JP2013041205A - Image reading lens and image reading apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exert favorable imaging performance by correcting various aberrations in an image reading lens.SOLUTION: The image reading lens includes, in order from an object side, a front group GF, an aperture stop St, and a back group GB, and has a telecentricity in the object side. The front group GF is disposed with: a first group G1 of a positive or negative cemented lens; a second group G2 of a positive or negative cemented lens; a third group G3 of a positive cemented lens with its convex surface on the object side; and a fourth group G4 of a cemented lens with its concave surface on an image side. The back group GB comprises three or four lens groups, and includes a fifth group G5 of a negative cemented lens with its concave surface on the object side, and a positive sixth group G6 with its convex surface on the image side. Three or more positive lenses constituting the front group GF and two or more positive lenses constituting the back group GB are configured to satisfy a conditional expression (1): νd>60.0, and one or more positive lenses constituting the front group GF and two or more positive lenses constituting the back group GB are configured to satisfy a conditional expression (1): Δθ>0.015.

Description

  The present invention relates to an image reading lens and an image reading apparatus provided with the image reading lens.

  2. Description of the Related Art Conventionally, there has been known an image scanner in which an original image such as a film disposed at a finite distance is taken into an image pickup device such as a CCD (Charge Coupled Device) via an imaging lens and converted into an electronic image. Also, in the field of movies, digitization is progressing, and an electronic image displayed on an image display device such as an LCD (Liquid Crystal Display) is converted into an optical image by an imaging lens and printed on a movie film, An image reading apparatus has been developed in which an image on a motion picture film is imaged on an imaging surface of an imaging element via an imaging lens and converted into an electronic image by the imaging element. Along with the development of the image reading apparatus, an image reading lens used as an image forming lens of the image reading apparatus is also developed.

  Since the image reading apparatus as described above is required to read the information of the original image faithfully, various aberrations such as distortion are corrected well, and the image reading lens is corrected from the center to the peripheral portion of the imaging region. It is required to have high resolution over a wide range. In recent years, since most of the originals are color originals, it is necessary for the image reading lens to be well corrected for both axial chromatic aberration and lateral chromatic aberration.

  In addition, in the image reading apparatus in the above field, particularly when a film image is captured by the image sensor, a minute scratch or dust on the film surface is detected as image information, and an unnecessary image generated by the scratch or dust is detected. There is a demand to digitally remove a portion by image processing. When detecting scratches or dust on the film surface, near infrared light is often used. For this reason, the axial lens chromatic aberration and the lateral chromatic aberration are corrected well in the wide wavelength range from the visible range to the near-infrared range (for example, about 900 nm) in the image reading lens. It is desired to have optical performance.

  As an image reading lens in which various aberrations are corrected from the visible region to the near infrared region, for example, lenses described in Patent Documents 1 to 4 below are known.

  Patent Document 1 describes an example in which two lens groups on the reduction side and the enlargement side adjacent to the aperture stop are each composed of two cemented lenses in a four-group six-lens configuration.

  Patent Document 2 describes an example in which two lens groups on the reduction side and the enlargement side adjacent to the aperture stop are each composed of three cemented lenses in a six-group configuration including 13 to 14 lenses. .

  Patent Document 3 describes an example in which two lens groups on the reduction side and the enlargement side adjacent to the aperture stop are each composed of two cemented lenses in a six-group configuration including 10 to 12 lenses. ing.

  Furthermore, Patent Document 4 describes an example in which a magnification is about 1.4 to 1.7 times in a seven-group configuration including 12 to 14 lenses.

Japanese Patent Laid-Open No. 2002-287022 JP 2002-148514 A JP 2008-26593 A JP 2010-276892 A

  As described above, the image reading lens is required to obtain a high-resolution and high-quality image in which various aberrations are suppressed from the central portion to the peripheral portion of the imaging region. In addition, with the recent increase in the number of pixels in an image sensor, an image reading lens capable of obtaining a higher quality image is required.

  More specifically, various aberrations, particularly distortion, magnification, and axial chromatic aberration, can be corrected well, for example, if light rays emitted from an LCD or received by a CCD have an angle, shading occurs and image quality is reduced. In order to deteriorate, it is required to suppress the occurrence of such shading.

  However, the lens systems described in Patent Documents 1 and 3 having a small number of lenses and a small number of lens groups are sufficiently corrected for aberrations compared to the performance required for recent image reading lenses. I can't say that.

  In addition, a lens system described in Patent Document 2 in which both the incident side and the exit side are not telecentric, and a lens system described in Patent Document 4 with a magnification of about 1.4 to 1.7 times are also available in recent years. It cannot be said that it has sufficient performance as compared with the required performance for the image reading lens.

  The present invention has been made in view of the above circumstances, and various aberrations, in particular, axial chromatic aberration and lateral chromatic aberration are corrected satisfactorily, and an image having good imaging performance from the central portion of the imaging region to the peripheral portion. An object of the present invention is to provide a reading lens and an image reading apparatus including the image reading lens.

