JP4065968B2

JP4065968B2 - Zoom lens

Info

Publication number: JP4065968B2
Application number: JP31919697A
Authority: JP
Inventors: 治夫佐藤
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 1997-11-06
Filing date: 1997-11-06
Publication date: 2008-03-26
Anticipated expiration: 2017-11-06
Also published as: JPH11142739A

Description

【０００１】
【発明の属する技術分野】
本発明は小型軽量でコストパフォーマンスに優れ、製造組み立てが比較的容易なズームレンズ、特にコンパクトな標準ズームレンズに関する。
【０００２】
【従来の技術】
近年、広角を含み、かつズーム比が３〜４倍のいわゆる標準ズームレンズは小型化と低コスト化の一途をたどり、カメラボディに装着されたまま持ち運ばれる場合が非常に多くなっている。このため、標準ズームレンズは小型で軽量、かつ充分な結像性能を有し、さらに安価であることが必須の条件になっている。かかる条件を満足するにはズームレンズの各レンズ群を強いパワーで構成し、かつ各レンズ群を出来る限り薄肉化する必要がある。薄肉化のためにレンズ枚数を軽減するには、非球面レンズを導入するのが効果的である。近年、非球面レンズが安価で生産できるようになり、例えば、特開平８−２４８３１９号公報に開示されるようなパワー配置が正負正正、正負負正である４群ズームレンズの第２群、第４群等に非球面レンズを使用する例が増えている。また、該非球面は正負正負正などの５群以上のズームレンズの後群などに使用することも可能であり、同様の薄肉化の効果が期待できる。さらに、非球面を使用せずに、標準ズームレンズの小型化と小径化を試みた例に、特公平４−４０６８９号公報、特公昭６１−６０４１８号公報、特公平１−４６０４４号公報、特開昭６２−２７０９１０号公報、特開平６−３３７３５４号公報等に開示されたズームレンズがある。
【０００３】
【本発明が解決しようとする課題】
しかしながら、特開平８−２４８３１９号公報に開示されたズームレンズに代表される正負正正４群ズームレンズにおいては、４群中の非球面レンズの加工が比較的難しく、また鏡筒組み込み時の偏心精度、空気間隔精度が厳しく、設計性能を十分維持したまま製造することが難しいという問題がある。また、組み立て調整にかかるコストも増加してしまうため、非球面レンズの採用によるレンズ枚数の軽減のコスト面での効果が相殺されてしまう傾向がある。
【０００４】
また、非球面を使用せずに、標準ズームレンズの小型化と小径化を試みた、特公平４−４０６８９号公報、特公昭６１−６０４１８号公報、特公平１−４６０４４号公報、特開昭６２−２７０９１０号公報、特開平６−３３７３５４号公報等に開示されたズームレンズは、比較的大型で、ズーム比も３倍程度のものが主流である。このため、ズーム比が大きくても大型で構成枚数も多く、光学性能も不十分である。
【０００５】
本発明は、上記問題に鑑みてなされたものであり、精度的に厳しい後方レンズ群に非球面を使用せずに、小径・小型であり、少ないレンズ構成枚数で、コストパフォーマンスに優れ、製造時の難易度のより少ない、変倍比３．５〜３．８倍程度で、かつ高性能なズームレンズを提供することを目的としている。
【０００６】
【課題を解決するための手段】
上記目的を達成するために、本発明のズームレンズは、物体側から順に、正の屈折カを有する第１レンズ群Ｇ１と、負の屈折力を有する第２レンズ群Ｇ２と、正の屈折力を有する第３レンズ群Ｇ３と、正の屈折力を有する第４レンズ群Ｇｍとからなり、前記第１レンズ群Ｇ１と前記第２レンズ群Ｇ２との空気間隔を変化させることにより変倍を行うズームレンズにおいて、
【０００７】
前記第４レンズ群Ｇｍは、物体側から順に、物体側に凸面を向けた正メニスカスレンズ成分Ｌ１と、物体側に凸面を向け負レンズと正レンズの接合からなる接合正レンズ成分Ｌ２と、正レンズ成分Ｌ３と、像側に凸面を向けた負メニスカスレンズ成分Ｌ４とからなり、
【０００８】
前記正メニスカスレンズ成分Ｌ１と前記接合正レンズ成分Ｌ２との間には物体側に凸面を向けたメニスカス形状からなる空気レンズを有し、かつ前記正レンズ成分Ｌ３と前記負レンズ成分Ｌ４との間には像側に凸を向けたメニスカス形状からなる空気レンズを有することを特徴としている。
【０００９】
【発明の実施の形態】
本発明のズームレンズは、基本的に正負正正タイプを代表とする凸先行ズームレンズの後群（マスタ一群）のレンズ構成を、極端に非球面レンズの効果を利用した設計方法をとること無しに、良好な性能を確保し、改良したレンズである。特に、本発明のズームレンズにおいて重要な構成は、凸レンズ先行型ズームレンズの後群（マスター群）にあたる前記レンズ群Ｇｍに、物体側に凸面を向け、強いメニスカス形状を持つ正メニスカスレンズ成分Ｌ１を有する点と、前記正メニスカスレンズ成分Ｌ１と前記接合正レンズ成分Ｌ２との間に物体側に凸面を向けたメニスカス形状からなる空気レンズを有し、かつ前記正レンズ成分Ｌ３と前記負レンズ成分Ｌ４との間に像側に凸を向けたメニスカス形状からなる空気レンズを有する点である。かかる構成により、それぞれのレンズにおいて、高次収差を発生させ、結果的に球面収差やコマ収差の補正を良好に行なっている。
【００１０】
また、前記空気レンズは、レンズ群Ｇｍの中心に向かってそれぞれ凹面を向けており、適切な形状とすることにより、非球面を使用することなく良好な収差補正が可能になる。また、前記接合正レンズ成分Ｌ２によってペッツバール和、軸上色収差の補正を行なっている。
【００１１】
以上説明したように、本発明のズームレンズでは、出来るかぎり凸先行ズームレンズの後群（マスター群）を単独の対物レンズ系として、可能な限りの収差補正自由度を与えるレンズ構成を採用している。この結果、良好な収差補正が可能で、かつ製造する事の容易な多群ズームレンズが達成できている。
