JP2005345919A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact imaging lens attaining high performance in spite of simple lens constitution of a small number of lenses. <P>SOLUTION: In the imaging lens, an aperture stop 14, a 1st lens 11 being a meniscus lens turning its convex surface to an object side and having positive refractive power, a 2nd lens 12 having negative refractive power and turning its concave surface to the object side, and a 3rd lens 13 having positive refractive power are arranged in order from the object side. The lens is constituted to satisfy conditional expressions; 0.6<f<SB>3</SB>/f≤1, 2<f<SB>12</SB>/f<7, -1.50<f<SB>2</SB>/f<-0.50, 0.8<Σd/f<1.5, 1.40≤n<SB>3</SB>≤1.85, 40≤ν<SB>1</SB>≤ 100 and 0≤ν<SB>1</SB>-ν<SB>3</SB>≤45, where f, f<SB>12</SB>, f<SB>2</SB>and f<SB>3</SB>mean the focal distance of the imaging lens 10, the composite focal distance of the 1st lens 11 and the 2nd lens 12, and the focal distances of the 2nd lens 12 and the 3rd lens 13, Σd means the entire length of the imaging lens 10, n<SB>3</SB>means the refractive index of the 3rd lens 13, ν<SB>1</SB>and ν<SB>3</SB>are the Abbe numbers of the 1st lens 11 and the 3rd lens 13. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a solid-state imaging device, such as a CCD (Charge Coupled Device) type image sensor, a CMOS (Complementary
The present invention relates to an imaging lens suitable for an optical system of a metal oxide semiconductor) type image sensor.

  Since various aberrations can be corrected with a small number of lenses, a triplet type which is a three-lens type is often used as an imaging lens for a mobile phone camera module or the like. As this type of triplet lens, a lens disclosed in Patent Document 1 is known.

Since such an imaging lens is particularly incorporated into a portable terminal, there is a restriction that the entire length must be shortened.
In addition, solid-state image sensors used for mobile phones are often imaged with an electronic shutter, and when a moving subject is photographed, the image may flow. In order to prevent such image flow from occurring, an optical system incorporating a mechanical shutter is often employed. Therefore, a more compact imaging lens is desired.
JP 2003-149545 A

  However, the imaging lens proposed in Patent Document 1 has a long overall lens length even though the field angle of view is relatively narrow, about 50 to 65 degrees, and the optical system when incorporated in a mobile phone or the like. It was difficult to reduce the thickness.

  The present invention has been made in view of the above circumstances, and can provide a compact imaging lens that achieves high performance while having a simple lens configuration with a small number of sheets.

In order to achieve the above object, an imaging lens according to the first aspect of the present invention provides:
In order from the object side, a meniscus first lens having a positive refractive power with a convex surface facing the object side, a second lens having a negative refractive power and a concave surface facing the object side, and a positive refractive power A third lens having
An aperture stop is provided on the object side of the first lens;
Each of the first lens, the second lens, and the third lens has an aspheric surface on at least one surface;
The focal length of the entire first lens, the second lens, and the third lens is f, the combined focal length of the first lens and the second lens is f ₁₂ , the focal length of the second lens is f ₂ , and the focal length of the third lens. F ₃ , the distance measured along the optical axis from the object-side surface of the first lens to the image-side surface of the third lens is Σd, the refractive index of the third lens is n ₃ , and the Abbe number of the first lens Is ν ₁ and the Abbe number of the third lens is ν ₃ ,
The following conditional expression (1) is satisfied.
0.6 <f ₃ / f ≦ 1 (1)

An imaging lens according to a second aspect of the present invention is
In order from the object side, a meniscus first lens having a positive refractive power facing the object side, a second lens having a negative refractive power and a concave surface facing the object side, and a positive refractive power A third lens having
An aperture stop is provided on the object side of the first lens;
Each of the first lens, the second lens, and the third lens has an aspheric surface on at least one surface;
When the focal length of the entire first lens, the second lens, and the third lens is f, the combined focal length of the first lens and the second lens is f ₁₂ , and the focal length of the second lens is f ₂ ,
The following conditional expressions (2) and (3) are satisfied.
_{2 <f 12 / f <7} ····· (2)
−1.50 <f ₂ /f<−0.50 (3)

