JP2007233423A - Photographic lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To thin a photographic lens applied to a mobile camera or the like. <P>SOLUTION: The photographic lens is constituted of an aperture diaphragm 1 having a predetermined aperture; a first lens 2 turning its convex surfaces to an object side and an image surface side and having positive refractive power; a second lens 3 turning its concave surface to the object side and having positive refractive power; and a third lens 4 turning its convex surface to the object side, having an aspherical surface on the image surface side, formed to have an inflection point midway and having negative refractive power, which are arranged, in order starting from the object side to the image surface side. By constituting the photographic lens of three lenses in three groups, the thin photographic lens with appropriate back focus being secured, whose aberrations are satisfactorily corrected, whose entire length is shortened, and which is adapted to a high-density imaging element, having 1,000,000 or more pixels, is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photographic lens applied to a mobile phone, a personal digital assistant (PDA), a mobile personal computer such as a portable personal computer, a digital camera, a video camera, and the like equipped with an image sensor such as a CCD.

As a photographing lens applied to an image pickup device such as a CCD, there is known a lens that is used for photographing a moving image such as a surveillance camera. This surveillance camera is mainly used for shooting moving images, and since the number of pixels of the image sensor is relatively small, the lens itself does not require high optical performance.
In image sensors used in conventional surveillance cameras, video cameras, etc., it has been pointed out that the image quality of captured images is worse than that of a silver salt film type camera, but due to remarkable technological progress of image sensors in recent years, An image with a quality close to that obtained by a silver salt film camera has been obtained. At the same time, downsizing and high density of the image sensor have been achieved, and as a photographic lens applied to a digital still camera or the like, it is strongly desired that it is high performance and at the same time small, thin and inexpensive. Yes.

On the other hand, a photographing lens used for a cellular phone, a personal digital assistant (PDA), etc. is a very small and thin lens having about 1 to 2 lenses, but is about 100,000 to 350,000 pixels. Therefore, the obtained image was not fully satisfactory.
In addition, in an image sensor such as a CCD, a microlens is conventionally provided on the surface of the image sensor in order to use light efficiently. Therefore, if the angle of light incident on the image sensor is too large, vignetting occurs and light does not enter the image sensor. Therefore, as a photographic lens applied to these, a lens in which the exit pupil is sufficiently away from the image plane and the angle at which the light beam enters the image sensor, that is, the exit angle is reduced to improve the telecentricity is generally used. (For example, see Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, Patent Literature 5, Patent Literature 6, and Patent Literature 7).

Japanese Patent Laid-Open No. 2000-171697 Japanese Patent Laid-Open No. 2001-133684 Japanese Patent Laid-Open No. 2002-98888 Japanese Patent Laid-Open No. 2002-162561 Japanese Patent Laid-Open No. 05-40220 Japanese Patent Laid-Open No. 05-157862 JP 05-188284 A

By the way, the recent technological advances in image sensors have led to demands for smaller, thinner, higher resolution, and cheaper imaging lenses, but conventional imaging lenses have improved telecentricity. The overall length of the lens is relatively long, which is not suitable for further thinning.
On the other hand, the conventional imaging device was limited by the limit of the light emission angle, and the photographic lens could not be made so thin (the total length of the lens system was so short). Can be used up to about 20 degrees. Therefore, there is a demand for a thinner photographic lens suitable for an image sensor having such a microlens.

The present invention has been made in view of the above points.
While eliminating the vignetting phenomenon, it is possible to reduce the size, thickness, weight, cost, etc. with a very simple lens configuration. An object of the present invention is to provide a high-performance photographic lens that can be used for a high-density imaging device having 1 million pixels or more mounted in a mobile camera such as a terminal, a digital still camera, a digital video camera, or the like.

