JP2007298719A - Imaging lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging lens used for image input of a cellular phone or a portable terminal, which has excellent telecentricity and can be reduced in size, has excellent resolution performance, other peripheral light quantity, distortion aberration characteristics, and necessary. An imaging lens having a back focus is provided.
In order from an object side, an aperture stop, a meniscus positive first lens having a convex surface facing the object side, a meniscus negative second lens having a convex surface facing the image surface side, and a convex surface facing the object side. A positive meniscus third lens having an aspheric surface on both sides is arranged. Further, the first lens and the second lens have at least an aspheric surface on the image plane side, and in each of the first lens, the second lens, and the third lens, the object side surface is the first surface and the image plane side. When the second surface is the second surface, 1.3 <f / f1 <1.5,
1.8 <R2 / (Nd1-1) / f <15, 1.0 <TL / f <1.3, 1.8 <TL / Y <2, 18 <α <23, 61 <2ω <64 Satisfy the conditional expression.
[Selection] Figure 1

Description

  The present invention relates to a small imaging lens used for image input of a mobile phone, a portable terminal, an electronic still camera, or the like using a solid-state imaging device such as a CCD image sensor or a CMOS image sensor.

In recent years, the pixel density of CCD image sensors and CMOS image sensors used for imaging cameras mounted on mobile phones and mobile terminals for image input has improved, and the imaging lenses used for them have a thin and high resolution performance. It has been demanded. Specifically, (1) The distance from the lens front surface to the image plane (optical total length TL) is small (low profile); (2) The incident angle of the principal ray on the image plane is small (telecentricity is good). ); (3) Large amount of peripheral light on the sensor image plane; (4) Aberration is well removed and resolution is high; (5) The image is not distorted and has a moderately large angle of view; (6) Long back focus And so on.
As lenses for such applications, various types of three-lens lens systems or four-lens lens systems have been proposed, which are superior in optical performance to a two-lens lens system. A four-lens lens system can obtain extremely high optical performance, but it is difficult to reduce the size and is expensive because each component requires high accuracy. On the other hand, the three-lens lens system cannot achieve performance as high as that of the four-lens configuration, but is thin, and can obtain higher optical performance than the two-lens configuration, and has an image sensor of 1 million pixels or more. Can be said to be suitable.

Examples of such a three-lens lens system include those described in the following patent documents.
Patent Document 1 includes a meniscus first lens having a positive power with a convex surface facing the object side, a meniscus second lens having a negative power with a concave surface facing the object side, and a positive third lens. An imaging lens is disclosed in which the second and third lenses are both aspheric.
Patent Document 2 includes a meniscus first lens having a positive power with a convex surface facing the object side, a meniscus second lens having a negative power with a concave surface facing the object side, and a third lens having a positive power. An imaging lens is disclosed in which the shape of at least one lens surface of the first to third lenses is defined by an aspheric shape in which an inflection point does not appear in the effective lens surface region.
Patent Document 3 discloses a meniscus first lens having a positive refractive power with a convex surface facing the object side, an aperture stop, a meniscus second lens having a negative refractive power with a concave surface facing the object side, and a positive third lens. An imaging lens in which both surfaces of the first to third lenses are aspherical is disclosed.
Patent Document 4 discloses an imaging lens that includes an aperture stop, a positive first lens, a negative second lens, and a positive third lens, and each lens has at least one aspheric surface.
Patent Document 5 includes an aperture stop, a first meniscus lens having a positive refractive power with a convex surface facing the object side, a second lens having a concave surface facing the object side, and a third lens having a positive refractive power, An imaging lens in which each lens has an aspheric surface on at least one surface is disclosed.

However, in the imaging lenses described in Patent Documents 1 to 3, if the incident angle to the sensor is reduced to improve the telecentricity, it is necessary to ensure a long distance between the diaphragm and the sensor, and the first lens This is disadvantageous in reducing the height because the thickness is increased by the thickness. That is, if the height is further reduced, the incident angle increases and the telecentricity decreases.
In the imaging lenses described in Patent Documents 4 to 5, the stop position is closer to the object side than the first lens. However, in Patent Document 4, the telecentricity is still loose even in the case where the incident angle of the chief ray on the image plane is optimal, and in Patent Document 5, the telecentricity is good, but the optical total length is still not sufficiently small. Further improvements are desired.

