JP4540261B2 - Electronic imaging device - Google Patents

Description

ただし、Ｒ_2C1 、Ｒ_2C2 、Ｒ_2C3 は第２群の接合レンズの物体側から１番目と２番目と３番目のレンズ面のそれぞれの光軸上の曲率半径、ｔ_2Nは第２群の接合レンズ中の負レンズの光軸上での厚み、ｔ₂ は第２群の最も物体側の面から最も像側の面までの光軸上での厚みである。
【００４４】
条件（３）は、前記第２群の接合レンズのそれぞれのレンズエレメント（正レンズ・負レンズ）のシェープファクターの比を規定したものである。下限値の−１．５を越えると、軸上色収差の補正に不利であり、上限値の−０．３を越えると、レンズエレメントが厚くなり、小型化には不利である。
【００４５】
条件（４）は、第２群の負レンズ（接合されている）の光軸上の厚みを規定したものである。この部位はある程度厚くしないと非点収差が補正し切れないが、光学系の各エレメントの厚みを薄くする目的の場合、これが足枷になる。したがって、非点収差の補正は、その像側のレンズに非球面を導入して補正する。それでも、下限値０．０５を越えると、非点収差は補正し切れなくなる。上限値０．３を越えると、厚さが許容できない。
【００４６】
なお、条件（３）、（４）を個別に若しくは共に次のようにすればなお好ましい。
【００４７】

さらに、条件（３）、（４）を個別に若しくは共に次のようにすればなお好ましい。
【００４８】

上記式の下限値又は上限値を各々個別に限定しても好ましい。
【００４９】
本発明は、また、物体側より順に、負の屈折力を有する第１群と正の屈折力を有する第２群と正の屈折力を有する第３群と正の屈折力を有する第４群よりなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、前記第２群と第３群の間隔が大きくなり、前記第３群を物体側に繰り出すことでより近距離の被写体に合焦することが可能であり、前記第２群が物体側から順に非球面を含む正レンズ成分と負レンズ成分１つずつからなり、前記第３群は正の屈折力を有する１枚の単レンズよりなり、以下の条件（５）を満足するズームレンズ及び電子撮像素子を有することを特徴とする電子撮像装置として構成してもよい。
【００５０】
（５） ０．０５＜ｔ_2NI ／ｔ₂ ＜０．３
ただし、ｔ_2NI は第２群中の最も像側の負レンズの光軸上での厚み、ｔ₂ は第２群の最も物体側の面から最も像側の面までの光軸上での厚みである。ここで、レンズ成分とは、単レンズか接合レンズを示す概念とする。
【００５１】
条件（５) は、条件（４) と同様に、非点収差の補正と第２群の厚さとのバランスをとるための条件である。
【００５２】
条件（５) は以下の条件（５−１）又は（５−２）としてもよく、また、以下の式の上限のみ若しくは下限のみ限定しても好ましい。
【００５３】
（５−１） ０．０６＜ｔ_2NI ／ｔ₂ ＜０．２８
（５−２） ０．０７＜ｔ_2NI ／ｔ₂ ＜０．２６
ところで、上記の各発明にてズームレンズの変倍比が２．３倍以上の場合、以下の条件（ａ）、（ｂ）を満足すると薄型化に寄与する。
【００５４】
（ａ） ０．９＜−β_23t ＜１．８
（ｂ） ２．０＜ｆ₂ ／ｆ_W ＜３．０
ただし、β_23t は第２と第３群の望遠端における無限遠物点合焦時の合成倍率、ｆ₂ は第２群の焦点距離、ｆ_W はズームレンズ全系の無限遠物点合焦時の広角端焦点距離である。
【００５５】
条件（ａ) は、第２群と第３群の望遠端における無限遠物点時倍率β_23t を規定したものである。これはできるだけ絶対値が大きい方が広角端における入射瞳位置を浅くできて第１群の径を小さくしやすく、ひいては厚みを小さくできる。下限の０．９を越えると、厚みを満足するのが困難で、上限の１．８を越えると、収差補正（球面収差、コマ、非点収差）が困難となる。
【００５６】
条件（ｂ) は、第２群の焦点距離ｆ₂ を規定したものである。焦点距離が短い方が第２群自身の薄型化には有利であるが、第２群の前側主点を物体側に、第１群の後側主点を像側に位置するようなパワー配置上の無理が出やすく、収差補正上好ましくない。下限の２．０を越えると、球面収差、コマ、非点収差等の補正が困難になる。上限の３．０を越えると、薄型化が困難となる。
【００５７】
なお、（ａ）、（ｂ）を各々個別に若しくは共に次のようにすればより好ましい。
【００５８】
（ａ−１) ０．９＜−β_23t ＜１．７
（ｂ−１) ２．１＜ｆ₂ ／ｆ_W ＜２．８
さらに、次のようにすればなお好ましい。
【００５９】
（ａ−２) １．１＜−β_23t ＜１．６
（ｂ−２) ２．２＜ｆ₂ ／ｆ_W ＜２．６
上記式の下限値又は上限値を各々個別に限定しても好ましい。
【００６０】
また、第１群の構成としては、物体側から順に、２枚の負レンズからなる負レンズ群と１枚の正レンズからなる正レンズ群によるか、物体側から順に、２枚以下の負レンズからなる負レンズ群と１枚の正レンズからなる正レンズ群とよりなり、前記負レンズ群の中少なくとも１枚の負レンズは非球面を含む構成とすれば、第２・３・４群の構成との収差補正上の相性が良好である。つまり、フォーカシング時の収差変動が少なく、全ての変倍域で収差補正が良好に行える。
【００６１】
並びに、前記第１群、第２群の総厚が以下の条件を満足するのもよい。
【００６２】
（６） ０．６＜ｔ₁ ／Ｙ＜２．２
（７） ０．３＜ｔ₂ ／Ｙ＜１．５
ただし、ｔ₁ は第１群の最も物体側の面から最も像側の面までの光軸上での厚みであり、ｔ₂ は第２群の最も物体側の面から最も像側の面までの光軸上での厚みであり、Ｙは撮像素子の有効撮像領域（略矩形）の対角長である。
【００６３】
条件（６）、（７）は、それぞれ第１群第２群の総厚を規定したものである。それぞれの上限値２．２、１．５を越えると、薄型化の妨げになりやすく、下限値０．６、０．３を越えると、各レンズ面の曲率半径を緩くせざるを得ず、近軸関係の成立や諸収差補正が困難になる。条件（６）、（７）の下限のそれぞれ０．６、０．３を越えて小さくなると、各レンズ厚が薄くなる。そのため、レンズ中心から周辺までの厚さ、縁肉を確保しようとすると、各レンズの曲率が緩くなるため、各レンズに必要なパワーを確保できなくなる。
【００６４】
なお、この条件範囲は縁肉・機械スペース確保上、Ｙの値によって変えることが好ましい。
【００６５】
具体的には、以下の条件（６−１）、（７−１）を満足することが望ましい。
【００６６】