The photographic lens of the present invention includes an aperture stop having a predetermined aperture, which is arranged in order from the object side to the image plane side, and a single positive refractive power with convex surfaces facing both the object side and the image plane side. A first lens having a positive refractive power with a concave surface facing the object side, a convex surface facing the object side, an aspheric surface on the image side, and an inflection point in the middle And a third lens having negative refractive power formed in the above.
According to this configuration, an aperture stop is disposed at the tip, and the first lens having a biconvex shape and the second lens having a concave surface on the object side both have a positive refractive power, and the third lens has a negative refractive power. By adopting a three-group, three-lens configuration, it is possible to obtain a thin photographic lens with an appropriate back focus and a short overall lens length. The third lens has an aspheric surface on the image surface side and is formed so as to have an inflection point in the middle. That is, the third lens has a concave shape at a position on the way to the outside in the radial direction within the effective range of the aspheric surface. By providing an inflection point that changes in a convex shape, the exit angle can be reduced while satisfactorily correcting various aberrations, particularly astigmatism and distortion.

In the above configuration, the second lens and the third lens may have aspheric surfaces on both the object side and the image side.
According to this configuration, the overall length of the lens system is shortened, and it becomes difficult to correct each aberration as the lens system is miniaturized. It is possible to obtain a photographic lens in which the light emission angle is 24 degrees or less and various aberrations are favorably corrected.

In the above-described configuration, the second lens may be configured to have an aspheric surface on the object side and to have a refractive power that decreases toward the periphery.
According to this configuration, various aberrations, in particular astigmatism and coma aberration, can be easily corrected and corrected satisfactorily.

The said structure WHEREIN: The structure currently formed with the resin material can be employ | adopted for the 2nd lens and the 3rd lens.
According to this configuration, the production cost can be reduced and the weight can be reduced by using the resin material. In addition, since the resin material is formed by injection molding, a complicated shape such as a curved surface having an inflection point can be easily formed.

In the above configuration, when the focal length of the entire lens system is f and the total length of the lens system from the object side front surface of the aperture stop to the image plane on which the subject is imaged is TL,
(1) TL / f <1.6
Can be adopted.
According to this configuration, by defining the relationship between the focal length of the entire lens system and the total length of the lens system as shown in equation (1), it is possible to easily achieve a reduction in size and thickness of the photographing lens.

In the above configuration, when the Abbe number of the first lens is ν1,
(2) ν1> 45
Can be adopted.
According to this configuration, the axial chromatic aberration and the lateral chromatic aberration can be particularly favorably corrected by determining the Abbe number of the first lens as shown in equation (2).

In the above configuration, the radius of curvature of the object side surface of the second lens is R4, the radius of curvature of the image side surface of the second lens is R5, the radius of curvature of the object side surface of the third lens is R6, and the third lens. When the radius of curvature of the surface on the image plane side is R7,
(3) 0.7 <| R4 | / | R5 | <2
(4) 1 <R6 / R7 <4
Can be adopted.
According to this configuration, the second lens is formed so that the radius of curvature satisfies the expression (3), and the curvature radius of the third lens is formed so as to satisfy the expression (4), thereby ensuring an appropriate back focus. However, various aberrations, particularly astigmatism and distortion can be corrected well, and good optical characteristics can be obtained.

In the above configuration, when the distance between the second lens and the third lens in the optical axis direction is D5, and the focal length of the entire lens system is f,
(5) D5 / f <0.15
Can be adopted.
According to this configuration, by forming the distance between the second lens and the third lens so as to satisfy the expression (5), various aberrations, particularly astigmatism and distortion can be corrected well.

In the above configuration, when the thickness of the second lens in the optical axis direction is D4 and the thickness of the third lens in the optical axis direction is D6,
(6) 0.8 <D4 / D6 <1.3
Can be adopted.
According to this configuration, the thickness of the second lens and the third lens is formed so as to satisfy the expression (6), so that various aberrations, particularly astigmatism, can be corrected satisfactorily while ensuring an appropriate back focus. And good optical properties can be obtained.