JP 2004-219982 A JP 2005-62680 A JP 2005-55751 A JP 2005-227755 A JP 2005-345919 A

  Accordingly, an object of the present invention relates to an imaging lens used for image input of a mobile phone or a mobile terminal, which is excellent in telecentricity and can be downsized, and has excellent resolution performance, other peripheral light quantity, and distortion aberration characteristics. An object of the present invention is to provide an imaging lens having a necessary back focus.

In order to solve the above-described problems, an imaging lens according to the present invention includes an aperture stop, a positive first lens, a negative second lens, and a positive third lens arranged in this order from the object side. Is a meniscus lens with a convex surface facing the object side,
The second lens is a meniscus lens having a convex surface facing the image surface side, and the third lens is a meniscus lens having both convex surfaces facing the object side and aspheric surfaces,
The first lens and the second lens have at least an aspheric surface on the image plane side, and in each of the first lens, the second lens, and the third lens, the object side surface is the first surface and the image plane side. When the surface is the second surface, the following conditional expressions [1] to [6] are satisfied.
[1] 1.3 <f / f1 <1.5
[2] 1.8 <R2 / (Nd1-1) / f <15
[3] 1.0 <TL / f <1.3
[4] 1.8 <TL / Y <2
[5] 18 <α <23
[6] 61 <2ω <64
(Where f is the focal length of the entire lens system, f1 is the focal length of the first lens, R2 is the radius of curvature of the second surface of the first lens, Nd1 is the refractive index of the first lens material at the d-line, and TL is The distance from the first surface of the first lens to the image plane (the parallel plane filter portion is converted to the air length), Y is the image height of the diagonal of the screen, α is the incident angle of the principal ray on the image plane at the maximum image height, ω represents a half angle of view.)

The imaging lens of the present invention preferably further satisfies the following conditional expression [7].
[7] -1.2 <f / f2 <-0.6
(Here, f2 represents the focal length of the second lens.)

The imaging lens of the present invention preferably further satisfies the following conditional expressions [8] and [9].
[8] 0.10 <f / f3 <0.50
[9] 0.5 <R6 / (Nd1-1) / f <1.5
(Where f3 is the focal length of the third lens, R6 is the radius of curvature of the second surface of the third lens, and Nd3 is the refractive index of the third lens material at the d-line).

The imaging lens of the present invention preferably further satisfies the following conditional expression [10].
[10] 0.5 <f / f (1-2) <1.0
(Here, f (1-2) represents the combined focal length of the first lens and the second lens.)

The imaging lens of the present invention preferably further satisfies the following conditional expression [11].
[11] 0.3 <bf / f <0.4
(Here, bf represents the distance on the optical axis from the second surface of the third lens to the image plane (the parallel surface filter portion is converted to the air length).)

The imaging lens of the present invention preferably further satisfies the following conditional expression [12].
[12] 53 <ν1
(Here, ν1 represents the Abbe number of the first lens material.)

  In the imaging lens of the present invention, it is preferable that the object side surface of the third lens is concave toward the object side as it goes from the optical axis to the periphery, and further convex toward the periphery of the side surface.

  In the imaging lens of the present invention, it is preferable to use a resin as a material constituting the first lens, the second lens, and the third lens.

  According to the present invention, the three-group three-lens configuration is arranged such that the absolute value of the refractive power decreases in the order of the first lens, the second lens, and the third lens, and the aspherical surface of each lens. By providing the inflection point to share the aberration correction, it is possible to realize an imaging lens corresponding to a high-order megapixel with a low profile and a high resolution and brightness to every corner of the screen.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of an imaging lens according to the present invention. The imaging lens shown in FIG. 1 includes an aperture stop 10, a first lens 11, a second lens 12, and a third lens 13 in order from the object side. The first lens 11 is a positive meniscus lens having a convex surface facing the object side, the second lens 12 is a negative meniscus lens having a convex surface facing the image surface side, and a third lens 13. Is a positive meniscus lens with a convex surface facing the object side. Further, both surfaces of the first lens, the second lens, and the third lens are aspherical surfaces. A cover glass or an infrared cut filter is disposed between the third lens 13 and the image plane (corresponding to 14 in FIG. 1). By placing the aperture stop 10 closest to the object side, the incident angle of the principal ray on the image plane can be reduced.
In the present invention, the first lens and the second lens are preferably aspheric both on the image side surface and the object side surface. Since the image side surface and the object side surface of the first lens and the second lens are aspherical surfaces, various aberrations caused by peripheral rays are reduced, and the edge thickness of the third lens is excessively reduced. Is suppressed.

