JP4426762B2 - Imaging optical system and imaging apparatus using the same - Google Patents

Description

【０１３５】

【０１３６】

【０１３７】

【０１３８】
上記実施例１〜４の無限遠にフォーカシングした場合の収差図をそれぞれ図５〜図８に示す。これら収差図において、“ＳＡ”は球面収差、“ＡＳ”は非点収差、“ＤＴ”は歪曲収差、“ＣＣ”は倍率色収差を示す。また、各収差図中、“ω”は半画角を示す。
【０１３９】
次に、上記各実施例における条件（１）〜（１３）の値を示す。
【０１４０】
条件式 実施例１ 実施例２ 実施例３ 実施例４
（１） 0.95 0.74 0.71 0.54
（２） 0.024 0.12 0.14 0.24
（３） -0.55 -0.45 -0.42 -0.46
（４） -1.30 -0.43 -3.30 -1.52
（５） -0.38 -0.17 -0.41 -0.41
（６） 0.38 1.06 2.51 2.43
（７） 3.06 4.20 1.45 2.90
（８） 18.9 ° 30.4 ° 15.8 ° 20.4 °
（９） 0.44 0.34 0.41 0.42
（10） 0.60 0.47 0.56 0.58
（11） 1.45 2.57 1.03 1.14
（12） -0.40 -0.33 -0.31 -0.34
（13） 1.05 1.87 0.75 0.83 。
【０１４１】
ここで、本発明において、像面における最大像高Ｉｈは、前記のように、撮像素子の有効撮像領域（略矩形）の対角長Ｌの２分の１で定義される。そして、撮像領域を規定する手段として視野枠を配する場合は、視野枠対角長Ｌの２分の１であり、固体撮像素子等の撮像素子を配する場合は、有効撮像領域の対角長Ｌの２分の１である。
【０１４２】
そこで、撮像記録媒体がＣＣＤ等の電子撮像素子の場合の有効撮像面（有効撮像領域）の対角長Ｌと画素間隔ａについて説明しておく。図９は、撮像素子の画素配列の１例を示す図であり、画素間隔ａでＲ（赤）、Ｇ（緑）、Ｂ（青）の画素がモザイク状に配されている。有効撮像面は撮影した映像の再生（パソコン上での表示、プリンターによる印刷等）に用いる撮像素子上の光電変換面内における領域を意味する。図中に示す有効撮像面は、光学系の性能（光学系の性能が確保し得るイメージサークル）に合わせて、撮像素子の全光電変換面よりも狭い領域に設定されている。有効撮像面の対角長Ｌは、この有効撮像面の対角長である。なお、映像の再生に用いる撮像範囲を種々変更可能としてよいが、そのような機能を有する撮像装置に本発明の結像光学系を用いる際は、その有効撮像面の対角長Ｌが変化する。そのような場合は、本発明において最大像高Ｉｈを定義する有効撮像面の対角長Ｌは、Ｌの取り得る範囲における最大値とする。
【０１４３】
図１０は、ＣＣＤ等の電子撮像素子の撮像面に視野枠を配する場合の視野枠対角長について説明するための図である。ＣＣＤ等の電子撮像素子に像を形成して撮影する場合、その有効撮影領域は撮像面直前の視野枠の開口によって決定される。ここでも、視野枠の形状の変更は種々行う構成としてよいが、図９の場合と同様に、本発明において最大像高Ｉｈを定義する有効撮像面の対角長Ｌは、Ｌのとり得る範囲における最大値とする。
【０１４４】
なお、以上の本発明の実施例において、絞りＳの直前にカバーガラスを配置するようにしてもよい。
【０１４５】
また、本発明の以上の実施例において、プラスチックで構成しているレンズをガラスで構成するようにしてもよい。例えば何れかの実施例のプラスチックより屈折率の高いガラスを用いれば、さらに高性能を達成できるのは言うまでもない。また、特殊低分散ガラスを用いれば、色収差の補正に効果があるのは言うまでもない。特にプラスチックで構成する場合には、低吸湿材料を用いることにより、環境変化による性能劣化が軽減されるので好ましい（例えば、日本ゼオン社のゼオネックス（商品名）等がある）。
【０１４６】
また、ゴースト、フレア等の不要光をカットするために、明るさ絞りＳ以外にフレア絞りＦＳを配置してもよい（図１〜図４にはその配置例を示す。）。フレア絞りＦＳは、上記実施例の明るさ絞りＳから第１レンズＬ１の間、第１レンズＬ１と第２レンズＬ２の間、第２レンズＬ２と第３レンズＬ３の間、第３レンズＬ３から像面Ｉの間の何れの場所に配置してもよい。図１〜図４のようにレンズ枠によりフレア光線をカットするように構成してもよいし、フレア絞りＦＳを別の部材で構成してもよい。また、光学系に直接印刷しても、塗装しても、シール等を接着しても構わない。また、その形状は、円形、楕円形、矩形、多角形、関数曲線で囲まれる範囲等、いかなる形状でも構わない。また、有害光束をカットするだけでなく、画面周辺のコマフレア等の光束をカットするようにしてもよい。
【０１４７】
また、各レンズには、反射防止コートを行い、ゴースト、フレアを軽減しても構わない。マルチコートであれば、効果的にゴースト、フレアを軽減できるので望ましい。また、赤外カットコートをレンズ面、カバーガラス等に行ってもよい。
【０１４８】
また、ピント調節を行うためにフォーカシングを行うようにしてもよい。レンズ系全体を繰り出してフォーカスを行ってもよいし、一部のレンズを繰り出すか、若しくは、繰り込みをしてフォーカスするようにしてもよい。
【０１４９】
また、画像周辺部の明るさ低下をＣＣＤのマイクロレンズをシフトすることにより軽減するようにしてもよい。例えば、各像高における光線の入射角に合わせて、ＣＣＤのマイクロレンズの設計を変えてもよい。また、画像処理により画像周辺部の低下量を補正するようにしてもよい。
【０１５０】
上記各実施例は小型でありながら、図５〜図８の収差図に示すように、良好な画像が得られている。
【０１５１】
ところで、以上の各実施例において、前記のように、カバーガラスＣＧの入射面側に近赤外シャープカットコートを施してもよい。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する。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。
【０１５２】
基 板 材質 物理的膜厚（ｎｍ） λ／４
───────────────────────────────
第１層 Ａｌ₂ Ｏ₃ ５８．９６ ０．５０
第２層 ＴｉＯ₂ ８４．１９ １．００
第３層 ＳｉＯ₂ １３４．１４ １．００
第４層 ＴｉＯ₂ ８４．１９ １．００
第５層 ＳｉＯ₂ １３４．１４ １．００
第６層 ＴｉＯ₂ ８４．１９ １．００
第７層 ＳｉＯ₂ １３４．１４ １．００
第８層 ＴｉＯ₂ ８４．１９ １．００
第９層 ＳｉＯ₂ １３４．１４ １．００
第10層 ＴｉＯ₂ ８４．１９ １．００
第11層 ＳｉＯ₂ １３４．１４ １．００
第12層 ＴｉＯ₂ ８４．１９ １．００
第13層 ＳｉＯ₂ １３４．１４ １．００
第14層 ＴｉＯ₂ ８４．１９ １．００
第15層 ＳｉＯ₂ １７８．４１ １．３３
第16層 ＴｉＯ₂ １０１．０３ １．２１
第17層 ＳｉＯ₂ １６７．６７ １．２５
第18層 ＴｉＯ₂ ９６．８２ １．１５
第19層 ＳｉＯ₂ １４７．５５ １．０５
第20層 ＴｉＯ₂ ８４．１９ １．００
第21層 ＳｉＯ₂ １６０．９７ １．２０
第22層 ＴｉＯ₂ ８４．１９ １．００
第23層 ＳｉＯ₂ １５４．２６ １．１５
第24層 ＴｉＯ₂ ９５．１３ １．１３
第25層 ＳｉＯ₂ １６０．９７ １．２０
第26層 ＴｉＯ₂ ９９．３４ １．１８
第27層 ＳｉＯ₂ ８７．１９ ０．６５
───────────────────────────────
空 気 。
【０１５３】
上記の近赤外シャープカットコートの透過率特性は図１１に示す通りである。
【０１５４】
また、ローパスフィルターの射出面側には、図１２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。
【０１５５】
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。
【０１５６】
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。
【０１５７】
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短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。
【０１５８】
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。
【０１５９】
上記各実施例では、図１２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。
【０１６０】
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。
【０１６１】
また、ローパスフィルターは、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することができ、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、モアレ抑制を行うことができる。ここで、ＳＱＲＴはスクエアルートであり平方根を意味する。
【０１６２】
また、ＣＣＤの撮像面Ｉ上には、図１３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。
【０１６３】
補色モザイクフィルターは、具体的には、図１３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。
【０１６４】
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。
【０１６５】
５１０ｎｍ＜Ｇ_P ＜５４０ｎｍ
５ｎｍ＜Ｙ_P −Ｇ_P ＜３５ｎｍ
−１００ｎｍ＜Ｃ_P −Ｇ_P ＜−５ｎｍ
４３０ｎｍ＜Ｍ_P1＜４８０ｎｍ
５８０ｎｍ＜Ｍ_P2＜６４０ｎｍ
さらに、グリーン、イエロー、シアンの色フィルターはそれぞれの分光強度のピークに対して波長５３０ｎｍでは８０％以上の強度を有し、マゼンダの色フィルターはその分光強度のピークに対して波長５３０ｎｍでは１０％から５０％の強度を有することが、色再現性を高める上でより好ましい。
【０１６６】
上記各実施例におけるそれぞれの波長特性の１例を図１４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。
【０１６７】
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。
【０１６８】
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の枚数も２枚でも１枚でも構わない。
【０１６９】
本発明の撮像装置において、光量調整のために、明るさ絞りＳを複数の絞り羽にて構成し、その開口形状を可変とすることで調整する可変絞りを用いてもよい。図１５は、開口時絞り形状の例を示す説明図、図１６は、２段絞り時の絞り形状の例を示す説明図である。図１５、図１６において、ＯＰは光軸、Ｄａは６枚の絞り板、Ｘａ、Ｘｂは開口部を示している。本発明においては、絞りの開口形状を開放状態（図１５）と、所定の条件を満たすＦ値となる絞り値（２段絞り、図１６）の２種類のみとすることができる。
【０１７０】
又は、形状又は透過率の異なる形状固定の複数の明るさ絞りを設けたターレットを用いて、必要な明るさに応じて、何れかの明るさ絞りを結像光学系の物体側光軸上に配置する構成とすると、絞り機構の薄型化が図れる。また、そのターレット上に配された複数の明るさ絞りの開口の中の最も光量を低減させる開口に、他の明るさ絞りの透過率よりも低い透過率の光量低減フィルターを配する構成としてもよい。それにより、絞りの開口径を絞り込みすぎることがなくなり、絞りの開口径が小さいことにより発生する回折による結像性能の悪化を抑えることができる。
【０１７１】
