JP2004061910A

JP2004061910A - Zoom lens provided with vibration-proofing function

Info

Publication number: JP2004061910A
Application number: JP2002220903A
Authority: JP
Inventors: Hiroshi Endo; 遠藤　宏志
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2002-07-30
Filing date: 2002-07-30
Publication date: 2004-02-26

Abstract

<P>PROBLEM TO BE SOLVED: To achieve an ultra-wide angle zoom lens provided with a vibration-proofing function of a 17-40/4 class. <P>SOLUTION: In the configuration having four lens groups of negative, positive, negative, and positive refracting power successively from an object side, vibration-proofing is performed by dividing the second positive lens group to a positive front group and a positive rear group, and moving the front group to a direction perpendicular to an optical axis. An aspheric surface is used for the second group. The front group and the rear group do not change the interval during variable magnification and focusing. The first negative lens group is divided to the negative front group and the negative rear group and focusing is performed by the rear group. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明はズームレンズに関し、特に一眼レフカメラ等のスティルカメラおよび電子スティルカメラに好適であり、防振機能を有し、超広角域をカバーした高変倍で良好な光学性能を有したズームレンズに関する。
【０００２】
【従来の技術】
進行中の車等移動物体上からの撮影では撮影系に振動が伝わり撮影画像にブレが生じる。また焦点距離の長いレンズやＦＮｏの大きいレンズでの手持ち撮影では手ブレにより、撮影画像にブレが生じることがある。近年、これらのブレを光学的または電気的に補正した銀塩カメラやビデオカメラが発売されている。
【０００３】
従来より防振機能を有したズームレンズとして、特開平５−２３２４１０号公報（キヤノンＬ５８）従来例１や特開平９−２３０２４２号公報（ニコン２群内防振）従来例２、特開平９―１１３８０８（ニコン２群内防振）従来例３等があった。従来例１は、物体側より順に正、負、正、正の屈折力の第１〜４レンズ群で構成された望遠ズームレンズであり、第２群を光軸と垂直方向に移動して防振を行っており、従来例２及び従来例３は、３５ｍｍ一眼レフカメラ換算で２８ｍｍから８５ｍｍの焦点距離をカバーした大口径標準ズームレンズであり、物体側より順に負、正、負、正のレンズ群より構成され第２レンズ群を正の前群と正の後群に分割し、前記前群でフォーカシングを行い、且つ該前群を光軸と垂直方向に変位させて防振を行ったものである。
【０００４】
【発明が解決しようとする課題】
本発明は、３５ｍｍ一眼レフカメラ換算で焦点距離１７ｍｍ程度の超広角域から４０ｍｍ程度の標準域までをカバーし、防振機能を有する、コンパクトで、特に防振時の収差も良好に補正されたズームレンズを提供することが目的である。
【０００５】
【課題を解決するための手段】
本発明は、物体側より順に負の屈折力の第１レンズ群と正の屈折力の第２レンズ群と負の屈折力の第３レンズ群と正の屈折力の第４レンズ群を有し、各群の間隔を変化させて変倍を行うズームレンズに於いて、前記第２レンズ群を複数のレンズ群に分割し、前記分割されたレンズ群中、正の屈折力の第２ａ群を光軸と略垂直方向に移動することで防振を行い、以下の条件式を満足することを特徴としている。
【０００６】
Ｄ１Ｗ　　　＞　　Ｄ１Ｔ　　　　　　　　　　…（イ）
Ｄ２Ｗ　　　＜　　Ｄ２Ｔ　　　　　　　　　　　　　　　　　　　…（ロ）
Ｄ３Ｗ　　　＜　　Ｄ３Ｔ　　　　　　　　　　　　　　　　　　　…（ハ）
０．４　　＜　ＴＳ２ａＷ　＜　１　　　　　　　　　　　…（１）
０．７　　＜　ＴＳ２ａＴ　　＜　１．５　　　…（２）
ここで、ＤｉＷ、ＤｉＴは各々広角端、望遠端での第ｉ群と第（ｉ＋１）群との間隔、ＴＳ２ａＷ、ＴＳ２ａＴは各々第２ａ群の広角端および望遠端での偏芯敏感度である。
【０００７】
この他、本発明の特徴は実施例において開示している。
【０００８】
【発明の実施の形態】
以下、実施例に基づいて本発明の詳細な説明をする。
【０００９】