The image reading lens of the present invention comprises, in order from the object side, a front group having positive refractive power, an aperture stop, and a rear group having positive refractive power, and has telecentricity on the object side. The front group includes, in order from the object side, a first lens group that is a cemented lens having a positive or negative refractive power as a whole, and a positive lens and a negative lens. The second lens group, which is a cemented lens having negative refractive power, and a positive lens and a negative lens have a positive refractive power as a whole, and the second lens group is a cemented lens in which the most object side surface is convex on the object side. The first lens group includes a three-lens group and a fourth lens group that is a cemented lens that includes a positive lens and a negative lens and has negative refractive power as a whole, and the most image-side surface is concave on the image side. , The second lens group, and the third lens group The rear group includes four positive lenses and at least two negative lenses, and includes three or four lens groups, and this rear group is configured to have a positive refractive power. The fifth lens group arranged closest to the object side is a cemented lens composed of a positive lens and a negative lens, and has a negative refractive power as a whole, and the most object side surface is concave on the object side. The sixth lens group in the rear group arranged on the image side of the fifth lens group includes at least one positive lens and has a positive refractive power as a whole, and the most image side surface is convex on the image side A positive lens constituting the front group, in which the lens portion in the rear group disposed on the image side of the fifth lens group has a positive refractive power as a whole. And at least two of the positive lenses constituting the rear group Equation (1): νd> 60.0 was filled, and, at least one of the positive lens constituting the front group, and at least two of the positive lenses of the rear group conditional expression (2): [Delta] [theta] _{g , D} > 0.015. Where νd is the Abbe number with respect to the d-line of the lens, Δθ _{g, d} is anomalous dispersion (Δθ _{g, d} = θ _{g, d} −1.365 + 0.00208 × νd), θ _{g, d} is the g-line, d-line Partial dispersion ratio (θ _{g, d} = (ng−nd) / (nF−nC)), ng is the refractive index for g-line, nd is the refractive index for d-line, nF is the refractive index for F-line, and nC is C The refractive index for the line.

  In the image reading lens, a rear group includes the four lens groups including a fifth lens group, a sixth lens group, a seventh lens group, and an eighth lens group in order from the object side. Includes at least one positive lens, has a positive or negative refractive power as a whole, the most image side surface is convex on the image side, and the eighth lens group includes at least one positive lens. And has a positive or negative refractive power as a whole, and the most image side surface is convex on the image side. Furthermore, in this image reading lens, at least three of the positive lenses constituting the rear group satisfy the conditional expression (1), at least two of the positive lenses constituting the front group, and the positive lens constituting the rear group. At least three of the lenses can satisfy the conditional expression (2).

  The image reading lens includes, in order from the object side, the three lens groups including a fifth lens group, a sixth lens group, and a seventh lens group in the rear group, and the sixth lens group includes at least two lenses. The seventh lens group includes at least one positive lens and has a positive refractive power as a whole, and the most image-side surface is convex on the image side. . Furthermore, in this image reading lens, at least three of the positive lenses constituting the rear group satisfy the conditional expression (1), at least two of the positive lenses constituting the front group, and the positive lens constituting the rear group. At least three of the lenses can satisfy the conditional expression (2).

  In the image reading lens, the rear group includes the four lens groups including a fifth lens group, a sixth lens group, a seventh lens group, and an eighth lens group in order from the object side. However, the most object side surface has a convex surface on the object side, the second lens group has a positive refractive power as a whole, and the most object side surface has a convex surface on the object side. The sixth lens group is a single lens, the seventh lens group is a single lens having positive refractive power, the most image side surface is convex on the image side, and the eighth lens group is a positive lens and a negative lens. And has a positive or negative refractive power as a whole, and can be a cemented lens in which the most image side surface is convex on the image side. Furthermore, the cemented lens constituting the eighth lens group may be formed by arranging a positive lens and a negative lens in order from the object side.

  In the image reading lens, the rear group includes the four lens groups including a fifth lens group, a sixth lens group, a seventh lens group, and an eighth lens group in order from the object side. Is a cemented lens having a positive refractive power as a whole, the most image side surface being convex on the image side, the sixth lens group is a single lens, and the seventh lens group is a positive lens and a negative lens. And has a positive or negative refractive power as a whole, a cemented lens with the most object-side surface facing the concave surface on the object side, and the eighth lens group has a positive refractive power with the convex surface facing the image side Can be a single lens. Furthermore, the cemented lens constituting the seventh lens group may be formed by disposing a negative lens and a positive lens in order from the object side.

  An image reading apparatus according to the present invention includes the image reading lens.

  The image reading lens may be substantially composed of seven or eight lens groups. The “lens substantially consisting of n lens groups” means a lens having substantially no refractive power, an optical element other than a lens such as a diaphragm or a cover glass, a lens flange, in addition to the n lens groups. A lens having a lens barrel, an image sensor, a mechanism portion such as a camera shake correction mechanism, and the like.

  The “positive lens” means one lens having positive refractive power, and the “negative lens” means one lens having negative refractive power. That is, when simply described as “positive lens”, it means one lens having positive refractive power, and when simply described as “negative lens”, one lens having negative refractive power. Means.

  When an aspherical lens is used as the lens constituting the image reading lens, the aspherical irregularities, the aspherical refractive power positive / negative, and the aspherical curvature radius positive / negative are irregularities in the aspherical paraxial region, It is defined by the positive / negative of the refractive power and the positive / negative of the radius of curvature.

  In general, an image reading lens can form an optical image representing a subject by passing light emitted from the subject from one side to the other side, and can emit light emitted from the subject on the other side. An optical image representing the subject can be formed through the one side to the other side. Therefore, the “object side” does not necessarily correspond to the subject side but may correspond to the imaging side. Similarly for the “image side”, the “image side” does not necessarily correspond to the image forming side but may correspond to the subject side.

  That is, the description on the “object side” or “image side” with respect to the image reading lens is provided for convenience, and does not limit the direction in which light passes through the image reading lens.

