JP4110599B2

JP4110599B2 - Zoom lens

Info

Publication number: JP4110599B2
Application number: JP31919797A
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: 2008-07-02
Anticipated expiration: 2017-11-06
Also published as: JPH11142740A

Description

【０００１】
【発明の属する技術分野】
本発明は、小型軽量でコストが安く、優れた光学性能を有し、かつ製造・組み立てが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、正屈折力を有する第３レンズ群Ｇ３と、正屈折力のレンズ群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】
前記レンズ群Ｇｍは、物体側から順に、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と、物体側に凸面を向けた接合または単レンズからなる正レンズ成分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】
前記レンズ成分Ｌ１と前記正レンズ成分Ｌ２との間には物体側に凸面を向けたメニスカス形状の空気レンズを有し、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の空気レンズを有し、
0.1≦|{(Rb+Ra)/(Rb-Ra)}/{(Rd+Rc)/(Rd-Rc)}|≦8 （１）
０＜（Ｒａ−Ｒ１）／（Ｒａ＋Ｒ１）＜０．３（２）
の条件を満足することを特徴としている。
【０００９】
ここで、Ｒ１は前記レンズ成分Ｌｌの最も物体側の面の曲率半径、
Ｒａは前記レンズ成分Ｌ１の最も像側の面の曲率半径、
Ｒｂは前記正レンズ成分Ｌ２の最も物体側の面の曲率半径、
Ｒｃは前記正レンズ成分Ｌ３の最も像側の面の曲率半径、
Ｒｄは前記負レンズ成分Ｌ４の最も物体側の面の曲率半径をそれぞれ表している。
【００１０】
【発明の実施の形態】
本発明のズームレンズは、基本的にパワー配置で正負正正を代表とする凸先行ズームレンズの後群（マスタ一群）に、極端な非球面レンズの効果を利用すること無しに、良好な性能を確保し、改良したズームレンズである。
【００１１】
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と、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との間に存在する像側に凸を向けたメニスカス形状の空気レンズの形状を相対的に規定する条件である。本発明におけるレンズ群Ｇｍは、前述の特開平８−２４８３１９号公報に代表されるズームレンズの４群と異なり、後述する実施例にも示すとおり、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いる。このためには本発明の上記構成が必須であり、上記２つの空気レンズのパワー及び形状が重要な要素となる。この空気レンズは、レンズ群Ｇｍの中心に向かって、それぞれ凹面を向けている。ここで、レンズ群Ｇｍ全体としてテレフォト型としているため、若干対称性をくずしてある。しかし、条件式に定める適切な範囲を満足することにより、極端に強い効果を有する非球面を使用すること無く良好な収差補正が可能である。
【００１２】
条件式（１）の上限値を上回ると、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）より、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）の方が曲率が強くなり、光軸に平行に入射する光束に対してレンズ群Ｇｍの中の物体側の空気レンズの偏角が著しく大きくなる。この結果、高次の球面収差が著しく発生するので好ましくない。また、レンズ製造の観点からも各精度に対する敏感度が増加する（許容誤差が小さくなる）傾向があるので好ましくない。さらに好ましくは、条件式（１）の上限値を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。加えて条件式（１）の上限値を５．５以下に設定すると本発明の効果を最大限に発揮できるので望ましい。逆に、条件式（１）の下限値を下回ると、上限値を上回る場合とは逆に、レンズ群Ｇｍの中の物体側の空気レンズに比較して、レンズ群Ｇｍの中の像側の空気レンズの方が曲率が強くなり、斜光線に対する空気レンズの偏角が著しく強くなる。このため、コマ収差、倍率色収差、歪曲等の軸外収差が悪化し、好ましくない。また、著しく強い曲率は強いゴーストの発生源になるので好ましくない。さらに好ましくは、条件式（１）の下限値を０．２以上に設定するとよりコマ収差、倍率色収差、歪曲等の軸外収差が良好に補正可能となる。また、条件式（１）の下限値を０．３５以上に設定するとより本発明の効果を最大限に発揮できる。
