JP3935896B2 - Imaging lens, imaging module, and portable terminal - Google Patents

Description

  The present invention relates to an imaging lens used in an imaging device using an imaging element such as a CCD or CMOS, an imaging module using the imaging lens, and a portable terminal.

  2. Description of the Related Art In recent years, technology related to an imaging device used for multimedia has been remarkably developed. For example, an imaging device using an imaging element such as a CCD or CMOS is used in a mobile phone, a digital camera, a portable computer, or the like. . Imaging lenses mounted on these imaging devices are required to have higher performance, smaller size, and lighter weight.

  Conventionally, an imaging lens having a single lens system or a dual lens system has been proposed for downsizing and weight reduction. 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, the technical development of an imaging lens corresponding to high image quality and high resolution with three or more lens configurations has been advanced, and imaging lens systems having various configurations have been proposed.
For example, in the case of a three-lens configuration, an aperture stop from the object side, a first lens having a positive power with a convex surface on the object side, a second lens having a negative power with a concave surface on the object side, and a third lens having a positive power An imaging lens system configured by sequentially arranging lenses is known. Proposals obtained by improving this technique are disclosed in, for example, Patent Documents 1 and 2. The imaging lens disclosed in Patent Document 1 is an imaging lens having features such as a wide angle of view and favorable correction of various aberrations. The imaging lens disclosed in Patent Document 2 is an imaging lens having features such as being small and correcting various aberrations satisfactorily.
JP 2001-750006 A Japanese Patent Laid-Open No. 2004-4466

However, the imaging lens disclosed in Patent Document 1 has insufficient points in terms of size reduction and weight reduction. Further, the imaging lens disclosed in Patent Document 2 has a slightly insufficient point in terms of resolution. In addition, the surface shape of a small and high-performance imaging lens is usually an aspherical shape having at least one complicated surface, and it is difficult to shape the lens surface into a desired shape as designed. Conventionally, there are few proposals that take into account this complicated shaping of the lens surface.
In view of these prior arts, the present invention is a three-lens imaging lens that is small and light, has various aberrations suitably corrected, has good resolution, and is easy to shape the lens surface, and uses this imaging lens. An object is to provide an imaging module and a portable terminal.

In order to achieve the above object, according to the first aspect of the present invention, there is provided, in order from the object side, an aperture stop, a positive-powered biconvex first lens having a larger radius of curvature on the image plane side than the object side , and an image side surface. In the imaging lens in which the convex-shaped negative power second lens and the positive lens third lens in which the vicinity of the optical axis on the side surface of the image has a concave shape and the outer peripheral portion has a convex shape are arranged in order, At least one of the surfaces of the first to third lenses has an aspheric shape, and the imaging lens satisfies the following conditional expression.
0.5 <f1 / f <0.8 (1)
0.3 <| f2 | / f <0.7 (2)
0.5 <f3 / f <1.0 (3)
0.4 <R1 / | R2 | <1.0 (4)
0.2 <| R3 | / | R4 | <0.6 (5)
0.1 <R5 / R6 <0.3 (6)
However,
f: focal length of the entire imaging lens of the present invention f1: focal length of the first lens f2: focal length of the second lens f3: focal length of the third lens
R1: central radius of curvature of the object side surface of the first lens
R2: center curvature radius of the image side surface of the first lens
R3: center radius of curvature of the object side surface of the second lens
R4: Center curvature radius of the image side surface of the second lens
R5: Center curvature radius of the object side surface of the third lens
R6: Center curvature radius of the image side surface of the third lens

