JP2008096621A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens suitable for a compact mobile camera. <P>SOLUTION: The imaging lens includes an aperture diaphragm SD having a predetermined aperture, a first lens 1 that is a biconvex lens having positive refractive power, a second lens 2 that is a meniscus lens having positive refractive power and turning its convex surface to an image surface side, and a third lens 3 having negative refractive power, whose surface on an image surface side is formed to be an aspherical surface having an inflection point where the direction of curvature is changed within an effective range in order from an object side. The focal length f1 of the first lens, the focal length f2 of the second lens, the focal length f3 of the third lens, and a distance D4 between the second lens and the third lens on an optical axis satisfy a conditional expression (1) (¾f1¾+¾f2¾+¾f3¾)/3≤3.73 and a conditional expression (2) 0.08 mm≤D4≤0.09 mm. Thus, the imaging lens whose aberration is satisfactorily corrected and which is miniaturized and thinned is obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging lens having a three-group, three-element configuration, and particularly suitable for a small mobile camera mounted on a mobile phone, a personal digital assistant (PDA), a portable personal computer, a portable music player, and the like. Related to lenses.

Conventionally, surveillance cameras, video cameras, and the like have been known as electronic imaging devices using a solid-state imaging device such as a CCD, and these have been mainly used for capturing moving images. Therefore, such a high performance is not required for the CCD and the imaging lens.
However, in recent years, with the spread of digital still cameras and the like, higher performance of solid-state imaging devices and imaging lenses has been desired.
As a result, due to significant technological advances in solid-state imaging devices such as CCDs, it has become possible to obtain images close to those of film cameras, and at the same time, miniaturization and high pixel counts of CCDs and the like have been achieved. As an imaging lens used for the above, there has been a strong demand for high performance and at the same time miniaturization, thickness reduction, and cost reduction.

By the way, as a conventional imaging lens, a meniscus first lens having a positive refractive power, sequentially arranged from the object side to the image plane side, an aperture stop having a predetermined aperture, and having a positive refractive power Known is a meniscus second lens, a third lens having a negative refractive power with a concave surface facing the image surface side, or a third lens having a positive refractive power with a convex surface facing the object side. (For example, see Patent Document 1 and Patent Document 2).
However, in these imaging lenses, since the aperture stop is arranged between the lenses, the exit pupil position is shortened, the exit angle is reduced, and the overall length of the lens is shortened in terms of thinning. Have difficulty.

As another imaging lens, an aperture stop having a predetermined aperture and sequentially arranged from the object side to the image plane side, a meniscus first lens having a positive refractive power with a convex surface facing the object side And a meniscus second lens having a negative refractive power facing the object side and a meniscus third lens having a negative refractive power facing the object side are known. (For example, refer to Patent Document 3).
However, in this imaging lens, the first lens is a meniscus lens, and it is difficult to improve the surface accuracy as compared with the biconvex lens. The conditions regarding the distance between the lens and the third lens are insufficient, and are not fully satisfactory in terms of cost reduction, aberration correction, size reduction, and the like.

Furthermore, as another imaging lens, an aperture stop having a predetermined aperture, which is sequentially arranged from the object side to the image plane side, and a meniscus first lens having a positive refractive power with a convex surface facing the object side And a meniscus second lens having a positive refractive power with a concave surface facing the object side, and a meniscus third lens having a negative refractive power with a convex surface facing the object side are known. (For example, refer to Patent Document 4).
However, in this imaging lens, since the first lens is made of a spherical lens made of a glass material, cost reduction, aberration correction and the like are not sufficient, and the F value is not so small, and the thickness is reduced. But it was not enough.

JP 2004-163786 A JP 2005-62680 A JP 2005-292235 A JP 2006-84720 A

  The present invention has been made in view of the above-described problems of the prior art, and the object of the present invention is to reduce aberrations while reducing size, thickness, weight, and cost. It is well corrected, bright (F value is small), high optical performance, and suitable for mobile cameras mounted on mobile phones, personal digital assistants (PDAs), portable personal computers, portable music players, etc. It is to provide an imaging lens.