  However, this image reading lens has telecentricity on the object side and does not have telecentricity on the image side. The image reading lens is configured such that the total number of lenses arranged on the object side of the aperture stop is larger than the total number of lenses arranged on the image side of the aperture stop. Yes.

  The image reading lens having telecentricity on the object side is not limited to being completely telecentric. Here, “object side” is described as “one side”, that is, “the image reading lens is telecentric on one side” means that the image reading lens is emitted toward one side. This is not limited to the case where the principal ray incident on the image reading lens from one side is completely parallel to the optical axis, but also includes cases where there is some error. To do. The case where there is a slight error is a case where the inclination of the principal ray with respect to the optical axis is ± 1 ° or less.

  It is more desirable for the image reading lens to have telecentricity such that the principal ray has an inclination of ± 0.6 ° or less with respect to the optical axis.

According to the image reading lens and the image reading apparatus of the present invention, in order from the object side, the front group having a positive refractive power, an aperture stop, and a rear group having a positive refractive power have telecentricity on the object side. The front group consists of a first lens group, which is a cemented lens having a positive or negative refractive power as a whole, and a positive lens and a negative lens. The second lens group, which is a cemented lens having a positive or negative refractive power, and a positive lens and a negative lens have a positive refractive power as a whole, and the surface arranged closest to the object side is convex on the object side. A third lens group which is a cemented lens, and a fourth lens group which is composed of a positive lens and a negative lens and has a negative refracting power as a whole, and is a cemented lens having a concave surface on the image side. The first lens group, the first The lens group and the third lens group are configured to have a positive refractive power, and the rear group includes four positive lenses and at least two negative lenses, and includes three or four lens groups. The fifth lens group arranged on the most object side in the rear group is composed of a positive lens and a negative lens, and has a negative refractive power as a whole, and the most object side surface is concave on the object side. The sixth lens group in the rear group, which is arranged adjacent to the image side of the fifth lens group, includes at least one positive lens and has a positive refractive power as a whole, The image side surface is convex on the image side, and the lens portion in the rear group disposed on the image side with respect to the fifth lens group is configured to have a positive refractive power as a whole. At least three of the positive lenses constituting the group and the positive lenses constituting the rear group At least two satisfy the conditional expression (1): νd> 60.0, and at least one of the positive lenses constituting the front group and at least two of the positive lenses constituting the rear group are conditional expressions (2): Since Δθ _{g, d} > 0.015 is satisfied, various aberrations, particularly longitudinal chromatic aberration and lateral chromatic aberration, are favorably corrected, and favorable imaging is performed from the center of the imaging region to the peripheral portion. Performance can be obtained.

  That is, this image reading lens can achieve good performance near the same magnification by adopting a substantially symmetrical power arrangement with an aperture stop in between. In addition, this image reading lens can suppress shading and reduce the sensitivity of magnification adjustment, for example, by making the side on which the CCD, LCD, etc. are arranged an object side having telecentricity. It becomes easy to adjust to a predetermined magnification set in advance.

  Further, coma and astigmatism can be favorably corrected by adopting a 4-group configuration on the object side from the aperture stop and a 3-4 group configuration on the image side from the aperture stop.

  Furthermore, by using a lot of glass with a large Abbe number and anomalous dispersion for the positive lens, various aberrations, especially on-axis and magnification chromatic aberration in the entire visible range, can be corrected more favorably. Chromatic aberration can be corrected more satisfactorily by using as a cemented lens all groups on the object side (telecentric side) from the stop and at least two groups on the image side (non-telecentric side) from the aperture stop.

  A more specific effect related to the image reading lens of the present invention will be described later.

Sectional drawing which shows schematic structure of the lens for image reading by embodiment of this invention Sectional drawing which shows the structure of the lens for image reading of Example 1. FIG. Sectional drawing which shows the structure of the lens for image reading of Example 2. FIG. Sectional drawing which shows the structure of the lens for image reading of Example 3. FIG. Sectional drawing which shows the structure of the lens for image reading of Example 4. FIG. Sectional drawing which shows the structure of the lens for image reading of Example 5. FIG. Sectional drawing which shows the structure of the lens for image reading of Example 6. FIG. Sectional drawing which shows the structure of the lens for image reading of Example 7. Sectional drawing which shows the structure of the lens for image reading of Example 8. FIG. Sectional drawing which shows the structure of the lens for image reading of Example 9. FIG. Sectional drawing which shows the structure of the lens for image reading of Example 10. FIG. 12A to 12D are aberration diagrams showing various aberrations of the image reading lens of Example 1. FIG. 13A to 13D are aberration diagrams showing various aberrations of the image reading lens of Example 2. FIG. 14A to 14D are aberration diagrams showing various aberrations of the image reading lens of Example 3. FIG. FIGS. 15A to 15D are aberration diagrams showing various aberrations of the image reading lens of Example 4. FIGS. FIGS. 16A to 16D are aberration diagrams showing various aberrations of the image reading lens of Example 5. FIGS. FIGS. 17A to 17D are aberration diagrams showing various aberrations of the image reading lens of Example 6. FIGS. 18A to 18D are aberration diagrams showing various aberrations of the image reading lens of Example 7. FIG. FIGS. 19A to 19D are aberration diagrams showing various aberrations of the image reading lens of Example 8. FIGS. 20A to 20D are aberration diagrams showing various aberrations of the image reading lens of Example 9. FIG. FIGS. 21A to 21D are aberration diagrams showing various aberrations of the image reading lens of Example 10. FIGS. 1 is a diagram showing a schematic configuration of an image reading apparatus according to an embodiment of the present invention.

