JP4639425B2

JP4639425B2 - Variable focal length lens system

Info

Publication number: JP4639425B2
Application number: JP2000103808A
Authority: JP
Inventors: 基之大竹
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2000-04-05
Filing date: 2000-04-05
Publication date: 2011-02-23
Anticipated expiration: 2020-04-05
Also published as: JP2001290076A

Description

【０００１】
【発明の属する技術分野】
本発明は、広角端状態において８０度を超える画角を包括することが可能な可変焦点距離レンズ系に関し、特に、口径比３．５程度の大口径比化が可能な可変焦点距離レンズ系に関する。
【０００２】
【従来の技術】
レンズシャッター式カメラの特徴は携帯性に優れることである。この携帯性は小型であること、軽量であることに分類される。撮影レンズの長さがカメラ本体の厚みに影響し、レンズ径がカメラ本体の高さと横幅に影響するので、撮影レンズ系を小さくすることが特にカメラの小型化に影響を与えてきた。
【０００３】
ズームレンズは被写体により近づいた撮影が可能であり、撮影者に自由度を与えるため、ズームレンズ付カメラが主流になってきた。そして、望遠端状態の焦点距離が大きいほど被写体に近付いた撮影が可能になるので、望遠端状態での焦点距離が長くなるように変倍比が高まる傾向だった。
【０００４】
ところで、レンズシャッター式カメラは携帯性に優れる点から旅行等に出掛ける際に使われる機会が多いが、一眼レフカメラのユーザー層がレンズシャッター式カメラを携行する場合、口径比の明るい単焦点レンズ付カメラが多かった。
【０００５】
【発明が解決しようとする課題】
しかしながら、従来のレンズシャッター式カメラ用ズームレンズは、望遠端状態での焦点距離が長くなるに従って、望遠端状態での開放Ｆナンバーが大きくなる傾向であり、ピンぼけが目立たず、遠近感に乏しい写真に仕上がる傾向であった。
【０００６】
一眼レフカメラのユーザー層が旅行時に携行する場合、口径比が大きく、画角が広い撮影系が好まれる。前者はストロボなしで自然な発色での撮影ができるからであり、後者は撮影者と被写体との距離が離れずに撮影できるからである。
【０００７】
本発明は上記問題に鑑みてさなれたものであり、広角端状態で８０度を超える画角を包括しながらも、明るく小型の可変焦点距離レンズ系を提供することを目的とする。
【０００８】
上記目的を達成するために本発明は、物体側より順に、負屈折力を有する第１レンズ群と、正屈折力を有する第２レンズ群と、負屈折力を有する第３レンズ群とを有し、広角端状態から望遠端状態までレンズ位置状態が変化する際に、前記第１レンズ群と前記第２レンズ群との間隔が減少し、前記第２レンズ群と前記第３レンズ群との間隔が減少するように、少なくとも前記第２レンズ群と前記第３レンズ群がそれぞれ物体側へ移動して、前記第２レンズ群は、物体側より順に、第１の正レンズ成分Ｌ21と、負レンズ成分Ｌ22と、第２の正レンズ成分Ｌ23との３つのレンズ成分を含み、開口絞りＳが前記負レンズ成分Ｌ22に隣接して配置され、前記負レンズ成分Ｌ22は該開口絞りＳに対して凹面を向けたメニスカス形状であり、以下の条件式（１）を満足することを特徴とする可変焦点距離レンズ系を提供する。
（１）０．１５＜Ｄａ／ｆｗ＜０．４０
但し、Ｄａは前記開口絞りを挟んだ物体側と像側の空気間隔の長さ，ｆｗは広角端状態での前記可変焦点距離レンズ系の焦点距離である。
【０００９】
【発明の実施の形態】
従来より可変焦点距離レンズ系は、レンズ系のもっとも物体側に正屈折力を有するレンズ群を配置する正先行型と負屈折力を有するレンズ群を配置する負先行型とに大別される。
【００１０】
正先行型ズームレンズは主に画角が狭く、画面対角長と比較して焦点距離が長いレンズ系に用いられ、レンズ全長の短縮に適している。また、負先行型ズームレンズは主に画角が広いレンズ系に用いられている。
【００１１】
負先行型ズームレンズは広角端状態で（もっとも物体側に配置される）第１レンズ群を通過する軸外光束が光軸に近い高さを通過するのでレンズ径の小型化が図れる。しかし、変倍比を高めると望遠端状態において、（第１レンズ群の像側に配置される）第２レンズ群を軸上光束が広がって通過するので、画面中心部で所定の光学性能を確保するのが困難である。
【００１２】
また、レンズシャッター式カメラに用いられるレンズ系は、レンズ系のもっとも像側に負レンズ群を配置することで、レンズ全長の短縮化とレンズ径の小型化を実現している。
【００１３】
本発明においては、ズーム比よりも大口径比と広い画角を優先し、レンズ系のもっとも像側に負屈折力を有する第１レンズ群を配置して、その像側に正屈折力を有する第２レンズ群を配置して、さらにその像側に負屈折力を有する第３レンズ群を配置している。また、広角端状態では第１レンズ群と第２レンズ群との間隔が広がった状態、第２レンズ群と第３レンズ群との間隔が広がった状態に配置して、望遠端状態に向かってレンズ位置状態が変化するに従って、各レンズ群同士の間隔が狭まるように、少なくとも第２レンズ群と第３レンズ群とを物体側へ移動させている。
【００１４】
また、画角の広い光学系では、開口絞りを配置する位置が重要であり、本発明では、第２レンズ群の内部に開口絞りを配置している。
【００１５】
広角端状態では各レンズ群同士の間隔を充分広げることで、第１レンズ群及び第３レンズ群を通過する軸外光束が光軸から離れるので、軸外収差の補正が充分良好に行える。また、望遠端状態へ向かってレンズ位置状態が変化するに従って、各レンズ群同士の間隔を狭めることで、第１レンズ群と第３レンズ群を通過する軸外光束の高さを積極的に変化させて、レンズ位置状態の変化に伴って発生する軸外収差の変動を良好に補正している。
【００１６】
本発明では第２レンズ群の物体側と像側に負屈折力の第１レンズ群と第３レンズ群をそれぞれ配置することにより、光学系全体での屈折力配置を対称型に近づけて、歪曲収差及び倍率色収差を良好に補正している。
【００１７】
第２レンズ群は主に軸上収差の補正を担う。第２レンズ群を物体側から順に、第１の正レンズ成分、負レンズ成分、第２の正レンズ成分の３レンズ成分で構成することで、軸上収差を特に良好に補正し、軸外収差の発生も抑えることができる。
【００１８】
特に、負レンズ成分を開口絞りに対して凹面を向けたメニスカス形状のレンズとすることで、軸外収差の発生を抑えている。
【００１９】
従来より、物体側より順に、負屈折力を有する第１レンズ群、正屈折力を有する第２レンズ群、負屈折力を有する第３レンズ群を配置した負正負３群型のズームレンズが知られている。例えば、特開昭６４−７２１１４号公報では広角端状態で７２度程度の画角を有するズームレンズが提案されている。しかし、このズームレンズは、第２レンズ群の像側に開口絞りが配置されているため、８０度を超える画角を包括すると、第１レンズ群のレンズ径が非常に大きくなってしまった。
【００２０】
本発明では、以上の構成から、広角端状態での画角が８０度を超える広い画角と、Ｆ３．５程度の大口径比化との両立化が達成できている。
【００２１】
以下、各条件式について説明する。
【００２２】
条件式（１）は第２レンズ群中に配置される開口絞りの物体側と像側の空気間隔の長さを規定する条件式であり、小型化を図るための条件である。
【００２３】
本発明においては、第２レンズ群が第１の正レンズ成分、負レンズ成分、第２の正レンズ成分の３つのレンズ成分で構成され、負レンズ成分に隣接して開口絞りが配置される。この開口絞りの前後に充分なスペースが確保できないと、シャッタースペースが確保できない。
【００２４】
また、本発明では、以下の条件式（１）と（２）のうち、少なくともいずれか一方を満足することが望ましい。
（１）０．１５＜Ｄａ／ｆｗ＜０．４０
（２）０．４＜Ｄ1W／Ｄ3W＜１．２
但し、
Ｄａ：前記開口絞りを挟んだ物体側と像側の空気間隔の長さ，
ｆｗ：広角端状態での前記可変焦点距離レンズ系の焦点距離，
Ｄ1W：広角端状態での前記第１レンズ群と前記第２レンズ群との軸上間隔，
Ｄ3W：広角端状態での前記第２レンズ群と前記第３レンズ群との軸上間隔．
条件式（１）の下限値を下回った場合、充分なシャッタースペースが確保できない。逆に、条件式（１）の上限値を上回った場合、レンズ厚が大きくなるので、各レンズ群を通過する軸外光束が光軸から離れて、レンズ径の大型化を引き起こしてしまう。
