JP4361120B2 - Imaging lens - Google Patents

Description

  The present invention relates to an imaging lens, and more particularly to an imaging lens suitable for a compact imaging device, a photosensor, a portable module camera, a WEB camera, and the like using a solid-state imaging device such as a high pixel CCD or CMOS.

  In recent years, various imaging devices using solid-state imaging devices such as CCD and CMOS have been widely used. As these imaging elements become smaller and higher in performance, imaging lenses used in imaging devices are required to be small, lightweight, and have high performance optical characteristics.

  Conventionally, a single lens system or a double lens system has been proposed for downsizing and weight reduction of an imaging lens. However, these lens systems are advantageous in reducing the size and weight, but it is well known that it is difficult to correct aberrations such as field curvature and that good optical characteristics cannot be expected. Therefore, in order to obtain an imaging lens having good high-performance optical characteristics, it is necessary to be composed of three or more lenses.

  However, even in the case of a three-lens imaging lens system, when used in a high pixel CCD, for example, a high pixel CCD having 2 million pixels or more, even if all three lenses are aspherical, the peripheral aberration correction is possible. It may be insufficient. Therefore, technical development relating to an imaging lens composed of four lenses that facilitates correction of various aberrations and obtains good optical characteristics from three-lens has been advanced, and imaging lenses having various four-lens configurations. Proposals have been made.

  In Patent Document 1, in order from the object side, a diaphragm, a first biconvex lens having positive power, a second biconcave lens having negative power, and a convex surface facing the image side having positive power In addition, there has been proposed an imaging lens in which a third lens and a fourth lens having a convex surface facing an object surface having negative power are arranged. According to this method, the power of the first lens and the second lens is strongly designed to reduce the size of the imaging lens. However, since a high-refractive-index lens is used as the second lens, it may be difficult to balance the power balance with other lenses, and it is difficult to shorten the focal length of the entire imaging lens and to correct aberrations. Sometimes it was enough.

  In Patent Document 2, in order from the object side, a diaphragm, a first biconvex lens having a positive power, a second biconcave lens having a negative power, and a convex surface facing an image side having a positive power. An imaging lens has been proposed in which a third lens and a fourth lens having a convex surface facing an object surface having negative power are arranged. According to this method, the power of the first lens and the second lens is strongly designed in order to reduce the size of the imaging lens. However, since the refractive index of the second lens is relatively small, it may be difficult to distribute the power of the entire imaging lens, and the focal length of the entire imaging lens may be shortened and aberration correction may be insufficient. It was.

  In Patent Document 3, a first lens group having a positive power, a second lens group having a negative power, a third lens having a positive or negative power, and a fourth lens having a positive or negative power are disclosed. An imaging lens including the above is disclosed. According to this method, since a high refractive index lens is used as the second lens, it may be difficult to balance the power with other lenses, particularly the first lens. Therefore, there is a problem that it is difficult to obtain an imaging lens that achieves both downsizing of the imaging lens and good optical characteristics. In the embodiments, an imaging lens in which a thin film filter or an optical filter for limiting a part of light between lens groups is incorporated is disclosed. These also have the problem that the number of parts of the imaging lens increases and the number of production steps increases.

JP 2002-365529 A Japanese Patent Laid-Open No. 2002-365531 JP 2007-17984 A

  An object of the present invention is to provide an imaging lens composed of four miniaturized lenses having good optical characteristics in which various aberrations are suitably corrected.

  In order to achieve the above object, the power balance of the first lens and the second lens, and the ratio of the focal length and the center thickness of the first lens, the third lens, and the fourth lens to the size and optical characteristics of the imaging lens are studied As a result, the present inventors have found that an imaging lens in which the problems of the prior art are improved can be obtained.