In the present invention, it is essential to satisfy the following conditional expressions [1] to [6].
[1] 1.3 <f / f1 <1.5
[2] 1.8 <R2 / (Nd1-1) / f <15
[3] 0.5 <R6 / (Nd3-1) / f <1.5
[3] 1.0 <TL / f <1.3
[4] 1.8 <TL / Y <2
[5] 18 <α <23
[6] 61 <2ω <64
(Where f is the focal length of the entire lens system, f1 is the focal length of the first lens, R2 is the radius of curvature of the second surface of the first lens, Nd1 is the refractive index of the first lens material at the d-line, and TL is The distance from the first surface of the first lens to the image plane (the parallel plane filter portion is converted to the air length), Y is the image height of the diagonal of the screen, α is the incident angle of the principal ray on the image plane at the maximum image height, ω represents a half angle of view.)

  Conditional expression [1] determines the power distribution of the first lens. When the upper limit is exceeded, it is advantageous for lowering the thickness (thinning), but the aberration increases. This is disadvantageous for low profile. A preferable range of the conditional expression [1] is 1.35 <f / f1 <1.45.

  Conditional expression [2] is a condition for appropriately setting the negative refractive power of the second surface of the first lens. By satisfying this condition, the burden of correction of field curvature due to the concave surfaces of the second lens and the third lens can be reduced, and the back focus can be appropriately maintained. That is, by setting the value within the upper limit, the field curvature is reduced, and the back focus is increased to secure a space for installing the filter, and when the lower limit is exceeded, the negative refractive power becomes stronger than necessary. The back focus is reduced by suppressing the occurrence of coma flare and distortion of off-axis light flux, and the overall optical length is kept small.

  Conditional expression [3] is a condition for reducing the height. If the upper limit is exceeded, the optical total length becomes long. Conversely, if the lower limit is not reached, it is difficult to ensure the back focus, which is not preferable. A preferable range of conditional expression [3] is 1.1 <TL / f <1.2.

  The conditional expression [4] is a condition for reducing the height as in the conditional expression [3]. If the upper limit is exceeded, it is not preferable for reducing the height, whereas if the lower limit is not reached, it is necessary to reduce the length from the first surface of the first lens to the second surface of the third lens, which makes manufacturing difficult.

  Conditional expression [5] is a condition for ensuring telecentricity. If the upper limit is exceeded, it will be difficult to increase the amount of light sufficiently with the microlens of the sensor. Conversely, if the lower limit is exceeded, it will be necessary to lengthen from the lens front surface to the imaging surface, making it difficult to achieve a desired low profile.

  Conditional expression [6] defines the angle of view to which the present invention is applied. If the upper limit is exceeded, it is possible to shoot a wider range, but it is inconvenient when shooting a narrow range, and conversely, if it falls below the lower limit, it is inconvenient to shoot a wide range.

In the present invention, it is preferable that the following conditional expression [7] is further satisfied.
[7] -1.2 <f / f2 <-0.6
Here, f2 represents the focal length of the second lens.
Conditional expression [7] is a condition for determining the power distribution of the second lens. Below the upper limit, the negative power becomes stronger, and the curvature of field is corrected by the negative contribution of the Petzval value. Conversely, exceeding the lower limit suppresses back focus to be small and avoids an increase in optical length, prevents deterioration of distortion, and suppresses decentration error sensitivity. A preferable range of the conditional expression [7] is −1.05 <f / f2 <−0.7.

In the present invention, it is preferable that the following conditional expressions [8] and [9] are satisfied.
[8] 0.10 <f / f3 <0.50
[9] 0.5 <R6 / (Nd3-1) / f <1.5
Here, f3 represents the focal length of the third lens, R6 represents the radius of curvature of the second surface of the third lens, and Nd3 represents the refractive index of the third lens material at the d-line.
Conditional expression [8] determines the power distribution of the third lens, but has the function of correcting aberrations as the lens closest to the image plane side and keeps the distribution small. By setting it as the said range, a back focus becomes long and the space of filter installation can be ensured, and also a refraction effect becomes strong and telecentricity can be made favorable. A preferred range of conditional expression [8] is 0.15 <f / f3 <0.45.

