JP4580510B2

JP4580510B2 - Zoom lens

Info

Publication number: JP4580510B2
Application number: JP2000187625A
Authority: JP
Inventors: 裕司宮内; 紳中村
Original assignee: Olympus Corp; Fujii Optical Co Ltd
Current assignee: Olympus Corp; Fujii Optical Co Ltd
Priority date: 2000-06-22
Filing date: 2000-06-22
Publication date: 2010-11-17
Anticipated expiration: 2020-06-22
Also published as: JP2002006216A

Description

【０００１】
【発明の属する技術分野】
本発明はズームレンズで、特にカムコーダーやデジタルカメラ等の電子撮像素子を用いたカメラに使用されるズームレンズに関するものである。
【０００２】
【従来の技術】
上記の分野のズームレンズの従来例のうち、民生用の小型で低コストの従来のズームレンズは、特開平３−２００１１３号、特開平６−９４９９７号、特開平６−１９４５７２号の各公報に記載されているように、物体側から順に、正の屈折力を有し変倍時固定の第１レンズ群と、負の屈折力を有し変倍時広角端から望遠端にかけて物体側から像側に移動する第２レンズ群と、正の屈折力を有し変倍時広角端から望遠端にかけて像側から物体側へ移動して若干変倍作用を助ける第３レンズ群と、正の屈折力を有し変倍時可動の第４レンズ群とよりなるレンズ系である。
【０００３】
これら従来例は、変倍比が５〜１２程度である。
【０００４】
また、前記構成のズームレンズで第３レンズ群の変倍作用を強くすることにより変倍比が３程度の従来例として特開平１０−６２６８７号、特開平１１−１１９１００号、特開平１１−２５８５０７号の各公報に記載されたレンズ系が知られている。
【０００５】
【発明が解決しようとする課題】
前記従来例のうち、変倍比が１０程度のズームレンズは、第２レンズ群の変倍作用が強く小型化の点で不十分である。
【０００６】
また変倍比が５程度の従来例のズームレンズは、フォーカシングも含めて考えると少ないレンズ枚数で、十分小型な構成であるとはいえない。
【０００７】
また、前記従来例のうちの変倍比が３程度のズームレンズは、変倍比が十分ではなく、これを超える変倍比のレンズ系にしようとすると性能が劣化し、特にフォーカシングの際の性能劣化が大きい。
【０００８】
本発明は、フォーカシングを含めて良好な光学性能を有していてまた製産性も良好であって、しかも少ないレンズ枚数にて構成したカムコーダーやデジタルカメラ等の電子撮像手段を用いたカメラに適した小型で低コストのズームレンズで、特に変倍比が５前後のズームレンズを提供するものである。
【０００９】
【課題を解決するための手段】
本発明のズームレンズは、物体側から順に、正の屈折力の第１レンズ群と負の屈折力の第２レンズ群と正の屈折力の第３レンズ群と正の屈折力の第４レンズ群とよりなり、各レンズ群間の間隔を変化させることにより変倍を行い、各レンズ群間のいずれかの空気間隔中につまり第１レンズ群と第２レンズ群の間、第２レンズ群と第３レンズ群の間、第３レンズ群と第４レンズ群の間のいずれかの空気間隔中に明るさ絞りが配置され、広角端から望遠端への変倍の際に第１レンズ群と明るさ絞りとは固定であり、第２レンズ群は光軸上を像側に常に移動し、第３レンズ群は光軸上を物体側へ常に移動し、第４レンズ群は光軸上を移動するもので、第３レンズ群と第４レンズ群の移動量が下記条件（１）を満足するようにしたものである。
（１）０≦ｔ４／ｔ３＜０．２
ただし、ｔ３，ｔ４は夫々第３レンズ群および第４レンズ群の広角端と望遠端の移動量の絶対値である。
【００１０】
一般に高変倍のズームレンズは、第２レンズ群のみに変倍作用を負担させ、第４レンズ群により像面位置を補正するようにしている。
【００１１】
本発明は、第２レンズ群の変倍作用の一部と第４レンズ群による像面位置の補正作用の一部を第３レンズ群に負担させることによってレンズ系の小型化を図ったもので、そのための条件が条件（１）である。
【００１２】
条件（１）の上限を超えると第４レンズ群による像面位置の補正作用の負担が大になりすぎるため第４レンズ群の変倍時の移動量（像面位置補正のための移動量）が大になり、レンズ系を十分小型にすることが出来ない。また第４レンズ群によりフォーカシングを行なうようにした場合、前記のように変倍の際の第４レンズ群の移動量が大であると、フォーカシング時の収差変動が大になり、またフォーカシングのための機構が複雑になる。更に第２、第３レンズ群は変倍時いずれも単調に移動するのでズーミングのためのカムの製作が容易であり、また条件（１）を満足することにより前述のように第４レンズ群の移動量を小さくできるためにズーミング時やフォーカシング時のモーターなどでの制御が短くメカスペースを小さくできる。
【００１３】
尚、条件（１）において下限値を超えることはあり得ない。
更には条件（１）の上限値を０．１５とするとより好ましい。
又、条件（１）の下限値を０．００５とすると、各レンズ群の移動量のバランスがよくなる。
【００１４】
前記本発明の第１の構成のズームレンズにおいて、正の屈折力の第４レンズ群を物体側から順に両凹負レンズと正レンズとを接合した負の接合レンズと正レンズの２群３枚構成にすることが好ましい。