According to the photographic lens of the present invention having the above configuration, various aberrations can be achieved with a simple configuration of three elements in three groups while eliminating the vignetting phenomenon in the image sensor and achieving downsizing, weight reduction, cost reduction, and the like. It is possible to obtain a thin photographic lens in which is corrected well.
In particular, the light emission angle is 20 degrees or less, the total lens length is as short as 4.5 mm or less (in a state where the back focus is not included), an appropriate back focus can be secured, various aberrations are corrected, and 1 million A small and thin photographic lens suitable for a high-density imaging device having pixels or more can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a basic configuration diagram showing an embodiment of a photographic lens according to the present invention. As shown in FIG. 1, the photographic lens according to this embodiment includes an aperture stop 1 having a predetermined aperture, a first lens group (I), and a second lens group (from the object side to the image plane side). II) and the third lens group (III) are sequentially arranged.

The first lens group (I) is formed by a first lens 2 having a positive refractive power with a convex surface facing the object side.
The second lens group (II) is formed by the second lens 3 having a positive refractive power with the concave surface facing the object side.
The third lens group (III) is formed by a third lens 4 having a negative refractive power with a convex surface facing the object side.
In this arrangement, a glass filter 5 made of a parallel plate as an infrared cut filter, a low-pass filter or the like is arranged closer to the image plane side than the third lens 4, and an image plane S such as a CCD is arranged behind the third lens 4. Will be.

  In the arrangement configuration including the aperture stop 1, the first lens 2, the second lens 3, the third lens 4, and the glass filter 5, as shown in FIG. 1, the aperture stop 1, the lenses 2 to 4, and the glass filter 5. Each surface of Si is i (i = 1 to 9), the radius of curvature of each surface Si is Ri (i = 1 to 9), and the refractive index of the first lens 2 to the third lens 4 with respect to the d-line is Ni (i = 1 to 3) and Abbe number are represented by νi (i = 1 to 3), and the refractive index of the glass filter 5 with respect to the d-line is represented by N4 and Abbe number by ν4. Further, the distance (thickness, air distance) in the optical axis direction L from the aperture stop 1 to the glass filter 5 is represented by Di (i = 1 to 8), and the back focus is represented by BF.

Here, when the focal length of the entire lens system is f and the distance from the object-side front surface S1 of the aperture stop 1 to the image plane S on which the subject is imaged (back focus is an air conversion distance) is TL, the following conditional expression (1),
(1) TL / f <1.6
It is configured to satisfy.
Conditional expression (1) defines an appropriate ratio between the dimension of the entire lens system in the optical axis direction and the focal length of the entire lens system, and is a condition relating to thinning of the lens. By forming so that the value of TL / f is less than 1.6, size reduction and thickness reduction can be easily achieved.

The first lens 2 is a lens having a positive refractive power with a convex surface facing the object side, particularly a lens having a positive refractive power with a convex surface facing both the object side and the image surface side, and is formed of a glass material. The Abbe number ν1 is expressed by the following conditional expression (2),
(2) ν1> 45
It is configured to satisfy.
Conditional expression (2) defines an appropriate Abbe number of the first lens 2, and unless this conditional expression is satisfied, axial chromatic aberration and lateral chromatic aberration are particularly increased. Therefore, by satisfying this conditional expression, axial chromatic aberration and lateral chromatic aberration can be corrected well.

The second lens 3 is a lens having a concave surface on the object side and a convex surface on the image surface side, and is formed of a resin material here. Further, the second lens 3 is formed such that both the object side and the image surface side S4 and S5 are aspherical. Furthermore, the aspherical surface formed on the object-side surface S4 of the second lens 3 is formed such that its refractive power decreases toward the periphery.
As the overall length of the lens becomes shorter and smaller, correction of each aberration becomes very difficult, and the exit angle tends to become very large. However, both surfaces S4 and S5 of the second lens 3 are not used. By using a spherical surface, various aberrations can be corrected satisfactorily while ensuring an appropriate back focus. In particular, astigmatism and coma can be easily corrected by reducing the refractive power of the peripheral portion.

