.

  The image reading apparatus according to the present invention photoelectrically illuminates a document, an imaging lens for reducing and imaging reflected light of the document irradiated by the illumination, and a document image formed by the imaging lens. An image reading apparatus including a line sensor for conversion includes the image reading lens according to any one of claims 1 to 3.

  An image forming apparatus according to the present invention includes the image reading device according to claim 4.

  According to the present invention, since the number of lenses is seven, the F-number is set to a very large aperture of 3.5, and the field curvature can be corrected satisfactorily at a half angle of view exceeding about 18 degrees. An image reading lens, an image reading apparatus, and an image forming apparatus provided with the same, in which the aperture efficiency is close to 100% up to the periphery, and chromatic aberration is also corrected well, and high contrast performance can be obtained in a high spatial frequency region Obtainable.

1 is a structural diagram showing a basic configuration of an image reading lens in an embodiment of the present invention. FIG. 2 is a structural diagram illustrating a configuration of an image reading lens in Embodiment 1 of the present invention. FIG. 3 is an aberration diagram of the image reading lens according to Example 1 of the present invention. FIG. 6 is a structural diagram illustrating a configuration of an image reading lens in Example 2 of the present invention. It is an aberration diagram of the image reading lens in Example 2 of the present invention. FIG. 6 is a structural diagram illustrating a configuration of an image reading lens in Example 3 of the present invention. It is an aberration diagram of the image reading lens in Example 3 of the present invention. 1 is a structural diagram illustrating a configuration of an image reading apparatus using an image reading lens according to an embodiment of the present invention. 1 is a structural diagram illustrating a configuration of an image forming apparatus using an image reading lens according to an embodiment of the present invention.

  Next, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified thru | or abbreviate | omitted suitably. First, the basic configuration of the image reading lens in the embodiment of the present invention will be described. FIG. 1 is a structural diagram showing a basic configuration of an image reading lens according to an embodiment of the present invention.

  As shown in FIG. 1, the configuration of the image reading lens in the embodiment of the present invention is the first having a positive refractive power from the contact glass side (left side in the figure) to the CCD cover glass side (right side in the figure). A group, a second group having a negative refractive power, a stop, a third group having a negative refractive power, a fourth group having a negative refractive power, and a fifth group having a positive refractive power are arranged.

  The first group consists of a positive meniscus first lens 1 with a convex surface facing the contact glass, and the second group is a biconvex lens with convex surfaces facing both the contact glass side and the CCD cover glass side. The second lens 2, the contact glass side, and the CCD cover glass side are joined to a third lens 3 of a biconcave lens with a concave surface facing the both sides, and the third group is a negative meniscus with a concave surface facing the contact glass side. The fourth lens unit 4 includes a fourth lens 5 having a positive meniscus shape with a concave surface facing the contact glass side, and the fifth group has a positive meniscus shape with a concave surface facing the contact glass side. It consists of a sixth lens 6 and a negative meniscus seventh lens 7 with a concave surface facing the contact glass, and constitutes an image reading lens as a whole. In FIG. 1, n_ represents the refractive index of the lens material, ν_ represents the Abbe number of the lens material, r_ represents the radius of curvature of the lens surface, and d_ represents the surface spacing.

  Here, as an index for evaluating the chromatic aberration (chromatic dispersion) of the lens material, a numerical value called Abbe number is used. In general, it is said that a lens material having a large degree of chromatic aberration (small chromatic dispersion) has a small Abbe number, and a lens material having a small degree of chromatic aberration (large chromatic dispersion) has a large Abbe number.

  The third lens and the fourth lens adjacent to the stop formed between the second group and the third group are formed of aspherical lenses on the surface facing the stop. Aspherical lenses are generally manufactured by molding. At this time, when the outer diameter of the lens is increased, restrictions on facilities are increased, for example, a very large molding machine is required for molding.

  Further, since the molding time is enormous, not only the cost of the spherical lens is increased, but also the surface accuracy of the lens cannot be kept good, and the imaging performance of the image reading lens is deteriorated. In view of this, in the image reading lens according to the embodiment of the present invention, an aspherical lens is adopted as a lens adjacent to the stop that can minimize the outer diameter in the lens system.

  Here, the aspherical lens refers to a lens whose lens surface is processed into a spherical or non-planar shape. In general, since spherical lenses generate aberrations, a plurality of lenses are often required to correct the aberrations. On the other hand, since the aspherical lens has no aberration, the number of lenses can be reduced to one.

