JP2004252312A - Imaging lens - Google Patents
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- JP2004252312A JP2004252312A JP2003044394A JP2003044394A JP2004252312A JP 2004252312 A JP2004252312 A JP 2004252312A JP 2003044394 A JP2003044394 A JP 2003044394A JP 2003044394 A JP2003044394 A JP 2003044394A JP 2004252312 A JP2004252312 A JP 2004252312A
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、ＣＣＤやＣＭＯＳ等の受光素子を用いた携帯電話搭載カメラ、ＰＣカメラ、監視カメラ、デジタルスチルカメラ等に用いられるコンパクトで、かつ高解像な３枚構成からなる撮像レンズに関する。
【０００２】
【従来の技術】
この種の小型カメラモジュールに用いられる撮像レンズとして、ガラス枚数を少なくし、またプラスチックレンズを使用し、コスト低減とコンパクト化を図ったレンズ系が提案されている（例えば、特許文献１および２参照）。
【０００３】
【特許文献１】
特願２００２−２１５７４５号公報
【０００４】
【特許文献２】
特開１９９８−１７０８１９号公報
【０００５】
【発明が解決しようとする課題】
しかし、今後ますますＣＣＤ、ＣＭＯＳが小型化し、携帯電話、モバイル等の小型機用に使用されるレンズ系は、従来のこの種のレンズよりも外径、全長ともに、極端に小さくまた、短くしなければ使用することができない。さらに、ＣＣＤ、ＣＭＯＳの高画素化、精細画素ピッチへの対応を考えると、できるだけ少ない枚数のレンズで構成しながら、かつ高い解像力を維持することが要求される。しかし、２枚構成からなる非球面の撮像レンズでは、非球面特有の中心ズレのために、レンズを組み込むことによって像性能の安定性に問題が生じる。また、３枚構成からなる撮像レンズでも高い解像力を維持しつつコンパクト化を図ることは十分に達成しているとはいえない。さらに、４枚以上のレンズ構成では小型化およびローコスト化を図ることが困難になる。したがって、上記公報記載の従来技術では高解像力を維持しつつも小型化、ローコスト化を達成するという要求を必ずしも満足することができず、解像力も十分でない。
【０００６】
本発明は上記事情を鑑みなされたものであり、３枚のレンズ構成とし、ローコスト化、組み立て精度を意識しつつも高解像、かつコンパクトなＣＣＤ用、ＣＭＯＳ用のカメラ、モニター、ＴＶ用等に利用できる撮像レンズを提供することを目的とするものである。
【０００７】
【課題を解決するための手段】
本発明のうち請求項１記載の撮像レンズは、物体側から像面側へと順に絞りと正の屈折力を有する第１レンズと、物体側に凹面を向けたメニスカス状の正の屈折力を有する第２レンズと、少なくとも１つの屈折面を非球面形状とした負の屈折力を有する第３レンズからなり、下記条件（１）及び（２）を満足していることを特徴とする。
【０００８】
（１）０．６ ＜ｆ１ ／ ｆ ＜ ２．５
（２）ＴＬ ／ ｆ ＜ １．９
但し、ｆ：全レンズ系の合成焦点距離
ｆ１：第１レンズの焦点距離
ＴＬ：絞りから像面までの距離
（ただし、平行平面ガラス部分は空気換算距離）