【００１５】
このように、第４レンズ群を前記の通りの２群３枚構成にすることにより、第３レンズ群の変倍作用の一部を負担したときの第４レンズ群の収差発生量を少なくし、また第４レンズ群の移動量を少なくしたまま諸収差を良好に補正するためには、負レンズ１枚と正レンズ２枚が必要になり、そのうちの物体側の負レンズと正レンズとを接合することにより、製造誤差によるレンズ系の性能への悪影響を小さくすることができ、フォーカシングによる収差変動も少なくし得る。
【００１６】
以上の理由から、第４レンズ群は、前述の通りの両凹レンズと正レンズの接合レンズと正レンズよりなる２群３枚構成にすることが望ましい。
【００１７】
また、本発明のズームレンズにおいて、第４レンズ群を前述の通りの２群３枚構成にした時、下記条件（２）を満足することが望ましい。
（２）０．２４＜｜ｆ４ｎ／ｆ４｜＜０．３３
ただし、ｆ４ｎは第４レンズ群の両凹レンズの単体での焦点距離、ｆ４は第４レンズ群の焦点距離である。
【００１８】
条件（２）において上限の０．３３を超えると負レンズのパワーが弱くなり色収差の補正が困難であり、また条件（２）の下限の０．２４を超えると負レンズのパワーが強くなりすぎ色収差やその他の諸収差の発生が大になる。
【００１９】
また、この条件（２）を満足すれば、フォーカシングによる収差変動を小さくできる。
更には条件（２）の上限値を０．３１とするとより好ましい。
又、条件（２）の下限値を０．２７とするとより好ましい。
【００２０】
本発明の第２の構成のズームレンズは、物体側から順に、正の屈折力の第１レンズ群と、負の屈折力の第２レンズ群と、正の屈折力の第３レンズ群と、正の屈折力の第４レンズ群とよりなり、各レンズ群間を変化させることにより変倍を行い、明るさ絞りが第１，第２レンズ群の間、第２，第３レンズ群の間、第３，第４レンズ群の間のいずれかのレンズ群間に配置されており、広角端から望遠端への変倍の際、第１レンズ群と明るさ絞りとが固定であり、第２，第３，第４レンズ群の四つのレンズ群が光軸上を移動するレンズ系で、広角端から望遠端にかけての変倍時第２レンズ群が常に像側へ移動し、第３レンズ群が常に物体側へ移動するもので、第４レンズ群は物体側から順に両凹負レンズと正レンズを貼り合わせた接合レンズと正レンズとよりなる２群３枚構成であり、前記の条件（２）を満足するレンズ系である。
【００２１】
本発明のズームレンズは、前述のように第３レンズ群に変倍作用と像面位置の補正作用を負担させるようにした。そのため発生する収差を補正するためには、第４レンズ群に負レンズ１枚と正レンズ２枚が必要になる。
【００２２】
前記第２の構成では、正の第４レンズ群を物体側から順に、両凹負レンズと正レンズとを接合した接合レンズと正レンズよりなる２群３枚構成にして、第３レンズ群にて発生する収差を補正するようにした。また、負レンズと正レンズとを接合することにより、製造誤差による光学性能に及ぼす影響を少なくした。
【００２３】
また、この第２の構成において、第４レンズ群による収差補正作用を大にするために条件（２）を満足するようにした。
【００２４】
前述の通り、この条件（２）の上限の０．３３を超えると負のパワーが弱くなり色収差を十分良好に補正し得ない。又条件（２）の下限の０．２４を超えると負レンズのパワーが強くなりすぎて色収差や他の諸収差が発生する。
【００２５】
また、この条件（２）を満足するようにすれば、フォーカシングの際の収差変動を小さくすることができる。
条件（２）の上限値を０．３１としてもよい。又、下限値を０．２７としてもよい。
【００２６】
本発明の第１、第２の構成のズームレンズは、第３レンズ群を少なくとも１枚の正レンズと最も像側に配置されていて像側に凹面を向けた負レンズを含んだ構成にすると、射出瞳を遠くにすることができ好ましい。
本発明の第３の構成のズームレンズは、物体側から順に、正の屈折力の第１レンズ群と、負の屈折力の第２レンズ群と、正の屈折力の第３レンズ群と、正の屈折力の第４レンズ群とよりなり、各レンズ群間の間隔を変化させることにより変倍を行い、明るさ絞りが第１，第２レンズ群の間、第２，第３レンズ群の間、第３，第４レンズ群の間のいずれかのレンズ群間に配置されており、広角端から望遠端への変倍の際、第１レンズ群と明るさ絞りとが固定であり、第２，第３，第４レンズ群の四つのレンズ群が光軸上を移動するレンズ系で、広角端から望遠端にかけての変倍時に、第２レンズ群が像側へ常に移動し、第３レンズ群が物体側へ常に移動するもので、正の第３レンズ群Ｇ３が少なくとも１枚の正レンズと１枚の負レンズを含んでおり、正の第４レンズ群が、物体側より順に、負の前群と正の後群とよりなり、負の前群が最も物体側の面と最も像側の面が物体側に凸面を向けた形状であり、正の後群が物体側に凸面を向けた単レンズよりなり、下記条件（３）を満足するレンズ系である。
（３）０．３＜｜ｆ４／ｆ４１｜＜０．６
ただし、ｆ４１は第４レンズ群の前群の焦点距離である。
【００２７】
本発明のズームレンズは、第３レンズ群にも変倍作用を持たせたもので、そのためこの第３レンズ群が正レンズと負レンズとを含んでいないと色収差を補正できない。
【００２８】
また、第４レンズ群を比較的パワーの小さい負の前群と正の単レンズよりなる正の後群とにて構成することにより諸収差特に色収差の発生を抑え変倍全域にわたってまたフォーカシング領域全域にわたって、収差変動を小さくし得る。
【００２９】