An imaging lens according to a first aspect of the present invention includes, in order from the object side, a stop, a first lens having a positive power in a biconvex shape, a second lens having a meniscus shape having a negative power with a convex surface facing the object side, and an image A meniscus third lens having a positive power with a convex surface facing the side and a meniscus fourth lens having a negative power with a convex power facing the object side are disposed, and the following conditional expression is satisfied: An imaging lens.
−0.95 <f1 / f2 ≦ −0.65 (1)
4.00 <f1 / d1 <10.00 (2)
2.80 <f3 / d5 <5.20 (3)
−10.00 <f4 / d7 ≦ −5.98 (4)
−0.45 <R1 / R2 <−0.05 (5)
2.50 <R3 / R4 <10.00 (6)
However,
f1: focal length of the first lens,
f2: focal length of the second lens,
f3: focal length of the third lens,
f4: focal length of the fourth lens,
d1: Center thickness of the first lens,
d5: center thickness of the third lens,
d7: center thickness of the fourth lens,
R1: radius of curvature of the side surface of the first lens object
R2: radius of curvature of the first lens image side surface
R3: radius of curvature of the second lens object side surface
R4: radius of curvature of the second lens image side surface .

  In the imaging lens according to the first aspect of the present invention, the entrance pupil position can be set at a position far from the image plane by disposing the stop closer to the object side than the first lens, and the incident angle with respect to the image plane is optimized. . In addition, the four lenses constituting the imaging lens have a specific surface shape, the lens power array is positive, negative, positive, and negative, and the power distribution between the first lens and the second lens, the first lens, and the third lens By setting the relationship between the focal length of each of the lens and the fourth lens and the center thickness of the lens within a specific range, various aberrations are preferably corrected, and an imaging lens having favorable optical characteristics and a reduced size is obtained. be able to. The power described in the present invention is a value represented by the reciprocal of the focal length.

Furthermore, in the first aspect of the invention, the power balance of both lenses is optimized by setting the shape of the first lens and the second lens within a specific range. Thereby, downsizing of the imaging lens becomes more advantageous.

  The imaging lens obtained by the present invention contributes to high functionality, high performance, and miniaturization of various digital input devices such as mobile phones.

  An embodiment of an imaging lens according to the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an imaging lens according to an embodiment of the present invention. The imaging lens LA has a four-lens configuration in which an aperture S1, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 are arranged in order from the object (not shown) side toward the image plane. Lens system. A glass flat plate GF is disposed between the fourth lens L4 and the image plane. As this glass flat plate GF, a glass having a function such as a cover glass, an IR cut filter, or a low-pass filter can be used.

  By disposing the stop S1 on the object side of the first lens L1, the entrance pupil position can be located 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 biconvex lens having a positive power, the second lens L2 is a meniscus negative lens having a convex surface directed toward the object side, and the third lens L3 is an image side. The fourth lens L4 is a meniscus lens having a negative power with a convex surface facing the object side. In order to reduce the size of the imaging lens LA, the first lens L1 and the second lens L2 are arranged with a large power as a so-called telephoto type in which the lens power array is positive, negative, positive, or negative. As a result, the imaging lens LA is miniaturized, and various on-axis aberrations are mainly corrected. Off-axis aberrations are mainly corrected by the third lens L3 and the fourth lens L4. . The surfaces of these four lenses are preferably aspherical on the entire surface in order to more appropriately correct various aberrations.

  The roles of the first lens L1 and the second lens L2 with respect to correction of aberrations such as downsizing and chromatic aberration of the imaging lens LA are important. When downsizing the imaging lens LA, increasing the positive power of the first lens L1 is advantageous for downsizing the imaging lens LA because the main point is on the object side. However, if the power of the first lens L1 becomes too large, high-order aberrations are likely to occur, and it becomes difficult to balance the power with other lenses, making it difficult to correct aberrations. In the present invention, the first lens L1 is a positive power biconvex lens. Since the biconvex lens has a converging function on both sides, even if a relatively large positive power is applied to the first lens L1, it is possible to suppress the occurrence of high-order aberrations, and the principal point of the optical system is the object side. Therefore, it is easy to reduce the size of the imaging lens.