【００２５】
条件式（２）はレンズ径とレンズ全長のバランス化を図るための条件である。
【００２６】
条件式（２）の上限値を上回った場合、第１レンズ群を通過する軸外光束が光軸から離れるので、レンズ径の小型化充分図れない。また、画面周縁部においてコマ収差が多量に発生するので高性能化も図れない。逆に、条件式（２）の下限値を下回った場合、第３レンズ群を通過する軸外光束が光軸から離れるので、レンズ径が大型化してしまう。また、バックフォーカスが短くなってしまうので、もっともフィルム面側のレンズ面上に付着したゴミの影がフィルム上に記録され、画質が劣化してしまう。
【００２７】
ところで、本発明においてより高性能化を図るには、各レンズ群毎に発生する収差量をできるだけ抑えることが肝要である。
【００２８】
そこで、第１レンズ群と第３レンズ群をそれぞれ２枚以上のレンズ枚数で構成することが望ましく、特に、第１レンズ群は像側に凹面を向けた負レンズとその像側に配置され、物体側に凸面を向けた正レンズ、第３レンズ群は像側に凸面を向けた正レンズとその像側に配置され、物体側に凹面を向けた負レンズをそれぞれ有することが望ましい。これは、レンズ径を小型化にすると同時に軸外収差の発生を抑えるためである。
【００２９】
さらに、本発明では、以下の条件式（３）と（４）のうち、少なくともいずれか一方を満足することにより、小型化を図りながら、より優れた性能が得られる。
（３）０．３＜ｆ３／ｆ１＜０．７（ｆ３＜０，ｆ１＜０）
（４）０．７＜ｆ２／ｆｗ＜０．８５
但し、
ｆ１：前記第１レンズ群の焦点距離，
ｆ２：前記第２レンズ群の焦点距離，
ｆ３：前記第３レンズ群の焦点距離，
ｆｗ：広角端状態での前記可変焦点距離レンズ系の焦点距離．
条件式（３）は第１レンズ群と第３レンズ群との焦点距離比を規定する条件式である。条件式（３）の上限値を上回った場合、望遠端状態で第２レンズ群を通過する軸上光束が広がってしまうので、軸上収差の補正が不足してしまう。逆に、条件式（３）の下限値を下回った場合、第３レンズ群を通過する軸外光束が光軸に近づき、画角によるコマ収差の変動を良好に補正できない。
【００３０】
条件式（４）は第２レンズ群の焦点距離を規定する条件式である。条件式（４）の上限値を上回った場合、レンズ全長の大型化を引き起こしてしまう。逆に、条件式（４）の下限値を下回った場合、第１レンズ群と第３レンズ群の屈折力も強まり、第１レンズ群と第３レンズ群を通過する軸外光束が光軸に近づくので、広角端状態で発生する画角によるコマ収差の変動が補正できない。
【００３１】
また、本発明においては、レンズ全長を短縮するために、開口絞りを第２レンズ群中の第１の正レンズ成分Ｌ21と負レンズ成分Ｌ22との間に配置することが望ましく、より高性能化を図るには開口絞りから離れて配置され、軸外光束が光軸からやや離れる第２の正レンズ成分Ｌ23のもっとも像側のレンズ面を非球面とすることが望ましい。さらに好ましくは、以下の条件式（５）を満足するように構成することが望ましい。
（５）０．１５＜Ｄｂ／ｆｗ＜０．３５
但し、
Ｄｂ：前記開口絞りから前記第２の正レンズ成分のもっとも像側のレンズ面までの光軸に沿った長さ．
条件式（５）は、第２の正レンズ成分Ｌ23のもっとも像側のレンズ面と開口絞りとの間隔を規定する条件式である。条件式（５）の上限値を上回った場合、第３レンズ群を通過する軸外光束が光軸から大きく離れてレンズ径が大型化してしまい、携帯性を損ねてしまう。逆に、条件式（５）の下限値を下回った場合、第２の正レンズ成分Ｌ23のもっとも像側のレンズ面を通過する軸外光束と軸上光束との高さの差が少なくなり、画角によるコマ収差の変動をより良く補正できなくなってしまう。
【００３２】
また、本発明においては、製造時に安定した品質を維持するため、以下の条件式（６）及び（７）を満足することが望ましい。
（６）−０．１＜（ｒ22ａ−ｒ23ｂ）／（ｒ22ａ＋ｒ23ｂ）＜０．１
（７）ｆｗ／│ｒ23ａ│＜０．５５
但し、ｒ22ａ：前記第２レンズ群中の前記負レンズ成分の物体側レンズ面の曲率半径，ｒ23ｂ：前記第２レンズ群中の前記第２の正レンズ成分の像側レンズ面の曲率半径，ｒ23ａ：前記第２レンズ群中の前記第２の正レンズ成分の物体側レンズ面の曲率半径である。
【００３３】
本発明においては、第２の正レンズ成分Ｌ23を通過する軸外光束を光軸から離すために、負レンズ成分Ｌ22の物体側のレンズ面で光束を強く発散させることが望ましく、これに伴って第２の正レンズ成分Ｌ23の像側のレンズ面で光束を強く収斂させる。
【００３４】
更なる高性能化を図るにはこのように構成することが望ましいが、レンズ室にレンズを組込んだ際の相互偏心による性能劣化が著しく大きくなるため、組込み時に負レンズ成分Ｌ22の物体側のレンズ面と第２の正レンズ成分L23の像側のレンズ面との芯ズレを少なくすることが重要である。
【００３５】
本発明では、条件式（６）を満足するように負レンズ成分Ｌ22の物体側のレンズ面と第２の正レンズ成分L23の像側のレンズ面のそれぞれの曲率半径を設定することで、偏心調整が比較的容易に行える。
【００３６】
また、レンズ室を構成する際に、（開口絞りから離れて）レンズ径の大きな第２の正レンズ成分L23を偏心調整時に動かす方が作業上好ましく、特に条件式（７）を満足するように第２の正レンズ成分L23の物体側のレンズ面の曲率半径を設定することで、作業効率が高められる。これは偏心調整時に第２の正レンズ成分Ｌ23の物体側レンズ面の曲率中心を回転中心にレンズが回転するため、回転中心位置が第２の正レンズ成分L23の像側のレンズ面から離れないと調整量が多量に必要になるからである。
【００３７】
以下の各実施例では、近距離合焦時に第２レンズ群を物体側へ移動させているが、第１レンズ群や第３レンズ群を移動させること、または複数のレンズ群を移動させることでも近距離合焦が行える。また、各実施例では、第１レンズ群に非球面レンズを配置しているが、例えば、さらに第３レンズ群中に非球面レンズを配置することで更なる高性能化が実現できるのは言うまでもない。
【００３８】
さらに、以下の各実施例は３つのレンズ群で構成されるが、第３レンズ群の像側に屈折力が弱い他のレンズ群を付加することも容易である。
【００３９】
本発明においては、別の観点によれば、撮影を行う際に、発生しがちな手ブレ等が原因の像ブレによる失敗を防ぐために、ブレを検出するブレ検出系と駆動手段とをレンズ系に組み合わせ、レンズ系を構成するレンズ群のうち、１つのレンズ群を全体か、あるいはその一部を偏心レンズ群として偏心させることにより、ブレをブレ検出系により検出し、検出されたブレを補正するように駆動手段により偏心レンズ群を偏心させ像をシフトさせて、像ブレを補正することで防振光学系とすることが可能である。
【００４０】
【実施例】
以下に、本発明にかかる数値実施例について説明する。
【００４１】
なお、各実施例において、非球面は以下の式で表される。
【００４２】
【数１】
ｘ＝ｃｙ²／｛１＋（１−κｃ²ｙ²）^1/2｝＋Ｃ₄ｙ⁴＋Ｃ₆ｙ⁶＋…
【００４３】
但し、ｙは光軸からの高さ、ｘはサグ量、ｃは曲率、κは円錐定数、Ｃ₄，Ｃ₆，…は非球面係数である。
【００４４】
図１は、本発明の各実施例による可変焦点距離レンズ系の屈折力配分を示す図である。物体側より順に、負屈折力を有する第１レンズ群Ｇ１と、正屈折力を有する第２レンズ群Ｇ２と、負屈折力を有する第３レンズ群Ｇ３とで構成される。そして、広角端状態より望遠端状態まで焦点距離が変化する際に、第１レンズ群Ｇ１と第２レンズ群Ｇ２との間隔が減少し、第２レンズ群Ｇ２と第３レンズ群Ｇ３との間隔が減少するように、少なくとも第２レンズ群Ｇ２と第３レンズ群Ｇ３が物体側へ移動する。
【００４５】
（第１実施例）
図２は、本発明の第１実施例にかかる可変焦点距離レンズ系のレンズ構成を示す図である。第１レンズ群Ｇ１は両凹レンズＬ１１と物体側に凸面を向けた正メニスカスレンズＬ１２とで構成され、第２レンズ群Ｇ２は物体側より順に、両凸レンズＬ２１と、物体側に凹面を向けたメニスカス形状のＬ２２と、両凸レンズＬ２３とで構成され、第３レンズ群Ｇ３は像側に凸面を向けたメニスカス形状の正レンズＬ３１と物体側に凹面を向けたメニスカス形状の負レンズＬ３２とで構成される。
【００４６】
本実施例では、開口絞りＳが両凸レンズＬ２１と負レンズＬ２２との間に配置され、レンズ位置状態が変化する際に、第２レンズ群Ｇ２と一緒に移動する。
【００４７】
以下の表１に、本実施例の諸元の値を掲げる。実施例の諸元表中のｆは焦点距離、ＦNOはＦナンバー、２ωは画角を表し、屈折率はｄ線（λ=587.6nm）に対する値である。また、表１中で曲率半径０とは平面を示す。なお、以下全ての実施例の諸元値において、本実施例の諸元値と同じ符号を用いる。
【００４８】
【表１】

