JP2009092803A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens composed of three lenses, which is compact and has satisfactory optical characteristics. <P>SOLUTION: The imaging lens comprises a diaphragm S1, a menicus-shaped first lens L1 having positive powder and turning its convex surface to an object side, and a menicus-shaped second lens L2 having negative power and turning its convex surface to an image side, and a menicus-shaped third lens L3 having negative power and turning its convex surface to the object side, which are arranged in the order from the object side, and satisfies the conditional expressions (1) to (3): (1)-4.0<f1/f2<-0.1, (2) 4.0<f1/d1<7.0 and (3)-80.0<f2/d3<-20.0, wherein f1: the focal distance of the first lens L1, f2: the focal distance of the second lens L2, d1: the center thickness of the first lens L1 and d3: the center thickness of the second lens L2. <P>COPYRIGHT: (C)2009,JPO&INPIT

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.

  In Patent Document 1, in order from an object, an aperture stop, 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 an object side An imaging lens that has a meniscus negative power third lens with a convex surface and satisfies a specific condition has been proposed. In this imaging lens, the power of the first lens is strong and the size is reduced. However, it is difficult to adjust the power of the first lens and the power of the second and third lenses, and correction of chromatic aberration and other aberrations may be insufficient.

  In Patent Document 2, in order from an object, an aperture stop, a meniscus positive first lens with a convex surface facing the object side, a second meniscus lens with a convex surface facing the image side, and a convex surface facing the object side In addition, an imaging lens that includes a meniscus third lens and satisfies a specific condition has been proposed. In this imaging lens, since the power of the second lens is kept lower than the power of the first lens, it may be difficult to correct the aberration of the central portion generated in the first lens with the second lens. In some cases, the optical characteristics may be insufficient.

Japanese Patent No. 3816095 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.

  As a result of intensive studies to achieve the above object, the power distribution of the first lens and the second lens constituting the imaging lens and the relationship between the focal length and the center thickness of each of the first lens and the second lens are set as a specific range. As a result, the inventors have found that the desired imaging lens can be obtained, and have reached the present invention. The power in the present invention is an amount represented by the reciprocal of the focal length.

The imaging lens according to the first aspect of the present invention includes, in order from the object, a diaphragm, 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 surface, The imaging lens satisfies the following conditional expressions (1) to (3) by disposing a meniscus negative third lens with a convex surface facing the object side.
−4.0 <f1 / f2 <−0.1 (1)
4.0 <f1 / d1 <7.0 (2)
−80.0 <f2 / d3 <−20.0 (3)
However,
f1: focal length of the first lens,
f2: focal length of the second lens,
d1: Center thickness of the first lens,
d3: the center thickness of the second lens.

According to a second aspect of the present invention, in the imaging lens according to the first aspect of the present invention, the imaging lens satisfies the following conditional expressions (4) and (5).
-10.0 <f2 / f <-2.0 (3)
0.01 <f2 / f3 <2.00 (4)
However,
f: focal length of the entire imaging lens system f2: focal length of the second lens f3: focal length of the third 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 includes a stop S1, a meniscus positive first lens L1 having a convex surface facing the object side from the object (not shown) side, and a meniscus having a convex surface facing the image surface side. This is a three-lens lens system in which a negative lens-shaped second lens L2 and a meniscus negative-power third lens L3 having a convex surface directed toward the object side are arranged. 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 with a convex surface facing the object side, the second lens L2 is a meniscus negative power lens with a convex surface facing the image side, and the third lens is the object side This is a meniscus negative power lens with a convex surface. In order to reduce the size of the imaging lens of the present invention, it is necessary to set the positive power of the first lens L1 strongly. Among the aberrations generated by the first lens L1, the aberration at the center is mainly, The correction is performed by the second lens L2 having a negative power, and the peripheral aberration is mainly corrected by the third lens L3 having a negative power. In order to more appropriately correct various aberrations, the surfaces of these three lenses are preferably aspherical on one or more surfaces, and more preferably aspherical on both surfaces.

  When the positive power of the first lens L1 is increased, the principal point is on the object side, so the imaging lens LA can be easily downsized. However, if the positive power of the first lens L1 becomes excessively strong, it may be difficult to adjust the positive power of the first lens L1 and the negative power of the second lens L2 and the third lens L3. For this reason, the first lens L1 has a convex surface toward the object side, a meniscus shape having a converging action on one side and a diverging action on the other side, preventing excessive power.

  In the imaging lens LA of the present invention, the aberration of the central part generated by the first lens L1 is mainly corrected by the second lens L2, and the aberration of the peripheral part is mainly corrected by the third lens L3. Therefore, in order to suitably correct the aberration at the center, the power distribution between the first lens L1 and the second lens L2 and the shapes of the first lens and the second lens L2 are important. In addition, in order to appropriately correct the peripheral aberration, it is important to distribute the negative power between the second lens L2 and the third lens L3.