The imaging lens of the present invention includes an aperture stop having a predetermined aperture, a biconvex first lens having a positive refractive power, and a positive refractive power, which are arranged in order from the object side to the image plane side. A second lens having a meniscus shape having a convex surface facing the image surface and an aspherical surface having a negative refractive power and an inflection point in which the direction of curvature changes within the effective range of the image surface side. The focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, and the air spacing on the optical axis of the second lens and the third lens. Is D4, the following conditional expressions (1), (2),
(1) (| f1 | + | f2 | + | f3 |) /3≦3.73
(2) 0.08 mm ≦ D4 ≦ 0.09 mm
It is characterized by satisfying.
According to this configuration, by arranging the lenses so that the first lens and the second lens have a positive refractive power and the third lens has a negative refractive power, an appropriate back focus can be secured, and the infrared light can be cut. Filters etc. can be easily arranged, and various aberrations are favorably corrected by forming an aspherical surface with an inflection point where the direction of curvature changes within the effective range on the image side surface of the third lens. Further, the emission angle can be suppressed while shortening the total lens length, and the overall size and thickness can be reduced.
Further, by satisfying conditional expression (1), it is possible to appropriately arrange the power, to properly correct various aberrations, particularly astigmatism, to reduce the manufacturing error sensitivity with respect to the lens axis, and to provide peripheral optical performance. Can be kept high.
Furthermore, by satisfying conditional expression (2), the total lens length can be shortened (thinned), and various aberrations, particularly astigmatism and distortion can be corrected well.

In the above configuration, a configuration in which the first lens, the second lens, and the third lens are all plastic lenses formed of a resin material can be employed.
According to this configuration, by using a plastic lens formed of a resin material, the production cost can be reduced and the weight can be reduced, the aspherical surface can be easily set, and the degree of freedom of aberration correction is increased. A compact configuration is possible, and a complicated shape can be easily processed as compared with a glass material.

In the above configuration, the first lens, the second lens, and the third lens may employ a configuration in which both the object side and the image plane side are all aspherical surfaces.
According to this configuration, since all surfaces are aspherical, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration can be favorably corrected, and the F value is small (bright). Thus, an imaging lens with high optical performance can be obtained.

In the above configuration, a configuration in which the first lens, the second lens, and the third lens are all formed of the same material can be employed.
According to this configuration, the production cost per lens can be reduced by using the same material, and the Abbe number is the same because of the same material, and the chromatic aberration of magnification from the center of the optical axis, An axial chromatic aberration can be satisfactorily corrected, and an imaging lens having a small F value (that is, bright) and high resolving power can be obtained.

In the above configuration, when the distance from the aperture stop to the image plane is TL, and the focal length of the first to third lenses is f, the following conditional expression (3):
(3) TL / f <1.32.
A configuration that satisfies the above can be adopted.
According to this configuration, the overall length of the lens system and the outer dimensions of the lens system can be reduced, and a reduction in size and thickness can be achieved, and various aberrations can be corrected well.

  According to the imaging lens having the above-mentioned configuration, various aberrations can be corrected well while achieving miniaturization, thinning, weight reduction, cost reduction, etc., bright (F value is small), and high optical performance. An imaging lens suitable for a mobile camera mounted on a mobile phone, a personal digital assistant (PDA), a portable personal computer, a portable music player, or the like can be obtained.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
1 and 2 show an embodiment of an imaging lens according to the present invention. FIG. 1 is a lens configuration diagram and FIG. 2 is an optical path diagram.
As shown in FIG. 1, the imaging lens includes an aperture stop SD having a predetermined aperture, a biconvex first lens 1 having a positive refractive power, arranged in order from the object side to the image plane side, A second meniscus lens 2 having a positive refractive power, and a third aspherical surface having a negative refractive power and an inflection point where the surface of the image side changes in the effective range within the effective range. A lens 3 is provided. Further, behind the third lens 3, glass plates 4 and 5 such as an infrared light cut filter or a cover glass are arranged, and an image plane P such as a CCD is arranged behind the glass plate 5. .

