JP2004004566A - Imaging lens and imaging apparatus equipped with same, imaging unit and mobile terminal equipped with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide imaging lenses which are smaller than that in the conventional practice and which satisfactorily compensate various aberrations. <P>SOLUTION: The imaging lenses are so constituted that an aperture diaphragm S, a biconvex first lens L1 with a positive refractive power, a second lens L2 with its concave surface facing to the object side and with a negative refractive power, and a third meniscus lens L3 with its convex surface facing to the object side are arranged successively from the object side. <P>COPYRIGHT: (C)2004,JPO

Description

【００５７】
（第１実施例）
撮像レンズデータを表１，２，３に示す。
【００５８】
【表１】

【００５９】
【表２】

【００６０】
【表３】

【００６１】
図５は第１実施例の撮像レンズ配置を示す説明図である。図中Ｌ１は第１レンズ、Ｌ２は第２レンズ、Ｌ３は第３レンズ、Ｓは開口絞りを示す。図６は実施例１の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
第１レンズＬ１および第３レンズＬ３は、ポリオレフィン系のプラスチックレンズで、飽和吸水率は０．０１％以下である。また、第２レンズＬ２はポリカーボネイト系のプラスチックレンズで、飽和吸水率は０．４％である。
【００６２】
（実施例２）
撮像レンズデータを表４，５，６に示す。
【００６３】
【表４】

【００６４】
【表５】

【００６５】
【表６】

【００６６】
図７は実施例２の撮像レンズ配置を示す説明図である。図中Ｌ１は第１レンズ、Ｌ２は第２レンズ、Ｌ３は第３レンズ、Ｓは開口絞りを示す。図８は実施例１の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
第１レンズＬ１および第３レンズＬ３は、アクリル系のプラスチックレンズで、飽和吸水率は１．３％である。また、第２レンズＬ２はポリカーボネイト系のプラスチックレンズで、飽和吸水率は０．４％である。
【００６７】
（実施例３）
レンズデータを表７，８，９に示す。
【００６８】
【表７】

【００６９】
【表８】

【００７０】
【表９】

【００７１】
図９は実施例３の撮像レンズ配置を示す説明図である。図中Ｌ１は第１レンズ、Ｌ２は第２レンズ、Ｌ３は第３レンズ、Ｓは開口絞りを示す。図１０は実施例１の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
第１レンズＬ１および第３レンズＬ３は、アクリル系のプラスチックレンズで、飽和吸水率は１．３％である。また、第２レンズＬ２はポリカーボネイト系のプラスチックレンズで、飽和吸水率は０．４％である。なお、本実施例は、最も像側に水晶のローパスフィルタ相当の平行平板を配置した設計例である。
【００７２】
（実施例４）
撮像レンズデータを表１０，１１，１２に示す。
【００７３】
【表１０】

【００７４】
【表１１】

【００７５】
【表１２】

【００７６】
図１１は実施例４の撮像レンズの断面図である。図中Ｌ１は第１レンズ、Ｌ２は第２レンズ、Ｌ３は第３レンズ、Ｓは開口絞りを示す。図１２は実施例１の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
第１レンズＬ１および第３レンズＬ３は、ポリオレフィン系のプラスチックレンズで、飽和吸水率は０．０１％以下である。また、第２レンズＬ２はポリカーボネイト系のプラスチックレンズで、飽和吸水率は０．４％である。
【００７７】
（第５実施例）
撮像レンズデータを表１３，１４，１５に示す。
【００７８】
【表１３】

【００７９】
【表１４】

【００８０】
【表１５】

【００８１】
図１３は第５実施例の撮像レンズ配置を示す説明図である。図中Ｌ１は第１レンズ、Ｌ２は第２レンズ、Ｌ３は第３レンズ、Ｓは開口絞りを示す。図１４は実施例５の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
第１レンズＬ１はガラスレンズである。また、第２レンズＬ２はポリエステル系のプラスチックレンズで、飽和吸水率は０．７％、第３レンズＬ３は、ポリオレフィン系のプラスチックレンズで、飽和吸水率は０．０１％以下である。
なお、本実施例は最も像側に、赤外線カットフィルタ及び固体撮像素子のシールガラス相当の平行平板を配置した設計例である。
【００８２】
（第６実施例）
撮像レンズデータを表１６，１７，１８に示す。
【００８３】
【表１６】

【００８４】
【表１７】

【００８５】
【表１８】

【００８６】
図１５は第６実施例の撮像レンズ配置を示す説明図である。図中Ｌ１は第１レンズ、Ｌ２は第２レンズ、Ｌ３は第３レンズ、Ｓは開口絞りを示す。図１６は実施例６の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
第１レンズＬ１はガラスレンズである。また、第２レンズＬ２はポリエステル系のプラスチックレンズで、飽和吸水率は０．７％、第３レンズＬ３は、ポリオレフィン系のプラスチックレンズで、飽和吸水率は０．０１％以下である。
なお、本実施例は最も像側に、赤外線カットフィルタ及び固体撮像素子のシールガラス相当の平行平板を配置した設計例である。
【００８７】
（第７実施例）
撮像レンズデータを表１９，２０，２１に示す。
【００８８】
【表１９】