この場合の１例の構成を示す斜視図を図１７に示す。結像光学系の第１正レンズＬ１の物体側の光軸上の絞りＳの位置に、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。
【０１７２】
ターレット１０には、０段の調整をする開口形状が最大絞り径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。
【０１７３】
そして、ターレット１０に設けた回転軸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。
【０１７４】
また、図１７に示すターレット１０に代えて、図１８の正面図に示すターレット１０’を用いることができる。結像光学系の第１正レンズＬ１の物体側の光軸上の絞りＳの位置に、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。
【０１７５】
ターレット１０’には、０段の調整をする開口形状が最大絞り径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となる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。
【０１７６】
そして、ターレット１０’に設けた回転軸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。
【０１７７】
また、より薄型化のために、明るさ絞りＳの開口を、形状、位置共に固定の絞りとし、光量調整は、撮像素子からの出力信号を電気的に調整するようにしもよい。また、レンズ系の他の空間、例えば第３正レンズＬ３とＣＣＤカバーガラスＣＧの間にＮＤフィルターを抜き差して光量調整を行う構成としてもよい。図１９はその１例を示す図であり、ターレット１０”の開口１Ａ”は素通し面又は中空の開口、開口１Ｂ”は透過率１／２のＮＤフィルター、開口１Ｃ”は透過率１／４のＮＤフィルター、開口１Ｄ”は透過率１／８のＮＤフィルター等を設けたターレット状のものを用い、中心の回転軸の周りの回動により何れかの開口を光路中の何れかの位置に配することで光量調節を行っている。
【０１７８】
また、光量調節のフィルターとして、光量ムラを抑えるように光量調節が可能なフィルター面を設けてもよい。例えば、暗い被写体に対しては中心部の光量確保を優先して透過率を均一とし、明るい被写体に対してのみ明るさムラを補うように、図２０に示すように、同心円状に光量が中心程低下するフィルターを配する構成としてもよい。
【０１７９】
また、絞りＳとしては、第１正レンズＬ１の入射面側の周辺部を黒塗りしたものでもよい。
【０１８０】
また、本発明による撮像装置を、カメラ等のように映像を静止画として保存するものとする場合、光量調整のためのシャッターを光路中に配置するとよい。
【０１８１】
そのようなシャッターとしては、ＣＣＤの直前に配置したフォーカルプレーンシャッターやロータリーシャッター、液晶シャッターでもよいし、開口絞り自体をシャッターとして構成してもよい。
【０１８２】
図２１にシャッターの１例を示す。図２１に示すものは、フォーカルプレーンシャッターの１つであるロータリーフォーカルプレーンシャッターの例であり、図２１（ａ）は裏面側から見た図、図２１（ｂ）は表面側から見た図である。１５はシャッター基板であり、像面の直前又は任意の光路位置に配される構成となっている。基板１５には、光学系の有効光束を透過する開口部１６が設けられている。１７はロータリーシャッター幕である。１８はロータリーシャッター幕１７の回転軸であり、回転軸１８は基板１５に対して回転し、ロータリーシャッター幕１７と一体化されている。回転軸１８は基板１５の表面のギヤ１９、２０と連結されている。このギア１９、２０は図示しないモーターと連結されている。
【０１８３】
このような構成において、図示しないモーターの駆動により、ギア１９、２０、回転軸１８を介して、ロータリーシャッター幕１７が回転軸１８を中心に回転するように構成されている。
【０１８４】
このロータリーシャッター幕１７は略半円型に構成され、回転により基板１５の開口部１６の遮蔽と退避を行い、シャッターの役割を果たしている。シャッタースピードはこのロータリーシャッター幕１７の回転するスピードを変えることで調整される。
【０１８５】
図２２（ａ）〜（ｄ）は、ロータリーシャッター幕１７が回転する様子を像面側からみた図である。時間を追って図の（ａ）、（ｂ）、（ｃ）、（ｄ）、（ａ）の順で移動する。
【０１８６】
以上のように、レンズ系の異なる位置に形状が固定の開口絞りＳと光量調整を行うフィルターあるいはシャッターを配置することにより、回折の影響を抑えて高画質を保ちつつ、フィルターやシャッターにより光量調整が行え、かつ、レンズ系の全長の短縮化も可能とした撮像装置を得ることができる。
【０１８７】
また、機械的なシャッターを用いずに、ＣＣＤの電気信号の一部を取り出して静止画を得るような電気的な制御で行う構成としてもよい。このような構成の１例を、図２３、図２４によりＣＣＤ撮像の動作を説明しながら説明する。図２３は、インターレース式（飛び越し走査式）で信号の順次読み出しを行っているＣＣＤ撮像の動作説明図である。図２３において、Ｐａ〜Ｐｃはフォトダイオードを用いた感光部、Ｖａ〜ＶｃはＣＣＤによる垂直転送部、ＨａはＣＣＤによる水平転送部である。Ａフィールドは奇数フィールド、Ｂフィールドは偶数フィールドを示している。
【０１８８】
図２３の構成では、基本動作が次のように行われる。すなわち、（１）感光部で光による信号電荷の蓄積（光電変換）、（２）感光部から垂直転送部への信号電荷のシフト（フィールドシフト）、（３）垂直転送部での信号電荷の転送（垂直転送）、（４）垂直転送部から水平転送部への信号電荷の転送（ラインシフト）、（５）水平転送部での信号電荷の転送（水平転送）、（６）水平転送部の出力端で信号電荷の検出（検出）。このような順次読み出しは、Ａフィールド（奇数フィールド）とＢフィールド（偶数フィールド）の何れか一方を用いて行うことができる。
【０１８９】
図２３のインターレース式（飛び越し走査式）ＣＣＤ撮像は、ＴＶ放送方式やアナログビデオ方式では、ＡフィールドとＢフィールドの蓄積タイミングが１／６０ずれている。これをそのままＤＳＣ（Ｄｉｊｉｔａｌ Ｓｐｅｃｔｒａｍ Ｃｏｍｐａｔｉｂｌｅ）用画像としてフレーム画を構成すると、動きのある被写体の場合、二重像のようなブレを起こす。そこで、このタイプのＣＣＤ撮像では、Ａ、Ｂフィールドを同時露光して隣接するフィールドの信号を混合する。そして、機械的なシャッターで露光終了時に湛光した後、ＡフィールドとＢフィールドそれぞれ別々に読み出して信号を合成する方法が取られている。
【０１９０】
本発明においては、機械的なシャッターの役割をスミア防止用のみとして、Ａフィールドのみの順次読み出し、あるいは、Ａ、Ｂフィールドを同時混合読み出しとすることにより、垂直解像度は低下するが、機械的なシャッターの駆動スピードに左右されず（電子的なシャッターのみでコントロールできるため）、高速シャッターを切ることができる。図２３の例では、垂直転送部のＣＣＤの数が感光部を構成するフォトダイオードの数の半分であるので、小型化しやすいという利点がある。
【０１９１】
図２４は、信号の順次読み出しをプログレッシブ式で行うＣＣＤ撮像の動作説明図である。図２４において、Ｐｄ〜Ｐｆはフォトダイオードを用いた感光部、Ｖｄ〜ＶｆはＣＣＤによる垂直転送部、ＨｂはＣＣＤによる水平転送部である。
【０１９２】
図２４においては、画素の並び順に読み出すことができるので、電荷蓄積読み出し作業を全て電子的にコントロールすることが可能となる。したがって、露光時間を（１／１００００秒）程度に短くすることができる。図２４の例では、図２３の場合よりも垂直ＣＣＤの数が多く、小型化が困難という不利な点があるが、前記したような利点があるので、本発明においては、図２３、図２４の何れの方式も採用することができる。
【０１９３】
さて、以上のような本発明の撮像装置は、結像光学系で物体像を形成しその像をＣＣＤ等の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。
【０１９４】
図２５〜図２７は、本発明による結像光学系をデジタルカメラの撮影光学系４１に組み込んだ構成の概念図を示す。図２５はデジタルカメラ４０の外観を示す前方斜視図、図２６は同後方斜視図、図２７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の結像光学系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ローパスフィルター作用を持たせたカバーガラスＣＧ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。
【０１９５】
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。
【０１９６】
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が高性能で小型であるので、高性能・小型化が実現できる。
【０１９７】
なお、図２７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。
【０１９８】
次に、本発明の結像光学系が対物光学系として内蔵された情報処理装置の１例であるパソコンが図２８〜図３０に示される。図２８はパソコン３００のカバーを開いた前方斜視図、図２９はパソコン３００の撮影光学系３０３の断面図、図３０は図２８の状態の側面図である。図２８〜図３０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。
【０１９９】
この撮影光学系３０３は、撮影光路３０４上に、本発明による結像光学系（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。
【０２００】
ここで、撮像素子チップ１６２上にはローパスフィルター作用を持たせたカバーガラスＣＧ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。
【０２０１】
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２８には、その１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。
【０２０２】
次に、本発明の結像光学系が撮影光学系として内蔵された情報処理装置の１例である電話、特に持ち運びに便利な携帯電話が図３１に示される。図３１（ａ）は携帯電話４００の正面図、図３１（ｂ）は側面図、図３１（ｃ）は撮影光学系４０５の断面図である。図３１（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結像光学系（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。
【０２０３】
ここで、撮像素子チップ１６２上にはローパスフィルター作用を持たせたカバーガラスＣＧ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。
【０２０４】
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。
【０２０５】
なお、以上の各実施例は、前記の特許請求の範囲の構成に合わせて種々変更することができる。
【０２０６】
【発明の効果】
本発明により、製造誤差に対する性能劣化が少なく、小型化しても高性能な結像光学系とそれを用いた小型で高性能の撮像装置を得ることができる。
【図面の簡単な説明】
【図１】本発明の結像光学系の実施例１の無限遠物点合焦時のレンズ断面図である。
【図２】実施例２の結像光学系の図１と同様のレンズ断面図である。
【図３】実施例３の結像光学系の図１と同様のレンズ断面図である。
【図４】実施例４の結像光学系の図１と同様のレンズ断面図である。
【図５】実施例１の無限遠物点合焦時の収差図である。
【図６】実施例２の無限遠物点合焦時の収差図である。
【図７】実施例３の無限遠物点合焦時の収差図である。
【図８】実施例４の無限遠物点合焦時の収差図である。
