JP2005292353A - Color image reading lens, color image reading lens unit, document reading apparatus, and image forming apparatus - Google Patents

Abstract

A good color image reading lens of Gaussian type is realized at low cost.
From the object side, a first group I composed of a positive first lens, a second group II having a negative refractive power by joining a positive second lens and a negative third lens, and a negative fourth lens. A third group III having a negative refractive power by joining a lens and a positive fifth lens, and a fourth group IV consisting of a positive sixth lens are arranged in the above order, and between the second group and the third group. A four-group, six-element color image reading lens having an aperture stop S, d-line refractive index: nd, c-line refractive index: nc, F-line refractive index: nF, g-line refractive index: ng The partial dispersion: θgd is defined as θgd = (ng-nd) / (nF-nc), and the partial dispersion: θgd and the Abbe number: coordinate point of reference material K7 on the coordinate plane having νd as two orthogonal axes: When a straight line connecting K7 (θgd, νd) and reference glass material: F2 coordinate point: F2 (θgd, νd) is defined as a reference line, partial dispersion of the material from the second lens to the fifth lens: reference of θgd line Deviation from: Δθgd is positive.
[Selection] Figure 1

Description

  The present invention relates to a color image reading lens, a color image reading lens unit, a document reading device, and an image forming apparatus.

  In a document reading unit or an image scanner in a facsimile machine or a digital copying machine, a “color image to be read” is reduced by a color image reading lens. For example, “light receiving elements having red, green and blue filters are arranged in three rows on one chip. A reduced image is formed on a solid-state image pickup device such as a so-called three-line CCD arranged in the image, and is separated into three primary colors, and image information is converted into a signal.

  Such a color image reading lens is required to have “a uniform and high contrast from the vicinity of the optical axis to the periphery in a high spatial frequency region”, and therefore, a color image reading lens can properly correct curvature of field. In particular, it is necessary to satisfactorily correct the “field curvature in the sagittal direction” and to keep the coma flare small in order to “uniformize the contrast in the sub-scanning direction”.

  In addition, in order to read a color image satisfactorily, it is necessary to make the imaging positions of red, green, and blue colors coincide with the optical axis direction on the light receiving surface of the solid-state imaging device. The secondary spectrum (axial chromatic aberration for other wavelengths when correcting “axial chromatic aberration” for two wavelengths) must be corrected very well. Furthermore, an aperture efficiency close to 100% is required up to the periphery of the field angle.

  In order to correct the curvature of field to a small extent, it is common practice to “reduce the Petzval sum to some extent”, and to correct axial chromatic aberration, the positive lens has a high refractive index and low dispersion (large Abbe number). It is necessary to use “a material with a low refractive index and high dispersion (small Abbe number) for the negative lens”.

  In order to suppress the “secondary spectrum of longitudinal chromatic aberration” to be small, a reference line (a straight line connecting the coordinate points of the reference material K7 and F2 on a coordinate plane having two axes orthogonal with partial dispersion: θgd and Abbe number: νd) It is preferable that the “deviation of partial dispersion of each lens material” from “” is positive for a positive lens and negative for a negative lens.

  However, when looking at optical glasses that are currently mass-produced, the high-refractive index / low-dispersion lanthanum crown-based and tantalum crown-based materials that are frequently used as positive lens materials are “partial dispersion from the reference line”. The “deviation” is negative, and the “low-refractive index, high-dispersion heavy flint material”, which is frequently used as a negative lens material, has a positive “partial dispersion deviation from the reference line”. It was difficult to “correctly correct” the sum, the axial chromatic aberration and the secondary spectrum at the same time.

  For this reason, conventionally, a color image reading lens can “correctly correct field curvature up to a half field angle of about 20 °, and can suppress coma flare generation even with a relatively large aperture, and has high chromatic aberration correction capability. In order to satisfactorily correct the secondary spectrum of longitudinal chromatic aberration in the “4 group 6 element gauss type”, at least one of the third and fourth lenses, which are negative lenses, has a partial dispersion deviation from the reference line. A material that realizes good performance using a so-called “anomalous dispersion glass” having a negative property is known (Patent Documents 1, 2, etc.).

