JP3652179B2

JP3652179B2 - Zoom lens

Info

Publication number: JP3652179B2
Application number: JP24527399A
Authority: JP
Inventors: 則廣難波
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1999-08-31
Filing date: 1999-08-31
Publication date: 2005-05-25
Anticipated expiration: 2019-08-31
Also published as: JP2001066503A

Description

【０００１】
【発明の属する技術分野】
本発明は、ズームレンズに関し、特に負の屈折力のレンズ群が先行する全体として３つのレンズ群を有し、これらの各レンズ群のレンズ構成を適切に設定することにより、レンズ系全体の小型化を図ったフィルム用のスチルカメラやビデオカメラ、そしてデジタルスチルカメラ等に好適な広画角のズームレンズに関するものである。
【０００２】
【従来の技術】
最近、固体撮像素子を用いたビデオカメラ、デジタルスチルカメラ等、撮像装置（カメラ）の高機能化にともない、それに用いる光学系には高性能で小型のズームレンズが求められている。この種のカメラには、レンズ最後部と撮像素子との間に、ローパスフィルターや色補正フィルターなどの各種光学部材を配置する為、それに用いる光学系には、比較的バックフォーカスの長いレンズ系が要求される。さらに、カラー画像用の撮像素子を用いたカラーカメラの場合、色シェーディングを避けるため、それに用いる光学系には像側のテレセントリック特性の良いものが望まれている。
【０００３】
従来より、負の屈折力の第１群と正の屈折力の第２群の２つのレンズ群より成り、双方のレンズ間隔を変えて変倍を行う。所謂ショートズームタイプの広角の２群ズームレンズが種々提案されている。これらのショートズームタイプの光学系では、正の屈折力の第２群を移動することで変倍を行い、負の屈折力の第１群を移動することで変倍に伴う像点位置の補正を行っている。
【０００４】
これらの２つのレンズ群よりなるレンズ構成においては、ズーム倍率は２倍程度である。さらに２倍以上の高い変倍比を有しつつレンズ全体をコンパクトな形状にまとめるため、例えば特公平7-3507号公報や、特公平6-40170 号公報等には２群ズームレンズの像側に負または正の屈折力の第３群を配置し、高倍化に伴って発生する諸収差の補正を行っている、所謂３群ズームレンズが提案されている。
【０００５】
しかしながら、これらの３群ズームレンズは主として３５ｍｍフィルム写真用に設計されているため、固体撮像素子を用いた光学系に求められるバックフォーカスの長さと、良好なテレセントリック特性を両立したものとは言い難かった。
【０００６】
【発明が解決しようとする課題】
バックフォーカスとテレセントリック特性を満足する広角の３群ズームレンズ系が、例えば、特開昭63-135913 号公報や、特開平7-261083号公報等で提案されている。また、特開平3-288113号公報には、３群ズームレンズにおいて負の屈折力の第１群を固定とし、正の屈折力の第２群と正の屈折力の第３群を移動させて変倍を行う光学系も開示されている。ところが、これらの従来例においては、各レンズ群の構成枚数が比較的多く、レンズ全長が長い、製造コストが高いなどの欠点を有していた。
【０００７】
また、特開平7-261083号公報に記載される例では、負の屈折力の第１群のもっとも物体側に凸レンズ（正レンズ）が配置されており、特に広角化した場合のレンズ外径の増大が避けられない欠点を有していた。さらに、この例では負の屈折力の第１群を移動させて近距離物体へのフォーカシングを行うため、ズーミングでの移動とあいまってメカ構造の複雑化する欠点があった。
【０００８】
また、米国特許第4,999,007 号公報には、３群ズームレンズにおいて、第１レンズ群、第２レンズ群をそれぞれ１枚の単レンズで構成したものも開示されている。ところが、広角端でのレンズ全長が比較的大きく、さらに広角端での第1 群と絞りが大きく離れているため軸外光線の入射高が大きく第１群を構成するレンズの径が増大してしまうため、レンズ系全体が大きくなってしまう欠点を有していた。
【０００９】
また、第１群、第２群は構成枚数が１枚のため群内における収差補正が不十分であった。特に変倍時の倍率色収差の変動は軸外光線の光軸の高さの変動が大きい第１群内にて発生しやすいが、第１群を凹レンズの１枚としているので群内での補正がされておらず、全系においても倍率色収差変動が大きいという課題を有する。
【００１０】
さらに、ズーム広角端での画角を大きくした場合の特有な問題として歪曲収差の補正不足の問題がある。また、比較的感度の低い高画素の撮影素子で用いるためには更なる大口径比化が求められる。
【００１１】
さらに、本出願人は特願平10-301684号公報において負−正−正の屈折力の３つのレンズ群より成る３群構成の撮影レンズを開示している。この撮影レンズではフィルター等を挿入するために必要なレンズバックの確保と、固体撮像素子用として必要なテレセントリック特性を両立した上で、極力全長を短縮しコンパクトなズームレンズを達成している。
【００１２】
一方、近年の固体撮像素子は多画素化が進んでおり、特定のイメージサイズにおける画素サイズは小さくなる傾向にある。これに伴い撮影レンズには同じイメージサイズの従来のものに比べてより高い空間周波数での解像力向上が求められている。特願平10-301684号公報で開示しているレンズ構成においては全系の収斂作用の大部分を担う第２群を物体側から順に正負正の所謂トリプレットで構成しており、諸収差の補正と小型化を両立している。
【００１３】
本発明では、本出願人は先に提案した特開平10-301684号公報で開示しているズームレンズを更に改良し、固体撮像素子を用いた撮影系に好適な、構成レンズ枚数の少ない、コンパクトで、小径化を達成した高変倍比で、特に色収差が良好に補正され、優れた光学性能を有するズームレンズの提供を目的とする。
【００１６】
【課題を解決するための手段】
請求項１の発明のズームレンズは、物体側より順に、負の屈折力の第１群、正の屈折力の第２群、そして正の屈折力の第３群から成り、広角端から望遠端へのズーミングに際して、第１群と第２群との間隔は縮まり、第２群と第３群との間隔は広がるズームレンズにおいて、該第１群は、像面側に凹面を向けたメニスカス状の負レンズ、物体側に凸面を向けたメニスカス状の正レンズを有し、該第２群は、両レンズ面が凹面の負レンズと、該負レンズより物体側に配置され、物体側に凸面を向けた正レンズと、さらに該負レンズより像面側に配置され負レンズと正レンズより構成された全体として正の屈折力の接合レンズとを有し、該第２群中の接合レンズの焦点距離をｆｃ、該第２群の焦点距離をｆ２、該接合レンズの物体側のレンズ面の曲率半径をＲａ、該両レンズ面が凹面の負レンズの像面側のレンズ面の曲率半径をＲｂとしたとき、
０．５＜ｆｃ／ｆ２＜２．０
０．５＜（Ｒａ＋Ｒｂ）／（Ｒａ−Ｒｂ）＜２．５
の条件式を満足することを特徴としている。
【００１７】
請求項２の発明は、請求項１の発明において、前記第２群中の両レンズ面が凹面の負レンズの焦点距離をｆｎ、前記第２群の焦点距離をｆ２、前記第２群中の最も物体側に配置され物体側に凸面を向けた正レンズの物体側のレンズ面の曲率半径をＲｃ、像面側のレンズ面の曲率半径をＲｄとしたとき、
０．３＜｜ｆｎ｜／ｆ２＜２．０
０＜（Ｒｄ＋Ｒｃ）／（Ｒｄ−Ｒｃ）＜２．５
の条件式を満足することを特徴としている。
【００１８】
請求項３の発明は、請求項１又は２の発明において、前記第３群は正レンズ１枚、もしくは正レンズと負レンズで構成され全体として正の接合レンズで構成されることを特徴としている。
【００１９】
請求項４の発明は、請求項１から３のいずれか１項の発明において、前記第１群中の負レンズの中の少なくとも１つのレンズ面は非球面であり、該非球面は光軸から周辺に向かってしだいに発散作用が弱まる形状であることを特徴としている。
【００２０】
請求項５の発明は、請求項１の発明において、前記第２群中の正レンズ中の少なくとも１つのレンズ面は非球面であり、該非球面は光軸から周辺に向かってしだいに収斂作用が弱まる形状であることを特徴としている。
【００２１】
請求項６の発明は、請求項１から５のいずれか１項の発明において、前記第３群は正レンズを有し、該正レンズの少なくとも１つのレンズ面は非球面であり、該非球面は光軸から周辺に向かってしだいに収斂作用が弱まる形状であることを特徴としている。
【００２２】
請求項７の発明は、請求項１から６のいずれか１項の発明において、前記第３群はズーミングに際して移動することを特徴としている。
