JP3733355B2

JP3733355B2 - Zoom lens

Info

Publication number: JP3733355B2
Application number: JP2003019904A
Authority: JP
Inventors: 勝啓高田
Original assignee: Olympus Corp
Current assignee: Olympus Corp
Priority date: 2003-01-29
Filing date: 2003-01-29
Publication date: 2006-01-11
Anticipated expiration: 2021-01-11
Also published as: JP2003262793A

Description

【０００１】
【産業上の利用分野】
本発明は、ズームレンズに関し、特に、撮像管や固体撮像素子を用いた電子カメラ、なかんずく近年の高精細画像を取り込む用途に適した画素数の多い撮像素子を用いた電子カメラに最適な高い光学性能を有するズームレンズに関するものである。
【０００２】
【従来の技術】
一般に、電子カメラは、撮像面積の小さな撮像管や固体撮像素子を用いて光学像を電気信号に変換するため、撮影レンズには明るいレンズ系が必要となり、また、レンズと撮像素子の間にローパスフィルタや赤外カットフィルタ等の光学部材や、ＲＧＢ三原色それぞれの画像をそれぞれの撮像素子で受光する所謂多板式の電子カメラのように、それぞれの撮像素子に光束を導く所謂色分解プリズム等の光学素子を配置する必要が生じ、焦点距離に比較して大きなバックフォーカスが必要となる。
【０００３】
さらに、動画像を撮影する用途が多く、撮影レンズとしては高変倍率のズームレンズを用いることが一般的であり、これらの要求を満たすレンズ系としては、物体側から順に、正の屈折力を持ちズーミングに際して固定の第１レンズ群と、ズーミングに際して光軸に沿って移動して変倍作用を有する負の屈折力を持つ第２レンズ群と、ズーミングに際して前後に移動して変倍の際に像面を一定に保つ作用の負の屈折力を持つ第３レンズ群と、ズーミングに際して固定の結像作用を有する正の屈折力を持つ第４レンズ群とからなる４群ズームレンズがよく知られている。
【０００４】
また、近年の電子カメラでは、フォーカシングも電気的にモータ等により行う場合が増えてきた。そこで、従来、第１レンズ群を繰り出してフォーカシングを行っていたのに対し、フォーカシングに際しての駆動力の省力化やレンズ全長を一定に保てる点等から、レンズ径が大きく重い第１レンズ群以外のレンズ群又はその一部を移動してフォーカシングを行う所謂インナーフォーカス方式が一般的になってきた。
【０００５】
物体側から順に、正・負・負・正の構成のズームレンズにインナーフォーカス方式を採用した従来例としては、特許文献１や特許文献２等のものがあり、第３レンズ群をフォーカシングに際して移動させる例が示されている。
【０００６】
また、撮像素子として１枚の固体撮像素子を用いた所謂単板式電子カメラでは、所謂色分解プリズムを必要としないため、バックフォーカスが比較的小さくて済むので、正・負・負・正の構成から第３レンズ群を省き、結像レンズ群の第４レンズ群を分割して、その一方に像面を一定に保つコンペンセータの役割を担わせた、物体側から順に、正の屈折力を持ちズーミングに際して固定の第１レンズ群と、ズーミングに際して光軸に沿って移動して変倍作用を有する負の屈折力を持つ第２レンズ群と、ズーミングに際して固定の正の屈折力を持つ第３レンズ群と、ズーミングに際して前後に移動して変倍の際に像面を一定に保つ作用の正の屈折力を持つ第４レンズ群とからなる４群ズームレンズがよく知られている。
【０００７】
このレンズタイプでは、第４レンズ群やその一部を移動させることによりフォーカシングを行うことが一般的であり、特許文献３や特許文献４や特許文献４等が知られている。
【０００８】
また、特に近年の製造技術の発展により、撮像範囲の大きさに比べて画素数の非常に多い固体撮像素子が開発され、例えばハイビジョン映像のように高精細な画像を得ることが可能となってきている。そのため、撮影レンズも撮像素子の性能を十分に引き出すことができる極めて高い光学性能を有するズームレンズが必要になってきた。撮像素子が小型化され、例えば固体撮像素子の各ピクセルの大きさが小さくなる程、高い解像力が必要となるため、撮影レンズに対する光学性能の要求はますます高くなっている。その要求に応えるズームレンズとしては、特許文献５のものが知られている。
【０００９】
【特許文献１】
特開昭６３−４４６１４号公報
【００１０】
【特許文献２】
特開平３−２５９２０９号公報
【００１１】
【特許文献３】
特開昭６２−１７８９１７号公報
【００１２】
【特許文献４】
特開昭６２−２１５２２５号公報
【００１３】
【特許文献５】
特開昭６３−１２３００９号公報
【００１４】
【特許文献６】
特開平１−１２６６１４号公報
【００１５】
【発明が解決しようとする課題】
一般に、高い光学性能を得るためには、光線をできるだけ少しずつ多くの回数屈折させて結像する方が、各屈折面での収差の発生量が少なくなるので望ましく、必然的に多くの枚数のレンズが用いられ、その結果、光学性能の向上に伴ってレンズ系も大型化する傾向が強い。
【００１６】
また、特にズームレンズでは可動群が多いため、ズーミングに伴う収差変動が生じる。理想的には、各レンズ群において収差が補正されていれば、ズーミングに伴う収差変動は生じないが、広角端から望遠端にかけて必ずしも一定の光線の通り方をする訳ではないので、若干の収差が残存し、高い光学性能を達成しようとすると、この残存収差による収差変動が無視できなくなる。そこで、可動群の数を増やし、広角端から望遠端にかけて複雑に移動させることにより、高度に収差変動を補正することが行われ、レンズ系の大型化につながる。
【００１７】
前述の従来例の特許文献６のものでは、高精細な画像を取り込むために高い光学性能を達成しているが、２つのコンペンセータを配置することによりこの収差変動を補正しており、群構成が複雑化している。また、大口径の第１レンズ群又はその一部を移動させてフォーカシングを行っており、大きな駆動力を必要とする問題もある。
【００１８】
そこで、比較的簡単な構成の従来の４群ズームレンズ構成をとりながら、高い光学性能を達成することにより、レンズ系の小型化を図ることが期待されている。
【００１９】
この点に鑑みて従来技術を眺めると、一般にズームレンズでは、移動距離の大きな変倍作用のレンズ群、所謂バリエータの屈折力を大きくし、移動距離を小さくすることによって、小型化を達成する方法がよく採用される。
【００２０】
しかし、この方法を採用すると、バリエータで発生する残存収差による収差変動をどの群において補正するかが問題となり、物体側から順に、正・負・負・正の４群ズームレンズでは、結像レンズ群である第４レンズ群が固定されているために、第１レンズ群乃至第３レンズ群でのズーミングによる収差変動を補正することが困難となる。また、物体側から順に、正・負・正・正の４群ズームレンズでは、屈折力の大きなバリエータの第２レンズ群とコンペンセータの第４レンズ群によって収差変動を補正することが容易となるが、収差変動の補正にも限界があり、第２レンズ群の負の屈折力をバックフォーカスを確保するために十分大きくすることは困難であり、所謂単板式の電子カメラ以外に適用することは難しく、所謂多板式の電子カメラと同等の解像力を得るには、数倍多くの画素数を持つ撮像素子が必要となる。
【００２１】
特許文献１や特許文献２等の、物体側から順に、正・負・負・正の４群ズームレンズの例や、特許文献３や特許文献４や特許文献５等の、物体側から順に、正・負・正・正の４群ズームレンズの例では残存収差が大きく、後記する本発明の目的である高精細な画像の取り込みには満足のゆく性能ではない。
【００２２】
以上のように、これらの従来例では、小型化、バックフォーカスの確保、高い光学性能の全てを満足するに至っていない。
【００２３】
本発明は上記事情に鑑みてなされたものであり、その目的は、比較的簡単なズームレンズ構成でありながら、撮像管や固体撮像素子等を用いた電子カメラ、特に近年の高精細画像を取り込む用途に適した画素数の多い撮像素子を用いた電子カメラに最適な、高い光学性能を有し、各種フィルタ類等の光学部材や光路分割用のプリズム等の光学素子をレンズと撮像素子の間に挿入可能な大きなバックフォーカスを有する小型のズームレンズを提供することにある。
【００２４】
また、本発明の別の目的は、無限遠物点から近距離物点に至るまで、安定した高い光学性能を有する、バックフォーカスの大きな、小型のズームレンズを提供することにある。
【００２５】
【課題を解決するための手段】
本発明のズームレンズは、上記の問題点を解決するために、物体側から順に、正の屈折力を持ちズーミングに際して固定の第１レンズ群、負の屈折力を持ちズーミングに際して光軸に沿って移動して変倍作用を持つ第２レンズ群、負の屈折力を持ち、第２レンズ群のズーミング移動に伴って変動する像面を光軸に沿って移動して一定に保つ作用の第３レンズ群、正の屈折力を持ちズーミングに際して固定で結像作用を持つ第４レンズ群からなり、
前記第３レンズ群は、物体側から順に、物体側に負の屈折力の強い方の面を向けた負レンズの第３−１サブレンズ群と、正の屈折力を持ち凹面を像側に向けた接合ダブレットレンズの第３−２サブレンズ群から構成され、
前記接合ダブレットレンズの接合面は、正の屈折力を有し、
前記第３レンズ群を物体側に繰り出すことによりフォーカシングを行うことを特徴とするものである。
本発明のもう１つのズームレンズは、物体側から順に、正の屈折力を持ちズーミングに際して固定の第１レンズ群、負の屈折力を持ちズーミングに際して光軸に沿って移動して変倍作用を持つ第２レンズ群、負の屈折力を持ち、第２レンズ群のズーミング移動に伴って変動する像面を光軸に沿って移動して一定に保つ作用の第３レンズ群、正の屈折力を持ちズーミングに際して固定で結像作用を持つ第４レンズ群からなり、
前記第３レンズ群は、物体側から順に、物体側に負の屈折力の強い方の面を向けた負レンズの第３−１サブレンズ群と、正の屈折力を持ち凹面を像側に向けた接合ダブレットレンズの第３−２サブレンズ群から構成され、以下の条件を満足することを特徴とすものである。
（５） −５．０＜ｆ_3-1／ｆ_W＜−３．０
（６）０．０＜１／ＳＦ_3-2＜０．１
ただし、ｆ_3-1は第３−１サブレンズ群の焦点距離、ＳＦ_3-2は第３−２サブレンズ群のシェイピングファクターである。ここで、シェイピングファクターＳＦは、レンズの物体側の面、像側の面の曲率半径をそれぞれｒ_F、ｒ_Rとするとき、以下の式で定義される。
ＳＦ＝（ｒ_F＋ｒ_R）／（ｒ_F−ｒ_R）
【００２６】
【作用】
以下、本発明において上記構成をとる理由と作用について説明する。
【００２７】
大きなバックフォーカスを確保するためには、物体側から順に、負・正の所謂レトロフォーカスタイプの構成にすることが望ましく、しかも、負の屈折力が強い程好ましい。しかし、物体側から順に、正・負・正・正の４群ズームレンズでは、負の屈折力を有するレンズ群が第２レンズ群のみであるため、変倍作用を有する第２レンズ群の屈折力を強くする必要があり、屈折力が過度に強いと、ズーミングに伴う収差変動が極めて大きなものとなり、好ましくない。
【００２８】
そこで、本発明のズームレンズのレンズタイプは、物体側から順に、正・負・負・正のタイプ、詳しくは、上記のレンズタイプを選択した。
【００２９】
このとき、前述のように、小型化を図るために大きな移動距離の可動群である第２レンズ群の屈折力を強めることは、収差変動が大になり好ましくない。
【００３０】
高い光学性能を得るには、特にズーミングに伴う収差変動の補正が重要であり、そのためには、各レンズ群、特に可動群での収差発生量を抑制することが望ましく、むしろ第２レンズ群の屈折力を弱めることが望まれる。
【００３１】
一方、物体側から順に、正・負・負・正の４群ズームレンズが大型化する別の理由としては、発散光束を収束光束に変換する結像レンズ群である第４レンズ群が大きな屈折力を持つために、一般に収差の発生が大きく、そのため、収差の発生を抑制する目的でレンズ枚数の増加又は各レンズ要素の屈折力の低下が図られ、第４レンズ群全体としては大型化する傾向が強い。
【００３２】
そこで、ズームレンズの例として、結像レンズ群である第４レンズ群を適切な構成とすることによって、小型でありながら良好に収差補正を行うことを可能とし、第２レンズ群の屈折力を弱めてズーミングに伴う収差変動を抑制し、可動群である第２レンズ群の移動距離が大となっても、レンズ系全体としての全長の小型化を達成したものがある。
【００３３】
具体的には、前述のように、第４レンズ群を、物体側から順に、正の屈折力を持つ第４−１サブレンズ群と、それから比較的間隔を空けて配置された正の屈折力を持つ第４−２サブレンズ群から構成し、第４−１サブレンズ群には、第１レンズ群乃至第３レンズ群による発散光束を平行光束に近い光束に変換する作用を、第４−２サブレンズ群には、収束光束に変換させる作用を持たせている。
【００３４】
さらに、第４−１サブレンズ群は、物体側から順に、少なくとも２枚の正レンズを配置して、屈折回数を多くして球面収差の発生を抑制すると共に、さらに像側に、少なくとも１枚の負レンズを配置することにより、正の球面収差を発生させ、第４−１サブレンズ群全体として正の球面収差を発生させ、第４−２サブレンズ群で発生する負の球面収差を打ち消す作用を持たせ、第４レンズ群全体として負の球面収差の発生を抑制している。また、この負レンズでは、負のコマ収差が発生し、第３レンズ群で発生する正のコマ収差を打ち消す作用を持たせている。
【００３５】
第４−２サブレンズ群は、物体側から順に、少なくとも１枚の正レンズと、少なくとも１枚の、接合面が負の屈折力を有する接合レンズから構成し、この接合面において正のコマ収差を発生させ、正レンズで発生する負のコマ収差を打ち消させることにより、第４−２サブレンズ群で発生するコマ収差を抑制している。
【００３６】
また、第４レンズ群では、一般に負の軸上色収差、負の倍率色収差が発生するが、第４−１サブレンズ群の負レンズ、及び、第４−２サブレンズ群の接合面において正の軸上色収差、正の倍率色収差を発生させ、色収差を補正している。
【００３７】
さらに、非点収差との補正バランスを考慮すると、この第４−１サブレンズ群は、物体側から順に、少なくとも２枚の正レンズと、少なくとも１枚の物体側に凹面を向けた負メニスカスレンズから構成し、非点収差の発生量を小さくせしめて、第４−１サブレンズ群の正レンズで発生する負の非点収差の補正に有効に使うことが望ましい。
【００３８】
また、第４−２サブレンズ群は、物体側から順に、少なくとも１枚の正レンズと、少なくとも１枚の、像側に凹面を向けた負メニスカスレンズと正レンズの接合レンズから構成し、この接合面で発生する正の球面収差、コマ収差等を適度な値に抑制し、過剰補正とならないようにすることが望ましい。
【００３９】
さらに良好に収差補正を行うためには、以下の条件を満足することが望ましい。
【００４０】
（１）２．５＜ｆ_4-1／ｆ_W＜４．５
（２）２．２＜ｆ_4-2／ｆ_W＜４．２
（３）０．８＜ｆ_4-1／ｆ_4-2＜１．２
（４）６．０＜ｆ_4C／ｆ_W＜１１．０
ただし、ｆ_4-1、ｆ_4-2はそれぞれ第４−１サブレンズ群、第４−２サブレンズ群の焦点距離、ｆ_4Cは第４−２サブレンズ群の構成要素である接合レンズの焦点距離、ｆ_Wは広角端におけるレンズ全系の焦点距離である。
【００４１】
条件式（１）乃至（３）は、第４−１サブレンズ群、第４−２サブレンズ群の屈折力及び配分を規定したものであり、条件式（１）の下限値２．５を越えて小さくなると、正の屈折力が強くなりすぎ、負レンズを配置しても十分大きな正の球面収差を発生させることができなくなり、第４レンズ群として負の球面収差が増大する。また、上限値４．５を越えて大きくなると、第４−１サブレンズ群では正の屈折力が弱まり、適切な正の屈折力を得るために第４−２サブレンズ群の正の屈折力が強まり、第４−１サブレンズ群では正の球面収差が、第４−２サブレンズ群では負の球面収差が増大する。広角端では、これらの球面収差がうまく打ち消すことができるが、望遠端では、第４−１サブレンズ群での正の球面収差が上回り、補正が極めて困難となる。
【００４２】
条件式（２）の下限値２．２を越えて小さくなると、第４−２サブレンズ群の正の屈折力が大きくなるために、負の球面収差が増大し、屈折力のバランスから第４−１サブレンズ群の屈折力が低下し、正の球面収差が増大しても補正が困難となる。また、第４−１サブレンズ群の屈折力低下に伴ってペッツバール和が負になり、像面の正方向への倒れが顕著になる。また、上限値４．２を越えて大きくなると、第４−２サブレンズ群の屈折力が小さくなり、負の球面収差が小さくなるものの、第４−１サブレンズ群の屈折力が増大し、正の球面収差が減少するため、第４レンズ群としては負の球面収差の増大を招く。また、正のコマ収差が大きくなるが、近軸的な屈折力の適正化から第３レンズ群の主点位置が物体側にシフトし、第３レンズ群で発生する正のコマ収差が減少するため、ズーミングに伴うコマ収差の変動が大きくなり、特に望遠端のコマ収差が極めて大きくなる。
【００４３】
条件式（３）の下限値０．８を越えて小さくなると、正の屈折力が第４−１サブレンズ群に偏り、バックフォーカスが小さくなると共に、第４−１サブレンズ群で発生する正の球面収差が減少し、第４レンズ群としての負の球面収差が増大する。また、上限値１．２を越えて大きくなると、正の屈折力が第４−２サブレンズ群に偏り、第４−１サブレンズ群の正の球面収差と第４−２サブレンズ群の負の球面収差が共に増大し、特に望遠端での補正バランスが崩れ、望遠端で正の球面収差が増大する。
【００４４】
条件式（４）は、第４−２サブレンズ群の接合レンズの屈折力を規定したものであり、下限値６．０を越えて小さくなると、接合レンズの物体側に位置する第４−２サブレンズ群の正レンズの屈折力が小さくなり、第４−２サブレンズ群での負の球面収差は小さくなるが、レンズ全長を大きくしないために第２レンズ群、第３レンズ群の主点位置の関係が変動することにより、第２レンズ群の正の球面収差が大きく、また、第３レンズ群の正の球面収差が小さくなり、ズーミングに伴う球面収差の変動が極めて大きくなる。また、上限値１１．０を越えて大きくなると、広角端では第３レンズ群の正の球面収差が増大し、望遠端では第２レンズ群の正の球面収差が増大することにより、正の球面収差が補正できなくなる。
【００４５】
さらに良好に収差補正を行うためには、以下の条件を満足することが望ましい。
【００４６】
（１）’２．９＜ｆ_4-1／ｆ_W＜３．７
（２）’２．９＜ｆ_4-2／ｆ_W＜３．６
（３）’０．９＜ｆ_4-1／ｆ_4-2＜１．１
（４）’７．０＜ｆ_4C／ｆ_W＜１０．０
また、極めて高い光学性能を満足し、かつ、十分なバックフォーカスを確保し、全長を小型に保つには、第１レンズ群乃至第３レンズ群の屈折力配分に関して、以下の条件を満足することが望ましい。
【００４７】
（７）７．０＜ｆ₁／ｆ_W＜１０．０
（８） −２．５＜ｆ₂／ｆ_W＜−１．３
（９） −５．２＜ｆ₃／ｆ_W＜−３．９
ただし、ｆ_iはそれぞれ第ｉレンズ群の焦点距離である。
【００４８】
条件式（７）の下限値７．０を越えて小さくなると、特に望遠端での負の非点収差が大きくなり、第２レンズ群の屈折力を大きくして大きな正の非点収差を発生させる必要が生じ、ズーミングに伴う非点収差の変動が大きくなる。また、第２レンズ群の屈折力の増大に伴って、特に望遠端での正の球面収差の発生が極めて大になり、補正が困難となる。上限値１０．０を越えて大きくなると、諸収差の補正から第２レンズ群の屈折力が弱く、第３レンズ群、第４レンズ群の屈折力が増大し、ズーミングに伴う球面収差、非点収差の変動が大きく、補正が困難となる。
【００４９】
条件式（８）の下限値−２．５を越えて小さくなると、第２レンズ群の負の屈折力が小さくなり、第３レンズ群の屈折力を増大させてバックフォーカスの確保に必要な負の屈折力を得なければならず、正の球面収差とコマ収差が増大し、補正が困難となる。また、上限値−１．３を越えて大きくなると、第２レンズ群で発生する負の歪曲収差と負のペッツバール和の補正をしなければならず、各群で収差発生量が増大し、好ましくない。
【００５０】
条件式（９）の下限値−５．２を越えて小さくなると、第３レンズ群の正の球面収差が小さくなり、第４レンズ群の負の球面収差を補正することができなくなる。第４レンズ群の屈折力を減少させて負の球面収差を小さくすると、負の非点収差が増大し、非点収差のバランスが崩れることとなる。また、上下値−３．９を越えて大きくなると、バックフォーカスを大きくするためには有利であるが、正の球面収差、コマ収差が増大し、第４レンズ群で発生する負の球面収差、コマ収差を大きくしないと、補正できなくなる。しかし、第４レンズ群の屈折力を増大させると、非点収差の発生量が増大し、補正できなくなる。
【００５１】
さらに良好に収差補正を行うためには、以下の条件を満足することが望ましい。
【００５２】
（７）’７．７＜ｆ₁／ｆ_W＜８．５
（８）’−２．２＜ｆ₂／ｆ_W＜−１．６
（９）’−５．０＜ｆ₃／ｆ_W＜−４．１
さて、特にフォーカシングに対して収差変動が少なく、無限遠物点から近距離物点まで安定して高い光学性能を得るためには、適切なフォーカシング方式とフォーカシングを行うレンズ群の適切な構成が重要であることは言うまでもない。本発明者は、特願平４−２８４９１１号において、物体側から順に、正・負・負・正の４群ズームレンズにおいて、負の第３レンズ群を、物体側から順に、物体側に強い負の屈折力の面を向けた負レンズと像側に負の屈折力の面を向けたメニスカスレンズで構成し、この第３レンズ群を物体側に繰り出すことによりフォーカシングを行う方法を考案した。このフォーカシング方式では、無限遠物点から近距離物点にフォーカシングした際に、負レンズで負の方向に変動する球面収差をメニスカスレンズでこの球面収差の変動を正にして打ち消すことにより、フォーカシングに伴う球面収差の変動を小さく保つことができる。
【００５３】
ここで、さらに光学性能の向上を考えると、前述のように、変倍作用を主に担う第２レンズ群の屈折力を弱めることが望ましいが、レンズ全長を大型化せずにバックフォーカスを確保するためには、適度な負の屈折力が必要であり、第２レンズ群の屈折力を弱める代りに、第３レンズ群の屈折力を強める必要が生じる。このとき、第３レンズ群の負レンズで発生する正の軸上色収差と負の倍率色収差が大きくなるが、像側に配置したメニスカスレンズを正の屈折力とし、その屈折力を強めると、色収差は補正できるが、フォーカシングに対する収差変動が大きく、本来の目的に反する。
【００５４】
そこで、本発明のズームレンズは、第３レンズ群を、物体側から順に、物体側に負の屈折力の強い方の面を向けた負レンズの第３−１サブレンズ群と、正の屈折力を持ち凹面を像側に向けた接合ダブレットレンズの第３−２サブレンズ群から構成し、色収差を良好に補正したものである。
【００５５】
さらに、この接合ダブレットレンズについて、接合面は正の屈折力を持たせることが望ましい。この構成により、接合面において負の軸上色収差と正の倍率色収差を発生させ、色収差補正を可能にすると共に、レンズ形状を強い正レンズとせずに済むため、フォーカシングに際して正の球面収差の変動を小さく保つことが可能となるのである。
【００５６】
また、さらに、この接合ダブレットレンズは、像側に凹面を向けたメニスカスレンズであるため、その構成は両凸レンズと両凹レンズの組み合せによるダブレットレンズが望ましく、他の組み合せでは、倍率色収差の補正を効果的に行うことが困難となる。
【００５７】
さらに良好に諸収差の補正を行うためには、以下の条件を満足することが望ましい。
【００５８】
（５） −５．０＜ｆ_3-1／ｆ_W＜−３．０
（６）０．０＜１／ＳＦ_3-2＜０．１
ただし、ｆ_3-1は第３−１サブレンズ群の焦点距離、ＳＦ_3-2は第３−２サブレンズ群のシェイピングファクターである。ここで、シェイピングファクターＳＦは、レンズの物体側の面、像側の面の曲率半径をそれぞれｒ_F、ｒ_Rとするとき、以下の式で定義される。
【００５９】
ＳＦ＝（ｒ_F＋ｒ_R）／（ｒ_F−ｒ_R）
条件式（５）の下限値−５．０を越えて小さくなると、負の屈折力を確保するために、第３−２サブレンズ群が負レンズ群となり、近軸的な関係から主点位置が変動するため、第３レンズ群で発生する正の球面収差が小さくなり、第４レンズ群で発生する負の球面収差を補正することが困難となる。また、第３レンズ群で発生する正の軸上色収差が大きくなり、他のレンズ群で負の軸上色収差を発生させると、ズーミングに伴う収差変動が極めて大きくなり、特に望遠端での軸上色収差を補正できなくなる。また、上限値−３．０を越えて大きくなると、第３−１サブレンズ群で発生する正の軸上色収差を補正するために、第３−２サブレンズ群の正の屈折力を大きくすることが必要になるが、フォーカシングに際しての収差変動を抑制するために、軸上色収差を打ち消すまで屈折力を大きくすることができず、広角端、望遠端での収差バランスをとるために第４レンズ群の負の軸上色収差、第２レンズ群の正の軸上色収差が大きくなり、それに伴って第２レンズ群で発生する負の倍率色収差が補正できなくなる。
【００６０】
条件式（６）の下限値０．０を越えて小さくなると、レンズ形状は正に強くなるため、接合面の曲率は正の屈折力を弱めるために緩くなり、また、物体側の面の曲率が強くなる。そのため、物体側の面で発生する負の球面収差と像側の面で発生する正の球面収差の変動が大きくなり、第３レンズ群として発生する正の球面収差が、広角端では小さく、望遠端では大きくなり、第４レンズ群で発生する負の球面収差をコントロールしても補正しきれない。また、フォーカシングに際しての収差変動が大きく、近距離物点に対する性能劣化を招く。また、上限値０．１を越えて大きくなると、負形状が強くなり、像側の屈折面で大きな正の球面収差が発生する。一方、適度な正の屈折力を確保するために接合面の曲率は強くなり、負の球面収差が大となるが、像側の面で発生する正の球面収差を補正するには至らない。そのため、正の球面収差が大きくなり、他のレンズ群を用いても補正できなくなる。
【００６１】
さらに良好に収差補正を行うには、以下の条件を満足することが望ましい。
【００６２】
（５）’−４．５＜ｆ_3-1／ｆ_W＜−３．６
（６）’０．０＜１／ＳＦ_3-2＜０．０５
以下の条件を満足すればさらに良い。
【００６３】
（６）”０．０＜１／ＳＦ_3-2＜０．０３。
【００６４】
【実施例】
以下に、図面を参照にして本発明の実施例１〜６のズームレンズについて説明する。
【００６５】
各実施例の数値データは後記するが、実施例１は、図１に広角端から標準状態を経て望遠端に至る各レンズ群の様子を示すように、その構成は、物体側から順に、全体として正の屈折力を持ちズーミングに際して固定の第１レンズ群Ｉと、全体として負の屈折力を持ちズーミングに際して光軸上を移動することにより変倍作用を有する第２レンズ群IIと、全体として負の屈折力を持ち、ズーミングに際して光軸上を前後に移動することにより像面を一定に保つ作用を有する第３レンズ群III と、全体として正の屈折力を持ちズーミングに際して固定で結像作用を有する第４レンズ群IVとからなる。
【００６６】
第１レンズ群Ｉは、物体側から順に、像側に凹面を向けた負メニスカスレンズと両凸レンズの接合レンズと、２枚の像側に凹面を向けた正メニスカスレンズからなる。
【００６７】
第２レンズ群IIは、物体側から順に、像側に凹面を向けた負メニスカスレンズと、両凹レンズと、像側に凹面を向けた正メニスカスレンズと、物体側に凹面を向けた負メニスカスレンズからなる。
【００６８】
第３レンズ群III は、物体側から順に、物体側に強い屈折力の方の面を向けた両凹レンズ（第３−１サブレンズ群III-1 ）と、両凸レンズと両凹レンズの接合レンズ（第３−２サブレンズ群III-2 ）からなる。
【００６９】
第４レンズ群IVは、物体側から順に、全体として正の屈折力を持つ第４−１サブレンズ群IV-1と、全体として正の屈折力を持つ第４−２サブレンズ群IV-2からなり、第４−１サブレンズ群IV-1は、物体側から順に、像側に強い屈折力の方の面を向けた両凸レンズと、物体側に凸面を向けた平凸レンズと、物体側に凹面を向けた負メニスカスレンズからなる。第４−２サブレンズ群IV-2は、物体側から順に、物体側に凹面を向けた正メニスカスレンズと、像側に凹面を向けた負メニスカスレンズと両凸レンズの接合レンズからなる。
【００７０】
絞りは、第３レンズ群III と第４レンズ群IVの間に配置され、ズーミングに際して固定である。
【００７１】
本実施例は、レンズと撮像面との間に、複数の撮像素子に光路を分割する等のためにプリズム等の光学部材を挿入するのに十分なバックフォーカスを有し、図に示したように、ＲＧＢ３原色の画像をそれぞれの撮像素子で得るために、光束をそれぞれの撮像素子に導くための光路分割用プリズムＰをレンズと撮像素子の間に配置している。
【００７２】
実施例１の広角端、標準状態、望遠端での無限遠物点に対する収差状況をそれぞれ図６、図７、図８に示す。また、望遠端における物点距離１ｍの場合の収差状況を図９に示す。なお、収差状況としては、球面収差、非点収差、歪曲収差、倍率色収差、軸外横収差を示す。以下、同じ。
【００７３】
これらの図から明らかなように、本実施例は、広角端から望遠端に至るズーミングに際して、また、無限遠物点から近距離物点に至るフォーカシングに際して、安定して極めて高い光学性能を有し、近年の高精細画像を取り込む用途に適した画素数の多い撮像素子を用いた電子カメラに最適な光学性能を有している。
【００７４】
実施例２は、図２に広角端での断面図を示すようなレンズ構成であり、実施例１と比較して、第２レンズ群IIが、物体側から順に、像側に凹面を向けた負メニスカスレンズと、両凹レンズと、物体側に凸面を向けた平凸レンズと、物体側に凹面を向けた負メニスカスレンズからなる点と、第４−１サブレンズ群IV-1が、物体側から順に、像側に強い屈折力の方の面を向けた両凸レンズと、物体側に強い屈折力の方の面を向けた両凸レンズと、物体側に凹面を向けた負メニスカスレンズからなる点で異なっている。実施例２の広角端、標準状態、望遠端での無限遠物点に対する収差状況をそれぞれ図１０、図１１、図１２に示す。また、望遠端における物点距離１ｍの場合の収差状況を図１３に示す。
【００７５】
実施例３は、図３に広角端での断面図を示すようなレンズ構成であり、実施例１と比較して、第４−１サブレンズ群IV-1が、物体側から順に、像側に強い屈折力の方の面を向けた両凸レンズと、物体側に強い屈折力の方の面を向けた両凸レンズと、物体側に凹面を向けた負メニスカスレンズからなる点で異なっている。実施例３の広角端、標準状態、望遠端での無限遠物点に対する収差状況をそれぞれ図１４、図１５、図１６に示す。また、望遠端における物点距離１ｍの場合の収差状況を図１７に示す。
【００７６】
実施例４は、実施例３と同様の構成を取っており、図示は省く。実施例４の広角端、標準状態、望遠端での無限遠物点に対する収差状況をそれぞれ図１８、図１９、図２０に示す。また、望遠端における物点距離１ｍの場合の収差状況を図２１に示す。
【００７７】
実施例５は、図４に広角端での断面図を示すようなレンズ構成であり、実施例１と比較して、第２レンズ群IIが、物体側から順に、像側に凹面を向けた負メニスカスレンズと、両凹レンズと、像側に凹面を向けた正メニスカスレンズと、物体側に凹面を向けた平凹レンズからなる点と、第４−１サブレンズ群IV-1が、物体側から順に、像側に強い屈折力の方の面を向けた両凸レンズと、物体側に強い屈折力の方の面を向けた両凸レンズ、物体側に凹面を向けた負メニスカスレンズからなる点で異なっている。図４より明らかに、本実施例は、ローパスフィルタや赤外カットフィルタ等の光学部材を挿入するには十分なバックフォーカスを確保しているが、実施例１乃至４のようにレンズと撮像面の間には複数の撮像素子に光路を分割する等のためにプリズム等の光学部材を挿入していない。その分レンズ全長を短くした例であり、本発明のズームレンズ系が、単板式電子カメラのように全長の短縮化の優先度を高めた場合にも、十分適用できることを示している。
【００７８】
実施例５の広角端、標準状態、望遠端での無限遠物点に対する収差状況をそれぞれ図２２、図２３、図２４に示す。また、望遠端における物点距離１ｍの場合の収差状況を図２５に示す。
【００７９】
実施例６は、図５に広角端での断面図を示すようなレンズ構成であり、実施例５と比較して、第２レンズ群IIが、物体側から順に、像側に凹面を向けた負メニスカスレンズと、両凹レンズと、像側に凹面を向けた正メニスカスレンズと、物体側に強い屈折力の方の面を向けた両凹レンズからなる点で異なっている。実施例６の広角端、標準状態、望遠端での無限遠物点に対する収差状況をそれぞれ図２６、図２７、図２８に示す。また、望遠端における物点距離１ｍの場合の収差状況を図２９に示す。
【００８０】
以上の各実施例では、第３レンズ群III を物体側に繰り出すことによりフォーカシングを行っているが、第１レンズ群Ｉ等の他のレンズ群や、第４−２サブレンズ群IV-2や第４−１サブレンズ群IV-1 等の他のレンズ群の一部、あるいは、第３レンズ群III と第４レンズ群IV等の他のレンズ群、あるいは、他のレンズ群の一部を組み合わせて移動することによりフォーカシングを行うことも可能である。
【００８１】
以下に、上記各実施例の数値データを示すが、記号は上記の外、ｆは全系焦点距離、Ｆ_NOはＦナンバー、２ωは画角、ｒ₁、ｒ₂…は各レンズ面の曲率半径、ｄ₁、ｄ₂…は各レンズ面間の間隔、ｎ_d1、ｎ_d2…は各レンズのｄ線の屈折率、ν_d1、ν_d2…は各レンズのアッベ数である。なお、ズーム間隔に関する表中、括弧内の数値は、物点距離１ｍにフォーカシングしたときの間隔を示す。
【００８２】
実施例１
ｆ＝ 9.200 〜25.567 〜72.007
Ｆ_NO＝ 2.0 〜 2.0 〜 2.0
２ω＝49.113°〜17.618°〜 6.258°
ｒ₁= 197.3081 ｄ₁= 2.0000 ｎ_d1 =1.83350 ν_d1 =21.00
ｒ₂= 105.1497 ｄ₂= 5.3000 ｎ_d2 =1.56907 ν_d2 =71.30
ｒ₃= -546.9522 ｄ₃= 0.1000
ｒ₄= 72.8412 ｄ₄= 5.0000 ｎ_d3 =1.43875 ν_d3 =94.97
ｒ₅= 547.8902 ｄ₅= 0.1000
ｒ₆= 52.3882 ｄ₆= 4.2300 ｎ_d4 =1.43875 ν_d4 =94.97
ｒ₇= 151.1643 ｄ₇=(可変)
ｒ₈= 61.0924 ｄ₈= 1.2000 ｎ_d5 =1.69680 ν_d5 =55.52
ｒ₉= 15.9872 ｄ₉= 5.3531
ｒ₁₀= -40.8139 ｄ₁₀= 1.0000 ｎ_d6 =1.61800 ν_d6 =63.38
ｒ₁₁= 64.0384 ｄ₁₁= 0.1000
ｒ₁₂= 30.5618 ｄ₁₂= 2.3000 ｎ_d7 =1.83350 ν_d7 =21.00
ｒ₁₃= 968.8110 ｄ₁₃= 1.4972
ｒ₁₄= -31.0496 ｄ₁₄= 1.0000 ｎ_d8 =1.72916 ν_d8 =54.68
ｒ₁₅= -805.0028 ｄ₁₅=(可変)
ｒ₁₆= -19.3481 ｄ₁₆= 1.2000 ｎ_d9 =1.48749 ν_d9 =70.20
ｒ₁₇= 1087.0698 ｄ₁₇= 0.1000
ｒ₁₈= 28.2827 ｄ₁₈= 5.9981 ｎ_d10=1.80610 ν_d10=40.95
ｒ₁₉= -30.0000 ｄ₁₉= 1.2000 ｎ_d11=1.77250 ν_d11=49.66
ｒ₂₀= 27.8186 ｄ₂₀=(可変)
ｒ₂₁= ∞（絞り）ｄ₂₁= 1.5000
ｒ₂₂= 621.8818 ｄ₂₂= 3.8793 ｎ_d12=1.60311 ν_d12=60.70
ｒ₂₃= -20.5472 ｄ₂₃= 0.1000
ｒ₂₄= 32.2619 ｄ₂₄= 3.7155 ｎ_d13=1.61375 ν_d13=56.36
ｒ₂₅= ∞ ｄ₂₅= 2.9102
ｒ₂₆= -18.9985 ｄ₂₆= 1.0000 ｎ_d14=1.80518 ν_d14=25.43
ｒ₂₇= -38.9775 ｄ₂₇= 8.2271
ｒ₂₈= -94.3367 ｄ₂₈= 6.3283 ｎ_d15=1.60311 ν_d15=60.70
ｒ₂₉= -24.5090 ｄ₂₉= 0.1000
ｒ₃₀= 31.2799 ｄ₃₀= 1.0000 ｎ_d16=1.87400 ν_d16=35.26
ｒ₃₁= 15.8062 ｄ₃₁= 3.5100 ｎ_d17=1.56907 ν_d17=71.30
ｒ₃₂= -95.3269 ｄ₃₂= 3.0000
ｒ₃₃= ∞ ｄ₃₃=25.3000 ｎ_d18=1.58267 ν_d18=46.33
ｒ₃₄= ∞ ｄ₃₄=11.1000 ｎ_d19=1.51633 ν_d19=64.15
ｒ₃₅= ∞
ズーム間隔