  However, anomalous dispersion glass having a relatively high dispersion (Abbe number in the vicinity of 40 to 45) generally used for a negative lens is caused by the action of a polishing agent or a cleaning chemical used for polishing or cleaning. There is a problem in processing that so-called “yake” is likely to occur, and it is difficult to realize high yield by “yake”, and the processing cost tends to increase.

  In addition, a Gauss type of 6 elements in 4 groups is known as “no anomalous dispersion glass is used for the negative lens” described in Patent Document 3, but the F / No is slightly dark as F4.5 and the surface of aberration But there is still room for improvement.

  Recently, from the viewpoint of saving resources in various fields of industry, recycling of processed materials has been requested, and recycling of lens glass materials is also intended. From the viewpoint of recycling the lens glass material, it goes without saying that it is preferable that the lens material does not contain harmful substances.

Japanese Patent No. 2729039 Japanese Patent No. 2790919 Japanese Patent Laid-Open No. 2002-116381

  In view of the above, the present invention is a Gauss type of 4 elements in 6 groups, bright as F / No: about 4.2, the aperture efficiency is close to 100% to the periphery, and the field curvature is corrected very well. The coma flare is small, the contrast is high in the high spatial frequency region from the vicinity of the axis to the outermost periphery, the axial chromatic aberration and its secondary spectrum are suppressed, and R (red), G (green), and B (blue). It is an object of the present invention to realize a high-performance color image reading lens that is small in size, low in cost, and suitable for reading full-color images.

  Another object of the present invention is to realize a color image reading lens in which materials can be recycled and there is no water contamination due to waste liquid during processing.

  It is another object of the present invention to realize a color image reading lens unit using the color image reading lens, an original reading apparatus, and an image forming apparatus using the original reading apparatus.

  As illustrated in FIG. 1, the color image reading lens according to the present invention includes, from the object side (left side in the figure), a first group I including a positive first lens, a positive second lens, and a negative third lens. Is a second group II having a negative refractive power and a fourth group consisting of a negative fourth lens and a positive fifth lens, a third group III having a negative refractive power, and a positive sixth lens. A color image reading lens having a four-group six-lens configuration in which the groups IV are arranged in the above-described order and the diaphragm S is provided between the second group II and the third group III, and has the following characteristics (claim 1): .

  That is, the deviation of the partial dispersion: θgd of the material from the second lens to the fifth lens constituting the second group II and the third group III from the reference line: δθgd is positive. Hereinafter, “partial dispersion: θgd deviation from reference line: Δθgd” is simply referred to as “partial dispersion deviation: Δθgd”.

  The color image reading lens described in claim 1 has positive, negative, negative, and positive power distribution as described above. In FIG. 1, reference numeral CG1 indicates a contact glass on which a document to be read is placed, and reference numeral CG2 indicates a cover glass of the solid-state image sensor.

"Partial dispersion: θgd" means d-line (587.56nm) refractive index: nd, c-line (656.27nm) refractive index: nc, F-line (486.13nm) refractive index: nF, g-line (435.83nm) The refractive index is defined by the following formula according to ng.
θgd = (ng-nd) / (nF-nc)
The “reference line” is a reference on a coordinate plane (partial points on this coordinate plane are determined by coordinates: (θgd, νd)) having the above-described partial dispersion: θgd and Abbe number: νd as two orthogonal axes. Glass material: Defined as a straight line connecting K7 coordinate point: K7 (θgd, νd) and reference glass material: F2 coordinate point F2 (θgd, νd).

  The above-mentioned “partial dispersion deviation: δθgd” is positive because the coordinate point of the glass material partial dispersion: θgd on the coordinate plane is located in the “region where the partial dispersion: θgd increases from the reference line”. Means that.

In the color image reading lens according to the first aspect, the second to fifth lenses constituting the second group and the third group, both of which are cemented lenses, are “partial dispersion deviation: glass material with positive δθgd”.
Such “partial dispersion deviation: glass material having positive δθgd” has a low refractive index and high dispersion, and is suitable as a material for a negative lens in terms of correcting axial chromatic aberration. By using the fifth lens as well, it is possible to satisfactorily correct the “secondary spectrum of longitudinal chromatic aberration” due to the positive partial dispersion deviation. Further, such a glass material is excellent in resistance to abrasives, cleaning chemicals, etc., and hardly causes the above-mentioned “burn”.