【００４９】
図３（ａ）より図３（ｃ）は、本実施例の無限遠合焦状態での諸収差図をそれぞれ示し、それぞれ広角端状態（ｆ＝25.20）、中間焦点距離状態（ｆ＝28.00）、望遠端状態（ｆ＝34.00）における諸収差図を示す。
【００５０】
各収差図において、球面収差図中の実線は球面収差、点線はサイン・コンディションを示し、ｙは像高を示し、非点収差図中の実線はサジタル像面、破線はメリディオナル像面を示す。コマ収差図は、像高ｙ＝０，１０．８，１５．１２，１８．３４，２１．６でのコマ収差を表し、Ａは画角を示す。
【００５１】
各収差図から、本実施例は諸収差が良好に補正され、優れた結像性能を有していることは明らかである。
【００５２】
（第２実施例）
図４は、本発明の第２実施例にかかる可変焦点距離レンズ系のレンズ構成を示す図である。第１レンズ群Ｇ１は両凹レンズＬ１１と物体側に凸面を向けた正メニスカスレンズＬ１２とで構成され、第２レンズ群Ｇ２は物体側より順に、物体側に凸面を向けたメニスカス形状の正レンズＬ２１と、物体側に凹面を向けたメニスカス形状のＬ２２と、両凸レンズＬ２３とで構成され、第３レンズ群Ｇ３は像側に凸面を向けたメニスカス形状の正レンズＬ３１と物体側に凹面を向けたメニスカス形状の負レンズＬ３２とで構成される。
【００５３】
本実施例では、開口絞りＳが正レンズＬ２１と負レンズＬ２２との間に配置され、レンズ位置状態が変化する際に、第２レンズ群Ｇ２と一緒に移動する。
【００５４】
以下の表２に、本実施例の諸元の値を掲げる。
【００５５】
【表２】