  The second lens L2 is designed to control the positive power of the first lens L1 and reduce the power load on the third and fourth lenses. The second lens L2 has a meniscus shape having a negative power with the convex surface facing the object side in consideration of the balance with the large positive power of the first lens L1. By making the second lens L2 a meniscus shape having a convex surface toward the object side, a converging action on one surface, and a diverging action on the other surface, it becomes easy to optimize the power balance with the first lens L1, Aberration correction is easy.

The first lens L1 and the second lens L2 have the above-described shape and power arrangement, and the relationship between the focal length f1 of the first lens L1 and the focal length f2 of the second lens L2 is in the range of the conditional expression (1). It is preferable. The relationship between the focal length f1 of the first lens L1 and the center thickness d1 is preferably in the range of conditional expression (2). These conditional expressions optimize the balance of the power of the first lens L1 and the second lens L2, correct the axial aberration including the axial chromatic aberration, and relate to the downsizing of the imaging lens LA. Outside the range of conditional expression (1) or (2), it may be difficult to reduce the size of the imaging lens LA.
−0.95 <f1 / f2 ≦ −0.65 (1)
4.00 <f1 / d1 <10.00 (2)
However,
f1: focal length of the first lens,
f2: focal length of the second lens,
d1: Center thickness of the first lens,
It is.

  The third lens L3 bears the positive power of the imaging lens LA of the present invention together with the first lens L1. In order to reduce the size, the first lens L1 is designed with a strong positive power. If the power of the first lens L1 is too strong, it becomes difficult to correct various aberrations. Therefore, the third lens L3 is designed to control that the power of the first lens L1 becomes excessive. In the third lens L3, it is necessary to perform off-axis aberration correction that is difficult to be corrected by the first lens L1 and the second lens L2. Accordingly, the third lens L3 is a meniscus lens having a relatively weak positive power with a convex surface facing the image side. By taking this shape, the third lens L3 optimizes the power of the first lens L1 and, in combination with the fourth lens L4, mainly enables off-axis aberration correction.

The relationship between the focal length f3 of the third lens L3 and the center thickness d5 is preferably in the range of conditional expression (3). By satisfying this range, various aberrations including off-axis chromatic aberration can be corrected by downsizing the imaging lens LA.
2.80 <f3 / d5 <5.20 (3)
However,
f3: focal length of the third lens L3,
d5: Center thickness of the third lens L3.

  The fourth lens L4 bears the negative power of the imaging lens LA of the present invention together with the second lens L2. Since the positive power of the first lens L1 is relatively strong, the power of the second lens L2 tends to increase inevitably. If the power of the second lens L2 becomes too strong, it becomes difficult to balance the power of the entire imaging lens LA, and it becomes difficult to obtain a good imaging lens LA. Therefore, the fourth lens L4 optimizes the power balance with the second lens L2 as a lens having a relatively weak negative power with a meniscus shape having a convex surface directed toward the object side.

The relationship between the focal length f4 of the fourth lens L4 and the center thickness d7 is preferably in the range of conditional expression (4). By satisfying this range, the imaging lens LA can be downsized, various aberrations including off-axis chromatic aberration can be corrected, and the incident angle with respect to the image plane can be made suitable.
−10.00 <f4 / d7 ≦ −5.98 (4)
However,
f4: focal length of the fourth lens,
d7: center thickness of the fourth lens,
It is.

The relationship between the radius of curvature of the object side surface and the image side surface of the first lens L1 is preferably in the range of the conditional expression (5). Outside the range of conditional expression (5), it may be difficult to correct high-order aberrations associated with downsizing of the imaging lens LA. −0.45 <R1 / R2 <−0.05 (5)
R1: radius of curvature of the first lens object side surface R2: radius of curvature of the first lens image side surface.

