JP2004219807A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens suitable for a compact high-performance camera using a solid-state imaging element such as a CCD or a CMOS sensor, having simple constitution and made inexpensive. <P>SOLUTION: The image pickup lens is constituted of a diaphragm, a 1st lens having positive refractive power, a 2nd lens having negative refractive power and a 3rd lens having positive refractive power in order from an object side, and the 1st lens has stronger refractive power on an image side and the 2nd lens is a meniscus lens turning its concave surface to the object side, and the image pickup lens satisfies following conditional expressions. The conditional expressions are -0.85<f<SB>2</SB>/f<-0.25 and ν<SB>2</SB><35, where f means the focal distance of the entire system, f<SB>2</SB>means the focal distance of the 2nd lens and ν<SB>2</SB>means the Abbe number of the 2nd lens. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００３７】
また、下記の実施例における各レンズはプラスチックより形成されている。
［実施例１］
焦点距離：ｆ＝３．４０ｍｍ
Ｆナンバー：Ｆ３．６０
画角：２ω＝５２．０°
実施例１におけるレンズデータを表１に、非球面係数を表２に示す。
【００３８】
【表１】

【００３９】
【表２】

【００４０】
条件式▲１▼，▲３▼〜▲８▼に対応する値は下記の如くなる。
ｆ_２／ｆ＝−０．３３
（ｒ_３＋ｒ_４）／（ｒ_３−ｒ_４）＝−１．２８
（ｒ_１＋ｒ_２）／（ｒ_１−ｒ_２）＝０．９４
ｆ_３／ｆ＝０．７１
実施例１におけるレンズ断面図を図１に、球面収差、非点収差及び歪曲収差の収差図を図２に、コマ収差の収差図を図３に示す。
【００４１】
なお、図１において、１０は絞り、１１は第１レンズ、１２は第２レンズ、１３は第３レンズ、１４はローパスフィルタ、１５は固体撮像素子である。
【００４２】
［実施例２］
焦点距離：ｆ＝３．２８ｍｍ
Ｆナンバー：Ｆ３．６０
画角：２ω＝５３．６°
実施例２におけるレンズデータを表３に、非球面係数を表４に示す。
【００４３】
【表３】

【００４４】
【表４】

【００４５】
条件式▲１▼，▲３▼〜▲８▼に対応する値は下記の如くなる。
ｆ_２／ｆ＝−０．３７
（ｒ_３＋ｒ_４）／（ｒ_３−ｒ_４）＝−１．４８
（ｒ_１＋ｒ_２）／（ｒ_１−ｒ_２）＝０．９１
ｆ_３／ｆ＝０．７３
実施例２におけるレンズ断面図を図４に、球面収差、非点収差及び歪曲収差の収差図を図５に、コマ収差の収差図を図６に示す。
【００４６】
なお、図４において、２０は絞り、２１は第１レンズ、２２は第２レンズ、２３は第３レンズ、２４はローパスフィルタ、２５は固体撮像素子である。
【００４７】
［実施例３］
焦点距離：ｆ＝３．２８ｍｍ
Ｆナンバー：Ｆ３．６０
画角：２ω＝５４．２°
実施例３におけるレンズデータを表５に、非球面係数を表６に示す。
【００４８】
【表５】

【００４９】
【表６】

【００５０】
条件式▲１▼，▲３▼〜▲８▼に対応する値は下記の如くなる。
ｆ_２／ｆ＝−０．３３
（ｒ_３＋ｒ_４）／（ｒ_３−ｒ_４）＝−１．４０
（ｒ_１＋ｒ_２）／（ｒ_１−ｒ_２）＝０．９５
ｆ_３／ｆ＝０．６９
実施例３におけるレンズ断面図を図７に、球面収差、非点収差及び歪曲収差の収差図を図８に、コマ収差の収差図を図９に示す。
【００５１】
なお、図７において、３０は絞り、３１は第１レンズ、３２は第２レンズ、３３は第３レンズ、３４はローパスフィルタ、３５は固体撮像素子である。
【００５２】
［実施例４］
焦点距離：ｆ＝３．２８ｍｍ
Ｆナンバー：Ｆ３．６０
画角：２ω＝５６．０°
実施例４におけるレンズデータを表７に、非球面係数を表８に示す。
【００５３】
【表７】

