JP2008176011A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact imaging lens LA having good optical properties, including a first lens having a positive power, a second lens having a negative power and a third lens having a positive power. <P>SOLUTION: The imaging lens is constituted by arranging, in order from an object side: a diaphragm; the first lens L1 as a positive meniscus lens having a convex surface facing the object side; the second lens L2 as a negative meniscus lens having a convex surface facing the image side; and the third lens L3 as a positive meniscus lens having a convex surface facing the object side, the imaging lens satisfies conditions (1) 0.22<R1/R2<0.50 and (2) 0.02<d3/¾f2¾<0.12, wherein R1 denotes the radius of curvature of the object-side surface of the first lens, R2 denotes the radius of curvature of the image-side surface of the first lens, f2 denotes focal length of the second lens, d3 denotes center thickness of the second lens. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging lens. In particular, the present invention relates to a compact imaging lens having good optical characteristics suitable for a small-sized imaging device using a solid-state imaging device such as a high-pixel CCD or CMOS, an optical sensor, a portable module camera, or a WEB camera.

  In recent years, various imaging devices using a solid-state imaging device such as a CCD or a CMOS have been widely used. As these image sensors become higher in performance and smaller in size, an image pickup lens used in an image pickup apparatus is required to be more compact and have better optical characteristics than before.

  Conventionally, an imaging lens having a single lens structure or a double lens structure has been proposed for downsizing and weight reduction of the imaging lens. However, these lens systems are advantageous for miniaturization and weight reduction, but are insufficient for high performance such as high image quality and high resolution required for the imaging lens.

  Therefore, technological development of an imaging lens corresponding to a high image quality and a high resolution by a three-lens configuration has been advanced, and imaging lens systems having various configurations have been proposed. For example, in order from the object side, an aperture, a first lens of a positive meniscus lens having a convex surface facing the object side, a second lens of a negative meniscus lens having a convex surface facing the image side, and a positive meniscus lens having a convex surface facing the object side Patent Documents 1 to 3 below disclose an imaging lens in which a third lens is arranged.

  The imaging lens disclosed in Patent Document 1 includes a first lens having a meniscus-shaped positive refractive power with a convex surface facing the object side, and a second lens having a negative meniscus-shaped refractive power having a concave surface facing the object side. The lens includes a meniscus third lens having a positive refractive power with the convex surface facing the object side. The image side surface of the first lens has a relatively gentle radius of curvature with a convex surface facing the object side, or a shape with a concave surface facing the object side. Therefore, the front principal point position of the first lens is close to the image plane side, and there is a limit to shortening the optical length, which is insufficient in terms of compactness.

  In the imaging lens disclosed in Patent Document 2, the first lens is a planoconvex or positive meniscus lens having a convex surface facing the object side, the second lens has at least one refracting surface aspherical, and A negative meniscus lens having a convex surface, and the third lens is a positive meniscus lens having at least one refracting surface having an aspherical shape and a convex surface facing the object side. The image side surface of the first lens has a planar shape or a shape having a relatively loose radius of curvature with a convex surface directed toward the object side. Therefore, like the imaging lens of Patent Document 1, it is insufficient in terms of compactness.

  In the imaging lens disclosed in Patent Document 3, the first lens is a meniscus lens having a convex surface on the object side and having a positive refractive power, and the second lens is a meniscus lens having a concave surface on the object side and having a negative refractive power. The third lens is a meniscus lens having a convex surface on the object side and a positive refractive power. The second lens has a strong negative power (the reciprocal of the focal length), and the core thickness of the second lens occupies the entire length of the lens. Therefore, it becomes difficult to correct spherical aberration and curvature of field as the lens becomes compact, and it is compact. It was insufficient to obtain good optical properties.

JP 2005-345919 A JP 2006-106321 A JP 2006-133270 A

  The present invention has been made in order to solve the above-described problems of the conventional example. In order from the object side, the aperture, the first lens of a positive meniscus lens having a convex surface directed toward the object side, and the negative lens having a convex surface directed toward the image side. An object of the present invention is to provide a compact imaging lens having good optical characteristics in an imaging lens in which a second lens of a meniscus lens and a third lens of a positive meniscus lens having a convex surface directed toward the object side are arranged.