図１〜図４は各々後述する数値実施例１〜４のズームレンズのレンズ断面図、図５〜図８は各々後述する数値実施例１〜４のズームレンズの縦収差図、図９〜図１２は各々後述する数値実施例１〜４のズームレンズの横収差図である。
【００１０】
図中、Ｉ〜ＩＶは各々、負、正、負、正の屈折力の第１レンズ群〜第４レンズ群、ＩＩａ、ＩＩｂは各々第２ａ群、第２ｂ群であり、Ｓは開口絞り、ＳＦはフレアーカッター、矢印は広角端から望遠端へ変倍する際の各レンズ群の移動軌跡を示している。広角端から望遠端の変倍に際して、条件式（イ）〜（ハ）を満足するように、各レンズ群が移動しており、絞りは第３群と一体で移動している。
【００１１】
広角端から望遠端への変倍に際して、条件式（イ）を満足しつつ第１レンズ群が像側へ凸の軌跡を描いて移動し、第２レンズ群と第４レンズ群が一体で像側へ移動し、条件式（ロ）、（ハ）を満足するように第３レンズ群が移動している。条件式（ロ）、（ハ）を満足するように第３レンズ群が移動することで、第２レンズ群から第４レンズ群までの合成の主点位置を物体側に移動させることで、条件式（イ）を満足した各レンズ群の移動による変倍効果を大きくし、コンパクトで高変倍なズームレンズの達成を可能としている。
【００１２】
また、本実施例のズームタイプは、第２レンズ群さらに詳しくは第２レンズ群中最も像側のレンズ群と第４レンズ群の製造誤差に起因する相対的な偏芯及び傾きによる光学性能の劣化が著しく発生する。従って、変倍時、第２レンズ群と第４レンズ群が別々の軌跡で移動すると鏡筒構造上偏芯及び倒れが発生するのが避けられず光学性能の劣化の原因の一つとなる。そこで、本実施例では、第２レンズ群さらに詳しくは第２レンズ群の最も像側のレンズ群と第４レンズ群を同一軌跡で移動させることにより、第２レンズ群と第４レンズ群を一体とした鏡筒構造とすることを可能としている。これにより前記製造誤差要因に起因する光学性能の劣化を小さく抑えることを可能としている。
【００１３】
また、本実施例では、前記第２レンズ群を正の屈折力の第２ａ群と正の屈折力の第２ｂ群に分割し、条件式（１）、（２）を満足する屈折力配置とし、前記第２ａ群を光軸と略垂直に移動させて防振を行っている。条件式（１）、（２）はどちらも第２ａ群すなわち防振レンズ群の光軸と垂直な方向の移動に対する像面の光軸と垂直な方向への移動量すなわち偏芯敏感度を規定したものである。条件式（１）、（２）の下限値を越えて偏芯敏感度が小さくなると防振のための防振レンズ群の変位が大きくなり、この変位を満足するための防振駆動装置が大型化し、このためレンズ外径が大きくなり好ましくない。条件式（１）、（２）の上限値を越えて偏芯敏感度が大きくなると防振駆動装置の小型化には有利であるが、防振レンズ群の正の屈折力が強くなるため第２レンズ群で発生する諸収差が増大し、広角端から望遠端への変倍および防振時の収差をバランス良く補正することが困難となる。
【００１４】
さらに本実施例では、防振レンズ群を１枚の負レンズと１枚の正レンズの接合レンズで構成し、
１．１　＜　ＥＡＩＳ　／　ＥＡｍｉｎ　　＜　１．３　　　・・・（３）
なる条件式を満足している。ここで、ＥＡＩＳは防振レンズ群の光線有効径の最大値であり、ＥＡｍｉｎは光学系中最小の光線有効径である。従来より防振レンズ群の駆動装置として、コイルとマグネットによる磁力を利用したものが知られている。（特開平２０００−１９５７７等参照。）該駆動装置の小型化及び省電力化のために、防振レンズ群の軽量化が求められている。このため防振レンズ群のレンズ枚数を極力少なくし、レンズ外径も小型化する必要がある。条件式（３）は防振レンズ群の光線有効径を規定するものであり、下限値を超えて有効径が小さくなると所定のスペックのズームレンズを達成不可となり、上限値を超えて有効径が大きくなると前記駆動装置が大型となり好ましくない。
また、本実施例では、第２レンズ群に非球面を用いることで第２ａ群（防振レンズ群）の球面収差係数を小さくすることができ、防振時の光学性能を良好に補正することを可能としている。
【００１５】
また、第４レンズ群に、中心から周辺へ行くに従って正の屈折力が弱くなる形状の非球面を用いることで、広角ズームレンズで問題となる最大像高付近の像面湾曲を良好に補正可能としている。
【００１６】
実施例２では、無限遠から至近へのフォーカシングを第２ａ群を像面側へ移動させて行っている。
【００１７】
実施例１、３、４では、無限遠から至近へのフォーカシングを第１ｂ群を物体側へ移動させて行っている。このようにインナーフォーカスとすることでオートフォーカスの際、フォーカスアクチュエータにかかる負荷を小さくし迅速な駆動と省電力を可能としている。また、実施例１、３、４では、
１．５＜　　ＥＳｆＴ　　＜３．５　　　　　　・・・（４）
０．９５＜ＥＳｆＴ×ｆＷ＾２／（ＥＳｆＷ×ｆＴ＾２）＜１．０５　・・・（５）
なる条件式を満足させている。
【００１８】
条件式（４）は同一物体距離におけるデフォーカス量が最も大きい焦点距離であるテレ端でのフォーカス群の位置敏感度を規定するものであり、下限値を超えて敏感度が小さくなるとフォーカシングのためのフォーカスレンズ群の移動量が大きくなり、レンズ系が大きくなり迅速なオートフォーカスが出来なくなってくる。上限値を超えて敏感度が大きくなることは第２群より物体側のレンズ群の屈折力が強くなることになり、収差補正が困難となる。条件式（５）は各焦点距離において同一物体距離へのフォーカシングの際のフォーカスレンズの移動量を一定とするためのものであり、条件式を外れると前記繰り出し量が焦点距離によってことなってしまう。このように前記繰り出し量を一定とすることで、レンズ鏡筒のフォーカス機構を簡単にできる。さらに、防振とフォーカシングを異なったレンズ群で行うことで鏡筒構造を簡略化できる。
【００１９】
さらに、本実施例では、第１レンズ群を２枚の負レンズと１枚の正レンズより構成し、最も物体側の負レンズに光軸中心から周辺へ行くに従って正の屈折力が強くなる形状の非球面を用い、第２レンズ群を１枚の負レンズと２枚の正レンズで構成し、第３レンズ群を２枚の負レンズと１枚の正レンズで構成し、第４レンズ群を１枚または２枚の負レンズと２枚の正レンズで構成し、以下の条件式を満足させている。
【００２０】
０．７　　＜｜ｆ１Ｗ｜／√（ｆＷ×ｆＴ）＜０．９　　　　・・・（６）
０．９８　＜　　　ｆ２Ｗ／√（ｆＷ×ｆＴ）　＜１．２５　　・・・（７）
１．４　　＜　｜ｆ３｜／√（ｆＷ×ｆＴ）　＜２．５　　・・・（８）
１．４　　＜　　　　　ｆ４／√（ｆＷ×ｆＴ）　＜２．　　　　・・・（９）
２．５　＜　　ｆ２ａ　／　ｆ２Ｗ　　　　　　　　＜　３．５　　　・・・（１０）
４．５　　＜　　ＯＴＬＷ／√（ｆＷ×ｆＴ）　＜　７　　　　　　　　・・・（１１）
ここで、ｆＷ、ｆＴは各々広角端、望遠端での全系の焦点距離、ｆ１Ｗ、ｆ２Ｗは広角端での第１レンズ群および第２レンズ群の焦点距離、ｆ３、ｆ４は第３レンズ群および第４レンズ群の焦点距離、ｆ２ａは第２ａ群の焦点距離、ＯＴＬＷは広角端での光学全長である。
【００２１】
第１レンズ群に前述の非球面を用いることで特に広角側で発生する樽型の歪曲を補正している。
【００２２】
条件式（６）は全系の広角端と望遠端の焦点距離の積の平方根に対し広角端での第１レンズ群の焦点距離の範囲を規定するものである。下限値を超えて広角端での第１レンズ群の負の屈折力が強くなると、第１レンズ群で発生する諸収差が大きくなり、これを他のレンズ群でバランス良く補正することが困難となる。又、上限値を超えて第１レンズ群の負の屈折力が弱くなると、収差補正上は有利だがレンズ系が大きくなり好ましくない。条件式（７）は全系の広角端と望遠端の焦点距離の積の平方根に対し広角端での第２レンズ群の焦点距離の範囲を規定するものである。下限値を超えて第２レンズ群の正の屈折力が強くなると、全長の短縮、絞り径の小型化には有利だが、第２レンズ群で発生する球面収差等諸収差が大きくなり、これをバランス良く他のレンズ群で補正することが困耕となる。又、上限値を超えて第２レンズ群の正の屈折力が弱くなると、収差補正には有利だがレンズ系が増大してくる。
【００２３】
条件式（８），（９）は、各々、全系の広角端と望遠端の焦点距離の積の平方根に対し第３レンズ群、第４レンズ群の焦点距離の範囲を規定するものであり、コンパクト化と高性能を両立させるためのものである。どちらも下限値を超えて第３レンズ群、第４レンズ群の屈折力が強くなると、第３レンズ群、第４レンズ群での球面収差、コマ収差、非点収差が大きく発生し、これらをバランス良く補正することが困難となる。又、上限値を超えて第３レンズ群、第４レンズ群の屈折力が弱くなると、レンズ全長が長くなってしまう。条件式（１０）は第２正レンズ群の焦点距離に対し第２ａ群すなわち防振レンズ群の焦点距離の範囲を規定するものである。下限値を超えて第２ａ群の正の屈折力が強くなると防振敏感度が大きくなり防振駆動装置を小型化できる利点があるが第２ａ群で発生する諸収差の発生が大きくなりこれをバランス良く他のレンズ群で補正することが困難となる。
【００２４】
上限値を超えて第２ａ群の正の屈折力が弱くなると防振敏感度が小さくなり所定の防振角度を満足するために防振駆動装置が大型化し好ましくない。ここで、防振敏感度とは、手振れ前の物点と最も物体側のレンズ面の光軸中心を結んだ軸と手振れ時の物点と最も物体側のレンズ面の光軸中心を結んだ軸との角度を防振角としたとき、防振レンズ群すなわち第２ａ群の光軸と垂直方向への移動量１ｍｍあたりの防振角である。条件式（１１）は全系の広角端と望遠端の焦点距離の積の平方根に対し広角端、物体距離無限遠での最も物体側のレンズ面から像面までの長さ、すなわち、光学全長を規定したものである。本実施例では最も像面側のレンズ面と像面との間にクイックリターンミラー及びまたはその他の部材を配置することを想定しており、これら部材を配置するためのスペースが必要となる。そのためレンズ系をテレフォトタイプとしバックフォーカスを長くしている。条件式（１１）の下限値を超えて広角端での光学全長が短くなると所定の変倍比を達成しつつバックフォーカスを確保することが困難となってくる。条件式（１１）の上限値を超えて広角端での光学全長が長くなるとバックフォーカスの確保及び収差補正に関しては有利となるがレンズ全長が長くなるため好ましくない。
【００２５】
（数値実施例）
次に、本発明の実施形態１〜４に各々対応する数値実施例１〜４を示す。各数値実施例においてｉは物体側からの光学面の順序を示し、ｒｉは第ｉ番目の光学面（第ｉ面）の曲率半径、ｄｉは第ｉ面と第ｉ＋１面との間の間隔、ｎｉとνｉはそれぞれｄ線に対する第ｉ番目の光学部材の屈折率、アッベ数を示す。ｆは焦点距離、ＦＮｏはＦナンバー、ωは半画角である。Ｓｋｉｎｆはフレアー絞りから像面までの距離である。ｂ、ｃ、ｄ、ｅを非球面係数、光軸からの高さｈの位置での光軸方向の変位を面頂点を基準にしてｘとするとき、非球面形状は、
ｘ＝（ｈ^２／Ｒ）／［１＋［１−（ｈ／Ｒ）^２］^１／２］＋ｂｈ^４＋ｃｈ^６＋ｄｈ^８＋ｅｈ^１０
で表示される。但しＲは曲率半径である。また、例えば「ｅ−Ｚ」の表示は「１０^−Ｚ」を意味する。又、各数値実施例における上述した条件式との対応を表１に示す。
【００２６】
【外１】

【００２７】
【外２】

【００２８】
【外３】

【００２９】
【外４】

【００３０】
【表１】

【００３１】
【発明の効果】
以上説明したように、本発明によれば、物体側より負の屈折力の第１レンズ群、正の屈折力の第２レンズ群、負の屈折力の第３レンズ群、正の屈折力の第４レンズ群で構成し、第２群を正の第２ａ群と正の第２ｂ群で構成し、前記第３ａ群を光軸と垂直方向に移動して防振を行い、適切な屈折力配置とレンズ構成を与えることで、コンパクトで良好な光学性能の超広角ズームレンズを達成することができた。
【図面の簡単な説明】
【図１】本発明の数値実施例１の広角端におけるレンズ断面図
【図２】本発明の数値実施例２の広角端におけるレンズ断面図
【図３】本発明の数値実施例３の広角端におけるレンズ断面図
【図４】本発明の数値実施例４の広角端におけるレンズ断面図
【図５Ａ】本発明の数値実施例１の広角端の縦収差図
【図５Ｂ】本発明の数値実施例１の望遠端の縦収差図
【図６Ａ】本発明の数値実施例２の広角端の縦収差図
【図６Ｂ】本発明の数値実施例２の望遠端の縦収差図
【図７Ａ】本発明の数値実施例３の広角端の縦収差図
【図７Ｂ】本発明の数値実施例３の望遠端の縦収差図
【図８Ａ】本発明の数値実施例４の広角端の縦収差図
【図８Ｂ】本発明の数値実施例４の望遠端の縦収差図
【図９Ａ】本発明の数値実施例１の広角端の横収差図
【図９Ｂ】本発明の数値実施例１の望遠端の横収差図
【図９Ｃ】本発明の数値実施例１の０．３度防振した状態での広角端の横収差図
【図９Ｄ】本発明の数値実施例１の０．３度防振した状態での望遠端の横収差図
【図１０Ａ】本発明の数値実施例２の広角端の横収差図
【図１０Ｂ】本発明の数値実施例２の望遠端の横収差図
【図１０Ｃ】本発明の数値実施例２の０．３度防振した状態での広角端の横収差図
【図１０Ｄ】本発明の数値実施例２の０．３度防振した状態での望遠端の横収差図
【図１１Ａ】本発明の数値実施例３の広角端の横収差図
【図１１Ｂ】本発明の数値実施例３の望遠端の横収差図
【図１１Ｃ】本発明の数値実施例３の０．３度防振した状態での広角端の横収差図
【図１１Ｄ】本発明の数値実施例３の０．３度防振した状態での望遠端の横収差図
【図１２Ａ】本発明の数値実施例４の広角端の横収差図
【図１２Ｂ】本発明の数値実施例４の望遠端の横収差図
【図１２Ｃ】本発明の数値実施例４の０．３度防振した状態での広角端の横収差図
【図１２Ｄ】本発明の数値実施例４の０．３度防振した状態での望遠端の横収差図
【符号の説明】
Ｉ〜ＩＶは各々第１レンズ群〜第４レンズ群、Ｓは絞り、ＳＰはフレアーカッター、実線矢印は広角端から望遠端へズーミングする際の各レンズ群の移動軌跡、球面収差において実線はｄ線、一点鎖線はｇ線、点線は正弦条件であり、非点収差において実線はサジタル光線、点線はメリディオナル光線を表す[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a zoom lens, and is particularly suitable for a still camera such as a single-lens reflex camera and an electronic still camera. The zoom lens has an image stabilizing function, has a high zoom ratio and has an excellent optical performance covering an ultra wide angle range. About.
[0002]
[Prior art]
In photographing from a moving object such as a car in progress, vibration is transmitted to the photographing system, and the photographed image is blurred. In hand-held shooting using a lens having a long focal length or a lens having a large FNo, camera shake may occur in a shot image due to camera shake. In recent years, silver halide cameras and video cameras that optically or electrically correct these blurs have been released.
[0003]
Conventionally, as a zoom lens having an anti-vibration function, Japanese Patent Application Laid-Open No. 5-232410 (Canon L58) Conventional Example 1 and Japanese Patent Application Laid-Open No. 9-230242 (Nikon 2 Group Anti-Vibration) Conventional Example 2, Japanese Patent Application Laid-Open 113808 (Nikon 2 Group Vibration Isolation) Conventional Example 3 and the like. Conventional example 1 is a telephoto zoom lens composed of first to fourth lens units having positive, negative, positive, and positive refractive powers in order from the object side, and moves the second unit in a direction perpendicular to the optical axis to prevent the telephoto zoom lens. Conventional examples 2 and 3 are large-aperture standard zoom lenses that cover a focal length of 28 mm to 85 mm in terms of a 35 mm single-lens reflex camera, and are negative, positive, negative, and positive in order from the object side. The second lens group constituted by a lens group was divided into a positive front group and a positive rear group, focusing was performed by the front group, and vibration was performed by displacing the front group in a direction perpendicular to the optical axis. Things.
[0004]
[Problems to be solved by the invention]
The present invention covers from a super wide angle range of about 17 mm focal length to a standard range of about 40 mm in terms of a 35 mm single-lens reflex camera, and has a vibration proof function, is compact, and satisfactorily corrects aberrations particularly during vibration proof. It is an object to provide a zoom lens.
[0005]
[Means for Solving the Problems]
The present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power. In a zoom lens that performs zooming by changing the distance between the respective groups, the second lens group is divided into a plurality of lens groups, and a second lens group having a positive refractive power is divided among the divided lens groups. It is characterized by performing vibration isolation by moving in a direction substantially perpendicular to the optical axis and satisfying the following conditional expression.
[0006]
D1W> D1T (a)
D2W <D2T ... (b)
D3W <D3T (C)
0.4 <TS2aW <1 ... (1)
0.7 <TS2aT <1.5 ... (2)
Here, DiW and DiT are the distance between the i-th group and the (i + 1) -th group at the wide angle end and the telephoto end, respectively, and TS2aW and TS2aT are the eccentric sensitivities at the wide angle end and the telephoto end of the 2a group, respectively. .
[0007]
In addition, the features of the present invention are disclosed in the embodiments.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail based on examples.
[0009]
1 to 4 are sectional views of zoom lenses according to Numerical Examples 1 to 4 to be described later. FIGS. 5 to 8 are longitudinal aberration diagrams of zoom lenses according to Numerical Examples 1 to 4 to be described later, and FIGS. 12 is a lateral aberration diagram of each of the zoom lenses of Numerical Examples 1 to 4 described later.
[0010]
In the figure, I to IV are a first lens group to a fourth lens group having negative, positive, negative, and positive refractive power, IIa and IIb are a 2a group and a 2b group, respectively, and S is an aperture stop. SF indicates a flare cutter, and arrows indicate the movement trajectories of the respective lens units when zooming from the wide-angle end to the telephoto end. At the time of zooming from the wide-angle end to the telephoto end, each lens unit moves so that the conditional expressions (a) to (c) are satisfied, and the stop moves integrally with the third unit.
[0011]
At the time of zooming from the wide-angle end to the telephoto end, the first lens group moves along a locus convex toward the image side while satisfying conditional expression (A), and the second lens group and the fourth lens group form an integral image. Side, and the third lens group moves so as to satisfy the conditional expressions (b) and (c). By moving the third lens group so as to satisfy the conditional expressions (b) and (c), the position of the principal point of synthesis from the second lens group to the fourth lens group is moved to the object side. The zooming effect by the movement of each lens group that satisfies the expression (a) is increased, and a compact and high zooming zoom lens can be achieved.
[0012]
Further, the zoom type of the present embodiment has the optical performance of the second lens group, more specifically, the relative eccentricity and tilt due to the manufacturing error of the lens group closest to the image and the fourth lens group in the second lens group. Deterioration occurs remarkably. Therefore, during zooming, if the second lens group and the fourth lens group move along different trajectories, eccentricity and tilting inevitably occur in the lens barrel structure, which is one of the causes of deterioration of optical performance. Therefore, in the present embodiment, the second lens group and the fourth lens group are moved together by moving the second image group and the fourth lens group closest to the image side in the same trajectory. It is possible to have a lens barrel structure. As a result, it is possible to minimize the deterioration of the optical performance due to the manufacturing error factor.
[0013]
In the present embodiment, the second lens group is divided into a second lens group having a positive refractive power and a second lens group having a positive refractive power, so that a refractive power arrangement satisfying conditional expressions (1) and (2) is obtained. The second lens group is moved substantially perpendicular to the optical axis to perform image stabilization. Conditional expressions (1) and (2) both define the amount of movement of the image plane in the direction perpendicular to the optical axis, that is, the eccentric sensitivity, with respect to the movement of the group 2a, that is, the vibration-proof lens group in the direction perpendicular to the optical axis. It was done. If the sensitivity to eccentricity is reduced below the lower limits of the conditional expressions (1) and (2), the displacement of the anti-vibration lens group for anti-vibration increases, and the anti-vibration driving device for satisfying this displacement is large. As a result, the outer diameter of the lens becomes large, which is not preferable. Increasing the eccentric sensitivity beyond the upper limits of the conditional expressions (1) and (2) is advantageous for miniaturization of the anti-vibration driving device. Various aberrations generated in the two lens groups increase, and it becomes difficult to correct aberrations during zooming from the wide-angle end to the telephoto end and in image stabilization in a well-balanced manner.
[0014]
Further, in the present embodiment, the image stabilizing lens group includes a cemented lens of one negative lens and one positive lens,
1.1 <EAIS / EAmin <1.3 (3)
The following conditional expression is satisfied. Here, EAIS is the maximum value of the effective beam diameter of the image stabilizing lens group, and EAmin is the minimum effective beam diameter of the optical system. 2. Description of the Related Art Conventionally, as a driving device for a vibration-proof lens group, a device using magnetic force generated by a coil and a magnet is known. (See Japanese Patent Application Laid-Open No. 2000-19577.) In order to reduce the size and power consumption of the driving device, it is required to reduce the weight of the vibration-proof lens group. For this reason, it is necessary to minimize the number of lenses in the image stabilizing lens group and to reduce the lens outer diameter. Conditional expression (3) defines the effective beam diameter of the anti-vibration lens group. If the effective diameter is smaller than the lower limit, a zoom lens having a predetermined specification cannot be achieved, and the effective diameter exceeds the upper limit. When the size is increased, the driving device becomes large, which is not preferable.
Further, in this embodiment, by using an aspherical surface for the second lens unit, the spherical aberration coefficient of the 2a-th unit (anti-vibration lens unit) can be reduced, and the optical performance at the time of anti-vibration can be satisfactorily corrected. Is possible.
[0015]
In addition, by using an aspheric surface in which the positive refractive power becomes weaker from the center to the periphery of the fourth lens group, it is possible to satisfactorily correct the field curvature near the maximum image height, which is a problem in a wide-angle zoom lens. And
[0016]
In the second embodiment, focusing from infinity to closest is performed by moving the second lens subunit toward the image plane side.
[0017]
In the first, third, and fourth embodiments, focusing from infinity to closest is performed by moving the first lens subunit toward the object side. By using the inner focus in this way, the load applied to the focus actuator during auto focus is reduced, enabling quick drive and power saving. In Examples 1, 3, and 4,
1.5 <ESfT <3.5 (4)
0.95 <ESfT × fW ＾ 2 / (ESfW × fT ＾ 2) <1.05 (5)
The following conditional expression is satisfied.
[0018]
Conditional expression (4) defines the position sensitivity of the focus group at the telephoto end where the defocus amount is the largest at the same object distance. The amount of movement of the focus lens group becomes large, the lens system becomes large, and rapid autofocus cannot be performed. If the sensitivity exceeds the upper limit, the refractive power of the lens unit on the object side becomes stronger than that of the second lens unit, and it becomes difficult to correct aberration. Conditional expression (5) is for making the moving amount of the focus lens constant at the time of focusing to the same object distance at each focal length. If the conditional expression is not satisfied, the above-mentioned extension amount varies depending on the focal length. . By keeping the extension amount constant in this way, the focus mechanism of the lens barrel can be simplified. Furthermore, the lens barrel structure can be simplified by performing vibration reduction and focusing with different lens groups.
[0019]
Further, in this embodiment, the first lens group is composed of two negative lenses and one positive lens, and the negative lens closest to the object has a shape in which the positive refractive power becomes stronger from the center of the optical axis toward the periphery. The second lens group is composed of one negative lens and two positive lenses, the third lens group is composed of two negative lenses and one positive lens, and the fourth lens group Is composed of one or two negative lenses and two positive lenses, and satisfies the following conditional expressions.
[0020]
0.7 <| f1W | / √ (fW × fT) <0.9 (6)
0.98 <f2W / √ (fW × fT) <1.25 (7)
1.4 <| f3 | / √ (fW × fT) <2.5 (8)
1.4 <f4 / √ (fW × fT) <2. ... (9)
2.5 <f2a / f2W <3.5 (10)
4.5 <OTLW / √ (fW × fT) <7 (11)
Here, fW and fT are the focal lengths of the entire system at the wide-angle end and the telephoto end, respectively, f1W and f2W are the focal lengths of the first and second lens groups at the wide-angle end, and f3 and f4 are the third lens groups. And the focal length of the fourth lens group, f2a is the focal length of the second lens group, and OTLW is the total optical length at the wide-angle end.
[0021]
By using the above-mentioned aspherical surface for the first lens group, barrel-shaped distortion particularly occurring on the wide-angle side is corrected.
[0022]
Conditional expression (6) defines the range of the focal length of the first lens unit at the wide-angle end with respect to the square root of the product of the focal length at the wide-angle end and the telephoto end of the entire system. If the negative refractive power of the first lens unit at the wide-angle end exceeds the lower limit value, various aberrations generated in the first lens unit increase, and it is difficult to correct these aberrations with other lens units in a well-balanced manner. Become. If the negative refractive power of the first lens unit is weakened beyond the upper limit, the lens system is unfavorably large in terms of aberration correction but large in size. Conditional expression (7) defines the range of the focal length of the second lens group at the wide-angle end with respect to the square root of the product of the focal length at the wide-angle end and the telephoto end of the entire system. When the positive refractive power of the second lens unit is increased beyond the lower limit, it is advantageous for shortening the overall length and reducing the diameter of the stop, but various aberrations such as spherical aberration generated in the second lens unit are increased. It is difficult to make corrections with other lens groups in a well-balanced manner. If the positive refractive power of the second lens group is weakened beyond the upper limit, the lens system increases, although it is advantageous for aberration correction.
[0023]
Conditional expressions (8) and (9) respectively define the range of the focal length of the third lens unit and the fourth lens unit with respect to the square root of the product of the focal length at the wide-angle end and the telephoto end of the entire system. , To achieve both compactness and high performance. If the refractive powers of the third lens unit and the fourth lens unit are both higher than the lower limit, spherical aberration, coma, and astigmatism in the third lens unit and the fourth lens unit are large. It is difficult to make a good correction. Further, if the refractive power of the third lens group and the fourth lens group becomes weaker than the upper limit, the overall length of the lens becomes longer. Conditional expression (10) defines a range of the focal length of the second positive lens group, ie, the focal length of the image stabilizing lens group, with respect to the focal length of the second positive lens group. If the positive refracting power of the second lens subunit becomes larger than the lower limit value, the image stabilization sensitivity increases, and there is an advantage that the image stabilization driving device can be downsized. However, the occurrence of various aberrations generated in the second lens unit becomes large. It becomes difficult to make a correction with another lens group in a well-balanced manner.
[0024]
If the positive refractive power of the second lens subunit becomes weaker than the upper limit, the image stabilization sensitivity decreases, and a predetermined image stabilization angle is satisfied. Here, the image stabilization sensitivity is defined as the axis connecting the object point before camera shake and the center of the optical axis of the lens surface closest to the object, and the object point at the time of camera shake connected to the center of the optical axis of the lens surface closest to the object. Assuming that the angle with respect to the axis is the anti-vibration angle, it is the anti-vibration angle per 1 mm of the amount of movement of the anti-vibration lens group, that is, the 2a group, in the direction perpendicular to the optical axis. Conditional expression (11) is the distance from the lens surface closest to the object side at the wide-angle end and infinity at the object distance to the image plane, that is, the total optical length, with respect to the square root of the product of the focal length at the wide-angle end and the telephoto end of the entire system. Is defined. In this embodiment, it is assumed that a quick return mirror and / or other members are arranged between the lens surface closest to the image plane and the image plane, and a space for disposing these members is required. For this reason, the lens system is a telephoto type, and the back focus is lengthened. If the lower limit of conditional expression (11) is exceeded and the total optical length at the wide-angle end becomes short, it becomes difficult to secure a back focus while achieving a predetermined zoom ratio. Exceeding the upper limit of conditional expression (11) and increasing the total optical length at the wide-angle end is advantageous for securing the back focus and correcting aberrations, but is not preferable because the total lens length becomes long.
[0025]
(Numerical example)
Next, Numerical Examples 1 to 4 respectively corresponding to Embodiments 1 to 4 of the present invention will be described. In each numerical example, i indicates the order of the optical surface from the object side, ri is the radius of curvature of the i-th optical surface (i-th surface), di is the distance between the i-th surface and the (i + 1) -th surface, ni and νi represent the refractive index and Abbe number of the i-th optical member with respect to the d-line, respectively. f is the focal length, FNo is the F number, and ω is the half angle of view. Skinf is the distance from the flare stop to the image plane. When b, c, d, and e are aspherical coefficients, and the displacement in the optical axis direction at a position of height h from the optical axis is x with respect to the surface vertex, the aspherical shape is
^{^{^{x = (h 2 / R)}}} / [1+ [1- (h / R) 2] 1/2] + bh 4 + ch 6 + dh 8 + eh 10
Displayed with. Here, R is a radius of curvature. Further, for example, "e-Z" means ^{"10 -Z".} Table 1 shows the correspondence between the numerical expressions and the conditional expressions described above.
[0026]
[Outside 1]

[0027]
[Outside 2]

[0028]
[Outside 3]

[0029]
[Outside 4]

[0030]
[Table 1]

[0031]
【The invention's effect】
As described above, according to the present invention, the first lens group having a negative refractive power, the second lens group having a positive refractive power, the third lens group having a negative refractive power, and the positive lens having a positive refractive power are arranged from the object side. The fourth lens group, the second group is composed of a positive 2a group and a positive 2b group, and the 3a group is moved in a direction perpendicular to the optical axis to perform image stabilization, and has an appropriate refractive power. By providing the arrangement and the lens configuration, it was possible to achieve a compact and wide-angle zoom lens with good optical performance.
[Brief description of the drawings]
FIG. 1 is a sectional view of a lens at a wide angle end according to a first numerical embodiment of the present invention. FIG. 2 is a sectional view of a lens at a wide angle end according to a second numerical embodiment of the present invention. FIG. 4 is a sectional view of a lens at a wide angle end according to a numerical example 4 of the present invention. FIG. 5A is a longitudinal aberration diagram at a wide angle end of a numerical example 1 of the present invention. FIG. 5B is a numerical example of the present invention. Fig. 6A is a longitudinal aberration diagram at the telephoto end of Fig. 6A. Fig. 6A is a longitudinal aberration diagram at the wide-angle end of Numerical Example 2 of the present invention. Fig. 6B is a longitudinal aberration diagram at the telephoto end of Numerical Example 2 of the present invention. FIG. 7B is a longitudinal aberration diagram at the wide-angle end of Numerical Example 3 of the present invention. FIG. 7B is a longitudinal aberration diagram at a telephoto end of Numerical Example 3 of the present invention. 8B: Longitudinal aberration diagram at the telephoto end of Numerical Embodiment 4 of the present invention [FIG. 9A] Transverse aberration diagram at the wide-angle end of Numerical Embodiment 1 of the present invention [FIG. 9B] Fig. 9C is a lateral aberration diagram at the telephoto end of Numerical Embodiment 1 of the present invention. Fig. 9C is a lateral aberration diagram of the wide-angle end of the Numerical Embodiment 1 in a state where vibration is suppressed by 0.3 degrees. FIG. 10A is a lateral aberration diagram at the telephoto end in a state where 0.3 degrees of vibration is reduced in Example 1. FIG. 10A is a lateral aberration diagram at a wide-angle end according to Numerical Embodiment 2 of the present invention. FIG. 10B is a telephoto diagram of Numerical Embodiment 2 of the present invention. FIG. 10C is a lateral aberration diagram at a wide-angle end in a state where 0.3-degree vibration is prevented in Numerical Embodiment 2 of the present invention. FIG. 10D is a 0.3-degree prevention in Numerical Embodiment 2 of the present invention. FIG. 11A is a lateral aberration diagram at the telephoto end in a shaken state. FIG. 11A is a lateral aberration diagram at the wide-angle end according to Numerical Example 3 of the present invention. FIG. 11B is a lateral aberration diagram at the telephoto end according to Numerical Example 3 of the present invention. FIG. 11D is a lateral aberration diagram at the wide-angle end in a state where 0.3-degree vibration is suppressed in Numerical Embodiment 3 of the present invention. FIG. 11D is a telephoto view in a state where 0.3-degree vibration is shaken in Numerical Embodiment 3 of the present invention. FIG. 12A is a lateral aberration diagram at the wide-angle end of Numerical Embodiment 4 of the present invention. FIG. 12B is a lateral aberration diagram at a telephoto end of Numerical Embodiment 4 of the present invention. FIG. 12C is a numerical embodiment of the present invention. FIG. 12D is a lateral aberration diagram at the wide-angle end in a state where the image is subjected to 0.3-degree vibration isolation. FIG. 12D is a lateral aberration diagram at a telephoto end in a state where the image is 0.3-degree vibration-proof according to Numerical Embodiment 4 of the present invention. ]
I to IV are the first to fourth lens groups, S is the aperture, SP is the flare cutter, solid arrows are the movement locus of each lens group when zooming from the wide-angle end to the telephoto end, and the solid line is d for spherical aberration. Line, dash-dot line is g-line, dotted line is sine condition, solid line is sagittal ray, dotted line is meridional ray in astigmatism

Claims

A first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power are arranged in order from the object side. In a zoom lens that changes magnification by changing an interval, at least one aspheric surface is used for the second lens group, and the second lens group is divided into a plurality of lens groups. A zoom lens, wherein the second lens unit having a positive refractive power is moved in a direction substantially perpendicular to the optical axis to perform image stabilization and satisfy the following conditional expression.
D1W> D1T
D2W <D2T
D3W <D3T
0.4 <TS2aW <1
0.7 <TS2aT <1.5
Here, DiW and DiT are the distance between the i-th group and the (i + 1) -th group at the wide angle end and the telephoto end, respectively, and TS2aW and TS2aT are the eccentric sensitivities at the wide angle end and the telephoto end of the 2a group, respectively. .

A first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power are arranged in order from the object side. In a zoom lens that changes magnification by changing an interval, the second lens group is divided into a plurality of lens groups, and the second lens group having a positive refractive power is substantially defined as an optical axis in the divided lens groups. A zoom lens which performs image stabilization by moving in a vertical direction, and does not change the distance within the second lens group during zooming and focusing, and satisfies the following conditional expression.
D1W> D1T
D2W <D2T
D3W <D3T
0.4 <TS2aW <1
0.7 <TS2aT <1.5
Here, DiW and DiT are the distance between the i-th group and the (i + 1) -th group at the wide angle end and the telephoto end, respectively, and TS2aW and TS2aT are the eccentric sensitivities at the wide angle end and the telephoto end of the 2a group, respectively. .

The zoom lens according to claim 2, wherein the second lens group has at least one aspheric surface.

The zoom lens according to claim 1, wherein the lens group closest to the image in the second group and the fourth lens group move together during zooming.

3. The zoom lens according to claim 1, wherein focusing is performed by a lens group other than the second group.

4. The zoom lens according to claim 3, wherein focusing is performed on all or a part of the lens unit on the object side of the second unit, and the following conditional expression is satisfied.
1.5 <ESfT <3.5
0.95 <ESfT × fW ＾ 2 / (ESfW × fT ＾ 2) <1.05
Here, ESfW and ESfT are the position sensitivities of the focus group at the wide-angle end, the telephoto end, and an infinite object distance, respectively.

The zoom lens according to claim 1, wherein the image stabilizing lens group includes one negative lens and one positive lens, and satisfies the following conditional expression.
1.1 <EAIS / EAmin <1.3
Here, EAIS is the maximum value of the effective beam diameter of the image stabilizing lens group, and EAmin is the minimum effective beam diameter of the optical system.

The first lens group includes at least one negative lens and at least one positive lens, uses an aspheric surface having a shape in which the positive refractive power increases from the center of the optical axis toward the periphery, and includes at least the second lens group. The third lens group includes one or two negative lenses and one positive lens, and the fourth lens group includes at least one negative lens. 3. The zoom lens according to claim 1, wherein the zoom lens comprises at least one positive lens and satisfies the following conditional expression.
0.7 <| f1W | / √ (fW × fT) <0.9
0.98 <f2W / √ (fW × fT) <1.25
1.4 <| f3 | / √ (fW × fT) <2.5
1.4 <f4 / √ (fW × fT) <2.5
2.5 <f2a / f2W <3.5
4.5 <OTLW / √ (fW × fT) <7
Here, fW and fT are the focal lengths of the entire system at the wide-angle end and the telephoto end, respectively, f1W and f2W are the focal lengths of the first and second lens groups at the wide-angle end, and f3 and f4 are the third lens groups. And the focal length of the fourth lens group, f2a is the focal length of the second lens group, and OTLW is the total optical length at the wide-angle end.

The zoom lens according to claim 1, wherein the fourth lens group has an aspheric surface having a shape in which positive refractive power becomes weaker from the center of the optical axis toward the periphery.

7. The method according to claim 6, wherein the first lens unit is divided into a negative first unit and a negative first unit, and focusing from infinity to a close position is performed by moving the first unit toward the object side. Zoom lens.