【図９】撮像素子にて撮影を行う場合の最大像高Ｉｈを定義する有効撮像面の対角長Ｌについて説明するための図である。
【図１０】撮像素子の撮像面に視野枠を配する場合の最大像高Ｉｈを定義する有効撮像面の対角長Ｌについて説明するための図である。
【図１１】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１２】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１３】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１４】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１５】絞りの開口形状を開放状態としたことを示す図である。
【図１６】絞りの開口形状を２段絞りとした状態を示す図である。
【図１７】形状と透過率の異なる形状固定の複数の明るさ絞りを設けたターレットを配置した本発明の結像光学系の構成を示す斜視図である。
【図１８】図１７に示すターレットに代わる別のターレットを示す正面図である。
【図１９】本発明において利用可能な別のターレット状の光量調整フィルターを示す図である。
【図２０】光量ムラを抑えるフィルターの例を示す図である。
【図２１】ロータリーフォーカルプレーンシャッターの例を示す裏面図と表面図である。
【図２２】図２１のシャッターのロータリーシャッター幕が回転する様子を示す図である。
【図２３】インターレース式ＣＣＤ撮像の動作説明図である。
【図２４】プログレッシブ式ＣＣＤ撮像の動作説明図である
【図２５】本発明による結像光学系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２６】図２５のデジタルカメラの後方斜視図である。
【図２７】図２５のデジタルカメラの断面図である。
【図２８】本発明による結像光学系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２９】パソコンの撮影光学系の断面図である。
【図３０】図２８の状態の側面図である。
【図３１】本発明による結像光学系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】
Ｓ …明るさ絞り
Ｌ１…第１正レンズ
Ｌ２…第２負レンズ
Ｌ３…第３正レンズ
ＣＧ…カバーガラス
Ｉ …像面
ＦＳ…フレア絞り
ＯＰ…光軸
Ｄａ…絞り板
Ｘａ、Ｘｂ…開口部
Ｐａ〜Ｐｆ…感光部
Ｖａ〜Ｖｆ…垂直転送部
Ｈａ、Ｈｂ…水平転送部
Ｅ …観察者眼球
１Ａ、１Ｂ、１Ｃ、１Ｄ、１Ｅ…開口
１Ａ’、１Ｂ’、１Ｃ’、１Ｄ’、１Ｅ’…開口
１Ａ”、１Ｂ”、１Ｃ”、１Ｄ”…開口
１０…ターレット
１０’…ターレット
１０”…ターレット
１１…回転軸
１５…シャッター基板
１６…開口部
１７…ロータリーシャッター幕
１８…回転軸
１９、２０…ギヤ
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 imaging optical system and an imaging apparatus using the imaging optical system, and is particularly mounted in a digital still camera, a digital video camera, a cellular phone, or a personal computer using a solid-state imaging device such as a CCD or a CMOS. The present invention relates to an imaging apparatus such as a small camera or a surveillance camera.
[0002]
[Prior art]
2. Description of the Related Art In recent years, electronic cameras that take a subject using a solid-state imaging device such as a CCD or a CMOS instead of a silver salt film have become widespread. Among such electronic cameras, an imaging device mounted on a portable computer, a cellular phone, or the like is particularly required to be small and light.
[0003]
As an image forming optical system used in such an image pickup apparatus, there is a conventional one having two or more lenses. However, as is apparent from the aberration theory, it is already known that field curvature cannot be corrected and high performance cannot be expected. Therefore, in order to satisfy high performance, it is necessary to configure with three or more lenses.
[0004]
On the other hand, in the case of a CCD, if the off-axis light beam emitted from the imaging lens system is incident at an excessively large angle with respect to the image plane, the condensing performance of the microlens is not fully exhibited, and the brightness of the image is at the center of the image. This causes the problem of extreme changes between the image and the image periphery. Therefore, the light incident angle to the CCD, that is, the exit pupil position is important in design. In the case of an optical system with a small number of sheets, the position of the aperture stop is important.
[0005]
Considering these problems, there is a triplet type with a front aperture. Such imaging lenses are disclosed in Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, Patent Literature 5, Patent Literature 6, and the like.
[0006]
[Patent Document 1]
JP-A-1-144007
[0007]
[Patent Document 2]
JP-A-2-191907
[0008]
[Patent Document 3]
JP-A-4-153612
[0009]
[Patent Document 4]
Japanese Patent Laid-Open No. 5-188284
[0010]
[Patent Document 5]
Japanese Patent Laid-Open No. 9-288235
[0011]
[Patent Document 6]
JP 2001-750006 A
[0012]
[Problems to be solved by the invention]
However, these prior examples have various problems as shown below.
[0013]
In Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5, since the first positive lens has a biconvex shape, it is difficult to correct coma and astigmatism of off-axis rays. It was. Therefore, in all cases, the half angle of view was about 25 °. Further, unless the glass having a high refractive index is used therefor, the optical performance cannot be sufficiently satisfied, so that it is difficult to achieve cost reduction and weight reduction.
[0014]
In Patent Document 6, the first positive lens is formed in a meniscus shape that is convex on the image side to reduce the above-described influence. However, the total length is large and it cannot be said that miniaturization has been achieved.
[0015]
The present invention has been made in view of such problems of the prior art, and an object thereof is to provide an imaging optical system that satisfies both high performance and miniaturization and an imaging apparatus using the same. .
[0016]
[Means for Solving the Problems]
The imaging optical system of the present invention that achieves the above object includes, in order from the object side, an aperture stop, a first positive meniscus lens having a convex surface facing the image side, a biconcave second negative lens, and a third positive lens. It is characterized by comprising three lenses.
[0017]
The imaging apparatus of the present invention includes, in order from the object side, an aperture stop, a first positive meniscus lens having a convex surface facing the image side, a biconcave second negative lens, and a third positive lens. The image forming optical system is provided.