The third lens 4 has a negative refractive power with a convex surface on the object side and a concave surface on the image surface side, and in particular, has a convex surface on the object side, an aspheric surface on the image surface side, and an inflection in the middle. It is a lens having negative refractive power formed so as to have a point, and here is formed of a resin material.
Here, in the third lens 4, both the object side and the image surface side S 6 and S 7 are formed as aspherical surfaces. The aspherical surface formed on the image plane side of the third lens 4 is formed so as to have an inflection point that changes from a concave shape to a convex shape on the way from the center toward the radially outer side.
In this case as well, as described above, as the overall length of the lens becomes shorter and the size is reduced, correction of each aberration becomes very difficult and the exit angle tends to become very large. By making the both surfaces S6 and S7 aspherical, various aberrations can be favorably corrected while ensuring an appropriate back focus.
In particular, by providing a shape with an inflection point, the exit angle can be reduced while satisfactorily correcting astigmatism and distortion, and the center and peripheral image planes can be easily matched. .

Here, a formula representing an aspheric surface formed on the second lens 3 and the third lens 4 is defined by the following formula.
Z = Cy ² / [1+ (1-εC ² y ² ) ^1/2 ] + Dy ⁴ + Ey ⁶ + Fy ⁸ + Gy ¹⁰ + Hy ¹² , where Z: height from the optical axis L from the tangential plane at the apex of the aspheric surface Is the distance to the point on the aspheric surface of y, y: height from the optical axis L, C: curvature (1 / R) at the apex of the aspheric surface, ε: conic constant, D, E, F, G, H : Aspheric coefficient.

In the above configuration, the second lens 3 and the third lens 4 have the following curvatures R4 and R5 of the second lens 3 and radii R6 and R7 of the third lens 4 in the following conditional expressions (3) and (4 ),
(3) 0.7 <| R4 | / | R5 | <2
(4) 1 <R6 / R7 <4
It is configured to satisfy.
Conditional expressions (3) and (4) define appropriate ratios of the curvature radii of the lenses in order to achieve good optical characteristics in the second lens 3 and the third lens 4. If these conditional expressions are not satisfied, it is difficult to secure an appropriate back focus, and it is difficult to correct various aberrations, particularly astigmatism and distortion. Therefore, by satisfying these conditional expressions, an appropriate back focus can be ensured, various aberrations can be corrected well, and sufficient optical characteristics can be obtained.

Further, the second lens 3 and the third lens 4 have a distance D5 between them in the optical axis direction and a focal length f of the entire lens system in the following conditional expression (5):
(5) D5 / f <0.15
It is configured to satisfy.
Conditional expression (5) defines an appropriate lens interval between the second lens 3 and the third lens 4 in the optical axis direction. If this conditional expression is not satisfied, it is advantageous because the distance to the exit pupil is increased and the angle of the light ray incident on the image sensor is reduced. However, the overall length of the lens system is increased and the outer diameter of the third lens 4 is increased. Is also undesirable, and correction of astigmatism and distortion is particularly difficult. Therefore, by satisfying this conditional expression, it is possible to satisfactorily correct various aberrations, particularly astigmatism and distortion, while achieving a reduction in thickness and size.

Further, the second lens 3 and the third lens 4 have a thickness D4 of the second lens 3 and a thickness D6 of the third lens 4 satisfying the following conditional expression (6),
(6) 0.8 <D4 / D6 <1.3
It is configured to satisfy.
Conditional expression (6) defines an appropriate thickness ratio on the optical axis of the second lens 3 and the third lens 4. If this conditional expression is not satisfied, it is difficult to secure an appropriate back focus, and it is difficult to correct various aberrations, particularly astigmatism. Therefore, by satisfying this conditional expression, an appropriate back focus is ensured, various aberrations, particularly astigmatism, can be favorably corrected, and good optical characteristics can be obtained.