According to the first aspect of the present invention, the aperture stop, the positive power first lens, the negative power second lens, and the positive power third lens are sequentially arranged from the object side. At least one of the third lenses has an aspheric shape, and the relationship between the focal length of each lens and the focal length of the entire imaging lens satisfies the conditional expressions (1), (2), and (3). By doing so, it is possible to obtain a three-lens imaging lens with good resolution, small size and light weight, and various aberrations suitably corrected. Further, the conditional expression (4) defines the ratio of the center curvature radius R5 of the object side surface to the center curvature radius R6 of the image side surface and the surface on the image surface side in a specific shape. The overall length is shortened, aberrations such as field curvature are suitably corrected, and the shape of the lens surface shape is improved. Further, the ratio of the central curvature radius of the object side surface and the central curvature radius of the image side surface of each of the first lens and the second lens is defined by conditional expressions (5) and (6), so that the total length of the imaging lens is increased. In addition to being shortened, various aberrations such as spherical aberration, coma and curvature of field are suitably corrected, and the shape of the lens surface shape is improved.

  The invention described in claim 2 is an imaging lens having the same configuration as that of the invention described in claim 1 and having all surfaces of the first to third lenses being aspherical.

According to the second aspect of the present invention, an imaging lens in which various aberrations are more preferably corrected can be obtained.

The invention described in claim 3 has the same configuration as that of the invention described in claim 1 or 2, and all the lenses of the first to third lenses are made of a plastic material. And an edge lens KB that does not contribute to image formation, and the ratio of the outer diameter LD of the curved surface end of the lens to the longest outer diameter KD of the edge KB satisfies the following conditional expression.
1.1 <KD / LD <4.0 ( 7 )

According to the third aspect of the present invention, formability of lenses surface shape is improved.

The invention described in claim 4 has the same configuration as that of any one of the inventions described in claims 1 to 3 , and the first lens and the third lens are d-line measured according to the ASTM D542 method. Polyolefin-based material having a refractive index of 1.500 to 1.540, a polycarbonate-based material or a polyester-based material having a second lens having a refractive index of d-line measured according to ASTM D542 method of 1.580 to 1.615 An imaging lens made of a material.

According to the invention of claim 4 , the plastic material constituting the imaging lens is made of polycycloolefin for the first lens and the third lens, and polycarbonate or polyester material for the second lens. The optical design of the imaging lens and the shaping of the lens surface shape become easier.

According to a fifth aspect of the present invention, there is provided an image sensor that obtains an image signal corresponding to light irradiated on its own photoelectric conversion surface, and an object is imaged on the photoelectric conversion surface of the image sensor. an imaging lens according to any one of the claim 4, having an opening for the light incident from the object side, holding the imaging lens, a lens barrel for fixing, incident from the imaging lens to the imaging element A transparent flat plate that transmits effective light speed, an image signal processing circuit having an external connection terminal that holds the image sensor and transmits and receives an electrical signal, and holds the transparent flat plate, the image sensor, and the image signal processing circuit, The imaging module is composed of parts including a housing to be fixed, and these are integrally formed. According to the fifth aspect of the present invention, it is possible to obtain a small and light imaging module with high image quality.

A sixth aspect of the present invention is a portable terminal including the imaging module according to the fifth aspect . According to the invention described in claim 6, it is possible to obtain a portable terminal having a small size and light weight and high image quality .

The imaging lens of the present invention, positive negative power is suitably balanced, and, since it is possible to suitably correct various aberrations, the resolution is good, the size and weight. Further, the overall length of the imaging lens is shortened, aberrations such as field curvature are preferably corrected, and the shape of the lens surface shape is improved. Furthermore, various aberrations such as spherical aberration, coma aberration, and curvature of field are suitably corrected, and the shape of the lens surface shape is improved. In addition, the imaging module and the portable terminal are small and light and have high resolution.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows one of the basic configurations of an imaging lens L according to the present invention.
From the left side of FIG. 1, the imaging lens L of the present embodiment includes an object (not shown), an aperture stop S, a first lens L1 having a positive power, a second lens L2 having a negative power, and a third lens having a positive power. L3 is a lens having a three-lens structure that is sequentially arranged. By placing the aperture stop S in front of the first lens L1, the exit pupil is separated from the image plane. A transparent flat plate P is placed between the third lens L3 and an image (not shown). This transparent flat plate P is installed between the imaging lens L and the imaging element 11 (not shown), and has a function such as an infrared cut filter, a low-pass filter, or a cover glass. The alternate long and short dash line indicates the optical axis.