【００５６】
図５（ａ）より図５（ｃ）は本実施例の無限遠合焦状態での諸収差図をそれぞれ示し、それぞれ広角端状態（ｆ＝25.20）、中間焦点距離状態（ｆ＝28 .00）、望遠端状態（ｆ＝34.00）における諸収差図を示す。
【００５７】
各収差図から、本実施例は諸収差が良好に補正され、優れた結像性能を有していることは明らかである。
【００５８】
（第３実施例）
図６は、本発明の第３実施例にかかる可変焦点距離レンズ系のレンズ構成を示す図である。第１レンズ群Ｇ１は両凹レンズＬ１１と物体側に凸面を向けた正メニスカスレンズＬ１２とで構成され、第２レンズ群Ｇ２は物体側より順に、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との接合正レンズＬ２１と、物体側に凹面を向けたメニスカス形状のＬ２２と、両凸レンズＬ２３とで構成され、第３レンズ群Ｇ３は像側に凸面を向けたメニスカス形状の正レンズＬ３１と物体側に凹面を向けたメニスカス形状の負レンズＬ３２とで構成される。
【００５９】
本実施例では、開口絞りＳが接合正レンズＬ２１と負レンズＬ２２との間に配置され、レンズ位置状態が変化する際に、第２レンズ群Ｇ２と一緒に移動する。
【００６０】
以下の表３に、本実施例の諸元の値を掲げる。
【００６１】
【表３】

【００６２】
図７（ａ）より図７（ｃ）は本実施例の無限遠合焦状態での諸収差図をそれぞれ示し、それぞれ広角端状態（ｆ＝25.20）、中間焦点距離状態（ｆ＝28.00）、望遠端状態（ｆ＝34.00）における諸収差図を示す。
【００６３】
各収差図から、本実施例は諸収差が良好に補正され、優れた結像性能を有していることは明らかである。
【００６４】
（第４実施例）
図８は、本発明の第４実施例にかかる可変焦点距離レンズ系のレンズ構成を示す図である。第１レンズ群Ｇ１は両凹レンズＬ１１と物体側に凸面を向けた正メニスカスレンズＬ１２とで構成され、第２レンズ群Ｇ２は物体側より順に、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との接合正レンズＬ２１と、物体側に凹面を向けたメニスカス形状のＬ２２と、両凸レンズＬ２３とで構成され、第３レンズ群Ｇ３は像側に凸面を向けたメニスカス形状の正レンズＬ３１と物体側に凹面を向けたメニスカス形状の負レンズＬ３２とで構成される。
【００６５】
本実施例では、開口絞りＳが接合正レンズＬ２１と負レンズＬ２２との間に配置され、レンズ位置状態が変化する際に、第２レンズ群Ｇ２と一緒に移動する。
【００６６】
以下の表４に、本実施例の諸元の値を掲げる。
【００６７】
【表４】

