JP2009116063A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide compact imaging lenses having satisfactory optical characteristics and composed of two lenses capable of reducing focal length and optical length of the whole imaging lenses. <P>SOLUTION: The imaging lenses are constituted by arranging an aperture stop S1, the first lens L1 having a meniscus shape with its convex face directed toward an object side and having positive power, and the second lens L2 with its convex face directed toward the object side and having positive power in this order from an object to an image face side to satisfy the following expressions: (1): 0.70<f2/f1<2.50, (2): 0.30<R1/R2<0.65, and (3): 0.60<d1/d2<1.80 (wherein, f1 is focal length of the first lens L1, f2 is focal length of the second lens L2, R1 is radius of curvature of an object side face of the first lens L1, R2 is radius of curvature of an image face side face of the first lens L1, d1 is thickness of the center of the first lens, and d2 is distance between the image face side face of the first lens and an object side face of the second lens). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging lens. In particular, it is composed of two lenses with small and good optical characteristics, which are suitable for small image pickup devices using solid-state image pickup devices such as CCD and COMS for high pixels, optical sensors, portable module cameras, and WEB cameras. The present invention relates to an imaging lens.

  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 pickup devices have higher performance and smaller size, there is a demand for an image pickup lens that is smaller, lighter, and has good optical characteristics than ever.

  Conventionally, much research and development has been conducted on an imaging lens that satisfies both downsizing and good optical characteristics. With the improvement in performance of solid-state imaging devices such as CCDs, the level of miniaturization and optical characteristics required for imaging lenses has increased. In order to reduce the size of the imaging lens, the smaller the number of lenses, the more advantageous. On the other hand, regarding the optical characteristics, the larger the number of lenses, the better the correction of various aberrations, and the easier it is to obtain an imaging lens having good optical characteristics. In consideration of these, an imaging lens composed of two lenses that balances downsizing and good optical characteristics has been proposed.

  Patent Document 1 discloses an imaging lens including a meniscus first lens having a positive power with a convex surface facing the object side and a second lens having a biconvex positive power in order from the object. Yes. In the disclosed imaging lens, the center thickness of the first lens is thick and the radius of curvature of the object side surface and the image side surface is large. Therefore, the focal length of the entire imaging lens tends to be relatively long, and miniaturization and correction of aberrations can be achieved. It may be insufficient.

    Patent Document 2 discloses an imaging lens including a meniscus first lens having a positive power with a convex surface facing the object side and a second lens having a biconvex positive power in order from the object. Yes. The disclosed imaging lens is similar to Patent Document 1, and since the center thickness of the first lens is thick and the curvature radius of the object side surface and the image side surface is large, the focal length of the entire imaging lens tends to be relatively long. Miniaturization and correction of aberrations may be insufficient.

  Patent Document 3 discloses an imaging lens including a meniscus first lens having a positive power with a convex surface facing the object side and a second lens having a biconvex positive power in order from the object. Yes. In the disclosed imaging lens, the power of the first lens tends to be too strong, and it may be difficult to correct the aberration generated in the first lens with the second lens. The power in the present invention means an amount represented by the reciprocal of the focal length.

Japanese Patent Application Laid-Open No. 2005-121585 JP 2006-350275 A JP 2007-156030 A

  The present invention has been made in order to solve the above-described problems of the conventional example, and is small in size and excellent in optical characteristics, which is composed of two lenses having a short focal length and a thin center thickness. An object is to provide a simple imaging lens.

  As a result of intensive studies to achieve the above object, it has been found that an imaging lens of the object of the present invention can be obtained by optimizing the power distribution between the first lens and the second lens and the shape of the first lens. Reached.

The imaging lens according to the first aspect of the present invention includes a meniscus first lens having a positive power with a diaphragm and a convex surface facing the object side in order from the object toward the image plane side, and a positive lens with the convex surface facing the object side. A second lens having power is arranged, the focal length of the first lens is f1, the focal length of the second lens is f2, the radius of curvature of the object side surface of the first lens is R1, and the first lens has an image plane side radius of curvature. When the radius of curvature of the surface is R2, the center thickness of the first lens is d1, and the distance between the image side surface of the first lens and the object side surface of the second lens is d2, the following conditional expression ( Satisfy 1) to (3).
0.70 <f2 / f1 <2.50 (1)
0.30 <R1 / R2 <0.65 (2)
0.60 <d1 / d2 <1.80 (3)

  The imaging lens according to a second aspect of the present invention is the imaging lens according to the first aspect, wherein the second lens is a biconvex positive power lens.

