JP4536301B2 - Variable magnification imaging optical system and electronic imaging apparatus having the same - Google Patents

Description

【００８９】

【００９０】

【００９１】

【００９２】

【００９３】
以上の実施例１の無限遠物点合焦時及び被写体距離２０ｃｍ合焦時の収差図をそれぞれ図４、図５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。
【００９４】
次に、上記各実施例におけるＬ、及び、条件（１）〜（２２）の値を示す。

【００９５】
なお、実施例１〜５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。
【００９６】
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６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９）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。
【００９７】
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。
【００９８】
また、実施例３〜５において、第４レンズ群Ｇ４の像側には、図示のように、入射面側に近赤外シャープカットコートを施したローパスフィルターＬＦを有している。こ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されている。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。
【００９９】

【０１００】
上記の近赤外シャープカットコートの透過率特性は図７に示す通りである。 また、ローパスフィルターＬＦの射出面側には、図８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。
【０１０１】
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。
【０１０２】
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。
【０１０３】
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。
【０１０４】
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。
【０１０５】
上記各実施例では、図８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。
【０１０６】
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。
【０１０７】
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。
【０１０８】
また、ＣＣＤの撮像面Ｉ上には、図９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。
【０１０９】
補色モザイクフィルターは、具体的には、図９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。
【０１１０】
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。
【０１１１】
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。
【０１１２】
上記各実施例におけるそれぞれの波長特性の一例を図１０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。
【０１１３】
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。
【０１１４】
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。
【０１１５】
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。
【０１１６】
図１１〜図１３は、本発明による変倍結像光学系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１１はデジタルカメラ４０の外観を示す前方斜視図、図１２は同後方斜視図、図１３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設けた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。
【０１１７】
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。
【０１１８】
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。
【０１１９】
なお、図１３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。
【０１２０】
以上の本発明の変倍結像光学系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。
【０１２１】
〔１〕 最も像側に配されるレンズ群が非球面を含みかつ合焦動作の際に固定され、該最も像側に配されるレンズ群の直前の合焦レンズ群の移動により合焦を行う変倍結像光学系において、
前記変倍結像光学系は、物体側から順に、負の屈折力を有する第１レンズ群と、開口絞りと、正の屈折力を有する第２レンズ群と、それに続く第３レンズ群と第４レンズ群とを有し、
変倍時に各々のレンズ群間が可変であり、
前記第２レンズ群は非球面を有する正レンズ成分と負レンズ成分の２つのレンズ成分からなりかつ変倍時に前記開口絞りと一体で光軸上を移動し、
前記第３レンズ群と第４レンズ群は各々２つ以下のレンズ成分で構成されていることを特徴とする変倍結像光学系。
【０１２２】
〔２〕 前記第３レンズ群が前記合焦レンズ群であり、前記第４レンズ群が前記最も像側に配されるレンズ群であることを特徴とする上記１記載の変倍結像光学系。
【０１２３】
〔３〕 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レンズ群と、最も像側に配されるレンズ群としての正の屈折力を有する第４レンズ群とよりなり、
変倍時に各々のレンズ群間が可変であり、
前記第３レンズ群を合焦レンズ群とし、物体側に繰り出すことにより近距離の被写体に合焦することが可能な変倍結像光学系であって、
前記第２レンズ群が非球面を含む正レンズ成分と負レンズ成分１つずつからなり、第３レンズ群は正の単レンズ１枚よりなることを特徴とする変倍結像光学系。
【０１２４】
〔４〕 前記合焦レンズ群は、変倍時にも移動することを特徴とする上記１から３の何れか１項記載の変倍結像光学系。
【０１２５】
〔５〕 前記第２レンズ群における正レンズ成分及び負レンズ成分の面形状が以下の条件（２）及び（３）を満足することを特徴とする上記１から４の何れか１項記載の変倍結像光学系。
【０１２６】
（２） −２＜（Ｒ₂₁＋Ｒ₂₂）／（Ｒ₂₁−Ｒ₂₂）＜−０．５
（３） １＜（Ｒ₂₃＋Ｒ₂₄）／（Ｒ₂₃−Ｒ₂₄）＜５
ただし、Ｒ₂₁、Ｒ₂₂は第２レンズ群正レンズ成分のそれぞれ物体側、像側の屈折面曲率半径、Ｒ₂₃、Ｒ₂₄は第２レンズ群負レンズ成分のそれぞれ物体側、像側の屈折面曲率半径である。なお、非球面の場合は光軸近傍の曲率半径とする。
【０１２７】
〔６〕 前記第２レンズ群における正レンズ成分及び負レンズ成分は、相互に分離されたものであり、前記正レンズ成分の像側の面よりも前記負レンズ成分の物体側の面の方が曲率が強いことを特徴とする上記１から５の何れか１項記載の変倍結像光学系。
【０１２８】
〔７〕 上記１から６の何れか１項記載の変倍結像光学系と、その像側に配された電子撮像素子とを有することを特徴とする電子撮像装置。
【０１２９】
〔８〕 前記合焦レンズ群は、無限遠物点合焦時に広角端から望遠端にかけて変倍するときの移動量ｍ_F に関して、以下の条件（１）を満足することを特徴とする上記７記載の電子撮像装置。
【０１３０】
（１） ０．１＜（ｍ_F −ｍ₂ ）／Ｌ＜１
ただし、ｍ₂ は前記第２レンズ群の無限遠物点合焦時に広角端から望遠端にかけて変倍するときの移動量、Ｌは前記撮像素子の有効撮像領域の対角長（ｍｍ）である。
【０１３１】
〔９〕 前記最も像側に配されるレンズ群は１つの正レンズ成分のみにて構成されており、以下の条件（８）及び（９）を満足することを特徴とする上記７又は８記載の電子撮像装置。
【０１３２】
（８） −１．２＜（Ｒ_R1＋Ｒ_R2）／（Ｒ_R1−Ｒ_R2）＜０．８
（９） ０＜Ｌ／ｆ_R ＜０．５
ただし、Ｒ_R1、Ｒ_R2は最も像側のレンズ成分のそれぞれ最も物体側、最も像側の屈折面曲率半径であり、非球面の場合は光軸近傍の曲率半径とする。Ｌは前記撮像素子の有効撮像領域の対角長（ｍｍ）、ｆ_R は最も像側のレンズ成分の合成焦点距離である。
【０１３３】
〔１０〕 前記最も像側に配されるレンズ群は正の単レンズ１枚のみから構成されていることを特徴とする上記９記載の電子撮像装置。
【０１３４】
〔１１〕 前記合焦レンズ群は１つの正レンズ成分のみにて構成されており、以下の条件（１０）及び（１１）を満足することを特徴とする上記７から１０の何れか１項記載の電子撮像装置。
【０１３５】
（10） −５＜（Ｒ_F1＋Ｒ_F2）／（Ｒ_F1−Ｒ_F2）＜−０．２
（11） ０．１＜Ｌ／ｆ_F ＜０．７
ただし、Ｒ_F1、Ｒ_F2はそのフォーカスのために移動するレンズ成分のそれぞれ最も物体側、最も像側の屈折面曲率半径であり、非球面の場合は光軸近傍の曲率半径とする。Ｌは前記撮像素子の有効撮像領域の対角長（ｍｍ）、ｆ_F はそのフォーカスのために移動するレンズ成分の合成焦点距離である。
【０１３６】
〔１２〕 前記合焦レンズ群は正の単レンズ１枚のみから構成されていることを特徴とする上記１１記載の電子撮像装置。
【０１３７】
〔１３〕 前記第１レンズ群、前記第２レンズ群の近軸量に関し、以下の条件（１２）〜（１６）を満たすことを特徴とする上記７から１２の何れか１項記載の電子撮像装置。
【０１３８】
（12） −０．３＜ｍ₁ ／Ｌ＜１．２
（13） −３＜ｍ₂ ／Ｌ＜−１
（14） ０．２＜Ｌ／ｆ₂ ＜０．６
（15） ０．３５＜Ｌ／ｆ_23W ＜０．７５
（16） −０．１＜Ｌ／ｆ_12T ＜０．５
ただし、ｍ₁ 、ｍ₂ はそれぞれ第１レンズ群、第２レンズ群の無限遠物点合焦時に広角端から望遠端にかけて変倍するときの移動量、Ｌは前記撮像素子の有効撮像領域の対角長（ｍｍ）、ｆ₂ は第２レンズ群の合成焦点距離、ｆ_23W は第２レンズ群と第３レンズ群の無限遠物点合焦時の広角端における合成焦点距離、ｆ_12T は第１レンズ群と第２レンズ群の無限遠物点合焦時の望遠端における合成焦点距離である。
【０１３９】
〔１４〕 前記第１レンズ群は、物体側から順に、屈折面に非球面を含む負の単レンズと、像側の屈折面よりも物体側の屈折面の方が曲率が強い正の単レンズの２枚からなり、以下の条件を満足することを特徴とする上記７から１３の何れか１項記載の電子撮像装置。
【０１４０】
（17） ０．７＜Ｒ₁₂／Ｌ＜１．４
ただし、Ｒ₁₂は第１レンズ群の屈折面に非球面を含む負レンズの像側の面の曲率半径であり、非球面の場合は光軸近傍の曲率半径とする。
【０１４１】
【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変倍結像光学系を得ることができ、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１の無限遠物点合焦時の収差図である。
【図５】実施例１の被写体距離２０ｃｍ合焦時の収差図である。
【図６】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７】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８】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９】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１０】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１１】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１２】図１１のデジタルカメラの後方斜視図である。
【図１３】図１１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
Ｇ４…第４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 variable magnification imaging optical system and an electronic image pickup apparatus having the same, and more particularly to a variable magnification imaging optical system in which a thinning in the depth direction is realized by devising an optical system portion such as a zoom lens. The present invention relates to an electronic imaging device such as a video camera or a digital camera. In addition, the variable magnification imaging optical system makes the rear focus possible.
[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 thinnest, Japanese Patent Laid-Open No. Hei 11- No. 194274, JP-A-11-287953, JP-A-2000-9997, and the like.
[0005]
In order to make the camera body thin, first reduce the total number of components, and then increase the combined magnification of all the lens units from the second lens unit onwards to reduce the entrance pupil position on the wide-angle side. One lens group can be made thin, and the lens movement at the time of focusing can be changed to a so-called rear focus system instead of the front group, and an optical system with little aberration fluctuation at the time of focusing can be selected. There is also a method of reducing the size of the image sensor, but 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. For that purpose, the F value must be brightened.