ｆ₁/ｆ_W ＝ 8.1595 ｆ₂/ｆ_W ＝-1.8699 ｆ₃/ｆ_W ＝-4.6529
ｆ_4-1/ｆ_W＝ 3.3008 ｆ_4-2/ｆ_W＝ 3.2201 ｆ_4-1/ｆ_4-2＝ 1.0251
ｆ_4C /ｆ_W＝ 7.3954 ｆ_3-1/ｆ_W＝-4.2373 1/ＳＦ_3-2 ＝ 0.0083 。
【００８３】
実施例２
ｆ＝ 9.244 〜25.601 〜71.927
Ｆ_NO＝ 2.0 〜 2.0 〜 2.0
２ω＝48.969°〜17.589°〜 6.264°
ｒ₁= 197.6120 ｄ₁= 2.0000 ｎ_d1 =1.83350 ν_d1 =21.00
ｒ₂= 104.8697 ｄ₂= 5.3000 ｎ_d2 =1.56907 ν_d2 =71.30
ｒ₃= -446.3652 ｄ₃= 0.1000
ｒ₄= 68.8505 ｄ₄= 5.0000 ｎ_d3 =1.43875 ν_d3 =94.97
ｒ₅= 417.5884 ｄ₅= 0.1000
ｒ₆= 54.1787 ｄ₆= 4.2300 ｎ_d4 =1.43875 ν_d4 =94.97
ｒ₇= 146.6534 ｄ₇=(可変)
ｒ₈= 63.0838 ｄ₈= 1.2000 ｎ_d5 =1.69680 ν_d5 =55.52
ｒ₉= 16.2826 ｄ₉= 5.3543
ｒ₁₀= -38.9621 ｄ₁₀= 1.0000 ｎ_d6 =1.61800 ν_d6 =63.38
ｒ₁₁= 55.1903 ｄ₁₁= 0.1000
ｒ₁₂= 32.3006 ｄ₁₂= 2.3000 ｎ_d7 =1.83350 ν_d7 =21.00
ｒ₁₃= ∞ ｄ₁₃= 1.5376
ｒ₁₄= -29.3192 ｄ₁₄= 1.0000 ｎ_d8 =1.72916 ν_d8 =54.68
ｒ₁₅= -149.4560 ｄ₁₅=(可変)
ｒ₁₆= -18.6422 ｄ₁₆= 1.2000 ｎ_d9 =1.48749 ν_d9 =70.20
ｒ₁₇= 512.8154 ｄ₁₇= 0.1000
ｒ₁₈= 31.0045 ｄ₁₈= 5.8971 ｎ_d10=1.78590 ν_d10=44.18
ｒ₁₉= -19.1922 ｄ₁₉= 1.2000 ｎ_d11=1.72916 ν_d11=54.68
ｒ₂₀= 29.3552 ｄ₂₀=(可変)
ｒ₂₁= ∞（絞り）ｄ₂₁= 1.5000
ｒ₂₂= 271.8809 ｄ₂₂= 3.8968 ｎ_d12=1.60311 ν_d12=60.70
ｒ₂₃= -21.8578 ｄ₂₃= 0.1000
ｒ₂₄= 35.0934 ｄ₂₄= 3.7018 ｎ_d13=1.61375 ν_d13=56.36
ｒ₂₅= -558.1239 ｄ₂₅= 3.1444
ｒ₂₆= -19.8361 ｄ₂₆= 1.0000 ｎ_d14=1.80518 ν_d14=25.43
ｒ₂₇= -43.8636 ｄ₂₇= 8.6035
ｒ₂₈= -537.6966 ｄ₂₈= 6.1330 ｎ_d15=1.60311 ν_d15=60.70
ｒ₂₉= -27.0630 ｄ₂₉= 0.1000
ｒ₃₀= 32.6168 ｄ₃₀= 1.0000 ｎ_d16=1.87400 ν_d16=35.26
ｒ₃₁= 15.8461 ｄ₃₁= 4.0882 ｎ_d17=1.56907 ν_d17=71.30
ｒ₃₂= -110.2597 ｄ₃₂= 3.0000
ｒ₃₃= ∞ ｄ₃₃=25.3000 ｎ_d18=1.58267 ν_d18=46.33
ｒ₃₄= ∞ ｄ₃₄=11.1000 ｎ_d19=1.51633 ν_d19=64.15
ｒ₃₅= ∞
ズーム間隔

ｆ₁/ｆ_W ＝ 8.1381 ｆ₂/ｆ_W ＝-1.8711 ｆ₃/ｆ_W ＝-4.5789
ｆ_4-1/ｆ_W＝ 3.4349 ｆ_4-2/ｆ_W＝ 3.1847 ｆ_4-1/ｆ_4-2＝ 1.0786
ｆ_4C /ｆ_W＝ 8.4447 ｆ_3-1/ｆ_W＝-3.9887 1/ＳＦ_3-2 ＝ 0.0273 。
【００８４】
実施例３
ｆ＝ 9.155 〜25.470 〜71.792
Ｆ_NO＝ 2.0 〜 2.0 〜 2.0
２ω＝49.282°〜17.658°〜 6.273°
ｒ₁= 189.8195 ｄ₁= 2.0000 ｎ_d1 =1.83350 ν_d1 =21.00
ｒ₂= 106.3382 ｄ₂= 5.3000 ｎ_d2 =1.49700 ν_d2 =81.61
ｒ₃= -363.5344 ｄ₃= 0.1000
ｒ₄= 73.3026 ｄ₄= 5.0000 ｎ_d3 =1.43875 ν_d3 =94.97
ｒ₅= 721.8012 ｄ₅= 0.1000
ｒ₆= 51.1180 ｄ₆= 4.2300 ｎ_d4 =1.43875 ν_d4 =94.97
ｒ₇= 140.5591 ｄ₇=(可変)
ｒ₈= 59.2368 ｄ₈= 1.2000 ｎ_d5 =1.69680 ν_d5 =55.52
ｒ₉= 15.9520 ｄ₉= 5.3453
ｒ₁₀= -42.2129 ｄ₁₀= 1.0000 ｎ_d6 =1.61800 ν_d6 =63.38
ｒ₁₁= 61.1428 ｄ₁₁= 0.1000
ｒ₁₂= 30.0722 ｄ₁₂= 2.3000 ｎ_d7 =1.83350 ν_d7 =21.00
ｒ₁₃= 543.5115 ｄ₁₃= 1.5641
ｒ₁₄= -30.0999 ｄ₁₄= 1.0000 ｎ_d8 =1.72916 ν_d8 =54.68
ｒ₁₅= -463.3256 ｄ₁₅=(可変)
ｒ₁₆= -19.0377 ｄ₁₆= 1.2000 ｎ_d9 =1.48749 ν_d9 =70.20
ｒ₁₇= 255.4218 ｄ₁₇= 0.1000
ｒ₁₈= 31.9211 ｄ₁₈= 5.9916 ｎ_d10=1.78590 ν_d10=44.18
ｒ₁₉= -20.4887 ｄ₁₉= 1.2000 ｎ_d11=1.72916 ν_d11=54.68
ｒ₂₀= 30.9715 ｄ₂₀=(可変)
ｒ₂₁= ∞（絞り）ｄ₂₁= 1.5000
ｒ₂₂= 239.2299 ｄ₂₂= 3.8935 ｎ_d12=1.60311 ν_d12=60.70
ｒ₂₃= -21.5818 ｄ₂₃= 0.1000
ｒ₂₄= 34.8649 ｄ₂₄= 3.5799 ｎ_d13=1.61772 ν_d13=49.83
ｒ₂₅= -319.6570 ｄ₂₅= 2.9338
ｒ₂₆= -19.8422 ｄ₂₆= 1.0000 ｎ_d14=1.80518 ν_d14=25.43
ｒ₂₇= -47.6130 ｄ₂₇= 8.4357
ｒ₂₈= -354.0919 ｄ₂₈= 6.0278 ｎ_d15=1.60311 ν_d15=60.70
ｒ₂₉= -26.2256 ｄ₂₉= 0.1000
ｒ₃₀= 32.9626 ｄ₃₀= 1.0000 ｎ_d16=1.87400 ν_d16=35.26
ｒ₃₁= 15.6412 ｄ₃₁= 3.6999 ｎ_d17=1.56907 ν_d17=71.30
ｒ₃₂= -104.6406 ｄ₃₂= 3.0000
ｒ₃₃= ∞ ｄ₃₃=25.3000 ｎ_d18=1.58267 ν_d18=46.33
ｒ₃₄= ∞ ｄ₃₄=11.1000 ｎ_d19=1.51633 ν_d19=64.15
ｒ₃₅= ∞
ズーム間隔

ｆ₁/ｆ_W ＝ 8.1919 ｆ₂/ｆ_W ＝-1.8780 ｆ₃/ｆ_W ＝-4.5943
ｆ_4-1/ｆ_W＝ 3.4269 ｆ_4-2/ｆ_W＝ 3.2182 ｆ_4-1/ｆ_4-2＝ 1.0648
ｆ_4C /ｆ_W＝ 8.6941 ｆ_3-1/ｆ_W＝-3.9640 1/ＳＦ_3-2 ＝ 0.0151 。
【００８５】
実施例４
ｆ＝ 9.192 〜25.517 〜71.615
Ｆ_NO＝ 2.0 〜 2.0 〜 2.0
２ω＝48.985°〜17.610°〜 6.287°
ｒ₁= 189.9135 ｄ₁= 2.0000 ｎ_d1 =1.83350 ν_d1 =21.00
ｒ₂= 105.6874 ｄ₂= 5.3000 ｎ_d2 =1.49700 ν_d2 =81.61
ｒ₃= -358.8365 ｄ₃= 0.1000
ｒ₄= 73.4031 ｄ₄= 5.0000 ｎ_d3 =1.43875 ν_d3 =94.97
ｒ₅= 727.2932 ｄ₅= 0.1000
ｒ₆= 51.1560 ｄ₆= 4.2300 ｎ_d4 =1.43875 ν_d4 =94.97
ｒ₇= 140.5501 ｄ₇=(可変)
ｒ₈= 59.3218 ｄ₈= 1.2000 ｎ_d5 =1.69680 ν_d5 =55.52
ｒ₉= 15.9171 ｄ₉= 5.3448
ｒ₁₀= -42.3113 ｄ₁₀= 1.0000 ｎ_d6 =1.61800 ν_d6 =63.38
ｒ₁₁= 60.0575 ｄ₁₁= 0.1000
ｒ₁₂= 30.1516 ｄ₁₂= 2.3000 ｎ_d7 =1.83350 ν_d7 =21.00
ｒ₁₃= 622.6014 ｄ₁₃= 1.5650
ｒ₁₄= -30.3946 ｄ₁₄= 1.0000 ｎ_d8 =1.72916 ν_d8 =54.68
ｒ₁₅= -439.3981 ｄ₁₅=(可変)
ｒ₁₆= -18.9565 ｄ₁₆= 1.2000 ｎ_d9 =1.48749 ν_d9 =70.20
ｒ₁₇= 283.3954 ｄ₁₇= 0.1000
ｒ₁₈= 32.0654 ｄ₁₈= 5.9912 ｎ_d10=1.78590 ν_d10=44.18
ｒ₁₉= -20.6565 ｄ₁₉= 1.2000 ｎ_d11=1.72916 ν_d11=54.68
ｒ₂₀= 31.1179 ｄ₂₀=(可変)
ｒ₂₁= ∞（絞り）ｄ₂₁= 1.5000
ｒ₂₂= 224.1327 ｄ₂₂= 3.8934 ｎ_d12=1.60311 ν_d12=60.70
ｒ₂₃= -21.5625 ｄ₂₃= 0.1000
ｒ₂₄= 34.8176 ｄ₂₄= 3.5800 ｎ_d13=1.61772 ν_d13=49.83
ｒ₂₅= -327.3882 ｄ₂₅= 2.9338
ｒ₂₆= -19.7780 ｄ₂₆= 1.0000 ｎ_d14=1.80518 ν_d14=25.43
ｒ₂₇= -47.8125 ｄ₂₇= 8.4361
ｒ₂₈= -352.3666 ｄ₂₈= 6.0280 ｎ_d15=1.60311 ν_d15=60.70
ｒ₂₉= -26.1466 ｄ₂₉= 0.1000
ｒ₃₀= 33.1453 ｄ₃₀= 1.0000 ｎ_d16=1.87400 ν_d16=35.26
ｒ₃₁= 15.5881 ｄ₃₁= 3.7000 ｎ_d17=1.56907 ν_d17=71.30
ｒ₃₂= -102.2519 ｄ₃₂= 3.0000
ｒ₃₃= ∞ ｄ₃₃=25.3000 ｎ_d18=1.58267 ν_d18=46.33
ｒ₃₄= ∞ ｄ₃₄=11.1000 ｎ_d19=1.51633 ν_d19=64.15
ｒ₃₅= ∞
ズーム間隔