ここで、上記条件式（１）はレンズ全系の合成焦点距離に対する第１レンズのパワーに関する条件式であり、この条件式（１）の下限を越えて第１レンズのパワーが強くなると、球面収差、コマ収差の補正が困難になり画面全体のコントラストが低下する。また第１レンズを構成しているレンズの球面の曲率半径が小さくなり、加工が困難となる。一方上限を越えて第１レンズのパワーが弱くなると、バックフォーカスが長くなり、撮像レンズの全長を小さくすることが困難となる。
上記条件式（２）はレンズ全長を規定するもので、この条件式（２）を越えると、コンパクト性を維持できなくなり、収差補正とのバランスがとれなくなる。
【０００９】
また、請求項２記載の撮像レンズは、請求項１記載の撮像レンズにおいて、第１レンズの物体側の面形状に関して下記条件（３）を満足していることが好ましい。
【００１０】
（３）０．４ ＜ ｒ２ ／ ｆ ＜ １．３
但し、ｒ２：第１レンズの物体側の曲率半径
ここで、条件式（３）は、第１レンズの物体側の面形状に関する条件式であり、下限を越えて曲率半径が小さくなると、負の球面収差の発生が過大となり、以降の面で補正が困難となる。また、上限を超えて曲率半径が大きくなると、像面湾曲が補正不足となる共に、レンズ全長が長くなってしまい望ましくない。
【００１１】
また、請求項３記載の撮像レンズは、請求項１または２記載の撮像レンズにおいて、第２レンズの物体側及び像側の面形状に関して下記条件（４）を満足していることが望ましい。
【００１２】
（４）０．２ ＜ｒ５ ／ｒ４ ＜ ０．８
但し、ｒ４：第２レンズの物体側の曲率半径
ｒ５：第２レンズの像側の曲率半径
ここで、条件式（４）は、第２レンズの物体側と像側の面形状に関する条件式であり、上下限を超えるといずれもコンセントリック形状、効果が崩れ、特に非点収差、歪曲収差及びテレセントリック性が急速に劣化してしまう。
【００１３】
また、請求項４記載の撮像レンズは、請求項１から３記載の撮像レンズにおいて、第３レンズのパワーに関して下記条件（５）を満足しており、また第３レンズの物体側及び像側の面形状に関して下記条件（６）を満足していることを特徴とする。
【００１４】
（５）− ７５ ＜ｆ３ ／ ｆ ＜ − ０．６
（６）０．２５ ＜ｒ７ ／ ｆ ＜ ０．８
但し、ｆ３：第３レンズの焦点距離
ｒ７：第３レンズの像側の曲率半径
ここで、条件式（５）は、第３レンズのパワーに関する条件式であり、下限を超えて第３レンズのパワーが大きくなると、小型化には有利であるが、周辺部のテレセントリック性、歪曲収差を補正することが困難となる。また、上限を超えて第３レンズのパワーが小さくなると、レンズ全系のバックフォーカスが長くなってしまいコンパクト性を維持することができなくなる。条件式（６）は、第３レンズの像側の面形状に関する条件式であり、下限を超えると、テレセントリック性を補正するために周辺部が極端な形状の非球面となり望ましくない。また、上限を超えると、像側の面のパワーが小さくなり、小型化に不利となる。
【００１５】
【発明の実施の形態】
以下、具体的な実施の形態について、添付図面を参照して説明する。
図１において、各実施例とも、第１レンズ２の物体側の直前に絞り１が配備されている。物体側から像面側へと順に、絞り１と、負の屈折力を有する第１レンズ２と、物体側に凹面を向けたメニスカス状の弱い正の屈折力を有する第２レンズ３と、少なくとも１つの屈折面を非球面形状とした負の屈折力を有する第３レンズ４からなり、その後方にローパスフィルタ５、像面６が配置される。
ここで、物体側から数えて第ｉ番目の面（絞り面を含む）の曲率半径をｒｉ、 第ｉ番目と第ｉ＋１番目の面の光軸上の面間隔をｄｉ、物体側から数えて第ｊ番目のレンズの屈折率およびアッベ数をそれぞれｎｉ、νｉで表す。＊の面は非球面を表し、それら各非球面は下記に示す非球面式により表される。またＦ／ＮＯは明るさ、ωは画角を表す。
【００１６】
非球面式 Ｚ ＝ ＣＹ２ ／ （ １ ＋ （ １−（１＋Ｋ）Ｃ２Ｙ２ ）１／２ ） ＋ ａ４Ｙ４ ＋ ａ６Ｙ６ ＋ ａ８Ｙ８ ＋ ａ１０Ｙ１０