【００５４】
【表８】

【００５５】
条件式▲１▼，▲３▼〜▲８▼に対応する値は下記の如くなる。
ｆ_２／ｆ＝−０．７９
（ｒ_３＋ｒ_４）／（ｒ_３−ｒ_４）＝−２．４８
（ｒ_１＋ｒ_２）／（ｒ_１−ｒ_２）＝０．６１
ｆ_３／ｆ＝３．０５
実施例４におけるレンズ断面図を図１０に、球面収差、非点収差及び歪曲収差の収差図を図１１に、コマ収差の収差図を図１２に示す。
【００５６】
なお、図１０において、４０は絞り、４１は第１レンズ、４２は第２レンズ、４３は第３レンズ、４５は固体撮像素子である。
【００５７】
【発明の効果】
本発明の撮像レンズによれば、ＣＣＤやＣＭＯＳセンサー等の固体撮像素子を用いた小型で高性能なカメラに好適であり、良好なテレセントリック性を確保して全長が短く、簡素な構成であり、且つ各レンズをプラスチックにして低コストにすることが可能であるという効果を奏する。
【図面の簡単な説明】
【図１】実施例１におけるレンズ断面図である。
【図２】実施例１における球面収差、非点収差及び歪曲収差の収差図である。
【図３】実施例１におけるコマ収差の収差図である。
【図４】実施例２におけるレンズ断面図である。
【図５】実施例２における球面収差、非点収差及び歪曲収差の収差図である。
【図６】実施例２におけるコマ収差の収差図である。
【図７】実施例３におけるレンズ断面図である。
【図８】実施例３における球面収差、非点収差及び歪曲収差の収差図である。
【図９】実施例３におけるコマ収差の収差図である。
【図１０】実施例４におけるレンズ断面図である。
【図１１】実施例４における球面収差、非点収差及び歪曲収差の収差図である。
【図１２】実施例４におけるコマ収差の収差図である。
【符号の説明】
１０，２０，３０，４０ 絞り
１１，２１，３１，４１ 第１レンズ
１２，２２，３２，４２ 第２レンズ
１３，２３，３３，４３ 第３レンズ
１４，２４，３４ ローパスフィルタ
１５，２５，３５，４５ 固体撮像素子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging lens suitable for a small, high-performance camera using a solid-state imaging device such as a CCD or a CMOS sensor, which is a camera built in a digital still camera, a video camera, a mobile phone, or the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a small imaging lens used for a small video camera, a digital still camera, or a camera built in a mobile phone or the like, various imaging lenses composed of three lenses have been proposed. It is disclosed in the patent literature.
[0003]
[Patent Document 1]
JP-A-4-153612
[Patent Document 2]
JP-A-5-188284 [0005]
[Patent Document 3]
JP-A-9-288235 [0006]
[Patent Document 4]
JP 2001-75006 A
[Patent Document 5]
JP 2001-83409 A
[Patent Document 6]
JP, 2002-221659, A
[Patent Document 7]
JP, 2002-244030, A
[Problems to be solved by the invention]
An imaging lens used for a solid-state imaging device such as a CCD or a CMOS sensor requires good telecentricity. However, the imaging lenses disclosed in Patent Literature 1, Patent Literature 2, and Patent Literature 3 require an object side of the first lens. By arranging the diaphragm at the center, it is easy to ensure good telecentricity. However, the imaging lenses disclosed in any of the patent documents use a high refractive index glass lens having a refractive index of 1.7 or more, which has a problem that the cost increases. Further, if a plastic lens that is advantageous in terms of cost is applied to these imaging lenses, the optical performance is degraded due to a low refractive index.
[0011]
Patent Document 4 discloses an example using a low-refractive-index material that can be made of plastic for cost reduction. However, the occurrence of chromatic aberration of magnification is slightly large, so that a high-pixel type camera is used. Is difficult to apply.
[0012]
Furthermore, in the imaging lenses disclosed in Patent Literature 5, Patent Literature 6, and Patent Literature 7, the aperture is disposed between the first lens and the second lens, and the telecentricity is slightly insufficient. Has become.
[0013]
The present invention has been made in view of such a problem, and is an imaging lens suitable for a small and high-performance camera using a solid-state imaging device such as a CCD or a CMOS sensor. It is an object of the present invention to propose an imaging lens that is short, has a simple configuration, and can be manufactured at low cost by using each lens as a plastic lens.
[0014]
[Means for Solving the Problems]
The imaging lens according to claim 1 includes, in order from the object side, an aperture, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power, The first lens has a stronger refractive power on the image side, and the second lens is a meniscus lens having a concave surface facing the object side, and has a configuration satisfying the following conditional expression.
[0015]
-0.85 _<f 2 /f<-0.25 ▲ 1 ▼
ν ₂ <35 ▲ 2 ▼
However,
f: focal length of the entire system f ₂ : focal length of the second lens ν ₂ : Abbe number of the second lens The imaging lens according to claim 2 has the same configuration as the imaging lens according to claim 1 and , The first lens, the second lens, and the third lens are formed of plastic.
[0016]
The imaging lens according to a third aspect has the same configuration as the imaging lens according to the first or second aspect, and also has a configuration that satisfies the following conditional expression.
[0017]
−0.45 <f ₂ /f<−0.28 (3)
The imaging lens according to a fourth aspect has the same configuration as the imaging lens according to any one of the first to third aspects, and also has a configuration that satisfies the following conditional expression.
[0018]
_{-2.80 <(r 3 + r 4} ) / (r 3 -r 4) <- 1.00 ▲ 4 ▼
However,
r ₃ : paraxial radius of curvature of the object-side surface of the second lens r ₄ : paraxial radius of curvature of the image-side surface of the second lens The imaging lens according to claim 5, the imaging lens according to claim 4. And a configuration that satisfies the following conditional expression.
[0019]
_{-2.00 <(r 3 + r 4} ) / (r 3 -r 4) <- 1.10 ▲ 5 ▼
An imaging lens according to a sixth aspect has the same configuration as the imaging lens according to any one of the first to fifth aspects, and also has a configuration that satisfies the following conditional expression.