  According to the image reading lens of the embodiment of the present invention, f1 is the focal length of the first group e-line, f23 is the combined focal length of the second group and the third group e-line, and f is the entire system e. The combined focal length of the lines, n convex is the average value of the refractive index of the d line of the positive lens, n concave is the average value of the refractive index of the d line of the negative lens, ν convex is the average value of the Abbe number of the positive lens, ν concave Is the average value of the Abbe number of the negative lens, the following conditional expression is satisfied.

(1) 1.1 <f / f1 <1.2
(2) -3.0 <f / f23 <-2.5
(3) -0.055 <n convex-n concave <-0.3
(4) 15.0 <ν convex−ν concave <18.5

  Conditional expression (1) determines the power of the first group. If the upper limit is exceeded, the power of the first group becomes too weak, and the lens diameter becomes large, leading to an increase in cost. Exceeding the lower limit value is advantageous for making the lens compact, but coma flare becomes large. Here, the coma flare means that the light flux forms an asymmetric blur and causes a reduction in sharpness.

  Conditional expression (2) determines the combined power of the second group and the third group having the negative power of the lens system of the present invention. If the upper limit is exceeded, both spherical aberration and field curvature are overcorrected, The coma aberration at the end will deteriorate. If the lower limit is exceeded, conversely, both spherical aberration and field curvature are insufficiently corrected, the astigmatic difference at the intermediate angle of view increases, and coma at the intermediate angle of view deteriorates.

  Conditional expression (3) defines the range of the refractive index of the convex lens and the concave lens constituting the image reading lens of the present invention. If the upper limit is exceeded, the Petzval sum becomes too small and the image plane is on the positive side. The tilted field curvature increases. On the contrary, if the lower limit is exceeded, the Petzval sum becomes too large, the image surface falls to the negative side, and the astigmatic difference becomes large.Under this condition, good imaging performance can be obtained over the entire screen. It becomes impossible.

  Here, the Petzval sum is a basic expression relating to the field curvature of a planar object, and refers to the amount by which the image plane is curved toward the front as it goes to the periphery of the screen. Zero is ideal and is determined by the curvature and refractive index of the lens. To reduce the Petzval sum, use a thick meniscus, make the two curvatures the same, use multiple convex and concave elements apart, and so on.

  Conditional expression (4) is a condition for satisfactorily correcting axial chromatic aberration. When the upper limit is exceeded, the axial chromatic aberration is overcorrected, and the axial chromatic aberration becomes larger on the positive side on the shorter wavelength side than the dominant wavelength. If the lower limit is exceeded, the axial chromatic aberration will be undercorrected, and the axial chromatic aberration will increase on the negative side on the shorter wavelength side than the dominant wavelength.

Next, specific examples of the present invention will be described below. The meaning of each symbol in each embodiment is as follows.
f: Composite focal length FNo of entire system FNo: F number (F value)
m: Reduction ratio ω: Half angle of view (degrees)
Y: object height ri (i = 1 to 13): radius of curvature of i-th lens surface counted from contact glass side di (i = 1 to 11): i-th surface interval nj (j counted from contact glass side) = 1-7): Refractive index vj of the j-th lens material counted from the contact glass side (j = 1-7): Abbe number rc1 of the j-th lens material counted from the contact glass side: Object-side curvature radius rc2: Image radius of contact glass rc3: Curvature radius of object rc4 of CCD cover glass: Curvature radius dc1 of CCD cover glass: Contact glass thickness dc3: CCD cover glass thickness Thickness nc1: Refractive index of CCD cover glass nc3: Refractive index of contact glass vc1: Abbe number of contact glass vc3: CCD cover glass Abbe number nd: d-line refractive index ne: e-line refractive index f1: focal length of the first group e-line f23: combined focal length of the second group and third group e-line n convex: positive Nd average n-concave of lens having refractive power: nd average ν-convex of lens having negative refractive power: nd average ν-concave of lens having positive refractive power: nd of lens having negative refractive power average

Also,
X: Distance from tangent plane at aspherical vertex of aspheric surface at height Y from optical axis Y: Height from optical axis R: Paraxial radius of curvature of aspheric surface K: Conical multipliers A4, A6, A8, A10: Assuming that the aspheric coefficient SQRT is the square root, the distance from the tangent plane at the aspheric vertex of the aspheric surface at the height Y from the optical axis (distance from the XY plane to the aspheric surface) X is calculated by the following equation.