【００２３】
請求項８の発明のズームレンズは、物体側より順に、負の屈折力の第１群、正の屈折力の第２群、そして正の屈折力の第３群から成り、広角端から望遠端へのズーミングに際して、第１群と第２群との間隔は縮まり、第２群と第３群との間隔は広がるズームレンズにおいて、第１群は、像面側に凹面を向けたメニスカス状の負レンズ、物体側に凸面を向けたメニスカス状の正レンズを有し、該第２群は、物体側より順に１つ又は２つの正レンズと、両レンズ面が凹面の負レンズＢ、そして負レンズと正レンズとの接合レンズＡとから成り、前記第２群中の接合レンズＡの焦点距離をｆｃ、前記第２群の焦点距離をｆ２、前記接合レンズＡの物体側のレンズ面の曲率半径をＲａ、前記レンズＢの像側面の曲率半径をＲｂ、前記第２群中のレンズＢの焦点距離をｆｎ、前記第２群中の最も物体側に配置され物体側に凸面を向けた正レンズの物体側面の曲率半径をＲｃ、像面側のレンズ面の曲率半径をＲｄとしたとき、
０．５＜ｆｃ／ｆ２＜２．０
０．５＜（Ｒａ＋Ｒｂ）／（Ｒａ−Ｒｂ）＜２．５
０．３＜｜ｆｎ｜／ｆ２＜２．０
０＜（Ｒｄ＋Ｒｃ）／（Ｒｄ−Ｒｃ）＜２．５
の条件式を満足することを特徴としている。
【００２４】
請求項９の発明のズームレンズは、請求項１〜８の発明のズームレンズが固体撮像素子に像を形成することを特徴としている。
請求項１０の撮像装置は、請求項１から９のいずれかい１項のズームレンズと、該ズームレンズによって形成される像を受光する固体撮像素子とを備えることを特徴としている。
【００２５】
【発明の実施の形態】
図１は本発明の後述する数値実施例１のレンズ断面図である。図２〜図４は本発明の数値実施例の広角端，中間，望遠端の収差図である。
【００２６】
図５は本発明の後述する数値実施例２のレンズ断面図である。図６〜図８は本発明の数値実施例の広角端，中間，望遠端の収差図である。
【００２７】
図９は本発明の後述する数値実施例３のレンズ断面図である。図１０〜図１２は本発明の数値実施例の広角端，中間，望遠端の収差図である。
【００２８】
図１３は本発明の後述する数値実施例４のレンズ断面図である。図１４〜図１６は本発明の数値実施例の広角端，中間，望遠端の収差図である。
【００２９】
図１７は本発明の後述する数値実施例５のレンズ断面図である。図１８〜図２０は本発明の数値実施例の広角端，中間，望遠端の収差図である。
【００３０】
レンズ断面図においてＬ１は負の屈折力の第１群（第１レンズ群）、Ｌ２は正の屈折力の第２群（第２レンズ群）、Ｌ３は正の屈折力の第３群（第３レンズ群）、ＳＰは開口絞り、ＩＰは像面である。Ｇはフィルターや色分解プリズム等のガラスブロックである。
【００３１】
本発明のズームレンズの基本構成は、負の屈折力の第１群と正の屈折力の第２群とで所謂広角ショートズーム系を構成しており、正の屈折力の第２群の移動により変倍を行い、負の屈折力の第１群を往復移動によって変倍に伴う像点の移動を補正している。正の屈折力の第３群はズーミング中固定の場合、変倍には寄与しないが、撮像素子の小型化に伴う撮影レンズの屈折力の増大を分担し、第１，第２群で構成されるショートズーム系の屈折力を減らすことで、特に第１群を構成する各レンズでの収差の発生を抑え、良好な光学性能を達成している。また、特に固体撮像素子等を用いた撮影装置に必要な像側のテレセントリックな結像を正の屈折力の第３群をフィールドレンズの役割を持たせることで達成している。また、第３群がズーミング中移動する場合は、第３群に入射する軸外光線の光軸の高さをコントロールできるため、軸外諸収差に対する補正能力が高まり、変倍全域に渡ってさらに良好な性能を実現している。
【００３２】
また、絞りＳＰを第２群内の物体側に置き、広角側での入射瞳と第１群との距離を縮めることで、第１群を構成するレンズの外径の増大をおさえるとともに、正の屈折力の第２群の物体側に配置した絞りを挟んで第１群と第３群とで軸外の諸収差を打ち消すことで構成レンズ枚数を増やさずに良好な光学性能を得ている。
【００３３】
本発明は前述の基本構成の基で、
(1-1)第１発明は、該第１群は像面側に凹面を向けたメニスカス状の負レンズ、物体側に凸面を向けたメニスカス状の正レンズを有し、該第２群は最も像面側に負レンズと正レンズより構成され全体として正の屈折力の接合レンズＡと、該接合レンズＡより物体側のレンズ中最も像面側のレンズＢは像面側のレンズ面が像面側に凹面を向けた形状であることを特徴としている。
【００３４】
尚、第１発明において更に好ましくは次の条件のうち少なくとも１つを満足させるのが良い。
【００３５】
(ア-1)前記第２群中の接合レンズＡの焦点距離をｆｃ、前記第２群の焦点距離をｆ２、前記接合レンズＡの物体側のレンズ面の曲率半径をＲａ、前記レンズＢの像面側のレンズ面の曲率半径をＲｂとしたとき、
０．５＜ｆｃ／ｆ２＜２．０…（１）
０．５＜（Ｒａ＋Ｒｂ）／（Ｒａ−Ｒｂ）＜２．５…（２）
の条件式を満足することである。
【００３６】
(ア-2)前記第２群は物体側より順に物体側に凸面を向けた正レンズ、像面側に凹面を向けた負レンズ、そして接合レンズを有することである。
【００３７】
(1-2)第２発明は、該第１群は像面側に凹面を向けたメニスカス状の負レンズ、物体側に凸面を向けたメニスカス状の正レンズを有し、該第２群は両レンズ面が凹面の負レンズと、該負レンズより物体側に配置され、物体側に凸面を向けた正レンズ、さらに該負レンズより像面側に配置され負レンズと正レンズより構成され、全体として正の屈折力の接合レンズを有することを特徴としている。
【００３８】
尚、第２発明において更に好ましくは次の条件のうちの少なくとも１つを満足させるのが良い。
【００３９】
(イ-1)前記第２群中の負レンズの焦点距離をｆｎ、前記第２群の焦点距離をｆ２、前記第２群中の最も物体側に配置され物体側に凸面を向けた正レンズの物体側のレンズ面の曲率半径をＲｃ、像面側のレンズ面の曲率半径をＲｄとしたとき、
０．３＜｜ｆｎ｜／ｆ２＜２．０…（３）
０＜（Ｒｄ＋Ｒｃ）／（Ｒｄ−Ｒｃ）＜２．５…（４）
の条件式を満足することである。
【００４０】
(イ-2)前記第３群は正レンズ１枚、もしくは正レンズと負レンズで構成され全体として正の接合レンズで構成されることである。
【００４１】
(1-3)第１群は像面側に凹面を向けたメニスカス状の負レンズ、物体側に凸面を向けたメニスカス状の正レンズを有し、該第２群は物体側より順に１つ又は２つの正レンズと、両レンズ面が凹面の負レンズＢ、そして負レンズと正レンズとの接合レンズＡとを有し、前記第２群中の接合レンズＡの焦点距離をｆｃ、前記第２群の焦点距離をｆ２、前記接合レンズＡの物体側のレンズ面の曲率半径をＲａ、前記レンズＢの像側面の曲率半径をＲｂ、前記第２群中のレンズＢの焦点距離をｆｎ、前記第２群中の最も物体側に配置され物体側に凸面を向けた正レンズの物体側面の曲率半径をＲｃ、像面側のレンズ面の曲率半径をＲｄとしたとき、
０．５＜ｆｃ／ｆ２＜２．０…（１）
０．５＜（Ｒａ＋Ｒｂ）／（Ｒａ−Ｒｂ）＜２．５…（２）
０．３＜｜ｆｎ｜／ｆ２＜２．０…（３）
０＜（Ｒｄ＋Ｒｃ）／（Ｒｄ−Ｒｃ）＜２．５…（４）
の条件式を満足するよう構成されたことである。
【００４２】
次に各発明の特徴について説明する。尚、第１，第２，第３発明を総称して「本発明」ともいう。
【００４３】
本発明のズームレンズは、負の屈折力の第１群を物体側から順に物体側に凸面を向けたメニスカス状の負レンズと物体側に凸面を向けたメニスカス状の正レンズの２つのレンズより構成し、または第１群を２枚の像側に凹面を向けた凹レンズ（負レンズ）１１、凹レンズ１２、そして物体側に凸面を向けた凸レンズ（正レンズ）１３の３枚で構成している。また、正の屈折力の第２群を物体側から順に物体側に凸面を向けた凸レンズ２１、両レンズ面が凹面の凹レンズ２２、負レンズと正レンズより成る接合レンズ２３の３群４枚構成で構成し、または、第２群を物体側より順に２つの正レンズ、両レンズ面が凹面の負レンズ２２、負レンズと正レンズより成る接合レンズ２３の４群５枚で構成している。
【００４４】
正の屈折力の第３群を凸レンズ１枚または正レンズと負レンズとの接合レンズで構成している。このように各群を所望の屈折力配置を収差補正とを両立する構成とすることにより、良好な性能を保ちつつ、レンズ系のコンパクト化を達成している。
【００４５】
負の屈折力の第１群は、軸外主光線を絞り中心に瞳結像させる役割を持っており、特に広角側においては軸外主光線の屈折量が大きいために軸外諸収差、特に非点収差と歪曲収差が発生しやすい。そこで、通常の広角レンズと同様に最も物体側のレンズ径の増大が抑えられる凹−凸の構成とした上で、主に負の屈折力を分担している２つの負レンズ１１，１２で屈折力の分担を図っている。第１群を構成する各レンズは、軸外主光線の屈折によって生じる軸外収差の発生を抑えるために絞り中心を中心とする同心球面に近い形状をとっている。すなわち、負レンズ１１，１２は像面に凹面を向けたメニスカス形状とし、正レンズ１３は物体側に凸面を向けたメニスカス形状としている。