The imaging lens according to a third aspect of the present invention is the imaging lens according to the first or second aspect, wherein the focal length of the second lens is f2, the center thickness of the first lens is d1, and the center of the second lens. When the thickness is d3, the following conditional expressions (4) and (5) are satisfied.
2.00 <f2 / d3 <10.00 (4)
0.40 <d1 / d3 <0.85 (5)

  According to the first aspect of the present invention, in order from the object toward the image surface side, the stop, the first meniscus lens having a positive power with the convex surface facing the object side, and the positive power with the convex surface facing the object side By disposing the second lens having the above and satisfying the above conditional expressions (1) to (3), it is possible to obtain a small imaging lens having a good optical characteristic with the two-lens configuration of the object of the present invention. . The obtained imaging lens is used for portable module cameras, WEB cameras, personal computers, digital cameras, optical sensors and monitors for automobiles and various industrial devices, and contributes to the reduction in size, weight and performance of these devices.

  According to the second aspect of the present invention, the second lens is a biconvex positive power lens, so that it is easy to obtain a compact imaging lens having a good optical characteristic with the objective of the present invention. It becomes.

  According to the invention of claim 3, in the imaging lens of the invention of claim 1 or 2, satisfying the conditional expressions (4) and (5), the two-lens object of the present invention It becomes easier to obtain an imaging lens having a small configuration and good optical characteristics.

  Hereinafter, an embodiment of an imaging lens LA according to the present invention will be described with reference to the drawings. The block diagram of the imaging lens concerning one Embodiment of this invention is shown in FIG. The imaging lens LA is a lens system including two lenses in which an aperture S1, a first lens L1, and a second lens L2 are arranged in order from the object side (not shown) toward the image plane. A glass flat plate GF is placed between the second lens L2 and the image plane. As the glass flat plate GF, a glass plate 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 (not shown) from the first lens L1, 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 meniscus lens having a positive power with one or more surfaces being aspheric, preferably both surfaces being aspheric and having a convex surface facing the object side. The second lens L2 is a lens having a positive power in which one or more surfaces are aspheric surfaces, and preferably both surfaces are aspheric surfaces, and the convex surface faces the object side. As the second lens L2, it is more preferable to use a biconvex lens having positive power in which one or more surfaces are aspheric surfaces, preferably both surfaces are aspheric surfaces.

In the imaging lens LA of the present invention, the focal length of the first lens L1 is f1, the focal length of the second lens L2 is f2, the radius of curvature of the object side surface of the first lens L1 is R1, and the image plane of the first lens L1. When the radius of curvature of the side surface is R2, the center thickness of the first lens L1 is d1, and the distance between the image side surface of the first lens and the object side surface of the second lens is d2, the following Conditional expressions (1) to (3) are satisfied.
0.70 <f2 / f1 <2.50 (1)
0.30 <R1 / R2 <0.65 (2)
0.60 <d1 / d2 <1.80 (3)

  The imaging lens LA can be easily downsized by increasing the power of the first lens L1. However, as the power of the first lens L1 increases, the generation of aberration increases. In order to correct the aberration generated in the first lens L1 with the second lens L2, it is necessary to optimize the power balance between the first lens L1 and the second lens L2. Conditional expression (1) defines the power balance of the first lens L1 and the second lens L2. In the present invention, it is preferable that the conditional expression (1) is satisfied, and the more preferable conditional expression is 0.75 <f2 / f1 <2.50. When the ratio f2 / f1 of the focal length f1 of the first lens L1 and the focal length f2 of the second lens L2 is equal to or lower than the lower limit of the conditional expression (1), correction of various aberrations is relatively easy, but the first lens L1 The position of the front principal point of the imaging lens approaches the image plane, and the optical length of the imaging lens LA may become long, making it difficult to reduce the size. On the other hand, when the value of f2 / f1 is equal to or greater than the upper limit of conditional expression (1), it is easy to reduce the size, but it is difficult to correct various aberrations, particularly spherical aberration (axial chromatic aberration) and lateral chromatic aberration. is there.

