JP2004205887A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain various kinds of aberrations and to realize miniaturization, thinning and the reduction in the cost. <P>SOLUTION: The imaging lens is constituted of a front end diaphragm, a 1st group lens 1 in meniscus shape pointing its convex surface toward an image surface side and having positive power, an intermediate diaphragm 4 intercepting unnecessary light and a 2nd group lens 2 in meniscus shape turning its convex surface toward the image surface side and having positive power in order from an object side. Both surfaces of the 1st group lens 1 and the 2nd group lens 2 are constituted of aspherical surfaces and the 1st group lens 1 and the 2nd group lens 2 satisfy following conditional expressions. (1) 0.45<f<SB>1</SB>/f<0.60, (2) 0.50<ΣD/f<0.80, and (3) 50<υ<SB>1</SB><60, 20<υ<SB>2</SB><35. Provided that f<SB>1</SB>means the focal distance of the 1st group, f means the focal distance of an entire system, ΣD means axial length from the object-side surface of the 1st group lens to the image-side surface of the 2nd group lens, υ<SB>1</SB>means the Abbe number of the 1st group lens and υ<SB>2</SB>means the Abbe number of the 2nd group lens. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a small imaging lens used for a mobile phone or the like.
[0002]
[Prior art]
2. Description of the Related Art In recent years, mobile phones have been widely used because of their convenience. In particular, camera-equipped mobile phones having a function of transmitting and receiving images have been rapidly spreading.
[0003]
A camera incorporated in a mobile phone uses a CCD element or a CMOS element. When the number of pixels of these elements reaches the level of 300,000 pixels, a high-resolution lens is required. For this reason, there is a demand for a lens having various aberrations and having good optical characteristics.
[0004]
As such a lens, a lens described in Patent Document 1 is known. It is said that this lens is a two-group, two-element lens used for mobile phone applications and the like, and has achieved high performance with a short optical path length and low distortion using an aspheric plastic lens.
[0005]
[Patent Document 1]
JP-A-2002-258155
[0006]
[Problems to be solved by the invention]
However, although the lens of Example 4 in Patent Document 1 described above has a short optical path length, the off-axis resolution is weak, and the MTF characteristics in which optical characteristics are important are not good. Further, the distortion characteristic is + 8.7% at the maximum, and the distortion is very conspicuous due to the pin winding type. Furthermore, since the peripheral light amount ratio is as low as 36% and the principal ray angle at the maximum image height is 31.8 °, four corners of the image become dark in combination with a CCD element or a CMOS element. For this reason, the conventional lens cannot be said to have various aberrations sufficiently corrected as a lens to be incorporated in a mobile phone.
[0007]
Further, since the image handled by the imaging lens in a mobile phone or the like is a color image, it is natural that various aberrations are small, but it is also required that the axial chromatic aberration and the chromatic aberration of magnification are small. Also, image distortion must be kept small and the four corners of the screen must be bright.
[0008]
On the other hand, since a plastic lens made of an acrylic resin has a large Abbe number (small wavelength dispersion), it works well for suppressing chromatic aberration. However, in the case of a camera in which the number of pixels of a CCD element or a CMOS element is at a level of 300,000 pixels, since a plurality of lenses are used, it is necessary to further suppress chromatic aberration. On the other hand, in the lens of Example 4 of Patent Document 1, the MTF characteristic was not good because the chromatic aberration of magnification was large.
[0009]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an imaging lens that is reduced in size, thickness, and cost while maintaining basic performance required for a lens. .
[0010]
[Means for Solving the Problems]
In order to solve such a problem, an imaging lens according to a first aspect includes, in order from the object side, a pre-aperture, a meniscus-shaped first group lens having a positive power with a convex surface facing the image surface side, An imaging lens comprising: an intermediate stop for blocking unnecessary light; and a meniscus-shaped second group lens having a negative power and a convex surface facing the image surface side, wherein the first group lens and the second group are included. The lenses are both aspherical on both sides and satisfy the following conditional expressions.