[0018]
In this case, it is desirable to include an image sensor disposed on the image side of the three lenses.
[0019]
Further, it is desirable that each of the three lenses is a single lens, and two air lenses formed by the three lenses are sandwiched between two refracting surfaces having different shapes. In that case, it is desirable that the two air lenses are configured to be sandwiched between two aspherical surfaces having different shapes.
[0020]
Another imaging device according to the present invention includes, in order from the object side, a first aperture of an aperture stop and a positive single lens whose absolute value of the curvature radius on the optical axis on the image side is smaller than the absolute value of the curvature radius on the optical axis on the object side A positive lens, a second negative lens of a negative single lens whose absolute value of the curvature radius on the optical axis on the image side is smaller than an absolute value of the curvature radius on the optical axis of the object side, and a third positive lens of the positive single lens It has an imaging optical system composed of three single lenses and an image sensor arranged on the image side, and satisfies the following conditions.
[0021]
0.30 <f₁/Ih<0.90 (10)
−0.75 <f₂/Ih<−0.1 (3)
0.70 <f_Three/Ih<2.00 (11)
Where f₁Is the focal length of the first positive lens, f₂Is the focal length of the second negative lens, f_ThreeIs the focal length of the third positive lens, and Ih is the maximum image height.
[0022]
Still another imaging apparatus according to the present invention includes, in order from the object side, an aperture stop and a positive single lens whose absolute value of the curvature radius on the optical axis on the image side is smaller than the absolute value of the curvature radius on the optical axis on the object side. A first positive lens, a second negative lens of a negative single lens whose absolute value of the curvature radius on the optical axis on the image side is smaller than the absolute value of the curvature radius on the optical axis of the object side, and a third positive lens of the positive single lens The image forming optical system composed of the three single lenses and an image pickup device disposed on the image side satisfy the following conditions.
[0023]
0.1 <f₁/F<0.46 (9-3)
−0.75 <f₂/F<−0.29 (12)
0.40 <f_Three/F<0.85 (13)
Where f₁Is the focal length of the first positive lens, f₂Is the focal length of the second negative lens, f_ThreeIs the focal length of the third positive lens, and f is the focal length of the entire system.
[0024]
In the above, it is desirable to satisfy the following conditional expression.
[0025]
−0.5 <(r_2f+ R_2r) / (R_2f-R_2r) <0.98 (1)
Where r_2fIs the radius of curvature on the optical axis of the object side surface of the second negative lens, r_2rIs the radius of curvature on the optical axis of the image side surface of the second negative lens.
[0026]
Moreover, it is desirable to satisfy the following conditional expression.
[0027]
0.01 <r_1r/ R_2f<0.75 (2)
Where r_1rIs the radius of curvature on the optical axis of the image side surface of the first positive lens, r_2fIs the radius of curvature on the optical axis of the object side surface of the second negative lens.
[0028]
Moreover, it is desirable to satisfy the following conditional expression.
[0029]
−0.75 <f₂/Ih<−0.1 (3)
Where f₂Is the focal length of the second negative lens, and Ih is the maximum image height.
[0030]
Moreover, it is desirable to satisfy the following conditional expression.
[0031]
−5.0 <f_2-3/F<−0.1 (4)
Where f_2-3Is the combined focal length of the second negative lens and the third positive lens, and f is the focal length of the entire system.
[0032]
Moreover, it is desirable to satisfy the following conditional expression.
[0033]
−0.8 <f₂/ F_Three<-0.1 (5)
Where f₂Is the focal length of the second negative lens, f_ThreeIs the focal length of the third positive lens.
[0034]
Further, it is desirable that the object-side surface of the second negative lens is an aspheric surface and satisfies the following conditional expression.
[0035]
0.01 <| (r_2fs+ R_2fa) / (R_2fs-R_2fa) -1 | <100 (6)
Where r_2fsIs the radius of curvature on the optical axis on the object side of the second negative lens, r_2faIs the value when the radius of curvature considering the aspherical surface of the object side surface of the second negative lens changes most within the optical effective range.
[0036]
Further, it is desirable that the image-side surface of the second negative lens is an aspherical surface and satisfies the following conditional expression.
[0037]
0.01 <| (r_2rs+ R_2ra) / (R_2rs-R_2ra) -1 | <100 (7)
Where r_2rsIs the radius of curvature on the optical axis on the image side of the second negative lens, r_2raIs the value when the radius of curvature considering the aspherical surface of the image side surface of the second negative lens changes most within the effective optical range.
[0038]
Moreover, it is desirable to satisfy the following conditional expression.
[0039]
10 ° <α <40 ° (8)
Where α is the incident angle of the chief ray on the image plane at the maximum image height.
[0040]
Moreover, it is desirable to satisfy the following conditional expression.
[0041]
0.1 <f₁/F<1.2 (9)
Where f₁Is the focal length of the first positive lens, and f is the focal length of the entire system.
[0042]
Hereinafter, the reason and effect | action which took the above structures in this invention are demonstrated.
[0043]
First, the number of lenses will be described. In the present invention, as a result of considering performance and miniaturization, the number of lenses is three. It is clear that the performance will be further improved if the number of lenses is increased to 4 or more. However, as the number of lenses increases, the thickness of the lens, the distance between the lenses, and the space of the frame will increase accordingly. Is inevitable. In addition, as described in the section of the prior art, the field curvature is not reduced when the number is two or less, and the peripheral performance is considerably deteriorated. Three sheets are optimal for both performance and size.
[0044]
Next, in order to reduce the light incident angle to the image pickup device such as a CCD, the aperture stop was disposed closest to the object side. The power of the lens may be configured so that the exit pupil position is far from the object side. However, since the number is small, it is most effective to arrange the position of the aperture stop on the object side.
[0045]
Here, when the aperture stop is disposed closest to the object side, since there is only one lens with respect to the stop, it is difficult to correct distortion and lateral chromatic aberration, which are peripheral performances, in the optical design. For this reason, by arranging a positive lens, a negative lens, and a positive lens in this order from the object side, powers having different signs are arranged and corrected by the second and third lenses having a higher light beam height. The central performance is achieved by correcting the spherical aberration and axial chromatic aberration that occur in the first positive lens with the second negative lens, thereby improving the overall performance of the screen.
[0046]
The first positive lens has a meniscus shape that is convex on the image side, as described in the section of the problem to be solved by the invention. As a result, off-axis aberrations can be corrected well, and high performance can be achieved.
[0047]
At this time, if the second negative lens is formed in a meniscus shape, a problem in optical performance occurs. First, in general, when a lens is formed in a meniscus shape, even one of the negative lenses has a positive power convergence effect. Therefore, when the power of this lens is increased, the curvature of the negative power surface, which is the other surface, becomes too strong. As a result, higher-order aberrations are generated and the performance tends to deteriorate. In addition, since aberrations are canceled out on both sides, there is also a problem that performance degradation is increased due to manufacturing errors due to relative decentering of each side. This is a factor that hinders downsizing because the effect becomes more prominent when the lens power is increased by shortening the overall length or the like.
[0048]
For miniaturization, it is better to move the principal point to the object side with respect to the focal length of the entire system as in the telephoto type, but when the second negative lens has a meniscus shape convex to the object side, The principal point is moved to the image side together with the first positive meniscus lens, which is disadvantageous for downsizing. Further, for correcting aberrations such as spherical aberration, it is effective to reduce the principal ray height between the first positive lens and the second negative lens so that the marginal ray height does not change significantly. The lens must move the principal point to the image side more, and the curvature on both sides, particularly the curvature on the exit side, becomes tight, making it difficult to balance performance.
[0049]
Therefore, in the present invention, the second negative lens is constituted by a biconcave. Thereby, even if the entire length is shortened, the occurrence of high-order aberrations is reduced, so that the performance is hardly deteriorated. Also, unlike the meniscus shape, the negative power is divided on each surface, so that the performance deterioration due to the relative eccentricity of each surface of the second negative lens is reduced. That is, even if the overall length is shortened, high performance can be achieved.
[0050]
Further, if each lens is a single lens, and both sides of the two air lenses sandwiched between the lenses are refracting surfaces having different shapes, it is easy to balance aberration correction of both on-axis aberration and off-axis aberration. In particular, when two air lenses formed by three lenses are sandwiched between two aspheric surfaces having different shapes, aberration correction can be performed more satisfactorily.
[0051]
In the above, it is desirable that the following conditional expression is satisfied.
[0052]
−0.5 <(r_2f+ R_2r) / (R_2f-R_2r) <0.98 (1)
Where r_2fIs the radius of curvature on the optical axis of the object side surface of the second negative lens, r_2rIs the radius of curvature on the optical axis of the image side surface of the second negative lens.
[0053]
If the upper limit of 0.98 in the conditional expression (1) is exceeded, the negative power on the object side becomes too weak and the aberration due to the first positive lens cannot be corrected satisfactorily. The power of the image side surface where the height of the light beam becomes high becomes too weak, and the lateral chromatic aberration is deteriorated.
[0054]
Preferably, the following conditional expression is satisfied.