  An example with specific numerical values of the embodiment configured as described above will be shown as Example 1 below. The main specification specifications, various numerical data (setting values), and numerical data related to the aspherical surface in Example 1 are as follows. In addition, the aberration diagrams regarding the spherical aberration, astigmatism, distortion (distortion), and lateral chromatic aberration in Example 1 are as shown in FIG. In FIG. 2, H represents the incident height, Y ′ represents the image height, d represents the aberration due to the d line, F represents the aberration due to the F line, c represents the aberration due to the c line, and SC represents the sine condition. It indicates an unsatisfactory amount, DS further indicates an aberration on the sagittal plane, and DT indicates an aberration on the meridional plane.

<Specification specifications>
Object distance = infinity, focal length f of the entire lens system = 4.35 mm, FNo. = 3.95, exit pupil position = −4.41 mm, exit angle of outermost ray = −18.9 °, total lens system length (front of aperture stop to third lens rear end) = 4.14 mm, back focus (air (Converted) = 1.58 mm, total lens system length (front of aperture stop to image plane; including glass filter 5) = 5.97 mm, total length of lens system (front of aperture stop to image plane; no glass filter 5) TL = 5.72 mm , Angle of view (2ω) = 60.4 °

<Curvature radius>
R1 = ∞ (aperture stop), R2 = 2.100 mm, R3 = -31.041 mm, R4 = −1.307 mm (aspherical), R5 = −1.415 mm (aspherical), R6 = 2.620 mm (non-aspheric) Spherical surface), R7 = 1.573 mm (aspherical surface), R8 = ∞, R9 = ∞
<Spacing on the optical axis>
D1 = 0.050 mm, D2 = 1.013 mm, D3 = 0.840 mm, D4 = 1.090 mm, D5 = 0.100 mm, D6 = 1.045 mm, D7 = 0.783 mm, D8 = 0.750 mm, BF = 0.30mm
<Refractive index (Nd)>
N1 = 1.49700, N2 = 1.50914, N3 = 1.50914, N4 = 1.51680
<Abbe number>
ν1 = 81.6, ν2 = 56.4, ν3 = 56.4, ν4 = 64.2

<Aspheric coefficient>
<S4>
ε = −1.6013550, D = −0.1373080, E = 0.609909190 × 10 ⁻¹ , F = 0.12222470 × 10 ⁻¹ , G = −0.4222570 × 10 ⁻¹ , H = 0.127620 × 10 ^-1
<S5>
ε = 0.4005340, D = −0.7267790 × 10 ⁻¹ , E = 0.6589860 × 10 ⁻¹ , F = 0.79947910 × 10 ⁻² , G = −0.4892700 × 10 ⁻² , H = 0.3645610 × 10 ⁻³
<S6>
ε = -2.8115860, D = -0.1355510, E = 0.4805600 x 10 ^-1 , F = -0.6459320 x 10 ^-2 , G = -0.1636780 x 10 ^-3 , H = 0. 5901350 × 10 ^-4
<S7>
ε = −0.3867960, D = −0.1251790, E = 0.26777310 × 10 ⁻¹ , F = −0.40885650 × 10 ⁻² , G = 0.4376590 × 10 ⁻³ , H = −0. 2920160 × 10 ⁻⁴

Here, the values of the conditional expressions (1) to (6) are
(1) TL / f = 1.31 (<1.6)
(2) ν1 = 81.6 (> 45)
(3) | R4 | / | R5 | = 0.92 (0.7 <0.92 <2)
(4) R6 / R7 = 1.67 (1 <1.67 <4)
(5) D5 / f = 0.02 (<0.15)
(6) D4 / D6 = 1.04 (0.8 <1.04 <1.3)
And all are satisfied.