【００４６】
正の屈折力の第２群は、両レンズ面が凹面の凹レンズ２２の前後に正レンズを配置し、屈折力配置上において対称的な構成としている。これは、変倍中大きく移動する群であることから、製造誤差による群相互の偏心等による製造劣化を未然に防ぐため、群単体で球面収差、コマ収差等をある程度取り除いたものとするためである。
【００４７】
第２群中のもっとも物体側の凸レンズ２１は第１群を射出した軸外主光線が大きく屈折して軸外諸収差が発生しないよう物体側に凸の形状にしている。また、第１群を発散状態で射出した軸上光束に対して球面収差の発生量を抑えるためにも凸レンズ２１は物体側に凸の形状としている。
【００４８】
さらに、凹レンズ２２は物体側と像面ともに凹面とし、前後の凸レンズ２１と正の接合レンズ２３とともに負の空気レンズを形成し、大口径比化に伴って発生する球面収差と、コマ収差の補正を良好に行っている。
【００４９】
さらに凹レンズ２２の像面側に接合レンズ２３を配置して色収差を良好に補正している。本発明のズームレンズの構成では第１群にて軸外光束が屈曲する高さは広角端で高く、望遠端で低くなるため、変倍に伴う倍率色収差の変動は特に第１群にて発生する。そこで、第１群の屈折力配置および硝材選択は特に倍率色収差の変動が最小となるように構成している。第１群をコンパクトにするために前述のように凹−凸の構成として、構成枚数を２から３枚程度とした場合、第１群内にて軸上色収差の変動成分が残存しやすい。そこで第２群内に接合レンズを用いることで軸上色収差を良好に補正している。
【００５０】
また、少しでも倍率色収差の補正を第２群内にも分担させるには接合レンズを絞りより離れた位置に配置するのが効果的であるため、本発明では凹レンズ２２の像側に配置している。
【００５１】
正の屈折力の第３群は、物体側に凸面を設けた形状の凸レンズより構成し、または正レンズと負レンズとの接合レンズより構成し、像側がテレセントリック系となるようにしている。また、フィールドレンズとしての役割も有するようにしている。
【００５２】
また、各レンズ群を少ない枚数で構成しつつ、更なる光学性能の向上を達成するため、本実施例では非球面を効果的に導入している。
【００５３】
図１に示す数値実施例１においては、第１群を構成する凹レンズ１１の像側面を周辺で発散作用が弱くなる形状の非球面とし、特に広角側での像面彎曲、非点収差および歪曲収差の補正を行い変倍に伴う収差変動を低減している。
【００５４】
また、第２群を構成する凸レンズ２１の物体側のレンズ面を周辺で収斂作用が弱くなる非球面としており、大口径化で顕著になる球面収差の補正を効果的におこなっている。
【００５５】
また、第３群を構成する凸レンズ３１の物体側のレンズ面を周辺で収斂作用が弱くなる非球面としており、変倍全域での像面彎曲、非点収差、歪曲収差の補正を効果的におこなっている。
【００５６】
本実施例のズームレンズを用いて近距離物体を撮影する場合には、第１群を物体側へ移動することで良好な性能を得られるが、第３群を物体側に移動するリアフォーカス式を用いても良い。これによれば、フォーカシングによる前玉径の増大が防げる、また、最短撮像距離が短縮でき、フォーカス群が軽量化できるといったメリットが得られる。
【００５７】
次に前述の各条件式の技術的意味について説明する。
【００５８】
条件式（１）は第２群の接合レンズの屈折力を規定している式である。本発明の第２群は前述にあるように、正，負，正の屈折力の対称型な屈折力配置としている。上記接合レンズの屈折力は第２群の像側の正の屈折力を担っており、第２群の屈折力と比してある範囲内にあるのが好ましい。
【００５９】
条件式（１）の上限を越えて接合レンズの屈折力が弱まると、第２群に必要な収斂作用をもたせるには第２群中の物体側の正レンズの屈折力を強めなければならず、過度の球面収差が発生し非球面を用いても補正不足となるため良くない。また、物体側の正レンズの屈折力を強めない場合は第２群の屈折力自体が弱まるため、変倍のための移動量が大きくなり、レンズ全長、前玉径の増大を招きコンパクトなズームレンズが構成できなくなるためよくない。
【００６０】
また、条件式（１）の下限を超えて接合レンズの屈折力が強まると、第２群内のペッツバール和が正方向に大きくなり、アンダーの像面彎曲が発生するため良くない。また、軸上色収差を補正するために接合レンズ面の曲率をきつくしなければならず、接合レンズを構成する正レンズのコバ厚を確保するために中心肉厚が大きくなりコンパクト化の点で良くない。
【００６１】
条件式（２）は第２群の像側に配置された接合レンズとその直前の凹レンズとで構成される負の屈折力の空気レンズの形状因子を規定している式である。
【００６２】
第２群中の絞りを物体側に配置すると第２群の物体側の正レンズの物体側のレンズ面と凹レンズの物体側のレンズ面とで同符合のコマ収差が発生する。これに対して空気レンズの物体側のレンズ面はこれらとは異符号のコマ収差が、像側のレンズ面は同符合のコマ収差が発生するため、空気レンズの物体側のレンズ面を像側に凹面を向けた状態で曲率をある程度きつくし、これとは反対に空気レンズの像側のレンズ面は比較的緩い曲率とするとコマ収差に対して補正効果がある。尚、形状因子が１より大きいとメニスカス形状、１より小さいと両凸レンズであり、像側のレンズ面の曲率半径は１より大きくなるにつれ像側に曲率中心を持ちながら小さくなり、反対に１より小さくなるにつれ物体側に曲率中心を持ちながら曲率が小さくなる。
【００６３】
条件式（２）の上限を超えて空気レンズのメニスカスの度合いが強まると空気レンズの像側のレンズ面の曲率が強くなりすぎ、空気レンズのコマ収差の補正能力が弱まる。結果として第２群はコマ収差が補正不足となるため良くない。
【００６４】
空気レンズの形状因子が１より小さくなると空気レンズの像側のレンズ面は物体側に曲率中心を持つため、空気レンズは両凸形状となる。これに伴い像側の接合レンズはメニスカス形状となる。接合レンズが条件式（１）を満足する屈折力を有するためには接合レンズの像側のレンズ面の曲率がきつくなってしまう。条件式（２）の下限値を超えると、結果的に接合レンズの像側のレンズ面の曲率がきつくなりすぎ、アンダーの球面収差が発生し非球面を用いても補正不足となるため良くない。
【００６５】
条件式（３）は第２群の両レンズ面が凹面の負レンズの屈折力を規定している式である。
【００６６】
条件式（３）の上限を超えて屈折力が弱まると第２群内のペッツバール和が正方向に大きくなりアンダーの像面彎曲が発生するため良くない。また、フィルター群を配置するための十分なバックフォーカスが得られない。更に、射出瞳を像面から十分遠ざけることができないといった問題が発生する。
【００６７】
条件式（３）の下限を超えて屈折力が強まると球面収差が補正過剰となる、オーバーの像面彎曲が発生する、バックフォーカスが長くなりすぎコンパクト化が困難となるため良くない。
【００６８】
条件式（４）は第２群中の物体側の正レンズの形状因子を規定した式である。
【００６９】
条件式（４）の上限を超え、像側のレンズ面の曲率が像側に曲率中心を有しながら状態できつくなると、特にコマ収差の発生が顕著になり、非球面を用いても補正困難となるため良くない。
【００７０】
条件式（４）の下限を超え、像側のレンズ面の曲率が物体側に曲率中心を有しながらきつくなると軸上ランド光線の像側面への入射角がきつくなりすぎアンダーの球面収差が発生するため良くない。
【００７１】
以下に、本発明の数値実施例を示す。各数値実施例においてｉは物体側からの面の順序を示し、Ｒｉは第ｉ面の曲率半径、Ｄｉは第ｉ面と第ｉ＋１面との間のレンズ肉厚又は空気間隔、Ｎｉ，νｉはそれぞれｄ線に対する屈折率、アッベ数を示す。また、もっとも像側の２面は水晶ローパスフィルター、赤外カットフィルター等のフィルター部材である。また、Ｂ，Ｃ，Ｄ，Ｅ，Ｆは非球面係数である。非球面形状は光軸からの高さｈの位置での光軸方向の変位を面頂点を基準にしてｘとするとき、
ｘ＝Ｒ｛１−（１−ｈ²／Ｒ²）^1/2｝＋Ｂｈ⁴＋Ｃｈ⁶＋Ｄｈ⁸＋Ｅｈ¹⁰＋Ｆｈ¹²で表される。但しＲは曲率半径である。「ｅ−０Ｘ」は「１０^-X」を意味している。また、前述の各条件式と数値実施例における諸数値との関係を表１に示す。
【００７２】
［数値実施例１］
本数値実施例の断面図を図１に、広角端，中間位置，望遠端での収差図を図２，３，４に示す。
【００７３】
本実施例は物体側から順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群で構成され、広角端から望遠端へのズーミングに際し、第１群は像側に凸状の往復運動、第２群は物体側へ移動、第３群は像側へ移動する。以下レンズデータを示す。
【００７４】
【外１】

