JP2013054295A - Image scanning lens, image scanner, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image scanning lens having a wide field angle of 35° or more and a short back focus, and providing a high image quality, and an apparatus using the same.SOLUTION: The image scanning lens has 5-group and 6-piece configuration comprising: a first group G1 consisting of a first lens L1 having negative refractive power; a second group G2 consisting of a biconvex second lens L2; a third group G3 consisting of a biconcave third lens L3; a fourth group G4 formed by joining a biconvex fourth lens L4 and a meniscus-shape fifth lens L5 with its concave surface on an object side, having negative refractive power; a fifth group G5 consisting of a sixth lens L6 having negative refractive power; and an aperture stop S located between the third group G3 and the fourth group G4. A distance TL from the lens first plane to an imaging plane, a focal distance f of an image scanning lens entire system, and a composite focal length fof the lens group in the object side with respect to the aperture stop S satisfy the following conditional expressions (1) and (2): (1)1.7<TL/f<2.1, and (2) -0.7<f/f<0.3.

Description

  The present invention relates to an image reading lens and an apparatus including the image reading lens, and more specifically, image information of a document is reduced and formed on an image pickup element in which elements are arranged in a line shape, and the image information is read by the image pickup element. The present invention relates to an image reading lens used for an image reading unit such as a digital copying machine and a facsimile and various image scanners, an image reading apparatus including the image reading lens, and an image forming apparatus.

  An image reading unit or an image scanner of a digital copying machine or a facsimile reduces the image information of an original to be read by an image reading lens and forms an image on an image pickup device such as a CCD (Charge Coupled Device) to signal the image information. Turn into. In order to read image information of a document for color, for example, a so-called 3-line CCD in which image sensors having red, green, and blue filters are arranged in three rows on one substrate is often used. There is an optical system that uses the three-line CCD and forms image information of a document on the surface of the image sensor to separate the three primary colors into a color image information signal.

  In general, such an image reading lens requires a high contrast in a high spatial frequency region on an image sensor that is an image plane, and has an aperture efficiency close to 100% up to the periphery of the angle of view. It is requested. Further, in order to read a color document satisfactorily, it is necessary to match the image forming positions of red, green, and blue colors on the image plane in the optical axis direction, and it is necessary to correct chromatic aberrations for each color.

  In recent years, an image reading lens and an image reading apparatus use an image reading lens with a wide angle of view in order to reduce the size and cost of the apparatus in addition to imaging performance, and integrate an illumination system, a mirror, and an image sensor. It is required to use the reading unit.

  As a wide-angle reading lens, an image reading lens (Patent Literature 1 and Patent Literature 2) having a concave lens of 4 groups, 5 elements, 4 groups, 6 elements constituted only by a spherical lens, and an aspheric lens are used. A lens (patent document 3) that aims to widen the angle of the image reading lens is proposed.

  However, since the image reading lenses described in Patent Document 1 and Patent Document 2 have an angle of view of around 24 degrees, the distance from the document surface to the image sensor increases, and the optical path is turned back when integrated as a reading unit. There is a problem that it is difficult to reduce the size of the reading unit by increasing the number of times. Furthermore, the distance from the image reading lens to the image sensor is also required for the angle of view.

  Between the image reading lens and the image sensor, it is necessary to shield the light beam directly irradiated from the illumination system and the document surface so that it does not enter the image sensor. The optical path cannot be drawn. Therefore, the distance between the image reading lens and the image sensor becomes long, and it is difficult to reduce the size of the reading unit, and it is also difficult to reduce the size of the image reading device.

  The image reading lens described in Patent Document 3 aims to further widen the angle by using an aspheric lens, but it is still around 30 degrees. Also, since a rotationally asymmetric aspherical lens is used, it is necessary to adjust the rotationally asymmetrical aspherical lens and the other spherical lens separately when assembling the lens. There is a problem that it is difficult to satisfy satisfactory imaging performance.

  In view of the above problems, the present invention provides an image reading that has a wide angle of view of 35 degrees or more, a short back focus necessary for forming image information, and a high image quality with little deterioration in imaging performance. It is an object of the present invention to provide a lens and an image reading apparatus and an image forming apparatus that can be miniaturized using the image reading lens.