【００１３】
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。後述する実施例に示すとおり、前記レンズ成分Ｌ１は単レンズまたは複数のレンズを有していても良い。そして条件式（２）は、複数レンズの場合はレンズ成分Ｌ１全体のベンディングを規定することとする。前記レンズ成分Ｌ１は、条件式（１）で説明した空気レンズの作用と相まって、本発明のズームレンズの特徴の１つとなっている。前記レンズ成分Ｌ１は球面収差、軸上色収差を補正する役割を担っている。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の各面の偏角の適切な値を設定することにより、良好な収差捕正が可能になる。
【００１４】
このため、条件式（２）の上限値を越えた場合は、前記レンズ成分Ｌ１の形状が平凸形状に近づき、特に、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パワーも減少することとなる。このため、最適な高次の球面収差が発生しなくなり、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。さらに好ましくは、条件式（２）の上限値を０．２３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。加えて、条件式（２）の上限値を０．２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の形状が逆方向を向くことになり、上限値を上回る場合と同様に、最適な高次の球面収差が発生しなくなり、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。
【００１５】
前記レンズ成分Ｌ１は正メニスカス単レンズよりなる構成または物体側に凸面を向けた正メニスカスレンズと物体側に凸面を向けた負メニスカスレンズの接合からなり、全体として負の屈折力を有する接合負メニスカスレンズよりなることが好ましい。前記レンズ成分Ｌ１を正メニスカス単レンズとするか接合負メニスカスレンズとするかの選択は、ズームレンズの仕様による。球面収差を良好に補正し明るいＦ値のズームレンズとするなら、正メニスカス単レンズを選択し、軸外収差を良好に補正し、広画角のズームレンズとするなら、接合負メニスカスレンズを選択する方がよい。
【００１６】
また、本発明のズームレンズでは、前記正レンズ成分Ｌ２は、両凸単レンズもしくは物体側に凸面を向けた負メニスカスレンズと物体側に凸面を向けた正レンズの接合からなり、全体として正の屈折力を有する接合正レンズ成分より構成されることが好ましい。
【００１７】
また、本発明のズームレンズでは、前記正レンズ成分Ｌ２は物体側に凸面を向けた正レンズよりなることが好ましい。
【００１８】
また、本発明のズームレンズでは、以下の条件式（３）、（４）、
０＜ｄ１２／ｄＦ≦０．７（３）
０＜ｄ３４／ｄＲ≦０．８５（４）
を満足することが好ましい。
【００１９】
ここで、ｄ１２は前記レンズ成分Ｌ１の最も像側の面から前記正レンズ成分Ｌ２の最も物体側の面までの光軸上の距離、
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、
ｄＦは前記レンズ成分Ｌ１の最も物体側の面から正レンズ成分Ｌ２の最も像側の面までの光輔上の合計の厚さ、
ｄＲは前記正レンズ成分Ｌ３の最も物体側の面からと前記負レンズ成分Ｌ４の最も像側の面までの光軸上の合計の厚さをそれぞれ表している。
【００２０】
条件式（３）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適切な厚さを規定している。条件式（３）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（３）の上限値を０．５以下に設定すると、球面収差球面収差等の諸収差をより良好に捕正できる。また、条件式（３）の上限値を０．２５以下、さらに０．１５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（３）の下限値を下回る場合は、前記レンズ成分Ｌ１と前記正レンズ成分Ｌ２が接合レンズであることを意味する。従って、前記レンズ成分Ｌ１と前記正レンズ成分Ｌ２との間には空気レンズが存在しないことになってしまう。