[0011]
0.45 <f ₁ /F<0.60 (1)
0.50 <ΣD / f <0.80 (2)
50 <υ ₁ <60,20 <υ ₂ <35… (3)
Where f ₁ : Focal length of the first group, f: focal length of the entire system, ΔD: axial length from the object side surface of the first lens unit to the image side surface of the second lens unit, Δ ₁ : Abbe number of the first lens unit, υ ₂ : Abbe number of the second lens group
According to the above configuration, it is possible to reduce the total thickness of the lens, suppress various aberrations, and realize an imaging lens having a high resolution, a peripheral light amount ratio of 50% or more, and a principal ray angle of 22 °.
[0012]
The imaging lens according to a second aspect of the present invention is the imaging lens according to the first aspect, wherein the plastic material for molding the first group lens is an acrylic resin, and the plastic material for molding the second group lens is polycarbonate. It is a resin.
[0013]
With the above configuration, the first group lens is formed of an acrylic resin, and the second group lens is formed of a polycarbonate resin, so that they can cooperate to suppress various aberrations, reduce the thickness, and achieve high resolution. An imaging lens having a peripheral light amount ratio of 50% or more and a principal ray angle of 22 ° can be realized.
[0014]
The imaging lens according to a third aspect of the present invention is the imaging lens according to the first aspect, wherein the plastic material for molding the first group lens is a polyolefin resin, and the plastic material for molding the second group lens is It is characterized by being a polycarbonate resin.
[0015]
According to the above configuration, by forming the first lens unit with a polyolefin resin and the second lens unit with a polycarbonate resin, they can cooperate to suppress various aberrations, reduce the thickness, and achieve high resolution. Thus, an imaging lens having a peripheral light amount ratio of 50% or more and a principal ray angle of 22 ° can be realized.
[0016]
The imaging lens according to a fourth aspect of the present invention is the imaging lens according to the first aspect, wherein the plastic material for molding the first group lens is an acrylic resin, and the plastic material for molding the second group lens is polyester. It is a resin.
[0017]
According to the above configuration, the first group lens is formed of an acrylic resin, and the second group lens is formed of a polyester resin. Thus, they can cooperate to suppress various aberrations and reduce the thickness. An imaging lens having a peripheral light amount ratio of 50% or more and a principal ray angle of 22 ° can be realized.
[0018]
The imaging lens according to a fifth aspect of the present invention is the imaging lens according to the first aspect, wherein the plastic material for molding the first group lens is a polyolefin resin, and the plastic material for molding the second group lens is It is a polyester resin.
[0019]
With the above configuration, the first group lens is formed of a polyolefin resin, and the second group lens is formed of a polyester resin. Thus, they can cooperate to suppress various aberrations, reduce the thickness, and achieve high resolution. Thus, an imaging lens having a peripheral light amount ratio of 50% or more and a principal ray angle of 22 ° can be realized.
[0020]
An imaging lens according to a sixth aspect of the present invention is the imaging lens according to any one of the first to fifth aspects, wherein the first group and the second group lens each include a lens unit and a bank. The bank portion is formed in a thick annular plate shape, and supports each of the lens portions at a set distance by contacting each other.
[0021]
According to the above configuration, each lens unit can be supported accurately at a set distance only by combining the first and second group lenses. This makes it possible to easily assemble the imaging lens by combining the first and second lens units.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of an imaging lens according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a side sectional view showing the imaging lens according to the present embodiment.
[0023]
The imaging lens according to the present embodiment includes a front stop (not shown), a first group lens 1, an intermediate stop 4, and a second group lens 2. A cover glass 3 is provided on the image side of the second group lens 2.
[0024]
The pre-aperture is generally used and has a generally known general configuration.
[0025]
The first lens unit 1 is a meniscus lens having a positive power with a convex surface facing the image surface side, and has a double-sided aspheric surface. Also, 0.45 <f ₁ /F<0.60(f ₁ : Focal length of the first group, f: focal length of the entire system), and comprises a lens portion 5 and a bank portion 6.
