JP2009098183A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens which is short in focal length as a whole, is composed of two lenses thin in center thickness, and is small in size and excellent in optical characteristics. <P>SOLUTION: The imaging lens includes, in order from an object side to an image side: a diaphragm; a first meniscus lens having a positive power, with a convex surface facing the object side; and a second meniscus lens having a positive power, with a convex surface facing the image side. Provided that the focal length of the whole imaging lens is expressed by f, the focal length of the first lens is expressed by f1, the focal length of the second lens is expressed by f2, the center thickness of the first lens is expressed by d1, the center thickness of the second lens is expressed by d3, the curvature radius on the object side of the first lens is expressed by R1, and the curvature radius on the image side of the same is expressed by R2, the imaging lens satisfies the following conditional inequalities: (1) 0.30<f1/f2<1.30; (2) 0.20<d1/f<0.30; (3) 0.28<d3/f<0.45; (4) 0.50<R1/R2<0.68. <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 miniaturization and good optical characteristics. With the improvement in performance of solid-state image sensors such as CCDs, the required level of miniaturization and optical characteristics is increasing. In order to reduce the size of the imaging lens, the smaller the number of lenses, the more advantageous. On the other hand, as the number of lenses increases, it becomes easier to correct various aberrations, and an imaging lens having good optical characteristics can be obtained. In consideration of these, an imaging lens composed of two lenses that balances downsizing and good optical characteristics has been proposed.

  The imaging lens described in Patent Document 1 includes, in order from an object, a positive meniscus first lens having a convex surface facing the object side and a second lens having a convex surface facing the image surface side. The disclosed imaging lens has an insufficient focal point because the focal length of the entire imaging lens is relatively long, and the first lens and the second lens are also thick.

  The imaging lens described in Patent Document 2 includes, in order from an object, an aperture, a positive meniscus first lens having a convex surface facing the object side, and a positive second lens having a convex surface facing the image surface side. Yes. The focal length of the entire imaging lens disclosed is relatively short, and the thickness of the first lens and the second lens is also thin. However, the optical length is still long and is insufficient in terms of miniaturization.

Japanese Patent Application Laid-Open No. 2005-121585 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 configured with two optical lenses having a short focal length and a thin center thickness. An object is to provide a good imaging lens.

  In order to achieve the above object, as a result of intensive studies on the power distribution between the first lens and the second lens and the relationship between the focal length of the entire imaging lens and the center thickness of the lens, the imaging lens of the object of the present invention is 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 toward the image plane side, a diaphragm, a first meniscus lens having a positive power with the convex surface facing the object side, and a positive lens with the convex surface facing the image plane side. A second meniscus lens having the following power is arranged, the focal length of the entire imaging lens is f, the focal length of the first lens is f1, the focal length of the second lens is f2, and the center thickness of the first lens is d1, Imaging satisfying the following conditional expressions (1) to (4), where d3 is the center thickness of the second lens, R1 is the radius of curvature on the first lens object side, and R2 is the radius of curvature on the first lens image surface side. It is a lens.
0.30 <f1 / f2 <1.30 (1)
0.20 <d1 / f <0.30 (2)
0.28 <d3 / f <0.45 (3)
0.50 <R1 / R2 <0.68 (4)

The imaging lens according to a second aspect of the present invention is the imaging lens according to the first aspect, wherein the radius of curvature on the second lens object side is R3 and the radius of curvature on the second lens image plane side is R4. This is an imaging lens satisfying 5).
4.00 <R3 / R4 <15.50 (5)

The imaging lens according to a third aspect of the present invention is the imaging lens according to the first or second aspect, wherein when the center thickness of the first lens is d1 and the center thickness of the second lens is d3, The imaging lens satisfies the following conditional expressions (6) and (7).
d1 <0.50 mm (6)
d3 <0.60 mm (7)

  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 surface with the convex surface facing the image surface side By disposing a meniscus second lens having power and satisfying the above conditional expressions (1) to (4), it is possible to obtain an image pickup lens having a small two-lens configuration and having good optical characteristics. Obtainable. 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 invention of claim 2, in the imaging lens of the invention of claim 1, further, by specifying the radius of curvature of the object side surface and the image side surface of the second lens, it is small and various aberrations, particularly astigmatism. An imaging lens in which aberration and distortion are corrected can be obtained more easily.

  According to the invention of claim 3, in the imaging lens of the invention of claim 1 or 2, the upper limit of the center thickness of the constituent lens is defined, thereby making it easier to reduce the size of the imaging lens. .