  Hereinafter, an image reading lens of the present invention and an image reading apparatus including the image reading lens will be described with reference to the drawings.

  FIG. 1 is a sectional view showing an image reading lens according to an embodiment of the present invention. In the figure, arrows X, Y, and Z indicate three directions orthogonal to each other, and the arrow Z direction indicates the same direction as the optical axis Z1.

  The illustrated image reading lens 100 includes a front group GF having a positive refractive power, an aperture stop St, and a rear lens having a positive refractive power in order from the object side (the arrow-Z direction side in the figure) which is one side. It consists of group GB and has telecentricity on the object side.

  The front group GF includes, in order from the object side, a first lens group G1, which is a cemented lens having a positive or negative refractive power as a whole, including a positive lens and a negative lens, and a positive lens and a negative lens as a whole. Alternatively, the second lens group G2, which is a cemented lens having a negative refractive power, and a positive lens and a negative lens have a positive refractive power as a whole, and the surface arranged closest to the object side is convex on the object side. The third lens group G3, which is a cemented lens, and a positive lens and a negative lens have a negative refractive power as a whole, and the surface arranged closest to the image side (the arrow + Z direction side in the figure, the other side) The fourth lens group G4, which is a cemented lens having a concave surface on the image side, is configured so that the refractive power of the first lens group G1, the second lens group G2, and the third lens group G3 is positive. It is a thing.

  The rear group GB includes four positive lenses and at least two negative lenses, and is composed of three or four lens groups. The fifth lens group G5 arranged on the most object side in the rear group GB is composed of a positive lens and a negative lens, and has a negative refractive power as a whole, and the surface arranged on the most object side is concave on the object side. This is a cemented lens. The sixth lens group G6 in the rear group disposed adjacent to the image side of the fifth lens group G5 includes at least one positive lens and has a positive refractive power as a whole, and is disposed closest to the image side. The lens surface in the rear group GB (not including the fifth lens group G5) arranged on the image side of the fifth lens group G5 is a convex surface on the image side. It is configured to have a positive refractive power.

Further, the image reading lens 100 includes at least three positive lenses among the positive lenses constituting the front group GF and at least two positive lenses among the positive lenses constituting the rear group GB. ): Satisfying νd> 60.0, and at least one positive lens among the positive lenses constituting the front group GF and at least two positive lenses among the positive lenses constituting the rear group GB are the following conditions: Expression (2): Δθ _{g, d} > 0.015 is satisfied.

Where νd is the Abbe number of the lens with respect to the d-line _{, and} Δθg _{, d} is anomalous dispersion (Δθg _{, d} = θg _{, d−} 1.365 + 0.00208 × νd). Here, θ _{g, d} is a partial dispersion ratio (θ _{g, d} = (ng−nd) / (nF−nC)) between g line and d line, ng is a refractive index with respect to g line, and nd is a refraction with respect to d line. Index, nF is the refractive index for the F-line, and nC is the refractive index for the C-line.

  The image reading lens 100 may have the following configuration in addition to the above basic configuration.

  The image reading lens 100 may be configured such that the imaging magnification is 0.7 times or more and 1.5 times or less.

  The rear group GB includes four lens groups in which a seventh lens group G7 and an eighth lens group G8 are arranged in this order in addition to the fifth lens group G5 and the sixth lens group G6. The group G7 includes at least one positive lens, has a positive or negative refractive power as a whole, and a surface disposed closest to the image side forms a convex surface on the image side, and an eighth lens group G8 includes: It may include at least one positive lens, and has a positive or negative refractive power as a whole, and a surface disposed closest to the image side forms a convex surface on the image side.

  The rear group GB includes three lens groups in which a seventh lens group G7 is arranged in this order in addition to the fifth lens group G5 and the sixth lens group G6. At least two sixth lens groups G6 are included. The seventh lens group G7 includes at least one positive lens and has a positive refractive power as a whole, and the surface disposed closest to the image side forms a convex surface on the image side. can do.

  In the image reading lens 100, at least three positive lenses among the positive lenses constituting the front group GF and at least three positive lenses among the positive lenses constituting the rear group GB satisfy the conditional expression (1). And at least two positive lenses among the positive lenses constituting the front group GF and at least three positive lenses among the positive lenses constituting the rear group GB may satisfy the conditional expression (2). .

  When the rear group GB is composed of the fifth lens group G5, the sixth lens group G6, the seventh lens group G7, and the eighth lens group G8 in order from the object side, the rear group GB is the first lens group. However, the surface arranged closest to the object side is convex on the object side, the second lens group G2 has a positive refractive power as a whole, and the surface arranged closest to the object side is convex on the object side. The sixth lens group G6 is a single lens, the seventh lens group G7 is a single lens having a positive refractive power, and the surface most disposed on the image side is convex on the image side. The eighth lens group includes a positive lens and a negative lens, and has a positive or negative refracting power as a whole, and is configured to be a cemented lens in which a surface disposed closest to the image side forms a convex surface on the image side. Can be. Further, the eighth lens group G8 may be a cemented lens including a positive lens and a negative lens in order from the object side.

  Similarly to the above, when the rear group GB is composed of the fifth lens group G5, the sixth lens group G6, the seventh lens group G7, and the eighth lens group G8 in order from the object side, this rear group GB. Is a cemented lens in which the first lens group G1 has a positive refractive power as a whole, and the surface disposed closest to the image side forms a convex surface on the image side, the sixth lens group G6 is a single lens, The seventh lens group G7 includes a positive lens and a negative lens, and is a cemented lens having a concave surface facing the object side having positive or negative refractive power as a whole. The eighth lens group G8 has a convex surface facing the image side. In addition, the lens may be configured to be a single lens having a positive refractive power. Furthermore, the seventh lens group G7 can be a cemented lens arranged in this order from the object side to the negative lens and then to the positive lens.