[0026]
The lens part 5 is the Abbe number ベ ₁ = 50-60 plastic material. An acrylic resin or a polyolefin resin is used as a plastic material of the lens portion 5. The bank 6 is a member that supports the lens unit 5 and maintains a set distance from the second group lens 2. The bank 6 is formed in a thick annular plate shape. The bank portion 6 abuts against a bank portion 9 of the second group lens 2, which will be described later, via the intermediate stop 4, so that the lens portion 5 of the first group lens 1 and the lens portion 8 of the second group lens 2. Are set to a thickness that can be supported at a set distance.
[0027]
The intermediate stop 4 is a member between the first group lens 1 and the second group lens 2 for blocking unnecessary light beams to prevent a decrease in contrast due to halation or the like. The intermediate diaphragm 4 is formed of a black annular plate having a thickness of 50 to 150 μm. The inner diameter of the intermediate stop 4 is set to a size that allows light rays irregularly reflected by the bank 6 and the like of the first group lens 1 not to reach the CCD element or the CMOS element when a light ray having a necessary angle of view or more enters. I do.
[0028]
The second group lens 2 is a meniscus lens having a negative power and a convex surface facing the image surface side, and has a double-sided aspheric surface. The second group lens 2 includes a lens section 8 and a bank section 9. The lens section 8 is composed of the Abbe number ₂ = 20-35. As a plastic material of the lens portion 8, a polycarbonate resin or a polyester resin is used. The bank 9 has the same configuration as the bank 6 of the first group lens 1. That is, the bank portion 9 is a member for supporting the lens portion 8 and maintaining a set distance from the first group lens 1. The bank 9 is formed in a thick annular plate shape. The bank portion 9 abuts against the bank portion 6 of the first group lens 1 via the intermediate stop 4 to set the lens portion 8 of the second group lens 2 and the lens portion 5 of the first group lens 1. The thickness is set so that it can be supported at a distance. Note that the bank portion 9 may be configured to increase the thickness toward the cover glass 3 and abut the cover glass 3 to support the cover glass 3.
[0029]
When the axial length from the object side surface of the first lens unit 1 to the image side surface of the second lens unit 2 is ΣD and the focal length f of the entire system is 0.50 <ΣD / f <0.80, This is a condition for determining the center thickness of the lens and the lens interval.
[0030]
The cover glass 3 is a glass that functions as a filter. The cover glass 3 has a low-pass filter function or is coated with a near-infrared cut filter.
[0031]
As described above, in order from the object side, the front stop, the meniscus-shaped first group lens 1 having a positive power with the convex surface facing the image plane side, the intermediate stop 4 for blocking unnecessary light, and the image plane An imaging lens comprising a meniscus-shaped second group lens 2 having a negative surface and a convex surface directed to the side. By satisfying the conditional expressions (1) to (3), they cooperate to suppress various aberrations and reduce the thickness, and at the same time, have a high resolution, a peripheral light intensity ratio of 50% or more, and a principal ray angle of 22 °. A lens can be realized.
[0032]
0.45 <f ₁ /F<0.60 (1)
0.50 <ΣD / f <0.80 (2)
50 <υ ₁ <60,20 <υ ₂ <35… (3)
Where f ₁ : Focal length of the first group, f: focal length of the entire system, ΔD: axial length from the object side surface of the first lens unit to the image side surface of the second lens unit, Δ ₁ : Abbe number of the first lens unit, υ ₂ : Abbe number of the second lens group
In addition, accurate positioning can be achieved only by combining the first group lens 1, the intermediate stop 4, and the second group lens 2. That is, the bank portion 6 of the first group lens 1, the intermediate stop 4, and the bank portion 9 of the second group lens 2 come into contact with each other, so that the lens portion 5 of the first group lens 1 and the lens of the second group lens 2 The part 8 is supported in a correct position, and can be assembled in that state. Thereby, the assembling work of the first group lens 1, the intermediate stop 4, and the second group lens 2 becomes easy, and the number of parts is reduced, so that the cost can be reduced.
[0033]
Further, the size and thickness of the imaging lens can be reduced while maintaining the basic performance required for the lens in a favorable state.
[0034]
[First embodiment]
The results of experiments with specific numerical values set for the imaging lens having the above configuration will be described below.
[0035]
Here, the first group lens 1 is made of acrylic resin. ₁ = 54.0, and the second lens unit 2 is made of polycarbonate resin. ₂ = 29.9.
[0036]
FIG. 2 is a table showing the values of the radius of curvature R, interval D, refractive index Nd, and Abbe number υd of each surface of the lens when the focal length f = 3.60 mm and the brightness F / no = 2.80. is there. Here, S1 to S8 are numbers indicating each surface. S2 is the object side surface of the lens unit 5 of the first group lens 1, S3 is the image side surface of the lens unit 5, S4 is the object side surface of the lens unit 8 of the second group lens 2, and S5 is the image side surface of the lens unit 8. Are respectively shown. The distance Di (i = 1, 2,..., 7) indicates the distance from the Si plane to the Si + 1 plane. The table in FIG. 3 shows the aspheric coefficients on the respective surfaces S2 to S5 of the lens portions 5 and 8 of the lenses 1 and 2.
[0037]
At this time, the focal length f of the first group lens 1 ₁ = 2.00 mm and the focal length f of the entire system f = 3.60 mm, f ₁ /F=0.556, which is within the condition of the above equation (1). From よ り D = 1.10 + 0.473 + 0.80 = 2.373, ΣD / f = 0.609, which is within the condition of the above equation (2).
[0038]
As a result, the coma aberration was as shown in FIG. Here, the maximum image height is 2.25 mm as shown in FIG. Light having three wavelengths in FIG. 4 (light having a wavelength of 656.28 nm indicated by a dashed line, light having a wavelength of 587.56 nm indicated by a solid line, and light having a wavelength of 486.13 nm indicated by a dotted line) is illustrated in FIG. Thus, in a state where the coma is eliminated on the axis, the coma is suppressed to a small value even at the maximum image height as shown in FIG. It can be seen that the value of the coma at the maximum image height is a better value than the experimental result (see FIG. 11B) of the imaging lens of the conventional example described later.
[0039]
In addition, the MTF characteristics are shown in FIG. 6, and it is understood that the MTF characteristics are better numerical values as compared with the experimental results (see FIG. 12) of the conventional imaging lens described later.
[0040]
Further, distortion and astigmatism resulted in the results shown in FIG. Here, the astigmatism shown in FIG. 7B is a good numerical value, similar to the experimental result (see FIG. 13B) of the imaging lens of the conventional example described later. It can be seen that the distortion shown in FIG. 7A is a better numerical value than the experimental result (see FIG. 13A) of the imaging lens of the conventional example described later.
[0041]
As described above, the first group lens 1 of the imaging lens is formed of an acrylic resin, the second group lens 2 is formed of a polycarbonate resin, and is set as shown in FIGS. , Distortion and astigmatism can be suppressed to small values, and the principal ray angle at the maximum image height can be 22 ° at a peripheral light amount ratio of 50% or more. That is, the basic performance required as a lens can be maintained in a good state.
[0042]
Furthermore, the size and thickness of the imaging lens can be reduced while maintaining the basic performance required for the lens in a favorable state. In the imaging lens used in this example, the diameter of the first group lens 1 and the second group lens 2 could be φ6 mm, and the total lens thickness could be 5.4 mm.
[0043]
[Conventional example]
Next, for comparison with the present embodiment, the results of experiments with specific numerical values set for the conventional imaging lens described in Embodiment 4 of Patent Document 1 will be described below.
[0044]
In the imaging lens, as shown in FIG. 8, the first lens group 11 is formed of a polyolefin resin, and the second lens group 12 is formed of a polyolefin resin. FIG. 9 shows the values of the radius of curvature R, interval D, refractive index Nd, and Abbe number υd of each surface of the lens when the focal length f is 3.624 mm and the brightness F / no is 2.80. And so on. Further, the aspherical coefficients on the respective surfaces of the lenses 11 and 12 are set as shown in FIG.
[0045]
As a result, the coma aberration was as shown in FIG. That is, as shown in FIG. 11A, the light of the three wavelengths has a large value of the coma aberration at the maximum image height as shown in FIG. Chromatic aberration of magnification is also a large value.
[0046]
For this reason, the MTF characteristics are as shown in FIG. 12, which is a value that cannot be said to be good. Further, distortion and astigmatism resulted in the results shown in FIG. The astigmatism shown in FIG. 13 (B) is a good numerical value, but the distortion shown in FIG. 13 (A) is greatly shifted, and has a maximum of + 8.7%. It is very noticeable due to pincushion distortion.
[0047]
Compared with such experimental results of the conventional imaging lens, the imaging lens of the present embodiment was able to obtain favorable results as described above and as described later.
[0048]
[Second embodiment]
Next, a second embodiment will be described.
[0049]
Here, the first lens group 1 is made of a polyolefin resin. ₁ = 55.6, and the second lens unit 2 is made of polycarbonate resin. ₂ = 29.9.
[0050]
FIG. 14 is a table showing the values of the radius of curvature R, interval D, refractive index Nd, and Abbe number υd of each surface of the lens when the focal length f is 3.60 mm and the brightness F / no is 2.80. is there. Here, the surfaces S1 to S8 and the intervals D2 to D7 are the same as in the first embodiment described above. The table in FIG. 15 shows the aspheric coefficients on the surfaces S2 to S5 of the lens portions 5 and 8 of the lenses 1 and 2.
[0051]
At this time, the focal length f of the first group lens 1 ₁ = 1.99 mm, and from the focal length f of the entire system f = 3.60 mm, f ₁ /F=0.553, which is within the condition of the above equation (1). From ΣD = 1.10 + 0.479 + 0.80 = 2.379, ΣD / f = 0.661, which is within the condition of the above equation (2).
[0052]
As a result, the coma aberration was as shown in FIG. Light having three wavelengths (light having a wavelength of 656.28 nm indicated by a dashed line, light having a wavelength of 587.56 nm indicated by a solid line, and light having a wavelength of 486.13 nm indicated by a dotted line) is, as shown in FIG. In a state where the coma aberration is eliminated above, as shown in FIG. 16B, the coma aberration is suppressed to a small value even at the maximum image height. It can be seen that the value of coma at the maximum image height is a better value than the experimental result (see FIG. 11B) of the imaging lens of the conventional example.
[0053]
The MTF characteristics are shown in FIG. 17, and it is understood that the MTF characteristics are better than the experimental results (see FIG. 12) of the conventional imaging lens (see FIG. 12).
[0054]
Further, distortion and astigmatism resulted in the results shown in FIG. Here, the astigmatism shown in FIG. 18B is a good numerical value, similar to the experimental result (see FIG. 13B) of the imaging lens of the conventional example. It can be seen that the distortion shown in FIG. 18A is a better numerical value than the experimental result (see FIG. 13A) of the imaging lens of the conventional example.
[0055]
As described above, the first group lens 1 of the imaging lens is formed of a polyolefin-based resin, and the second group lens 2 is formed of a polycarbonate resin, and is set as shown in FIG. 14 and FIG. Characteristics, distortion, and astigmatism can be suppressed to small values, and the principal ray angle at the maximum image height can be 22 ° at a peripheral light amount ratio of 50% or more. That is, the basic performance required as a lens can be maintained in a good state.
[0056]
Furthermore, the size, thickness, and cost of the imaging lens can be reduced while maintaining the basic performance required for the lens in a favorable state.
[0057]
[Third embodiment]
Next, a third embodiment will be described.
[0058]
Here, the first group lens 1 is made of acrylic resin. ₁ = 54.0, and the second lens group 2 is made of polyester resin. ₂ = 24.0.
[0059]
FIG. 19 is a table showing the values of the radius of curvature R, interval D, refractive index Nd, and Abbe number υd of each surface of the lens when the focal length f = 3.60 mm and the brightness F / no = 2.80. is there. Here, the surfaces S1 to S8 and the intervals D2 to D7 are the same as in the first embodiment described above. The table in FIG. 20 shows the aspherical coefficients on the surfaces S2 to S5 of the lens portions 5 and 8 of the lenses 1 and 2.
[0060]
At this time, the focal length f of the first group lens 1 ₁ = 1.97 mm, the focal length f of the entire system f = 3.60 mm, f ₁ /F=0.47, which is within the condition of the above equation (1). From ΣD = 1.10 + 0.465 + 0.80 = 2.365, ΣD / f = 0.657, which is within the condition of the above equation (2).
[0061]
As a result, the coma aberration was as shown in FIG. Light having three wavelengths (light having a wavelength of 656.28 nm indicated by a dashed line, light having a wavelength of 587.56 nm indicated by a solid line, and light having a wavelength of 486.13 nm indicated by a dotted line) is, as shown in FIG. In the state where the coma aberration has been eliminated, as shown in FIG. 21B, the coma aberration is suppressed to a small value even at the maximum image height. It can be seen that the value of coma at the maximum image height is a better value than the experimental result (see FIG. 11B) of the imaging lens of the conventional example.
[0062]
In addition, the MTF characteristics are shown in FIG. 22, which indicates that the MTF characteristics are better than the experimental results (see FIG. 12) of the conventional imaging lens (see FIG. 12).
[0063]
Further, distortion and astigmatism resulted in the results shown in FIG. Here, the astigmatism shown in FIG. 23 (B) is a good numerical value, similar to the experimental result (see FIG. 13 (B)) of the imaging lens of the conventional example. It can be seen that the distortion shown in FIG. 23 (A) has a better numerical value than the experimental result (see FIG. 13 (A)) of the conventional imaging lens.
[0064]
As described above, the first group lens 1 of the imaging lens is formed of acrylic resin, and the second group lens 2 is formed of polyester resin, and is set as shown in FIG. 19 and FIG. , Distortion and astigmatism can be suppressed to small values, and the principal ray angle at the maximum image height can be 22 ° at a peripheral light amount ratio of 50% or more. That is, the basic performance required as a lens can be maintained in a good state.
[0065]
Furthermore, the size, thickness, and cost of the imaging lens can be reduced while maintaining the basic performance required for the lens in a favorable state.
[0066]
[Fourth embodiment]
Next, a fourth embodiment will be described.
[0067]
Here, the first lens group 1 is made of a polyolefin resin. ₁ = 55.6, and the second lens group 2 is made of polyester resin. ₂ = 24.0.
[0068]
FIG. 24 is a table showing the values of the radius of curvature R, interval D, refractive index Nd, and Abbe number υd of each surface of the lens when the focal length f is 3.60 mm and the brightness F / no is 2.80. is there. Here, the surfaces S1 to S8 and the intervals D2 to D7 are the same as in the first embodiment described above. The table in FIG. 25 shows the aspheric coefficients on the surfaces S2 to S5 of the lens portions 5 and 8 of the lenses 1 and 2.
[0069]
At this time, the focal length f of the first group lens 1 ₁ = 1.97 mm, the focal length f of the entire system f = 3.60 mm, f ₁ /F=0.47, which is within the condition of the above equation (1). From ΣD = 1.10 + 0.475 + 0.80 = 2.375, ΣD / f = 0.660, which is within the condition of the above equation (2).
[0070]
As a result, the coma aberration was as shown in FIG. Light having three wavelengths (light having a wavelength of 656.28 nm indicated by a dashed line, light having a wavelength of 587.56 nm indicated by a solid line, and light having a wavelength of 486.13 nm indicated by a dotted line) is, as shown in FIG. In the state where the coma aberration is eliminated, as shown in FIG. 26B, the coma aberration is suppressed to a small value even at the maximum image height. It can be seen that the value of coma at the maximum image height is a better value than the experimental result (see FIG. 11B) of the imaging lens of the conventional example.
[0071]
Further, the MTF characteristics are as shown in FIG. 27, and it can be seen that the MTF characteristics are better values as compared with the experimental results (see FIG. 12) using the imaging lens of the conventional example.
[0072]
Further, distortion and astigmatism resulted in the results shown in FIG. Here, the astigmatism shown in FIG. 28B is a good numerical value, similar to the experimental result (see FIG. 13B) of the imaging lens of the conventional example. It can be seen that the distortion shown in FIG. 28A is a favorable numerical value as compared with the experimental result (see FIG. 13A) of the imaging lens of the conventional example.
[0073]
As described above, the first lens group 1 of the imaging lens is formed of a polyolefin-based resin, and the second lens group 2 is formed of a polyester resin, and is set as shown in FIGS. Characteristics, distortion, and astigmatism can be suppressed to small values, and the principal ray angle at the maximum image height can be 22 ° at a peripheral light amount ratio of 50% or more. That is, the basic performance required for the lens can be maintained in a good state.
[0074]
Further, the size, thickness, and cost of the imaging lens can be reduced while maintaining the basic performance required for the lens in a favorable state.
[0075]
[Modification]
In the above-described embodiment, a mobile phone has been described as an example. However, the present invention is not limited to a mobile phone and can be applied to other small devices. That is, it can be widely used as an imaging lens for a PC monitor lens or a small camera.
[0076]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
[0077]
(1) In order from the object side, a front stop, a meniscus-shaped first lens unit having a positive surface with a convex surface facing the image surface side, an intermediate stop for blocking unnecessary light, and a convex surface on the image surface side And a meniscus-shaped second lens unit having a negative power directed to the first lens unit. Both the first lens unit and the second lens unit are aspherical on both surfaces.
0.45 <f ₁ /F<0.60 (1)
0.50 <ΣD / f <0.80 (2)
50 <υ ₁ <60,20 <υ ₂ <35… (3)
Where f ₁ : Focal length of the first group, f: focal length of the entire system, ΔD: axial length from the object side surface of the first lens unit to the image side surface of the second lens unit, Δ ₁ : Abbe number of the first lens unit, υ ₂ : Abbe number of the second lens group
Is satisfied so that the total thickness of the lens can be reduced, the various aberrations can be suppressed, the resolution is high, and the principal ray angle at the maximum image height is 22 ° at a peripheral light intensity ratio of 50% or more. realizable.
[0078]
(2) Since the plastic material for forming the first lens unit is made of acrylic resin and the plastic material for forming the second lens unit is made of polycarbonate resin, they work together to suppress various aberrations and reduce the thickness. In addition, an imaging lens having high resolution and high contrast in a low frequency region can be realized.
[0079]
(3) The plastic materials used for molding the first lens group and the second lens group are polyolefin resin and polycarbonate resin, acrylic resin and polyester resin, or polyolefin resin and polyester resin, respectively. Aberrations can be suppressed and the thickness can be reduced, and a chief ray angle of 22 ° at a maximum image height can be realized at a high resolution with a peripheral light amount ratio of 50% or more.
[0080]
(4) The first and second group lenses are composed of a lens portion and a bank portion, and the bank portions are formed in a thick annular plate shape, and each lens is brought into contact with each other via an intermediate diaphragm. Since the lens units are supported at a set distance, only the first group lens 1, the intermediate stop 4, and the second group lens 2 can be combined to support each lens unit accurately at the set distance. . Thus, the imaging lens can be easily assembled by combining the first group lens 1, the intermediate stop 4, and the second group lens 2.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing an imaging lens according to an embodiment of the present invention.
FIG. 2 is a table showing values of a radius of curvature R, an interval D, a refractive index Nd, and an Abbe number νd of each surface of the imaging lens according to the embodiment of the present invention.
FIG. 3 is a table showing aspheric coefficients on respective surfaces of the imaging lens of the present invention.
FIG. 4 is a graph showing coma aberration of the imaging lens of the present invention.
FIG. 5 is a side sectional view showing a maximum image height of the imaging lens according to the embodiment of the present invention.
FIG. 6 is a graph showing MTF characteristics of the present invention.
FIG. 7 is a graph showing distortion and astigmatism of the present invention.
FIG. 8 is a side sectional view showing a conventional imaging lens.
FIG. 9 is a table showing values of a radius of curvature R, an interval D, a refractive index Nd, and an Abbe number νd of each surface of a conventional imaging lens.
FIG. 10 is a table showing the aspheric coefficient on each surface of a conventional imaging lens.
FIG. 11 is a graph showing coma aberration of a conventional imaging lens.
FIG. 12 is a graph showing MTF characteristics of a conventional imaging lens.
FIG. 13 is a graph showing distortion and astigmatism of a conventional imaging lens.
FIG. 14 is a table showing values of a radius of curvature R, an interval D, a refractive index Nd, and an Abbe number νd of each surface of the imaging lens according to Example 2 of the present invention.
FIG. 15 is a table showing aspherical coefficients on respective surfaces of the imaging lens of the second example.
FIG. 16 is a graph showing the coma aberration of the imaging lens of the second example.
FIG. 17 is a characteristic diagram showing MTF characteristics of the second embodiment.
FIG. 18 is a characteristic diagram showing distortion and astigmatism of the second example.
FIG. 19 is a table showing values of a radius of curvature R, an interval D, a refractive index Nd, and an Abbe number νd of each surface of the imaging lens according to Example 3 of the present invention.
FIG. 20 is a table showing aspherical coefficients on respective surfaces of each lens of the third example.
FIG. 21 is a graph showing the coma aberration of the imaging lens of the third example.
FIG. 22 is a graph showing MTF characteristics of the third embodiment.
FIG. 23 is a graph showing distortion and astigmatism of the third example.
FIG. 24 is a table showing values of a radius of curvature R, an interval D, a refractive index Nd, and an Abbe number νd of each surface of the imaging lens according to Example 4 of the present invention.
FIG. 25 is a table showing aspheric coefficients on respective surfaces of the imaging lens of the fourth example.
FIG. 26 is a graph showing the coma aberration of the imaging lens of the fourth example.
FIG. 27 is a graph showing MTF characteristics of the fourth embodiment.
FIG. 28 is a graph showing distortion and astigmatism of the fourth example.
[Explanation of symbols]
1: 1st group lens, 2: 2nd group lens, 3: cover glass, 4: intermediate stop, 5: lens section, 6: ridge section, 8: lens section, 9: ridge section.

Claims (6)

In order from the object side, a front stop, a meniscus-shaped first group lens having a positive surface with a convex surface facing the image surface side, an intermediate stop for blocking unnecessary light, and a negative lens with a convex surface facing the image surface side An imaging lens constituted by a meniscus-shaped second group lens having a power of
An imaging lens, wherein both the first lens unit and the second lens unit are aspherical on both surfaces and satisfy the following conditional expressions.
0.45 <f ₁ /f<0.60 (1)
0.50 <ΣD / f <0.80 (2)
50 <υ ₁ <60, 20 <υ ₂ <35… (3)
Where f ₁ : focal length of the first group, f: focal length of the entire system, ΔD: axial length from the object side surface of the first lens unit to the image side surface of the second lens unit, Δ ₁ : first lens unit Abbe number of lens, υ ₂ : Abbe number of second lens group The imaging lens according to claim 1,
The plastic material for molding the first group lens is an acrylic resin,
An imaging lens, wherein the plastic material for forming the second group lens is a polycarbonate resin. The imaging lens according to claim 1,
The plastic material for forming the first lens group is a polyolefin resin,
An imaging lens, wherein the plastic material for forming the second group lens is a polycarbonate resin. The imaging lens according to claim 1,
The plastic material for molding the first group lens is an acrylic resin,
An imaging lens, wherein the plastic material for forming the second group lens is a polyester resin. The imaging lens according to claim 1,
The plastic material for forming the first lens group is a polyolefin resin,
An imaging lens, wherein the plastic material for forming the second group lens is a polyester resin. The imaging lens according to any one of claims 1 to 5,
The first group and the second group lenses each include a lens unit and a bank,
An imaging lens, wherein the bank portion is formed in a thick annular plate shape, and supports each of the lens portions at a set distance by being in contact with each other.

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