In order to achieve the above object, the invention of claim 1 comprises, in order from the object side, an aperture, a first lens of a positive meniscus lens having a convex surface facing the object side, and a second lens of a negative meniscus lens having a convex surface facing the image side. A third lens of a positive meniscus lens having a convex surface facing the object side,
0.22 <R1 / R2 <0.50 (1)
0.02 <d3 / | f2 | <0.12 (2)
However,
R1: radius of curvature of object side surface of first lens R2: radius of curvature of image side surface of first lens f2: focal length of second lens d3: condition of core thickness of second lens is satisfied.

The invention of claim 2 is the imaging lens of claim 1,
The refractive index at the d-line of the first lens is n1,
n1> 1.53 (3)
It satisfies the following conditions.

  According to the first aspect of the present invention, in order from the object side, the stop, the first lens of the positive meniscus lens having the convex surface facing the object side, the second lens of the negative meniscus lens having the convex surface facing the image side, the convex surface toward the object side By arranging the third lens of the positive meniscus lens facing, and satisfying conditional expressions (1) and (2), a compact imaging lens having good optical characteristics can be obtained.

  According to the second aspect of the present invention, the imaging lens is compact and has good aberrations corrected by satisfying the condition of n1> 1.53, where n1 is the refractive index of the first lens at the d-line. It becomes easy to get.

  Embodiments of an imaging lens according to the present invention will be described with reference to the drawings. A configuration diagram of an imaging lens according to an embodiment of the present invention is shown in FIG. The imaging lens LA is a three-lens lens system in which an aperture S1, a first lens L1, a second lens L2, and a third lens L3 are arranged in order from the object (not shown) side toward the image plane. . A glass flat plate GF is disposed between the third lens L3 and the image plane. As this glass flat plate GF, what has functions, such as a cover glass, IR cut filter, or a low pass filter, can be used.

  By disposing the stop S1 on the object side of the first lens, the entrance pupil position can be set at a position far from the image plane. As a result, high telecentricity can be ensured, and the incident angle with respect to the image plane can be made suitable.

  The first lens L1 is a positive meniscus lens having a convex surface facing the object side, the second lens L2 is a negative meniscus lens having a convex surface facing the image side, and the third lens has a convex surface facing the object side. It is a positive meniscus lens. The lens surfaces of these three lenses can suitably correct various aberrations by forming one or more surfaces into an aspherical shape, and preferably both surfaces into an aspherical shape.

In order from the object side, stop S1, first lens L1 of a positive meniscus lens having a convex surface directed toward the object side, second lens L2 of a negative meniscus lens having a convex surface directed toward the image side, and a positive meniscus lens having a convex surface directed toward the object side The third lens L3 is disposed, and the following conditional expressions (1) and (2), more preferably, the conditional expressions (1-A) and (2-A) are satisfied. An imaging lens having optical characteristics can be obtained.
0.22 <R1 / R2 <0.50 (1)
0.30 <R1 / R2 <0.50 (1-A)
0.02 <d3 / | f2 | <0.12 (2)
0.02 <d3 / | f2 | <0.10 (2-A)

  Conditional expressions (1) and (1-A) are conditional expressions regarding the meniscus degree of the first lens L1. If the value of R1 / R2 exceeds the upper limit of conditional expression (1), it may be difficult to correct distortion. On the other hand, if the lower limit is not reached, the meniscus degree becomes loose, so the front principal point position of the first lens may approach the image plane and the optical length may become long, which is not preferable in terms of downsizing the imaging lens.

  Conditional expressions (2) and (2-A) are conditional expressions concerning the focal length and the core thickness of the second lens L2. If the value of d3 / | f2 | is less than the lower limit of the conditional expression (2), it is easy to make it compact, but the core thickness of the second lens L2 becomes too thin, and it may be difficult to manufacture. On the other hand, if the upper limit is exceeded, the core thickness of the second lens L2 becomes large and the manufacture becomes easy, but it is difficult to correct spherical aberration and curvature of field, and the optical length may become long, which is not preferable. . Accordingly, it is difficult to obtain a compact imaging lens having good optical characteristics outside the range of the conditional expressions (1) and (2).

By making the refractive index n1 of the d-line of the first lens L1 occupying the imaging lens LA in the range of the following conditional expression (3), it becomes easy to obtain a compact imaging lens having good optical characteristics.
n1> 1.53 (3)
If the value of n1 is 1.53 or less, it may be difficult to correct aberrations with downsizing.