【００６８】
図９（ａ）より図９（ｃ）は本実施例の無限遠合焦状態での諸収差図をそれぞれ示し、それぞれ広角端状態（ｆ＝25.20）、中間焦点距離状態（ｆ＝28.00）、望遠端状態（ｆ＝34.00）における諸収差図を示す。
【００６９】
各収差図から、本実施例は諸収差が良好に補正され、優れた結像性能を有していることは明らかである。
【００７０】
【発明の効果】
以上説明したように、本発明によれば、広角端状態での画角が８０度を超え、Ｆ３．５程度の明るく、小型の可変焦点距離レンズ系が達成できる。
【図面の簡単な説明】
【図１】本発明による可変焦点距離レンズ系の屈折力配置図
【図２】第１実施例にかかる可変焦点距離レンズ系の構成を示す断面図
【図３】第１実施例の、（ａ）は広角端状態における収差図（無限遠合焦状態）（ｂ）は中間焦点距離状態における収差図（無限遠合焦状態）、（ｃ）は望遠端状態における収差図（無限遠合焦状態）
【図４】第２実施例にかかる可変焦点距離レンズ系の構成を示す断面図
【図５】第２実施例の、（ａ）は広角端状態における収差図（無限遠合焦状態）（ｂ）は中間焦点距離状態における収差図（無限遠合焦状態）、（ｃ）は望遠端状態における収差図（無限遠合焦状態）
【図６】第３実施例にかかる可変焦点距離レンズ系の構成を示す断面図
【図７】第３実施例の、（ａ）は広角端状態における収差図（無限遠合焦状態）（ｂ）は中間焦点距離状態における収差図（無限遠合焦状態）、（ｃ）は望遠端状態における収差図（無限遠合焦状態）
【図８】第４実施例にかかる可変焦点距離レンズ系の構成を示す断面図
【図９】第４実施例の、（ａ）は広角端状態における収差図（無限遠合焦状態）（ｂ）は中間焦点距離状態における収差図（無限遠合焦状態）、（ｃ）は望遠端状態における収差図（無限遠合焦状態）
【符号の説明】
Ｇ１：第１レンズ群
Ｇ２：第２レンズ群
Ｇ３：第３レンズ群
Ｓ：開口絞り
Ｌ１１〜Ｌ３２各レンズ成分[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable focal length lens system that can include an angle of view exceeding 80 degrees in a wide-angle end state, and more particularly, to a variable focal length lens system that can have a large aperture ratio of about 3.5. .
[0002]
[Prior art]
The feature of the lens shutter type camera is that it is excellent in portability. This portability is classified as being small and lightweight. Since the length of the photographic lens affects the thickness of the camera body, and the lens diameter affects the height and width of the camera body, reducing the photographic lens system has particularly affected the miniaturization of the camera.
[0003]
Zoom lenses can be taken closer to the subject, and cameras with zoom lenses have become mainstream in order to give the photographer freedom. And as the focal length in the telephoto end state increases, it becomes possible to shoot closer to the subject, so the zoom ratio tends to increase so that the focal length in the telephoto end state becomes longer.
[0004]
By the way, lens shutter cameras are often used when going on a trip because of their excellent portability. However, when single-lens reflex camera users carry lens shutter cameras, they have a single aperture lens with a bright aperture ratio. There were many cameras.
[0005]
[Problems to be solved by the invention]
However, conventional zoom lenses for shutter-type cameras tend to have a wide open F-number in the telephoto end state as the focal length in the telephoto end state becomes long, blurring is not noticeable, and the perspective is poor. It was a tendency to be finished.
[0006]
When users of single-lens reflex cameras carry around when traveling, an imaging system with a large aperture ratio and a wide angle of view is preferred. This is because the former allows photographing with natural color without a strobe, and the latter allows photographing without leaving the distance between the photographer and the subject.
[0007]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a bright and small variable focal length lens system that covers a field angle exceeding 80 degrees in the wide-angle end state.
[0008]
In order to achieve the above object, the present invention includes, in order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power. When the lens position changes from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, and the second lens group and the third lens group At least the second lens group and the third lens group are moved to the object side so that the distance is decreased, and the second lens group, in order from the object side, has a first positive lens component L21 and a negative value. It includes three lens components, a lens component L22 and a second positive lens component L23, and an aperture stop S is disposed adjacent to the negative lens component L22, and the negative lens component L22 is in relation to the aperture stop S. It is a meniscus shape with a concave surface, and the following conditional expression (1 And a variable focal length lens system satisfying the above.
(1) 0.15 <Da / fw <0.40
Where Da is the length of the air gap between the object side and the image side across the aperture stop, and fw is the focal length of the variable focal length lens system in the wide-angle end state .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Conventionally, the variable focal length lens system is roughly classified into a positive leading type in which a lens group having positive refractive power is arranged on the most object side of the lens system and a negative leading type in which a lens group having negative refractive power is arranged.
[0010]
The front-first zoom lens has a narrow angle of view and is used in a lens system having a long focal length compared to the diagonal length of the screen, and is suitable for shortening the total lens length. The negative leading zoom lens is mainly used in a lens system having a wide angle of view.
[0011]
In the negative leading zoom lens, the off-axis light beam passing through the first lens group in the wide-angle end state (mostly arranged on the object side) passes through a height close to the optical axis, so that the lens diameter can be reduced. However, when the zoom ratio is increased, in the telephoto end state, the axial light beam spreads and passes through the second lens group (arranged on the image side of the first lens group), so that a predetermined optical performance is obtained at the center of the screen. It is difficult to secure.
[0012]
In addition, the lens system used in the lens shutter type camera realizes a reduction in the overall lens length and a reduction in the lens diameter by disposing the negative lens group on the most image side of the lens system.
[0013]
In the present invention, priority is given to a large aperture ratio and a wide angle of view over a zoom ratio, and a first lens group having negative refractive power is arranged closest to the image side of the lens system and has positive refractive power on the image side. A second lens group is arranged, and a third lens group having negative refractive power is arranged on the image side. Further, in the wide-angle end state, the first lens group and the second lens group are spaced apart from each other, and the second lens group and the third lens group are spaced apart from each other toward the telephoto end state. As the lens position changes, at least the second lens group and the third lens group are moved to the object side so that the distance between the lens groups is narrowed.
[0014]
Further, in an optical system having a wide angle of view, the position where the aperture stop is disposed is important. In the present invention, the aperture stop is disposed inside the second lens group.
[0015]
In the wide-angle end state, by sufficiently widening the distance between the lens groups, the off-axis light beam passing through the first lens group and the third lens group is separated from the optical axis, so that the off-axis aberration can be corrected sufficiently satisfactorily. In addition, as the lens position state changes toward the telephoto end state, the height of the off-axis light beam passing through the first lens group and the third lens group is positively changed by narrowing the distance between the lens groups. Thus, the fluctuation of the off-axis aberration that occurs with the change in the lens position state is corrected well.
[0016]
In the present invention, the first lens unit and the third lens unit having negative refractive power are arranged on the object side and the image side of the second lens unit, respectively, so that the refractive power arrangement in the entire optical system becomes close to a symmetric type and is distorted. Aberration and lateral chromatic aberration are corrected well.
[0017]
The second lens group is mainly responsible for correcting axial aberrations. By constructing the second lens group in order from the object side with three lens components including a first positive lens component, a negative lens component, and a second positive lens component, axial aberrations are corrected particularly well, and off-axis aberrations are achieved. Can also be suppressed.
[0018]
In particular, the negative lens component is a meniscus lens having a concave surface facing the aperture stop, thereby suppressing the occurrence of off-axis aberrations.
[0019]
Conventionally, in order from the object side, there is known a negative positive / negative three group type zoom lens in which a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power are arranged. It has been. For example, JP-A-64-72114 proposes a zoom lens having a field angle of about 72 degrees in the wide-angle end state. However, since this aperture lens has an aperture stop on the image side of the second lens group, the lens diameter of the first lens group becomes very large when an angle of view exceeding 80 degrees is included.
[0020]
In the present invention, from the above configuration, it is possible to achieve both a wide angle of view in which the angle of view in the wide-angle end state exceeds 80 degrees and a large aperture ratio of about F3.5.
[0021]
Hereinafter, each conditional expression will be described.
[0022]
Conditional expression (1) is a conditional expression that defines the length of the air gap between the object side and the image side of the aperture stop arranged in the second lens group, and is a condition for reducing the size.
[0023]
In the present invention, the second lens group includes three lens components, a first positive lens component, a negative lens component, and a second positive lens component, and an aperture stop is disposed adjacent to the negative lens component. If there is not enough space before and after the aperture stop, the shutter space cannot be secured.
[0024]
In the present invention, it is desirable that at least one of the following conditional expressions (1) and (2) is satisfied.
(1) 0.15 <Da / fw <0.40
(2) 0.4 <D1W / D3W <1.2
However,
Da: the length of the air gap between the object side and the image side across the aperture stop,
fw: focal length of the variable focal length lens system in the wide-angle end state,
D1W: axial distance between the first lens group and the second lens group in the wide-angle end state,
D3W: On-axis distance between the second lens group and the third lens group in the wide-angle end state.
If the lower limit of conditional expression (1) is not reached, sufficient shutter space cannot be secured. On the other hand, when the upper limit value of conditional expression (1) is exceeded, the lens thickness increases, so that the off-axis light beam passing through each lens group is separated from the optical axis, causing an increase in the lens diameter.
[0025]
Conditional expression (2) is a condition for balancing the lens diameter and the total lens length.
[0026]