【００８９】
【表２０】

【００９０】
【表２１】

【００９１】
図１７は第７実施例の撮像レンズ配置を示す説明図である。図中Ｌ１は第１レンズ、Ｌ２は第２レンズ、Ｌ３は第３レンズ、Ｓは開口絞りを示す。図１８は実施例７の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
第１レンズＬ１及び第３レンズＬ３は、ポリオレフィン系のプラスチックレンズで、飽和吸水率は０．０１％以下である。また、第２レンズＬ２はポリエステル系のプラスチックレンズで、飽和吸水率は０．７％、である。
なお、本実施例は最も像側に、赤外線カットフィルタ及び固体撮像素子のシールガラス相当の平行平板を配置した設計例である。
【００９２】
なお、本実施例は、像側光束のテレセントリック特性については必ずしも十分な設計にはなっていない。テレセントリック特性とは、各像点に対する光束の主光線が、撮像レンズ最終面を射出した後、光軸とほぼ平行になることをいい、換言すれば光学系の射出瞳位置が像面から十分離れることである。テレセントリック特性が悪くなると、光束が固体撮像素子に対し斜めより入射し、画面周辺部において実質的な開口効率が減少する現象（シェーディング）が生じ、周辺光量不足となってしまう。しかし、最近の技術では、固体撮像素子の色フィルタやマイクロレンズアレイの配列の見直し等によって、前述のシェーディング現象を軽減することができる。従って、本実施例は、テレセントリック特性の要求が緩和された分について、より小型化を目指した設計例となっている。
【００９３】
【発明の効果】
請求項１記載の発明は、最も物体側に開口絞りを配置することで射出瞳位置を像面から遠ざけることが可能となるため、例えば、固体撮像素子用の撮像レンズとして本発明を使用した場合に、固体撮像素子に必要な像側テレセントリック特性を良好に確保することが可能となる。
また、本発明は、比較的屈折力の大きい正の両凸形状の第１レンズと、負の第２レンズとを物体側前方に配置していることから、撮像レンズ全長の小型化を図っている。
【００９４】
そして、第１レンズを両凸形状とすることで、当該第１レンズとして屈折力が大きなものを使用した場合に発生する球面収差の低減を図っている。
さらに、負の第２レンズの凹面を第１レンズ側に向けることで、凸面を向けた第１レンズとの近接配置を可能とし、これにより、球面収差、コマ収差、色収差等の諸収差の補正を良好且つ簡易に行うことを可能としている。
また、第３レンズを物体側に凸面を向けたメニスカス形状としているので、特に、像側の画面周辺部でのテレセントリック特性を良好に確保することを可能としている。
【００９５】
以上のことから、本発明により、球面収差，コマ収差，色収差等の諸収差を有効に低減でき、テレセントリック特性を良好に維持しつつも、光軸方向の小型化を実現した撮像レンズを提供することが可能となる。
【００９６】
請求項２記載の発明は、第３レンズが正の屈折力を有する構成としたことから、いわゆるトリプレットタイプの撮像レンズ構成となり、歪曲収差等の軸外諸収差の補正や、テレセントリック特性の確保がより容易に行うことが可能となる。
【００９７】
請求項３記載の発明は、正の第１レンズに非球面を用いことにより球面収差，コマ収差の補正を可能とし、負の第２レンズに非球面を用いることによりコマ収差，非点収差の補正が可能となる。
さらに、正の第３レンズは、最も像面に近接した位置に配置したことにより生じる軸上光線と周辺光線の通過高さの格差を利用して、画面周辺部の諸収差を軸上性能に影響を与えることなく非球面によって補正することが可能となる。特に、第２レンズの負の屈折力を強く設定した場合に発生する糸巻き型の歪曲収差の補正や像面湾曲の補正を効果的に行うことが可能となる。換言すれば、第２レンズの負の屈折力を強化することも可能となる。
従って、本発明により、より良好な収差補正が可能となる。
【００９８】
請求項４記載の発明は、撮像レンズ全長を規定し，小型化を達成するための条件式（１）により、その上限値を下回る設定とすることで、撮像レンズ全長を短くでき相乗的に撮像レンズ外径も小さくできる。従って、これにより、撮像装置全体の小型軽量化が可能となる。
さらに、正の第１レンズの屈折力を規定する条件式（２）に従い、その下限値を上回る設定とすることで、第１レンズの正の屈折力の増大を押さえ、第１レンズで発生する球面収差やコマ収差を小さく抑えることが可能となる。また極端に小さな曲率半径にはならないため、撮像レンズの加工性の観点からも好ましい。一方、式（２）の上限値を下回る設定とすることで、第１レンズの正の屈折力の過度の低下を抑制し、撮像レンズ全長の小型化に有利となる。
【００９９】
また、正の第３レンズの屈折力を規定する条件式（３）に従い、その下限値を上回る設定とすることで、第３レンズの正の屈折力が過度に増大することを抑制するので、第１レンズとの正の屈折力配分が適切になり、撮像レンズ全長の小型化を図ることが可能となる。一方、その上限値を下回る設定とすることで、第３レンズの正の屈折力の過度の低下を防ぎ、歪曲収差の補正を良好に行うことができ、また像側光束のテレセントリック特性を確保することが可能となる。
【０１００】
請求項５記載の発明は、条件式（４）に従うことにより、第２レンズ物体面側の負の屈折力が過大とならず、軸外光束のコマフレアの発生を抑えることができ、良好な画質を得ることが可能となる。
また、第２レンズ物体面側の負の屈折力を適切に維持されるので、正のペッツバール和が減少し、像面湾曲の補正が容易になると共に、正の第１レンズで発生する球面収差やコマ収差を良好に補正することが可能となる。
【０１０１】
請求項６記載の発明は、正の第１レンズと負の第２レンズでの色収差補正の条件式（５）の下限値を上回る設定とすることにより、軸上色収差，倍率色収差をバランス良く補正することが可能となる。
【０１０２】
請求項７記載の発明では、第１レンズ、第２レンズ、第３レンズ全てを射出成形により製造されるプラスチックレンズで構成しているため、曲率半径や外径の小さなレンズであっても、研磨加工により製造されるガラスレンズよりも大量生産が可能となる。
また、プラスチックレンズは、非球面化が容易なため、収差補正最寄り容易且つ的確に行うことが可能となる。
さらに、プラスチックレンズを用いるもう一つのメリットとしては、撮像レンズ有効径外側のフランジ部の形状を自由に設計できるため、取り付け部品点数の低減化を図ることができ、これにより、取り付け誤差を効果的に低減し、フランジ部の内径部または外径部を利用して、各レンズの光軸を容易に一致させることができる構造をとる等、光学系の組み立て精度の向上を図ることが可能となる。さらに、組み立てが容易となり、生産性も向上する。
【０１０３】
請求項８記載の発明では、各レンズについて、飽和吸水率が０．７％以下のプラスチック材料を用いることにより、急激な湿度変化による屈折率の不均一化を抑制し、より良好な結像性能を維持しながら、プラスチックレンズの利点をも得ることが可能となる。
【０１０４】
請求項９記載の発明は、第１−第２レンズの間隔，或いは第２−第３レンズの間隔の、少なくとも一方の間隔に、周辺光束を規制する遮光マスクを配置しているので、上記各レンズのいずれかに外周部にフランジ部を設けた場合であっても、結像に必要な光束のみを通過させ、且つフランジ部への光の入射を最小限に抑えることができる。従って、フランジ部の存在によるゴーストやフレアの発生を抑えることが可能となる。このため、遮光マスクの配置に応じて、第１〜３の各レンズの取り付けや位置決めを容易化するフランジ部を積極的にレンズ外周に設けることが可能となる。
【０１０５】
請求項１０記載の発明は、第１レンズをガラス材料とすることにより、第１レンズの温度変化時の屈折率変化が無視でき、撮像レンズ全系での温度変化時の像点位置変動を小さく抑えることが可能となる。
さらに、第２，第３レンズをプラスチック材料とすることから、一体成形により撮像レンズ有効径外側のフランジ部の形状を自由に設計することも可能となる。仮に、各レンズのフランジ部を相互に嵌合自在とした場合には、複数枚のレンズの光軸を容易に一致させることができる構造をとることができる。さらに、フランジが各レンズ間隔を規定する構造とした場合には、スペーサーを不要とし、部品点数の軽減により生産性の向上を図ることが可能となる。
また、レンズをプラスチック材料を形成することからレンズに非球面を容易に形成することが可能となり、収差補正を容易に行うことが可能となる。
従って、プラスチック材料による影響を低減した上で、プラスチック材料がもたらす効果である小型軽量化と低コスト化を実現することが可能となる。
また、第１レンズをガラスレンズとすることで、傷つきやすいプラスチックレンズを露出させる必要がなく保守性の向上を図ることが可能である。
【０１０６】
請求項１１記載の発明は、条件式（６）を満たすように設定することにより、プラスチックレンズの合成焦点距離を大きく設定して屈折力の総和を小さく抑え、温度変化時の像点位置変動を小さく抑えることが可能となる。
【０１０７】
請求項１２記載の発明では、第２，第３レンズについて、飽和吸水率が０．７％以下のプラスチック材料を用いることにより、急激な湿度変化による屈折率の不均一化を抑制し、より良好な結像性能を維持しながら、プラスチックレンズの利点をも得ることが可能となる。
【０１０８】
請求項１３記載の発明は、第１−第２レンズの間隔，或いは第２−第３レンズの間隔の、少なくとも一方の間隔に、周辺光束を規制する遮光マスクを配置しているので、上記第２，第３レンズのいずれかに外周部にフランジ部を設けた場合であっても、当該フランジ部の存在によるゴーストやフレアの発生を抑えることが可能となる。このため、遮光マスクの配置に応じて、第２，第３レンズの取り付けや位置決めを容易化するフランジ部を積極的にレンズ外周に設けることが可能となる。
【０１０９】
請求項１４記載の発明によれば、上述した各効果を実現可能な撮像レンズを搭載することにより、小型化、軽量化、高画質化等の利点を備える撮像装置を提供することが可能である。
【０１１０】
請求項１５記載の発明によれば、上述した各効果を実現可能な撮像レンズを搭載することにより、小型化、軽量化、高画質化等の利点を備える撮像ユニットを提供することが可能である。
【０１１１】
請求項１６記載の発明によれば、上述した各効果を実現可能な撮像ユニットを搭載することにより、小型化、軽量化を図りつつ、高画質な撮像が可能な携帯端末を提供することが可能である。
【図面の簡単な説明】
【図１】発明の実施形態たる撮像ユニットの斜視図である。
【図２】本発明の実施形態たる撮像レンズユニットの各レンズの光軸を含む断面における断面図を示している。
【図３】図３（Ａ）は撮像ユニットを適用した携帯電話機の正面図、図３（Ｂ）は撮像ユニットを適用した携帯電話機の背面図を示す。
【図４】図３の携帯電話機の制御ブロック図である。
【図５】実施例１のレンズ配置を示す説明図である。
【図６】実施例１の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
【図７】実施例２の撮像レンズ配置を示す説明図である。
【図８】実施例２の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
【図９】実施例３の撮像レンズ配置を示す説明図である。
【図１０】実施例３の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
【図１１】実施例４の撮像レンズ配置を示す説明図である。
【図１２】実施例４の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
【図１３】実施例５の撮像レンズ配置を示す説明図である。
【図１４】実施例５の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
【図１５】実施例６の撮像レンズ配置を示す説明図である。
【図１６】実施例６の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
【図１７】実施例７の撮像レンズ配置を示す説明図である。
【図１８】実施例７の収差図（球面収差、非点収差、歪曲収差、メリディオナルコマ収差）である。
【符号の説明】
１０　撮像光学系（撮像レンズ）
５０　撮像ユニット
１００　携帯電話機（携帯端末）
Ｌ１　第１レンズ
Ｌ２　第２レンズ
Ｌ３　第３レンズ
Ｓ　　開口絞り[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging lens suitable as an optical system of a solid-state imaging device such as a CCD image sensor and a CMOS image sensor, and an imaging device, an imaging unit, and a mobile terminal including the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, as an imaging device using a solid-state imaging device such as a CCD (Charged Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor becomes higher in performance and miniaturized, a mobile phone equipped with the imaging device has been developed. Personal computers are becoming popular.
With the miniaturization of these mobile phones and personal computers and the increase in density due to the increase in functions, there is a demand for further miniaturization of the imaging lens mounted on the imaging device in order to reduce the size of these imaging devices. Is growing.
[0003]
In recent years, as an imaging lens for such a small-sized imaging device, a first lens having a positive refractive power has been arranged in order from the object side because it can have higher performance than an imaging lens having one or two lenses. , A second lens having a negative refractive power and a third lens having a third lens having a positive refractive power are becoming common. Such a so-called triplet type imaging lens is disclosed in Patent Document 1.
[0004]
[Patent Document 1]
JP 2001-75006 A (FIG. 1)
[0005]
[Problems to be solved by the invention]
However, the imaging lens of the type described in Patent Literature 1 is a type in which various aberrations are well corrected while securing a wide angle of view, but on the other hand, the entire length of the imaging lens (the most object of the entire imaging lens system) However, the distance from the side surface to the image-side focal point (however, in an imaging lens in which an aperture stop is arranged closest to the object side, the distance from the aperture stop to the image-side focal point) is not suitable for miniaturization.
In view of such problems, an object of the present invention is to provide a triplet-type imaging lens which is smaller than a conventional type, and which has well corrected various aberrations.
[0006]
[Means for Solving the Problems]
The invention according to claim 1 includes, in order from the object side, an aperture stop, a biconvex first lens having a positive refractive power, a second lens having a negative refractive power and a concave surface facing the object side, and an object. A configuration is adopted in which a meniscus-shaped third lens having a convex surface facing the side is disposed.
[0007]
In the above configuration, since the aperture stop is arranged closest to the object side, the exit pupil position can be moved away from the image plane. When the exit pupil is farther from the image plane, the principal ray of the light beam emitted from the final lens surface enters the solid-state imaging device at an angle close to perpendicular, that is, the telecentric characteristics can be secured well, and the shading phenomenon in the peripheral portion of the screen Can be reduced.
The basic configuration of the above-mentioned imaging lens includes a first positive lens, a second negative lens, and a third lens. In addition, by arranging a positive biconvex first lens having relatively large refractive power and a negative second lens in front, a configuration close to a telephoto type is achieved, and the overall length of the imaging lens is reduced. I have.
[0008]
The invention described in claim 2 has the same configuration as that of the invention described in claim 1, and adopts a configuration in which the third lens has a positive refractive power. With such a configuration, the positive first lens, the negative second lens, and the positive third lens are arranged in this order from the object side, and constitute a so-called triplet type.
[0009]
According to a third aspect of the present invention, the first lens, the second lens, and the third lens each have an aspheric surface on at least one of the first lens, the second lens, and the third lens. It has a configuration of having.
[0010]
In the above configuration, when an aspheric surface is used for the positive first lens, spherical aberration and coma are corrected by this. When an aspheric surface is used for the negative second lens, Correction of coma and astigmatism is performed. Further, the positive third lens is arranged at the position closest to the image plane, so that a difference occurs in the passing height between the on-axis ray and the peripheral ray. It is possible to correct various aberrations at a peripheral portion of a distant screen.
[0011]
A fourth aspect of the present invention has the same configuration as the first, second, or third aspect of the present invention, and has a distance L on the optical axis from the aperture stop to the image-side focal point, an effective screen diagonal length of 2Y, When the focal length of one lens is f1, the focal length of the third lens is f3, and the focal length of the entire imaging lens system is f, the following conditional expressions (1) to (3) are satisfied. ing.
L / 2Y <1.50 (1)
0.50 <f1 / f <0.95 (2)
1.00 <f3 / f <1.40 (3)
[0012]