  The power distribution of the first lens L1, the second lens L2, and the third lens L3 of the imaging lens LA is as follows: the focal length f1 of the first lens L1, the focal length f2 of the second lens L2, and the focal length f3 of the third lens L3. Then, it is preferable that the value of f1 / | f2 | is in the range of 0.20 to 0.87 and the value of f1 / f3 is in the range of 0.15 to 0.80. By setting the value of f1 / | f2 | and the value of f1 / f3 in the above ranges, it is easy to obtain a compact imaging lens having good optical characteristics.

  The first lens L1 to the third lens L3 are each formed of glass or a resin material, but are preferably formed of a resin material from the viewpoint of productivity. As the resin material used for the first lens L1, a resin material having a d-line refractive index in the range of 1.53 to 1.64 measured according to the ASTM D542 method is used. The resin material may be a thermoplastic resin or a thermosetting resin as long as the light transmittance in the wavelength range of 450 to 600 nm is 80% or more, more preferably 85% or more. Good.

  Specific examples of the resin material used in the first lens L1 include a non-crystalline polyolefin-based resin, a polystyrene-based resin, a polycarbonate-based resin, 9,9-bis (4- Examples thereof include highly transparent polyester-based resins, epoxy-based resins, silicon-based resins, and the like including structures such as hydroxynphenyl) fluorene. Among these, polyolefins containing cycloolefin and polyolefins containing cyclic olefin are preferable. When a resin material is used as the lens material, the lens can be manufactured using a known molding method such as injection molding, compression molding, cast molding, transfer molding, or the like.

  As the resin material used for the second lens L2 and the third lens L3, those having a refractive index of d-line measured in accordance with ASTM D542 method in the range of 1.49 to 1.64 are used. The resin material may be a thermoplastic resin or a thermosetting resin as long as the light transmittance in the wavelength range of 450 to 600 nm is 80% or more, more preferably 85% or more. Good.

  Specific examples of the resin material used in the second lens L2 and the third lens L3 include a non-crystalline polyolefin resin, polystyrene resin, acrylic resin, and polycarbonate resin having a cyclo ring and other ring structures. , 9,9-bis (4-hydroxylphenyl) fluorene, and other highly transparent polyester resins, epoxy resins, and silicon resins. Among these, polyolefin containing cycloolefin, polyolefin containing cyclic olefin, and polycarbonate resin are preferable. When a resin material is used as the lens material, the lens can be manufactured using a known molding method such as injection molding, compression molding, cast molding, transfer molding, or the like.

  When the lens is manufactured from a resin material, an edge can be provided on the outer periphery of each of the first lens L1, the second lens L2, and the third lens L3. The edge shape is not particularly limited as long as the performance of the lens is not impaired. From the viewpoint of lens moldability, the edge thickness is preferably in the range of 70 to 130% of the thickness of the outer periphery of the lens. When the edge is provided on the outer peripheral portion of the lens, if light enters the edge portion, it may cause ghost or flare. In that case, a light-emitting mask that restricts incident light may be provided between the lenses as necessary.

    The imaging lens LA is a known surface treatment such as antireflection or surface hardening on the object-side and image-side lens surfaces of the first lens L1, the second lens L2, and the third lens L3 before being used in an imaging module. May be applied. The imaging module using the imaging lens LA is used for a portable module camera, a WEB camera, a personal computer, a digital camera, an optical sensor of an automobile or various industrial devices, a monitor, and the like.

Hereinafter, specific examples of the imaging lens LA of the present invention will be described. The symbols described in each example indicate the following. The unit of distance is mm.
f: focal length f1 of the imaging lens LA: focal length f2 of the first lens L1: focal length f3 of the second lens L2: focal length Fno of the third lens L3: F number S1: aperture R: radius of curvature of the optical surface In the case of a lens, the center radius of curvature R1: the radius of curvature R2 of the object side surface of the first lens L1: the radius of curvature R3 of the image side surface of the first lens L1: the radius of curvature R4 of the object side surface of the second lens L2: the second lens L2 Radius of curvature R5 of the object side surface of the third lens L3: radius of curvature R6 of the image side surface of the third lens L3: radius of curvature R7 of the object side surface of the glass plate GF: radius of curvature R8 of the object side surface of the glass plate GF Curvature radius d: Lens thickness or inter-lens distance d1: Core thickness d2 of the first lens L1: Distance between the image plane side of the first lens L1 and the object side surface of the second lens L2 d3: Core of the second lens L2 Thickness d4: Distance between image plane side of second lens L2 and object side surface of third lens L3 d5: Core thickness of third lens L3 d6: Distance between image plane side of third lens L3 and object side surface of glass flat plate GF Distance d7: Thickness of glass flat plate GF nd: Refractive index n1 of d line: Refractive index n2 of first lens L1: Refractive index n3 of second lens L2: Refractive index νd of third lens L3: Abbe number at d line ν1: Abbe number of the first lens ν2: Abbe number of the second lens ν3: Abbe number of the third lens ν4: Abbe number of the glass plate GF

