JP4418844B2 - Imaging lens - Google Patents

Description

  The present invention relates to an imaging lens. In particular, it is composed of two small lenses with good optical characteristics, which are suitable for compact imaging devices using solid-state imaging devices such as high-pixel CCDs and CMOSs, 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.

  In terms of downsizing the imaging lens, an imaging lens composed of a single lens is advantageous. However, it is difficult to correct aberrations in the periphery of the imaging lens, which is composed of a single lens. It is well known that it is difficult to obtain optical characteristics. Accordingly, an imaging lens composed of two lenses has been proposed as an imaging lens that balances downsizing and good optical characteristics.

  Patent Document 1 proposes an imaging lens composed of a positive meniscus first lens having a convex surface facing the object side and a biconcave second lens. In the proposed imaging lens, since the negative power of the second lens is weak, it is difficult to correct chromatic aberration, and it is insufficient for obtaining a small size and good optical characteristics.

JP 2006-178026 A

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

  As a result of diligent studies to achieve the above object, by specifying the power (reciprocal of focal length) distribution and Abbe number ratio of the first lens and the second lens, the imaging lens of the object of the present invention can be obtained. The present invention has been found.

The imaging lens according to the first aspect of the present invention includes, in order from the object side to the image surface side, a stop, a meniscus first lens having a positive power with a convex surface facing the object side, and a biconcave negative power. An imaging lens comprising: a second lens having the following conditional expression (1) to (4):
−2.5 <f2 / f1 <−0.8 (1)
0.8 <ν1 / ν2 <1.2 (2)
0.1 <R1 / R2 ≦ 0.28 (3)
2.0 <f1 / d1 <4.2 (4)
However,
f1: Focal length of the first lens f2: Focal length of the second lens ν1: Abbe number of the first lens ν2: Abbe number of the second lens R1: Radius of curvature of the first lens object side surface R2: Side surface of the first lens image curvature radius
f1: Focal length of the first lens
d1: the center thickness of the first lens .

According to the first aspect of the present invention, in order from the object side to the image surface side, the stop, the first meniscus lens having a positive power with the convex surface facing the object side, and the negative power of the biconcave shape It is easy to correct various aberrations such as on-axis and off-axis chromatic aberration by specifying the power distribution of the first lens and the second lens, the Abbe number, and the meniscus degree of the first lens. Furthermore, by specifying the ratio between the focal length and the center thickness of the first lens, it is possible to obtain a small and good optical characteristic.

  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 includes a diaphragm S1, a meniscus first lens L1 having a positive power with a convex surface facing the object side from the object (not shown) side to the image plane, and a biconcave negative power. This is a two-lens configuration lens system in which a second lens L2 having the above is disposed. In FIG. 1, a glass flat plate is not inserted between the second lens image side and the image plane, but a glass flat plate having a function such as a cover glass, an IR cut filter, or a low-pass filter may be inserted. .

  By inserting the diaphragm 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. As a result, high telecentricity can be ensured, and the incident angle with respect to the image plane can be made suitable.

  Both the first lens L1 and the second lens L2 have one or more lens surfaces having an aspherical shape, and preferably two surfaces having an aspherical shape, thereby facilitating correction of various aberrations.

  The first lens L1 has a meniscus shape with a convex surface directed toward the object side, and the second lens L2 has a biconcave shape, so that various aberrations such as downsizing and astigmatism can be corrected and good optical characteristics can be obtained.

By setting the focal length f1 of the first lens L1 and the focal length f2 of the second lens L2 of the imaging lens LA, and setting the power distribution of the first lens L1 and the second lens L2 within the range of the following conditional expression (1), Good optical characteristics in which various aberrations such as axial chromatic aberration are corrected can be obtained with a small size.
−2.5 <f2 / f1 <−0.8 (1)

By making the Abbe numbers ν1 and ν2 of the first lens L1 and the second lens L2 of the imaging lens LA within the range of the following conditional expression (2), it is small and excellent in various aberrations such as off-axis chromatic aberration are corrected Optical characteristics can be obtained.
0.8 <ν1 / ν2 <1.2 (2)

By setting the focal length f1 of the first lens L1 and the center thickness d1 of the first lens L1 of the imaging lens LA within the range of the following conditional expression (4) , the optical characteristics are small and the distortion is corrected. Obtainable.
2.0 <f1 / d1 <4.2 (4)

The radius of curvature of the object side surface of the first lens L1 of the imaging lens LA R1, a curvature radius of the image side surface and R2, which are, to suppress that the first lens L1 becomes excessive power, error sensitivity is increased, in meniscus shape, it is not preferable in the range of the following conditional expression (3).
0.1 <R1 / R2 ≦ 0.28 (3)

  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.

  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 is in the range of the refractive index of d-line measured according to ASTM D542 method in the range of 1.45 to 1.60 and in the wavelength range of 450 to 600 nm. 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. The first lens L1 and the second lens L2 may be made of the same resin material or different materials.