【００１２】
また、本発明のズームレンズは、以下の条件式（１）、
０＜（Ｒｂ−Ｒａ）／（Ｒｂ＋Ｒａ）≦ｌ（１）
を満足することが望ましい。
【００１３】
ここで、Ｒａは前記正メニスカスレンズ成分Ｌ１の像側の面の曲率半径を、
Ｒｂは前記接合正レンズ成分Ｌ２の物体側の面の曲率半径をそれぞれ表している。
【００１４】
条件式（１）はレンズ群Ｇｍの中のレンズ成分Ｌ１と前記正レンズ成分Ｌ２との間に存在する物体側に凸面を向けたメニスカス形状の空気レンズの形状の適切な範囲を規定している。本発明のズームレンズでは、後記する実施例にも示すとおり、特開平８−２４８３１９号公報に代表されるズームレンズの４群と異なり、マスターレンズ群でもあるレンズ群Ｇｍが比較的独立して良好に収差補正を行なっており、前記の空気レンズの形状が重要な要素となる。条件式（１）の上限値を上回る場合、レンズ群Ｇｍの中のレンズ成分Ｌ１と前記正レンズ成分Ｌ２との間の物体側に凸面を向けたメニスカス形状からなる空気レンズ（以下、「レンズ群Ｇｍの中の物体側の空気レンズ」という）の形状が平凸形状になり、レンズ群Ｇｍの中の物体側の空気レンズの偏角が著しく変化してしまう。この結果、球面収差の良好な補正と、各焦点距離における球面収差の変化を抑えることが困難になり好ましくない。さらに好ましくは、条件式（１）の上限値を０．６以下または０．４以下に設定すると、球面収差等の諸収差をより良好に補正できる。また、条件式（１）の上限値を０．３以下に設定すると本発明の効果を最大限に発揮できる。逆に、条件式（１）の下限値を下回る場合、レンズ群Ｇｍの中の物体側の空気レンズの形状が像側に凸形状を向けた逆向きの形状になる。このため、上限値を上回る場合と同様に、レンズ群Ｇｍの中の物体側の空気レンズの偏角が著しく変化し、結果的に球面収差の良好な補正と、各焦点距離における球面収差の変化を抑えることが困難になり好ましくない。
【００１５】
また、本発明のズームレンズでは、以下の条件式（２）、
０＜（Ｒａ−Ｒ１）／（Ｒａ＋Ｒ１）≦１（２）
を満足することが望ましい。
【００１６】
ここで、Ｒ１は前記正メニスカスレンズ成分Ｌ１の物体側の面の曲率半径を、Ｒａは前記正メニスカスレンズ成分Ｌ１の像側の面の曲率半径をそれぞれ表している。
【００１７】
条件式（２）は、前記レンズ群Ｇｍ中の物体側に凸面を向け全体としてメニスカス形状を有するレンズ成分Ｌ１の適切なベンディング形状を規定している。前記レンズ成分Ｌ１は単レンズまたは接合レンズを有していても良く、接合レンズの場合、レンズ成分Ｌ１全体の形状を規定することとする。前記レンズ成分Ｌ１は主に球面収差、軸上色収差の補正を行っている。特に、高次の球面収差を発生させ、各焦点距離における球面収差の変動を抑えている。したがって、光軸に平行に入射する光束に対する前記レンズ成分Ｌ１の各面の偏角を適切な値に設定することにより、良好な収差補正が可能になる。条件式（２）の上限値を上回る場合、前記レンズ成分Ｌ１の形状が平凸形状に近づくため、像側の面の偏角が減少する方向に変化する。また、直後の空気レンズの収差補正効果も減少するために最適な高次の球面収差が発生しなくなる。この結果、各焦点距離における球面収差の変動を抑えることが困難になる。さらに好ましくは、条件式（２）の上限値を０．６以下に設定すると、球面収差等の諸収差をより良好に補正できる。また、条件式（２）の上限値を０．３以下に設定すると本発明の効果を最大限に発揮できる。逆に、、条件式（２）の下限値を下回る場合、前記レンズ成分Ｌ１の形状が像側に凸形状を向けた逆向きの形状になってしまう。このため、上限値を上回る場合と同様に、前記レンズ成分Ｌ１各面における偏角が著しく変化する。このため、球面収差の良好な補正と、各焦点距離における球面収差の変化を抑えることが困難になり好ましくない。
【００１８】
また、本発明のズームレンズでは、以下の条件式（３）、
−１≦（Ｒｄ−Ｒｃ）／（Ｒｄ＋Ｒｃ）＜０（３）
を満足することが望ましい。
【００１９】
ここで、Ｒｃは前記正レンズ成分Ｌ３の像側の面の曲率半径を、
Ｒｄは前記負レンズ成分Ｌ４の物体側の面の曲率半径をそれぞれ表している。
【００２０】
条件式（３）は、前記レンズ群Ｇｍの中の正レンズ成分Ｌ３と前記負レンズ成分Ｌ４との間の像側に凸を向けたメニスカス形状からなる空気レンズの形状の適切な範囲を規定している。本発明のズームレンズでは、後記する実施例にも示すとおり、特開平８−２４８３１９号公報に代表されるズームレンズの４群と異なり、マスターレンズ群でもあるレンズ群Ｇｍが比較的独立して良好に収差補正を行なう必要があり、前記の空気レンズの形状が重要である。条件式（３）の上限値を上回る場合、レンズ群Ｇｍの中の正レンズ成分Ｌ３と前記負レンズ成分Ｌ４との間の像側に凸面を向けたメニスカス形状からなる空気レンズ（以下、「レンズ群Ｇｍの中の像側の空気レンズ」という）の形状が物体側に凸形状を向けた逆向きの形状になってしまう。このため、空気レンズの偏角が著しく変化し、結果的に上方コマ収差、倍率色収差をはじめとする軸外諸収差の補正が困難になる。逆に、条件式（３）の下限値を下回る場合、レンズ群Ｇｍの中の像側の空気レンズの形状が平凸形状になってしまう。このため、空気レンズの偏角が著しく変化し、上限を上回る場合と同様に、上方コマ収差、倍率色収差をはじめとする軸外諸収差の補正が困難になる。さらに好ましくは、条件式（３）の下限値を−０．８以下または−０．７以下に設定すると、上方コマ収差、倍率色収差をはじめとする軸外諸収差をより良好に補正できる。また、条件式（３）の下限値を−０．６以下に設定すると本発明の効果を最大限に発揮できる。
【００２１】
また、本発明のズームレンズでは、以下の条件式（４）、
ｎ凸＜ｎ凹（４）
を満足することが望ましい。
【００２２】
ここで、ｎ凹は前記接合正レンズ成分Ｌ２中の物体側の負レンズのｄ線（λ＝５８７．５６ｎｍ）に対する屈折率を、
ｎ凸は前記接合正レンズ成分Ｌ２中の像側の正レンズのｄ線に対する屈折率をそれぞれ表している。