【００２１】
条件式（４）は前記正レンズ成分Ｌ３と前記負レンズ成分Ｌ４との間の空気レンズの光軸上の適切な厚さを規定している。条件式（４）の上限値を上回る場合は、前記レンズ成分Ｌ３と前記正レンズ成分Ｌ４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、特に上方コマ収差、歪曲等の軸外収差の補正が困難になる。さらに好ましくは、条件式（４）の上限値を０．７以下に設定すると、コマ収差等の諸収差をより良好に補正できる。また、条件式（４）の上限値を０．６以下、さらに０．５以下に設定すると本発明の効果を最大限に発揮できる。
【００２２】
また、本発明のズームレンズでは、以下の条件式（５）、（６）、
−８≦ｆ３／ｆ４≦−０．８（５）
−１≦ｆ４／ｆｍ≦−０．１（６）
を満足することが好ましい。
【００２３】
ここで、ｆ３は前記正レンズ成分Ｌ３の焦点距離、
ｆ４は前記負メニスカスレンズ成分Ｌ４の焦点距離、
ｆｍは前記レンズ群Ｇｍの全体の焦点距離をそれぞれ表している。
【００２４】
条件式（５）は前記正レンズ成分Ｌ３と前記負レンズ成分Ｌ４の焦点距離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、前記負レンズ成分Ｌ４より前記正レンズ成分Ｌ３のパワーが著しく大きくなり、パワーのバランスを大きく崩してしまう。この結果、上方コマ収差等の軸外収差、球面収差の補正が困難になる。また、直前のレンズ群とのデッドスペースの確保が困難になり、好ましくない。さらに好ましくは、条件式（５）の上限値を−１以上に設定すると、コマ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−１．１以上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、前記正レンズ成分Ｌ３より前記負レンズ成分Ｌ４のパワーが著しく大きくなり、パワーのバランスを大きく崩してしまう。この結果、上方コマ収差、歪曲等の軸外収差の補正が困難になる。また、バックフォーカスの確保が困難になるので好ましくない。さらに好ましくは、条件式（５）の下限値を−６以上に設定すると、コマ収差等の諸収差をより良好に捕正できる。また、条件式（５）の下限値を−５以上に設定すると本発明の効果を最大限に発揮できる。
【００２５】
条件式（６）は前記負レンズ成分Ｌ４の焦点距離の適切な範囲を規定している。条件式（６）の上限値を上回る場合、前記負レンズ成分Ｌ４のパワーが著しく大きくなり、パワーのバランスを大きく崩してしまう。この結果、上方コマ収差、歪曲等の軸外収差の補正が困難になる。また、バックフォーカスの確保が困難になるので好ましくない。さらに好ましくは、条件式（６）の上限値を−０．２以下に設定すると、コマ収差等の諸収差をより良好に捕正できる。また、条件式（６）の上限値を−０．３以下、さらに−０．５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、前記負レンズ成分Ｌ４のパワーが著しく小さくなり、パワーのバランスを大きく崩してしまう。また、直前のレンズ群とのデッドスペースの確保が困難になり、好ましくない。さらに好ましくは、条件式（６）の下限値を−０．９５以上に設定すると、よりバックフォーカスの確保が容易になり、条件式（６）の下限値を−０．９以上に設定すると本発明の効果を最大限に発揮できる。
【００２６】
【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。
【００２７】
（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。
【００２８】
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。
【００２９】
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。
【００３０】
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。
【００３１】
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。
【００３２】
【数１】