また、条件（３）の上限の０．６を超えると負の前群のパワーが強くなりすぎ、色収差や諸収差が発生する。条件（３）の下限の０．３を超えると、負の前群のパワーが弱くなりすぎて色収差を補正できなくなる。
【００３０】
また、第４レンズ群の負の前群の最も物体側の面と最も像側の面を物体側に凸面を向けた形状にすれば、第４レンズ群の製造誤差による悪影響を小さくすることが可能になる。
更に、条件（３）の上限値を０．５３とするとより好ましい。
又、条件（３）の下限値を０．３８とするとより好ましい。
【００３１】
本発明の第３の構成のズームレンズにおいて、第４レンズ群の負の前群をメニスカスレンズ１枚にて構成すればレンズ系の部品点数の削減および小型化に寄与し得るため望ましい。特に負メニスカス単レンズとすればより部品点数の削減に寄与し得る。
【００３２】
また前記の負の前群のメニスカスレンズをメニスカス形状の接合レンズにすれば、この前群における収差補正能力が一層向上するため望ましい。また、接合レンズであれば、この前群での製造誤差によるレンズ系に及ぼす悪影響を少なくできるため好ましい。
【００３３】
本発明の第３の構成のズームレンズにおいて、正の第３レンズ群を最も像側に配置された像側に凹面を向けた負レンズと、少なくとも１枚の正レンズを含む構成にすることが望ましい。
【００３４】
このように第３レンズ群の最も像側に像側に凹面を向けた負レンズを配置することにより射出瞳を遠くすることができるため望ましい。
【００３５】
また、本発明のズームレンズは、この第３レンズ群にも変倍作用を持たせており、したがって、前記最も像側の負レンズの他に少なくとも１枚の正レンズを含むようにし、少なくとも正レンズと負レンズとを配置してこのレンズ群での色収差を良好に補正する必要がある。このように、正レンズと負レンズを配置しないと第３レンズ群での色収差を十分良好に補正することが困難になる。
【００３６】
また、このように第３の構成で、第３レンズ群を最も像側に配置された像側に凹面を向けた負レンズと、この負レンズの他に少なくとも１枚の正レンズを含むようにしたズームレンズの場合も正の第４レンズ群の前群を負のメニスカスレンズ１枚にて構成することが望ましい。またこのメニスカスレンズをメニスカス形状の接合レンズとしてもよい。また、メニスカス単レンズ１枚にて構成してもよい。
【００３７】
本発明のズームレンズつまり前述の第１〜第３の構成のズームレンズは、フォーカシングを第４レンズ群にて行なうのが望ましい。
また、本発明のズームレンズは明るさ絞りを第２レンズ群と第３レンズ群との間に配置すると、光学系全体の小型化と、像側へのテレセントリック性が両立でき好ましい。
以上の構成は変倍比が２．８から６．９のズームレンズに適している。
【００３８】
【発明の実施の形態】
次に本発明の実施の形態を図１〜４に示す構成で下記データを有する実施例１〜４にもとづいて説明する。尚、実施例１、４は参考例である。
実施例１
ｆ＝5.900 〜10.219〜17.551 ，Ｆナンバー＝2.83〜3.68〜3.99
２ω＝60.6°〜21.3°
ｒ₁ ＝60.780 ｄ₁ ＝1.00 ｎ₁ ＝1.80518 ν₁ ＝25.42
ｒ₂ ＝22.057 ｄ₂ ＝5.46 ｎ₂ ＝1.62280 ν₂ ＝57.05
ｒ₃ ＝-931.750 ｄ₃ ＝0.20
ｒ₄ ＝25.036 ｄ₄ ＝3.16 ｎ₃ ＝1.80610 ν₃ ＝40.92
ｒ₅ ＝100.658 ｄ₅ ＝Ｄ₁ （可変）
ｒ₆ ＝83.957 ｄ₆ ＝1.00 ｎ₄ ＝1.80440 ν₄ ＝39.59
ｒ₇ ＝6.667 ｄ₇ ＝3.67
ｒ₈ ＝-20.662 ｄ₈ ＝1.00 ｎ₅ ＝1.51633 ν₅ ＝64.14
ｒ₉ ＝8.622 ｄ₉ ＝2.93 ｎ₆ ＝1.80518 ν₆ ＝25.42
ｒ₁₀＝60.380 ｄ₁₀＝Ｄ₂ （可変）
ｒ₁₁＝∞（絞り）ｄ₁₁＝Ｄ₃ （可変）
ｒ₁₂＝11.405 ｄ₁₂＝2.95 ｎ₇ ＝1.69350 ν₇ ＝53.24
ｒ₁₃＝-23.743 （非球面）ｄ₁₃＝0.22
ｒ₁₄＝7.908 ｄ₁₄＝2.62 ｎ₈ ＝1.69100 ν₈ ＝54.82
ｒ₁₅＝40.704 ｄ₁₅＝1.01 ｎ₉ ＝1.84666 ν₉ ＝23.78
ｒ₁₆＝5.180 ｄ₁₆＝Ｄ₄ （可変）
ｒ₁₇＝32.444 ｄ₁₇＝1.00 ｎ₁₀＝1.80440 ν₁₀＝39.59
ｒ₁₈＝8.384 ｄ₁₈＝2.32 ｎ₁₁＝1.49700 ν₁₁＝81.54
ｒ₁₉＝32.662 ｄ₁₉＝0.76
ｒ₂₀＝11.234 ｄ₂₀＝2.82 ｎ₁₂＝1.65844 ν₁₂＝50.88
ｒ₂₁＝-20.977 ｄ₂₁＝Ｄ₅ （可変）
ｒ₂₂＝∞ ｄ₂₂＝3.40 ｎ₁₃＝1.51633 ν₁₃＝64.14
ｒ₂₃＝∞ ｄ₂₃＝1.00
ｒ₂₄＝∞（撮像面）
非球面係数
（第１３面）Ｋ＝-4.537 ，Ａ₄ ＝1.12339 ×10^-4 ，Ａ₆ ＝8.46541 ×10^-6
Ａ₈ ＝-6.78805×10^-7 ，Ａ₁₀＝2.00622 ×10^-8
ｆ 5.900 10.219 17.551
Ｄ₁ 1.03 4.60 9.50
Ｄ₂ 14.42 10.85 5.95
Ｄ₃ 5.76 2.45 0.43
Ｄ₄ 3.06 6.43 6.17
Ｄ₅ 1.25 1.19 3.45
ｔ３＝5.306 ，ｔ４＝2.203 ，ｔ４／ｔ３＝2.203 ／5.306 ＝0.415
ｆ４＝15.686 ，ｆ４１＝-37.535
｜ｆ４／ｆ４１｜＝｜15.686／-37.535 ｜＝0.418 ，変倍比 2.97
撮像素子の画素ピッチ３．２μｍ〜４．２μｍ
【００３９】