  The aspheric shapes of the lens surfaces of the first lens L1, the second lens L2, and the third lens L3 of the imaging lens LA are such that y is an optical axis with the light traveling direction as positive and x is orthogonal to the optical axis. The direction axis is represented by the following aspheric polynomial (4).

y = (x ² / R) / [1+ {1− (k + 1) (x / R ² } ^1/2 ]
+ A4x ⁴ + A6x ⁶ + A8x ⁸ + A10. x10 ^.
+ A12x ¹² + A14x ¹⁴ + A16x ¹⁶ (4)
Here, R is a radius of curvature on the optical axis, k is a conical coefficient, and A4, A6, A8, A10, A12, A14, and A16 are aspherical coefficients.

  As an aspheric surface of each lens surface, an aspheric surface represented by the above formula (4) is used for convenience. However, the present invention is not particularly limited to the aspheric polynomial of the formula (4).

(Example 1)
The arrangement and configuration of the imaging lens of Example 1 are shown in FIG. Curvature radius R, refractive index nd, Abbe number νd, lens thickness or the object side and image plane side of each of first lens L1, second lens L2, and third lens L3 constituting imaging lens LA of Example 1 Table 1 shows values such as the distance d between the lenses, the conical coefficient k, and the aspheric coefficient.

Under these conditions, Fno = 3.2, f = 2.999 mm, f1 = 2.617 mm,
f2 = −6.049 mm, f3 = 9.342 mm, n1 = 1.544,
R1 / R2 = 0.439, d3 / | f2 | = 0.051, f1 / | f2 | = 0.433,
f1 / f3 = 0.28.

  The spherical aberration of the imaging lens of Example 1 is shown in FIG. 3, and astigmatism and distortion are shown in FIG. From the above results, it can be seen that the imaging lens LA of Example 1 is compact and has good optical characteristics. In addition, in the spherical aberration, it is an aberration result with respect to three wavelengths of 486 nm, 588 nm, and 656 nm, and in the drawing, the aberrations are 486 nm, 588 nm, and 656 nm in order from the left. Astigmatism and distortion are aberration results at a wavelength of 588 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface.

(Example 2)
The arrangement and configuration of the imaging lens of Example 2 are shown in FIG. The radius of curvature R, the refractive index nd, the Abbe number νd, the thickness of the lens or the object side and the image plane side of the first lens L1, the second lens L2, and the third lens L3 constituting the imaging lens LA of the second embodiment. Table 2 shows values such as the distance d between the lenses, the conical coefficient k, and the aspheric coefficient.

Under these conditions, Fno = 3.2, f = 3.010 mm, f1 = 2.613 mm,
f2 = −6.492 mm, f3 = 10.571 mm, n1 = 1.544,
R1 / R2 = 0.274, d3 / | f2 | = 0.052, f1 / | f2 | = 0.402,
f1 / f3 = 0.247.

  The spherical aberration of the imaging lens of Example 2 is shown in FIG. 6, and astigmatism and distortion are shown in FIG. From the above results, it can be seen that the imaging lens LA of Example 2 is compact and has good optical characteristics. In addition, in the spherical aberration, it is an aberration result with respect to three wavelengths of 486 nm, 588 nm, and 656 nm, and in the drawing, the aberrations are 486 nm, 588 nm, and 656 nm in order from the left. Astigmatism and distortion are aberration results at a wavelength of 588 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface.

(Example 3)
The arrangement and configuration of the imaging lens of Example 3 are shown in FIG. Curvature radius R, refractive index nd, Abbe number νd, lens thickness of each of the first lens L1, the second lens L2, and the third lens L3 constituting the imaging lens LA of Example 3 Table 3 shows values such as the distance d between the lenses, the conical coefficient k, and the aspheric coefficient.

Under these conditions, Fno = 3.2, f = 2.748 mm, f1 = 2.569 mm,
f2 = −7.550 mm, f3 = 9.950 mm, n1 = 1.544,
R1 / R2 = 0.317, d3 / | f2 | = 0.034, f1 / | f2 | = 0.340,
f1 / f3 = 0.258.