【００３３】
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。
【００３４】
【表１】

【００３５】
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。
【００３６】
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。
【００３７】
（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。
【００３８】
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。
【００３９】
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。
【００４０】
【表２】

【００４１】
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。
【００４２】
（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。
【００４３】
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。
【００４４】
【表３】

【００４５】
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。
【００４６】
（第４実施例）
図１３は本発明の第４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４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。
【００４７】
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成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と物体側に凸面を向けた負メニスカスレンズとの接合によりなる接合負メニスカスレンズＬ１、両凸レンズＬ２、固定絞りＡ、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。
【００４８】
【表４】

【００４９】
図１４乃至図１６は第４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１４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１５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１６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。
【００５０】
【発明の効果】
以上の説明したように本発明によれば、２ω＝７５度〜２３度程度の画角を有し、約３．５倍の変倍比を有し小径化・小型化され、かつ精度的に厳しい後群に非球面を使用せず、少ない構成枚数で、コストパフォーマンスに優れ、製造が容易な、高性能なズームレンズを得ることができる。
【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。
【図１３】本発明の第４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１４】本発明の第４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１５】本発明の第４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１６】本発明の第４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 lightweight, has low cost, has excellent optical performance, and is 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, the zoom lens of the present invention includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power; A third lens group G3 having positive refractive power; Positive refractive power lens group Gm Consist of In the zoom lens that performs zooming by changing the air gap between the first lens group G1 and the second lens group G2,
[0007]
The lens group Gm includes, in order from the object side, a lens component L1 having a meniscus shape as a whole with a convex surface facing the object side, a positive lens component L2 composed of a cemented or single lens with a convex surface facing the object side, and a positive lens component L3, and a negative meniscus lens component L4 having a convex surface facing the image side Consist of ,
[0008]
A meniscus air lens having a convex surface facing the object side is provided between the lens component L1 and the positive lens component L2, and an image side is provided between the positive lens component L3 and the negative lens component L4. Has a meniscus air lens with a convex facing
0.1 ≦ | {(Rb + Ra) / (Rb-Ra)} / {(Rd + Rc) / (Rd-Rc)} | ≦ 8 (1)
0 <(Ra−R1) / (Ra + R1) <0.3 (2)
It is characterized by satisfying the following conditions.
[0009]
Here, R1 is the radius of curvature of the surface closest to the object side of the lens component Ll,
Ra is the radius of curvature of the surface closest to the image side of the lens component L1,
Rb is the radius of curvature of the surface closest to the object side of the positive lens component L2,
Rc is the radius of curvature of the surface closest to the image side of the positive lens component L3,
Rd represents the radius of curvature of the most object side surface of the negative lens component L4.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The zoom lens of the present invention basically has good performance without using the extreme aspherical lens effect in the rear group (master group) of the convex preceding zoom lens that is representative of positive / negative positive / positive in power arrangement. This is a zoom lens that has been improved and improved.
[0011]
Conditional expression (1) indicates that the shape of a 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, and the lens group Gm This is a condition that relatively defines the shape of a meniscus air lens having a convex surface facing the image side existing between the positive lens component L3 and the negative lens component L4. The lens group Gm in the present invention is different from the four zoom lens groups represented by the above-mentioned JP-A-8-248319, and the lens group Gm, which is also a master lens group, is relatively independent as shown in the examples described later. Thus, aberration correction is performed satisfactorily. For this purpose, the above-described configuration of the present invention is indispensable, and the power and shape of the two air lenses are important factors. Each air lens has a concave surface directed toward the center of the lens group Gm. Here, since the entire lens group Gm is a telephoto type, the symmetry is slightly broken. However, satisfactory aberration correction is possible without using an aspherical surface having an extremely strong effect by satisfying an appropriate range defined in the conditional expression.
[0012]