  In Example 1 described above, the total length of the lens is 4.14 mm, the back focus (air conversion) is 1.58 mm, the emission angle of the outermost ray is │−18.9 ° │, and the F-number is not including the back focus. 3.95, angle of view becomes 60.4 °, a thin lens (short dimension in the optical axis direction), various aberrations are corrected well, and a photographing lens with high optical performance suitable for an image sensor with high density pixels is obtained. It is done.

  FIG. 3 is a basic configuration diagram showing another embodiment of the taking lens according to the present invention. This photographing lens has the same configuration as that of the above-described embodiment except that the specification of each lens is changed.

  An example with specific numerical values of this embodiment is shown as Example 2 below. Main specification specifications, various numerical data (setting values), and numerical data related to the aspherical surface in Example 2 are as follows. In addition, the aberration diagrams regarding the spherical aberration, astigmatism, distortion (distortion), and lateral chromatic aberration in Example 2 are as shown in FIG. In FIG. 4, H represents the incident height, Y ′ represents the image height, d represents the aberration due to the d line, F represents the aberration due to the F line, c represents the aberration due to the c line, and SC represents the sine condition. It indicates an unsatisfactory amount, DS further indicates an aberration on the sagittal plane, and DT indicates an aberration on the meridional plane.

<Specification specifications>
Object distance = infinity, focal length f of the entire lens system = 4.32 mm, FNo. = 4.00, exit pupil position = -5.30 mm, exit angle of outermost light ray = -17.8 °, total lens system length (front of aperture stop to third lens rear end) = 4.40 mm, back focus (air (Converted) = 1.79 mm, lens system total length (front of aperture stop to image surface; including glass filter 5) = 6.36 mm, lens system total length (front of aperture stop to image surface; no glass filter 5) TL = 6.19 mm , Angle of view (2ω) = 60.6 °

<Curvature radius>
R1 = ∞ (aperture stop), R2 = 3.146 mm, R3 = 12.111 mm, R4 = −1.550 mm (aspherical), R5 = −1.345 mm (aspherical), R6 = 2.182 mm (aspherical) ), R7 = 1.450 mm (aspherical surface), R8 = ∞, R9 = ∞
<Spacing on the optical axis>
D1 = 0.000 mm, D2 = 1.000 mm, D3 = 1.100 mm, D4 = 1.100 mm, D5 = 0.200 mm, D6 = 1.000 mm, D7 = 1.158 mm, D8 = 0.500 mm, BF = 0.30mm
<Refractive index (Nd)>
N1 = 1.71300, N2 = 1.50914, N3 = 1.50914, N4 = 1.51680
<Abbe number>
ν1 = 53.9, ν2 = 56.4, ν3 = 56.4, ν4 = 64.2

<Aspheric coefficient>
<S4>
ε = −5.2212236, D = −0.14211075, E = 0.4925830 × 10 ⁻¹ , F = −0.1896358 × 10 ⁻² , G = −0.1048479 × 10 ⁻² , H = 0. 1270435 × 10 ^-4
<S5>
ε = 0.38888039, D = −0.9013852 × 10 ⁻² , E = 0.9477626 × 10 ⁻² , F = 0.0.44367 × 10 ⁻² , G = −0.4583173 × 10 ⁻³ , H = 0.1708697 × 10 ⁻⁴
<S6>
ε = −7.102434, D = −0.5224621 × 10 ⁻¹ , E = 0.247356 × 10 ⁻¹ , F = −0.5362617 × 10 ⁻² , G = 0.41312775 × 10 ⁻³ , H = 0.1368477 × 10 ⁻⁴
<S7>
ε = −3.9418225, D = −0.4667482 × 10 ⁻¹ , E = 0.14969927 × 10 ⁻¹ , F = −0.2858500 × 10 ⁻² , G = 0.15772929 × 10 ⁻³ , H = −0.2558601 × 10 ⁻⁵

Here, the values of the conditional expressions (1) to (6) are
(1) TL / f = 1.43 (<1.6)
(2) ν1 = 53.9 (> 45)
(3) | R4 | / | R5 | = 1.15 (0.7 <1.15 <2)
(4) R6 / R7 = 1.50 (1 <1.50 <4)
(5) D5 / f = 0.05 (<0.15)
(6) D4 / D6 = 1.1 (0.8 <1.1 <1.3)
And all are satisfied.

  In Example 2 described above, the total length of the lens is 4.40 mm, the back focus (air equivalent) is 1.79 mm, the emission angle of the outermost ray is │−17.8 ° │, and the F-number is not including the back focus. It is 4.00 and the angle of view is 60.6 °. It is thin (short in the optical axis direction), has various aberrations corrected, and has a high optical performance suitable for high-density pixel image sensors. It is done.

  FIG. 5 is a basic configuration diagram showing still another embodiment of the photographing lens according to the present invention. This photographing lens has the same configuration as that of the above-described embodiment except that the specification of each lens is changed.

  An example with specific numerical values of this embodiment is shown as Example 3 below. Main specification specifications, various numerical data (setting values), and numerical data related to the aspherical surface in Example 3 are as follows. In addition, the aberration diagrams regarding the spherical aberration, astigmatism, distortion (distortion), and lateral chromatic aberration in Example 3 are as shown in FIG. In FIG. 6, H represents the incident height, Y ′ represents the image height, d represents the aberration due to the d line, F represents the aberration due to the F line, c represents the aberration due to the c line, and SC represents the sine condition. It indicates an unsatisfactory amount, DS further indicates an aberration on the sagittal plane, and DT indicates an aberration on the meridional plane.

<Specification specifications>
Object distance = infinity, focal length f of the entire lens system = 4.35 mm, FNo. = 3.96, exit pupil position = −4.35 mm, exit angle of outermost ray = −18.9 °, total length of lens system (front of aperture stop to third lens rear end) = 4.15 mm, back focus (air (Converted) = 1.56 mm, lens system total length (aperture stop front surface to image surface; including glass filter 5) = 5.97 mm, lens system total length (aperture stop front surface to image surface; no glass filter 5) TL = 5.71 mm , Angle of view (2ω) = 60.8 °

<Curvature radius>
R1 = ∞ (aperture stop), R2 = 2.100 mm, R3 = −22.790 mm, R4 = −1.318 mm (aspheric surface), R5 = −1.155 mm (aspheric surface), R6 = 4.766 mm (non-surface) Spherical surface), R7 = 1.546 mm (aspherical surface), R8 = ∞, R9 = ∞
<Spacing on the optical axis>
D1 = 0.100 mm, D2 = 1.032 mm, D3 = 0.821 mm, D4 = 1.097 mm, D5 = 0.100 mm, D6 = 1.000 mm, D7 = 0.769 mm, D8 = 0.750 mm, BF = 0.30mm
<Refractive index (Nd)>
N1 = 1.49700, N2 = 1.50914, N3 = 1.50914, N4 = 1.51680
<Abbe number>
ν1 = 81.6, ν2 = 56.4, ν3 = 56.4, ν4 = 64.2

<Aspheric coefficient>
<S4>
ε = −0.670092, D = −0.1125650, E = 0.1230170, F = 0.156666 × 10 ⁻¹ , G = −0.5996650 × 10 ⁻¹ , H = 0.1961910 × 10 ⁻¹
<S5>
ε = 0.175880, D = −0.2461630 × 10 ⁻¹ , E = 0.5475240 × 10 ⁻¹ , F = 0.8936770 × 10 ⁻² , G = −0.3604610 × 10 ⁻² , H = −0.26233760 × 10 ⁻³
<S6>
ε = −17.3319785, D = −0.9529140 × 10 ⁻¹ , E = 0.3618380 × 10 ⁻¹ , F = −0.5356020 × 10 ⁻² , G = −0.7287330 × 10 ⁻⁴ , H = 0.4659120 × 10 ⁻⁴
<S7>
ε = −1.1226510, D = −0.1108290, E = 0.24959010 × 10 ⁻¹ , F = −0.3897190 × 10 ⁻² , G = 0.4121550 × 10 ⁻³ , H = −0. 2865440 × 10 ⁻⁴

Here, the values of the conditional expressions (1) to (6) are
(1) TL / f = 1.31 (<1.6)
(2) ν1 = 81.6 (> 45)
(3) | R4 | / | R5 | = 1.14 (0.7 <1.14 <2)
(4) R6 / R7 = 3.08 (1 <3.08 <4)
(5) D5 / f = 0.02 (<0.15)
(6) D4 / D6 = 1.097 (0.8 <1.097 <1.3)
And all are satisfied.

  In Example 3 above, the total lens length is 4.15 mm without back focus, the back focus (air equivalent) is 1.56 mm, the emission angle of the outermost ray is │−18.9 ° │, and the F number is 3.96, a field angle of 60.8 °, a thin lens (short dimension in the optical axis direction), various aberrations are corrected well, and a high-performance imaging lens suitable for a high-density pixel imaging device is obtained. It is done.

It is a block diagram which shows one Embodiment of the imaging lens which concerns on this invention. FIG. 4 shows aberration diagrams of spherical aberration, astigmatism, distortion, and lateral chromatic aberration of the photographing lens according to Example 1. It is a block diagram which shows other embodiment of the imaging lens which concerns on this invention. FIG. 4 shows aberration diagrams of spherical aberration, astigmatism, distortion, and lateral chromatic aberration of the photographing lens according to Example 2. It is a block diagram which shows other embodiment of the imaging lens which concerns on this invention. FIG. 5 shows aberration diagrams of spherical aberration, astigmatism, distortion, and lateral chromatic aberration of the photographing lens according to Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aperture stop 2 1st lens 3 2nd lens 4 3rd lens 5 Glass filter D1-D8 Space | interval BF on optical axis Back focus R1-R9 Radius of curvature S1-S9 Surface L Optical axis

Claims (9)

Arranged in order from the object side to the image plane side,
An aperture stop having a predetermined aperture;
A first lens having a positive refractive power and having convex surfaces facing both the object side and the image side;
A second lens having a positive refractive power with a concave surface facing the object side;
A third lens having a negative refractive power and having a convex surface on the object side, an aspheric surface on the image surface side, and an inflection point in the middle;
A photographic lens characterized by comprising: The second lens and the third lens have aspheric surfaces on both the object side and the image side.
The photographic lens according to claim 1. The second lens has an aspherical surface on the object side and is formed such that its refractive power decreases as it goes toward the periphery.
The photographic lens according to claim 1, wherein the photographic lens is provided. The second lens and the third lens are formed of a resin material,
The photographic lens according to claim 1, wherein: When the focal length of the entire lens system is f, and the total length of the lens system from the object side front surface of the aperture stop to the image plane on which the subject is imaged is TL,
(1) TL / f <1.6
The photographic lens according to claim 1, wherein: When the Abbe number of the first lens is ν1,
(2) ν1> 45
The photographic lens according to claim 1, wherein: The radius of curvature of the object side surface of the second lens is R4, the radius of curvature of the image side surface of the second lens is R5, the radius of curvature of the object side surface of the third lens is R6, and the third lens. When the radius of curvature of the surface on the image plane side is R7,
(3) 0.7 <| R4 | / | R5 | <2
(4) 1 <R6 / R7 <4
The photographic lens according to claim 1, wherein: When the distance in the optical axis direction between the second lens and the third lens is D5, and the focal length of the entire lens system is f,
(5) D5 / f <0.15
The photographic lens according to claim 1, wherein: When the thickness of the second lens in the optical axis direction is D4, and the thickness of the third lens in the optical axis direction is D6,
(6) 0.8 <D4 / D6 <1.3
The photographic lens according to claim 1, wherein:

Images