[0006]
[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 that has image performance, and further reduce the lens element thickness to reduce the total thickness of each group, or consider the selection of filters, etc. The aim is to achieve a thorough thickness reduction in the depth direction when storing the system.
[0007]
[Means for Solving the Problems]
The variable magnification imaging optical system of the present invention that achieves the above object includes a lens group that is disposed closest to the image side and includes a non-spherical lens surface that is fixed during focusing, and is disposed closest to the image side. In the variable magnification imaging optical system that performs focusing by moving the focusing lens group immediately before
The variable magnification imaging optical system includes, in order from the object side, a first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, a subsequent third lens group, 4 lens groups,
Each lens group is variable during zooming,
The second lens group is composed of two lens components, a positive lens component (positive single lens or cemented lens) having an aspherical surface and a negative lens component (negative single lens or cemented lens). Move on the optical axis as a unit,
The third lens group and the fourth lens group are each composed of two or less lens components.
[0008]
Hereinafter, the reason and effect | action which take the said structure in this invention are demonstrated.
[0009]
In the present invention, the lens component means a single lens or a cemented lens.
[0010]
In the variable magnification imaging optical system employed in the electronic image pickup apparatus of the present invention, the lens group disposed closest to the image side includes an aspheric surface, which is fixed at the time of focusing, and the lens group immediately before this is in focus. This is a rear focus zoom lens that is moved to the position. Therefore, it is possible to ensure a stable and high imaging performance from infinity to a short distance while being a rear focus system. This is particularly effective when a lens unit having a positive refractive power that moves monotonously on the object side when zooming from the wide-angle end to the telephoto end is effective. In a zoom lens having such a lens group, an aspherical surface is introduced into the final group in order to reduce the aberration variation in the entire zooming range from the wide-angle end to the telephoto end, and to correct the aberration to be small in any state. In particular, off-axis aberrations such as coma and astigmatism are corrected. Therefore, when focusing is performed on the final group having an aspheric surface, fluctuations in off-axis aberrations such as coma and astigmatism accompanying movement in the optical axis direction tend to increase, leading to performance degradation. Therefore, it is preferable that the final group having an aspheric surface is fixed at the time of focusing (if it is also fixed at the time of zooming, it is preferable in terms of mechanical configuration), and focusing is preferably performed on the group immediately before that (the aspherical surface of this group). It ’s better to avoid making it possible.)
[0011]
Note that the first lens group of such a zoom lens is more compact when it is constituted by a negative lens group, but the above problem is more conspicuous than when the first lens group is a positive lens group. Specifically, for example, the following optical system may be selected for such a problem. In order from the object side, the first lens group having a negative refractive power, an aperture stop, and a positive lens and a negative lens that can move on the optical axis integrally with the aperture stop and include an aspheric surface as a refractive surface. A second lens group having a positive refractive power and at least two lens groups following the second lens group. The most image side lens group includes an aspheric surface and is fixed at the time of zooming and focusing. This is an imaging optical system including a lens group in which the immediately preceding lens group moves for focusing.
[0012]
One method for reducing the thickness of the first lens group is to set the combined magnification of all the lens groups (including the second lens group) after the second lens group to be high. In this case, Since the effective F value of the composite system of all the lens groups after the second lens group tends to be dark, this composite system must be made to have a large aperture ratio. On the other hand, the number of components cannot be increased in order to reduce the thickness when the lens system is housed. Therefore, the synthesis system consisting of all the lens groups after the second lens group is divided into three components, each group is composed of two or less lens elements, and a part of them is movable, and correction of zooming / focus / residual aberration is performed. , It is better not to carry out each group independently, but to carry out it in relation to each other. In particular, the lens unit closest to the object side (that is, the second lens group) of the synthesis system is composed of only two lenses, a positive lens and a negative lens that include an aspheric surface on the refractive surface. Note that there is only one lens group that moves for focusing, the second lens group from the image side, and this lens group is movable during zooming and has a positive refractive power.
[0013]
The lens group that moves for this focus is the amount of movement m when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity._FIt is desirable that the following conditions are satisfied.
[0014]
(1) 0.1 <(m_F-M₂) / L <1
Where m₂Is the amount of movement of the second lens group when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, and L is the diagonal length (mm) of the effective imaging area of the image sensor.
[0015]
If the upper limit of 1 of the condition (1) is exceeded, the movable space of the lens group that moves for focusing is insufficient on the telephoto side, and short-range focusing becomes difficult. If the lower limit of 0.1 is exceeded, the amount of relative movement with respect to the second lens group tends to increase, making it difficult to correct aberration fluctuations during zooming with the second lens group having a small number of elements.
[0016]
It is better to do the following.
[0017]
(1) ′ 0.1 <(m_F-M₂) / L <0.7
Furthermore, it is best to do the following.
[0018]
(1) "0.1 <(m_F-M₂) / L <0.4
Since the second lens group is the main power among the combined powers of all the groups after the second lens group, its aberration correction is important. Thus, in particular, spherical aberration correction is performed by introducing an aspheric surface on the object side surface of the positive lens in the second lens group. In addition, in order to set the magnification of the synthesis system of all the groups after the second lens group to be high, the lens system is reduced in size by positioning the principal point of the synthesis system itself as far as possible on the object side. Yes.
