JP4145952B1 - Imaging lens - Google Patents

Abstract

Provided is an imaging lens that is small and includes three lenses having good optical characteristics.
In order from an object, an aperture S1, a meniscus positive first lens L1 having a convex surface facing the object side, a meniscus negative power second lens L2 having a convex surface facing the image side, and toward the object side. An imaging lens LA, wherein a meniscus positive third lens L3 having a convex surface is disposed and satisfies the following conditional expressions (1) to (3). 0.20 <R1 / R2 <0.60 (1) −0.85 <f1 / f2 <−0.20 (2) 0.70 <d1 / d2 <0.95 (3)
[Selection] Figure 1

Description

  The present invention relates to an imaging lens. In particular, it is composed of three lenses with small and good optical characteristics, which are suitable for small image pickup devices using solid-state image sensors such as CCD and CMOS 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 sensors become smaller and have higher performance, image pickup lenses used in image pickup apparatuses are also required to be smaller and have better optical characteristics.

  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 an object, a stop, a meniscus first positive power lens with a convex surface facing the object side, a meniscus negative power second lens with a convex surface facing the image side, and a meniscus with a convex surface facing the object side An imaging lens having a third lens having a shape is disclosed. The power in the present invention is an amount represented by the reciprocal of the focal length.

  The imaging lens disclosed in Patent Document 1 includes, in order from an object, a plano-convex or positive meniscus first lens having a convex surface facing the object side, a negative meniscus second lens having a convex surface facing the image side, and the object side. An imaging lens composed of a positive meniscus third lens having a convex surface facing the surface has been proposed. According to the proposed imaging lens, the image side surface of the first lens is an image in which the image side surface of the first lens has a planar shape or a relatively loose radius of curvature with a convex surface facing the object side. It is close to the surface side, and the lens shape is naturally limited to shorten the optical length, which is insufficient in terms of miniaturization.

  The imaging lens disclosed in Patent Document 2 includes, in order from the object side, an aperture stop, a positive first meniscus lens with a convex surface facing the object side, and a second positive or negative meniscus shape with a convex surface facing the image side. An imaging lens composed of a lens and a positive or negative third meniscus lens having a convex surface facing the object side has been proposed. According to the proposed imaging lens, since the power distribution of the second lens is positive or negative of weak power, there is an insufficient point for correcting chromatic aberrations on and off the axis.

JP 2006-106321 A JP 2007-10773 A

  The present invention has been made to solve the conventional problems, and provides an imaging lens that is composed of three lenses that are small and have good optical characteristics in which various aberrations are suitably corrected. Objective.

  In order to achieve the above object, as a result of intensive studies, the meniscus degree of the first lens, the power distribution of the first lens and the second lens, the center thickness of the first lens, the first lens image side surface, and the second lens object side surface The inventors have found that the objective imaging lens can be obtained by specifying the distance relationship, and have reached the present invention.

The imaging lens according to the first aspect of the present invention includes, in order from an object, an aperture, a meniscus positive first lens having a convex surface facing the object side, a meniscus negative power second lens having a convex surface facing the image side, An imaging lens having a meniscus positive power third lens with a convex surface facing the object side and satisfying the following conditional expressions (1) to (3).
0.20 <R1 / R2 <0.60 (1)
−0.85 <f1 / f2 <−0.20 (2)
0.70 <d1 / d2 <0.95 (3)
However,
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 f1: focal length of the first lens f2: focal length of the second lens d1: center thickness of the first lens d2: first This is the distance between the image side surface of the lens and the object side surface of the second lens.

The imaging lens according to a second aspect of the present invention is the imaging lens according to the first aspect, wherein the following conditional expression (4) is satisfied.
4.50 <f1 / d1 <6.50 (4)
However,
f1: Focal length of the first lens d1: Center thickness of the first lens.

  The imaging lens of the invention of claim 1 is improved in the problems of the prior art, is small, and has good optical characteristics. The imaging lens obtained by the present invention 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 miniaturization and high performance of these devices. .

  The imaging lens according to the second aspect of the invention can more easily obtain a small imaging lens having good optical characteristics, which is the object of the present invention.

  An embodiment of an imaging lens LA according to the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an imaging lens LA according to an embodiment of the present invention. 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 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, a glass having a function such as a cover glass, an IR cut filter, or a low-pass filter can be used.

  By inserting the stop S1 closer to the object side than the first lens L1, the entrance pupil position can be set at a position far from the image plane. Thereby, it becomes easy to ensure high telecentricity, and the incident angle with respect to the image plane can be made suitable.

  The first lens L1 is a meniscus positive power lens having a convex surface facing the object side, the second lens L2 is a meniscus negative power lens having a convex surface facing the image side, and the third lens L3 is an object. This is a meniscus positive power lens with a convex surface facing the side. In order to more appropriately correct various aberrations, the surfaces of these three lenses preferably have one or more aspherical surfaces, and more preferably both aspherical surfaces.

  By making the first lens L1 and the second lens L2 into a meniscus shape, it is easy to suppress both lenses from becoming excessive power.

The downsizing of the imaging lens LA can be easily achieved by appropriately controlling the power and shape of the first lens L1. In addition, it is desirable to correct most of the aberrations generated in the first lens L1 with the second lens L2. Therefore, the relationship between the power distribution of the first lens L1 and the second lens L2 and the distance between the lenses is optimized. Is required. In the present invention, the curvature radius R1 on the object plane side and the curvature radius R2 on the image plane side of the first lens L1 are conditional expressions (1), and the focal length f1 of the first lens L1 and the focal length f2 of the second lens L2 are conditional. Expression (2) and the distance d2 between the center thickness d1 of the first lens L1 and the image side surface of the first lens L1 and the object side surface of the second lens L2 are set to satisfy the conditional expression (3).
0.20 <R1 / R2 <0.60 (1)
−0.85 <f1 / f2 <−0.20 (2)
0.70 <d1 / d2 <0.95 (3)

  Conditional expression (1) defines the meniscus degree of the first lens L1. In the present invention, it is preferable that the conditional expression (1) is satisfied, and the more preferable conditional expression is 0.22 <R1 / R2 <0.60. When 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 less than or equal to the lower limit of the conditional expression (1), the meniscus degree becomes loose. Therefore, the front principal point position of the first lens L1 approaches the image plane side, the optical length of the imaging lens LA becomes long, and it may be difficult to reduce the size. On the other hand, above the upper limit, it may be difficult to correct distortion.

  Conditional expression (2) defines the power distribution of the first lens L1 and the second lens L2. In the present invention, it is preferable that the conditional expression (2) is satisfied, and the more preferable conditional expression is −0.85 <f1 / f2 <−0.27. When the ratio of the focal length f1 of the first lens L1 to the second lens f2, f1 / f2 is outside the range of the conditional expression (2), it is possible to obtain a small imaging lens in which off-axis chromatic aberration is well corrected. It can be difficult.

  Conditional expression (3) defines the relationship 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. In the present invention, it is preferable that the conditional expression (3) is satisfied, and a more preferable conditional expression is 0.75 <d1 / d2 <0.95. When the ratio of the center thickness d1 of the first lens L1 to 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 outside the range of the conditional expression (3), the image accompanying the size reduction is obtained. It may be difficult to control the angular increase.

Furthermore, by setting the focal length f1 of the first lens L1 and the center thickness d1 of the first lens L1 as the conditional expression (4), the imaging lens LA can be easily reduced in size and obtain good optical characteristics. It was.
4.50 <f1 / d1 <6.50 (4)

  Conditional expression (4) defines the power and center thickness d1 of the first lens L1. In the present invention, it is preferable that the conditional expression (4) is satisfied. If the ratio of the focal length f1 of the first lens L1 to the center thickness d1 of the first lens L1, f1 / d1, is not more than the lower limit of the conditional expression (4), it may be difficult to correct spherical aberration and astigmatism. On the other hand, if the upper limit is exceeded, it may be difficult to reduce the size of the imaging lens LA.

  The first to third lenses constituting the imaging lens LA of the present invention 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.

  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. The three lenses constituting the imaging lens LA of the present invention are preferably formed of a resin material. When a resin material is used as the lens material, the light transmittance in a wavelength range of 450 to 600 nm with a d-line refractive index measured according to the ASTM D542 method is in the range of 1.45 to 1.65. As long as the resin material is 80% or more, more preferably 85% or more, it may be a thermoplastic resin or a thermosetting resin.

  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 polyester resin, an epoxy resin, a silicon resin, etc. Is mentioned. Among these, polyolefins containing cycloolefins, polyolefins containing cyclic olefins, polycarbonate resins and the like 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 and dimensions of resin materials vary with temperature. In order to suppress these fluctuations, the above-mentioned 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. can do.

  When the lens is manufactured from a resin material, each of the three lenses constituting the imaging lens LA 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.

  Before the imaging lens LA of the present invention is used in an imaging module or the like, the three lenses constituting the imaging lens LA are provided with an antireflection film, an IR cut film on the object-side and image-side lens surfaces, You may perform well-known surface treatments, such as surface hardening. 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 image 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 image side surface of the third lens L3: radius of curvature R8 of the object side surface of the glass plate GF: Radius of curvature d: Lens thickness or inter-lens distance d1: Center thickness of first lens L1 d2: Distance between image side surface of first lens L1 and object side surface of second lens L2 d3: Center of second lens L2 d4: Distance between the image side surface of the second lens L2 and the object side surface of the third lens L3 d5: Center thickness of the third lens L3 d6: Between the image side surface of the third lens L2 and the object side surface of the glass flat plate GF Distance d7: center 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 n4 of third lens L3: of glass flat plate GF Refractive index νd: Abbe number ν1 at d line: Abbe number ν2 of first lens: Abbe number ν3 of second lens: Abbe number ν4 of third lens: Abbe number TTL of glass plate GF: Optical length of imaging lens LA 2ω: All angle of view of imaging lens LA

  The aspherical shape of each lens surface of the first lens L1, the second lens L2, and the third lens L3 constituting the imaging lens LA is such that y is an optical axis with the traveling direction of light as positive and x is an optical axis. The axis in the orthogonal direction is represented by the following aspheric polynomial.

Where R is the radius of curvature on the optical axis, k is the cone coefficient, A4, A6, A8, A10, A12,
A14 and A16 are aspheric coefficients.

As an aspheric surface of each lens surface, an aspheric surface represented by Expression (5) is used for convenience. However, the present invention is not particularly limited to the aspheric polynomial of Expression (5).

(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 and the image side surface of each of the first lens L1 to the third lens L3 constituting the imaging lens LA of Example 1, the lens thickness or inter-lens distance d, the refractive index nd, and the Abbe number νd Table 1 shows the values of the cone coefficient k and the aspheric coefficient.

  Under these conditions, conditional expressions (1) to (4) are satisfied as shown in Table 9, the optical length TTL is short, and the imaging lens LA is small.

  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. From the above results, it can be seen that the imaging lens LA of Example 1 is small and has good optical characteristics. In addition, the aberration of each figure is each result in three wavelengths, wavelength 486nm, wavelength 588nm, and wavelength 656nm. In the 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, it can be seen that 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 and the image side surface of each of the first lens L1 to the third lens L3 constituting the imaging lens LA of Example 2, the lens thickness or inter-lens distance d, the refractive index nd, and the Abbe number νd are set. Table 3 shows the values of the conical coefficient k and the aspheric coefficient.

  Under these conditions, conditional expressions (1) to (4) are satisfied as shown in Table 9, the optical length TTL is short, and the imaging lens LA is small.

  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. From the above results, it can be seen that the imaging lens LA of Example 2 is small and has good optical characteristics. In addition, the aberration of each figure is each result in three wavelengths, wavelength 486nm, wavelength 588nm, and wavelength 656nm. In the 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, it can be seen that 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 and the image side surface of each of the first lens L1 to the third lens L3 constituting the imaging lens LA of Example 3, the lens thickness or inter-lens distance d, the refractive index nd, and the Abbe number νd Table 5 shows the values of the cone coefficient k and the aspheric coefficient.

  Under these conditions, conditional expressions (1) to (4) are satisfied as shown in Table 9, the optical length TTL is short, and the imaging lens LA is small.

  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. From the above results, it can be seen that the imaging lens LA of Example 3 is small and has good optical characteristics. In addition, the aberration of each figure is each result in three wavelengths, wavelength 486nm, wavelength 588nm, and wavelength 656nm. In the 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, it can be seen that 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 and the image side surface of each of the first lens L1 to the third lens L3 constituting the imaging lens LA of Example 4, the lens thickness or inter-lens distance d, the refractive index nd, and the Abbe number νd are set. Table 7 shows the values of the cone coefficient k and the aspheric coefficient.

  Under these conditions, conditional expressions (1) to (4) are satisfied as shown in Table 9, the optical length TTL is short, and the imaging lens LA is small.

  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. From the above results, it can be seen that the imaging lens LA of Example 4 is small and has good optical characteristics. In addition, the aberration of each figure is each result in three wavelengths, wavelength 486nm, wavelength 588nm, and wavelength 656nm. In the 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, it can be seen that the imaging lens LA of Example 4 is small and has good optical characteristics.

  Table 9 shows values corresponding to the parameters defined in the numerical values and conditional expressions (1) to (4) of each numerical example. The units of values shown in Table 9 are TTL (mm), 2ω (°), f (mm), f1 (mm), f2 (mm), and f3 (mm).

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: aperture L1: first lens L2: second lens L3: third lens GF: glass flat plate R1: radius of curvature R2 of the object side surface of the first lens L1: radius of curvature 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: radius of curvature of object side surface of third lens L3 R6: radius of curvature of image side surface of third lens L3 R7: Curvature radius R8 of object side surface of glass flat plate GF: Radius of curvature of image side surface of glass flat plate GF d1: Center thickness d2 of first lens L1: Between image side surface of first lens L1 and object side surface of second lens L2 Distance d3: Center thickness d4 of the second lens L2: Distance d5 between the image side surface of the second lens L2 and the object side surface of the third lens L3: Center thickness d6 of the third lens L3: Image side surface of the third lens L2 And glass plate GF The distance between the object side surface d7: center thickness of the glass plate GF

Claims (2)

In order from the object, stop, first meniscus positive power lens with convex surface facing the object side, second meniscus negative power lens with convex surface facing the image side, meniscus shape with convex surface facing the object side An imaging lens comprising a third lens having a positive power and satisfying the following conditional expressions (1) to (3):
0.20 <R1 / R2 <0.60 (1)
−0.85 <f1 / f2 <−0.20 (2)
0.70 <d1 / d2 <0.95 (3)
However,
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 f1: focal length of the first lens f2: focal length of the second lens d1: center thickness of the first lens d2: first This is the distance between the image side surface of the lens and the object side surface of the second lens. The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied.
4.50 <f1 / d1 <6.50 (4)
However,
f1: Focal length of the first lens d1: Center thickness of the first lens.

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