JP4007789B2 - Electronic imaging device - Google Patents

Description

【００８９】

【００９０】

【００９１】

【００９２】
以上の実施例２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３、図４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。
【００９３】
次に、上記各実施例における条件（１）〜（８）、（１０）〜（１５）の値、条件（９）に関するAsp_2MAX 、Asp_3MAX 、最大絞り径（直径）φ、及び、Ｌの値を示す。

【００９４】
なお、実施例１〜４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。
【００９５】
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６）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。
【００９６】
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。
【００９７】
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。
【００９８】

【００９９】
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。
【０１００】
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。
【０１０１】
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。
【０１０２】
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。
【０１０３】
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。
【０１０４】
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。
【０１０５】
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。
【０１０６】
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。
【０１０７】
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。
【０１０８】
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。
【０１０９】
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。
【０１１０】
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。
【０１１１】
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。
【０１１２】
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。
【０１１３】
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。
【０１１４】
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。
【０１１５】
図１１〜図１３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。
【０１１６】
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。
【０１１７】
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。
【０１１８】
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。
【０１１９】
以上の本発明の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。
【０１２０】
〔１〕 ズームレンズ及びその像側に配された撮像素子を備えた電子撮像装置において、
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、各レンズ群の間隔を変化させつつ、前記第２レンズ群が物体側へのみ移動し、かつ、前記第３レンズ群は第２レンズ群とは異なる軌跡で移動し、
前記第２レンズ群は、物体側から順に、物体側面に非球面を有する正又は負の第１レンズＬ２１、正の第２レンズＬ２２、負の第３レンズＬ２３の３枚のレンズよりなると共に、前記第２レンズＬ２２と第３レンズＬ２３とは接合されており、
以下の条件を満足することを特徴とする電子撮像装置。
【０１２１】
（１） ０．６５＜Ｒ_21R ／Ｒ_21F ＜１．０５
（２） ０．３＜Ｌ／ｆ_2R＜０．９
ただし、Ｒ_21F 、Ｒ_21R はそれぞれ第２レンズ群の第１レンズＬ２１の物体側面及び像側面の光軸上の曲率半径、Ｌは撮像素子の有効撮像領域の対角長、ｆ_2Rは第２レンズ群の第２レンズＬ２２と第３レンズＬ２３との合成焦点距離である。
【０１２２】
〔２〕 前記第２レンズ群における第２レンズＬ２２及び第３レンズＬ２３が以下の条件を満足することを特徴とする上記１記載の電子撮像装置。
【０１２３】
（３） １０＜ν₂₂−ν₂₃
（４） −１．５＜（Ｒ_22F ＋Ｒ_23R ）／（Ｒ_22F −Ｒ_23R ）＜−０．１ただし、ν₂₂は第２レンズ群の第２レンズＬ２２のｄ線基準アッベ数、ν₂₃は第２レンズ群の第３レンズＬ２３のｄ線基準アッベ数、Ｒ_22F 、Ｒ_23R はそれぞれ第２レンズ群の第２レンズＬ２２の物体側面、第３レンズＬ２３の像側面における光軸上の曲率半径である。
【０１２４】
〔３〕 前記第３レンズ群は１つの正レンズ成分からなり、以下の条件を満足することを特徴とする上記１又は２記載の電子撮像装置。
【０１２５】
（５） −１．０＜（Ｒ_3F＋Ｒ_3R）／（Ｒ_3F−Ｒ_3R）＜０．５
ただし、Ｒ_3F、Ｒ_3Rはそれぞれ第３レンズ群の正レンズ成分の物体側面及び像側面の光軸上の曲率半径である。
【０１２６】
〔４〕 前記第３レンズ群は１つの正の単レンズからなることを特徴とする上記３記載の電子撮像装置。
【０１２７】
〔５〕 前記第３レンズ群は球面のみで構成されていることを特徴とする上記１から４の何れか１項記載の電子撮像装置。
【０１２８】
〔６〕 光路中に開口絞りを有し、かつ、前記第３レンズ群の屈折面の面形状が以下の条件を満足することを特徴とする上記１から４の何れか１項記載の電子撮像装置。
【０１２９】
（９） ０≦｜Asp_3MAX ｜／｜Asp_2MAX ｜≦０．５
ただし、Asp_3MAX は第３レンズ群における各々の屈折面の光軸上での曲率半径を有する球面に対し、光軸からの高さが絞り半径最大値の０．７倍の位置における非球面偏倚量の最大値、Asp_2MAX は第２レンズ群における各々の屈折面の光軸上での曲率半径を有する球面に対し、光軸からの高さが絞り半径最大値の０．７倍の位置における非球面偏倚量の最大値である。
【０１３０】
〔７〕 広角端から望遠端への変倍に際して、前記第３レンズ群は物体側に凸の形状の軌跡で移動することを特徴とする上記１から６の何れか１項記載の電子撮像装置。
【０１３１】
〔８〕 前記第１レンズ群は、非球面を含む負レンズと正レンズの２枚のレンズで構成され、以下の条件式を満足することを特徴とする上記１から７の何れか１項記載の電子撮像装置。
【０１３２】
（６） ２０＜ν₁₁−ν₁₂
（７） −１０＜（Ｒ₁₃＋Ｒ₁₄）／（Ｒ₁₃−Ｒ₁₄）＜−２．０
ただし、ν₁₁は第１レンズ群の負レンズのｄ線基準アッベ数、ν₁₂は第１レンズ群の正レンズのｄ線基準アッベ数、Ｒ₁₃、Ｒ₁₄はそれぞれ第１レンズ群の正レンズの物体側面及び像側面の光軸上の曲率半径である。
【０１３３】
〔９〕 前記第１レンズ群は、空気間隔を挟んで負レンズと正レンズの２枚のレンズで構成され、以下の条件式を満足することを特徴とする上記１から８の何れか１項記載の電子撮像装置。
【０１３４】
（８） ０．２＜ｄ₁₁／Ｌ＜０．６５
ただし、ｄ₁₁は第１レンズ群の負レンズと正レンズとの光軸上の空気間隔である。
【０１３５】
〔１０〕 前記撮像素子の有効撮像領域の対角長Ｌが以下の条件を満足することを特徴とする上記１から９の何れか１項記載の電子撮像装置。
【０１３６】
３．０ｍｍ ＜ L ＜ １２．０ｍｍ
〔１１〕 前記ズームレンズの広角端半画角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１０の何れか１項記載の電子撮像装置。
【０１３７】
〔１２〕 前記第３レンズ群はフォーカシング時に単独で移動することを特徴とする上記１から１１の何れか１項記載の電子撮像装置。
【０１３８】
〔１３〕 前記第１レンズ群と前記第２レンズ群との間に配された開口絞りを有することを特徴とする上記１から１２の何れか１項記載の電子撮像装置。
【０１３９】
〔１４〕 前記開口絞りは前記第２レンズ群と一体で移動することを特徴とする上記１３記載の電子撮像装置。
【０１４０】
【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３】実施例２の無限遠物点合焦時の収差図である。
【図４】実施例２の被写体距離１０ｃｍ合焦時の収差図である。
【図５】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
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 an electronic image pickup apparatus, and more particularly to an electronic image pickup apparatus such as a video camera or a digital camera that is thinned in the depth direction by devising an optical system portion such as a zoom lens. 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 object is to have a small number of components, a small and simple mechanism layout such as a rear focus method, and a stable and high connection from infinity to a short distance. Select a zoom method or zoom configuration that has image performance, and further reduce the total thickness of each group by thinning the lens elements, or considering the selection of filters, and thoroughly adopt video cameras and digital cameras. It is to reduce the thickness.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an electronic image pickup apparatus according to the present invention includes a zoom lens and an image pickup element provided on an image side of the zoom lens,
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. At the time of zooming from the wide-angle end to the telephoto end at the time of focusing, the second lens group moves only to the object side while changing the distance between the lens groups, and the third lens group is the second lens. Move in a different trajectory from the group,
The second lens group includes, in order from the object side, three lenses, a positive or negative first lens L21 having an aspheric surface on the object side, a positive second lens L22, and a negative third lens L23. The second lens L22 and the third lens L23 are cemented,
An electronic imaging apparatus characterized by satisfying the following conditions.
[0009]
(1) 0.65 <R _21R / R _21F <1.05
(2) 0.3 <L / f _2R <0.9
Here, R _21F and R _21R are the curvature radii on the optical axis of the object side surface and the image side surface of the first lens L21 of the second lens group, L is the diagonal length of the effective imaging region of the image sensor, and f _2R is the second This is the combined focal length of the second lens L22 and the third lens L23 of the lens group.
[0010]
Hereinafter, the reason and effect | action which take the said structure in this invention are demonstrated.
[0011]
An electronic image pickup apparatus according to the present invention includes, in an electronic image pickup apparatus including a zoom lens and an image pickup element disposed on an image side thereof, as a zoom lens, in order from the object side, a first lens group having negative refractive power, and a positive lens unit. The second lens group having a refracting power and a third lens group having a positive refracting power, and the distance between the lens groups is changed upon zooming from the wide angle end to the telephoto end when focusing on an object point at infinity. The second lens group moves only toward the object side, the third lens group moves along a different locus from the second lens group, and the second lens group moves in order from the object side to the object side surface. The first and second lenses L21, L22, L22 and negative lens L23 having an aspheric surface are joined together, and the second lens L22 and the third lens L23 are cemented. Adopting a different type of zoom lens By that.
[0012]
In the present invention, the term “lens” refers to a lens made of a single medium as a unit, and the cemented lens consists of a plurality of lenses. Moreover, a lens component means the lens group which does not arrange | position an air space | interval between them, and means a single lens or a cemented lens.
[0013]
In a negative-positive two-group zoom lens that has been used as a zoom lens for silver halide film cameras 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 of the zoom lens. However, for this purpose, a positive lens component is added as a third lens group further to 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. Is well known. Further, the third lens group has a possibility of being used for focusing.
[0014]
In order to achieve the object of the present invention, that is, to reduce the fluctuation of off-axis aberrations such as astigmatism when the third lens unit is focused while the total thickness of the lens unit is reduced when retracted. In addition, the second lens group includes, in order from the object side, a single positive or negative lens L21 whose surface closest to the object side is an aspheric surface, and a positive lens component formed by joining the positive lens L22 and the negative lens L23 in that order. In particular, it is preferable that the lens component closest to the object side has a strong meniscus shape with the convex surface facing the object side and the curvature radius of both surfaces being close.
[0015]
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.
[0016]
Therefore, the third lens group is constituted by a spherical system or a small amount of aspherical surface, the aperture stop is arranged on the object side of the second lens group, and the second lens group is a single lens having an aspheric surface on the object side surface. It is preferable that the lens is composed of a positive or negative lens L21, and a cemented lens component in order of the positive lens L22 and the negative lens L23.
[0017]
Further, in this type, since the front lens diameter is difficult to increase, the aperture stop is integrated with the second lens group (in the embodiments described later of the present invention, it is disposed immediately before the second lens group and integrated with the second lens group). ) Is not only simple in terms of mechanism but also difficult to generate a dead space when retracted, and the difference in F-number between the wide-angle end and the telephoto end is small.
[0018]
In addition, since the positive lens L22 of the second lens group and the negative lens L23 on the image side generate remarkable aberrations due to their relative decentration, they should be joined together. In the case of cementing, it is preferable to cancel the aberration in the cemented lens (L22, L23) as much as possible to reduce the decentration sensitivity.
[0019]
In order to reduce the relative decentration sensitivity between the single positive or negative lens L21 and the cemented components of the positive lens L22 and the negative lens L23, the following conditions should be satisfied.
[0020]
(1) 0.65 <R _21R / R _21F <1.05
(2) 0.3 <L / f _2R <0.9
Where R _21F and R _21R are the curvature radii on the optical axis of the object side surface and the image side surface of the first lens L21 of the second lens group, respectively, L is the diagonal length of the effective imaging region (substantially rectangular) of the image sensor, f _2R is a combined focal length of the second lens L22 and the third lens L23 of the second lens group.
[0021]
Exceeding the upper limit of 1.05 to condition (1) is advantageous for correcting spherical aberration, coma aberration, and astigmatism of the entire system aberration, but has little effect of reducing decentration sensitivity by bonding. When the lower limit of 0.65 is exceeded, correction of spherical aberration, coma aberration, and astigmatism of the total system aberration tends to be difficult.
[0022]
If the lower limit of 0.3 of the condition (2) is exceeded, the exit pupil position tends to approach the image plane and cause shading, and the cemented components of the first lens L21, the second lens L22, and the third lens L23 The sensitivity of eccentricity tends to increase. If the upper limit of 0.9 is exceeded, it is difficult to ensure a small and high zoom ratio.
[0023]
Note that it is better to set one or both of the conditions (1) and (2) as follows.
[0024]
(1) '0.7 <R _21R / R _21F <1
(2) ′ 0.35 <L / f _2R <0.8
Furthermore, it is better to set one or both of the conditions (1) and (2) as follows. In particular, it is best to do both as follows.
[0025]
(1) ”0.75 <R _21R / R _21F <0.95
(2) "0.4 <L / f _2R <0.7
Moreover, it is preferable that the following conditional expressions are satisfied for the cemented components of the second lens L22 and the third lens L23.
[0026]
(3) 10 <ν ₂₂ −ν ₂₃
(4) −1.5 <(R _22F + R _23R ) / (R _22F −R _23R ) <− 0.1
Where ν ₂₂ is the d-line reference Abbe number of the second lens L22 of the second lens group, ν ₂₃ is the d-line reference Abbe number of the third lens L23 of the second lens group, and R _22F and R _23R are the second lens, respectively. This is the radius of curvature on the optical axis of the object side surface of the second lens L22 and the image side surface of the third lens L23 in the group.
[0027]
If the lower limit of 10 to condition (3) is exceeded, both axial chromatic aberration and lateral chromatic aberration will be insufficiently corrected. The upper limit is not particularly set because there is no more suitable medium combination, but if an upper limit is added, the upper limit should be set to 75 and ν ₂₃ −ν ₂₂ should be less than that. . If the upper limit value 75 is exceeded, the lens material becomes expensive.
[0028]
Condition (4) is a rule regarding the shape factor of the cemented components (L22, L23) of the second lens group. If the lower limit of −1.5 is exceeded, the air gap d ₂₁ of the second lens group can be easily reduced, but it becomes difficult to correct coma and astigmatism. If the upper limit of −0.1 is exceeded, d ₂₁ tends to increase due to mechanical interference between the first lens L21 and the second lens L22, which is a foothold for reducing the collapsed thickness.
[0029]
In addition, it is better to set one or both of the conditions (3) and (4) as follows.
[0030]
(3) '12 <ν ₂₂ −ν ₂₃
(4) ′ − 1.4 <(R _22F + R _23R ) / (R _22F −R _23R ) <− 0.2
Furthermore, it is better to set one or both of the conditions (3) and (4) as follows. In particular, it is best to do both as follows.
[0031]
(3) ”14 <ν ₂₂ −ν ₂₃
(4) ”− 1.3 <(R _22F + R _23R ) / (R _22F −R _23R ) <− 0.3 On the other hand, the third lens group can be composed of one positive lens component. Satisfy the conditions.
[0032]
(5) −1.0 <(R _3F + R _3R ) / (R _3F −R _3R ) <0.5
Here, R _3F and R _3R are the radii of curvature on the optical axis of the object side surface and the image side surface of the positive lens component of the third lens group, respectively.
[0033]
If the upper limit of 0.5 of the condition (5) is exceeded, the fluctuation of astigmatism due to the rear focus becomes too large, and even if the astigmatism can be corrected well at an infinite object point, Astigmatism tends to deteriorate. When the lower limit of −1.0 is exceeded, astigmatism fluctuation due to rear focus is small, but it is difficult to correct aberrations for infinite object points.
[0034]
The third lens group may be composed of one positive lens. Practical aberration level correction is possible and contributes to thinning.
[0035]
It is better to do the following.
[0036]
(5) ′ − 0.9 <(R _3F + R _3R ) / (R _3F −R _3R ) <0.3
Furthermore, it is best to do the following.
[0037]
(5) "-0.8 <(R 3F + R 3R) / (R 3F -R 3R) <0.1
Next, if the first lens group is composed of only two lenses, a negative lens including an aspherical surface and a positive lens, while satisfying the following conditions, chromatic aberration and each Seidel off-axis aberration can be corrected well. Contributes to thinning.
[0038]
(6) 20 <ν ₁₁ −ν ₁₂
(7) −10 <(R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ) <− 2.0
Where ν ₁₁ is the d-line reference Abbe number of the negative lens of the first lens group, ν ₁₂ is the d-line reference Abbe number of the positive lens of the first lens group, and R ₁₃ and R ₁₄ are positive lenses of the first lens group, respectively. Are the radii of curvature on the optical axis of the object side surface and the image side surface.
[0039]
Condition (6) is defined with respect to fluctuations in axial and magnification chromatic aberration during zooming. If the lower limit of 20 is exceeded, the variation in axial and lateral chromatic aberration tends to increase. The upper limit is not particularly set because there is no medium more suitable for reality, but if an upper limit value is added, the upper limit value is set to 75, and ν ₁₁ −ν ₁₂ should be less than that. If the upper limit 75 is exceeded, the glass material becomes expensive.
[0040]
Condition (7) defines the shape factor of the positive lens in the first lens group. Exceeding the lower limit of −10 is disadvantageous in correcting astigmatism, and also disadvantageous in that it requires an extra space with the second lens group in order to avoid mechanical interference during zooming. When the upper limit of −2.0 is exceeded, correction of distortion tends to be disadvantageous.
[0041]
In addition, it is better to set one or both of the conditions (6) and (7) as follows.
[0042]
(6) '22 <ν ₁₁ −ν ₁₂
(7) ′ −9 <(R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ) <− 2.5
Furthermore, it is better to set one or both of the conditions (6) and (7) as follows. In particular, it is best to do both as follows.
[0043]
(6) ”24 <ν ₁₁ −ν ₁₂
(7) "-8 <(R 13 + R 14) / (R 13 -R 14) <- 3
In addition, the following conditions should be satisfied.
[0044]
(8) 0.2 <d ₁₁ /L<0.65
However, d ₁₁ is the air gap along the optical axis between the negative lens and the positive lens in the first lens group.
[0045]
If the upper limit of 0.65 is exceeded, it is advantageous for correction of coma, astigmatism, and distortion, but the optical system becomes thicker, and if the lower limit of 0.2 is exceeded, these aberrations are reduced. Correction is difficult despite the introduction of an aspherical surface.
[0046]
It is better to do the following.
[0047]
(8) ′ 0.25 <d ₁₁ /L<0.6
Furthermore, it is best to do the following.
[0048]
(8) ”0.3 <d ₁₁ /L<0.55
Previously, it has been described that it is preferable to configure the third lens unit with a spherical system or a small amount of aspherical surface in order to suppress aberration fluctuations during focusing. More specifically, a configuration that satisfies the following conditions: It is preferable that
[0049]
(9) 0 ≦ | Asp _3MAX | / | Asp _2MAX | ≦ 0.5
However, Asp _3MAX is an aspherical deviation at a position where the height from the optical axis is 0.7 times the maximum aperture radius with respect to the spherical surface having the radius of curvature on the optical axis of each refractive surface in the third lens group. The maximum value, Asp _2MAX, is at a position where the height from the optical axis is 0.7 times the maximum aperture radius relative to the spherical surface having the radius of curvature on the optical axis of each refractive surface in the second lens group. This is the maximum value of the aspherical deviation.
[0050]
Since the lower limit value of the condition (9) is set to 0, which is a value corresponding to a value in which the third lens group is entirely composed of a spherical surface or a flat surface, the lower limit value 0 of this condition is not exceeded and becomes smaller. On the other hand, if the aspherical deviation amount in the third lens unit increases beyond the upper limit of 0.5, the aberration fluctuation during focusing increases.
[0051]
In the present invention, as shown in FIG. 5, the aspherical deviation amount has a height from the optical axis with respect to a spherical surface (reference spherical surface) having a radius of curvature r on the optical axis of the target aspherical surface. This is the amount of deviation of the aspheric surface at a position 0.7 times the maximum aperture radius.
[0052]
In addition, the corresponding values of condition (9) in Examples 1 to 3 described later are all zero. In the table | surface regarding Examples 1-4 mentioned later, it is set as the largest aperture diameter (diameter), and an aperture shape is circular. In the present invention, the diaphragm may be variable in shape or fixed in shape.
[0053]
Note that the zoom lens of the present invention is advantageous in constructing an electronic imaging device including a wide angle region. In particular, it is preferably used for an electronic imaging apparatus in which the half angle of view ω _W in the diagonal direction at the wide angle end satisfies the following conditions (the wide angle end half angle of view described in each example described later corresponds to ω _W. ).
[0054]
27 ° <ω _W <42 °
If the wide angle end half angle of view becomes narrower beyond the lower limit of 27 ° under this condition, it becomes advantageous for aberration correction, but it is not a practical angle of view 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.
[0055]
In addition, since the zoom lens used in the electronic image sensor of the present invention can guide the off-axis principal ray to the image sensor in a nearly vertical state, a good image can be obtained up to the periphery of the image. At that time, it is more preferable that the diagonal length L of the effective imaging region of the imaging device is 3.0 mm to 12.0 mm in order to achieve both good image quality and downsizing.
[0056]
If the image sensor becomes smaller than the lower limit of 3.0 mm of this condition, insufficient sensitivity will be difficult to cover. On the other hand, if the image sensor becomes larger than the upper limit of 12.0 mm, the zoom lens tends to become larger accordingly, and the effect of thinning is reduced.
[0057]
It should be noted that satisfying the following condition simultaneously with the above-described condition (1) is advantageous for correcting off-axis aberrations including astigmatism.
[0058]
(10) 0.3 <R _21R /L<0.7
It is better to do the following.
[0059]
(10) '0.35 <R _21R /L<0.65
Furthermore, it is best to do the following.
[0060]
(10) ”0.4 <R _21R /L<0.6
As described above, a means for improving the imaging performance while reducing the retractable thickness of the zoom lens unit has been provided.
[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. A near-infrared sharp cut coat with a transmittance (τ ₆₀₀ ) at a wavelength of 600 nm of 80% or more and a transmittance (τ ₇₀₀ ) at ₇₀₀ nm of 8% or less on the object side of the image sensor behind the zoom lens system When introduced, 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, which is a disadvantage of a solid-state imaging device such as a CCD having a complementary color mosaic filter. The magenta tendency on the side is alleviated by gain adjustment, and color reproduction similar to that of a solid-state imaging device such as a CCD having a primary color filter can be obtained.
[0062]
That is,
(11) τ ₆₀₀ / τ ₅₅₀ ≧ 0.8
(12) τ ₇₀₀ / τ ₅₅₀ ≦ 0.08
It is desirable to satisfy. However, (tau) ₅₅₀ is the transmittance | permeability in wavelength 550nm.
[0063]
In addition, it is better to set one or both of the conditions (11) and (12) as follows.
[0064]
(11) 'τ ₆₀₀ / τ ₅₅₀ ≧ 0.85
(12) 'τ ₇₀₀ / τ ₅₅₀ ≦ 0.05
Furthermore, it is better to set one or both of the conditions (11) and (12) as follows. In particular, it is best to do both as follows.
[0065]
(11) ”τ ₆₀₀ / τ ₅₅₀ ≧ 0.9
(12) ”τ ₇₀₀ / τ ₅₅₀ ≦ 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 ratio of transmittance (τ ₄₀₀ ) at a wavelength of 400 nm to that at 550 nm (τ ₅₅₀ ) is less than 0.08, and the ratio of the transmittance at ₄₄₀ nm (τ ₄₄₀ ) to that at 550 nm (τ ₅₅₀ ). Inserting an absorber or reflector that exceeds 0.4 on the optical path does not lose the wavelength range necessary for color reproduction (while maintaining good color reproduction), and significantly reduces noise such as color bleeding. Is done.
[0066]
That is,
(13) τ ₄₀₀ / τ ₅₅₀ ≦ 0.08
(14) τ ₄₄₀ / τ ₅₅₀ ≧ 0.4
It is desirable to satisfy.
[0067]
Note that it is better to set one or both of the conditions (13) and (14) as follows.
[0068]
(13) 'τ ₄₀₀ / τ ₅₅₀ ≦ 0.06
(14) 'τ ₄₄₀ / τ ₅₅₀ ≧ 0.5
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.
[0069]
(13) ”τ ₄₀₀ / τ ₅₅₀ ≦ 0.04
(14) ”τ ₄₄₀ / τ ₅₅₀ ≧ 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 has substantially higher sensitivity than a CCD with a primary color filter and is advantageous in terms of resolution. It is. For the optical low-pass filter as the other filter, the total thickness t _LPF (mm) should satisfy the following condition.
[0071]
(15) 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 to satisfy the condition (15) including filter specifications other than those described above, for example, when 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 (15) ′ 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]
(15) ”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 an F value such that a (μm) / F number <0.4, the medium having different transmittances for 550 nm and less than 80% in the opening. An electronic imaging device having For example, if the medium is not within the above range from the open value, or a dummy medium with a transmittance of 550 nm or more is set to 91% or more, and the aperture diameter is within the range, the aperture stop diameter is reduced to such an extent that the influence of diffraction occurs. 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 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 4 of the zoom lens used in the electronic imaging apparatus of the present invention will be described below. FIGS. 1 and 2 show lens cross-sectional views at the wide-angle end (a), the intermediate state (b), and the telephoto end (c), respectively, when focusing on an object point at infinity in Examples 1 and 3. Since Examples 2 and 4 are the same as those in FIG. 1, illustration is omitted. In the figure, the first lens group is G1, the aperture 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 cover glass is an electronic image sensor. The image plane of CG and 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. .
[0080]
As shown in FIG. 1, the zoom lenses according to the first, second, and fourth embodiments include a first lens group G1 having a negative refractive power that includes a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side. A second lens group G2 having a positive refractive power composed of an aperture stop S, a negative meniscus lens convex on the object side, a cemented lens of a biconvex lens and a negative meniscus lens convex on the image side, and a single biconvex positive lens. Consists of a third lens group G3 having positive refractive power, and when zooming from the wide-angle end to the telephoto end, the first lens group G1 moves with a concave locus on the object side, and at the telephoto end, the image plane is larger than the wide-angle end. 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 is slightly more objected at the telephoto end than at the wide-angle end. It becomes the position of the side. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0081]
As for the aspherical surface, Example 1 is used for the two surfaces of the image surface side surface of the negative meniscus lens of the first lens group G1 and the object side surface of the single negative meniscus lens of the second lens group G2. .
[0082]
Example 2 is used for the three surfaces of the image plane side surface of the negative meniscus lens of the first lens group G1 and the both surfaces of the single negative meniscus lens of the second lens group G2.
[0083]
In Example 4, the image side surface of the negative meniscus lens of the first lens group G1, the object side surface of the single negative meniscus lens of the second lens group G2, and the object side surface of the third lens group G3 are three. Used on the surface.
[0084]
As shown in FIG. 2, the zoom lens according to the third exemplary embodiment includes a first lens group G1 having a negative refractive power including a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, Second lens group G2 having a positive refractive power composed of a negative meniscus lens convex on the object side, a cemented lens of a biconvex lens and a negative meniscus lens convex on the image side, a negative meniscus lens convex on the object side and a biconvex positive The third lens group G3 having a positive refractive power composed of a cemented lens of the lens, 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 the telephoto end , 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 the telephoto end. Then, it is slightly 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.
[0085]
The aspherical surface is used for two surfaces, that is, the image side surface of the negative meniscus lens of the first lens group G1 and the object side surface of the single negative meniscus lens of the second lens group G2.
[0086]
The numerical data of each of the above embodiments are shown below. Symbols are the above, f is the total focal length, ω is the half field angle, _FNO is the F number, WE is the wide angle end, ST is the intermediate state, TE telephoto end, r _1, r ₂ ... curvature radius of each lens surface, d _1, d ₂ ... the spacing between the lens surfaces, n _d1, n _d2 ... d-line refractive index of each lens, [nu _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 = (y ² / r) / [1+ {1- (K + 1) (y / r) ² } ^1/2 ]
+ A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰
Here, r is a paraxial radius of curvature, K is a conical coefficient, and A ₄ , A ₆ , A ₈ , and A ₁₀ are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.
[0088]

[0089]

[0090]

[0091]

[0092]
FIG. 3 and FIG. 4 show aberration diagrams in Example 2 when focusing on an object point at infinity and focusing on a subject distance of 10 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.
[0093]
Next, conditions in the above respective embodiments (1) to (8), (10) the value of - (15), Asp conditions on (9) _2MAX, Asp _3MAX, maximum aperture diameter (diameter) phi, and, of L Indicates the value.

[0094]
Note that the total thickness t _LPF of the low-pass filters LF of Examples 1 to 4 is 1.500 (mm) and is configured 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.
[0095]
Here, the diagonal length L of the effective imaging surface and the pixel interval a will be described. FIG. 6 is a diagram illustrating an example of a 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. 6) 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.
[0096]
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.
[0097]
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.
[0098]

[0099]
The transmittance characteristics of the near infrared sharp cut coat are as shown in FIG. In addition, the color reproducibility of the electronic image is further improved by providing or coating a color filter that reduces the transmission of colors in the short wavelength region as shown in FIG. 8 on the emission surface side of the low-pass filter LF. ing.
[0100]
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.
[0101]
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.
[0102]
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.
[0103]
Such means for limiting the wavelength is more effective in an imaging system using a complementary color mosaic filter.
[0104]
In each of the above embodiments, as shown in FIG. 8, the transmittance is 0% at a wavelength of 400 nm, the transmittance at 420 nm is 90%, and the transmittance peak is 100% at 440 nm.
[0105]
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.
[0106]
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.
[0107]
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 becomes possible.
[0108]
Specifically, the complementary color mosaic filter is composed of at least four types of color filters as shown in FIG. 9, and the characteristics of the four types of color filters are preferably as follows.
[0109]
The green color filter G has a spectral intensity peak at the wavelength _GP ,
Yellow filter element Y _e has a spectral strength peak at a wavelength Y _P,
Each cyan filter element C has a spectral strength peak at a wavelength C _P,
The magenta color filter M has peaks at wavelengths M _P1 and M _P2 and satisfies the following conditions.
[0110]
510 nm <G _P <540 nm
5 nm <Y _P −G _P <35 nm
−100 nm <C _P −G _P <−5 nm
430 nm <M _P1 <480 nm
580 nm <M _P2 <640 nm
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%.
[0111]
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. The yellow color filter Y _e has 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. In each color filter at 530 nm, G is 99%, _Ye is 95%, C is 97%, and M is 38% with respect to the respective spectral intensity peaks.
[0112]
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.
[0113]
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.
[0114]
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.
[0115]
FIGS. 11 to 13 are conceptual diagrams of a configuration in which the zoom lens 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 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.
[0116]
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.
[0117]
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.
[0118]
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.
[0119]
The electronic imaging apparatus of the present invention described above can be configured as follows, for example.
[0120]
[1] In an electronic image pickup apparatus including a zoom lens and an image pickup element arranged on the image side thereof,
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. At the time of zooming from the wide-angle end to the telephoto end at the time of focusing, the second lens group moves only to the object side while changing the distance between the lens groups, and the third lens group is the second lens. Move in a different trajectory from the group,
The second lens group includes, in order from the object side, three lenses, a positive or negative first lens L21 having an aspheric surface on the object side, a positive second lens L22, and a negative third lens L23. The second lens L22 and the third lens L23 are cemented,
An electronic imaging apparatus characterized by satisfying the following conditions.
[0121]
(1) 0.65 <R _21R / R _21F <1.05
(2) 0.3 <L / f _2R <0.9
Here, R _21F and R _21R are the curvature radii on the optical axis of the object side surface and the image side surface of the first lens L21 of the second lens group, L is the diagonal length of the effective imaging region of the image sensor, and f _2R is the second This is the combined focal length of the second lens L22 and the third lens L23 of the lens group.
[0122]
[2] The electronic imaging apparatus as described in 1 above, wherein the second lens L22 and the third lens L23 in the second lens group satisfy the following conditions.
[0123]
(3) 10 <ν ₂₂ −ν ₂₃
(4) −1.5 <(R _22F + R _23R ) / (R _22F −R _23R ) <− 0.1 where ν ₂₂ is the d-line reference Abbe number of the second lens L22 of the second lens group, ν ₂₃ Is the d-line reference Abbe number of the third lens L23 of the second lens group, and R _22F and R _23R are curvatures on the optical axis of the object side surface of the second lens L22 and the image side surface of the third lens L23, respectively. Radius.
[0124]
[3] The electronic imaging apparatus as described in [1] or [2], wherein the third lens group includes one positive lens component and satisfies the following condition.
[0125]
(5) −1.0 <(R _3F + R _3R ) / (R _3F −R _3R ) <0.5
Here, R _3F and R _3R are the radii of curvature on the optical axis of the object side surface and the image side surface of the positive lens component of the third lens group, respectively.
[0126]
[4] The electronic image pickup apparatus according to [3], wherein the third lens group includes one positive single lens.
[0127]
[5] The electronic imaging apparatus as described in any one of [1] to [4], wherein the third lens group includes only a spherical surface.
[0128]
[6] The electronic imaging as described in any one of [1] to [4], wherein an aperture stop is included in the optical path, and a surface shape of a refracting surface of the third lens group satisfies the following condition: apparatus.
[0129]
(9) 0 ≦ | Asp _3MAX | / | Asp _2MAX | ≦ 0.5
However, Asp _3MAX is an aspherical deviation at a position where the height from the optical axis is 0.7 times the maximum aperture radius with respect to the spherical surface having the radius of curvature on the optical axis of each refractive surface in the third lens group. The maximum value, Asp _2MAX, is at a position where the height from the optical axis is 0.7 times the maximum aperture radius relative to the spherical surface having the radius of curvature on the optical axis of each refractive surface in the second lens group. This is the maximum value of the aspherical deviation.
[0130]
[7] The electronic imaging apparatus according to any one of [1] to [6], wherein the third lens group moves along a locus having a convex shape toward the object side upon zooming from the wide angle end to the telephoto end. .
[0131]
[8] The first lens group includes two lenses, a negative lens including an aspherical surface and a positive lens, and satisfies the following conditional expression: Electronic imaging device.
[0132]
(6) 20 <ν ₁₁ −ν ₁₂
(7) −10 <(R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ) <− 2.0
Where ν ₁₁ is the d-line reference Abbe number of the negative lens of the first lens group, ν ₁₂ is the d-line reference Abbe number of the positive lens of the first lens group, and R ₁₃ and R ₁₄ are positive lenses of the first lens group, respectively. Are the radii of curvature on the optical axis of the object side surface and the image side surface.
[0133]
[9] The first lens group includes two lenses, a negative lens and a positive lens, with an air gap therebetween, and satisfies the following conditional expression: The electronic imaging device described.
[0134]
(8) 0.2 <d ₁₁ /L<0.65
However, d ₁₁ is the air gap along the optical axis between the negative lens and the positive lens in the first lens group.
[0135]
[10] The electronic imaging apparatus according to any one of 1 to 9, wherein a diagonal length L of an effective imaging region of the imaging element satisfies the following condition.
[0136]
3.0mm <L <12.0mm
[11] The electronic imaging apparatus according to any one of [1] to [10], wherein a wide angle end half field angle ω _{W of the} zoom lens is in a range of 27 ° to 42 °.
[0137]
[12] The electronic imaging apparatus according to any one of [1] to [11], wherein the third lens group moves independently during focusing.
[0138]
[13] The electronic imaging apparatus as described in any one of [1] to [12], further comprising an aperture stop disposed between the first lens group and the second lens group.
[0139]
[14] The electronic imaging apparatus as described in [13], wherein the aperture stop moves integrally with the second lens group.
[0140]
【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 cross-sectional view of a lens 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 3. FIG.
FIG. 3 is an aberration diagram for Example 2 upon focusing on an object point at infinity.
FIG. 4 is an aberration diagram for Example 2 upon focusing on a subject distance of 10 cm.
FIG. 5 is a diagram for explaining the definition of the amount of aspherical deviation in the present invention.
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 ... 1st lens group G2 ... 2nd lens group G3 ... 3rd 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 ... Optical system 42 ... Optical path for photographing 43 ... Viewfinder optical system 44 ... Optical path for viewfinder 45 ... Shutter 46 ... Flash 47 ... Liquid crystal display monitor 49 ... CCD
DESCRIPTION OF SYMBOLS 50 ... Cover member 51 ... Processing means 52 ... Recording means 53 ... Finder objective optical system 55 ... Porro prism 57 ... Field frame 59 ... Eyepiece optical system

Claims (14)

In an electronic imaging device including a zoom lens and an imaging device arranged on the image side thereof,
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. At the time of zooming from the wide-angle end to the telephoto end at the time of focusing, the second lens group moves only to the object side while changing the distance between the lens groups, and the third lens group is the second lens. Move in a different trajectory from the group,
The second lens group includes, in order from the object side, three lenses, a positive or negative first lens L21 having an aspheric surface on the object side, a positive second lens L22, and a negative third lens L23. The second lens L22 and the third lens L23 are cemented,
An electronic imaging apparatus characterized by satisfying the following conditions.
(1) 0.65 <R _21R / R _21F <1.05
(2) 0.3 <L / f _2R <0.9
Here, R _21F and R _21R are the curvature radii on the optical axis of the object side surface and the image side surface of the first lens L21 of the second lens group, L is the diagonal length of the effective imaging region of the image sensor, and f _2R is the second This is the combined focal length of the second lens L22 and the third lens L23 of the lens group. The electronic imaging apparatus according to claim 1, wherein the second lens L22 and the third lens L23 in the second lens group satisfy the following conditions.
(3) 10 <ν ₂₂ −ν ₂₃
(4) −1.5 <(R _22F + R _23R ) / (R _22F −R _23R ) <− 0.1 where ν ₂₂ is the d-line reference Abbe number of the second lens L22 of the second lens group, ν ₂₃ Is the d-line reference Abbe number of the third lens L23 of the second lens group, and R _22F and R _23R are curvatures on the optical axis of the object side surface of the second lens L22 and the image side surface of the third lens L23, respectively. Radius. The electronic imaging apparatus according to claim 1, wherein the third lens group includes one positive lens component and satisfies the following condition.
(5) −1.0 <(R _3F + R _3R ) / (R _3F −R _3R ) <0.5
Here, R _3F and R _3R are the radii of curvature on the optical axis of the object side surface and the image side surface of the positive lens component of the third lens group, respectively.   The electronic imaging apparatus according to claim 3, wherein the third lens group includes one positive single lens.   The electronic imaging apparatus according to claim 1, wherein the third lens group includes only a spherical surface. 5. The electronic imaging apparatus according to claim 1, wherein the electronic imaging apparatus has an aperture stop in an optical path, and a surface shape of a refractive surface of the third lens group satisfies the following condition.
(9) 0 ≦ | Asp _3MAX | / | Asp _2MAX | ≦ 0.5
However, Asp _3MAX is an aspherical deviation at a position where the height from the optical axis is 0.7 times the maximum aperture radius with respect to the spherical surface having the radius of curvature on the optical axis of each refractive surface in the third lens group. The maximum value, Asp _2MAX, is at a position where the height from the optical axis is 0.7 times the maximum aperture radius relative to the spherical surface having the radius of curvature on the optical axis of each refractive surface in the second lens group. This is the maximum value of the aspherical deviation.   7. The electronic imaging apparatus according to claim 1, wherein the third lens unit moves along a locus having a convex shape toward the object side upon zooming from the wide-angle end to the telephoto end. The electron according to any one of claims 1 to 7, wherein the first lens group includes two lenses, a negative lens including an aspherical surface and a positive lens, and satisfies the following conditional expression. Imaging device.
(6) 20 <ν ₁₁ −ν ₁₂
(7) −10 <(R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ) <− 2.0
Where ν ₁₁ is the d-line reference Abbe number of the negative lens of the first lens group, ν ₁₂ is the d-line reference Abbe number of the positive lens of the first lens group, and R ₁₃ and R ₁₄ are positive lenses of the first lens group, respectively. Are the radii of curvature on the optical axis of the object side surface and the image side surface. The said 1st lens group is comprised with two lenses, a negative lens and a positive lens on both sides of an air space | interval, The following conditional expression is satisfied, The any one of Claim 1 to 8 characterized by the above-mentioned. Electronic imaging device.
(8) 0.2 <d ₁₁ /L<0.65
However, d ₁₁ is the air gap along the optical axis between the negative lens and the positive lens in the first lens group. The electronic imaging apparatus according to claim 1, wherein a diagonal length L of an effective imaging region of the imaging element satisfies the following condition.
3.0mm <L <12.0mm 11. The electronic imaging apparatus according to claim 1, wherein a wide angle end half field angle ω _{W of the} zoom lens is in a range of 27 ° to 42 °.   The electronic imaging apparatus according to claim 1, wherein the third lens group moves independently during focusing.   The electronic image pickup apparatus according to claim 1, further comprising an aperture stop disposed between the first lens group and the second lens group.   14. The electronic imaging apparatus according to claim 13, wherein the aperture stop moves integrally with the second lens group.

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