The first lens L1 is a biconvex lens, the object side surface of the second lens L2 is a concave surface, the object side surface of the third lens L3 is a convex surface, and is at least one surface of the first to third lenses L3. The above-mentioned aspherical shape corrects various aberrations. The power balance of the imaging lens L is that the power of the first lens L1 is such that the ratio f1 / f between the focal length f1 of the first lens L1 and the focal length f of the entire imaging lens of the present invention is the following conditional expression (1): The power of the second lens L2 is such that the ratio | f2 | / f of the focal length f2 of the second lens L2 and the focal length f of the entire imaging lens of the present invention falls within the range of the following conditional expression (2). The power of the three lenses L3 is high because the ratio f3 / f of the focal length f3 of the third lens L3 and the focal length f of the entire imaging lens of the present invention is defined in the range of the following conditional expression (3). Therefore, it is possible to reduce the size and weight and to improve the shape of the lens surface shape.
0.5 <f1 / f <0.8 (1)
0.3 <| f2 | / f <0.7 (2)
0.5 <f3 / f <1.0 (3)

The conditional expression will be further described.
If the f1 / f value of the first lens L1 is smaller than the lower limit value of the conditional expression (1), the positive power of the first lens L1 becomes excessively large, and the error sensitivity after the second lens L2 is large. This is not preferable. On the other hand, when the value is larger than the upper limit value, the positive power becomes too small and it is difficult to shorten the entire length of the imaging lens.

  The second lens L2 is a negative power lens. Since both the first lens L1 and the third lens L3 have positive power, the negative power of the second lens L2 is defined by the conditional expression (2) to optimize the power of the entire imaging lens. The ratio between the focal length f2 of the second lens 2 and the focal length f of the entire imaging lens of the present invention is defined by conditional expression (2), but more preferably 0.4 <| f2 | / f <0. .6. If the value of | f2 | / f is smaller than the lower limit, the positive power of the imaging lens becomes too large, and the error sensitivity of the first lens L2 and the third lens L3 becomes large, which is not preferable. On the other hand, if the value exceeds the upper limit value, the correction of chromatic aberration becomes insufficient.

  The positive power of the third lens L3 is defined by the conditional expression (3), and the positive power distribution with the first lens L1 is optimized. The ratio f3 / f between the focal length f3 of the third lens L3 and the focal length f of the entire imaging lens of the present invention is defined by conditional expression (3), but more preferably 0.6 <f3 / f <. 0.9. If the value of f3 / f is smaller than the lower limit value, the difference in thickness between the center portion and the peripheral portion of the lens becomes large, and it becomes difficult to shape the lens surface shape. In addition, positive power distribution with the first lens L1 may be inappropriate, and it may be difficult to correct distortion. On the other hand, if the value is larger than the upper limit value, the incident angle to the sensor becomes large, which is not preferable, and it is difficult to shorten the entire length of the imaging lens L.

  Also, by making all the surfaces of the first to third lenses L3 aspherical, the spherical aberration and coma are mainly corrected in the first lens L1, and mainly coma and astigmatism are corrected in the second lens L2. Aberrations are corrected, and in the third lens L3, various aberrations in the periphery of the screen such as curvature of field and distortion are mainly corrected, and each lens is appropriately assigned the aberration correction to obtain a good imaging lens L. Can do.