The relationship between the radius of curvature of the object side surface and the image side surface of the second lens L2 is preferably in the range of conditional expression (6). Outside the range of the conditional expression (6), it is difficult to control the power of the second lens L2 with the downsizing of the imaging lens LA, and the correction of axial chromatic aberration may be insufficient.
2.50 <R3 / R4 <10.00 (6)
However,
R3: radius of curvature of the second lens object side surface R4: radius of curvature of the second lens image side surface.

  When the four lenses constituting the imaging lens LA satisfy the above-described configuration and conditional expressions, respectively, it is possible to obtain a small imaging lens having good optical characteristics with various aberrations corrected.

  The first lens L1 to the fourth lens L4 are made of either glass or resin. When glass is used as the lens material, it is preferable to use a glass material having a glass transition temperature of 400 ° C. or lower. Thereby, it becomes possible to improve the durability of the mold.

  A resin material can efficiently manufacture a lens having a complicated surface shape, and is more preferable than a glass material in terms of productivity. When a resin material is used as the lens material, the light transmittance in the range of the refractive index of d-line measured in accordance with ASTM D542 method is 1.500 to 1.650 and the wavelength is 450 to 600 nm. If the resin material is 80% or more, more preferably 85% or more, either a thermoplastic resin or a thermosetting resin can be used. The first lens L1, the third lens L3, and the fourth lens L4 may be the same resin material or different materials. For the second lens L2, a resin material different from that of the first lens L1 is usually used. A lens made of a resin material can be manufactured by a known molding method such as injection molding, compression molding, cast molding, transfer molding, or the like. Hereinafter, specific examples of resins used for the first lens L1 to the fourth lens L4 are shown.

  A commercially available transparent resin can be used for the first lens L1, and the refractive index n1 of the d-line measured according to the ASTM D542 method is 1.500 to 1.600, and the Abbe number υ1 is 50.0 to A 60.0 transparent resin is used. Specific examples of the transparent resin that is preferably used include a non-crystalline polyolefin resin, a polycarbonate resin, and an epoxy resin having a cyclo ring and other cyclic structures.

  A commercially available transparent resin can be used for the second lens L2, and the refractive index n2 of the d-line measured according to the ASTM D542 method is 1.580 to 1.650, the Abbe number υ2 is 20. A transparent resin of 0 to 35.0 is preferably used. Specific examples of transparent resins that are preferably used include polyester resins containing structures such as 9,9-bis (4-hydroxylphenyl) fluorene, special polycarbonates (SP series, manufactured by Teijin), epoxy resins, heat Examples include curable resins.

  A commercially available transparent resin can be used for the third lens L3. The refractive index n3 of the d-line measured according to the ASTM D542 method is 1.500 to 1.650, and the Abbe number υ3 is 50.0 to A 60.0 transparent resin is used. Specific examples of the transparent resin preferably used include a non-crystalline polyolefin resin, a polystyrene resin, a polycarbonate resin, and an epoxy resin having a cyclo ring and other cyclic structures.

  A commercially available transparent resin can be used for the fourth lens L4. The refractive index n4 of the d-line measured according to the ASTM D542 method is 1.500 to 1.650, and the Abbe number υ4 is 20.0. A transparent resin of ˜60.0 is preferably used. Specific examples of the resin preferably used include a non-crystalline polyolefin resin having a cyclo ring or other cyclic structure, a polystyrene resin, a polycarbonate resin, or 9,9-bis (4-hydroxynephenyl) fluorene. Polyester resins including such structures, special polycarbonate (SP series, manufactured by Teijin) epoxy resins, silicon resins and the like.

  It is well known that the refractive index of a resin material varies with temperature. In order to suppress this variation, the resin material having transparency described above in which fine particles such as silica, niobium oxide, titanium oxide, and aluminum oxide having an average particle diameter of 100 nm or less, more preferably 50 nm or less are dispersed and mixed is used as a lens material. be able to.