  In order to reduce the size of the imaging lens LA and suppress the aberration generated in the first lens L1, in the present invention, the shape of the first lens L1 is a specific meniscus shape with a convex surface facing the object side. The center thickness d1 of the lens L1 and the distance d2 between the image side surface of the first lens L1 and the object side surface of the second lens L2 need to have a specific relationship. Conditional expression (2) defines the meniscus degree of the first lens L1. In the present invention, it is preferable that the conditional expression (2) is satisfied, and the more preferable conditional expression is 0.40 <R1 / R2 <0.65. The ratio of the radius of curvature R1 of the object side surface of the first lens L1 to the radius of curvature R2 of the image side surface of the first lens L1, R1 / R2 is equal to or lower than the lower limit of the conditional expression (2), the first lens L1 The front principal point may approach the image side, and it may be difficult to reduce the size of the imaging lens LA. On the other hand, above the upper limit, it becomes difficult to correct distortion.

  Conditional expression (3) defines the relationship between the center thickness d1 of the first lens L1, the distance d2 between the image-side surface of the first lens L1 and the object-side surface of the second lens L2. In the present invention, it is preferable that the conditional expression (3) is satisfied, and the more preferable conditional expression is 0.65 <d1 / d2 <1.75. The ratio between the center thickness d1 of the first lens L1 and the distance d2 between the image side surface of the first lens L1 and the object side surface of the second lens L2, d1 / d2 is the lower limit of the conditional expression (3) Below, the distance between the 1st lens L1 and the 2nd lens L2 becomes long, and size reduction may become difficult. On the other hand, above the upper limit, it may be difficult to correct various aberrations, particularly chromatic aberration.

The aberration generated by the first lens L1 is corrected by the second lens L2. Therefore, the second lens L2 has a shape with a convex surface on the object side, more preferably a biconvex shape, the focal length of the second lens L2 is f2, the center thickness of the first lens L1 is d1, and the second lens When the center thickness of L2 is d3, it is preferable that the following conditional expressions (4) and (5) are satisfied.
2.00 <f2 / d3 <10.00 (4)
0.40 <d1 / d3 <0.85 (5)

  The second lens L2 controls the positive power of the first lens L1, and compensates for the aberration that occurs in the first lens L1. Conditional expression (4) relates to power control and downsizing of the second lens L2 in consideration of aberration correction. The focal length f2 of the second lens L2 and the center thickness d3 of the second lens L2 preferably satisfy the conditional expression (4), and a more preferable conditional expression is 3.00 <f2 / d3 <10.00. is there. If the ratio of the focal length f2 of the second lens L2 to the center thickness d3 of the second lens L2, f2 / d3 is equal to or greater than the upper limit of the conditional expression (4), the optical length of the imaging lens LA tends to be long and it is difficult to reduce the size. It may become. Below the lower limit, the power of the second lens L2 becomes strong, and it may be difficult to correct aberrations at the center, particularly chromatic aberration.

  In order to effectively correct the aberration by the second lens L2, it is preferable that the center thickness d1 of the first lens L1 is thinner than the center thickness d3 of the second lens L2. The center thickness d1 of the first lens L1 and the center thickness d3 of the second lens L2 preferably satisfy the conditional expression (5), and the more preferable conditional expression is 0.50 <d1 / d3 <0.80. is there. When the ratio d1 / d3 of the center thickness d1 of the first lens L1 to the center thickness d3 of the second lens L2 is not more than the lower limit of the conditional expression (5), it is difficult to reduce the size of the imaging lens LA. On the other hand, if the upper limit is exceeded, the center thickness d1 of the first lens L1 becomes thick, which may make it difficult to reduce the size of the imaging lens LA and correct aberrations.

  The first lens L1 and the second lens L2 can be formed of glass or a resin material. 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.

  The lens material has a d-line refractive index measured according to the ASTM D542 method in the range of 1.450 to 1.650, more preferably in the range of 1.500 to 1.600, and a wavelength of 450. A material having a light transmittance of 80% or more, more preferably 85% or more in a range of ˜600 nm is used.

  A resin material can efficiently manufacture a lens having a complicated surface shape, and is a preferable lens material over a glass material in terms of productivity. The resin material may be a thermoplastic resin or a thermosetting resin. Further, the first lens L1 and the second lens L2 may be the same material or different materials.

  Specific examples of the resin material include a non-crystalline polyolefin resin having a cyclo ring or other cyclic structure, a polystyrene resin, an acrylic resin, a polycarbonate resin, a transparent polyester resin, an epoxy resin, silicon. Based resins and the like. Among these, polyolefins containing a cycloolefin system and polyolefins containing a cyclic olefin are preferably used. The lens production using a resin material is performed using a known molding method such as an injection molding method, a compression molding method, a casting molding method, or a transfer molding method.