  Hereinafter, the operation and effect of the above-described configuration of the image reading lens 100 will be described. In this description, the image reading lens 100 is described as being formed by passing light from the “object side” to the “image side” to form an optical image representing the subject. An optical image of the subject may be formed through light in the opposite direction (from the “image side” to the “object side”) with respect to the reading lens.

  Since this image reading lens 100 has telecentricity on the object side (one side), an electronic device (LCD, CCD, etc.) is arranged on the object side having this telecentricity, thereby disposing the electronic device. It is possible to prevent the occurrence of shading due to angle dependency, which is a problem when used, and maintain good image quality from the center to the periphery. Further, since the distance fluctuation on the object side having telecentricity hardly affects the imaging magnification, the sensitivity of magnification adjustment is suppressed, and it becomes easy to match the desired imaging magnification.

  The image reading lens 100 having telecentricity means that the angle between the principal ray and the optical axis Z1 is 1 ° or less. The image reading lens 100 desirably has telecentricity on the object side such that the angle between the principal ray and the optical axis Z1 is 0.6 ° or less. The image reading lens 100 does not have telecentricity on the image side.

  In order to realize good optical performance while configuring the image reading lens 100 so that the imaging magnification is 0.7 times or more and 1.5 times or less, the image reading lens 100 is It is desirable to have a nearly symmetrical power arrangement on both sides with the aperture stop St in between. The lens groups (fourth lens group G4 and fifth lens group G5) arranged adjacent to the object side and the image side of the aperture stop St are both positive and negative cemented lenses having a concave surface facing the aperture stop St. This is a negative lens group. Further, the third lens group G3 disposed on the object side of the fourth lens group G4 is a lens group having a positive refractive power with the convex surface facing the object side, and the third lens group G3 disposed on the image side of the fifth lens group G5. The six lens group G6 is a lens group having a positive refractive power with the convex surface facing the image side, so that a so-called double Gauss type optical system can be formed by four groups from the third lens group G3 to the sixth lens group G6. Can be configured. In addition, all the lens groups arranged on the object side of the fourth lens group G4 (excluding the fourth lens group G4) have positive refractive power as a whole, and are on the image side of the fifth lens group G5. And all the lens groups (not including the fifth lens group G5) having positive refractive power as a whole constitute a double Gauss type optical system as the entire lens system. It has become. The double Gauss type optical system has an advantage that it can reduce field curvature and distortion, and is advantageous for designing a bright optical system.

  Further, in order to achieve the resolution required for the motion picture film in the entire image forming region, it is necessary to satisfactorily correct not only spherical aberration but also coma and astigmatism. For this purpose, the front group GF arranged on the object side from the aperture stop St has a four-group configuration to achieve good optical performance. Further, in order to satisfactorily correct axial chromatic aberration and lateral chromatic aberration while ensuring telecentricity, all four lens groups in the front group GF are cemented lenses of a positive lens and a negative lens.

  In order to make the lens configuration symmetrical with the aperture stop St interposed therebetween, four positive lenses are arranged on the image side of the aperture stop St as well as on the object side of the aperture stop St. Further, in order to suppress the occurrence of various aberrations on the image side from the aperture stop St, at least two negative lenses are arranged on the image side. When focusing on the balance of various aberrations, it is desirable that the rear group GB has a four-group configuration that is symmetrical to the front group GF. However, when emphasizing correction of chromatic aberration, two positive lenses and one negative lens are joined. It is also possible to adopt a three-group configuration including the three-joint lens group.

Further, in order to suppress the occurrence of chromatic aberration and correct it satisfactorily, at least three of the positive lenses in the front group GF and at least two of the positive lenses in the rear group GB are conditional expression (1): νd> Conditional expression (2): Δθ _{g, d} satisfying 60.0, and at least one positive lens among the positive lenses in the front group GF and at least two positive lenses among the positive lenses in the rear group GB > 0.015. By satisfying the above conditions, the amount of axial chromatic aberration and lateral chromatic aberration can be suppressed. In order to more effectively correct chromatic aberration, at least three of the positive lenses in the rear group GB satisfy the conditional expression (1): νd> 60.0, and at least two of the positive lenses in the front group GF It is desirable that at least three of the positive lenses in the rear group GB satisfy the conditional expression (2): Δθ _{g, d} > 0.015.

  Further, in order to correct various aberrations generated on the image side from the aperture stop St, it is necessary to dispose a negative lens in any group on the image side from the sixth lens group G6. When this negative lens is arranged closer to the image side than the sixth lens group G6 in the rear group GB, astigmatism can be favorably corrected by arranging the negative lens as close to the image side as possible. Further, since the chromatic aberration of magnification can be favorably corrected by making this negative lens a cemented lens with a positive lens, the sixth lens group G6 is a positive single lens, the seventh lens group G7 is a positive single lens, It is desirable that the eight lens group G8 is composed of a positive and negative cemented lens.

  Furthermore, by disposing the cemented lens of the eighth lens group G8 in the order of the positive lens and the negative lens, the negative lens can be disposed closest to the image side, so that it is possible to achieve a desirable arrangement for aberration correction.

  Note that the cemented lens arranged in the eighth lens group G8 can take either positive or negative values depending on the specifications required for the optical system. Therefore, the power arrangement of the rear group GB in the above case is negative. A fifth lens group G5, a positive sixth lens group G6, a positive seventh lens group G7, and a positive or negative eighth lens group G8. In such a case, in order to make the power arrangement of the entire lens symmetrical with the aperture stop St in between, the power arrangement of the front group GF is positive or negative for the first lens group G1, and the second lens It is desirable that the group G2 is positive, the third lens group G3 is positive, and the fourth lens group G4 is negative.

  Further, when the image reading lens 100 is configured by eight lens groups, a negative lens disposed after the sixth lens group G6 is disposed between the four positive lenses in the rear group GB. Axial chromatic aberration can be corrected satisfactorily. Furthermore, since this negative lens is a cemented lens with a positive lens, axial chromatic aberration and lateral chromatic aberration can be corrected in a balanced manner, so that the sixth lens group G6 is a positive single lens and the seventh lens group G7 is positive. It is desirable that the negative cemented lens and the eighth lens group G8 be composed of a single positive lens.

  Further, the cemented lens constituting the seventh lens group G7 is arranged in the order of the negative lens and the positive lens from the object side, and the cemented lens constituting the fifth lens group G5 is also arranged in the order of the negative lens and the positive lens from the object side. As a result, the negative lens in the seventh lens group G7 can be arranged at the center of the four positive lenses, which can be a more desirable arrangement for aberration correction.

  Since the cemented lens arranged in the seventh lens group G7 can take either positive or negative values depending on the specifications required for the optical system, the power arrangement of the rear group GB in the above case is negative. The lens group G5, the positive sixth lens group G6, the positive or negative seventh lens group G7, and the positive eighth lens group G8. In such a case, in order to make the power arrangement of the entire lens symmetrical with the aperture stop St interposed therebetween, the power arrangement of the front group GF is such that the first lens group G1 is positive and the second lens group is positive. It is desirable that G2 is positive or negative, the third lens group G3 is positive, and the fourth lens group G4 is negative.

  Next, Examples 1 to 10 showing specific numerical data of the image reading lens according to the present invention will be described collectively with reference to FIGS. 2 to 11, FIGS. 12 to 21, and Tables 1 to 10. . Note that the reference numerals in FIGS. 2 to 11 that correspond to the reference numerals in FIG. 1 showing the above-described image reading lens 100 indicate the corresponding components.

  As in the case described above, the side in the arrow -Z direction in the figure is the object side (side having telecentricity), and the side in the arrow + Z direction in the figure is the image side (side not having telecentricity).

  In the embodiments described below, each cemented lens and each single lens constituting each of the image reading lenses of Embodiments 1 to 10 corresponds to one group.

<Example 1>
FIG. 2 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the first embodiment.

  The image reading lens of Example 1 corresponds to an image reading lens including eight lens groups.

  Table 1 shows lens data and various data of the image reading lens of Example 1. The upper part of Table 1 shows lens data, and the lower part shows various data.

  In the upper lens data in Table 1, the surface number i is the number of the i-th (i = 1, 2, 3,...) Surface Si that sequentially increases toward the image side, with the surface arranged closest to the object side being the first. Indicates the surface number. This lens data is given a surface number including the aperture stop St.

  The upper symbol Ri in Table 1 indicates the radius of curvature of the i-th (i = 1, 2, 3,...) Surface, and the symbol Di indicates the i (i = 1, 2, 3,...) -Th surface and the (i + 1) th surface. The surface interval on the optical axis Z1 with respect to this surface is shown. Symbols Ri and Di correspond to numbers corresponding to symbols Si (i = 1, 2, 3,...) Indicating each lens surface and aperture stop St.

  Further, the symbol Ndj in the upper part of Table 1 indicates the d-line (wavelength 587) of the j-th (j = 1, 2, 3,. .6 nm), and vdj represents the Abbe number of the j-th optical element with respect to the d-line.

The column of θ _{g, d} j shows the partial dispersion ratio θ _{g, d} between the g-line and the d-line of the j-th lens, and the column of Δθ _{g, d} j shows the anomalous dispersion Δθ _g of the j-th lens. _{, D.}

  The various data in the lower part of Table 1 are the focal length f of the entire lens system, the magnification M, the incident angle V1 of the principal ray on the object side having telecentricity, the emission angle V2 of the principal ray, the first lens group to the first lens group. The values for the combined focal length f13 of all the lenses included in the three lens groups and the combined focal length f6A of all the lenses arranged on the image side of the sixth lens group are shown. Note that the values of various data are obtained based on the e-line (wavelength 546.07 nm).

In the upper part of Table 1, the radius of curvature is positive when convex on the object side and negative when convex on the image side. The unit of the radius of curvature, the surface interval, and the focal length is mm. However, since the optical system as described above can maintain a predetermined performance even if the size of an optical element such as a lens is generally proportionally enlarged or reduced, the entire lens data is proportionally enlarged or reduced. An image reading lens can also be an embodiment according to the present invention.

  12A to 12D show various aberrations of the image reading lens of Example 1. FIG. 12A shows spherical aberration, FIG. 12B shows astigmatism, FIG. 12C shows distortion (distortion aberration), and FIG. 12D shows chromatic aberration of magnification (chromatic aberration of magnification). Each aberration diagram is created using e-line (wavelength 546.07 nm) as a reference wavelength. The spherical aberration diagram and the lateral chromatic aberration diagram also show aberrations for the C-line (wavelength 656.27 nm) and g-line (wavelength 435.84 nm). The solid line in the astigmatism diagram indicates the sagittal aberration, and the broken line indicates the tangential aberration.