[0019]
It is desirable that the following conditions are satisfied with respect to the shapes of the positive lens component and the negative lens component of the second lens group.
[0020]
(2) -2 <(R_{twenty one}+ R_{twenty two}) / (R_{twenty one}-R_{twenty two}<0.5
(3) 1 <(R_{twenty three}+ R_{twenty four}) / (R_{twenty three}-R_{twenty four}<5
However, R_{twenty one}, R_{twenty two}Is the refracting surface curvature radius on the object side and the image side of the positive lens component of the second lens group, and R_{twenty three}, R_{twenty four}Is the refracting surface curvature radius on the object side and the image side of the second lens group negative lens component, respectively. In the case of an aspheric surface, the radius of curvature is in the vicinity of the optical axis.
[0021]
If the upper limit value −0.5 and the lower limit value 1 are exceeded in each of the conditions (2) and (3), the total length of the optical system becomes long, and the amount of lens movement when stored from the use state becomes too large. Easy to enlarge. On the other hand, if the lower limit value −2 and the upper limit value 5 are exceeded, the exit pupil position is close to the image plane on the wide angle side, which is likely to cause shading.
[0022]
In addition, it is better to set one or both of the conditions (2) and (3) as follows.
[0023]
(2) '-1.7 <(R_{twenty one}+ R_{twenty two}) / (R_{twenty one}-R_{twenty two}<0.6
(3) ’1.2 <(R_{twenty three}+ R_{twenty four}) / (R_{twenty three}-R_{twenty four}) <4.5
Furthermore, it is better to set one or both of the conditions (2) and (3) as follows. In particular, it is best to do both as follows.
[0024]
(2) "-1.5 <(R_{twenty one}+ R_{twenty two}) / (R_{twenty one}-R_{twenty two}) <-0.7
(3) "1.4 <(R_{twenty three}+ R_{twenty four}) / (R_{twenty three}-R_{twenty four}<4
In addition, the second lens group is composed of two components, a positive lens component including an aspherical surface and a negative lens component. In order to correct spherical aberration, coma aberration, and reduce the relative decentration sensitivity of each component,
(4) 0.6 <R_{twenty four}/ R_{twenty one}<1.0
It is desirable to satisfy.
[0025]
It is better to do the following.
[0026]
(4) '0.65 <R_{twenty four}/ R_{twenty one}<0.95
Furthermore, it is best to do the following.
[0027]
(4) "0.7 <R_{twenty four}/ R_{twenty one}<0.9
Further, in order to establish the paraxial relationship of the focus, it is necessary that the magnification range taken by the focus group following the second lens group does not include -1x or approach -1x. It is important to make the combined power of the lens group as positive as possible. Therefore, it is assumed that the two lens components are separated from each other, and the image side surface R of the positive lens component._{twenty two}Surface R on the object side of the negative lens component than_{twenty three}It is desirable that the curvature be stronger on the image side.
[0028]
If this condition shows the numerical range,
(5) R_{twenty three}/ R_{twenty two}<1.0
It becomes.
[0029]
It is better to do the following.
[0030]
(5) '-0.4 <R_{twenty three}/ R_{twenty two}<0.4
Furthermore, it is best to do the following.
[0031]
(5) "-0.3 <R_{twenty three}/ R_{twenty two}<0.3
Next, the role and configuration of the lens group closest to the image side will be described. In the movable group at the time of zooming, the aberration variation in the entire zooming range is corrected as much as possible to remove almost uniform aberrations, particularly off-axis aberrations, by adding an aspheric surface to the final group. However, especially in the case of coma aberration, correction cannot be performed unless the lens surface for correction is separated from the image plane to some extent. Therefore, the air equivalent distance D on the optical axis between the final lens and the image plane._RShould satisfy the following conditions.
[0032]
(6) 0.3 <D_R/L<2.5
When the lower limit of 0.3 of the condition (6) is exceeded, correction of distortion due to the aspherical surface of the final lens is easy, but correction of coma becomes difficult. When the upper limit of 2.5 is exceeded, the total length of the optical system and the lens diameter of the group apart from the aperture stop tend to be enlarged.
[0033]
It is better to do the following.
[0034]
(6) '0.4 <D_R/L<2.0
Furthermore, it is best to do the following.
[0035]
(6) "0.5 <D_R/L<1.5
Furthermore, in order to cover the spatial loss caused by the above as much as possible, the distance between the fixed final group including the aspherical surface and the focus group immediately before (the wide-angle end when focusing on an object point at infinity) is as follows: It is better to meet the conditions.
[0036]
(7) 0.1 <D_34W/L<1.2
If the upper limit of 1.2 of the condition (7) is exceeded, the total length of the optical system tends to be long, or it is difficult to secure a zoom ratio. The lower limit of 0.1 is provided to avoid mechanical interference between the two groups.
[0037]
It is better to do the following.
[0038]
(7) ’0.1 <D_34W/L<1.0
Furthermore, it is best to do the following.
[0039]
(7) "0.1 <D_34W/L<0.8
Furthermore, the lens group closest to the image side is composed of one positive lens component, and the following conditions should be satisfied.
[0040]
(8) -1.2 <(R_R1+ R_R2) / (R_R1-R_R2<0.8
(9) 0 <L / f_R<0.5
However, R_R1, R_R2Is the most object-side and image-side refractive radius of curvature of the lens component closest to the image side, and in the case of an aspherical surface, the radius of curvature near the optical axis. f_RIs the combined focal length of the lens component closest to the image side.
[0041]
When the upper limit of 0.8 of the condition (8) is exceeded, astigmatism and coma, and when the lower limit of −1.2 is exceeded, distortion and coma are likely to deteriorate. In addition, a meniscus shape increases the dead space when the lens system is accommodated, which is not preferable in reducing the thickness. If the lower limit of 0 to condition (9) is exceeded, the exit pupil position tends to approach the image plane at the wide-angle end, and shading tends to occur. If the upper limit of 0.5 is exceeded, the variation of the exit pupil position when zooming from the wide-angle end to the telephoto end tends to be large, and shading tends to occur at either the wide-angle end or the telephoto end. If the lens group closest to the image side is composed of only one positive lens, there is almost no aberration deterioration, which contributes to a reduction in thickness.
[0042]
Note that it is better to set one or both of the conditions (8) and (9) as follows.
[0043]
(8) '-1.0 <(R_R1+ R_R2) / (R_R1-R_R2) <0.6
(9) '0.05 <L / f_R<0.45
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.