[0055]
0 <(r_2f+ R_2r) / (R_2f-R_2r) <0.95 (1-1)
More preferably, the following conditional expression is satisfied.
[0056]
0.3 <(r_2f+ R_2r) / (R_2f-R_2r<0.8 (1-2)
Further, since the image-side surface of the first positive lens has a strong positive power, it is desirable to effectively correct the residual aberration on the object-side surface of the second negative lens, which is the next surface. At this time, the following conditional expression should be satisfied.
[0057]
0.01 <r_1r/ R_2f<0.75 (2)
Where r_1rIs the radius of curvature on the optical axis of the image side surface of the first positive lens, r_2fIs the radius of curvature on the optical axis of the object side surface of the second negative lens.
[0058]
If the upper limit of 0.75 of the conditional expression (2) is exceeded, the negative power of the object side surface of the second negative lens becomes too strong, resulting in overcorrection. The power becomes too weak and the correction becomes insufficient, and the performance deteriorates.
[0059]
Preferably, the following conditional expression is satisfied.
[0060]
0.05 <r_1r/ R_2f<0.6 (2-1)
More preferably, the following conditional expression is satisfied.
[0061]
0.1 <r_1r/ R_2f<0.4 (2-2)
In addition, since the second negative lens is disposed between the first positive lens and the third positive lens, the aberration generation of both positive lenses cannot be corrected effectively unless this power is set appropriately. End up. Therefore, the following conditional expression should be satisfied.
[0062]
−0.75 <f₂/Ih<−0.1 (3)
Where f₂Is the focal length of the second negative lens, and Ih is the maximum image height.
[0063]
If the upper limit of -0.1 in this conditional expression (3) is exceeded, the power of the second negative lens becomes too strong and overcorrected. If the lower limit of -0.75 is exceeded, the power becomes too weak. , The correction becomes insufficient, and the performance deteriorates.
[0064]
Here, the maximum image height Ih of the imaging device is half of the diagonal length of the field frame when a field frame that restricts the imaging region is arranged on the image plane side of the imaging optical system. When an element is arranged, it is half the diagonal length of the effective imaging area.
[0065]
Preferably, the following conditional expression is satisfied.
[0066]
−0.6 <f₂/Ih<−0.25 (3−1)
Further, since the second negative lens has a diverging action, it works in a disadvantageous direction with respect to the incident angle to the image plane. Therefore, the configuration of the next third positive lens is important. Therefore, the following conditional expression should be satisfied.
[0067]
−5.0 <f_2-3/F<−0.1 (4)
Where f_2-3Is the combined focal length of the second negative lens and the third positive lens, and f is the focal length of the entire system.
[0068]
If the upper limit of -0.1 in conditional expression (4) is exceeded, the negative power becomes too strong and the incident angle on the image surface becomes too tight. If the lower limit of -5.0 is exceeded, the negative power becomes weak. Too much will increase the overall length.
[0069]
Preferably, the following conditional expression is satisfied.
[0070]
−2.0 <f_2-3/F<−0.3 (4-1)
Further, since the second and third lenses are arranged far from the aperture stop and the off-axis ray height becomes high, the occurrence of lateral chromatic aberration and distortion tends to increase. Therefore, the following conditional expression should be satisfied.
[0071]
−0.8 <f₂/ F_Three<-0.1 (5)
Where f₂Is the focal length of the second negative lens, f_ThreeIs the focal length of the third positive lens.
[0072]
If both the upper limit −0.1 and the lower limit −0.8 of the conditional expression (5) are exceeded, the lateral chromatic aberration and distortion will be overcorrected or undercorrected, and the peripheral performance will deteriorate.
[0073]
Preferably, the following conditional expression is satisfied.
[0074]
−0.5 <f₂/ F_Three<-0.2 (5-1)
If the object-side surface of the second negative lens is an aspherical surface, it is possible to correct aberrations satisfactorily, and it is desirable that the following conditional expression is satisfied.
[0075]
0.01 <| (r_2fs+ R_2fa) / (R_2fs-R_2fa) -1 | <100 (6)
Where r_2fsIs the radius of curvature on the optical axis on the object side of the second negative lens, r_2faIs the value when the radius of curvature considering the aspherical surface of the object side surface of the second negative lens changes most within the optical effective range.
[0076]
Here, the radius of curvature r considering the aspherical surface_ASPIs defined by the following equation, where f (y) is the aspherical definition equation. same as below.
[0077]
r_ASP= Y · (1 + f ′ (y)²)^1/2/ F ’(y)
Here, y is the height from the optical axis, and f ′ (y) is the first derivative of f (y).
[0078]
If the upper limit of 100 of the conditional expression (6) is exceeded, the aspherical effect becomes too weak and the correction becomes insufficient, coma aberration and astigmatism deteriorate, and if the lower limit of 0.01 is exceeded, The aspherical effect becomes too strong and overcorrected, resulting in degraded performance and difficult lens processing.
[0079]
Preferably, the following conditional expression is satisfied.
[0080]
0.05 <| (r_2fs+ R_2fa) / (R_2fs-R_2fa) -1 | <5.0 (6-1)
More preferably, the following conditional expression is satisfied.
[0081]
0.1 <| (r_2fs+ R_2fa) / (R_2fs-R_2fa) -1 | <3.0 (6-2)
In addition, when the image-side surface of the second negative lens is formed of an aspherical surface, it is possible to satisfactorily correct aberrations, and it is desirable that the following conditional expression is satisfied.
[0082]
0.01 <| (r_2rs+ R_2ra) / (R_2rs-R_2ra) -1 | <100 (7)
Where r_2rsIs the radius of curvature on the optical axis on the image side of the second negative lens, r_2raIs the value when the radius of curvature considering the aspherical surface of the image side surface of the second negative lens changes most within the effective optical range.
[0083]
If the upper limit of 100 of the conditional expression (7) is exceeded, the aspherical effect becomes too weak and the correction becomes insufficient, coma aberration and astigmatism deteriorate, and if the lower limit of 0.01 is exceeded, The aspherical effect becomes too strong and overcorrected, resulting in degraded performance and difficult lens processing.
[0084]
Preferably, the following conditional expression is satisfied.
[0085]
0.05 <| (r_2rs+ R_2ra) / (R_2rs-R_2ra) -1 | <10.0
... (7-1)
More preferably, the following conditional expression is satisfied.
[0086]
0.1 <| (r_2rs+ R_2ra) / (R_2rs-R_2ra) -1 | <5.0
... (7-2)
In addition, when a CCD is used as the image sensor, if the off-axis light beam emitted from the imaging optical system is incident at an excessively large angle with respect to the image plane, the brightness of the image changes at the image center and the image periphery. End up. On the other hand, if the light is incident on the image plane at a small angle, this problem is reduced, but the total length of the optical system is increased. Therefore, the following conditional expression should be satisfied.
[0087]
10 ° <α <40 ° (8)
Where α is the incident angle of the chief ray on the image plane at the maximum image height.
[0088]
If the upper limit of 40 ° in the conditional expression (8) is exceeded, the incident angle to the CCD becomes too large and the brightness of the peripheral portion of the image decreases. If the lower limit of 10 ° is exceeded, the total length becomes too large. End up.
[0089]
Preferably, the following conditional expression is satisfied.
[0090]
15 ° <α <35 ° (8-1)
More preferably, the following conditional expression is satisfied.
[0091]
17.5 ° <α <25 ° (8-2)
Further, since the first positive lens is closest to the aperture stop, all light rays from the center of the screen to the periphery gather and pass through substantially the same point. Therefore, unless the first positive lens is set appropriately, the performance of the entire screen is involved. Therefore, the following conditional expression should be satisfied.
[0092]
0.1 <f₁/F<1.2 (9)
Where f₁Is the focal length of the first positive lens, and f is the focal length of the entire system.
[0093]
If the upper limit of 1.2 in the conditional expression (9) is exceeded, the power of the positive lens becomes too weak and the total length becomes large. If the lower limit of 0.1 is exceeded, the power of the positive lens becomes too strong. As a result, spherical aberration, coma aberration, etc. occur, and the performance of the entire screen deteriorates.
[0094]
Preferably, the following conditional expression is satisfied.
[0095]
0.2 <f₁/F<0.7 (9-1)
More preferably, the following conditional expression is satisfied.
[0096]
0.25 <f₁/F<0.5 (9-2)
In another imaging apparatus of the present invention, the imaging optical system is configured with three single lenses in the order of positive, negative, and positive in the configuration of the front diaphragm, and the focal length of the first positive lens is reduced. By making the lens have a main positive refracting power, the overall length can be shortened by using a telephoto type of positive and negative order as a whole and moving the principal point closer to the object.
[0097]
At this time, by increasing the curvature radius of the image side surface of the first positive lens, the refraction angle of the off-axis light beam incident from the aperture stop is moderated while maintaining the appropriate refractive power of the first positive lens, and the off-axis is maintained. Aberration correction can be performed.
[0098]
In addition, the third positive lens has a function of bringing the light beam incident on the image sensor closer to the vertical direction, but the second and third lenses can have a strong refractive power on the image side surface of the second negative lens. The lens jointly suppresses the occurrence of lateral chromatic aberration and off-axis aberration.