  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 two-lens lens system 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 positive power with one or more surfaces being aspherical, preferably both surfaces being aspherical and having a convex surface facing the object side, and the second lens L2 has one or more surfaces being aspherical. Preferably, it is a meniscus lens having a positive power with the convex surface facing the image surface side having both aspheric surfaces.

The imaging lens LA of the present invention includes a first meniscus lens having a positive power with a diaphragm and a convex surface facing the object side in order from the object side to the image surface side, and a positive lens with the convex surface facing the image surface side. A second meniscus lens having power is arranged, the focal length of the entire imaging lens LA is f, the focal length of the first lens L1 is f1, the focal length of the second lens L2 is f2, and the center thickness of the first lens L1 Is d1, and the center thickness of the second lens L2 is d3, it is necessary to satisfy the conditional expressions (1) to (3) in order to obtain the objective imaging lens LA of the present invention.
0.30 <f1 / f2 <1.30 (1)
0.20 <d1 / f <0.30 (2)
0.28 <d3 / f <0.45 (3)

  Conditional expression (1) is a conditional expression that defines the power balance between the first lens L1 and the second lens L2. The ratio of the focal length f2 of the second lens L2 to the focal length f1 of the first lens L1, and a more preferable range of f1 / f2 is 0.35 <f1 / f2 <1.30. If f1 / f2 is less than the lower limit of conditional expression (1), it is easy to reduce the size, but it may be difficult to correct various aberrations, particularly spherical aberration and lateral chromatic aberration. On the other hand, when the value of f1 / f2 exceeds the upper limit of the conditional expression (1), correction of various aberrations is relatively easy, but the front principal point position of the first lens approaches the image plane, and the imaging lens LA The optical length may become long, and miniaturization becomes difficult.

  Conditional expression (2) is a relational expression between the center thickness d1 of the first lens L1 and the focal length f of the entire imaging lens LA. The ratio of the focal length f of the entire imaging lens LA to the center thickness d1 of the first lens L1, and a more preferable range of d1 / f is 0.22 <d1 / f <0.27. If d1 / f exceeds the upper limit of the conditional expression (2), the optical length of the imaging lens LA becomes long, and if it falls below the lower limit, it is difficult to manufacture the first lens L1.

  The center thickness d1 of the first lens is less than 0.5 mm, and more preferably 0.25 mm <d1 <0.45 mm. When d1 is 0.5 mm or more in thickness, the optical length tends to be long, and downsizing may be difficult. If the thickness is less than 0.25 mm, it is difficult to manufacture the lens.

  Conditional expression (3) is a relational expression between the center thickness d3 of the second lens L2 and the focal length f of the entire imaging lens LA. The ratio of the focal length f of the entire imaging lens LA to the center thickness d3 of the second lens L2, that is, when d3 / f exceeds the upper limit of the conditional expression (3), the optical length of the imaging lens LA tends to be long. It becomes difficult to manufacture the two lenses L2.

  The center thickness d3 of the second lens is less than 0.6 mm, more preferably 0.25 mm <d3 <0.55 mm. If d3 is 0.6 mm or more in thickness, the optical length of the imaging lens LA tends to be long, and downsizing may be difficult. If the thickness is less than 0.25 mm, it may be difficult to manufacture the lens.

Further, both the first lens L1 and the second lens L2 have a meniscus shape and define the meniscus degree of each lens. The radius of curvature of the first lens L1 on the object side is R1, the radius of curvature of the image plane side of the first lens L1 is R2, the radius of curvature of the object side of the second lens L2 is R3, and the curvature of the second lens L2 is on the image plane side. By satisfying the following conditional expressions (4) and (5) when the radius is R4, a compact two-lens imaging lens having excellent optical characteristics with various aberrations suitably corrected is obtained. It can be obtained more easily.
0.50 <R1 / R2 <0.68 (4)
4.00 <R3 / R4 <15.50 (5)

  Conditional expression (4) is an expression that defines the meniscus degree of the first lens L1. If the ratio R1 / R2 of the curvature radius R2 on the object side of the first lens L1 to the curvature radius R2 on the image plane side of the first lens L1 exceeds the upper limit of the conditional expression (4), it becomes difficult to correct distortion aberration. If the lower limit is exceeded, the position of the front principal point of the first lens L1 approaches the image side, and it becomes difficult to reduce the size of the imaging lens LA. In addition, with a bright Fno lens, the edge thickness of the first lens L1 may be secured. It can be difficult.