【００４０】

【００４１】

ただしｒ₁ ，ｒ₂ ，・・・は各レンズ面の曲率半径、ｄ₁ ，ｄ₂ ，・・・は各レンズの肉厚および空気間隔、ｎ₁ ，ｎ₂ ，・・・は各レンズの屈折率、ν₁ ，ν₂ ，・・・は各レンズのアッベ数である。
【００４２】
実施例１は、図１に示す通りの構成で、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Ｇ４とよりなり、明るさ絞りＳは第２レンズ群Ｇ２と第３レンズ群Ｇ３との間に配置されている。
【００４３】
第１レンズ群Ｇ１と絞りＳは変倍中固定であり、また広角端から望遠端への変倍の際に第２レンズ群Ｇ２は物体側から像側へ移動し、第３レンズ群Ｇ３は像側から物体側へ移動し、第４レンズ群Ｇ４は図１に示すように光軸上を移動する。
【００４４】
この実施例１のレンズ系は、第１レンズ群Ｇ１が正の接合レンズと正レンズとよりなり、第２レンズ群Ｇ２が負レンズと負の接合レンズとよりなる。
【００４５】
また、第３レンズ群Ｇ３は正レンズと、正レンズと負レンズの接合負レンズよりなり、第４レンズ群Ｇ４は負の接合レンズと正レンズの２群３枚よりなる。
【００４６】
この実施例は、第３の構成のズームレンズで、第４レンズ群が負の前群Ｇ４１と正の後群Ｇ４２よりなり負の前群Ｇ４１が最も物体側の面（ｒ₁₇）と最も像側の面（ｒ₁₉）とが物体側に凸のメニスカス形状の接合レンズからなり、正の後群Ｇ４２が正レンズ１枚よりなる。
【００４７】
この実施例１は条件（３）を満足する。
【００４８】
実施例２は、図２に示す通りの構成であって、第１レンズ群Ｇ１と第２レンズ群Ｇ２は実施例１と同様のレンズ構成であるが、第３レンズ群Ｇ３が正レンズと負レンズのみからなり、第４レンズ群Ｇ４が両凹負レンズと正レンズの接合レンズと正レンズの２群３枚構成である点で実施例１と相違する。
【００４９】
この実施例２は条件（１）、（２）を満足する。
【００５０】
実施例３は、図３に示すような構成のズームレンズで、実施例２と類似の構成のレンズ系である。
【００５１】
この実施例３も条件（１）、（２）を満足する。
【００５２】
これら実施例２、３は第１及び第２の構成のズームレンズである。
【００５３】
実施例４は図４に示す構成であって、第１レンズ群Ｇ１と第２レンズ群Ｇ２とは他の実施例と類似の構成である。また第３レンズ群Ｇ３は、２枚の正レンズと１枚の負レンズとよりなり、第４レンズ群Ｇ４は負レンズと正レンズとよりなる。
【００５４】
つまり、この実施例４は第１、第３の構成のレンズ系であって、第３レンズ群Ｇ３は少なくとも１枚の正レンズと１枚の負レンズとよりなり、第４レンズ群Ｇ４は負の前群Ｇ４１と正の後群Ｇ４２とよりなり、負の前群Ｇ４１が最も物体側と最も像側の面が物体側に凸のメニスカス単レンズであり、正の後群Ｇ４２が正レンズよりなる。
【００５５】
この実施例４は条件（１）、（３）を満足する。
【００５６】
上記各実施例にて用いられる非球面の形状は、光軸上の光が進む方向をｘ軸、光軸と直交する方向をｙ軸としたとき、次の式にて表わされる。