  The first lens L1 to the fourth lens L4 made of resin can be provided with edges and ribs on the outer periphery of the lens. The shape of the edge and rib 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 for limiting incident light can be provided between the lenses as necessary.

  Before the imaging lens LA is used in an imaging module or the like, an antireflection film, an IR cut film, or a surface hardening is applied to the object-side and image-side lens surfaces of the first lens L1 to the fourth lens L4. For example, a known process may be performed. The imaging module using the imaging lens LA of the present invention is used for a portable module camera, a WEB camera, a personal computer, a digital camera, a photo sensor, a monitor, and the like of automobiles and various industrial devices.

Hereinafter, the imaging lens LA of the present invention will be described using examples and comparative examples. Symbols described in each example and comparative example indicate the following. The unit of distance, radius, and center thickness is mm.
f: focal length of the entire imaging lens LA f1: focal length f2 of the first lens L1: focal length f3 of the second lens L2: focal length f4 of the third lens L3: focal length Fno of the fourth lens L4: F number S1 : Diaphragm R: Radius of curvature of optical surface, center radius of curvature R1 in the case of lens: Curvature radius of object side R2 of first lens L1: Radius of curvature R3 of image side of first lens L1: Object side of second lens L2 Radius of curvature R4: radius of curvature R5 of the image side surface of the second lens L2: radius of curvature R6 of the object side surface of the third lens L3: radius of curvature R7 of the image side surface of the third lens L3: curvature of the object side surface of the fourth lens L4 Radius R8: Radius of curvature of image side surface of fourth lens L4 R9: Radius of curvature of object side surface of glass flat plate GL R10: Radius of curvature of image side surface of glass flat plate GL d: Lens thickness or inter-lens distance d 1: Center thickness d2 of the first lens L1: Distance d3 between the image plane side of the first lens L1 and the object side surface of the second lens L2: Center thickness d4 of the second lens L2: Image plane of the second lens L2 Distance d5 between the lens side and the object side surface of the third lens L3: center thickness d6 of the third lens L3: distance d7 between the image surface side of the third lens L3 and the object side surface of the fourth lens d4: fourth lens Center thickness d8 of L4: Distance between the image plane side of the fourth lens L4 and the object side surface of the glass flat plate GF d9: Center thickness of the glass flat plate GF nd: Refractive index of d-line n1: Refractive index of the first lens L1 n2: Refractive index n3 of the second lens L2: Refractive index n4 of the third lens L3: Refractive index νd of the fourth lens L4: Abbe number ν1 at d-line: Abbe number ν2 of the first lens L1: Second lens L2 Abbe number ν3: Abbe number ν4 of the third lens L3: Abbe number ν of the fourth lens L4 : Abbe number of the glass plate GF

  The aspherical shape of each lens surface of the first lens L1 to the fourth lens L4 of the imaging lens LA is such that y is an optical axis with the traveling direction of light as positive and x is a direction orthogonal to the optical axis. The following aspheric polynomial is used.

y = (x ² / R) / [1+ {1- (k + 1) (x / R ² )} ^1/2 ]
+ A4x ⁴ + A6x ⁶ + A8x ⁸ + A10x ¹⁰ + A12x ¹² (7)

  However, R is a radius of curvature on the optical axis, k is a conical coefficient, and A4, A6, A8, A10, and A12 are aspherical coefficients.

  As an aspheric surface of each lens surface, an aspheric surface represented by Expression (7) is used for convenience. However, the present invention is not particularly limited to the aspheric polynomial of the formula (7).

(Example 1)
FIG. 2 is a configuration diagram illustrating an arrangement of the imaging lens LA according to the first embodiment. The curvature radius r on the object side and the image plane side of each of the first lens L1 to the fourth lens L4 constituting the imaging lens LA of Example 1, the lens center thickness or the distance d between the lenses, the refractive index nd, and the Abbe number νd Table 1 shows the conical coefficient k and the aspheric coefficient.