Conditional expression (1) in the above configuration defines the overall length of the imaging lens and is a condition for achieving miniaturization. By falling below the upper limit value in Expression (1), the overall length of the imaging lens can be shortened, and the outer diameter of the imaging lens can be reduced synergistically. L used in the calculation of the conditional expression (1) is a distance from the aperture stop to the image-side focal point. The image-side focal point is an image point when a parallel ray parallel to the optical axis enters the imaging lens. Say. When a parallel plate-shaped optical member such as a low-pass filter is disposed between the image side surface of the third lens and the image side focal point, the optical member is converted to an air-equivalent distance and then the expression (1) is satisfied. Cases are included.
[0013]
Further, conditional expression (2) defines the refractive power of the positive first lens. Exceeding the lower limit in Equation (2) avoids an excessive increase in the positive refractive power of the first lens, and does not result in an extremely small radius of curvature. On the other hand, when the value is below the upper limit, an excessive decrease in the positive refractive power of the first lens is avoided, which is advantageous in reducing the overall length of the imaging lens.
[0014]
Conditional expression (3) defines the refractive power of the positive third lens. By exceeding the lower limit value in the expression (3), an excessive increase in the positive refractive power of the third lens is avoided, and the positive refractive power distribution with the first lens becomes appropriate (f1 <f3 in the present invention. More preferred). On the other hand, by falling below the upper limit, an excessive decrease in the positive refractive power of the third lens is avoided.
[0015]
The invention according to claim 5 has the same configuration as the invention according to claim 1, 2, 3, or 4, and further has a refractive index for the d-line of the second lens of N2 and a radius of curvature of the object side surface of the second lens. When the focal length of R3 and the entire imaging lens system is f, the following conditional expression (4) is satisfied.
−0.60 <R3 / ((N2-1) · f) <− 0.20 (4)
[0016]
Conditional expression (4) in the above configuration is a condition for facilitating the correction of the curvature of field and making the image plane flat by appropriately setting the negative refractive power on the object plane side of the second lens. (Here, the focal length of the object side surface of the second lens is calculated by R3 / (N2-1) using the radius of curvature (R3) and the refractive power (N2) of the second lens. ) Is an expression representing the ratio of the focal length of the second lens object plane side to the focal length of the entire imaging lens system).
By exceeding the lower limit, the negative refracting power on the object surface side of the second lens does not become excessively large, and the occurrence of coma flare of the off-axis light beam can be suppressed, and good image quality can be obtained. On the other hand, when the value is below the upper limit, the negative refractive power on the object side of the second lens can be maintained, so that the positive Petzval sum is reduced and the correction of the curvature of field becomes easy. Further, spherical aberration and coma generated by the positive first lens can be corrected well.
[0017]
The invention according to claim 6 has the same configuration as the invention according to claim 1, 2, 3, 4 or 5, and the Abbe number of the first lens is ν1, and the Abbe number of the second lens is ν2. To
25 <ν1-ν2 (5)
Is satisfied.
[0018]
Conditional expression (5) in the above configuration is a condition for correcting chromatic aberration in the positive first lens and the negative second lens. By setting the lower limit value to be greater, the correction of axial chromatic aberration and lateral chromatic aberration can be performed. Do.
[0019]
The invention according to claim 7 has the same configuration as the invention according to claim 1, 2, 3, 4, 5, or 6, and the first, second, and third lenses are all formed of a plastic material. Is adopted. Here, forming from a plastic material includes a case where the surface of the plastic material is subjected to a coating treatment for the purpose of preventing reflection and improving surface hardness using the plastic material as a base material. The same applies to the following description.
[0020]
When producing an imaging lens having a small radius of curvature or outer diameter, plastic is more suitable for mass production by using a manufacturing method such as injection molding than glass. Therefore, in the above configuration, the first lens, the second lens, and the third lens are all formed of plastic lenses.
Here, as a lens that can be manufactured relatively easily even with a small-diameter lens, a glass mold lens may be employed, but it can be said that a plastic lens is more suitable for mass production with reduced manufacturing costs.
[0021]
The invention according to claim 8 has the same configuration as the invention according to claim 7, and the first, second, and third lenses are all formed of a plastic material having a saturated water absorption of 0.7% or less. It has a configuration.
Plastic lenses have a higher saturated water absorption than glass lenses, so if there is a sudden change in humidity, a non-uniform distribution of the water absorption will occur transiently, and the refractive index will not be uniform and good imaging performance will be obtained. It tends to disappear. Therefore, the use of plastic having a low saturated water absorption rate as the material of the lens as a material of the lens is intended to eliminate performance deterioration due to a change in humidity.
[0022]
According to a ninth aspect of the present invention, there is provided the same configuration as that of the seventh or eighth aspect, and at least one of an interval between the first lens and the second lens or an interval between the second lens and the third lens. In addition, a configuration is adopted in which a light-shielding mask for regulating the peripheral light beam is arranged.
[0023]
Generally, a plastic lens can be easily formed into a shape having a flange portion that does not contribute to image formation on an outer peripheral portion. If light enters this flange portion, it causes ghost or flare. Therefore, it is preferable to arrange a light-shielding mask that regulates a peripheral light beam at at least one of the two lens intervals. Thereby, only the light beam necessary for image formation can be passed, and the incidence of light on the flange portion can be minimized. As a result, ghost and flare can be suppressed. The light-shielding mask referred to herein is not limited to a light-shielding member having a light-transmitting opening at the center, and includes, for example, a mask formed by applying a light-shielding paint to a flange portion of a lens. In the case of using the light-shielding member, the overall shape is not limited to the sheet-like member. The same applies to the following description.
[0024]
The tenth aspect of the present invention has the same configuration as the first, second, third, fourth, fifth, or sixth aspect of the present invention, the first lens is made of a glass material, and the second and third lenses are both made. It is made of plastic material.
[0025]
When the lens constituting the imaging lens is formed of a plastic lens manufactured by injection molding, it is advantageous for reducing the size and weight of the imaging lens and reducing the cost. However, since the plastic material has a large change in the refractive index when the temperature changes, if all the lenses are made of plastic lenses, there is a disadvantage that the image point position of the entire imaging lens fluctuates depending on the temperature.
Such a change in the image point position due to a temperature change is particularly problematic in an image pickup device equipped with a solid-state image pickup device having a large number of pixels and without an autofocus mechanism (a so-called pan-focus type image pickup device). In the case of a solid-state imaging device having a large number of pixels, the pixel pitch is small, and the depth of focus proportional to the pixel pitch is narrow, so that the allowable range of the image point position fluctuation is narrow. The pan-focus type imaging apparatus is a method that originally focuses on a subject having a reference distance of several tens of centimeters and covers a close distance from infinity with a depth of field. Therefore, the image quality of a subject at infinity or a close distance is slightly out of focus compared to the image quality of a subject at a reference distance. Image quality is extremely deteriorated, which is not preferable.
[0026]
In the configuration of the present invention, the first positive lens is formed of a glass material, and the second negative lens and the third positive lens are formed of a plastic material. By using a glass lens as the first lens having a relatively large positive refractive power, a change in the refractive index when the temperature of the first lens changes can be ignored, and the change in the image point position when the temperature changes in the entire imaging lens system can be reduced. It is a configuration that can be suppressed.
Further, by using a glass lens as the first lens, it is not necessary to expose a plastic lens that is easily damaged, which is a preferable configuration.
Here, when a glass mold lens is used as the first lens, generally, in a glass having a high glass transition point (Tg), it is necessary to set a high press temperature at the time of performing a mold press, and consequently a molding die tends to be consumed. . As a result, the number of times of changing the molding die and the number of maintenances increase, which leads to an increase in cost. Therefore, when a glass mold lens is employed, it is desirable to use a glass material having a Tg of 400 [° C.] or less.
[0027]
The invention according to claim 11 has the same configuration as the invention according to claim 10, and when the combined focal length of the second and third lenses is f23 and the focal length of the entire imaging lens system is f, (6) is satisfied.
f / | f23 | <0.4 (6)
[0028]
Conditional expression (6) defines the combined focal length of the second and third lenses formed of plastic. By increasing the combined focal length so as to satisfy the conditional expression, it becomes possible to offset the contribution of the plastic lens to the image point position variation due to the temperature change by the negative second lens and the positive third lens, Variations in image point position when the temperature changes can be reduced.
[0029]
A twelfth aspect of the present invention has the same configuration as the tenth or eleventh aspect, and both the second and third lenses are formed of a plastic material having a saturated water absorption of 0.7% or less. The configuration is adopted.
In the above configuration, by using plastic having a low saturated water absorption as the lens material, the uneven distribution of the water absorption due to a rapid change in humidity is suppressed, and the refractive index is made uniform.
[0030]
A thirteenth aspect of the present invention has the same configuration as that of the tenth, eleventh, or twelfth aspect, and at least one of an interval between the first lens and the second lens or an interval between the second lens and the third lens. A light-shielding mask that regulates the peripheral light flux is disposed at the interval of.
As described above, the configuration in which the light shielding mask is provided restricts the peripheral light flux and allows only the light flux necessary for image formation to pass, so that the second and third lenses made of a plastic material are provided with a flange portion. Even so, the incidence of light on the flange portion can be minimized, and as a result, ghost and flare can be suppressed.
[0031]
According to a fourteenth aspect of the present invention, there is provided a solid-state imaging device having a photoelectric conversion unit, and the imaging lens according to any one of the first to thirteenth aspects, for forming a subject image on the photoelectric conversion unit of the solid-state imaging device. Is provided.
With the above-described configuration, by mounting the imaging lens described in each of the above-described claims, an imaging apparatus having the above-described advantages such as miniaturization, weight reduction, and high image quality is realized.
Here, the imaging device includes an electronic device having an imaging function, such as a mobile terminal such as a mobile phone or a PDA, in addition to a camera mainly for imaging.
[0032]
According to a fifteenth aspect of the present invention, there is provided a solid-state imaging device having a photoelectric conversion unit, and the imaging lens according to any one of the first to thirteenth aspects, for imaging a subject image on the photoelectric conversion unit of the solid-state imaging device. A substrate having an external connection terminal for holding a solid-state imaging device and transmitting and receiving an electric signal, and a housing made of a light shielding member having an opening for light incidence from the object side are integrally formed. In this case, the height of the imaging unit in the direction of the optical axis of the imaging lens is 10 mm or less.
[0033]
In the above configuration, by using any one of the imaging lenses according to the first to thirteenth aspects, it is possible to obtain an imaging unit having advantages such as smaller size and higher image quality.
In addition, the "opening portion for light incidence" is not necessarily limited to one that forms a space such as a hole, but refers to a portion where a region that can transmit incident light from the object side is formed.
Also, “the length of the imaging lens of the imaging unit in the optical axis direction is 10 mm or less” means the entire length of the imaging unit having all the above-described configurations along the optical axis direction. Therefore, for example, when the housing is provided on the front surface of the substrate and electronic components and the like are mounted on the rear surface of the substrate, the electronic components protruding on the rear surface from the front end on the object side of the housing. It is assumed that the distance to the tip of the component is 10 [mm] or less.
[0034]
According to a sixteenth aspect of the present invention, there is provided a configuration including the imaging unit according to the fifteenth aspect.
In the above configuration, by mounting the above-described imaging unit, a portable terminal capable of performing high-quality imaging while realizing a reduction in size and weight as described above.
[0035]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of the imaging unit 50 according to the present embodiment, and FIG. 2 is a cross-sectional view of the imaging unit 50 along the optical axis of the imaging optical system.
The imaging unit 50 includes a CMOS image sensor 51 as a solid-state imaging device having a photoelectric conversion unit 51a, an imaging optical system 10 as an imaging lens for causing the photoelectric conversion unit 51a of the image sensor 51 to capture a subject image, A substrate 52 having an external connection terminal 54 for holding the sensor 51 and transmitting and receiving an electric signal thereof, and a housing 53 as a lens barrel having an opening for light incidence from the object side and made of a light shielding member. And these are integrally formed.
[0036]
In the image sensor 51, a photoelectric conversion unit 51a as a light receiving unit in which pixels (photoelectric conversion elements) are two-dimensionally arranged is formed in the center of a plane on the light receiving side, and a signal is provided around the photoelectric conversion unit 51a. A processing circuit 51b is formed. Such a signal processing circuit includes a driving circuit unit that sequentially drives each pixel to obtain a signal charge, an A / D conversion unit that converts each signal charge into a digital signal, and a signal that forms an image signal output using the digital signal. It is composed of a processing unit and the like. A number of pads (not shown) are arranged near the outer edge of the light receiving side plane of the image sensor 51, and are connected to the substrate 52 via wires W. The image sensor 51 converts the signal charge from the photoelectric conversion unit 51a into an image signal such as a digital YUV signal or the like, and outputs the signal to a predetermined circuit on the substrate 52 via the wire W. Here, Y is a luminance signal, U (= RY) is a color difference signal between red and luminance, and V (= BY) is a color difference signal between blue and the luminance signal.
The image sensor is not limited to the CMOS image sensor described above, and other devices such as a CCD may be used.
[0037]
The substrate 52 includes a support plate 52a that supports the image sensor 51 and the housing 53 on one plane, and a flexible substrate having one end connected to the back surface (the surface opposite to the image sensor 51) of the support plate 52a. 52b.
The support plate 52a has a large number of signal transmission pads provided on the front and back surfaces, and is connected to the wire W of the image sensor 51 on one plane side and to the flexible substrate 52b on the back side. I have.
One end of the flexible substrate 52b is connected to the support plate 52a as described above, and the support plate 52a and an external circuit (for example, a higher-level device having an imaging unit mounted thereon) are connected to the support plate 52a via an external output terminal 54 provided at the other end. And a supply of a voltage and a clock signal for driving the image sensor 51 from an external circuit, and a digital YUV signal to an external circuit. Further, the intermediate portion in the longitudinal direction of the flexible substrate 52b has flexibility or deformability, and the deformation gives flexibility to the direction and arrangement of the external output terminals with respect to the support plate 52a.
[0038]
Next, the housing 53 and the imaging optical system 10 will be described. The housing 53 is fixedly mounted on the support plate 52a of the substrate 52 on a plane on which the image sensor 51 is provided, with the image sensor 51 housed inside the image sensor 51 by bonding. The imaging optical system 10 is stored and held inside the housing 53. The housing 53 includes a cylindrical body 55 fixed and attached by adhesive so as to surround the image sensor 51 on the supporting flat plate 52a, and a first lens L1, a second lens L2, and a third lens L3 of the imaging optical system 10 described later. And a lens barrel 21 for storing and supporting the lens.
Then, the lens barrel 21 is screwed into the inside of the cylindrical body 55 to form a connection between them. Further, the lens barrel 21 is formed of a bottomed cylindrical body having an opening at the image sensor 51 side and an opening at the other end, and the end at which the opening is provided. Used for object side. The aperture of the lens barrel 21 is a part of the configuration of the imaging optical system 10 and also forms an aperture stop S that determines the F number of the entire imaging lens system.
[0039]
As shown in FIG. 2, the imaging optical system 10 includes an IR (infrared) cut filter 23 for preventing the incidence of infrared rays from the object side, and an external light shielding mask 26 further disposed on the object side than the IR cut filter 23. An imaging lens arranged in the order of an aperture S, a first lens L1, a second lens L2, and a third lens L3 from the object side, and a lens holder 22 for fixing the lenses L1, L2, L3 in the lens barrel 21. Have.
The imaging optical system 10 is used to form a subject image on a solid-state imaging device such as a CCD using the stop S and the lenses L1, L2, and L3 as optical systems. In FIG. 1, the upper side is the object side, and the lower side is the image side, and the chain line in FIG. 2 is the common optical axis of the lenses L1, L2, L3.
[0040]
The IR cut filter 23 is formed in a rectangular shape, and is held on the object-side end surface of the lens barrel 21 by bonding. The IR cut filter 23 may have a circular shape.
Further, the external light-shielding mask 26 is fixed on the object-side end surface of the lens barrel 21 on the object side of the IR cut filter 23 by bonding. The external light-shielding mask 26 is a light-shielding plate, and an opening through which external light can pass is provided at the center of the light-shielding plate. The external light-shielding mask 26 is provided to minimize the incidence of unnecessary light from the outside.
[0041]
The lenses L1, L2, and L3 are housed inside the lens barrel 21 in a state where the center line of the lens barrel 21 and the optical axes of the lenses L1, L2, and L3 match. The inside of the lens barrel 21 is set such that the inner diameter gradually increases in three stages from the end on the object side to the end on the image sensor side.
[0042]
On the other hand, each of the lenses L1, L2 and L3 is set to a range of an effective diameter having a function as an imaging lens from a center thereof to a predetermined range, and a portion outside the range is a flange portion which does not function as an imaging lens. (The portions indicated by hatching in the lenses L1, L2, and L3). In addition, at the part having the smallest inner diameter on the object side end side of the lens barrel 21, the outer periphery of the flange portion of the first lens L1 is set to be fitted. Therefore, the first lens L1 is held inside the lens barrel 21 by such a structure.
[0043]
Further, a circular concave portion is formed on a surface of the flange portion of the first lens L1 facing the second lens L2. Correspondingly, a convex portion that can be fitted into the concave portion of the first lens L1 is formed on the flange portion of the second lens L2 and on the surface facing the first lens L1. Then, the first lens L1 and the second lens L2 can accurately match their optical axes with the convex portion fitted in the concave portion.
[0044]
Further, the outer diameter of the flange portion of the third lens L3 is set to be larger than the outer diameter of the flange portion of the second lens L2, and the flange portion of the third lens L3 faces the second lens L2. A circular recess is formed on the surface. The inner diameter of the concave portion of the third lens L3 is set so that the outer peripheral portion of the flange portion of the second lens L2 can be fitted. Then, in a state where the second lens L2 is fitted in the concave portion, the optical axes of the third lens L3 and the second lens L2 can be accurately matched with each other.
[0045]
As described above, the lenses L1, L2, and L3 are fitted to each other with the above-described structure with the optical axes aligned. Further, the lens barrel 21 has a structure in which the first lens L1 is supported only by the above-described minimum diameter inner peripheral portion on the bottom surface side, and none of the other inner peripheral portions is in contact with each of the lenses L1, L2, L3. I have.
[0046]
In recent years, in order to reduce the size of the entire imaging device, even with a solid-state imaging device having the same number of pixels, a solid-state imaging device having a small pixel pitch and consequently a small light receiving unit (photoelectric conversion unit) has been developed. . Such an imaging lens for a solid-state imaging device having a small screen size requires a short focal length of the entire system in order to secure the same angle of view. turn into. Therefore, it becomes difficult to process glass lenses manufactured by polishing. Therefore, it is desirable that each of the lenses L1, L2, L3 is formed by injection molding using plastic as a raw material. Further, when it is desired to suppress the image point position fluctuation of the entire imaging lens system at the time of temperature change as an imaging apparatus, it is preferable that the first lens is a glass mold lens.
[0047]
The optical axes of the lenses L1, L2, and L3 are configured to be matched in accordance with the mutual fitting accuracy. Therefore, the lenses L1, L2, and L3 easily coincide with the optical axes of the lenses L1, L2, and L3 within a range of accuracy that can be achieved by injection molding, regardless of the accuracy of the support member of the imaging lens such as the lens barrel 21. Take the structure that can be made. Furthermore, since the axial accuracy of each concave portion and each convex portion of each lens L1, L2, L3 can be made as high as possible by injection molding, the distance between the lenses L1, L2, L3 in the optical axis direction is also predetermined. It is possible to maintain accuracy. For these reasons, it is possible to improve the assembly accuracy of the optical system. Further, assembling is facilitated and productivity is improved.
The detailed specifications of each of the lenses L1, L2, L3 will be described using a plurality of specific examples in embodiments described later.
[0048]
Next, the lens holder 22 is a ring-shaped member made of a light-shielding material, and an opening is provided at a central portion thereof so that light can pass therethrough. The outer diameter of the lens holder 22 is set slightly larger than the inner diameter of the end portion of the lens barrel 21 on the image sensor side, and the lenses L1, L2, and L3 are stored in the lens barrel 21 in a state of being stored in the lens barrel 21. Pressed into. The lens holder 22 is press-fitted toward the object-side end of the lens barrel 21 until the lens holders 22 cannot move so as not to form a gap between the lenses L1, L2, and L3. Then, the fixed state is maintained together with the lenses L1, L2, L3 by the frictional force based on the stress generated between the lens barrel 21 and the lens holder 22.
[0049]
The lens holder 22 only needs to be mounted on the lens barrel 21 in a state where the axial movement of each of the lenses L1, L2, L3 can be regulated, and the means is not limited to the above-described method. For example, at positions where the outer peripheral surface of the lens barrel 21 and the inner peripheral surface of the lens holder 22 are opposed to each other, one of the projections is provided, and the other is provided with a recess to be fitted to the projection. A connection structure that is elastically supported so as to be movable in a direction away from each other, or a thread groove may be provided between them so as to be coupled by screwing.
[0050]
A first light-shielding mask 24 and a second light-shielding mask 25 are arranged between the lenses L1, L2, and L3. The first light-shielding mask 24 is disposed in a circular depression centered on the optical axis provided on the axial front end surface of the convex portion of the second lens L2. The first light-shielding mask 24 has a ring shape, and the inner diameter of the center hole is set slightly smaller than the effective diameter of the imaging lens on the object side of the second lens L2. The first light-shielding mask 24 is arranged in the above-described recess, so that the first lens L1 and the second lens L2 are in a state where the center line thereof is aligned with the optical axis of each of the lenses L1, L2, L3. Held between. Note that the depth of the depression is set slightly deeper than the thickness of the first light shielding mask 24, and does not affect the mutual distance in the fitted state between the first lens L1 and the second lens L2. It has a structure.
[0051]
The second light-shielding mask 25 is disposed in a circular recess centered on the optical axis provided on the inner bottom surface of the concave portion of the third lens L3. The second light-shielding mask 25 also has a ring shape, and the inner diameter of the center hole is set to be slightly smaller than the effective diameter of the imaging lens on the image side of the second lens L2. The second light-shielding mask 25 is arranged in the above-described recess, so that the second lens L2 and the third lens L3 are in a state where the center line thereof is aligned with the optical axes of the lenses L1, L2, and L3. Held between. In this case as well, the depth of the depression is set slightly deeper than the thickness of the second light shielding mask 25, and the distance between the second lens L2 and the third lens L3 in the fitted state is set. It does not affect the structure.
[0052]
The interaction between the stop S and each of the light-shielding masks 24 and 25 prevents light incident from the stop S from entering outside the effective diameter of the imaging lenses of the lenses L1, L2, and L3, thereby preventing ghost and flare. Can be suppressed.
[0053]
A usage mode of the above-described imaging unit 50 will be described. FIG. 3 shows a state in which the imaging unit 50 is mounted on a mobile terminal 100 as a mobile terminal or an imaging device. FIG. 4 is a control block diagram of the mobile phone 100.
The imaging unit 50 is provided, for example, at a position where the object-side end surface of the housing 53 in the imaging optical system is provided on the back surface of the mobile phone 100 (the liquid crystal display unit side is the front) and below the liquid crystal display unit. Is done.
The external connection terminal 54 of the imaging unit 50 is connected to the control unit 101 of the mobile phone 100 and outputs an image signal such as a luminance signal and a color difference signal to the control unit 101.
On the other hand, as shown in FIG. 4, the mobile phone 100 controls a whole unit, controls a unit (CPU) 101 that executes a program corresponding to each process, and supports and inputs numbers and the like with keys. An input unit 60, a display unit 70 that displays captured images in addition to predetermined data, a wireless communication unit 80 for realizing various types of information communication with an external server, a system program of the mobile phone 100, A storage unit (ROM) 91 storing various processing programs and necessary data such as a terminal ID, and various processing programs and data to be executed by the control unit 101, or processing data, or imaging data and the like by the imaging unit 50 And a temporary storage unit (RAM) 92 which is used as a work area for temporarily storing.
Then, the image signal input from the imaging unit 50 is stored in the storage unit 92 or displayed on the display unit 70 by the control system of the mobile phone 100, and further, the video information is transmitted via the wireless communication unit 80. Sent to the outside.
[0054]
【Example】
Next, the specifications of the imaging lens will be described based on Examples 1 to 7, but each specification is not limited thereto. Here, the symbols used in each embodiment are as follows.
f: focal length
fB: Back focus
F: F number
2Y: diagonal length of effective screen (diagonal length on rectangular light receiving surface of solid-state imaging device)
R: radius of curvature of the refraction surface
D: Refraction surface spacing
Nd: refractive index of the imaging lens material at d-line
νd: Abbe number of imaging lens material
[0055]
In each embodiment, the shape of the aspheric surface is such that, in an orthogonal coordinate system in which the vertex of the surface is the origin and the optical axis direction is the X axis, the vertex curvature is C, the conic constant is K, and the aspheric coefficients are A4 and A6. A8, A10, and A12 are represented by the following “Formula 1”.
[0056]
(Equation 1)

[0057]
(First embodiment)
Tables 1, 2 and 3 show the imaging lens data.
[0058]
[Table 1]

[0059]
[Table 2]

[0060]
[Table 3]

[0061]
FIG. 5 is an explanatory diagram showing the arrangement of the imaging lenses of the first embodiment. In the figure, L1 denotes a first lens, L2 denotes a second lens, L3 denotes a third lens, and S denotes an aperture stop. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the first embodiment.
The first lens L1 and the third lens L3 are polyolefin-based plastic lenses, and have a saturated water absorption of 0.01% or less. The second lens L2 is a polycarbonate plastic lens having a saturated water absorption of 0.4%.
[0062]
(Example 2)
Tables 4, 5, and 6 show the imaging lens data.
[0063]
[Table 4]

[0064]
[Table 5]

[0065]
[Table 6]

[0066]
FIG. 7 is an explanatory diagram illustrating the arrangement of the imaging lenses according to the second embodiment. In the figure, L1 denotes a first lens, L2 denotes a second lens, L3 denotes a third lens, and S denotes an aperture stop. FIG. 8 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the first embodiment.
The first lens L1 and the third lens L3 are acrylic plastic lenses and have a saturated water absorption of 1.3%. The second lens L2 is a polycarbonate plastic lens having a saturated water absorption of 0.4%.
[0067]
(Example 3)
Tables 7, 8, and 9 show the lens data.
[0068]
[Table 7]

[0069]
[Table 8]

[0070]
[Table 9]

[0071]
FIG. 9 is an explanatory diagram illustrating the arrangement of the imaging lenses according to the third embodiment. In the figure, L1 denotes a first lens, L2 denotes a second lens, L3 denotes a third lens, and S denotes an aperture stop. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the first embodiment.
The first lens L1 and the third lens L3 are acrylic plastic lenses and have a saturated water absorption of 1.3%. The second lens L2 is a polycarbonate plastic lens having a saturated water absorption of 0.4%. This embodiment is a design example in which a parallel flat plate corresponding to a low-pass filter made of quartz is arranged closest to the image side.
[0072]
(Example 4)
Tables 10, 11, and 12 show the imaging lens data.
[0073]
[Table 10]

[0074]
[Table 11]

[0075]
[Table 12]

[0076]
FIG. 11 is a sectional view of the imaging lens of the fourth embodiment. In the figure, L1 denotes a first lens, L2 denotes a second lens, L3 denotes a third lens, and S denotes an aperture stop. FIG. 12 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the first embodiment.
The first lens L1 and the third lens L3 are polyolefin-based plastic lenses, and have a saturated water absorption of 0.01% or less. The second lens L2 is a polycarbonate plastic lens having a saturated water absorption of 0.4%.
[0077]
(Fifth embodiment)
Tables 13, 14, and 15 show the imaging lens data.
[0078]
[Table 13]

[0079]
[Table 14]

[0080]
[Table 15]

[0081]
FIG. 13 is an explanatory diagram showing the arrangement of the imaging lenses of the fifth embodiment. In the figure, L1 denotes a first lens, L2 denotes a second lens, L3 denotes a third lens, and S denotes an aperture stop. FIG. 14 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the fifth embodiment.
The first lens L1 is a glass lens. The second lens L2 is a polyester plastic lens having a saturated water absorption of 0.7%, and the third lens L3 is a polyolefin plastic lens having a saturated water absorption of 0.01% or less.
This embodiment is a design example in which an infrared cut filter and a parallel flat plate equivalent to a seal glass of a solid-state imaging device are arranged closest to the image.
[0082]
(Sixth embodiment)
Tables 16, 17, and 18 show the imaging lens data.
[0083]
[Table 16]

[0084]
[Table 17]

[0085]
[Table 18]

[0086]
FIG. 15 is an explanatory diagram showing the arrangement of the imaging lenses of the sixth embodiment. In the figure, L1 denotes a first lens, L2 denotes a second lens, L3 denotes a third lens, and S denotes an aperture stop. FIG. 16 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the sixth embodiment.
The first lens L1 is a glass lens. The second lens L2 is a polyester plastic lens having a saturated water absorption of 0.7%, and the third lens L3 is a polyolefin plastic lens having a saturated water absorption of 0.01% or less.
This embodiment is a design example in which an infrared cut filter and a parallel flat plate equivalent to a seal glass of a solid-state imaging device are arranged closest to the image.
[0087]
(Seventh embodiment)
Tables 19, 20, and 21 show the imaging lens data.
[0088]
[Table 19]

[0089]
[Table 20]

[0090]
[Table 21]

[0091]
FIG. 17 is an explanatory diagram showing the arrangement of the imaging lenses of the seventh embodiment. In the figure, L1 denotes a first lens, L2 denotes a second lens, L3 denotes a third lens, and S denotes an aperture stop. FIG. 18 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the seventh embodiment.
The first lens L1 and the third lens L3 are polyolefin-based plastic lenses and have a saturated water absorption of 0.01% or less. The second lens L2 is a polyester-based plastic lens having a saturated water absorption of 0.7%.
This embodiment is a design example in which an infrared cut filter and a parallel flat plate equivalent to a seal glass of a solid-state imaging device are arranged closest to the image.
[0092]
In this embodiment, the telecentric characteristic of the image-side light beam is not always sufficiently designed. The telecentric characteristic means that the principal ray of the luminous flux for each image point becomes almost parallel to the optical axis after exiting the final surface of the imaging lens. In other words, the exit pupil position of the optical system is sufficiently separated from the image plane. That is. When the telecentric characteristic is deteriorated, a light beam is obliquely incident on the solid-state imaging device, and a phenomenon (shading) in which the aperture efficiency is substantially reduced at the periphery of the screen occurs, resulting in insufficient peripheral light quantity. However, with the recent technology, the above-described shading phenomenon can be reduced by reviewing the arrangement of the color filters of the solid-state imaging device and the microlens array. Therefore, the present embodiment is a design example aiming at further miniaturization for the part where the requirement of the telecentric characteristic is relaxed.
[0093]
【The invention's effect】
According to the first aspect of the invention, since the exit pupil position can be kept away from the image plane by disposing the aperture stop closest to the object side, for example, when the present invention is used as an imaging lens for a solid-state imaging device In addition, the image side telecentric characteristic required for the solid-state imaging device can be secured well.
Further, in the present invention, since the positive biconvex first lens having relatively large refractive power and the negative second lens are arranged in front of the object side, the overall length of the imaging lens can be reduced. I have.
[0094]
By forming the first lens in a biconvex shape, spherical aberration generated when a lens having a large refractive power is used as the first lens is reduced.
Furthermore, by directing the concave surface of the negative second lens toward the first lens, it is possible to arrange the first lens close to the convex surface, thereby correcting various aberrations such as spherical aberration, coma aberration, and chromatic aberration. Can be performed satisfactorily and easily.
In addition, since the third lens has a meniscus shape with the convex surface facing the object side, it is possible to ensure good telecentric characteristics particularly at the image-side peripheral portion of the screen.
[0095]
As described above, according to the present invention, an imaging lens that can effectively reduce various aberrations such as spherical aberration, coma, and chromatic aberration, and achieves downsizing in the optical axis direction while maintaining good telecentric characteristics is provided. It becomes possible.
[0096]
According to the second aspect of the present invention, since the third lens has a configuration having a positive refractive power, a so-called triplet type imaging lens configuration is provided, and it is possible to correct off-axis aberrations such as distortion and secure telecentric characteristics. This can be performed more easily.
[0097]
According to the third aspect of the present invention, spherical aberration and coma can be corrected by using an aspheric surface for the first positive lens, and coma and astigmatism can be corrected by using an aspheric surface for the negative second lens. Correction becomes possible.
Furthermore, the positive third lens uses the difference between the passing height of the on-axis ray and the marginal ray caused by disposing it at the position closest to the image plane to reduce various aberrations at the periphery of the screen to on-axis performance. The correction can be made by the aspherical surface without affecting. In particular, it becomes possible to effectively correct pincushion-type distortion and field curvature that occur when the negative refractive power of the second lens is set strong. In other words, it is possible to enhance the negative refractive power of the second lens.
Therefore, the present invention enables better aberration correction.
[0098]
According to a fourth aspect of the present invention, the total length of the imaging lens can be shortened by defining the total length of the imaging lens and setting the value to be less than the upper limit value by the conditional expression (1) for achieving miniaturization. The outer diameter of the lens can be reduced. Therefore, this makes it possible to reduce the size and weight of the entire imaging device.
Further, in accordance with the conditional expression (2) for defining the refractive power of the first positive lens, by setting the lower limit value to be exceeded, the increase in the positive refractive power of the first lens is suppressed, and the first lens is generated. It is possible to suppress spherical aberration and coma aberration to a small value. Since the radius of curvature does not become extremely small, it is preferable from the viewpoint of workability of the imaging lens. On the other hand, by setting the value to be less than the upper limit value of the expression (2), an excessive decrease in the positive refractive power of the first lens is suppressed, which is advantageous for reducing the overall length of the imaging lens.
[0099]
According to conditional expression (3) for defining the refractive power of the positive third lens, by setting the lower limit to be larger than the lower limit, the positive refractive power of the third lens is prevented from excessively increasing. Positive refractive power distribution with the first lens is appropriate, and the overall length of the imaging lens can be reduced. On the other hand, by setting the value below the upper limit, an excessive decrease in the positive refractive power of the third lens can be prevented, distortion can be corrected well, and the telecentric characteristic of the image-side luminous flux can be secured. It becomes possible.
[0100]
According to the fifth aspect of the present invention, by satisfying the conditional expression (4), the negative refracting power on the object side of the second lens does not become excessive, and the occurrence of the coma flare of the off-axis light beam can be suppressed. Can be obtained.
Further, since the negative refractive power on the object surface side of the second lens is appropriately maintained, the positive Petzval sum is reduced, the field curvature is easily corrected, and the spherical aberration generated by the positive first lens is obtained. And coma can be satisfactorily corrected.
[0101]
According to a sixth aspect of the present invention, axial chromatic aberration and chromatic aberration of magnification are corrected in a well-balanced manner by setting the lower limit of conditional expression (5) for chromatic aberration correction of the first positive lens and the negative second lens. It is possible to do.
[0102]
According to the seventh aspect of the present invention, since the first lens, the second lens, and the third lens are all made of plastic lenses manufactured by injection molding, even if the lens has a small radius of curvature or outside diameter, it is polished. Mass production is possible compared to glass lenses manufactured by processing.
In addition, since the plastic lens can be easily made aspherical, it can be easily and accurately performed near the aberration correction.
Another advantage of using a plastic lens is that since the shape of the flange portion outside the effective diameter of the imaging lens can be freely designed, the number of mounting components can be reduced, thereby effectively reducing mounting errors. It is possible to improve the assembling accuracy of the optical system, for example, by adopting a structure in which the optical axis of each lens can be easily matched using the inner diameter portion or the outer diameter portion of the flange portion. . Further, assembling is facilitated and productivity is improved.
[0103]
According to the eighth aspect of the present invention, for each lens, by using a plastic material having a saturated water absorption of 0.7% or less, non-uniformity of the refractive index due to a sudden change in humidity is suppressed, and better imaging performance is achieved. , While also obtaining the advantages of the plastic lens.
[0104]
According to the ninth aspect of the present invention, a light-shielding mask that regulates a peripheral light beam is disposed at at least one of the distance between the first and second lenses or the distance between the second and third lenses. Even when a flange portion is provided on the outer periphery of any of the lenses, it is possible to pass only a light beam necessary for image formation and minimize the incidence of light on the flange portion. Therefore, it is possible to suppress the occurrence of ghost and flare due to the presence of the flange portion. For this reason, according to the arrangement of the light shielding mask, it is possible to positively provide a flange portion on the outer periphery of the lens for facilitating attachment and positioning of the first to third lenses.
[0105]
According to the tenth aspect of the present invention, since the first lens is made of a glass material, the change in the refractive index of the first lens when the temperature changes can be ignored, and the change in the image point position when the temperature changes in the entire imaging lens system can be reduced. It can be suppressed.
Further, since the second and third lenses are made of a plastic material, the shape of the flange portion outside the effective diameter of the imaging lens can be freely designed by integral molding. If the flange portions of the lenses can be freely fitted to each other, it is possible to adopt a structure in which the optical axes of a plurality of lenses can be easily matched. Further, when the flange is configured to define the distance between the lenses, the spacer is not required, and the number of components can be reduced to improve the productivity.
In addition, since the lens is formed of a plastic material, an aspherical surface can be easily formed on the lens, and aberration correction can be easily performed.
Therefore, it is possible to reduce the size, weight, and cost, which are the effects provided by the plastic material, while reducing the influence of the plastic material.
In addition, by using a glass lens as the first lens, it is not necessary to expose a plastic lens that is easily damaged, thereby improving maintainability.
[0106]
According to the eleventh aspect of the present invention, by setting the conditional expression (6) to be satisfied, the synthetic focal length of the plastic lens is set large to suppress the total refractive power small, and the image point position variation due to temperature change is reduced. It is possible to keep it small.
[0107]
According to the twelfth aspect of the present invention, the use of a plastic material having a saturated water absorption of 0.7% or less for the second and third lenses suppresses non-uniformity of the refractive index due to a rapid change in humidity, and is more favorable. It is possible to obtain the advantages of a plastic lens while maintaining excellent imaging performance.
[0108]
According to a thirteenth aspect of the present invention, the light-shielding mask for regulating the peripheral light beam is arranged at at least one of the interval between the first and second lenses or the interval between the second and third lenses. Even when a flange portion is provided on the outer peripheral portion of any of the second and third lenses, it is possible to suppress the occurrence of ghost and flare due to the presence of the flange portion. For this reason, according to the arrangement of the light-shielding mask, it is possible to positively provide a flange portion on the outer periphery of the lens to facilitate attachment and positioning of the second and third lenses.
[0109]
According to the fourteenth aspect, by mounting an imaging lens capable of realizing each of the effects described above, it is possible to provide an imaging apparatus having advantages such as miniaturization, weight reduction, and high image quality. .
[0110]
According to the fifteenth aspect, by mounting an imaging lens capable of realizing the above-described effects, it is possible to provide an imaging unit having advantages such as miniaturization, weight reduction, and high image quality. .
[0111]
According to the sixteenth aspect of the present invention, it is possible to provide a portable terminal capable of high-quality imaging while reducing the size and weight by mounting an imaging unit capable of realizing the above-described effects. It is.
[Brief description of the drawings]
FIG. 1 is a perspective view of an imaging unit according to an embodiment of the present invention.
FIG. 2 is a sectional view showing a section including an optical axis of each lens of the imaging lens unit according to the embodiment of the present invention.
3A is a front view of a mobile phone to which an imaging unit is applied, and FIG. 3B is a rear view of the mobile phone to which the imaging unit is applied.
FIG. 4 is a control block diagram of the mobile phone of FIG. 3;
FIG. 5 is an explanatory diagram illustrating a lens arrangement according to the first embodiment.
FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the first embodiment.
FIG. 7 is an explanatory diagram illustrating an arrangement of imaging lenses according to a second embodiment.
8 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of Example 2. FIG.
FIG. 9 is an explanatory diagram illustrating an arrangement of imaging lenses according to a third embodiment.
FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the third embodiment.
FIG. 11 is an explanatory diagram illustrating an image pickup lens arrangement according to a fourth embodiment.
12 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of Example 4. FIG.
FIG. 13 is an explanatory diagram illustrating an arrangement of an imaging lens according to a fifth embodiment.
14 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of Example 5. FIG.
FIG. 15 is an explanatory diagram illustrating an imaging lens arrangement according to a sixth embodiment.
16 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of Example 6. FIG.
FIG. 17 is an explanatory diagram illustrating an arrangement of an imaging lens according to a seventh embodiment.
FIG. 18 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the seventh embodiment.
[Explanation of symbols]
10. Imaging optical system (imaging lens)
50 Imaging unit
100 Mobile phone (mobile terminal)
L1 First lens
L2 Second lens
L3 Third lens
S aperture stop

Claims (16)

In order from the object side, an aperture stop, a biconvex first lens having a positive refractive power, a second lens having a negative refractive power and having a concave surface facing the object side, and having a convex surface facing the object side An imaging lens, wherein a third lens having a meniscus shape is arranged. The imaging lens according to claim 1, wherein the third lens has a positive refractive power. The imaging lens according to claim 1, wherein each of the first lens, the second lens, and the third lens has an aspheric surface on at least one of the surfaces. The distance on the optical axis from the aperture stop to the image-side focal point is L, the effective screen diagonal length is 2Y, the focal length of the first lens is f1, the focal length of the third lens is f3, and the focal point of the entire imaging lens system. 4. The imaging lens according to claim 1, wherein the following conditional expressions (1) to (3) are satisfied when the distance is f.
L / 2Y <1.50 (1)
0.50 <f1 / f <0.95 (2)
1.00 <f3 / f <1.40 (3) When the refractive index of the second lens with respect to the d-line is N2, the radius of curvature of the object side surface of the second lens is R3, and the focal length of the entire imaging lens system is f, the following conditional expression (4) is satisfied. The imaging lens according to claim 1, 2, 3, or 4, wherein:
−0.60 <R3 / ((N2-1) · f) <− 0.20 (4) The conditional expression (5) below is satisfied when the Abbe number of the first lens is ν1 and the Abbe number of the second lens is ν2. The imaging lens according to the above.
25 <ν1-ν2 (5) 7. The imaging lens according to claim 1, wherein each of the first, second, and third lenses is formed of a plastic material. The imaging lens according to claim 7, wherein each of the first, second, and third lenses is formed of a plastic material having a saturated water absorption of 0.7% or less. 9. A light-shielding mask for regulating a peripheral light beam is arranged at at least one of the distance between the first lens and the second lens or the distance between the second lens and the third lens. Imaging lens. The first lens is made of a glass material,
7. The imaging lens according to claim 1, wherein each of the second and third lenses is formed of a plastic material. The imaging lens according to claim 10, wherein the following conditional expression (6) is satisfied, where f23 is the combined focal length of the second and third lenses, and f is the focal length of the entire imaging lens system. .
f / | f23 | <0.4 (6) 12. The imaging lens according to claim 10, wherein each of the second and third lenses is formed of a plastic material having a saturated water absorption of 0.7% or less. 12. A light-shielding mask for regulating a peripheral light beam is arranged at at least one of the distance between the first lens and the second lens or the distance between the second lens and the third lens. 13. The imaging lens according to 12. A solid-state imaging device having a photoelectric conversion unit,
An imaging apparatus comprising: the imaging lens according to any one of claims 1 to 13 for forming a subject image on the photoelectric conversion unit of the solid-state imaging device. A solid-state imaging device having a photoelectric conversion unit,
An imaging lens according to any one of claims 1 to 13, for forming a subject image on the photoelectric conversion unit of the solid-state imaging device,
A substrate having an external connection terminal for transmitting and receiving an electric signal while holding the solid-state imaging device,
An imaging unit in which a housing having an opening for light incidence from the object side and made of a light shielding member is integrally formed,
The height of the imaging unit in the direction of the optical axis of the imaging lens is 10 [mm] or less. A mobile terminal comprising the imaging unit according to claim 15.

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