【００７５】
［数値実施例２］
本実施例の断面図を図５に、広角端，中間位置，望遠端での収差図を図６，７，８に示す。
【００７６】
本実施例は物体側から順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群で構成され、広角端から望遠端へのズーミングに際し、第１群は像側に凸状の往復運動、第２群は物体側へ移動、第３群は像側へ移動する。以下レンズデータを示す。
【００７７】
【外２】

【００７８】
［数値実施例３］
本実施例の断面図を図９に、広角端，中間位置，望遠端での収差図を図１０，１１，１２に示す。
【００７９】
本実施例は物体側から順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群で構成され、広角端から望遠端へのズーミングに際し、第１群は像側に凸状の往復運動、第２群は物体側へ移動、第３群は像側へ移動する。
【００８０】
本実施例が数値実施例１と異なるのは、第１群の構成枚数を２枚とした点である。本実施例では像側に凹面を向けたメニスカス状の負レンズと、物体側に凸面を向けたメニスカス状の正レンズで構成されており、数値実施例１の２枚の凹レンズを１枚で構成している。これにより、レンズ枚数が削減されコストダウンにつながる、前玉が軽量化されるといったメリットがある。以下レンズデータを示す。
【００８１】
【外３】

【００８２】
［数値実施例４］
本実施例の断面図を図１３に、広角端，中間位置，望遠端での収差図を図１４，１５，１６に示す。
【００８３】
本実施例は物体側から順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群で構成され、広角端から望遠端へのズーミングに際し、第１群は像側に凸状の往復運動、第２群は物体側へ移動、第３群は像側へ移動する。
【００８４】
本実施例が数値実施例１と異なるのは、第２群の構成枚数４群５枚とした点である。本実施例の第２群は物体側より順に、物体側に凸面を向けたメニスカス状の正レンズ、両レンズ面が凸面の凸レンズ、両レンズ面が凹面の凹レンズ、凹レンズと凸レンズで構成され全体として正の接合レンズで構成されており、数値実施例１の物体側の正レンズ１枚を２枚で構成している。これにより、第１群を発散状態で発した軸上光束を収斂させる作用をレンズ２枚で分担させることができるため、球面収差の発生を低減でき、より大口径な撮影レンズを構成できるというメリットがある。以下レンズデータを示す。
【００８５】
【外４】

【００８６】
［数値実施例５］
本実施例の断面図を図１７に、広角端，中間位置，望遠端での収差図を図１８，１９，２０に示す。
【００８７】
本実施例は物体側から順に正の屈折力の第１群、負の屈折力の第２群、正の屈折力の第３群で構成され、広角端から望遠端へのズーミングに際し、第１群は像側に凸状の往復運動、第２群は物体側へ移動、第３群は固定である。
【００８８】
本実施例が数値実施例１と異なるのは、第３群の構成枚数を１群２枚とした点である。本実施例の第３群は凹レンズと凸レンズで構成され全体として正の接合レンズで構成されており、数値実施例１の単レンズ１枚を接合で構成している。これにより、第３群にて特に倍率色収差の補正が可能となる。倍率色収差は前述のように第１群にてズーム変動が大きいが、本実施例の場合は返変動成分を第１群で補正し、絶対量を第３群にて補正分担することができる。これにより、ズーム比を上げた場合にも変倍全域に渡って倍率色収差が良好に補正できるというメリットがある。
【００８９】
また、変倍に際して第３群を固定としている点が数値実施例１と異なる。第３群を固定とすることにより移動機構が必要なく、鏡筒構成が簡素化されるというメリットがある。以下レンズデータを示す。
【００９０】
【外５】

【００９１】
以下、本発明の実施例における各条件式の値を示す。
【００９２】
【表１】

【００９３】
【発明の効果】
本発明によれば、固体撮像素子を用いた撮影系に好適な、構成レンズ枚数の少ない、コンパクトで、小径化を達成した高変倍比で、特に色収差が良好に補正され、優れた光学性能を有するズームレンズを達成することができる。
【図面の簡単な説明】
【図１】本発明の数値実施例１のレンズ断面図
【図２】本発明の数値実施例１の広角端の収差図
【図３】本発明の数値実施例１の中間の収差図
【図４】本発明の数値実施例１の望遠端の収差図
【図５】本発明の数値実施例２のレンズ断面図
【図６】本発明の数値実施例２の広角端の収差図
【図７】本発明の数値実施例２の中間の収差図
【図８】本発明の数値実施例２の望遠端の収差図
【図９】本発明の数値実施例３のレンズ断面図
【図１０】本発明の数値実施例３の広角端の収差図
【図１１】本発明の数値実施例３の中間の収差図
【図１２】本発明の数値実施例３の望遠端の収差図
【図１３】本発明の数値実施例４のレンズ断面図
【図１４】本発明の数値実施例４の広角端の収差図
【図１５】本発明の数値実施例４の中間の収差図
【図１６】本発明の数値実施例４の望遠端の収差図
【図１７】本発明の数値実施例５のレンズ断面図
【図１８】本発明の数値実施例５の広角端の収差図
【図１９】本発明の数値実施例５の中間の収差図
【図２０】本発明の数値実施例５の望遠端の収差図
【符号の説明】
Ｌ１第１群
Ｌ２第２群
Ｌ３第３群
ＳＰ絞り
ＩＰ像面
ｄｄ線
ｇｇ線
Ｓサジタル像面
Ｍメリディオナル像面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens, and in particular, has a total of three lens groups preceded by a lens unit having a negative refractive power. By appropriately setting the lens configuration of each lens group, the entire lens system can be made compact. The present invention relates to a zoom lens having a wide angle of view suitable for a still camera for a film, a video camera, a digital still camera, and the like.
[0002]
[Prior art]
Recently, along with the enhancement of functions of an imaging apparatus (camera) such as a video camera or a digital still camera using a solid-state imaging device, a high-performance and compact zoom lens is required for an optical system used therefor. In this type of camera, various optical members such as a low-pass filter and a color correction filter are arranged between the last lens part and the image sensor, so that the optical system used therefor has a lens system with a relatively long back focus. Required. Furthermore, in the case of a color camera using an image pickup device for color images, in order to avoid color shading, an optical system with good telecentric characteristics on the image side is desired.
[0003]
Conventionally, it consists of two lens groups, a first group having a negative refractive power and a second group having a positive refractive power, and zooming is performed by changing the distance between both lenses. Various so-called short zoom type wide-angle two-group zoom lenses have been proposed. In these short zoom type optical systems, zooming is performed by moving the second group having a positive refractive power, and correction of the image point position accompanying zooming is performed by moving the first group having a negative refractive power. It is carried out.
[0004]
In a lens configuration composed of these two lens groups, the zoom magnification is about twice. Furthermore, in order to collect the entire lens into a compact shape while having a high zoom ratio of 2 times or more, for example, Japanese Patent Publication No. 7-3507 and Japanese Patent Publication No. 6-40170 disclose the image side of a two-group zoom lens. A so-called three-group zoom lens has been proposed in which a third group having a negative or positive refractive power is arranged to correct various aberrations that occur as the magnification increases.
[0005]
However, since these three-group zoom lenses are mainly designed for 35 mm film photography, it is difficult to say that both the back focus length required for an optical system using a solid-state imaging device and good telecentric characteristics are compatible. It was.
[0006]
[Problems to be solved by the invention]
A wide-angle three-group zoom lens system that satisfies the back focus and telecentric characteristics has been proposed in, for example, Japanese Patent Laid-Open Nos. 63-135913 and 7-261083. Japanese Patent Laid-Open No. 3-288113 discloses that a first lens unit having a negative refractive power is fixed in a three-group zoom lens, and a second group having a positive refractive power and a third group having a positive refractive power are moved. An optical system that performs zooming is also disclosed. However, these conventional examples have the disadvantages that the number of components of each lens group is relatively large, the total lens length is long, and the manufacturing cost is high.
[0007]
Further, in the example described in Japanese Patent Laid-Open No. 7-261083, a convex lens (positive lens) is disposed on the most object side of the first group having a negative refractive power, and the outer diameter of the lens particularly when the angle is widened. It had the disadvantage that an increase was inevitable. Further, in this example, since the first group having a negative refractive power is moved to perform focusing on a short-distance object, there is a disadvantage that the mechanical structure becomes complicated in combination with the movement by zooming.
[0008]
U.S. Pat. No. 4,999,007 discloses a three-group zoom lens in which the first lens group and the second lens group are each composed of one single lens. However, the overall length of the lens at the wide-angle end is relatively large, and the first group at the wide-angle end is far away from the stop, so that the incident height of off-axis rays is large and the diameter of the lens constituting the first group is increased. As a result, the entire lens system becomes large.
[0009]
In addition, since the first group and the second group have one component, aberration correction within the group was insufficient. In particular, the variation in lateral chromatic aberration during zooming is likely to occur in the first group where the variation in the optical axis height of off-axis rays is large. However, since the first group is a single concave lens, correction is performed within the group. However, there is a problem that the chromatic aberration of magnification variation is large even in the entire system.
[0010]
Furthermore, there is a problem of insufficient correction of distortion aberration as a particular problem when the angle of view at the wide angle end of the zoom is increased. Further, in order to use it in a high-pixel imaging element with a relatively low sensitivity, a larger aperture ratio is required.
[0011]
Further, the present applicant has disclosed a photographic lens having a three-group structure comprising three lens groups having negative-positive-positive refractive power in Japanese Patent Application No. 10-301684. This photographic lens achieves a compact zoom lens by shortening the total length as much as possible, while ensuring both the lens back necessary for inserting a filter and the like and the telecentric characteristics necessary for a solid-state image sensor.
[0012]
On the other hand, the number of pixels in recent solid-state imaging devices is increasing, and the pixel size in a specific image size tends to be small. Along with this, the photographic lens is required to improve the resolution at a higher spatial frequency than the conventional lens having the same image size. In the lens configuration disclosed in Japanese Patent Application No. 10-301684, the second group that plays a major part in the converging action of the entire system is composed of so-called triplets that are positive and negative in order from the object side. And miniaturization.
[0013]
In the present invention, the applicant further improves the zoom lens disclosed in Japanese Patent Laid-Open No. 10-301684 previously proposed, and is suitable for a photographing system using a solid-state imaging device, and is compact with a small number of constituent lenses. Accordingly, it is an object of the present invention to provide a zoom lens that has a high zoom ratio that achieves a small diameter and that has particularly good chromatic aberration correction and excellent optical performance.
[0016]
[Means for Solving the Problems]
The zoom lens according to the first aspect of the present invention includes, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. During zooming, in the zoom lens in which the distance between the first group and the second group is reduced and the distance between the second group and the third group is increased, the first group has a meniscus shape with a concave surface facing the image surface side. Negative lens, meniscus-shaped positive lens with a convex surface facing the object side, the second lens group is a negative lens whose concave lens surfaces are disposed on the object side from the negative lens, and convex surface on the object side And a cemented lens having a positive refractive power as a whole, which is composed of a negative lens and a positive lens, which is disposed on the image plane side of the negative lens. The focal length is fc, the focal length of the second lens unit is f2, and the object-side lens surface of the cemented lens is When the rate radius Ra, the both lens surfaces of the radius of curvature of the lens surface on the image side of the concave surface of the negative lens and Rb,
0.5 <fc / f2 <2.0
0.5 <(Ra + Rb) / (Ra−Rb) <2.5
It satisfies the following conditional expression.
[0017]
According to a second aspect of the present invention, in the first aspect of the present invention, the focal length of the negative lens in which both lens surfaces in the second group are concave surfaces is fn, the focal length of the second group is f2, and the second group has a focal length of f2. When the radius of curvature of the lens surface on the object side of the positive lens disposed closest to the object side and having the convex surface facing the object side is Rc, and the radius of curvature of the lens surface on the image plane side is Rd,
0.3 <| fn | / f2 <2.0
0 <(Rd + Rc) / (Rd−Rc) <2.5
It satisfies the following conditional expression.
[0018]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the third group is composed of one positive lens, or a positive lens and a negative lens, and a positive cemented lens as a whole. .
[0019]
According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, at least one lens surface of the negative lens in the first group is an aspherical surface, and the aspherical surface is peripheral from the optical axis. It is characterized by a shape in which the diverging action gradually weakens toward.
[0020]
According to a fifth aspect of the present invention, in the first aspect of the invention, at least one lens surface in the positive lens in the second group is an aspherical surface, and the aspherical surface gradually converges from the optical axis toward the periphery. It is characterized by a weakened shape.
[0021]
The invention of claim 6 is the invention of any one of claims 1 to 5, wherein the third group has a positive lens, and at least one lens surface of the positive lens is an aspheric surface, It is characterized by a shape in which the convergence action gradually decreases from the optical axis toward the periphery.
[0022]
The invention of claim 7 is the invention of any one of claims 1 to 6, characterized in that the third group moves during zooming.
[0023]
The zoom lens according to an eighth aspect of the present invention includes, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. During zooming, in the zoom lens in which the distance between the first group and the second group is reduced and the distance between the second group and the third group is widened, the first group has a meniscus shape with a concave surface facing the image surface side. The second lens unit has a negative lens, a meniscus positive lens having a convex surface directed toward the object side, and the second group includes one or two positive lenses in order from the object side, a negative lens B whose both lens surfaces are concave surfaces, and a negative lens A cemented lens A of a lens and a positive lens; Consist of The focal length of the cemented lens A in the second group is fc, the focal length of the second group is f2, the radius of curvature of the object-side lens surface of the cemented lens A is Ra, and the curvature of the image side surface of the lens B is The radius is Rb, the focal length of the lens B in the second group is fn, the radius of curvature of the object side surface of the positive lens disposed closest to the object side in the second group with the convex surface facing the object side is Rc, the image plane When the radius of curvature of the lens surface on the side is Rd,
0.5 <fc / f2 <2.0
0.5 <(Ra + Rb) / (Ra−Rb) <2.5
0.3 <| fn | / f2 <2.0
0 <(Rd + Rc) / (Rd−Rc) <2.5
It satisfies the following conditional expression.
[0024]
A zoom lens according to a ninth aspect of the invention is characterized in that the zoom lens according to the first to eighth aspects forms an image on a solid-state imaging device.
An imaging device according to a tenth aspect includes the zoom lens according to any one of the first to ninth aspects, and a solid-state imaging device that receives an image formed by the zoom lens.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a lens cross-sectional view of Numerical Example 1 described later according to the present invention. 2 to 4 are aberration diagrams at the wide-angle end, middle, and telephoto end of the numerical example of the present invention.
[0026]
FIG. 5 is a lens cross-sectional view of Numerical Example 2 described later according to the present invention. FIGS. 6 to 8 are aberration diagrams at the wide-angle end, in the middle, and at the telephoto end of the numerical example of the present invention.
[0027]
FIG. 9 is a lens cross-sectional view of Numerical Example 3 described later according to the present invention. 10 to 12 are aberration diagrams of the numerical example of the present invention at the wide-angle end, in the middle, and at the telephoto end.
[0028]
FIG. 13 is a lens cross-sectional view of Numerical Example 4 described later according to the present invention. FIGS. 14 to 16 are aberration diagrams at the wide-angle end, in the middle, and at the telephoto end of the numerical example of the present invention.
[0029]
FIG. 17 is a lens cross-sectional view of Numerical Example 5 described later according to the present invention. 18 to 20 are aberration diagrams at the wide-angle end, middle, and telephoto end of the numerical example of the present invention.
[0030]
In the lens cross-sectional view, L1 is a first group (first lens group) having a negative refractive power, L2 is a second group (second lens group) having a positive refractive power, and L3 is a third group (first lens) having a positive refractive power. 3 lens group), SP is an aperture stop, and IP is an image plane. G is a glass block such as a filter or a color separation prism.
[0031]
The basic configuration of the zoom lens of the present invention is a so-called wide-angle short zoom system composed of a first group having a negative refractive power and a second group having a positive refractive power, and movement of the second group having a positive refractive power. Thus, the zooming is performed, and the movement of the image point accompanying the zooming is corrected by reciprocating the first group having a negative refractive power. The third group of positive refractive power does not contribute to zooming when it is fixed during zooming, but it shares the increase in refractive power of the taking lens accompanying the downsizing of the image sensor, and is composed of the first and second groups. By reducing the refracting power of the short zoom system, it is possible to suppress the occurrence of aberrations in each lens constituting the first group and to achieve good optical performance. In addition, telecentric imaging on the image side necessary for a photographing apparatus using a solid-state imaging device or the like is achieved by providing the third lens unit having a positive refractive power as a field lens. In addition, when the third group moves during zooming, the height of the optical axis of off-axis rays incident on the third group can be controlled, so that the ability to correct off-axis aberrations is increased, and the entire zoom range is further increased. Good performance is achieved.
[0032]
Further, by placing the stop SP on the object side in the second group and reducing the distance between the entrance pupil and the first group on the wide angle side, the increase in the outer diameter of the lenses constituting the first group can be suppressed. By canceling off-axis aberrations between the first group and the third group with a diaphragm disposed on the object side of the second group having a refractive power of 2 mm, good optical performance can be obtained without increasing the number of constituent lenses. .
[0033]
The present invention is based on the basic configuration described above.
(1-1) In the first invention, the first group includes a meniscus negative lens having a concave surface facing the image side, and a meniscus positive lens having a convex surface facing the object side. The cemented lens A is composed of a negative lens and a positive lens on the most image surface side and has a positive refractive power as a whole. It is characterized by having a concave surface facing the image surface side.
[0034]
In the first invention, it is more preferable that at least one of the following conditions is satisfied.
[0035]
(A-1) The focal length of the cemented lens A in the second group is fc, the focal length of the second group is f2, the radius of curvature of the object-side lens surface of the cemented lens A is Ra, and the lens B When the curvature radius of the lens surface on the image side is Rb,
0.5 <fc / f2 <2.0 (1)
0.5 <(Ra + Rb) / (Ra−Rb) <2.5 (2)
Is satisfied.
[0036]
(A-2) The second group includes a positive lens having a convex surface directed toward the object side, a negative lens having a concave surface directed toward the image surface side, and a cemented lens in order from the object side.
[0037]
(1-2) In the second invention, the first group includes a meniscus negative lens having a concave surface facing the image surface side, and a meniscus positive lens having a convex surface facing the object side. Both lens surfaces are concave negative lenses, arranged on the object side from the negative lens, a positive lens having a convex surface facing the object side, further arranged on the image plane side from the negative lens, and composed of a negative lens and a positive lens, As a whole, it has a cemented lens having a positive refractive power.
[0038]
In the second invention, it is more preferable to satisfy at least one of the following conditions.
[0039]
(A-1) A positive lens in which the negative lens in the second lens unit has a focal length of fn, the focal length of the second lens unit has a focal length of f2, and is located closest to the object side in the second lens unit and has a convex surface facing the object side. When the radius of curvature of the object-side lens surface is Rc and the radius of curvature of the image-side lens surface is Rd,
0.3 <| fn | / f2 <2.0 (3)
0 <(Rd + Rc) / (Rd−Rc) <2.5 (4)
Is satisfied.
[0040]
(A-2) The third group is composed of one positive lens or a positive and negative lens and a positive cemented lens as a whole.
[0041]
(1-3) The first group has a meniscus negative lens having a concave surface facing the image surface side and a meniscus positive lens having a convex surface facing the object side. The second group is one in order from the object side. Or, there are two positive lenses, a negative lens B whose both lens surfaces are concave, and a cemented lens A of a negative lens and a positive lens, and the focal length of the cemented lens A in the second group is fc, The focal length of the second group is f2, the radius of curvature of the object-side lens surface of the cemented lens A is Ra, the radius of curvature of the image side surface of the lens B is Rb, and the focal length of the lens B in the second group is fn, When the radius of curvature of the object side surface of the positive lens disposed closest to the object side in the second lens unit and having the convex surface facing the object side is Rc, and the radius of curvature of the lens surface on the image side is Rd,
0.5 <fc / f2 <2.0 (1)
0.5 <(Ra + Rb) / (Ra−Rb) <2.5 (2)
0.3 <| fn | / f2 <2.0 (3)
0 <(Rd + Rc) / (Rd−Rc) <2.5 (4)
This is to satisfy the following conditional expression.
[0042]
Next, features of each invention will be described. The first, second, and third inventions are collectively referred to as “the present invention”.
[0043]
The zoom lens according to the present invention includes a meniscus negative lens in which the first lens unit having negative refractive power has a convex surface directed toward the object side in order from the object side and a meniscus positive lens having a convex surface directed toward the object side. Or the first lens group is composed of two lenses, a concave lens (negative lens) 11 having a concave surface facing the image side, a concave lens 12, and a convex lens (positive lens) 13 having a convex surface facing the object side. . Further, the second group having positive refractive power is composed of a convex lens 21 having a convex surface facing the object side in order from the object side, a concave lens 22 having concave surfaces, and a cemented lens 23 composed of a negative lens and a positive lens. Or the second group is composed of five positive elements in the four groups of two positive lenses in order from the object side, a negative lens 22 whose concave surfaces are concave, and a cemented lens 23 composed of a negative lens and a positive lens.
[0044]
The third group having a positive refractive power is composed of a single convex lens or a cemented lens of a positive lens and a negative lens. In this way, each lens unit is configured to achieve both desired refractive power arrangement and aberration correction, thereby achieving a compact lens system while maintaining good performance.
[0045]
The first group having a negative refractive power has a role of focusing off-axis chief rays on the center of the aperture, and especially on the wide-angle side, since the amount of refraction of off-axis chief rays is large, various off-axis aberrations, particularly Astigmatism and distortion are likely to occur. Therefore, like a normal wide-angle lens, a concave-convex configuration that can suppress the increase in the lens diameter closest to the object side is used, and the light is refracted by two

negative lenses

11 and 12 that mainly share negative refractive power. We are trying to share power. Each lens constituting the first group has a shape close to a concentric spherical surface centered on the stop center in order to suppress the occurrence of off-axis aberration caused by refraction of the off-axis principal ray. That is, the

negative lenses

11 and 12 have a meniscus shape with a concave surface facing the image surface, and the positive lens 13 has a meniscus shape with a convex surface facing the object side.
[0046]
In the second group having positive refractive power, positive lenses are arranged before and after the concave lens 22 whose both lens surfaces are concave, and the configuration is symmetrical on the refractive power arrangement. This is because the group moves greatly during zooming, so that spherical aberration, coma aberration, etc. are removed to some extent by the group alone in order to prevent manufacturing deterioration due to mutual eccentricity due to manufacturing errors. is there.
[0047]
The convex lens 21 closest to the object side in the second group has a convex shape on the object side so that off-axis chief rays exiting the first group are largely refracted and no off-axis aberrations occur. The convex lens 21 has a convex shape on the object side in order to suppress the amount of spherical aberration generated with respect to the axial light beam emitted from the first group in a divergent state.
[0048]
Further, the concave lens 22 has a concave surface on both the object side and the image surface, and forms a negative air lens together with the front and rear convex lenses 21 and the positive cemented lens 23, and corrects spherical aberration and coma aberration that occur with a large aperture ratio. Have done well.
[0049]
Further, a cemented lens 23 is arranged on the image surface side of the concave lens 22 to correct chromatic aberration well. In the configuration of the zoom lens according to the present invention, the height at which the off-axis light beam bends in the first group is high at the wide-angle end and low at the telephoto end. To do. Therefore, the refractive power arrangement of the first group and the selection of the glass material are particularly configured so that the variation of the lateral chromatic aberration is minimized. As described above, in order to make the first group compact, the concave-convex structure is used, and when the number of constituent elements is about 2 to 3, the variation component of the axial chromatic aberration tends to remain in the first group. Therefore, axial chromatic aberration is favorably corrected by using a cemented lens in the second group.
[0050]
Further, in order to share the correction of lateral chromatic aberration in the second group as much as possible, it is effective to dispose the cemented lens at a position away from the stop. Therefore, in the present invention, it is disposed on the image side of the concave lens 22. Yes.
[0051]
The third group having positive refractive power is composed of a convex lens having a convex surface on the object side, or composed of a cemented lens of a positive lens and a negative lens so that the image side is a telecentric system. It also has a role as a field lens.
[0052]
In addition, in order to achieve further improvement in optical performance while constituting each lens group with a small number of lenses, an aspherical surface is effectively introduced in this embodiment.
[0053]
In Numerical Example 1 shown in FIG. 1, the image side surface of the concave lens 11 constituting the first group is an aspherical surface having a shape in which the diverging action is weak at the periphery, and particularly, field curvature, astigmatism and distortion on the wide angle side. Aberration correction is performed to reduce aberration fluctuations accompanying zooming.
[0054]
In addition, the lens surface on the object side of the convex lens 21 constituting the second group is an aspheric surface in which the converging action is weakened in the periphery, and the spherical aberration that becomes conspicuous when the aperture is increased is effectively corrected.
[0055]
Further, the object-side lens surface of the convex lens 31 constituting the third lens group is an aspheric surface in which the convergence action is weakened in the periphery, and it is effective to correct field curvature, astigmatism, and distortion aberration in the entire zooming range. I'm doing it.
[0056]
When photographing a short-distance object using the zoom lens of the present embodiment, good performance can be obtained by moving the first group to the object side, but a rear focus type that moves the third group to the object side. May be used. According to this, an advantage can be obtained that an increase in the front lens diameter due to focusing can be prevented, the shortest imaging distance can be shortened, and the focus group can be reduced in weight.
[0057]
Next, the technical meaning of each conditional expression described above will be described.
[0058]
Conditional expression (1) defines the refractive power of the cemented lens of the second group. As described above, the second group of the present invention has a symmetrical refractive power arrangement of positive, negative and positive refractive powers. The refractive power of the cemented lens bears a positive refractive power on the image side of the second group, and is preferably in a certain range as compared with the refractive power of the second group.
[0059]
If the refractive power of the cemented lens is weakened beyond the upper limit of conditional expression (1), the refractive power of the positive lens on the object side in the second group must be increased in order to give the second group the necessary converging action. Even if an excessive spherical aberration occurs and an aspherical surface is used, correction is insufficient, which is not good. In addition, when the refractive power of the positive lens on the object side is not increased, the refractive power of the second group itself is weakened, so that the amount of movement for zooming increases, leading to an increase in the total lens length and the front lens diameter, and a compact zoom. This is not good because the lens cannot be constructed.
[0060]
Further, if the refractive power of the cemented lens is increased beyond the lower limit of the conditional expression (1), the Petzval sum in the second lens unit increases in the positive direction, which causes an under field curvature and is not good. In addition, the curvature of the cemented lens surface must be tight in order to correct axial chromatic aberration, and the center thickness is increased to secure the edge thickness of the positive lens constituting the cemented lens, which is good in terms of compactness. Absent.
[0061]
Conditional expression (2) is an expression that defines the form factor of an air lens having a negative refractive power composed of a cemented lens disposed on the image side of the second group and a concave lens immediately before it.
[0062]
When the aperture stop in the second group is arranged on the object side, coma aberration having the same sign is generated between the object side lens surface of the positive lens in the second group and the object side lens surface of the concave lens. On the other hand, the object-side lens surface of the air lens generates coma aberration with a different sign, and the image-side lens surface generates coma with the same sign. On the other hand, the curvature of the lens surface on the concave side faces a certain degree of curvature. On the other hand, if the lens surface on the image side of the air lens has a relatively gentle curvature, the coma aberration can be corrected. If the shape factor is greater than 1, it is a meniscus shape, and if it is less than 1, it is a biconvex lens. As the radius of curvature of the lens surface on the image side becomes larger than 1, it becomes smaller while having the center of curvature on the image side. As it becomes smaller, the curvature becomes smaller while having the center of curvature on the object side.
[0063]
If the upper limit of conditional expression (2) is exceeded and the meniscus degree of the air lens increases, the curvature of the lens surface on the image side of the air lens becomes too strong, and the coma aberration correction capability of the air lens decreases. As a result, the second lens group is not good because coma is undercorrected.
[0064]
When the shape factor of the air lens becomes smaller than 1, the lens surface on the image side of the air lens has a center of curvature on the object side, so that the air lens has a biconvex shape. Accordingly, the cemented lens on the image side has a meniscus shape. In order for the cemented lens to have a refractive power that satisfies the conditional expression (1), the curvature of the lens surface on the image side of the cemented lens becomes tight. If the lower limit value of conditional expression (2) is exceeded, the result is that the curvature of the lens surface on the image side of the cemented lens becomes too tight, and an under spherical aberration occurs. .
[0065]
Conditional expression (3) is an expression defining the refractive power of a negative lens in which both lens surfaces of the second group are concave.
[0066]
If the refractive power is weakened beyond the upper limit of the conditional expression (3), the Petzval sum in the second lens unit increases in the positive direction and an under field curvature occurs, which is not good. In addition, a sufficient back focus for arranging the filter group cannot be obtained. Furthermore, there arises a problem that the exit pupil cannot be sufficiently separated from the image plane.
[0067]
If the refractive power is increased beyond the lower limit of the conditional expression (3), the spherical aberration is overcorrected, over-curvature curvature occurs, the back focus becomes too long, and it is difficult to make it compact.
[0068]
Conditional expression (4) defines the form factor of the object side positive lens in the second lens group.
[0069]
If the upper limit of Conditional Expression (4) is exceeded and the curvature of the lens surface on the image side is in a state with the center of curvature on the image side, coma will be particularly noticeable and difficult to correct even using an aspherical surface. It is not good because it becomes.
[0070]
If the lower limit of conditional expression (4) is exceeded and the curvature of the lens surface on the image side is tight with the center of curvature on the object side, the incident angle of the axial land ray on the image side becomes too tight and under spherical aberration occurs. Not good to do.
[0071]
The numerical examples of the present invention are shown below. In each numerical example, i indicates the order of the surfaces from the object side, Ri is the radius of curvature of the i-th surface, Di is the lens thickness or air space between the i-th surface and the i + 1-th surface, and Ni and νi are The refractive index and Abbe number for d line are shown. The two surfaces closest to the image side are filter members such as a quartz low-pass filter and an infrared cut filter. B, C, D, E, and F are aspheric coefficients. When the aspherical shape is x with the displacement in the optical axis direction at the position of the height h from the optical axis as x based on the surface vertex,
x = R {1- (1-h ² / R ² ) ^1/2 } + Bh ^Four + Ch ⁶ + Dh ⁸ + Eh ^Ten + Fh ¹² It is represented by Where R is the radius of curvature. “E-0X” is “10 ^-X "Means. Table 1 shows the relationship between the conditional expressions described above and the numerical values in the numerical examples.
[0072]
[Numerical Example 1]
FIG. 1 shows a cross-sectional view of this numerical example, and FIGS. 2, 3 and 4 show aberration diagrams at the wide-angle end, the intermediate position, and the telephoto end.
[0073]
This embodiment is composed of a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side, and the first group is used for zooming from the wide angle end to the telephoto end. The group moves back and forth convex toward the image side, the second group moves toward the object side, and the third group moves toward the image side. Lens data is shown below.
[0074]
[Outside 1]

[0075]
[Numerical Example 2]
FIG. 5 is a cross-sectional view of this embodiment, and FIGS. 6, 7, and 8 are aberration diagrams at the wide-angle end, the intermediate position, and the telephoto end.
[0076]
This embodiment is composed of a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side, and the first group is used for zooming from the wide angle end to the telephoto end. The group moves back and forth convex toward the image side, the second group moves toward the object side, and the third group moves toward the image side. Lens data is shown below.
[0077]
[Outside 2]

[0078]
[Numerical Example 3]
FIG. 9 is a cross-sectional view of this embodiment, and FIGS. 10, 11, and 12 are aberration diagrams at the wide-angle end, the intermediate position, and the telephoto end.
[0079]
This embodiment is composed of a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side, and the first group is used for zooming from the wide angle end to the telephoto end. The group moves back and forth convex toward the image side, the second group moves toward the object side, and the third group moves toward the image side.
[0080]
This embodiment is different from Numerical Embodiment 1 in that the number of constituent members of the first group is two. In this embodiment, it is composed of a meniscus negative lens having a concave surface facing the image side and a meniscus positive lens having a convex surface facing the object side, and the two concave lenses of Numerical Example 1 are composed of one lens. doing. This has the advantage that the number of lenses is reduced, leading to cost reduction, and the weight of the front lens is reduced. Lens data is shown below.
[0081]
[Outside 3]

