JP2009103896A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens, having a short focal distance for the imaging lens as a whole, a small size, and forming a two-lens configuration having proper optical characteristics. <P>SOLUTION: This imaging lens is constituted by arranging, in the order starting from the object side going toward the image plane side; a diaphragm; a first lens L1 as a positive meniscus lens, having a convex surface facing the object side; and a second lens L2 as a negative meniscus lens, having a convex surface facing the image plane side. The imaging lens satisfies the conditions (1) to (3): (1) 2.50<f1/d1<4.10, (2) 3.00<f1/d2<6.30; and (3)-30.00<f2/d3<-2.00, where the focal distance of the first lens L1 is f1, the focal distance of the second lens L2 is f2, the center thickness of the first lens is d1, the center thickness of the second lens L2 is d3, and the distance between the surface on the image plane side of the first lens L1 and the surface on the object side of the second lens L2 is d2. <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. 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.

  Example 5 of Patent Document 1 includes a meniscus first lens having a positive power with a convex surface facing the object side and a meniscus second lens having a negative power with a convex surface facing the image surface side. A configured imaging lens is disclosed. In the disclosed imaging lens, the power of the first lens is suppressed, and the power of the second lens corresponding thereto is set weak. For this reason, the focal length of the entire imaging lens becomes long, and the required miniaturization is still insufficient. In addition, since the power of the second lens is weak, correction of chromatic aberration may be insufficient. The power in the present invention is an amount represented by the reciprocal of the focal length.

JP 2004-170460 A

  The present invention has been made in order to solve the above-described problems of the conventional example, and is a two-lens lens in which the focal length of the entire imaging lens is short, compact, and optical characteristics, particularly chromatic aberration, are well corrected. An object is to provide a configured imaging lens.

  As a result of intensive studies to achieve the above object, it has been found that the objective imaging lens can be obtained when the relationship between the power and the center thickness of each of the first lens and the second lens satisfies a specific condition. The present invention has been reached.

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 negative lens with the convex surface facing the image plane side. A second meniscus-shaped lens having the following power is arranged, the focal length of the first lens is f1, the focal length of the second lens is f2, the center thickness of the first lens is d1, and the surface on the image plane side of the first lens When the distance between the second lens and the object side surface of the second lens is d2, and the center thickness of the second lens is d3, the following conditional expressions (1) to (3) are satisfied.
2.50 <f1 / d1 <4.10 (1)
3.00 <f1 / d2 <6.30 (2)
−30.00 <f2 / d3 <−2.00 (3)

The imaging lens according to a second aspect of the invention is the imaging lens according to the first aspect, wherein the following conditional expression (4) is satisfied, where d1 is the center thickness of the first lens and d3 is the center thickness of the second lens. To do.
0.25 <d1 / d3 <0.60 (4)

An imaging lens according to a third aspect of the present invention is the imaging lens according to the first or second aspect, wherein the radius of curvature of the object-side surface of the first lens is R1, and the image-side surface of the first lens Where R2 is the radius of curvature of the second lens, R3 is the radius of curvature of the object-side surface of the second lens, and R4 is the radius of curvature of the image-side surface of the second lens, the following conditional expressions (5) and (6) Satisfied.
0.10 <R1 / R2 <1.00 (5)
0.03 <R3 / R4 <1.00 (6)

  The imaging lens obtained by the invention of claim 1 has a meniscus first lens having a positive power with an aperture and a convex surface facing the object side in order from the object toward the image surface side, and a convex surface facing the image surface side. In addition, by disposing a meniscus second lens having negative power and satisfying the above conditional expressions (1) to (3), the focal length and optical length of the entire imaging lens are short, small, various aberrations, In particular, chromatic aberration is preferably corrected. 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 miniaturization, weight reduction and high performance of these devices. .

  The imaging lens obtained by the invention of claim 2 is reduced in size and size in the imaging lens of the invention of claim 1 by setting the ratio between the center thickness of the first lens and the center thickness of the second lens within a specific range. Various aberrations can be corrected more easily.

    The imaging lens obtained by the invention of claim 3 is the imaging lens according to claim 1 or 2, wherein the meniscus degree of each of the first lens and the second lens is in a specific range. This makes it easier to reduce the size and correct various aberrations.

  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. Thereby, it becomes possible to ensure high telecentricity, and it becomes easy to make the incident angle with respect to the image plane 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 negative power with both surfaces aspherical and having a convex surface facing the image surface side.