【００２３】
条件式（４）は、前記接合正レンズ成分Ｌ２中の物体側の負レンズと像側の正レンズの適切な屈折率差を規定している。条件式（４）を満たさない場合、ペッツバール和が適切な値に設定できなくなり、結果的に非点収差および像面湾曲を良好に保てなくなり好ましくない。
【００２４】
また、本発明のズームレンズでは、以下の条件式（５）、（６）、
０．１＜ｄ１２／ｄ３４＜７（５）
０．０１＜ｄ２３／ｄ３４＜５（６）
を満足することが望ましい。
【００２５】
ここで、ｄ１２は前記正メニスカスレンズ成分Ｌ１の最も像側の面から前記接合正レンズ成分Ｌ２の最も物体側の面までの光軸上の距離を、
ｄ２３は前記接合正レンズ成分Ｌ２の最も像側の面から前記正レンズ成分Ｌ３の最も物体側の面までの光軸上の距離を、
ｄ３４は前記正レンズ成分Ｌ３の最も像側の面から前記負レンズ成分Ｌ４の最も物体側の面までの光軸上の距離をそれぞれ表している。
【００２６】
条件式（５）は、前記レンズ成分Ｌ１と前記正レンズ成分Ｌ２との間の空気レンズの光軸上の厚さと、正レンズ成分Ｌ３と前記負レンズ成分Ｌ４との間の空気レンズの厚さの適切な比を規定している。条件式（５）の上限値を上回る場合、前記レンズ成分Ｌ１と前記正レンズ成分Ｌ２との間隔が著しく大きくなってしまう。このため、空気レンズの収差補正効果が著しく減少し、特に各焦点距離における球面収差の変動を抑えることが困難になる。さらに好ましくは、条件式（５）の上限値を５以下に設定すると、球面収差等の諸収差をより良好に補正できる。また、条件式（５）の上限値を３以下に設定すると本発明の効果を最大限に発揮できる。逆に、条件式（５）の下限値を下回る場合、前記レンズ成分Ｌ１と前記正レンズ成分Ｌ２との間隔が著しく小さくなる。このため、空気レンズの収差補正効果が著しく減少し、上限を上回る場合と同様、結果的に各焦点距離における球面収差の変動を抑えることが困難になる。また、条件式（５）の下限値を０．３以上に設定すると、球面収差等の諸収差をより良好に補正できる。また、条件式（５）の下限値を０．４以上に設定すると本発明の効果を最大限に発揮できる。
【００２７】
条件式（６）は、前記接合正レンズ成分Ｌ２と前記正レンズ成分Ｌ３との間の空気間隔の光軸上の厚さと、正レンズ成分Ｌ３と前記負レンズ成分Ｌ４との間の空気レンズの厚さの適切な比を規定している。条件式（６）の上限値を上回る場合、前記接合正レンズ成分Ｌ２と前記正レンズ成分Ｌ３との間隔が著しく大きくなるか、または正レンズ成分Ｌ３と前記負レンズ成分Ｌ４との間の空気レンズの厚さが著しく小さくなってしまう。前者の場合、レンズ群Ｇｍの総厚が著しく大きくなり、コンパクト化の要請に反し好ましくない。また、後者の場合、空気レンズが著しく薄くなり、空気レンズの収差補正効果が減少し、軸外収差の補正が困難になり好ましくない。さらに好ましくは、条件式（６）の上限値を３以下、さらに１以下に設定すると本発明の効果を最大限に発揮できる。逆に、条件式（６）の下限値を下回る場合、前記接合正レンズ成分Ｌ２と前記正レンズ成分Ｌ３との間隔が著しく小さくなるか、または前記正レンズ成分Ｌ３と負レンズ成分Ｌ４との間の空気レンズの厚みが著しく大きくなってしまう。このことは、上限を上回る場合と同様に、空気レンズの収差補正効果が減少し、結果的に上方コマ収差、倍率色収差をはじめとする軸外諸収差の補正が困難になる。また、条件式（６）の下限値を０．０２以上、さらに０．０３以上に設定すると本発明の効果を最大限に発揮できる。
【００２８】
【実施例】
以下に添付図面に基づいて本発明の実施の形態にかかるズームレンズを説明する。
【００２９】
（第１実施例）
図１は本発明の第１実施例にかかるズームレンズのレンズ構成と広角端から望遠端にいたる各レンズ群の移動軌跡を示す図である。第１実施例にかかるズームレンズは、物体側から順に、正の屈折力を有する第１レンズ群Ｇ１と、負の屈折力を有する第２レンズ群Ｇ２と、正の屈折力を有する第３レンズ群Ｇ３と、正の屈折力を有する第４レンズ群Ｇｍの正・負・正・正の４つのレンズ群から構成されている。
【００３０】
第１レンズ群Ｇ１は物体側から、物体側に凸面を向けた負メニスカスレンズと正メニスカスレンズとの接合よりなる接合正レンズＬ１１、物体側に凸面を向けた正メニスカスレンズＬ１２より構成され、第２レンズ群Ｇ２は物体側から、物体側に非球面を有し、樹脂とガラス部材の複合からなる負メニスカスレンズＬ２１、両凹レンズＬ２２、両凸レンズＬ２３、両凹レンズと両凸レンズとの接合により成り物体側に凹面を向けた接合負メニスカスレンズＬ２４より構成され、第３レンズ群Ｇ３は物体側から、開口絞りＳ、両凸レンズＬ３１、両凸レンズと両凹レンズとの接合より成る接合正レンズＬ３２より構成され、第４レンズ群Ｇｍは物体側から、物体側に凸面を向けた正メニスカスレンズＬ１、物体側に凸面を向けた負メニスカスレンズと両凸レンズとの接合よりなる接合正レンズＬ２、物体側に凹面を向けた正メニスカスレンズＬ３、物体側に凹面を向けた負メニスカスレンズＬ４より構成されている。
【００３１】
変倍は広角端から望遠端に向かって、第１レンズ群Ｇ１と第２レンズ群Ｇ２との間の空気間隔が拡大し、第２レンズ群Ｇ２と第３レンズ群Ｇ３との間の空気間隔が縮小し、第３レンズ群Ｇ３と第４レンズ群Ｇｍとの間の空気間隔が縮小するように全レンズ群を独立して移動することによって行なう。また、近距離合焦は第２レンズ群Ｇ２を物体方向に移動して行なう。
【００３２】
以下の表１に第１実施例にかかるズームレンズの諸元値を示す。表において、面番号は物体側から数えたレンズ面の番号、ｒは曲率半径、ｄは面間隔、ｎｄはｄ線（λ＝５８７．５６ｎｍ）に対する屈折率、νｄはアッベ数である。また、ｆは焦点距離、ＦＮＯはＦナンバー、２ωは画角、Ｂｆはバックフォーカスをそれぞれ示している。
【００３３】
また、非球面は、光軸から垂直方向の高さｙにおける各非球面の頂点の接平面から光軸方向に沿った距離（サグ量）をＳ（ｙ）とし、基準曲率半径をＲ、円錐係数をｋ、ｎ次の非球面係数をＣｎとするとき、以下の非球面式で与えられるものとする。
【００３４】
【数１】