Next, the shape of the third lens L3 will be described with reference to FIG. The focal length of the third lens L3 is defined by the conditional expression (3). Further, the ratio R5 / R6 of the central curvature radius R5 of the object side surface and the central curvature radius R6 of the image side surface of the third lens L3 is a conditional expression (4 ) And the shape of the image side surface is a substantially concave surface at the central portion A and a substantially convex surface at the peripheral portion B.
0.1 <R5 / R6 <0.3 (4)

If the value of R5 / R6 is smaller than the lower limit, field curvature and astigmatism will deteriorate. If it exceeds the upper limit value, the incident angle to the sensor increases and it becomes difficult to shorten the entire length of the imaging lens L.
The value of R5 / R6 is within the range of conditional expression (4), and the lens surface shape of the image side surface is such that the central portion A is a substantially concave surface and the peripheral portion B is a substantially convex surface, thereby correcting various aberrations. This makes it possible to improve the image quality, prevent the lens size from increasing, and facilitate the shaping of the surface shape of the third lens L3. Here, the area of the central part A and the peripheral part B varies depending on the desired optical characteristics of the lens. Referring to FIG. 2, a region within 80%, preferably within 60% of the lens diameter LD with the center C as the intersection of the lens surface on the image side surface of the third lens L3 and the optical axis is substantially concave. In addition, a peripheral portion of the lens diameter of 80 to 100%, preferably 60 to 100% may be a substantially convex surface. An area of 60 to 80% of the lens diameter LD where the concave surface and the convex surface overlap may be a concave surface continuing from the central portion A as appropriate depending on the optical design of the lens in consideration of the optical characteristics of the lens and the appropriateness of correction of various aberrations. In other words, the region is a convex surface continuing from the peripheral portion B.

In the first lens L1, the ratio R1 / | R2 | of the center curvature radius R1 of the object side surface and the center curvature radius R2 of the image side surface satisfies the conditional expression (5), and the second lens L2 is the center of the object side surface. The ratio between the curvature radius R3 and the central curvature radius R4 of the image side surface satisfies the conditional expression (6).
0.4 <R1 / | R2 | <1.0 (5)
0.2 <| R3 | / | R4 | <0.6 (6)

  When the value of R1 / | R2 | of the first lens L1 is smaller than the lower limit, it is difficult to correct off-axis aberrations. On the other hand, when it becomes larger than the upper limit, the entire length of the imaging lens L becomes longer. If the value of | R3 | / | R4 | of the second lens L2 is smaller than the lower limit, the error sensitivity of the second lens L2 and the third lens L3 becomes too large, which is not preferable. On the other hand, if it exceeds the upper limit, it is difficult to correct off-axis aberrations. Further, when the first lens L1 satisfies the conditional expression (5) and the second lens L2 satisfies the conditional expression (6), the shape of the lens surface shape is improved.

Next, the material constituting the lens will be described. All the lenses of the first to third lenses L3 are made of a plastic material, and all the lenses have an edge KB that does not contribute to image formation on the outer peripheral portion.
A plastic material is useful as a material for an imaging lens because a molded product having a complicated shape can be manufactured with high productivity by a method such as an injection molding method and the weight can be easily reduced. However, even if a plastic material is used, it is difficult to accurately shape the surface shape of a small imaging lens having an aspherical complicated surface shape. In particular, when the lens diameter is 10 mm or less, shaping is difficult. As a method for improving the formability of the lens surface, a method of improving the plastic molding processability when manufacturing an imaging lens by providing an edge KB that does not contribute to image formation on the outer periphery of the lens is conventionally known. However, there is no suggestion about the shape of the edge KB effective for forming processability.

Therefore, as a result of examining a suitable shape of the edge KB of the imaging lens L, it has been found that the relationship between the outer diameter LD of the lens and the outer diameter KD of the edge affects the shaping of the complex surface shape of the imaging lens L. It was. That is, in the case of the larger surface of the lens, the third lens, the length of the lens curved surface ends X and X ′ on the image side surface is the lens outer diameter LD, and the ratio with the longest outer diameter KD of the edge KB is
1.1 <KD / LD <4.0 (7)
More preferably, by satisfying 1.1 <KD / LD <3.0, the shape of the surface shape of the lens was good.