  The spherical aberration of the image pickup lens of Example 3 is shown in FIG. 9, and astigmatism and distortion are shown in FIG. From the above results, it can be seen that the imaging lens LA of Example 3 is compact and has good optical characteristics. In addition, in the spherical aberration, it is an aberration result with respect to three wavelengths of 486 nm, 588 nm, and 656 nm, and in the drawing, the aberrations are 486 nm, 588 nm, and 656 nm in order from the left. Astigmatism and distortion are aberration results at a wavelength of 588 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface.

Example 4
The arrangement and configuration of the imaging lens of Example 4 are shown in FIG. Curvature radius R, refractive index nd, Abbe number νd, lens thickness of each of the first lens L1, second lens L2, and third lens L3 constituting the imaging lens LA of Example 4 on the object side and the image plane side Table 4 shows values such as the distance d between the lenses, the conical coefficient k, and the aspheric coefficient.

Under these conditions, Fno = 3.2, f = 2.364 mm, f1 = 1.742 mm,
f2 = −3.030 mm, f3 = 7.600 mm, n1 = 1.544,
R1 / R2 = 0.233, d3 / | f2 | = 0.099, f1 / | f2 | = 0.575,
f1 / f3 = 0.229.

  The spherical aberration of the imaging lens of Example 4 is shown in FIG. 12, and astigmatism and distortion are shown in FIG. From the above results, it can be seen that the imaging lens LA of Example 4 is compact and has good optical characteristics. In addition, in the spherical aberration, it is an aberration result with respect to three wavelengths of 486 nm, 588 nm, and 656 nm, and in the drawing, the aberrations are 486 nm, 588 nm, and 656 nm in order from the left. Astigmatism and distortion are aberration results at a wavelength of 588 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface.

The figure which shows the structure of the imaging lens which concerns on-embodiment of this invention. The figure which shows the structure of the specific Example 1 of the said imaging lens. FIG. 3 is a spherical aberration diagram of the imaging lens of Example 1. FIG. 3 is an astigmatism diagram and a distortion diagram of the imaging lens of Example 1. The figure which shows the structure of the specific Example 2 of the said imaging lens. FIG. 6 is a spherical aberration diagram of the imaging lens of Example 2. FIG. 6 is an astigmatism diagram and a distortion diagram of the imaging lens of Example 2. The figure which shows the structure of the specific Example 3 of the said imaging lens. FIG. 6 is a spherical aberration diagram of the imaging lens of Example 3. FIG. 6 is an astigmatism diagram and a distortion diagram of the imaging lens of Example 3. The figure which shows the structure of the specific Example 4 of the said imaging lens. FIG. 6 is a spherical aberration diagram of the imaging lens of Example 4. FIG. 6 is an astigmatism diagram and a distortion diagram of the imaging lens of Example 4.

LA: Imaging lens S1: Diaphragm L1: First lens L2: Second lens L3: Third lens GF: Glass flat plate R: Radius of curvature of optical surface, central radius of curvature R1 for lens: Object side surface of first lens L1 Radius of curvature R2: radius of curvature R3 of the image side surface of the first lens L1: radius of curvature R4 of the object side surface of the second lens L2: radius of curvature R5 of the image side surface of the second lens L2: curvature of the object side surface of the third lens L3 Radius R6: Radius of curvature of image side surface of third lens L3 R7: Radius of curvature of object side surface of glass flat plate GF R8: Radius of curvature of image side surface of glass flat plate GF d1: Core thickness d2 of first lens L1: First lens L1 Distance d3 between the image surface side of the second lens L2 and the object side surface of the second lens L2: core thickness d4 of the second lens L2: distance d5 between the image surface side of the second lens L2 and the object side surface of the third lens L3: third lens L3 core thickness 6: the distance between the image side and the object side surface of the glass plate GF of the third lens L3 d7: thickness of the glass plate GF

Claims (2)

In order from the object side, a stop, a first lens of a positive meniscus lens having a convex surface facing the object side, a second lens of a negative meniscus lens having a convex surface facing the image side, and a third of a positive meniscus lens having a convex surface facing the object side Place the lens,
0.22 <R1 / R2 <0.50 (1)
0.02 <d3 / | f2 | <0.12 (2)
However,
R1: radius of curvature of object side surface of first lens R2: radius of curvature of image side surface of first lens f2: focal length of second lens d3: imaging lens satisfying condition of core thickness of second lens . The refractive index at the d-line of the first lens is n1,
n1> 1.53 (3)
The imaging lens according to claim 1, wherein the following condition is satisfied.

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