Ｃ：非球面頂点の曲率
Ｋ：円錐定数
ａＩ：非球面定数
Ｙ：光軸からの高さ
Ｚ：非球面上の点のレンズ面頂点における接平面からの距離
ここで、各実施例が満足している条件式について説明する。
本発明のうち請求項１記載の撮像レンズは、物体側から像面側へと順に絞りと正の屈折力を有する第１レンズと、物体側に凹面を向けたメニスカス状の正の屈折力を有する第２レンズと、少なくとも１つの屈折面を非球面形状とした負の屈折力を有する第３レンズからなり、下記条件（１）及び（２）を満足していることを特徴とする。
【００１７】
（１）０．６ ＜ｆ１ ／ ｆ ＜ ２．５
（２）ＴＬ ／ ｆ ＜ １．９
但し、ｆ：全レンズ系の合成焦点距離
ｆ１：第１レンズの焦点距離
ＴＬ：絞りから像面までの距離
（ただし、平行平面ガラス部分は空気換算距離）
ここで、上記条件式（１）はレンズ全系の合成焦点距離に対する第１レンズのパワーに関する条件式であり、この条件式（１）の下限を越えて第１レンズのパワーが強くなると、球面収差、コマ収差の補正が困難になり画面全体のコントラストが低下する。また第１レンズを構成しているレンズの球面の曲率半径が小さくなり、加工が困難となる。一方上限を越えて第１レンズのパワーが弱くなると、バックフォーカスが長くなり、撮像レンズの全長を小さくすることが困難となる。上記条件式（２）はレンズ全長を規定するもので、この条件式（２）を越えると、コンパクト性を維持できなくなり、収差補正とのバランスがとれなくなる。
【００１８】
また、請求項２記載の撮像レンズは、請求項１記載の撮像レンズにおいて、第１レンズの物体側の面形状に関して下記条件（３）を満足していることが好ましい。
【００１９】
（３）０．４ ＜ ｒ２ ／ ｆ ＜ １．３
但し、ｒ２：第１レンズの物体側の曲率半径
ここで、条件式（３）は、第１レンズの物体側の面形状に関する条件式であり、下限を越えて曲率半径が小さくなると、負の球面収差の発生が過大となり、以降の面で補正が困難となる。また、上限を超えて曲率半径が大きくなると、像面湾曲が補正不足となる共に、レンズ全長が長くなってしまい望ましくない。
【００２０】
また、請求項３記載の撮像レンズは、請求項１または２記載の撮像レンズにおいて、第２レンズの物体側及び像側の面形状に関して下記条件（４）を満足していることが望ましい。
【００２１】
（４）０．２ ＜ｒ５ ／ｒ４ ＜ ０．８
但し、ｒ４：第２レンズの物体側の曲率半径
ｒ５：第２レンズの像側の曲率半径
ここで、条件式（４）は、第２レンズの物体側と像側の面形状に関する条件式であり、上下限を超えるといずれもコンセントリック形状、効果が崩れ、特に非点収差、歪曲収差及びテレセントリック性が急速に劣化してしまう。
【００２２】
また、請求項４記載の撮像レンズは、請求項１から３記載の撮像レンズにおいて、第３レンズのパワーに関して下記条件（５）を満足しており、また第３レンズの物体側及び像側の面形状に関して下記条件（６）を満足していることを特徴とする。
【００２３】
（５）− ７５ ＜ｆ３ ／ ｆ ＜ − ０．６
（６）０．２５ ＜ｒ７ ／ ｆ ＜ ０．８
但し、ｆ３：第３レンズの焦点距離
ｒ７：第３レンズの像側の曲率半径
ここで、条件式（５）は、第３レンズのパワーに関する条件式であり、下限を超えて第３レンズのパワーが大きくなると、小型化には有利であるが、周辺部のテレセントリック性、歪曲収差を補正することが困難となる。また、上限を超えて第３レンズのパワーが小さくなると、レンズ全系のバックフォーカスが長くなってしまいコンパクト性を維持することができなくなる。条件式（６）は、第３レンズの像側の面形状に関する条件式であり、下限を超えると、テレセントリック性を補正するために周辺部が極端な形状の非球面となり望ましくない。また、上限を超えると、像側の面のパワーが小さくなり、小型化に不利となる。
【００２４】
なお、さらに好ましくは条件式（１）〜（５）の数値範囲を次のごとく設定するのがよい。
（１ａ） ０．７ ＜ｆ１ ／ ｆ ＜ １．３
（２ａ） １．１ ＜ＴＬ ／ ｆ ＜ １．６
（３ａ） ０．６ ＜ ｒ２ ／ ｆ ＜ １．０
（５ａ） − ５ ＜ｆ３ ／ ｆ ＜ − ０．７
ここで、上記条件式（１ａ）の下限を越えると、第１レンズのパワーが強くなり、バックフォーカスが短くなるため、撮像素子とレンズの間にローパスフィルタ等を配置することが困難になる。一方、上限を越えて第１レンズのパワーが弱くなると、バックフォーカスが長くなり、撮像レンズの全長を小さくすることが困難になる。
【００２５】
上記条件式（２ａ）の下限を超えると、各レンズ群のパワーが強くなるため、非球面を用いてもテレセントリック性を維持することが困難になる。一方、上限を超えるとテレセントリック性は良好になるが、全長が大きくなってしまう。
【００２６】
上記条件式（３ａ）の下限を超えて曲率半径が小さくなると、製造が困難になる。一方、上限を超えて曲率半径が大きくなると、コマ収差が補正不足なり、高い解像力を得るためには望ましくない。
【００２７】
上記条件式（５ａ）の下限を超えると、第３レンズのパワーが強くなる。そこで、テレセントリック性を維持するために、第３レンズの像側の非球面を周辺にいくに従いパワーの強い形状、つまり像側に凸の形状になっていく。そのため、レンズは変曲点を持つ形状となり製造が困難になる。一方、上限を超えると、像面湾曲が補正不足となり、十分な解像力を持つレンズとすることができない。
さらに、第２レンズ及び第３レンズが樹脂材により製作されていることが好ましい。
【００２８】
以下に、実施例を５例上げて、各実施例について数値例を示す。
【００２９】
【表１】
実施例１の球面収差、非点収差及び歪曲収差を図２に示す。
【００３１】
【表２】
実施例２の球面収差、非点収差及び歪曲収差を図３に示す。
【００３３】
【表３】
実施例３の球面収差、非点収差及び歪曲収差を図４に示す。
【００３５】
【表４】
実施例４の球面収差、非点収差及び歪曲収差を図５に示す。
【００３７】
【表５】
実施例５の球面収差、非点収差及び歪曲収差を図６に示す。
【００３９】
【発明の効果】
本発明によれば前述の如く撮像レンズの各レンズ群のレンズ構成を適切に設定すると共に各条件式を満足させることにより、小型化を図ることができると共に各収差を良好に抑え、高解像な撮像レンズを達成できる。さらに、量産する際もローコスト化を図ることができるので各種の小型カメラモジュールに用いられる撮像レンズとして好適である。
【図面の簡単な説明】
【図１】本発明のレンズの構成図
【図２】本発明の数値実施例１の諸収差図
【図３】本発明の数値実施例２の諸収差図
【図４】本発明の数値実施例３の諸収差図
【図５】本発明の数値実施例４の諸収差図
【図６】本発明の数値実施例５の諸収差図
【符号の説明】
１ 絞り
２ 第１レンズ
３ 第２レンズ
４ 第３レンズ
５ ローパスフィルタ
６ 像面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compact and high-resolution three-lens imaging lens used for a camera mounted on a mobile phone, a PC camera, a surveillance camera, a digital still camera, and the like using a light receiving element such as a CCD or a CMOS.