ｆ₁/ｆ_W ＝ 8.1667 ｆ₂/ｆ_W ＝-1.8783 ｆ₃/ｆ_W ＝-4.5869
ｆ_4-1/ｆ_W＝ 3.4088 ｆ_4-2/ｆ_W＝ 3.2082 ｆ_4-1/ｆ_4-2＝ 1.0625
ｆ_4C /ｆ_W＝ 8.7193 ｆ_3-1/ｆ_W＝-3.9599 1/ＳＦ_3-2 ＝ 0.0150 。
【００８６】
実施例５
ｆ＝ 9.160 〜25.558 〜71.950
Ｆ_NO＝ 2.0 〜 2.0 〜 2.0
２ω＝49.220°〜17.602°〜 6.256°
ｒ₁= 214.8678 ｄ₁= 2.0000 ｎ_d1 =1.83350 ν_d1 =21.00
ｒ₂= 114.8112 ｄ₂= 5.3000 ｎ_d2 =1.49700 ν_d2 =81.61
ｒ₃= -280.1195 ｄ₃= 0.1000
ｒ₄= 69.2733 ｄ₄= 5.0000 ｎ_d3 =1.43875 ν_d3 =94.97
ｒ₅= 498.1384 ｄ₅= 0.1000
ｒ₆= 51.4092 ｄ₆= 4.2300 ｎ_d4 =1.43875 ν_d4 =94.97
ｒ₇= 132.3773 ｄ₇=(可変)
ｒ₈= 66.7529 ｄ₈= 1.2000 ｎ_d5 =1.69680 ν_d5 =55.52
ｒ₉= 16.0594 ｄ₉= 5.3649
ｒ₁₀= -41.9645 ｄ₁₀= 1.0000 ｎ_d6 =1.61800 ν_d6 =63.38
ｒ₁₁= 93.3191 ｄ₁₁= 0.1000
ｒ₁₂= 30.3487 ｄ₁₂= 2.3000 ｎ_d7 =1.83350 ν_d7 =21.00
ｒ₁₃= 243.7892 ｄ₁₃= 1.6437
ｒ₁₄= -32.4908 ｄ₁₄= 1.0000 ｎ_d8 =1.72916 ν_d8 =54.68
ｒ₁₅= ∞ ｄ₁₅=(可変)
ｒ₁₆= -19.0018 ｄ₁₆= 1.2000 ｎ_d9 =1.48749 ν_d9 =70.20
ｒ₁₇= 267.3031 ｄ₁₇= 0.1000
ｒ₁₈= 25.7142 ｄ₁₈= 5.3023 ｎ_d10=1.78590 ν_d10=44.18
ｒ₁₉= -47.5733 ｄ₁₉= 1.2000 ｎ_d11=1.72916 ν_d11=54.68
ｒ₂₀= 24.9853 ｄ₂₀=(可変)
ｒ₂₁= ∞（絞り）ｄ₂₁= 1.5000
ｒ₂₂= 242.0915 ｄ₂₂= 3.6544 ｎ_d12=1.60311 ν_d12=60.70
ｒ₂₃= -19.3814 ｄ₂₃= 0.1000
ｒ₂₄= 29.3715 ｄ₂₄= 2.9821 ｎ_d13=1.60311 ν_d13=60.70
ｒ₂₅= -1456.1020 ｄ₂₅= 1.6402
ｒ₂₆= -19.3088 ｄ₂₆= 1.0000 ｎ_d14=1.80518 ν_d14=25.43
ｒ₂₇= -47.7151 ｄ₂₇=10.7574
ｒ₂₈= -142.1109 ｄ₂₈= 6.0592 ｎ_d15=1.60311 ν_d15=60.70
ｒ₂₉= -24.9286 ｄ₂₉= 0.1000
ｒ₃₀= 29.8304 ｄ₃₀= 1.0000 ｎ_d16=1.87400 ν_d16=35.26
ｒ₃₁= 14.9246 ｄ₃₁= 4.3524 ｎ_d17=1.56907 ν_d17=71.30
ｒ₃₂= -163.9926
ズーム間隔

ｆ₁/ｆ_W ＝ 8.1905 ｆ₂/ｆ_W ＝-1.8921 ｆ₃/ｆ_W ＝-4.4614
ｆ_4-1/ｆ_W＝ 3.2068 ｆ_4-2/ｆ_W＝ 3.3069 ｆ_4-1/ｆ_4-2＝ 0.9697
ｆ_4C /ｆ_W＝ 8.7237 ｆ_3-1/ｆ_W＝-3.9675 1/ＳＦ_3-2 ＝ 0.0144 。
【００８７】
実施例６
ｆ＝ 9.003 〜25.492 〜71.972
Ｆ_NO＝ 2.0 〜 2.0 〜 2.0
２ω＝49.949°〜17.642°〜 6.253°
ｒ₁= 214.6492 ｄ₁= 2.0000 ｎ_d1 =1.83350 ν_d1 =21.00
ｒ₂= 113.0438 ｄ₂= 5.3000 ｎ_d2 =1.49700 ν_d2 =81.61
ｒ₃= -292.9631 ｄ₃= 0.1000
ｒ₄= 69.7853 ｄ₄= 5.0000 ｎ_d3 =1.43875 ν_d3 =94.97
ｒ₅= 708.8696 ｄ₅= 0.1000
ｒ₆= 50.0471 ｄ₆= 4.2300 ｎ_d4 =1.43875 ν_d4 =94.97
ｒ₇= 122.1518 ｄ₇=(可変)
ｒ₈= 58.2294 ｄ₈= 1.2000 ｎ_d5 =1.69680 ν_d5 =55.52
ｒ₉= 15.4000 ｄ₉= 5.2784
ｒ₁₀= -40.5987 ｄ₁₀= 1.0000 ｎ_d6 =1.61800 ν_d6 =63.38
ｒ₁₁= 98.4973 ｄ₁₁= 0.1000
ｒ₁₂= 28.7904 ｄ₁₂= 2.3000 ｎ_d7 =1.83350 ν_d7 =21.00
ｒ₁₃= 195.0991 ｄ₁₃= 1.6170
ｒ₁₄= -32.0483 ｄ₁₄= 1.0000 ｎ_d8 =1.72916 ν_d8 =54.68
ｒ₁₅= 1284.2129 ｄ₁₅=(可変)
ｒ₁₆= -17.9064 ｄ₁₆= 1.2000 ｎ_d9 =1.48749 ν_d9 =70.20
ｒ₁₇= 1249.1440 ｄ₁₇= 0.1000
ｒ₁₈= 22.5533 ｄ₁₈= 4.2041 ｎ_d10=1.78590 ν_d10=44.18
ｒ₁₉= -46.4740 ｄ₁₉= 1.2000 ｎ_d11=1.72916 ν_d11=54.68
ｒ₂₀= 21.2975 ｄ₂₀=(可変)
ｒ₂₁= ∞（絞り）ｄ₂₁= 1.5000
ｒ₂₂= 208.7578 ｄ₂₂= 3.1994 ｎ_d12=1.60311 ν_d12=60.70
ｒ₂₃= -19.6135 ｄ₂₃= 0.1000
ｒ₂₄= 26.3003 ｄ₂₄= 2.9996 ｎ_d13=1.60311 ν_d13=60.70
ｒ₂₅= -1108.9644 ｄ₂₅= 1.4438
ｒ₂₆= -19.4039 ｄ₂₆= 1.0000 ｎ_d14=1.80518 ν_d14=25.43
ｒ₂₇= -51.1011 ｄ₂₇=10.5712
ｒ₂₈= -116.8701 ｄ₂₈= 2.6008 ｎ_d15=1.60311 ν_d15=60.70
ｒ₂₉= -23.0163 ｄ₂₉= 0.1000
ｒ₃₀= 26.6785 ｄ₃₀= 1.0000 ｎ_d16=1.87400 ν_d16=35.26
ｒ₃₁= 13.4925 ｄ₃₁= 3.8121 ｎ_d17=1.56907 ν_d17=71.30
ｒ₃₂= -374.3053
ズーム間隔