If the upper limit of conditional expression (1) is exceeded, a meniscus air lens (hereinafter referred to as “lens group Gm”) having a convex surface facing the image side between the positive lens component L3 and the negative lens component L4 in the lens group Gm. Air lens (hereinafter referred to as “lens”) having a convex surface facing the object side between the lens component L1 and the positive lens component L2 in the lens group Gm. The curvature of the object-side air lens in the group Gm) is stronger, and the deflection angle of the object-side air lens in the lens group Gm is remarkably large with respect to the light beam incident parallel to the optical axis. . As a result, high-order spherical aberration is remarkably generated, which is not preferable. Also, from the viewpoint of lens manufacturing, sensitivity to each accuracy tends to increase (allowable error decreases), which is not preferable. More preferably, when the upper limit value of conditional expression (1) is set to 6 or less, various aberrations such as spherical aberration can be corrected more favorably. In addition, it is desirable to set the upper limit of conditional expression (1) to 5.5 or less because the effects of the present invention can be maximized. Conversely, if the lower limit value of conditional expression (1) is not reached, the image side in the lens group Gm is compared with the air lens on the object side in the lens group Gm, contrary to the case where the upper limit value is exceeded. The curvature of the air lens is stronger, and the deflection angle of the air lens with respect to oblique rays is remarkably increased. For this reason, off-axis aberrations such as coma, lateral chromatic aberration, and distortion are deteriorated, which is not preferable. In addition, a remarkably strong curvature is not preferable because it causes a strong ghost. More preferably, when the lower limit of conditional expression (1) is set to 0.2 or more, off-axis aberrations such as coma, lateral chromatic aberration, and distortion can be corrected more favorably. Further, when the lower limit value of conditional expression (1) is set to 0.35 or more, the effect of the present invention can be exhibited to the maximum.
[0013]
Conditional expression (2) defines an appropriate bending shape of the lens component L1 having a meniscus shape as a whole with a convex surface facing the object side in the lens group Gm. As shown in the examples described later, the lens component L1 may include a single lens or a plurality of lenses. Conditional expression (2) prescribes bending of the entire lens component L1 in the case of a plurality of lenses. The lens component L1 is one of the features of the zoom lens of the present invention, coupled with the action of the air lens described in the conditional expression (1). The lens component L1 has a role of correcting 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. Accordingly, by setting an appropriate value of the deviation angle of each surface of the lens component L1 with respect to the light beam incident in parallel to the optical axis, good aberration correction can be performed.
[0014]
For this reason, when the upper limit value of conditional expression (2) is exceeded, the shape of the lens component L1 approaches a plano-convex shape, and in particular, changes in the direction in which the declination of the image side surface decreases. In addition, the power of the air lens immediately after that also decreases. For this reason, optimal high-order spherical aberration does not occur, and as a result, it becomes difficult to suppress the variation of spherical aberration at each focal length. More preferably, when the upper limit value of conditional expression (2) is set to 0.23 or less, various aberrations such as spherical aberration can be corrected more favorably. In addition, if the upper limit value of conditional expression (2) is set to 0.2 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 is directed in the opposite direction, and the optimum higher-order spherical aberration does not occur as in the case where the upper limit value is exceeded. As a result, it becomes difficult to suppress variations in spherical aberration at each focal length.
[0015]
The lens component L1 is composed of a single positive meniscus lens or a cemented negative meniscus having a negative refractive power as a whole, consisting of a positive meniscus lens having a convex surface facing the object side and a negative meniscus lens having a convex surface facing the object side. It is preferable to consist of a lens. The selection of whether the lens component L1 is a positive meniscus single lens or a cemented negative meniscus lens depends on the specifications of the zoom lens. Select a positive meniscus single lens to correct spherical aberration well and obtain a bright F-number zoom lens, and select a cemented negative meniscus lens to correct off-axis aberrations well and wide-angle zoom lenses. Better to do.
[0016]
In the zoom lens according to the present invention, the positive lens component L2 is formed by cementing a biconvex single lens or a negative meniscus lens having a convex surface on the object side and a positive lens having a convex surface on the object side. It is preferable that the lens is composed of a cemented positive lens component having refractive power.
[0017]
In the zoom lens of the present invention, it is preferable that the positive lens component L2 is a positive lens having a convex surface facing the object side.
[0018]
In the zoom lens of the present invention, the following conditional expressions (3), (4),
0 <d12 / dF ≦ 0.7 (3)
0 <d34 / dR ≦ 0.85 (4)
Is preferably satisfied.
[0019]
Here, d12 is a distance on the optical axis from the most image side surface of the lens component L1 to the most object side surface of the positive lens component L2,
d34 is 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;
dF is the total thickness on the Kosuke from the most object side surface of the lens component L1 to the most image side surface of the positive lens component L2,
dR represents the total thickness on the optical axis from the most object side surface of the positive lens component L3 to the most image side surface of the negative lens component L4.
[0020]