  It is well known that the refractive index of a resin material varies with temperature. In order to suppress this variation, the above-described transparent resin material in which fine particles such as silica, niobium oxide, titanium oxide, 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.

  When the lens is manufactured from a resin material, the first lens L1 and the second lens L2 can be provided with an edge on the outer periphery of the lens. 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 shielding mask for restricting incident light may be provided between the lenses as necessary.

  The imaging lens LA of the present invention is used in an imaging module or the like before the anti-reflection film, IR cut film, and surface hardening on the object-side and image-side lens surfaces of the first lens L1 and the second lens L2. For example, a known surface treatment may be performed. 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 the center thickness and distance is mm.
f: focal length f1 of the imaging lens LA as a whole: focal length f2 of the first lens L1: focal length Fno of the second lens L2: F number S1: aperture R: radius of curvature of the optical surface, or center radius of curvature R1 in the case of a lens : Curvature radius R2 of the object side surface of the first lens L1: curvature radius R3 of the image side surface of the first lens L1: curvature radius R4 of the object side surface of the second lens L2: image of the second lens L2 Curvature radius R5 of the surface side: Object side surface R6 of glass flat plate GF: Image plane side surface of glass flat plate GF d: Center thickness of lens or inter-lens distance d1: Center thickness d2 of first lens L1: No. 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 object side surface of the glass plate GF Distance d5: Center thickness of glass flat plate GF d: Refractive index n1 of d line: Refractive index n2 of first lens L1: Refractive index n3 of second lens L2: Refractive index νd of glass flat plate GF: Abbe number ν1 at d line: Abbe number of first lens L1 ν2: Abbe number of second lens L2 ν3: Abbe number TTL of glass flat plate GF: Optical length

  The aspherical shape of each lens surface of the first lens L1 and the second lens L2 of the imaging lens LA is such that y is an optical axis with the light traveling direction 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 + A14x ¹⁴ (6)

  However, R is a radius of curvature on the optical axis, k is a conical coefficient, and A4, A6, A8, A10, A12, and A14 are aspherical coefficients.

  As an aspheric surface of each lens surface, an aspheric surface represented by Expression (6) is used for convenience. However, the present invention is not particularly limited to the aspheric polynomial of Expression (6).

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 of the object side surface and the image surface side surface of each of the first lens L1 and the second lens L2 constituting the imaging lens LA of Example 1, the center thickness of the lens or the inter-lens distance d, the refractive index nd, and the Abbe number νd. Table 1 shows the conic coefficient k and the aspheric coefficient values.

  The imaging lens LA of Example 1 satisfies the conditional expressions (1) to (5) as shown in Table 9, and the focal length f and the optical length TTL of the entire imaging lens LA are short.

  FIG. 3 shows spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 1, FIG. 4 shows astigmatism and distortion, and FIG. 5 shows lateral chromatic aberration. In addition, the aberration of each figure is a result of each aberration in three wavelengths, wavelength 486nm, wavelength 588nm, and wavelength 656nm. 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. From the above results, the imaging lens LA of Example 1 is small and has good optical characteristics.

(Example 2)
FIG. 6 is a configuration diagram illustrating the arrangement of the imaging lens LA according to the second embodiment. The curvature radius R of the object side surface and the image surface side surface of each of the first lens L1 and the second lens L2 constituting the imaging lens LA of Example 2, the lens center thickness or the inter-lens distance d, the refractive index nd, and the Abbe number νd. Table 3 shows the conic coefficient k and the aspheric coefficient values.

  The imaging lens LA of Example 2 satisfies the conditional expressions (1) to (5) as shown in Table 9, and the focal length f and the optical length TTL of the entire imaging lens LA are short.

  FIG. 7 shows spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 2, FIG. 8 shows astigmatism and distortion, and FIG. 9 shows lateral chromatic aberration. In addition, the aberration of each figure is a result of each aberration in three wavelengths, wavelength 486nm, wavelength 588nm, and wavelength 656nm. 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. From the above results, the imaging lens LA of Example 2 is small and has good optical characteristics.

(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 of the object side surface and the image surface side surface of each of the first lens L1 and the second lens L2 constituting the imaging lens LA of Embodiment 3, the lens center thickness or the inter-lens distance d, the refractive index nd, and the Abbe number νd. Table 5 shows the values of the conical coefficient k and the aspheric coefficient.