ｆ₁/ｆ_W ＝ 8.2930 ｆ₂/ｆ_W ＝-1.9015 ｆ₃/ｆ_W ＝-4.4611
ｆ_4-1/ｆ_W＝ 3.1052 ｆ_4-2/ｆ_W＝ 3.3149 ｆ_4-1/ｆ_4-2＝ 0.9367
ｆ_4C /ｆ_W＝ 9.2481 ｆ_3-1/ｆ_W＝-4.0210 1/ＳＦ_3-2 ＝ 0.0286 。
【００８８】
以上の本発明のズームレンズは、以下のように構成することができる。
〔１〕物体側から順に、正の屈折力を持ちズーミングに際して固定の第１レンズ群、負の屈折力を持ちズーミングに際して光軸に沿って移動して変倍作用を持つ第２レンズ群、負の屈折力を持ち、第２レンズ群のズーミング移動に伴って変動する像面を光軸に沿って移動して一定に保つ作用の第３レンズ群、正の屈折力を持ちズーミングに際して固定で結像作用を持つ第４レンズ群からなり、前記第４レンズ群は、物体側から順に、正の屈折力を持つ第４−１サブレンズ群と、それから比較的間隔を空けて配置された正の屈折力を持つ第４−２サブレンズ群から構成され、前記第４−１サブレンズ群は、物体側から順に、少なくとも２枚の正レンズと少なくとも１枚の負レンズからなり、前記第４−２サブレンズ群は、物体側から順に、少なくとも１枚の正レンズと接合面が負の屈折力である少なくとも１枚の接合レンズからなることを特徴とするズームレンズ。
〔２〕前記第４−１サブレンズ群は、物体側から順に、少なくとも２枚の正レンズと、物体側に凹面を向けた少なくとも１枚の負メニスカスレンズから構成されることを特徴とする上記〔１〕記載のズームレンズ。
〔３〕物体側から順に、正の屈折力を持ちズーミングに際して固定の第１レンズ群、負の屈折力を持ちズーミングに際して光軸に沿って移動して変倍作用を持つ第２レンズ群、負の屈折力を持ち、第２レンズ群のズーミング移動に伴って変動する像面を光軸に沿って移動して一定に保つ作用の第３レンズ群、正の屈折力を持ちズーミングに際して固定で結像作用を持つ第４レンズ群からなり、前記第３レンズ群は、物体側から順に、物体側に負の屈折力の強い方の面を向けた負レンズの第３−１サブレンズ群と、正の屈折力を持ち凹面を像側に向けた接合ダブレットレンズの第３−２サブレンズ群から構成されることを特徴とするズームレンズ。
〔４〕前記第４−２サブレンズ群は、物体側から順に、少なくとも１枚の正レンズと、少なくとも１枚の、像側に凹面を向けた負メニスカスレンズと正レンズの接合レンズから構成されることを特徴とする上記〔１〕記載のズームレンズ。
〔５〕以下の条件を満足することを特徴とする上記〔１〕記載のズームレンズ：
（１）２．５＜ｆ_4-1／ｆ_W＜４．５
ただし、ｆ_4-1は第４−１サブレンズ群の焦点距離、ｆ_Wは広角端におけるレンズ全系の焦点距離である。
〔６〕以下の条件を満足することを特徴とする上記〔１〕記載のズームレンズ：
（２）２．２＜ｆ_4-2／ｆ_W＜４．２
ただし、ｆ_4-2は第４−２サブレンズ群の焦点距離、ｆ_Wは広角端におけるレンズ全系の焦点距離である。
〔７〕以下の条件を満足することを特徴とする上記〔１〕記載のズームレンズ：
（３）０．８＜ｆ_4-1／ｆ_4-2＜１．２
ただし、ｆ_4-1、ｆ_4-2はそれぞれ第４−１サブレンズ群、第４−２サブレンズ群の焦点距離である。
〔８〕以下の条件を満足することを特徴とする上記〔１〕記載のズームレンズ：
（４）６．０＜ｆ_4C／ｆ_W＜１１．０
ただし、ｆ_4Cは第４−２サブレンズ群の構成要素である接合レンズの焦点距離、ｆ_Wは広角端におけるレンズ全系の焦点距離である。
〔９〕前記第３レンズ群を物体側に繰り出すことによりフォーカシングを行うことを特徴とする上記〔３〕記載のズームレンズ。
〔１０〕前記第３−２サブレンズ群の接合面は正の屈折力であることを特徴とする上記〔３〕記載のズームレンズ。
〔１１〕前記第３−２サブレンズ群の接合ダブレットレンズは、両凸レンズと両凹レンズからなることを特徴とする上記〔３〕記載のズームレンズ。
〔１２〕以下の条件を満足することを特徴とする上記〔３〕記載のズームレンズ：
（５） −５．０＜ｆ_3-1／ｆ_W＜−３．０
ただし、ｆ_3-1は第３−１サブレンズ群の焦点距離、ｆ_Wは広角端におけるレンズ全系の焦点距離である。
〔１３〕以下の条件を満足することを特徴とする上記〔３〕記載のズームレンズ：
（６）０．０＜１／ＳＦ_3-2＜０．１
ただし、ＳＦ_3-2は第３−２サブレンズ群のシェイピングファクターであり、ここで、シェイピングファクターＳＦは、レンズの物体側の面、像側の面の曲率半径をそれぞれｒ_F、ｒ_Rとするとき、以下の式で定義される。
【００８９】
ＳＦ＝（ｒ_F＋ｒ_R）／（ｒ_F−ｒ_R）。
【００９０】
【発明の効果】
以上に詳細に説明したように、また各実施例からも明らかなように、本発明によれば、比較的簡単なズームレンズ構成でありながら、撮像管や固体撮像素子等を用いた電子カメラ、特に、近年の高精細画像を取り込む用途に適した画素数の多い撮像素子を用いた電子カメラに最適な高い光学性能を有し、各種フィルタ類等の光学部材や光路分割用のプリズム等の光学素子をレンズと撮像素子の間に挿入可能な大きなバックフォーカスを有する、小型のズームレンズを実現することができる。
【００９１】
また、本発明の別の発明によれば、無限遠物点から近距離物点に至るまで、安定した高い光学性能を有する、バックフォーカスの大きな、小型の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】本発明の実施例１のズームレンズの広角端から標準状態を経て望遠端に至る各レンズ群の様子を示す図である。
【図２】実施例２の広角端でのレンズ断面図である。
【図３】実施例３の広角端でのレンズ断面図である。
【図４】実施例５の広角端でのレンズ断面図である。
【図５】実施例６の広角端でのレンズ断面図である。
【図６】実施例１の広角端での無限遠物点に対する収差状況を示す収差図である。
【図７】実施例１の標準状態での無限遠物点に対する収差状況を示す収差図である。
【図８】実施例１の望遠端での無限遠物点に対する収差状況を示す収差図である。
【図９】実施例１の望遠端における物点距離１ｍの場合の収差状況を示す収差図である。
【図１０】実施例２の広角端での無限遠物点に対する収差状況を示す収差図である。
【図１１】実施例２の標準状態での無限遠物点に対する収差状況を示す収差図である。
【図１２】実施例２の望遠端での無限遠物点に対する収差状況を示す収差図である。
【図１３】実施例２の望遠端における物点距離１ｍの場合の収差状況を示す収差図である。
【図１４】実施例３の広角端での無限遠物点に対する収差状況を示す収差図である。
【図１５】実施例３の標準状態での無限遠物点に対する収差状況を示す収差図である。
【図１６】実施例３の望遠端での無限遠物点に対する収差状況を示す収差図である。
【図１７】実施例３の望遠端における物点距離１ｍの場合の収差状況を示す収差図である。
【図１８】実施例４の広角端での無限遠物点に対する収差状況を示す収差図である。
【図１９】実施例４の標準状態での無限遠物点に対する収差状況を示す収差図である。
【図２０】実施例４の望遠端での無限遠物点に対する収差状況を示す収差図である。
【図２１】実施例４の望遠端における物点距離１ｍの場合の収差状況を示す収差図である。
【図２２】実施例５の広角端での無限遠物点に対する収差状況を示す収差図である。
【図２３】実施例５の標準状態での無限遠物点に対する収差状況を示す収差図である。
【図２４】実施例５の望遠端での無限遠物点に対する収差状況を示す収差図である。
【図２５】実施例５の望遠端における物点距離１ｍの場合の収差状況を示す収差図である。
【図２６】実施例６の広角端での無限遠物点に対する収差状況を示す収差図である。
【図２７】実施例６の標準状態での無限遠物点に対する収差状況を示す収差図である。
【図２８】実施例６の望遠端での無限遠物点に対する収差状況を示す収差図である。
【図２９】実施例６の望遠端における物点距離１ｍの場合の収差状況を示す収差図である。
【符号の説明】
Ｉ …第１レンズ群
II …第２レンズ群
III …第３レンズ群
III-1 …第３−１サブレンズ群
III-2 …第３−２サブレンズ群
IV …第４レンズ群
IV-1…第４−１サブレンズ群
IV-2…第４−２サブレンズ群
Ｐ …光路分割用プリズム[0001]
[Industrial application fields]
The present invention relates to a zoom lens, and in particular, an optical camera that uses an image pickup tube or a solid-state image sensor, and in particular, a high optical optimum for an electronic camera that uses an image sensor with a large number of pixels suitable for use in capturing a recent high-definition image. The present invention relates to a zoom lens having performance.
[0002]
[Prior art]
In general, an electronic camera converts an optical image into an electrical signal using an imaging tube or a solid-state imaging device having a small imaging area. Therefore, a photographing lens requires a bright lens system, and a low-pass between the lens and the imaging device. Optical elements such as so-called color separation prisms that guide light beams to the respective image sensors, such as optical members such as filters and infrared cut filters, and so-called multi-plate electronic cameras that receive the images of the three primary colors of RGB with the respective image sensors. An element needs to be arranged, and a large back focus is required compared to the focal length.
[0003]
Furthermore, there are many uses for capturing moving images, and it is common to use a zoom lens with a high zoom ratio as a photographic lens.A lens system that satisfies these requirements has a positive refractive power in order from the object side. A first lens group that is fixed during zooming, a second lens group that moves along the optical axis during zooming and has a negative refracting power, and a zoom lens that moves back and forth during zooming. A four-group zoom lens is well known which includes a third lens group having a negative refractive power that keeps the image surface constant and a fourth lens group having a positive refractive power that has a fixed image-forming action during zooming. ing.
[0004]
In recent electronic cameras, there is an increasing number of cases where focusing is also performed electrically by a motor or the like. Conventionally, the first lens group has been extended to perform focusing. On the other hand, other than the first lens group, which has a large lens diameter and is heavy, from the viewpoint of saving the driving force during focusing and keeping the entire lens length constant. A so-called inner focus system in which focusing is performed by moving a lens group or a part thereof has become common.
[0005]
In order from the object side, there are conventional examples in which the inner focus method is adopted for zoom lenses having positive, negative, negative, and positive configurations, such as Patent Document 1 and Patent Document 2, and the third lens group is moved during focusing. An example is shown.
[0006]
A so-called single-plate electronic camera using a single solid-state image sensor as an image sensor does not require a so-called color separation prism, so that the back focus can be relatively small. The third lens group is omitted, the fourth lens group of the imaging lens group is divided, and one of them has a function of a compensator that keeps the image plane constant. A first lens group that is fixed during zooming, a second lens group that moves along the optical axis during zooming and has a negative refractive power, and a third lens that has positive refractive power that is fixed during zooming A four-group zoom lens is well known that includes a group and a fourth lens group that has a positive refractive power that moves back and forth during zooming and keeps the image plane constant during zooming.
[0007]
In this lens type, it is common to perform focusing by moving the fourth lens group or a part thereof, and Patent Document 3, Patent Document 4, Patent Document 4, and the like are known.
[0008]
In particular, due to recent developments in manufacturing technology, solid-state imaging devices with a very large number of pixels compared to the size of the imaging range have been developed, making it possible to obtain high-definition images such as high-definition images. ing. For this reason, a zoom lens having extremely high optical performance that can sufficiently bring out the performance of the image sensor has been required. As the image sensor is miniaturized, for example, the smaller the size of each pixel of the solid-state image sensor, the higher the resolution, the higher the optical performance requirements for the photographic lens. As a zoom lens that meets this requirement, one disclosed in Patent Document 5 is known.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 63-44614
[0010]
[Patent Document 2]
JP-A-3-259209
[0011]
[Patent Document 3]
Japanese Patent Laid-Open No. 62-178717
[0012]
[Patent Document 4]
JP-A-62-215225
[0013]
[Patent Document 5]
Japanese Unexamined Patent Publication No. 63-123209
[0014]
[Patent Document 6]
JP-A-1-126614
[0015]
[Problems to be solved by the invention]
In general, in order to obtain high optical performance, it is desirable to refract a light beam as many times as possible to form an image because the amount of aberration generated on each refracting surface is reduced. Lenses are used, and as a result, there is a strong tendency to increase the size of lens systems as optical performance improves.
[0016]
In particular, since there are many movable groups in a zoom lens, aberration fluctuations occur due to zooming. Ideally, if aberrations are corrected in each lens group, aberration fluctuations due to zooming will not occur, but there will be some aberrations because they do not necessarily pass a certain ray from the wide-angle end to the telephoto end. Therefore, if an attempt is made to achieve high optical performance, aberration fluctuations due to the residual aberration cannot be ignored. Therefore, by increasing the number of movable groups and moving them in a complicated manner from the wide-angle end to the telephoto end, aberration variations are highly corrected, leading to an increase in the size of the lens system.
[0017]
In the above-mentioned conventional example of Patent Document 6, high optical performance is achieved in order to capture a high-definition image, but this aberration variation is corrected by arranging two compensators, and the group configuration is It is getting complicated. Further, focusing is performed by moving the first lens unit having a large aperture or a part of the first lens unit, and there is a problem that a large driving force is required.
[0018]
Therefore, it is expected to reduce the size of the lens system by achieving high optical performance while adopting a conventional 4-group zoom lens configuration having a relatively simple configuration.
[0019]
Looking at the prior art in view of this point, in general, in a zoom lens, a method of achieving miniaturization by increasing the refractive power of a so-called variator having a large moving distance, that is, a variator, and reducing the moving distance. Is often adopted.
[0020]
However, when this method is adopted, it becomes a problem in which group the aberration variation due to the residual aberration generated in the variator is corrected. In the four-group zoom lens of positive / negative / negative / positive in order from the object side, the imaging lens Since the fourth lens group, which is a group, is fixed, it is difficult to correct aberration variation due to zooming in the first to third lens groups. Further, in the positive, negative, positive, and positive four-group zoom lenses in order from the object side, it is easy to correct aberration fluctuations by the second lens group of the variator and the fourth lens group of the compensator having a large refractive power. In addition, there is a limit to correction of aberration fluctuations, and it is difficult to increase the negative refractive power of the second lens group sufficiently to ensure the back focus, and it is difficult to apply to applications other than so-called single-plate electronic cameras. In order to obtain a resolving power equivalent to that of a so-called multi-plate electronic camera, an image sensor having a pixel number several times larger is required.
[0021]
Examples of positive, negative, negative, and positive four-group zoom lenses in order from the object side, such as Patent Document 1 and Patent Document 2, and in order from the object side, such as Patent Document 3, Patent Document 4, and Patent Document 5, In the example of the positive / negative / positive / positive four-group zoom lens, the residual aberration is large, and it is not a satisfactory performance for capturing a high-definition image which is the object of the present invention described later.
[0022]
As described above, these conventional examples have not yet satisfied all of downsizing, securing of back focus, and high optical performance.
[0023]
The present invention has been made in view of the above circumstances, and an object of the present invention is to capture an electronic camera using an imaging tube, a solid-state imaging device, or the like, particularly a recent high-definition image, while having a relatively simple zoom lens configuration. Optimal for electronic cameras using image sensors with a large number of pixels suitable for the application, having high optical performance, optical members such as various filters and optical elements such as optical path splitting prisms between the lens and the image sensor Another object of the present invention is to provide a small zoom lens having a large back focus that can be inserted into the zoom lens.
[0024]
Another object of the present invention is to provide a small zoom lens having a large back focus and stable high optical performance from an object point at infinity to a near object point.
[0025]
[Means for Solving the Problems]
In order to solve the above problems, the zoom lens according to the present invention, in order from the object side, has a positive first refractive power having a positive refractive power and a fixed first lens group during zooming, and has a negative refractive power along the optical axis during zooming. A second lens group that moves and has a zooming action, a third lens that has a negative refractive power and moves along the optical axis to keep the image plane that fluctuates with the zooming movement of the second lens group constant. A fourth lens unit having a positive refractive power and a fixed imaging function during zooming,
The third lens group includes, in order from the object side, a negative lens third-first sub-lens group having a surface having a strong negative refractive power directed toward the object side, and a negative surface having a positive refractive power on the image side. Composed of the 3-2 sub lens group of the cemented doublet lens
The cemented surface of the cemented doublet lens has a positive refractive power,
Focusing is performed by extending the third lens group toward the object side.
Another zoom lens according to the present invention has, in order from the object side, a first lens unit having a positive refractive power and fixed during zooming, and having a negative refractive power and moving along the optical axis during zooming to perform a zooming action. A second lens group having a negative refractive power, and a third lens group having a function of moving along the optical axis to keep the image plane fluctuating with the zooming movement of the second lens group constant, a positive refractive power It consists of a fourth lens group that has a fixed and imaging function during zooming,
The third lens group includes, in order from the object side, a negative lens third-first sub-lens group having a surface having a strong negative refractive power directed toward the object side, and a negative surface having a positive refractive power on the image side. It consists of the 3-2 sub lens group of the directing doublet lens, and satisfies the following conditions.
(5) -5.0 <f _3-1 / F _W <-3.0
(6) 0.0 <1 / SF _3-2 <0.1
Where f _3-1 Is the focal length of the 3-1 sub lens group, SF _3-2 Is the shaping factor of the 3-2 sub lens group. Here, the shaping factor SF is the radius of curvature of the object side surface and the image side surface of the lens. _F , R _R Is defined by the following equation.
SF = (r _F + R _R ) / (R _F -R _R )
[0026]
[Action]
Hereinafter, the reason and effect | action which take the said structure in this invention are demonstrated.
[0027]
In order to ensure a large back focus, it is desirable to adopt a negative / positive so-called retrofocus type structure in order from the object side, and it is more preferable that the negative refractive power is stronger. However, in the positive, negative, positive, and positive four-group zoom lenses in order from the object side, the second lens group has only a negative refracting power. Therefore, the second lens group having a variable power action is refracted. It is necessary to increase the force, and if the refractive power is excessively strong, aberration fluctuations accompanying zooming become extremely large, which is not preferable.
[0028]
Therefore, as the lens type of the zoom lens according to the present invention, positive, negative, negative, and positive types, specifically, the above lens types were selected in order from the object side.
[0029]
At this time, as described above, it is not preferable to increase the refractive power of the second lens group, which is a movable group having a large moving distance, in order to reduce the size, because aberration fluctuations increase.
[0030]
In order to obtain high optical performance, it is particularly important to correct aberration fluctuations caused by zooming. For this purpose, it is desirable to suppress the amount of aberration generated in each lens group, particularly the movable group. It is desirable to weaken the refractive power.
[0031]
On the other hand, another reason why the positive, negative, negative, and positive four-unit zoom lenses increase in size from the object side is that the fourth lens unit, which is an imaging lens unit that converts a divergent beam into a convergent beam, has a large refraction. In general, the occurrence of aberrations is large due to the power, and therefore the number of lenses is increased or the refractive power of each lens element is reduced for the purpose of suppressing the occurrence of aberrations, and the entire fourth lens group is enlarged. The tendency is strong.
[0032]
Therefore, as an example of a zoom lens, by appropriately configuring the fourth lens group that is an imaging lens group, it is possible to correct aberrations satisfactorily while being small, and the refractive power of the second lens group can be increased. Some lenses achieve a reduction in the overall length of the entire lens system even when the movement distance of the second lens group, which is a movable group, is increased by weakening to suppress aberration fluctuations associated with zooming.
[0033]
Specifically, as described above, the fourth lens group is arranged in order from the object side, the 4-1 sub lens group having a positive refractive power, and the positive refractive power disposed at a relatively long distance from the fourth sub lens group. 4-2 sub-lens group, and the 4-1 sub-lens group has an action of converting the divergent light beam from the first lens group to the third lens group into a light beam close to a parallel light beam. The two sub-lens group has an effect of converting into a convergent light beam.
[0034]
Further, in the fourth-first sub lens group, at least two positive lenses are arranged in order from the object side, the number of refractions is increased to suppress the occurrence of spherical aberration, and at least one lens is further provided on the image side. By arranging the negative lens, positive spherical aberration is generated, positive spherical aberration is generated as a whole of the 4-1 sub lens group, and negative spherical aberration generated in the 4-2 sub lens group is canceled. Thus, the fourth lens unit as a whole suppresses the occurrence of negative spherical aberration. Further, in this negative lens, a negative coma aberration is generated, and the positive coma aberration generated in the third lens group is canceled.
[0035]
The 4-2 sub lens group includes, in order from the object side, at least one positive lens and at least one cemented lens having a negative refractive power at the cemented surface. And the negative coma generated in the positive lens is canceled, thereby suppressing the coma generated in the 4-2 sub lens group.
[0036]
In the fourth lens group, negative axial chromatic aberration and negative lateral chromatic aberration generally occur. However, the fourth lens group is positive on the cemented surface of the negative lens of the 4-1 sub lens group and the 4-2 sub lens group. On-axis chromatic aberration and positive lateral chromatic aberration are generated to correct chromatic aberration.
[0037]
Further, considering the correction balance with astigmatism, the fourth-first sub-lens group includes, in order from the object side, at least two positive lenses and at least one negative meniscus lens having a concave surface facing the object side. It is desirable to reduce the amount of astigmatism and effectively use it to correct negative astigmatism generated in the positive lens of the fourth-first sub-lens group.
[0038]
The 4-2 sub lens group includes, in order from the object side, at least one positive lens, and at least one cemented lens of a negative meniscus lens having a concave surface facing the image side and a positive lens. It is desirable to suppress positive spherical aberration, coma, and the like generated on the cemented surface to appropriate values so as not to cause overcorrection.
[0039]
In order to correct aberrations more satisfactorily, it is desirable to satisfy the following conditions.
[0040]
(1) 2.5 <f _4-1 / F _W <4.5
(2) 2.2 <f _4-2 / F _W <4.2
(3) 0.8 <f _4-1 / F _4-2 <1.2
(4) 6.0 <f _4C / F _W <11.0
Where f _4-1 , F _4-2 Are the focal lengths of the 4-1 sub lens group and the 4-2 sub lens group, respectively, f _4C Is the focal length of the cemented lens, which is a component of the 4-2 sub lens group, f _W Is the focal length of the entire lens system at the wide-angle end.
[0041]
Conditional expressions (1) to (3) define the refractive power and distribution of the 4-1 sub lens group and the 4-2 sub lens group, and the lower limit value 2.5 of the conditional expression (1) is set. If the value is too small, the positive refractive power becomes too strong, and even if a negative lens is arranged, a sufficiently large positive spherical aberration cannot be generated, and the negative spherical aberration increases as the fourth lens group. On the other hand, when the value exceeds the upper limit of 4.5, the positive refractive power of the fourth-first sub-lens group becomes weak, and the positive refractive power of the fourth-second sub-lens group is obtained in order to obtain an appropriate positive refractive power. Increases, positive spherical aberration increases in the 4-1 sub lens group, and negative spherical aberration increases in the 4-2 sub lens group. At the wide-angle end, these spherical aberrations can be canceled well, but at the telephoto end, the positive spherical aberration in the fourth-first sub-lens group is higher and correction becomes extremely difficult.
[0042]
When the value exceeds the lower limit of 2.2 in the conditional expression (2), the positive refractive power of the 4-2 sub lens unit increases, so that the negative spherical aberration increases, and the fourth from the balance of refractive power. -Even if the refractive power of the sub lens group decreases and the positive spherical aberration increases, correction becomes difficult. Further, the Petzval sum becomes negative as the refractive power of the 4th-1 sub lens group decreases, and the tilt of the image plane in the positive direction becomes significant. On the other hand, when the value exceeds the upper limit of 4.2, the refractive power of the 4-2 sub-lens group decreases and the negative spherical aberration decreases, but the refractive power of the 4-1 sub-lens group increases. Since the positive spherical aberration decreases, the fourth lens group causes an increase in negative spherical aberration. Further, the positive coma increases, but the principal point position of the third lens group shifts to the object side due to the paraxial optimization of the refractive power, and the positive coma generated in the third lens group decreases. Therefore, the fluctuation of coma accompanying zooming becomes large, and especially the coma at the telephoto end becomes extremely large.
