JP4256443B1 - 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, a diaphragm S1, a meniscus first positive lens L1 with a convex surface facing the object side, a meniscus second negative lens L2 with a convex surface facing the image side, and toward the object side. An imaging lens in which a meniscus positive third lens L3 having a convex surface is disposed and satisfies the following conditional expressions (1) to (3). 0.07 <R1 / R2 <0.40 (1) 5.30 <f1 / d1 <6.50 (2) -40.00 <f2 / d3 <−6.00 (3) where R1: first Radius of curvature R2 of the object side surface of the lens: radius of curvature f1 of the image surface 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 d3: center of the second lens It is thickness.
[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 diaphragm, 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 object side, and a meniscus with a convex surface facing the object side An imaging lens having a third lens having a shape is disclosed.

  Patent Document 1 includes a first lens having a positive power with a convex surface facing the object side, a second meniscus lens with a concave surface facing the object side, and a third lens having a meniscus shape with a convex surface facing the object side. An imaging lens that is configured and satisfies specific conditions has been proposed. In this imaging lens, the first lens has a biconvex shape or is formed of a meniscus lens having a large curvature radius on the image side surface and a convex surface facing the object side. The main surface position approaches the image surface side, and the optical length of the imaging lens becomes long, which is insufficient for miniaturization. The power in the present invention is an amount expressed by the reciprocal of the focal length.

JP 2007-279597 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.

  As a result of intensive studies to achieve the above object, the objective imaging lens can be obtained by specifying the relationship between the meniscus degree of the first lens and the focal length and the center thickness of each of the first lens and the second lens. The present invention has been reached.

The imaging lens according to the first aspect of the present invention includes, in order from the 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 comprising a meniscus positive power third lens having a convex surface directed toward the object side and satisfying the following conditional expressions (1) to (3):
0.07 <R1 / R2 ≦ 0.339 (1)
5.30 <f1 / d1 <6.50 (2)
-40.00 <f2 / d3 <-6.00 (3)
However,
R1: radius of curvature of object side surface of first lens R2: radius of curvature of image surface side surface of first lens f1: focal length of first lens f2: focal length of second lens d1: center thickness of first lens d3: first It is the center thickness of two lenses.

An imaging lens according to a second aspect of the present invention is the imaging lens according to the first aspect, wherein the following conditional expressions (4) and (5) are satisfied.
0.90 <f1 / f <1.10 (4)
26.0 <ν1-ν2 <35.0 (5)
However,
f: focal length of the entire imaging lens f1: focal length of the first lens ν1: Abbe number of the first lens ν2: Abbe number of the second 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 of the invention according to claim 2 can more easily achieve downsizing and good optical characteristics.

  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 optimized.

  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 surfaces being aspherical, and more preferably both surfaces are aspherical.

In order from the object, the stop, the meniscus first positive power lens L1 with the convex surface facing the object side, the meniscus negative power second lens L2 with the convex surface facing the image side, and the meniscus with the convex surface facing the object side. By disposing the shape-shaped positive power third lens L3 and satisfying the following conditional expressions (1) to (3), it is possible to obtain a compact imaging lens having good optical characteristics.
0.07 <R1 / R2 ≦ 0.339 (1)
5.30 <f1 / d1 <6.50 (2)
-40.00 <f2 / d3 <-6.00 (3)

  In order to prevent the first lens L1 and the second lens L2 from having excessive power, it is preferable that both have a meniscus shape.

  Conditional expression (1) is an expression defining the degree of meniscus of the first lens L1. Below the lower limit of conditional expression (1), the degree of meniscus becomes loose, so the front principal point position of the first lens L1 approaches the image plane side, and the optical length of the imaging lens LA becomes long, which is not preferable. On the other hand, if the upper limit is exceeded, it becomes difficult to correct distortion, which is not preferable.

  Conditional expression (2) defines the focal length f1 and the center thickness d1 of the first lens L1. Below the lower limit of conditional expression (2), correction of spherical aberration and astigmatism tends to be difficult. If the upper limit is exceeded, it may be difficult to reduce the size of the imaging lens LA.

  Conditional expression (3) defines the focal length f2 and the center thickness d3 of the second lens L2. Below the lower limit of conditional expression (3), it is not preferable because it is difficult to correct on-axis and off-axis chromatic aberration. Above the upper limit, on-axis and off-axis chromatic aberration correction is easy, but distortion aberration correction may be difficult.

Furthermore, the imaging lens LA is small and can obtain good optical characteristics by satisfying conditional expression (4). Conditional expression (4) is a relational expression that defines the power of the first lens L1. Below the lower limit of conditional expression (4), the positive power of the first lens L1 becomes too large, and the error sensitivity after the second lens L2 tends to be tight. On the other hand, if the upper limit is exceeded, the positive power becomes small, and the optical length of the imaging lens LA becomes long.
0.90 <f1 / f <1.10 (4)

Furthermore, the relationship between the Abbe number ν1 of the first lens L1 and the Abbe number ν2 of the second lens L2 of the imaging lens LA satisfies the conditional expression (5), more preferably (5-a). Outside the range of conditional expression (5), it becomes difficult to correct aberrations, in particular, on-axis and off-axis chromatic aberrations.
26.0 <ν1-ν2 <35.0 (5)
29.0 <ν1-ν2 <32.0 (5-a)

  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.