(5) X = [{( 1 / R) * Y 2} / {1 + SQRT (1- (1 + K) * (Y / R) 2)}] + A4 * Y 4 + A6 * Y 6 + A8 * Y 8 + A10 * Y ^Ten

  In the aberration diagrams in each example, the e-line, g-line, c-line, and F-line are the Fraunhofer line e-line (546.07 nm), g-line (436.83 nm), and c-line (656), respectively. .27 nm) and the aberration corresponding to the F-line (486.13 nm). Further, in the spherical aberration diagram, the wavy line represents the sine condition, and in the astigmatism diagram, the solid line represents the sagittal ray, and the dotted line represents the meridional ray.

Example 1 is an example in which each lens constituting the image reading lens is configured as shown in FIG. FIG. 2 is a structural diagram showing the configuration of the image reading lens in Example 1 of the present invention. The conditions in Example 1 are as follows:
f = 46.17, F = 3.48, m = 0.110102, Y = 152.4, and ω = 18.3 degrees.

なお、数値中、Ｅ−ＸＹは、１０^-XYを意味する。 The aspheric coefficient in the aspheric surface number 7 is as follows.

It should be noted that, in the numerical value, E-XY means 10 ^-XY.

The values of conditional expressions (1), (2), and (3) are as follows.

  Aberration diagrams in Example 1 are shown in FIG. FIG. 3 is an aberration diagram of the image reading lens according to Example 1 of the present invention. The e-line, g-line, c-line, and F-line in this aberration diagram are as described above.

Example 2 is an example in which each lens constituting the image reading lens is configured as shown in FIG. FIG. 4 is a structural diagram showing the configuration of the image reading lens in Example 2 of the present invention. The conditions in Example 2 are as follows:
f = 46.25, F = 3.50, m = 0.1102, Y = 152.4, and ω = 18.2 degrees.

なお、数値中、Ｅ−ＸＹは、１０^-XYを意味する。 The aspheric coefficient in the aspheric surface number 7 is as follows.

It should be noted that, in the numerical value, E-XY means 10 ^-XY.

The values of conditional expressions (1), (2), and (3) are as follows.

  Aberration diagrams in Example 2 are shown in FIG. FIG. 5 is an aberration diagram of the image reading lens according to Example 2 of the present invention. The e-line, g-line, c-line, and F-line in this aberration diagram are as described above.

Example 3 is an example in which each lens constituting the image reading lens is configured as shown in FIG. FIG. 6 is a structural diagram showing the configuration of the image reading lens in Example 3 of the present invention. The conditions in Example 3 are as follows:
f = 46.40, F = 3.51, m = 0.110102, Y = 152.4, and ω = 18.2 degrees.

なお、数値中、Ｅ−ＸＹは、１０^-XYを意味する。 The aspheric coefficient in the aspheric surface number 7 is as follows.

It should be noted that, in the numerical value, E-XY means 10 ^-XY.

The values of conditional expressions (1), (2), and (3) are as follows.

  Aberration diagrams in Example 3 are shown in FIG. FIG. 6 is an aberration diagram of the image reading lens according to Example 3 of the present invention. The e-line, g-line, c-line, and F-line in this aberration diagram are as described above.

The focal length f1 in the conditional expression (1) is
n is the refractive index of the lens material, r1 is the radius of curvature of the front surface of the lens, r2 is the radius of curvature of the rear surface of the lens, and d is the thickness of the lens.
(6) f1 = 1 / [(n-1) * (1 / r1-1 / r2) + (n-1) ² * d / (n * r1 * r2)])

The combined focal length fs in the conditional expressions (1) and (2) is
f1, f2: When the focal length of each lens is d: the distance between the lenses, it is calculated by the following equation.
(7) fs = f1 * f2 / (f1 + f2-d)

  In the present invention, all seven lenses constituting the image reading lens are glass lenses, and the glass material does not contain harmful substances such as lead and arsenic. As a result, all lenses can be made of optical glass that is chemically stable and does not contain harmful substances such as lead and arsenic, so that materials can be recycled, and there is no water pollution caused by waste liquid during processing. It is possible to reduce the CO2 and the like generated at the time of resource recycling and processing, and it is possible to provide a small and low-cost image reading lens considering the global environment.