  The imaging lens LA of Example 3 satisfies the conditional expressions (1) to (5) as shown in Table 9, and the focal length f and the optical length TTL of the entire imaging lens LA are short.

  FIG. 11 shows spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 3, FIG. 12 shows astigmatism and distortion, and FIG. 13 shows lateral chromatic aberration. In addition, the aberration of each figure is a result of each aberration in three wavelengths, wavelength 486nm, wavelength 588nm, and wavelength 656nm. 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. From the above results, the imaging lens LA of Example 3 is small and has good optical characteristics.

Example 4
FIG. 14 is a configuration diagram illustrating the arrangement of the imaging lens LA according to the fourth embodiment. The curvature radius R of the object side surface and the image surface side surface of each of the first lens L1 and the second lens L2 constituting the imaging lens LA of Example 4, the lens center thickness or inter-lens distance d, the refractive index nd, and the Abbe number νd Table 7 shows the conic coefficient k and aspheric coefficient values.

  The imaging lens LA of Example 4 satisfies the conditional expressions (1) to (5) as shown in Table 9, and the focal length f and the optical length TTL of the entire imaging lens LA are short.

  FIG. 15 shows spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 4, FIG. 16 shows astigmatism and distortion, and FIG. 17 shows lateral chromatic aberration. In addition, the aberration of each figure is a result of each aberration in three wavelengths, wavelength 486nm, wavelength 588nm, and wavelength 656nm. 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. From the above results, the imaging lens LA of Example 4 is small and has good optical characteristics.

1 is a schematic configuration diagram showing an embodiment of an imaging lens of the present invention. 1 is a schematic configuration diagram illustrating Example 1 of an imaging lens according to the present invention. Spherical aberration diagram of the imaging lens of Example 1 Astigmatism diagram and distortion diagram of the imaging lens of Example 1 Magnification Aberration Diagram of Imaging Lens of Example 1 Schematic block diagram showing Example 2 of the imaging lens of the present invention Spherical aberration diagram of the imaging lens of Example 2 Astigmatism diagram and distortion diagram of the imaging lens of Example 2 Magnification Aberration Chart of Imaging Lens of Example 2 Schematic block diagram showing Example 3 of the imaging lens of the present invention Spherical aberration diagram of the imaging lens of Example 3 Astigmatism diagram and distortion diagram of the imaging lens of Example 3 Magnification Aberration Diagram of Imaging Lens of Example 3 Schematic block diagram showing Example 4 of the imaging lens of the present invention Spherical aberration diagram of the imaging lens of Example 4 Astigmatism diagram and distortion diagram of the imaging lens of Example 4 Magnification Aberration Chart of Imaging Lens of Example 4

Explanation of symbols

LA: Imaging lens S1: Diaphragm L1: First lens L2: Second lens GF: Glass flat plate R1: Curvature radius of the object side surface of the first lens L1 R2: Curvature radius of the image side surface of the first lens L1 R3: radius of curvature of object side surface of second lens L2 R4: radius of curvature of image side surface of second lens L2 R5: object side surface of glass plate GF R6: image side surface of glass plate GF d1: Center thickness of the first lens L1 d2: Distance between the image surface side surface of the first lens L1 and the object side surface of the second lens L2 d3: Center thickness of the second lens L2 d4: Image surface of the second lens L2 Distance d5 between side surface and object side surface of glass flat plate GF: center thickness of glass flat plate GF

Claims (3)

In order from the object side toward the image plane side, a diaphragm, a meniscus first lens having a positive power with a convex surface facing the object side, and a second lens having a positive power with a convex surface facing the object side are arranged, An imaging lens satisfying the following conditional expressions (1) to (3):
0.70 <f2 / f1 <2.50 (1)
0.30 <R1 / R2 <0.65 (2)
0.60 <d1 / d2 <1.80 (3)
However,
f1: focal length of the first lens f2: focal length of the second lens R1: radius of curvature of the object side surface of the first lens R2: radius of curvature of the image side surface of the first lens d1: center of the first lens Thickness d2: distance between the image side surface of the first lens and the object side surface of the second lens   The imaging lens according to claim 1, wherein the second lens is a biconvex positive lens. The imaging lens according to claim 1, wherein the following conditional expressions (4) and (5) are satisfied.
2.00 <f2 / d3 <10.00 (4)
0.40 <d1 / d3 <0.85 (5)
However,
f2: Focal length of the second lens d1: Center thickness of the first lens d3: Center thickness of the second lens

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