In order to solve the above-described problem, an image reading lens according to the present invention includes:
In order from the object side to the image side, a first group including a first lens having a negative refractive power, a second group including a biconvex second lens, and a third group including a biconcave third lens. And a fourth group formed by joining a biconvex fourth lens and a meniscus fifth lens having negative refractive power with a concave surface facing the object side, and a sixth lens having negative refractive power. An image reading lens having a five-group, six-element configuration, which is configured by a fifth group and has a diaphragm between the third group and the fourth group,
When a lens TL the distance to the image plane from the first surface, the focal length of the image reading lens system f, and the combined focal length of the lens group disposed on the object side of the aperture and f _123, they condition An image reading lens satisfying the expressions (1) and (2).
(1) 1.7 <TL / f <2.1
(2) -0.7 <f / f ₁₂₃ <0.3

In order to solve the above-described problems, an image reading apparatus according to the present invention includes:
The image reading lens of the present invention, an illumination system for illuminating a document placed on a document placement surface, a line-shaped image sensor on which image information of the document illuminated by the illumination system is imaged, and at least one sheet The image reading apparatus comprises an image reading unit that is integrally held with the mirror, and scans the image reading unit to read image information of the document.
In order to solve the above problems, an image forming apparatus according to the present invention provides:
An image forming apparatus for forming an image by writing an image corresponding to an image signal, wherein the image reading apparatus according to the present invention is used as a means for reading image information of a document into an image signal. Forming device.

According to the image reading lens of the present invention, an image having a wide angle of view of 35 degrees or more, a short back focus necessary for imaging image information, little imaging performance degradation, and high image quality can be obtained. A reading lens can be provided.
Further, it is possible to provide an image reading apparatus and an image forming apparatus that include the image reading lens and can be downsized.

It is a schematic sectional drawing which shows an example of a structure of the image reading lens of this invention. It is a schematic sectional drawing which shows the lens structure which concerns on a 1st embodiment. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of FIG. 2. It is a schematic sectional drawing which shows the lens structure which concerns on a 2nd embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in the lens configuration of the second embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 3rd embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in the lens configuration of the third embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 4th embodiment. FIG. 9 is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of the fourth embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 5th embodiment. It is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration in the fifth embodiment. It is a schematic sectional drawing which shows the lens structure which concerns on a 6th embodiment. FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion, and coma aberration in the lens configuration of the sixth embodiment. It is a schematic perspective view which shows an example of the lens structure whose 6th lens is a non-circular lens. It is a schematic sectional drawing which shows an example of a structure of the image reading apparatus of this invention. 1 is a schematic cross-sectional view illustrating an example of a configuration of an image forming apparatus of the present invention.

  Hereinafter, an image reading lens, an image reading apparatus, and an image forming apparatus according to the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments of the examples shown below, and other embodiments, additions, modifications, deletions, and the like can be changed within a range that can be conceived by those skilled in the art. Any aspect is included in the scope of the present invention as long as the operations and effects of the present invention are exhibited.

An example of the configuration of the image reading lens of the present invention is shown in FIG.
As shown in FIG. 1, the image reading lens of the present invention includes, in order from the object side to the image side, a first group (G1) composed of a first lens L1 having negative refractive power, a biconvex second lens. The second group (G2) composed of the lens L2, the third group (G3) composed of the biconcave third lens L3, the biconvex fourth lens L4, and negative refractive power with the concave surface facing the object side. A fourth group (G4) formed by cementing the fifth meniscus lens L5 and a fifth group (G5) including a sixth lens L6 having negative refractive power, and the third group (G3). This is a 5-group 6-lens configuration having an aperture S between the fourth group (G4).
A contact glass CG1 is disposed on the object side of the first group (G1), and a CCD cover glass CG2 is disposed on the image side of the fifth group (G5).

In addition, the meaning of the code | symbol in FIG. 1 is as follows.
r _j (j = 1 to 12): radius of curvature of the i-th lens surface counted from the object side d _j (j = 1 to 11): i-th surface interval counted from the object side n _j (j = 1, 1) 3, 5, 8, 9, 11): Refractive index of the lens material with the j-th surface interval counted from the object side νd _j (j = 1, 3, 5, 8, 9, 11): Counted from the object side Abbe number of the lens material with the j-th surface spacing r _c1 : radius of curvature of the contact glass on the object side r _c2 : radius of curvature of the contact glass on the image side r _c3 : radius of curvature of the CCD cover glass on the object side r _c4 : CCD cover Radius of curvature on the image side of the glass d _c1 : thickness of the contact glass d _c3 : thickness of the CCD cover glass n _c1 : refractive index of the contact glass n _c3 : refractive index of the CCD cover glass νd _c1 : Abbe number of the contact glass νd _c3: CCD mosquitoes Abbe number of the-glass