[0020]
_{0.50 <(r 1 + r 2} ) / (r 1 -r 2) <1.20 ▲ 6 ▼
However,
r ₁ : paraxial curvature radius of the object-side surface of the first lens r ₂ : paraxial curvature radius of the image-side surface of the first lens The imaging lens according to claim 7, wherein: A configuration similar to that of the imaging lens described in item 1 is provided, and the configuration satisfies the following conditional expression.
[0021]
0.50 <f ₃ /f<3.30 (7)
However,
f ₃ : focal length of the third lens The imaging lens described in claim 8 has the same configuration as the imaging lens described in claim 7 and has a configuration that satisfies the following conditional expression.
[0022]
0.50 <f ₃ /f<1.00 (8)
In the imaging lens of the present invention, good telecentricity is ensured by arranging the diaphragm closest to the object side, and the first lens having a positive refractive power, the second lens having a negative refractive power, By including the third lens having a refractive power, an imaging lens having a short overall length is realized while favorably correcting axial chromatic aberration and lateral chromatic aberration. Although the second lens is a meniscus lens having a concave surface on the object side, such a configuration makes it easy to secure a sufficient back focus for arranging a low-pass filter and a CCD face plate, and furthermore, is telecentric. It is possible to improve the properties.
[0023]
Next, conditional expressions (1) to (8) will be described.
The conditional expressions (1) to (3) are all conditional expressions for favorably correcting chromatic aberration.
[0024]
If the refractive power of the second lens becomes too small below the lower limit of the conditional expression (1), the axial chromatic aberration increases in the direction in which the g-line becomes lower than the d-line, and the chromatic aberration of magnification changes in the d-line. In comparison, the image height of the g-line increases in the direction in which the image height decreases. When the value exceeds the upper limit, any chromatic aberration increases in the direction opposite to the case where the value exceeds the lower limit.
[0025]
When the value falls outside the range of the conditional expression (2), the axial chromatic aberration increases in the direction in which the g-line becomes lower than the d-line, and the chromatic aberration of magnification decreases in the direction in which the image height of the g-line becomes smaller than the d-line. It becomes big.
[0026]
Further, by satisfying conditional expression (3), chromatic aberration can be corrected more favorably.
[0027]
Conditional expressions (4) and (5) are for facilitating the workability of the second lens while ensuring the telecentricity and better correcting the coma.
[0028]
If the lower limit of conditional expression (4) is exceeded, the angle between the off-axis ray emitted from the image-side surface of the second lens and the optical axis becomes large, so that the telecentricity tends to deteriorate. Further, if the refractive power of the third lens is increased in order to secure the telecentricity, the coma aberration is likely to deteriorate. When the value exceeds the upper limit of conditional expression (4), the radius of curvature of the second lens on the object side becomes small, so that the workability of the second lens tends to deteriorate.
[0029]
By satisfying conditional expression (5), it is possible to secure telecentricity, correct coma, and improve the workability of the second lens.
[0030]
Conditional expression (6) is for ensuring a sufficient back focus for arranging the low-pass filter and the CCD face plate, and facilitating workability of the first lens while improving telecentricity. If the lower limit of conditional expression (6) is exceeded, the back focus tends to be short and the telecentricity tends to deteriorate. If the upper limit of conditional expression (6) is exceeded, the radius of curvature of the first lens on the image side becomes too small, and the workability of the first lens tends to deteriorate.
[0031]
Conditional expressions (7) and (8) are for better correction of coma aberration and chromatic aberration of magnification while further improving telecentricity. If the lower limit of conditional expression (7) is exceeded, lateral chromatic aberration and coma generated by the third lens tend to increase. Conversely, if the upper limit is exceeded, the telecentricity tends to deteriorate.
[0032]
By satisfying conditional expression (8), telecentricity, coma, and chromatic aberration of magnification can be further improved.
[0033]
【Example】
Hereinafter, examples of the imaging lens of the present invention will be described.
[0034]
Here, r is the radius of curvature of each lens surface, d is the lens thickness or lens interval, nd is the refractive index, and νd is the Abbe number.
[0035]
The shape of the aspherical surface is such that the optical axis direction is the Z axis, the direction orthogonal to the optical axis is the Y axis, the paraxial radius of curvature is r, the conic constant is K, and the aspherical coefficients are A, B, C, D, and E. Then, it is expressed by the following equation.
[0036]
(Equation 1)