Conditional expression (3) defines an appropriate thickness on the optical axis of the air lens between the lens component L1 and the positive lens component L2. If the upper limit value of conditional expression (3) 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 (3) is set to 0.5 or less, various aberrations such as spherical aberration and spherical aberration can be corrected better. Further, when the upper limit value of the conditional expression (3) is set to 0.25 or less, and further 0.15 or less, the effect of the present invention can be maximized. On the contrary, when the lower limit value of conditional expression (3) is not reached, it means that the lens component L1 and the positive lens component L2 are cemented lenses. Accordingly, there is no air lens between the lens component L1 and the positive lens component L2.
[0021]
Conditional expression (4) defines an appropriate thickness on the optical axis of the air lens between the positive lens component L3 and the negative lens component L4. When the upper limit value of conditional expression (4) is exceeded, the distance between the lens component L3 and the positive lens component L4 becomes remarkably large. For this reason, the aberration correction effect of the air lens is remarkably reduced, and it becomes difficult to correct off-axis aberrations such as upper coma and distortion. More preferably, when the upper limit value of conditional expression (4) is set to 0.7 or less, various aberrations such as coma can be corrected more favorably. Further, when the upper limit value of the conditional expression (4) is set to 0.6 or less, and further 0.5 or less, the effect of the present invention can be maximized.
[0022]
In the zoom lens of the present invention, the following conditional expressions (5), (6),
−8 ≦ f3 / f4 ≦ −0.8 (5)
−1 ≦ f4 / fm ≦ −0.1 (6)
Is preferably satisfied.
[0023]
Here, f3 is a focal length of the positive lens component L3,
f4 is a focal length of the negative meniscus lens component L4,
fm represents the overall focal length of the lens group Gm.
[0024]
Conditional expression (5) defines an appropriate ratio of the focal lengths of the positive lens component L3 and the negative lens component L4. When the upper limit of conditional expression (5) is exceeded, the power of the positive lens component L3 is significantly greater than that of the negative lens component L4, and the power balance is greatly lost. As a result, it becomes difficult to correct off-axis aberrations such as upper coma and spherical aberration. Further, it becomes difficult to secure a dead space with the immediately preceding lens group, which is not preferable. More preferably, when the upper limit value of conditional expression (5) is set to −1 or more, various aberrations such as coma can be corrected more favorably. Further, when the upper limit value of the conditional expression (5) is set to −1.1 or more, the effect of the present invention can be maximized. On the other hand, if the lower limit value of conditional expression (5) is not reached, the power of the negative lens component L4 is significantly greater than that of the positive lens component L3, and the power balance is greatly lost. As a result, it becomes difficult to correct off-axis aberrations such as upper coma and distortion. Further, it is not preferable because it is difficult to ensure the back focus. More preferably, when the lower limit value of the conditional expression (5) is set to −6 or more, various aberrations such as coma aberration can be corrected better. Further, when the lower limit value of the conditional expression (5) is set to -5 or more, the effect of the present invention can be maximized.
[0025]
Conditional expression (6) defines an appropriate range of the focal length of the negative lens component L4. When the upper limit value of conditional expression (6) is exceeded, the power of the negative lens component L4 becomes remarkably large, and the balance of power is greatly lost. As a result, it becomes difficult to correct off-axis aberrations such as upper coma and distortion. Further, it is not preferable because it is difficult to ensure the back focus. More preferably, when the upper limit value of conditional expression (6) is set to −0.2 or less, various aberrations such as coma aberration can be corrected better. Further, when the upper limit value of conditional expression (6) is set to -0.3 or less, and further to -0.5 or less, the effect of the present invention can be exhibited to the maximum. On the other hand, when the lower limit value of conditional expression (6) is not reached, the power of the negative lens component L4 is remarkably reduced and the power balance is greatly lost. Further, it becomes difficult to secure a dead space with the immediately preceding lens group, which is not preferable. More preferably, when the lower limit value of conditional expression (6) is set to −0.95 or more, it becomes easier to secure the back focus, and when the lower limit value of conditional expression (6) is set to −0.9 or more, this The effects of the invention can be maximized.
[0026]
【Example】
A zoom lens according to an embodiment of the present invention will be described below with reference to the accompanying drawings.
[0027]
(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.
[0028]
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. Positive cemented 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.
[0029]
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.
[0030]
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.
[0031]
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-th order aspheric coefficient is Cn, it is given by the following aspheric expression.
[0032]
[Expression 1]