[0099]
In this configuration, it is desirable that the following conditional expression is satisfied.
[0100]
0.30 <f₁/Ih<0.90 (10)
−0.75 <f₂/Ih<−0.1 (3)
0.70 <f_Three/Ih<2.00 (11)
Where f₁Is the focal length of the first positive lens, f₂Is the focal length of the second negative lens, f_ThreeIs the focal length of the third positive lens, and Ih is the maximum image height.
[0101]
Alternatively, it is desirable that the following conditional expression is satisfied.
[0102]
0.1 <f₁/F<0.46 (9-3)
−0.75 <f₂/F<−0.29 (12)
0.40 <f_Three/F<0.85 (13)
Where f₁Is the focal length of the first positive lens, f₂Is the focal length of the second negative lens, f_ThreeIs the focal length of the third positive lens, and f is the focal length of the entire system.
[0103]
Conditional expressions (10), (3), and (11) define the focal length of each lens with the maximum image height Ih.
[0104]
Conditional expression (10) is set so that the total length can be shortened while keeping the refractive power of the first positive lens, which bears the main refractive power, in balance with the aberration, based on the size of the image plane. Expressions (3) and (11) determine the refractive powers of the second negative lens and the third positive lens for performing aberration correction on the basis of the maximum image height as in the conditional expression (10). It is a condition.
[0105]
Satisfying these conditional expressions at the same time balances shortening of the overall length, widening of the angle of view, and aberration correction.
[0106]
In conditional expression (10), if the lower limit value of 0.30 is exceeded, it will be difficult to correct aberrations that occur in the first positive lens. On the other hand, if the upper limit value of 0.90 is exceeded, the entire lens will be telephoto type. The effect of shortening the overall length is reduced.
[0107]
Further, if the lower limit value of conditional expression (10) is 0.35 or 0.40, it is preferable for aberration correction, and if the upper limit value is 0.75 or 0.70, the overall length can be shortened. Therefore, it is more preferable.
[0108]
In conditional expression (3), if the upper and lower limits of −0.75 and −0.1 are exceeded, aberration correction becomes difficult.
[0109]
In conditional expression (11), if the lower limit of 0.70 is exceeded, the refractive power of the third positive lens becomes strong, and the thickness on the optical axis of the third positive lens becomes large, making it difficult to reduce the thickness. On the other hand, aberration correction becomes difficult. On the other hand, when the upper limit of 2.00 is exceeded, the effect of bringing the most off-axis light beam perpendicular to the image plane becomes weak.
[0110]
In conditional expression (11), if the lower limit value is further set to 0.80 or 0.90, aberration correction is easy, and if the upper limit value is set to 1.80 or 1.60, the off-axis principal ray is It can be close to vertical, which is preferable.
[0111]
Conditional expressions (9-3), (12), and (13) define the focal length of each lens by the focal length of the entire system.
[0112]
Conditional expression (9-3) means that the main refractive power of the imaging optical system is borne by the first positive lens, and conditional expressions (12) and (13) are for correcting aberrations on the first positive lens. This is a condition that determines the refractive power of the second negative lens and the third positive lens.
[0113]
Satisfying these conditional expressions at the same time balances shortening of the overall length, widening of the angle of view, and aberration correction.
[0114]
In conditional expression (9-3), if the lower limit of 0.1 is exceeded, it will be difficult to correct aberrations occurring in the first positive lens. On the other hand, if the upper limit of 0.46 is exceeded, the whole will be telephoto type. Thus, the effect of shortening the overall length is reduced.
[0115]
Further, when the lower limit value of conditional expression (9-3) is 0.2 or 0.25, it is preferable for aberration correction, and when the upper limit value is 0.44 or 0.43, the total length is shortened. It is more preferable because of
[0116]
In conditional expression (12), if the upper and lower limits of −0.75 and −0.29 are exceeded, aberration correction becomes difficult.
[0117]
In conditional expression (12), if the lower limit value is further set to -0.6 or -0.37, or the upper limit value is set to -0.3 or -0.31, it becomes easier to correct aberrations.
[0118]
In conditional expression (13), if the lower limit of 0.40 is exceeded, the refractive power of the third positive lens will increase, and the thickness on the optical axis of the third positive lens will increase, making it difficult to reduce the thickness. On the other hand, when the upper limit of 0.85 is exceeded, the action of bringing the most off-axis light beam perpendicular to the image plane becomes weak.
[0119]
In conditional expression (13), if the lower limit value is further set to 0.60 or 0.70, aberration correction is easy to perform, and if the upper limit value is set to 0.84 or 0.83, the off-axis principal ray. Can be brought close to vertical.
[0120]
These conditional expressions (10), (3), (11), and (9-3), (12), (13) may be satisfied simultaneously. Moreover, you may make it satisfy | fill simultaneously the above-mentioned conditional expression (1)-(9-2) of one or several conditional expressions.
[0121]
In addition, in common with each of the above conditional expressions, only the upper limit value of the lower conditional expression that limits each conditional expression range or only the lower limit value is limited as the upper limit value or lower limit value of the higher conditional expression. It may be.
[0122]
Moreover, the effect of this invention can be heightened more by combining the above conditional expressions arbitrarily.
[0123]
DETAILED DESCRIPTION OF THE INVENTION
Examples 1 to 4 of the imaging optical system of the present invention will be described below. FIGS. 1 to 4 show lens cross-sectional views of Examples 1 to 4 when focusing on an object point at infinity, respectively. In the drawing, the aperture stop is indicated by S, the first positive lens is indicated by L1, the second negative lens is indicated by L2, the third positive lens is indicated by L3, the cover glass of the electronic image sensor is indicated by CG, and the image plane is indicated by I. In addition, you may give the multilayer film for wavelength range limitation to the surface of the cover glass CG. Further, the cover glass CG may have a low-pass filter function.
[0124]
As shown in FIG. 1, the imaging optical system of Example 1 includes, in order from the object side, an aperture stop S, a double-sided aspherical first positive meniscus lens L1 having a convex surface facing the image side, and a double-concave double-sided surface. It includes a spherical second negative lens L2, a biconvex double-sided aspherical third positive lens L3, and a cover glass CG. In this embodiment, the first lens L1 to the third lens L3 are all made of plastic, the first lens L1 and the third lens L3 are made of amorphous polyolefin ZEONEX (trade name), and the second lens L2 is made of polycarbonate. Yes.
[0125]
The specification of this example is a wide-angle optical system with a focal length f = 3.3 mm, an image height Ih = 2.4 mm, and a half angle of view ω = 36 °. In addition, each optical effective diameter (one side) of each lens is the second surface r.₂~ Seventh surface r₇In this order, they are 0.664 mm, 0.962 mm, 1.144 mm, 1.247 mm, 1.526 mm, and 1.815 mm.
[0126]
As shown in FIG. 2, the imaging optical system of Example 2 includes, in order from the object side, an aperture stop S, a double-sided aspherical first positive meniscus lens L1 with a convex surface facing the image side, and a biconcave double-sided non-side surface. The lens includes a spherical second negative lens L2, a double-sided aspherical third positive meniscus lens L3 having a convex surface facing the object side, and a cover glass CG. In the present embodiment, the first lens L1 to the second lens L2 are made of glass, the third lens L3 is made of plastic, and the third lens L3 is made of amorphous polyolefin ZEONEX (trade name).
[0127]
The specification of this example is a wide-angle optical system with a focal length f = 3.3 mm, an image height Ih = 2.4 mm, and a half angle of view ω = 36 °. In addition, each optical effective diameter (one side) of each lens is the second surface r.₂~ Seventh surface r₇In order of 0.667 mm, 1.043 mm, 1.088 mm, 1.062 mm, 1.195 mm, and 1.641 mm.
[0128]
As shown in FIG. 3, the imaging optical system of Example 3 includes, in order from the object side, the aperture stop S, the first aspherical positive meniscus lens L1 with the convex surface facing the image side, and the double-sided double-sided non-side surface. It includes a spherical second negative lens L2, a biconvex double-sided aspherical third positive lens L3, and a cover glass CG. In the present embodiment, the first lens L1 and the third lens L3 are made of plastic, the second lens L2 is made of glass, and the first lens L1 and the third lens L3 are made of amorphous polyolefin ZEONEX (trade name). .
[0129]
The specification of this example is a wide-angle optical system with a focal length f = 3.3 mm, an image height Ih = 2.4 mm, and a half angle of view ω = 36 °. In addition, each optical effective diameter (one side) of each lens is the second surface r.₂~ Seventh surface r₇In this order, they are 0.670 mm, 1.163 mm, 1.309 mm, 1.641 mm, 1.624 mm, and 1.791 mm.