The imaging lens LA of the present invention includes a first meniscus lens having a positive power with a convex surface facing the object side and a negative surface with the convex surface facing the image surface side in order from the object side to the image surface side. A second meniscus lens having power is arranged, the focal length of the first lens L1 is f1, the focal length of the second lens L2 is f2, the center thickness of the first lens L1 is d1, and the center thickness of the second lens L2 Where d3 is the distance between the image-side surface of the first lens L1 and the object-side surface of the second lens L2, and the conditional expressions (1) to (3) are satisfied. It is possible to obtain an imaging lens having a two-lens configuration in which the focal length and the optical length of the entire lens are short, that is, small in size, and various aberrations, in particular, chromatic aberration is suitably corrected.
2.50 <f1 / d1 <4.10 (1)
3.00 <f1 / d2 <6.30 (2)
−30.00 <f2 / d3 <−2.00 (3)

  When the power of the first lens L1 is increased, the imaging lens LA can be easily reduced in size, but aberrations are increased. Conditional expression (1) defines the power of the first lens L1, and is a conditional expression for controlling the downsizing of the imaging lens LA and the generation of aberration. A more preferable conditional expression of the ratio between the focal length f1 of the first lens L1 and the center thickness d1, f1 / d1, is 3.00 <f1 / d1 <4.00. If f1 / d1 falls below the lower limit of conditional expression (1), the power of the first lens L1 becomes too strong, and miniaturization is easy, but correction of chromatic aberration such as spherical aberration and lateral chromatic aberration may be difficult. is there. On the other hand, when f1 / d1 exceeds the upper limit of 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 optical length of the imaging lens LA is increased. May become long, and miniaturization becomes difficult.

  Conditional expression (2) relates to field curvature and size reduction of the imaging lens LA. A more preferable conditional expression of the focal length of the first lens L1 as f1 and the distance d2 between the image side surface of the first lens L1 and the object side surface of the second lens L2 is 3.50 <f1 /. d2 <6.00. The ratio f1 / d2 between the focal length of the first lens L1 and the distance d2 between the image side surface of the first lens L1 and the object side surface of the second lens L2 is a lower limit of the conditional expression (2). If it is less than 1, the power of the first lens L1 becomes too strong and the size can be easily reduced, but the balance of field curvature may be deteriorated. On the other hand, if the upper limit is exceeded, downsizing may be difficult.

  The second lens L2 controls the positive power of the first lens L1 and corrects aberrations. Conditional expression (3) relates to power control and downsizing of the second lens L2. A more preferable conditional expression between the focal length f2 of the second lens L2 and the center thickness d3 of the second lens L2 is −25.00 <f2 / d3 <−3.00. If the ratio of the focal length f2 of the second lens L2 to the center thickness d3 of the second lens L2, f2 / d3 exceeds the upper limit of the conditional expression (3), the optical length of the imaging lens LA tends to be long, and miniaturization becomes difficult. easy. If the lower limit is not reached, the power of the second lens L2 becomes strong, and it may be difficult to correct the aberration at the center.

In the imaging lens LA, the center thickness d3 of the second lens L2 is thicker than the center thickness d1 of the first lens L1 by design. As a factor for reducing the size of the imaging lens LA, it is important to increase the power of the first lens L1 described above, but it is also a factor to suppress the thickness of the center thickness of the second lens L2. It is preferable that the center thickness d1 of the first lens L1 and the center thickness d3 of the second lens L2 satisfy the conditional expression (4).
0.25 <d1 / d3 <0.60 (4)

  A more preferable conditional expression of the center thickness d1 of the first lens L1 and the center thickness d3 of the second lens L2 is 0.30 <d1 / d3 <0.60. If the ratio d1 / d3 between the center thickness d1 of the first lens L1 and the center thickness d3 of the second lens L2 is below the lower limit of the numerical range of the conditional expression (4), it is difficult to reduce the size of the imaging lens LA. On the other hand, when the upper limit is exceeded, the center thickness d1 of the first lens L1 becomes thick, and the imaging lens LA may be downsized and aberration correction may be insufficient.

Both the first lens L1 and the second lens L2 have a meniscus shape. By making both surfaces of the lens aspherical as a specific meniscus shape, it becomes easy to correct the aberration generated in the first lens L1. The radius of curvature of the object side surface of the first lens L1 is R1, the radius of curvature of the image side surface of the first lens L1 is R2, the radius of curvature of the object side surface of the second lens L2 is R3, and the second lens L2 By satisfying the following conditional expressions (5) and (6) when the radius of curvature of the surface on the image plane side is R4, an imaging lens having a small two-lens structure with good optical characteristics can be obtained. It can be obtained more easily.
0.10 <R1 / R2 <1.00 (5)
0.01 <R3 / R4 <1.00 (6)

  Conditional expression (5) is an expression defining the meniscus degree of the first lens L1. A more preferable conditional expression is 0.20 <R1 / R2 <0.60. The ratio of the curvature radius R1 of the object-side surface of the first lens L1 to the curvature radius R2 of the image-side surface of the first lens L1, that is, when R1 / R2 exceeds the upper limit of the conditional expression (5), the curvature on the image side. The radius R2 becomes tight and it becomes difficult to correct distortion and the like. On the other hand, if the value is below the lower limit, the front principal point position of the first lens L1 approaches the image side and it becomes difficult to reduce the size of the imaging lens LA, and in addition, the edge thickness of the first lens L1 is secured in a bright Fno lens. May be difficult to do.

