JP2012123271A - Reading lens and image reader, image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reading lens capable of realizing a wider field angle and excellent performance in addition to having as large a diameter as the previous lenses.SOLUTION: This image reader is composed of six groups and seven lens; the first group having a first positive lens L1, the second group having a cemented lens of a second positive lens L2 and a third negative lens L3, the third group III having a fourth negative lens L4, the fourth group IV having a fifth positive lens L5, the fifth group V having a sixth positive lens VI, and the sixth group VI having a seventh negative lens L7. φ4, defined as φ4=f4/f, φ5, defined as φ5=f5/f, the Abbe number ν5 of material of the fifth lens and the Abbe number ν6 of material of the sixth lens are so set as to satisfy the conditions: (1)φ4/ν5+φ5/ν6<0.04, and (2)|φ4-φ5|<0.12, where f is the focal length of the whole system to the e line, f4 is the focal length of the fifth lens L5 to the e line and f5 is the focal length of the sixth lens L6 to the e line.

Description

  The present invention relates to a reading lens for reading a document image, an image reading apparatus using the reading lens, and an image forming apparatus. The reading lens can be used for a document reading unit of a facsimile or a digital copying machine and various image scanners.

In a facsimile, a digital copying apparatus, or the like, an image reading apparatus that reads an image of a transmission original or a copy original reduces the image to be read with a reading lens and forms an image on a solid-state image pickup device such as a CCD 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 to form a document image on the light receiving surface. Thus, there is an optical system that performs color separation into three primary colors and converts a color image into a signal.

A reading lens used for such image reading generally requires a high contrast in a high spatial frequency region on the image plane, and is required to have an aperture efficiency close to 100% up to the periphery of the angle of view. It is necessary to correct the surface curvature very well.
Further, in order to read a color original satisfactorily, it is necessary to match the image forming positions of red, green, and blue colors on the light receiving surface in the optical axis direction, and chromatic aberration of each color must be corrected extremely well.

  Further, there is a demand for downsizing of the image reading apparatus, particularly for reducing the conjugate distance between the original and the light receiving surface. For this purpose, it is necessary to widen the angle of view of the reading lens.

  In addition, speeding up of image reading is also demanded. For this purpose, a lens having a large aperture and a bright lens is required.

  Conventionally, as a reading lens realizing a large aperture, many Gauss type lenses having four groups and six elements are known. The Gauss-type lens system is a “lens type that can suppress the occurrence of coma flare to a small size” even with a large aperture, but the majority of currently known lenses have a half angle of view of about 18 degrees, which is a relatively large image. Even with a wide angle, the half angle of view remains at about 20 degrees.

  For this reason, a Gaussian reading lens is effective in terms of brightness, but is not necessarily sufficient to meet the demand for downsizing of an image forming apparatus.

  There is known a reading lens in which one lens is further added to a Gauss type lens configuration to form a five-group seven-lens configuration (Patent Document 1). This reading lens has a large aperture of F number: about 4.0, but has a half angle of view of about 20 degrees, and is not necessarily sufficient to sufficiently achieve downsizing of the image reading apparatus.

  The reading lens described in Patent Document 1 also employs an aspherical surface. The use of an aspherical surface not only makes it difficult to form an aspherical surface, but it is not only a factor in increasing the cost of the reading lens, but also a lens with a large outer diameter cannot maintain good surface accuracy, and the imaging performance of the reading lens. It also causes deterioration.

  In view of the above, the present invention has a wide half field angle of about 24 °, corrects the field curvature well, has a bright F number of about 4.0, and has an aperture efficiency of 100 up to the periphery. %, With various aberrations corrected well, high contrast in the high spatial frequency region, and capable of full-color reading, realizing a “compact reading lens with only a spherical surface” consisting of 7 elements in 6 groups The challenge is to make it possible.

  Another object is to realize an image reading apparatus and an image forming apparatus using such a reading lens.

  The reading lens of the present invention is used in an image reading apparatus for reading an image of a transmission original or a copy original in a facsimile or a digital copying apparatus, etc. An image reading lens ”is configured as follows.

  That is, as illustrated in FIG. 1, the reading lens moves from the object side (left side in the figure) to the image side (right side in the figure), positive first group I, negative second group II, negative A third group III, a positive fourth group IV, a positive fifth group V, and a negative sixth group VI are arranged, and a stop ST is provided between the second group II and the third group III.