[0044]
(8) "-0.8 <(R_R1+ R_R2) / (R_R1-R_R2<0.4
(9) "0.1 <L / f_R<0.4
Next, the role and configuration of the lens group that moves for the focus will be described. In order to perform inner focusing, it is essential that there is little variation in aberration due to movement of the lens group by focusing. Since the increase in the number of components is fatal in terms of miniaturization, the lens group that moves for focusing must be composed of only one lens component. At this time, aberration fluctuations due to focusing are minimized by satisfying the following conditions.
[0045]
(10) -5 <(R_F1+ R_F2) / (R_F1-R_F2) <-0.2
(11) 0.1 <L / f_F<0.7
However, R_F1, R_F2Is the radius of curvature of the refractive surface closest to the object side and the image side of the lens component moving for focusing, and in the case of an aspherical surface, it is the radius of curvature near the optical axis. f_FIs the combined focal length of the lens components that move for that focus.
[0046]
From the condition (1), the relative positional relationship between the aperture stop and the lens group that moves for focusing is less changed by zooming and the distance itself is closer, so the off-axis chief ray height is generally low and there is little change. The variation of off-axis aberration is reduced. Therefore, the shape of the spherical aberration is less changed due to focusing. If the upper limit of -0.2 of the condition (10) is exceeded, the variation in spherical aberration tends to increase. When the lower limit of −5 is exceeded, fluctuations in off-axis aberrations such as astigmatism increase. When the lower limit of 0.1 of the condition (11) is exceeded, the amount of movement necessary for focusing of the lens group that moves for focusing becomes too large, and at the same time, fluctuations in various aberrations due to focusing become large. If the upper limit of 0.7 is exceeded, the principal point of the synthesis system of all the lens groups after the second lens group tends to go backward, the magnification of the synthesis system becomes small, and the first lens group tends to be enlarged.
[0047]
If the lens group that moves for focusing is composed of only one positive lens, there is almost no aberration variation due to focusing, which contributes to a reduction in thickness.
[0048]
In addition, it is better to set one or both of the conditions (10) and (11) as follows.
[0049]
(10) '-4 <(R_F1+ R_F2) / (R_F1-R_F2<0.4
(11) '0.15 <L / f_F<0.55
Furthermore, it is better to set one or both of the conditions (10) and (11) as follows. In particular, it is best to do both as follows.
[0050]
(10) "-3 <(R_F1+ R_F2) / (R_F1-R_F2<0.6
(11) ”0.2 <L / f_F<0.4
In addition, the following conditions may be satisfied with respect to the paraxial amounts of the first and second lens groups.
[0051]
(12) -0.3 <m₁ /L<1.2
(13) -3 <m₂/ L <-1
(14) 0.2 <L / f₂<0.6
(15) 0.35 <L / f_23W<0.75
(16) -0.1 <L / f_12T<0.5
Where m₁ , M₂Is the amount of movement when zooming from the wide-angle end to the telephoto end when the first lens unit and the second lens unit are focused on an object point at infinity, f₂Is the combined focal length of the second lens group, f_23WIs the combined focal length at the wide-angle end when focusing on an object point at infinity of the second lens group and the third lens group, f_12TIs the combined focal length at the telephoto end when the first lens unit and the second lens unit are focused on an object point at infinity.
[0052]
The locus of the first lens group is ideal in terms of the size of the lens system, starting from the wide-angle end and substantially returning at the telephoto end (that is, the amount of movement is zero). If the upper limit of 1.2 of the condition (12) is exceeded, the lens diameter of the first lens group becomes large and therefore tends to be thick. Since the second lens group is a main driver of zooming, it moves from the wide-angle end to the telephoto end in a substantially monotonous manner toward the object side. However, if the amount is too large and exceeds the upper limit of -1 in the condition (13), the F value at the telephoto end tends to be dark. Further, since the amount of variation in the exit pupil position is large, shading is likely to occur at either the wide-angle end or the telephoto end. The second lens group greatly contributes to zooming while having only two lenses. Due to this relationship, the amount of generated aberration tends to increase. Therefore, the focal length of the second lens group is made as long as possible to borrow the power of the third lens group. If the upper limit of 0.6 of the condition (14) is exceeded, the aberration fluctuation at the time of zooming tends to be large. If the lower limit of 0.2 is exceeded, the lens group that moves for focusing tends to be burdened, and aberration fluctuations during focusing tend to increase. If the lower limit of 0.35 of the condition (15) is exceeded, the amount of movement of the second lens group during zooming tends to increase. When the upper limit of 0.75 is exceeded, the exit pupil is likely to approach the image plane at the wide-angle end. In order to reduce the variation of spherical aberration due to focusing, it is preferable to make the axial light beam incident so that the amount of spherical aberration generated in the focusing lens group is as small as possible. For this purpose, the condition (16) indirectly defines the angle of the axially emitted light beams of the first lens group and the second lens group with respect to the optical axis. If the upper limit of 0.5 and the lower limit of −0.1 are exceeded, the variation in spherical aberration due to focusing tends to increase.
[0053]
In addition, it is better to set one or more of the conditions (12) to (16) as follows.
[0054]
(12) '-0.2 <m₁ / L <1
(13) '-2.6 <m₂/L<-1.3
(14) ’0.25 <L / f₂<0.55
(15) ’0.4 <L / f_23W<0.7
(16) '-0.08 <L / f_12T<0.3
Furthermore, it is better to set one or more of the conditions (12) to (16) as follows. In particular, it is best to do everything as follows.
[0055]
(12) "-0.1 <m₁ /L<0.8
(13) ”-2.2 <m₂/L<-1.6
(14) "0.3 <L / f₂<0.5
(15) "0.45 <L / f_23W<0.65
(16) "-0.05 <L / f_12T<0.1
Finally, conditions for thinning the first lens group will be described. In order from the object side, the first lens group is composed of two lenses, a negative lens having an aspheric surface on the refractive surface and a positive lens having a refractive surface with a stronger curvature on the object side, and preferably satisfies the following conditions.
[0056]
(17) 0.7 <R₁₂/L<1.4
However, R₁₂Is the radius of curvature of the image side surface of the negative lens including an aspherical surface on the refractive surface of the first lens group. In the case of an aspheric surface, the radius of curvature is in the vicinity of the optical axis.
[0057]
If the lower limit of 0.7 in condition (17) is exceeded, it will be difficult to correct distortion and coma even if an aspherical surface is introduced. If the upper limit of 1.4 is exceeded, it will be difficult to correct lateral chromatic aberration. Become.