  Conditional expression (6) is an expression defining the meniscus degree of the second lens L2. A more preferable conditional expression is 0.05 <R3 / R4 <0.75. When the ratio R3 / R4 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 exceeds the upper limit of the conditional expression (6), 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.

  The lens material has a d-line refractive index measured according to the ASTM D542 method in the range of 1.450 to 1.650, more preferably in the range of 1.500 to 1.600, and a wavelength of 450. A material having a light transmittance in the range of ˜600 nm of 80% or more, more preferably 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, a thermosetting resin, or the same or different materials.

  Specific examples of the resin material include a non-crystalline polyolefin resin having a cyclo ring or other cyclic structure, a polystyrene resin, an acrylic resin, a polycarbonate resin, a transparent polyester resin, an epoxy resin, silicon. Based resins and the like. Among these, polyolefins containing a cycloolefin system and polyolefins containing a cyclic olefin 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. A known surface treatment can be applied. 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 side surface 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 side surface of the second lens L2 and the object side surface of the glass plane GL: Center thickness nd of glass plane GL: d Refractive index n1 of the line: 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 the d-line: Abbe number ν2 of the first lens: second Abbe number ν3 of lens: 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 <sup>6
+ A8x 8 + A10x 10 + A12x</sup> 12 + A14x 14 + A16x 16 (7)

  Here, R is a radius of curvature on the optical axis, k is a conical coefficient, and A4, A6, A8, A10, A12, A14, and A16 are aspherical coefficients.

  As an aspheric surface of each lens surface, an aspheric surface represented by Expression (7) is used for convenience. However, the present invention is not particularly limited to the aspheric 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. Curvature radius R, lens thickness or inter-lens distance d, refractive index nd, Abbe number νd of the object-side and image-side surfaces of the first lens L1 and the second lens L2 constituting the imaging lens LA of Embodiment 1. Table 1 shows the conic coefficient k and the aspheric coefficient values.

  The imaging lens LA of Example 1 satisfies the conditional expressions (1) to (6) as shown in Table 9, and the focal length f and the optical length TTL of the entire 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. 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. 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 radius of curvature R of the object side and image side surfaces of the first lens L1 and the second lens L2 constituting the imaging lens LA of Example 2, 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.

  The imaging lens LA of Example 2 satisfies conditional expressions (1) to (6) as shown in Table 9, and the focal length f and the optical length TTL of the entire 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 lateral chromatic aberration. 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. 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 image plane side surfaces of the first lens L1 and the second lens L2 constituting the imaging lens LA of Example 3, the lens thickness or the 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.

  The imaging lens LA of Example 3 satisfies the conditional expressions (1) to (6) as shown in Table 9, and the focal length f and the optical length TTL of the entire 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. 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. 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 radius of curvature R of the object side and image side surfaces 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 conic coefficient k and aspheric coefficient values.

  The imaging lens LA of Example 4 satisfies the conditional expressions (1) to (6) as shown in Table 9, and the focal length f and the optical length TTL of the entire 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. 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. From the above results, the imaging lens LA of Example 4 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 surface 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 of the second lens L2 Distance d5 between side surface and object side surface of glass plane GL: center thickness of glass plane GL

Claims (3)

In order from the object side to the image surface side, a first lens having a positive power with a diaphragm and a convex surface facing the object side, and a second meniscus lens having a negative power with a convex surface facing the image surface side And an imaging lens characterized by satisfying the following conditional expressions (1) to (3):
2.50 <f1 / d1 <4.10 (1)
3.00 <f1 / d2 <6.30 (2)
−30.00 <f2 / d3 <−2.00 (3)
However,
f1: focal length of the first lens f2: focal length of the second lens d1: center thickness of the first lens d2: distance d3 between the image side surface of the first lens and the object side surface of the second lens : Center thickness of the second lens The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied.
0.25 <d1 / d3 <0.60 (4)
However,
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 (5) and (6) are satisfied.
0.10 <R1 / R2 <1.00 (5)
0.03 <R3 / R4 <1.00 (6)
However,
R1: radius of curvature of the object side surface of the first lens R2: radius of curvature of the image side surface of the first lens R3: radius of curvature of the object side surface of the second lens R4: radius of curvature of the second lens on the image side Radius of curvature of face

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