[0043]
When the lower limit value 0.8 of conditional expression (3) is exceeded, the positive refractive power is biased toward the 4th-1 sub-lens group, the back focus is reduced, and the positive generated at the 4th-1 sub-lens group. And the negative spherical aberration as the fourth lens group increases. When the value exceeds the upper limit of 1.2, the positive refractive power is biased toward the 4-2 sub lens group, and the positive spherical aberration of the 4-1 sub lens group and the negative of the 4-2 sub lens group. Both of the spherical aberration increases, particularly, the balance of correction at the telephoto end is lost, and the positive spherical aberration increases at the telephoto end.
[0044]
Conditional expression (4) defines the refractive power of the cemented lens of the 4-2 sub-lens group. When the lower limit value 6.0 is exceeded, the 4-2 is located on the object side of the cemented lens. Although the refractive power of the positive lens in the sub lens group is reduced and the negative spherical aberration in the 4-2 sub lens group is reduced, the main points of the second lens group and the third lens group in order not to increase the total lens length. When the positional relationship fluctuates, the positive spherical aberration of the second lens group becomes large, the positive spherical aberration of the third lens group becomes small, and the fluctuation of the spherical aberration accompanying zooming becomes extremely large. When the value exceeds the upper limit of 11.0, the positive spherical aberration of the third lens unit increases at the wide-angle end, and the positive spherical aberration of the second lens unit increases at the telephoto end. Aberration cannot be corrected.
[0045]
In order to correct aberrations more satisfactorily, it is desirable to satisfy the following conditions.
[0046]
(1) '2.9 <f _4-1 / F _W <3.7
(2) '2.9 <f _4-2 / F _W <3.6
(3) '0.9 <f _4-1 / F _4-2 <1.1
(4) '7.0 <f _4C / F _W <10.0
In addition, in order to satisfy extremely high optical performance, ensure sufficient back focus, and keep the overall length small, the following conditions must be satisfied regarding the refractive power distribution of the first to third lens groups. Is desirable.
[0047]
(7) 7.0 <f ₁ / F _W <10.0
(8) -2.5 <f ₂ / F _W <-1.3
(9) -5.2 <f _Three / F _W <-3.9
Where f _i Is the focal length of the i-th lens group.
[0048]
When the value exceeds the lower limit of 7.0 in conditional expression (7), negative astigmatism increases particularly at the telephoto end, and the refractive power of the second lens group is increased to generate large positive astigmatism. Astigmatism variation due to zooming increases. In addition, as the refractive power of the second lens group increases, the generation of positive spherical aberration, particularly at the telephoto end, becomes extremely large, making correction difficult. When the value exceeds the upper limit of 10.0, the refractive power of the second lens group becomes weak due to correction of various aberrations, the refractive power of the third lens group and the fourth lens group increases, and spherical aberrations caused by zooming, astigmatism. Variations in aberrations are large, making correction difficult.
[0049]
When the value exceeds the lower limit of −2.5 in conditional expression (8), the negative refractive power of the second lens group decreases, and the refractive power of the third lens group increases to reduce the negative power necessary to secure the back focus. Refractive power must be obtained, positive spherical aberration and coma increase, and correction becomes difficult. On the other hand, if the value exceeds the upper limit of −1.3, the negative distortion and negative Petzval sum generated in the second lens group must be corrected, and the amount of aberration generated increases in each group. Absent.
[0050]
If the lower limit -5.2 of conditional expression (9) is exceeded, the positive spherical aberration of the third lens group becomes small, and the negative spherical aberration of the fourth lens group cannot be corrected. If the negative spherical aberration is reduced by reducing the refractive power of the fourth lens group, negative astigmatism increases and the balance of astigmatism is lost. On the other hand, when the value exceeds the upper and lower values of −3.9, it is advantageous for increasing the back focus. However, positive spherical aberration and coma increase, and negative spherical aberration generated in the fourth lens group. If coma is not increased, correction cannot be performed. However, when the refractive power of the fourth lens group is increased, the amount of astigmatism increases and correction cannot be performed.
[0051]
In order to correct aberrations more satisfactorily, it is desirable to satisfy the following conditions.
[0052]
(7) '7.7 <f ₁ / F _W <8.5
(8) '-2.2 <f ₂ / F _W <-1.6
(9) '-5.0 <f _Three / F _W <-4.1
Now, in order to obtain stable and high optical performance from an infinite object point to a short distance object point, an appropriate focusing method and an appropriate configuration of the lens group that performs the focusing are important, especially when there is little aberration variation for focusing. Needless to say. In the Japanese Patent Application No. Hei 4-284911, the inventor in the positive, negative, negative, and positive four-group zoom lens in order from the object side, the negative third lens group is strong on the object side in order from the object side. A negative lens having a negative refractive power surface and a meniscus lens having a negative refractive power surface facing the image side, and a method of focusing by extending the third lens group toward the object side have been devised. In this focusing method, when focusing from an infinite object point to a close object point, the spherical aberration that changes in the negative direction with the negative lens is corrected by using the meniscus lens to cancel the change of the spherical aberration positively. The fluctuation of the accompanying spherical aberration can be kept small.
[0053]
Here, considering further improvement in optical performance, as mentioned above, it is desirable to weaken the refractive power of the second lens group, which mainly handles zooming, but it ensures back focus without increasing the overall length of the lens. In order to achieve this, an appropriate negative refractive power is required, and instead of reducing the refractive power of the second lens group, it is necessary to increase the refractive power of the third lens group. At this time, positive axial chromatic aberration and negative lateral chromatic aberration generated in the negative lens of the third lens group increase. However, if the meniscus lens arranged on the image side has a positive refractive power and the refractive power is increased, the chromatic aberration is increased. Can be corrected, but the fluctuation of aberration with respect to focusing is large, which is contrary to the original purpose.
[0054]
Therefore, in the zoom lens of the present invention, the third lens group, in order from the object side, the negative third 3-1 sub-lens group with the surface having the strong negative refractive power facing the object side, and the positive refraction. This lens is composed of a 3-2 sub lens group of a cemented doublet lens having a force and a concave surface facing the image side, and chromatic aberration is corrected well.
[0055]
Further, for this cemented doublet lens, it is desirable that the cemented surface has a positive refractive power. With this configuration, negative axial chromatic aberration and positive lateral chromatic aberration are generated on the cemented surface, enabling chromatic aberration correction and eliminating the need for a strong positive lens shape. It is possible to keep it small.
[0056]
Further, since this cemented doublet lens is a meniscus lens having a concave surface facing the image side, a doublet lens comprising a combination of a biconvex lens and a biconcave lens is desirable, and other combinations are effective in correcting lateral chromatic aberration. It is difficult to do it automatically.
[0057]
In order to further correct various aberrations, it is desirable to satisfy the following conditions.
[0058]
(5) -5.0 <f _3-1 / F _W <-3.0
(6) 0.0 <1 / SF _3-2 <0.1
Where f _3-1 Is the focal length of the 3-1 sub lens group, SF _3-2 Is the shaping factor of the 3-2 sub lens group. Here, the shaping factor SF is the radius of curvature of the object side surface and the image side surface of the lens. _F , R _R Is defined by the following equation.
[0059]
SF = (r _F + R _R ) / (R _F -R _R )
If the lower limit of −5.0 is exceeded in conditional expression (5), the third sub-lens group becomes a negative lens group to secure negative refractive power, and the principal point position is determined from a paraxial relationship. Therefore, the positive spherical aberration generated in the third lens group becomes small, and it becomes difficult to correct the negative spherical aberration generated in the fourth lens group. In addition, if the positive axial chromatic aberration that occurs in the third lens group increases and negative axial chromatic aberration occurs in the other lens groups, the aberration fluctuations associated with zooming become extremely large, especially on the axis at the telephoto end. Chromatic aberration cannot be corrected. On the other hand, when the value exceeds the upper limit of −3.0, the positive refractive power of the third-second sub-lens group is increased in order to correct positive axial chromatic aberration occurring in the third-first sub-lens group. In order to suppress aberration fluctuations during focusing, the refractive power cannot be increased until the axial chromatic aberration is canceled, and the fourth lens is used to balance aberrations at the wide-angle end and the telephoto end. The negative on-axis chromatic aberration of the lens group and the positive on-axis chromatic aberration of the second lens group become large, and accordingly, the negative magnification chromatic aberration generated in the second lens group cannot be corrected.
[0060]
If the lower limit value 0.0 of the conditional expression (6) is exceeded, the lens shape becomes positively strong, so that the curvature of the cemented surface becomes loose to weaken the positive refractive power, and the curvature of the object-side surface Becomes stronger. Therefore, the variation of the negative spherical aberration generated on the object side surface and the positive spherical aberration generated on the image side surface becomes large, and the positive spherical aberration generated as the third lens group is small at the wide-angle end, and the telephoto Even if the negative spherical aberration generated in the fourth lens group is controlled, it cannot be corrected. In addition, aberration fluctuations during focusing are large, leading to performance degradation for short-distance object points. On the other hand, when the value exceeds the upper limit of 0.1, the negative shape becomes strong, and a large positive spherical aberration occurs on the refracting surface on the image side. On the other hand, in order to secure an appropriate positive refractive power, the curvature of the cemented surface becomes strong and negative spherical aberration increases, but it does not lead to correction of positive spherical aberration occurring on the image side surface. For this reason, positive spherical aberration increases, and correction cannot be performed even if another lens group is used.
[0061]
For better aberration correction, it is desirable to satisfy the following conditions.
[0062]
(5) '-4.5 <f _3-1 / F _W <-3.6
(6) '0.0 <1 / SF _3-2 <0.05
It is even better if the following conditions are satisfied.
[0063]
(6) “0.0 <1 / SF _3-2 <0.03.
[0064]
【Example】
Hereinafter, zoom lenses according to first to sixth embodiments of the present invention will be described with reference to the drawings.
[0065]
Numerical data of each embodiment will be described later. In the first embodiment, as shown in FIG. 1, the configuration of each lens group from the wide-angle end to the telephoto end through the standard state is arranged in order from the object side. A first lens group I having a positive refractive power and fixed during zooming, a second lens group II having a negative refractive power as a whole and moving on the optical axis during zooming, and a zooming action as a whole A third lens unit III having a negative refractive power and maintaining the image plane constant by moving back and forth on the optical axis during zooming, and a positive imaging power as a whole with a positive refractive power and a fixed refractive power And a fourth lens unit IV.
[0066]
The first lens unit I includes, in order from the object side, a negative meniscus lens having a concave surface facing the image side, a cemented lens of a biconvex lens, and a positive meniscus lens having a concave surface facing the image side.
[0067]
The second lens group II includes, in order from the object side, a negative meniscus lens having a concave surface facing the image side, a biconcave lens, a positive meniscus lens having a concave surface facing the image side, and a negative meniscus lens having a concave surface facing the object side. Consists of.
[0068]
The third lens group III includes, in order from the object side, a biconcave lens (3-1 sub lens group III-1) having a surface with a strong refractive power directed toward the object side, and a cemented lens of a biconvex lens and a biconcave lens ( And a third sub-lens group III-2).
[0069]
The fourth lens group IV includes, in order from the object side, a 4-1 sub lens group IV-1 having a positive refractive power as a whole and a 4-2 sub lens group IV-2 having a positive refractive power as a whole. The fourth sub lens group IV-1 includes, in order from the object side, a biconvex lens having a surface with a strong refractive power directed to the image side, a plano-convex lens having a convex surface directed to the object side, and an object side. It consists of a negative meniscus lens with a concave surface facing the surface. The fourth-second sub lens unit IV-2 includes, in order from the object side, a positive meniscus lens having a concave surface facing the object side, a negative meniscus lens having a concave surface facing the image side, and a cemented lens of a biconvex lens.
[0070]
The stop is disposed between the third lens group III and the fourth lens group IV, and is fixed during zooming.
[0071]
The present embodiment has a back focus sufficient to insert an optical member such as a prism between the lens and the imaging surface to divide the optical path into a plurality of imaging elements, as shown in the figure. In addition, in order to obtain RGB three primary color images with the respective image sensors, optical path dividing prisms P for guiding the light beams to the respective image sensors are arranged between the lens and the image sensor.
[0072]
FIG. 6, FIG. 7, and FIG. 8 show the aberration states for the object point at infinity at the wide-angle end, the standard state, and the telephoto end, respectively. Further, FIG. 9 shows an aberration situation when the object point distance is 1 m at the telephoto end. The aberration status includes spherical aberration, astigmatism, distortion, lateral chromatic aberration, and off-axis lateral aberration. same as below.
[0073]
As is apparent from these figures, this embodiment has a stable and extremely high optical performance during zooming from the wide-angle end to the telephoto end, and during focusing from an infinite object point to a short-distance object point. The optical performance is optimal for an electronic camera using an image sensor with a large number of pixels suitable for recent high-definition image capturing applications.
[0074]
Example 2 has a lens configuration as shown in a cross-sectional view at the wide-angle end in FIG. 2. Compared with Example 1, the second lens group II has a concave surface directed toward the image side in order from the object side. A point consisting of a negative meniscus lens, a biconcave lens, a plano-convex lens with a convex surface facing the object side, a negative meniscus lens with a concave surface facing the object side, and the 4-1 sub lens group IV-1 In order, it consists of a biconvex lens with a strong refractive surface facing the image side, a biconvex lens with a strong refractive surface facing the object side, and a negative meniscus lens with a concave surface facing the object side. Is different. FIG. 10, FIG. 11, and FIG. 12 show the aberration states for the object point at infinity at the wide-angle end, the standard state, and the telephoto end, respectively. In addition, FIG. 13 shows an aberration situation when the object point distance is 1 m at the telephoto end.
[0075]
Example 3 has a lens configuration as shown in a cross-sectional view at the wide-angle end in FIG. 3. Compared to Example 1, the fourth sub-lens group IV-1 has an image side in order from the object side. This is different in that it consists of a biconvex lens having a surface with a strong refractive power facing the surface, a biconvex lens having a surface with a strong refractive power facing the object side, and a negative meniscus lens having a concave surface facing the object side. FIG. 14, FIG. 15, and FIG. 16 show the aberration states for the object point at infinity at the wide-angle end, the standard state, and the telephoto end, respectively, in Example 3. In addition, FIG. 17 shows an aberration situation when the object point distance is 1 m at the telephoto end.
[0076]
The fourth embodiment has the same configuration as that of the third embodiment and is not illustrated. FIG. 18, FIG. 19, and FIG. 20 show the aberration states for the object point at infinity at the wide angle end, the standard state, and the telephoto end, respectively, in Example 4. Further, FIG. 21 shows an aberration state when the object point distance is 1 m at the telephoto end.
[0077]
Example 5 has a lens configuration as shown in a cross-sectional view at the wide-angle end in FIG. 4. Compared with Example 1, the second lens group II has a concave surface directed toward the image side in order from the object side. A point consisting of a negative meniscus lens, a biconcave lens, a positive meniscus lens having a concave surface facing the image side, and a plano-concave lens having a concave surface facing the object side, and the 4-1 sub lens group IV-1 are arranged from the object side. In order, it consists of a biconvex lens with a strong refractive power facing the image side, a biconvex lens with a strong refractive power facing the object side, and a negative meniscus lens with a concave surface facing the object side. ing. As apparent from FIG. 4, the present embodiment secures a sufficient back focus for inserting an optical member such as a low-pass filter or an infrared cut filter, but the lens and the imaging surface as in the first to fourth embodiments. An optical member such as a prism is not inserted between them in order to divide the optical path among a plurality of image sensors. This is an example in which the total lens length is shortened accordingly, and shows that the zoom lens system of the present invention can be sufficiently applied even when the priority of shortening the total length is increased as in a single-plate electronic camera.
[0078]
FIG. 22, FIG. 23, and FIG. 24 show aberration states for the object point at infinity at the wide-angle end, the standard state, and the telephoto end, respectively, in Example 5. Further, FIG. 25 shows an aberration state when the object point distance is 1 m at the telephoto end.
[0079]
Example 6 has a lens configuration as shown in a cross-sectional view at the wide-angle end in FIG. 5. Compared with Example 5, the second lens group II has a concave surface directed toward the image side in order from the object side. It is different in that it comprises a negative meniscus lens, a biconcave lens, a positive meniscus lens having a concave surface facing the image side, and a biconcave lens having a surface having a strong refractive power facing the object side. FIG. 26, FIG. 27, and FIG. 28 show aberration states for the object point at infinity at the wide-angle end, the standard state, and the telephoto end, respectively, in Example 6. In addition, FIG. 29 shows an aberration state when the object point distance is 1 m at the telephoto end.
[0080]
In each of the above embodiments, focusing is performed by extending the third lens group III to the object side, but other lens groups such as the first lens group I, the 4-2 sub-lens group IV-2, Part of other lens groups such as the 4-1 sub lens group IV-1, or other lens groups such as the third lens group III and the fourth lens group IV, or part of other lens groups It is also possible to perform focusing by moving in combination.
[0081]
The numerical data of each of the above embodiments is shown below, where the symbols are outside the above, f is the total focal length, F _NO Is the F number, 2ω is the angle of view, r ₁ , R ₂ ... is the radius of curvature of each lens surface, d ₁ , D ₂ ... is the distance between each lens surface, n _d1 , N _d2 ... is the refractive index of d-line of each lens, ν _d1 , Ν _d2 ... is the Abbe number of each lens. In the table relating to the zoom interval, the numerical value in parentheses indicates the interval when focusing on an object point distance of 1 m.
[0082]
Example 1
f = 9.200 to 25.567 to 72.007
F _NO = 2.0 to 2.0 to 2.0
2ω = 49.113 ° -17.618 ° -6.258 °
r ₁ = 197.3081 d ₁ = 2.0000 n _d1 = 1.83350 ν _d1 = 21.00
r ₂ = 105.1497 d ₂ = 5.3000 n _d2 = 1.56907 ν _d2 = 71.30
r _Three = -546.9522 d _Three = 0.1000
r _Four = 72.8412 d _Four = 5.0000 n _d3 = 1.43875 ν _d3 = 94.97
r _Five = 547.8902 d _Five = 0.1000
r ₆ = 52.3882 d ₆ = 4.2300 n _d4 = 1.43875 ν _d4 = 94.97
r ₇ = 151.1643 d ₇ = (Variable)
r ₈ = 61.0924 d ₈ = 1.2000 n _d5 = 1.69680 ν _d5 = 55.52
r ₉ = 15.9872 d ₉ = 5.3531
r _Ten = -40.8139 d _Ten = 1.0000 n _d6 = 1.61800 ν _d6 = 63.38
r ₁₁ = 64.0384 d ₁₁ = 0.1000
r ₁₂ = 30.5618 d ₁₂ = 2.3000 n _d7 = 1.83350 ν _d7 = 21.00
r ₁₃ = 968.8110 d ₁₃ = 1.4972
r ₁₄ = -31.0496 d ₁₄ = 1.0000 n _d8 = 1.72916 ν _d8 = 54.68
r ₁₅ = -805.0028 d ₁₅ = (Variable)
r ₁₆ = -19.3481 d ₁₆ = 1.2000 n _d9 = 1.48749 ν _d9 = 70.20
r ₁₇ = 1087.0698 d ₁₇ = 0.1000
r ₁₈ = 28.2827 d ₁₈ = 5.9981 n _d10 = 1.80610 ν _d10 = 40.95
r ₁₉ = -30.0000 d ₁₉ = 1.2000 n _d11 = 1.77250 ν _d11 = 49.66
r ₂₀ = 27.8186 d ₂₀ = (Variable)
r _{twenty one} = ∞ (aperture) d _{twenty one} = 1.5000
r _{twenty two} = 621.8818 d _{twenty two} = 3.8793 n _d12 = 1.60311 ν _d12 = 60.70
r _{twenty three} = -20.5472 d _{twenty three} = 0.1000
r _{twenty four} = 32.2619 d _{twenty four} = 3.7155 n _d13 = 1.61375 ν _d13 = 56.36
r _{twenty five} = ∞ d _{twenty five} = 2.9102
r ₂₆ = -18.9985 d ₂₆ = 1.0000 n _d14 = 1.80518 ν _d14 = 25.43
r ₂₇ = -38.9775 d ₂₇ = 8.2271
r ₂₈ = -94.3367 d ₂₈ = 6.3283 n _d15 = 1.60311 ν _d15 = 60.70
r ₂₉ = -24.5090 d ₂₉ = 0.1000
r ₃₀ = 31.2799 d ₃₀ = 1.0000 n _d16 = 1.87400 ν _d16 = 35.26
r ₃₁ = 15.8062 d ₃₁ = 3.5100 n _d17 = 1.56907 ν _d17 = 71.30
r ₃₂ = -95.3269 d ₃₂ = 3.0000
r ₃₃ = ∞ d ₃₃ = 25.3000 n _d18 = 1.58267 ν _d18 = 46.33
r ₃₄ = ∞ d ₃₄ = 11.1000 n _d19 = 1.51633 ν _d19 = 64.15
r ₃₅ = ∞
Zoom interval