  Under the conditions of Example 1, as shown in Table 9, the conditional expressions (1) to (6) are satisfied.

  The spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 1 is shown in FIG. 3, the lateral chromatic aberration is shown in FIG. 4, and astigmatism and distortion are shown in FIG. From the above results, the imaging lens LA of Example 1 has a four-lens configuration, but the focal length f of the imaging lens LA as a whole is short, downsized, and has good optical characteristics. Recognize. 3 to 5 show the aberration results for three wavelengths of 486 nm, 588 nm, and 656 nm. In each figure, the aberration results at a wavelength of 486 nm, a wavelength of 588 nm, and a wavelength of 656 nm are shown in order from the left. 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 measurement wavelength in the aberration diagram is the same in Examples 2 to 4.

(Example 2)
FIG. 6 is a configuration diagram illustrating the arrangement of the imaging lens LA according to the second embodiment. The object-side and image-plane curvature radii r, the lens center thickness or the distance d between the lenses, the refractive index nd, and the Abbe number νd of the first lens L1 to the fourth lens L4 constituting the imaging lens LA of Example 2. Table 3 shows the conical coefficient k and the aspheric coefficient.

  In the conditions of Example 2, as shown in Table 9, conditional expressions (1) to (6) are satisfied.

  The spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 2 is shown in FIG. 7, the lateral chromatic aberration is shown in FIG. 8, and astigmatism and distortion are shown in FIG. From the above results, the imaging lens LA of Example 2 has a four-lens configuration, but the focal length f of the imaging lens LA as a whole is short, downsized, and has good optical characteristics. Recognize.

( Example 3 )
FIG. 10 is a configuration diagram illustrating an arrangement of the imaging lens LA according to the third embodiment . The curvature radius r on the object side and the image plane side of each of the first lens L1 to the fourth lens L4 constituting the imaging lens LA of Example 3 , the lens center thickness or the distance d between the lenses, the refractive index nd, and the Abbe number νd Table 5 shows the conical coefficient k and the aspheric coefficient.

Under the conditions of Example 3, as shown in Table 9, conditional expressions (1) to (6) are satisfied.

FIG. 11 shows spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 3 , FIG. 12 shows chromatic aberration of magnification, and FIG. 13 shows astigmatism and distortion aberration. From the above results, the imaging lens LA of Example 3 has a four-lens configuration, but the focal length f of the imaging lens LA as a whole is short, downsized, and has good optical characteristics. Recognize.

( Example 4 )
FIG. 14 is a configuration diagram illustrating the arrangement of the imaging lens LA according to the fourth embodiment . The radius of curvature r on the object side and the image plane side of each of the first lens L1 to the fourth lens L4 constituting the imaging lens LA of Example 4 , the lens center thickness or the distance d between the lenses, the refractive index nd, and the Abbe number νd Is shown in Table 7, and the conic coefficient k and the aspheric coefficient are shown in Table 8.

In the conditions of Example 4, as shown in Table 9, conditional expressions (1) to (6) are satisfied.

FIG. 15 shows spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 4 , FIG. 16 shows chromatic aberration of magnification, and FIG. 17 shows astigmatism and distortion aberration. From the above results, the imaging lens LA of Example 4 has a four-lens configuration, but the focal length f of the imaging lens LA as a whole is short, downsized, and has good optical characteristics. Recognize.

  Table 9 shows values corresponding to various values of the numerical examples and parameters defined by the conditional expressions (1) to (6). The units of values shown in Table 9 are f (mm), f1 (mm), f2 (mm), f3 (mm), and f4 (mm).