  Here, in the aperture stop SD, the first lens 1 to the third lens 3, and the glass plates 4, 5 to the image plane P, each surface is Si (i = 0 to 10), as shown in FIG. The radius of curvature of the surface Si is Ri (i = 0 to 10), the refractive index of the i-th lens with respect to the d-line is Ni and the Abbe number is νi (i = 1 to 3), and the refractive index of the glass plates 4 and 5 is Ni. And the Abbe number is represented by νi (i = 4, 5). Further, the distance (thickness, air distance) in the direction of the optical axis L from the aperture stop SD to the image plane P is represented by Di (i = 0 to 10) as shown in FIG. Furthermore, the focal length of the lens system of the first lens 1 to the third lens 3 is f, the focal length of the first lens 1 is f1, the focal length of the second lens 2 is f2, and the focal length of the third lens 3 is f3, A distance (lens system total length) from the aperture stop SD to the image plane P is represented by TL.

The first lens 1 is preferably a plastic lens formed of a plastic material, and as shown in FIG. 1, positive refraction in which the object-side surface S1 is convex and the image-side surface S2 is convex. It is a biconvex lens with power.
Here, the surfaces S1 and S2 are preferably both aspherical.

The second lens 2 is preferably a plastic lens formed of a plastic material. As shown in FIG. 1, the second lens 2 has a positive refractive power in which the object-side surface S3 is concave and the image-side surface S4 is convex. This is a meniscus lens.
Here, the surfaces S3 and S4 are preferably formed as aspherical surfaces.

The third lens 3 is preferably a plastic lens formed of a plastic material. As shown in FIG. 1, the object-side surface S5 is formed in a convex surface in the vicinity of the optical axis L, and the image-side surface S6 is light. A lens having a negative refractive power formed on an aspheric surface having a concave surface near the axis L and a convex surface having an inflection point where the direction of curvature changes within an effective range.
Here, the surface S5 is preferably formed as an aspheric surface in the same manner as the surface S6.

Here, the aspherical surface applied in the first lens 1 to the third lens 3 is defined by the following equation.
Z = Cy ² / [1+ (1-εC ² y ² ) ^1/2 ] + Dy ⁴ + Ey ⁶ + Fy ⁸ + Gy ¹⁰
Where Z: distance from the tangent plane of the aspheric vertex of the point on the aspheric surface whose height is y from the optical axis, y: height from the optical axis, C: curvature of the aspheric vertex (1 / r), ε: conic constant, D, E, F, G: aspheric coefficient.

In addition to the above configuration, the focal length f1 of the first lens 1, the focal length f2 of the second lens 2, the focal length f3 of the third lens 3, and the optical axis L of the second lens 2 and the third lens 3 are on the optical axis L. The air gap D4 is defined by conditional expressions (1), (2),
(1) (| f1 | + | f2 | + | f3 |) /3≦3.73
(2) 0.08 mm ≦ D4 ≦ 0.09 mm
It is formed to satisfy.
Conditional expression (1) defines the focal length of each lens. When the value of (| f1 | + | f2 | + | f3 |) / 3 exceeds the upper limit, the power of the focal length is shifted and correction of astigmatism becomes difficult, and the manufacturing error sensitivity with respect to the optical axis L of the lens is reduced. It becomes high and it becomes difficult to maintain the peripheral performance of the lens.
Therefore, when the value of (| f1 | + | f2 | + | f3 |) / 3 satisfies the conditional expression (1), the power can be appropriately arranged, and various aberrations, particularly astigmatism, can be corrected well. The manufacturing error sensitivity with respect to the lens axis can be reduced, and the peripheral optical performance can be kept high.
Conditional expression (2) defines the distance D4 on the optical axis L between the second lens 2 and the third lens 3. When the value of D4 exceeds the lower limit, it becomes difficult to correct astigmatism. On the other hand, when the value of D4 exceeds the upper limit, the entire length of the lens becomes longer, and further, it becomes difficult to correct distortion.
Therefore, when the value of D4 satisfies the conditional expression (2), the entire lens length can be shortened (thinned), and various aberrations, particularly astigmatism and distortion can be corrected well.

  That is, according to the imaging lens having the above-described configuration, by arranging the lenses so that the first lens 1 and the second lens 2 have positive refracting power and the third lens 3 has negative refracting power, an appropriate back surface can be obtained. A focus can be secured, an infrared light cut filter or the like can be easily arranged, and an aspherical surface having an inflection point in which the direction of curvature changes within the effective range is formed on the image surface side surface S6 of the third lens 3. As a result, various aberrations can be corrected satisfactorily, and the emission angle can be suppressed while shortening the overall lens length, and the overall size and thickness can be reduced. In particular, astigmatism and distortion can be corrected satisfactorily, the manufacturing error sensitivity with respect to the lens axis can be reduced, and the peripheral optical performance can be kept high.

In the above-described configuration, plastic lenses that are all formed of a resin material are preferably used as the first lens 1, the second lens 2, and the third lens 3.
According to this, the production cost can be reduced and the weight can be reduced, the aspherical surface can be easily set, and the degree of freedom of aberration correction is increased, so that a compact configuration is possible, which is more complicated than glass materials. The shape can be easily processed.

In the above configuration, both the object side and image side S1, S2, S3, S4, S5, and S6 of the first lens 1, the second lens 2, and the third lens 3 are preferably aspherical. Formed.
Thus, by making all the surfaces aspherical, it is possible to satisfactorily correct various aberrations such as spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and the F value is small (bright). An imaging lens with high optical performance can be obtained.

In the above configuration, the first lens 1, the second lens 2, and the third lens 3 are preferably all made of the same material.
In this way, by using the same material for all lenses, the production cost per lens can be reduced, and because the same material is used, the Abbe number is the same, and the magnification from the center of the optical axis. Chromatic aberration and axial chromatic aberration can be satisfactorily corrected, and an imaging lens having a small F value (that is, bright) and high resolving power can be obtained.

Furthermore, in the imaging lens having the above configuration, the distance (lens system total length) TL from the aperture stop SD to the image plane P and the focal length f of the first lens 1 to the third lens 3 are preferably the following conditional expression (3 )
(3) TL / f <1.32.
It is formed so as to satisfy.
Conditional expression (3) defines the ratio between the total length TL of the lens system and the focal length f of the lens system. If the value of TL / f exceeds the upper limit, the total lens length becomes long, and further, it becomes difficult to correct distortion. Therefore, when the value of TL / f satisfies the conditional expression (3), the overall length of the lens system and the outer dimensions of the lens system can be reduced, and a reduction in size and thickness can be achieved, and various aberrations can be improved. It can be corrected.

    Next, specific numerical examples of the imaging lens will be described below as Example 1 and Example 2.

Numerical data of the conditional expressions (1) to (3) in the first embodiment, main specifications of the first lens 1 to the third lens 3, and the glass plates 4 and 5, and various numerical data (setting values) are as follows. It is as follows. In addition, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration in Example 1 are as shown in FIG. In FIG. 3, astigmatism, S represents an aberration on the sagittal plane, and M represents an aberration on the meridional plane.
In the first embodiment, the first lens 1 to the third lens 3 are all formed as plastic lenses, and both surfaces S1 and S2 of the first lens 1, both surfaces S3 and S4 of the second lens 2, and the third lens 3 are formed. Both surfaces S5 and S6 are formed as aspherical surfaces.

<Value of conditional expression>
(1) (| f1 | + | f2 | + | f3 |) / 3 = (| 3.69 | + | 3.76 | + | −3.74 |) /3→3.73≦3.73
(2) 0.08 mm ≦ D4 ≦ 0.09 mm → 0.08 mm ≦ 0.09 mm ≦ 0.09 mm
(3) TL / f <1.32 → 4.65 / 3.53 <1.32 → 1.317 <1.32.

<Specification specifications>
Object distance = 60 cm, focal length f of the lens system of the first lens 1 to the third lens 3 = 3.53 mm, focal length f1 of the first lens 1 = 3.69 mm, focal length f2 of the second lens 2 = 3. 76 mm, focal length f3 of the third lens 3 = −3.74 mm, F number (FNo.) = 2.87, exit pupil position = −3.46 mm, exit angle of outermost ray = −22.5 °, lens System overall length (aperture stop SD to image plane P) = 4.65 mm, lens overall length (aperture stop SD to rear surface S6 of the third lens 3) = 3.04 mm, back focus = 0.538 mm, field angle (2ω) = 64 0.0 °, distortion (at 600 mm) = 0.2%, outer diameter of the first lens = 1.58 mm, outer diameter of the second lens = 2.25 mm, outside of the third lens 3 Diameter dimension = 3.80 mm

<Curvature radius>
R0 = ∞ (aperture stop SD), R1 = 1.950 mm (aspheric surface), R2 = −300.000 mm (aspheric surface), R3 = −1.022 mm (aspheric surface), R4 = −0.813 mm (aspheric surface) ), R5 = 3.638 mm (aspherical surface), R6 = 1.184 mm (aspherical surface), R7 = ∞, R8 = ∞, R9 = ∞, R10 = ∞

<Spacing on the optical axis>
D0 = 0.000 mm, D1 = 0.600 mm, D2 = 0.979 mm, D3 = 0.615 mm, D4 = 0.090 mm, D5 = 0.753 mm, D6 = 0.738 mm, D7 = 0.300 mm, D8 = 0.125mm, D9 = 0.400mm, D10 = 0.045mm

<Refractive index (Ni)>
N1 = 1.525, N2 = 1.525, N3 = 1.525, N4 = 1.517, N5 = 1.517
<Abbe number (νi)>
ν1 = 56.3, ν2 = 56.3, ν3 = 56.3, ν4 = 64.2, ν5 = 64.2

<Numerical data of aspheric coefficient>
<S1 surface>
ε = −1.014 × 10 ⁻² , D = −2.095 × 10 ⁻² , E = −3.949 × 10 ⁻³ , F = 2.079 × 10 ⁻³ , G = −2.852 × ^10-2
<S2 surface>
ε = −3.576 × 10 ⁻² , D = −2.778 × 10 ⁻² , E = −9.677 × 10 ⁻³ , F = −7.283 × 10 ⁻³ , G = −9.332 × 10 ^-3
<S3 surface>
ε = −3.502 × 10 ⁻¹ , D = 1.541 × 10 ⁻¹ , E = 2.269 × 10 ⁻¹ , F = −1.542 × 10 ⁻¹ , G = 1.508 × 10 ^{− 2}
<S4 surface>
ε = 1.394 × 10 ⁻¹ , D = −1.747 × 10 ⁻¹ , E = 2.085 × 10 ⁻¹ , F = −4.746 × 10 ⁻² , G = −1.249 × 10 ^-3
<S5 surface>
ε = −1.053 × 10 ⁻¹ , D = 5.631 × 10 ⁻² , E = −2.228 × 10 ⁻² , F = 2.676 × 10 ⁻³ , G = 7.897 × 10 ^{− 5}
<S6 surface>
ε = −6.566 × 10 ⁻² , D = 2.405 × 10 ⁻² , E = −6249 × 10 ⁻³ , F = 4.779 × 10 ⁻⁴ , G = −1.028 × 10 ⁻⁶

  In the first embodiment, the lens system total length TL is as short as 4.65 mm, the F value (F number) is as small as 2.87 and is bright, a desired resolving power can be secured, and optical performance such as peripheral light quantity is deteriorated. As shown in FIG. 3, a small imaging lens having various optical aberrations corrected and high optical performance, suitable for a mobile camera mounted on a mobile phone, a portable personal computer, a portable music player, etc. was gotten.

Numerical data of the conditional expressions (1) to (3) in the second embodiment, main specifications of the first lens 1 to the third lens 3, and the glass plates 4 and 5, and various numerical data (setting values) are as follows. It is as follows. In addition, various aberrations such as spherical aberration, astigmatism, distortion, and lateral chromatic aberration in Example 2 are as shown in FIG. In the astigmatism in FIG. 4, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane.
In Example 2, the first lens 1 to the third lens 3 are all formed as plastic lenses. Both surfaces S1 and S2 of the first lens 1, both surfaces S3 and S4 of the second lens 2, and both surfaces of the third lens 3 are formed. S5 and S6 are formed as aspherical surfaces.

<Value of conditional expression>
(1) (| f1 | + | f2 | + | f3 |) / 3 = (| 3.69 | + | 3.76 | + | −3.74 |) /3→3.73≦3.73
(2) 0.08 ≦ D3 ≦ 0.09 → 0.08 ≦ 0.09 ≦ 0.09
(3) 1.30 <TL / f <1.32 = 1.30 <4.64 / 3.52 <1.32 → 1.30 <1.315 <1.32.

<Specification specifications>
Object distance = 60 cm, focal length f of the lens system of the first lens 1 to the third lens 3 = 3.52 mm, focal length f1 of the first lens 1 = 3.69 mm, focal length f2 of the second lens 2 = 3. 76 mm, focal length f3 of the third lens 3 = −3.74 mm, F number (FNo.) = 2.88, exit pupil position = −3.46 mm, exit angle of outermost ray = −25.0 °, lens System overall length (aperture stop SD to image plane P) = 4.63 mm, lens overall length (aperture stop SD to rear surface S6 of the third lens 3) = 3.02 mm, back focus = 0.745 mm, field angle (2ω) = 64 0.0 °, distortion (at 600 mm) = 0.11%, outer diameter of the first lens = 1.59 mm, outer diameter of the second lens = 2.27 mm, outside of the third lens 3 Diameter dimension = 3.79 mm

<Curvature radius>
R0 = ∞ (aperture stop SD), R1 = 1.950 mm (aspheric surface), R2 = −300.000 mm (aspheric surface), R3 = −1.022 mm (aspheric surface), R4 = −0.813 mm (aspheric surface) ), R5 = 3.624 mm (aspherical surface), R6 = 1.183 mm (aspherical surface), R7 = ∞, R8 = ∞, R9 = ∞, R10 = ∞

<Spacing on the optical axis>
D0 = 0.000 mm, D1 = 0.600 mm, D2 = 0.967 mm, D3 = 0.615 mm, D4 = 0.090 mm, D5 = 0.756 mm, D6 = 0.756 mm, D7 = 0.300 mm, D8 = 0.125mm, D9 = 0.400mm, D10 = 0.045mm

<Refractive index (Ni)>
N1 = 1.525, N2 = 1.525, N3 = 1.525, N4 = 1.517, N5 = 1.517
<Abbe number (νi)>
ν1 = 56.3, ν2 = 56.3, ν3 = 56.3, ν4 = 64.2, ν5 = 64.2

<Numerical data of aspheric coefficient>
<S1 surface>
ε = −9.057 × 10 ⁻³ , D = −2.033 × 10 ⁻² , E = −3.496 × 10 ⁻³ , F = 2.544 × 10 ⁻³ , G = −2.799 × ^10-2
<S2 surface>
ε = −3.423 × 10 ⁻² , D = −2.639 × 10 ⁻² , E = −9.212 × 10 ⁻³ , F = −2.604 × 10 ⁻³ , G = −9.176 × 10 ^-3
<S3 surface>
ε = −3.517 × 10 ⁻¹ , D = −1.748 × 10 ⁻¹ , E = 2.271 × 10 ⁻¹ , F = −1.540 × 10 ⁻¹ , G = 1.505 × 10 ^-2
<S4 surface>
ε = 1.398 × 10 ⁻¹ , D = −1.748 × 10 ⁻¹ , E = 2.083 × 10 ⁻¹ , F = −4.768 × 10 ⁻² , G = −1.371 × 10 ^-3
<S5 surface>
ε = −1.053 × 10 ⁻¹ , D = 5.628 × 10 ⁻² , E = −2.228 × 10 ⁻² , F = 2.675 × 10 ⁻³ , G = 7.823 × 10 ^{− 5}
<S6 surface>
ε = −6.606 × 10 ⁻² , D = 2.403 × 10 ⁻² , E = −6.224 × 10 ⁻³ , F = 4.809 × 10 ⁻⁴ , G = −4.836 × 10 ^-8

  In the second embodiment, the lens system total length TL is as short as 4.63 mm, the F value (F number) is as small as 2.88 and is bright, a desired resolving power can be ensured, and optical performance such as peripheral light quantity is deteriorated. As shown in FIG. 4, a small imaging lens having various optical characteristics corrected and high optical performance, suitable for a mobile camera mounted on a mobile phone, a portable personal computer, a portable music player, etc. was gotten.

  As described above, the imaging lens according to the present invention achieves reductions in size, thickness, weight, cost, and the like, can correct various aberrations favorably, and is bright (small F value). Therefore, it can be applied to mobile cameras mounted on cellular phones, portable personal computers, portable music players, etc., as well as digital cameras, fixed cameras as well as portable cameras, and other lens optical systems Is also useful.

It is a lens block diagram which shows one Embodiment of the imaging lens which concerns on this invention. FIG. 2 is an optical path diagram of the imaging lens shown in FIG. 1. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration in Example 1. FIG. 5 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration in Example 2.

Explanation of symbols

SD Aperture stop 1 First lens 2 Second lens 3 Third lens 4, 5 Glass plate P Image plane L Optical axis f Focal length f1 of lens system Focal length f2 of first lens Focal length f3 of second lens Third lens Focal length D4 Air distance TL on the optical axis of the second lens and the third lens Distance from aperture stop to image plane (lens system total length)

Claims (5)

Arranged in order from the object side to the image plane side,
An aperture stop having a predetermined aperture;
A biconvex first lens having positive refractive power;
A second meniscus lens having positive refractive power and having a convex surface facing the image surface side;
A third lens having a negative refracting power and an aspherical surface having an inflection point at which the image side surface has an inflection point in which the direction of curvature changes within an effective range,
The focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, and the air space on the optical axis of the second lens and the third lens is D4. When the following conditional expressions (1), (2),
(1) (| f1 | + | f2 | + | f3 |) /3≦3.73
(2) 0.08 mm ≦ D4 ≦ 0.09 mm
An imaging lens characterized by satisfying The first lens, the second lens, and the third lens are all plastic lenses formed of a resin material.
The imaging lens according to claim 1. The first lens, the second lens, and the third lens are both aspheric on both the object side and the image side.
The imaging lens according to claim 1 or 2, wherein The first lens, the second lens, and the third lens are all formed of the same material.
The imaging lens according to any one of claims 1 to 3. When the distance from the aperture stop to the image plane is TL and the focal length of the first lens to the third lens is f, the following conditional expression (3):
(3) TL / f <1.32.
The imaging lens according to any one of claims 1 to 4, wherein:

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