If the value of KD / LD is smaller than the lower limit, the moldability may be deteriorated. If the value is larger than the upper limit, there is no big problem with the moldability, but the amount of resin used increases and the mold clamping pressure increases. This is not preferable because it requires a molding apparatus. In the case of FIG. 2, the outer diameter LD of the lens is the length between the curved end point XX ′ on the image side surface, and this length is usually longer than the effective screen diagonal length of the lens.
The shape of the edge KB is preferably circular, but may be oval. Further, a part of the edge KB may have a notch as shown in FIG.

Referring to FIG. 1, when a specific example of KD / LD is given, the KD / LD of the first lens L1 is 2.1 (
KD = 2.38 mm, LD = 5.00 mm) , KD / LD of the second lens L2 is 2.3 (KD = 7.30 mm, LD = 3.12 mm) , and KD / LD of the third lens L3 is 1. 3 (KD = 7.50 mm, LD = 5.74 mm) .
When the imaging lens L is molded by plastic injection molding or the like, the thickness of the edge KB affects not only the outer diameter KD of the edge. However, the thickness of the edge KB is determined by factors other than molding processability, such as the shape of the imaging lens L, for example, whether it is concave or convex, the lens thickness, and the distance from other lenses combined. It is difficult to define clearly because there are.

  In the case of the imaging lens L of the present invention, when the ratio of the thickness LT of the center C of the imaging lens to the thickness KT of the thinnest edge is in the range of 0.2 <KT / LT <3.0, imaging is performed. The shape of the surface shape of the lens L was good.

  In the case where the edge KB is provided on the outer periphery of the lens, if light enters the edge KB, it causes ghost and flare. In that case, as shown in FIG. 4, the peripheral luminous flux is limited between the first lens L1 and the second lens L2 and between at least one of the two lenses between the second lens L2 and the third lens L3. By providing the light shielding mask 16, it is possible to minimize the incidence of light on the edge KB and to suppress the occurrence of ghosts and flares. In the imaging lens L of the present invention, a light shielding mask 16 can be provided as necessary.

  The light shielding mask 16 has a special material or shape as long as it is a light shielding member having an opening for light transmission at the center and a light shielding paint is applied to the edge KB to limit the incidence of light on the edge KB. There are no limitations.

  The selection of the plastic material is important because the light transmittance, refractive index, and molding processability vary depending on the type. The imaging lens L of the present invention is preferably a polyolefin-based material having a d-line refractive index of 1.500 to 1.540 measured according to ASTM D542 for the first lens L1 and the third lens L3. For the second lens L2, a polycarbonate-based material or a polyester-based material having a d-line refractive index of 1.580 to 1.615 measured according to the ASTM D542 method is preferably used. By using these plastic materials, the optical design of the imaging lens L is easy, and a lens shape in which the surface shape can be easily shaped can be obtained.

  Specific examples of the polyolefin-based material used for the first lens L1 and the third lens L3 include amorphous polyolefins having a cyclo ring or other cyclic structures. The polycarbonate material used for the second lens L2 is a bisphenol type polycarbonate, and the polyester material is a polyester containing a raw material having a fluorene structure such as 9,9-bis (4-hydroxyphenyl) fluorene as one component. .

  The imaging lens L of the present invention is preferably used for the imaging module 10 after the surface of the object side surface and the image side surface of all the lenses has been subjected to surface treatment for the purpose of improving the antireflection film and surface hardness. . The antireflection film is applied to all surfaces of the first to third lenses of the present invention by a known vacuum deposition method. The light transmittance of each lens provided with the antireflection film is 90% or more in the wavelength range of 450 to 750 nm, more preferably 95% in the wavelength range of 450 to 750 nm, as measured with a spectrophotometer. That's it.

FIG. 4 is an example of a cross section of an imaging module 10 using the imaging lens L of the present invention.
The imaging module 10 includes an imaging device 11 made of either CCD or CMOS, imaging lenses L1, L2, and L3 of the present invention, a barrel 12 that fixes and holds these imaging lenses, an infrared cut filter, a low-pass filter, or A transparent flat plate P made of any one of cover glasses, an image signal processing device 13 having an external connection terminal capable of transmitting and receiving electrical signals to and from the outside, such as a flexible substrate, a connector, etc. The housing 14 holds the image signal processing device 13. The transparent flat plate P may be an infrared cut filter or a combination of a low-pass filter and a cover glass.

  The lens barrel 12 is made of a light-shielding material having a light incident opening from the object side, and a plastic material is usually used. The imaging lens L is attached to the lens barrel 12 at a predetermined interval in the order of the first lens L1, the second lens L2, and the third lens L3 from the object side. Each lens has an edge KB, and the edge KB may be fixed to the lens barrel 12 with an adhesive or the like. The lens holder 15 is used to fix the lens position, the lens holder 15 and the mirror. The cylinder 12 may be fixed with an adhesive or the like. In order to suppress ghosts and flares caused by edge KB between the first lens L1 and the second lens L2 and between the second lens L2 and the third lens L3, the light shielding mask 16 is used. May be incorporated. The lens holder 15 and the light shielding mask 16 are preferably made of a plastic material having a light shielding property. The distance between the lenses is set to a desired distance depending on the distance between the lens barrel 12 and each lens and the shape of the edge KB. The image sensor 11 is disposed on an image signal processing device 13 having a signal terminal for external connection, and is connected to the image signal processing device 13 through a wire not shown.

  The transparent flat plate P and the image signal processing device 13 are fixed to the housing 14 with an adhesive or the like, and the lens barrel 12 is screwed into the inside of the housing 14 with screws 17 and connected to each other.

  The imaging module 10 is used not only for portable terminals such as notebook computers, mobile phones, and digital cameras, but also for monitoring parts for automobiles and industrial equipment.

Examples of the imaging lens L according to the present invention will be described below. The symbols used in each example are as follows.
f: focal length of the entire imaging lens f1: focal length of the first lens L1 f2: focal length of the second lens L2 f3: focal length of the third lens L3 FB: back focus F: F number R1: of the first lens L1 Center curvature radius of object side surface R2: Center curvature radius of image side surface of first lens L1 R3: Center curvature radius of object side surface of second lens L2 R4: Center curvature radius of image side surface of second lens L2 R5: Third lens Center radius of curvature of object side surface of L3 R6: Center radius of curvature of image side surface of third lens L3 Tt: Distance between refractive surfaces nd: Refractive index at d line νd: Appe number

  The aspherical shape of each lens of the imaging lens L is Z axis in the optical axis direction, X is the direction perpendicular to the optical axis, the axis is taken, the light traveling direction is positive, and K, a, b, c are When an aspheric coefficient is used, it is expressed by the following equation.

Example 1
FIG. 5 is an explanatory diagram illustrating the arrangement of the imaging lenses of the first embodiment. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and P is a transparent plate. In FIG. 5, the edge KB on the outer periphery of the lens is not shown. The first lens L1 and the third lens L3, the refractive index of the d line was measured according to ASTM D542 method, polycycloolefin (trade name ZEONEX, Nippon Zeon) is 1.509 using the second lens L No. 2 was produced by injection molding using bisphenol-type polycarbonate having a d-line refractive index of 1.585 measured according to the ASTM D542 method. The imaging lens L of Example 1 is set under the following conditions. Aspherical coefficients are shown in Table 1.

f = 4.635 mm, f1 = 3.333 mm, f2 = −2.404 mm, f3 = 3.417 mm, fB = 1.101 mm, optical length = 6.410 mm, F = 3.200

Surface number Curvature radius R (mm) Refractive surface spacing Tt (mm) Refractive index nd Upe number νd
Aperture stop ∞ 0.05
1 2.476 1.47 1.509 56.0
2 -4.315 0.77
3 -0.668 0.55 1.585 30.0
4-1.659 0.05
5 1.454 1.72 1.509 56.0
6 5.331 0.50
7 ∞ 0.50 1.517 64.2

Under such conditions, f1 / f = 0.719, | f2 | /f=0.518, f3 / f = 0.737, R1 / | R2 | = 0.574, | R3 | / | R4 | = 0.403,
R5 / R6 = 0.273. An imaging lens that achieves the object of the present invention.