  Conditional expression [9] is a condition for appropriately setting the negative refractive power of the second surface of the third lens. By satisfying this condition, the burden of correction of field curvature due to the concave surfaces of the first lens and the second lens is reduced, and the back focus is appropriately maintained. That is, by making it within the upper limit of the above formula, the field curvature is reduced, and the back focus is increased to secure a space for arranging the filter. It is not strong and suppresses the occurrence of coma flare and distortion of off-axis luminous flux, and the back focus is reduced and the optical total length is kept small.

In the present invention, it is preferable that the following conditional expression [10] is further satisfied.
[10] 0.5 <f / f (1-2) <1.0
Here, f (1-2) represents the combined focal length of the first lens and the second lens.
Conditional expression [10] sets the positive combined focal length, that is, refractive power of the first lens and the second lens within an appropriate range. By setting it as the said range, a full length can be shortened and spherical aberration and coma aberration can be suppressed small. A preferable range of conditional expression [10] is 0.6 <f / f (1-2) <0.85.

In the present invention, it is preferable that the following conditional expression [11] is further satisfied.
[11] 0.3 <bf / f <0.4
Here, bf represents the distance on the optical axis from the second surface of the third lens to the imaging surface (the parallel surface filter portion is converted into the air length).
Conditional expression [11] is a conditional expression for ensuring the back focus. By setting it as the said range, optical full length TL can be made small, and the height reduction is attained, ensuring the space which puts a filter.

In the present invention, it is preferable that the following conditional expression [12] is satisfied.
[12] 53 <ν1
Here, ν1 represents the Abbe number of the first lens material.
Conditional expression [12] is a condition for suppressing the occurrence of chromatic aberration as much as possible. By setting it as the above range, chromatic aberration can be suppressed low.

In the present invention, it is preferable that the third lens has a concave surface on the object side as it goes from the optical axis to the periphery, and further becomes a convex surface as it goes to the periphery of the side surface.
This is a condition for improving the telecentricity by removing peripheral distortion, coma, and astigmatism. This realizes a stable and high resolving power from the center of the image to the effective range of the image, and at the same time increases the chief ray incident angle to the image plane as monotonously as possible with respect to the image height. Can be prevented from growing.

In the present invention, it is preferable to use a resin as a material constituting the first lens, the second lens, and the third lens. By using a resin material, mass production can be performed at low cost by an injection molding method.
The resin is not particularly limited, and examples thereof include a resin having an alicyclic structure, polymethyl methacrylate, and polycarbonate. The resin having an alicyclic structure is a resin having a cycloalkane structure in the main chain and / or side chain. Specific examples of the resin having an alicyclic structure include (1) norbornene polymer, (2) monocyclic olefin polymer, (3) cyclic conjugated diene polymer, and (4) vinyl alicyclic carbonization. Examples thereof include hydrogen polymers and hydrogenated products thereof.
When resin is used as the material constituting the first lens, the second lens, and the third lens, the method for producing the lens is not particularly limited, and a known molding method such as injection molding may be used.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

Example 1
FIG. 2 is a diagram illustrating a lens arrangement and an optical path of the imaging lens of the first embodiment. An aperture stop 10, a first lens 11, a second lens 12, a third lens 13, and a cover glass 14 are formed in this order from the object side to the image side. The first lens 11 is a meniscus positive lens having a convex surface facing the object side, the second lens 12 is a meniscus negative lens having a convex surface facing the image surface side, and the third lens 13 is It is a meniscus positive lens with a convex surface facing the object side.
Both surfaces of the first lens, the second lens, and the third lens are aspheric. The object side surface of the third lens becomes concave toward the object side as it goes from the optical axis to the periphery, and further becomes convex as it goes toward the periphery of the side surface. The image side surface of the third lens becomes a convex surface on the image plane side from the optical axis toward the periphery.
Here, a norbornene polymer (manufactured by ZEON Corporation, ZEONEX E48R) is used as a material constituting the first lens and the third lens, and a polycarbonate resin is used as a material constituting the second lens.

Table 1 shows lens configuration data of Example 1. The symbols used in this description are as follows. Further, as will be described later, the imaging lens of Example 1 satisfies the conditional expressions [1] to [12].
f: Lens focal length of the entire system FNO: F number R: radius of curvature of bent surface D: distance between bent surfaces Nd: refractive index with respect to d line υd: Abbe number with respect to d line 1 to 8 in Table 1 are from the object side The surface numbers are counted in order toward the image side. These symbols and numbers are the same in Table 3 and Table 5 described later.