When the upper limit value of conditional expression (2) is exceeded, the off-axis light beam passing through the first lens group is separated from the optical axis, so that the lens diameter cannot be sufficiently reduced. In addition, since a large amount of coma occurs at the peripheral edge of the screen, high performance cannot be achieved. Conversely, when the lower limit value of conditional expression (2) is not reached, the off-axis light beam passing through the third lens group is separated from the optical axis, and the lens diameter is increased. Also, since the back focus is shortened, the shadow of dust adhering to the lens surface closest to the film surface is recorded on the film, and the image quality deteriorates.
[0027]
By the way, in order to achieve higher performance in the present invention, it is important to suppress the aberration amount generated for each lens group as much as possible.
[0028]
Therefore, it is desirable that each of the first lens group and the third lens group is composed of two or more lenses. In particular, the first lens group is disposed on the image side with a negative lens having a concave surface on the image side, It is desirable that the positive lens with the convex surface facing the object side and the third lens group have a positive lens with the convex surface facing the image side and a negative lens with the concave surface facing the object side. This is to reduce the lens diameter and suppress the occurrence of off-axis aberrations.
[0029]
Furthermore, in the present invention, by satisfying at least one of the following conditional expressions (3) and (4), more excellent performance can be obtained while reducing the size.
(3) 0.3 <f3 / f1 <0.7 (f3 <0, f1 <0)
(4) 0.7 <f2 / fw <0.85
However,
f1: the focal length of the first lens group,
f2: focal length of the second lens group,
f3: focal length of the third lens group,
fw: focal length of the variable focal length lens system in the wide-angle end state.
Conditional expression (3) is a conditional expression that defines the focal length ratio between the first lens group and the third lens group. If the upper limit value of conditional expression (3) is exceeded, the axial light beam that passes through the second lens group in the telephoto end state spreads, so that correction of axial aberration is insufficient. On the other hand, when the lower limit value of conditional expression (3) is not reached, the off-axis light beam passing through the third lens group approaches the optical axis, and the coma variation due to the angle of view cannot be corrected well.
[0030]
Conditional expression (4) is a conditional expression that defines the focal length of the second lens group. If the upper limit of conditional expression (4) is exceeded, the overall length of the lens will be increased. Conversely, when the lower limit value of conditional expression (4) is not reached, the refractive power of the first lens group and the third lens group also increases, and the off-axis light beam passing through the first lens group and the third lens group approaches the optical axis. Therefore, fluctuations in coma due to the angle of view that occurs in the wide-angle end state cannot be corrected.
[0031]
In the present invention, in order to shorten the overall length of the lens, it is desirable to dispose the aperture stop between the first positive lens component L21 and the negative lens component L22 in the second lens group, thereby improving performance. In order to achieve this, it is desirable that the lens surface closest to the image side of the second positive lens component L23, which is arranged away from the aperture stop and whose off-axis light beam is slightly away from the optical axis, is an aspherical surface. More preferably, it is desirable to configure so as to satisfy the following conditional expression (5).
(5) 0.15 <Db / fw <0.35
However,
Db: a length along the optical axis from the aperture stop to the lens surface closest to the image side of the second positive lens component.
Conditional expression (5) is a conditional expression that defines the distance between the lens surface closest to the image side of the second positive lens component L23 and the aperture stop. If the upper limit value of conditional expression (5) is exceeded, the off-axis light beam passing through the third lens group will be far away from the optical axis and the lens diameter will increase, impairing portability. Conversely, if the lower limit of conditional expression (5) is not reached, the difference in height between the off-axis light beam passing through the lens surface closest to the image side of the second positive lens component L23 and the on-axis light beam is reduced. The fluctuation of coma due to the angle of view cannot be corrected better.
[0032]
In the present invention, it is desirable to satisfy the following conditional expressions (6) and (7) in order to maintain stable quality during production.
(6) -0.1 <(r22a-r23b) / (r22a + r23b) <0.1
(7) fw / | r23a | <0.55
Where r22a: radius of curvature of the object side lens surface of the negative lens component in the second lens group, r23b : radius of curvature of the image side lens surface of the second positive lens component in the second lens group, r23a : The radius of curvature of the object-side lens surface of the second positive lens component in the second lens group.
[0033]
In the present invention, in order to separate the off-axis light beam passing through the second positive lens component L23 from the optical axis, it is desirable to strongly diverge the light beam on the object side lens surface of the negative lens component L22. The light beam is strongly converged on the image side lens surface of the second positive lens component L23.
[0034]
Such a configuration is desirable for further improvement in performance, but the performance deterioration due to mutual eccentricity when the lens is incorporated into the lens chamber is significantly increased. It is important to reduce the misalignment between the lens surface and the image-side lens surface of the second positive lens component L23.
[0035]
In the present invention, by setting the respective curvature radii of the object-side lens surface of the negative lens component L22 and the image-side lens surface of the second positive lens component L23 so as to satisfy the conditional expression (6), decentration is achieved. Adjustment is relatively easy.
[0036]
Further, when constructing the lens chamber, it is preferable in terms of work to move the second positive lens component L23 having a large lens diameter (away from the aperture stop) at the time of decentering adjustment, and in particular, the conditional expression (7) is satisfied. By setting the radius of curvature of the object-side lens surface of the second positive lens component L23, the working efficiency can be improved. This is because the lens rotates around the center of curvature of the object-side lens surface of the second positive lens component L23 during the decentering adjustment, so that the position of the rotation center does not move away from the image-side lens surface of the second positive lens component L23. This is because a large amount of adjustment is required.
[0037]
In each of the following embodiments, the second lens group is moved to the object side when focusing at a short distance, but it is also possible to move the first lens group or the third lens group, or to move a plurality of lens groups. Can focus at close range. In each embodiment, an aspheric lens is disposed in the first lens group. Needless to say, further performance enhancement can be realized by further disposing an aspheric lens in the third lens group, for example. Yes.
[0038]
Further, each of the following embodiments is configured by three lens groups, but it is easy to add another lens group having a weak refractive power to the image side of the third lens group .
[0039]
According to another aspect of the present invention, in order to prevent a failure due to an image blur caused by a camera shake or the like that is likely to occur when taking a picture, a blur detection system that detects a blur and a driving unit are provided in the lens system. In combination with the lens group, one lens group is made entirely or partly decentered as an eccentric lens group, and blur is detected by the blur detection system, and the detected blur is corrected. As described above, it is possible to obtain an image stabilizing optical system by correcting the image blur by decentering the decentering lens group by the driving means and shifting the image.
[0040]
【Example】
Hereinafter, numerical examples according to the present invention will be described.
[0041]
In each embodiment, the aspherical surface is expressed by the following equation.
[0042]
[Expression 1]
x = cy ² / {1+ (1-κc ² y ² ) ^1/2 } + C ₄ y ⁴ + C ₆ y ⁶ +...
[0043]
Where y is the height from the optical axis, x is the sag amount, c is the curvature, κ is the conic constant, and C ₄ , C ₆ ,... Are aspherical coefficients.
[0044]
FIG. 1 is a diagram showing refractive power distribution of a variable focal length lens system according to each embodiment of the present invention. In order from the object side, the lens unit includes a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. When the focal length changes from the wide-angle end state to the telephoto end state, the distance between the first lens group G1 and the second lens group G2 decreases, and the distance between the second lens group G2 and the third lens group G3. At least the second lens group G2 and the third lens group G3 move toward the object side.
[0045]
(First embodiment)
FIG. 2 is a diagram showing a lens configuration of the variable focal length lens system according to the first embodiment of the present invention. The first lens group G1 is composed of a biconcave lens L11 and a positive meniscus lens L12 having a convex surface facing the object side, and the second lens group G2 is arranged in order from the object side, the biconvex lens L21 and the meniscus having a concave surface facing the object side. The third lens group G3 is composed of a meniscus positive lens L31 having a convex surface facing the image side and a meniscus negative lens L32 having a concave surface facing the object side. The
[0046]
In this embodiment, the aperture stop S is disposed between the biconvex lens L21 and the negative lens L22, and moves together with the second lens group G2 when the lens position state changes.
[0047]
Table 1 below lists values of specifications of the present example. In the specification table of the embodiment, f represents the focal length, FNO represents the F number, 2ω represents the angle of view, and the refractive index is a value with respect to the d-line (λ = 587.6 nm). In Table 1, the curvature radius 0 indicates a plane. In addition, in the following, the same sign as the specification value of a present Example is used in the specification value of all Examples.
[0048]
[Table 1]