[0130]
As shown in FIG. 4, the imaging optical system of Example 4 includes, in order from the object side, an aperture stop S, a first aspherical first positive meniscus lens L1 having a convex surface facing the image side, and a double-concave double-sided non-surface. It includes a spherical second negative lens L2, a biconvex double-sided aspherical third positive lens L3, and a cover glass CG. In this embodiment, the first lens L1 to the third lens L3 are all made of plastic, the first lens L1 and the third lens L3 are made of amorphous polyolefin ZEONEX (trade name), and the second lens L2 is made of polycarbonate. Yes.
[0131]
The specification of this example is a wide-angle optical system with a focal length f = 3.3 mm, an image height Ih = 2.4 mm, and a half angle of view ω = 36 °. In addition, each optical effective diameter (one side) of each lens is the second surface r.₂~ Seventh surface r₇In this order, they are 0.652 mm, 0.962 mm, 1.097 mm, 1.291 mm, 1.397 mm, and 1.682 mm.
[0132]
The numerical data of each of the above examples is shown below, but the symbols are the above, 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.
[0133]
x = (y²/ R) / [1+ {1- (K + 1) (y / r)²}^1/2] + A_Foury^Four+ A₆y⁶+ A₈y⁸+ A_Teny^Ten
Where r is the radius of curvature on the optical axis, K is the cone coefficient, A_Four, A₆, A₈, A_TenAre the 4th, 6th, 8th and 10th order aspherical coefficients, respectively.
[0134]

[0135]

[0136]

[0137]

[0138]
Aberration diagrams in Examples 1 to 4 when focusing to infinity are shown in FIGS. In these aberration diagrams, “SA” indicates spherical aberration, “AS” indicates astigmatism, “DT” indicates distortion, and “CC” indicates lateral chromatic aberration. In each aberration diagram, “ω” indicates a half angle of view.
[0139]
Next, the values of the conditions (1) to (13) in the above embodiments will be shown.
[0140]
Conditional Example Example 1 Example 2 Example 3 Example 4
(1) 0.95 0.74 0.71 0.54
(2) 0.024 0.12 0.14 0.24
(3) -0.55 -0.45 -0.42 -0.46
(4) -1.30 -0.43 -3.30 -1.52
(5) -0.38 -0.17 -0.41 -0.41
(6) 0.38 1.06 2.51 2.43
(7) 3.06 4.20 1.45 2.90
(8) 18.9 ° 30.4 ° 15.8 ° 20.4 °
(9) 0.44 0.34 0.41 0.42
(10) 0.60 0.47 0.56 0.58
(11) 1.45 2.57 1.03 1.14
(12) -0.40 -0.33 -0.31 -0.34
(13) 1.05 1.87 0.75 0.83.
[0141]
Here, in the present invention, the maximum image height Ih in the image plane is defined as one half of the diagonal length L of the effective imaging region (substantially rectangular) of the imaging device as described above. When the field frame is arranged as a means for defining the imaging region, the field frame diagonal length L is ½, and when an imaging element such as a solid-state imaging element is arranged, the diagonal of the effective imaging region is used. One half of the length L.
[0142]
Accordingly, the diagonal length L and the pixel interval a of the effective imaging surface (effective imaging area) when the imaging recording medium is an electronic imaging element such as a CCD will be described. FIG. 9 is a diagram illustrating an example of a pixel array of the image sensor, and R (red), G (green), and B (blue) pixels are arranged in a mosaic pattern at a pixel interval a. The effective image pickup surface means a region in the photoelectric conversion surface on the image pickup element used for reproduction (display on a personal computer, printing by a printer, etc.) of a taken image. The effective image pickup surface shown in the figure is set to a region narrower than the entire photoelectric conversion surface of the image pickup device in accordance with the performance of the optical system (image circle that can ensure the performance of the optical system). The diagonal length L of the effective imaging surface is the diagonal length of this effective imaging surface. It should be noted that the imaging range used for image reproduction may be variously changed. However, when the imaging optical system of the present invention is used in an imaging apparatus having such a function, the diagonal length L of the effective imaging surface changes. . In such a case, the diagonal length L of the effective imaging surface that defines the maximum image height Ih in the present invention is the maximum value in a range that L can take.
[0143]
FIG. 10 is a diagram for explaining the diagonal length of the field frame when the field frame is arranged on the imaging surface of an electronic image sensor such as a CCD. When an image is formed on an electronic imaging device such as a CCD, the effective imaging area is determined by the opening of the field frame immediately before the imaging surface. Here, the shape of the field frame may be changed variously. However, as in the case of FIG. 9, the diagonal length L of the effective imaging surface that defines the maximum image height Ih in the present invention is a range that L can take. The maximum value at.
[0144]
In the embodiment of the present invention described above, a cover glass may be disposed immediately before the diaphragm S.
[0145]
In the above embodiments of the present invention, the lens made of plastic may be made of glass. For example, it is needless to say that higher performance can be achieved by using a glass having a higher refractive index than the plastic of any of the embodiments. Needless to say, the use of special low dispersion glass is effective in correcting chromatic aberration. In particular, when it is made of plastic, it is preferable to use a low moisture-absorbing material because performance deterioration due to environmental changes is reduced (for example, ZEONEX (trade name) manufactured by ZEON Corporation).
[0146]
Further, in order to cut unnecessary light such as ghost and flare, a flare stop FS may be arranged in addition to the brightness stop S (an arrangement example is shown in FIGS. 1 to 4). The flare stop FS is provided between the brightness stop S and the first lens L1, between the first lens L1 and the second lens L2, between the second lens L2 and the third lens L3, and from the third lens L3. You may arrange | position in any place between the image surfaces I. The flare ray may be cut by a lens frame as shown in FIGS. 1 to 4, or the flare stop FS may be constituted by another member. Further, it may be printed directly on the optical system, painted, or bonded with a seal or the like. Further, the shape may be any shape such as a circle, an ellipse, a rectangle, a polygon, or a range surrounded by a function curve. Further, not only the harmful light flux but also the light flux such as coma flare around the screen may be cut.
[0147]
Each lens may be provided with an antireflection coating to reduce ghost and flare. A multi-coat is desirable because it can effectively reduce ghosts and flares. Moreover, you may perform an infrared cut coat on a lens surface, a cover glass, etc.
[0148]
Further, focusing may be performed to adjust the focus. Focusing may be performed by extending the entire lens system, or a part of the lenses may be extended, or focusing may be performed by retraction.
[0149]
Further, the brightness decrease in the peripheral portion of the image may be reduced by shifting the micro lens of the CCD. For example, the design of the CCD microlens may be changed in accordance with the incident angle of the light beam at each image height. Further, the amount of decrease in the peripheral portion of the image may be corrected by image processing.
[0150]
Although each of the above examples is small, good images are obtained as shown in the aberration diagrams of FIGS.
[0151]
By the way, in each above-mentioned Example, you may give a near-infrared sharp cut coat to the entrance plane side of cover glass CG as mentioned above. This near-infrared sharp cut coat is configured such that the transmittance at a wavelength of 600 nm is 80% or more and the transmittance at a wavelength of 700 nm is 10% or less. Specifically, it is a multilayer film composed of the following 27 layers, for example. However, the design wavelength is 780 nm.
[0152]
Substrate material Physical film thickness (nm) λ / 4
───────────────────────────────
1st layer Al₂O_Three    58.96 0.50
Second layer TiO₂      84.19 1.00
Third layer SiO₂    134.14 1.00
4th layer TiO₂      84.19 1.00
5th layer SiO₂    134.14 1.00
6th layer TiO₂      84.19 1.00
7th layer SiO₂    134.14 1.00
8th layer TiO₂      84.19 1.00
9th layer SiO₂    134.14 1.00
10th layer TiO₂      84.19 1.00
11th layer SiO₂    134.14 1.00
12th layer TiO₂      84.19 1.00
13th layer SiO₂    134.14 1.00
14th layer TiO₂      84.19 1.00
15th layer SiO₂    178.41 1.33
16th layer TiO₂    101.03 1.21
17th layer SiO₂    167.67 1.25
18th layer TiO₂      96.82 1.15
19th layer SiO₂    147.55 1.05
20th layer TiO₂      84.19 1.00
21st layer SiO₂    160.97 1.20
22nd layer TiO₂      84.19 1.00
23rd layer SiO₂    154.26 1.15
24th layer TiO₂      95.13 1.13
25th layer SiO₂    160.97 1.20
26th layer TiO₂      99.34 1.18
27th layer SiO₂      87.19 0.65
───────────────────────────────
Air.
[0153]
The transmittance characteristics of the near infrared sharp cut coat are as shown in FIG.
[0154]
Further, by providing or coating a color filter that reduces the transmission of colors in the short wavelength region as shown in FIG. 12 on the emission surface side of the low-pass filter, the color reproducibility of the electronic image is further improved. Yes.
[0155]
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.
[0156]
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.
[0157]
If the ratio of the transmittance at the wavelength of 400 nm exceeds 6%, the short wavelength castle that is difficult to be recognized by the human eye is regenerated to a wavelength that can be recognized. Conversely, the ratio of the transmittance at the wavelength of 420 nm is reversed. If the value is smaller than 15%, the reproduction of the wavelength castle that can be recognized by humans becomes low, and the color balance becomes poor.