[0002]
[Prior art]
As an imaging lens used in such a small camera module, a lens system has been proposed in which the number of glasses is reduced and a plastic lens is used to reduce cost and make the lens compact (for example, see Patent Documents 1 and 2). ).
[0003]
[Patent Document 1]
Japanese Patent Application No. 2002-215745
[Patent Document 2]
JP-A-1998-170819
[Problems to be solved by the invention]
However, in the future, CCDs and CMOSs will become smaller and the lens system used for small machines such as mobile phones and mobiles will be extremely smaller and shorter in both outer diameter and overall length than conventional lenses of this type. It cannot be used without it. Further, in consideration of the increase in the number of pixels and the fine pixel pitch of the CCD and the CMOS, it is required to maintain a high resolution while being configured with as few lenses as possible. However, in the case of an aspherical imaging lens having a two-element configuration, a problem arises in the stability of image performance due to the incorporation of the lens due to the center shift peculiar to the aspherical surface. Further, even with an imaging lens having a three-lens configuration, achieving compactness while maintaining high resolving power has not been sufficiently achieved. Further, it is difficult to reduce the size and cost with a configuration of four or more lenses. Therefore, the prior art described in the above-mentioned publication does not always satisfy the requirement of achieving downsizing and low cost while maintaining high resolution, and the resolution is not sufficient.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a three-lens configuration, a low-resolution, high-resolution and compact CCD, CMOS camera, monitor, TV, etc. while being aware of assembly accuracy. It is an object of the present invention to provide an imaging lens that can be used for a camera.
[0007]
[Means for Solving the Problems]
The imaging lens according to claim 1 of the present invention has a diaphragm and a first lens having a positive refractive power in order from the object side to the image surface side, and a meniscus-shaped positive refractive power having a concave surface facing the object side. And a third lens having a negative refractive power with at least one refracting surface being aspherical, and satisfying the following conditions (1) and (2).
[0008]
(1) 0.6 <f 1 / f <2.5
(2) TL / f <1.9
Here, f: combined focal length of all lens systems f 1 : focal length of the first lens TL: distance from the stop to the image plane (however, the parallel plane glass portion is the air equivalent distance)
Here, the above conditional expression (1) is a conditional expression relating to the power of the first lens with respect to the combined focal length of the entire lens system. If the power of the first lens becomes larger than the lower limit of the conditional expression (1), the spherical surface becomes larger. It becomes difficult to correct aberration and coma, and the contrast of the entire screen is reduced. In addition, the radius of curvature of the spherical surface of the lens constituting the first lens becomes small, and processing becomes difficult. On the other hand, if the power of the first lens becomes weaker than the upper limit, the back focus becomes longer, and it becomes difficult to reduce the overall length of the imaging lens.
Conditional expression (2) defines the total lens length. If conditional expression (2) is exceeded, compactness cannot be maintained and balance with aberration correction cannot be achieved.
[0009]
It is preferable that the imaging lens described in
[0010]
(3) 0.4 <r 2 / f <1.3
Here, r 2 is the radius of curvature of the first lens on the object side. Here, conditional expression (3) is a conditional expression relating to the surface shape of the first lens on the object side. Is excessively generated, and it becomes difficult to correct the subsequent surface. On the other hand, if the radius of curvature is increased beyond the upper limit, the field curvature will be insufficiently corrected and the overall length of the lens will be undesirably increased.
[0011]
It is preferable that the imaging lens described in
[0012]
(4) 0.2 <r 5 / r 4 <0.8
Where r 4 is the radius of curvature of the second lens on the object side, and r 5 is the radius of curvature of the second lens on the image side. Here, conditional expression (4) is a condition relating to the surface shapes of the second lens on the object side and the image side. If the upper and lower limits are exceeded, the concentric shape and the effect are lost, and astigmatism, distortion, and telecentricity are rapidly deteriorated.