[0058]
It is better to do the following.
[0059]
(17) ’0.75 <R₁₂/L<1.2
Furthermore, it is best to do the following.
[0060]
(17) ”0.8 <R₁₂/L<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.
[0061]
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.
[0062]
That is,
(18) τ₆₀₀/ Τ₅₅₀≧ 0.8
(19) τ₇₀₀/ Τ₅₅₀≦ 0.08
It is desirable to satisfy. Where τ₅₅₀Is the transmittance at a wavelength of 550 nm.
[0063]
Note that it is better to set one or both of the conditions (18) and (19) as follows.
[0064]
(18) ’τ₆₀₀/ Τ₅₅₀≧ 0.85
(19) ’τ₇₀₀/ Τ₅₅₀≦ 0.05
Furthermore, it is better to set one or both of the conditions (18) and (19) as follows. In particular, it is best to do both as follows.
[0065]
(18) “τ₆₀₀/ Τ₅₅₀≧ 0.9
(19) “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.
[0066]
That is,
(20) τ₄₀₀/ Τ₅₅₀≦ 0.08
(21) τ₄₄₀/ Τ₅₅₀≧ 0.4
It is desirable to satisfy.
[0067]
Note that it is better to set one or both of the conditions (20) and (21) as follows.
[0068]
(20) ’τ₄₀₀/ Τ₅₅₀≦ 0.06
(21) ’τ₄₄₀/ Τ₅₅₀≧ 0.5
Furthermore, it is better to set one or both of the conditions (20) and (21) as follows. In particular, it is best to do both as follows.
[0069]
(20) “τ₄₀₀/ Τ₅₅₀≦ 0.04
(21) “τ₄₄₀/ Τ₅₅₀≧ 0.6
These filters are preferably installed between the imaging optical system and the image sensor.
[0070]
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.
[0071]
(22) 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.
[0072]
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.
[0073]
It is preferable that the condition (22) is satisfied, including the case where filter specifications other than those described above, for example, 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.
[0074]
If a is 4 μm or less, it is more susceptible to diffraction.
(22) ’0.13 <t_LPF/A<0.42
It is good.
[0075]
Further, the following may be performed according to the number of low-pass filters superimposed on the horizontal pixel pitch.
[0076]
(22) "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).
[0077]
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.
[0078]
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.
[0079]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments 1 to 5 of the zoom lens used in the imaging optical system of the electronic image pickup apparatus of the present invention will be described below. FIGS. 1 to 3 show sectional views of lenses at the wide-angle end (a), the intermediate state (b), and the telephoto end (c) when focusing on an object point at infinity according to the first to third embodiments. Since Examples 4 and 5 are the same as Example 3, illustration is omitted. In each figure, the first lens group is G1, the stop is S, the second lens group is G2, the third lens group is G3, the fourth lens group is G4, the infrared cut absorption filter is IF, the low-pass filter is LF, and the electron The cover glass of the CCD, which is an image sensor, 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. (Examples 3 to 5).
[0080]
As shown in FIG. 1, the zoom lens of Embodiment 1 includes a negative lens first lens group G1, which includes a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, and an object. Positive refraction comprising a cemented lens of a positive meniscus lens convex to the side, a second lens group G2 having a positive refracting power consisting of a negative meniscus lens convex to the object side, and a negative meniscus lens convex to the image side. A third lens group G3 having a positive force and a fourth lens group G4 having a positive refractive power made up of one biconvex positive lens. When zooming from the wide angle end to the telephoto end, the first lens group G1 is concave on the object side. The second lens group G2 moves to the object side together with the aperture stop S, and the third lens group G3 moves to the second lens group G2. The fourth lens group G It is fixed. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0081]
The aspheric surfaces are 3 of the image side surface of the negative meniscus lens of the first lens group G1, the object side surface of the positive meniscus lens of the second lens group G2, and the object side surface of the positive lens of the fourth lens group G4. Used on the surface.
[0082]
As shown in FIG. 2, the zoom lens of Example 2 includes a plano-concave negative lens, a negative lens first lens group G1 composed of a positive meniscus lens convex on the object side, an aperture stop S, and a biconvex positive lens. From the second lens group G2 having a positive refractive power composed of a negative meniscus lens convex on the object side, the third lens group G3 having a positive refractive power composed of one positive meniscus lens convex on the object side, and one biconvex positive lens The first lens unit G1 moves along a concave locus on the object side when zooming from the wide-angle end to the telephoto end. At the telephoto end, the image is seen from the wide-angle end. Located on the surface side, the second lens group G2 moves to the object side integrally with the aperture stop S, the third lens group G3 moves to the object side while widening the gap with the second lens group G2, The four lens group G4 is fixed. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0083]
The aspheric surfaces are the three surfaces of the negative lens image side surface of the first lens group G1, the object side surface of the positive lens of the second lens group G2, and the object side surface of the positive lens of the fourth lens group G4. It is used.
[0084]
As shown in FIG. 3, the zoom lenses of Examples 3 to 5 are a negative lens first lens group G1 including a planoconcave negative lens and a positive meniscus lens convex on the object side, an aperture stop S, and a biconvex positive lens. A second lens group G2 having a positive refractive power composed of a lens and a negative meniscus lens convex on the object side, a third lens group G3 having a positive refractive power composed of one positive meniscus lens convex on the object side, and a biconvex positive lens 1 The fourth lens unit G4 is composed of a fourth lens unit having positive refractive power, 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, the wide-angle end. Located closer to the image plane side, the second lens group G2 moves to the object side together with the aperture stop S, and the third lens group G3 moves to the object side while increasing the distance from the second lens group G2. The fourth lens group G4 is fixed. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0085]
The aspheric surfaces are the three surfaces of the negative lens image side surface of the first lens group G1, the object side surface of the positive lens of the second lens group G2, and the object side surface of the positive lens of the fourth lens group G4. It is used.
[0086]
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.
[0087]
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.
[0088]