Regarding the balance of power of the first lens L1 and the second lens L2, it is preferable that the ratio of the focal length f1 of the first lens L1 and the focal length f2 of the second lens L2 satisfies the conditional expression (1). If the value of f1 / f2 is below the lower limit of conditional expression (1), it may be difficult to correct the aberration at the center, while if it exceeds the upper limit, downsizing may be difficult.
−4.0 <f1 / f2 <−0.1 (1)

Moreover, in order to suppress that the 1st lens L1 and the 2nd lens L2 become excessive power, it is preferable that both are meniscus shape. Further, in the first lens L1, the ratio between the focal length f1 and the center thickness d1 of the first lens L1 is conditional expression (2), more preferably conditional expression (2-a), and further preferably conditional expression (2- b) is satisfied. By satisfying conditional expression (2), the first lens L1 suppresses excessive aberration of the first lens L1, and prevents the center thickness d1 from increasing. If the value of f1 / d1 is less than the lower limit of conditional expression (2), it may be difficult to correct the aberration at the center, while if it exceeds the upper limit, it may be difficult to reduce the size.
4.0 <f1 / d1 <7.0 (2)
4.5 <f1 / d1 <6.0 (2-a)
5.0 <f1 / d1 <6.0 (2-b)

The second lens L2 is designed to control the positive power of the first lens L1 and reduce the power load of the third lens L3. In the second lens L2, the ratio between the focal length f2 of the second lens L2 and the center thickness d3 satisfies the conditional expression (3). If the value of f2 / d3 is below the lower limit of conditional expression (3), it may be difficult to reduce the size, while if it exceeds the upper limit, correction of the aberration at the center may be difficult. When the first lens L1 and the second lens L2 satisfy the conditional expressions (1) to (3), it is possible to reduce the size of the imaging lens LA and appropriately correct the aberration at the center. .
−80.0 <f2 / d3 <−20.0 (3)

Further, the second lens L2 is formed of a material having a higher refractive index than the first lens L1, and the power distribution in the imaging lens LA is such that the focal length f2 of the second lens L2 and the focal length f of the entire imaging lens LA. The ratio satisfies the conditional expression (4), more preferably the conditional expression (4-a). When the value of f2 / f falls outside the range of conditional expression (4), the power balance between the second lens L2, the first lens L1, and the third lens L3 may be difficult.
-10.0 <f2 / f <-20.0 (4)
−8.0 <f2 / f <−20.0 (4-a)

Both the second lens L2 and the third lens L3 have negative power. The distribution of negative power is optimized so that the second lens L2 can mainly correct aberrations in the central portion and the third lens L3 can mainly correct aberrations in the peripheral portion. In the power distribution between the second lens L2 and the third lens L3, the ratio between the focal length f2 of the second lens L2 and the focal length f3 of the third lens L3 is conditional expression (5), more preferably (5-a ) Is satisfied. When the value of f2 / f3 satisfies the range of the conditional expression (5), the second lens L2 corrects the central aberration, and the third lens L3 corrects the peripheral aberration. Becomes easy.
0.01 <f2 / f3 <2.00 (5)
0.03 <f2 / f3 <1.50 (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.

  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 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.

  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, and a silicon resin. Etc. 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 distance is mm.
f: focal length f1 of the imaging lens LA: focal length f2 of the first lens L1: focal length f2 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 plane 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 of image surface R5: radius of curvature R6 of object side surface of third lens L3: radius of curvature of image surface of third lens L3 d: lens thickness or inter-lens distance d1: center thickness d2 of first lens L1 : Distance d3 between the image plane of the first lens L1 and the object side surface of the second lens L2: center thickness d4 of the second lens L2: distance d5 between the image plane of the second lens L2 and the object side surface of the third lens L3 : Inside the third lens L3 Thickness nd: refractive index n1 of d-line: refractive index n2 of first lens L1: refractive index n3 of second lens L2: refractive index νd of third lens L3: Abbe number ν1 at d-line: first lens Abbe number ν2 of the second lens Abbe number ν3 of the second lens: Abbe number of the third lens

  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 (7) is used for convenience. However, it is not particularly limited to the aspherical polynomial of the formula (7).

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 this condition, as shown in Table 7, it is within the range of conditional expressions (1) to (6).

  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.

(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 this condition, as shown in Table 7, it is within the range of conditional expressions (1) to (6).

  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.

(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 this condition, as shown in Table 7, it is within the range of conditional expressions (1) to (6).

  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.

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

Explanation of symbols

LA: imaging lens S1: aperture L1: first lens L2: second lens L3: third lens R1: radius of curvature R2 of the object side surface of the first lens L1: radius of curvature R3 of the image plane of the first lens L1: second Radius of curvature R4 of object side surface of lens L2: Radius of curvature R2 of image surface of second lens L2: Radius of curvature of object side surface of third lens L3 R6: Radius of curvature of image surface of third lens L3 d1: First lens L1 Center thickness d2: distance d3 between the image plane of the first lens L1 and the object side surface of the second lens L2: center thickness d4 of the second lens L2: the image plane of the second lens L2 and the object side surface of the third lens L3 Distance d5: center thickness of the third lens L3

Claims (2)

In order from the object, a diaphragm, a first meniscus-shaped positive power lens with a convex surface facing the object side, a second meniscus-shaped negative 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 negative power and satisfying the following conditional expressions (1) to (3):
−4.0 <f1 / f2 <−0.1 (1)
4.0 <f1 / d1 <7.0 (2)
−80.0 <f2 / d3 <−20.0 (3)
However,
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. The imaging lens according to claim 1, wherein the following conditional expressions (4) and (5) are satisfied.
-10.0 <f2 / f <-2.0 (3)
0.01 <f2 / f3 <2.00 (4)
However,
f: focal length of the entire system f2: focal length of the second lens f3: focal length of the third lens.

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