[0049]
FIGS. 3 (a) to 3 (c) show various aberration diagrams in the infinitely focused state according to the present embodiment, respectively, and are in the wide-angle end state (f = 25.20) and the intermediate focal length state (f = 28.00). The aberration diagrams in the telephoto end state (f = 34.00) are shown.
[0050]
In each aberration diagram, the solid line in the spherical aberration diagram indicates the spherical aberration, the dotted line indicates the sine condition, y indicates the image height, the solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane. The coma aberration diagram shows coma aberration at image heights y = 0, 10.8, 15.12, 18.34, and 21.6, and A indicates an angle of view.
[0051]
From each aberration diagram, it is clear that the present example has excellent image forming performance with various aberrations corrected well.
[0052]
(Second embodiment)
FIG. 4 is a diagram showing a lens configuration of a variable focal length lens system according to the second embodiment of the present invention. The first lens group G1 includes a biconcave lens L11 and a positive meniscus lens L12 having a convex surface facing the object side. The second lens group G2 is a meniscus positive lens L21 having a convex surface facing the object side in order from the object side. A meniscus L22 having a concave surface facing the object side, and a biconvex lens L23. The third lens group G3 has a meniscus positive lens L31 having a convex surface facing the image side and a concave surface facing the object side. It is composed of a meniscus negative lens L32.
[0053]
In this embodiment, the aperture stop S is disposed between the positive lens L21 and the negative lens L22, and moves together with the second lens group G2 when the lens position state changes.
[0054]
Table 2 below lists values of specifications of this example.
[0055]
[Table 2]

[0056]
FIGS. 5 (a) to 5 (c) show various aberration diagrams in the infinite focus state according to the present embodiment, respectively, and are in the wide-angle end state (f = 25.20) and the intermediate focal length state (f = 28.00), respectively. ) Shows various aberration diagrams in the telephoto end state (f = 34.00).
[0057]
From each aberration diagram, it is clear that the present example has excellent image forming performance with various aberrations corrected well.
[0058]
(Third embodiment)
FIG. 6 is a diagram showing a lens configuration of a variable focal length lens system according to the third example of the present invention. The first lens group G1 includes a biconcave lens L11 and a positive meniscus lens L12 having a convex surface facing the object side. The second lens group G2 is a negative meniscus lens having a biconvex lens and a concave surface facing the object side in order from the object side. Positive lens L21 having a concave surface facing the object side, a biconvex lens L23, and a third lens group G3 having a meniscus positive lens L31 having a convex surface facing the image side and the object And a negative meniscus lens L32 having a concave surface on the side.
[0059]
In the present embodiment, the aperture stop S is disposed between the cemented positive lens L21 and the negative lens L22, and moves together with the second lens group G2 when the lens position state changes.
[0060]
Table 3 below lists values of specifications of the present example.
[0061]
[Table 3]

[0062]
7 (a) to 7 (c) show various aberration diagrams in the infinite focus state of the present embodiment, respectively, and are respectively at the wide-angle end state (f = 25.20), the intermediate focal length state (f = 28.00), The aberration diagrams in the telephoto end state (f = 34.00) are shown.
[0063]
From each aberration diagram, it is clear that the present example has excellent image forming performance with various aberrations corrected well.
[0064]
(Fourth embodiment)
FIG. 8 is a diagram showing a lens configuration of a variable focal length lens system according to the fourth example of the present invention. The first lens group G1 includes a biconcave lens L11 and a positive meniscus lens L12 having a convex surface facing the object side. The second lens group G2 is a negative meniscus lens having a biconvex lens and a concave surface facing the object side in order from the object side. Positive lens L21 having a concave surface facing the object side, a biconvex lens L23, and a third lens group G3 having a meniscus positive lens L31 having a convex surface facing the image side and the object And a negative meniscus lens L32 having a concave surface on the side.
[0065]
In the present embodiment, the aperture stop S is disposed between the cemented positive lens L21 and the negative lens L22, and moves together with the second lens group G2 when the lens position state changes.
[0066]
Table 4 below lists values of specifications of the present example.
[0067]
[Table 4]

[0068]
9 (a) to 9 (c) show various aberration diagrams in the infinitely focused state according to the present embodiment, respectively. The wide-angle end state (f = 25.20), the intermediate focal length state (f = 28.00), respectively. The aberration diagrams in the telephoto end state (f = 34.00) are shown.
[0069]
From each aberration diagram, it is clear that the present example has excellent image forming performance with various aberrations corrected well.
[0070]
【The invention's effect】
As described above, according to the present invention, it is possible to achieve a bright and compact variable focal length lens system in which the angle of view in the wide-angle end state exceeds 80 degrees and is approximately F3.5.
[Brief description of the drawings]
FIG. 1 is a refractive power arrangement diagram of a variable focal length lens system according to the present invention. FIG. 2 is a cross-sectional view showing a configuration of a variable focal length lens system according to a first embodiment. (B) is an aberration diagram in the intermediate focal length state (infinite focus state), and (c) is an aberration diagram in the telephoto end state (infinite focus state). )
4 is a cross-sectional view showing a configuration of a variable focal length lens system according to a second embodiment. FIG. 5A is an aberration diagram in the wide-angle end state (infinite focus state) (b). ) Is an aberration diagram in the intermediate focal length state (infinitely focused state), and (c) is an aberration diagram in the telephoto end state (infinitely focused state).
FIG. 6 is a cross-sectional view showing the configuration of a variable focal length lens system according to a third example. FIG. 7A is an aberration diagram in the wide-angle end state (infinite focus state) (b). ) Is an aberration diagram in the intermediate focal length state (infinitely focused state), and (c) is an aberration diagram in the telephoto end state (infinitely focused state).
FIG. 8 is a cross-sectional view showing the configuration of a variable focal length lens system according to a fourth example. FIG. 9A is an aberration diagram in the wide-angle end state (infinite focus state) (b). ) Is an aberration diagram in the intermediate focal length state (infinitely focused state), and (c) is an aberration diagram in the telephoto end state (infinitely focused state).
[Explanation of symbols]
G1: 1st lens group G2: 2nd lens group G3: 3rd lens group S: Aperture stop L11-L32 Each lens component

Claims

In order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power,
When the lens position changes from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, and the distance between the second lens group and the third lens group decreases. So that at least the second lens group and the third lens group move toward the object side, respectively, so as to decrease,
The second lens group includes three lens components of a first positive lens component, a negative lens component, and a second positive lens component in order from the object side,
An aperture stop is disposed adjacent to the negative lens component, and the negative lens component has a meniscus shape with a concave surface facing the aperture stop, and satisfies the following conditional expression (1): Focal length lens system.
(1) 0.15 <Da / fw <0.40
However,
Da: the length of the air gap between the object side and the image side across the aperture stop,
fw: focal length of the variable focal length lens system in the wide-angle end state.

The variable focal length lens system according to claim 1, wherein the following conditional expression (2) is satisfied.
(2) 0.4 <D1W / D3W <1.2
However,
D1W: axial distance between the first lens group and the second lens group in the wide-angle end state,
D3W: On-axis distance between the second lens group and the third lens group in the wide-angle end state.

The first lens group includes a negative lens component having a concave surface directed to the image side, and a positive lens component disposed with an air gap on the image side of the negative lens component and having a convex surface directed to the object side,
The third lens group includes a positive lens component having a convex surface directed toward the image side, and a negative lens component disposed with an air gap on the image side of the positive lens component and having a concave surface directed toward the object side. The variable focal length lens system according to claim 1 or 2 .

The variable focal length lens system according to any one of claims 1 to 3 , wherein at least one of the following conditional expressions (3) and (4) is satisfied.
(3) 0.3 <f3 / f1 <0.7 (f3 <0, f1 <0)
(4) 0.7 <f2 / fw <0.85
However,
f1: the focal length of the first lens group,
f2: focal length of the second lens group,
f3: focal length of the third lens group,
fw: focal length of the variable focal length lens system in the wide-angle end state.

The aperture stop is disposed between the first positive lens component and the negative lens component;
The second most image side lens surface of the positive lens component is a non-spherical shape, and according to claims 1 to any one of 4, characterized by satisfying the following conditional expression (5) Variable focal length lens system.
(5) 0.15 <Db / fw <0.35
However,
fw: focal length of the variable focal length lens system in the wide-angle end state,
Db: Length along the optical axis from the aperture stop to the lens surface closest to the image side of the second positive lens component.

The variable focal length lens system according to any one of claims 1 to 5 , wherein the following conditional expressions (6) and (7) are satisfied.
(6) -0.1 <(r22a-r23b) / (r22a + r23b) <0.1
(7) fw / | r23a | <0.55
However,
r22a: radius of curvature of the object side lens surface of the negative lens component in the second lens group,
r23b: radius of curvature of the image side lens surface of the second positive lens component in the second lens group,
r23a: radius of curvature of the object-side lens surface of the second positive lens component in the second lens group.

The first lens group, the variable focal length lens system according to any one of claims 1 6, characterized in that it has an aspherical surface.

The variable focal length lens system according to any one of claims 1 to 7 , wherein the second lens group has an aspherical surface.