[0089]

[0090]

[0091]

[0092]

[0093]
FIG. 4 and FIG. 5 show aberration diagrams in Example 1 when focusing on an object point at infinity and focusing on a subject distance of 20 cm, 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.
[0094]
Next, L and the values of the conditions (1) to (22) in the above embodiments will be shown.

[0095]
The total thickness t of the low-pass filter LF of Examples 1 to 5_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.
[0096]
Here, the diagonal length L of the effective imaging surface and the pixel interval a will be described. FIG. 6 is a diagram showing an example of the pixel array of the image sensor, and R (red), G (green), and B (blue) pixels or cyan, magenta, yellow, and green (green) pixels with a pixel interval a. Four color pixels (FIG. 9) 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.
[0097]
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.
[0098]
In Examples 3 to 5, the image side of the fourth lens group G4 has a low-pass filter LF having a near-infrared sharp cut coat on the incident surface side as illustrated. This near-infrared sharp cut coat has a transmittance of 80% or more at a wavelength of 600 nm and a transmittance of 10% or less at a wavelength of 700 nm. Specifically, it is a multilayer film composed of the following 27 layers, for example. However, the design wavelength is 780 nm.
[0099]

[0100]
The transmittance characteristics of the near infrared sharp cut coat are as shown in FIG. Further, the color reproducibility of the electronic image is further improved by providing a color filter for reducing the transmission of colors in the short wavelength region as shown in FIG. 8 or coating on the exit surface side of the low-pass filter LF. ing.
[0101]
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.
[0102]
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.
[0103]
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.
[0104]
Such means for limiting the wavelength is more effective in an imaging system using a complementary color mosaic filter.
[0105]
In each of the above-described embodiments, as shown in FIG. 8, 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.
[0106]
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.
[0107]
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.
[0108]
Further, on the image pickup surface I of the CCD, as shown in FIG. 9, a complementary color mosaic filter in which four color filters of cyan, magenta, yellow, and green are provided in a mosaic pattern corresponding to the image pickup pixels is provided. 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.
[0109]
Specifically, as shown in FIG. 9, the complementary color mosaic filter includes at least four types of color filters, and the characteristics of the four types of color filters are preferably as follows.
[0110]
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.
[0111]
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%.
[0112]
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%.
[0113]
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.
[0114]
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.
[0115]
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.
[0116]
FIGS. 11 to 13 are conceptual diagrams of a configuration in which the variable magnification imaging optical system according to the present invention is incorporated in a photographing optical system 41 of a digital camera. 11 is a front perspective view showing the appearance of the digital camera 40, FIG. 12 is a rear perspective view thereof, and FIG. 13 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 through an optical low-pass filter LF provided with a near infrared cut coat. 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.
[0117]
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.
[0118]
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.
[0119]
In the example of FIG. 13, a parallel plane plate is disposed as the cover member 50, but a lens having power may be used.
[0120]
The variable magnification imaging optical system of the present invention and the electronic image pickup apparatus having the same can be configured as follows, for example.
[0121]
[1] The lens unit disposed closest to the image side includes an aspherical surface and is fixed during the focusing operation, and is focused by moving the focusing lens unit immediately before the lens unit disposed closest to the image side. In the variable magnification imaging optical system to perform,
The variable magnification imaging optical system includes, in order from the object side, a first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, a subsequent third lens group, 4 lens groups,
Each lens group is variable during zooming,
The second lens group is composed of two lens components, a positive lens component having an aspherical surface and a negative lens component, and moves on the optical axis integrally with the aperture stop at the time of zooming,
The zoom lens system according to claim 1, wherein each of the third lens group and the fourth lens group includes two or less lens components.
[0122]
[2] The variable magnification imaging optical system according to [1], wherein the third lens group is the focusing lens group, and the fourth lens group is a lens group arranged closest to the image side. .
[0123]
[3] In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a third lens group having a positive refractive power are arranged closest to the image side. A fourth lens group having a positive refractive power as a lens group,
Each lens group is variable during zooming,
A variable magnification imaging optical system capable of focusing on a short-distance object by extending the third lens group to a focusing lens group and extending it toward the object side,
A variable magnification imaging optical system, wherein the second lens group includes one positive lens component including an aspherical surface and one negative lens component, and the third lens group includes one positive single lens.
[0124]
[4] The variable magnification imaging optical system according to any one of [1] to [3], wherein the focusing lens group also moves during zooming.
[0125]
[5] The variation according to any one of the above items 1 to 4, wherein the surface shapes of the positive lens component and the negative lens component in the second lens group satisfy the following conditions (2) and (3): Double imaging optical system.
[0126]
(2) -2 <(R_{twenty one}+ R_{twenty two}) / (R_{twenty one}-R_{twenty two}<0.5
(3) 1 <(R_{twenty three}+ R_{twenty four}) / (R_{twenty three}-R_{twenty four}<5
However, R_{twenty one}, R_{twenty two}Is the refracting surface curvature radius on the object side and the image side of the positive lens component of the second lens group, and R_{twenty three}, R_{twenty four}Is the refracting surface curvature radius on the object side and the image side of the second lens group negative lens component, respectively. In the case of an aspheric surface, the radius of curvature is in the vicinity of the optical axis.
[0127]
[6] The positive lens component and the negative lens component in the second lens group are separated from each other, and the object side surface of the negative lens component is closer to the image side surface of the positive lens component. 6. The variable magnification imaging optical system according to any one of 1 to 5, wherein the curvature is strong.
[0128]
[7] An electronic imaging apparatus comprising: the variable magnification imaging optical system according to any one of 1 to 6 above; and an electronic imaging device arranged on the image side.
[0129]
[8] The focusing lens group moves m when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity._F8. The electronic imaging device as described in 7 above, wherein the following condition (1) is satisfied.
[0130]
(1) 0.1 <(m_F-M₂) / L <1
Where m₂Is the amount of movement of the second lens group when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, and L is the diagonal length (mm) of the effective imaging region of the image sensor.
[0131]
[9] The above 7 or 8, wherein the lens group arranged closest to the image side is composed of only one positive lens component, and satisfies the following conditions (8) and (9): Electronic imaging device.
[0132]
(8) -1.2 <(R_R1+ R_R2) / (R_R1-R_R2<0.8
(9) 0 <L / f_R<0.5
However, R_R1, R_R2Is the most object-side and image-side refractive radius of curvature of the lens component closest to the image side, and in the case of an aspherical surface, the radius of curvature near the optical axis. L is the diagonal length (mm) of the effective imaging area of the imaging device, f_RIs the combined focal length of the lens component closest to the image side.
[0133]
[10] The electronic image pickup apparatus as described in [9], wherein the lens group arranged closest to the image side includes only one positive single lens.
[0134]
[11] The focusing lens group includes only one positive lens component, and satisfies the following conditions (10) and (11): Electronic imaging device.
[0135]
(10) -5 <(R_F1+ R_F2) / (R_F1-R_F2) <-0.2
(11) 0.1 <L / f_F<0.7
However, R_F1, R_F2Is the radius of curvature of the refractive surface closest to the object side and the image side of the lens component moving for focusing, and in the case of an aspherical surface, it is the radius of curvature near the optical axis. L is the diagonal length (mm) of the effective imaging area of the imaging device, f_FIs the combined focal length of the lens components that move for that focus.
[0136]
[12] The electronic imaging apparatus as described in [11], wherein the focusing lens group is composed of only one positive single lens.
[0137]
[13] The electronic imaging according to any one of 7 to 12, wherein the following conditions (12) to (16) are satisfied with respect to paraxial amounts of the first lens group and the second lens group: apparatus.
[0138]
(12) -0.3 <m₁ /L<1.2
(13) -3 <m₂/ L <-1
(14) 0.2 <L / f₂<0.6
(15) 0.35 <L / f_23W<0.75
(16) -0.1 <L / f_12T<0.5
Where m₁ , M₂Is the amount of movement when the first lens group and the second lens group are zoomed from the wide-angle end to the telephoto end when focusing on an object point at infinity, L is the diagonal length (mm) of the effective imaging area of the image sensor, f₂Is the combined focal length of the second lens group, f_23WIs the combined focal length at the wide-angle end when focusing on an object point at infinity of the second lens group and the third lens group, f_12TIs the combined focal length at the telephoto end when the first lens unit and the second lens unit are focused on an object point at infinity.
[0139]
[14] The first lens group includes, in order from the object side, a negative single lens including an aspheric surface on the refractive surface, and a positive single lens having a curvature on the object side refractive surface that is stronger than that on the image side refractive surface. 14. The electronic imaging apparatus according to any one of 7 to 13, wherein the electronic imaging apparatus satisfies the following condition.
[0140]
(17) 0.7 <R₁₂/L<1.4
However, R₁₂Is the radius of curvature of the image side surface of the negative lens including an aspheric surface on the refractive surface of the first lens group. In the case of an aspheric surface, the radius of curvature is near the optical axis.
[0141]
【The invention's effect】
The present invention makes it possible to obtain a variable magnification imaging optical system with a small retractable thickness, excellent storage, and excellent imaging performance even at high magnification and rear focus. Can be achieved.
[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.
FIG. 4 is an aberration diagram for Example 1 upon focusing on an object point at infinity.
FIG. 5 is an aberration diagram for Example 1 upon focusing on a subject distance of 20 cm.
FIG. 6 is a diagram for explaining a diagonal length of an effective imaging surface when photographing with an electronic imaging element.
FIG. 7 is a diagram showing transmittance characteristics of an example of a near-infrared sharp cut coat.
FIG. 8 is a diagram illustrating a transmittance characteristic of an example of a color filter provided on an emission surface side of a low-pass filter.
FIG. 9 is a diagram illustrating a color filter arrangement of a complementary color mosaic filter.
FIG. 10 is a diagram illustrating an example of wavelength characteristics of a complementary color mosaic filter.
FIG. 11 is a front perspective view showing the external appearance of a digital camera incorporating a zoom lens according to the present invention.
12 is a rear perspective view of the digital camera of FIG. 11. FIG.
13 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
G4 ... Fourth 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 (11)