An imaging lens according to a third aspect of the present invention is
In order from the object side, a meniscus first lens having a positive refractive power facing the object side, a second lens having a negative refractive power and a concave surface facing the object side, and a positive refractive power A third lens having
An aperture stop is provided on the object side of the first lens;
Each of the first lens, the second lens, and the third lens has an aspheric surface on at least one surface;
The focal length of the entire first lens, the second lens and the third lens is f, the distance measured along the optical axis from the object side surface of the first lens to the image side surface of the third lens is Σd, and the third When the refractive index of the lens is n ₃ , the Abbe number of the first lens is ν ₁ , and the Abbe number of the third lens is ν ₃ ,
The following conditional expressions (4), (5), (6) and (7) are satisfied.
0.8 <Σd / f <1.5 (4)
1.40 ≦ n ₃ ≦ 1.85 (5)
40 ≦ ν ₁ ≦ 100 (6)
0 ≦ ν ₁ −ν ₃ ≦ 45 (7)

  Further, the first lens, the second lens, and the third lens may all be made of a plastic material.

  The second lens and the third lens may be made of a plastic material, and the first lens may be made of a glass material.

  The first lens and the third lens may be made of a glass material, and the second lens may be made of a plastic material.

  According to the present invention, it is possible to provide a compact imaging lens that achieves high performance while having a simple lens configuration with a small number of sheets.

  An imaging lens according to an embodiment of the present invention will be described below with reference to the drawings. In FIGS. 1 to 6 showing configuration examples of the imaging lens according to the embodiment of the present invention, Ri (i = 1 to 6) represents the paraxial curvature radius of the i-th lens in order from the object side. Dk (k = 1 to 8) represents the thickness of the lens or the like on the kth optical axis X or the air space between the lenses in order from the object side.

  The imaging lens 10 has, in order from the object side, a first lens 11 having a meniscus positive refractive power with a convex surface facing the object side along the optical axis X, a negative refractive power, and a negative refractive power on the object side. It is a triplet lens having a three-lens configuration including a second lens 12 having a concave surface and a third lens 13 having a positive refractive power. The aperture stop 14 adjusts the amount of subject light reaching the imaging surface of the image sensor 16 and is provided on the object side of the first lens 11. The parallel flat glass 15 corresponds to a filter or a cover glass, and is disposed on the imaging surface side of the third lens 13.

  The image sensor 16 captures a subject image formed by the imaging lens 10 and converts it into an electrical signal. The image sensor 16 is configured by, for example, a CCD image sensor, a CMOS image sensor, or the like. The image sensor 16 is electrically connected to and held by a substrate (not shown).

  In the imaging lens 10 or the like, when light enters from the object side, the subject light amount is adjusted by the aperture stop 14, and sequentially passes through the first lens 11, the second lens 12, and the third lens 13, and passes through the parallel flat glass 15. Thus, the light is condensed on the image pickup surface of the image pickup device 16.

  All of the first lens 11, the second lens 12, and the third lens 13 have aspheric surfaces on both surfaces (the object side and the imaging surface side). The first lens 11, the second lens 12, and the third lens 13 may be configured such that at least one surface has an aspherical shape.

  In general, since a triplet lens composed of three lenses has a small number of lenses, there are few degrees of freedom only with the radius of curvature, lens thickness, and lens spacing in order to correct various aberrations. However, the imaging lens 10 of the present embodiment can be designed using the total thickness of the lens and the distribution of refractive power by making the spherical surface an aspherical surface.

The imaging lens 10 is
f: focal length f ₁₂ of imaging lens 10: combined focal length f _{2 of} first lens 11 and second lens 12: focal length f ₃ of second lens 12: focal length Σd of third lens 13: first lens 11 distance n ₃ a from the object side to the imaging side surface of the third lens 13 measured I along the optical axis X of the _refractive index (e.g., the wavelength lambda = 5 of the light incident on the third lens 13 of the third lens 13 (When 87.56 nm)
When ν _{1 is} the Abbe number of the first lens 11 ν _{3 is} the Abbe number of the third lens 13, the following conditional expressions (1) to (7) are satisfied.

0.6 <f ₃ / f ≦ 1 (1)
_{2 <f 12 / f <7} ····· (2)
−1.50 <f ₂ /f<−0.50 (3)
0.8 <Σd / f <1.5 (4)
1.40 ≦ n ₃ ≦ 1.85 (5)
40 ≦ ν ₁ ≦ 100 (6)
0 ≦ ν ₁ −ν ₃ ≦ 45 (7)

  By the way, the most important and difficult point in shortening the overall length of the imaging lens 10 which is a triplet lens, widening the angle, and further reducing the incident angle of the principal ray on the image plane side to an appropriate angle of 22 degrees or less. Is correction of distortion aberration, astigmatism, etc. and securing of the peripheral light quantity.