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

  Specific examples of the resin material include a non-crystalline polyolefin resin having a cyclo ring and other cyclic structures, a polystyrene resin, an acrylic resin, a polycarbonate resin, a polyester resin, an epoxy resin, a silicon resin, and the like. Is mentioned. Of 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 thickness and 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 Radius of curvature R5 on the image side surface of L2: Radius of curvature of the object side surface of the third lens L3 R6: Radius of curvature of the image side surface of the third lens L3 R7: Radius of curvature of the object side surface of the glass plate GF R8: Radius of curvature of the glass plate GF Radius of curvature d of the image side surface: lens thickness or inter-lens distance d1: center thickness d2 of the first lens L1: distance d3 between the image side surface of the first lens L1 and the object side surface of the second lens L2. : Second Ren Center thickness d4 of L2: Distance d5 between the image side surface of the second lens L2 and the object side surface of the third lens L3 d5: Center thickness d6 of the third lens L3: Image side surface of the third lens L2 and glass Distance d7 between object side surface of flat plate GF: Center thickness of glass flat plate nd: Refractive index n1 of d line: Refractive index n2 of first lens L1: Refractive index n3 of second lens L2: Third lens L3 Refractive index n4: Refractive index νd of glass plate GF: Abbe number ν1 at d-line: Abbe number ν2 of first lens L1: Abbe number ν3 of second lens L2: Abbe number ν4 of third lens L3: Glass plate GF Abbe number TTL: Optical length

  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.

^{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 + A16x ¹⁶
(6)

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 (6) is used for convenience. However, the present invention is not particularly limited to the aspheric polynomial of Expression (6).

( Reference Example 1)
FIG. 2 is a configuration diagram illustrating the arrangement of the imaging lens LA of Reference Example 1. The curvature radius R of the object side surface and the image surface side surface of each of the first lens L1 to the third lens L3 constituting the imaging lens LA of Reference Example 1, the lens thickness or 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.

FIG. 3 shows spherical aberration (axial chromatic aberration) of the imaging lens LA of Reference Example 1, FIG. 4 shows astigmatism and distortion, and FIG. 5 shows chromatic aberration of magnification. From the above results, it can be seen that the imaging lens LA of Reference 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.

(Example 1 )
FIG. 6 is a configuration diagram illustrating the 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 to the third lens L3 constituting the imaging lens LA of Example 1 , the lens thickness or the inter-lens distance d, the refractive index nd, and the Abbe number νd. Table 3 shows the values of the conical coefficient k and the aspheric coefficient.

Under the conditions of Example 1 , as shown in Table 9, conditional expressions (1) to (5) are satisfied, 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 1 , FIG. 8 shows astigmatism and distortion, and FIG. 9 shows chromatic aberration of magnification. 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.

(Example 2 )
FIG. 10 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 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 Table 5 shows the values of the conical coefficient k and the aspheric coefficient.

Under the conditions of Example 2 , as shown in Table 9, conditional expressions (1) to (5) are satisfied, the optical length TTL is short, and the imaging lens LA is small.

FIG. 11 shows the spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 2 , FIG. 12 shows astigmatism and distortion, and FIG. 13 shows the 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.

(Example 3 )
FIG. 14 is a configuration diagram illustrating the 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 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 7 shows the conic coefficient k and aspheric coefficient values.

In the conditions of Example 3 , as shown in Table 9, conditional expressions (1) to (5) are satisfied, 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 3 , 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 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.

1 is a schematic configuration diagram showing an embodiment of an imaging lens of the present invention. Schematic configuration diagram showing Reference Example 1 of the imaging lens of the present invention Spherical aberration diagram of the imaging lens of Reference Example 1 Astigmatism diagram and distortion diagram of the imaging lens of Reference Example 1 Magnification chromatic aberration diagram of the imaging lens of Reference Example 1 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

Explanation of symbols

LA: Imaging lens S1: Diaphragm L1: First lens L2: Second lens L3: Third 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 of the object side surface of the second lens L2 R4: Radius of curvature of the image surface side surface of the second lens L2 R5: Radius of curvature of the object side surface of the third lens L3 R6: Curvature of the image surface side surface of the third lens L3 Radius R7: Curvature radius of object side surface of glass flat plate GF R8: Radius of curvature of image surface side surface of glass flat plate GF d1: Center thickness of first lens L1 d2: Object surface side of first lens L1 and object of second lens L2 Distance d3 between side surfaces: Center thickness d4 of second lens L2: Distance d5 between image side surface of second lens L2 and object side surface of third lens L3: Center thickness d6 of third lens L3: First 3 Lens L2 image Distance d7 between the surface side surface and the object side surface of the glass flat plate GF: Center thickness of the glass flat plate GF

Claims (2)

In order from the object, an aperture, a meniscus positive first 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 shape with a 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):
0.07 <R1 / R2 ≦ 0.339 (1)
5.30 <f1 / d1 <6.50 (2)
-40.00 <f2 / d3 <-6.00 (3)
However,
R1: radius of curvature of object side surface of first lens R2: radius of curvature of image surface side surface of first lens f1: focal length of first lens f2: focal length of second lens d1: center thickness of first lens d3: first It is the center thickness of two lenses. The imaging lens according to claim 1, wherein the following conditional expressions (4) and (5) are satisfied.
0.90 <f1 / f <1.10 (4)
26.0 <ν1-ν2 <35.0 (5)
However,
f: focal length of the entire imaging lens f1: focal length of the first lens ν1: Abbe number of the first lens ν2: Abbe number of the second lens.

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