A zooming unit in which the lens unit disposed closest to the image side includes an aspherical surface and is fixed during focusing, and is focused by moving the focusing lens unit immediately before the lens unit disposed closest to the image side. In an electronic imaging device comprising an imaging optical system and an electronic imaging device,
The variable magnification imaging optical system includes, in order from the object side, a first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, and a third lens having a positive refractive power. A lens group and a fourth lens group having positive refractive power;
Each lens group is variable during zooming,
The first lens group includes, in order from the object side, a negative single lens including an aspheric surface on the refracting surface, and a positive single lens whose refractive surface on the object side has a stronger curvature than the refracting surface on the image side. Consists of
The second lens group comprises two lens components, a positive lens component having an aspherical surface and a negative lens component, and moves on the optical axis integrally with the aperture stop at the time of zooming,
The third lens group and the fourth lens group are each composed of two or less lens components,
An electronic imaging apparatus characterized by satisfying the following conditions (2), (3), and (17):
_{(2) -2 <(R 21} + R 22) / (R 21 -R 22) <- 0.5
(3) 1 <(R ₂₃ + R ₂₄ ) / (R ₂₃ −R ₂₄ ) <5
(17) 0.7 <R ₁₂ /L<1.4
Where R ₂₁ and R ₂₂ are the object side and image side refractive radius of curvature of the second lens group positive lens component , and R ₂₃ and R ₂₄ are the object side and image side refraction of the second lens group negative lens component, respectively. The surface radius of curvature, R _12, is the radius of curvature of the image side surface of the negative lens including an aspheric surface on the refractive surface of the first lens group. When the refractive surface is an aspheric surface, the radius of curvature is near the optical axis. , L is the diagonal length of the effective imaging area of the electronic imaging device. In an electronic imaging device comprising a variable magnification imaging optical system and an electronic imaging device,
The variable magnification imaging optical system 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; A fourth lens unit having a positive refractive power as a lens unit disposed closest to the image side,
Each lens group is variable during zooming,
The third lens group is a focusing lens group, and it is possible to focus on an object at a short distance by extending to the object side,
The first lens group includes, in order from the object side, a negative single lens including an aspheric surface on the refracting surface, and a positive single lens whose refractive surface on the object side has a stronger curvature than the refracting surface on the image side. Consists of
The second lens group is composed of one positive lens component including an aspheric surface and one negative lens component,
The third lens group consists of one positive single lens,
The lens group arranged closest to the image side is composed of only one positive lens component,
An electronic imaging apparatus characterized by satisfying the following conditions (8), (9), and (17):
(8) -1.2 <(R _R1 + R _R2 ) / (R _R1 -R _R2 ) <0.8
(9) 0 <L / f _R <0.5
(17) 0.7 <R ₁₂ /L<1.4
Where R _R1 and R _R2 are the radii of curvature of the most object-side and image-side refracting surfaces of the most image-side lens components, respectively, and R ₁₂ is a negative including an aspherical surface on the refracting surface of the first lens group. The radius of curvature of the image-side surface of the lens. When the refracting surface is an aspherical surface, the radius of curvature is near the optical axis, L is the diagonal length of the effective imaging area of the electronic image sensor , and f _R is the most image-side. Is the combined focal length of the lens components .   The electronic imaging apparatus according to claim 1, wherein the focusing lens group moves even during zooming. In an electronic imaging device comprising a variable magnification imaging optical system and an electronic imaging device,
The variable magnification imaging optical system 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; A fourth lens unit having a positive refractive power as a lens unit disposed closest to the image side,
Each lens group is variable during zooming,
The third lens group is a focusing lens group, and it is possible to focus on an object at a short distance by extending to the object side,
The first lens group includes, in order from the object side, a negative single lens including an aspheric surface on the refracting surface, and a positive single lens whose refractive surface on the object side has a stronger curvature than the refracting surface on the image side. Consists of
The second lens group is composed of one positive lens component including an aspheric surface and one negative lens component,
The third lens group consists of one positive single lens,
An electronic imaging apparatus, wherein the surface shapes of the positive lens component and the negative lens component in the second lens group satisfy the following conditions (2) and (3), and satisfy the following condition (17):
_{(2) -2 <(R 21} + R 22) / (R 21 -R 22) <- 0.5
(3) 1 <(R ₂₃ + R ₂₄ ) / (R ₂₃ −R ₂₄ ) <5
(17) 0.7 <R ₁₂ /L<1.4
However, R ₂₁ and R ₂₂ are the object-side and image-side refracting surface radii of the second lens group positive lens component, and R ₂₃ and R ₂₄ are the object-side and image-side refractions of the second lens group negative lens component, respectively. surface radius of curvature, R ₁₂ is the radius of curvature der of the image-side surface of the negative lens including an aspheric surface on the refractive surface of the first lens group is, if each refractive surface is aspherical curvature radius near the optical axis and then, L is Ru diagonal length der of the effective image pickup area of the electronic image pickup device.   The positive lens component and the negative lens component in the second lens group are separated from each other, and the curvature of the object side surface of the negative lens component is stronger than that of the image side surface of the positive lens component. The electronic imaging device according to claim 1, wherein the electronic imaging device is an electronic imaging device. 6. The focusing lens group satisfies the following condition (1) with respect to a moving amount m _F when zooming from a wide-angle end to a telephoto end when focusing on an object point at infinity. The electronic imaging device according to any one of the above.
(1) 0.1 <(m _F −m ₂ ) / L <1
Here, m ₂ is the amount of movement when the second lens group is zoomed from the wide-angle end to the telephoto end when focusing on an object point at infinity, and L is the diagonal length (mm) of the effective imaging area of the image sensor. . A zooming unit in which the lens unit disposed closest to the image side includes an aspherical surface and is fixed during focusing, and is focused by moving the focusing lens unit immediately before the lens unit disposed closest to the image side. In an electronic imaging device comprising an imaging optical system and an electronic imaging device,
The variable magnification imaging optical system includes, in order from the object side, a first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, and a third lens having a positive refractive power. A lens group and a fourth lens group having positive refractive power;
Each lens group is variable during zooming,
The first lens group includes, in order from the object side, a negative single lens including an aspheric surface on the refracting surface, and a positive single lens whose refractive surface on the object side has a stronger curvature than the refracting surface on the image side. Consists of
The second lens group is composed of two lens components, a positive lens component having an aspherical surface and a negative lens component, and moves on the optical axis integrally with the aperture stop at the time of zooming,
The third lens group and the fourth lens group are each composed of two or less lens components,
The lens group arranged closest to the image side is composed of only one positive lens component,
An electronic imaging apparatus characterized by satisfying the following conditions (8), (9) and (17):
(8) -1.2 <(R _R1 + R _R2 ) / (R _R1 -R _R2 ) <0.8
(9) 0 <L / f _R <0.5
(17) 0.7 <R ₁₂ /L<1.4
Where R _R1 and R _R2 are the radii of curvature of the most object-side and image-side refracting surfaces of the most image-side lens components, respectively, and R ₁₂ is a negative including an aspheric surface on the refracting surface of the first lens group. The radius of curvature of the image-side surface of the lens. When each refracting surface is an aspherical surface, the radius of curvature is near the optical axis . L is the diagonal length (mm) of the effective imaging area of the electronic imaging device, f _R Is the combined focal length of the lens component closest to the image side.   8. The electronic image pickup apparatus according to claim 7, wherein the lens group disposed closest to the image side includes only one positive single lens. The electron according to any one of claims 1 to 8, wherein the focusing lens group includes only one positive lens component, and satisfies the following conditions (10) and (11). Imaging device.
(10) −5 <(R _F1 + R _F2 ) / (R _F1 −R _F2 ) <− 0.2
(11) 0.1 <L / f _F <0.7
However, R _F1 and R _F2 are the radiuses of curvature of the refractive surfaces of the lens components moving for the focus on the most object side and the image side, respectively. In the case of an aspherical surface, the radius of curvature is near the optical axis. L is the diagonal length (mm) of the effective imaging region of the image sensor, and f _F is the combined focal length of the lens components that move for the focus.   The electronic imaging apparatus according to claim 9, wherein the focusing lens group includes only one positive single lens. 11. The electronic imaging apparatus according to claim 1, wherein the following conditions (12) to (16) are satisfied with respect to paraxial amounts of the first lens group and the second lens group.
(12) −0.3 <m ₁ /L<1.2
(13) −3 <m ₂ / L <−1
(14) 0.2 <L / f ₂ <0.6
(15) 0.35 <L / f _23W <0.75
(16) -0.1 <L / f _12T <0.5
Where m ₁ and m ₂ are the movement amounts of the first lens group and the second lens group when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, and L is the effective amount of the electronic image sensor. The diagonal length (mm) of the imaging region, f ₂ is the combined focal length of the second lens group, and f _23W is the combined at the wide angle end when the second lens group and the third lens group are focused on an object point at infinity. The focal length, f _12T, is the combined focal length at the telephoto end when the first lens group and the second lens group are focused on an object point at infinity.

Images