  In FIG. 1, reference numeral CG denotes a document placement glass or contact glass, which is drawn closely to the first group I for the sake of simplicity of illustration. Reference numeral F represents the cover glass and various filters of the image sensor as “one transparent parallel plate having optical characteristics equivalent to these”, and for the sake of simplicity of illustration, it is placed close to the sixth group VI. I draw.

The first group I includes a positive first lens L1, and the second group II includes a positive second lens L2 and a negative third lens L3 cemented. The second lens L2 and the third lens L3 are cemented to form the second group II having “negative refractive power”.
The third group III includes a negative fourth lens L4, and the fourth group IV includes a positive fifth lens L5. The fifth group V includes a positive sixth lens L6, and the sixth group VI includes a negative seventh lens L7.
Accordingly, the entire system of the reading lens has a configuration of 7 elements in 6 groups, and the refractive power distribution is positive / negative / negative / positive / positive / negative toward the object side or the naked image side. The refractive power distribution of the 7 lens L7 is positive / positive / negative / negative / positive / positive / negative.

The reading lens satisfies the following conditions (1) and (2).
(1) φ4 / ν5 + φ5 / ν6 <0.04
(2) | φ4-φ5 | <0.12
Here, the “focal length with respect to the e line” of the entire system is f (> 0), the “focal length with respect to the e line” of the positive fifth lens L5 that forms the fourth group IV is f4, and the positive focal length that forms the fifth group V. Φ4 and φ5 are defined as φ4 = f4 / f and φ5 = f5 / f, respectively, where f5 is the “focal length with respect to the e-line” of the sixth lens L6.
ν5 and ν6 represent Abbe numbers of materials of the fifth lens and the sixth lens, respectively.

  In the reading lens according to claim 1, the first lens L1 is “a positive meniscus lens having a convex surface facing the object side”, the second lens L2 is “a positive lens having a convex surface on the object side surface”, and the third lens L3 is “an image”. The negative lens having a concave side surface ”, the fourth lens L4“ a negative meniscus lens having a concave surface facing the object side ”, the fifth lens L5“ a positive lens having a convex surface on the image side ”, and the sixth lens L6“ The “biconvex lens” and the seventh lens L7 can be configured as a “biconcave lens” (claim 2).

  In the lens configuration of claim 2, the third lens L3 can be a “negative meniscus lens”, and the fifth lens L5 can be a “positive meniscus lens” (claim 3).

  In the lens configuration of claim 2, the second lens L2 can be a “positive meniscus lens”, the third lens L3 can be a “negative meniscus lens”, and the fifth lens L5 can be a “biconvex lens” (claim 4). .

  In the reading lens according to the second aspect, the second lens L2 can be a “biconvex lens”, the third lens L3 can be a “biconcave lens”, and the fifth lens L5 can be a “positive meniscus lens”. ).

  In the reading lens according to any one of claims 1 to 5, it is preferable that all of the first to seventh lenses are “glass lenses made of glass containing no harmful substances such as lead and arsenic”. Item 6).

  The image reading apparatus according to the present invention includes an “illumination system for illuminating a document, an imaging lens for reducing and imaging reflected light of the document illuminated by the illumination system, and a document image formed by the imaging lens. An image reading apparatus having a line sensor for photoelectric conversion ”, wherein the reading lens according to any one of claims 1 to 6 is used as an imaging lens (claim 7).

  The image forming apparatus according to the present invention is an "image forming apparatus that uses the image reading apparatus according to claim 7 and forms an image using the read image information" (claim 8).

Supplement the explanation.
The reading lens of the present invention has seven groups in six groups and has thirteen lens surfaces, and in particular, the second, third, and fifth lenses have a degree of freedom as in the second to fourth aspects. Therefore, as compared with the conventionally known Gauss type, there are many design parameters and the degree of freedom in design is high, so that various aberrations can be corrected satisfactorily.

  Further, since all the lens surfaces are formed as spherical surfaces, it is easy to form the lens surfaces, and the reading lens can be realized at low cost.

Condition (1) is a condition for ensuring an achromatic function by the lenses of the fourth group and the fifth group (the fifth lens and the sixth lens).
“Φ4” in condition (1) represents “the strength of positive refractive power with respect to the entire system” of the positive fifth lens, and “φ5” represents “positive refractive power with respect to the entire system” of the positive sixth lens. Of strength ". The sum of the ratios of these positive refractive power lenses to the Abbe number is the parameter of the condition (1), and the positive power of the fifth lens and the sixth lens and the “negative power of the second group” are combined. And good chromatic aberration correction.

  If the upper limit of condition (1) is exceeded, the positive power of the fifth lens and the sixth lens will be small, and even if the Abbe number of these lenses is selected, a sufficient achromatic effect will not be obtained, and the chromatic aberration of the entire system will be large. turn into.

  Condition (2) is a condition that regulates the “difference in power distribution (f4 / f, f5 / f)” in the lenses of the fourth group and the fifth group (the fifth lens and the sixth lens). The difference in power distribution between both lenses becomes too large, and the “difference in lens outer diameter” between the fifth and sixth lenses becomes large, which is disadvantageous for making the reading lens compact.

As described above, in the reading lens of the present invention, the first to seventh lenses constituting the reading lens are all “spherical lenses” and do not use aspherical surfaces. Accordingly, these first to seventh lenses can be easily “all composed of glass lenses”.
If all the lenses are glass lenses, the reading lens has high environmental resistance, and even if the temperature in the image reading apparatus fluctuates due to the movement of the illumination system, the change in optical characteristics can be suppressed to a small level.

When all the lenses are glass lenses, the first to seventh lenses are all made of “glass that does not contain harmful substances such as lead and arsenic” as in the reading lens of claim 6. The glass material can be easily recycled, and there is no water pollution due to waste liquid during lens processing, so that resources can be saved and CO ₂ generated during processing can be reduced.

As described above, according to the present invention, a novel reading lens can be realized.
The reading lens according to the present invention has the above-described configuration. As shown in the examples described later, the reading lens has a large aperture of about 4.0 and a wide angle of view of about 24 degrees. It has a high contrast in the frequency domain ”, an aperture efficiency close to 100% up to the periphery of the angle of view, chromatic aberration is well corrected, and can be realized compactly.
Therefore, by using such a “wide viewing angle reading lens”, the conjugate length from the document surface to the line sensor can be set short, and a compact image reading apparatus and image forming apparatus can be realized.

It is a figure for demonstrating a reading lens. FIG. 3 is a diagram illustrating a lens configuration of a reading lens of Example 1. FIG. 6 is an aberration diagram for Example 1. FIG. 6 is a diagram illustrating a lens configuration of a reading lens of Example 2. FIG. 6 is an aberration diagram for Example 2. 6 is a diagram illustrating a lens configuration of a reading lens according to Example 3. FIG. FIG. 6 is an aberration diagram for Example 3. 6 is a diagram illustrating a lens configuration of a reading lens of Example 4. FIG. FIG. 6 is an aberration diagram for Example 4. 6 is a diagram illustrating a lens configuration of a reading lens according to Example 5. FIG. FIG. 9 is an aberration diagram for Example 5. It is a figure for demonstrating one Embodiment of an image reading apparatus. It is a figure for demonstrating one Embodiment of an image forming apparatus.

Hereinafter, embodiments will be described.
2, 4, 6, 8, and 10 show embodiments of the reading lens. These embodiments correspond to Examples 1 to 5 described later in the order of the drawings. In order to avoid complications, the reference numerals in these figures are made common, and as shown in FIG. 1, the document placement glass or contact glass by CG, the filter by reference numeral F, etc., the first to seventh lenses sequentially by reference numerals L1 to L7. The aperture is indicated by the symbol ST.

  The reading lens shown in each of the above figures, in order from the object side (left side of the figure), is a positive first group, a negative second group, a negative third group, a positive fourth group, a positive fifth group, A negative sixth group is disposed, and a stop ST is provided between the second group and the third group. The first group includes a positive first lens L1, and the second group includes a positive second lens. The lens L2 and the negative third lens L3 are cemented, the third group is composed of a negative fourth lens L4, the fourth group is composed of a positive fifth lens L5, and the fifth group is positive. The sixth lens unit L6 includes a sixth lens unit L6, and the sixth lens unit includes a negative seventh lens L7.

  The first lens L1 is “a positive meniscus lens having a convex surface facing the object side”, the second lens L2 is “a positive lens having a convex surface on the object side surface”, and the third lens L3 is “a negative lens having a concave surface on the image side surface”, The fourth lens L4 is “a negative meniscus lens having a concave surface facing the object side”, the fifth lens L5 is “a positive lens having a convex surface on the image side surface”, the sixth lens L6 is a “biconvex lens”, and the seventh lens L7 is “ It is a “biconcave lens”.

  In the reading lenses shown in FIGS. 2, 4, and 6, the third lens L3 is a negative meniscus lens, and the fifth lens L5 is a positive meniscus lens. In the reading lens shown in FIG. 8, the second lens L2 is a positive meniscus lens, the third lens L3 is a negative meniscus lens, and the fifth lens L5 is a biconvex lens.

  In the reading lens shown in FIG. 10, the second lens L2 is a biconvex lens, the third lens L3 is a biconcave lens, and the fifth lens is a positive meniscus lens.

  The reading lenses of Examples 1 to 5 corresponding to these embodiments all satisfy the conditions (1) and (2).

  In the reading lenses of Examples 1 to 5, the first lens L1 to the seventh lens L7 are all “glass lenses made of glass containing no harmful substances such as lead and arsenic”. Also, none of the examples employs “aspheric surfaces”, and the first to seventh lenses are all “glass lenses”.

Hereinafter, embodiments of the image reading apparatus and the image forming apparatus will be described.
FIG. 12 is a diagram showing an embodiment of an “image reading apparatus”.
In FIG. 12, a document 112 having an image to be read is placed flat on a contact glass 111, and an illumination unit 113A using an “Xe lamp, LED light source, etc.” is disposed below the contact glass 111, and the illumination is performed. Light illuminates a “slit-like portion long in a direction perpendicular to the drawing” of the document surface of the placed document.
Reflected light from the illuminated portion of the document 112 (reflected light from the image) is reflected by the first mirror 113B provided on the first traveling body 113, and then provided on the second traveling body 114. 114A and the third mirror 114B are sequentially reflected, pass through the reading lens 115, and form a reduced image of the original image on the imaging surface of the line sensor 116 as a solid-state imaging device that performs photoelectric conversion.

The first to third mirrors 113B, 114A, and 114B constitute a “reflective optical system”, and the first traveling body 113 and the second traveling body 114 are each moved in the direction of the arrow (to the right in the figure) by driving means (not shown). Can be run.
The traveling speed of the first traveling body 113 is “V”, the traveling speed of the second traveling body 114 is “V / 2”, and the first traveling body 113 and the second traveling body 114 are indicated by “broken lines” shown in the drawings. Displacement to “shown position”.
The illumination unit 113 </ b> A and the first mirror 113 </ b> B move integrally with the first traveling body 113 to “illuminate and scan” the entire document 112 on the contact glass 1. Since the moving speed ratio of the first and second traveling bodies is “V: V / 2”, “the optical path length from the original scanned portion to the reading lens” is kept unchanged.

  The line sensor 116 indicates that “photoelectric conversion elements (116A, 116B, 116C) having filters of red (R), green (G), and blue (B) as color separation means are arranged in three rows on one chip. Line CCD (3-line sensor) ”, which converts the document image into an image signal as the document 112 is illuminated and scanned. In this way, reading of the original 112 is executed, and the color image of the original 112 is read by color separation into three primary colors of red, green, and blue.

  The image reading apparatus according to this embodiment is an apparatus that reads an image in full color, and includes “color separation means (red, green, red, green, etc. provided in the three-line CCD” provided in the imaging optical path of the image reading lens 115. Blue filter) ”.

  As another form of the image reading apparatus, “illuminating means for illuminating the original on the contact glass in a slit shape, a line sensor, and a plurality of mirrors forming an imaging optical path from the illuminated part of the original to the line sensor; The image reading lens arranged on the image forming optical path and the reading unit integrated with each other are moved relative to the document by the driving means so as to read and scan the document. You can also.

  In the “color separation”, a color separation prism or filter is selectively inserted between the reading lens 115 and the line sensor (CCD) separately from the above, and R (red), G (green), and B (blue). Or a “method of illuminating a document by sequentially turning on R, G, and B light sources”.

FIG. 13 is a diagram illustrating one embodiment of an image forming apparatus.
The image forming apparatus of FIG. 13 includes an image reading apparatus 200 located at the upper part of the apparatus and an “image forming part” located at the lower part thereof. The parts of the image reading apparatus 200 are the same as those described with reference to FIG. 12, and the same reference numerals as those shown in FIG.

  The image signal output from the three-line line sensor 116 of the image reading apparatus 200 is sent to the image processing unit 1200 and processed by the image processing unit 1200 to “write signals (yellow, magenta, cyan, and black colors). Signal for writing) ”.

  The image forming unit has a photoconductive photosensitive member 1100 formed in a cylindrical shape as a “latent image carrier”, and around it, a charging roller 1110 as a charging unit, a revolver type developing device 1130, a transfer belt. 1140 and a cleaning device 1150 are provided. As the charging means, a “corona charger” can be used instead of the charging roller 1110.

  An optical scanning device 1170 that receives a writing signal from the signal processing unit 1200 and writes on the photosensitive member 1100 by optical scanning performs optical scanning of the photosensitive member 1100 between the charging roller 1110 and the developing device 1130. ing.

  Reference numeral 1160 denotes a fixing device, reference numeral 1180 denotes a cassette, reference numeral 1190 denotes a registration roller pair, reference numeral 1220 denotes a paper feed roller, reference numeral 1210 denotes a tray, and reference numeral S denotes a transfer sheet as a “recording medium”.

  When image formation is performed, the photoconductive photoreceptor 1100 is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by the charging roller 1110, and is subjected to exposure by optical writing of the laser beam of the optical scanning device 1170. 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 1100, 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 1140 by the transfer voltage application roller 114A, and the respective color toner images are superimposed on the transfer belt 1140 to form a color image.

  The cassette 1180 containing the transfer paper S is detachable from the main body of the image forming apparatus, and the uppermost sheet of the stored transfer paper S is fed by the paper feed roller 1220 when mounted as shown in the figure. The leading edge of the fed transfer paper S is caught by the registration roller pair 1190.

  The registration roller pair 1190 feeds the transfer sheet S to the transfer unit at the timing when the “color image by toner” on the transfer belt 1140 moves to the transfer position. The transferred transfer paper S 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 sheet S on which the color image is transferred is sent to the fixing device 1160, where the color image is fixed in the fixing device 1160, passes through a conveyance path by a guide means (not shown), and is discharged onto the tray 1210 by a pair of paper discharge rollers (not shown). The Each time each color toner image is transferred, the surface of the photoreceptor 1100 is cleaned by a cleaning device 1150 to remove residual toner, paper dust, and the like.

  Hereinafter, five specific examples of the reading lens will be described. The meanings of the symbols in each example are as follows (see FIG. 1).

f: Composite focal length of e-line of the entire system FNo: F number m: Reduction ratio ω: Half angle of view Y: Object height ri (i = 1 to 14): Curvature radius of i-th surface counted from the object side di (I = 1 to 13): i-th surface interval counted from the object side nj (j = 1 to 7): Refractive index of the material of the j-th lens counted from the object side νj (j = 1 to 7): Abbe number of the material of the j-th lens from the object side rc1: radius of curvature of the contact glass on the object side rc2: radius of curvature of the contact glass on the image side rc3: radius of curvature of the CCD cover glass on the object side rc4: CCD cover glass Radius of curvature of the image side dc1: contact glass thickness dc3: CCD cover glass thickness nc1: contact glass refractive index nc3: CCD cover glass refractive index νc1: contact glass CG Abbe number νc : Abbe number of the CCD cover glass F nd: refractive index of d line [nu] d: Abbe number of d line ne: refractive index of the e-line
Unless otherwise specified, the unit of the quantity having the length element is “mm”.

"Example 1"
FIG. 2 shows the lens configuration of Example 1.
f = 65.880, FNo = 3.97, m = 0.36222, Y = 152.4, ω = 23.8 °
The data of Example 1 is shown in Table 1.

"Example 2"
FIG. 4 shows the lens configuration of Example 2.
f = 65.163, FNo = 3.99, m = 0.36222, Y = 152.4, ω = 24.1 °
The data of Example 2 is shown in Table 2.

"Example 3"
FIG. 6 shows the lens configuration of Example 2.
f = 65.471, FNo = 3.98, m = 0.36222, Y = 152.4, ω = 24.0 °
The data of Example 3 is shown in Table 3.

Example 4
FIG. 8 shows the lens configuration of the reading lens of Example 4.
f = 66.051, FNo = 3.98, m = 0.36222, Y = 152.4, ω = 24.1 °
The data of Example 4 is shown in Table 4.

"Example 5"
FIG. 10 shows the lens configuration of the reading lens of Example 5.
f = 66.415, FNo = 4.02, m = 0.36222, Y = 152.4, ω = 23.7 °
The data of Example 5 is shown in Table 5.

  Table 6 shows values relating to the condition (1) of the reading lenses of Examples 1 to 5.

  Table 7 shows parameter values of the condition (2) for the reading lenses of Examples 1 to 5.

FIG. 3 shows aberration diagrams relating to the reading lens of Example 1. FIG.
In the aberration diagrams, “e” is e-line (546.07 nm), “g” is g-line (436.83 nm), “c” is c-line (656.27 nm), “F” is F-line (486.13 nm) Indicates. The broken line in the spherical aberration diagram indicates the “sine condition”, the solid line in the astigmatism diagram indicates the sagittal ray, and the broken line indicates the meridional ray. The same applies to the aberration diagrams of the other examples.

  FIG. 5 is an aberration diagram for the reading lens of Example 2, FIG. 7 is an aberration diagram for the reading lens of Example 3, FIG. 9 is an aberration diagram for the reading lens of Example 4, and FIG. 11 is an aberration for the reading lens of Example 5. The figure is shown.

  Each of the reading lenses of Examples 1 to 5 has a large aperture of about FNo: 4.0 and a wide angle of about half of an angle of view: about 24 degrees. As shown in each aberration diagram, the performance is also good.

L1 first lens
L2 second lens
L3 3rd lens
ST Aperture
L4 4th lens
L5 5th lens
L6 6th lens
L7 7th lens

JP 2005-351973 A

Claims (8)

From the object side, a positive first group, a negative second group, a negative third group, a positive fourth group, a positive fifth group, and a negative sixth group are arranged, and the second group and the third group With a diaphragm in between
The first group consists of a positive first lens,
The second group is formed by joining a positive second lens and a negative third lens,
The third group consists of a negative fourth lens,
The fourth group consists of a positive fifth lens,
The fifth group consists of a positive sixth lens,
The sixth group is a six-group seven-element configuration composed of a negative seventh lens,
The focal length with respect to the e-line of the entire system is f, the focal length with respect to the e-line of the positive fifth lens forming the fourth group is f4, and the focal length with respect to the e-line of the positive sixth lens forming the fifth group is f5. Then, φ4, φ5 defined by φ4 = f4 / f, φ5 = f5 / f, Abbe number of the material of the fifth lens: ν5, Abbe number of the material of the sixth lens: ν6, conditions:
(1) φ4 / ν5 + φ5 / ν6 <0.04
(2) | φ4-φ5 | <0.12
A reading lens characterized by satisfying The reading lens according to claim 1.
The first lens is a positive meniscus lens having a convex surface facing the object side, the second lens is a positive lens having a convex surface on the object side, the third lens is a negative lens having a concave surface on the image side, and the fourth lens has a concave surface on the object side. A reading lens, wherein the negative meniscus lens is directed, the fifth lens is a positive lens having a convex image side surface, the sixth lens is a biconvex lens, and the seventh lens is a biconcave lens. The reading lens according to claim 2, wherein
A reading lens, wherein the third lens is a negative meniscus lens and the fifth lens is a positive meniscus lens. The reading lens according to claim 2, wherein
A reading lens, wherein the second lens is a positive meniscus lens, the third lens is a negative meniscus lens, and the fifth lens is a biconvex lens. The reading lens according to claim 2, wherein
A reading lens, wherein the second lens is a biconvex lens, the third lens is a biconcave lens, and the fifth lens is a positive meniscus lens. The reading lens according to any one of claims 1 to 5,
A reading lens, wherein all of the first to seventh lenses are glass lenses made of glass containing no harmful substances such as lead and arsenic. An illumination system that illuminates the document; an imaging lens that reduces and images the reflected light of the document illuminated by the illumination system; a line sensor that receives and photoelectrically converts the document image formed by the imaging lens; An image reading apparatus comprising:
An image reading apparatus using the reading lens according to any one of claims 1 to 6 as an imaging lens.   An image forming apparatus that forms an image using the read image information using the image reading apparatus according to claim 7.

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