  Therefore, in the present embodiment, in the conditional expressions (1), (2), and (3), the imaging lens 10 is widened, the entire length is shortened, and the incident angle of the principal ray on the image plane side is 22 The optimal refractive power distribution is specified to make it less than or equal to the degree, and both good correction of distortion, astigmatism and the like and securing of the peripheral light quantity are compatible.

Conditional expression (1) is a conditional expression related to the refractive power of the third lens 13 component. If the lower limit value is not reached, the refractive power of the third lens 13 component increases, which is advantageous for shortening the total lens length. This is undesirable because it causes negative distortion. On the other hand, if the value exceeds the upper limit, the back focus increases and the total lens length increases, which is not preferable.
Note that the imaging lens can be configured to satisfy only the conditional expression (1).

  Conditional expression (2) is a conditional expression related to the refractive power of the first lens 11 component and the combined refractive power of the second lens 12 component, and below this lower limit, the refractive power of the first lens 11 component becomes excessive. The peripheral light quantity is insufficient due to the aberration of the pupil. On the other hand, if the value exceeds the upper limit, the refractive power of the first lens 11 component is small, so that the height of the on-axis peripheral ray in the second lens 12 component increases, and the occurrence of high-order spherical aberration is significant, which is not preferable. .

Conditional expression (3) is a conditional expression for improving the Petzval sum and the curvature of the image plane with respect to the refractive power of the second lens 12 component. If the lower limit of the conditional expression (3) is not reached, it is advantageous for reducing the Petzval sum and is advantageous for correcting the curvature of field. This is not preferable because the incident angle of the light beam cannot be controlled. On the contrary, if the upper limit is exceeded, the Petzval sum becomes excessive, and the field curvature at the sagittal image plane remains negative.
It is also possible to configure the imaging lens so as to satisfy only conditional expressions (2) and (3).

  Furthermore, in the present embodiment, the conditional expression (4) is set to achieve both good aberration correction and compactness.

  In correcting aberrations, it is desirable that the total thickness of the lens is somewhat large. However, if the upper limit of (4) is exceeded, it becomes difficult to make the lens compact, which is contrary to the lens compactification. Conversely, if the lower limit is exceeded, it becomes difficult to ensure the lens edge thickness and middle thickness, the incident angle of the principal ray on the sensor surface at the periphery of the image cannot be controlled, and various aberrations, in particular, Since it becomes difficult to correct coma and spherical aberration, the brightness of F number 2.8 to 3.5 cannot be maintained.

  Conditional expression (5) relates to a good image plane correction. In correcting the Petzval sum, it is desirable to increase the refractive index of the third lens 13 component having a large role as positive refractive power as much as possible. Therefore, if the lower limit of (5) is not reached, correction of Petzval sum becomes difficult. On the other hand, if the upper limit of (5) is exceeded, it will be difficult to maintain the balance between the third lens 13 and the first and second lenses 11 and 12. In consideration of the balance between the third lens and the first lens 11 and the second lens 12, it is preferable that the refractive indexes of the third lens 13 and the first lens 11 are the same. Further, when cost is given priority, it is more preferable to use a plastic material for the third lens 13.

Conditional expression (6) relates to correction of chromatic aberration. In general, it is difficult to correct off-axis aberrations in front aperture lenses, and chromatic aberration is no exception. In particular, the chromatic aberration of magnification due to the angle of view becomes more pronounced as the angle becomes wider, making it difficult to widen the angle. The reason for this is that the contribution of the third lens 13 component to the oblique rays increases sharply as the angle of view increases compared to the first lens 11 component and the second lens 12 component.
Therefore, it is desirable to use a low-dispersion glass material for the first lens 11 component, but it is desirable to use a plastic material if cost is a priority.

  Lowering the lower limit of conditional expression (6) to make the first lens 11 component highly dispersed is not preferable because it increases chromatic aberration of magnification. On the contrary, if the upper limit of (6) is exceeded, the longitudinal chromatic aberration will be excessively corrected.