f ₁ / f _W = 8.1595 f ₂ / f _W = -1.8699 f _Three / f _W = -4.6529
f _4-1 / f _W = 3.3008 f _4-2 / f _W = 3.2201 f _4-1 / f _4-2 = 1.0251
f _4C / f _W = 7.3954 f _3-1 / f _W = -4.2373 1 / SF _3-2 = 0.0083.
[0083]
Example 2
f = 9.244 to 25.601 to 71.927
F _NO = 2.0 to 2.0 to 2.0
2ω = 48.969 ° -17.589 ° -6.264 °
r ₁ = 197.6120 d ₁ = 2.0000 n _d1 = 1.83350 ν _d1 = 21.00
r ₂ = 104.8697 d ₂ = 5.3000 n _d2 = 1.56907 ν _d2 = 71.30
r _Three = -446.3652 d _Three = 0.1000
r _Four = 68.8505 d _Four = 5.0000 n _d3 = 1.43875 ν _d3 = 94.97
r _Five = 417.5884 d _Five = 0.1000
r ₆ = 54.1787 d ₆ = 4.2300 n _d4 = 1.43875 ν _d4 = 94.97
r ₇ = 146.6534 d ₇ = (Variable)
r ₈ = 63.0838 d ₈ = 1.2000 n _d5 = 1.69680 ν _d5 = 55.52
r ₉ = 16.2826 d ₉ = 5.3543
r _Ten = -38.9621 d _Ten = 1.0000 n _d6 = 1.61800 ν _d6 = 63.38
r ₁₁ = 55.1903 d ₁₁ = 0.1000
r ₁₂ = 32.3006 d ₁₂ = 2.3000 n _d7 = 1.83350 ν _d7 = 21.00
r ₁₃ = ∞ d ₁₃ = 1.5376
r ₁₄ = -29.3192 d ₁₄ = 1.0000 n _d8 = 1.72916 ν _d8 = 54.68
r ₁₅ = -149.4560 d ₁₅ = (Variable)
r ₁₆ = -18.6422 d ₁₆ = 1.2000 n _d9 = 1.48749 ν _d9 = 70.20
r ₁₇ = 512.8154 d ₁₇ = 0.1000
r ₁₈ = 31.0045 d ₁₈ = 5.8971 n _d10 = 1.78590 ν _d10 = 44.18
r ₁₉ = -19.1922 d ₁₉ = 1.2000 n _d11 = 1.72916 ν _d11 = 54.68
r ₂₀ = 29.3552 d ₂₀ = (Variable)
r _{twenty one} = ∞ (aperture) d _{twenty one} = 1.5000
r _{twenty two} = 271.8809 d _{twenty two} = 3.8968 n _d12 = 1.60311 ν _d12 = 60.70
r _{twenty three} = -21.8578 d _{twenty three} = 0.1000
r _{twenty four} = 35.0934 d _{twenty four} = 3.7018 n _d13 = 1.61375 ν _d13 = 56.36
r _{twenty five} = -558.1239 d _{twenty five} = 3.1444
r ₂₆ = -19.8361 d ₂₆ = 1.0000 n _d14 = 1.80518 ν _d14 = 25.43
r ₂₇ = -43.8636 d ₂₇ = 8.6035
r ₂₈ = -537.6966 d ₂₈ = 6.1330 n _d15 = 1.60311 ν _d15 = 60.70
r ₂₉ = -27.0630 d ₂₉ = 0.1000
r ₃₀ = 32.6168 d ₃₀ = 1.0000 n _d16 = 1.87400 ν _d16 = 35.26
r ₃₁ = 15.8461 d ₃₁ = 4.0882 n _d17 = 1.56907 ν _d17 = 71.30
r ₃₂ = -110.2597 d ₃₂ = 3.0000
r ₃₃ = ∞ d ₃₃ = 25.3000 n _d18 = 1.58267 ν _d18 = 46.33
r ₃₄ = ∞ d ₃₄ = 11.1000 n _d19 = 1.51633 ν _d19 = 64.15
r ₃₅ = ∞
Zoom interval