  Next, the configuration of the image reading apparatus using the image reading lens in the embodiment of the present invention will be described. FIG. 8 is a structural diagram illustrating the configuration of the image reading apparatus using the image reading lens according to the embodiment of the present invention.

  In FIG. 8, a document 2 is disposed on the contact glass 1, and the document is illuminated by an illumination optical system (not shown) disposed below the contact glass 1. The illumination light of the document is reflected by the first mirror 3-a of the first traveling body 3, and then reflected by the first mirror 4-a and the second mirror 4-b of the second traveling body 4, thereby reducing the image. The light is guided to the lens 5 and imaged on the line sensor 6 by the reduction imaging lens 5.

  When the longitudinal direction of the document is read, the first traveling body 3 moves to 3 ′ at a speed of V, and at the same time, the second traveling body 4 has a speed 1 / 2V that is half that of the first traveling body 3 and 4 Move to 'and scan the entire document. As another example of the image reading apparatus, it is possible to fold the optical path compactly by a plurality of mirrors, to form a unit integrated with the line sensor, and to scan the entire document to read the document information. (A so-called ADF (Auto Document Feeder)) can also be used as a back side reading lens when reading both sides of a document.

  Next, the configuration of the image forming apparatus including the image reading apparatus using the image reading lens according to the embodiment of the present invention will be described. FIG. 9 is a structural diagram illustrating a configuration of an image forming apparatus using the image reading lens according to the embodiment of the present invention.

  In FIG. 9, an image forming apparatus 300 includes an image reading apparatus 200 and an image forming unit (laser printer) 100. The image reading apparatus 200 outputs document information as an electrical signal from the line sensor 6 with the same configuration and operation as described in FIG. The image forming unit 100 has a photoconductive photoconductor formed in a cylindrical shape as the latent image carrier 111. Around the latent image carrier 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are provided.

  A corona charger can also be used as the charging means. Further, an optical scanning device 117 that receives document information from the line sensor 6 and performs optical scanning with the laser beam LB is provided, and exposure by optical writing is performed between the charging roller 112 and the developing device 113. ing.

  In addition, the image forming unit 100 includes a fixing device 116, a cassette 118, a registration roller pair 119, a paper feed roller 120, a conveyance path 121, a paper discharge roller pair 122, a tray 123, and a transfer paper P as a recording medium. Yes.

  When image formation is performed, the latent image carrier 111 that is a photoconductive photosensitive member rotates at a constant speed in the clockwise direction, and the surface thereof is uniformly charged by the charging roller 112, so that the laser beam LB of the optical scanning device 117 is obtained. An electrostatic latent image is formed upon exposure by optical writing. The formed electrostatic latent image is a so-called negative latent image, and the image portion is exposed.

  This electrostatic latent image is reversed and developed by the developing device 113, and a toner image is formed on the latent image carrier 111. The cassette 118 storing the transfer paper P is detachable from the main body of the image forming apparatus 100, and when the transfer paper P is loaded as shown in FIG. The transfer paper P that has been fed and fed is caught by the registration roller pair 119 at its leading end.

  The registration roller pair 119 feeds the transfer paper P to the transfer unit at the timing when the toner image on the latent image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114. The transfer paper P to which the toner image is transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the discharge roller pair 122.

  The surface of the latent image carrier 111 after the toner image is transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like. The latent image carrier 111 is a photoconductive photoconductor, and an electrostatic latent image is formed by uniform charging and optical scanning, and the formed electrostatic latent image is visualized as a toner image.

  In FIG. 9, in the image forming apparatus including the image reading apparatus using the image reading lens according to the embodiment of the present invention, no mention is made of the print color. Needless to say, a color original reading apparatus having a color separation function in the optical path and reading original information in full color may be used.

  For color separation, a color separation prism or a filter is selectively inserted between the image reading lens and the CCD to separate the colors into R, G, and B. For example, the R, G, and B light sources are sequentially turned on and the document is turned on. Or by using a so-called three-line CCD in which light receiving elements having R, G, and B filters are arranged in three rows on one chip and forming a color image on this light receiving surface Any method such as a method of separating the colors into the three primary colors may be used.