In the image reading lens of the present invention, the distance from the first lens surface to the imaging surface is TL, the focal length of the entire image reading lens system is f, and the combined focal length of the lens group disposed on the object side from the stop S is the combined focal length. When f ₁₂₃ is satisfied, these satisfy the following conditional expressions (1) and (2).
(1) 1.7 <TL / f <2.1
(2) -0.7 <f / f ₁₂₃ <0.3

  Conditional expression (1) defines the distance (size) from the image reading lens to the image sensor. The distance TL from the first lens surface to the imaging surface is a value that must be considered separately from the optical path from the document surface to the image reading lens. A smaller value indicates that the apparatus including the image reading lens can be made smaller.

Conditional expression (2) defines the ratio of the combined focal length f ₁₂₃ of the lens group (first to third groups) arranged on the object side of the stop S with respect to the focal length f of the entire image reading lens system. is there.
When the value of f / f ₁₂₃ is decreased, the power of the lens on the object side (front side) becomes weak, and there is an effect that the principal point position is arranged in front of the lens. As a result, the distance from the last lens surface to the imaging surface can be shortened, and the distance from the first lens surface to the imaging surface can be reduced, which is advantageous for miniaturization. When the lower limit (−0.7) or less is reached, the spherical aberration falls negatively, making it difficult to obtain a high resolution of the lens. On the other hand, when the upper limit (0.3) of conditional expression (2) is exceeded, the distance from the first lens surface to the imaging surface increases, which is disadvantageous for miniaturization.
Therefore, the conditional expressions (1) and (2) are conditions necessary for obtaining a good resolving power and achieving downsizing of the apparatus including the image reading lens in an image reading lens having a wide angle of view. .

In the image reading lens of the present invention, it is preferable that at least the first lens L1 and the sixth lens L6 have rotationally symmetric aspheric surfaces.
That is, the concave lenses of the first lens L1 and the sixth lens L6 that are farthest from the stop S on the object side and the image side are respectively rotationally symmetric aspheric surfaces. By making both negative lenses aspherical, it is not necessary to increase the aspherical amount of each lens, and the processing of the lens can be facilitated. In addition, since corrections can be made at different positions for the light rays for each image height, it is possible to correct field curvature and coma well, and to achieve a wide field depth by correcting field curvature. Can do. Furthermore, high assembly stability and temperature compensation performance can be obtained.
Thus, making both negative lenses aspherical is a necessary condition for matching the image plane in a wide-angle reading lens.

Further, the image reading lens of the present invention, when the combined focal length of the fourth group (G4) and f _45, it is preferable to satisfy the following condition (3).
(3) 0.3 <f ₄₅ /f<0.8
Conditional expression (3) represents the ratio of the combined focal length f ₄₅ after the fourth lens L4 and the fifth lens L5 of the fourth group (G4) are joined to the focal length f of the entire image reading lens system. Conditional expression (3) is a condition necessary for reducing the size of the image reading lens and ensuring a good image plane depth.
When the value of f ₄₅ / f is equal to or greater than the upper limit (0.8), the entire length of the image reading lens increases, leading to an increase in the distance TL from the first lens surface to the imaging surface. On the other hand, a smaller value is advantageous for downsizing the image reading lens, but as the lower limit (0.3) or less, astigmatism of the lens increases and it is difficult to ensure the depth of field. Become.

In the image reading lens of the present invention, it is preferable that all six lenses are glass lenses, and that the glass material of the glass lens does not contain lead, arsenic, and similar harmful substances.
All lenses are 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. The reading lens can be obtained.

Hereinafter, various aberrations and specific numerical data of the image reading lens according to the embodiment of the present invention will be described. The meanings of symbols in each embodiment (Example) are as follows.
f: Total focal length FNo: F number m: Reduction ratio Y: Object height ω: Half angle of view (degrees)
r: radius of curvature of lens surface d: surface spacing nd: refractive index of lens material vd: Abbe number of lens material

  The surface number j is given in order from the object side. C1 and C2 indicate the first and second surfaces of the contact glass on which the document is placed, and C3 and C4 indicate the first and second surfaces of the cover glass of the image sensor.

The aspherical surface shape is expressed using the following mathematical formula.