[0013]
According to a fourth aspect of the present invention, in the imaging lens of the first to third aspects, the following condition (5) is satisfied with respect to the power of the third lens, and the third lens has an object side and an image side. The surface shape satisfies the following condition (6).
[0014]
(5) - 75 <f 3 / f <- 0.6
(6) 0.25 <r 7 / f <0.8
Where f 3 : focal length of the third lens r 7 : radius of curvature of the third lens on the image side where conditional expression (5) is a conditional expression relating to the power of the third lens. When the power of the lens increases, it is advantageous for miniaturization, but it becomes difficult to correct the telecentricity and distortion of the peripheral portion. Further, when the power of the third lens becomes smaller than the upper limit, the back focus of the entire lens system becomes longer, and compactness cannot be maintained. The conditional expression (6) is a conditional expression relating to the image-side surface shape of the third lens. If the lower limit of the conditional expression (6) is exceeded, the peripheral portion becomes an extremely aspherical surface in order to correct telecentricity, which is not desirable. If the value exceeds the upper limit, the power of the image-side surface is reduced, which is disadvantageous for downsizing.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments will be described with reference to the accompanying drawings.
In FIG. 1, in each embodiment, an aperture 1 is provided immediately before the
Here, the radius of curvature of the i-th surface (including the stop surface) counted from the object side is r i , the distance between the i-th surface and the (i + 1) -th surface on the optical axis is d i , counted from the object side. The refractive index and Abbe number of the j-th lens are represented by n i and v i , respectively. The * surface represents an aspheric surface, and each aspheric surface is represented by the following aspheric surface equation. F / NO represents brightness, and ω represents the angle of view.
[0016]
Aspheric expression Z = CY 2 / (1 + (1- (1 + K) C 2 Y 2) 1/2) + a 4 Y 4 + a 6 Y 6 + a 8 Y 8 + a 10 Y 10
C: curvature of the aspherical vertex K: conical constant a I : aspherical constant Y: height from the optical axis Z: distance of the point on the aspherical surface from the tangent plane at the vertex of the lens surface Here, each embodiment is satisfied. The following describes the conditional expression.
The imaging lens according to claim 1 of the present invention has a diaphragm and a first lens having a positive refractive power in order from the object side to the image surface side, and a meniscus-shaped positive refractive power having a concave surface facing the object side. And a third lens having a negative refractive power with at least one refracting surface being aspherical, and satisfying the following conditions (1) and (2).
[0017]
(1) 0.6 <f 1 / f <2.5
(2) TL / f <1.9
Here, f: combined focal length of all lens systems f 1 : focal length of the first lens TL: distance from the stop to the image plane (however, the parallel plane glass portion is the air equivalent distance)
Here, the above conditional expression (1) is a conditional expression relating to the power of the first lens with respect to the combined focal length of the entire lens system. If the power of the first lens becomes larger than the lower limit of the conditional expression (1), the spherical surface becomes larger. It becomes difficult to correct aberration and coma, and the contrast of the entire screen is reduced. In addition, the radius of curvature of the spherical surface of the lens constituting the first lens becomes small, and processing becomes difficult. On the other hand, if the power of the first lens becomes weaker than the upper limit, the back focus becomes longer, and it becomes difficult to reduce the overall length of the imaging lens. Conditional expression (2) defines the total lens length. If conditional expression (2) is exceeded, compactness cannot be maintained and balance with aberration correction cannot be achieved.
[0018]
It is preferable that the imaging lens described in
[0019]
(3) 0.4 <r 2 / f <1.3
Here, r 2 is the radius of curvature of the first lens on the object side. Here, conditional expression (3) is a conditional expression relating to the surface shape of the first lens on the object side. Is excessively generated, and it becomes difficult to correct the subsequent surface. On the other hand, if the radius of curvature is increased beyond the upper limit, the field curvature will be insufficiently corrected and the overall length of the lens will be undesirably increased.
[0020]
It is preferable that the imaging lens described in
[0021]
(4) 0.2 <r 5 / r 4 <0.8
Where r 4 is the radius of curvature of the second lens on the object side, and r 5 is the radius of curvature of the second lens on the image side. Here, conditional expression (4) is a condition relating to the surface shapes of the second lens on the object side and the image side. If the upper and lower limits are exceeded, the concentric shape and the effect are lost, and astigmatism, distortion, and telecentricity are rapidly deteriorated.
[0022]
According to a fourth aspect of the present invention, in the imaging lens of the first to third aspects, the following condition (5) is satisfied with respect to the power of the third lens, and the third lens has an object side and an image side. The surface shape satisfies the following condition (6).
[0023]
(5) - 75 <f 3 / f <- 0.6
(6) 0.25 <r 7 / f <0.8
Where f 3 : focal length of the third lens r 7 : radius of curvature of the third lens on the image side where conditional expression (5) is a conditional expression relating to the power of the third lens. When the power of the lens increases, it is advantageous for miniaturization, but it becomes difficult to correct the telecentricity and distortion of the peripheral portion. Further, when the power of the third lens becomes smaller than the upper limit, the back focus of the entire lens system becomes longer, and compactness cannot be maintained. The conditional expression (6) is a conditional expression relating to the image-side surface shape of the third lens. If the lower limit of the conditional expression (6) is exceeded, the peripheral portion becomes an extremely aspherical surface in order to correct telecentricity, which is not desirable. If the value exceeds the upper limit, the power of the image-side surface is reduced, which is disadvantageous for downsizing.
[0024]
It is more preferable to set the numerical ranges of the conditional expressions (1) to (5) as follows.
(1a) 0.7 <f 1 / f <1.3
(2a) 1.1 <TL / f <1.6
(3a) 0.6 <r 2 / f <1.0
(5a) −5 <f 3 /f<−0.7
Here, if the lower limit of the conditional expression (1a) is exceeded, the power of the first lens becomes strong and the back focus becomes short, so that it is difficult to arrange a low-pass filter or the like between the imaging element and the lens. On the other hand, when the power of the first lens becomes weaker than the upper limit, the back focus becomes longer, and it becomes difficult to reduce the overall length of the imaging lens.
[0025]
If the lower limit of conditional expression (2a) is exceeded, the power of each lens unit will be strong, and it will be difficult to maintain telecentricity even with an aspheric surface. On the other hand, if it exceeds the upper limit, the telecentricity will be good, but the overall length will be large.
[0026]
If the radius of curvature is smaller than the lower limit of the conditional expression (3a), manufacturing becomes difficult. On the other hand, when the radius of curvature is increased beyond the upper limit, coma aberration is insufficiently corrected, which is not desirable for obtaining high resolution.
[0027]
If the lower limit of conditional expression (5a) is exceeded, the power of the third lens will be strong. Therefore, in order to maintain the telecentricity, the shape of the third lens becomes stronger as it approaches the image-side aspherical surface on the image side, that is, the shape becomes convex toward the image side. Therefore, the lens has a shape having an inflection point, and it is difficult to manufacture the lens. On the other hand, when the value exceeds the upper limit, the field curvature becomes insufficiently corrected, and a lens having a sufficient resolving power cannot be obtained.
Further, it is preferable that the second lens and the third lens are made of a resin material.
[0028]
In the following, five examples are given, and numerical examples are shown for each example.
[0029]
[Table 1]
FIG. 2 shows the spherical aberration, astigmatism, and distortion of the first embodiment.
[0031]
[Table 2]
FIG. 3 shows the spherical aberration, astigmatism, and distortion of the second embodiment.
[0033]
[Table 3]
FIG. 4 shows the spherical aberration, astigmatism, and distortion of the third embodiment.
[0035]
[Table 4]
FIG. 5 shows the spherical aberration, astigmatism, and distortion of the fourth embodiment.
[0037]
[Table 5]
FIG. 6 shows the spherical aberration, astigmatism, and distortion of the fifth embodiment.
[0039]
【The invention's effect】
According to the present invention, as described above, by appropriately setting the lens configuration of each lens unit of the imaging lens and satisfying each conditional expression, it is possible to achieve downsizing, favorably suppress each aberration, and achieve high resolution. A simple imaging lens can be achieved. Furthermore, since the cost can be reduced even in mass production, it is suitable as an imaging lens used for various small camera modules.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a lens of the present invention. FIG. 2 is a diagram showing various aberrations of Numerical Example 1 of the present invention. FIG. 3 is a diagram showing various aberrations of Numerical Example 2 of the present invention. Various aberration diagrams of Example 3 [FIG. 5] Various aberration diagrams of Numerical Example 4 of the present invention [FIG. 6] Various aberration diagrams of Numerical Example 5 of the present invention [Description of symbols]
1
Claims (4)
（１）０．６ ＜ｆ１ ／ ｆ ＜ ２．５
（２）ＴＬ ／ ｆ ＜ １．９
但し、ｆ：全レンズ系の合成焦点距離
ｆ１：第１レンズの焦点距離
ＴＬ：絞りから像面までの距離An aperture and a first lens having a positive refractive power in order from the object side to the image surface side, a meniscus-shaped second lens having a positive refractive power with a concave surface facing the object side, and at least one refractive surface being An imaging lens comprising a third lens having a negative refractive power and having a spherical shape, and satisfying the following conditions (1) and (2).
(1) 0.6 <f 1 / f <2.5
(2) TL / f <1.9
Where f: composite focal length of all lens systems f 1 : focal length of first lens TL: distance from aperture to image plane
（３）０．４ ＜ ｒ２ ／ ｆ ＜ １．３
但し、ｒ２：第１レンズの物体側の曲率半径2. The imaging lens according to claim 1, wherein the following condition (3) is satisfied with respect to the object-side surface shape of the first lens.
(3) 0.4 <r 2 / f <1.3
Here, r 2 is the radius of curvature of the first lens on the object side.
（４）０．２ ＜ｒ５ ／ｒ４ ＜ ０．８
但し、ｒ４：第２レンズの物体側の曲率半径
ｒ５：第２レンズの像側の曲率半径3. The imaging lens according to claim 1, wherein the surface shape of the second lens on the object side and the image side satisfies the following condition (4). 4.
(4) 0.2 <r 5 / r 4 <0.8
Here, r 4 : radius of curvature of the second lens on the object side r 5 : radius of curvature of the second lens on the image side
（５）− ７５ ＜ｆ３ ／ ｆ ＜ − ０．６
（６）０．２５ ＜ｒ７ ／ ｆ ＜ ０．８
但し、ｆ３：第３レンズの焦点距離
ｒ７：第３レンズの像側の曲率半径4. The imaging lens according to claim 1, wherein the following condition (5) is satisfied with respect to the power of the third lens, and the following condition (6) is satisfied with respect to the object-side and image-side surface shapes of the third lens. An imaging lens characterized by being satisfied.
(5) - 75 <f 3 / f <- 0.6
(6) 0.25 <r 7 / f <0.8
Here, f 3 : focal length of the third lens r 7 : radius of curvature of the third lens on the image side
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| JP2003044394A JP4235007B2 (en) | 2003-02-21 | 2003-02-21 | Imaging lens |
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| JP2003044394A JP4235007B2 (en) | 2003-02-21 | 2003-02-21 | Imaging lens |
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| JP2004252312A5 JP2004252312A5 (en) | 2005-11-04 |
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