  Specific examples of the resin material include a cyclo ring, an amorphous polyolefin resin having other cyclic structure, a polystyrene resin, an acrylic resin, a polycarbonate resin, a transparent polyester resin, an epoxy resin, Examples thereof include silicon-based resins. Of these, polyolefins containing cycloolefins and polyolefins containing cyclic olefins 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 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: curvature radius d of the image side surface of the second lens L2: lens Or distance between lenses d1: 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 nd of the second lens L2 nd: refractive index of d line n1: Refractive index n1 of the first lens L1: Refractive index νd of the second lens L2: Abbe number ν1 at d-line: Abbe number ν2 of the first lens: Abbe number of the second lens

  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 ]
+ 4x ⁴ + A6x ⁶ + A8x ⁸ + A10x ¹⁰ + A12x ¹² + A14x ¹⁴ (5)

  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 (5) is used for convenience. However, the present invention is not particularly limited to the aspheric polynomial of the formula (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 and the second lens L2 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.

  The imaging lens LA of Example 1 satisfies the conditional expressions (1) to (4) as shown in Table 11, and the focal length and optical length TTL of the 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. The aberrations in each figure are the results of the respective aberrations at three wavelengths, a wavelength of 486 nm, a wavelength of 588 nm, and a wavelength of 656 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface. 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 and the image side surface of each of the first lens L1 and the second lens L2 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.

  The imaging lens LA of Example 2 satisfies the conditional expressions (1) to (4) as shown in Table 11, and the focal length and optical length TTL of the 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 chromatic aberration of magnification. The aberrations in each figure are the results of the respective aberrations at three wavelengths, a wavelength of 486 nm, a wavelength of 588 nm, and a wavelength of 656 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface. 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 and the image side surface of each of the first lens L1 and the second lens L2 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 are set. Table 5 shows the values of the cone coefficient k and the aspheric coefficient.

  The imaging lens LA of Example 3 satisfies the conditional expressions (1) to (4) as shown in Table 11, and the focal length and optical length TTL of the 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. The aberrations in each figure are the results of the respective aberrations at three wavelengths, a wavelength of 486 nm, a wavelength of 588 nm, and a wavelength of 656 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface. 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 and the image side surface of each of the first lens L1 and the second lens L2 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. Table 7 shows the values of the cone coefficient k and the aspheric coefficient.

  The imaging lens LA of Example 4 satisfies the conditional expressions (1) to (4) as shown in Table 11, and the focal length and optical length TTL of the 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. The aberrations in each figure are the results of the respective aberrations at three wavelengths, a wavelength of 486 nm, a wavelength of 588 nm, and a wavelength of 656 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface. From the above results, the imaging lens LA of Example 4 is small and has good optical characteristics.

(Reference Example 1)
FIG. 18 is a configuration diagram illustrating the arrangement of the imaging lens LA of Reference Example 1 . The curvature radius R of the object side and the image side surface of each of the first lens L1 and the second lens L2 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 9 shows the values of the cone coefficient k and the aspheric coefficient.

As shown in Table 11, the imaging lens LA of Reference Example 1 satisfies the conditional expressions (1) to (4), and the focal length and optical length TTL of the imaging lens LA are short. However, it is comparatively long compared with Examples 1-4.

FIG. 19 shows spherical aberration (axial chromatic aberration) of the imaging lens LA of Reference Example 1, FIG. 21 shows astigmatism and distortion, and FIG. 22 shows lateral chromatic aberration. The aberrations in each figure are the results of the respective aberrations at three wavelengths, a wavelength of 486 nm, a wavelength of 588 nm, and a wavelength of 656 nm. Further, astigmatism S is an aberration with respect to the sagittal image surface, and T is an aberration with respect to the tangential image surface. From the above results , the imaging lens LA of Reference Example 1 is small and has good optical characteristics. However, the focal length and optical length are relatively long .

  Table 11 shows values corresponding to the values defined in the numerical examples and the parameters defined by the conditional expressions (1) to (4). The unit of values shown in Table 11 is f (mm), f1 (mm), f2 (mm), and TTL (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 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

Explanation of symbols

LA: imaging lens TTL: distance from the object side surface of the first lens L1 to the image plane S1: aperture L1: first lens L2: second lens R1: radius of curvature R2 of the object side surface of the first lens L1: first lens L1 Radius of curvature R3 of the image side surface of the second lens L2, radius of curvature R4 of the object side surface of the second lens L2, radius of curvature d1 of the image side surface of the second lens L2, thickness d2 of the center of the first lens L1, and the image surface side of the first lens L1. Distance d3 between second lens L2 and object side surface: thickness of center of second lens L2

Claims (1)

In order from the object side to the image surface side, a stop, a first meniscus lens having a positive power with a convex surface facing the object side, and a second lens having a negative power with a biconcave shape are arranged as follows. An imaging lens characterized by satisfying conditional expressions (1) to (4):
−2.5 <f2 / f1 <−0.8 (1)
0.8 <ν1 / ν2 <1.2 (2)
0.1 <R1 / R2 ≦ 0.28 (3)
2.0 <f1 / d1 <4.2 (4)
However,
f1: Focal length of the first lens f2: Focal length of the second lens ν1: Abbe number of the first lens ν2: Abbe number of the second lens R1: Radius of curvature of the first lens object side surface R2: Side surface of the first lens image curvature radius
f1: Focal length of the first lens
d1: the center thickness of the first lens .

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