The figure which shows the structure of the imaging lens LA which concerns on-embodiment of this invention. FIG. 3 is a diagram illustrating a configuration of a specific example 1 of the imaging lens LA. FIG. 4 is a spherical aberration (axial chromatic aberration) diagram of the imaging lens LA of Example 1. FIG. 3 is a chromatic aberration diagram of magnification of the imaging lens LA of Example 1. FIG. 2 is an astigmatism diagram and a distortion diagram of the imaging lens LA of Example 1. The figure which shows the structure of the specific Example 2 of the said imaging lens LA. FIG. 6 is a spherical aberration (axial chromatic aberration) diagram of the imaging lens LA of Example 2. FIG. 6 is a chromatic aberration diagram of magnification of the imaging lens LA of Example 2. FIG. 6 is an astigmatism diagram and a distortion diagram of the imaging lens LA of Example 2. FIG. 6 is a diagram illustrating a configuration of a specific example 3 of the imaging lens LA. FIG. 10 is a spherical aberration (axial chromatic aberration) diagram of the imaging lens LA of Example 3 . FIG. 4 is a chromatic aberration diagram of magnification of the imaging lens LA of Example 3 . FIG. 6 is an astigmatism diagram and a distortion diagram of the imaging lens LA of Example 3 . The figure which shows the structure of the specific Example 4 of the said imaging lens LA. FIG. 10 is a spherical aberration (axial chromatic aberration) diagram of the imaging lens LA of Example 4 . FIG. 7 is a chromatic aberration diagram of magnification of the imaging lens LA of Example 4 . FIG. 6 is an astigmatism diagram and a distortion diagram of the imaging lens LA of Example 4 .

Explanation of symbols

LA: Imaging lens
S1: Aperture L1: First lens L2: Second lens L3: Third lens L4: Fourth lens GF: Glass flat plate R1: Curvature radius R2 of the object side surface of the first lens L1: Curvature of the image side surface of the first lens L1 Radius R3: 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: radius of curvature R6 of the object side surface of the third lens L3: radius of curvature R7 of the image side surface of the third lens L3 : Radius of curvature R8 of the object side surface of the fourth lens L4: radius of curvature R9 of the image side surface of the fourth lens L4: radius of curvature R10 of the object side surface of the glass flat plate GF: radius of curvature d1 of the image side surface of the glass flat plate GF: first lens L1 center thickness d2: distance d3 between the image side surface of the first lens L1 and the object side surface of the second lens L2: center thickness d4 of the second lens L2: between the image side surface of the second lens L2 and the third lens L3 The side of the object Distance d5: center thickness d6 of the third lens L3: distance d7 between the image side surface of the third lens L3 and the object side surface of the fourth lens L4: center thickness d8 of the fourth lens L4: fourth lens L4 The distance d9 between the image side surface of the glass plate GF and the object side surface of the glass plate GF: the thickness d10 of the glass plate GF: the distance between the image side surface of the glass plate GF and the image surface

Claims (1)

In order from the object side, stop, first lens with positive power in biconvex shape, second lens with meniscus shape with negative power with convex surface facing object side, positive power with convex surface toward image side An imaging lens comprising: a third meniscus lens having a meniscus shape having a negative power with a convex surface directed toward the object side; and satisfying the following conditional expression:
−0.95 <f1 / f2 ≦ −0.65 (1)
4.00 <f1 / d1 <10.00 (2)
2.80 <f3 / d5 <5.20 (3)
−10.00 <f4 / d7 ≦ −5.98 (4)
−0.45 <R1 / R2 <−0.05 (5)
2.50 <R3 / R4 <10.00 (6)
However,
f1: focal length of the first lens,
f2: focal length of the second lens,
f3: focal length of the third lens,
f4: focal length of the fourth lens,
d1: Center thickness of the first lens,
d5: center thickness of the third lens,
d7: center thickness of the fourth lens,
R1: radius of curvature of the side surface of the first lens object
R2: radius of curvature of the first lens image side surface
R3: radius of curvature of the second lens object side surface
R4: radius of curvature of the second lens image side surface .

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