  The upper part of the vertical axis of the spherical aberration diagram indicates the F number (Fno.) Value, and the upper part of the vertical axis of each of the astigmatism diagram, distortion, and lateral chromatic aberration diagram shows the various data in the above table on the object side. Indicates the maximum image height determined by the object height.

  From the above data, in the image reading lens of Example 1, various aberrations, in particular axial chromatic aberration and lateral chromatic aberration, are corrected well at about the same magnification, and a good result is obtained from the center of the imaging region to the periphery. It turns out that it has image performance.

  Note that FIG. 2 showing the configuration of the image reading lens of Example 1 above, FIGS. 12A to 12D showing the aberrations, and reading of Table 1 showing the lens data and various data will be described later. Since the same applies to the second to seventh embodiments, detailed description thereof will be omitted for the later-described embodiments.

<Example 2>
FIG. 3 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the second embodiment. FIGS. 13A to 13D are graphs showing various aberrations of the image reading lens of Example 2. FIGS.

  The upper part of Table 3 below shows lens data of the image reading lens of Example 2, and the lower part shows various data.

The image reading lens of Example 2 corresponds to an image reading lens composed of eight lens groups.

<Example 3>
FIG. 4 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the third embodiment. 14A to 14D are graphs showing various aberrations of the image reading lens of Example 3. FIG.

  The upper part of Table 4 below shows lens data of the image reading lens of Example 3, and the lower part shows various data.

The image reading lens of Example 3 corresponds to an image reading lens composed of eight lens groups.

<Example 4>
FIG. 5 is a cross-sectional view illustrating a schematic configuration of the image reading lens of Example 4. FIGS. 15A to 15D are graphs showing various aberrations of the image reading lens of Example 4. FIGS.

  The upper part of Table 4 below shows lens data of the image reading lens of Example 4, and the lower part shows various data.

The image reading lens of Example 4 corresponds to an image reading lens including eight lens groups.

<Example 5>
FIG. 6 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the fifth embodiment. 16A to 16D are graphs showing various aberrations of the image reading lens of Example 5. FIG.

  The upper part of Table 5 below shows lens data of the image reading lens of Example 5, and the lower part shows various data.

The image reading lens of Example 5 corresponds to an image reading lens including eight lens groups.

<Example 6>
FIG. 7 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the sixth embodiment. FIGS. 17A to 17D are graphs showing various aberrations of the image reading lens of Example 6. FIGS.

  The upper part of Table 6 below shows lens data of the image reading lens of Example 6, and the lower part shows various data.

The image reading lens of Example 6 corresponds to an image reading lens including eight lens groups.

<Example 7>
FIG. 8 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the seventh embodiment. FIGS. 18A to 18D are graphs showing various aberrations of the image reading lens of Example 7. FIGS.

  The upper part of Table 7 below shows lens data of the image reading lens of Example 7, and the lower part shows various data.

The image reading lens of Example 7 corresponds to an image reading lens including eight lens groups.

<Example 8>
FIG. 9 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the eighth embodiment. FIGS. 19A to 19D are graphs showing various aberrations of the image reading lens of Example 8. FIGS.

  The upper part of Table 8 below shows lens data of the image reading lens of Example 8, and the lower part shows various data.

The image reading lens of Example 8 corresponds to an image reading lens composed of seven lens groups.

<Example 9>
FIG. 10 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the ninth embodiment. 20A to 20D are graphs showing various aberrations of the image reading lens of Example 9. FIG.

  The upper part of Table 9 below shows lens data of the image reading lens of Example 9, and the lower part shows various data.

The image reading lens of Example 9 corresponds to an image reading lens including eight lens groups.

<Example 10>
FIG. 11 is a cross-sectional view illustrating a schematic configuration of the image reading lens of the tenth embodiment. FIGS. 21A to 21D are graphs showing various aberrations of the image reading lens of Example 10. FIGS.

  The upper part of Table 10 below shows lens data of the image reading lens of Example 10, and the lower part shows various data.

The image reading lens of Example 10 corresponds to an image reading lens including eight lens groups.

  Next, an image reading apparatus according to an embodiment of the present invention will be described. FIG. 22 is a diagram showing a schematic configuration of the image reading apparatus according to the embodiment of the present invention.

  The illustrated image reading apparatus 200 includes the above-described image reading lens 100, a document placing table 3 on which a document 2 such as a movie film to be read is placed, and an image pickup device 4 such as a CCD that captures an image of the document 2. It has. The image reading lens 100 is disposed between the document 2 and the image sensor 4. If necessary, an optical member 5 such as an attachment lens that changes a color filter or an imaging magnification may be attached to the image reading lens 100.

  The image reading apparatus 200 can be applied to either a reflective original method or a transparent original method. In the case of a reflection original type image reading apparatus, light from a light source (not shown) is applied to the front side of the original 2. Then, the reflected light from the original 2 is imaged on the image sensor 4 through the image reading lens 100. An optical image representing the original 2 imaged on the image sensor 4 is captured by the image sensor 4 as image information.

  In the case of a transparent original type image reading apparatus, the original placing table 3 is constituted by a transparent member that transmits light, and the original 2 is constituted by a transparent original such as a negative film or a positive film. A light source (not shown) is disposed on the back side of the document placing table 3, and illumination light is irradiated from the back side of the document 2 toward the document 2. Then, the transmitted light from the document 2 is transmitted through the image reading lens 100 and receives an image forming action, whereby an optical image representing the document 2 is formed on the image sensor 4. The imaged optical image is captured as image information by the image sensor 4.