[0037]
Each lens in the following embodiments is formed of plastic.
[Example 1]
Focal length: f = 3.40 mm
F number: F3.60
Angle of view: 2ω = 52.0 °
Table 1 shows lens data in Example 1, and Table 2 shows aspheric coefficients.
[0038]
[Table 1]

[0039]
[Table 2]

[0040]
Values corresponding to conditional expressions (1), (3) to (8) are as follows.
f ₂ /f=-0.33
_{(R 3 + r 4) /} (r 3 -r 4) = - 1.28
(R ₁ + r ₂ ) / (r ₁ -r ₂ ) = 0.94
f ₃ /f=0.71
FIG. 1 is a sectional view of a lens in Example 1, FIG. 2 is an aberration diagram of spherical aberration, astigmatism, and distortion, and FIG. 3 is an aberration diagram of coma aberration.
[0041]
In FIG. 1, reference numeral 10 denotes an aperture, 11 denotes a first lens, 12 denotes a second lens, 13 denotes a third lens, 14 denotes a low-pass filter, and 15 denotes a solid-state image sensor.
[0042]
[Example 2]
Focal length: f = 3.28 mm
F number: F3.60
Angle of view: 2ω = 53.6 °
Table 3 shows lens data in Example 2, and Table 4 shows aspheric coefficients.
[0043]
[Table 3]

[0044]
[Table 4]

[0045]
Values corresponding to conditional expressions (1), (3) to (8) are as follows.
f ₂ /f=-0.37
_{(R 3 + r 4) /} (r 3 -r 4) = - 1.48
(R ₁ + r ₂ ) / (r ₁ -r ₂ ) = 0.91
f ₃ /f=0.73
FIG. 4 is a lens cross-sectional view in Example 2, FIG. 5 is an aberration chart of spherical aberration, astigmatism, and distortion, and FIG. 6 is a coma aberration chart.
[0046]
In FIG. 4, reference numeral 20 denotes an aperture, 21 denotes a first lens, 22 denotes a second lens, 23 denotes a third lens, 24 denotes a low-pass filter, and 25 denotes a solid-state image sensor.
[0047]
[Example 3]
Focal length: f = 3.28 mm
F number: F3.60
Angle of view: 2ω = 54.2 °
Table 5 shows the lens data in Example 3, and Table 6 shows the aspheric coefficient.
[0048]
[Table 5]

[0049]
[Table 6]

[0050]
Values corresponding to conditional expressions (1), (3) to (8) are as follows.
f ₂ /f=-0.33
_{(R 3 + r 4) /} (r 3 -r 4) = - 1.40
(R ₁ + r ₂ ) / (r ₁ -r ₂ ) = 0.95
f ₃ /f=0.69
FIG. 7 is a lens cross-sectional view of Example 3, FIG. 8 is an aberration diagram of spherical aberration, astigmatism, and distortion, and FIG. 9 is an aberration diagram of coma aberration.
[0051]
In FIG. 7, reference numeral 30 denotes an aperture, 31 denotes a first lens, 32 denotes a second lens, 33 denotes a third lens, 34 denotes a low-pass filter, and 35 denotes a solid-state image sensor.
[0052]
[Example 4]
Focal length: f = 3.28 mm
F number: F3.60
Angle of view: 2ω = 56.0 °
Table 7 shows lens data in Example 4, and Table 8 shows aspherical surface coefficients.
[0053]
[Table 7]