  FIG. 6 shows the lateral aberration of the imaging lens L of Example 1, FIG. 7 shows the spherical aberration, FIG. 8 shows the astigmatism and distortion aberration, and shows the relationship between the contrast on the axis of MTF (transfer function, modulated transfer function) and the spatial frequency. 9 shows the relationship between the off-axis / vertical contrast of MTF and the spatial frequency in FIG. 10, FIG. 11 shows the relationship between the off-axis / horizontal contrast of MTF and the spatial frequency, and FIG. The relationship is shown in FIG. From these data, the imaging lens L of Example 1 has various aberrations corrected well, has high resolution, and the shape of the imaging lens on the lens surface is good. 6 to 8 are data at wavelengths of 436 nm, 486 nm, 546 nm, 588 nm, and 656 nm. In the MTF data, S represents a sagittal image plane, and T represents a tangential image plane.

(Example 2)
FIG. 13 is an explanatory diagram illustrating the arrangement of the imaging lenses of the second embodiment. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and P is a transparent flat plate. In FIG. 13, the edge KB on the outer periphery of the lens is not shown. The first lens L1 and the third lens L3, the refractive index of the d line was measured according to ASTM D542 method, polycycloolefin (trade name ZEONEX, Nippon Zeon) is 1.509 using the second lens L No. 2 was produced by injection molding using bisphenol-type polycarbonate having a d-line refractive index of 1.585 measured according to the ASTM D542 method. The imaging lens L of Example 2 is set under the following conditions. The aspheric coefficients are shown in Table 2.
f = 4.341 mm, f1 = 2.876 mm, f2 = −2.007 mm, f3 = 3.0867 mm, fB = 0.630 mm, optical length = 6.0000 mm, F = 2.8

Surface number Curvature radius R (mm) Refractive surface spacing T (mm) Refractive index nd Upe number νd
Aperture stop ∞ 0.08
1 2.294 1.20 1.509 56.0
2 -3.334 0.74
3 -0.570 0.50 1.585 30.0
4-1.466 0.03
5 1.392 1.57 1.509 56.0
6 7.545 0.50
7 ∞ 0.75 1.517 64.2

Under such conditions, f1 / f = 0.663, | f2 | /f=0.462, f3 / f = 0.711, R1 / | R2 | = 0.688, | R3 | / | R4 | = 0.388,
R5 / R6 = 0.184. An imaging lens that achieves the object of the present invention.

  FIG. 14 shows the relationship between the MTF axis contrast and spatial frequency of the imaging lens L of Example 2, FIG. 15 shows the relationship between the MTF off-axis / vertical contrast and spatial frequency, and FIG. 15 shows the MTF off-axis / horizontal contrast and space. FIG. 16 shows the relationship between frequencies, and FIG. 17 shows the relationship between the off-axis / diagonal contrast of MTF and the spatial frequency. From these data, the imaging lens L of Example 2 has various aberrations corrected favorably, has high resolution, and has good shapeability of the imaging lens on the lens surface.

The schematic block diagram which shows the imaging lens 1 form of this invention. The figure which shows the external shape of a 3rd lens. The top view of a lens with a notch in the edge. Sectional drawing which shows one example of an imaging module. FIG. 2 is a schematic configuration diagram illustrating an imaging lens of Example 1. FIG. 4 is a lateral aberration diagram of Example 1. FIG. 3 is a spherical aberration diagram of Example 1. FIG. 3 is an astigmatism and distortion diagram of Example 1. The figure which shows the relationship between MTF of Example 1, the contrast on an axis | shaft, and a spatial frequency. The figure which shows the MTF of Example 1, the off-axis / vertical contrast, and the spatial frequency. The figure which shows the relationship of MTF of Example 1, off-axis and horizontal contrast, and a spatial frequency. The figure which shows the relationship between the MTF of Example 1, the off-axis / diagonal contrast, and the spatial frequency. FIG. 4 is a schematic configuration diagram illustrating an imaging lens of Example 2. The figure which shows the MTF of Example 2, and the relationship between on-axis contrast and spatial frequency. The figure which shows the relationship of MTF of Example 2, off-axis and perpendicular | vertical contrast, and a spatial frequency. The figure which shows the relationship of MTF of Example 2, off-axis and horizontal contrast, and a spatial frequency. The figure which shows the relationship of MTF of Example 2, off-axis and diagonal contrast, and a spatial frequency.