That is, the aspherical surface shape is a paraxial curvature (reciprocal of the paraxial curvature radius), and Y is a distance from the optical axis in a direction orthogonal to the optical axis, the aspherical surface shape is an arbitrary distance Y , It can be expressed by a distance X in the direction of the optical axis from the vertex of the surface that intersects the optical axis.
In the above formula, k is a conic constant, and Ai is an aspheric coefficient for the degree i.

[First Embodiment (Example 1)]
FIG. 2 shows a configuration diagram of a lens according to the first embodiment of the present invention.
Table 1 shows a lens configuration table.

  Table 2 shows the conic constant k and the aspheric coefficient Ai of the aspheric surface of the first embodiment.

FIG. 3 shows aberration diagrams in the lens configuration shown in FIG.
In the aberration diagrams, the e-line (e) indicates 546.07 nm, the g-line (g) indicates 436.83 nm, the c-line (c) indicates 656.27 nm, and the F-line (F) indicates 486.13 nm. 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. The same applies to aberration diagrams of other embodiments (examples) described below.

[Second Embodiment (Example 2)]
FIG. 4 shows a configuration diagram of a lens according to the second embodiment of the present invention. The lens configuration table is shown below.

  Table 4 shows the conic constant and aspheric coefficient of the aspheric surface of the second embodiment.

  FIG. 5 shows aberration diagrams in the lens configuration shown in FIG.

[Third Embodiment (Example 3)]
FIG. 6 shows a configuration diagram of a lens according to the third embodiment of the present invention. The lens configuration table is shown below.

  Table 6 shows the conic constant and aspheric coefficient of the aspheric surface of the third embodiment.

  FIG. 7 shows aberration diagrams in the lens configuration shown in FIG.

[Fourth Embodiment (Example 4)]
FIG. 8 shows a configuration diagram of a lens according to the fourth embodiment of the present invention. The lens configuration table is shown below.

  Table 8 shows the conic constant and aspheric coefficient of the aspheric surface of the fourth embodiment.

  FIG. 9 shows aberration diagrams of the lens configuration shown in FIG.

[Fifth Embodiment (Example 5)]
FIG. 10 is a structural diagram of a lens according to the fifth embodiment of the present invention. The lens configuration table is shown below.

  Table 10 shows the conic constant and aspheric coefficient of the aspheric surface of the fifth embodiment.

  FIG. 11 shows aberration diagrams in the lens configuration shown in FIG.

[Sixth Embodiment (Example 6)]
FIG. 12 shows a configuration diagram of a lens according to the sixth embodiment of the present invention. The lens configuration table is shown below.

  Table 12 shows the conic constant and aspheric coefficient of the aspheric surface of the sixth embodiment.

  FIG. 13 shows aberration diagrams in the lens configuration shown in FIG.

  The values of conditional expressions in the above-described embodiments (examples) are shown below.

In the image reading lens of the present invention, it is preferable that at least one of the lenses has a non-circular outer shape.
FIG. 14 shows an example of an image reading lens in which the sixth lens L6 has a non-circular lens outer shape. From the object side, a first group (G1) comprising a first lens L1 having negative refractive power, a second group (G2) comprising a biconvex second lens L2, and a third group comprising a biconcave third lens L3. Group (G3), a fourth group (G4) formed by cementing a biconvex fourth lens L4 and a meniscus fifth lens L5 having a negative refractive power facing the object side toward the object side, and negative refraction An image of 5 groups, 6 elements, comprising a fifth lens group (G5) comprising a sixth lens L6 having power, and having a diaphragm (not shown) between the third lens group (G3) and the fourth lens group (G4). In the reading lens, with respect to the direction orthogonal to the arrangement direction of the photoelectric conversion elements of the CCD line sensor, the sixth lens L6 of the fifth group (G5) has a size that allows the same amount of light flux as other lenses to pass. Therefore, a non-circular lens with the top and bottom cut off as shown in FIG. By, it is possible to further downsize the image reading lens. In FIG. 14, A indicates the optical axis, and B indicates the arrangement direction of the imaging elements.

The lens having a non-circular outer shape is not limited to the sixth lens L6 shown in FIG. 14, but the first lens L1 and the sixth lens are likely to have a large lens diameter because the height of the light beam is higher than other lenses. Making the outer shape of the lens L6 non-circular is advantageous for downsizing.
When the line sensor is used in the apparatus using the image reading lens of the present invention, the light beam passes only in the direction perpendicular to the direction of the line sensor in the direction perpendicular to the line sensor. It becomes possible to make the lens small.
Therefore, the size of the apparatus can be reduced by using at least one of the first lens L1 and the sixth lens L2 as a non-arc-shaped lens whose direction perpendicular to the line sensor is small.