ただし、ｒは基準球面の曲率半径、ｋは円錐係数、Ａ₄ ，Ａ₆ ，Ａ₈ ，Ａ₁₀は非球面係数である。
【００５７】
また、各実施例の断面図を示す図１〜図４において、上段は広角端、中段は中間焦点距離、下段は望遠端における図である。尚図中Ｆはローパスフィルターや不要波長域を制限するフィルターである。
【００５８】
また図５は実施例１の収差図であり、この図のように諸収差は良好に補正されている。
【００５９】
また、他の実施例２〜４も実施例１と同様の収差状況で諸収差は良好に補正されている。
【００６０】
本発明のズームレンズは、以上述べたような構成であって、特許請求の範囲に記載したレンズ系のほか、次の各項に記載する構成のレンズ系も本発明の目的を達成し得る。
【００６１】
（１）特許請求の範囲の請求項５に記載するレンズ系で、第４レンズ群の前群が負の屈折力を有するメニスカス単レンズであることを特徴とするズームレンズ。
【００６２】
（２）特許請求の範囲の請求項５に記載するレンズ系であって、第４レンズ群の前群が負の屈折力を有するメニスカス形状の接合レンズであることを特徴とするズームレンズ。
【００６３】
（３）特許請求の範囲の請求項１、２、３、４又は５あるいは前記の（１）又は（２）の項に記載するレンズ系で、第３レンズ群が少なくとも１枚の正レンズと最も像側に配置されていて像側に凹面を向けた負レンズとを含むことを特徴とするズームレンズ。
【００６４】
（４）特許請求の範囲の請求項１、２、３、４又は５あるいは前記の（１）、（２）又は（３）の項に記載するレンズ系で、第４レンズ群を光軸上を移動させることにより近接物点に合焦するようにしたことを特徴とするズームレンズ。
【００６５】
（５）特許請求の範囲の請求項１、２、３、４又は５あるいは前記の（１）、（２）、（３）又は（４）の項に記載するレンズ系で、変倍比が２．８から６．９であることを特徴とするズームレンズ。
【００６６】
【発明の効果】
本発明によれば、少ないレンズ枚数で、フォーカシングも含め良好な光学性能で小型で低コストなカムコーダーやデジタルカメラ等に適したズームレンズを実現し得る。
【図面の簡単な説明】
【図１】本発明の実施例１の断面図
【図２】本発明の実施例２の断面図
【図３】本発明の実施例３の断面図
【図４】本発明の実施例４の断面図
【図５】本発明の実施例１の広角端における収差曲線図
【図６】本発明の実施例２の望遠端における収差曲線図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens, and more particularly to a zoom lens used in a camera using an electronic image sensor such as a camcorder or a digital camera.
[0002]
[Prior art]
Among conventional zoom lens examples in the above-mentioned fields, conventional small zoom lenses for consumer use are disclosed in JP-A-3-200113, JP-A-6-94997, and JP-A-6-194572. As described, in order from the object side, a first lens unit having a positive refractive power and fixed at the time of zooming, and an image from the object side having a negative refractive power from the wide-angle end to the telephoto end at the time of zooming. A second lens group that moves to the side, a third lens group that has positive refractive power, moves from the image side to the object side from the wide-angle end to the telephoto end at the time of zooming, and assists the zooming function slightly, and positive refraction This is a lens system that includes a fourth lens unit that has power and is movable during zooming.
[0003]
These conventional examples have a zoom ratio of about 5 to 12.
[0004]
Further, as a conventional example having a zoom ratio of about 3 by strengthening the zooming action of the third lens unit with the zoom lens having the above configuration, JP-A-10-62687, JP-A-11-119100, JP-A-11-258507. The lens system described in each publication of No. is known.
[0005]
[Problems to be solved by the invention]
Among the conventional examples, a zoom lens having a zoom ratio of about 10 is insufficient in terms of downsizing because the zooming action of the second lens group is strong.
[0006]
Further, the zoom lens of the conventional example having a zoom ratio of about 5 cannot be said to be a sufficiently small configuration with a small number of lenses in consideration of focusing.
[0007]
Also, the zoom lens having a zoom ratio of about 3 in the conventional example has an insufficient zoom ratio, and if a lens system having a zoom ratio exceeding this is attempted, the performance deteriorates, especially during focusing. The performance degradation is large.
[0008]
The present invention has good optical performance including focusing and good manufacturability, and is suitable for a camera using electronic imaging means such as a camcorder or a digital camera configured with a small number of lenses. The present invention provides a zoom lens that is a small and low-cost zoom lens, and particularly has a zoom ratio of around 5.
[0009]
[Means for Solving the Problems]
The zoom lens of the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens having a positive refractive power. The zoom lens system is configured to perform zooming by changing the interval between the lens groups, and during any air interval between the lens groups, that is, between the first lens group and the second lens group, the second lens group. And a third lens group, and an aperture stop is disposed in any one of the air gaps between the third lens group and the fourth lens group, and the first lens group during zooming from the wide-angle end to the telephoto end And the aperture stop are fixed, the second lens group always moves to the image side on the optical axis, the third lens group always moves to the object side on the optical axis, and the fourth lens group on the optical axis. The movement amount of the third lens group and the fourth lens group satisfies the following condition (1).
(1) 0 ≦ t4 / t3 <0.2
However, t3 and t4 are absolute values of the movement amounts of the third lens group and the fourth lens group at the wide-angle end and the telephoto end, respectively.
[0010]
In general, in a zoom lens having a high zoom ratio, only the second lens group is subjected to a zooming action, and the image plane position is corrected by the fourth lens group.
[0011]
The present invention reduces the size of the lens system by causing the third lens group to bear a part of the zooming action of the second lens group and a part of the correction of the image plane position by the fourth lens group. The condition for this is the condition (1).
[0012]
If the upper limit of condition (1) is exceeded, the burden of the correction operation of the image plane position by the fourth lens group becomes too great, and the movement amount during zooming of the fourth lens group (movement amount for correcting the image plane position) Becomes large, and the lens system cannot be made sufficiently small. Further, when focusing is performed by the fourth lens group, if the amount of movement of the fourth lens group at the time of zooming is large as described above, the aberration fluctuation at the time of focusing becomes large, and also for focusing. The mechanism becomes complicated. Further, since the second and third lens groups move monotonously at the time of zooming, it is easy to make a cam for zooming, and satisfying the condition (1) allows the fourth lens group to function as described above. Since the amount of movement can be reduced, the control with the motor during zooming and focusing is short and the mechanical space can be reduced.
[0013]
In the condition (1), the lower limit cannot be exceeded.
Furthermore, it is more preferable that the upper limit value of the condition (1) is 0.15.
Further, when the lower limit value of the condition (1) is set to 0.005, the movement amount balance of each lens group is improved.
[0014]
In the zoom lens having the first configuration according to the present invention, the fourth lens group having a positive refractive power is made up of a negative cemented lens in which a biconcave negative lens and a positive lens are cemented in this order from the object side, and two groups of two lenses of a positive lens. A configuration is preferable.
[0015]
In this way, by forming the fourth lens group in the two-group three-lens configuration as described above, the amount of aberration generated in the fourth lens group when a part of the zooming action of the third lens group is borne is reduced. Also, in order to correct various aberrations satisfactorily while reducing the amount of movement of the fourth lens group, one negative lens and two positive lenses are required, of which the negative lens and positive lens on the object side are By joining, adverse effects on the performance of the lens system due to manufacturing errors can be reduced, and aberration fluctuations due to focusing can also be reduced.
[0016]
For the above reasons, it is desirable that the fourth lens group has a two-group three-lens configuration including a cemented lens of a biconcave lens, a positive lens, and a positive lens as described above.
[0017]
In the zoom lens according to the present invention, it is desirable that the following condition (2) is satisfied when the fourth lens group has the two-group three-lens structure as described above.
(2) 0.24 <| f4n / f4 | <0.33
Here, f4n is the focal length of the biconcave lens in the fourth lens group alone, and f4 is the focal length of the fourth lens group.
[0018]
If the upper limit of 0.33 is exceeded in condition (2), the power of the negative lens will be weak and correction of chromatic aberration will be difficult, and if the lower limit of 0.24 of condition (2) is exceeded, the power of the negative lens will be too strong. Occurrence of chromatic aberration and other various aberrations increases.
[0019]
Further, if this condition (2) is satisfied, the aberration fluctuation due to focusing can be reduced.
Furthermore, it is more preferable that the upper limit value of the condition (2) is 0.31.
Further, it is more preferable that the lower limit value of the condition (2) is 0.27.
[0020]
A zoom lens having a second configuration according to the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power; The fourth lens unit has a positive refractive power, and zooming is performed by changing between the lens units, and the aperture stop is between the first and second lens units and between the second and third lens units. The first lens unit and the aperture stop are fixed during zooming from the wide-angle end to the telephoto end, and the first lens unit is fixed between the third lens unit and the fourth lens unit. Four lens groups of the second, third, and fourth lens groups move on the optical axis, and the second lens group always moves to the image side during zooming from the wide-angle end to the telephoto end, and the third lens The group always moves toward the object side. The fourth lens group has a positive lens and a cemented lens in which a biconcave negative lens and a positive lens are bonded in order from the object side. It is more becomes 2 group three-lens structure with's, a lens system satisfying the condition (2).
[0021]
In the zoom lens according to the present invention, as described above, the third lens group is caused to bear a zooming action and an image plane position correcting action. Therefore, in order to correct the generated aberration, one negative lens and two positive lenses are required in the fourth lens group.
[0022]
In the second configuration, the positive fourth lens group is configured in order from the object side, a two-group three-lens configuration including a cemented lens obtained by cementing a biconcave negative lens and a positive lens, and a positive lens. The aberration that occurs is corrected. In addition, by joining the negative lens and the positive lens, the influence on the optical performance due to the manufacturing error is reduced.
[0023]
Further, in this second configuration, the condition (2) is satisfied in order to increase the aberration correction action by the fourth lens group.
[0024]
As described above, if the upper limit of 0.33 of the condition (2) is exceeded, the negative power becomes weak and chromatic aberration cannot be corrected sufficiently satisfactorily. If the lower limit of 0.24 of the condition (2) is exceeded, the power of the negative lens becomes too strong, and chromatic aberration and other various aberrations occur.
[0025]
Further, if this condition (2) is satisfied, aberration fluctuations during focusing can be reduced.
The upper limit of condition (2) may be set to 0.31. The lower limit value may be set to 0.27.
[0026]
In the zoom lenses having the first and second configurations of the present invention, the third lens group includes at least one positive lens and a negative lens that is disposed closest to the image side and has a concave surface facing the image side. The exit pupil can be made far away, which is preferable.
A zoom lens having a third configuration according to the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power; The fourth lens unit has a positive refractive power, and zooming is performed by changing the distance between the lens units, and the brightness stop is between the first and second lens units, and the second and third lens units. Between the third lens group and the fourth lens group, and the first lens group and the aperture stop are fixed during zooming from the wide-angle end to the telephoto end. In the lens system in which the four lens groups of the second, third and fourth lens groups move on the optical axis, the second lens group always moves to the image side at the time of zooming from the wide angle end to the telephoto end, The third lens group always moves toward the object side, and the positive third lens group G3 includes at least one positive lens and one negative lens. The positive fourth lens group is composed of a negative front group and a positive rear group in order from the object side. The negative front group has the most object side surface and the most image side surface convex on the object side. This is a lens system that is formed by a single lens whose positive rear group has a convex surface facing the object side, and satisfies the following condition (3).
(3) 0.3 <| f4 / f41 | <0.6
Here, f41 is the focal length of the front group of the fourth lens group.
[0027]
In the zoom lens according to the present invention, the third lens group is also provided with a zooming action. Therefore, if the third lens group does not include a positive lens and a negative lens, chromatic aberration cannot be corrected.
[0028]
In addition, the fourth lens group is composed of a negative front group with relatively small power and a positive rear group consisting of a positive single lens, thereby suppressing the occurrence of various aberrations, particularly chromatic aberration, over the entire zooming area and over the entire focusing area. Aberration variation can be reduced over a wide range.
[0029]
If the upper limit of 0.6 of the condition (3) is exceeded, the power of the negative front group becomes too strong, and chromatic aberration and various aberrations occur. If the lower limit of 0.3 of the condition (3) is exceeded, the power of the negative front group becomes too weak to correct chromatic aberration.
[0030]
Further, if the negative lens front side of the fourth lens unit is formed so that the most object side surface and the most image side surface are convex on the object side, adverse effects due to manufacturing errors of the fourth lens unit can be reduced. It becomes possible.
Furthermore, it is more preferable that the upper limit value of the condition (3) is 0.53.
Further, it is more preferable that the lower limit value of the condition (3) is 0.38.
[0031]
In the zoom lens having the third configuration according to the present invention, it is desirable to form the negative front group of the fourth lens group with a single meniscus lens, since this can contribute to a reduction in the number of parts of the lens system and a reduction in size. In particular, a negative meniscus single lens can contribute to a reduction in the number of parts.
[0032]
In addition, it is desirable that the meniscus lens of the negative front group be a meniscus cemented lens, since the aberration correction capability in the front group is further improved. In addition, a cemented lens is preferable because adverse effects on the lens system due to manufacturing errors in the front group can be reduced.
[0033]
In the zoom lens having the third configuration according to the present invention, the positive third lens group may include a negative lens having a concave surface facing the image side disposed closest to the image side, and at least one positive lens. desirable.
[0034]
In this way, it is desirable to dispose the negative lens with the concave surface facing the image side closest to the image side of the third lens group because the exit pupil can be made far.
[0035]
In the zoom lens according to the present invention, the third lens group also has a zooming action. Therefore, the zoom lens includes at least one positive lens in addition to the most negative lens on the image side. It is necessary to arrange a lens and a negative lens and correct chromatic aberration in this lens group satisfactorily. As described above, unless the positive lens and the negative lens are arranged, it is difficult to correct the chromatic aberration in the third lens group sufficiently satisfactorily.
[0036]
In this way, in the third configuration, the third lens group includes a negative lens having a concave surface facing the image side disposed closest to the image side, and at least one positive lens in addition to the negative lens. Also in the case of the zoom lens, it is desirable that the front group of the positive fourth lens group is composed of one negative meniscus lens. The meniscus lens may be a meniscus cemented lens. Moreover, you may comprise with one meniscus single lens.
[0037]
In the zoom lens of the present invention, that is, the zoom lens having the first to third configurations described above, it is desirable that focusing be performed by the fourth lens group.
In the zoom lens according to the present invention, it is preferable that the aperture stop be disposed between the second lens group and the third lens group, since both the miniaturization of the entire optical system and the telecentricity toward the image side can be achieved.
The above configuration is suitable for a zoom lens having a zoom ratio of 2.8 to 6.9.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described based on Examples 1 to 4 having the following data with the configuration shown in FIGS. Examples 1 and 4 are reference examples.
Example 1
f = 5.900-10.219-17.551, F number = 2.83-3.68-3.99
2ω = 60.6 ° ~ 21.3 °
r ₁ = 60.780 d ₁ = 1.00 n ₁ = 1.80518 ν ₁ = 25.42
r ₂ = 22.057 d ₂ = 5.46 n ₂ = 1.62280 ν ₂ = 57.05
r ₃ = -931.750 d ₃ = 0.20
r ₄ = 25.036 d ₄ = 3.16 n ₃ = 1.80610 ν ₃ = 40.92
r ₅ = 100.658 d ₅ = D ₁ (variable)
r ₆ = 83.957 d ₆ = 1.00 n ₄ = 1.80440 ν ₄ = 39.59
r ₇ = 6.667 d ₇ = 3.67
r ₈ = -20.662 d ₈ = 1.00 n ₅ = 1.51633 ν ₅ = 64.14
r ₉ = 8.622 d ₉ = 2.93 n ₆ = 1.80518 ν ₆ = 25.42
r ₁₀ = 60.380 d ₁₀ = D ₂ (variable)
r ₁₁ = ∞ (aperture) d ₁₁ = D ₃ (variable)
r ₁₂ = 11.405 d ₁₂ = 2.95 n ₇ = 1.69350 ν ₇ = 53.24
r ₁₃ = -23.743 (aspherical surface) d ₁₃ = 0.22
r ₁₄ = 7.908 d ₁₄ = 2.62 n ₈ = 1.69100 ν ₈ = 54.82
r ₁₅ = 40.704 d ₁₅ = 1.01 n ₉ = 1.84666 ν ₉ = 23.78
r ₁₆ = 5.180 d ₁₆ = D ₄ (variable)
r ₁₇ = 32.444 d ₁₇ = 1.00 n ₁₀ = 1.80440 ν ₁₀ = 39.59
r ₁₈ = 8.384 d ₁₈ = 2.32 n ₁₁ = 1.49700 ν ₁₁ = 81.54
r ₁₉ = 32.662 d ₁₉ = 0.76
r ₂₀ = 11.234 d ₂₀ = 2.82 n ₁₂ = 1.65844 ν ₁₂ = 50.88
r ₂₁ = -20.977 d ₂₁ = D ₅ (variable)
r ₂₂ = ∞ d ₂₂ = 3.40 n ₁₃ = 1.51633 ν ₁₃ = 64.14
r ₂₃ = ∞ d ₂₃ = 1.00
r ₂₄ = ∞ (imaging surface)
Aspheric coefficient (13th surface) K = -4.537, A ₄ = 1.12339 × 10 ⁻⁴ , A ₆ = 8.46541 × 10 ⁻⁶
A ₈ = -6.78805 × 10 ⁻⁷ , A ₁₀ = 2.00622 × 10 ⁻⁸
f 5.900 10.219 17.551
D ₁ 1.03 4.60 9.50
D ₂ 14.42 10.85 5.95
D ₃ 5.76 2.45 0.43
D ₄ 3.06 6.43 6.17
D ₅ 1.25 1.19 3.45
t3 = 5.306, t4 = 2.203, t4 / t3 = 2.203 / 5.306 = 0.415
f4 = 15.686, f41 = −37.535
| F4 / f41 | = | 15.686 / -37.535 | = 0.418, zoom ratio 2.97
Pixel pitch of image sensor 3.2 μm to 4.2 μm
[0039]