  Conditional expression (5) is an expression defining the degree of meniscus of the second lens L2. The ratio of the curvature radius R3 on the object side of the second lens L2 to the curvature radius R4 on the image plane side of the second lens L2, R3 / R4 exceeds the upper limit of the conditional expression (5), and the positive power of the second lens L2 Therefore, if the optical length of the imaging lens LA becomes long and falls below the lower limit, it is difficult to correct various aberrations, particularly astigmatism and distortion.

  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, it is a resin having a d-line refractive index in the range of 1.450 to 1.650 measured according to ASTM D542 method. More preferably, the refractive index n1 of the first lens L1 is in the range of 1.535 to 1.600, and the refractive index n2 of the second lens L2 is in the range of 1.500 to 1.525. Refractive index n1> refractive index n2 of the second lens L2. By using the resin having the refractive index as the lens material, it is possible to easily obtain a small imaging lens LA having good optical characteristics. Further, the type of the resin may be a thermoplastic resin or a thermosetting resin, but the light transmittance in the wavelength range of 450 to 600 nm is 80% or more, more preferably 85% or more. Is used. The first lens L1 and the second lens L2 may be resin materials of the same system or different resin 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: image of the second lens L2 Curvature radius R5 of the surface side: Object side surface R6 of the glass plane GL: Image plane side surface d of the glass plane GL: Lens or inter-lens distance d1: Center thickness d2 of the first lens L1: First lens L1 Distance d3 between the image plane side of the second lens L2 and the object side surface of the second lens L2: center thickness d4 of the second lens L2: distance d5 between the image plane side of the second lens L2 and the object side surface of the glass plane GL: of the glass plane GL Center thickness nd: d-line refractive index n 1: Refractive index n2 of the first lens L1: Refractive index n3 of the second lens L2: Refractive index νd of the glass plane GL: Abbe number ν1 at d-line: Abbe number ν2 of the first lens: Abbe number of the second lens ν3: Abbe number TTL of glass plane GL: 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 (8)

  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 (8) is used for convenience. However, the present invention is not particularly limited to the aspheric polynomial of the formula (8).

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.

This condition is within the range of conditional expressions (1) to (5) as shown in Table 9.

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 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.
The obtained imaging lens LA has a short focal length f and an optical length TTL, 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.

  This condition is within the range of conditional expressions (1) to (5) as shown in Table 9.

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 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.
The obtained imaging lens LA has a short focal length f and an optical length TTL, 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.

This condition is within the range of conditional expressions (1) to (5) as shown in Table 9.

  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 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. The obtained imaging lens LA has a short focal length f and an optical length TTL, 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.

  This condition is within the range of conditional expressions (1) to (5) as shown in Table 9.

  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 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. The obtained imaging lens LA has a short focal length f and an optical length TTL, 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: object side surface R6 of glass plane GL: image side surface of glass plane GL d1: Center thickness of the first lens L1 d2: Distance between the image surface side 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 side of the second lens L2 Distance d5 from the object side surface of the glass plane GL: Thickness of the center of the glass plane nd: Refractive index n1 of the d-line: Refractive index n2 of the first lens L1: Refractive index n3 of the second lens L2: Refractive index of the glass plane GL

Claims (3)

In order from the object side toward the image surface side, the first lens having a positive meniscus shape having a positive power with a diaphragm and a convex surface facing the object side, and the following meniscus shape having a positive power with a convex surface facing the image surface side An imaging lens comprising two lenses and satisfying the following conditional expressions (1) to (4):
0.30 <f1 / f2 <1.30 (1)
0.20 <d1 / f <0.30 (2)
0.28 <d3 / f <0.45 (3)
0.50 <R1 / R2 <0.68 (4)
However,
f: focal length of the entire imaging lens f1: focal length of the first lens f2: focal length of the second lens d1: center thickness of the first lens d3: center thickness of the second lens R1: radius of curvature on the first lens object side R2: radius of curvature on the first lens image plane side The imaging lens according to claim 1, wherein the following conditional expression (5) is satisfied.
4.00 <R3 / R4 <15.50 (5)
However,
R3: radius of curvature on the second lens object side R4: radius of curvature on the second lens image plane side The imaging lens according to claim 1, wherein the following conditional expressions (6) and (7) are satisfied.
d1 <0.50 mm (6)
d3 <0.60 mm (7)
However,
d1: Center thickness of the first lens d3: Center thickness of the second lens

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