以上、ズームレンズ部について沈胴厚を薄くしつつも結像性能を良好にする手段を提供した。
【００６７】
次に、フィルター類を薄くする点について言及する。電子撮像装置には通常赤外光が撮像面に入射しないように一定の厚みのある赤外吸収フィルターを撮像素子よりも物体側に挿入している。これを厚みのないコーティングに置き換えることを考える。当然その分薄くなる訳だが、副次的効果がある。ズームレンズ系後方にある撮像素子よりも物体側に、波長６００ｎｍでの透過率が８０％以上、波長７００ｎｍでの透過率が１０％以下の近赤外シャープカットコートを導入すると、吸収タイプよりも相対的に赤側の透過率が高くなり、補色モザイクフィルターを有するＣＣＤの欠点である青紫側のマゼンタ化傾向がゲイン調整により緩和され、原色フィルターを有するＣＣＤ並みの色再現を得ることができる。一方、補色フィルターの場合、その透過光エネルギーの高さから原色フィルター付きＣＣＤと比べ実質的感度が高く、かつ、解像的にも有利であるため、小型ＣＣＤを使用したときのメリットが大である。
【００６８】
もう一方のフィルターである光学的ローパスフィルターについても、その光軸上の総厚ｔ_LPF が以下の条件を満たすようにするとよい。
【００６９】
（８） ０．１５×１０³ ＜ｔ_LPF ／ａ＜０．４５×１０³
ただし、ａは電子撮像素子の水平画素ピッチである。
【００７０】
沈胴厚を薄くするには光学的ローパスフィルターを薄くすることも効果的であるが、一般的にはモアレ抑制効果が減少して好ましくない。一方、画素ピッチが小さくなるにつれて結像レンズ系の回折の影響によりナイキスト限界以上の周波数成分のコントラストは減少し、モアレ抑制効果の減少はある程度許容されるようになる。例えば、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する場合、かなりモアレ抑制効果があることが知られている。この場合のフィルターが最も薄くなる仕様としては、 水平にａμｍ、±４５°方向にそれぞれSQRT(1/2) ×ａだけずらせるものが知られている。ここで、ＳＱＲＴはスクエアルートであり平方根を意味する。このときのフィルター厚は、およそ［１＋２×SQRT(1/2) ］×ａ×１０³ ／５．８８（ｍｍ）となる。これは、ちょうどナイキスト限界に相当する周波数においてコントラストをゼロにする仕様である。これよりは数％ないし数十％程度薄くすると、ナイキスト限界に相当する周波数のコントラストが少し出てくるが、上記回折の影響で抑えることが可能になる。上記以外のフィルター仕様、例えば２枚重ねあるいは１枚で実施する場合も含めて、条件（８）を満足するのがよい。上限値の０．４５×１０³ を越えると、光学的ローパスフィルターが厚すぎ薄型化の妨げになる。下限値の０．１５×１０³ を越えると、モアレ除去が不十分になる。ただし、これを実施する場合のａの条件は５μｍ以下であることが望ましい。
【００７１】
さらに、ａが４μｍ以下の場合、より回折の影響を受けやすいので、以下の条件（８−１）を満足することが好ましい。
【００７２】
（８−１） ０．１３×１０³ ＜ｔ_LPF ／ａ＜０．４２×１０³
また、以下のようにしてもよい。ローパスフィルターが３枚のローパスフィルターを重ね合わせたものであり、４μｍ≦ａ＜５μｍのとき、
（８−２） ０．３×１０³ ＜ｔ_LPF ／ａ＜０．４×１０³
を満足するとよい。
【００７３】
また、ローパスフィルターが２枚のローパスフィルターを重ね合わせたものであり、４μｍ≦ａ＜５μｍのとき、
（８−３） ０．２×１０³ ＜ｔ_LPF ／ａ＜０．２８×１０³
を満足するとよい。
【００７４】
また、ローパスフィルターが１枚のローパスフィルターであり、４μｍ≦ａ＜５μｍのとき、
（８−４） ０．１×１０³ ＜ｔ_LPF ／ａ＜０．１６×１０³
を満足するとよい。
【００７５】
また、ローパスフィルターが３枚のローパスフィルターを重ね合わせたものであり、ａ＜４μｍのとき、
（８−５） ０．２５×１０³ ＜ｔ_LPF ／ａ＜０．３７×１０³
を満足するとよい。
【００７６】
また、ローパスフィルターが２枚のローパスフィルターを重ね合わせたものであり、ａ＜４μｍのとき、
（８−６） ０．１６×１０³ ＜ｔ_LPF ／ａ＜０．２５×１０³
を満足するとよい。
【００７７】
また、ローパスフィルターが１枚のローパスフィルターからなり、ａ＜４μｍのとき、
（８−７） ０．０８×１０³ ＜ｔ_LPF ／ａ＜０．１４×１０³
を満足するとよい。
【００７８】
また、画素ピッチの小さな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、開口形状が固定の複数の開口を有し、その中の１つを第１群の最も像側のレンズ面と第３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、他のものと交換可能とすることで、像面照度を調節することができる電子撮像装置としておき、具体的には、その複数の開口の中一部の開口内に、波長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し、他の一部の開口の波長５５０ｎｍに対する透過率を８０％以上とすることで光量調節を行なうのがよい。
【００７９】
あるいは、ズームレンズの焦点距離ｆと入射瞳の直径ＩＤから求まるＦナンバー（ｆ／ＩＤ）をＦ_no、前記開口における波長５５０ｎｍにおける透過率をＴとしたときのＦ_no／√Ｔを実効ＦナンバーＦ_no' とし、電子撮像素子の水平画素ピッチをａとするとき、Ｆ_no' ＞ａ／０．４μｍとなるような実効Ｆナンバーに相当する光量になるように調節を実施する場合は、開口内に波長５５０ｎｍに対する透過率Ｔが８０％未満の媒体を備えた開口をズームレンズの光路に挿入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波長５５０ｎｍに対する透過率が９１％以上のダミー媒質若しくは空間としておき、その範囲内のときは、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。
【００８０】
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空間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。絞り込むにつれて絞り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空間周波数特性を高く設定しておくことが好ましい。ここで、空間周波数特性がより高いとは、物体像の空間周波数のコントラストを他のものより高く保つことを意味している。別の言い方をすれば、例えばカットオフ周波数が大きいということを意味している。
【００８１】
【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１〜６について説明する。なお、実施例５〜６は参考例である。これらの実施例の無限遠物点合焦時の広角端でのレンズ断面図をそれぞれ図１〜図６に示す。各図中、第１群はＧ１、第２群はＧ２、第３群はＧ３、第４群はＧ４、３枚重ねの光学的ローパスフィルターであってその第１面（物体側の表面）に近赤外カットコートが設けられている光学的ローパスフィルターＦ、電子撮像素子であるＣＣＤのカバーガラスをＣ、ＣＣＤの像面であって補色モザイクフィルターが設けられている像面をＩで示してあり、物体側から順に配置された、光学的ローパスフィルターＦ、カバーガラスＣは、第４群Ｇ４と像面Ｉの間に固定して配置されている。なお、また、各図中、フォーカス群は“ｆｏｃｕｓ”と図示され、その近距離への合焦方向が矢印で図示してある。
【００８２】
実施例１のズームレンズは、図１に示すように、負屈折力の第１群Ｇ１、正屈折力の第２群Ｇ２、正屈折力の第３群Ｇ３、正屈折力の第４群Ｇ４からなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、第１群Ｇ１は一旦像側へ移動しその後物体側に反転して移動し、望遠端では広角端の位置より物体側になり、第２群Ｇ２は物体側に移動し、第３群Ｇ３は一旦像側へ若干移動しその後物体側に反転して、望遠端では広角端の位置と同じになり、第４群Ｇ４は固定レンズ群であり、第２群Ｇ２と第３群Ｇ３の間隔は広角端から望遠端に変倍する際に大きくなる。そして、第３群Ｇ３を物体側に繰り出して近距離の被写体にフォーカスするようになっている。
【００８３】
実施例１の第１群Ｇ１は、物体側に凸面を向けた負メニスカスレンズと、両凹レンズと、物体側に凸面を向けた正メニスカスレンズとからなり、第２群Ｇ２は、絞りとその後に配置された両凸レンズと、両凸レンズと両凹レンズの接合レンズとからなり、第３群Ｇ３は物体側に凹面を向けた正メニスカスレンズ１枚からなり、第４群Ｇ４は物体側に凸面を向けた正メニスカスレンズ１枚からなる。非球面は、第１群Ｇ１の真中の両凹レンズの物体側の面、第２群Ｇ２の最も物体側の面、第４群Ｇ４の物体側の面の３面に用いられている。
【００８４】
実施例２のズームレンズは、図２に示すように、負屈折力の第１群Ｇ１、正屈折力の第２群Ｇ２、正屈折力の第３群Ｇ３、正屈折力の第４群Ｇ４からなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、第１群Ｇ１は一旦像側へ移動しその後物体側に反転して移動し、望遠端では広角端の位置より物体側になり、第２群Ｇ２は物体側に移動し、第３群Ｇ３は物体側に移動し、第４群Ｇ４は固定レンズ群であり、第２群Ｇ２と第３群Ｇ３の間隔は広角端から望遠端に変倍する際に大きくなる。そして、第３群Ｇ３を物体側に繰り出して近距離の被写体にフォーカスするようになっている。
【００８５】
実施例２の第１群Ｇ１は、物体側に凸面を向けた負メニスカスレンズと、両凹レンズと、物体側に凸面を向けた正メニスカスレンズとからなり、第２群Ｇ２は、絞りとその後に配置された両凸レンズと、物体側に凸面を向けた正メニスカスレンズと物体側に凸面を向けた負メニスカスレンズの接合レンズとからなり、第３群Ｇ３は物体側に凹面を向けた正メニスカスレンズ１枚からなり、第４群Ｇ４は物体側に凸面を向けた正メニスカスレンズ１枚からなる。非球面は、第１群Ｇ１の真中の両凹レンズの物体側の面、第２群Ｇ２の最も物体側の面、第４群Ｇ４の物体側の面の３面に用いられている。
【００８６】
実施例３のズームレンズは、図３に示すように、負屈折力の第１群Ｇ１、正屈折力の第２群Ｇ２、正屈折力の第３群Ｇ３、正屈折力の第４群Ｇ４からなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、第１群Ｇ１は一旦像側へ移動しその後物体側に反転して移動し、望遠端では広角端の位置より物体側になり、第２群Ｇ２は物体側に移動し、第３群Ｇ３は一旦像側へ若干移動しその後物体側に反転して、望遠端では広角端の位置と同じになり、第４群Ｇ４は固定レンズ群であり、第２群Ｇ２と第３群Ｇ３の間隔は広角端から望遠端に変倍する際に大きくなる。そして、第３群Ｇ３を物体側に繰り出して近距離の被写体にフォーカスするようになっている。
【００８７】
実施例３の第１群Ｇ１は、物体側に凸面を向けた負メニスカスレンズと、両凹レンズと、物体側に凸面を向けた正メニスカスレンズとからなり、第２群Ｇ２は、絞りとその後に配置された両凸レンズと、両凸レンズと両凹レンズの接合レンズとからなり、第３群Ｇ３は物体側に凹面を向けた正メニスカスレンズ１枚からなり、第４群Ｇ４は物体側に凸面を向けた正メニスカスレンズ１枚からなる。非球面は、第１群Ｇ１の真中の両凹レンズの物体側の面、第２群Ｇ２の最も物体側の面、第４群Ｇ４の物体側の面の３面に用いられている。
【００８８】
実施例４のズームレンズは、図４に示すように、負屈折力の第１群Ｇ１、正屈折力の第２群Ｇ２、正屈折力の第３群Ｇ３、正屈折力の第４群Ｇ４からなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、第１群Ｇ１は一旦像側へ移動しその後物体側に反転して移動し、望遠端では広角端の位置より若干像側になり、第２群Ｇ２は物体側に移動し、第３群Ｇ３は一旦像側へ若干移動しその後物体側に反転して、望遠端では広角端の位置と同じになり、第４群Ｇ４は固定レンズ群であり、第２群Ｇ２と第３群Ｇ３の間隔は広角端から望遠端に変倍する際に大きくなる。そして、第３群Ｇ３を物体側に繰り出して近距離の被写体にフォーカスするようになっている。
【００８９】
実施例４の第１群Ｇ１は、両凹レンズと、物体側に凸面を向けた正メニスカスレンズとからなり、第２群Ｇ２は、絞りとその後に配置された両凸レンズと、両凸レンズと両凹レンズの接合レンズとからなり、第３群Ｇ３は物体側に凹面を向けた正メニスカスレンズ１枚からなり、第４群Ｇ４は物体側に凸面を向けた正メニスカスレンズ１枚からなる。非球面は、第１群Ｇ１の両凹レンズの像側の面、第２群Ｇ２の最も物体側の面、第４群Ｇ４の物体側の面の３面に用いられている。
【００９０】
実施例５のズームレンズは、図５に示すように、負屈折力の第１群Ｇ１、正屈折力の第２群Ｇ２、正屈折力の第３群Ｇ３、正屈折力の第４群Ｇ４からなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、第１群Ｇ１は一旦像側へ移動しその後物体側に反転して移動し、望遠端では広角端の位置より若干像側になり、第２群Ｇ２は物体側に移動し、第３群Ｇ３は一旦像側へ若干移動しその後物体側に反転して、望遠端では広角端の位置と同じになり、第４群Ｇ４は固定レンズ群であり、第２群Ｇ２と第３群Ｇ３の間隔は広角端から望遠端に変倍する際に大きくなる。そして、第３群Ｇ３を物体側に繰り出して近距離の被写体にフォーカスするようになっている。
【００９１】
実施例５の第１群Ｇ１は、物体側に凸面を向けた負メニスカスレンズと、物体側に凸面を向けた正メニスカスレンズとからなり、第２群Ｇ２は、絞りとその後に配置された両凸レンズと物体側に凹面を向けた負メニスカスレンズの接合レンズと、物体側に凸面を向けた負メニスカスレンズとからなり、第３群Ｇ３は物体側に凹面を向けた正メニスカスレンズ１枚からなり、第４群Ｇ４は物体側に凸面を向けた正メニスカスレンズ１枚からなる。非球面は、第１群Ｇ１の負メニスカスレンズの像側の面、第２群Ｇ２の最も物体側の面、第４群Ｇ４の物体側の面の３面に用いられている。
【００９２】
実施例６のズームレンズは、図６に示すように、負屈折力の第１群Ｇ１、正屈折力の第２群Ｇ２、正屈折力の第３群Ｇ３、正屈折力の第４群Ｇ４からなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、第１群Ｇ１は一旦像側へ移動しその後物体側に反転して移動し、望遠端では広角端の位置より若干像側になり、第２群Ｇ２は物体側に移動し、第３群Ｇ３は一旦物体側へ若干移動しその後像側に反転して、望遠端では広角端の位置より若干物体側になり、第４群Ｇ４は固定レンズ群であり、第２群Ｇ２と第３群Ｇ３の間隔は広角端から望遠端に変倍する際に大きくなる。そして、第３群Ｇ３を物体側に繰り出して近距離の被写体にフォーカスするようになっている。
【００９３】
実施例６の第１群Ｇ１は、物体側に凸面を向けた負メニスカスレンズと、物体側に凸面を向けた正メニスカスレンズとからなり、第２群Ｇ２は、絞りとその後に配置された両凸レンズと、物体側に凸面を向けた負メニスカスレンズとからなり、第３群Ｇ３は物体側に凸面を向けた正メニスカスレンズ１枚からなり、第４群Ｇ４は物体側に凹面を向けた正メニスカスレンズ１枚からなる。非球面は、第１群Ｇ１の負メニスカスレンズの像側の面、第２群Ｇ２の最も物体側の面、第４群Ｇ４の像側の面の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、ＦＢはバックフォーカス、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】

【０１０２】
以上の実施例１の無限遠物点合焦時の収差図を図７に示す。この収差図において、（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。ただし、図中、“ＦＩＹ”は像高を表している。
【０１０３】
次に、上記各実施例における条件式（１）〜（８）、（ａ）、（ｂ）の値を以下に示す。

【０１０４】
以上の各実施例において、第４群Ｇ４の像側には、図示のように、入射面側に近赤外シャープカットコートを施したローパスフィルターＦを有している。この近赤外シャープカットコートは、波長６００ｎｍでの透過率が８０％以上、波長７００ｎｍでの透過率が１０％以下となるように構成されている。具体的には、例えば次のような２７層の層構成からなる多層膜である。ただし、設計波長は７８０ｎｍである。
【０１０５】

【０１０６】
上記の近赤外シャープカットコートの透過率特性は図８に示す通りである。
【０１０７】
また、ローパスフィルターＦの射出面側には、図９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。
【０１０８】
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。
【０１０９】
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。
【０１１０】
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。
【０１１１】
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。
【０１１２】
上記各実施例では、図９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。
【０１１３】
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。
【０１１４】
また、ローパスフィルターＦ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。
【０１１５】
また、ＣＣＤの撮像面Ｉ上には、図１０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。
【０１１６】
補色モザイクフィルターは、具体的には、図１０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。
【０１１７】
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。
【０１１８】
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の大きい方のピークでは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。
【０１１９】
上記各実施例におけるそれぞれの波長特性の一例を図１１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。
【０１２０】
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。
【０１２１】
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Ｆの枚数も前記した通り２枚でも１枚でも構わない。
【０１２２】
また、各実施例の明るさ絞りの部分についての詳細を図１２示す。撮像光学系の第１群Ｇ１と第２群Ｇ２との間の光軸上の絞り位置に、０段、−１段、−２段、−３段、−４段の明るさ調節を可能とするターレット１０を配置している。ターレット１０には、０段の調整をする開口形状が直径約４ｍｍの円形で固定の空間からなる開口１Ａ（波長５５０ｎｍに対する透過率は１００％) と、−１段補正するために開口１Ａの開口面積の約半分の開口面積を有する開口形状が固定の透明な平行平板（波長５５０ｎｍに対する透過率は９９％）からなる開口１Ｂと、開口１Ｂと同じ面積の円形開口部を有し、−２段、−３段、−４段に補正するため、各々波長５５０ｎｍに対する透過率が５０％、２５％、１３％のＮＤフィルターが設けられた開口部１Ｃ、１Ｄ、１Ｅとを有している。
【０１２３】
そして、ターレット１０の回転軸１１の周りの回動により何れかの開口を絞り位置に配することで光量調節を行っている。
【０１２４】
また、実効ＦナンバーＦ_no' がＦ_no' ＞ａ／０．４μｍとなるときに、開口内に波長５５０ｎｍに対する透過率が８０％未満のＮＤフィルターが配される構成としている。具体的には、実施例１では、望遠端の実効Ｆ値が上記式を満たすのは、絞り開放時（０段）に対して−２段とした実行Ｆ値が９．０となるときであり、そのときに対応する開口は１Ｃとなる。それにより、絞りの回折現象による像の劣化を抑えている。
【０１２５】
また、図１２に示すターレット１０に代えて、図１３（ａ）に示すターレット１０’を用いた例を示す。撮像光学系の第１群Ｇ１と第２群Ｇ２との間の光軸上の明るさ絞り位置に、０段、−１段、−２段、−３段、−４段の明るさ調節を可能とするターレット１０’を配置している。ターレット１０’には、０段の調整をする開口形状が直径約４ｍｍの円形で固定の開口１Ａ' と、−１段補正するために開口１Ａ’の開口面積の約半分の開口面積を有する開口形状が固定の開口１Ｂ' と、さらに開口面積が順に小さくなり、−２段、−３段、−４段に補正するための形状が固定の開口部１Ｃ' 、１Ｄ' 、１Ｅ' とを有している。そして、ターレット１０’の回転軸１１の周りの回動により何れかの開口を絞り位置に配することで光量調節を行っている。
【０１２６】
また、これら複数の開口の中の１Ａ' から１Ｄ' にそれぞれ空間周波数特性の異なる光学的ローパスフィルターを配している。そして、図１３（ｂ）に示すように、開口径が小さくなる程光学フィルターの空間周波数特性を高く設定しており、それにより絞り込むことによる回折現象による像の劣化を抑えている。なお、図１３（ｂ）の各曲線は、ローパスフィルターのみの空間周波数特性を示すものであり、各絞りの回折も含めた特性は何れも等しくなるように設定しているものである。
【０１２７】
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や銀塩フィルムといった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。
【０１２８】
図１４〜図１６は、本発明によるの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１４はデジタルカメラ４０の外観を示す前方斜視図、図１５は同後方斜視図、図１６はデジタルカメラ４０の構成を示す断面図である。デジタルカメラ４０は、この例の場合、撮影用光路４２を有する撮影光学系４１、ファインダー用光路４４を有するファインダー光学系４３、シャッター４５、フラッシュ４６、液晶表示モニター４７等を含み、カメラ４０の上部に配置されたシャッター４５を押圧すると、それに連動して撮影光学系４１、例えば実施例１のズームレンズを通して撮影が行われる。撮影光学系４１によって形成された物体像が、近赤外カットコートを設けた光学的ローパスフィルターＦ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。
【０１２９】
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。
【０１３０】
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。
【０１３１】
なお、図１６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。
【０１３２】
次に、本発明のズームレンズが対物光学系として内蔵された情報処理装置の一例であるパソコンが図１７〜図１９に示される。図１７はパソコン３００のカバーを開いた前方斜視図、図１８はパソコン３００の撮影光学系３０３の断面図、図１９は図１７の状態の側面図である。図１７〜図１９に示されるように、パソコン３００は、外部から繰作者が情報を入力するためのキーボード３０１と、図示を省略した情報処理手段や記録手段と、情報を操作者に表示するモニター３０２と、操作者自身や周辺の像を撮影するための撮影光学系３０３とを有している。ここで、モニター３０２は、図示しないバックライトにより背面から照明する透過型液晶表示素子や、前面からの光を反射して表示する反射型液晶表示素子や、ＣＲＴディスプレイ等であってよい。また、図中、撮影光学系３０３は、モニター３０２の右上に内蔵されているが、その場所に限らず、モニター３０２の周囲や、キーボード３０１の周囲のどこであってもよい。
【０１３３】
この撮影光学系３０３は、撮影光路３０４上に、本発明によるズームレンズ（図では略記）からなる対物レンズ１１２と、像を受光する撮像素子チップ１６２とを有している。これらはパソコン３００に内蔵されている。
【０１３４】
ここで、撮像素子チップ１６２上には光学的ローパスフィルターＦが付加的に貼り付けられて撮像ユニット１６０として一体に形成され、対物レンズ１１２の鏡枠１１３の後端にワンタッチで嵌め込まれて取り付け可能になっているため、対物レンズ１１２と撮像素子チップ１６２の中心合わせや面間隔の調整が不要であり、組立が簡単となっている。また、鏡枠１１３の先端には、対物レンズ１１２を保護するためのカバーガラス１１４が配置されている。なお、鏡枠１１３中のズームレンズの駆動機構は図示を省いてある。
【０１３５】
撮像素子チップ１６２で受光された物体像は、端子１６６を介して、パソコン３００の処理手段に入力され、電子画像としてモニター３０２に表示される、図１７には、その一例として、操作者の撮影された画像３０５が示されている。また、この画像３０５は、処理手段を介し、インターネットや電話を介して、遠隔地から通信相手のパソコンに表示されることも可能である。
【０１３６】
次に、本発明のズームレンズが撮影光学系として内蔵された情報処理装置の一例である電話、特に持ち運びに便利な携帯電話が図２０に示される。図２０（ａ）は携帯電話４００の正面図、図２０（ｂ）は側面図、図２０（ｃ）は撮影光学系４０５の断面図である。図２０（ａ）〜（ｃ）に示されるように、携帯電話４００は、操作者の声を情報として入力するマイク部４０１と、通話相手の声を出力するスピーカ部４０２と、操作者が情報を入力する入力ダイアル４０３と、操作者自身や通話相手等の撮影像と電話番号等の情報を表示するモニター４０４と、撮影光学系４０５と、通信電波の送信と受信を行うアンテナ４０６と、画像情報や通信情報、入力信号等の処理を行う処理手段（図示せず）とを有している。ここで、モニター４０４は液晶表示素子である。また、図中、各構成の配置位置は、特にこれらに限られない。この撮影光学系４０５は、撮影光路４０７上に配置された本発明によるズームレンズ（図では略記）からなる対物レンズ１１２と、物体像を受光する撮像素子チップ１６２とを有している。これらは、携帯電話４００に内蔵されている。
【０１３７】
ここで、撮像素子チップ１６２上には光学的ローパスフィルターＦが付加的に貼り付けられて撮像ユニット１６０として一体に形成され、対物レンズ１１２の鏡枠１１３の後端にワンタッチで嵌め込まれて取り付け可能になっているため、対物レンズ１１２と撮像素子チップ１６２の中心合わせや面間隔の調整が不要であり、組立が簡単となっている。また、鏡枠１１３の先端には、対物レンズ１１２を保護するためのカバーガラス１１４が配置されている。なお、鏡枠１１３中のズームレンズの駆動機構は図示を省いてある。
【０１３８】
撮影素子チップ１６２で受光された物体像は、端子１６６を介して、図示していない処理手段に入力され、電子画像としてモニター４０４に、又は、通信相手のモニターに、又は、両方に表示される。また、通信相手に画像を送信する場合、撮像素子チップ１６２で受光された物体像の情報を、送信可能な信号へと変換する信号処理機能が処理手段には含まれている。
【０１３９】
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。
【０１４０】
〔１〕 結像光学系と前記結像光学系の像側に配された電子撮像素子とを備えた電子撮像装置において、
前記結像光学系は、非球面を含みかつ常時固定である最も像側の最終レンズと、前記最終レンズより物体側直前に配され、かつ、フォーカスのために移動するフォーカスレンズ群とを含むことを特徴とする電子撮像装置。
【０１４１】
〔２〕 前記結像光学系は、広角端から望遠端にかけて変倍する際に物体側にのみ移動する正の屈折力のレンズ群を有することを特徴とする上記１記載の電子撮像装置。
【０１４２】
〔３〕 前記結像光学系は、物体側から順に、負の屈折力の第１レンズ群、広角端から望遠端にかけて変倍する際に物体側にのみ移動する正の屈折力の第２レンズ群を有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。
【０１４３】
〔４〕 前記結像光学系は、物体側から順に、負の屈折力の第１レンズ群、広角端から望遠端にかけて変倍する際に物体側にのみ移動する複数の正の屈折力のレンズ群を有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。
【０１４４】
〔５〕 結像光学系と前記結像光学系の像側に配された電子撮像素子とを備えた電子撮像装置において、
前記結像光学系は、最も物体側に配された負の屈折力を有する第１レンズ群と、その像側に配された少なくとも３つのレンズ群とを含み、
物体側より引き続く４つ目のレンズ群までの相互の間隔は、変倍あるいはフォーカスのために変化し、
最も像側のレンズ群は固定で１枚の非球面レンズにて構成され、
変倍時に前記第１レンズ群の像側直後のレンズ群と一体で移動する開口絞りを有することを特徴とする電子撮像装置。
【０１４５】
〔６〕 ズームレンズと前記ズームレンズの像側に配された電子撮像素子と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レンズ群と、第４レンズ群からなり、
前記第３レンズ群を物体側に繰り出すことでより近距離の被写体に合焦することが可能であり、
前記第４レンズ群が非球面を含む常時固定の１枚のレンズよりなることを特徴とする電子撮像装置。
【０１４６】
〔７〕 ズームレンズと前記ズームレンズの像側に配された電子撮像素子と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レンズ群と、第４レンズ群からなり、
前記第３レンズ群を物体側に繰り出すことでより近距離の被写体に合焦することが可能であり、
前記第２レンズ群は、非球面を含む１枚の単レンズと、物体側より順に正レンズと負レンズとからなる接合レンズとからなり、
前記第３レンズ群は、正の単レンズ１枚よりなることを特徴とする電子撮像装置。
【０１４７】
〔８〕 ズームレンズと前記ズームレンズの像側に配された電子撮像素子と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レンズ群と、第４レンズ群とからなり、
前記第３レンズ群を物体側に繰り出すことでより近距離の被写体に合焦することが可能であり、
前記第２レンズ群は、非球面を含む１つの正レンズと、１つの負レンズとからなり、
前記第３レンズ群は、正の単レンズ１枚よりなることを特徴とする電子撮像装置。
【０１４８】
〔９〕 前記第１レンズ群が変倍時移動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。
【０１４９】
〔１０〕 最も物体側に、負の屈折力を有する第１群を有し、４つ以上の群より構成され、物体側より４つ目までの群は変倍中に相互の間隔が変化し、最も像側の群は固定で正の屈折力を有する１枚の非球面単レンズにて構成され、変倍時に第２群と一体で移動する開口絞りを有し、かつ、以下の条件（１）を満足するズームレンズ及び電子撮像素子を有することを特徴とする電子撮像装置。
【０１５０】
（１） １．５＜Ｌ₂ ／Ｙ＜３．５
ただし、Ｌ₂ は第２群の広角端から望遠端にかけての移動量、Ｙは撮像素子の有効撮像領域の対角長である。
【０１５１】
〔１１〕 物体側より順に、負の屈折力を有する第１群と正の屈折力を有する第２群と正の屈折力を有する第３群と正の屈折力を有する第４群とよりなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、前記第２群と第３群の間隔が大きくなり、前記第３群を物体側に繰り出すことでより近距離の被写体に合焦することが可能であり、前記第４群は正の屈折力を有する１枚の非球面単レンズにて構成され、以下の条件（２）を満足するズームレンズ及び電子撮像素子を有することを特徴とする電子撮像装置。
【０１５２】
（２） −１．２＜^exＰ_W ／^exＰ_T ＜０
ただし、^exＰ_W 、^exＰ_T はそれぞれ無限遠物点合焦時における広角端及び望遠端での像面から測った射出瞳位置である。
【０１５３】
〔１２〕 物体側より順に、負の屈折力を有する第１群と正の屈折力を有する第２群と正の屈折力を有する第３群と正の屈折力を有する第４群とよりなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、前記第２群と第３群の間隔が大きくなり、前記第３群を物体側に繰り出すことでより近距離の被写体に合焦することが可能であり、前記第２群が物体側から順に非球面を含む１枚の単レンズと物体側から正レンズ、負レンズの順で構成した接合レンズとからなり、前記第３群は正の屈折力を有する１枚の単レンズよりなり、以下の条件（３）と条件（４）を満足するズームレンズ及び電子撮像素子を有することを特徴とする電子撮像装置。
【０１５４】

ただし、Ｒ_2C1 、Ｒ_2C2 、Ｒ_2C3 は第２群の接合レンズの物体側から１番目と２番目と３番目のレンズ面のそれぞれの光軸上の曲率半径、ｔ_2Nは第２群の接合レンズ中の負レンズの光軸上での厚み、ｔ₂ は第２群の最も物体側の面から最も像側の面までの光軸上での厚みである。
【０１５５】
〔１３〕 物体側より順に、負の屈折力を有する第１群と正の屈折力を有する第２群と正の屈折力を有する第３群と正の屈折力を有する第４群よりなり、無限遠物点合焦時に広角端から望遠端に変倍する際は、前記第２群と第３群の間隔が大きくなり、前記第３群を物体側に繰り出すことでより近距離の被写体に合焦することが可能であり、前記第２群が物体側から順に非球面を含む正レンズ成分と負レンズ成分１つずつからなり、前記第３群は正の屈折力を有する１枚の単レンズよりなり、以下の条件（５）を満足するズームレンズ及び電子撮像素子を有することを特徴とする電子撮像装置。
【０１５６】
（５） ０．０５＜ｔ_2NI ／ｔ₂ ＜０．３
ただし、ｔ_2NI は第２群中の最も像側の負レンズの光軸上での厚み、ｔ₂ は第２群の最も物体側の面から最も像側の面までの光軸上での厚みである。
【０１５７】
〔１４〕 前記第１群は、物体側から順に、２枚の負レンズからなる負レンズ群と１枚の正レンズからなる正レンズ群とよりなることを特徴とする上記１０から１３の何れか１項記載の電子撮像装置。
【０１５８】
〔１５〕 前記第１群は、物体側から順に、２枚以下の負レンズからなる負レンズ群と１枚の正レンズからなる正レンズ群とよりなり、前記負レンズ群の中少なくとも１枚の負レンズは非球面を含むことを特徴とする上記１０から１３の何れか１項記載の電子撮像装置。
【０１５９】
〔１６〕 前記第１群、第２群の各々の総厚が以下の条件（６）、（７）を満足することを特徴とする上記９から１５の何れか１項記載の電子撮像装置。
【０１６０】
（６） ０．６＜ｔ₁ ／Ｙ＜２．２
（７） ０．３＜ｔ₂ ／Ｙ＜１．５
ただし、ｔ₁ は第１群の最も物体側の面から最も像側の面までの光軸上での厚みであり、ｔ₂ は第２群の最も物体側の面から最も像側の面までの光軸上での厚みであり、Ｙは撮像素子の有効撮像領域の対角長である。
【０１６１】
〔１７〕 前記ズームレンズの後方にある撮像素子よりも物体側に、波長６００ｎｍでの透過率が８０％以上であり、波長７００ｎｍでの透過率が１０％以下である近赤外シャープカットコートを有することを特徴とする上記９から１６の何れか１項記載の電子撮像装置。
【０１６２】
〔１８〕 前記撮像素子が、カラー化フィルターとして補色モザイクフィルターを有することを特徴とする上記１７記載の電子撮像装置。
【０１６３】
〔１９〕 前記補色モザイクフィルターは少なくとも４種類の色フィルターからなり、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ことを特徴とする上記１８記載の電子撮像装置。
【０１６４】
〔２０〕 前記補色モザイクフィルターは少なくとも４種類の色フィルターから構成され、前記４種類の色フィルターの特性は以下の通りであることを特徴とする上記１８又は１９記載の電子撮像装置。
【０１６５】
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、
シアンの色ブィルター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。
【０１６６】
５１０ｎｍ＜Ｇ_P ＜５４０ｎｍ
５ｎｍ＜Ｙ_P −Ｇ_P ＜３５ｎｍ
−１００ｎｍ＜Ｃ_P −Ｇ_P ＜−５ｎｍ
４３０ｎｍ＜Ｍ_P1＜４８０ｎｍ
５８０ｎｍ＜Ｍ_P2＜６４０ｎｍ
〔２１〕 前記グリーン、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５３０ｎｍでは８０％以上の強度を有し、前記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の大きい方のピークでは１０％から５０％の強度を有することを特徴とする上記２０記載のの電子撮像装置。
【０１６７】
〔２２〕 前記撮像素子より物体側に光軸上の総厚ｔ_LPF が以下の条件（８）を満たす光学的ローパスフィルターを配したことを特徴とする上記１０から２１の何れか１項記載の電子撮像装置。
【０１６８】
（８） ０．１５×１０³ ＜ｔ_LPF ／ａ＜０．４５×１０³
ただし、ａは電子撮像素子の水平画素ピッチである。
【０１６９】
〔２３〕 開口形状が固定の複数の開口を有し、その中の１つ開口を前記第１群の最も像側の面と前記第３群の最も物体側の面の間の何れかの光路内に挿入可能であり、かつ、他の開口と入れ替え可能とすることで像面照度の調節を行うことを特徴とする上記１０から２２の何れか１項記載の電子撮像装置。
【０１７０】
〔２４〕 前記複数の開口の中、一部の開口内に波長５５０ｎｍに対する透過率が８０％未満の媒体を有すると共に、他の一部の開口の波長５５０ｎｍに対する透過率を８０％以上としたことを特徴とする上記２３記載の電子撮像装置。
【０１７１】
〔２５〕 ズームレンズの焦点距離と入射瞳の直径から求まるＦナンバーをＦ_no、前記開口における波長５５０ｎｍにおける透過率をＴとしたときのＦ_no／√Ｔを実効ＦナンバーＦ_no' とし、電子撮像素子の水平画素ピッチをａとするとき、Ｆ_no' ＞ａ／０．４μｍとなるような実効Ｆナンバーに相当する光量になるように調節を実施する場合は、開口内に波長５５０ｎｍに対する透過率Ｔが８０％未満の媒体を備えた開口を前記ズームレンズの光路に挿入することを特徴とする上記２３記載の電子撮像装置。
【０１７２】
〔２６〕 前記複数の開口の中の複数にそれぞれ空間周波数特性の異なる光学的ローパスフィルターを有することを特徴とする上記２３から２５の何れか１項記載の電子撮像装置。
【０１７３】
以上の説明から明らかなように、本発明によると、物体側より順に、負の屈折力を有する第１レンズ群と、広角端から望遠端にかけて変倍する際に物体側にのみ移動する正の屈折力を有する第２レンズ群と、正の屈折力を有する第３レンズ群と、第４レンズ群からなるズームレンズを有する電子撮像装置において、第４レンズ群の構成枚数が少なく、リアフォーカス方式により、機構レイアウト上小型で簡素にしやすく、変倍比を確保しても薄型化と諸収差の補正を両立させ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でのレンズ断面図である。
【図２】実施例２のズームレンズの図１と同様のレンズ断面図である。
【図３】実施例３のズームレンズの図１と同様のレンズ断面図である。
【図４】実施例４のズームレンズの図１と同様のレンズ断面図である。
【図５】実施例５のズームレンズの図１と同様のレンズ断面図である。
【図６】実施例６のズームレンズの図１と同様のレンズ断面図である。
【図７】実施例１の無限遠物点合焦時の収差図である。
【図８】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９】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１０】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１１】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１２】各実施例の明るさ絞りの部分の一例の詳細を示す斜視図である。
【図１３】各実施例の明るさ絞りの部分の別の例の詳細を示す図である。
【図１４】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１５】図１４のデジタルカメラの後方斜視図である。
【図１６】図１４のデジタルカメラの断面図である。
【図１７】本発明によるズームレンズが対物光学系として組み込れたパソコンのカバーを開いた前方斜視図である。
【図１８】パソコンの撮影光学系の断面図である。
【図１９】図１７の状態の側面図である。
【図２０】本発明によるズームレンズが対物光学系として組み込れた携帯電話の正面図、側面図、その撮影光学系の断面図である。
【符号の説明】
Ｇ１…第１群
Ｇ２…第２群
Ｇ３…第３群
Ｇ４…第４群
Ｆ…光学的ローパスフィルター
Ｃ…カバーガラス
Ｉ…像面
Ｅ…観察者眼球
１Ａ、１Ｂ、１Ｃ、１Ｄ、１Ｅ…開口
１Ａ’、１Ｂ’、１Ｃ’、１Ｄ’、１Ｅ’…開口
１０…ターレット
１０’…ターレット
１１…回転軸
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
１１２…対物レンズ
１１３…鏡枠
１１４…カバーガラス
１６０…撮像ユニット
１６２…撮像素子チップ
１６６…端子
３００…パソコン
３０１…キーボード
３０２…モニター
３０３…撮影光学系
３０４…撮影光路
３０５…画像
４００…携帯電話
４０１…マイク部
４０２…スピーカ部
４０３…入力ダイアル
４０４…モニター
４０５…撮影光学系
４０６…アンテナ
４０７…撮影光路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic imaging apparatus that is thin in the depth direction by devising an optical system portion such as a zoom lens, and more particularly to a video camera and a digital camera. In addition, the zoom lens 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. The present invention pays attention to the category of portable popular types in particular, and aims to provide a technology for realizing a video camera and a digital camera with a thin depth while ensuring 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 a mainstream to employ a so-called collapsible lens barrel that projects an optical system from the camera body during shooting and stores the optical system in the camera body when carried. 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 high specifications such as zoom ratio and F value, 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, so Even so, 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). Among the currently known examples, those suitable for electronic imaging devices and having good imaging performance including zoom ratio, angle of view, F number, etc., and the possibility of making the collapsible thickness the thinnest are disclosed in JP-A-11 No. 194274, JP-A-11-287953, JP-A-2000-9997, and the like.
[0003]
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, it is only necessary to reduce the size of the image sensor. 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.
[0004]
Also, in order to make the camera body thin, so-called rear focus is effective for the layout of the drive system instead of the front group for lens movement during focusing. Then, it becomes necessary to select an optical system with less aberration fluctuation when rear focus is performed.
[0005]
[Problems to be solved by the invention]
  An object of the present invention is, in order from the object side, a first lens group having negative refractive power, and a second lens group having positive refractive power that moves only to the object side when zooming from the wide-angle end to the telephoto end. In the electronic imaging device having the third lens group having positive refractive power and the zoom lens composed of the fourth lens group, the number of the fourth lens group is small, and the rear focus system is used to reduce the size and the mechanism layout. It is easy to reduce the thickness and correct various aberrations even if the zoom ratio is secured.
[0006]
[Means for Solving the Problems]
  In order to achieve the above object, an electronic imaging apparatus of the present invention includes an imaging optical system and an electronic imaging device arranged on the image side of the imaging optical system.
  The imaging optical system includes a final lens group closest to the image side that is a single lens that includes an aspherical surface and is always fixed, and a focus lens that is disposed immediately before the object side from the final lens group and moves for focusing It is characterized by including a group.
[0007]
In this case, it is desirable that the imaging optical system has a lens unit having a positive refractive power that moves only to the object side when zooming from the wide-angle end to the telephoto end.
[0008]
The imaging optical system includes, in order from the object side, a first lens group having a negative refractive power, and a second lens group having a positive refractive power that moves only to the object side when zooming from the wide-angle end to the telephoto end. It can have.
[0009]
The imaging optical system includes, in order from the object side, a first lens group having a negative refractive power, and a plurality of lens groups having a positive refractive power that move only to the object side when zooming from the wide-angle end to the telephoto end. It can have.
[0010]
  Another electronic imaging device of the present invention is an electronic imaging device comprising an imaging optical system and an electronic imaging device disposed on the image side of the imaging optical system.
  The imaging optical system includes a first lens group having a negative refractive power arranged on the most object side, and at least three lens groups arranged on the image side,
  The mutual distance from the object side to the fourth lens group that follows is changed due to zooming or focusing.
  The last lens group on the most image side is fixed and is composed of one aspheric lens,
  The zoom lens has an aperture stop that moves together with the lens group immediately after the image side of the first lens group at the time of zooming.
[0011]
Yet another electronic imaging device of the present invention is an electronic imaging device comprising a zoom lens and an electronic imaging device arranged on the 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, a third lens group having a positive refractive power, and a fourth lens group. Consists of
It is possible to focus on a closer subject by extending the third lens group toward the object side,
The fourth lens group is composed of one lens that is always fixed including an aspherical surface.
[0012]
Another electronic imaging device of the present invention is an electronic imaging device comprising a zoom lens and an electronic imaging device disposed on the 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, a third lens group having a positive refractive power, and a fourth lens group. Consists of
It is possible to focus on a closer subject by extending the third lens group toward the object side,
The second lens group includes a single lens including an aspheric surface and a cemented lens including a positive lens and a negative lens in order from the object side.
The third lens group comprises a single positive single lens.
[0013]
Still another electronic imaging device of the present invention is an electronic imaging device comprising a zoom lens and an electronic imaging device arranged on the 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, a third lens group having a positive refractive power, and a fourth lens group. And consist of
It is possible to focus on a closer subject by extending the third lens group toward the object side,
The second lens group includes one positive lens including an aspherical surface and one negative lens.
The third lens group comprises a single positive single lens.
[0014]
In the above, the first lens group can be moved during zooming.
[0015]
In the imaging optical system employed in the electronic image pickup apparatus of the present invention, the lens closest to the image (single lens or cemented lens) includes an aspherical surface, which is always fixed, and the lens group immediately before this moves for focusing. This is a rear focus type zoom lens. Therefore, it is possible to ensure a stable and high imaging performance from infinity to a short distance while using the rear focus method. This is particularly effective when a lens unit having a positive refractive power that moves monotonously on the object side when zooming from the wide-angle end to the telephoto end is effective. In a zoom lens having such a lens group, an aspherical surface is introduced in the final group in order to reduce aberration fluctuations in the entire zooming range from the wide-angle end to the telephoto end, and to correct aberrations in a small amount in any state. In particular, correction of off-axis aberrations such as coma and astigmatism is performed. Therefore, when focusing is performed on the final group having an aspheric surface, fluctuations in off-axis aberrations such as coma and astigmatism accompanying movement in the optical axis direction are likely to increase, leading to performance degradation. For this reason, it is preferable that the final group having an aspheric surface is fixed, and focusing is performed in the group immediately before that.
[0016]
Note that the first lens group of such a zoom lens is more compact when it is constituted by a negative lens group, but the above problem is more conspicuous than when the first lens group is a positive lens group.
[0017]
For example, specifically, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group. An imaging optical system that includes a lens group and includes a zoom lens that can focus on an object at a shorter distance by extending the third lens group toward the object side, and the fourth lens group includes an aspherical surface An imaging optical system composed of a single lens with a fixed position, or a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a positive refractive power in order from the object side. A zoom lens that includes a third lens group and a fourth lens group, and is capable of focusing on a subject at a closer distance by extending the third lens group toward the object side. Including a single lens and a single positive / negative lens The third lens group is composed of a single lens and an imaging optical system consisting of a single positive lens, or a first lens group having a negative refractive power and a first lens group having a positive refractive power in order from the object side. A zoom lens that includes two lens groups, a third lens group having positive refractive power, and a fourth lens group, and is capable of focusing on an object at a shorter distance by extending the third lens group to the object side. The second lens group is composed of one positive lens (single lens or cemented lens) including an aspheric surface and one negative lens (single lens or cemented lens), and the third lens group is composed of one positive lens that is a single lens. This is the case with an imaging optical system.
[0018]
In addition, it is more preferable that the fourth lens group which is the final lens group has a positive refractive power because the incident angle to the electronic imaging element can be made nearly vertical. In order to reduce the number of parts, this lens group can be an aspherical single lens.
[0019]
As described above, in the group movable during zooming, the aberration variation in the entire zooming range is corrected as much as possible to remove substantially uniform aberrations, particularly off-axis aberrations, by adding an aspheric surface to the final lens group. Yes. However, especially in the case of coma aberration, correction cannot be made unless the lens surface for correction is separated from the image plane to some extent. Therefore, the air conversion distance DR on the optical axis between the last lens group and the image plane should satisfy the following condition.
[0020]
(X) 0.3 <DR / Y <2.5
However, Y is the diagonal length of the effective imaging area (substantially rectangular) of an image sensor.
[0021]
When the lower limit of 0.3 of the condition (x) is exceeded, correction of distortion due to the aspherical surface of the final lens group is easy, but correction of coma becomes difficult. When the upper limit of 2.5 is exceeded, the total length of the optical system and the lens diameter of the group apart from the aperture stop tend to be enlarged.
[0022]
Moreover,
(X-1) 0.4 <DR / Y <2.0
It is more preferable.
[0023]
In addition,
(X-2) 0.5 <DR / Y <1.5
It is more preferable.
[0024]
In order to cover as much as possible the space loss caused by the above-described configuration, the distance D between the last lens group including the aspheric surface and the fixed last lens group and the focus group immediately before it is D._34W(However, it is better to satisfy the following conditions for the wide-angle end when focusing on an object point at infinity).
[0025]
(Y) 0.05 <D_34W/Y<0.8
If the upper limit of 0.8 of the condition (y) is exceeded, the total length of the optical system tends to be long or it is difficult to ensure a zoom ratio. The lower limit of 0.05 is provided to avoid mechanical interference between the two groups.
[0026]
Moreover,
(Y-1) 0.05 <D_34W/Y<0.6
It is more preferable.
[0027]
In addition,
(Y-2) 0.05 <D_34W/Y<0.4
It is more preferable.
[0028]
Further, by making the first lens group, which is the most object side lens group, movable with zooming, the first lens group can have the function of a compensator. Since ratio can be expanded, it is more preferable.
[0029]
Next, an invention to which the above invention is applied will be described.
[0030]
In order to achieve the above object, another electronic imaging apparatus of the present invention has a first group having a negative refractive power closest to the object side, is composed of four or more groups, and a fourth group from the object side. The distance between the two groups changes during zooming, and the most image side group is composed of a single aspherical single lens having a fixed positive refractive power, and is integrated with the second group during zooming. It has a zoom lens and an electronic image sensor characterized by having a moving aperture stop and satisfying the following condition (1).
[0031]
(1) 1.5 <L₂/Y<3.5
However, L₂Is the amount of movement of the second group from the wide-angle end to the telephoto end, and Y is the diagonal length of the effective image pickup area (substantially rectangular) of the image sensor.
[0032]
The configuration of the zoom lens as in the present invention is easy to reduce the thickness of each group and is simple in configuration, and also has stable imaging performance during zooming and focusing. In addition, there is little fluctuation in the F value due to zooming. However, there is a drawback that the variation of the exit pupil position is large. This is because the amount of movement of the diaphragm during zooming is large. Exceeding the upper limit 3.5 of condition (1) is not preferable because the angle of the principal ray on the imaging surface becomes too large at the wide-angle end or the telephoto end. If the lower limit of 1.5 is exceeded, aberration fluctuations such as astigmatism during zooming or focusing tend to increase, which is not preferable.
[0033]
In addition, it is more preferable to replace the condition (1) as follows.
[0034]
(1-1) 1.6 <L₂/Y<3.3
Furthermore, the following is more preferable.
[0035]
(1-2) 1.7 <L₂/Y<3.0
It is also preferable to individually limit the lower limit value or the upper limit value of the above formula.
[0036]
In the present invention, the first group having a negative refractive power, the second group having a positive refractive power, the third group having a positive refractive power, and the fourth group having a positive refractive power in order from the object side. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the distance between the second group and the third group becomes larger, and the third group is moved closer to the object side. It is possible to focus on a subject at a distance, and the fourth group includes a single aspherical single lens having a positive refractive power, and satisfies the following condition (2) and electronic imaging An electronic imaging device including an element may be used.
[0037]
(2) -1.2 <^exP_W/^exP_T<0
However,^exP_W,^exP_TAre respectively the exit pupil positions measured from the image planes at the wide-angle end and the telephoto end when focusing on an object point at infinity.
[0038]
In the case of this zoom method, since the amount of change in the exit pupil position is large from the wide angle to the telephoto, it is necessary to be within the condition (2). When the upper limit of 0 is exceeded, shading tends to occur at the wide-angle end, and when the lower limit of −1.2 is exceeded, shading tends to occur at the telephoto end.
[0039]
In addition, it is better if it is as follows.
[0040]
(2-1) -1.1 <^exP_W/^exP_T<-0.2
Furthermore, it is even better to do the following.
[0041]
(2-2) -1.0 <^exP_W/^exP_T<-0.4
It is also preferable to individually limit the lower limit value or the upper limit value of the above formula.
[0042]
In the present invention, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the distance between the second group and the third group becomes larger, and the third group is moved closer to the object side. It is possible to focus on an object at a distance, and the second group includes a single lens including an aspheric surface in order from the object side, and a cemented lens configured in this order from the object side to a positive lens and a negative lens. The third group is composed of one single lens having a positive refractive power, and has a zoom lens and an electronic image sensor that satisfy the following conditions (3) and (4): It is good.
[0043]

However, R_2C1, R_2C2, R_2C3Is the radius of curvature on the optical axis of each of the first, second and third lens surfaces from the object side of the cemented lens of the second group, t_2NIs the thickness on the optical axis of the negative lens in the cemented lens of the second group, t₂Is the thickness on the optical axis from the most object side surface of the second group to the most image side surface.
[0044]
Condition (3) defines the ratio of the shape factor of each lens element (positive lens / negative lens) of the cemented lens of the second group. When the lower limit value of −1.5 is exceeded, it is disadvantageous for correction of axial chromatic aberration, and when the upper limit value of −0.3 is exceeded, the lens element becomes thick, which is disadvantageous for miniaturization.
[0045]
Condition (4) defines the thickness on the optical axis of the negative lens (joined) of the second group. The astigmatism cannot be corrected unless this part is thickened to some extent, but this is a problem for the purpose of reducing the thickness of each element of the optical system. Accordingly, astigmatism is corrected by introducing an aspherical surface into the image side lens. Still, if the lower limit of 0.05 is exceeded, astigmatism cannot be corrected completely. If the upper limit of 0.3 is exceeded, the thickness is unacceptable.
[0046]
Note that it is more preferable that the conditions (3) and (4) are as follows individually or together.
[0047]

Furthermore, it is more preferable that the conditions (3) and (4) are individually or together as follows.
[0048]

It is also preferable to individually limit the lower limit value or the upper limit value of the above formula.
[0049]
In the present invention, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the distance between the second group and the third group becomes large, and the third group is extended toward the object side to be closer to the object side. The second group is composed of one positive lens component and one negative lens component including an aspherical surface in order from the object side, and the third group has a positive refractive power. You may comprise as an electronic imaging device characterized by having a zoom lens and an electronic imaging device which consist of a single lens, and satisfy the following conditions (5).
[0050]
(5) 0.05 <t_2NI/ T₂<0.3
Where t_2NIIs the thickness on the optical axis of the most image side negative lens in the second lens unit, t₂Is the thickness on the optical axis from the most object side surface of the second group to the most image side surface. Here, the lens component is a concept indicating a single lens or a cemented lens.
[0051]
Condition (5) is a condition for balancing the correction of astigmatism and the thickness of the second group, as in condition (4).
[0052]
Condition (5) may be the following condition (5-1) or (5-2), and it is also preferable to limit only the upper limit or the lower limit of the following formula.
[0053]
(5-1) 0.06 <t_2NI/ T₂<0.28
(5-2) 0.07 <t_2NI/ T₂<0.26
When the zoom lens zoom ratio is 2.3 times or more in each of the above inventions, the following conditions (a) and (b) are satisfied, which contributes to a reduction in thickness.
[0054]
(A) 0.9 <−β_23t<1.8
(B) 2.0 <f₂/ F_W<3.0
However, β_23tIs the combined magnification when focusing on an object point at infinity at the telephoto end of the second and third groups, f₂Is the focal length of the second group, f_WIs the focal length at the wide-angle end when focusing on an object point at infinity of the entire zoom lens system.
[0055]
Condition (a) is that the infinite object time magnification β at the telephoto ends of the second group and the third group_23tIs specified. As the absolute value is as large as possible, the entrance pupil position at the wide angle end can be made shallower, the diameter of the first group can be easily reduced, and the thickness can be reduced. When the lower limit of 0.9 is exceeded, it is difficult to satisfy the thickness, and when the upper limit of 1.8 is exceeded, aberration correction (spherical aberration, coma, astigmatism) becomes difficult.
[0056]
Condition (b) is that the focal length f of the second group₂Is specified. A shorter focal length is advantageous for reducing the thickness of the second group itself, but the power arrangement is such that the front principal point of the second group is located on the object side and the rear principal point of the first group is located on the image side. Unreasonableness is likely to occur, which is not preferable for aberration correction. Exceeding the lower limit of 2.0 makes it difficult to correct spherical aberration, coma, astigmatism, and the like. If the upper limit of 3.0 is exceeded, thinning becomes difficult.
[0057]
It is more preferable if (a) and (b) are individually or together as follows.
[0058]
(A-1) 0.9 <−β_23t<1.7
(B-1) 2.1 <f₂/ F_W<2.8
Furthermore, it is more preferable to do the following.
[0059]
(A-2) 1.1 <−β_23t<1.6
(B-2) 2.2 <f₂/ F_W<2.6
It is also preferable to individually limit the lower limit value or the upper limit value of the above formula.
[0060]
In addition, the first group is configured by a negative lens group including two negative lenses and a positive lens group including one positive lens in order from the object side, or two or less negative lenses in order from the object side. And a positive lens group including one positive lens, and at least one negative lens in the negative lens group includes an aspherical surface. Good compatibility with the configuration for aberration correction. In other words, there is little aberration variation during focusing, and aberration correction can be satisfactorily performed in all zooming ranges.
[0061]
In addition, the total thickness of the first group and the second group may satisfy the following conditions.
[0062]
(6) 0.6 <t₁/Y<2.2
(7) 0.3 <t₂/Y<1.5
Where t₁Is the thickness on the optical axis from the most object-side surface to the most image-side surface of the first group, and t₂Is the thickness on the optical axis from the most object-side surface to the most image-side surface of the second group, and Y is the diagonal length of the effective imaging region (substantially rectangular) of the image sensor.
[0063]
Conditions (6) and (7) define the total thickness of the first group and the second group, respectively. If the upper limit values of 2.2 and 1.5 are exceeded, thinning tends to be hindered, and if the lower limit values of 0.6 and 0.3 are exceeded, the curvature radius of each lens surface must be loosened. It becomes difficult to establish a paraxial relationship and correct various aberrations. If the lower limit of each of the conditions (6) and (7) is reduced to 0.6 and 0.3, the thickness of each lens becomes thinner. For this reason, if the thickness from the lens center to the periphery and the edge thickness are to be secured, the curvature of each lens becomes loose, and the power required for each lens cannot be secured.
[0064]
In addition, it is preferable to change this condition range according to the value of Y in order to secure the rim and the machine space.
[0065]
Specifically, it is desirable to satisfy the following conditions (6-1) and (7-1).
[0066]

As described above, a means for improving the imaging performance while reducing the retractable thickness of the zoom lens unit has been provided.
[0067]
Next, mention will be made of thinning the filters. In an electronic imaging device, an infrared absorption filter having a certain thickness is usually inserted closer to the object side than the imaging device 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. If a near-infrared sharp cut coat having a transmittance at a wavelength of 600 nm of 80% or more and a transmittance at a wavelength of 700 nm of 10% or less is introduced closer to the object side than the image pickup device behind the zoom lens system, it is more than the absorption type. The transmittance on the red side becomes relatively high, and the magenta tendency on the bluish-purple side, which is a defect of the CCD having the complementary color mosaic filter, is alleviated by gain adjustment, and color reproduction similar to that of the CCD having the primary color filter can be obtained. On the other hand, in the case of a complementary color filter, since the transmitted light energy is high, the sensitivity is substantially higher than that of a CCD with a primary color filter and it is advantageous in terms of resolution. is there.
[0068]
For the other optical low-pass filter, the total thickness t on its optical axis_LPFShould satisfy the following conditions.
[0069]
(8) 0.15 × 10^Three<T_LPF/A<0.45×10^Three
Where a is the horizontal pixel pitch of the electronic image sensor.
[0070]
Although it is effective to reduce the optical low-pass filter to reduce the collapsed thickness, it is generally not preferable because the moire suppressing effect is reduced. On the other hand, as the pixel pitch decreases, the contrast of frequency components above the Nyquist limit decreases due to the diffraction effect of the imaging lens system, and a reduction in 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, one that is horizontally shifted by aμm and ± 45 ° direction by SQRT (1/2) × a is known. Here, SQRT is a square route and means a square root. The filter thickness at this time is approximately [1 + 2 × SQRT (1/2)] × a × 10^Three/5.88 (mm). This is a specification that makes the contrast 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. It is preferable that the condition (8) is satisfied, including the case where filter specifications other than the above, for example, two sheets are stacked or one sheet is used. Upper limit of 0.45 × 10^ThreeExceeding the value causes the optical low-pass filter to be too thick and hinder thinning. Lower limit of 0.15 × 10^ThreeExceeding this will result in insufficient moire removal. However, it is desirable that the condition of a in carrying out this is 5 μm or less.
[0071]
Furthermore, when a is 4 μm or less, it is more susceptible to diffraction, so it is preferable to satisfy the following condition (8-1).
[0072]
(8-1) 0.13 × 10^Three<T_LPF/A<0.42×10^Three
The following may also be used. The low-pass filter is a superposition of three low-pass filters. When 4μm ≦ a <5μm,
(8-2) 0.3 × 10^Three<T_LPF/A<0.4×10^Three
It is good to satisfy.
[0073]
The low-pass filter is a superposition of two low-pass filters, and when 4 μm ≦ a <5 μm,
(8-3) 0.2 × 10^Three<T_LPF/A<0.28×10^Three
It is good to satisfy.
[0074]
The low-pass filter is a single low-pass filter, and when 4 μm ≦ a <5 μm,
(8-4) 0.1 × 10^Three<T_LPF/A<0.16×10^Three
It is good to satisfy.
[0075]
The low-pass filter is a superposition of three low-pass filters. When a <4 μm,
(8-5) 0.25 × 10^Three<T_LPF/A<0.37×10^Three
It is good to satisfy.
[0076]
The low-pass filter is a superposition of two low-pass filters. When a <4 μm,
(8-6) 0.16 × 10^Three<T_LPF/A<0.25×10^Three
It is good to satisfy.
[0077]
The low-pass filter consists of a single low-pass filter, and when a <4 μm,
(8-7) 0.08 × 10^Three<T_LPF/A<0.14×10^Three
It is good to satisfy.
[0078]
In addition, when an image sensor with a small pixel pitch is used, the image quality deteriorates due to the diffraction effect due to narrowing down. Accordingly, there are a plurality of apertures having a fixed aperture shape, and one of them is in any optical path between the lens surface closest to the image side of the first group and the lens surface closest to the object side of the third group. An electronic imaging device that can be inserted and exchanged with other devices to adjust the illuminance of the image plane. It is preferable to adjust the amount of light by having a medium having different transmittances for 550 nm and less than 80%, and setting the transmittance for the wavelength 550 nm of the other part of the apertures to 80% or more.
[0079]
Alternatively, the F number (f / ID) obtained from the focal length f of the zoom lens and the diameter ID of the entrance pupil is F_noF where T is the transmittance at a wavelength of 550 nm in the aperture._no/ √T is the effective F number F_no', And when the horizontal pixel pitch of the electronic image sensor is a, F_no'When adjusting the light quantity to correspond to an effective F number such that> a / 0.4 μm, zoom the aperture provided with a medium having a transmittance T for the wavelength of 550 nm of less than 80% in the aperture. It is preferable that the electronic imaging device be inserted into the optical path of the lens. For example, if it is outside the range of the above condition from the open value, it is left as a dummy medium or space with no medium or with a transmittance of 91% or more for a wavelength of 550 nm, and within that range, the aperture stop is sufficiently affected by diffraction. Instead of reducing the diameter, it is better to adjust the amount of light with an ND filter.
[0080]
Further, the plurality of openings may be arranged with their diameters reduced in inverse proportion to the F value, and optical low-pass filters having different spatial frequency characteristics may be placed in the openings instead of the ND filters. . The diaphragm diffraction deterioration increases as the aperture is narrowed down. Therefore, it is preferable to set the spatial frequency characteristics of the optical low-pass filter higher as the aperture diameter decreases. Here, the higher spatial frequency characteristic means that the contrast of the spatial frequency of the object image is kept higher than the others. In other words, it means that the cutoff frequency is high, for example.
[0081]
DETAILED DESCRIPTION OF THE INVENTION
  Embodiments 1 to 6 of the zoom lens used in the electronic imaging device of the present invention will be described below. Examples 5 to 6 are reference examples. 1 to 6 show lens cross-sectional views at the wide-angle end when focusing on an object point at infinity according to these embodiments. In each figure, the first group is G1, the second group is G2, the third group is G3, the fourth group is G4, a three-layer optical low-pass filter on its first surface (object side surface). An optical low-pass filter F provided with a near-infrared cut coat, a cover glass of a CCD which is an electronic imaging device, C, and an image plane which is a CCD image plane and provided with a complementary color mosaic filter is indicated by I. The optical low-pass filter F and the cover glass C, which are sequentially arranged from the object side, are fixedly disposed between the fourth group G4 and the image plane I. In addition, in each figure, the focus group is illustrated as “focus”, and the in-focus direction to the short distance is illustrated by an arrow.
[0082]
As shown in FIG. 1, the zoom lens of Example 1 includes a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, a third group G3 having a positive refractive power, and a fourth group G4 having a positive refractive power. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then reverses to the object side and then moves to the position of the wide-angle end at the telephoto end. The second group G2 moves to the object side, the third group G3 once moves slightly to the image side and then reverses to the object side, and at the telephoto end becomes the same as the wide-angle end position. The fourth group G4 is a fixed lens group, and the distance between the second group G2 and the third group G3 increases when zooming from the wide-angle end to the telephoto end. Then, the third group G3 is extended toward the object side to focus on a subject at a short distance.
[0083]
The first group G1 of Example 1 includes a negative meniscus lens having a convex surface facing the object side, a biconcave lens, and a positive meniscus lens having a convex surface facing the object side. It is composed of a biconvex lens, a cemented lens of a biconvex lens and a biconcave lens, the third group G3 is composed of a single positive meniscus lens having a concave surface on the object side, and the fourth group G4 has a convex surface on the object side. It consists of one positive meniscus lens. The aspheric surfaces are used for the three surfaces of the object side surface of the middle biconcave lens in the first group G1, the most object side surface of the second group G2, and the object side surface of the fourth group G4.
[0084]
As shown in FIG. 2, the zoom lens of Example 2 includes a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, a third group G3 having a positive refractive power, and a fourth group G4 having a positive refractive power. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then reverses to the object side and then moves to the position of the wide-angle end at the telephoto end. The second group G2 moves to the object side, the third group G3 moves to the object side, the fourth group G4 is a fixed lens group, and the distance between the second group G2 and the third group G3 Increases when zooming from the wide-angle end to the telephoto end. Then, the third group G3 is extended toward the object side to focus on a subject at a short distance.
[0085]
The first group G1 of Example 2 includes a negative meniscus lens having a convex surface facing the object side, a biconcave lens, and a positive meniscus lens having a convex surface facing the object side. The third lens unit G3 is composed of a biconvex lens arranged, a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side. The third group G3 has a positive meniscus lens having a concave surface facing the object side. The fourth group G4 includes one positive meniscus lens having a convex surface directed toward the object side. The aspheric surfaces are used for the three surfaces of the object side surface of the middle biconcave lens in the first group G1, the most object side surface of the second group G2, and the object side surface of the fourth group G4.
[0086]
As shown in FIG. 3, the zoom lens of Example 3 includes a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, a third group G3 having a positive refractive power, and a fourth group G4 having a positive refractive power. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then reverses to the object side and then moves to the position of the wide-angle end at the telephoto end. The second group G2 moves to the object side, the third group G3 once moves slightly to the image side and then reverses to the object side, and at the telephoto end becomes the same as the wide-angle end position. The fourth group G4 is a fixed lens group, and the distance between the second group G2 and the third group G3 increases when zooming from the wide-angle end to the telephoto end. Then, the third group G3 is extended toward the object side to focus on a subject at a short distance.
[0087]
The first group G1 of Example 3 is composed of a negative meniscus lens having a convex surface facing the object side, a biconcave lens, and a positive meniscus lens having a convex surface facing the object side. It is composed of a biconvex lens, a cemented lens of a biconvex lens and a biconcave lens, the third group G3 is composed of a single positive meniscus lens having a concave surface on the object side, and the fourth group G4 has a convex surface on the object side. It consists of one positive meniscus lens. The aspheric surfaces are used for the three surfaces of the object side surface of the middle biconcave lens in the first group G1, the most object side surface of the second group G2, and the object side surface of the fourth group G4.
[0088]
As shown in FIG. 4, the zoom lens of Example 4 includes a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, a third group G3 having a positive refractive power, and a fourth group G4 having a positive refractive power. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then reverses to the object side and then moves to the position of the wide-angle end at the telephoto end. The second group G2 moves to the object side, the third group G3 once moves slightly to the image side and then reverses to the object side, and at the telephoto end becomes the same as the wide-angle end position. The fourth group G4 is a fixed lens group, and the distance between the second group G2 and the third group G3 increases when zooming from the wide-angle end to the telephoto end. Then, the third group G3 is extended toward the object side to focus on a subject at a short distance.
[0089]
The first group G1 of Example 4 includes a biconcave lens and a positive meniscus lens having a convex surface facing the object side. The second group G2 includes a diaphragm, a biconvex lens disposed thereafter, a biconvex lens, and a biconcave lens. The third group G3 is composed of one positive meniscus lens having a concave surface facing the object side, and the fourth group G4 is composed of one positive meniscus lens having a convex surface facing the object side. The aspheric surfaces are used for the three surfaces of the image side surface of the biconcave lens of the first group G1, the most object side surface of the second group G2, and the object side surface of the fourth group G4.
[0090]
As shown in FIG. 5, the zoom lens of Example 5 includes a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, a third group G3 having a positive refractive power, and a fourth group G4 having a positive refractive power. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then reverses to the object side and then moves to the position of the wide-angle end at the telephoto end. The second group G2 moves to the object side, the third group G3 once moves slightly to the image side and then reverses to the object side, and at the telephoto end becomes the same as the wide-angle end position. The fourth group G4 is a fixed lens group, and the distance between the second group G2 and the third group G3 increases when zooming from the wide-angle end to the telephoto end. Then, the third group G3 is extended toward the object side to focus on a subject at a short distance.
[0091]
The first group G1 of Example 5 includes a negative meniscus lens having a convex surface facing the object side and a positive meniscus lens having a convex surface facing the object side, and the second group G2 includes both a diaphragm and a lens disposed thereafter. It consists of a cemented lens of a convex lens and a negative meniscus lens having a concave surface facing the object side, and a negative meniscus lens having a convex surface facing the object side, and the third group G3 is composed of a single positive meniscus lens having a concave surface facing the object side. The fourth group G4 includes one positive meniscus lens having a convex surface facing the object side. The aspheric surfaces are used for the three surfaces of the negative meniscus lens of the first group G1, the most object side surface of the second group G2, and the object side surface of the fourth group G4.
[0092]
As shown in FIG. 6, the zoom lens of Example 6 includes a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, a third group G3 having a positive refractive power, and a fourth group G4 having a positive refractive power. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then reverses to the object side and then moves to the position of the wide-angle end at the telephoto end. The second group G2 moves to the object side slightly, the third group G3 temporarily moves slightly to the object side, and then reverses to the image side, and at the telephoto end, slightly closer to the object side than the wide-angle end position. Thus, the fourth group G4 is a fixed lens group, and the distance between the second group G2 and the third group G3 increases when zooming from the wide-angle end to the telephoto end. Then, the third group G3 is extended toward the object side to focus on a subject at a short distance.
[0093]
The first group G1 of Example 6 includes a negative meniscus lens having a convex surface facing the object side and a positive meniscus lens having a convex surface facing the object side, and the second group G2 includes both a diaphragm and a lens disposed thereafter. The third lens group G3 is composed of one positive meniscus lens having a convex surface facing the object side, and the fourth lens group G4 is a positive lens having a concave surface facing the object side. Consists of a single meniscus lens. The aspherical surfaces are used for three surfaces, that is, the image side surface of the negative meniscus lens of the first group G1, the most object side surface of the second group G2, and the image side surface of the fourth group G4.
[0094]
In the following, the numerical data of each of the above embodiments is shown._NOIs the F number, FB is the back focus, WE is the wide angle end, ST is the intermediate state, TE is the telephoto end, r₁, R₂... is the radius of curvature of each lens surface, d₁, D₂... is the distance between each lens surface, n_d1, N_d2... is the refractive index of d-line of each lens, ν_d1, Ν_d2... is the Abbe number of each lens. The aspherical shape is represented by the following formula, where x is an optical axis with the light traveling direction being positive, and y is a direction orthogonal to the optical axis.
[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]

[0102]
FIG. 7 shows aberration diagrams of Example 1 when focusing on an object point at infinity. In this aberration diagram, (a) shows the wide-angle end, (b) shows the intermediate state, and (c) shows the spherical aberration SA, astigmatism AS, distortion DT, and lateral chromatic aberration CC at the telephoto end. In the figure, “FIY” represents the image height.
[0103]
Next, the values of conditional expressions (1) to (8), (a), and (b) in the above-described embodiments are shown below.

[0104]
In each of the above embodiments, on the image side of the fourth group G4, as shown in the figure, a low-pass filter F having a near-infrared sharp cut coat on the incident surface side is provided. This near-infrared sharp cut coat has a transmittance of 80% or more at a wavelength of 600 nm and a transmittance of 10% or less at a wavelength of 700 nm. Specifically, it is a multilayer film composed of the following 27 layers, for example. However, the design wavelength is 780 nm.
[0105]

[0106]
The transmittance characteristics of the near infrared sharp cut coat are as shown in FIG.
[0107]
Further, the color reproducibility of the electronic image is further improved by providing a color filter for reducing the transmission of colors in the short wavelength region as shown in FIG. ing.
[0108]
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.
[0109]
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.
[0110]
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.
[0111]
Such means for limiting the wavelength is more effective in an imaging system using a complementary color mosaic filter.
[0112]
In each of the above-described embodiments, as shown in FIG. 9, 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.
[0113]
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.
[0114]
In addition, the low-pass filter F uses three types of filters with 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.
[0115]
Further, as shown in FIG. 10, 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 CCD imaging surface I. ing. These four types of color filters are arranged in a mosaic so that each of them has approximately the same number and adjacent pixels do not correspond to the same type of color filter. Thereby, more faithful color reproduction is possible.
[0116]
Specifically, the complementary color mosaic filter is composed of at least four types of color filters as shown in FIG. 10, and the characteristics of the four types of color filters are preferably as follows.
[0117]
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.
[0118]
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 a larger wavelength at 530 nm with respect to the peak of spectral intensity. In order to improve color reproducibility, it is more preferable that the peak has an intensity of 10% to 50%.
[0119]
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%.
[0120]
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.
[0121]
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 F may be two or one as described above.
[0122]
Details of the aperture stop portion of each embodiment are shown in FIG. Brightness can be adjusted in 0, −1, −2, −3, and −4 steps at the stop position on the optical axis between the first group G1 and the second group G2 of the imaging optical system. A turret 10 is arranged. The turret 10 has an opening 1A having a circular shape with a diameter of about 4 mm and a fixed space (the transmittance for a wavelength of 550 nm is 100%), and the opening of the opening 1A for −1 correction. An opening 1B made of a transparent parallel plate having a fixed opening shape having an opening area that is about half the area (the transmittance for the wavelength of 550 nm is 99%), a circular opening having the same area as the opening 1B, and −2 steps In order to correct to -3 and -4 stages, apertures 1C, 1D, and 1E provided with ND filters having transmittances of 50%, 25%, and 13% for a wavelength of 550 nm, respectively, are provided.
[0123]
The amount of light is adjusted by arranging one of the openings at the aperture position by turning the turret 10 around the rotation shaft 11.
[0124]
Effective F number F_no'Is F_no'> When a> 0.4 μm, an ND filter having a transmittance of less than 80% for a wavelength of 550 nm is arranged in the opening. Specifically, in the first embodiment, the effective F value at the telephoto end satisfies the above equation when the effective F value, which is -2 steps with respect to the full aperture (0 steps), is 9.0. There is a corresponding opening of 1C. This suppresses image degradation due to the diffraction phenomenon of the stop.
[0125]
Moreover, it replaces with the turret 10 shown in FIG. 12, and the example using the turret 10 'shown to Fig.13 (a) is shown. Adjust the brightness of the 0th, -1st, -2nd, -3rd, and -4th steps to the aperture stop position on the optical axis between the first group G1 and the second group G2 of the imaging optical system. The possible turret 10 'is arranged. The turret 10 'has an opening shape with an opening of 0A that is adjusted to be zero and a circular and fixed opening 1A' that has a diameter of about 4mm, and an opening that has an opening area that is about half of the opening area of the opening 1A 'for correcting -1 step. The opening 1B ′ having a fixed shape and the opening area are further reduced in order, and the openings 1C ′, 1D ′, and 1E ′ having fixed shapes for correction to −2, 3 and 4 steps are provided. is doing. The amount of light is adjusted by arranging one of the openings at the stop position by turning the turret 10 ′ around the rotation shaft 11.
[0126]
Further, optical low-pass filters having different spatial frequency characteristics are arranged from 1A ′ to 1D ′ in the plurality of openings. Then, as shown in FIG. 13B, the spatial frequency characteristic of the optical filter is set higher as the aperture diameter becomes smaller, thereby suppressing image deterioration due to diffraction phenomenon due to narrowing down. Each curve in FIG. 13B shows the spatial frequency characteristics of only the low-pass filter, and the characteristics including diffraction of each diaphragm are set to be equal.
[0127]
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 on an image pickup device such as a CCD or a silver salt film to take a picture, particularly a digital camera or video camera, The present invention can be used for personal computers and telephones, which are examples of information processing apparatuses, particularly mobile phones that are convenient to carry. The embodiment is illustrated below.
[0128]
14 to 16 are conceptual diagrams of a configuration in which the zoom lens according to the present invention is incorporated in the photographing optical system 41 of the digital camera. 14 is a front perspective view showing the appearance of the digital camera 40, FIG. 15 is a rear perspective view thereof, and FIG. 16 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 optical low-pass filter F provided with a near-infrared cut coat. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the processing means 51. Further, the processing means 51 is connected to a recording means 52 so that a photographed electronic image can be recorded. The recording means 52 may be provided separately from the processing means 51, or may be configured to perform recording / writing electronically using a floppy disk, memory card, MO, or the like. Further, it may be configured as a silver salt camera in which a silver salt film is arranged in place of the CCD 49.
[0129]
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.
[0130]
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.
[0131]
In the example of FIG. 16, a parallel plane plate is disposed as the cover member 50, but a lens having power may be used.
[0132]
Next, a personal computer which is an example of an information processing apparatus in which the zoom lens of the present invention is incorporated as an objective optical system is shown in FIGS. 17 is a front perspective view with the cover of the personal computer 300 opened, FIG. 18 is a sectional view of the photographing optical system 303 of the personal computer 300, and FIG. 19 is a side view of the state of FIG. As shown in FIGS. 17 to 19, the personal computer 300 includes a keyboard 301 for the writer to input information from the outside, information processing means and recording means (not shown), and a monitor for displaying information to the operator. 302 and a photographing optical system 303 for photographing the operator himself and surrounding images. Here, the monitor 302 may be a transmissive liquid crystal display element that is illuminated from the back by a backlight (not shown), a reflective liquid crystal display element that reflects and displays light from the front, a CRT display, or the like. Further, in the drawing, the photographing optical system 303 is built in the upper right of the monitor 302. However, the imaging optical system 303 is not limited to the place, and may be anywhere around the monitor 302 or the keyboard 301.
[0133]
The photographic optical system 303 includes an objective lens 112 including a zoom lens (abbreviated in the drawing) according to the present invention and an image sensor chip 162 that receives an image on a photographic optical path 304. These are built in the personal computer 300.
[0134]
Here, an optical low-pass filter F is additionally attached on the image sensor chip 162 to be integrally formed as an image pickup unit 160, and can be fitted and attached to the rear end of the lens frame 113 of the objective lens 112 with one touch. Therefore, the center alignment of the objective lens 112 and the image sensor chip 162 and the adjustment of the surface interval are unnecessary, and the assembly is simple. A cover glass 114 for protecting the objective lens 112 is disposed at the tip of the lens frame 113. The zoom lens driving mechanism in the lens frame 113 is not shown.
[0135]
The object image received by the image sensor chip 162 is input to the processing means of the personal computer 300 via the terminal 166 and is displayed on the monitor 302 as an electronic image. FIG. A rendered image 305 is shown. The image 305 can also be displayed on the personal computer of the communication partner from a remote location via the processing means, the Internet, or the telephone.
[0136]
Next, FIG. 20 shows a telephone which is an example of an information processing apparatus in which the zoom lens of the present invention is incorporated as a photographing optical system, particularly a portable telephone which is convenient to carry. 20A is a front view of the mobile phone 400, FIG. 20B is a side view, and FIG. 20C is a cross-sectional view of the photographing optical system 405. As shown in FIGS. 20A to 20C, the mobile phone 400 includes a microphone unit 401 that inputs an operator's voice as information, a speaker unit 402 that outputs a voice of a call partner, and an operator who receives information. An input dial 403 for inputting information, a monitor 404 for displaying information such as a photographed image and a telephone number of the operator and the other party, a photographing optical system 405, an antenna 406 for transmitting and receiving communication radio waves, and an image And processing means (not shown) for processing information, communication information, input signals, and the like. Here, the monitor 404 is a liquid crystal display element. In the drawing, the arrangement positions of the respective components are not particularly limited to these. The photographing optical system 405 includes an objective lens 112 including a zoom lens (abbreviated in the drawing) according to the present invention disposed on a photographing optical path 407, and an image sensor chip 162 that receives an object image. These are built in the mobile phone 400.
[0137]
Here, an optical low-pass filter F is additionally attached on the image sensor chip 162 to be integrally formed as an image pickup unit 160, and can be fitted and attached to the rear end of the lens frame 113 of the objective lens 112 with one touch. Therefore, the center alignment of the objective lens 112 and the image sensor chip 162 and the adjustment of the surface interval are unnecessary, and the assembly is simple. A cover glass 114 for protecting the objective lens 112 is disposed at the tip of the lens frame 113. The zoom lens driving mechanism in the lens frame 113 is not shown.
[0138]
The object image received by the imaging element chip 162 is input to the processing means (not shown) via the terminal 166 and displayed as an electronic image on the monitor 404, the monitor of the communication partner, or both. . Further, when transmitting an image to a communication partner, the processing means includes a signal processing function for converting information of an object image received by the image sensor chip 162 into a signal that can be transmitted.
[0139]
The electronic imaging apparatus of the present invention described above can be configured as follows, for example.
[0140]
[1] In an electronic imaging device comprising an imaging optical system and an electronic imaging device arranged on the image side of the imaging optical system,
The imaging optical system includes a final lens on the most image side that includes an aspheric surface and is always fixed, and a focus lens group that is disposed immediately before the final lens and moves for focusing. An electronic imaging device characterized by the above.
[0141]
[2] The electronic imaging apparatus as described in 1 above, wherein the imaging optical system has a lens unit having a positive refractive power that moves only to the object side when zooming from the wide-angle end to the telephoto end.
[0142]
[3] The imaging optical system includes, in order from the object side, a first lens unit having a negative refractive power, and a second lens having a positive refractive power that moves only to the object side when zooming from the wide-angle end to the telephoto end. 3. The electronic imaging device as described in 1 or 2 above, comprising a group.
[0143]
[4] The imaging optical system includes, in order from the object side, a first lens unit having a negative refractive power, and a plurality of lenses having a positive refractive power that move only to the object side when zooming from the wide-angle end to the telephoto end. 3. The electronic imaging device as described in 1 or 2 above, comprising a group.
[0144]
[5] In an electronic imaging device comprising an imaging optical system and an electronic imaging device arranged on the image side of the imaging optical system,
The imaging optical system includes a first lens group having a negative refractive power arranged on the most object side, and at least three lens groups arranged on the image side,
The mutual distance from the object side to the fourth lens group that follows is changed due to zooming or focusing.
The lens group closest to the image side is composed of a fixed aspherical lens,
An electronic imaging apparatus comprising an aperture stop that moves together with a lens group immediately after the first lens group on the image side during zooming.
[0145]
[6] In an electronic imaging device including a zoom lens and an electronic imaging device disposed on the 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, a third lens group having a positive refractive power, and a fourth lens group. Consists of
It is possible to focus on a closer subject by extending the third lens group toward the object side,
The electronic imaging apparatus, wherein the fourth lens group is composed of one lens that is always fixed including an aspherical surface.
[0146]
[7] In an electronic imaging apparatus comprising a zoom lens and an electronic imaging device disposed on the 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, a third lens group having a positive refractive power, and a fourth lens group. Consists of
It is possible to focus on a closer subject by extending the third lens group toward the object side,
The second lens group includes a single lens including an aspheric surface and a cemented lens including a positive lens and a negative lens in order from the object side.
The electronic lens apparatus according to claim 3, wherein the third lens group includes one positive single lens.
[0147]
[8] In an electronic imaging device comprising a zoom lens and an electronic imaging device disposed on the 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, a third lens group having a positive refractive power, and a fourth lens group. And consist of
It is possible to focus on a closer subject by extending the third lens group toward the object side,
The second lens group includes one positive lens including an aspherical surface and one negative lens.
The electronic lens apparatus according to claim 3, wherein the third lens group includes one positive single lens.
[0148]
[9] The electronic imaging apparatus as described in any one of [1] to [8], wherein the first lens group moves during zooming.
[0149]
[10] The first group having the negative refractive power on the most object side has four or more groups, and the fourth group from the object side changes the mutual distance during zooming. The most image side group is composed of a single aspherical single lens having a fixed and positive refractive power, has an aperture stop that moves together with the second group at the time of zooming, and has the following conditions ( 1. An electronic imaging apparatus comprising a zoom lens and an electronic imaging element satisfying 1).
[0150]
(1) 1.5 <L₂/Y<3.5
However, L₂Is the amount of movement from the wide-angle end to the telephoto end of the second group, and Y is the diagonal length of the effective image pickup area of the image sensor.
[0151]
[11] In order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power. When zooming from the wide-angle end to the telephoto end at the time of focusing on an object point at infinity, the distance between the second group and the third group becomes large, and the third group is extended toward the object side, so that the subject at a shorter distance The fourth group includes a single aspherical single lens having a positive refractive power, and has a zoom lens and an electronic image sensor that satisfy the following condition (2): An electronic imaging apparatus characterized by that.
[0152]
(2) -1.2 <^exP_W/^exP_T<0
However,^exP_W,^exP_TAre respectively the exit pupil positions measured from the image planes at the wide-angle end and the telephoto end when focusing on an object point at infinity.
[0153]
[12] In order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power. When zooming from the wide-angle end to the telephoto end at the time of focusing on an object point at infinity, the distance between the second group and the third group becomes large, and the third group is extended toward the object side, so that the subject at a shorter distance The second group is composed of a single lens including an aspheric surface in order from the object side, and a cemented lens configured in the order of a positive lens and a negative lens from the object side. An electronic image pickup apparatus comprising a zoom lens and an electronic image pickup element that satisfy the following conditions (3) and (4): the third group includes one single lens having positive refractive power.
[0154]

However, R_2C1, R_2C2, R_2C3Is the radius of curvature on the optical axis of each of the first, second and third lens surfaces from the object side of the cemented lens of the second group, t_2NIs the thickness on the optical axis of the negative lens in the cemented lens of the second group, t₂Is the thickness on the optical axis from the most object side surface of the second group to the most image side surface.
[0155]
[13] In order from the object side, the first group having negative refractive power, the second group having positive refractive power, the third group having positive refractive power, and the fourth group having positive refractive power, When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the distance between the second lens group and the third lens group becomes large, and the third lens group is extended to the object side to make it closer to the subject. The second group is composed of one positive lens component and one negative lens component including an aspheric surface in order from the object side, and the third group is a single unit having a positive refractive power. An electronic image pickup apparatus comprising a zoom lens and an electronic image pickup element that are made of a lens and satisfy the following condition (5).
[0156]
(5) 0.05 <t_2NI/ T₂<0.3
Where t_2NIIs the thickness on the optical axis of the most image side negative lens in the second lens unit, t₂Is the thickness on the optical axis from the most object side surface of the second group to the most image side surface.
[0157]
[14] Any one of 10 to 13, wherein the first group includes a negative lens group including two negative lenses and a positive lens group including one positive lens in order from the object side. The electronic imaging device according to 1.
[0158]
[15] The first group includes, in order from the object side, a negative lens group including two or less negative lenses and a positive lens group including one positive lens, and at least one of the negative lens groups. 14. The electronic imaging apparatus according to any one of 10 to 13, wherein the negative lens includes an aspherical surface.
[0159]
[16] The electronic imaging device as described in any one of 9 to 15 above, wherein the total thickness of each of the first group and the second group satisfies the following conditions (6) and (7).
[0160]
(6) 0.6 <t₁/Y<2.2
(7) 0.3 <t₂/Y<1.5
Where t₁Is the thickness on the optical axis from the most object-side surface to the most image-side surface of the first group, and t₂Is the thickness on the optical axis from the most object-side surface to the most image-side surface of the second group, and Y is the diagonal length of the effective imaging region of the image sensor.
[0161]
[17] A near-infrared sharp cut coat having a transmittance at a wavelength of 600 nm of 80% or more and a transmittance at a wavelength of 700 nm of 10% or less closer to the object side than the imaging device behind the zoom lens. 17. The electronic imaging apparatus according to any one of 9 to 16, characterized by comprising:
[0162]
[18] The electronic imaging device as described in 17 above, wherein the imaging device has a complementary color mosaic filter as a colorization filter.
[0163]
[19] The complementary color mosaic filter is composed of at least four types of color filters, and is 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. 19. The electronic imaging apparatus as described in 18 above.
[0164]
[20] The electronic imaging device as described in 18 or 19 above, wherein the complementary color mosaic filter includes at least four types of color filters, and the characteristics of the four types of color filters are as follows.
[0165]
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.
[0166]
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
[21] The green, yellow, and cyan color filters have an intensity of 80% or more at 530 nm with respect to each spectral intensity peak, and the magenta color filter has a wavelength of 530 nm with respect to the spectral intensity peak. 21. The electronic imaging device as described in 20 above, wherein the larger peak has an intensity of 10% to 50%.
[0167]
[22] Total thickness t on the optical axis closer to the object side than the image sensor_LPFThe electronic imaging apparatus according to any one of 10 to 21, wherein an optical low-pass filter satisfying the following condition (8) is disposed:
[0168]
(8) 0.15 × 10^Three<T_LPF/A<0.45×10^Three
Where a is the horizontal pixel pitch of the electronic image sensor.
[0169]
[23] There are a plurality of apertures having a fixed aperture shape, and one of the apertures is an optical path between the most image side surface of the first group and the most object side surface of the third group. 23. The electronic imaging device as described in any one of 10 to 22 above, wherein the image plane illuminance is adjusted by being insertable inside and being interchangeable with other openings.
[0170]
[24] Among the plurality of openings, a part of the openings has a medium having a transmittance of less than 80% for a wavelength of 550 nm, and the transmittance of the other part of the openings for a wavelength of 550 nm is set to 80% or more. 24. The electronic imaging apparatus as described in 23 above.
[0171]
[25] F number obtained from the focal length of the zoom lens and the diameter of the entrance pupil is F_noF where T is the transmittance at a wavelength of 550 nm in the aperture._no/ √T is the effective F number F_no', And when the horizontal pixel pitch of the electronic image sensor is a, F_noIn the case where adjustment is performed so that the light amount corresponds to an effective F number such that> a / 0.4 μm, an opening provided with a medium having a transmittance T of less than 80% for a wavelength of 550 nm is set in the opening. 24. The electronic imaging apparatus as described in 23 above, wherein the electronic imaging apparatus is inserted into an optical path of a zoom lens.
[0172]
[26] The electronic imaging apparatus as described in any one of [23] to [25], wherein an optical low-pass filter having a different spatial frequency characteristic is provided in each of the plurality of openings.
[0173]
  As is clear from the above description, according to the present invention, in order from the object side, the first lens group having negative refractive power and the positive lens that moves only to the object side when zooming from the wide angle end to the telephoto end. In an electronic imaging apparatus having a zoom lens composed of a second lens group having a refractive power, a third lens group having a positive refractive power, and a fourth lens group, the number of constituent lenses of the fourth lens group is small, and the rear focus method Thus, the mechanism layout is small and easy to simplify, and it is possible to achieve both reduction in thickness and correction of various aberrations even if the zoom ratio is ensured.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view at a wide-angle end when focusing on an object point at infinity according to Embodiment 1 of a zoom lens used in an electronic image pickup apparatus of the present invention.
2 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 2. FIG.
3 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 3. FIG.
4 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 4. FIG.
FIG. 5 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Example 5;
6 is a lens cross-sectional view similar to FIG. 1 illustrating a zoom lens according to Embodiment 6. FIG.
FIG. 7 is an aberration diagram for Example 1 upon focusing on an object point at infinity.
FIG. 8 is a diagram showing transmittance characteristics of an example of a near-infrared sharp cut coat.
FIG. 9 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. 10 is a diagram illustrating a color filter arrangement of a complementary color mosaic filter.
FIG. 11 is a diagram illustrating an example of wavelength characteristics of a complementary color mosaic filter.
FIG. 12 is a perspective view showing details of an example of an aperture stop portion of each embodiment.
FIG. 13 is a diagram showing details of another example of the aperture stop portion of each embodiment.
FIG. 14 is a front perspective view showing the appearance of a digital camera incorporating a zoom lens according to the present invention.
15 is a rear perspective view of the digital camera of FIG. 14. FIG.
16 is a cross-sectional view of the digital camera of FIG.
FIG. 17 is a front perspective view in which a cover of a personal computer in which a zoom lens according to the present invention is incorporated as an objective optical system is opened.
FIG. 18 is a cross-sectional view of a photographing optical system of a personal computer.
FIG. 19 is a side view of the state shown in FIG.
FIG. 20 is a front view, a side view, and a sectional view of the photographing optical system of a mobile phone in which the zoom lens according to the present invention is incorporated as an objective optical system.
[Explanation of symbols]
G1 ... 1st group
G2 ... Second group
G3 ... Third group
G4 ... 4th group
F: Optical low-pass filter
C ... Cover glass
I ... Image plane
E ... Observer eyeball
1A, 1B, 1C, 1D, 1E ... Opening
1A ', 1B', 1C ', 1D', 1E '... opening
10 ... Turret
10 '... Turret
11 ... Rotating shaft
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
112 ... Objective lens
113 ... Mirror frame
114 ... cover glass
160: Imaging unit
162. Image sensor chip
166 ... Terminal
300 ... PC
301 ... Keyboard
302 ... Monitor
303 ... Shooting optical system
304: Optical path for photographing
305 ... Image
400 ... mobile phone
401: Microphone unit
402: Speaker unit
403 ... Input dial
404 ... Monitor
405 ... Shooting optical system
406 ... Antenna
407: Photography optical path

Claims (21)

In an electronic imaging device comprising a zoom lens and an electronic imaging device disposed on the image side of the zoom lens,
The zoom lens includes, in order from the object side, a first lens group having negative refractive power, and a second lens group having positive refractive power that moves only to the object side when zooming from the wide-angle end to the telephoto end. A third lens group having a positive refractive power and a fourth lens group having a positive refractive power ,
It is possible to focus on a closer subject by extending the third lens group toward the object side,
The second lens group includes a single lens including an aspheric surface and a cemented lens including a positive lens and a negative lens in order from the object side.
The third lens group includes one positive single lens,
The fourth lens group is composed of one lens that is always fixed including an aspheric surface,
The zoom ratio is 12.88288 / 4.59300 times or more,
An electronic imaging apparatus characterized by satisfying the following conditions (a) and (b) ′.
(A) 0.9 <−β _23t <1.8
(B) '2.0 <f ₂ / f _W ≦ 2.5660
Where β _23t is the combined magnification at the infinite object point at the telephoto end of the second and third lens _units , f ₂ is the focal length of the second lens unit, and f _W is the infinite object point of the entire zoom lens system. This is the wide-angle end focal length at the time of focusing.   2. The electronic imaging apparatus according to claim 1, wherein the second lens group and the third lens group move only to the object side when zooming from the wide-angle end to the telephoto end. The mutual distance from the object side to the fourth lens group that follows is changed due to zooming or focusing.
3. The electronic image pickup apparatus according to claim 1, further comprising an aperture stop that moves together with the second lens group during zooming. Electronic imaging device according to any one of claims 1-3, wherein the first lens group is thus being moved during zooming. The distance from the object side to the fourth lens group changes during zooming, and the fourth lens group is composed of a single aspherical single lens having positive refractive power. It has an aperture stop that moves integrally with the second lens group, and the following conditions (1) according to claim 1, characterized by satisfying the electronic imaging device according to any one of the 4.
(1) 1.5 <L ₂ /Y<3.5
Here, L ₂ is the amount of movement of the second lens group from the wide-angle end to the telephoto end, and Y is the diagonal length of the effective imaging area of the image sensor. When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the distance between the second lens group and the third lens group is increased, and the fourth lens group is a single piece having a positive refractive power. aspheric is constituted by a single lens, the following condition (2) an electronic imaging device according to any one of the preceding claims, characterized by satisfying the 5.
(2) −1.2 < ^ex P _W / ^ex P _T <0
Here, ^ex P _W and ^ex P _T are exit pupil positions measured from the image planes at the wide-angle end and the telephoto end when focusing on an object point at infinity. The fourth lens group has a positive refractive power, and when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the distance between the second lens group and the third lens group is increased, The second lens group includes a single lens including an aspheric surface in order from the object side, and a cemented lens configured in the order of a positive lens and a negative lens from the object side, and the third lens group has a positive refractive power. The electronic imaging apparatus according to any one of claims 1 to 6 , comprising a single lens and satisfying the following condition (3) and condition (4).
(3) −1.5 <(R _2C1 + R _2C2 ) · (R _2C2 −R _2C3 ) /
(R _2C1 −R _2C2 ) · (R _2C2 + R _2C3 ) <− 0.3 (4) 0.05 <t _2N / t ₂ <0.3
Here, R _2C1 , R _2C2 , and R _2C3 are the radii of curvature on the optical axes of the first, second, and third lens surfaces from the object side of the cemented lens of the second lens group, and t _2N is the second lens group. In the cemented lens, the thickness of the negative lens on the optical axis, t ₂ is the thickness of the second lens group on the optical axis from the most object side surface to the most image side surface. The fourth lens group has a positive refractive power, and when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the distance between the second lens group and the third lens group is increased, The second lens group includes one positive lens component including an aspheric surface and one negative lens component in order from the object side, and the third lens group includes one single lens having a positive refractive power. 5) the electronic imaging apparatus of any one of claims 1, wherein 7 to satisfy.
(5) 0.05 <t _2NI / t ₂ <0.3
Where t _2NI is the thickness of the negative lens on the most image side in the second lens group on the optical axis, and t ₂ is on the optical axis from the most object side surface to the most image side surface of the second lens group. Of the thickness. Wherein the first lens group comprises, in order from the object side, either the two negative lens consisting of a negative lens group and a positive lens group composed of one positive lens and more made that claim 5, wherein 8 1 The electronic imaging device according to item. The first lens group includes, in order from the object side, a negative lens group including two or less negative lenses and a positive lens group including one positive lens, and at least one negative lens in the negative lens group. electronic imaging device according to any one of claims 5, wherein 9 comprises a non-spherical surface. The first lens group, the total thickness of the following conditions for each of the second lens group (6), the electronic imaging device of any one of claims 4 to 10, characterized by satisfying the expression (7).
(6) 0.6 <t ₁ /Y<2.2
(7) 0.3 <t ₂ /Y<1.5
Where t ₁ is the thickness on the optical axis from the most object side surface of the first lens group to the most image side surface, and t ₂ is the most image side distance from the most object side surface of the second lens group. It is the thickness on the optical axis to the surface, and Y is the diagonal length of the effective imaging area of the imaging device. A near-infrared sharp cut coat having a transmittance at a wavelength of 600 nm of 80% or more and a transmittance at a wavelength of 700 nm of 10% or less on the object side of the image pickup device behind the zoom lens. electronic imaging device according to any one of claims 4, wherein 11. 13. The electronic image pickup apparatus according to claim 12 , wherein the image pickup element has a complementary color mosaic filter as a colorizing filter. The complementary color mosaic filter is composed of at least four types of color filters, and is arranged in a mosaic so that each of them is approximately the same number and adjacent pixels do not correspond to the same type of color filter. The electronic imaging device according to claim 13 . The complementary mosaic filter is composed of at least four kinds of color filters, the four types of electronic imaging device according to claim 13 or 14, wherein the characteristics of the color filter are as follows.
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,
Cyan Buiruta 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.
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 The green, yellow, and cyan color filters have an intensity of 80% or more at 530 nm with respect to the respective spectral intensity peaks, and the magenta color filter has a larger wavelength of 530 nm with respect to the spectral intensity peaks. 16. The electronic image pickup apparatus according to claim 15, wherein the peak has an intensity of 10% to 50%. Electronic imaging of any one of claims 5 to 16, characterized in that the total thickness t _LPF on the optical axis on the object side of the imaging element is arranged an optical low-pass filter satisfying the following condition (8) apparatus.
(8) 0.15 × 10 ³ <t _LPF /a<0.45×10 ³
Where a is the horizontal pixel pitch of the electronic image sensor. A plurality of apertures having a fixed aperture shape are provided, and one of the apertures is inserted into any optical path between the most image side surface of the first group and the most object side surface of the third group. possible and, and electronic imaging apparatus according to any one of claims 5, characterized in that for regulating the image plane illuminance by the interchangeable with another opening 17. Among the plurality of openings, a part of the openings has a medium having a transmittance of less than 80% for a wavelength of 550 nm, and the transmittance of the other part of the openings for a wavelength of 550 nm is 80% or more. The electronic imaging device according to claim 18 . The F number obtained from the focal length of the zoom lens and the diameter of the entrance pupil is F _no , and F _no / √T when the transmittance at the wavelength of 550 nm in the aperture is T is the effective F number F _no ′. When the horizontal pixel pitch is a, and the adjustment is performed so that the amount of light corresponds to the effective F number such that F _no '> a / 0.4 μm, the transmittance T for the wavelength of 550 nm in the aperture is 19. The electronic imaging apparatus according to claim 18 , wherein an aperture having a medium of less than 80% is inserted into an optical path of the zoom lens. Wherein the plurality of plurality of electronic imaging apparatus according to any one of claims 18, wherein 20 to have different optical low-pass filter spatial frequency characteristic respectively in the opening.

Images