f ₁ / f _W = 8.1381 f ₂ / f _W = -1.8711 f _Three / f _W = -4.5789
f _4-1 / f _W = 3.4349 f _4-2 / f _W = 3.1847 f _4-1 / f _4-2 = 1.0786
f _4C / f _W = 8.4447 f _3-1 / f _W = -3.9887 1 / SF _3-2 = 0.0273.
[0084]
Example 3
f = 9.155-25.470-71.792
F _NO = 2.0 to 2.0 to 2.0
2ω = 49.282 ° -17.658 ° -6.273 °
r ₁ = 189.8195 d ₁ = 2.0000 n _d1 = 1.83350 ν _d1 = 21.00
r ₂ = 106.3382 d ₂ = 5.3000 n _d2 = 1.49700 ν _d2 = 81.61
r _Three = -363.5344 d _Three = 0.1000
r _Four = 73.3026 d _Four = 5.0000 n _d3 = 1.43875 ν _d3 = 94.97
r _Five = 721.8012 d _Five = 0.1000
r ₆ = 51.1180 d ₆ = 4.2300 n _d4 = 1.43875 ν _d4 = 94.97
r ₇ = 140.5591 d ₇ = (Variable)
r ₈ = 59.2368 d ₈ = 1.2000 n _d5 = 1.69680 ν _d5 = 55.52
r ₉ = 15.9520 d ₉ = 5.3453
r _Ten = -42.2129 d _Ten = 1.0000 n _d6 = 1.61800 ν _d6 = 63.38
r ₁₁ = 61.1428 d ₁₁ = 0.1000
r ₁₂ = 30.0722 d ₁₂ = 2.3000 n _d7 = 1.83350 ν _d7 = 21.00
r ₁₃ = 543.5115 d ₁₃ = 1.5641
r ₁₄ = -30.0999 d ₁₄ = 1.0000 n _d8 = 1.72916 ν _d8 = 54.68
r ₁₅ = -463.3256 d ₁₅ = (Variable)
r ₁₆ = -19.0377 d ₁₆ = 1.2000 n _d9 = 1.48749 ν _d9 = 70.20
r ₁₇ = 255.4218 d ₁₇ = 0.1000
r ₁₈ = 31.9211 d ₁₈ = 5.9916 n _d10 = 1.78590 ν _d10 = 44.18
r ₁₉ = -20.4887 d ₁₉ = 1.2000 n _d11 = 1.72916 ν _d11 = 54.68
r ₂₀ = 30.9715 d ₂₀ = (Variable)
r _{twenty one} = ∞ (aperture) d _{twenty one} = 1.5000
r _{twenty two} = 239.2299 d _{twenty two} = 3.8935 n _d12 = 1.60311 ν _d12 = 60.70
r _{twenty three} = -21.5818 d _{twenty three} = 0.1000
r _{twenty four} = 34.8649 d _{twenty four} = 3.5799 n _d13 = 1.61772 ν _d13 = 49.83
r _{twenty five} = -319.6570 d _{twenty five} = 2.9338
r ₂₆ = -19.8422 d ₂₆ = 1.0000 n _d14 = 1.80518 ν _d14 = 25.43
r ₂₇ = -47.6130 d ₂₇ = 8.4357
r ₂₈ = -354.0919 d ₂₈ = 6.0278 n _d15 = 1.60311 ν _d15 = 60.70
r ₂₉ = -26.2256 d ₂₉ = 0.1000
r ₃₀ = 32.9626 d ₃₀ = 1.0000 n _d16 = 1.87400 ν _d16 = 35.26
r ₃₁ = 15.6412 d ₃₁ = 3.6999 n _d17 = 1.56907 ν _d17 = 71.30
r ₃₂ = -104.6406 d ₃₂ = 3.0000
r ₃₃ = ∞ d ₃₃ = 25.3000 n _d18 = 1.58267 ν _d18 = 46.33
r ₃₄ = ∞ d ₃₄ = 11.1000 n _d19 = 1.51633 ν _d19 = 64.15
r ₃₅ = ∞
Zoom interval

f ₁ / f _W = 8.1919 f ₂ / f _W = -1.8780 f _Three / f _W = -4.5943
f _4-1 / f _W = 3.4269 f _4-2 / f _W = 3.2182 f _4-1 / f _4-2 = 1.0648
f _4C / f _W = 8.6941 f _3-1 / f _W = -3.9640 1 / SF _3-2 = 0.0151.
[0085]
Example 4
f = 9.192 to 25.517 to 71.615
F _NO = 2.0 to 2.0 to 2.0
2ω = 48.985 ° -17.610 ° -6.287 °
r ₁ = 189.9135 d ₁ = 2.0000 n _d1 = 1.83350 ν _d1 = 21.00
r ₂ = 105.6874 d ₂ = 5.3000 n _d2 = 1.49700 ν _d2 = 81.61
r _Three = -358.8365 d _Three = 0.1000
r _Four = 73.4031 d _Four = 5.0000 n _d3 = 1.43875 ν _d3 = 94.97
r _Five = 727.2932 d _Five = 0.1000
r ₆ = 51.1560 d ₆ = 4.2300 n _d4 = 1.43875 ν _d4 = 94.97
r ₇ = 140.5501 d ₇ = (Variable)
r ₈ = 59.3218 d ₈ = 1.2000 n _d5 = 1.69680 ν _d5 = 55.52
r ₉ = 15.9171 d ₉ = 5.3448
r _Ten = -42.3113 d _Ten = 1.0000 n _d6 = 1.61800 ν _d6 = 63.38
r ₁₁ = 60.0575 d ₁₁ = 0.1000
r ₁₂ = 30.1516 d ₁₂ = 2.3000 n _d7 = 1.83350 ν _d7 = 21.00
r ₁₃ = 622.6014 d ₁₃ = 1.5650
r ₁₄ = -30.3946 d ₁₄ = 1.0000 n _d8 = 1.72916 ν _d8 = 54.68
r ₁₅ = -439.3981 d ₁₅ = (Variable)
r ₁₆ = -18.9565 d ₁₆ = 1.2000 n _d9 = 1.48749 ν _d9 = 70.20
r ₁₇ = 283.3954 d ₁₇ = 0.1000
r ₁₈ = 32.0654 d ₁₈ = 5.9912 n _d10 = 1.78590 ν _d10 = 44.18
r ₁₉ = -20.6565 d ₁₉ = 1.2000 n _d11 = 1.72916 ν _d11 = 54.68
r ₂₀ = 31.1179 d ₂₀ = (Variable)
r _{twenty one} = ∞ (aperture) d _{twenty one} = 1.5000
r _{twenty two} = 224.1327 d _{twenty two} = 3.8934 n _d12 = 1.60311 ν _d12 = 60.70
r _{twenty three} = -21.5625 d _{twenty three} = 0.1000
r _{twenty four} = 34.8176 d _{twenty four} = 3.5800 n _d13 = 1.61772 ν _d13 = 49.83
r _{twenty five} = -327.3882 d _{twenty five} = 2.9338
r ₂₆ = -19.7780 d ₂₆ = 1.0000 n _d14 = 1.80518 ν _d14 = 25.43
r ₂₇ = -47.8125 d ₂₇ = 8.4361
r ₂₈ = -352.3666 d ₂₈ = 6.0280 n _d15 = 1.60311 ν _d15 = 60.70
r ₂₉ = -26.1466 d ₂₉ = 0.1000
r ₃₀ = 33.1453 d ₃₀ = 1.0000 n _d16 = 1.87400 ν _d16 = 35.26
r ₃₁ = 15.5881 d ₃₁ = 3.7000 n _d17 = 1.56907 ν _d17 = 71.30
r ₃₂ = -102.2519 d ₃₂ = 3.0000
r ₃₃ = ∞ d ₃₃ = 25.3000 n _d18 = 1.58267 ν _d18 = 46.33
r ₃₄ = ∞ d ₃₄ = 11.1000 n _d19 = 1.51633 ν _d19 = 64.15
r ₃₅ = ∞
Zoom interval