【００３５】
表中のレンズデータにおいて、非球面には＊印を付してあり、曲率半径ｒには近軸曲率半径を掲げる。また、以下のすべての実施例において、諸元値、非球面式などは第１実施例と同様のものを用いる。
【００３６】
【表１】

【００３７】
図２乃至図４は第１実施例にかかるズームレンズの諸収差を示す図である。図中、ＦＮＯはＦナンバー、Ｙは像高、ｄ，ｇはそれぞれｄ線，ｇ線の収差曲線であることを示している。また、非点収差図において、実線はサジタル像面、点線はメリジオナル像面を示している。以下、すべての実施例の収差図において第１実施例と同様の符号を用いる。
【００３８】
図２は、広角端での無限遠合焦時の収差図である。大画角まで十分カバーし、良好に収差補正が成されていることがわかる。図３は、中間焦点距離での無限遠合焦時の収差図である。広角端同様、良好に収差補正が成されていることがわかる。図４は、望遠端の無限遠合焦時の収差図である。広角端同様、良好に収差捕正が成されていることがわかる。
【００３９】
（第２実施例）
図５は本発明の第２実施例にかかるズームレンズのレンズ構成と広角端から望遠端にいたる各レンズ群の移動軌跡を示す図である。第２実施例にかかるズームレンズは、物体側から順に、正の屈折力を有する第１レンズ群Ｇ１と、負の屈折力を有する第２レンズ群Ｇ２と、正の屈折力を有する第３レンズ群Ｇ３と、正の屈折力を有する第４レンズ群Ｇｍの正・負・正・正の４つの群から構成されている。
【００４０】
第１レンズ群Ｇ１は物体側から、物体側に凸面を向けた負メニスカスレンズと正メニスカスレンズとの接合よりなる接合正レンズＬ１１と、物体側に凸面を向けた正メニスカスレンズＬ１２より構成され、第２レンズ群Ｇ２は物体側から、物体側に非球面を有する負メニスカスレンズＬ２１、物体側に凸面を向けた負メニスカスレンズＬ２２、両凸レンズＬ２３、両凹レンズと両凸レンズとの接合により成り物体側に凹面を向けた接合負メニスカスレンズＬ２４より構成され、第３レンズ群Ｇ３は物体側から、開口絞りＳ、両凸レンズＬ３１、両凸レンズと両凹レンズとの接合より成る接合正レンズＬ３２より構成され、第４レンズ群Ｇｍは物体側から、物体側に凸面を向けた正メニスカスレンズＬ１、物体側に凸面を向けた負メニスカスレンズと両凸レンズとの接合より成る接合正レンズＬ２、両凸レンズＬ３、物体側に凹面を向けた負メニスカスレンズＬ４より構成されている。変倍は広角端から望遠端に向かって、第１レンズ群Ｇ１と第２レンズ群Ｇ２との間の空気間隔が拡大し、第２レンズ群Ｇ２と第３レンズ群Ｇ３との間の空気間隔が縮小し、第３レンズ群Ｇ３と第４レンズ群Ｇｍとの間の空気間隔が縮小するように全レンズ群を独立して移動することによって行なう。また、近距離合焦は第２レンズ群Ｇ２を物体方向に移動して行なう。
【００４１】
表２に第２実施例にかかるズームレンズの諸元値を掲げる。
【００４２】
【表２】

【００４３】
図６乃至図８は第２実施例にかかるズームレンズの諸収差を示す図である。図６は、広角端での無限遠合焦時の収差図である。大画角まで十分カバーし、良好に収差捕正が成されていることがわかる。図７は、中間焦点距離での無限遠合焦時の収差図である。広角端同様、良好に収差補正が成されていることがわかる。図８は、望遠端の無限遠合焦時の収差図である。広角端同様、良好に収差補正が成されている。
【００４４】
（第３実施例）
図９は本発明の第３実施例にかかるズームレンズのレンズ構成と広角端から望遠端にいたる各レンズ群の移動軌跡を示す図である。第３実施例にかかるズームレンズは、物体側から順に、正の屈折力を有する第１レンズ群Ｇ１と、負の屈折力を有する第２レンズ群Ｇ２と、正の屈折力を有する第３レンズ群Ｇ３と、正の屈折力を有する第４レンズ群Ｇｍの正・負・正・正の４つの群から構成されている。第１レンズ群Ｇ１は物体側から、物体側に凸面を向けた負メニスカスレンズと正メニスカスレンズとの接合より成る接合正レンズＬ１１、物体側に凸面を向けた正メニスカスレンズＬ１２より構成され、第２レンズ群Ｇ２は物体側から、物体側に非球面を有する負メニスカスレンズＬ２１、両凹レンズＬ２２、両凸レンズＬ２３、両凹レンズと両凸レンズとの接合により成り物体側に凹面を向けた接合負メニスカスレンズＬ２４より構成され、第３レンズ群Ｇ３は物体側から、開口絞りＳ、両凸レンズＬ３１、両凸レンズＬ３２、物体側に凹面を向けた負メニスカスレンズＬ３３より構成され、第４レンズ群Ｇｍは物体側から、物体側に凸面を向けた正メニスカスレンズＬ１、物体側に凸面を向けた負メニスカスレンズと両凸レンズとの接合よりなる接合正レンズＬ２、物体側に凹面を向けた正メニスカスレンズＬ３、物体側に凹面を向けた負メニスカスレンズＬ４より構成されている。変倍は広角端から望遠端に向かって、第１レンズ群Ｇ１と第２レンズ群Ｇ２との間の空気間隔が拡大し、第２レンズ群Ｇ２と第３レンズ群Ｇ３との間の空気間隔が縮小し、第３レンズ群Ｇ３と第４レンズ群Ｇｍとの間の空気間隔が縮小するように全レンズ群を独立して移動することによって行なう。また、近距離合焦は第２レンズ群Ｇ２を物体方向に移動して行なう。
【００４５】
以下の表３に第３実施例にかかるズームレンズの諸元値を掲げる。
【００４６】
【表３】

【００４７】
図１０乃至図１２は第３実施例にかかるズームレンズの諸収差を示す図である。図１０は、広角端での無限遠合焦時の収差図である。大画角まで十分カバーし、良好に収差捕正が成されていることがわかる。図１１は、中間焦点距離での無限遠合焦時の収差図である。広角端同様、良好に収差補正が成されていることがわかる。図１２は、望遠端の無限遠合焦時の収差図である。広角端同様、良好に収差補正が成されている。
【図面の簡単な説明】
【図１】本発明の第１実施例にかかるズームレンズのレンズ構成と移動軌跡を示す図である。
【図２】本発明の第１実施例にかかるズームレンズの広角端での無限遠合焦時の諸収差を示す図である。
【図３】本発明の第１実施例にかかるズームレンズの中間焦点距離での無限遠合焦時の諸収差を示す図である。
【図４】本発明の第１実施例にかかるズームレンズの望遠端での無限遠合焦時の諸収差を示す図である。
【図５】本発明の第２実施例にかかるズームレンズのレンズ構成と移動軌跡を示す図である。
【図６】本発明の第２実施例にかかるズームレンズの広角端での無限遠合焦時の諸収差を示す図である。
【図７】本発明の第２実施例にかかるズームレンズの中間焦点距離での無限遠合焦時の諸収差を示す図である。
【図８】本発明の第２実施例にかかるズームレンズの望遠端での無限遠合焦時の諸収差を示す図である。
【図９】本発明の第３実施例にかかるズームレンズのレンズ構成と移動軌跡を示す図である。
【図１０】本発明の第３実施例にかかるズームレンズの広角端での無限遠合焦時の諸収差を示す図である。
【図１１】本発明の第３実施例にかかるズームレンズの中間焦点距離での無限遠合焦時の諸収差を示す図である。
【図１２】本発明の第３実施例にかかるズームレンズの望遠端での無限遠合焦時の諸収差を示す図である。
【符号の説明】
Ｇｌ第１レンズ群
Ｇ２第２レンズ群
Ｇ３第３レンズ群
Ｇｍ第４レンズ群（マスターレンズ群）
Ｓ開口絞り
Ａ固定絞り[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens, particularly a compact standard zoom lens, which is small and light, has excellent cost performance, and is relatively easy to manufacture and assemble.
[0002]
[Prior art]
In recent years, so-called standard zoom lenses that include a wide angle and have a zoom ratio of 3 to 4 times continue to be reduced in size and cost, and are often carried while attached to the camera body. For this reason, the standard zoom lens is required to be small and light, have sufficient imaging performance, and be inexpensive. In order to satisfy such conditions, it is necessary to construct each lens group of the zoom lens with a strong power and to make each lens group as thin as possible. In order to reduce the number of lenses for thinning, it is effective to introduce an aspheric lens. In recent years, it has become possible to produce aspheric lenses at low cost. For example, the second group of a four-group zoom lens having positive / negative positive / positive positive / negative positive / negative power arrangement as disclosed in JP-A-8-248319, An example of using an aspheric lens for the fourth group and the like is increasing. The aspherical surface can also be used for the rear group of five or more zoom lenses such as positive, negative, positive and negative, and the same thinning effect can be expected. Furthermore, examples of attempts to reduce the size and diameter of a standard zoom lens without using an aspherical surface include Japanese Patent Publication No. 4-40689, Japanese Patent Publication No. 61-60418, Japanese Patent Publication No. 1-446044, There are zoom lenses disclosed in Japanese Laid-Open Patent Publication Nos. 62-270910 and 6-337354.
[0003]
[Problems to be solved by the present invention]
However, in the positive / negative positive / positive four-group zoom lens represented by the zoom lens disclosed in Japanese Patent Laid-Open No. 8-248319, it is relatively difficult to process the aspherical lens in the fourth group, and the eccentricity when the lens barrel is incorporated. There is a problem that it is difficult to manufacture while maintaining a sufficient design performance because the accuracy and air spacing accuracy are severe. In addition, since the cost for assembly adjustment increases, the cost effect of reducing the number of lenses by using an aspheric lens tends to be offset.
[0004]
In addition, Japanese Patent Publication No. 4-40689, Japanese Patent Publication No. 61-60418, Japanese Patent Publication No. 1-446044, Japanese Patent Publication No. Sho, JP-A-4-40689, which attempted to reduce the size and diameter of a standard zoom lens without using an aspherical surface. The zoom lenses disclosed in JP-A-62-270910 and JP-A-6-337354 are relatively large and have a zoom ratio of about 3 times. For this reason, even if the zoom ratio is large, the zoom lens is large and has a large number of components, and the optical performance is insufficient.
[0005]
The present invention has been made in view of the above-mentioned problems, and has a small diameter and a small size without using an aspherical surface in a precisely strict rear lens group. An object of the present invention is to provide a high-performance zoom lens having a zoom ratio of about 3.5 to 3.8 times, which is less difficult.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a zoom lens according to the present invention includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a positive refractive power. a third lens group G3 having made a fourth lens group Gm having a positive refractive power, and performs zooming by varying the air gap between the first lens group G1 and the second lens group G2 In zoom lenses,
[0007]
The fourth lens group Gm includes, in order from the object side, a positive meniscus lens component L1 having a convex surface facing the object side, a cemented positive lens component L2 composed of a negative lens and a positive lens having a convex surface facing the object side, and a positive lens a lens component L3, and a negative meniscus lens component L4 Metropolitan having a convex surface directed toward the image side,
[0008]
Between the positive meniscus lens component L1 and the cemented positive lens component L2, there is an air lens having a meniscus shape with a convex surface facing the object side, and between the positive lens component L3 and the negative lens component L4. Is characterized in that it has an air lens having a meniscus shape with the convex side facing the image side.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The zoom lens of the present invention basically does not adopt a design method that uses the effect of an aspherical lens in the lens configuration of the rear group (master group) of the convex preceding zoom lens represented by the positive, negative, positive and positive types. In addition, it is an improved lens that ensures good performance. In particular, an important configuration of the zoom lens according to the present invention is that the positive meniscus lens component L1 having a strong meniscus shape and a convex surface facing the object side is directed to the lens group Gm, which is the rear group (master group) of the convex leading zoom lens. And an air lens having a meniscus shape with a convex surface facing the object side between the positive meniscus lens component L1 and the cemented positive lens component L2, and the positive lens component L3 and the negative lens component L4. And an air lens having a meniscus shape with a convex toward the image side. With such a configuration, high-order aberration is generated in each lens, and as a result, spherical aberration and coma are corrected well.
[0010]
Further, the air lens has a concave surface directed toward the center of the lens group Gm. When the air lens has an appropriate shape, it is possible to correct aberrations without using an aspherical surface. Further, Petzval sum and axial chromatic aberration are corrected by the cemented positive lens component L2.
[0011]
As described above, in the zoom lens of the present invention, the rear lens group (master group) of the convex leading zoom lens is used as a single objective lens system as much as possible, and the lens configuration that gives as much aberration correction freedom as possible is adopted. Yes. As a result, a multi-group zoom lens capable of excellent aberration correction and easy to manufacture has been achieved.
[0012]
The zoom lens according to the present invention includes the following conditional expression (1),
0 <(Rb−Ra) / (Rb + Ra) ≦ l (1)
It is desirable to satisfy
[0013]
Here, Ra is the radius of curvature of the image-side surface of the positive meniscus lens component L1,
Rb represents the radius of curvature of the object-side surface of the cemented positive lens component L2.
[0014]
Conditional expression (1) defines an appropriate range of the shape of the meniscus air lens having a convex surface facing the object side existing between the lens component L1 and the positive lens component L2 in the lens group Gm. . In the zoom lens of the present invention, the lens group Gm, which is also the master lens group, is relatively independent and good, unlike the four zoom lens groups represented by Japanese Patent Application Laid-Open No. 8-248319, as shown in the examples described later. Aberration correction is performed, and the shape of the air lens is an important factor. When the upper limit of conditional expression (1) is exceeded, an air lens (hereinafter, “lens group”) having a meniscus shape with a convex surface facing the object side between the lens component L1 and the positive lens component L2 in the lens group Gm. The object-side air lens in Gm ”becomes a plano-convex shape, and the deflection angle of the object-side air lens in the lens group Gm changes significantly. As a result, it becomes difficult to satisfactorily correct spherical aberration and suppress changes in spherical aberration at each focal length, which is not preferable. More preferably, when the upper limit value of conditional expression (1) is set to 0.6 or less or 0.4 or less, various aberrations such as spherical aberration can be corrected more favorably. Further, when the upper limit value of conditional expression (1) is set to 0.3 or less, the effects of the present invention can be maximized. On the other hand, when the lower limit value of conditional expression (1) is not reached, the shape of the air lens on the object side in the lens group Gm becomes a reverse shape with the convex shape facing the image side. For this reason, as in the case of exceeding the upper limit value, the declination of the air lens on the object side in the lens group Gm changes remarkably, resulting in good correction of spherical aberration and change of spherical aberration at each focal length. It is difficult to suppress this, which is not preferable.
[0015]
In the zoom lens of the present invention, the following conditional expression (2),
0 <(Ra−R1) / (Ra + R1) ≦ 1 (2)
It is desirable to satisfy
[0016]
Here, R1 represents the radius of curvature of the object side surface of the positive meniscus lens component L1, and Ra represents the radius of curvature of the image side surface of the positive meniscus lens component L1.
[0017]
Conditional expression (2) defines an appropriate bending shape of the lens component L1 having a meniscus shape as a whole with the convex surface facing the object side in the lens group Gm. The lens component L1 may include a single lens or a cemented lens. In the case of a cemented lens, the shape of the entire lens component L1 is defined. The lens component L1 mainly corrects spherical aberration and axial chromatic aberration. In particular, high-order spherical aberration is generated to suppress the variation of spherical aberration at each focal length. Therefore, by setting the declination of each surface of the lens component L1 with respect to the light beam incident in parallel to the optical axis to an appropriate value, it is possible to correct aberrations satisfactorily. When the upper limit value of conditional expression (2) is exceeded, the shape of the lens component L1 approaches a plano-convex shape, so that the declination of the image-side surface changes in a decreasing direction. In addition, since the aberration correction effect of the air lens immediately after is reduced, the optimum higher-order spherical aberration does not occur. As a result, it becomes difficult to suppress variations in spherical aberration at each focal length. More preferably, when the upper limit value of conditional expression (2) is set to 0.6 or less, various aberrations such as spherical aberration can be corrected more favorably. Further, when the upper limit value of conditional expression (2) is set to 0.3 or less, the effects of the present invention can be maximized. On the other hand, when the lower limit value of conditional expression (2) is not reached, the shape of the lens component L1 becomes a reverse shape with the convex shape facing the image side. For this reason, as in the case where the upper limit value is exceeded, the deflection angle on each surface of the lens component L1 changes significantly. For this reason, it is difficult to satisfactorily correct spherical aberration and suppress changes in spherical aberration at each focal length.
[0018]
In the zoom lens of the present invention, the following conditional expression (3),
−1 ≦ (Rd−Rc) / (Rd + Rc) <0 (3)
It is desirable to satisfy
[0019]
Here, Rc is the radius of curvature of the image side surface of the positive lens component L3,
Rd represents the radius of curvature of the object side surface of the negative lens component L4.
[0020]
Conditional expression (3) defines an appropriate range of the shape of the air lens having a meniscus shape with the convex facing the image side between the positive lens component L3 and the negative lens component L4 in the lens group Gm. ing. In the zoom lens of the present invention, the lens group Gm, which is also the master lens group, is relatively independent and good, unlike the four zoom lens groups represented by Japanese Patent Application Laid-Open No. 8-248319, as shown in the examples described later. Therefore, it is necessary to correct aberrations, and the shape of the air lens is important. When the upper limit of conditional expression (3) is exceeded, an air lens (hereinafter referred to as “lens”) having a meniscus shape with a convex surface facing the image side between the positive lens component L3 and the negative lens component L4 in the lens group Gm. The shape of the “air lens on the image side in the group Gm” becomes a reverse shape with the convex shape facing the object side. For this reason, the declination of the air lens changes remarkably, and as a result, it becomes difficult to correct various off-axis aberrations including upper coma and lateral chromatic aberration. On the contrary, when the lower limit value of conditional expression (3) is not reached, the shape of the air lens on the image side in the lens group Gm becomes a plano-convex shape. For this reason, the declination of the air lens changes remarkably, and it becomes difficult to correct off-axis aberrations such as upward coma and lateral chromatic aberration, as in the case where the upper limit is exceeded. More preferably, when the lower limit value of conditional expression (3) is set to −0.8 or less or −0.7 or less, various off-axis aberrations including upper coma and lateral chromatic aberration can be corrected more favorably. Moreover, when the lower limit value of the conditional expression (3) is set to −0.6 or less, the effect of the present invention can be maximized.
[0021]
In the zoom lens of the present invention, the following conditional expression (4),
n convex <n concave (4)
It is desirable to satisfy
[0022]
Here, n concave is the refractive index with respect to the d-line (λ = 587.56 nm) of the negative lens on the object side in the cemented positive lens component L2.
The n-convex represents the refractive index for the d-line of the positive lens on the image side in the cemented positive lens component L2.
[0023]
Conditional expression (4) defines an appropriate refractive index difference between the object-side negative lens and the image-side positive lens in the cemented positive lens component L2. If the conditional expression (4) is not satisfied, the Petzval sum cannot be set to an appropriate value, and astigmatism and curvature of field cannot be maintained well as a result.
[0024]
In the zoom lens of the present invention, the following conditional expressions (5), (6),
0.1 <d12 / d34 <7 (5)
0.01 <d23 / d34 <5 (6)
It is desirable to satisfy
[0025]
Here, d12 is the distance on the optical axis from the most image side surface of the positive meniscus lens component L1 to the most object side surface of the cemented positive lens component L2.
d23 is the distance on the optical axis from the most image side surface of the cemented positive lens component L2 to the most object side surface of the positive lens component L3,
d34 represents the distance on the optical axis from the most image side surface of the positive lens component L3 to the most object side surface of the negative lens component L4.
[0026]
Conditional expression (5) indicates that the thickness on the optical axis of the air lens between the lens component L1 and the positive lens component L2 and the thickness of the air lens between the positive lens component L3 and the negative lens component L4. An appropriate ratio is specified. If the upper limit value of conditional expression (5) is exceeded, the distance between the lens component L1 and the positive lens component L2 will be significantly large. For this reason, the aberration correction effect of the air lens is remarkably reduced, and it becomes difficult to suppress the variation of the spherical aberration particularly at each focal length. More preferably, when the upper limit value of conditional expression (5) is set to 5 or less, various aberrations such as spherical aberration can be corrected more favorably. Further, when the upper limit value of conditional expression (5) is set to 3 or less, the effect of the present invention can be maximized. On the other hand, when the lower limit value of conditional expression (5) is not reached, the distance between the lens component L1 and the positive lens component L2 becomes remarkably small. For this reason, the aberration correction effect of the air lens is remarkably reduced, and as a result, as in the case where the upper limit is exceeded, it is difficult to suppress the variation of spherical aberration at each focal length. If the lower limit value of conditional expression (5) is set to 0.3 or more, various aberrations such as spherical aberration can be corrected more favorably. Moreover, when the lower limit value of the conditional expression (5) is set to 0.4 or more, the effect of the present invention can be maximized.
[0027]
Conditional expression (6) indicates that the thickness of the air interval between the cemented positive lens component L2 and the positive lens component L3 on the optical axis, and the air lens between the positive lens component L3 and the negative lens component L4. An appropriate ratio of thickness is specified. When the upper limit value of conditional expression (6) is exceeded, the distance between the cemented positive lens component L2 and the positive lens component L3 becomes significantly large, or the air lens between the positive lens component L3 and the negative lens component L4. The thickness will be significantly reduced. In the former case, the total thickness of the lens group Gm is remarkably increased, which is not preferable against the demand for compactness. In the latter case, the air lens is remarkably thinned, the aberration correction effect of the air lens is reduced, and correction of off-axis aberrations becomes difficult, which is not preferable. More preferably, when the upper limit value of conditional expression (6) is set to 3 or less, and further 1 or less, the effect of the present invention can be maximized. Conversely, when the lower limit value of conditional expression (6) is not reached, the distance between the cemented positive lens component L2 and the positive lens component L3 is remarkably reduced or between the positive lens component L3 and the negative lens component L4. The thickness of the air lens is significantly increased. As in the case where the upper limit is exceeded, this reduces the aberration correction effect of the air lens, and as a result, it becomes difficult to correct various off-axis aberrations including upper coma and lateral chromatic aberration. Further, when the lower limit value of conditional expression (6) is set to 0.02 or more, and further 0.03 or more, the effect of the present invention can be maximized.
[0028]
【Example】
A zoom lens according to an embodiment of the present invention will be described below with reference to the accompanying drawings.
[0029]
(First embodiment)
FIG. 1 is a diagram showing the lens configuration of the zoom lens according to the first embodiment of the present invention and the movement locus of each lens group from the wide-angle end to the telephoto end. The zoom lens according to the first example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens having a positive refractive power. The lens group G3 is composed of four lens groups, that is, positive, negative, positive, and positive, of a fourth lens group Gm having a positive refractive power.
[0030]
The first lens group G1 includes a cemented positive lens L11 made of a cemented negative meniscus lens having a convex surface facing the object side and a positive meniscus lens, and a positive meniscus lens L12 having a convex surface facing the object side. The two-lens group G2 has an aspheric surface from the object side to the object side, and is composed of a negative meniscus lens L21 made of a composite of a resin and a glass member, a biconcave lens L22, a biconvex lens L23, and a biconcave lens and a biconvex lens. The third lens group G3 includes, from the object side, an aperture stop S, a biconvex lens L31, and a cemented positive lens L32 formed by cementing a biconvex lens and a biconcave lens from the object side. The fourth lens group Gm includes, from the object side, a positive meniscus lens L1 having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side. It cemented positive lens L2 made of junction between's and a biconvex lens, a positive meniscus lens having a concave surface directed toward the object side L3, and is composed of a negative meniscus lens L4 having a concave surface directed toward the object side.
[0031]
In zooming, the air gap between the first lens group G1 and the second lens group G2 increases from the wide-angle end toward the telephoto end, and the air gap between the second lens group G2 and the third lens group G3. Is reduced, and all the lens groups are moved independently so that the air gap between the third lens group G3 and the fourth lens group Gm is reduced. The short distance focusing is performed by moving the second lens group G2 in the object direction.
[0032]
Table 1 below shows specification values of the zoom lens according to the first example. In the table, the surface number is the number of the lens surface counted from the object side, r is the radius of curvature, d is the surface spacing, nd is the refractive index with respect to the d line (λ = 587.56 nm), and νd is the Abbe number. Further, f indicates the focal length, FNO indicates the F number, 2ω indicates the angle of view, and Bf indicates the back focus.
[0033]
In the aspherical surface, the distance (sag amount) along the optical axis direction from the tangent plane of each aspherical surface at the height y in the vertical direction from the optical axis is S (y), the reference radius of curvature is R, and the cone. When the coefficient is k and the n-order aspheric coefficient is Cn, it is given by the following aspheric expression.
[0034]
[Expression 1]

