JP4511089B2 - Zoom lens and electronic imaging apparatus having the same - Google Patents

Description

【０１１７】

【０１１８】

【０１１９】

【０１２０】

【０１２１】

【０１２２】

【０１２３】

【０１２４】

【０１２５】

【０１２６】
以上の実施例１の無限遠物点合焦時及び被写体距離１０ｃｍ合焦時の収差図をそれぞれ図１１、図１２に示す。これらの収差図において、（ａ）は広角端、（ｂ）は中間状態、（ｃ）は望遠端における球面収差ＳＡ、非点収差ＡＳ、歪曲収差ＤＴ、倍率色収差ＣＣを示す。図中、“ＦＩＹ”は像高を表す。
【０１２７】
なお、上記実施例中で開示した非球面について、その面の偏倚量の基準となる基準球面の曲率半径ｒはその面のｒ_a （ａは面番号）として示してある。
【０１２８】
次に、上記各実施例における条件（１）〜（５）、（７）〜（１７）の値、条件（６）に関するAsp21F、Asp2R 及びＬの値を示す。

【０１２９】
なお、実施例１〜１０のローパスフィルターＬＦの総厚ｔ_LPF は何れも１．５００（ｍｍ）で３枚重ねで構成している。もちろん、上述の実施例は、例えばローパスフィルターＬＦを１枚で構成する等、前記した構成の範囲内で種々変更可能である。
【０１３０】
ここで、有効撮像面の対角長Ｌと画素間隔ａについて説明しておく。図１４は、撮像素子の画素配列の１例を示す図であり、画素間隔ａでＲ（赤）、Ｇ（緑）、Ｂ（青）の画素あるいはシアン、マゼンダ、イエロー、グリーン（緑）の４色の画素（図１４）がモザイク状に配されている。有効撮像面は撮影した映像の再生（パソコン上での表示、プリンターによる印刷等）に用いる撮像素子上の光電変換面内における領域を意味する。図中に示す有効撮像面は、光学系の性能（光学系の性能が確保し得るイメージサークル）に合わせて、撮像素子の全光電変換面よりも狭い領域に設定されている。有効撮像面の対角長Ｌは、この有効撮像面の対角長である。なお、映像の再生に用いる撮像範囲を種々変更可能としてよいが、そのような機能を有する撮像装置に本発明のズームレンズを用いる際は、その有効撮像面の対角長Ｌが変化する。そのような場合は、本発明における有効撮像面の対角長Ｌは、Ｌのとり得る範囲における最大値とする。
【０１３１】
また、赤外カット手段については、赤外カット吸収フィルターＩＦと赤外シャープカットコートとがあり、赤外カット吸収フィルターＩＦはガラス中に赤外吸収体が含有される場合で、赤外シャープカットコートは吸収でなく反射によるカットである。したがって、前記したように、この赤外カット吸収フィルターＩＦを除去して、ローパスフィルターＬＦに直接赤外シャープカットコートを施してもよいし、ダミー透明平板上に施してもよい。
【０１３２】
この場合の近赤外シャープカットコートは、波長６００ｎｍでの透過率が８０％以上、波長７００ｎｍでの透過率が１０％以下となるように構成することが望ましい。具体的には、例えば次のような２７層の層構成からなる多層膜である。ただし、設計波長は７８０ｎｍである。
【０１３３】

【０１３４】
上記の近赤外シャープカットコートの透過率特性は図１５に示す通りである。
【０１３５】
また、ローパスフィルターＬＦの射出面側には、図１６に示すような短波長域の色の透過を低滅する色フィルターを設けるか若しくはコーティングを行うことで、より一層電子画像の色再現性を高めている。
【０１３６】
具体的には、このフィルター若しくはコーティングにより、波長４００ｎｍ〜７００ｎｍで透過率が最も高い波長の透過率に対する４２０ｎｍの波長の透過率の比が１５％以上であり、その最も高い波長の透過率に対する４００ｎｍの波長の透過率の比が６％以下であることが好ましい。
【０１３７】
それにより、人間の目の色に対する認識と、撮像及び再生される画像の色とのずれを低減させることができる。言い換えると、人間の視覚では認識され難い短波長側の色が、人間の目で容易に認識されることによる画像の劣化を防止することができる。
【０１３８】
上記の４００ｎｍの波長の透過率の比が６％を越えると、人間の目では認識され難い単波長城が認識し得る波長に再生されてしまい、逆に、上記の４２０ｎｍの波長の透過率の比が１５％よりも小さいと、人間の認識し得る波長城の再生が低くなり、色のバランスが悪くなる。
【０１３９】
このような波長を制限する手段は、補色モザイクフィルターを用いた撮像系においてより効果を奏するものである。
【０１４０】
上記各実施例では、図１６に示すように、波長４００ｎｍにおける透過率を０％、４２０ｎｍにおける透過率を９０％、４４０ｎｍにて透過率のピーク１００％となるコーティングとしている。
【０１４１】
前記した近赤外シャープカットコートとの作用の掛け合わせにより、波長４５０ｎｍの透過率９９％をピークとして、４００ｎｍにおける透過率を０％、４２０ｎｍにおける透過率を８０％、６００ｎｍにおける透過率を８２％、７００ｎｍにおける透過率を２％としている。それにより、より忠実な色再現を行っている。
【０１４２】
また、ローパスフィルターＬＦは、像面上投影時の方位角度が水平（＝０°）と±４５°方向にそれぞれ結晶軸を有する３種類のフィルターを光軸方向に重ねて使用しており、それぞれについて、水平にａμｍ、±４５°方向にそれぞれSQRT(1/2) ×ａだけずらすことで、モアレ抑制を行っている。ここで、ＳＱＲＴは前記のようにスクエアルートであり平方根を意味する。
【０１４３】
また、ＣＣＤの撮像面Ｉ上には、図１７に示す通り、シアン、マゼンダ、イエロー、グリーン（緑）の４色の色フィルターを撮像画素に対応してモザイク状に設けた補色モザイクフィルターを設けている。これら４種類の色フィルターは、それぞれが略同じ数になるように、かつ、隣り合う画素が同じ種類の色フィルターに対応しないようにモザイク状に配置されている。それにより、より忠実な色再現が可能となる。
【０１４４】
補色モザイクフィルターは、具体的には、図１７に示すように少なくとも４種類の色フィルターから構成され、その４種類の色フィルターの特性は以下の通りであることが好ましい。
【０１４５】
グリーンの色フイルターＧは波長Ｇ_P に分光強度のピークを有し、
イエローの色フィルターＹ_e は波長Ｙ_P に分光強度のピークを有し、
シアンの色フィルターＣは波長Ｃ_P に分光強度のピークを有し、
マゼンダの色フィルターＭは波長Ｍ_P1とＭ_P2にピークを有し、以下の条件を満足する。
【０１４６】
５１０ｎｍ＜Ｇ_P ＜５４０ｎｍ
５ｎｍ＜Ｙ_P −Ｇ_P ＜３５ｎｍ
−１００ｎｍ＜Ｃ_P −Ｇ_P ＜−５ｎｍ
４３０ｎｍ＜Ｍ_P1＜４８０ｎｍ
５８０ｎｍ＜Ｍ_P2＜６４０ｎｍ
さらに、グリーン、イエロー、シアンの色フィルターはそれぞれの分光強度のピークに対して波長５３０ｎｍでは８０％以上の強度を有し、マゼンダの色フィルターはその分光強度のピークに対して波長５３０ｎｍでは１０％から５０％の強度を有することが、色再現性を高める上でより好ましい。
【０１４７】
上記各実施例におけるそれぞれの波長特性の一例を図１８に示す。グリーンの色フィルターＧは５２５ｎｍに分光強度のビークを有している。イエローの色フィルターＹ_e は５５５ｎｍに分光強度のピークを有している。シアンの色フイルターＣは５１０ｎｍに分光強度のピークを有している。マゼンダの色フィルターＭは４４５ｎｍと６２０ｎｍにピークを有している。また、５３０ｎｍにおける各色フィルターは、それぞれの分光強度のピークに対して、Ｇは９９％、Ｙ_e は９５％、Ｃは９７％、Ｍは３８％としている。
【０１４８】
このような補色フイルターの場合、図示しないコントローラー（若しくは、デジタルカメラに用いられるコントローラー）で、電気的に次のような信号処理を行い、
輝度信号
Ｙ＝｜Ｇ＋Ｍ＋Ｙ_e ＋Ｃ｜×１／４
色信号
Ｒ−Ｙ＝｜（Ｍ＋Ｙ_e ）−（Ｇ＋Ｃ）｜
Ｂ−Ｙ＝｜（Ｍ＋Ｃ）−（Ｇ＋Ｙ_e ）｜
の信号処理を経てＲ（赤）、Ｇ（緑）、Ｂ（青）の信号に変換される。
【０１４９】
ところで、上記した近赤外シャープカットコートの配置位置は、光路上のどの位置であってもよい。また、ローパスフィルターＬＦの枚数も前記した通り２枚でも１枚でも構わない。
【０１５０】
さて、以上のような本発明の電子撮像装置は、ズームレンズで物体像を形成しその像をＣＣＤ等の電子撮像素子に受光させて撮影を行う撮影装置、とりわけデジタルカメラやビデオカメラ、情報処理装置の例であるパソコン、電話、特に持ち運びに便利な携帯電話等に用いることができる。以下に、その実施形態を例示する。
【０１５１】
図１９〜図２１は、本発明によるズームレンズをデジタルカメラの撮影光学系４１に組み込んだ構成の概念図を示す。図１９はデジタルカメラ４０の外観を示す前方斜視図、図２０は同後方斜視図、図２１はデジタルカメラ４０の構成を示す断面図である。デジタルカメラ４０は、この例の場合、撮影用光路４２を有する撮影光学系４１、ファインダー用光路４４を有するファインダー光学系４３、シャッター４５、フラッシュ４６、液晶表示モニター４７等を含み、カメラ４０の上部に配置されたシャッター４５を押圧すると、それに連動して撮影光学系４１、例えば実施例１のズームレンズを通して撮影が行われる。撮影光学系４１によって形成された物体像が、近赤外カットコートをダミー透明平板上に施してなる赤外カット吸収フィルターＩＦ、光学的ローパスフィルターＬＦを介してＣＣＤ４９の撮像面上に形成される。このＣＣＤ４９で受光された物体像は、処理手段５１を介し、電子画像としてカメラ背面に設けられた液晶表示モニター４７に表示される。また、この処理手段５１には記録手段５２が接続され、撮影された電子画像を記録することもできる。なお、この記録手段５２は処理手段５１と別体に設けてもよいし、フロッピーディスクやメモリーカード、ＭＯ等により電子的に記録書込を行うように構成してもよい。また、ＣＣＤ４９に代わって銀塩フィルムを配置した銀塩カメラとして構成してもよい。
【０１５２】
さらに、ファインダー用光路４４上にはファインダー用対物光学系５３が配置してある。このファインダー用対物光学系５３によって形成された物体像は、像正立部材であるポロプリズム５５の視野枠５７上に形成される。このポリプリズム５５の後方には、正立正像にされた像を観察者眼球Ｅに導く接眼光学系５９が配置されている。なお、撮影光学系４１及びファインダー用対物光学系５３の入射側、接眼光学系５９の射出側にそれぞれカバー部材５０が配置されている。
【０１５３】
このように構成されたデジタルカメラ４０は、撮影光学系４１が広画角で高変倍比であり、収差が良好で、明るく、フィルター等が配置できるバックフォーカスの大きなズームレンズであるので、高性能・低コスト化が実現できる。
【０１５４】
なお、図２１の例では、カバー部材５０として平行平面板を配置しているが、パワーを持ったレンズを用いてもよい。
【０１５５】
以上の本発明のズームレンズ及びそれを有する電子撮像装置は例えば次のように構成することができる。
【０１５６】
〔１〕 物体側より順に、負の屈折力を有する第１レンズ群と、正の屈折力を有する第２レンズ群と、正の屈折力を有する第３レンズ群よりなり、無限遠物点合焦時における広角端から望遠端への変倍に際して、前記第２レンズ群が物体側へのみ移動し、前記第３レンズ群が第２レンズ群との間隔を変化させつつ移動し、前記第２レンズ群は、物体側から順に、正レンズＬ２１、負レンズＬ２２、正レンズＬ２３、負レンズＬ２４にて構成され、前記第２レンズ群中の正レンズＬ２３又は負レンズＬ２４の少なくとも何れかのレンズは非球面を有し、かつ、以下の条件（１）を満足することを特徴とするズームレンズ。
【０１５７】
（１） ０．６＜Ｒ_22R ／Ｒ_21F ＜２．２
ただし、Ｒ_21F 、Ｒ_22R はそれぞれ第２レンズ群の正レンズＬ２１の物体側の面、第２レンズ群の負レンズＬ２２の像側の面の光軸上の曲率半径である。
【０１５８】
〔２〕 像側に配される電子撮像素子と一体化されたことを特徴とする上記１記載ズームレンズ。
【０１５９】
〔３〕 電子撮像素子の撮像面側に配されるズームレンズにおいて、
前記ズームレンズは、物体側より順に、負の屈折力を有する第１レンズ群と、正の屈折力を有する第２レンズ群と、正の屈折力を有する第３レンズ群よりなり、無限遠物点合焦時における広角端から望遠端への変倍に際して、前記第２レンズ群が物体側へのみ移動し、前記第３レンズ群が第２レンズ群との間隔を変化させつつ移動し、前記第２レンズ群は、物体側から順に、正レンズＬ２１、負レンズＬ２２、正レンズＬ２３、負レンズＬ２４にて構成され、前記第２レンズ群中の正レンズＬ２３又は負レンズＬ２４の少なくとも何れかのレンズは非球面を有し、かつ、以下の条件（２）、（３）、（４）を満足することを特徴とするズームレンズ。
【０１６０】
（２） ０＜（Ｃ_24F −Ｃ_23R ）・Ｌ＜１．６
（３） ０．０１＜ｄ₂₃／Ｌ＜０．２
（４） −０．４＜Ｌ／ｆ_2R＜０．８
ただし、Ｃ_23R ＝１／Ｒ_23R 、Ｃ_24F ＝１／Ｒ_24F であり、ここで、Ｒ_23R 、Ｒ_24F はそれぞれ第２レンズ群の正レンズＬ２３の像側の面、第２レンズ群の負レンズＬ２４の物体側の面の光軸上の曲率半径、Ｌは撮像素子の有効撮像領域（略矩形）の対角長（ｍｍ）、ｄ₂₃は第２レンズ群の正レンズＬ２３と負レンズＬ２４との光軸上の空気間隔、ｆ_2Rは第２レンズ群の正レンズＬ２３と負レンズＬ２４との合成焦点距離である。
【０１６１】
〔４〕 像側に配される電子撮像素子と一体化され、かつ、以下の条件（２）、（３）、（４）を満足することを特徴とする上記１記載のズームレンズ。
【０１６２】
（２） ０＜（Ｃ_24F −Ｃ_23R ）・Ｌ＜１．６
（３） ０．０１＜ｄ₂₃／Ｌ＜０．２
（４） −０．４＜Ｌ／ｆ_2R＜０．８
ただし、Ｃ_23R ＝１／Ｒ_23R 、Ｃ_24F ＝１／Ｒ_24F であり、ここで、Ｒ_23R 、Ｒ_24F はそれぞれ第２レンズ群の正レンズＬ２３の像側の面、第２レンズ群の負レンズＬ２４の物体側の面の光軸上の曲率半径、Ｌは撮像素子の有効撮像領域（略矩形）の対角長（ｍｍ）、ｄ₂₃は第２レンズ群の正レンズＬ２３と負レンズＬ２４との光軸上の空気間隔、ｆ_2Rは第２レンズ群の正レンズＬ２３と負レンズＬ２４との合成焦点距離である。
【０１６３】
〔５〕 前記第２レンズ群の正レンズＬ２１と負レンズＬ２２とが接合されていることを特徴とする上記２から４の何れか１項記載のズームレンズ。
【０１６４】
〔６〕 前記第２レンズ群が以下の条件（５）を満足することを特徴とする上記２から５の何れか１項記載のズームレンズ。
【０１６５】
（５） ２５＜ν₂₁−ν₂₂＋ν₂₃−ν₂₄＜５５
ただし、ν₂₁、ν₂₂、ν₂₃、ν₂₄はそれぞれ第２レンズ群の正レンズＬ２１、負レンズＬ２２、正レンズＬ２３、負レンズＬ２４の媒質のアッベ数（ｄ線基準）である。
【０１６６】
〔７〕 前記第２レンズ群における正レンズＬ２３又は負レンズＬ２４の少なくとも何れかに配された前記非球面の少なくとも何れかが以下の条件（６）を満足することを特徴とする上記２から６の何れか１項記載のズームレンズ。
【０１６７】
（６） ７．５×１０^-3・Ｌ＞｜Asp2R ｜＞｜Asp21F｜
ただし、Asp21F、Asp2R はそれぞれ正レンズＬ２１の物体側の面、正レンズＬ２３又は負レンズＬ２４の面の光軸上での曲率半径を有する球面に対し、光軸からの高さが０．３Ｌでの非球面偏倚量、Ｌは撮像素子の有効撮像領域（略矩形）の対角長（ｍｍ）であり、正レンズＬ２１の物体側面が球面の場合は非球面偏倚量Asp21Fを０とする。
【０１６８】
〔８〕 以下の条件（７）を満足することを特徴とする上記２から７の何れか１項記載のズームレンズ。
【０１６９】
（７） −０．５＜（Ｒ_21F −Ｒ_22R ）／（Ｒ_21F ＋Ｒ_22R ）＜０．３
ただし、Ｒ_21F 、Ｒ_22R はそれぞれ第２レンズ群の正レンズＬ２１の物体側の面と負レンズＬ２２の像側の面の光軸上の曲率半径である。
【０１７０】
〔９〕 以下の条件（８）及び（９）を満足することを特徴とする上記２から８の何れか１項記載のズームレンズ。
【０１７１】
（８） −１＜ｆ₃ ／ｆ_2R＜１．６
（９） ０．０２＜ｄ₂₂／Ｌ＜０．５
ただし、ｆ_2Rとｆ₃ はそれぞれ第２レンズ群の正レンズＬ２３と負レンズＬ２４との合成焦点距離と第３レンズ群の焦点距離、ｄ₂₂は第２レンズ群の負レンズＬ２２の像側面と正レンズＬ２３の物体側面との間隔、Ｌは撮像素子の有効撮像領域（略矩形）の対角長（ｍｍ）である。
【０１７２】
〔１０〕 以下の条件（１０）を満足する上記１乃至９の何れか１項に記載のズームレンズ。
【０１７３】
（10） −１＜ｆ_2F／Ｒ_21R ＜２．５
ただし、Ｒ_21R は第２レンズ群の正レンズＬ２１の像側の面の曲率半径、ｆ_2Fは第２レンズ群の正レンズＬ２１と負レンズＬ２２との合成焦点距離である。
【０１７４】
〔１１〕 広角端から望遠端に変倍する際、前記第３レンズ群は像側に凸の軌跡で移動することを特徴とする上記１から１０の何れか１項記載のズームレンズ。
【０１７５】
〔１２〕 前記第３レンズ群を光軸に沿って移動することにより合焦することを特徴とする上記１から１１の何れか１項記載のズームレンズ。
【０１７６】
〔１３〕 広角端半画角ω_W が２７°から４２°の範囲にあることを特徴とする上記１から１２の何れか１項記載のズームレンズ。
【０１７７】
〔１４〕 上記１から１３の何れか１項記載のズームレンズを備えたことを特徴とする電子撮像装置。
【０１７８】
【発明の効果】
本発明により、沈胴厚が薄く収納性に優れ、かつ、高倍率でリアフォーカスにおいても結像性能の優れたズームレンズを得ることができ、ビデオカメラやデジタルカメラの徹底的薄型化を図ることが可能となる。
【図面の簡単な説明】
【図１】本発明の電子撮像装置に用いられるズームレンズの実施例１の無限遠物点合焦時の広角端（ａ）、中間状態（ｂ）、望遠端（ｃ）でのレンズ断面図である。
【図２】実施例２のズームレンズの図１と同様のレンズ断面図である。
【図３】実施例３のズームレンズの図１と同様のレンズ断面図である。
【図４】実施例４のズームレンズの図１と同様のレンズ断面図である。
【図５】実施例５のズームレンズの図１と同様のレンズ断面図である。
【図６】実施例６のズームレンズの図１と同様のレンズ断面図である。
【図７】実施例７のズームレンズの図１と同様のレンズ断面図である。
【図８】実施例８のズームレンズの図１と同様のレンズ断面図である。
【図９】実施例９のズームレンズの図１と同様のレンズ断面図である。
【図１０】実施例１０のズームレンズの図１と同様のレンズ断面図である。
【図１１】実施例１の無限遠物点合焦時の収差図である。
【図１２】実施例１の被写体距離１０ｃｍ合焦時の収差図である。
【図１３】本発明のおける非球面偏倚量の定義を説明するための図である。
【図１４】電子撮像素子にて撮影を行う場合の有効撮像面の対角長について説明するための図である。
【図１５】近赤外シャープカットコートの一例の透過率特性を示す図である。
【図１６】ローパスフィルターの射出面側に設ける色フィルターの一例の透過率特性を示す図である。
【図１７】補色モザイクフィルターの色フィルター配置を示す図である。
【図１８】補色モザイクフィルターの波長特性の一例を示す図である。
【図１９】本発明によるズームレンズを組み込んだデジタルカメラの外観を示す前方斜視図である。
【図２０】図１９のデジタルカメラの後方斜視図である。
【図２１】図１９のデジタルカメラの断面図である。
【符号の説明】
Ｇ１…第１レンズ群
Ｇ２…第２レンズ群
Ｇ３…第３レンズ群
Ｓ…開口絞り
ＩＦ…赤外カット吸収フィルター
ＬＦ…ローパスフィルター
ＣＧ…カバーガラス
Ｉ…像面
Ｅ…観察者眼球
４０…デジタルカメラ
４１…撮影光学系
４２…撮影用光路
４３…ファインダー光学系
４４…ファインダー用光路
４５…シャッター
４６…フラッシュ
４７…液晶表示モニター
４９…ＣＣＤ
５０…カバー部材
５１…処理手段
５２…記録手段
５３…ファインダー用対物光学系
５５…ポロプリズム
５７…視野枠
５９…接眼光学系[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens and an electronic image pickup apparatus having the same, and more particularly to an electronic image pickup apparatus such as a video camera or a digital camera or a zoom lens that is thinned in the depth direction by devising an optical system part such as a zoom lens. Is. In addition, the zoom lens relates to a lens that enables rear focus.
[0002]
[Prior art]
In recent years, digital cameras (electronic cameras) have attracted attention as next-generation cameras that replace silver salt 35 mm film (commonly known as Leica version) cameras. Furthermore, it has come to have a number of categories in a wide range from a high-function type for business use to a portable popular type.
[0003]
In the present invention, focusing on the category of portable popular type, it is aimed to provide a technology for realizing a video camera and a digital camera with a small depth while ensuring a high image quality. The biggest bottleneck in reducing the depth direction of the camera is the thickness from the most object-side surface to the imaging surface of the optical system, particularly the zoom lens system. Recently, it has become the mainstream to adopt a so-called collapsible lens barrel that protrudes the optical system from the camera body during shooting and stores the optical system in the camera body when carried.
[0004]
However, the thickness when the optical system is retracted varies greatly depending on the lens type and filter used. In particular, in order to set the specifications such as the zoom ratio and F value high, the so-called positive leading zoom lens in which the lens unit closest to the object side has positive refractive power has a large thickness and dead space of each lens element, Even if the lens barrel is retracted, the thickness is not reduced (Japanese Patent Laid-Open No. 11-258507). The negative leading type, especially the zoom lens having 2 to 3 groups, is advantageous in this respect, but it is retracted even when the number of elements in the group is large, the thickness of the element is large, or the most object side lens is a positive lens. However, it does not become thin (Japanese Patent Laid-Open No. 11-52246). As an example of what is currently known and suitable for an electronic image pickup device, has good imaging performance including a zoom ratio, an angle of view, an F value, and the like, and has the possibility of making the collapsible thickness the smallest, JP-A-11 No. 287953, Japanese Patent Laid-Open No. 2000-267209, Japanese Patent Laid-Open No. 2000-275520, and the like.
[0005]
In order to make the first group thinner, it is preferable to make the entrance pupil position shallower. For this purpose, the magnification of the second group is increased. On the other hand, this not only increases the burden on the second group and makes it difficult to reduce the thickness of the second group, but also increases the difficulty of aberration correction and the effect of manufacturing errors. In order to reduce the thickness and size of the image sensor, the image sensor can be made smaller. However, in order to obtain the same number of pixels, it is necessary to reduce the pixel pitch, and the lack of sensitivity must be covered by the optical system. The same is true for diffraction.
[0006]
In order to obtain a camera body with a small depth, it is effective in terms of the layout of the drive system to move the lens at the time of focusing with the so-called rear focus instead of the front group. Then, it becomes necessary to select an optical system with less aberration fluctuation when rear focus is performed.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of such a situation in the prior art, and its purpose is to have a small number of components, a small and simple mechanism layout such as a rear focus method, and a stable high connection from infinity to a short distance. Select a zoom system or zoom configuration with image performance, and further reduce the total lens thickness of each lens element of the zoom lens, or consider the selection of filters, video cameras and digital cameras. The aim is to make the camera thinner.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the zoom lens of the present invention has, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a positive refractive power. The second lens unit is composed of a third lens unit, and the second lens unit is moved only to the object side during zooming from the wide-angle end to the telephoto end during focusing on an object point at infinity, and the third lens unit and the second lens unit The second lens group includes, in order from the object side, a positive lens L21, a negative lens L22, a positive lens L23, and a negative lens L24. The positive lens in the second lens group At least one of L23 and negative lens L24 has an aspheric surface and satisfies the following condition (1).
[0009]
(1) 0.6 <R_22R/ R_21F<2.2
However, R_21F, R_22RAre curvature radii on the optical axis of the object side surface of the positive lens L21 of the second lens group and the image side surface of the negative lens L22 of the second lens group, respectively.
[0010]
In this case, it is desirable to be integrated with an electronic image pickup device arranged on the image side.
[0011]
Further, the zoom lens of the present invention is a zoom lens arranged on the imaging surface side of the electronic imaging element.
The zoom lens includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. When zooming from the wide-angle end to the telephoto end during point focusing, the second lens group moves only to the object side, the third lens group moves while changing the distance from the second lens group, The second lens group includes, in order from the object side, a positive lens L21, a negative lens L22, a positive lens L23, and a negative lens L24, and at least one of the positive lens L23 and the negative lens L24 in the second lens group. The lens has an aspherical surface and satisfies the following conditions (2), (3), and (4).
[0012]
(2) 0 <(C_24F-C_23R) ・ L <1.6
(3) 0.01 <d_{twenty three}/L<0.2
(4) -0.4 <L / f_2R<0.8
However, C_23R= 1 / R_23R, C_24F= 1 / R_24FWhere R_23R, R_24FIs the radius of curvature on the optical axis of the image side surface of the positive lens L23 of the second lens group, the object side surface of the negative lens L24 of the second lens group, and L is the effective imaging area (substantially rectangular) of the image sensor. Diagonal length (mm), d_{twenty three}Is the air space on the optical axis between the positive lens L23 and the negative lens L24 of the second lens group, f_2RIs the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group.
[0013]
The present invention includes an electronic imaging apparatus provided with these zoom lenses.
[0014]
Hereinafter, the reason and effect | action which take the said structure in this invention are demonstrated.
[0015]
In the present invention, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, and an object point at infinity In a zoom lens in which zooming from the wide-angle end to the telephoto end during focusing is performed by monotonous movement of the second lens group toward the object side and movement of a different amount from the second lens group of the third lens group, The two lens groups employ a zoom lens composed of a positive lens L21, a negative lens L22, a positive lens L23, and a negative lens L24 in order from the object side.
[0016]
In the present invention, a lens means a lens composed of a single medium as a unit, and a cemented lens means a lens composed of a plurality of lenses.
[0017]
In the negative-positive two-group zoom that has been often used as a zoom lens for a silver halide film camera for a long time, the magnification of the positive rear group (second lens group) at each focal length is increased in order to reduce the size. For this purpose, one positive lens is added as a third lens group further on the image side of the second lens group, and the distance from the second lens group is changed when zooming from the wide angle end to the telephoto end. The method is well known. Further, the third lens group has a possibility of being used for focusing. Then, when the objective of the present invention is achieved, that is, when the total thickness of the lens unit when retracted is reduced and the third lens group is focused, fluctuations in off-axis aberrations including astigmatism are suppressed. For this reason, it is indispensable to configure the second lens group by adding a positive lens, a negative lens, and at least a positive lens in order from the object side, and a negative lens may be further added to the image side.
[0018]
When focusing with the third lens group, fluctuations in aberrations become a problem, but if an amount of aspherical surface more than necessary enters the third lens group, the first lens group and the second lens group are used to produce the effect. Astigmatism remaining in step 3 is corrected by the third lens group. If the third lens group moves for focusing, the balance is lost, which is not preferable. Therefore, when focusing with the third lens group, astigmatism must be substantially removed over the entire zoom range with the first lens group and the second lens group. Therefore, the third lens group is constituted by a spherical system or a small aspheric amount, and the aperture stop is disposed on the object side of the second lens group. The second lens group includes a positive lens, a negative lens, a positive lens, and a negative lens. It is preferable to configure in the order of lenses. In addition, since the diameter of the front lens is difficult to increase with this type, the aperture stop is integrated with the second lens group (in the embodiment of the present invention described later, it is disposed immediately before the second lens group and integrated with the second lens group). In addition to being simple in terms of mechanism, dead space during retraction is less likely to occur, and the F-number difference between the wide-angle end and the telephoto end is small. In addition, since the positive lens and the negative lens on the object side of the second lens group generate remarkable aberrations due to their relative decentration, they should be cemented lenses. In the case of cementing, it is preferable to cancel the aberration in the cemented lens (positive lens L21, negative lens L22) as much as possible to reduce the decentration sensitivity.
[0019]
Therefore, it is preferable to satisfy the following conditional expression regarding the positive lens 21 and the negative lens L22 of the second lens group.
[0020]
(1) 0.6 <R_22R/ R_21F<2.2
However, R_21F, R_22RAre curvature radii on the optical axis of the object side surface of the positive lens L21 of the second lens group and the image side surface of the negative lens L22 of the second lens group, respectively.
[0021]
Exceeding the upper limit of 2.2 of the condition (1) is advantageous for correcting spherical aberration, coma aberration, and astigmatism of the entire system aberration, but has little effect of reducing the eccentric sensitivity due to the joining. If the lower limit of 0.6 is exceeded, it will be difficult to correct spherical aberration, coma aberration, and astigmatism of the total system aberration.
[0022]
It is better to do the following.
[0023]
(1-1) 1.0 <R_22R/ R_21F<2.0
Furthermore, it is best to do the following.
[0024]
(1-2) 1.4 <R_22R/ R_21F<1.8
Furthermore, it is preferable that the following conditional expression is satisfied with respect to the positive lens L23 and the negative lens L24 of the second lens group.
[0025]
(2) 0 <(C_24F-C_23R) ・ L <1.6
(3) 0.01 <d_{twenty three}/L<0.2
(4) -0.4 <L / f_2R<0.8
However, C_23R= 1 / R_23R, C_24F= 1 / R_24FWhere R_23R, R_24FIs the radius of curvature on the optical axis of the image side surface of the positive lens L23 of the second lens group, the object side surface of the negative lens L24 of the second lens group, and L is the effective imaging area (substantially rectangular) of the image sensor. Diagonal length (mm), d_{twenty three}Is the air space on the optical axis between the positive lens L23 and the negative lens L24 of the second lens group, f_2RIs the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group.
[0026]
If the lower limit of 0 in condition (2) is exceeded, spherical aberration is likely to occur, and if the upper limit of 1.6 is exceeded, astigmatism cannot be corrected even if an aspheric surface is introduced into the first lens group. .
[0027]
An object of the present invention is to effectively use the shape of the adjacent surfaces of both the positive lens L23 and the negative lens L24 of the second lens group for aberration correction without being cemented. When the lower limit of 0.01 of the condition (3) is exceeded, the surface interference between the positive lens L23 and the negative lens L24 tends to reach the effective diameter. If the upper limit of 0.2 is exceeded, the lens diameter tends to increase.
[0028]
When the lower limit of −0.4 in condition (4) is exceeded, the exit pupil position approaches the image plane and shading is likely to occur, and when the positive lens L21 and the negative lens L22 are cemented, the decentering sensitivity is positive. Since it is more convenient to concentrate on the lens L21 and the negative lens L22, it is better to set a positive value if possible. If the upper limit of 0.8 is exceeded, it is difficult to secure a high zoom ratio with a small size.
[0029]
In addition, it is better to set one or more of the conditions (2) to (4) as follows.
[0030]
(2) ′ 0.15 <(C_24F-C_23R) ・ L <1.3
(3) ’0.01 <d_{twenty three}/L<0.15
(4) '-0.3 <L / f_2R<0.5
Furthermore, it is better to set one or more of the conditions (2) to (4) as follows. In particular, it is best to do everything as follows.
[0031]
(2) "0.3 <(C_24F-C_23R) ・ L <1
(3) "0.01 <d_{twenty three}/L<0.1
(4) "-0.2 <L / f_2R<0.2
In addition, the aspherical lens for correcting the aberration includes one lens for correcting distortion, astigmatism, and coma in the first lens group, and two lenses for correcting the aberration in the second lens group. A total of 3 is recommended. Adding more than that will have little effect and only increase costs.
[0032]
In addition, it is preferable that the following conditions be satisfied for axial chromatic aberration and magnification chromatic aberration correction.
[0033]
(5) 25 <ν_{twenty one}−ν_{twenty two}+ Ν_{twenty three}−ν_{twenty four}<55
Where ν_{twenty one}, Ν_{twenty two}, Ν_{twenty three}, Ν_{twenty four}Are respectively the Abbe numbers (d-line reference) of the medium of the positive lens L21, the negative lens L22, the positive lens L23, and the negative lens L24 of the second lens group.
[0034]
If the lower limit value 25 of the condition (5) is exceeded, the longitudinal chromatic aberration and lateral chromatic aberration are likely to be undercorrected, and if the upper limit value 55 is exceeded, these are likely to be overcorrected.
[0035]
It is better to do the following.
[0036]
(5) ’25 <ν_{twenty one}−ν_{twenty two}+ Ν_{twenty three}−ν_{twenty four}<50
Furthermore, it is best to do the following.
[0037]
(5) 30 <ν_{twenty one}−ν_{twenty two}+ Ν_{twenty three}−ν_{twenty four}<50
Next, the following conditions may be satisfied for the aspheric surfaces of the positive lens L23 and the negative lens L24 in the second lens group.
[0038]
(6) 7.5 × 10^-3・ L> | Asp2R | >> | Asp21F |
However, Asp21F and Asp2R have a height of 0.3 L from the optical axis with respect to a spherical surface having a radius of curvature on the optical axis of the object side surface of the positive lens L21, the surface of the positive lens L23 or the negative lens L24, respectively. Is the diagonal length (mm) of the effective imaging area (substantially rectangular) of the image sensor, and the aspherical deviation amount Asp21F is 0 when the object side surface of the positive lens L21 is spherical.
[0039]
That is, as shown in FIG. 13, the amount of aspherical deviation referred to in the present invention is an effective imaging area of the electronic imaging device with respect to a spherical surface (reference spherical surface) having a radius of curvature r on the optical axis of the target aspherical surface. When the diagonal length of L is L, the aspherical deviation amount at a position where the height from the optical axis is 0.3 L is said.
[0040]
As in the condition (6), unless some aspheric surface is introduced into the positive lens L23 or the negative lens L24, spherical aberration, coma aberration, and astigmatism cannot be corrected sufficiently. If the asphericity is less than that of the positive lens L21, correction of coma and astigmatism tends to be insufficient. The upper limit of 7.5 × 10^-3-Exceeding L is not preferable because the decentration sensitivity of the positive lens L23 or the negative lens L24 becomes too large, and the accuracy of parts and assembly becomes severe. The object side surface of the positive lens L21 may be a spherical surface.
[0041]
It is better to do the following.
[0042]
(6) ’5.0 × 10^-3・ L> | Asp2R | >> | Asp21F |
Furthermore, it is best to do the following.
[0043]
(6) ”2.5 × 10^-3・ L> | Asp2R | >> | Asp21F |
As another condition, it is better to satisfy the following.
[0044]
(6-2) | Asp2R |> 3 ・ | Asp21F |
Furthermore, it is best to do the following.
[0045]
(6-3) | Asp2R |> 6 ・ | Asp21F |
Further, if the following condition is further satisfied with respect to the condition (2) system, the spherical aberration can be corrected.
[0046]
(7) -0.5 <(R_21F-R_22R) / (R_21F+ R_22R<0.3
However, R_21F, R_22RAre the curvature radii on the optical axis of the object side surface of the positive lens L21 and the image side surface of the negative lens L22 of the second lens group, respectively. Incidentally, this conditional expression is a reciprocal of a normal shape factor.
[0047]
If the lower limit of −0.5 is exceeded, spherical aberration correction tends to be insufficient, and the lens thickness tends to increase. In addition, the workability of the object side positive lens L21 is also deteriorated. When the upper limit of 0.3 is exceeded, conversely, higher-order spherical aberration occurs or the workability of the deep concave surface on the negative lens side deteriorates.
[0048]
It is better to do the following.
[0049]
(7) '-0.4 <(R_21F-R_22R) / (R_21F+ R_22R<0.2
Furthermore, it is best to do the following.
[0050]
(7) "-0.3 <(R_21F-R_22R) / (R_21F+ R_22R<0.1
Further, with respect to the condition (2) system or the (7) system, it is advantageous with respect to the exit pupil position, that is, shading, if the following condition is satisfied, either (8) or (9).
[0051]
(8) -1 <f_Three/ F_2R<1.6
(9) 0.02 <d_{twenty two}/L<0.5
Where f_2RAnd f_ThreeAre the combined focal length of the positive lens L23 and negative lens L24 of the second lens group, the focal length of the third lens group, d_{twenty two}Is the distance between the image side surface of the negative lens L22 of the second lens group and the object side surface of the positive lens L23, and L is the diagonal length (mm) of the effective imaging region (substantially rectangular) of the imaging device.
[0052]
If the upper limit of 1.6 of condition (8) is exceeded, it is advantageous for the exit pupil position at the wide-angle end, that is, shading, but the amount of change in the exit pupil position when zooming to the telephoto end is large, and at the telephoto end. It is disadvantageous for shading. If the lower limit of −1 is exceeded, the exit pupil at the wide-angle end is too close and shading is likely to occur, and the amount of movement becomes too large when focusing with the third lens group, resulting in a space disadvantage. is there. In addition, since it is necessary to strengthen the positive lens on the image side of the second lens group having a high axial ray height paraxially, the principal point position of the second lens group moves backward, making it difficult to obtain a high magnification. The first lens group tends to be huge.
[0053]
When the lower limit of 0.02 to condition (9) is exceeded, shading tends to occur due to the relationship between astigmatism correction and the exit pupil position at the wide-angle end. If the upper limit of 0.5 is exceeded, the thickness of the second lens group will be thick, and it will be a footstep to reduce the collapsed thickness.
[0054]
It should be noted that the effect of the relative position error between the partial group of the positive lens L21 and the negative lens L22 in the second lens group and the partial group of the positive lens L23 and the negative lens L24 together on performance degradation is small (however, In this case, it is desirable that the amount of aspherical surface of the positive lens L23 be small.) Therefore, a constant interval or a changing interval may be provided larger during zooming or imaging, and the size may be reduced only when retracted. d_{twenty two}It is advantageous to secure the performance of the peripheral portion to make the image larger when imaging.
[0055]
Note that it is better to set one or both of the conditions (8) and (9) as follows.
[0056]
(8) '-0.7 <f_Three/ F_2R<1.0
(9) '0.04 <d_{twenty two}  /L<0.4
Furthermore, it is better to set one or both of the conditions (8) and (9) as follows. In particular, it is best to do both as follows.
[0057]
(8) "-0.4 <f_Three/ F_2R<0.4
(9) "0.06 <d_{twenty two}  /L<0.3
Apart from this, if the following condition is further satisfied with respect to the condition (2) or (5), it is advantageous for downsizing at the time of collapse.
[0058]
(10) -1 <f_2F/ R_21R<2.5
However, R_21RIs the radius of curvature of the image side surface of the positive lens L21 of the second lens group, f_2FIs the combined focal length of the positive lens L21 and the negative lens L22 of the second lens group.
[0059]
If the upper limit of 2.5 of the condition (10) is exceeded, the total thickness of the positive lens L21 and the negative lens L22 of the second lens group can be easily reduced, but it is difficult to correct axial chromatic aberration. Exceeding the lower limit of −1 is advantageous for correcting axial chromatic aberration, but the total thickness of the positive lens L21 and the negative lens L22 of the second lens group must be increased, and the collapsible thickness is decreased. Become a footpad.
[0060]
It is better to do the following.
[0061]
(10) '-0.8 <f_2F/ R_21R<0.8
Furthermore, it is best to do the following.
[0062]
(10) "-0.6 <f_2F/ R_21R<0.5
If the following conditions are further satisfied with respect to the condition (2) system, (7) system, or (10) system, it is advantageous for downsizing at the time of collapse.
[0063]
(11) -0.5 <f₂/ F_2R<1
Where f₂Is the combined focal length of the entire second lens group, f_2RIs the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group.
[0064]
Condition (11) defines the ratio between the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group and the combined focal length of the entire second lens group. If the upper limit of 1 is exceeded, the principal point of the second lens group will be closer to the image side, so the magnification of the second lens group will not be increased, and the amount of movement of the first lens group will be easily increased or increased in size. In this case, a dead space is easily formed behind the second lens group, the entire length is increased, and the lens frame mechanical structure is complicated or enlarged in order to reduce the retractable thickness. Or it cannot be made too thin. If the lower limit of −0.5 is exceeded, it will be difficult to correct astigmatism.
[0065]
It is better to do the following.
[0066]
(11) '-0.4 <f₂/ F_2R<0.7
Furthermore, it is best to do the following.
[0067]
(11) "-0.3 <f₂/ F_2R<0.4
In addition, the third lens group is preferably composed of substantially spherical surfaces for all lens surfaces, but in this case, the following conditions should be satisfied in terms of shape.
[0068]
(12) -1.0 <(R₃₁+ R₃₂) / (R₃₁-R₃₂<1.2
However, R₃₁And R₃₂Are the radii of curvature of the most object side and image side surfaces of the positive lens in the third lens group.
[0069]
When the upper limit of 1.2 of the condition (12) is exceeded, the fluctuation of astigmatism due to the rear focus becomes too large, and even if the astigmatism can be corrected well at the infinite object point, Astigmatism tends to deteriorate. When the lower limit of −1.0 is exceeded, astigmatism fluctuations due to rear focus are small, but it is difficult to correct aberrations for infinite object points.
[0070]
It is better to do the following.
[0071]
(12) '-0.3 <(R₃₁+ R₃₂) / (R₃₁-R₃₂<1.2
Furthermore, it is best to do the following.
[0072]
(12) ”0.0 <(R₃₁+ R₃₂) / (R₃₁-R₃₂<1.0
As described above, there has been provided means for improving the imaging performance while reducing the retractable thickness of the zoom lens unit.
[0073]
Note that the zoom lens of the present invention is advantageous in constructing an electronic imaging device including a wide angle region. In particular, the half angle of view ω in the diagonal direction at the wide-angle end_WIs preferably used for an electronic imaging apparatus that satisfies the following conditions (the wide angle end half angle of view described in each of the examples below is ω)._WIt corresponds to. ).
[0074]
27 ° <ω_W<42 °
If the wide angle end half field angle becomes narrower than the lower limit of 27 ° under this condition, the aberration correction is advantageous, but it is not a practical field angle at the wide angle end. On the other hand, when the upper limit of 42 ° is exceeded, distortion and chromatic aberration of magnification tend to occur, and the number of lenses increases.
[0075]
Next, mention is made of thinning filters. In an electronic imaging apparatus, an infrared absorption filter having a certain thickness is usually inserted closer to the object side than the imaging element so that infrared light does not enter the imaging surface. Consider replacing this with a thin coating. Naturally, it will be thinner, but it has a side effect. The transmittance (τ) at a wavelength of 600 nm is located closer to the object side than the image sensor behind the zoom lens system.₆₀₀) Is 80% or more and transmittance at 700 nm (τ)₇₀₀) Of 8% or less near infrared sharp cut coat, the transmittance in the near infrared region of 700 nm or more is lower than that of the absorption type, and the transmittance on the red side is relatively high. The magenta tendency on the bluish-purple side, which is a defect of a solid-state image pickup device such as a CCD having the above, is alleviated by gain adjustment, and color reproduction similar to that of a solid-state image pickup device such as a CCD having a primary color filter can be obtained.
[0076]
That is,
(13) τ₆₀₀/ Τ₅₅₀≧ 0.8
(14) τ₇₀₀/ Τ₅₅₀≦ 0.08
It is desirable to satisfy. Where τ₅₅₀Is the transmittance at a wavelength of 550 nm.
[0077]
Note that it is better to set one or both of the conditions (13) and (14) as follows.
[0078]
(13) ’τ₆₀₀/ Τ₅₅₀≧ 0.85
(14) ’τ₇₀₀/ Τ₅₅₀≦ 0.05
Furthermore, it is better to set one or both of the conditions (13) and (14) as follows. In particular, it is best to do both as follows.
[0079]
(13) “τ₆₀₀/ Τ₅₅₀≧ 0.9
(14) “τ₇₀₀/ Τ₅₅₀≦ 0.03
Another drawback of a solid-state imaging device such as a CCD is that the sensitivity to the near-ultraviolet wavelength of 550 nm is considerably higher than that of the human eye. This also highlights the color blur at the edge of the image due to chromatic aberration in the near ultraviolet region. In particular, it is fatal to downsize the optical system. Therefore, the transmittance at the wavelength of 400 nm (τ₄₀₀) At 550 nm (τ)₅₅₀) Ratio below 0.08, and transmittance at 440 nm (τ₄₄₀) At 550 nm (τ)₅₅₀) If an absorber or reflector with a ratio of more than 0.4 is inserted in the optical path, the wavelength range required for color reproduction is not lost (while maintaining good color reproduction), and noise such as color bleeding Is considerably reduced.
[0080]
That is,
(15) τ₄₀₀/ Τ₅₅₀≦ 0.08
(16) τ₄₄₀/ Τ₅₅₀≧ 0.4
It is desirable to satisfy.
[0081]
Note that it is better to set one or both of the conditions (15) and (16) as follows.
[0082]
(15) ’τ₄₀₀/ Τ₅₅₀≦ 0.06
(16) ’τ₄₄₀/ Τ₅₅₀≧ 0.5
Furthermore, it is better to set one or both of the conditions (15) and (16) as follows. In particular, it is best to do both as follows.
[0083]
(15) “τ₄₀₀/ Τ₅₅₀≦ 0.04
(16) “τ₄₄₀/ Τ₅₅₀≧ 0.6
These filters are preferably installed between the imaging optical system and the image sensor.
[0084]
On the other hand, in the case of a complementary color filter, because of its high transmitted light energy, it is substantially more sensitive than a CCD with a primary color filter and is advantageous in terms of resolution. It is. The total thickness t of the other optical low-pass filter is also t._LPF(Mm) should satisfy the following conditions.
[0085]
(17) 0.15 <t_LPF/A<0.45
However, a is a horizontal pixel pitch (unit: μm) of the image sensor, and is 5 μm or less.
[0086]
In order to reduce the collapsed thickness, it is effective to make the optical low-pass filter thinner, but in general, the moire suppressing effect is reduced, which is not preferable. On the other hand, as the pixel pitch decreases, the contrast of frequency components above the Nyquist limit decreases due to the influence of diffraction of the imaging lens system, and the phenomenon of the moire suppression effect is allowed to some extent. For example, when three types of filters having crystal axes in the horizontal (= 0 °) and ± 45 ° directions are projected in the direction of the optical axis when projected on the image plane, the effect of suppressing moiré is considerably improved. It has been known. As a specification in which the filter is the thinnest in this case, it is known that the filter is shifted by SQRT (1/2) * a μm horizontally by aμm and ± 45 °. The filter thickness at this time is approximately [1 + 2 * SQRT (1/2)] * a / 5.88 (mm). Here, SQRT is a square route and means a square root. This is a specification in which the contrast is zero at a frequency corresponding to the Nyquist limit. If it is made thinner by several percent to several tens of percent than this, a little frequency contrast corresponding to the Nyquist limit appears, but it can be suppressed by the influence of the diffraction.
[0087]
It is preferable that the condition (17) is satisfied, including the case where the filter specification is other than the above, for example, the case where two sheets are stacked or one sheet is used. If the upper limit of 0.45 is exceeded, the optical low-pass filter is too thick and hinders thinning. When the lower limit of 0.15 is exceeded, moire removal becomes insufficient. However, the condition of a in carrying out this is 5 μm or less.
[0088]
If a is 4 μm or less, it is more susceptible to diffraction.
(17) ’0.13 <t_LPF/A<0.42
It is good.
[0089]
Further, the following may be performed according to the number of low-pass filters superimposed on the horizontal pixel pitch.
[0090]
(17) ”0.3 <t_LPF/A<0.4
However, when 3 sheets are stacked and 4 ≦ a <5 (μm),
0.2 <t_LPF/A<0.28
However, when two sheets are stacked and 4 ≦ a <5 (μm),
0.1 <t_LPF/A<0.16
However, when only one sheet and 4 ≦ a <5 (μm),
0.25 <t_LPF/A<0.37
However, when 3 sheets are stacked and a <4 (μm),
0.16 <t_LPF/A<0.25
However, when two sheets are stacked and a <4 (μm),
0.08 <t_LPF/A<0.14
However, when only one sheet and a <4 (μm).
[0091]
When an electronic image sensor with a small pixel pitch is used, the image quality deteriorates due to the diffraction effect due to narrowing down. Therefore, there are a plurality of apertures having a fixed aperture size, and one of them is any one of the optical paths between the lens surface closest to the image side of the first lens group and the lens surface closest to the object side of the third lens group. An electronic imaging device that can be inserted into and can be exchanged with other apertures to adjust the illuminance of the image plane. Among the plurality of apertures, some of the apertures have transmittance for 550 nm. It is preferable to adjust the amount of light so as to have media that are different and less than 80%. Alternatively, when adjustment is performed so that the amount of light corresponds to the F value such that a (μm) / F number <0.4, the medium having different transmittances for 550 nm and less than 80% in the aperture An electronic imaging device having For example, if the medium is not within the range of the above condition from the open value, or a dummy medium with a transmittance of 550 nm or more is set to 91% or more, and if within the range, the aperture stop diameter is reduced to such an extent that diffraction is affected. It is better to adjust the amount of light with something like an ND filter.
[0092]
Alternatively, the plurality of openings may be arranged such that their diameters are reduced in inverse proportion to the F value, and optical low-pass filters having different frequency characteristics may be placed in the openings instead of the ND filters. Since the diffraction degradation increases as the aperture is narrowed down, the frequency characteristic of the optical low-pass filter is set higher as the aperture diameter decreases.
[0093]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, Examples 1 to 10 of the zoom lens used in the electronic imaging apparatus of the present invention will be described. FIGS. 1 to 10 show lens cross sections at the wide-angle end (a), the intermediate state (b), and the telephoto end (c) when focusing on an object point at infinity in Examples 1 to 10, respectively. In each figure, the first lens group is G1, the diaphragm is S, the second lens group is G2, the third lens group is G3, the infrared cut absorption filter is IF, the low-pass filter is LF, and the CCD is an electronic image sensor. The glass is indicated by CG, and the image plane of the CCD is indicated by I. Instead of the infrared cut absorption filter IF, a transparent flat plate incident surface with a near infrared sharp cut coat may be used, or the low pass filter LF may be directly provided with a near infrared sharp cut coat. .
[0094]
As shown in FIG. 1, the zoom lens according to the first exemplary embodiment includes a negative lens first lens group G1, which includes a biconcave negative lens and a positive meniscus lens convex on the object side, an aperture stop S, and a biconvex positive lens. And a second lens group G2 having a positive refractive power composed of a cemented lens of a biconcave negative lens, a biconvex positive lens, a negative meniscus lens convex on the object side, and a positive refractive power first composed of one biconvex positive lens. Consists of three lens groups G3, and when zooming from the wide-angle end to the telephoto end, the first lens group G1 moves along a concave locus on the object side, and at the telephoto end is positioned closer to the image plane side than the wide-angle end. The second lens group G2 moves together with the aperture stop S toward the object side, and the third lens group G3 moves along a locus convex toward the image plane side. At the telephoto end, the position is closer to the object side than the wide-angle end. . In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0095]
The aspherical surface is used for three surfaces, that is, the image side surface of the biconcave negative lens of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the biconvex positive lens. ing.
[0096]
As shown in FIG. 2, the zoom lens of Embodiment 2 includes a negative lens first lens group G1 including a biconcave negative lens and a biconvex positive lens, an aperture stop S, and a positive meniscus lens convex on the object side. A second lens group G2 having a positive refractive power composed of a cemented lens of a negative meniscus lens convex to the object side, a biconvex positive lens, and a plano-concave negative lens, and a positive refractive power first composed of one biconvex positive lens. The first lens group G1 moves along a concave locus on the object side when zooming from the wide-angle end to the telephoto end. The first lens group G1 moves at a substantially same position at the telephoto end and the wide-angle end. The second lens group G2 moves to the object side integrally with the aperture stop S, and the third lens group G3 moves to the image plane side. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0097]
The aspherical surface is used for three surfaces, that is, the image side surface of the biconcave negative lens of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the biconvex positive lens. ing.
[0098]
As shown in FIG. 3, the zoom lens of Example 3 includes a first lens group G1 having a negative refractive power composed of a biconcave negative lens and a positive meniscus lens convex on the object side, an aperture stop S, and a convex on the object side. A second lens group G2 having a positive refractive power, a biconvex positive lens 1 having a positive meniscus lens, a cemented lens of a negative meniscus lens convex on the object side, a biconvex positive lens, and a negative meniscus lens convex on the object side. The first lens unit G1 is composed of a third lens unit G3 having positive refractive power, and when zooming from the wide-angle end to the telephoto end, the first lens unit G1 moves along a concave locus on the object side, and the telephoto end and the wide-angle end. Then, the second lens group G2 moves to the object side together with the aperture stop S, and the third lens group G3 is fixed. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0099]
The aspherical surface is used for three surfaces, that is, the image side surface of the biconcave negative lens of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the biconvex positive lens. ing.
[0100]
As shown in FIG. 4, the zoom lens according to the fourth exemplary embodiment includes a first lens group G1 having a negative refractive power including two negative meniscus lenses convex on the object side and a biconvex positive lens, an aperture stop S, and an object side. A second lens group G2 having a positive refractive power composed of a cemented lens of a positive convex meniscus lens, a negative meniscus lens convex on the object side, a biconvex positive lens, and a negative meniscus lens convex on the object side; The first lens unit G1 includes a third lens unit G3 having a positive refracting power consisting of a single lens. When zooming from the wide-angle end to the telephoto end, the first lens unit G1 moves along a concave locus on the object side. The second lens group G2 moves to the object side integrally with the aperture stop S, the third lens group G3 moves along a locus convex toward the object side, and moves at the telephoto end. It is located on the object side from the wide angle end. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0101]
The aspherical surfaces are the three surfaces of the object side surface of the negative meniscus lens on the object side of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the biconvex positive lens. It is used.
[0102]
As shown in FIG. 5, the zoom lens of Example 5 includes a first lens group G1 having a negative refracting power composed of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, A second lens group G2 having a positive refractive power composed of a cemented lens of a convex plano positive lens and a plano-concave negative lens, a biconvex positive lens, and a biconcave negative lens, and a third positive refractive power comprising a single biconvex positive lens. When the lens unit G3 is used to change the magnification from the wide-angle end to the telephoto end, the first lens unit G1 moves along a concave locus on the object side, and at the telephoto end is positioned on the image plane side from the wide-angle end. The second lens group G2 moves to the object side integrally with the aperture stop S, and the third lens group G3 moves to the object side. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0103]
The aspherical surfaces are used for three surfaces: the image side surface of the negative meniscus lens of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the biconvex positive lens. Yes.
[0104]
As shown in FIG. 6, the zoom lens of Example 6 includes a first lens group G1 having a negative refractive power that includes a biconcave negative lens and a positive meniscus lens convex on the object side, an aperture stop S, and a biconvex positive lens. And a second lens group G2 having a positive refractive power composed of a cemented lens of a biconcave negative lens, a biconvex positive lens and a biconcave negative lens, and a third lens group G3 having a positive refractive power composed of one biconvex positive lens. When zooming from the wide-angle end to the telephoto end, the first lens group G1 moves along a concave locus on the object side, and at the telephoto end is positioned on the image plane side from the wide-angle end. The group G2 moves together with the aperture stop S toward the object side, and the third lens group G3 moves along a locus that is convex toward the object side, and at the telephoto end is positioned on the image plane side from the wide angle end. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0105]
The aspherical surface is used for three surfaces, that is, the image side surface of the biconcave negative lens of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the biconvex positive lens. ing.
[0106]
As shown in FIG. 7, the zoom lens of Example 7 includes a first lens group G1 having a negative refractive power including a biconcave negative lens and a positive meniscus lens convex on the object side, an aperture stop S, and a biconvex positive lens. And a second lens group G2 having a positive refractive power composed of a cemented lens of a biconcave negative lens, a biconvex positive lens and a biconcave negative lens, and a third lens group G3 having a positive refractive power composed of one biconvex positive lens. When zooming from the wide-angle end to the telephoto end, the first lens group G1 moves along a concave locus on the object side, and at the telephoto end, the position is closer to the object side than the wide-angle end. G2 moves to the object side integrally with the aperture stop S, and the third lens group G3 moves along a locus convex toward the object side, and is at the same position at the telephoto end and the wide-angle end. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0107]
The aspherical surface is used for three surfaces, that is, the image side surface of the biconcave negative lens of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the biconvex positive lens. ing.
[0108]
As shown in FIG. 8, the zoom lens according to the eighth embodiment includes a negative lens first lens group G1, an aperture stop S, and a convex surface facing the object side. The first lens group G1 includes a biconcave negative lens and a positive meniscus lens convex toward the object side. Second lens group G2 having a positive refracting power, a biconvex positive lens composed of a cemented lens of a positive meniscus lens, a negative meniscus lens convex on the object side, a biconvex positive lens, and a negative meniscus lens convex on the image side The first lens unit G1 is composed of a single third lens unit G3 having positive refracting power. When zooming from the wide-angle end to the telephoto end, the first lens unit G1 moves along a concave locus on the object side, and at the telephoto end a wide-angle The second lens group G2 moves to the object side integrally with the aperture stop S, the third lens group G3 moves along a locus convex toward the image plane side, and is wide at the telephoto end. It is located on the image plane side from the edge. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0109]
The aspherical surface is used for three surfaces, that is, the image side surface of the biconcave negative lens of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the biconvex positive lens. ing.
[0110]
As shown in FIG. 9, the zoom lens of Example 9 includes a first lens group G1 having a negative refractive power composed of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, Positive refraction made up of a second lens group G2 having a positive refractive power composed of a cemented lens of a convex plano-positive lens and a plano-concave negative lens, a biconvex positive lens, a negative meniscus lens convex on the object side, and a single biconvex positive lens The first lens unit G1 is composed of a third lens unit G3 having a force, and when zooming from the wide-angle end to the telephoto end, the first lens unit G1 moves in a concave locus on the object side, and at the telephoto end is closer to the image side than the wide-angle end. The second lens group G2 moves to the object side integrally with the aperture stop S, and the third lens group G3 moves to the object side. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0111]
The aspherical surfaces are used for the three surfaces of the negative meniscus lens image surface side of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the image surface side surface of the biconvex positive lens. ing.
[0112]
As shown in FIG. 10, the zoom lens of Example 10 includes a negative lens first lens group G1 having a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, The positive refracting power is composed of a cemented lens composed of a positive meniscus lens convex on the object side and a negative meniscus lens convex on the object side, a positive meniscus lens convex on the image side, and a negative meniscus lens convex on the image side. The first lens unit G1 has a concave locus on the object side when zooming from the wide-angle end to the telephoto end. At the telephoto end, it is positioned closer to the image plane side than the wide-angle end, the second lens group G2 moves to the object side together with the aperture stop S, and the third lens group G3 has a convex locus on the object side. It draws and moves, and at the telephoto end, it is positioned closer to the object side than the wide-angle end. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0113]
The aspherical surface is used for three surfaces, that is, the image side surface of the negative meniscus lens of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the image side surface of the single positive meniscus lens. It has been.
[0114]
In the following, the numerical data of each of the above embodiments is shown._NOIs the F number, WE is the wide angle end, ST is the intermediate state, TE is the telephoto end, r₁, R₂... is the radius of curvature of each lens surface, d₁, D₂... is the distance between each lens surface, n_d1, N_d2... is the refractive index of d-line of each lens, ν_d1, Ν_d2... is the Abbe number of each lens. The aspherical shape is represented by the following formula, where x is an optical axis with the light traveling direction being positive, and y is a direction orthogonal to the optical axis.
[0115]
x = (y²/ R) / [1+ {1- (K + 1) (y / r)²}^1/2]
+ A_Foury^Four+ A₆y⁶+ A₈y⁸+ A_Teny^Ten
Where r is the paraxial radius of curvature, K is the cone coefficient, A_Four, A₆, A₈, A_TenAre the 4th, 6th, 8th and 10th order aspherical coefficients, respectively.
[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126]
FIG. 11 and FIG. 12 show aberration diagrams when focusing on an object point at infinity and focusing on a subject distance of 10 cm in Example 1 above, respectively. In these aberration diagrams, (a) shows the wide-angle end, (b) the intermediate state, and (c) spherical aberration SA, astigmatism AS, distortion DT, and lateral chromatic aberration CC at the telephoto end. In the figure, “FIY” represents the image height.
[0127]
For the aspherical surface disclosed in the above embodiment, the radius of curvature r of the reference sphere serving as a reference for the amount of deviation of the surface is the r of the surface._a(A is a surface number).
[0128]
Next, the values of conditions (1) to (5) and (7) to (17) and the values of Asp21F, Asp2R and L relating to condition (6) in each of the above-described embodiments are shown.

[0129]
The total thickness t of the low-pass filter LF of Examples 1 to 10_LPFEach of them is 1.500 (mm) and is constituted by three layers. Of course, the above-described embodiment can be variously modified within the above-described configuration, for example, a single low-pass filter LF is configured.
[0130]
Here, the diagonal length L of the effective imaging surface and the pixel interval a will be described. FIG. 14 is a diagram illustrating an example of the pixel arrangement of the image sensor, and R (red), G (green), and B (blue) pixels or cyan, magenta, yellow, and green (green) with a pixel interval a. Four color pixels (FIG. 14) are arranged in a mosaic pattern. The effective image pickup surface means a region in the photoelectric conversion surface on the image pickup element used for reproduction (display on a personal computer, printing by a printer, etc.) of a taken image. The effective image pickup surface shown in the figure is set to a region narrower than the entire photoelectric conversion surface of the image pickup device in accordance with the performance of the optical system (image circle that can ensure the performance of the optical system). The diagonal length L of the effective imaging surface is the diagonal length of this effective imaging surface. Note that the imaging range used for video reproduction may be variously changed. However, when the zoom lens of the present invention is used in an imaging apparatus having such a function, the diagonal length L of the effective imaging surface changes. In such a case, the diagonal length L of the effective imaging surface in the present invention is the maximum value in the range that L can take.
[0131]
As for the infrared cut means, there are an infrared cut absorption filter IF and an infrared sharp cut coat, and the infrared cut absorption filter IF is a case where an infrared absorber is contained in the glass. The coat is cut by reflection rather than absorption. Therefore, as described above, the infrared cut absorption filter IF may be removed, and the infrared sharp cut coat may be directly applied to the low-pass filter LF, or may be applied on a dummy transparent flat plate.
[0132]
In this case, the near-infrared sharp cut coat is preferably configured so that the transmittance at a wavelength of 600 nm is 80% or more and the transmittance at a wavelength of 700 nm is 10% or less. Specifically, it is a multilayer film composed of the following 27 layers, for example. However, the design wavelength is 780 nm.
[0133]

[0134]
The transmittance characteristics of the near infrared sharp cut coat are as shown in FIG.
[0135]
Further, the color reproducibility of the electronic image is further improved by providing or coating a color filter for reducing the transmission of colors in the short wavelength region as shown in FIG. 16 on the emission surface side of the low-pass filter LF. ing.
[0136]
Specifically, with this filter or coating, the ratio of the transmittance of the wavelength of 420 nm to the transmittance of the wavelength having the highest transmittance at a wavelength of 400 nm to 700 nm is 15% or more, and 400 nm to the transmittance of the highest wavelength. It is preferable that the ratio of the transmittances of the wavelengths is 6% or less.
[0137]
Thereby, it is possible to reduce the difference between the recognition of the color of the human eye and the color of the image to be captured and reproduced. In other words, it is possible to prevent deterioration of the image due to the human eye easily recognizing a short wavelength color that is difficult to be recognized by human vision.
[0138]
If the ratio of the transmittance at the wavelength of 400 nm exceeds 6%, the single wavelength castle which is difficult to be recognized by the human eye is regenerated to a recognizable wavelength. If the ratio is less than 15%, the reproduction of wavelength castles that can be recognized by humans becomes low, and the color balance becomes poor.
[0139]
Such means for limiting the wavelength is more effective in an imaging system using a complementary color mosaic filter.
[0140]
In each of the above-described embodiments, as shown in FIG. 16, the coating has a transmittance of 0% at a wavelength of 400 nm, a transmittance of 90% at 420 nm, and a transmittance peak of 100% at 440 nm.
[0141]
By multiplying the action with the above-mentioned near infrared sharp cut coat, the transmittance at 400 nm is peaked at 99%, the transmittance at 400 nm is 0%, the transmittance at 420 nm is 80%, and the transmittance at 600 nm is 82%. The transmittance at 700 nm is 2%. As a result, more faithful color reproduction is performed.
[0142]
In addition, the low-pass filter LF uses three types of filters having crystal axes in the horizontal (= 0 °) and ± 45 ° directions when projected on the image plane in the optical axis direction, respectively. In this case, moire suppression is performed by shifting by SQRT (1/2) × a horizontally in the direction of a μm and ± 45 °. Here, SQRT is a square route and means a square root as described above.
[0143]
Also, on the image pickup surface I of the CCD, as shown in FIG. 17, a complementary color mosaic filter is provided in which four color filters of cyan, magenta, yellow, and green are provided in a mosaic pattern corresponding to the image pickup pixels. ing. These four types of color filters are arranged in a mosaic so that each of them has approximately the same number and adjacent pixels do not correspond to the same type of color filter. Thereby, more faithful color reproduction is possible.
[0144]
Specifically, the complementary color mosaic filter is composed of at least four types of color filters as shown in FIG. 17, and the characteristics of the four types of color filters are preferably as follows.
[0145]
Green color filter G has wavelength G_PHas a peak of spectral intensity,
Yellow color filter Y_eIs the wavelength Y_PHas a peak of spectral intensity,
Cyan color filter C has wavelength C_PHas a peak of spectral intensity,
Magenta color filter M has wavelength M_P1And M_P2And satisfy the following conditions.
[0146]
510nm <G_P<540 nm
5nm <Y_P-G_P<35nm
−100 nm <C_P-G_P<-5nm
430 nm <M_P1<480nm
580 nm <M_P2<640nm
Further, the green, yellow, and cyan color filters have an intensity of 80% or more at a wavelength of 530 nm with respect to each spectral intensity peak, and the magenta color filter has an intensity of 10% at a wavelength of 530 nm. From the viewpoint of improving the color reproducibility, it is more preferable that the strength is 50% to 50%.
[0147]
An example of each wavelength characteristic in each of the above embodiments is shown in FIG. The green color filter G has a spectral intensity beak at 525 nm. Yellow color filter Y_eHas a spectral intensity peak at 555 nm. The cyan color filter C has a spectral intensity peak at 510 nm. The magenta color filter M has peaks at 445 nm and 620 nm. Each color filter at 530 nm has a G of 99% and Y_e95%, C 97%, M 38%.
[0148]
In the case of such a complementary color filter, the following signal processing is performed electrically with a controller (not shown) (or a controller used in a digital camera),
Luminance signal
Y = | G + M + Y_e+ C | × 1/4
Color signal
R−Y = | (M + Y_e)-(G + C) |
B−Y = | (M + C) − (G + Y_e) ｜
The signal is converted into R (red), G (green), and B (blue) signals.
[0149]
By the way, the arrangement position of the above-mentioned near infrared sharp cut coat may be any position on the optical path. Further, the number of low-pass filters LF may be two or one as described above.
[0150]
The electronic image pickup apparatus of the present invention as described above is an image pickup apparatus that forms an object image with a zoom lens and receives the image with an electronic image pickup device such as a CCD, and particularly, a digital camera, a video camera, and an information processing apparatus. It can be used for personal computers, telephones, and especially mobile phones that are convenient to carry. The embodiment is illustrated below.
[0151]
19 to 21 are conceptual diagrams of a configuration in which the zoom lens according to the present invention is incorporated in the photographing optical system 41 of the digital camera. 19 is a front perspective view showing the appearance of the digital camera 40, FIG. 20 is a rear perspective view thereof, and FIG. 21 is a cross-sectional view showing the configuration of the digital camera 40. In this example, the digital camera 40 includes a photographing optical system 41 having a photographing optical path 42, a finder optical system 43 having a finder optical path 44, a shutter 45, a flash 46, a liquid crystal display monitor 47, and the like. When the shutter 45 disposed in the position is pressed, photographing is performed through the photographing optical system 41, for example, the zoom lens of the first embodiment, in conjunction therewith. An object image formed by the photographing optical system 41 is formed on the imaging surface of the CCD 49 via an infrared cut absorption filter IF obtained by applying a near infrared cut coat on a dummy transparent flat plate and an optical low-pass filter LF. . The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the processing means 51. Further, the processing means 51 is connected to a recording means 52 so that a photographed electronic image can be recorded. The recording means 52 may be provided separately from the processing means 51, or may be configured to perform recording / writing electronically using a floppy disk, memory card, MO, or the like. Further, it may be configured as a silver salt camera in which a silver salt film is arranged in place of the CCD 49.
[0152]
Further, a finder objective optical system 53 is disposed on the finder optical path 44. The object image formed by the finder objective optical system 53 is formed on the field frame 57 of the Porro prism 55 which is an image erecting member. Behind this polyprism 55 is an eyepiece optical system 59 that guides the erect image to the observer eyeball E. Note that cover members 50 are disposed on the incident side of the photographing optical system 41 and the finder objective optical system 53 and on the exit side of the eyepiece optical system 59, respectively.
[0153]
The digital camera 40 configured in this manner is a zoom lens with a large back focus, a photographing optical system 41 having a wide angle of view and a high zoom ratio, good aberration, bright, and a filter that can be arranged with a high back focus. Performance and cost reduction can be realized.
[0154]
In the example of FIG. 21, a parallel plane plate is disposed as the cover member 50, but a lens having power may be used.
[0155]
The zoom lens of the present invention and the electronic imaging apparatus having the same can be configured as follows, for example.
[0156]
[1] In order from the object side, the first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. During zooming from the wide-angle end to the telephoto end, the second lens group moves only to the object side, the third lens group moves while changing the distance from the second lens group, and the second lens group moves. The lens group includes, in order from the object side, a positive lens L21, a negative lens L22, a positive lens L23, and a negative lens L24. At least one of the positive lens L23 and the negative lens L24 in the second lens group is a lens group. A zoom lens having an aspherical surface and satisfying the following condition (1):
[0157]
(1) 0.6 <R_22R/ R_21F<2.2
However, R_21F, R_22RAre curvature radii on the optical axis of the object side surface of the positive lens L21 of the second lens group and the image side surface of the negative lens L22 of the second lens group, respectively.
[0158]
[2] The zoom lens as described in [1] above, which is integrated with an electronic image sensor disposed on the image side.
[0159]
[3] In a zoom lens arranged on the imaging surface side of the electronic imaging device,
The zoom lens includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. When zooming from the wide-angle end to the telephoto end during point focusing, the second lens group moves only to the object side, the third lens group moves while changing the distance from the second lens group, The second lens group includes, in order from the object side, a positive lens L21, a negative lens L22, a positive lens L23, and a negative lens L24, and at least one of the positive lens L23 and the negative lens L24 in the second lens group. A zoom lens characterized in that the lens has an aspherical surface and satisfies the following conditions (2), (3), and (4).
[0160]
(2) 0 <(C_24F-C_23R) ・ L <1.6
(3) 0.01 <d_{twenty three}/L<0.2
(4) -0.4 <L / f_2R<0.8
However, C_23R= 1 / R_23R, C_24F= 1 / R_24FWhere R_23R, R_24FIs the radius of curvature on the optical axis of the image side surface of the positive lens L23 of the second lens group, the object side surface of the negative lens L24 of the second lens group, and L is the effective imaging area (substantially rectangular) of the image sensor. Diagonal length (mm), d_{twenty three}Is the air space on the optical axis between the positive lens L23 and the negative lens L24 of the second lens group, f_2RIs the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group.
[0161]
[4] The zoom lens as described in 1 above, which is integrated with an electronic image pickup device arranged on the image side and satisfies the following conditions (2), (3) and (4).
[0162]
(2) 0 <(C_24F-C_23R) ・ L <1.6
(3) 0.01 <d_{twenty three}/L<0.2
(4) -0.4 <L / f_2R<0.8
However, C_23R= 1 / R_23R, C_24F= 1 / R_24FWhere R_23R, R_24FIs the radius of curvature on the optical axis of the image side surface of the positive lens L23 of the second lens group, the object side surface of the negative lens L24 of the second lens group, and L is the effective imaging area (substantially rectangular) of the image sensor. Diagonal length (mm), d_{twenty three}Is the air space on the optical axis between the positive lens L23 and the negative lens L24 of the second lens group, f_2RIs the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group.
[0163]
[5] The zoom lens according to any one of 2 to 4, wherein a positive lens L21 and a negative lens L22 of the second lens group are cemented.
[0164]
[6] The zoom lens according to any one of 2 to 5, wherein the second lens group satisfies the following condition (5).
[0165]
(5) 25 <ν_{twenty one}−ν_{twenty two}+ Ν_{twenty three}−ν_{twenty four}<55
Where ν_{twenty one}, Ν_{twenty two}, Ν_{twenty three}, Ν_{twenty four}Are respectively the Abbe numbers (d-line reference) of the medium of the positive lens L21, the negative lens L22, the positive lens L23, and the negative lens L24 of the second lens group.
[0166]
[7] At least one of the aspheric surfaces arranged in at least one of the positive lens L23 and the negative lens L24 in the second lens group satisfies the following condition (6): The zoom lens according to any one of the above.
[0167]
(6) 7.5 × 10^-3・ L> | Asp2R | >> | Asp21F |
However, Asp21F and Asp2R have a height of 0.3 L from the optical axis with respect to a spherical surface having a radius of curvature on the optical axis of the object side surface of the positive lens L21, the surface of the positive lens L23 or the negative lens L24, respectively. Is the diagonal length (mm) of the effective imaging area (substantially rectangular) of the image sensor, and the aspherical deviation amount Asp21F is 0 when the object side surface of the positive lens L21 is spherical.
[0168]
[8] The zoom lens according to any one of 2 to 7, wherein the following condition (7) is satisfied.
[0169]
(7) -0.5 <(R_21F-R_22R) / (R_21F+ R_22R<0.3
However, R_21F, R_22RAre the curvature radii on the optical axis of the object side surface of the positive lens L21 and the image side surface of the negative lens L22 of the second lens group, respectively.
[0170]
[9] The zoom lens as described in any one of 2 to 8 above, wherein the following conditions (8) and (9) are satisfied.
[0171]
(8) -1 <f_Three/ F_2R<1.6
(9) 0.02 <d_{twenty two}/L<0.5
Where f_2RAnd f_ThreeAre the combined focal length of the positive lens L23 and negative lens L24 of the second lens group, the focal length of the third lens group, d_{twenty two}Is the distance between the image side surface of the negative lens L22 of the second lens group and the object side surface of the positive lens L23, and L is the diagonal length (mm) of the effective imaging region (substantially rectangular) of the imaging device.
[0172]
[10] The zoom lens according to any one of 1 to 9, which satisfies the following condition (10):
[0173]
(10) -1 <f_2F/ R_21R<2.5
However, R_21RIs the radius of curvature of the image side surface of the positive lens L21 of the second lens group, f_2FIs the combined focal length of the positive lens L21 and the negative lens L22 of the second lens group.
[0174]
[11] The zoom lens as described in any one of [1] to [10], wherein, when zooming from the wide-angle end to the telephoto end, the third lens group moves along a locus convex toward the image side.
[0175]
[12] The zoom lens according to any one of [1] to [11], wherein the third lens group is focused by moving along the optical axis.
[0176]
[13] Wide angle half angle of view ω_W13. The zoom lens according to any one of 1 to 12 above, wherein the angle is in the range of 27 ° to 42 °.
[0177]
[14] An electronic imaging apparatus comprising the zoom lens according to any one of 1 to 13 above.
[0178]
【The invention's effect】
According to the present invention, it is possible to obtain a zoom lens having a small retractable thickness and excellent storage property, and excellent imaging performance even at a high magnification and in a rear focus. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view at a wide-angle end (a), an intermediate state (b), and a telephoto end (c) when focusing on an object point at infinity according to Embodiment 1 of a zoom lens used in an electronic imaging device of the present invention. It is.
2 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 2. FIG.
3 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 3. FIG.
4 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 4. FIG.
FIG. 5 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Example 5;
6 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 6. FIG.
7 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 7. FIG.
8 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 8. FIG.
9 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Example 9; FIG.
10 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Example 10. FIG.
FIG. 11 is an aberration diagram for Example 1 upon focusing on an object point at infinity.
12 is an aberration diagram for Example 1 upon focusing on a subject distance of 10 cm. FIG.
FIG. 13 is a diagram for explaining the definition of the amount of aspherical deviation in the present invention.
FIG. 14 is a diagram for explaining a diagonal length of an effective imaging surface when imaging is performed with an electronic imaging element.
FIG. 15 is a diagram showing transmittance characteristics of an example of a near-infrared sharp cut coat.
FIG. 16 is a diagram illustrating a transmittance characteristic of an example of a color filter provided on the emission surface side of the low-pass filter.
FIG. 17 is a diagram illustrating a color filter arrangement of a complementary color mosaic filter.
FIG. 18 is a diagram illustrating an example of wavelength characteristics of a complementary color mosaic filter.
FIG. 19 is a front perspective view showing the appearance of a digital camera incorporating a zoom lens according to the present invention.
20 is a rear perspective view of the digital camera of FIG. 19. FIG.
21 is a cross-sectional view of the digital camera of FIG.
[Explanation of symbols]
G1: First lens group
G2: Second lens group
G3 ... Third lens group
S ... Aperture stop
IF ... Infrared cut absorption filter
LF: Low-pass filter
CG ... Cover glass
I ... Image plane
E ... Observer eyeball
40 ... Digital camera
41. Photography optical system
42. Optical path for photographing
43. Viewfinder optical system
44. Optical path for viewfinder
45 ... Shutter
46 ... Flash
47 ... LCD monitor
49 ... CCD
50. Cover member
51. Processing means
52. Recording means
53. Objective optical system for viewfinder
55 ... Porro prism
57 ... View frame
59 ... Eyepiece optical system

Claims (14)

In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, and at the time of focusing on an object point at infinity. During zooming from the wide-angle end to the telephoto end, the second lens group moves only to the object side, the third lens group moves while changing the distance from the second lens group, and the second lens group In order from the object side, a positive lens L21, a negative lens L22, a positive lens L23, and a negative lens L24 are configured. At least one of the positive lens L23 and the negative lens L24 in the second lens group has an aspherical surface. And a zoom lens characterized by satisfying the following condition (1):
(1) 0.6 <R _22R / R _21F <2.2
R _21F and R _22R are radii of curvature on the optical axis of the object side surface of the positive lens L21 of the second lens group and the image side surface of the negative lens L22 of the second lens group, respectively.   2. The zoom lens according to claim 1, wherein the zoom lens is integrated with an electronic image pickup device arranged on the image side. In the zoom lens arranged on the imaging surface side of the electronic imaging device,
The zoom lens includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. When zooming from the wide-angle end to the telephoto end during point focusing, the second lens group moves only to the object side, the third lens group moves while changing the distance from the second lens group, The second lens group includes, in order from the object side, a positive lens L21, a negative lens L22, a positive lens L23, and a negative lens L24, and at least one of the positive lens L23 and the negative lens L24 in the second lens group. A zoom lens characterized in that the lens has an aspherical surface and satisfies the following conditions (2), (3), and (4).
(2) 0 <(C _24F -C _23R ) · L <1.6
(3) 0.01 <d ₂₃ /L<0.2
(4) −0.4 <L / f _2R <0.8
However, C _23R = 1 / R _23R and C _24F = 1 / R _24F , where R _23R and R _24F are the image side surface of the positive lens L23 of the second lens group and the negative value of the second lens group, respectively. radius of curvature on the optical axis of the object-side surface of the lens L24, L is the diagonal length of an effective image pickup area (substantially rectangular) of the image pickup device (mm), d ₂₃ is the positive lens L23 in the second lens group negative lens L24 F _2R is the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group. 2. The zoom lens according to claim 1, wherein the zoom lens is integrated with an electronic imaging device disposed on the image side and satisfies the following conditions (2), (3), and (4): 3.
(2) 0 <(C _24F -C _23R ) · L <1.6
(3) 0.01 <d ₂₃ /L<0.2
(4) −0.4 <L / f _2R <0.8
However, C _23R = 1 / R _23R and C _24F = 1 / R _24F , where R _23R and R _24F are the image side surface of the positive lens L23 of the second lens group and the negative value of the second lens group, respectively. radius of curvature on the optical axis of the object-side surface of the lens L24, L is the diagonal length of an effective image pickup area (substantially rectangular) of the image pickup device (mm), d ₂₃ is the positive lens L23 in the second lens group negative lens L24 F _2R is the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group.   The zoom lens according to any one of claims 2 to 4, wherein a positive lens L21 and a negative lens L22 of the second lens group are cemented. 6. The zoom lens according to claim 2, wherein the second lens group satisfies the following condition (5).
(5) 25 <ν ₂₁ −ν ₂₂ + ν ₂₃ −ν ₂₄ <55
Here, ν ₂₁ , ν ₂₂ , ν ₂₃ , and ν ₂₄ are the Abbe numbers (d-line reference) of the medium of the positive lens L21, negative lens L22, positive lens L23, and negative lens L24 of the second lens group, respectively. 7. The system according to claim 2, wherein at least one of the aspheric surfaces arranged in at least one of the positive lens L <b> 23 and the negative lens L <b> 24 in the second lens group satisfies the following condition (6). A zoom lens according to claim 1.
(6) 7.5 × 10 ⁻³ · L> | Asp2R |> | Asp21F |
However, Asp21F and Asp2R have a height of 0.3 L from the optical axis with respect to a spherical surface having a radius of curvature on the optical axis of the object side surface of the positive lens L21, the surface of the positive lens L23 or the negative lens L24, respectively. Is the diagonal length (mm) of the effective imaging area (substantially rectangular) of the image sensor, and the aspherical deviation amount Asp21F is 0 when the object side surface of the positive lens L21 is spherical. The zoom lens according to any one of claims 2 to 7, wherein the following condition (7) is satisfied.
(7) −0.5 <(R _21F −R _22R ) / (R _21F + R _22R ) <0.3
Here, R _21F and R _22R are the radii of curvature on the optical axis of the object side surface of the positive lens L21 and the image side surface of the negative lens L22 of the second lens group, respectively. 9. The zoom lens according to claim 2, wherein the following conditions (8) and (9) are satisfied.
(8) -1 <f ₃ / f _2R <1.6
(9) 0.02 <d ₂₂ /L<0.5
Here, f _2R and f ₃ are the combined focal length of the positive lens L23 and the negative lens L24 of the second lens group and the focal length of the third lens group, respectively, and d ₂₂ is the image side surface of the negative lens L22 of the second lens group. The distance from the object side surface of the positive lens L23, L is the diagonal length (mm) of the effective imaging region (substantially rectangular) of the imaging device. The zoom lens according to any one of claims 1 to 9, wherein the following condition (10) is satisfied.
(10) -1 <f _2F / R _21R <2.5
Where R _21R is the radius of curvature of the image side surface of the positive lens L21 of the second lens group, and f _2F is the combined focal length of the positive lens L21 and the negative lens L22 of the second lens group.   11. The zoom lens according to claim 1, wherein when zooming from the wide-angle end to the telephoto end, the third lens group moves along a locus convex toward the image side.   The zoom lens according to claim 1, wherein the third lens group is focused by moving along the optical axis. The zoom lens according to any one of claims 1 to 12, wherein the wide angle end half field angle ω _W is in a range of 27 ° to 42 °.   An electronic imaging apparatus comprising the zoom lens according to claim 1.

Images