f ₁ / f _W = 8.1667 f ₂ / f _W = -1.8783 f _Three / f _W = -4.5869
f _4-1 / f _W = 3.4088 f _4-2 / f _W = 3.2082 f _4-1 / f _4-2 = 1.0625
f _4C / f _W = 8.7193 f _3-1 / f _W = -3.9599 1 / SF _3-2 = 0.0150.
[0086]
Example 5
f = 9.160 to 25.558 to 71.950
F _NO = 2.0 to 2.0 to 2.0
2ω = 49.220 ° -17.602 ° -6.256 °
r ₁ = 214.8678 d ₁ = 2.0000 n _d1 = 1.83350 ν _d1 = 21.00
r ₂ = 114.8112 d ₂ = 5.3000 n _d2 = 1.49700 ν _d2 = 81.61
r _Three = -280.1195 d _Three = 0.1000
r _Four = 69.2733 d _Four = 5.0000 n _d3 = 1.43875 ν _d3 = 94.97
r _Five = 498.1384 d _Five = 0.1000
r ₆ = 51.4092 d ₆ = 4.2300 n _d4 = 1.43875 ν _d4 = 94.97
r ₇ = 132.3773 d ₇ = (Variable)
r ₈ = 66.7529 d ₈ = 1.2000 n _d5 = 1.69680 ν _d5 = 55.52
r ₉ = 16.0594 d ₉ = 5.3649
r _Ten = -41.9645 d _Ten = 1.0000 n _d6 = 1.61800 ν _d6 = 63.38
r ₁₁ = 93.3191 d ₁₁ = 0.1000
r ₁₂ = 30.3487 d ₁₂ = 2.3000 n _d7 = 1.83350 ν _d7 = 21.00
r ₁₃ = 243.7892 d ₁₃ = 1.6437
r ₁₄ = -32.4908 d ₁₄ = 1.0000 n _d8 = 1.72916 ν _d8 = 54.68
r ₁₅ = ∞ d ₁₅ = (Variable)
r ₁₆ = -19.0018 d ₁₆ = 1.2000 n _d9 = 1.48749 ν _d9 = 70.20
r ₁₇ = 267.3031 d ₁₇ = 0.1000
r ₁₈ = 25.7142 d ₁₈ = 5.3023 n _d10 = 1.78590 ν _d10 = 44.18
r ₁₉ = -47.5733 d ₁₉ = 1.2000 n _d11 = 1.72916 ν _d11 = 54.68
r ₂₀ = 24.9853 d ₂₀ = (Variable)
r _{twenty one} = ∞ (aperture) d _{twenty one} = 1.5000
r _{twenty two} = 242.0915 d _{twenty two} = 3.6544 n _d12 = 1.60311 ν _d12 = 60.70
r _{twenty three} = -19.3814 d _{twenty three} = 0.1000
r _{twenty four} = 29.3715 d _{twenty four} = 2.9821 n _d13 = 1.60311 ν _d13 = 60.70
r _{twenty five} = -1456.1020 d _{twenty five} = 1.6402
r ₂₆ = -19.3088 d ₂₆ = 1.0000 n _d14 = 1.80518 ν _d14 = 25.43
r ₂₇ = -47.7151 d ₂₇ = 10.7574
r ₂₈ = -142.1109 d ₂₈ = 6.0592 n _d15 = 1.60311 ν _d15 = 60.70
r ₂₉ = -24.9286 d ₂₉ = 0.1000
r ₃₀ = 29.8304 d ₃₀ = 1.0000 n _d16 = 1.87400 ν _d16 = 35.26
r ₃₁ = 14.9246 d ₃₁ = 4.3524 n _d17 = 1.56907 ν _d17 = 71.30
r ₃₂ = -163.9926
Zoom interval

f ₁ / f _W = 8.1905 f ₂ / f _W = -1.8921 f _Three / f _W = -4.4614
f _4-1 / f _W = 3.2068 f _4-2 / f _W = 3.3069 f _4-1 / f _4-2 = 0.9697
f _4C / f _W = 8.7237 f _3-1 / f _W = -3.9675 1 / SF _3-2 = 0.0144.
[0087]
Example 6
f = 9.003 to 25.492 to 71.972
F _NO = 2.0 to 2.0 to 2.0
2ω = 49.949 ° -17.642 ° -6.253 °
r ₁ = 214.6492 d ₁ = 2.0000 n _d1 = 1.83350 ν _d1 = 21.00
r ₂ = 113.0438 d ₂ = 5.3000 n _d2 = 1.49700 ν _d2 = 81.61
r _Three = -292.9631 d _Three = 0.1000
r _Four = 69.7853 d _Four = 5.0000 n _d3 = 1.43875 ν _d3 = 94.97
r _Five = 708.8696 d _Five = 0.1000
r ₆ = 50.0471 d ₆ = 4.2300 n _d4 = 1.43875 ν _d4 = 94.97
r ₇ = 122.1518 d ₇ = (Variable)
r ₈ = 58.2294 d ₈ = 1.2000 n _d5 = 1.69680 ν _d5 = 55.52
r ₉ = 15.4000 d ₉ = 5.2784
r _Ten = -40.5987 d _Ten = 1.0000 n _d6 = 1.61800 ν _d6 = 63.38
r ₁₁ = 98.4973 d ₁₁ = 0.1000
r ₁₂ = 28.7904 d ₁₂ = 2.3000 n _d7 = 1.83350 ν _d7 = 21.00
r ₁₃ = 195.0991 d ₁₃ = 1.6170
r ₁₄ = -32.0483 d ₁₄ = 1.0000 n _d8 = 1.72916 ν _d8 = 54.68
r ₁₅ = 1284.2129 d ₁₅ = (Variable)
r ₁₆ = -17.9064 d ₁₆ = 1.2000 n _d9 = 1.48749 ν _d9 = 70.20
r ₁₇ = 1249.1440 d ₁₇ = 0.1000
r ₁₈ = 22.5533 d ₁₈ = 4.2041 n _d10 = 1.78590 ν _d10 = 44.18
r ₁₉ = -46.4740 d ₁₉ = 1.2000 n _d11 = 1.72916 ν _d11 = 54.68
r ₂₀ = 21.2975 d ₂₀ = (Variable)
r _{twenty one} = ∞ (aperture) d _{twenty one} = 1.5000
r _{twenty two} = 208.7578 d _{twenty two} = 3.1994 n _d12 = 1.60311 ν _d12 = 60.70
r _{twenty three} = -19.6135 d _{twenty three} = 0.1000
r _{twenty four} = 26.3003 d _{twenty four} = 2.9996 n _d13 = 1.60311 ν _d13 = 60.70
r _{twenty five} = -1108.9644 d _{twenty five} = 1.4438
r ₂₆ = -19.4039 d ₂₆ = 1.0000 n _d14 = 1.80518 ν _d14 = 25.43
r ₂₇ = -51.1011 d ₂₇ = 10.5712
r ₂₈ = -116.8701 d ₂₈ = 2.6008 n _d15 = 1.60311 ν _d15 = 60.70
r ₂₉ = -23.0163 d ₂₉ = 0.1000
r ₃₀ = 26.6785 d ₃₀ = 1.0000 n _d16 = 1.87400 ν _d16 = 35.26
r ₃₁ = 13.4925 d ₃₁ = 3.8121 n _d17 = 1.56907 ν _d17 = 71.30
r ₃₂ = -374.3053
Zoom interval

f ₁ / f _W = 8.2930 f ₂ / f _W = -1.9015 f _Three / f _W = -4.4611
f _4-1 / f _W = 3.1052 f _4-2 / f _W = 3.3149 f _4-1 / f _4-2 = 0.9367
f _4C / f _W = 9.2481 f _3-1 / f _W = -4.0210 1 / SF _3-2 = 0.0286.
[0088]
The above zoom lens of the present invention can be configured as follows.
[1] In order from the object side, a first lens unit that has positive refractive power and is fixed during zooming, a second lens unit that has negative refractive power and moves along the optical axis during zooming, and has a zooming function, negative A third lens unit that has a refractive power of 2 mm and has a function of moving the image plane that fluctuates with the zooming movement of the second lens unit along the optical axis to keep it constant. The fourth lens group includes a fourth lens group having an image function. The fourth lens group includes, in order from the object side, a 4-1 sub-lens group having a positive refractive power, and a positive lens disposed at a relatively long distance from the sub lens group. The 4-2 sub lens group has a refractive power, and the 4-1 sub lens group includes, in order from the object side, at least two positive lenses and at least one negative lens. Two sub-lens groups are arranged in order from the object side. Both zoom lens, characterized in that the bonding surface and one positive lens is formed of at least one cemented lens of negative refractive power.
[2] The 4-1 sub-lens group includes, in order from the object side, at least two positive lenses and at least one negative meniscus lens having a concave surface facing the object side. [1] The zoom lens according to [1].
[3] In order from the object side, a first lens unit having a positive refractive power and fixed during zooming, a second lens unit having a negative refractive power and moving along the optical axis during zooming, and having a zooming effect, negative A third lens unit that has a refractive power of 2 mm and has a function of moving the image plane that fluctuates with the zooming movement of the second lens unit along the optical axis to keep it constant. A fourth lens group having an image action, and the third lens group includes, in order from the object side, a third lens sub-lens group 3-1 of a negative lens having a surface with a strong negative refractive power facing the object side; A zoom lens comprising a third and second sub-lens group of a cemented doublet lens having a positive refractive power and a concave surface facing the image side.
[4] The 4-2 sub lens group includes, in order from the object side, at least one positive lens, and at least one cemented lens of a negative meniscus lens having a concave surface facing the image side and a positive lens. The zoom lens as set forth in [1], wherein
[5] The zoom lens according to [1], wherein the following condition is satisfied:
(1) 2.5 <f _4-1 / F _W <4.5
Where f _4-1 Is the focal length of the 4-1 sub lens group, f _W Is the focal length of the entire lens system at the wide-angle end.
[6] The zoom lens according to [1], wherein the following condition is satisfied:
(2) 2.2 <f _4-2 / F _W <4.2
Where f _4-2 Is the focal length of the 4-2 sub lens group, f _W Is the focal length of the entire lens system at the wide-angle end.
[7] The zoom lens according to [1], wherein the following condition is satisfied:
(3) 0.8 <f _4-1 / F _4-2 <1.2
Where f _4-1 , F _4-2 Are the focal lengths of the 4-1 sub lens group and the 4-2 sub lens group, respectively.
[8] The zoom lens according to [1], wherein the following condition is satisfied:
(4) 6.0 <f _4C / F _W <11.0
Where f _4C Is the focal length of the cemented lens, which is a component of the 4-2 sub lens group, f _W Is the focal length of the entire lens system at the wide-angle end.
[9] The zoom lens according to [3], wherein focusing is performed by extending the third lens group toward the object side.
[10] The zoom lens as described in [3] above, wherein the cemented surface of the 3-2 sub lens group has a positive refractive power.
[11] The zoom lens according to [3], wherein the cemented doublet lens of the third-second sub-lens group includes a biconvex lens and a biconcave lens.
[12] The zoom lens according to [3], wherein the following condition is satisfied:
(5) -5.0 <f _3-1 / F _W <-3.0
Where f _3-1 Is the focal length of the 3-1 sub lens group, f _W Is the focal length of the entire lens system at the wide-angle end.
[13] The zoom lens according to [3], wherein the following condition is satisfied:
(6) 0.0 <1 / SF _3-2 <0.1
However, SF _3-2 Is a shaping factor of the third-second sub-lens group. Here, the shaping factor SF is the radius of curvature of the object-side surface and the image-side surface of the lens. _F , R _R Is defined by the following equation.
[0089]
SF = (r _F + R _R ) / (R _F -R _R )
[0090]
【The invention's effect】
As described in detail above and as is clear from each example, according to the present invention, an electronic camera using an imaging tube, a solid-state imaging device, etc., while having a relatively simple zoom lens configuration, In particular, it has high optical performance that is optimal for electronic cameras using an image sensor with a large number of pixels suitable for recent high-definition image capture applications, and includes optical members such as various filters and optical path splitting prisms A small zoom lens having a large back focus in which the element can be inserted between the lens and the imaging element can be realized.
[0091]
According to another invention of the present invention, it is possible to realize a small zoom lens having a large back focus and a stable and high optical performance from an infinite object point to a short distance object point.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a state of each lens group from a wide-angle end to a telephoto end through a standard state of a zoom lens according to Embodiment 1 of the present invention.
2 is a lens cross-sectional view at a wide angle end according to Embodiment 2. FIG.
3 is a lens cross-sectional view at a wide angle end according to Embodiment 3. FIG.
4 is a lens cross-sectional view at a wide angle end according to Embodiment 5. FIG.
5 is a lens cross-sectional view at a wide angle end according to Embodiment 6. FIG.
6 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the wide-angle end according to Example 1. FIG.
7 is an aberration diagram illustrating an aberration state with respect to an object point at infinity in the standard state according to Example 1. FIG.
FIG. 8 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the telephoto end according to the first embodiment.
FIG. 9 is an aberration diagram illustrating an aberration state when the object point distance is 1 m at the telephoto end according to the first embodiment.
10 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the wide-angle end according to Example 2. FIG.
FIG. 11 is an aberration diagram showing an aberration state with respect to an object point at infinity in the standard state according to Example 2.
12 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the telephoto end according to Example 2. FIG.
13 is an aberration diagram illustrating an aberration state when the object point distance is 1 m at the telephoto end according to Example 2. FIG.
FIG. 14 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the wide-angle end according to Example 3.
15 is an aberration diagram illustrating an aberration state with respect to an object point at infinity in the standard state according to Example 3. FIG.
FIG. 16 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the telephoto end according to the third embodiment.
17 is an aberration diagram illustrating an aberration state when the object point distance is 1 m at the telephoto end according to Example 3. FIG.
FIG. 18 is an aberration diagram showing an aberration state with respect to an object point at infinity at the wide-angle end according to Example 4.
19 is an aberration diagram illustrating an aberration state with respect to an object point at infinity in the standard state according to Example 4. FIG.
FIG. 20 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the telephoto end according to the fourth embodiment.
21 is an aberration diagram illustrating an aberration state when the object point distance is 1 m at the telephoto end according to Example 4. FIG.
22 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the wide-angle end according to Example 5. FIG.
FIG. 23 is an aberration diagram showing an aberration state with respect to an object point at infinity in the standard state according to Example 5.
FIG. 24 is an aberration diagram illustrating an aberration state with respect to an object point at infinity at the telephoto end according to the fifth embodiment.
25 is an aberration diagram illustrating an aberration state when the object point distance is 1 m at the telephoto end according to Example 5. FIG.
FIG. 26 is an aberration diagram showing an aberration state with respect to an object point at infinity at the wide-angle end according to Example 6.
FIG. 27 is an aberration diagram showing an aberration state with respect to an object point at infinity in the standard state according to Example 6.
FIG. 28 is an aberration diagram showing an aberration state with respect to an infinite object point at the telephoto end according to Example 6.
29 is an aberration diagram illustrating an aberration state when the object point distance is 1 m at the telephoto end according to Example 6. FIG.
[Explanation of symbols]
I: First lens group
II ... 2nd lens group
III ... Third lens group
III-1 ... 3-1 sub lens group
III-2 ... 3-2 sub lens group
IV ... 4th lens group
IV-1 ... 4-1 sub lens group
IV-2 ... 4-2 sub lens group
P: Optical path splitting prism

Claims

In order from the object side, the first lens unit having a positive refractive power and fixed during zooming, the second lens unit having a negative refractive power and moving along the optical axis during zooming, and having a zooming action, negative refractive power A third lens unit that has a function of moving along the optical axis to keep the image plane that fluctuates with the zooming movement of the second lens unit constant, and has a positive refractive power and has a fixed imaging function during zooming. Consisting of a fourth lens group
The third lens group includes, in order from the object side, a negative lens third-first sub-lens group having a surface having a strong negative refractive power directed toward the object side, and a negative surface having a positive refractive power on the image side. consists 3-2 sub lens group of the cemented doublet lens toward,
The cemented surface of the cemented doublet lens has a positive refractive power,
A zoom lens, wherein focusing is performed by extending the third lens group toward the object side .

In order from the object side, the first lens unit having a positive refractive power and fixed during zooming, the second lens unit having a negative refractive power and moving along the optical axis during zooming, and having a zooming action, negative refractive power A third lens unit that has a function of moving along the optical axis to keep the image plane that fluctuates with the zooming movement of the second lens unit constant, and has a positive refractive power and has a fixed imaging function during zooming. Consisting of a fourth lens group
The third lens group includes, in order from the object side, a negative lens third-first sub-lens group having a surface having a strong negative refractive power directed toward the object side, and a negative surface having a positive refractive power on the image side. consists 3-2 sub lens group of the cemented doublet lens toward, features and to Luz Murenzu that satisfies the following conditions.
(5) −5.0 <f _3-1 / f _W <−3.0
(6) 0.0 <1 / SF _3-2 <0.1
Here, f _3-1 is the focal length of the 3-1 sub lens group, and SF _3-2 is the shaping factor of the 3-2 sub lens group. Here, the shaping factor SF is defined by the following equation, where r _F and r _R are the curvature radii of the object-side surface and the image-side surface of the lens, respectively.
SF = (r _F + r _R ) / (r _F −r _R )