  On the other hand, “partial dispersion deviation: glass material with positive Δθgd” does not reach the high refractive index of “lanthanum crown-based and tantalum crown-based materials” frequently used for positive lenses in terms of refractive index. Therefore, if “partial dispersion deviation: glass material with positive δθgd” is used for the second and fifth lenses, the refractive index n in Petzval sum (= Σ (1 / nf)) becomes small, and Petzval sum becomes large. However, this is disadvantageous from the viewpoint of the “image plane flattening (correction of field curvature)” of the color image reading lens. Alternatively, this can be solved by using the above-mentioned “lanthanum crown-based or tantalum crown-based material” having a high refractive index for the sixth lens.

  As described above, both positive and negative lenses of the cemented lens are made of “glass material having a positive partial dispersion deviation”, so that the glass material price is low, and it is good at low cost by using a heavy flint glass material excellent in workability. A color image reading lens with high performance can be realized.

The color image reading lens according to claim 1 is the sum of the partial dispersion deviations of the positive lenses (second and fifth lenses) in the cemented lens: δθgd25 (= the partial dispersion deviation of the second lens and the partial dispersion deviation of the fifth lens). Sum), the sum of the partial dispersion deviations of the negative lenses (third and fourth lenses) in the cemented lens: δθgd34 (= the sum of the partial dispersion deviation of the third lens and the partial dispersion deviation of the fourth lens), i = 1, 2 , 6 and 7, the refractive index: ni and the Abbe number: νi of the material of the i-th lens from the object side with respect to the d-line are:
(1) 0.0 <δθgd34−δθgd25 <0.02
(2) 0.023 <(n2 / ν2 + n5 / ν5) / 2 <0.042
(3) 0.032 <(n1 / ν1 + n6 / ν6) / 2 <0.041
Is preferably satisfied (claim 2).

  In the color image reading lens according to claim 1, the partial dispersion deviation of the cemented lens is all positive, but the conditions (1) to (3) are such that “the partial dispersion deviation of the cemented lens is all positive”. In this case, the axial chromatic aberration, its secondary spectrum, and the curvature of field are conditions for correcting more satisfactorily.

  The parameter of condition (1) is obtained by subtracting “sum of partial dispersions of positive lenses (second and fifth lenses)” from “sum of partial dispersions of negative lenses (third and fourth lenses)” in the cemented lens. If the value of this parameter exceeds the upper limit, the secondary spectrum becomes insufficiently corrected in the wavelength region “outside the wavelength for correcting axial chromatic aberration” and becomes “positive and large”. On the other hand, if the lower limit is exceeded, the secondary spectrum becomes too “negative and large” in the wavelength region “between two wavelengths for correcting axial chromatic aberration”.

  When the upper limit of the condition (2) is exceeded, the Abbe number of the positive lens in the cemented lens becomes too small and the axial chromatic aberration is undercorrected, and negative on the short wavelength side than the reference wavelength and positive on the long wavelength side. growing. On the other hand, if the lower limit is exceeded, the refractive index of the positive lens of the cemented lens decreases, the Petzval sum increases positively, and field curvature correction becomes difficult.

  The condition (3) is a condition for realizing good performance when the material of the cemented lens is in a range where the conditions (1) and (2) are satisfied. The Abbe number of the six lenses becomes too small, and “first axial chromatic aberration that cannot be corrected by the cemented lens” occurs in the first and sixth lenses. If the lower limit is exceeded, the refractive indexes of the first and sixth lenses will be too small, and the radius of curvature of the first and final surfaces of the color image reading lens will have to be reduced, increasing coma flare and increasing the total lens length. Invite "Longening".

  3. The color image reading lens according to claim 1, wherein the second group, which is a cemented lens of the second and third lenses, has a “meniscus shape with a convex surface facing the object side”, and the fourth and fifth lenses. It is preferable that the third lens group is a “meniscus shape with the convex surface facing the image surface” (Claim 3).

  In this way, the “lens close to the stop” is formed in a meniscus shape, and spherical light and image are obtained by making “a light beam incident as concentrically as possible” to the stop disposed between the second group and the third group. It becomes possible to suppress surface curvature small.

  In the color image reading lens according to claim 3, the first lens is “a meniscus shape with a convex surface facing the object side”, and the sixth lens is “a meniscus shape with a convex surface facing the image surface”. (Claim 4).

  In this way, by making all of the first group to the fourth group have meniscus shapes, the light beams are incident “as concentrically as possible” to all the groups with respect to the diaphragm arranged between the second group and the third group. In addition, it is possible to maintain symmetry with respect to the stop, and to suppress spherical aberration, distortion, and lateral chromatic aberration.

The color image reading lens according to any one of claims 1 to 4, wherein the total focal length of the entire system for the e-line: f, the focal length of the first group (first lens) for the e-line: f1, the second group. The combined focal length f25 for the e-line of the (second and third lenses) and the third group (fourth and fifth lenses) is:
(4) 0.6 <f1 / f <1.0
(5) -0.93 <f25 / f <-0.47
Is preferably satisfied (Claim 5).
By satisfying the conditions (4) and (5), it becomes possible to correct each aberration better.

  Condition (4) determines the power of the first lens group. If the upper limit is exceeded, the power of the first lens group becomes too weak, and it is necessary to enlarge the entire lens to ensure performance, leading to a cost increase. On the contrary, if the lower limit is exceeded, it is advantageous for making the color image reading lens compact, but the power of the first lens unit becomes too strong, so the coma flare becomes large, and in particular, “contrast at low frequency” is lowered.

  Condition (5) determines the combined power of the second group and the third group having negative power. If the upper limit is exceeded, both spherical aberration and field curvature are overcorrected, and coma around the periphery deteriorates. If the lower limit is exceeded, on the contrary, both spherical aberration and curvature of field become insufficiently corrected, the astigmatic difference at the intermediate angle of view increases, and the coma aberration at the intermediate angle of view deteriorates.

  The color image reading lens according to any one of claims 1 to 5, wherein the first to sixth lenses are all glass lenses, and the glass material preferably does not contain harmful substances such as lead and arsenic ( Claim 6).

  All lenses are made of “chemically stable optical glass that does not contain toxic substances such as lead and arsenic”, which makes it possible to recycle materials, eliminate water pollution from waste liquid during processing, and protect the global environment. A compact and low-cost color image reading lens can be realized.

The color image reading lens according to any one of claims 1 to 6 can be "all the lens surfaces of the first to sixth lenses are spherical surfaces" (claim 7).
In recent years, various aspherical lenses have been used in various lens systems. However, as the outer diameter of the aspherical lens increases, it takes time to mold, and it is difficult to increase processing costs and maintain a good surface shape. . By not using an aspherical surface, there is no limitation on the size of the lens, and a lens with good workability and surface shape accuracy can be obtained.

The “color image reading lens unit” according to the present invention is the color image reading lens according to any one of claims 1 to 7 that is “assembled and integrated into a lens barrel” (claim 8).
The document reading device of the present invention is a “device for reading a color image of a document in full color”, and includes a document support means, an illumination means, a color image reading lens, a color separation means, and an imaging means. 9).
“Original support means” is means for supporting an original from which a color image is to be read.
“Illuminating means” is means for illuminating the original document supported by the original document supporting means.
The “color image reading lens” forms an image of the illuminated document.

The “color separation means” is arranged on the image forming optical path of the color image reading lens and performs color separation.
The “imaging unit” receives an image of the original image formed by the color image reading lens (color-separated by the color separation unit) and converts it into an electrical signal.
The color image reading lens according to any one of claims 1 to 7 is used as the color image reading lens.

  The document reading apparatus according to claim 9, wherein the document supporting means is “contact glass for placing a document in a plane”, and illumination means is “illuminating the document placed on the contact glass in a slit shape, It is possible to employ a configuration in which a “line sensor” is used as an image pickup means using an apparatus having “a means for scanning a document in a direction crossing the section”.