Table 2 shows the lens cone coefficient K and the aspheric coefficient A of the aspherical lenses of the first lens, the second lens, and the third lens used in Example 1. In the numerical values representing the aspherical surface shown in Table 2, the symbol “E” indicates that the subsequent numerical value is a “power exponent” with 10 as the base, and is represented by an exponential function with 10 as the base. Indicates that the numerical value before "E" is multiplied. For example, “1.0E-02” indicates “1.0 × 10 ⁻² ”. The same applies to Tables 4 and 6 described later.

上記非球面係数は、光軸にＺ軸、光軸と垂直方向にＸ軸をとり、光の進行方向を正とすると、以下の非球面公式であらわされる。

The aspheric coefficient is expressed by the following aspheric formula, where the Z axis is the optical axis, the X axis is perpendicular to the optical axis, and the light traveling direction is positive.

ここで、Ｒは各レンズの頂点の曲率半径、ｈはレンズの光軸からの高さ、ｋは円錐係数、Ａ３〜Ａ１０は非球面係数を示す。

Here, R is the radius of curvature of the apex of each lens, h is the height from the optical axis of the lens, k is a conical coefficient, and A3 to A10 are aspherical coefficients.

  3 and 4 show aberration diagrams of the imaging lens of Example 1. FIG. In spherical aberration, curve 1 represents the d line, curve 2 represents the g line, curve 3 represents the C line, and curve 4 represents the sine condition. In the astigmatism, M represents meridional and S represents sagittal aberration. In coma aberration, curve 1 represents d-line, curve 2 represents g-line, and curve 3 represents C-line. The meanings of these symbols are the same in FIGS. 6, 7, 9, and 10 described later.

(Example 2)
FIG. 5 is a diagram illustrating a lens arrangement and an optical path of the imaging lens obtained in the second embodiment. An aperture stop 10, a first lens 11, a second lens 12, a third lens 13, and a cover glass 14 are formed in this order from the object side to the image side. The first lens 11 is a meniscus positive lens having a convex surface facing the object side, the second lens 12 is a meniscus negative lens having a convex surface facing the image surface side, and the third lens 13 is It is a meniscus positive lens with a convex surface facing the object side.
Both surfaces of the first lens, the second lens, and the third lens are aspheric. The object side surface of the third lens becomes concave toward the object side as it goes from the optical axis to the periphery, and further becomes convex as it goes toward the periphery of the side surface. The image side surface of the third lens becomes a convex surface on the image plane side from the optical axis toward the periphery.
Here, the material constituting each lens is the same as the material used in Example 1.

  Table 3 shows lens configuration data of Example 2. Further, as will be described later, the imaging lens of Example 2 satisfies the conditional expressions [1] to [12].

実施例２で使用した第１レンズ、第２レンズ、及び第３レンズの非球面レンズのレンズ円錐係数Ｋ、及び非球面係数Ａを表４に示す。

Table 4 shows the lens cone coefficient K and the aspheric coefficient A of the aspherical lenses of the first lens, the second lens, and the third lens used in Example 2.

  6 and 7 show aberration diagrams in the imaging lens of Example 2. FIG.

(Example 3)
FIG. 8 is a diagram illustrating a lens arrangement and an optical path of the imaging lens obtained in the third embodiment. An aperture stop 10, a first lens 11, a second lens 12, a third lens 13, and a cover glass 14 are formed in this order from the object side to the image side. The first lens 11 is a meniscus positive lens having a convex surface facing the object side, the second lens 12 is a meniscus negative lens having a convex surface facing the image surface side, and the third lens 13 is It is a meniscus positive lens with a convex surface facing the object side.
Both surfaces of the first lens, the second lens, and the third lens are aspheric. The object side surface of the third lens becomes concave toward the object side as it goes from the optical axis to the periphery, and further becomes convex as it goes around the side surface. The image side surface of the third lens becomes a convex surface on the image plane side from the optical axis toward the periphery.
Here, the material constituting each lens is the same as the material used in Example 1.

  Table 5 shows lens configuration data of Example 3. Further, as will be described later, the imaging lens of Example 2 satisfies the conditional expressions [1] to [12].

実施例３で使用した第１レンズ、第２レンズ、及び第３レンズの非球面レンズのレンズ円錐係数Ｋ、及び非球面係数Ａを表６に示す。

Table 6 shows the lens cone coefficient K and the aspheric coefficient A of the aspherical lenses of the first lens, the second lens, and the third lens used in Example 3.