  The aberration structure of the triplet lens is such that the first lens 11 component and the second lens 12 component are overcorrected including chromatic aberration, and the excess is canceled out by the undercorrected third lens 13 component. . Therefore, in the case of the front aperture lens, if the third lens component 13 has a low dispersion compared to the first lens 11 component, the chromatic aberration with respect to the oblique ray is overcorrected compared to the on-axis, and so-called color coma aberration occurs. Occurs, and off-axis performance deteriorates.

Therefore, the above problem is solved by defining the dispersion of the third lens 13 component relative to the dispersion of the first lens 11 component in the conditional expression (7). If the upper limit of conditional expression (7) is exceeded, in other words, if the third lens 13 component is excessively highly dispersed with respect to the first lens 11 component, the third lens 13 component will increase chromatic aberration, so Incorrect chromatic aberration correction. On the other hand, if the lower limit of conditional expression (7) is not reached, the axial chromatic aberration will be overcorrected, making it difficult to correct axial chromatic aberration, lateral chromatic aberration, and chromatic coma at the peripheral image height.
Note that the imaging lens can be configured to satisfy the conditional expressions (4) to (7).

  Moreover, it is preferable that all of the first lens 11, the second lens 12, and the third lens 13 are made of a plastic material. The first lens 11, the second lens 12, and the third lens 13 made of a plastic material include those in which the surface of the plastic material is subjected to a coating process for the purpose of preventing reflection and improving surface hardness.

  The first lens 11, the second lens 12 and the third lens 13 are made of plastic lenses as described above. In the production of microlenses, the plastic is more suitable for manufacturing methods such as injection molding than glass. This is because it is suitable for mass production.

  The first lens 11 may be made of a glass material, and the second lens 12 and the third lens 13 may be made of a plastic material.

  Constructing all of the first lens 11, the second lens 12, and the third lens 13 with plastic lenses is advantageous for reducing the size and weight and reducing the cost as described above. However, since the plastic lens material has a large change in refractive index when the temperature changes, if all the lenses are made of plastic lenses, there is a possibility that aberrations in the peripheral portion of the image may occur due to temperature fluctuations.

  Therefore, in the configuration of the present embodiment, the positive first lens 11 is made of a glass material, the negative second lens 12 is made of a plastic material, and the third lens 13 having a small positive refractive power is made of plastic. By using the lens, the refractive index change at the time of the temperature change of the first lens 11 can be ignored, and the aberration at the peripheral portion of the image at the time of the temperature change in the entire imaging lens system can be suppressed. A glass mold lens is one of lenses that can be manufactured relatively easily even if it is a small-diameter lens.

  Further, in order to achieve further improvement in performance than the imaging lens 10 in which the first lens 11 is made of a glass material and the second lens 12 and the third lens 13 are made of a plastic material, the aberration of the image peripheral portion with respect to temperature fluctuations. In order to suppress the occurrence of this, a glass material may be employed for the first lens 11 and the third lens 13, and the second lens may be configured of a plastic material.

  In general, a plastic lens can be easily formed in a shape having a flange portion that does not contribute to image formation on the outer peripheral portion, but if light enters the flange portion, it may cause ghost or flare. Therefore, by making the third lens 13 into a glass lens, it is not necessary to have a shape having a flange portion on the outer peripheral portion, and it is possible to reduce the possibility of ghosts and flares that adversely affect the captured image. It is.

  As described above, in the present embodiment, the aperture stop 14 is disposed on the object side of the first lens 11, and the first lens 11, the second lens 12, and the third lens 13 are aspherical lenses and have a power distribution and surface. Since the shape, material, etc. are appropriately set, a sufficient amount of peripheral light can be maintained and various aberrations can be corrected satisfactorily. As a result, the imaging lens of the present embodiment can achieve high performance and can be made compact while having a simple lens configuration with a small number of lenses.

  In this embodiment, since the distance (height) from the aperture stop 14 to the image sensor 16 can be suppressed to 10 mm or less, a portable terminal capable of downsizing, lightening, and high-quality imaging is realized. Is possible.