[0035]
In the lens data in the table, an aspherical surface is marked with *, and the curvature radius r is a paraxial curvature radius. In all the following embodiments, the specification values, aspherical formulas, and the like are the same as those in the first embodiment.
[0036]
[Table 1]

[0037]
2 to 4 are graphs showing various aberrations of the zoom lens according to the first example. In the figure, FNO is an F number, Y is an image height, and d and g are aberration curves of d-line and g-line, respectively. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dotted line indicates the meridional image plane. Hereinafter, the same symbols as those in the first embodiment are used in the aberration diagrams of all the embodiments.
[0038]
FIG. 2 is an aberration diagram when focusing on infinity at the wide-angle end. It can be seen that the lens sufficiently covers up to a large angle of view and that aberrations are corrected well. FIG. 3 is an aberration diagram at the time of focusing at infinity at the intermediate focal length. As with the wide-angle end, it can be seen that aberration correction is satisfactorily performed. FIG. 4 is an aberration diagram when focusing on infinity at the telephoto end. As with the wide-angle end, it can be seen that aberration correction is performed well.
[0039]
(Second embodiment)
FIG. 5 is a diagram showing the lens configuration of the zoom lens according to the second embodiment of the present invention and the movement locus of each lens group from the wide-angle end to the telephoto end. The zoom lens according to the second example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens having a positive refractive power. The lens group G3 includes four groups of positive, negative, positive, and positive groups of the fourth lens group Gm having a positive refractive power.
[0040]
The first lens group G1 includes a cemented positive lens L11 composed of a negative meniscus lens having a convex surface facing the object side and a positive meniscus lens, and a positive meniscus lens L12 having a convex surface facing the object side. The second lens group G2 is composed of a negative meniscus lens L21 having an aspheric surface on the object side, a negative meniscus lens L22 having a convex surface on the object side, a biconvex lens L23, and a biconcave lens and a biconvex lens. The third lens group G3 includes, from the object side, an aperture stop S, a biconvex lens L31, and a cemented positive lens L32 composed of a cemented biconvex lens and a biconcave lens. The fourth lens group Gm includes a positive meniscus lens L1 having a convex surface directed toward the object side from the object side, and a negative meniscus lens having a convex surface directed toward the object side. It cemented positive lens L2 made of junction between's and a biconvex lens, a biconvex lens L3, and is composed of a negative meniscus lens L4 having a concave surface directed toward the object side. In zooming, the air gap between the first lens group G1 and the second lens group G2 increases from the wide-angle end toward the telephoto end, and the air gap between the second lens group G2 and the third lens group G3. Is reduced, and all the lens groups are moved independently so that the air gap between the third lens group G3 and the fourth lens group Gm is reduced. The short distance focusing is performed by moving the second lens group G2 in the object direction.
[0041]
Table 2 lists specifications of the zoom lens according to the second example.
[0042]
[Table 2]