[0082]
[Numerical Example 4]
FIG. 13 is a cross-sectional view of this example, and FIGS. 14, 15, and 16 are aberration diagrams at the wide-angle end, the intermediate position, and the telephoto end.
[0083]
This embodiment is composed of a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side, and the first group is used for zooming from the wide angle end to the telephoto end. The group moves back and forth convex toward the image side, the second group moves toward the object side, and the third group moves toward the image side.
[0084]
This embodiment is different from Numerical Embodiment 1 in that the second group is composed of 4 groups and 5 groups. The second group of this embodiment is composed of a meniscus positive lens having a convex surface facing the object side in order from the object side, both lens surfaces are convex convex lenses, both lens surfaces are concave concave lenses, concave lenses and convex lenses as a whole. It is composed of a positive cemented lens, and one positive lens on the object side in Numerical Example 1 is composed of two lenses. As a result, the function of converging the axial light beam emitted from the first group in a divergent state can be shared by two lenses, so that the occurrence of spherical aberration can be reduced and a larger aperture photographing lens can be constructed. There is. Lens data is shown below.
[0085]
[Outside 4]

[0086]
[Numerical Example 5]
FIG. 17 is a cross-sectional view of the present embodiment, and FIGS. 18, 19, and 20 are aberration diagrams at the wide-angle end, the intermediate position, and the telephoto end.
[0087]
This embodiment is composed of a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side, and the first group is used for zooming from the wide angle end to the telephoto end. The group has a reciprocating motion convex toward the image side, the second group moves toward the object side, and the third group is fixed.
[0088]
This embodiment is different from Numerical Embodiment 1 in that the number of elements in the third group is two in one group. The third group of the present embodiment is composed of a concave lens and a convex lens, and is composed of a positive cemented lens as a whole, and a single lens of Numerical Example 1 is composed of a cemented lens. This makes it possible to correct the lateral chromatic aberration particularly in the third group. As described above, the chromatic aberration of magnification has a large zoom variation in the first group, but in this embodiment, the return variation component can be corrected by the first group and the absolute amount can be shared by the third group. Thereby, there is an advantage that the chromatic aberration of magnification can be satisfactorily corrected over the entire zooming range even when the zoom ratio is increased.
[0089]
Further, the third embodiment is different from Numerical Example 1 in that the third group is fixed at the time of zooming. By fixing the third group, there is an advantage that a moving mechanism is not required and the configuration of the lens barrel is simplified. Lens data is shown below.
[0090]
[Outside 5]

[0091]
Hereafter, the value of each conditional expression in the Example of this invention is shown.
[0092]
[Table 1]

[0093]
【The invention's effect】
According to the present invention, it is suitable for a photographing system using a solid-state image sensor, has a small number of constituent lenses, is compact, has a high zoom ratio that achieves a small diameter, and particularly has excellent optical performance with excellent correction of chromatic aberration. A zoom lens with can be achieved.
[Brief description of the drawings]
FIG. 1 is a sectional view of a lens according to Numerical Example 1 of the present invention.
FIG. 2 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention.
FIG. 3 is an intermediate aberration diagram of Numerical Example 1 of the present invention.
FIG. 4 is an aberration diagram at the telephoto end according to Numerical Example 1 of the present invention.
FIG. 5 is a lens cross-sectional view of Numerical Example 2 according to the present invention.
FIG. 6 is an aberration diagram at the wide-angle end according to Numerical Example 2 of the present invention.
FIG. 7 is an intermediate aberration diagram of Numerical Example 2 of the present invention.
FIG. 8 is an aberration diagram at the telephoto end according to Numerical Example 2 of the present invention.
FIG. 9 is a sectional view of a lens according to Numerical Example 3 of the present invention.
FIG. 10 is an aberration diagram at the wide-angle end according to Numerical Example 3 of the present invention.
FIG. 11 is an intermediate aberration diagram of Numerical Example 3 according to the present invention.
FIG. 12 is an aberration diagram at the telephoto end according to Numerical Example 3 of the present invention.
FIG. 13 is a lens cross-sectional view of Numerical Example 4 of the present invention.
FIG. 14 is an aberration diagram at the wide-angle end according to Numerical Example 4 of the present invention.
FIG. 15 is an intermediate aberration diagram of Numerical Example 4 according to the present invention.
FIG. 16 is an aberration diagram at the telephoto end according to Numerical Example 4 of the present invention.
FIG. 17 is a lens cross-sectional view of Numerical Example 5 of the present invention.
FIG. 18 is an aberration diagram at the wide-angle end according to Numerical Example 5 of the present invention.
FIG. 19 is an intermediate aberration diagram of Numerical Example 5 according to the present invention.
FIG. 20 is an aberration diagram at the telephoto end according to Numerical Example 5 of the present invention.
[Explanation of symbols]
L1 first group
L2 second group
L3 3rd group
SP Aperture
IP image plane
d d line
g g line
S Sagittal image plane
M Meridional image

Claims

In order from the object side, the first group having a negative refractive power, the second group having a positive refractive power, and the third group having a positive refractive power. In zooming from the wide-angle end to the telephoto end, In a zoom lens in which the distance between the second group is reduced and the distance between the second group and the third group is increased, the first group has a meniscus negative lens with a concave surface on the image surface side and a convex surface on the object side. The second lens unit includes a negative lens having both concave lens surfaces, a positive lens disposed closer to the object side than the negative lens and having a convex surface facing the object side, and the negative lens. A negative lens disposed on the image plane side of the lens and a positive lens as a whole, and a cemented lens having a positive refractive power as a whole, and the focal length of the cemented lens in the second group is fc, The focal length is f2, the radius of curvature of the object-side lens surface of the cemented lens is Ra, and both lens surfaces are concave. The radius of curvature of the lens surface on the image side of the negative lens when the Rb of,
0.5 <fc / f2 <2.0
0.5 <(Ra + Rb) / (Ra−Rb) <2.5
A zoom lens that satisfies the following conditional expression:

A negative lens whose both lens surfaces in the second group are concave surfaces has a focal length of fn, a focal length of the second group is f2, and a positive lens which is disposed closest to the object side in the second group and has a convex surface facing the object side. When the radius of curvature of the lens surface on the object side of the lens is Rc and the radius of curvature of the lens surface on the image plane side is Rd,
0.3 <| fn | / f2 <2.00 <(Rd + Rc) / (Rd−Rc) <2.5
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.

3. The zoom lens according to claim 1, wherein the third group includes one positive lens, or a positive cemented lens as a whole that includes a positive lens and a negative lens.

The at least one lens surface of the negative lens in the first group is an aspherical surface, and the aspherical surface has a shape in which the diverging action gradually decreases from the optical axis toward the periphery. 4. The zoom lens according to any one of 3 above.

The at least one lens surface in the positive lens in the second group is an aspherical surface, and the aspherical surface has a shape in which the convergence action gradually decreases from the optical axis toward the periphery. Zoom lens.

The third group includes a positive lens, and at least one lens surface of the positive lens is an aspherical surface, and the aspherical surface has a shape that gradually converges toward the periphery from the optical axis. The zoom lens according to claim 1.

The zoom lens according to claim 1, wherein the third group moves during zooming.

In order from the object side, the first group having a negative refractive power, the second group having a positive refractive power, and the third group having a positive refractive power. In zooming from the wide-angle end to the telephoto end, In the zoom lens in which the distance between the second group is reduced and the distance between the second group and the third group is increased, the first group has a meniscus negative lens having a concave surface on the image surface side and a convex surface on the object side. The second lens group has one or two positive lenses in order from the object side, a negative lens B whose both lens surfaces are concave, and a cemented lens A composed of a negative lens and a positive lens. from made, the focal length fc of the second cemented lens a in the group, the focal length of the second lens group f2, the radius of curvature of the lens surface on the object side of the cemented lens a Ra, the image side surface of the lens B Is the radius of curvature Rb, the focal length of the lens B in the second group is fn, and in the second group When the most is disposed on the object side curvature radius of the object side surface of the positive lens having a convex surface on the object side and Rc, and Rd of the radius of curvature of the lens surface on the image side,
0.5 <fc / f2 <2.0 0.5 <(Ra + Rb) / (Ra−Rb) <2.5
0.3 <| fn | / f2 <2.0
0 <(Rd + Rc) / (Rd−Rc) <2.5
A zoom lens that satisfies the following conditional expression:

The zoom lens according to claim 1, wherein an image is formed on a solid-state imaging device.

An image pickup apparatus comprising: the zoom lens according to claim 1; and a solid-state image pickup device that receives an image formed by the zoom lens.