Hereinafter, the configuration of the imaging lens 10 embodying the present invention will be described more specifically with reference to construction data and aberration diagrams. Note that the configuration of the imaging lens 10 is not limited to the present embodiment. Here, symbols used in each example are as follows.
f: focal length f ₁₂ of the imaging lens 10: combined focal length f _{2 of} the first lens 11 and second lens 12: focal length f ₃ of the second lens 12: focal length Σd of the third lens 13: first lens The distance measured along the optical axis X from the object side surface of 11 to the imaging side surface of the third lens 13 ω: half angle of view F: F number R: radius of curvature (mm)
D: Thickness of the lens, etc., or air space between the lenses, etc. (mm)
Nd: Refractive index νd of each lens at d-line: Abbe number of each lens at d-line

In each embodiment, the shape of the aspheric surface is represented by the following aspheric expression (8) in an orthogonal coordinate system in which the vertex of the surface is the origin and the optical axis direction is the X axis.
Z = C × h ² / {1+ (1−K × C ² × h ² ) ^1/2 } + A ₄ h ⁴ + A ₆ h ⁶ + A ₈ h ⁸ + A ₁₀ h ¹⁰ (8)

here,
h: height in the vertical direction from the optical axis X Z: vertical line drawn from the point on the aspherical surface at a height h in the vertical direction from the optical axis to the tangential plane (plane perpendicular to the optical axis) of the aspheric surface Length C: Reciprocal number of aspherical paraxial radius of curvature K: Eccentricity A ₄ , A ₆ , A ₈ , A ₁₀ : _4th , _6th , _8th , 10th order aspherical coefficients.

  The configuration example of the imaging lens 10 illustrated in FIGS. 1 to 6 in the above embodiment corresponds to the configuration example of the imaging lens according to Examples 1 to 6.

(Example 1)
Tables 1 and 2 show the construction data of Example 1.

  FIG. 7 shows the aberration performance (spherical aberration, astigmatism, distortion) of the imaging lens 10 according to Example 1 shown in Tables 1 and 2. The astigmatism diagram shows aberrations with respect to the tangential image surface and the sagittal image surface. FIG. 8 shows the coma aberration performance of the imaging lens 10 according to Example 1.

  7 and 8 that the imaging lens according to Example 1 has good optical performance.

  Further, as will be described later, the present example satisfies the conditional expressions (1) to (7).

(Example 2)
Tables 3 and 4 show the construction data of Example 2.

  FIG. 9 shows the aberration performance (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 2 shown in Tables 3 and 4. FIG. 10 shows the coma aberration performance of the imaging lens 10 according to the second example. 9 and 10 that the imaging lens according to Example 2 has good optical performance.

  Further, as will be described later, the present example satisfies the conditional expressions (1) to (7).

(Example 3)
Tables 5 and 6 show the construction data of Example 3.

  FIG. 11 shows the aberration performance (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 3 shown in Tables 5 and 6. FIG. 12 shows the coma aberration performance of the imaging lens 10 according to Example 3. 11 and 12 that the imaging lens according to Example 3 has good optical performance.

  Further, as will be described later, the present example satisfies the conditional expressions (1) to (7).

Example 4
Tables 7 and 8 show the construction data of Example 4.

  FIG. 13 shows the aberration performance (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 4 shown in Tables 7 and 8. FIG. 14 shows the coma aberration performance of the imaging lens 10 according to Example 4. 13 and 14 that the imaging lens according to Example 4 has good optical performance.

  Further, as will be described later, the present example satisfies the conditional expressions (1) to (7).

(Example 5)
Tables 9 and 10 show the construction data of Example 5.

  FIG. 15 shows the aberration performance (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 5 shown in Table 9 and Table 10. FIG. 16 shows the coma aberration performance of the imaging lens 10 according to Example 5. 15 and 16 that the imaging lens according to Example 5 has good optical performance.

  Further, as will be described later, the present example satisfies the conditional expressions (1) to (7).

(Example 6)
Tables 11 and 12 show the construction data of Example 6.

  FIG. 17 shows the aberration performance (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 6 shown in Tables 11 and 12. FIG. 18 illustrates the coma aberration performance of the imaging lens 10 according to the sixth example. 17 and 18 that the imaging lens according to Example 6 has good optical performance.

  Further, as will be described later, the present example satisfies the conditional expressions (1) to (7).

  Table 13 shows values corresponding to the conditional expressions (1) to (7) in the imaging lenses of the first to sixth embodiments.

  Each Example 1-6 is satisfied about the said conditional expressions (1)-(7).

  While the present invention has been described with reference to the embodiment and each example, the present invention is not limited to the above embodiment and each example, and various modifications can be made. For example, in the said embodiment and each Example, although the example which provides the parallel plate glass 15 was demonstrated, the parallel plate glass 15 does not necessarily need to be provided.

  Further, the data given in each of the above embodiments is merely an example, and may take other values as long as the requirements of the present invention are satisfied.

1 is a configuration diagram of an imaging lens according to an embodiment of the present invention, and is a configuration diagram of an imaging lens according to Example 1. FIG. 2 is a configuration diagram of an imaging lens according to an embodiment of the present invention, and is a configuration diagram of an imaging lens according to Example 2. FIG. FIG. 3 is a configuration diagram of an imaging lens according to an embodiment of the present invention, and is a configuration diagram of an imaging lens according to Example 3; FIG. 6 is a configuration diagram of an imaging lens according to an embodiment of the present invention, and a configuration diagram of an imaging lens according to Example 4; FIG. 6 is a configuration diagram of an imaging lens according to an embodiment of the present invention, and is a configuration diagram of an imaging lens according to Example 5; FIG. 6 is a configuration diagram of an imaging lens according to an embodiment of the present invention, and is a configuration diagram of an imaging lens according to Example 6; FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 1; 3 is a coma aberration diagram of the imaging lens according to Example 1. FIG. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 2. 6 is a coma aberration diagram of the imaging lens according to Example 2. FIG. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 3. 4 is a coma aberration diagram of the imaging lens according to Example 3. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 4; 6 is a coma aberration diagram of the imaging lens according to Example 4. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 5. FIG. 9 is a coma aberration diagram of the imaging lens according to Example 5. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens according to Example 6; FIG. 10 is a coma aberration diagram of the imaging lens according to Example 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Imaging lens 11 1st lens 12 2nd lens 13 3rd lens 14 Aperture stop 15 Parallel plate glass 16 Image sensor

Claims (6)

In order from the object side, a meniscus first lens having a positive refractive power with a convex surface facing the object side, a second lens having a negative refractive power and a concave surface facing the object side, and a positive refractive power A third lens having
An aperture stop is provided on the object side of the first lens;
Each of the first lens, the second lens, and the third lens has an aspheric surface on at least one surface;
The first lens, the focal length of the entire second lens and the third lens f, and the focal length of the third lens when the f _3,
An imaging lens that satisfies the following conditional expression (1):
0.6 <f ₃ / f ≦ 1 (1) In order from the object side, a meniscus first lens having a positive refractive power with a convex surface facing the object side, a second lens having a negative refractive power and a concave surface facing the object side, and a positive refractive power A third lens having
An aperture stop is provided on the object side of the first lens;
Each of the first lens, the second lens, and the third lens has an aspheric surface on at least one surface;
When the focal length of the entire first lens, the second lens, and the third lens is f, the combined focal length of the first lens and the second lens is f ₁₂ , and the focal length of the second lens is f ₂ ,
An imaging lens satisfying the following conditional expressions (2) and (3):
_{2 <f 12 / f <7} ····· (2)
−1.50 <f ₂ /f<−0.50 (3) In order from the object side, a meniscus first lens having a positive refractive power with a convex surface facing the object side, a second lens having a negative refractive power and a concave surface facing the object side, and a positive refractive power A third lens having
An aperture stop is provided on the object side of the first lens;
Each of the first lens, the second lens, and the third lens has an aspheric surface on at least one surface;
The focal length of the entire first lens, the second lens and the third lens is f, the distance measured along the optical axis from the object side surface of the first lens to the image side surface of the third lens is Σd, and the third When the refractive index of the lens is n ₃ , the Abbe number of the first lens is ν ₁ , and the Abbe number of the third lens is ν ₃ ,
An imaging lens characterized by satisfying the following conditional expressions (4), (5), (6) and (7).
0.8 <Σd / f <1.5 (4)
1.40 ≦ n ₃ ≦ 1.85 (5)
40 ≦ ν ₁ ≦ 100 (6)
0 ≦ ν ₁ −ν ₃ ≦ 45 (7)   4. The imaging lens according to claim 1, wherein each of the first lens, the second lens, and the third lens is made of a plastic material. 5.   The imaging lens according to any one of claims 1 to 3, wherein the second lens and the third lens are made of a plastic material, and the first lens is made of a glass material.   The imaging lens according to any one of claims 1 to 3, wherein the first lens and the third lens are made of a glass material, and the second lens is made of a plastic material.

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