  Note that an image display device such as an LCD may be disposed as the document 2, or a movie film or the like may be disposed in place of the image sensor 4. Thus, the electronic image displayed on the image display device can be converted into an optical image by the image reading lens and printed on a movie film or the like.

  The present invention has been described with reference to the embodiment and examples. However, the present invention is not limited to the above embodiment and example, and various modifications can be made. For example, the values of the radius of curvature, the surface spacing, the refractive index, the Abbe number, etc. of each lens element are not limited to the values shown in the above numerical examples, but can take other values.

GF Front group St Aperture stop GB Rear group G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G5 Fifth lens group G6 Sixth lens group

Claims (10)

In order from the object side, it consists of a front group having positive refractive power, an aperture stop, and a rear group having positive refractive power, and has telecentricity on the object side,
The front group is
In order from the object side, the first lens group, which is a cemented lens having a positive or negative refractive power as a whole, including a positive lens and a negative lens, and has a positive or negative refractive power as a whole, which includes a positive lens and a negative lens. A second lens group that is a cemented lens, and a third lens group that is composed of a positive lens and a negative lens and has a positive refractive power as a whole, and a cemented lens in which the most object side surface is convex on the object side; The fourth lens group includes a positive lens and a negative lens, and has a negative refracting power as a whole. The fourth lens group is a cemented lens whose surface closest to the image side is concave on the image side. The lens group and the third lens group are configured to have a positive refractive power,
The rear group is
Comprising four positive lenses and at least two negative lenses, consisting of three or four lens groups,
The fifth lens group arranged closest to the object side in the rear group is composed of a positive lens and a negative lens, and has a negative refractive power as a whole, and a cemented lens in which the most object side surface is concave on the object side And
The sixth lens group in the rear group arranged on the image side of the fifth lens group includes at least one positive lens and has a positive refractive power as a whole, and the most image side surface is the image side. The lens portion in the rear group arranged on the image side of the fifth lens group is configured to have a positive refractive power as a whole,
At least three of the positive lenses constituting the front group and at least two of the positive lenses constituting the rear group satisfy the following conditional expression (1), and the positive lens constituting the front group An image reading lens, wherein at least one of them and at least two of the positive lenses constituting the rear group satisfy the following conditional expression (2).
νd> 60.0 (1)
Δθ _{g, d} > 0.015 (2)
However,
[nu] d: Abbe number [Delta] [theta] _g to the d-line of the _{lens, d:} anomalous dispersion _{(Δθ g, d = θ g} , d -1.365 + 0.00208 × νd)
θ _{g, d} : Partial dispersion ratio of g line and d line (θ _{g, d} = (ng−nd) / (nF−nC))
ng: refractive index for g line nd: refractive index for d line nF: refractive index for F line nC: refractive index for C line The rear group is composed of the four lens groups including the fifth lens group, the sixth lens group, the seventh lens group, and the eighth lens group in order from the object side.
The seventh lens group includes at least one positive lens and has a positive or negative refractive power as a whole, and the most image side surface is convex on the image side,
2. The eighth lens group includes at least one positive lens, and has a positive or negative refractive power as a whole, and the most image side surface is convex on the image side. The lens for image reading as described. At least three of the positive lenses constituting the rear group satisfy the conditional expression (1),
The image according to claim 1, wherein at least two of the positive lenses constituting the front group and at least three of the positive lenses constituting the rear group satisfy the conditional expression (2). Reading lens. The rear group is composed of the three lens groups including the fifth lens group, the sixth lens group, and the seventh lens group in order from the object side.
The sixth lens group includes at least two positive lenses;
2. The image according to claim 1, wherein the seventh lens group includes at least one positive lens and has a positive refractive power as a whole, and a surface closest to the image side is convex on the image side. Reading lens. At least three of the positive lenses constituting the rear group satisfy the conditional expression (1),
5. The image reading device according to claim 4, wherein at least two of the positive lenses constituting the front group and at least three of the positive lenses constituting the rear group satisfy the conditional expression (2). lens. The rear group is composed of the four lens groups including the fifth lens group, the sixth lens group, the seventh lens group, and the eighth lens group in order from the object side.
The first lens group is such that the most object side surface is convex on the object side,
The second lens group has a positive refractive power as a whole, and the most object side surface is convex on the object side;
The sixth lens group is a single lens;
The seventh lens group is a single lens having positive refractive power, and the most image side surface is convex on the image side;
The eighth lens group is composed of a positive lens and a negative lens, and has a positive or negative refractive power as a whole, and is a cemented lens in which the most image side surface is convex on the image side. The lens for image reading according to any one of 1 to 3.   The image reading lens according to claim 6, wherein the eighth lens group is the cemented lens in which a positive lens and a negative lens are arranged in order from the object side. The rear group is composed of the four lens groups including the fifth lens group, the sixth lens group, the seventh lens group, and the eighth lens group in order from the object side.
The first lens group has a positive refractive power as a whole, and is a cemented lens in which the most image side surface is convex on the image side,
The sixth lens group is a single lens;
The seventh lens group includes a positive lens and a negative lens, has a positive or negative refractive power as a whole, and is a cemented lens in which the most object-side surface faces a concave surface toward the object side;
4. The image reading lens according to claim 1, wherein the eighth lens group is a single lens having a positive refractive power with a convex surface facing the image side. 5.   9. The image reading lens according to claim 8, wherein the seventh lens group is the cemented lens in which a negative lens and a positive lens are arranged in order from the object side.   An image reading apparatus comprising the image reading lens according to claim 1.