Explanation of symbols

A: Near lens optical axis B: Lens outer periphery C: Optical axis L: Imaging lens L1: First lens L2: Second lens L3: Third lens Ln: Lens part St: Aperture aperture P: Transparent flat plate KB: Edge 10: Imaging module 11: Imaging element 12: Lens tube 13: Transparent flat plate incorporated in the imaging module 14; Image signal processing device 15: Housing 16: Lens presser 17: Light shielding mask

Claims (6)

In order from the object side, an aperture stop, a first lens of a double convex radius of curvature is large positive power of the image side from the object side, a second lens image side of the negative power of the convex of the image side surface In an imaging lens in which the vicinity of the optical axis has a concave shape and the outer peripheral portion has a convex shape and a positive power third lens is sequentially arranged, at least one of the surfaces of the first to third lenses is not An imaging lens having a spherical shape and satisfying the following conditional expression:
0.5 <f1 / f <0.8 (1)
0.3 <| f2 | / f <0.7 (2)
0.5 <f3 / f <1.0 (3)
0.4 <R1 / | R2 | <1.0 (4)
0.2 <| R3 | / | R4 | <0.6 (5)
0.1 <R5 / R6 <0.3 (6)
However,
f: focal length of the entire imaging lens of the present invention f1: focal length of the first lens f2: focal length of the second lens f3: focal length of the third lens
R1: central radius of curvature of the object side surface of the first lens
R2: center curvature radius of the image side surface of the first lens
R3: center radius of curvature of the object side surface of the second lens
R4: Center curvature radius of the image side surface of the second lens
R5: Center curvature radius of the object side surface of the third lens
R6: Center curvature radius of the image side surface of the third lens   The imaging lens according to claim 1, wherein all surfaces of the first to third lenses are aspherical. The first to third lenses are all made of a plastic material, and all these lenses have an edge that does not contribute to image formation on the outer periphery, and the longest diameter KD of the edge and the diameter LD of the curved surface end of the lens, the imaging lens according to claim 1 or claim 2 ratio is characterized by satisfying the following conditional expression.
1.1 <KD / LD <4.0 (7)
However,
LD: Diameter of lens end of curved surface KD: Longest diameter of edge The first lens and the third lens are composed of a polyolefin-based material having a refractive index of d-line of 1.500 to 1.540 measured according to the ASTM D542 method, and the second lens is measured according to the ASTM D542 method. The imaging lens according to any one of claims 1 to 3 , wherein the imaging lens is made of a polycarbonate-based material or a polyester-based material having a refractive index of d-line of 1.580 to 1.615. An image sensor that obtains an image signal corresponding to the light irradiated on its own photoelectric conversion surface;
The imaging lens according to any one of claims 1 to 4 , wherein a subject is imaged on a photoelectric conversion surface of the imaging element;
A lens barrel having an opening for light incidence from the object side, and holding and fixing the imaging lens;
A transparent flat plate that transmits an effective light beam incident on the image sensor from the imaging lens;
An image signal processing circuit having an external connection terminal for holding the image sensor and transmitting and receiving an electrical signal;
A housing for holding and fixing the transparent flat plate, the imaging device, and the image signal processing circuit;
An imaging module in which these are integrally formed. A portable terminal comprising the imaging module according to claim 5 .

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