  As described in detail above, according to the present invention, the number of constituent lenses is seven, so that the F value is 3.5 and the aperture is very large, with a half angle of view exceeding about 18 degrees. The field curvature is well corrected, the aperture efficiency is close to 100% up to the periphery, the chromatic aberration is also corrected well, and it is possible to obtain good performance with high contrast in a high spatial frequency region. Therefore, it is possible to reduce the input power of the apparatus, and can greatly contribute to the power saving of the apparatus using the image reading lens.

  In addition, by arranging the aspheric lens on the lens adjacent to the stop, the aspheric lens can be made at low cost and with high accuracy, and the cost and performance of the lens can be reduced. By satisfying the above-described conditional expressions (1) to (4), it becomes possible to correct each aberration more favorably, and an image reading lens having good imaging performance can be obtained.

  Furthermore, all lenses are made of glass materials that do not contain harmful substances such as lead and arsenic, so they can be easily recycled, do not cause water pollution due to waste liquid during processing, contribute to the preservation of the global environment, and have a large diameter. By using the compact and low-cost image reading lens, it is possible to read document information satisfactorily, and the image reading apparatus can be made very compact and low-cost with low power consumption.

  In an image reading apparatus having a color separation function in an optical system, it is possible to read a full color with good performance by using a lens in which axial chromatic aberration is corrected, so that the image reading apparatus It is possible to achieve higher functionality and higher performance, and by providing an image reading device using the image reading lens, an image is formed based on good read image quality. A forming apparatus can be obtained at low cost.

  The present invention has been described above by the preferred embodiments of the present invention. While the invention has been described with reference to specific embodiments thereof, various modifications and changes can be made to these embodiments without departing from the broader spirit and scope of the invention as defined in the claims. is there.

DESCRIPTION OF SYMBOLS 1 Contact glass 100 Image forming part 111 Latent image carrier 112 Charging roller 113 Developing device 114 Transfer roller 115 Cleaning device 116 Fixing device 117 Optical scanning device 118 Cassette 119 Registration roller pair 120 Paper feed roller 121 Transport path 122 Paper discharge roller pair 123 Tray 2 Document 200 Image reading device 3 First traveling body 300 Image forming device 4 Second traveling body 5 Reduction imaging lens 6 Line sensor

JP 58-063911 A Japanese Patent Laid-Open No. 04-127109 Japanese Patent Laid-Open No. 04-127110 Japanese Patent No. 3073786

Claims (5)

In order from the object side to the image side, a first group having a positive refractive power, a second group having a negative refractive power as a whole, a third group having a negative refractive power, and a first group having a positive refractive power In the image reading lens having four groups, the fifth group having positive refractive power as a whole,
The first group includes a positive meniscus first lens arranged with a convex surface facing the object side,
The second group includes a biconvex lens-shaped second lens having convex surfaces facing both the object side and the image side, and a biconcave lens-shaped second lens having concave surfaces facing both the object side and the image side. 3 lenses are joined,
The third group includes a negative meniscus fourth lens having a concave surface facing the object side,
The fourth group includes a positive meniscus fifth lens having a concave surface facing the object side,
The fifth group has a five-group, seven-element configuration including a positive meniscus sixth lens having a concave surface facing the object side and a negative mechanistic seventh lens having a concave surface facing the object side,
An image reading lens, wherein a diaphragm is formed between the second group and the third group.   2. The image reading lens according to claim 1, wherein the fourth lens adjacent to the stop has an aspheric surface facing the stop. 3. f1 is the focal length of the e-line of the first group, f23 is the combined focal length of the e-lines of the second group and the third group, f is the combined focal length of the e-line of the entire system, and n convex is the positive lens When the average value of the refractive index of the d-line, n concave is the average value of the refractive index of the d-line of the negative lens, ν convex is the average value of the Abbe number of the positive lens, and ν concave is the average value of the Abbe number of the negative lens The image reading lens according to claim 1, wherein the following conditional expression is satisfied.
(1) 1.1 <f / f1 <1.2
(2) -3.0 <f / f23 <-2.5
(3) -0.055 <n convex-n concave <-0.3
(4) 15.0 <ν convex−ν concave <18.5   Image reading comprising: illumination for illuminating a document; an imaging lens for reducing and imaging reflected light of the document illuminated by the illumination; and a line sensor for photoelectrically converting a document image formed by the imaging lens An image reading apparatus comprising the image reading lens according to claim 1. An image forming apparatus comprising the image reading apparatus according to claim 4.

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