[0043]
6 to 8 are graphs showing various aberrations of the zoom lens according to the second example. FIG. 6 is an aberration diagram when focusing on infinity at the wide-angle end. It can be seen that the lens sufficiently covers up to a large angle of view and that aberrations are corrected well. FIG. 7 is an aberration diagram at the time of focusing on infinity at the intermediate focal length. As with the wide-angle end, it can be seen that aberration correction is satisfactorily performed. FIG. 8 is an aberration diagram when focusing on infinity at the telephoto end. As with the wide-angle end, aberration correction is performed satisfactorily.
[0044]
(Third embodiment)
FIG. 9 is a diagram showing the lens configuration of the zoom lens according to the third embodiment of the present invention and the movement locus of each lens unit from the wide-angle end to the telephoto end. The zoom lens according to the third example includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens having a positive refractive power. The lens group G3 includes four groups of positive, negative, positive, and positive groups of the fourth lens group Gm having a positive refractive power. The first lens group G1 includes a cemented positive lens L11 made of a cemented negative meniscus lens having a convex surface facing the object side and a positive meniscus lens, and a positive meniscus lens L12 having a convex surface facing the object side. The two-lens group G2 includes a negative meniscus lens L21 having an aspheric surface on the object side, a biconcave lens L22, a biconvex lens L23, and a cemented negative meniscus lens having a concave surface facing the object side, which is formed by cementing the biconcave lens and the biconvex lens. The third lens group G3 includes an aperture stop S, a biconvex lens L31, a biconvex lens L32, a negative meniscus lens L33 having a concave surface facing the object side, and the fourth lens group Gm includes an object side. A positive meniscus lens L1 having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side and a biconvex lens Li Cheng cemented positive lens L2, the positive meniscus lens having a concave surface directed toward the object side L3, and is composed of a negative meniscus lens L4 having a concave surface directed toward the object side. In zooming, the air gap between the first lens group G1 and the second lens group G2 increases from the wide-angle end toward the telephoto end, and the air gap between the second lens group G2 and the third lens group G3. Is reduced, and all the lens groups are moved independently so that the air gap between the third lens group G3 and the fourth lens group Gm is reduced. The short distance focusing is performed by moving the second lens group G2 in the object direction.
[0045]
Table 3 below lists specifications of the zoom lens according to the third example.
[0046]
[Table 3]

[0047]
10 to 12 are graphs showing various aberrations of the zoom lens according to the third example. FIG. 10 is an aberration diagram when focusing on infinity at the wide-angle end. It can be seen that the lens sufficiently covers up to a large angle of view and that aberrations are corrected well. FIG. 11 is an aberration diagram at the time of focusing at infinity at the intermediate focal length. As with the wide-angle end, it can be seen that aberration correction is satisfactorily performed. FIG. 12 is an aberration diagram when focusing on infinity at the telephoto end. As with the wide-angle end, aberration correction is performed satisfactorily.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a lens configuration and a movement locus of a zoom lens according to a first example of the present invention.
FIG. 2 is a diagram showing various aberrations at the time of focusing on infinity at the wide angle end of the zoom lens according to the first example of the present invention.
FIG. 3 is a diagram illustrating various aberrations during focusing at infinity at an intermediate focal length of the zoom lens according to the first example of the present invention.
FIG. 4 is a diagram illustrating various aberrations at the time of focusing on infinity at the telephoto end of the zoom lens according to the first example of the present invention.
FIG. 5 is a diagram illustrating a lens configuration and a movement locus of a zoom lens according to a second example of the present invention.
FIG. 6 is a diagram illustrating various aberrations during infinite focus at the wide angle end of the zoom lens according to Example 2 of the present invention.
FIG. 7 is a diagram illustrating various aberrations during infinite focus at the intermediate focal length of the zoom lens according to Example 2 of the present invention.
FIG. 8 is a diagram illustrating various aberrations at the time of focusing on infinity at the telephoto end of the zoom lens according to Example 2 of the present invention.
FIG. 9 is a diagram illustrating a lens configuration and a movement locus of a zoom lens according to a third example of the present invention.
FIG. 10 is a diagram illustrating various aberrations at the time of focusing on infinity at the wide angle end of the zoom lens according to Example 3 of the present invention.
FIG. 11 is a diagram showing various aberrations during infinite focus at the intermediate focal length of the zoom lens according to Example 3 of the present invention.
FIG. 12 is a diagram illustrating various aberrations at the time of focusing on infinity at the telephoto end of the zoom lens according to Example 3 of the present invention.
[Explanation of symbols]
Gl 1st lens group G2 2nd lens group G3 3rd lens group Gm 4th lens group (master lens group)
S Aperture stop A Fixed stop

Claims

In order from the object side, the first lens group G1 having a positive refractive power, the second lens group G2 having a negative refractive power, the third lens group G3 having a positive refractive power , and a positive refractive power . consists of a fourth lens group Gm, in the zoom lens to perform zooming by changing the air gap between the first lens group G1 and the second lens unit G2,
The fourth lens group Gm includes, in order from the object side, a positive meniscus lens component L1 having a convex surface facing the object side, a cemented positive lens component L2 composed of a negative lens and a positive lens having a convex surface facing the object side, and a positive lens a lens component L3, and a negative meniscus lens component L4 Metropolitan having a convex surface directed toward the image side,
Between the positive meniscus lens component L1 and the cemented positive lens component L2, there is an air lens having a meniscus shape with a convex surface facing the object side, and between the positive lens component L3 and the negative lens component L4. The zoom lens has an air lens having a meniscus shape with a convex surface facing the image side.

When the radius of curvature of the image side surface of the positive meniscus lens component L1 is Ra and the radius of curvature of the object side surface of the cemented positive lens component L2 is Rb,
0 <(Rb−Ra) / (Rb + Ra) ≦ 1 (1)
The zoom lens according to claim 1, wherein the following condition is satisfied.

When the radius of curvature of the object side surface of the positive meniscus lens component L1 is R1, and the radius of curvature of the image side surface of the positive meniscus lens component L1 is Ra,
0 <(Ra−R1) / (Ra + R1) ≦ 1 (2)
According to claim 1 or 2, wherein the zoom lens satisfies the condition.

When the radius of curvature of the image side surface of the positive lens component L3 is Rc and the radius of curvature of the object side surface of the negative lens component L4 is Rd,
−1 ≦ (Rd−Rc) / (Rd + Rc) <0 (3)
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition.

The refractive index for the d-line (λ = 587.56 nm) of the negative lens on the object side in the cemented positive lens component L2 is n-concave, and the refractive index for the d-line of the positive lens on the image side in the cemented positive lens component L2 is When n convex
n convex <n concave (4)
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition.

The distance on the optical axis from the most image side surface of the positive meniscus lens component L1 to the most object side surface of the cemented positive lens component L2 is d12, and the distance from the most image side surface of the cemented positive lens component L2 is The distance on the optical axis to the most object side surface of the positive lens component L3 is d23, and the distance on the optical axis from the most image side surface of the positive lens component L3 to the most object side surface of the negative lens component L4. When the distance is d34,
0.1 <d12 / d34 <7 (5)
0.01 <d23 / d34 <5 (6)
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition.