JP4039837B2 - Electronic imaging device - Google Patents

Description

【００８１】
画素ピッチの小さな電子撮像素子を使用する場合、絞り込みによる回折効果の影響で画質が劣化する。したがって、開口サイズが固定の複数の開口を有し、その中の１つを第１レンズ群の最も像側のレンズ面と第３レンズ群の最も物体側のレンズ面の間の何れかの光路内に挿入でき、かつ、他の開口と交換可能とすることで像面照度の調節することができる電子撮像装置としておき、その複数の開口の中、一部の開口内に５５０ｎｍに対する透過率がそれぞれ異なり、かつ、８０％未満であるような媒体を有するようにして光量調節を行なうのがよい。あるいは、ａ（μｍ）／Ｆナンバー＜０．４となるようなＦ値に相当する光量になるように調節を実施する場合は、開口内に５５０ｎｍに対する透過率がそれぞれ異なりかつ８０％未満の媒体を有する電子撮像装置とするのがよい。例えば、開放値から上記条件の範囲外ではその媒体なしかあるいは５５０ｎｍに対する透過率が９１％以上のダミー媒質としておき、範囲内のときは回折の影響が出る程に開口絞り径を小さくするのではなく、ＮＤフィルターのようなもので光量調節するのがよい。
【００８２】
また、その複数の開口をそれぞれ径をＦ値に反比例して小さくしたものにして揃えておき、ＮＤフィルターの代わりにそれぞれ周波数特性の異なる光学的ローパスフィルターを開口内に入れておくのでもよい。絞り込むにつれて回折劣化が大きくなるので、開口径が小さくなる程光学的ローパスフィルターの周波数特性を高く設定しておく。
【００８３】
【発明の実施の形態】
以下、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１〜５について説明する。実施例１〜５の無限遠物点合焦時の広角端（ａ）、中間状態（ｂ）、望遠端（ｃ）でのレンズ断面図をそれぞれ図１〜図５に示す。各図中、第１レンズ群はＧ１、絞りはＳ、第２レンズ群はＧ２、第３レンズ群はＧ３、赤外カット吸収フィルターはＩＦ、ローパスフィルターはＬＦ、電子撮像素子であるＣＣＤのカバーガラスはＣＧ、ＣＣＤの像面はＩで示してある。なお、赤外カット吸収フィルターＩＦに代えて、透明平板の入射面に近赤外シャープカットコートとしたものを用いてもよいし、ローパスフィルターＬＦに直接近赤外シャープカットコートを施してもよい（実施例２）。
【００８４】
実施例１のズームレンズは、図１に示すように、物体側に凸の負メニスカスレンズと、物体側に凸の正メニスカスレンズとからなる負屈折力の第１レンズ群Ｇ１、開口絞りＳ、前群が物体側に凸の正メニスカスレンズと物体側に凸の負メニスカスレンズの接合レンズからなり、後群が物体側に凸の負メニスカスレンズと両凸レンズの正接合レンズからなる正屈折力の第２レンズ群Ｇ２、両凸正レンズ１枚からなる正屈折力の第３レンズ群Ｇ３からなり、広角端から望遠端に変倍する際は、第１レンズ群Ｇ１は物体側に凹の軌跡を描いて移動し、望遠端では広角端より像面側の位置になり、第２レンズ群Ｇ２は開口絞りＳと一体に物体側に移動し、第３レンズ群Ｇ３は像面側に凸の軌跡を描いて移動し、望遠端では広角端より物体側の位置になる。近距離の被写体にフォーカシングするために、第３レンズ群Ｇ３は物体側に繰り出される。
【００８５】
非球面は、第１レンズ群Ｇ１の負メニスカスレンズの像面側の面、第２レンズ群Ｇ２の前群の接合レンズの物体側の面、後群の接合レンズの像面側の面の３面に用いられている。
【００８６】
実施例２のズームレンズは、図２に示すように、物体側に凸の正メニスカスレンズと、物体側に凸の負メニスカスレンズと、両凹負レンズと、物体側に凸の正メニスカスレンズとからなる負屈折力の第１レンズ群Ｇ１、開口絞りＳ、前群が物体側に凸の正メニスカスレンズと物体側に凸の負メニスカスレンズの接合レンズからなり、後群が両凸正レンズからなる正屈折力の第２レンズ群Ｇ２、両凸正レンズ１枚からなる正屈折力の第３レンズ群Ｇ３からなり、広角端から望遠端に変倍する際は、第１レンズ群Ｇ１は物体側に凹の軌跡を描いて移動し、望遠端では広角端より像面側の位置になり、第２レンズ群Ｇ２は開口絞りＳと一体に物体側に移動し、第３レンズ群Ｇ３は像面側に凸の軌跡を描いて移動し、望遠端では広角端より像面側の位置になる。近距離の被写体にフォーカシングするために、第３レンズ群Ｇ３は物体側に繰り出される。
【００８７】
非球面は、第２レンズ群Ｇ２の接合レンズの物体側の面、両凸正レンズの物体側の面の２面に用いられている。
【００８８】
実施例３のズームレンズは、図３に示すように、物体側に凸の負メニスカスレンズと、物体側に凸の正メニスカスレンズとからなる負屈折力の第１レンズ群Ｇ１、開口絞りＳ、前群が物体側に凸の正メニスカスレンズと物体側に凸の負メニスカスレンズの接合レンズからなり、後群が両凸正レンズからなる正屈折力の第２レンズ群Ｇ２、両凸正レンズ１枚からなる正屈折力の第３レンズ群Ｇ３からなり、広角端から望遠端に変倍する際は、第１レンズ群Ｇ１は物体側に凹の軌跡を描いて移動し、望遠端では広角端より像面側の位置になり、第２レンズ群Ｇ２は開口絞りＳと一体に物体側に移動し、第３レンズ群Ｇ３は像面側に凸の軌跡を描いて移動し、望遠端では広角端と略同じ位置になる。近距離の被写体にフォーカシングするために、第３レンズ群Ｇ３は物体側に繰り出される。
【００８９】
非球面は、第１レンズ群Ｇ１の負メニスカスレンズの像面側の面、第２レンズ群Ｇ２の接合レンズの物体側の面、後群の両凸正レンズの像面側の面の３面に用いられている。
【００９０】
実施例４のズームレンズは、図４に示すように、物体側に凸の負メニスカスレンズと、物体側に凸の正メニスカスレンズとからなる負屈折力の第１レンズ群Ｇ１、開口絞りＳ、前群が物体側に凸の正メニスカスレンズと物体側に凸の負メニスカスレンズの接合レンズからなり、後群が両凸正レンズからなる正屈折力の第２レンズ群Ｇ２、両凸正レンズ１枚からなる正屈折力の第３レンズ群Ｇ３からなり、広角端から望遠端に変倍する際は、第１レンズ群Ｇ１は物体側に凹の軌跡を描いて移動し、望遠端では広角端より像面側の位置になり、第２レンズ群Ｇ２は開口絞りＳと一体に物体側に移動し、第３レンズ群Ｇ３は像面側に凸の軌跡を描いて移動し、望遠端では広角端と略同じ位置になる。近距離の被写体にフォーカシングするために、第３レンズ群Ｇ３は物体側に繰り出される。
【００９１】
非球面は、第１レンズ群Ｇ１の負メニスカスレンズの像面側の面、第２レンズ群Ｇ２の接合レンズの物体側の面、後群の両凸正レンズの物体側の面の３面に用いられている。
【００９２】
実施例５のズームレンズは、図５に示すように、物体側に凸の負メニスカスレンズと、物体側に凸の正メニスカスレンズとからなる負屈折力の第１レンズ群Ｇ１、開口絞りＳ、前群が物体側に凸の正メニスカスレンズと物体側に凸の負メニスカスレンズの接合レンズからなり、後群が両凸正レンズからなる正屈折力の第２レンズ群Ｇ２、両凸正レンズ１枚からなる正屈折力の第３レンズ群Ｇ３からなり、広角端から望遠端に変倍する際は、第１レンズ群Ｇ１は物体側に凹の軌跡を描いて移動し、望遠端では広角端より像面側の位置になり、第２レンズ群Ｇ２は開口絞りＳと一体に物体側に移動し、第３レンズ群Ｇ３は像面側に凸の軌跡を描いて移動し、望遠端では広角端と略同じ位置になる。近距離の被写体にフォーカシングするために、第３レンズ群Ｇ３は物体側に繰り出される。
【００９３】
非球面は、第１レンズ群Ｇ１の負メニスカスレンズの像面側の面、第２レンズ群Ｇ２の接合レンズの物体側の面、後群の両凸正レンズの像面側の面の３面に用いられている。
【００９４】
以下に、上記各実施例の数値データを示すが、記号は上記の外、ｆは全系焦点距離、ωは半画角、Ｆ_NOはＦナンバー、ＷＥは広角端、ＳＴは中間状態、ＴＥは望遠端、ｒ₁ 、ｒ₂ …は各レンズ面の曲率半径、ｄ₁ 、ｄ₂ …は各レンズ面間の間隔、ｎ_d1、ｎ_d2…は各レンズのｄ線の屈折率、ν_d1、ν_d2…は各レンズのアッベ数である。なお、非球面形状は、ｘを光の進行方向を正とした光軸とし、ｙを光軸と直交する方向にとると、下記の式にて表される。
【００９５】

ただし、ｒは近軸曲率半径、Ｋは円錐係数、A₄、A₆、A₈、A₁₀ はそれぞれ４次、６次、８次、１０次の非球面係数である。
【００９６】

【００９７】

【００９８】

【００９９】

【０１００】

【０１０１】
以上の実施例１の無限遠物点合焦時及び被写体距離１０ｃｍ合焦時の収差図をそれぞれ図６、図７に示す。また、実施例２、３の無限遠物点合焦時の収差図をそれぞれ図８、図９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。
【０１０２】
次に、上記各実施例における条件（１）〜（３）、（５）〜（１９）の値、条件（４）に関するAsp2F 、Asp2R 及びＬの値を示す。

【０１０３】
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。
【０１０４】
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１１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１１）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。
【０１０５】
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。
【０１０６】
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。
【０１０７】
基 板 材質 物理的膜厚（ｎｍ） λ／４
───────────────────────────────
第１層 Ａｌ₂ Ｏ₃ ５８．９６ ０．５０
第２層 ＴｉＯ₂ ８４．１９ １．００
第３層 ＳｉＯ₂ １３４．１４ １．００
第４層 ＴｉＯ₂ ８４．１９ １．００
第５層 ＳｉＯ₂ １３４．１４ １．００
第６層 ＴｉＯ₂ ８４．１９ １．００
第７層 ＳｉＯ₂ １３４．１４ １．００
第８層 ＴｉＯ₂ ８４．１９ １．００
第９層 ＳｉＯ₂ １３４．１４ １．００
第10層 ＴｉＯ₂ ８４．１９ １．００
第11層 ＳｉＯ₂ １３４．１４ １．００
第12層 ＴｉＯ₂ ８４．１９ １．００
第13層 ＳｉＯ₂ １３４．１４ １．００
第14層 ＴｉＯ₂ ８４．１９ １．００
第15層 ＳｉＯ₂ １７８．４１ １．３３
第16層 ＴｉＯ₂ １０１．０３ １．２１
第17層 ＳｉＯ₂ １６７．６７ １．２５
第18層 ＴｉＯ₂ ９６．８２ １．１５
第19層 ＳｉＯ₂ １４７．５５ １．０５
第20層 ＴｉＯ₂ ８４．１９ １．００
第21層 ＳｉＯ₂ １６０．９７ １．２０
第22層 ＴｉＯ₂ ８４．１９ １．００
第23層 ＳｉＯ₂ １５４．２６ １．１５
第24層 ＴｉＯ₂ ９５．１３ １．１３
第25層 ＳｉＯ₂ １６０．９７ １．２０
第26層 ＴｉＯ₂ ９９．３４ １．１８
第27層 ＳｉＯ₂ ８７．１９ ０．６５
───────────────────────────────
空 気 。
【０１０８】
上記の近赤外シャープカットコートの透過率特性は図１２に示す通りである。
【０１０９】
また、ローパスフィルターＬＦの射出面側には、図１３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。
【０１１０】
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。
【０１１１】
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。
【０１１２】
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。
【０１１３】
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。
【０１１４】
上記各実施例では、図１３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。
【０１１５】
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。
【０１１６】
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。
【０１１７】
また、ＣＣＤの撮像面Ｉ上には、図１４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。
【０１１８】
補色モザイクフィルターは、具体的には、図１４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。
【０１１９】
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。
【０１２０】
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。
【０１２１】
上記各実施例におけるそれぞれの波長特性の一例を図１５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。
【０１２２】
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。
【０１２３】
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。
【０１２４】
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。
【０１２５】
図１６〜図１８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１６はデジタルカメラ４０の外観を示す前方斜視図、図１７は同後方斜視図、図１８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。
【０１２６】
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。
【０１２７】
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。
【０１２８】
なお、図１８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。
【０１２９】
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。
【０１３０】
〔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前記第２レンズ群が物体側へのみ移動し、前記第３レンズ群が第２レンズ群との間隔を変化させつつ移動し、前記第２レンズ群は、空間を挟んで物体側から順に、第２群前群、第２群後群からなり、前記第２群前群は、物体側から順に、非球面を有する正レンズ、負レンズの２枚接合レンズ成分からなり、前記第２群後群は、非球面を有する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電子撮像装置。
【０１３１】
（１） ０．６＜Ｒ₂₃／Ｒ₂₁＜１．０
（２） ０．０５＜ｆ_2R／Ｒ₂₂＜１．５
（３） ν₂₂＜２６．５
（４） ２．５×１０^-3・Ｌ＞｜Asp2R ｜＞０．１・｜Asp2F ｜
ただし、Ｒ₂₁、Ｒ₂₂、Ｒ₂₃はそれぞれ第２群前群の最も物体側の面、接合面、最も像側の面の光軸上の曲率半径、ｆ_2Rは第２群後群の合成焦点距離、ν₂₂は第２群前群の負レンズの媒質のｄ線基準アッベ数、Ｌは撮像素子の有効撮像領域の対角長、Asp2F 、Asp2R はそれぞれ第２群前群の正レンズに設けられた非球面と第２群後群に設けられた非球面が有する光軸上の曲率半径を持つ基準球面に対し、光軸からの高さが０．３Ｌでの非球面偏倚量である。
【０１３２】
〔２〕 前記第２群後群は正屈折力の単レンズにて構成され、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。
【０１３３】
（６） ０．０４＜ｔ_2N／ｔ₂ ＜０．２
ただし、ｔ_2Nは第２群前群における負レンズの光軸上の厚み、ｔ₂ は第２レンズ群の最も物体側のレンズ面から最も像側のレンズ面までの光軸上の厚みである。
【０１３４】
〔３〕 以下の条件を満足することを特徴とする上記２記載の電子撮像装置。
【０１３５】
（７） −１．５＜（Ｒ_2RF ＋Ｒ_2RR ）／（Ｒ_2RF −Ｒ_2RR ）＜０
（８） ０．７＜ｆ_2R／ｆ₂ ＜２
ただし、Ｒ_2RF 、Ｒ_2RR はそれぞれ第２群後群の最も物体側の面及び最も像側の面の光軸上の曲率半径、ｆ_2Rは第２群後群の焦点距離、ｆ₂ は第２レンズ群全系の合成焦点距離である。
【０１３６】
〔４〕 前記第２群後群は、物体側から順に、負レンズと正レンズの接合レンズ成分にて構成され、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。
【０１３７】
（９） ０＜ν_2RN −ν₂₂＜３５、かつ、ν₂₂≦２６．５
ただし、ν₂₂は第２群前群の負レンズのｄ線基準のアッベ数、ν_2RN は第２群後群の負レンズのｄ線基準のアッベ数である。
【０１３８】
〔５〕 以下の条件を満足することを特徴とする上記４記載の電子撮像装置。
【０１３９】
（10） −２．０＜（Ｒ_2RF ＋Ｒ_2RR ）／（Ｒ_2RF −Ｒ_2RR ）＜−０．５
（11） ０．７＜ｆ_2R／ｆ₂ ＜２
ただし、Ｒ_2RF 、Ｒ_2RR はそれぞれ第２群後群の最も物体側の面及び最も像側の面の光軸上の曲率半径、ｆ_2Rは第２群後群の焦点距離、ｆ₂ は第２レンズ群全系の合成焦点距離である。
【０１４０】
〔６〕 前記第３レンズ群が以下の条件を満足することを特徴とする上記１から５の何れか１項記載の電子撮像装置。
【０１４１】
（12） −０．２＜（Ｒ_3F＋Ｒ_3R）／（Ｒ_3F−Ｒ_3R）＜１．５
ただし、Ｒ_3F、Ｒ_3Rはそれぞれ第３レンズ群の最も物体側の面及び最も像側の面の光軸上の曲率半径である。
【０１４２】
〔７〕 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枚で構成されており、以下の条件を満足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。
【０１４３】
（13） ２０＜ν₁₁−ν₁₂
（14） −１０＜（Ｒ₁₃＋Ｒ₁₄）／（Ｒ₁₃−Ｒ₁₄）＜−２
ただし、ν₁₁、ν₁₂はそれぞれ第１レンズ群の負レンズと正レンズの媒質のｄ線基準のアッベ数、Ｒ₁₃、Ｒ₁₄はそれぞれ第１レンズ群正レンズの物体側の面、像側の面の光軸上の曲率半径である。
【０１４４】
〔８〕 無限遠物点合焦時における広角端から望遠端への変倍に際して、前記第３レンズ群が像側に凸の軌跡で移動することを特徴とする上記１から７の何れか１項記載の電子撮像装置。
【０１４５】
〔９〕 前記第３レンズ群は１枚の正レンズのみで構成されてい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。
【０１４６】
〔１０〕 前記第２群前群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。
【０１４７】
（５） ０．０１＜ｎ₂₂−ｎ₂₁＜０．２０
ただし、ｎ₂₁、ｎ₂₂はそれぞれ第２群前群の正レンズ、負レンズのｄ線に対する媒質屈折率である。
【０１４８】
〔１１〕 前記第１レンズ群と第２レンズ群との間に絞りを配した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。
【０１４９】
〔１２〕 変倍時に前記絞りが第２レンズ群と一体で移動することを特徴とする上記１１に記載の電子撮像装置。
【０１５０】
〔１３〕 前記第３レンズ群の移動により近距離物点への合焦を行う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。
【０１５１】
〔１４〕 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１３の何れか１項記載の電子撮像装置。
【０１５２】
【発明の効果】
本発明により、沈胴厚が薄く収納性に優れ、かつ、高倍率でリアフォーカスにおいても結像性能の優れたズームレンズを得ることができ、ビデオカメラやデジタルカメラの徹底的薄型化を図ることが可能となる。
【図面の簡単な説明】
【図１】本発明の電子撮像装置に用いられるズームレンズの実施例１の無限遠物点合焦時の広角端（ａ）、中間状態（ｂ）、望遠端（ｃ）でのレンズ断面図である。
【図２】実施例２のズームレンズの図１と同様のレンズ断面図である。
【図３】実施例３のズームレンズの図１と同様のレンズ断面図である。
【図４】実施例４のズームレンズの図１と同様のレンズ断面図である。
【図５】実施例５のズームレンズの図１と同様のレンズ断面図である。
【図６】実施例１の無限遠物点合焦時の収差図である。
【図７】実施例１の被写体距離１０ｃｍ合焦時の収差図である。
【図８】実施例２の無限遠物点合焦時の収差図である。
【図９】実施例３の無限遠物点合焦時の収差図である。
【図１０】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１１】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１２】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１３】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１４】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１５】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１６】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１７】図１６のデジタルカメラの後方斜視図である。
【図１８】図１６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 thinnest, Japanese Patent Laid-Open No. Hei 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. The second lens group moves only to the object side during zooming from the wide-angle end to the telephoto end during point focusing, and the third lens group moves while changing the distance from the second lens group. The second lens group includes a front group of the second group and a rear group of the second group in order from the object side across the space, and the second group front group includes a positive lens and an negative lens having an aspheric surface in order from the object side. The second group rear group is composed of a positive lens component having an aspherical surface, and satisfies the following conditions.
[0009]
(1) 0.6 <R_{twenty three}/ R_{twenty one}<1.0
(2) 0.05 <f_2R/ R_{twenty two}<1.5
(3) ν_{twenty two}<26.5
(4) 2.5 × 10^-3・ L> | Asp2R |> 0.1 ・ | Asp2F |
However, R_{twenty one}, R_{twenty two}, R_{twenty three}Is the radius of curvature on the optical axis of the surface closest to the object side, the cemented surface, and the surface closest to the image side in the second group front group, f_2RIs the combined focal length of the second group, ν_{twenty two}Is the d-line reference Abbe number of the medium of the negative lens in the second lens unit front group, L is the diagonal length of the effective imaging area of the image sensor, and Asp2F and Asp2R are aspherical surfaces provided on the positive lens in the second lens unit front group, respectively. The aspherical deviation amount when the height from the optical axis is 0.3 L with respect to the reference spherical surface having the radius of curvature on the optical axis of the aspherical surface provided in the rear group of the second group.
[0010]
Hereinafter, the reason and effect | action which take the said structure in this invention are demonstrated.
[0011]
The electronic imaging device of the present invention is an electronic imaging device including a zoom lens and an imaging device disposed on the image side thereof, and the zoom lens includes, in order from the object side, a first lens group having negative refractive power; A second lens group having a positive refractive power and a third lens group having a positive refractive power, and the second lens group is located on the object side upon zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity. And the third lens group moves while changing the distance from the second lens group. The second lens group is arranged in order from the object side across the space, the second group front group, the second group. It consists of a rear group, and the second group front group is composed of, in order from the object side, a positive lens component having an aspherical surface and a negative cemented lens component of a negative lens, and the second group rear group is a positive lens component having an aspheric surface A zoom lens with the following structure is adopted.
[0012]
In the following description, it is assumed that the second lens unit front group positive lens is L21, the negative lens lens is L22, and the second lens group rear lens positive lens component is L23.
[0013]
Further, in the present invention, a lens is a single lens made of a single medium, and a cemented lens is made 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.
[0014]
In a negative-positive two-group zoom lens that has been used as a zoom lens for silver salt 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.
[0015]
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 is preferably composed of two lens components in order from the object side: a cemented lens component of a positive lens and a negative lens and a positive lens component having an aspherical surface.
[0016]
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.
[0017]
Therefore, the third lens group is constituted by a spherical system or a small amount of aspheric surface, the aperture stop is arranged on the object side of the second lens group, and the second lens group is a positive lens having an aspheric surface in order from the object side. It is preferable to use two lens components, a cemented lens component of the negative lens and a positive lens component having an aspherical surface.
[0018]
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. In addition, since the positive lens L21 and the negative lens L22 on the object side of the second lens group are prone to aberrations due to their relative decentration, they should be joined together. Further, regarding the second lens group, it is preferable that the following conditional expression is satisfied.
[0019]
(1) 0.6 <R_{twenty three}/ R_{twenty one}<1.0
(2) 0.05 <f_2R/ R_{twenty two}<1.5
(3) ν_{twenty two}<26.5
(4) 2.5 × 10^-3・ L> | Asp2R |> 0.1 ・ | Asp2F |
However, R_{twenty one}, R_{twenty two}, R_{twenty three}Is the radius of curvature on the optical axis of the surface closest to the object side, the cemented surface, and the surface closest to the image side in the second group front group, f_2RIs the combined focal length of the second group, ν_{twenty two}Is the d-line reference Abbe number of the medium of the negative lens in the second lens unit front group, L is the diagonal length of the effective imaging area of the image sensor, and Asp2F and Asp2R are aspherical surfaces provided on the positive lens in the second lens unit front group, respectively. The aspherical deviation amount when the height from the optical axis is 0.3 L with respect to the reference spherical surface having the radius of curvature on the optical axis of the aspherical surface provided in the rear group of the second group. That is, as shown in FIG. 10, the amount of aspherical deviation referred to in the present invention is the effective imaging area of the imaging device with respect to a spherical surface (reference spherical surface) having a radius of curvature r on the optical axis of the target aspherical surface. When the diagonal length is L, it means the amount of deviation of the aspheric surface at a position where the height from the optical axis is 0.3L.
[0020]
The objective of the second group front group is to cancel the aberration coefficient in the cemented lens component to reduce the decentration sensitivity. Exceeding the upper limit of 1.0 of the condition (1) is advantageous for correcting spherical aberration, coma aberration, and astigmatism of the entire system aberration, but the effect of reducing the decentration sensitivity by the joining is small. If the lower limit of 0.6 is exceeded, it will be difficult to correct spherical aberration, coma aberration, and astigmatism of the total system aberration.
[0021]
Conditions (2) and (3) are regulations relating to correction of longitudinal and lateral chromatic aberration. If the upper limit of 1.5 of condition (2) is exceeded, the thickness of the cemented lens of the second lens group can be easily reduced. This makes it difficult to correct axial chromatic aberration. If the lower limit of 0.05 is exceeded, it is advantageous for correcting axial chromatic aberration, but it is necessary to increase the thickness of the cemented lens, and it becomes a foothold to reduce the collapsed thickness.
[0022]
If the upper limit of 26.5 of the condition (3) is exceeded, the axial chromatic aberration will be insufficiently corrected. The lower limit is not particularly set because there is no medium suitable for reality below, but if a lower limit is added, the lower limit is set to 20 and ν_{twenty two}Should be more than that. If the lower limit 20 is exceeded, the lens material becomes expensive.
[0023]
By the way, since the third lens group can introduce only a spherical surface or only a small amount of aspherical surface, an aspherical surface having a certain amount of deviation with respect to the spherical surface of the radius of curvature in the vicinity of the optical axis is not introduced accordingly. Then, spherical aberration, coma and astigmatism cannot be corrected sufficiently. On the other hand, since it is necessary to emphasize the relative decentration sensitivity of each component in the second lens group, it is preferable to satisfy the condition (4) for the aspheric surface. Upper limit of 2.5 × 10^-3When L is exceeded, the relative decentration sensitivity between the front group and the rear group in the second lens group tends to increase. If the lower limit of 0.1 · | Asp2F | is exceeded, spherical aberration, coma aberration, and astigmatism cannot be corrected sufficiently.
[0024]
If possible, the following conditions should be satisfied.
[0025]
(5) 0.01 <n_{twenty two}-N_{twenty one}<0.20
Where n_{twenty one}, N_{twenty two}Are the medium refractive indices for the d-line of the positive lens and negative lens in the second group front group, respectively.
[0026]
This condition stipulates the medium refractive index difference between the positive lens and the negative lens in the second group front group. If the lower limit of 0.01 is exceeded, the relative eccentric sensitivity of the front group and rear group in the second group However, it is difficult to correct the entire coma aberration. If the upper limit of 0.20 is exceeded, it is advantageous for correcting each aberration in the entire zoom range, but it is disadvantageous for improving the relative eccentric sensitivity of the front group and the rear group in the second group.
[0027]
In addition, it is better to set one or more or all of the conditions (1) to (5) as follows.
[0028]
(1) '0.65 <R_{twenty three}/ R_{twenty one}<0.95
(2) '0.08 <f_2R/ R_{twenty two}<1.4
(3) ’ν_{twenty two}<26
(4) '3.0 × 10^-3・ L> | Asp2R |> 0.1 ・ | Asp2F |
(5) '0.02 <n_{twenty two}-N_{twenty one}<0.18
Furthermore, it is better to set one or more of the conditions (1) to (5) as follows. In particular, it is best to do everything as follows.
[0029]
(1) ”0.7 <R_{twenty three}/ R_{twenty one}<0.9
(2) "0.1 <f_2R/ R_{twenty two}<1.3
(3) "ν_{twenty two}<25.5
(4) ”2.5 × 10^-3・ L> | Asp2R |> 0.1 ・ | Asp2F |
(5) "0.03 <n_{twenty two}-N_{twenty one}<0.16
Further, when the second group rear group is constituted by a positive single lens, the following conditions should be satisfied.
[0030]
(6) 0.04 <t_2N/ T₂<0.2
Where t_2NIs the thickness on the optical axis of the negative lens in the front group of the second group, t₂Is the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the second lens group.
[0031]
Condition (6) is that the thickness t on the optical axis of the negative lens of the cemented lens of the second group front group_2NIs specified. The astigmatism cannot be corrected unless this part is made thick to some extent, but this is a foothold for the purpose of reducing the thickness of each element of the optical system. Therefore, astigmatism is corrected by introducing an aspheric surface on any surface of the first lens group. If the lower limit of 0.04 is still exceeded, astigmatism cannot be corrected completely. If the upper limit of 0.2 is exceeded, the thickness is unacceptable.
[0032]
It is better to do the following.
[0033]
(6) '0.06 <t_2N/ T₂<0.18
Furthermore, it is best to do the following.
[0034]
(6) "0.08 <t_2N/ T₂<0.16
Further, when the rear group of the second group is constituted by a positive single lens, the following conditions are preferably satisfied.
[0035]
(7) -1.5 <(R_2RF+ R_2RR) / (R_2RF-R_2RR) <0
(8) 0.7 <f_2R/ F₂<2
However, R_2RF, R_2RRIs the radius of curvature on the optical axis of the most object-side surface and the most image-side surface of the second group rear group, f_2RIs the focal length of the rear group of the second group, f₂Is the combined focal length of the entire second lens group.
[0036]
Condition (7) is a rule concerning the shape factor of the positive single lens in the second group rear group. If the lower limit of −1.5 is exceeded, the air gap d of the second lens group_{twenty two}However, it is difficult to correct coma and astigmatism. When the upper limit of 0 is exceeded, d is caused by mechanical interference between the negative lens L22 (second group front group negative lens) and L23 (second group rear group positive lens)._{twenty two}Tends to be large, and it becomes a footpad to reduce the collapsed thickness.
[0037]
When the upper limit of 2 of the condition (8) is exceeded, the exit pupil position tends to cause shading close to the image plane, and the relative eccentric sensitivity of the second group front group and the rear group increases. When the lower limit of 0.7 is exceeded, it is difficult to sufficiently correct spherical aberration, coma aberration, and astigmatism, and it is difficult to ensure a compact and high zoom ratio.
[0038]
In addition, it is better to set one or both of the conditions (7) and (8) as follows.
[0039]
(7) '-1.4 <(R_2RF+ R_2RR) / (R_2RF-R_2RR<0.1
(8) '0.75 <f_2R/ F₂<1.9
Furthermore, it is better to set one or both of the conditions (7) and (8) as follows. In particular, it is best to do both as follows.
[0040]
(7) "-1.3 <(R_2RF+ R_2RR) / (R_2RF-R_2RR) <-0.2
(8) "0.8 <f_2R/ F₂<1.8
On the other hand, when the rear group of the second group is composed of a cemented lens component of a negative lens and a positive lens in order from the object side, the following conditions should be satisfied.
[0041]
(9) 0 <ν_2RN−ν_{twenty two}<35 (ν_{twenty two}≦ 26.5)
Where ν_{twenty two}Is the Abbe number based on the d-line of the negative lens in the second lens unit, ν_2RNIs the d-line-based Abbe number of the negative lens in the second group rear group. The parentheses indicate preconditions.
[0042]
Condition (9) is a condition for correcting axial chromatic aberration and lateral chromatic aberration in a balanced manner. When the lower limit of 0 is exceeded, the longitudinal chromatic aberration tends to be undercorrected, and the lateral chromatic aberration tends to be overcorrected. If the upper limit of 35 is exceeded, the opposite will be true.
[0043]
It is better to do the following.
[0044]
(9) ’5 <ν_2RN−ν_{twenty two}<30 (ν_{twenty two}≦ 26)
Furthermore, it is best to do the following.
[0045]
(9) ”10 <ν_2RN−ν_{twenty two}<25 (ν_{twenty two}≦ 25.5)
Furthermore, when the second group rear group is composed of a cemented lens component of a negative lens and a positive lens in order from the object side, the following conditions may be satisfied.
[0046]
(10) -2.0 <(R_2RF+ R_2RR) / (R_2RF-R_2RR<0.5
(11) 0.7 <f_2R/ F₂<2
However, R_2RF, R_2RRIs the radius of curvature on the optical axis of the most object-side surface and the most image-side surface of the second group rear group, f_2RIs the focal length of the rear group of the second group, f₂Is the combined focal length of the entire second lens group.
[0047]
The condition (10) is for the same reason as the condition (7) and the conditions (11) and (8).
[0048]
In addition, it is better to set one or both of the conditions (10) and (11) as follows.
[0049]
(10) '-1.9 <(R_2RF+ R_2RR) / (R_2RF-R_2RR<0.6
(11) ’0.75 <f_2R/ F₂<1.9
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) "-1.8 <(R_2RF+ R_2RR) / (R_2RF-R_2RR) <-0.7
(11) ”0.8 <f_2R/ F₂<1.8
Next, regarding the third lens group that is also movable for focusing, the following conditions should be satisfied.
[0051]
(12) -0.2 <(R_3F+ R_3R) / (R_3F-R_3R<1.5
However, R_3F, R_3RAre the radii of curvature on the optical axis of the most object-side surface and the most image-side surface of the third lens group, respectively.
[0052]
If the upper limit of 1.5 of this condition 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 −0.2 is exceeded, astigmatism variation due to rear focus is small, but it is difficult to correct aberrations for object points at infinity.
[0053]
When zooming from the wide-angle end to the telephoto end, the third lens unit moves along a convex locus toward the image side, so that it is easy to secure an adjustment margin especially at the telephoto end where there is a large variation in focus position due to performance error. become. The third lens group may be composed of one positive lens. Practical aberration level correction is possible and contributes to thinning.
[0054]
It is better to do the following.
[0055]
(12) ’0.0 <(R_3F+ R_3R) / (R_3F-R_3R) <1.4
Furthermore, it is best to do the following.
[0056]
(12) ”0.2 <(R_3F+ R_3R) / (R_3F-R_3R<1.3
The first lens group is preferably composed of two lenses, a negative lens including an aspherical surface and a positive lens, and satisfies the following conditions.
[0057]
(13) 20 <ν₁₁−ν₁₂
(14) -10 <(R₁₃+ R₁₄) / (R₁₃-R₁₄<-2
Where ν₁₁, Ν₁₂Are respectively the Abbe numbers of the d-line reference of the medium of the negative lens and the positive lens of the first lens group, R₁₃, R₁₄Are the radii of curvature on the optical axis of the object-side surface and the image-side surface of the first lens group positive lens, respectively.
[0058]
The condition (13) is defined with respect to the variation of the on-axis and lateral chromatic aberration at the time of 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 is added, the upper limit is set to 75, and ν₁₁−ν₁₂Should be less than that. If the upper limit value 75 is exceeded, the lens material becomes expensive.
[0059]
Condition (14) 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. If the upper limit of −2 is exceeded, correction of distortion aberration tends to be disadvantageous.
[0060]
In addition, it is better to set one or both of the conditions (13) and (14) as follows.
[0061]
(13) ’22 <ν₁₁−ν₁₂
(14) ′ −9 <(R₁₃+ R₁₄) / (R₁₃-R₁₄<2.5
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.
[0062]
(13) ”24 <ν₁₁−ν₁₂
(14) "-8 <(R₁₃+ R₁₄) / (R₁₃-R₁₄) <-3
As described above, a means for improving the imaging performance while reducing the retractable thickness of the zoom lens unit has been provided.
[0063]
Note that the zoom lens of the present invention is advantageous in constructing an electronic imaging device including a wide angle region. In particular, the half angle of view ω in the diagonal direction at the wide-angle end_WIs preferably used in an electronic imaging device that satisfies the following conditions (the wide angle end half angle of view described in each example below is ω_WIt corresponds to. ).
[0064]
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, if the upper limit of 42 ° is exceeded, distortion and chromatic aberration of magnification tend to occur, and the number of lenses increases.
[0065]
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.
[0066]
That is,
(15) τ₆₀₀/ Τ₅₅₀≧ 0.8
(16) τ₇₀₀/ Τ₅₅₀≦ 0.08
It is desirable to satisfy. Where τ₅₅₀Is the transmittance at a wavelength of 550 nm.
[0067]
Note that it is better to set one or both of the conditions (15) and (16) as follows.
[0068]
(15) ’τ₆₀₀/ Τ₅₅₀≧ 0.85
(16) ’τ₇₀₀/ Τ₅₅₀≦ 0.05
Furthermore, it is better to set one or both of the conditions (15) and (16) as follows. In particular, it is best to do both as follows.
[0069]
(15) “τ₆₀₀/ Τ₅₅₀≧ 0.9
(16) “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 necessary for color reproduction is not lost (while maintaining good color reproduction), and noise such as color bleeding Is considerably reduced.
[0070]
That is,
(17) τ₄₀₀/ Τ₅₅₀≦ 0.08
(18) τ₄₄₀/ Τ₅₅₀≧ 0.4
It is desirable to satisfy.
[0071]
Note that it is better to set one or both of the conditions (17) and (18) as follows.
[0072]
(17) ’τ₄₀₀/ Τ₅₅₀≦ 0.06
(18) ’τ₄₄₀/ Τ₅₅₀≧ 0.5
Furthermore, it is better to set one or both of the conditions (17) and (18) as follows. In particular, it is best to do both as follows.
[0073]
(17) “τ₄₀₀/ Τ₅₅₀≦ 0.04
(18) “τ₄₄₀/ Τ₅₅₀≧ 0.6
These filters are preferably installed between the imaging optical system and the image sensor.
[0074]
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. The total thickness t of the other optical low-pass filter is also t._LPF(Mm) should satisfy the following conditions.
[0075]
(19) 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.
[0076]
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.
[0077]
It is preferable that the condition (19) is satisfied, including the case where filter specifications other than those described above are carried out, 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.
[0078]
If a is 4 μm or less, it is more susceptible to diffraction.
(19) ’0.13 <t_LPF/A<0.42
It is good.
[0079]
Further, the following may be performed according to the number of low-pass filters superimposed on the horizontal pixel pitch.
[0080]

[0081]
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 there is no medium or a dummy medium having a transmittance for 550 nm of 91% or more outside the range of the above conditions from the open value, and if it is within the range, the aperture stop diameter should be made small enough to affect the diffraction. It is better to adjust the amount of light with something like an ND filter.
[0082]
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.
[0083]
DETAILED DESCRIPTION OF THE INVENTION
Examples 1 to 5 of the zoom lens used in the electronic imaging device of the present invention will be described below. FIGS. 1 to 5 show lens cross-sectional views at the wide-angle end (a), the intermediate state (b), and the telephoto end (c) when focusing on an object point at infinity in Examples 1 to 5, respectively. In each 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 is an electronic image sensor. The glass is indicated by CG, and the image plane of the CCD is indicated by I. Instead of the infrared cut absorption filter IF, a transparent flat plate incident surface with a near infrared sharp cut coat may be used, or the low pass filter LF may be directly provided with a near infrared sharp cut coat. (Example 2).
[0084]
As shown in FIG. 1, the zoom lens of Example 1 includes a first lens group G1 having a negative refractive power composed of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, The front group consists of a positive meniscus lens convex on the object side and a negative meniscus lens convex on the object side, and the rear group has a positive refractive power consisting of a negative meniscus lens convex on the object side and a positive cemented lens of a biconvex lens. The second lens group G2 includes a third lens group G3 having a positive refractive power composed of one biconvex positive lens. When zooming from the wide angle end to the telephoto end, the first lens group G1 has a concave locus 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 is convex toward the image plane side. Moves in a locus, and at the telephoto end is closer to the object side than the wide-angle end. . In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0085]
The aspherical surface is a surface on the image side of the negative meniscus lens of the first lens group G1, an object side surface of the cemented lens in the front group of the second lens group G2, and an image surface side surface of the cemented lens in the rear group. Used on the surface.
[0086]
As shown in FIG. 2, the zoom lens of Example 2 includes a positive meniscus lens convex on the object side, a negative meniscus lens convex on the object side, a biconcave negative lens, and a positive meniscus lens convex on the object side. A first lens group G1 having a negative refractive power, an aperture stop S, a front lens group consisting of a cemented lens of a positive meniscus lens convex on the object side and a negative meniscus lens convex on the object side, and a rear group consisting of a biconvex positive lens The second lens group G2 having a positive refractive power and the third lens group G3 having a positive refractive power composed of one biconvex positive lens. When zooming from the wide angle end to the telephoto end, the first lens group G1 is an object. The telephoto end moves to a position closer to the image plane side than the wide-angle end, the second lens group G2 moves to the object side together with the aperture stop S, and the third lens group G3 moves to the image side. It moves with a convex locus on the surface side, and the telephoto end is closer to the image plane side than the wide-angle end. To become. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0087]
The aspheric surfaces are used for the two surfaces of the cemented lens of the second lens group G2 on the object side and the biconvex positive lens on the object side.
[0088]
As shown in FIG. 3, the zoom lens of Embodiment 3 includes a first lens group G1 having a negative refractive power composed of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, A second lens group G2 having a positive refractive power and a biconvex positive lens 1 consisting of a cemented lens composed of a positive meniscus lens convex toward the object side and a negative meniscus lens convex toward the object side. The first lens unit G1 includes a third lens unit G3 having a positive refractive power and includes a concave locus on the object side when zooming from the wide-angle end to 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 image plane side, and is wide at the telephoto end. It is in the same position as the edge. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0089]
The aspherical surfaces are the three surfaces of the negative meniscus lens image surface side of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the image surface side surface of the rear biconvex positive lens. It is used for.
[0090]
As shown in FIG. 4, the zoom lens of Embodiment 4 includes a first lens group G1 having a negative refractive power composed of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, A second lens group G2 having a positive refractive power and a biconvex positive lens 1 consisting of a cemented lens composed of a positive meniscus lens convex on the object side and a negative meniscus lens convex on the object side, and a rear group consisting of a biconvex positive lens. The first lens unit G1 includes a third lens unit G3 having a positive refractive power and includes a concave locus on the object side when zooming from the wide-angle end to 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 image plane side, and is wide at the telephoto end. It is in the same position as the edge. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0091]
The aspherical surfaces are the three surfaces of the negative meniscus lens surface of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the object side surface of the rear biconvex positive lens. It is used.
[0092]
As shown in FIG. 5, the zoom lens of Example 5 includes a first lens group G1 having a negative refracting power composed of a negative meniscus lens convex on the object side and a positive meniscus lens convex on the object side, an aperture stop S, A second lens group G2 having a positive refractive power and a biconvex positive lens 1 consisting of a cemented lens composed of a positive meniscus lens convex on the object side and a negative meniscus lens convex on the object side, and a rear group consisting of a biconvex positive lens. The first lens unit G1 includes a third lens unit G3 having a positive refractive power and includes a concave locus on the object side when zooming from the wide-angle end to 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 image plane side, and is wide at the telephoto end. It is in the same position as the edge. In order to focus on a subject at a short distance, the third lens group G3 is extended toward the object side.
[0093]
The aspherical surfaces are the three surfaces of the negative meniscus lens image surface side of the first lens group G1, the object side surface of the cemented lens of the second lens group G2, and the image surface side surface of the rear biconvex positive lens. It is used for.
[0094]
In the following, numerical data of each of the above embodiments is shown. Symbols are the above, f is the total focal length, ω is the half angle of view, F_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 expression, where x is an optical axis with the light traveling direction being positive, and y is a direction orthogonal to the optical axis.
[0095]

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.
[0096]

[0097]

[0098]

[0099]

[0100]

[0101]
Aberration diagrams at the time of focusing on an object point at infinity and focusing on a subject distance of 10 cm are shown in FIGS. 6 and 7, respectively. Aberration diagrams at the time of focusing on an object point at infinity in Examples 2 and 3 are shown in FIGS. 8 and 9, 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.
[0102]
Next, the values of the conditions (1) to (3) and (5) to (19) and the values of Asp2F, Asp2R and L relating to the condition (4) in each of the above embodiments are shown.

[0103]
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.
[0104]
Here, the diagonal length L of the effective imaging surface and the pixel interval a will be described. FIG. 11 is a diagram illustrating an example of a pixel array 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. 11) 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.
[0105]
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.
[0106]
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.
[0107]
Substrate material Physical film thickness (nm) λ / 4
───────────────────────────────
1st layer Al₂O_Three    58.96 0.50
Second layer TiO₂      84.19 1.00
3rd layer SiO₂    134.14 1.00
4th layer TiO₂      84.19 1.00
5th layer SiO₂    134.14 1.00
6th layer TiO₂      84.19 1.00
7th layer SiO₂    134.14 1.00
8th layer TiO₂      84.19 1.00
9th layer SiO₂    134.14 1.00
10th layer TiO₂      84.19 1.00
11th layer SiO₂    134.14 1.00
12th layer TiO₂      84.19 1.00
13th layer SiO₂    134.14 1.00
14th layer TiO₂      84.19 1.00
15th layer SiO₂    178.41 1.33
16th layer TiO₂    101.03 1.21
17th layer SiO₂    167.67 1.25
18th layer TiO₂      96.82 1.15
19th layer SiO₂    147.55 1.05
20th layer TiO₂      84.19 1.00
21st layer SiO₂    160.97 1.20
22nd layer TiO₂      84.19 1.00
23rd layer SiO₂    154.26 1.15
24th layer TiO₂      95.13 1.13
25th layer SiO₂    160.97 1.20
26th layer TiO₂      99.34 1.18
27th layer SiO₂      87.19 0.65
───────────────────────────────
Air.
[0108]
The transmittance characteristics of the near infrared sharp cut coat are as shown in FIG.
[0109]
Further, 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. 13 on the emission surface side of the low-pass filter LF. ing.
[0110]
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.
[0111]
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.
[0112]
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.
[0113]
Such means for limiting the wavelength is more effective in an imaging system using a complementary color mosaic filter.
[0114]
In each of the above embodiments, as shown in FIG. 13, 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.
[0115]
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.
[0116]
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.
[0117]
Further, as shown in FIG. 14, a complementary color mosaic filter in which four color filters of cyan, magenta, yellow, and green (green) are provided in a mosaic pattern corresponding to the imaging pixels is provided on the imaging surface I of the CCD. 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.
[0118]
Specifically, the complementary color mosaic filter is composed of at least four types of color filters as shown in FIG. 14, and the characteristics of the four types of color filters are preferably as follows.
[0119]
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.
[0120]
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 enhancing the color reproducibility, it is more preferable that the strength is 50 to 50%.
[0121]
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%.
[0122]
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.
[0123]
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.
[0124]
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.
[0125]
FIGS. 16 to 18 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. 16 is a front perspective view showing the appearance of the digital camera 40, FIG. 17 is a rear perspective view thereof, and FIG. 18 is a cross-sectional view showing the configuration of the digital camera 40. In this example, the digital camera 40 includes a photographic optical system 41 having a photographic 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.
[0126]
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.
[0127]
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.
[0128]
In the example of FIG. 18, a parallel plane plate is disposed as the cover member 50, but a lens having power may be used.
[0129]
The electronic imaging apparatus of the present invention described above can be configured as follows, for example.
[0130]
[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. The second lens group moves only to the object side during zooming from the wide-angle end to the telephoto end during point focusing, and the third lens group moves while changing the distance from the second lens group. The second lens group includes a front group of the second group and a rear group of the second group in order from the object side across the space, and the second group front group includes a positive lens and an negative lens having an aspheric surface in order from the object side. An electronic image pickup apparatus comprising: a two-lens cemented lens component, wherein the second group rear group is composed of a positive lens component having an aspheric surface, and satisfies the following conditions.
[0131]
(1) 0.6 <R_{twenty three}/ R_{twenty one}<1.0
(2) 0.05 <f_2R/ R_{twenty two}<1.5
(3) ν_{twenty two}<26.5
(4) 2.5 × 10^-3・ L> | Asp2R |> 0.1 ・ | Asp2F |
However, R_{twenty one}, R_{twenty two}, R_{twenty three}Is the radius of curvature on the optical axis of the surface closest to the object side, the cemented surface, and the surface closest to the image side in the second group front group, f_2RIs the combined focal length of the second group, ν_{twenty two}Is the d-line reference Abbe number of the medium of the negative lens in the second lens unit front group, L is the diagonal length of the effective imaging area of the image sensor, and Asp2F and Asp2R are aspherical surfaces provided on the positive lens in the second lens unit front group, respectively. The aspherical deviation amount when the height from the optical axis is 0.3 L with respect to the reference spherical surface having the radius of curvature on the optical axis of the aspherical surface provided in the rear group of the second group.
[0132]
[2] The electronic imaging apparatus as described in [1] above, wherein the rear group of the second group is composed of a single lens having a positive refractive power and satisfies the following conditions.
[0133]
(6) 0.04 <t_2N/ T₂<0.2
Where t_2NIs the thickness on the optical axis of the negative lens in the front group of the second group, t₂Is the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the second lens group.
[0134]
[3] The electronic imaging apparatus as described in 2 above, wherein the following condition is satisfied.
[0135]
(7) -1.5 <(R_2RF+ R_2RR) / (R_2RF-R_2RR) <0
(8) 0.7 <f_2R/ F₂<2
However, R_2RF, R_2RRIs the radius of curvature on the optical axis of the most object-side surface and the most image-side surface of the second group rear group, f_2RIs the focal length of the rear group of the second group, f₂Is the combined focal length of the entire second lens group.
[0136]
[4] The electronic imaging apparatus as described in 1 above, wherein the rear group of the second group is composed of a cemented lens component of a negative lens and a positive lens in order from the object side, and satisfies the following conditions.
[0137]
(9) 0 <ν_2RN−ν_{twenty two}<35 and ν_{twenty two}≦ 26.5
Where ν_{twenty two}Is the Abbe number based on the d-line of the negative lens in the second lens unit, ν_2RNIs the d-line-based Abbe number of the negative lens in the second group rear group.
[0138]
[5] The electronic imaging apparatus as described in 4 above, wherein the following condition is satisfied.
[0139]
(10) -2.0 <(R_2RF+ R_2RR) / (R_2RF-R_2RR<0.5
(11) 0.7 <f_2R/ F₂<2
However, R_2RF, R_2RRIs the radius of curvature on the optical axis of the most object-side surface and the most image-side surface of the second group rear group, f_2RIs the focal length of the rear group of the second group, f₂Is the combined focal length of the entire second lens group.
[0140]
[6] The electronic imaging apparatus as described in any one of [1] to [5], wherein the third lens group satisfies the following condition.
[0141]
(12) -0.2 <(R_3F+ R_3R) / (R_3F-R_3R<1.5
However, R_3F, R_3RAre the radii of curvature on the optical axis of the most object-side surface and the most image-side surface of the third lens group, respectively.
[0142]
[7] The first lens group includes two lenses, a negative lens including an aspherical surface and a positive lens, and satisfies the following condition. Electronic imaging device.
[0143]
(13) 20 <ν₁₁−ν₁₂
(14) -10 <(R₁₃+ R₁₄) / (R₁₃-R₁₄<-2
Where ν₁₁, Ν₁₂Are respectively the Abbe numbers of the d-line reference of the medium of the negative lens and the positive lens of the first lens group, R₁₃, R₁₄Are the radii of curvature on the optical axis of the object-side surface and the image-side surface of the first lens group positive lens, respectively.
[0144]
[8] The zoom lens according to any one of 1 to 7, wherein the third lens unit moves along a locus convex toward the image side upon zooming from the wide-angle end to the telephoto end during focusing on an object point at infinity. The electronic imaging device according to item.
[0145]
[9] The electronic imaging apparatus according to any one of [1] to [8], wherein the third lens group includes only one positive lens.
[0146]
[10] The electronic imaging apparatus according to any one of [1] to [9], wherein the second group front group satisfies the following conditions.
[0147]
(5) 0.01 <n_{twenty two}-N_{twenty one}<0.20
Where n_{twenty one}, N_{twenty two}Are the medium refractive indices for the d-line of the positive lens and negative lens in the second group front group, respectively.
[0148]
[11] The electronic imaging apparatus as described in any one of [1] to [10], wherein a diaphragm is disposed between the first lens group and the second lens group.
[0149]
[12] The electronic imaging apparatus as described in [11], wherein the diaphragm moves integrally with the second lens group during zooming.
[0150]
[13] The electronic imaging apparatus according to any one of [1] to [12], wherein focusing on a short-distance object point is performed by movement of the third lens group.
[0151]
[14] Wide angle end half field angle ω of the zoom lens_W14. The electronic imaging apparatus according to any one of 1 to 13, wherein the angle is in a range of 27 ° to 42 °.
[0152]
【The invention's effect】
According to the present invention, it is possible to obtain a zoom lens having a small retractable thickness and excellent storage property, and excellent imaging performance even at a high magnification and in a rear focus. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view at a wide-angle end (a), an intermediate state (b), and a telephoto end (c) when focusing on an object point at infinity according to Embodiment 1 of a zoom lens used in an electronic imaging device of the present invention. It is.
2 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 2. FIG.
3 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 3. FIG.
4 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 4. FIG.
FIG. 5 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Example 5;
FIG. 6 is an aberration diagram for Example 1 upon focusing on an object point at infinity.
7 is an aberration diagram for Example 1 upon focusing on a subject distance of 10 cm. FIG.
FIG. 8 is an aberration diagram for Example 2 upon focusing on an object point at infinity.
FIG. 9 is an aberration diagram for Example 3 upon focusing on an object point at infinity.
FIG. 10 is a diagram for explaining the definition of the amount of aspherical deviation in the present invention.
FIG. 11 is a diagram for explaining a diagonal length of an effective imaging surface when imaging is performed with an electronic imaging element.
FIG. 12 is a diagram showing transmittance characteristics of an example of a near-infrared sharp cut coat.
FIG. 13 is a diagram illustrating a transmittance characteristic of an example of a color filter provided on the emission surface side of the low-pass filter.
FIG. 14 is a diagram illustrating a color filter arrangement of a complementary color mosaic filter.
FIG. 15 is a diagram illustrating an example of wavelength characteristics of a complementary color mosaic filter.
FIG. 16 is a front perspective view showing the appearance of a digital camera incorporating a zoom lens according to the present invention.
17 is a rear perspective view of the digital camera of FIG. 16. FIG.
18 is a cross-sectional view of the digital camera of FIG.
[Explanation of symbols]
G1: First lens group
G2: Second lens group
G3 ... Third lens group
S ... Aperture stop
IF ... Infrared cut absorption filter
LF: Low-pass filter
CG ... Cover glass
I ... Image plane
E ... Observer eyeball
40 ... Digital camera
41. Photography optical system
42. Optical path for photographing
43. Viewfinder optical system
44. Optical path for viewfinder
45 ... Shutter
46 ... Flash
47 ... LCD monitor
49 ... CCD
50. Cover member
51. Processing means
52. Recording means
53. Objective optical system for viewfinder
55 ... Porro prism
57 ... View frame
59 ... Eyepiece optical system

Claims (14)

In 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. The second lens group moves only to the object side during zooming from the wide-angle end to the telephoto end during point focusing, and the third lens group moves while changing the distance from the second lens group. The second lens group includes a front group of the second group and a rear group of the second group in order from the object side across the space, and the second group front group includes a positive lens and an negative lens having an aspheric surface in order from the object side. An electronic image pickup apparatus comprising: a two-lens cemented lens component, wherein the second group rear group is composed of a positive lens component having an aspheric surface, and satisfies the following conditions.
(1) 0.6 <R ₂₃ / R ₂₁ <1.0
(2) 0.05 <f _2R / R ₂₂ <1.5
(3) ν ₂₂ <26.5
(4) 2.5 × 10 ⁻³ · L> | Asp2R |> 0.1 · | Asp2F |
However, R ₂₁ , R ₂₂ , and R ₂₃ are the radius of curvature on the optical axis of the most object side surface, the junction surface, and the most image side surface of the second group front group, respectively, and f _2R is the composition of the second group rear group. Focal length, ν ₂₂ is the d-line reference Abbe number of the medium of the negative lens in the second group front group, L is the diagonal length of the effective imaging area of the image sensor, and Asp2F and Asp2R are the positive lenses in the second group front group, respectively. The aspherical deviation amount when the height from the optical axis is 0.3 L with respect to the reference spherical surface having the radius of curvature on the optical axis of the aspherical surface provided and the aspherical surface provided in the second group rear group. . The electronic imaging apparatus according to claim 1, wherein the rear group of the second group includes a single lens having a positive refractive power and satisfies the following condition.
(6) 0.04 <t _2N / t ₂ <0.2
However, t _2N is the thickness on the optical axis of the negative lens in the second group front group, and t ₂ is the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side in the second lens group. . The electronic imaging apparatus according to claim 2, wherein the following condition is satisfied.
(7) −1.5 <(R _2RF + R _2RR ) / (R _2RF −R _2RR ) <0
(8) 0.7 <f _2R / f ₂ <2
Where R _2RF and R _2RR are the radius of curvature on the optical axis of the most object-side surface and the most image-side surface of the second group rear group, f _2R is the focal length of the second group rear group, and f ₂ is the first This is the combined focal length of the entire two-lens group system. 2. The electronic imaging apparatus according to claim 1, wherein the second group rear group includes a cemented lens component of a negative lens and a positive lens in order from the object side, and satisfies the following condition.
(9) 0 <ν _2RN −ν ₂₂ <35 and ν ₂₂ ≦ 26.5
Where ν ₂₂ is the d-line reference Abbe number of the negative lens in the second group front group, and ν _2RN is the d-line reference Abbe number of the negative lens in the second group rear group. The electronic imaging apparatus according to claim 4, wherein the following condition is satisfied.
(10) −2.0 <(R _2RF + R _2RR ) / (R _2RF −R _2RR ) <− 0.5 (11) 0.7 <f _2R / f ₂ <2
Where R _2RF and R _2RR are the radius of curvature on the optical axis of the most object-side surface and the most image-side surface of the second group rear group, f _2R is the focal length of the second group rear group, and f ₂ is the first This is the combined focal length of the entire two-lens group system. 6. The electronic imaging apparatus according to claim 1, wherein the third lens group satisfies the following condition.
(12) −0.2 <(R _3F + R _3R ) / (R _3F −R _3R ) <1.5
Here, R _3F and R _3R are the radii of curvature on the optical axis of the most object side surface and the most image side surface of the third lens group, respectively. The electronic imaging according to any one of claims 1 to 6, wherein the first lens group includes two lenses, a negative lens including an aspherical surface and a positive lens, and satisfies the following condition. apparatus.
(13) 20 <ν ₁₁ −ν _{12
(14) -10 <(R 13} + R 14) / (R 13 -R 14) <- 2
Where ν ₁₁ and ν ₁₂ are d-line reference Abbe numbers of the negative lens and positive lens medium of the first lens group, respectively, and R ₁₃ and R ₁₄ are the object side surface and image side of the first lens group positive lens, respectively. Is the radius of curvature on the optical axis of the surface.   8. The zoom lens according to claim 1, wherein the third lens unit moves along a locus convex toward the image side upon zooming from the wide-angle end to the telephoto end during focusing on an object point at infinity. Electronic imaging device.   The electronic imaging apparatus according to claim 1, wherein the third lens group includes only one positive lens. The electronic imaging apparatus according to claim 1, wherein the front group of the second group satisfies the following condition.
(5) 0.01 <n ₂₂ −n ₂₁ <0.20
Here, n ₂₁ and n ₂₂ are medium refractive indexes with respect to the d-line of the positive lens and negative lens in the second group front group, respectively.   The electronic imaging apparatus according to claim 1, wherein a diaphragm is disposed between the first lens group and the second lens group.   The electronic imaging apparatus according to claim 11, wherein the diaphragm moves integrally with the second lens group at the time of zooming.   The electronic imaging apparatus according to claim 1, wherein focusing on a short-distance object point is performed by movement of the third lens group. 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 °.

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