  In the document reading device according to claim 10, “a document placed in a plane on the contact glass is illuminated and scanned by the illumination means”, but according to claim 9, the document reading device includes “illumination device, color image reading lens and line While fixing the positional relationship with the sensor and illuminating the original to be read in a slit shape on the contact glass placed at a position conjugate to the line sensor, the original is moved in the direction intersecting the slit-like illumination position to You may comprise so that illumination scanning is performed. In this case, the contact glass has only to have “a narrow width necessary for illuminating the original”.

  The document reading device according to claim 9 may be arranged such that a document to be read is placed flat on a document glass and the entire surface of the document is illuminated with a predetermined illuminance distribution, and a reduced image on the entire surface of the document is It is also possible to configure so that an image is formed on the light receiving surface and the entire surface of the original is read simultaneously. Further, as the color separation means, it is possible to use one that switches the illumination light of the document at a high speed in the order of red, green, and blue.

  The image forming apparatus according to the present invention is an "apparatus for writing an image corresponding to an image signal to form an image", and as a means for reading an original image in full color and converting it to an image signal, It has a reading device (claim 11).

  In this image forming apparatus, the image signal can be written by various known methods such as an ink jet method, an ink ribbon method, a heat sensitive method, and the like. “The image corresponding to the image signal is written by optical writing. (Claim 12). In this case, writing by optical writing may be performed on a silver salt film or the like, but “optical writing is performed on a photoconductive photoreceptor to form an electrostatic latent image corresponding to an image to be formed”. It can also be set as a structure (Claim 13).

  As described above, according to the present invention, it is a Gauss type of 4 elements in 6 groups, bright as F / No: about 4.2, aperture efficiency is close to 100% up to the peripheral part, and field curvature is corrected very well. In addition, the coma flare is small, and the high chromatic aberration and the secondary spectrum thereof are suppressed to be small in the high spatial frequency region from the vicinity of the axis to the outermost periphery, and R (red), G (green), and B (blue). It is possible to realize a high-performance color image reading lens that is small in size and low in cost and is suitable for reading a full-color image because the “image position difference” of each color light is small.

In the color image reading lens according to the sixth aspect, each constituent lens material can be recycled, and there is no water contamination due to waste liquid during processing.
An original reading apparatus using such a color image reading lens can read a color image of the original satisfactorily, and an image forming apparatus using such an original reading apparatus is excellent on the basis of the color image information read well. Image formation can be realized.

FIG. 10 shows only a main part of one embodiment of the “document reading apparatus”.
In FIG. 10, a document 2 to be read is placed in a plane on a contact glass 1 as a document supporting means, and is “long in a direction perpendicular to the drawing” by an illumination optical system (not shown) disposed under the contact glass 1. The “slit-like part” is illuminated.

  The reflected light from the illuminated portion of the document 1 is reflected by the first mirror 3A provided on the first traveling body 3, and then the second mirror 4A and the second mirror 4B provided on the second traveling body 4. Are sequentially reflected and transmitted through the color image reading lens assembled in the lens barrel of the color image reading lens unit 5 to form a reduced image of the document 1 on the light receiving portion of the line sensor 6 as the imaging means.

  As the “color image reading lens”, the one described in any one of claims 1 to 7, specifically, for example, any one of the color image reading lenses of Examples 1 to 4 described later is used.

  The first traveling body 3 and the second traveling body 4 are caused to travel in the direction of the arrow (to the right in the figure) by driving means (not shown). The traveling speed of the first traveling body 3 is “V”, and the traveling speed of the second traveling body 4 is “V / 2”. By this traveling, the first traveling body 3 and the second traveling body 4 are displaced to positions indicated by broken lines, respectively.

  An illumination optical system (not shown) moves integrally with the first traveling body 3 and “illuminates and scans” the entire document 2 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 color image reading lens” is kept unchanged.

  The line sensor 6 is a so-called three-line CCD (three-line line sensor) in which light receiving elements having red, green, and blue filters as color separation means are arranged in three rows on one chip. Along with the illumination scanning, the document image is converted into an image signal. In this way, the document 2 is read, and the color image of the document 2 is separated into the three primary colors red, green, and blue and read.

  That is, the document reading device shown in FIG. 9 is a device that reads a color image of a document in full color. The document support unit 1 that supports the document 2 and the illumination that illuminates the document 2 supported by the document support unit 1. Means (illumination optical system not shown, first and second traveling bodies 3 and 4, first to third mirrors 3A, 4A and 4B held by these traveling bodies, and a drive (not shown) for running the traveling body A color image reading lens (installed in a lens barrel of the color image reading lens unit 5) for forming an image of the illuminated original 2, and a color image reading lens unit 5 Receiving the color image of the original image formed by the “color separation means (red, green and blue filters provided on the three-line CCD)” provided in the imaging optical path and the color image reading lens. Telegraph And an imaging device 6 for converting the a those using a color image reading lens according to any one of claims 1 to 7 as a color image reading lens (Claim 9).

  Further, the “document supporting means” is the contact glass 1 for placing the document 2 in a plane, and the illumination means illuminates the document 2 placed on the contact glass 1 in a slit shape, and the slit-shaped illumination section. It has means for scanning the document in the intersecting direction, and the “imaging means” is the line sensor 6 (claim 10).

  As another form of the document reading device, “illumination means for illuminating the document on the contact glass in a slit shape, a line sensor, a plurality of mirrors forming an imaging optical path from the non-illuminated portion of the document to the line sensor, A reading unit in which a color image reading lens disposed on the imaging optical path is integrated with each other is driven relative to the document by driving means so as to read and scan the document. You can also.

  Further, the color image reading lens can be used in “document back side reading” when reading both sides of a document by placing it in a document feeder (so-called ADF).

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

FIG. 11 shows an embodiment of the image forming apparatus.
This image forming apparatus includes a document reading apparatus 200 positioned at the upper part of the apparatus and an “image forming unit” positioned at a lower position thereof. The portion of the document reading apparatus 200 is the same as that described with reference to FIG. 10, and the same reference numerals as those in FIG.

  The image signal output from the three-line line sensor (imaging means) 6 in the document reading apparatus 200 is sent to the signal processing unit 120 and processed by the signal processing unit 120 to generate a “writing signal (yellow, magenta, cyan, Signal for writing each color of black) ”.

  The image forming unit includes a photoconductive photosensitive member 110 formed in a cylindrical shape as a “latent image carrier”, and a charging roller 111 as a charging unit, a revolver type developing device 113, and a transfer belt around the photosensitive member 110. 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 120 denotes a paper feed roller, reference numeral 121 denotes a tray, and reference numeral S 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 S 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 feeding roller 120. 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 S to the transfer unit at a timing when the color image formed by the toner on the transfer belt 114 moves to the transfer position. The transferred transfer paper S is superimposed on the color image at the transfer portion, and contacts the transfer belt 114 while the toner image of each color is transferred from the photoconductor 110 to the transfer belt 114. The color image is electrostatically transferred by the action of retreating from the position.

  The transfer sheet S on 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.

  That is, the image forming apparatus shown in the embodiment in FIG. 11 is an image forming apparatus that forms an image by writing an image corresponding to the image signal, and as means for converting a document image into an image signal. To the image forming apparatus 200 according to any one of (9) to (9). The image corresponding to the image signal is written by optical writing (claim 12), and an electrostatic latent image corresponding to the image to be formed is formed on the photoconductive photosensitive member 110 by optical writing (claim). Item 13).

  Hereinafter, four specific numerical examples of the color image reading lens will be described.

The meanings of symbols in each embodiment are as follows. The surfaces of the lens and the diaphragm are first to eleventh surfaces in order from the object side.
f: Composite focal length for the e-line of the entire system F: F / No
m: Reduction ratio ω: Half angle of view (degrees)
Y: object height R: radius of curvature D: surface spacing c1: object side surface of contact glass c2: image side surface of contact glass c3: object side surface of CCD cover glass c4: image side surface of CCD cover glass nd: d line (587.56 nm) Refractive index for ne: Refractive index for e-line (546.07 nm) ng: Refractive index for g-line (435.83 nm) nF: Refractive index for F-line (486.13 nm) nC: Refractive index for C-line (656.27 nm) νd: Abbe Number nj (j = 1 to 6): Refractive index of the jth lens
νj (j = 1 to 6): Abbe number of the j-th lens δθgdj (j = 2 to 5): partial dispersion deviation of the material of the j-th lens Also, the name of the producer is shown in parentheses in the material name column in the examples The “H” is “HOYA”.

f = 89.894, F = 4.19, m = 0.36222, Y = 152.4, ω = 17.9 ° Table 1 shows the data of Example 1.

Parameter values of conditional expression Table 2 shows the parameter values of condition (1).

  Table 3 shows parameter values of the conditions (2) and (3).

  Table 4 shows the parameter values of the conditions (4) and (5).

  FIG. 2 shows the lens configuration of the color image reading lens of Example 1, and FIG. 3 shows aberration diagrams.

f = 90.968, F = 4.19, m = 0.36222, Y = 152.4, ω = 17.8 ° The data of Example 2 are shown in Table 5.

Parameter values of conditional expression Table 6 shows the parameter values of condition (1).

  Table 7 shows parameter values of the conditions (2) and (3).

  Table 8 shows parameter values of the conditions (4) and (5).

  FIG. 4 shows the lens configuration of the color image reading lens of Example 2, and FIG. 5 shows aberration diagrams.

f = 90.925, F = 4.20, m = 0.36222, Y = 152.4, ω = 17.8 ° The data of Example 3 are shown in Table 9.

Parameter values of conditional expression Table 10 shows the parameter values of condition (1).

  Table 11 shows parameter values of the conditions (2) and (3).

  Table 12 shows parameter values of the conditions (5) and (6).

  FIG. 6 shows the lens configuration of the color image reading lens of Example 3, and FIG. 7 shows aberration diagrams.

f = 90.931, F = 4.16, m = 0.36222, Y = 152.4, ω = 17.8 ° The data of Example 4 are shown in Table 13.

Table 14 shows the parameter values of the conditional expression (1).

  Table 15 shows the parameter values of the conditions (2) and (3).

  Table 16 shows parameter values of the conditions (4) and (5).

  FIG. 8 shows a lens configuration of the color image reading lens of Example 4, and FIG. 9 shows aberration diagrams.

  In each aberration diagram, “e” indicates e-line (546.07 nm), “g” indicates g-line (436.83 nm), “c” indicates c-line (656.27 nm), and “F” indicates F-line (486.13 nm). . In the diagram of spherical aberration, “broken line indicates sine condition”, and in astigmatism diagram, “solid line indicates sagittal ray and broken line indicates meridional ray”.

  As is apparent from each aberration diagram, the color image reading lens of each example is a Gauss type of 6 elements in 4 groups, and an F / No of about 4.2 is used even though an inexpensive glass material is used. With a large aperture and an aperture efficiency of nearly 100%, chromatic aberration is well corrected with a reduction ratio of 0.23622, and the on-axis and off-axis aberrations are well balanced, as is apparent from the coma aberration diagram. High contrast in the high spatial frequency region.

  Therefore, by using these color image reading lenses, original information can be read in monochrome, and satisfactory reading can be performed in full color with little variation in the SN ratio of each color of red, green, and blue.

It is a block diagram of a color image reading lens. 1 is a configuration diagram of a color image reading lens of Example 1. FIG. FIG. 6 is an aberration diagram for Example 1. 3 is a configuration diagram of a color image reading lens of Example 2. FIG. FIG. 6 is an aberration diagram for Example 2. FIG. 6 is a configuration diagram of a color image reading lens of Example 3. FIG. 6 is an aberration diagram for Example 3. 5 is a configuration diagram of a color image reading lens of Example 4. FIG. FIG. 6 is an aberration diagram for Example 4. 1 is a diagram conceptually illustrating an embodiment of a document reading apparatus. 1 is a diagram conceptually illustrating an embodiment of an image forming apparatus.

Explanation of symbols

I Group 1
II Second group
III Group 3
IV Group 4 S Aperture

Claims (13)

From the object side, a first group consisting of a positive first lens, a second group having a negative refractive power by joining a positive second lens and a negative third lens, a negative fourth lens and a positive fifth lens A fourth group consisting of a third lens group having a negative refractive power and a fourth lens group consisting of a positive sixth lens arranged in the above order and having a stop between the second lens group and the third lens group. In a color image reading lens having a single sheet configuration,
d-line (587.56 nm) refractive index: nd, c-line (656.27 nm) refractive index: nc, F-line (486.13 nm) refractive index: nF, g-line (435.83 nm) refractive index: ng Dispersion: θgd θgd = (ng-nd) / (nF-nc)
In the coordinate plane having the above partial dispersion: θgd and Abbe number: νd as two orthogonal axes, the reference material: K7 coordinate point: K7 (θgd, νd) and the reference glass material: F2 coordinate point: F2 (θgd , νd) is defined as the reference line,
A color image reading lens, wherein the partial dispersion of the material from the second lens to the fifth lens: θgd has a positive deviation from the reference line: δθgd. The color image reading lens according to claim 1.
Sum of deviation from reference line of partial dispersion of positive lens (second and fifth lenses) in cemented lens: δθgd25, deviation of reference lens from reference line of partial dispersion of negative lens (third and fourth lenses) in cemented lens Sum: δθgd34, i = 1, 2, 6, 7, and the refractive index: ni and Abbe number: νi of the material of the i-th lens from the object side with respect to the d-line are:
(1) 0.0 <δθgd34−δθgd25 <0.02
(2) 0.023 <(n2 / ν2 + n5 / ν5) / 2 <0.042
(3) 0.032 <(n1 / ν1 + n6 / ν6) / 2 <0.041
A color image reading lens characterized by satisfying The color image reading lens according to claim 1 or 2,
The second group, which is a cemented lens of the second lens and the third lens, has a meniscus shape with the convex surface facing the object side,
A color image reading lens, wherein the third group which is a cemented lens of the fourth lens and the fifth lens has a meniscus shape with a convex surface facing the image surface. The color image reading lens according to claim 3.
The first lens has a meniscus shape with a convex surface facing the object side,
The sixth lens is a color image reading lens having a meniscus shape with a convex surface facing the image surface. The color image reading lens according to any one of claims 1 to 4,
Total focal length for the e-line of the entire system: f, focal length for the e-line of the first group (first lens): f1, second group (second and third lenses) and third group (fourth and fifth lenses) The combined focal length for the e-line: f25 is the condition:
(4) 0.6 <f1 / f <1.0
(5) -0.93 <f25 / f <-0.47
A color image reading lens characterized by satisfying The color image reading lens according to any one of claims 1 to 5,
A color image reading lens, wherein the first to sixth lenses are all glass lenses, and the glass material does not contain harmful substances such as lead and arsenic. The color image reading lens according to any one of claims 1 to 6,
A color image reading lens, wherein the lens surfaces of the first to sixth lenses are all spherical.   A color image reading lens unit obtained by assembling and integrating the color image reading lens according to any one of claims 1 to 7 into a lens barrel. A device that reads a color image of a document in full color,
Document support means for supporting the document;
Illuminating means for illuminating the original document supported by the original document supporting means;
A color image reading lens for forming an image of a document illuminated by the illumination means;
Color separation means disposed on the imaging optical path of the color image reading lens;
Image pickup means for receiving an image of an original image formed by the color image reading lens and converting it into an electric signal;
An original reading apparatus using the color image reading lens according to any one of claims 1 to 7 as the color image reading lens. The document reading device according to claim 9, wherein
The document support means is a contact glass for placing the document in a plane,
The illumination means has a means for illuminating the document placed on the contact glass in a slit shape, and scans the document in a direction crossing the slit-shaped illumination portion, and the imaging means is a line sensor Reader. An image forming apparatus for forming an image by writing an image corresponding to an image signal,
11. An image forming apparatus comprising the document reading device according to claim 9 or 10 as means for reading a document image in full color and converting it into an image signal. The image forming apparatus according to claim 11.
An image forming apparatus, wherein an image corresponding to an image signal is written by optical writing. The image forming apparatus according to claim 12.
An image forming apparatus, wherein an electrostatic latent image corresponding to an image to be formed is formed on a photoconductive photosensitive member by optical writing.

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