[Image reading device]
An image reading apparatus according to the present invention includes an image reading lens according to the present invention, an illumination system that illuminates a document placed on a document placement surface, and a line shape on which image information of the document illuminated by the illumination system is imaged. And an image reading unit in which at least one mirror is integrally held, and the image reading unit is scanned to read image information of the document.
FIG. 15 shows an example of the image reading apparatus of the present invention.

As shown in FIG. 15, a document 42 having an image to be read is placed in a plane on a contact glass 41 as a document table.
The image reading unit 43 holds mirrors 43e, 43f, and 43g that are arranged with the mirror surface tilted with respect to the document placement surface of the document table 41, with the direction orthogonal to the drawing as the longitudinal direction. It moves at a constant speed V from the indicated position to the position indicated by reference numeral 43 '.
The image reading unit 43 holds fluorescent lamps 43a and 43c and reflecting mirrors 43b and 43d that are long in the direction orthogonal to the drawing as an illumination system for illuminating the document 42. The fluorescent lamps 43 a and 43 c emit light when the image reading unit 43 is displaced to the right in FIG. 15 and illuminate the document 42 on the document table 41. Accordingly, the document 42 is illuminated and scanned while the image reading unit 43 is displaced to the position indicated by reference numeral 43 '.
As the fluorescent lamps 43a and 43c, a halogen lamp, a xenon lamp, a tube lamp such as a cold cathode tube, or a light source that converts a point light source into a linear light source is used. A linear light source can be used, and a surface light source represented by organic EL can also be used.

  When the document 42 is illuminated and scanned, the reflected light from the illuminated portion of the document 42 is sequentially reflected by the mirrors 43e, 43f, and 43g, and enters the image reading lens 44 as an imaging light beam. At this time, since all the mirrors are integrally held by the image reading unit 43, the optical path length from the original illuminated portion to the image reading lens 44 is constant during the illumination scanning of the original 42.

The imaging light beam incident on the image reading lens 44 forms a reduced image of the document 4 on the light receiving surface of the image sensor 45 by the imaging action of the image reading lens 44.
The image sensor 45 is a CCD line sensor, and minute photoelectric conversion units are closely arranged in a direction orthogonal to the drawing, and outputs a document image as an electrical signal in pixel units as the document 42 is illuminated and scanned. This electrical signal undergoes signal processing such as A / D conversion to become an image signal, and is stored in a memory (not shown) as necessary.

The image sensor 45 can color-separate the formed image into three colors (red, green, and blue) to read color information, and synthesizes the electrical signals converted by the respective photoelectric conversion units to produce a color document. Can be read. As a method of performing color separation, a color separation prism or filter is selectively inserted between the image reading lens 44 and the line sensor (CCD) 45, and R (red), G (green), and B (blue). A method of color separation, a method of illuminating a document by sequentially turning on R, G, and B light sources can be used.
It is also possible to read the document information as monochrome without having a color separation element in the imaging optical path.

  By forming the image reading unit 43 integrally using the image reading lens 44 of the present invention having a wide angle of view, the image reading apparatus can be further reduced in size, and the image reading is performed in order to move integrally. It becomes possible to suppress the performance degradation when the unit 43 moves.

[Image forming apparatus]
The image forming apparatus of the present invention is an image forming apparatus that forms an image by writing an image corresponding to an image signal, and uses the image reading apparatus of the present invention as a means for reading image information of a document into an image signal. .
The configuration of an example of the image forming apparatus of the present invention is shown in FIG.

  As shown in FIG. 16, the image forming apparatus includes an image reading apparatus 200 positioned at the upper part of the apparatus and an image forming unit 100 positioned at a lower position. The portion of the image reading apparatus 200 is the same as that described with reference to FIG. 15, and the same reference numerals as those in FIG.

  An image signal output from the three-line CCD line sensor (imaging device) 45 of the image reading unit 43 of the image reading apparatus 200 is sent to the signal processing unit 120 and processed by the signal processing unit 120 to obtain a “writing signal ( Signals for writing yellow, magenta, cyan, and black colors).

The image forming unit includes a photoconductive photosensitive member 110 formed in a cylindrical shape as a “latent image carrier”, and around it, a charging roller 111 as a charging unit, a revolver type developing device 113, and a transfer belt. 114 and a cleaning device 115 are provided. As the charging means, a “corona charger” can be used instead of the charging roller 111.
An optical scanning device 117 that receives a signal for writing from the signal processing unit 120 and writes on the photosensitive member 110 by optical scanning performs optical scanning of the photosensitive member 110 between the charging roller 111 and the developing device 113. ing.

Reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a registration roller pair, reference numeral 122 denotes a paper feed roller, reference numeral 121 denotes a tray, and reference numeral 130 denotes a transfer sheet as a “recording medium”.
When image formation is performed, the photoconductive photosensitive member 110 is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 111, and is subjected to exposure by optical writing of the laser beam of the optical scanning device 117. An electrostatic latent image is formed. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

  “Image writing” is performed in the order of a yellow image, a magenta image, a cyan image, and a black image in accordance with the rotation of the photoconductor 110, and the formed electrostatic latent image is stored in each developing unit Y ( Development with yellow toner), M (development with magenta toner), C (development with cyan toner), K (development with black toner) are sequentially reversed and visualized as a positive image. The respective color toner images are sequentially transferred onto the transfer belt 114 by the transfer voltage application roller 114A, and the respective color toner images are superimposed on the transfer belt 114 to form a color image.

The cassette 118 storing the transfer paper 130 is detachable from the main body of the image forming apparatus. When the cassette 118 is mounted as shown in the figure, the uppermost sheet of the stored transfer paper S is fed by the paper feed roller 122. The leading edge of the fed transfer sheet S is caught by the registration roller pair 119.
The registration roller pair 119 feeds the transfer sheet 130 to the transfer unit at the timing when the “color image by toner” on the transfer belt 114 moves to the transfer position. The transferred transfer paper 130 is superimposed on the color image at the transfer portion, and the color image is electrostatically transferred by the action of the transfer roller 114B. The transfer roller 114B presses the transfer sheet S against the color image during transfer.

  The transfer paper 130 onto which the color image has been transferred is sent to the fixing device 116, where the color image is fixed, passes through a conveyance path by a guide means (not shown), and is discharged onto the tray 121 by a pair of paper discharge rollers (not shown). The Each time each color toner image is transferred, the surface of the photoreceptor 110 is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like.

  The image forming apparatus according to the present invention may be a so-called tandem type image forming apparatus in which a plurality of photoconductors are arranged corresponding to respective colors. Of course, it goes without saying that the image forming apparatus can be “configured to perform monochrome image formation”.

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens CG1 Contact glass CG2 CCD cover glass 41 Document table (contact glass)
42 Document 43 Image reading unit 44 Image reading lens 45 Line sensor (CCD)
200 Image reader

Japanese Patent Laying-Open No. 2005-266771 JP 2006-285158 A Japanese Patent No. 3862446

Claims (7)

In order from the object side to the image side, a first group including a first lens having a negative refractive power, a second group including a biconvex second lens, and a third group including a biconcave third lens. And a fourth group formed by joining a biconvex fourth lens and a meniscus fifth lens having negative refractive power with a concave surface facing the object side, and a sixth lens having negative refractive power. An image reading lens having a five-group, six-element configuration, which is configured by a fifth group and has a diaphragm between the third group and the fourth group,
When a lens TL the distance to the image plane from the first surface, the focal length of the image reading lens system f, and the combined focal length of the lens group disposed on the object side of the aperture and f _123, they less An image reading lens characterized by satisfying conditional expressions (1) and (2):
(1) 1.7 <TL / f <2.1
(2) -0.7 <f / f ₁₂₃ <0.3   The image reading lens according to claim 1, wherein at least the first lens and the sixth lens have a rotationally symmetric aspherical surface. 3. The image reading lens according to claim 1, wherein the following conditional expression (3) is satisfied when a combined focal length of the fourth group is f ₄₅ .
(3) 0.3 <f ₄₅ /f<0.8   The six lenses are all glass lenses, and the glass material of the glass lenses does not contain lead, arsenic, and similar harmful substances. Image reading lens.   The image reading lens according to claim 1, wherein at least one of the lenses has a non-circular outer shape.   6. An image reading lens according to claim 1, an illumination system for illuminating a document placed on a document placement surface, and a line shape on which image information of the document illuminated by the illumination system is imaged An image reading apparatus comprising: an image reading unit in which the image pickup element and at least one mirror are integrally held, and scanning the image reading unit to read image information of the document.   7. An image forming apparatus for forming an image by writing an image corresponding to an image signal, wherein the image reading apparatus according to claim 6 is used as means for reading image information of a document into an image signal. An image forming apparatus.

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