[0040]

[0041]

Where r ₁ , r ₂ ,... Are the radius of curvature of each lens surface, d ₁ , d ₂ ,... Are the thickness and air spacing of each lens, and n ₁ , n ₂ ,. Refractive index, ν ₁ , ν ₂ ,... Is the Abbe number of each lens.
[0042]
In the first embodiment, the first lens group G1 having a positive refractive power, the second lens group G2 having a negative refractive power, and the third lens group G3 having a positive refractive power are configured as shown in FIG. The fourth lens group G4 has a positive refractive power, and the aperture stop S is disposed between the second lens group G2 and the third lens group G3.
[0043]
The first lens group G1 and the stop S are fixed during zooming, and the second lens group G2 moves from the object side to the image side during zooming from the wide-angle end to the telephoto end, and the third lens group G3 Moving from the image side to the object side, the fourth lens group G4 moves on the optical axis as shown in FIG.
[0044]
In the lens system of Example 1, the first lens group G1 includes a positive cemented lens and a positive lens, and the second lens group G2 includes a negative lens and a negative cemented lens.
[0045]
The third lens group G3 is composed of a positive lens and a cemented negative lens composed of a positive lens and a negative lens, and the fourth lens group G4 is composed of two groups consisting of a negative cemented lens and a positive lens.
[0046]
This embodiment is a zoom lens having a third configuration, and the fourth lens group is composed of a negative front group G41 and a positive rear group G42, and the negative front group G41 is the most object-side surface (r ₁₇ ) and the most image. The side surface (r ₁₉ ) is composed of a meniscus cemented lens convex on the object side, and the positive rear group G42 is composed of one positive lens.
[0047]
This Example 1 satisfies the condition (3).
[0048]
The second embodiment has a configuration as shown in FIG. 2, and the first lens group G1 and the second lens group G2 have the same lens configuration as that of the first embodiment, but the third lens group G3 has a positive lens and a negative lens. The fourth lens group G4 is different from the first embodiment in that the fourth lens group G4 has a two-group three-lens configuration including a cemented lens of a biconcave negative lens, a positive lens, and a positive lens.
[0049]
This Example 2 satisfies the conditions (1) and (2).
[0050]
The third embodiment is a zoom lens having a configuration as shown in FIG. 3 and a lens system having a configuration similar to that of the second embodiment.
[0051]
This Example 3 also satisfies the conditions (1) and (2).
[0052]
These Examples 2 and 3 are zoom lenses having the first and second configurations.
[0053]
The fourth embodiment has the configuration shown in FIG. 4, and the first lens group G1 and the second lens group G2 have a configuration similar to that of the other embodiments. The third lens group G3 is composed of two positive lenses and one negative lens, and the fourth lens group G4 is composed of a negative lens and a positive lens.
[0054]
That is, Example 4 is a lens system having the first and third configurations, and the third lens group G3 includes at least one positive lens and one negative lens, and the fourth lens group G4 is negative. The front group G41 and the positive rear group G42, and the negative front group G41 is a meniscus single lens with the most object-side and most image-side surfaces convex toward the object side, and the positive rear group G42 from the positive lens Become.
[0055]
This Example 4 satisfies the conditions (1) and (3).
[0056]
The shape of the aspherical surface used in each of the above embodiments is represented by the following equation, where the x-axis is the direction in which light travels on the optical axis and the y-axis is the direction orthogonal to the optical axis.

Here, r is the radius of curvature of the reference sphere, k is the conic coefficient, and A ₄ , A ₆ , A ₈ , and A ₁₀ are aspheric coefficients.
[0057]
Moreover, in FIGS. 1-4 which show sectional drawing of each Example, the upper stage is a wide angle end, the middle stage is an intermediate | middle focal distance, and the lower stage is a figure in a telephoto end. In the figure, F is a low-pass filter or a filter for limiting an unnecessary wavelength region.
[0058]
FIG. 5 is an aberration diagram of Example 1, and various aberrations are corrected favorably as shown in FIG.
[0059]
In the other Examples 2 to 4, various aberrations are satisfactorily corrected in the same aberration situation as in Example 1.
[0060]
The zoom lens of the present invention is configured as described above, and in addition to the lens system described in the claims, the lens system configured as described in each of the following items can also achieve the object of the present invention.
[0061]
(1) A zoom lens system according to claim 5, wherein the front group of the fourth lens group is a meniscus single lens having negative refractive power.
[0062]
(2) A lens system according to claim 5, wherein the front group of the fourth lens group is a meniscus cemented lens having negative refractive power.
[0063]
(3) In the lens system according to

claim

1, 2, 3, 4 or 5 or (1) or (2), the third lens group includes at least one positive lens. A zoom lens comprising: a negative lens disposed closest to the image side and having a concave surface facing the image side.
[0064]
(4) In the lens system according to

claim

1, 2, 3, 4 or 5 of the claims or the item (1), (2) or (3), the fourth lens group is on the optical axis. A zoom lens characterized by focusing on a nearby object point by moving the lens.
[0065]
(5) In the lens system according to

claim

1, 2, 3, 4 or 5 of the claims or the above-mentioned item (1), (2), (3) or (4), the zoom ratio is A zoom lens characterized by being from 2.8 to 6.9.
[0066]
【The invention's effect】
According to the present invention, it is possible to realize a zoom lens suitable for a camcorder, a digital camera, and the like with a small number of lenses, good optical performance including focusing, and a small size and low cost.
[Brief description of the drawings]
1 is a cross-sectional view of a first embodiment of the present invention. FIG. 2 is a cross-sectional view of a second embodiment of the present invention. FIG. 3 is a cross-sectional view of a third embodiment of the present invention. FIG. 5 is an aberration curve diagram at the wide-angle end of Example 1 of the present invention. FIG. 6 is an aberration curve diagram at the telephoto end of Example 2 of the present invention.

Claims

In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens having a positive refractive power This is a lens system in which the magnification is changed by changing the distance between each lens group, and an aperture stop is placed in one of the air intervals between each lens group. From the wide-angle end to the telephoto end. During zooming, the first lens group and the aperture stop are fixed, the second lens group always moves on the optical axis from the object side to the image side, and the third lens group always images on the optical axis. The fourth lens group moves on the optical axis from the lens side to the object side, and the fourth lens group is a cemented lens having negative refractive power, which is composed of a biconcave negative lens and a positive lens in order from the object side. And a positive lens, a zoom lens that satisfies the following conditions (1) and (2) .
(1) 0 ≦ t4 / t3 <0.2
(2) 0.24 <| f4n / f4 | <0.33
Where t3 and t4 are the absolute values of the movement amounts of the third lens group and the fourth lens group at the wide-angle end and the telephoto end , f4 is the focal length of the fourth lens group, and f4n is both the cemented lenses of the fourth lens group. This is the focal length of a single concave lens .

2. The zoom lens according to claim 1, wherein the third lens group includes at least one positive lens and a negative lens disposed closest to the image side and having a concave surface facing the image side.

3. The zoom lens according to claim 1, wherein the fourth lens group is focused on an adjacent object point by moving on the optical axis. 4.

At least any one of the zoom lens according to claim 1 to 3 zoom ratio, characterized in that 6.9 to 2.8.