[0054]
[Table 8]

[0055]
Values corresponding to conditional expressions (1), (3) to (8) are as follows.
f ₂ /f=-0.79
_{(R 3 + r 4) /} (r 3 -r 4) = - 2.48
(R ₁ + r ₂ ) / (r ₁ -r ₂ ) = 0.61
f ₃ /f=3.05
FIG. 10 is a sectional view of a lens in Example 4, FIG. 11 is an aberration diagram of spherical aberration, astigmatism, and distortion, and FIG. 12 is an aberration diagram of coma aberration.
[0056]
In FIG. 10, reference numeral 40 denotes an aperture, 41 denotes a first lens, 42 denotes a second lens, 43 denotes a third lens, and 45 denotes a solid-state imaging device.
[0057]
【The invention's effect】
According to the imaging lens of the present invention, it is suitable for a small and high-performance camera using a solid-state imaging device such as a CCD or a CMOS sensor, has a short overall length and secures good telecentricity, and has a simple configuration. In addition, there is an effect that each lens can be made of plastic to reduce the cost.
[Brief description of the drawings]
FIG. 1 is a sectional view of a lens according to a first embodiment.
FIG. 2 is an aberration diagram of spherical aberration, astigmatism, and distortion in Example 1.
FIG. 3 is an aberration diagram of coma aberration in the first embodiment.
FIG. 4 is a sectional view of a lens according to a second embodiment.
FIG. 5 is an aberration diagram of spherical aberration, astigmatism, and distortion in Example 2.
FIG. 6 is an aberration diagram of coma aberration in the second embodiment.
FIG. 7 is a sectional view of a lens according to a third embodiment.
FIG. 8 is an aberration diagram of a spherical aberration, an astigmatism, and a distortion in the third embodiment.
FIG. 9 is an aberration diagram of coma aberration in the third embodiment.
FIG. 10 is a sectional view of a lens according to a fourth embodiment.
FIG. 11 is an aberration diagram of a spherical aberration, an astigmatism, and a distortion in the fourth embodiment.
FIG. 12 is an aberration diagram of coma aberration in the fourth embodiment.
[Explanation of symbols]
10, 20, 30, 40 Apertures 11, 21, 31, 41 First lenses 12, 22, 32, 42 Second lenses 13, 23, 33, 43 Third lenses 14, 24, 34 Low-pass filters 15, 25, 35 , 45 solid-state imaging device

Claims (8)

An aperture, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power are arranged in order from the object side. The first lens has a stronger refractive power on the image side. An imaging lens having power, wherein the second lens is a meniscus lens having a concave surface facing the object side, and satisfies the following conditional expression.
-0.85 _<f 2 /f<-0.25
ν ₂ <35
However,
f: focal length of the entire system f ₂ : focal length of the second lens ν ₂ : Abbe number of the second lens The imaging lens according to claim 1, wherein the first lens, the second lens, and the third lens are formed of plastic. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
-0.45 _<f 2 /f<-0.28 The imaging lens according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
_{-2.80 <(r 3 + r 4} ) / (r 3 -r 4) <- 1.00
However,
r ₃ : paraxial radius of curvature of the object-side surface of the second lens r ₄ : paraxial radius of curvature of the image-side surface of the second lens The imaging lens according to claim 4, wherein the following conditional expression is satisfied.
−2.00 <(r ₃ + r ₄ ) / (r ₃ −r ₄ ) <− 1.10 The imaging lens according to any one of claims 1 to 5, wherein the following conditional expression is satisfied.
_{0.50 <(r 1 + r 2} ) / (r 1 -r 2) <1.20
However,
r ₁ : paraxial radius of curvature of the object-side surface of the first lens r ₂ : paraxial radius of curvature of the image-side surface of the first lens The imaging lens according to any one of claims 1 to 6, wherein the following conditional expression is satisfied.
0.50 <f ₃ /f<3.30
However,
f ₃ : focal length of the third lens The imaging lens according to claim 7, wherein the following conditional expression is satisfied.
0.50 <f ₃ /f<1.00

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