[0033]
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.
[0034]
[Table 1]

[0035]
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.
[0036]
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.
[0037]
(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.
[0038]
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 from the object side, 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 cemented from the object side. The third lens group G3 is composed of an aperture stop S, a biconvex lens L31, and a cemented positive lens L32 composed of a cemented biconvex lens and a biconcave lens, from the object side. 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.
[0039]
Table 2 lists specifications of the zoom lens according to the second example.
[0040]
[Table 2]

[0041]
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.
[0042]
(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, 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.
[0043]
Table 3 below lists specifications of the zoom lens according to the third example.
[0044]
[Table 3]

[0045]
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.
[0046]
(Fourth embodiment)
FIG. 13 is a diagram showing the lens configuration of the zoom lens according to the fourth 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 fourth 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.
[0047]
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 aspherical 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 an aperture stop S, a biconvex lens L31, a biconvex lens L32 from the object side, and a negative meniscus lens L33 with a concave surface facing the object side. The fourth lens group Gm includes a positive meniscus lens having a convex surface facing the object side and a negative meniscus having a convex surface facing the object side. Cemented negative meniscus lens L1 made by bonding the lens, biconvex lens L2, fixed throttle A, 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. 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.
[0048]
[Table 4]

[0049]
14 to 16 are graphs showing various aberrations of the zoom lens according to the fourth example. FIG. 14 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. 15 is an aberration diagram when focusing on infinity at an intermediate focal length. As with the wide-angle end, it can be seen that aberration correction is satisfactorily performed. FIG. 16 is an aberration diagram when focusing on infinity at the telephoto end. As with the wide-angle end, aberration correction is performed satisfactorily.
[0050]
【The invention's effect】
As described above, according to the present invention, the angle of view is about 2ω = 75 degrees to 23 degrees, the zoom ratio is about 3.5 times, and the diameter is reduced and the size is reduced. It is possible to obtain a high-performance zoom lens that does not use an aspherical surface for a strict rear group, has a small number of components, has excellent cost performance, and is easy to manufacture.
[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 showing various aberrations at the time of focusing at infinity 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.
FIG. 13 is a diagram illustrating a lens configuration and a movement locus of a zoom lens according to a fourth example of the present invention.
FIG. 14 is a diagram illustrating various aberrations at the time of focusing on infinity at the wide angle end of a zoom lens according to Example 4 of the present invention.
FIG. 15 is a diagram illustrating various aberrations during infinite focus at the intermediate focal length of the zoom lens according to Example 4 of the present invention.
FIG. 16 is a diagram showing various aberrations at the time of focusing on infinity at the telephoto end of the zoom lens according to Example 4 of the present invention.
[Explanation of symbols]
Gl first lens group
G2 second lens group
G3 Third lens group
Gm 4th lens group (master lens group)
S Aperture stop
A Fixed iris

Claims

In order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a lens group Gm of positive refractive power In the zoom lens that performs zooming by changing the air gap between the first lens group G1 and the second lens group G2,
The lens group Gm includes, in order from the object side, a lens component L1 having a meniscus shape as a whole with a convex surface facing the object side, a positive lens component L2 composed of a cemented or single lens with a convex surface facing the object side, and a positive lens component and L3, and a negative meniscus lens component L4 Metropolitan having a convex surface directed toward the image side,
A meniscus air lens having a convex surface facing the object side is provided between the lens component L1 and the positive lens component L2, and an image side is provided between the positive lens component L3 and the negative lens component L4. Has a meniscus air lens with a convex facing
The radius of curvature of the surface closest to the object side of the lens component Ll is R1, the radius of curvature of the surface of the lens component L1 closest to the image side is Ra,
The curvature radius of the most object side surface of the positive lens component L2 is Rb, and the curvature radius of the most image side surface of the positive lens component L3 is Rc,
When the radius of curvature of the surface closest to the object side of the negative lens component L4 is Rd,
0.1 ≦ | {(Rb + Ra) / (Rb-Ra)} / {(Rd + Rc) / (Rd-Rc)} | ≦ 8 (1)
0 <(Ra−R1) / (Ra + R1) <0.3 (2)
A zoom lens that satisfies the following conditions.

2. The zoom lens according to claim 1, wherein the lens component L1 is a positive meniscus single lens.

The lens component L1 is a cemented negative meniscus lens having a negative refractive power as a whole, which is composed of a positive meniscus lens having a convex surface facing the object side and a negative meniscus lens having a convex surface facing the object side. The zoom lens according to claim 1.

The positive lens component L2 is composed of a negative meniscus lens having a convex surface facing the object side and a positive lens having a convex surface facing the object side, and is a cemented positive lens component having a positive refractive power as a whole. The zoom lens according to claim 1, 2 or 3.

4. The zoom lens according to claim 1, wherein the positive lens component L2 is a positive lens having a convex surface directed toward the object side.

The distance on the optical axis from the most image side surface of the lens component L1 to the most object side surface of the positive lens component L2 is d12,
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 is d34,
The total thickness of the light component from the most object side surface of the lens component L1 to the most image side surface of the positive lens component L2 is dF, and the negative lens from the most object side surface of the positive lens component L3 When the total thickness on the optical axis to the surface closest to the image side of the component L4 is dR,
0 <d12 / dF ≦ 0.7 (3)
0 <d34 / dR ≦ 0.85 (4)
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition.

The focal length of the positive lens component L3 is f3,
The focal length of the negative meniscus lens component L4 is f4,
−8 ≦ f3 / f4 ≦ −0.8 when the focal length of the entire lens group Gm is fm (5)
−1 ≦ f4 / fm ≦ −0.1 (6)
The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditional expression: