JP4564625B2

JP4564625B2 - Zoom lens and optical apparatus using the same

Info

Publication number: JP4564625B2
Application number: JP2000138906A
Authority: JP
Inventors: 昭永堀内
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2000-05-11
Filing date: 2000-05-11
Publication date: 2010-10-20
Anticipated expiration: 2020-05-11
Also published as: JP2001318315A

Description

【０００１】
【発明の属する技術分野】
本発明はズームレンズ及びそれを用いた光学機器に関し、特にビデオカメラやデジタルスチルカメラ等の電子カメラに好適なものである。この他本発明はズーム比が１０倍と高変倍比でありながら、広角端のＦナンバーが１．６程度と大口径比で全長の短いズームレンズ及びそれを用いた光学機器に関するものである。
【０００２】
【従来の技術】
従来より、レンズ系全体が小型であって比較的高い変倍比を有したズームレンズが例えば特開昭５６−１１４９２０号公報や特開昭５８−１６０９１３号公報で提案されている。これらは物体側より順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群、そして正の屈折力の第４群から構成され、変倍に際して第１群と第２群更に第４群を移動させており、これによってレンズ系全体が小型でありながらも比較的高いズーム比を得ている。
【０００３】
一方、特開昭６２−２４２１３号公報や特開昭６３−２４７３１６号公報では、物体側より順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群、正の屈折力の第４群の４つのレンズ群を有し、第２群を移動させて変倍を行ない、変倍に伴う像面変動を第４群を移動させて補正すると共に第４群でフォーカスを行なっている。
【０００４】
また、特開平４−１４００７号公報では、物体側より順に正の屈折力の第１群、負の屈折力の第２群、絞り、正の屈折力の第３群、そして正の屈折力の第４群で構成され、広角端から望遠端へのズーミングのために第１群を物体側へ第２群を像側へ移動させ、第４群をズーミングとフォーカシングのために移動させ、更に開口絞りを中間焦点距離から望遠端へのズーミングで像面側に移動するズームレンズを開示している。
【０００５】
特開昭５８−１２９４０４号公報、特開昭６１−２５８２１７号公報では物体側より順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群、正の屈折力の第４群、そして負の屈折力の第５群の５つのレンズ群より成るズームレンズにおいて、該第５群または該第５群を含む複数のレンズ群を移動させてフォーカスを行なっている。
【０００６】
また、特開平４−３０１８１１号公報では、物体側より順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群、正の屈折力の第４群そして負の屈折力の第５群の５つのレンズ群を有し、該第１群を物体側へ、該第２群を像面側へ移動させて広角端から望遠端への変倍を行い、変倍に伴う像面変動を該第４群を移動させて補正すると共に該第４群を移動させてフォーカスを行っている。
【０００７】
米国再発行特許明細書第３２９２３号には、物体側より順に第1正レンズ群、第２負レンズ群、絞り、そして第３正レンズ群、第４正レンズ群を配し、第1と第４レンズ群は変倍の際、同じ方向に動き、絞りは変倍の際に固定されるズームレンズが開示されている。
【０００８】
【発明が解決しようとする課題】
一般にズームレンズにおいて、レンズ系全体の小型化を図りつつ高変倍比を有し、かつ全変倍範囲において高い光学性能を得るためには、レンズ構成、各群の屈折力等を適切に設定する必要がある。
【０００９】
例えば変倍に伴う各レンズ群の移動条件や各レンズ群の屈折力そして変倍作用をするレンズ群のレンズ構成、フォーカスを行う為のレンズ群の選定及びそのレンズ構成そして開口絞りの光学的作用等を適切に設定しないと変倍およびフォーカスの際に諸収差の発生が増大し、高変倍化を図りつつ良好なる画質の映像を得るのが難しくなってくる。
【００１０】
本発明は変倍に伴う所定のレンズ群の移動条件や各レンズ群の屈折力、そしてレンズ構成等を適切に設定することにより、レンズ構成の簡素化を図りつつ、全変倍範囲にわたり、また、高い光学性能を有するレンズ全長の短い小型ズームレンズ及びそれを用いた光学機器の提供を目的とする。
【００１１】
この他本発明は、ズーム比が１０倍と高変倍比にもかかわらずレンズ系全体を小型化することを目的とする。また、Ｆナンバーが１．６程度と大口径比でありながら、高い光学性能を有しレンズの構成枚数が少ないズームレンズを提供することである。
【００１２】
【課題を解決するための手段】
請求項１の発明のズームレンズは、物体側より像側へ順に、正の屈折力の第１群、負の屈折力の第２群、開口絞り、正の屈折力の第３群、正の屈折力の第４群、負の屈折力の第５群より構成され、広角端から望遠端への変倍に際して、前記第１群は物体側に移動し、前記第２群は像面側に移動し、該開口絞りは移動し、前記第３群は固定であり、前記第４群は物体側に凸状の軌跡で移動し、前記第５群は固定であり、前記第４群を移動させてフォーカスを行い、広角端と望遠端における全系の焦点距離をｆｗ、ｆｔ、前記第２群の焦点距離をｆ２、前記第２群を構成する負レンズの屈折率の平均値をＮｎとするとき、
０．１９＜｜ｆ２／√（ｆｗ・ｆｔ）｜≦０．２５
１．８０＜Ｎｎ＜１．９６
なる条件式を満足することを特徴としている。
【００１３】
請求項２の発明は請求項１の発明において、前記開口絞りは、広角端から望遠端への変倍に際して、像面側に移動することを特徴としている。
【００１４】
請求項３の発明は請求項１の発明において、前記開口絞りは、広角端から望遠端への変倍に際して、変倍範囲の中間位置から望遠端にかけて像面側に移動することを特徴としている。
【００１５】
請求項４の発明は請求項１の発明において、前記開口絞りは、広角端から望遠端への変倍に際して、変倍範囲の中間位置で最も物体側に位置するように移動することを特徴としている。
【００１６】
請求項５の発明は請求項１乃至４のいずれか１項の発明において、前記第３群に対して前記開口絞りが光軸上最も離れる変倍位置と望遠端における前記第２群と該開口絞りの間隔を各々Ｌ２ｓ、Ｌ２ｔ、前記第３群に対して前記開口絞りが光軸上最も離れる変倍位置と望遠端における前記開口絞りと前記第３群の間隔を各々Ｌｓ３、Ｌ３ｔとするとき、
０．４＜（Ｌ２ｓ−Ｌ２ｔ）／（Ｌｓ３−Ｌ３ｔ）＜１．３
を満足することを特徴としている。
【００１７】
請求項６の発明は請求項１乃至５のいずれか１項の発明において、前記ズームレンズの広角端における最も物体側のレンズ面と像面の間隔をＬ、広角端と望遠端における全系の焦点距離をそれぞれｆｗ、ｆｔとするとき、
２．２２＜Ｌ／√（ｆｗ・ｆｔ）＜３．３６
なる条件式を満足することを特徴としている。
【００１８】
請求項７の発明は請求項１乃至６のいずれか１項の発明において、広角端から望遠端への変倍における前記第１群と前記第２群の移動量をそれぞれＳ１、Ｓ２とするとき、
０．６＜Ｓ１／Ｓ２＜１．２
なる条件式を満足することを特徴としている。
【００１９】
請求項８の発明は請求項１乃至７のいずれか１項の発明において、前記第３群を光軸に対して垂直方向に移動させて、前記ズームレンズが振動したときの結像位置の変動を補正することを特徴としている。
【００２０】
請求項９の発明は請求項１乃至８のいずれか１項の発明において、前記第２群は、物体側に凸面を向けたメニスカス状の負レンズ、両レンズ面が凹面の負レンズ、両レンズ面が凸面の正レンズと負レンズとを接合した接合レンズより成り、前記第２群を構成する正レンズのアッベ数の平均値をνｐ，前記第２群を構成する負レンズのアッベ数の平均値をνｎとするとき、
２０＜νｐ＜３５
３６＜νｎ＜６５
を満足することを特徴としている。
【００２１】
請求項１０の発明は請求項１乃至９のいずれか１項の発明において、第２群の物体側から第ｉ番目のレンズ面の曲率半径をＲ２ｉとしたとき、
０．６＜｜Ｒ２２／Ｒ２３｜＜０．８２
を満足することを特徴としている。
【００２２】
請求項１１の発明の光学機器は、請求項１から１０のいずれか１項に記載のズームレンズを有することを特徴としている。
【００３６】
【発明の実施の形態】
図１は本発明の数値実施例１のレンズ断面図、図２〜図４は本発明の数値実施例１の広角端，中間，望遠端の収差図である。図５は本発明の数値実施例２のレンズ断面図、図６〜図８は本発明の数値実施例２の広角端，中間，望遠端の収差図である。図９は本発明の数値実施例３のレンズ断面図、図１０〜図１２は本発明の数値実施例３の広角端，中間，望遠端の収差図である。
【００３７】
レンズ断面図においてＬ１は正の屈折力の第１群、Ｌ２は負の屈折力の第２群、Ｌ３は正の屈折力の第３群、Ｌ４は正の屈折力の第４群、Ｌ５は負の屈折力の第５群、ＳＰは絞り（開口絞り）であり第２群と第３群の間に設けている。絞りＳＰは変倍に伴って所定の条件で移動している。
【００３８】
Ｇは赤外カットフィルター，ローパスフィルター等のフィルターであり、ガラスブロックとして示している。ＩＰは像面である。
【００３９】
本実施形態では広角端から望遠端への変倍に際して矢印のように第１群を物体側へ第２群を象面側へ移動させると共に、変倍に伴う象面変動を第４群を物体側に凸状の軌跡を有しつつ移動させて補正している
また、第４群を光軸上移動させてフォーカスを行うリアフォーカス式を採用している。同図に示す第４群の実線の曲線４ａと点線の曲線４ｂは各々無限遠物体と近距離物体にフォーカスしているときの広角端から望遠端への変倍に伴う際の像面変動を補正する為の移動軌跡を示している。なお、第３群と第５群は変倍及びフォーカスの際固定である。
【００４０】
本実施形態において、例えば望遠端において無限遠物体から近距離物体へフォーカスを行う場合は、同図の直線４ｃに示すように第４群を前方へ繰り出すことにより行っている。
【００４１】
また、広角端から望遠端への変倍に際して絞りＳＰを所定の条件下で移動させている。
【００４２】
次に具体的に各数値実施例のズームレンズのレンズ構成を説明する。
【００４３】
図１の数値実施例１は、物体側から順に正の屈折力の第１群、負の屈折力の第２群、開口絞り、常時固定の正の屈折力の第3群、正の屈折力の第４群、そして常時固定の負の屈折力の第5群の５つのレンズ群を有し、広角端から望遠端への変倍に際して矢印のように該第１群を物体側に、該第２群を像面側へ移動させると同時に該開口絞りも像面側に移動させ、変倍に伴う像面変動を該第４群を移動させて補正している。また、第４群を光軸上移動させてフォーカスを行うリアフォーカス式を採用している。
【００４４】
図５の数値実施例２は物体側から順に正の屈折力の第１群、負の屈折力の第２群、開口絞り、常時固定の正の屈折力の第3群、正の屈折力の第４群、そして常時固定の負の屈折力の第5群の５つのレンズ群を有し、広角端から望遠端への変倍に際して矢印のように該第１群を物体側に、該第２群を像面側へ移動させると共に変倍に伴う像面変動を該第４群を移動させて補正している。そして該開口絞りは、変倍に際して広角端から中間焦点距離まではほぼ不動の状態で、中間焦点距離から望遠端にかけては像面側に移動させている。また、第４群を光軸上移動させてフォーカスを行うリアフォーカス式を採用している。
【００４５】
図９の数値実施例３は物体側から順に正の屈折力の第１群、負の屈折力の第２群、開口絞り、常時固定の正の屈折力の第3群、正の屈折力の第４群、そして常時固定の負の屈折力の第5群の５つのレンズ群を有し、広角端から望遠端への変倍に際して矢印のように該第１群を物体側に、該第２群を像面側へ移動させると共に変倍に伴う像面変動を該第４群を移動させて補正している。そして該開口絞りは、変倍に際して広角端から中間焦点距離までは物体側に移動させ、中間焦点距離から望遠端にかけては像面側に移動させている。また、第４群を光軸上移動させてフォーカスを行うリアフォーカス式を採用している。
【００４６】
また、いずれの実施例においても、ズーミング中固定の第３群を光軸方向に略垂直に移動させて、被写体像の像面移動を補正することも可能である。
【００４７】
本発明のズームレンズでは、このように変倍の際に第１，第２，第４のレンズ群そして絞りを移動させることにより複数のレンズ群に変倍をバランス良く分担させ，レンズ系全体の小型化を図りつつ効率よく変倍を行うと共に，全ズーム領域での収差補正を良好に行っている。
【００４８】
本発明の目的とするズームレンズは以上の構成により達成されるが、更に本発明において広角端から望遠端に至り、また、物体距離全般にわたり良好なる光学性能を有し、小型のズームレンズを得るには次の諸条件のうちの少なくとも１つを満足させるのが良い。
【００４９】
（ア−１）前記第1群は物体側に移動して広角端から望遠端への変倍を行なうことを特徴とすることである。これにより該第１群にも増倍作用を持たせてズーム比の高倍化を図っている。
【００５０】
（アー２）変倍に伴う像面変動を該第4群を移動させて補正すると共に該第4群を移動させてフォーカスを行なうことを特徴とすることである。つまりリアフォーカス方式を採用することである。第１群を移動させてフォーカスを行うズームレンズに比べて第１群の有効径が小さくなり、レンズ系全体の小型化が容易になる。また、近接撮影、特に超至近撮影が容易となる。更に比較的軽量のレンズ群を移動させて行うため、レンズ群の駆動力が小さくてすみ迅速な焦点合わせを行うことができる等の特長がある。
【００５１】
（ア−３）該第４群は、変倍に際して物体側に凸状の軌跡で移動することを特徴とすることである。これによれば（ア−２）と同様の効果が得られる。
【００５２】
（ア−４）前記開口絞りは、広角端から望遠端への変倍の際、像面側に移動することを特徴とすることである。
【００５３】
（ア−５）前記開口絞りは、広角端から望遠端への変倍の際、変倍範囲の中間位置から望遠端にかけて像面側に移動することを特徴とすることである。
【００５４】
（ア−６）前記開口絞りは、広角端から望遠端への変倍の際、変倍範囲の中間位置でもっとも物体側に位置するような軌跡で移動することを特徴とすることである。前記構成のズームレンズの重量の大部分を決めているのは、第１群であり全体の約９０％を占めている。これをいかに小さくするかがレンズの軽量小型化に大きく寄与してくる。
【００５５】
該ズームレンズにおいて、第１群の有効径を決定しているのは変倍の中間位置における周辺の光線束である。これをレンズ光軸に近づけることにより第１群を小型化することが可能となる。すなわち開口絞りを可能な限り第１群に近づけることである。ただし近づけすぎると逆に像面近傍のレンズ系が大きくなったり、光学性能が劣化してしまうことがある。
【００５６】
構成（ｐ−４），（ｐ−５），（ｐ−６）は以上の理由により第１群の有効径を小さくしつつ，画面周辺で十分な光量を得るためのものである。
【００５７】
（ア−７）前記第3群に対して前記開口絞りが光軸上最も離れる変倍位置と望遠端における第2群と該開口絞りの間隔を各々Ｌ２ｓ、Ｌ２ｔ、該変倍位置と望遠端における該開口絞りと第3群の間隔を各々Ｌｓ３、Ｌ３ｔとするとき、
０．４＜（Ｌ２ｓ−Ｌ２ｔ）／（Ｌｓ３−Ｌ３ｔ）＜１．３・・・（１）
を満足する該開口絞りの位置が存在することを特徴とすることである。
【００５８】
条件式（１）の上限値を超えて開口絞りを第３群側に近づけると，第１群と開口絞りの距離が大きくなり，第１群の有効径の小型化を図るのが困難になってくる。逆に、下限値を越えて第２群に近づきすぎると、像面近傍のレンズ群の有効径が大きくなり、光学性能を良好に保つことが困難になってくるので好ましくない。
【００５９】
（ア−８）広角端と望遠端における全系の焦点距離をｆｗ、ｆｔ、第2群の焦点距離をｆ２とおいたとき、
【００６０】
【数７】

【００６１】
とする。
【００６２】
０．１９＜｜ｆ２／ｆＡ｜≦０．２５・・・（２）
なる条件式を満足することを特徴とすることである。これは第２群の焦点距離を適正にするための条件である。条件式（２）の上限値を超えて第２群の焦点距離が長くなると、収差上は好ましいが所望のズーム比を得るためには該第２群の移動量を大きくしなくてはならず、レンズ系全体の大型化を招き好ましくない。逆に下限値を越えるとペッツバール和が負の方向に大きくなり、像面が倒れてくるので良好な光学性能を保つのが困難になる。
【００６３】
（ア−９）広角端で無限遠物体の合焦状態において最終レンズ面から像面までの距離を空気に換算し、物体側の第1レンズ面から近軸像面までの距離（最も物体側のレンズ面と像面の間隔）をＬ、広角端と望遠端における全系の焦点距離をｆｗ、ｆｔ、
【００６４】
【数８】

【００６５】
とおいたとき
２．２２＜Ｌ／ｆＡ＜３．３６・・・（３）
なる条件式を満足することを特徴とすることである。条件式（３）の上限値を超えるとレンズ全長が長くなり好ましくない。逆に下限値を越えるとペッツバール和が負に大きくなり、像面が倒れてくるので良好な光学性能を保つのが困難になる。
【００６６】
（ア−１０）広角端から望遠端への変倍における前記第1群と第2群の移動量をＳ１、Ｓ２とおいたとき、
０．６＜Ｓ１／Ｓ２＜１．２・・・（４）
なる条件式を満足することを特徴とすることである。条件式（４）は広角端から望遠端への変倍の際の第１群と第２群の移動量の比に関し、主に変倍の際の収差変動を良好に補正しつつ第１群の有効径の小型化及びレンズ全長の短縮化の両方をバランス良く行うための条件である。上限値を越えて第１郡の移動量が増加すると、中間焦点距離から望遠端において該開口絞りからの距離が遠くなり、軸外光束がレンズ光軸から離れて第１群の有効径が大きくなってくるので好ましくない。逆に下限値を越えて第１群の移動量が少なくなると広角端でのレンズ全長を短くすることが難しくなったり、所望の変倍比を売るのが困難となってくる。
【００６７】
（ア−１１）前記第5群は、変倍に際し常時固定であることを特徴とすることである。
【００６８】
（ア−１２）前記第3群を光軸方向にほぼ垂直に移動させて、前記ズームレンズが振動したときの被写体象の像面位置を補正することを特徴とすることである。
【００６９】
（ア−１３）該第２群は物体側より順に像面側に強い凹面を向けた負の２１レンズ、両レンズ面が凹面の負の第２２レンズ、そして像側に比べ物体側に強い凸面を向けた正レンズと負レンズとを接合した正の第２３接合レンズを有することが望ましい。
【００７０】
本発明のようなズームタイプで変倍比を上げる場合、変倍機能に大きく寄与する第２群の移動量を大きくするか、該第２群の焦点距離を短くする必要がある。
【００７１】
前記の方法は、ズームレンズの大型化を招き好ましくなく、後記の方法はレンズは大きくならないものの第２群に負担が大きくかかり、光学性能を良好に保つ事が困難になってくる。そこで上述の如く第２群を構成することにより光学性能を良好に補正することができる。
【００７２】
（ア−１４）第２群は少なくとも１つの非球面を有することである。非球面を配置することにより軸外の光学性能を向上することができる。また、第２群の屈折力を強くすることも可能になり、結果的に第２群の移動量を少なくすることができ、レンズ全長を短くすることができる。また、該第２群中の非球面は、曲率半径の小さい、負の第２１レンズの像面側の面、または負の第２２レンズの物体側の面、または正の第２３レンズの物体側の面に配置することにより、より効果的に収差を補正することが可能になる。特に軸外のフレアーを良好に補正できる。なお、非球面は、レンズの周辺部にいくにしたがって屈折力が弱くなる形状となることが望ましい。
【００７３】
（ア−１５）該第２群の正レンズの材質の平均アッベ数をνｐ、負レンズの材質の平均アッベ数をνｎとおいたとき
２０＜νｐ＜３５・・・（５）
３６＜νｎ＜６５・・・（６）
なる条件式を少なくとも１つ満足することが望ましい。これは第２群で発生する色収差を良好に補正している。該第２群は変倍に大きく寄与しているのでここで発生する収差は良好に補正しておかなければならない。特に変倍比が１０倍程度の高変倍比のズームレンズにおいては色収差も良好に補正することが重要である。
【００７４】
条件式（５）の上限値を超えると軸上色収差がオーバーになり補正過剰となる。逆に、下限値を超えると軸上色収差がアンダーになり補正不足となる。条件式（６）は条件式（５）の場合と現象の発生は逆になるが、上限値あるいは下限値を超えるとやはり色収差を良好に補正することが難しい。
【００７５】
（ア−１６）前記第２群の負レンズの材質の平均屈折力をＮｎとおいたとき、
１．８０＜Ｎｎ＜１．９６・・・（７）
なる条件式を満足することである。これは条件式（２）とも関係してくるが、負レンズに高屈折率ガラスを用いてペッツバール和の悪化を防ぐ為の条件で、限界値を超えると像面湾曲が悪化してくる。
（ア−１７）該第２群のレンズの曲率半径を物体側から順にＲ２ｉとおいたとき
０．６０＜｜Ｒ２２／Ｒ２３｜＜０．８２・・・（８）
なる条件式を満足することである。これらはコマ収差と像面湾曲そしてフレアーをバランス良く補正する条件である。条件式（８）の上限値を超えるとコマ収差が大きくなってくる。逆に下限値を超えると像面が物体側に凹となるように湾曲し好ましくない。更に、上限値または下限値を超えると共にフレアーが大きくなり好ましくない。
【００７６】
次に本発明のズームレンズを用いたビデオカメラ（光学機器）の実施形態を図１３を用いて説明する。
【００７７】
図１３において、１０はビデオカメラ本体、１１は本発明のズームレンズによって構成された撮影光学系、１２は撮影光学系１１によって被写体像を受光するＣＣＤ等の撮像素子、１３は撮像素子１２が受光した被写体像を記録する記録手段、１４は不図示の表示素子に表示された被写体像を観察するためのファインダーである。上記表示素子は液晶パネル等によって構成され、撮像素子１２上に形成された被写体像が表示される。
【００７８】
このように本発明のズームレンズをビデオカメラやデジタルスチルカメラ等の電子カメラに適用することにより、小型で高い光学性能を有する光学機器を実現している。
【００７９】
以下に、本発明の各数値実施例を記載する。
【００８０】
数値実施例において、Ｒｉは物体側より順に第ｉ番目の面の曲率半径、Ｄｉは物体側より順に第ｉ番目のレンズ厚及び空気間隔、Ｎｉとνｉはそれぞれ物体側より順に第ｉ番目の光学部材の材質の屈折率とアッベ数である。
【００８１】
非球面形状は、光軸方向にＸ軸、光軸と垂直方向Ｈ軸、光の進行方向を正とし、Ｒを近軸曲率半径、各非球面係数をＫ，Ｂ，Ｃ，Ｄ，Ｅ，Ｆとしたとき、
【００８２】
【数９】

【００８３】
なる式で表している。
【００８４】
また、例えば「ｅ−Ｚ」の表示は「１０^-Z」を意味する。前述の各条件式と数値実施例における諸数値との関係を表−１に示す。
【００８５】
【外１】

【００８６】
【外２】

【００８７】
【外３】

【００８８】
【表１】

【００８９】
【発明の効果】
本発明によれば、変倍に伴う所定のレンズ群の移動条件や各レンズ群の屈折力、そしてレンズ構成等を適切に設定することにより、レンズ構成の簡素化を図りつつ、全変倍範囲にわたり、また、高い光学性能を有するレンズ全長の短い小型ズームレンズ及びそれを用いた光学機器を達成することができる。
【００９０】
この他本発明によれば、以上説明したように構成することにより、ズーム比が10倍と高変倍比にもかかわらずレンズ系全体を小型化し、さらにＦナンバーが１．６程度と大口径比でありながら、高い光学性能を有しレンズの構成枚数が少ないズームレンズを実現することができる。
【図面の簡単な説明】
【図１】本発明の数値実施例1のレンズ断面図
【図２】本発明の数値実施例1の広角端における収差図
【図３】本発明の数値実施例1の中間における収差図
【図４】本発明の数値実施例1の望遠端における収差図
【図５】本発明の数値実施例２のレンズ断面図
【図６】本発明の数値実施例２の広角端における収差図
【図７】本発明の数値実施例２の中間における収差図
【図８】本発明の数値実施例２の望遠端における収差図
【図９】本発明の数値実施例３のレンズ断面図
【図１０】本発明の数値実施例３の広角端における収差図
【図１１】本発明の数値実施例３の中間における収差図
【図１２】本発明の数値実施例３の望遠端における収差図
【図１３】本発明の光学機器の要部概略図
【符号の説明】
Ｌ１第１群
Ｌ２第２群
Ｌ３第３群
Ｌ４第４群
Ｌ５第５群
ｄｄ線
ｇｇ線
ΔＭメリディオナル像面
ΔＳサジタル像面
１０ビデオカメラ本体
１１ズームレンズ
１２撮像素子
１３記録手段
１４ファインダー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens and an optical apparatus using the same, and is particularly suitable for an electronic camera such as a video camera or a digital still camera. In addition, the present invention relates to a zoom lens having a zoom ratio of 10 times and a high zoom ratio, and an F number at the wide-angle end of about 1.6, a large aperture ratio and a short overall length, and an optical apparatus using the same. .
[0002]
[Prior art]
Conventionally, zoom lenses having a small lens system and a relatively high zoom ratio have been proposed in, for example, Japanese Patent Laid-Open Nos. 56-114920 and 58-160913. These are composed of a first group of positive refractive power, a second group of negative refractive power, a third group of positive refractive power, and a fourth group of positive refractive power in order from the object side. The first group, the second group, and the fourth group are moved, so that a relatively high zoom ratio is obtained while the entire lens system is small.
[0003]
On the other hand, in Japanese Patent Laid-Open Nos. 62-24213 and 63-247316, a first group having a positive refractive power, a second group having a negative refractive power, and a third having a positive refractive power in order from the object side. A fourth lens group having a positive refractive power, and moving the second group to perform zooming, and correcting the image plane variation accompanying zooming by moving the fourth group and correcting the first lens group. Focusing is done in 4 groups.
[0004]
In JP-A-4-14007, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, a stop, a third group having a positive refractive power, and a positive refractive power. Consists of a fourth group, the first group is moved to the object side for zooming from the wide-angle end to the telephoto end, the second group is moved to the image side, the fourth group is moved for zooming and focusing, and the aperture is further opened A zoom lens is disclosed in which the stop is moved to the image plane side by zooming from the intermediate focal length to the telephoto end.
[0005]
In JP-A-58-129404 and JP-A-61-258217, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, In a zoom lens composed of five lens units of a fourth group having a refractive power of 5 and a fifth group having a negative refractive power, focusing is performed by moving the fifth group or a plurality of lens groups including the fifth group. ing.
[0006]
In Japanese Patent Laid-Open No. 4-301811, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power. Then, it has five lens groups of negative fifth refractive power, and the first group is moved to the object side and the second group is moved to the image plane side to perform zooming from the wide angle end to the telephoto end. The image plane variation due to zooming is corrected by moving the fourth group, and the fourth group is moved for focusing.
[0007]
In US Reissued Patent Specification No. 32923, a first positive lens group, a second negative lens group, a stop, and a third positive lens group and a fourth positive lens group are arranged in order from the object side. A zoom lens is disclosed in which the four lens groups move in the same direction during zooming, and the diaphragm is fixed during zooming.
[0008]
[Problems to be solved by the invention]
In general, in a zoom lens, in order to have a high zoom ratio while reducing the size of the entire lens system and to obtain high optical performance in the entire zoom range, the lens configuration, the refractive power of each group, etc. are set appropriately. There is a need to.
[0009]
For example, the movement conditions of each lens group accompanying zooming, the refractive power of each lens group, the lens configuration of the lens group that performs zooming, the selection of the lens group for focusing, the lens configuration, and the optical action of the aperture stop If these are not set appropriately, the occurrence of various aberrations increases during zooming and focusing, and it becomes difficult to obtain an image with good image quality while achieving high zooming.
[0010]
In the present invention, by appropriately setting the movement conditions of the predetermined lens units accompanying the zooming, the refractive power of each lens unit, and the lens configuration, etc., the lens configuration can be simplified and the entire zooming range can be achieved. Another object of the present invention is to provide a small zoom lens having high optical performance and a short overall lens length, and an optical apparatus using the same.
[0011]
Another object of the present invention is to reduce the size of the entire lens system in spite of a high zoom ratio of 10 times. Another object of the present invention is to provide a zoom lens having high optical performance and a small number of lenses, while having a large aperture ratio of F number of about 1.6.
[0012]
[Means for Solving the Problems]
The zoom lens according to the first aspect of the present invention includes, in order from the object side to the image side, a first group having a positive refractive power, a second group having a negative refractive power, an aperture stop, a third group having a positive refractive power, and a positive group. The zoom lens is composed of a fourth group having a refractive power and a fifth group having a negative refractive power. Upon zooming from the wide angle end to the telephoto end, the first group moves toward the object side, and the second group moves toward the image plane side. The aperture stop moves, the third group is fixed, the fourth group moves with a convex locus toward the object side, the fifth group is fixed, and the fourth group moves. The focal length of the entire system at the wide-angle end and the telephoto end is fw, ft, the focal length of the second group is f2, and the average refractive index of the negative lens constituting the second group is Nn. and when,
0.19 <| f2 / √ (fw · ft) | ≦ 0.25
1.80 <Nn <1.96
It satisfies the following conditional expression.
[0013]
According to a second aspect of the present invention, in the first aspect of the present invention, the aperture stop moves to the image plane side upon zooming from the wide-angle end to the telephoto end.
[0014]
According to a third aspect of the present invention, in the first aspect of the invention, the aperture stop moves toward the image plane from the middle position of the zoom range to the telephoto end when zooming from the wide-angle end to the telephoto end. .
[0015]
According to a fourth aspect of the present invention, in the first aspect of the invention, the aperture stop moves so as to be located closest to the object side in the middle position of the zooming range when zooming from the wide-angle end to the telephoto end. Yes.
[0016]
According to a fifth aspect of the present invention, there is provided the zoom lens according to any one of the first to fourth aspects, wherein the aperture stop is farthest on the optical axis relative to the third group, and the second group and the aperture at the telephoto end. When the distance between the aperture stops is L2s and L2t, and the distance between the aperture stop and the third group at the telephoto end where the aperture stop is farthest on the optical axis with respect to the third group is Ls3 and L3t, respectively. ,
0.4 <(L2s-L2t) / (Ls3-L3t) <1.3
It is characterized by satisfying.
[0017]
According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the distance between the lens surface closest to the object side and the image plane at the wide-angle end of the zoom lens is L, and the entire system at the wide-angle end and the telephoto end is When the focal lengths are fw and ft, respectively.
2.22 <L / √ (fw · ft) <3.36
It satisfies the following conditional expression.
[0018]
The invention of claim 7 is the invention of any one of claims 1 to 6, wherein the movement amounts of the first group and the second group in zooming from the wide-angle end to the telephoto end are S1 and S2, respectively. ,
0.6 <S1 / S2 <1.2
It satisfies the following conditional expression.
[0019]
According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the imaging position is changed when the third lens group is moved in the direction perpendicular to the optical axis and the zoom lens vibrates. It is characterized by correcting.
[0020]
The invention of claim 9 is the invention according to any one of claims 1 to 8, wherein the second group includes a meniscus negative lens having a convex surface facing the object side, a negative lens having concave both lens surfaces, and both lenses. It consists of a cemented lens in which a positive lens having a convex surface and a negative lens are cemented together, and the average Abbe number of the positive lens constituting the second group is νp, and the average Abbe number of the negative lens constituting the second group When the value is νn,
20 <νp <35
36 <νn <65
It is characterized by satisfying.
[0021]
The invention of claim 10 is the invention of any one of claims 1 to 9, wherein the radius of curvature of the i-th lens surface from the object side of the second group is R2i.
0.6 <| R22 / R23 | <0.82
It is characterized by satisfying.
[0022]
An optical apparatus according to an eleventh aspect of the present invention includes the zoom lens according to any one of the first to tenth aspects.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention, and FIGS. 2 to 4 are aberration diagrams at the wide-angle end, middle, and telephoto end of Numerical Example 1 of the present invention. FIG. 5 is a lens cross-sectional view of Numerical Example 2 of the present invention, and FIGS. 6 to 8 are aberration diagrams at the wide-angle end, middle, and telephoto end of Numerical Example 2 of the present invention. FIG. 9 is a lens cross-sectional view of Numerical Example 3 of the present invention, and FIGS. 10 to 12 are aberration diagrams at the wide-angle end, middle, and telephoto end of Numerical Example 3 of the present invention.
[0037]
In the lens sectional view, L1 is a first group having positive refractive power, L2 is a second group having negative refractive power, L3 is a third group having positive refractive power, L4 is a fourth group having positive refractive power, and L5 is The fifth group, SP, having a negative refractive power, is a stop (aperture stop), and is provided between the second group and the third group. The aperture stop SP is moved under a predetermined condition with zooming.
[0038]
G is a filter such as an infrared cut filter or a low-pass filter, and is shown as a glass block. IP is the image plane.
[0039]
In this embodiment, when zooming from the wide-angle end to the telephoto end, the first group is moved to the object side as indicated by the arrow, and the second group is moved to the elephant side. It is corrected by moving it while having a convex locus on the side, and a rear focus method is adopted in which focusing is performed by moving the fourth lens unit on the optical axis. The solid curve 4a and the dotted curve 4b of the fourth group shown in the figure show the image plane fluctuations accompanying the zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at close distance, respectively. The movement trajectory for correction is shown. The third group and the fifth group are fixed during zooming and focusing.
[0040]
In the present embodiment, for example, when focusing from an infinitely distant object to a close object at the telephoto end, the fourth group is moved forward as indicated by a straight line 4c in the figure.
[0041]
Further, the aperture stop SP is moved under a predetermined condition at the time of zooming from the wide angle end to the telephoto end.
[0042]
Next, the lens configuration of the zoom lens of each numerical example will be specifically described.
[0043]
Numerical example 1 of FIG. 1 is the first group having positive refractive power, the second group having negative refractive power, the aperture stop, the third group having always positive positive power, and the positive refractive power in order from the object side. And a fifth lens group having a negative refractive power that is always fixed, and the first group is moved to the object side as indicated by an arrow when zooming from the wide-angle end to the telephoto end. At the same time when the second group is moved to the image plane side, the aperture stop is also moved to the image plane side, and the image plane variation accompanying zooming is corrected by moving the fourth group. In addition, a rear focus type is employed in which focusing is performed by moving the fourth group on the optical axis.
[0044]
Numerical Example 2 in FIG. 5 shows the first group of positive refractive power, the second group of negative refractive power, the aperture stop, the third group of positive refractive power that is always fixed, and the positive refractive power in order from the object side. There are five lens groups, a fourth group and a fifth lens group having a negative refractive power that is always fixed, and the first group is placed on the object side as indicated by an arrow when zooming from the wide-angle end to the telephoto end. The second group is moved to the image plane side, and the image plane variation accompanying zooming is corrected by moving the fourth group. The aperture stop is substantially stationary from the wide angle end to the intermediate focal length during zooming, and is moved to the image plane side from the intermediate focal length to the telephoto end. In addition, a rear focus type is employed in which focusing is performed by moving the fourth group on the optical axis.
[0045]
In numerical example 3 of FIG. 9, in order from the object side, the first group of positive refractive power, the second group of negative refractive power, the aperture stop, the third group of always positive positive refractive power, the positive refractive power There are five lens groups, a fourth group and a fifth lens group having a negative refractive power that is always fixed, and the first group is placed on the object side as indicated by an arrow when zooming from the wide-angle end to the telephoto end. The second group is moved to the image plane side, and the image plane variation accompanying zooming is corrected by moving the fourth group. The aperture stop is moved to the object side from the wide-angle end to the intermediate focal length during zooming, and is moved to the image plane side from the intermediate focal length to the telephoto end. In addition, a rear focus type is employed in which focusing is performed by moving the fourth group on the optical axis.
[0046]
In any of the embodiments, it is also possible to correct the image plane movement of the subject image by moving the third group fixed during zooming substantially perpendicularly to the optical axis direction.
[0047]
In the zoom lens according to the present invention, the first, second, and fourth lens groups and the diaphragm are moved during zooming so that the zooming is distributed among the plurality of lens groups in a well-balanced manner. While zooming in efficiently while miniaturizing, aberration correction is well performed in the entire zoom range.
[0048]
The zoom lens that is the object of the present invention is achieved by the above configuration. In the present invention, the zoom lens extends from the wide-angle end to the telephoto end, and has a good optical performance over the entire object distance, thereby obtaining a small zoom lens. It is preferable to satisfy at least one of the following conditions.
[0049]
(A-1) The first group is characterized in that it moves toward the object side and performs zooming from the wide-angle end to the telephoto end. As a result, the first lens group also has a multiplying action to increase the zoom ratio.
[0050]
(Ar 2) The present invention is characterized in that the image plane variation caused by zooming is corrected by moving the fourth group, and focusing is performed by moving the fourth group. That is, the rear focus method is adopted. The effective diameter of the first lens unit is smaller than that of a zoom lens that moves the first lens unit to focus, and the entire lens system can be easily downsized. In addition, close-up photography, particularly ultra close-up photography is facilitated. Further, since the relatively light lens group is moved, the driving force of the lens group is small, so that quick focusing can be performed.
[0051]
(A-3) The fourth group is characterized by moving along a convex locus toward the object side upon zooming. According to this, the same effect as (A-2) can be obtained.
[0052]
(A-4) The aperture stop moves to the image plane side upon zooming from the wide-angle end to the telephoto end.
[0053]
(A-5) The aperture stop moves to the image plane side from the intermediate position of the zooming range to the telephoto end when zooming from the wide-angle end to the telephoto end.
[0054]
(A-6) The aperture stop moves along a trajectory that is located closest to the object side in the middle position of the zooming range when zooming from the wide-angle end to the telephoto end. It is the first group that determines most of the weight of the zoom lens configured as described above, which occupies about 90% of the total. How to reduce this greatly contributes to the reduction in weight and size of the lens.
[0055]
In the zoom lens, the effective diameter of the first lens unit is determined by the peripheral light flux at the intermediate position of zooming. By bringing this closer to the lens optical axis, the first group can be reduced in size. That is, to bring the aperture stop as close to the first group as possible. However, if it is too close, the lens system in the vicinity of the image plane may become large or the optical performance may deteriorate.
[0056]
The configurations (p-4), (p-5), and (p-6) are for obtaining a sufficient amount of light around the screen while reducing the effective diameter of the first group for the above reasons.
[0057]
(A-7) The distance between the second lens unit and the aperture stop at the zoom position at which the aperture stop is farthest on the optical axis with respect to the third lens unit and the aperture stop at L2s and L2t, respectively, and the zoom position and the telephoto end When the distance between the aperture stop and the third lens unit is Ls3 and L3t, respectively,
0.4 <(L2s-L2t) / (Ls3-L3t) <1.3 (1)
There exists a position of the aperture stop that satisfies the following.
[0058]
If the upper limit value of conditional expression (1) is exceeded and the aperture stop is brought closer to the third group side, the distance between the first group and the aperture stop will increase, making it difficult to reduce the effective diameter of the first group. Come. On the other hand, if the value exceeds the lower limit and is too close to the second group, the effective diameter of the lens group in the vicinity of the image surface becomes large, and it becomes difficult to maintain good optical performance.
[0059]
(A-8) When the focal length of the entire system at the wide-angle end and the telephoto end is fw, ft, and the focal length of the second group is f2,
[0060]
[Expression 7]

[0061]
And
[0062]
0.19 <| f2 / fA | ≦ 0.25 (2)
The following conditional expression is satisfied. This is a condition for making the focal length of the second group appropriate. When the focal length of the second group becomes longer than the upper limit value of conditional expression (2), it is preferable in terms of aberration, but in order to obtain a desired zoom ratio, the movement amount of the second group must be increased. This is not preferable because it increases the size of the entire lens system. On the other hand, if the lower limit is exceeded, the Petzval sum increases in the negative direction and the image plane falls, making it difficult to maintain good optical performance.
[0063]
(A-9) The distance from the last lens surface to the image plane is converted to air in the in- focus state of an object at infinity at the wide angle end, and the distance from the first lens surface on the object side to the paraxial image plane (most object side) L ) between the lens surface and the image plane) , and the focal lengths of the entire system at the wide-angle end and the telephoto end are fw, ft,
[0064]
[Equation 8]

[0065]
2.22 <L / fA <3.36 (3)
The following conditional expression is satisfied. Exceeding the upper limit of conditional expression (3) is not preferable because the total lens length becomes long. On the other hand, if the lower limit is exceeded, the Petzval sum will become negative and the image plane will fall, making it difficult to maintain good optical performance.
[0066]
(A-10) When the movement amounts of the first group and the second group in zooming from the wide-angle end to the telephoto end are set as S1 and S2,
0.6 <S1 / S2 <1.2 (4)
The following conditional expression is satisfied. Conditional expression (4) relates to the ratio of the amount of movement between the first group and the second group at the time of zooming from the wide-angle end to the telephoto end, and mainly corrects aberration fluctuations at the time of zooming while favorably correcting the first group. This is a condition for achieving both a reduction in the effective diameter of the lens and a reduction in the total lens length in a balanced manner. When the movement amount of the first group increases beyond the upper limit value, the distance from the aperture stop is increased from the intermediate focal length to the telephoto end, the off-axis light beam is separated from the lens optical axis, and the effective diameter of the first group is increased. This is not preferable. On the other hand, if the amount of movement of the first lens unit decreases beyond the lower limit, it becomes difficult to shorten the total lens length at the wide-angle end, and it becomes difficult to sell a desired zoom ratio.
[0067]
(A-11) The fifth group is characterized in that it is always fixed during zooming.
[0068]
(A-12) The third group is moved substantially perpendicularly to the optical axis direction to correct the image plane position of the subject image when the zoom lens vibrates .
[0069]
(A-13) The second lens group has a negative 21 lens with a strong concave surface facing the image surface side in order from the object side, a negative 22nd lens whose both lens surfaces are concave surfaces, and a strong convex surface on the object side compared to the image side. It is desirable to have a positive twenty-third cemented lens in which the positive lens and the negative lens directed are cemented.
[0070]
When the zoom ratio is increased in the zoom type as in the present invention, it is necessary to increase the movement amount of the second group that greatly contributes to the zooming function or shorten the focal length of the second group.
[0071]
The method described above is not preferable because it leads to an increase in the size of the zoom lens, and the method described below is burdensome on the second group, although the lens does not become large, and it becomes difficult to maintain good optical performance. Therefore, by configuring the second group as described above, the optical performance can be favorably corrected.
[0072]
(A-14) The second group has at least one aspherical surface. By arranging an aspherical surface, off-axis optical performance can be improved. In addition, the refractive power of the second group can be increased, and as a result, the amount of movement of the second group can be reduced, and the overall lens length can be shortened. The aspherical surface in the second group has a small curvature radius, the image side surface of the negative 21st lens, the object side surface of the negative 22nd lens, or the object side of the positive 23rd lens. By disposing the lens on the surface, aberration can be corrected more effectively. The off-axis of the flare can be satisfactorily corrected, especially. It is desirable that the aspherical surface has a shape in which the refractive power becomes weaker toward the periphery of the lens.
[0073]
(A-15) 20 <νp <35 (5) where the average Abbe number of the material of the positive lens in the second group is νp and the average Abbe number of the material of the negative lens is νn.
36 <νn <65 (6)
It is desirable to satisfy at least one of the following conditional expressions. This corrects the chromatic aberration generated in the second group well. Since the second group greatly contributes to zooming, the aberration generated here must be corrected well. In particular, in a zoom lens having a high zoom ratio of about 10 times, it is important to correct chromatic aberration well.
[0074]
If the upper limit of conditional expression (5) is exceeded, the axial chromatic aberration will be over and overcorrected. On the contrary, if the lower limit is exceeded, the axial chromatic aberration will be under and correction will be insufficient. Conditional expression (6) reverses the occurrence of the phenomenon as in conditional expression (5), but if the upper limit value or lower limit value is exceeded, it is difficult to correct chromatic aberration well.
[0075]
(A-16) When the average refractive power of the material of the negative lens of the second group is Nn,
1.80 <Nn <1.96 (7)
The following conditional expression is satisfied. This is also related to conditional expression (2), but it is a condition for preventing the Petzval sum from deteriorating by using a high refractive index glass for the negative lens. When the limit value is exceeded, curvature of field deteriorates.
(A-17) 0.62 <| R22 / R23 | <0.82 (8) when the radius of curvature of the second lens group is set to R2i in order from the object side.
The following conditional expression is satisfied. These are conditions for correcting coma aberration, field curvature and flare in a well-balanced manner. When the upper limit value of conditional expression (8) is exceeded, coma aberration increases. On the contrary, when the lower limit is exceeded, the image surface is curved so as to be concave toward the object side, which is not preferable. Further, the upper limit value or the lower limit value is exceeded, and the flare becomes unfavorable.
[0076]
Next, an embodiment of a video camera (optical apparatus) using the zoom lens of the present invention will be described with reference to FIG.
[0077]
In FIG. 13, 10 is a video camera body, 11 is a photographic optical system constituted by the zoom lens of the present invention, 12 is an image sensor such as a CCD that receives a subject image by the photographic optical system 11, and 13 is received by the image sensor 12. A recording means 14 for recording the subject image, and a finder for observing the subject image displayed on a display element (not shown). The display element is constituted by a liquid crystal panel or the like, and a subject image formed on the image sensor 12 is displayed.
[0078]
In this way, by applying the zoom lens of the present invention to an electronic camera such as a video camera or a digital still camera, a small optical device having high optical performance is realized.
[0079]
Hereinafter, each numerical example of the present invention will be described.
[0080]
In numerical examples, Ri is the radius of curvature of the i-th surface in order from the object side, Di is the i-th lens thickness and air spacing in order from the object side, and Ni and νi are the i-th optical in order from the object side. The refractive index and Abbe number of the material of the member.
[0081]
The aspherical shape has an X axis in the optical axis direction, an H axis perpendicular to the optical axis, a positive light traveling direction, R is a paraxial radius of curvature, and each aspheric coefficient is K, B, C, D, E, When F
[0082]
[Equation 9]

[0083]
It is expressed by the following formula.
[0084]
For example, “e-Z” means “10 ^−Z ”. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.
[0085]
[Outside 1]

[0086]
[Outside 2]

[0087]
[Outside 3]

[0088]
[Table 1]

[0089]
【The invention's effect】
According to the present invention, it is possible to simplify the lens configuration by appropriately setting the movement condition of the predetermined lens unit accompanying the zooming, the refractive power of each lens unit, the lens configuration, and the like. In addition, a small zoom lens having a high overall optical performance and a short overall lens length and an optical apparatus using the same can be achieved.
[0090]
In addition to this, according to the present invention, the lens system as a whole is miniaturized in spite of the zoom ratio of 10 times and the high zoom ratio, and the F-number is about 1.6. Although the ratio is high, a zoom lens having high optical performance and a small number of lenses can be realized.
[Brief description of the drawings]
1 is a lens cross-sectional view of Numerical Example 1 of the present invention. FIG. 2 is an aberration diagram at the wide-angle end of Numerical Example 1 of the present invention. FIG. 3 is an aberration diagram in the middle of Numerical Example 1 of the present invention. FIG. 5 is an aberration diagram at the telephoto end of Numerical Example 1 of the present invention. FIG. 5 is a lens cross-sectional view of Numerical Example 2 of the present invention. FIG. 8 is an aberration diagram at the telephoto end of Numerical Example 2 of the present invention. FIG. 9 is a lens cross-sectional view of Numerical Example 3 of the present invention. FIG. 11 is an aberration diagram in the middle of Numerical Example 3 of the present invention. FIG. 12 is an aberration diagram at the telephoto end of Numerical Example 3 in the present invention. Schematic diagram of essential parts of the optical apparatus of the invention
L1 1st group L2 2nd group L3 3rd group L4 4th group L5 5th group d d line g g line ΔM meridional image plane ΔS sagittal image plane 10 video camera body 11 zoom lens 12 image sensor 13 recording means 14 viewfinder

Claims

In order from the object side to the image side, a first group having a positive refractive power, a second group having a negative refractive power, an aperture stop, a third group having a positive refractive power, a fourth group having a positive refractive power, and a negative refraction. The first group is moved to the object side, the second group is moved to the image plane side, and the aperture stop is moved during zooming from the wide-angle end to the telephoto end. The third group is fixed, the fourth group moves with a convex locus toward the object side, the fifth group is fixed, and the fourth group is moved to perform focusing, and the wide-angle end and the telephoto end When the focal length of the entire system at the end is fw, ft, the focal length of the second group is f2, and the average value of the refractive index of the negative lens constituting the second group is Nn,
0.19 <| f2 / √ (fw · ft) | ≦ 0.25
1.80 <Nn <1.96
A zoom lens satisfying the following conditional expression:

2. The zoom lens according to claim 1, wherein the aperture stop moves to the image plane side upon zooming from the wide-angle end to the telephoto end.

2. The zoom lens according to claim 1, wherein the aperture stop moves toward the image plane from the middle position of the zooming range to the telephoto end when zooming from the wide-angle end to the telephoto end.

2. The zoom lens according to claim 1, wherein the aperture stop moves so as to be located closest to the object side at an intermediate position in the zooming range when zooming from the wide-angle end to the telephoto end.

The distance between the second group and the aperture stop at the zoom position where the aperture stop is farthest on the optical axis with respect to the third group and the telephoto end are L2s and L2t, respectively, and the aperture stop is relative to the third group. When the distance between the aperture stop and the third group at the zoom position most distant from the optical axis and the telephoto end is Ls3 and L3t, respectively.
0.4 <(L2s-L2t) / (Ls3-L3t) <1.3
5. The zoom lens according to claim 1, wherein the zoom lens satisfies the following.

When the distance between the lens surface closest to the object side and the image plane at the wide-angle end of the zoom lens is L, and the focal lengths of the entire system at the wide-angle end and the telephoto end are fw and ft, respectively.
2.22 <L / √ (fw · ft) <3.36
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.

When the movement amounts of the first group and the second group in zooming from the wide-angle end to the telephoto end are S1 and S2, respectively,
0.6 <S1 / S2 <1.2
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.

8. The variation in the imaging position when the zoom lens vibrates is corrected by moving the third group in a direction perpendicular to the optical axis. Zoom lens.

The second group includes a meniscus negative lens having a convex surface directed toward the object side, a negative lens having concave surfaces on both lens surfaces, and a cemented lens in which a positive lens and a negative lens having convex surfaces are cemented to each other. When the average value of Abbe numbers of the positive lenses constituting the second group is νp and the average value of Abbe numbers of the negative lenses constituting the second group is νn,
20 <νp <35
36 <νn <65
The zoom lens according to claim 1, wherein the zoom lens satisfies the following.

When the radius of curvature of the i-th lens surface from the object side of the second group is R2i,
0.6 <| R22 / R23 | <0.82
The zoom lens according to claim 1, wherein the zoom lens satisfies the following.

An optical apparatus comprising the zoom lens according to claim 1.