  FIGS. 8 and 9 are aberration diagrams of the imaging lens of Example 2. FIG.

Table 7 shows values corresponding to the conditional expressions [1] to [12] of the respective examples.
From Table 7, it can be seen that the imaging lenses of Examples 1 to 3 satisfy the conditional expressions [1] to [12].

It is a figure which shows the lens structure of the imaging lens of this invention. 2 is a diagram illustrating a lens arrangement and an optical path of an imaging lens of Example 1. FIG. FIG. 3 is a diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens of Example 1. 6 is a diagram illustrating coma aberration in a meridional direction of the imaging lens of Example 1. FIG. 6 is a diagram illustrating a lens arrangement and an optical path of an imaging lens of Example 2. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens of Example 2. FIG. 6 is a diagram illustrating coma aberration in a meridional direction of the imaging lens of Example 2. FIG. 6 is a diagram illustrating a lens arrangement and an optical path of an imaging lens according to Example 3. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens of Example 3. FIG. 6 is a diagram illustrating coma aberration in the meridional direction of the imaging lens of Example 3. FIG.

Explanation of symbols

10: Aperture stop, 11: First lens, 12: Second lens, 13: Third lens, 14: Infrared cut filter or cover glass, 1: Spherical aberration or coma aberration at d line, 2: Spherical aberration at g line Or coma, 3: spherical aberration or coma on C line, 4: spherical aberration under sine condition, S: sagittal, M: meridional

Claims (8)

In order from the object side, an aperture stop, a positive first lens, a negative second lens, and a positive third lens are arranged,
The first lens is a meniscus lens having a convex surface facing the object side,
The second lens is a meniscus lens having a convex surface facing the image surface side,
The third lens is a meniscus lens having aspheric surfaces on both sides with convex surfaces facing the object side,
The first lens and the second lens have at least an aspheric surface on the image plane side,
In each of the first lens, the second lens, and the third lens, when the object side surface is the first surface and the image surface side surface is the second surface, the following conditional expressions [1] to [6]: An imaging lens characterized by satisfying
[1] 1.3 <f / f1 <1.5
[2] 1.8 <R2 / (Nd1-1) / f <15
[3] 1.0 <TL / f <1.3
[4] 1.8 <TL / Y <2
[5] 18 <α <23
[6] 61 <2ω <64
(Where f is the focal length of the entire lens system, f1 is the focal length of the first lens, R2 is the radius of curvature of the second surface of the first lens, Nd1 is the refractive index of the first lens material at the d-line, and TL is The distance from the first surface of the first lens to the image plane (the parallel plane filter portion is converted to the air length), Y is the image height of the diagonal of the screen, α is the incident angle of the principal ray on the image plane at the maximum image height, ω represents a half angle of view.) Furthermore, the imaging lens of Claim 1 which satisfy | fills the conditional expression of following [7].
[7] -1.2 <f / f2 <-0.6
(Here, f2 represents the focal length of the second lens.) The imaging lens according to claim 1, further satisfying conditional expressions [8] and [9] below.
[8] 0.10 <f / f3 <0.50
[9] 0.5 <R6 / (Nd3-1) / f <1.5
(Where f3 is the focal length of the third lens, R6 is the radius of curvature of the second surface of the third lens, and Nd3 is the refractive index of the third lens material at the d-line). Furthermore, the imaging lens in any one of Claims 1-3 which satisfy | fill the conditional expression of following [10].
[10] 0.5 <f / f (1-2) <1.0
(Here, f (1-2) represents the combined focal length of the first lens and the second lens.) Furthermore, the imaging lens in any one of Claims 1-4 which satisfy | fill the conditional expression of following [11].
[11] 0.3 <bf / f <0.4
(Here, bf represents the distance on the optical axis from the second surface of the third lens to the image plane (the parallel surface filter portion is converted to the air length).) Furthermore, the imaging lens in any one of Claims 1-5 which satisfy | fills conditional expression of following [12].
[12] 53 <ν1
(Here, ν1 represents the Abbe number of the first lens material.) The imaging lens according to any one of claims 1 to 6, wherein the third lens has a concave surface on the object side as it goes from the optical axis to the periphery, and further becomes a convex surface as it goes to the periphery of the side surface. The imaging lens according to claim 1, wherein a resin is used as a material constituting the first lens, the second lens, and the third lens.

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