[0158]
Such means for limiting the wavelength is more effective in an imaging system using a complementary color mosaic filter.
[0159]
In each of the above embodiments, as shown in FIG. 12, 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.
[0160]
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.
[0161]
The low-pass filter can be used by superimposing 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. Can be suppressed 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.
[0162]
Further, on the image pickup surface I of the CCD, as shown in FIG. 13, 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 image pickup pixels is provided. ing. These four types of color filters are arranged in a mosaic so that each of them has approximately the same number and adjacent pixels do not correspond to the same type of color filter. Thereby, more faithful color reproduction is possible.
[0163]
Specifically, as shown in FIG. 13, the complementary color mosaic filter is composed of at least four types of color filters, and the characteristics of the four types of color filters are preferably as follows.
[0164]
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.
[0165]
510nm <G_P<540 nm
5nm <Y_P-G_P<35nm
−100 nm <C_P-G_P<-5nm
430 nm <M_P1<480nm
580 nm <M_P2<640nm
Further, the green, yellow, and cyan color filters have an intensity of 80% or more at a wavelength of 530 nm with respect to each spectral intensity peak, and the magenta color filter has an intensity of 10% at a wavelength of 530 nm. From the viewpoint of improving the color reproducibility, it is more preferable that the strength is 50% to 50%.
[0166]
FIG. 14 shows an example of each wavelength characteristic in each of the above embodiments. 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%.
[0167]
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.
[0168]
By the way, the arrangement position of the above-mentioned near infrared sharp cut coat may be any position on the optical path. The number of low-pass filters may be two or one.
[0169]
In the image pickup apparatus of the present invention, for adjusting the light amount, a variable aperture may be used in which the brightness stop S is configured with a plurality of aperture blades and the aperture shape is variable. FIG. 15 is an explanatory diagram illustrating an example of the aperture shape at the time of opening, and FIG. 16 is an explanatory diagram illustrating an example of the aperture shape at the time of two-stage aperture. 15 and 16, OP represents the optical axis, Da represents six diaphragm plates, and Xa and Xb represent openings. In the present invention, the aperture shape of the aperture can be set to only two types: an open state (FIG. 15) and an aperture value (a two-stage aperture, FIG. 16) that provides an F value that satisfies a predetermined condition.
[0170]
Or, using a turret provided with a plurality of fixed-shaped brightness stops with different shapes or transmittances, depending on the required brightness, place any brightness stop on the object-side optical axis of the imaging optical system. With the arrangement, the diaphragm mechanism can be thinned. In addition, a configuration in which a light amount reduction filter having a transmittance lower than the transmittance of other aperture stops is arranged in the aperture that reduces the amount of light most among the apertures of the aperture stops arranged on the turret. Good. Accordingly, the aperture diameter of the diaphragm is not excessively narrowed, and deterioration of the imaging performance due to diffraction that occurs due to the small aperture diameter of the diaphragm can be suppressed.
[0171]
FIG. 17 is a perspective view showing a configuration of an example in this case. Brightness can be adjusted in 0, −1, −2, −3, and −4 stages at the position of the stop S on the optical axis on the object side of the first positive lens L1 of the imaging optical system. A turret 10 is arranged.
[0172]
The turret 10 has an opening 1A (a transmittance of 100% for a wavelength of 550 nm) having a circular aperture with a maximum aperture diameter and a fixed aperture of 0 stage, and an opening of the opening 1A for -1 stage 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.
[0173]
The light quantity is adjusted by arranging one of the apertures at the aperture position by turning around the rotation shaft 11 provided in the turret 10.
[0174]
Moreover, it can replace with the turret 10 shown in FIG. 17, and the turret 10 'shown in the front view of FIG. 18 can be used. Brightness can be adjusted in 0, −1, −2, −3, and −4 stages at the position of the stop S on the optical axis on the object side of the first positive lens L1 of the imaging optical system. A turret 10 'is arranged.
[0175]
The turret 10 ′ has an opening shape for adjusting the zero stage having a circular and fixed opening 1 A ′ having a maximum aperture diameter, and an opening area that is about half of the opening area of the opening 1 A ′ for −1 stage correction. The opening 1B ′ having a fixed opening shape and the opening areas 1C ′, 1D ′, and 1E ′ having fixed shapes for the correction to the −2 step, the −3 step, and the −4 step are further reduced in order. Have.
[0176]
The light quantity is adjusted by arranging any opening at the stop position by turning around the rotation shaft 11 provided in the turret 10 '.
[0177]
In order to reduce the thickness, the aperture of the aperture stop S may be an aperture having a fixed shape and position, and the light amount adjustment may be performed by electrically adjusting an output signal from the image sensor. Alternatively, the light amount may be adjusted by inserting and removing an ND filter between other spaces in the lens system, for example, the third positive lens L3 and the CCD cover glass CG. FIG. 19 is a diagram showing an example of this. The opening 1A ″ of the turret 10 ″ is a through surface or hollow opening, the opening 1B ″ is an ND filter having a transmittance of 1/2, and the opening 1C ″ is having a transmittance of 1/4. The ND filter, aperture 1D ″ is a turret-shaped filter provided with an ND filter having a transmittance of 1/8, and any aperture is arranged at any position in the optical path by rotation around the central rotation axis. To adjust the light intensity.
[0178]
Further, as a filter for adjusting the light amount, a filter surface capable of adjusting the light amount so as to suppress unevenness in the light amount may be provided. For example, as shown in FIG. 20, the light intensity is centered concentrically so that the transmittance is uniform with priority given to securing the light intensity at the center for dark subjects and the uneven brightness is compensated only for bright subjects. It is good also as a structure which arrange | positions the filter which falls so much.
[0179]
Further, as the diaphragm S, the peripheral portion on the incident surface side of the first positive lens L1 may be painted black.
[0180]
When the imaging apparatus according to the present invention stores an image as a still image like a camera or the like, a shutter for adjusting the amount of light may be disposed in the optical path.
[0181]
As such a shutter, a focal plane shutter, a rotary shutter, or a liquid crystal shutter disposed immediately before the CCD may be used, or the aperture stop itself may be configured as a shutter.
[0182]
FIG. 21 shows an example of the shutter. FIG. 21 shows an example of a rotary focal plane shutter which is one of the focal plane shutters. FIG. 21A is a view seen from the back side, and FIG. 21B is a view seen from the front side. is there. A shutter substrate 15 is arranged immediately before the image plane or at an arbitrary optical path position. The substrate 15 is provided with an opening 16 that transmits an effective light beam of the optical system. Reference numeral 17 denotes a rotary shutter curtain. Reference numeral 18 denotes a rotary shaft of the rotary shutter curtain 17. The rotary shaft 18 rotates with respect to the substrate 15 and is integrated with the rotary shutter curtain 17. The rotating shaft 18 is connected to gears 19 and 20 on the surface of the substrate 15. The gears 19 and 20 are connected to a motor (not shown).
[0183]
In such a configuration, the rotary shutter curtain 17 is configured to rotate about the rotation shaft 18 via the gears 19 and 20 and the rotation shaft 18 by driving a motor (not shown).
[0184]
The rotary shutter curtain 17 is formed in a substantially semicircular shape and shields and retreats the opening 16 of the substrate 15 by rotation, thereby serving as a shutter. The shutter speed is adjusted by changing the rotating speed of the rotary shutter curtain 17.
[0185]
22A to 22D are views of the rotary shutter curtain 17 rotating from the image plane side. It moves in the order of (a), (b), (c), (d), and (a) in the figure with time.
[0186]
As described above, the aperture stop S with a fixed shape and a filter or shutter that adjusts the amount of light are placed at different positions in the lens system. In addition, an imaging apparatus capable of reducing the overall length of the lens system can be obtained.
[0187]
Further, a configuration may be adopted in which electrical control is performed so as to obtain a still image by extracting a part of the electrical signal of the CCD without using a mechanical shutter. One example of such a configuration will be described with reference to FIG. 23 and FIG. FIG. 23 is a diagram for explaining the operation of CCD imaging in which signals are sequentially read out by an interlace method (interlaced scanning method). In FIG. 23, Pa to Pc are photosensitive sections using photodiodes, Va to Vc are vertical transfer sections using CCD, and Ha is a horizontal transfer section using CCD. The A field indicates an odd field, and the B field indicates an even field.
[0188]
In the configuration of FIG. 23, the basic operation is performed as follows. That is, (1) signal charge accumulation (photoelectric conversion) by light in the photosensitive part, (2) signal charge shift (field shift) from the photosensitive part to the vertical transfer part, and (3) signal charge in the vertical transfer part. Transfer (vertical transfer), (4) transfer of signal charges from the vertical transfer unit to the horizontal transfer unit (line shift), (5) transfer of signal charges in the horizontal transfer unit (horizontal transfer), (6) horizontal transfer unit The signal charge is detected (detected) at the output terminal. Such sequential reading can be performed using either the A field (odd field) or the B field (even field).
[0189]
In the interlaced (interlaced scanning) CCD imaging shown in FIG. 23, the accumulation timing of the A field and the B field is shifted by 1/60 in the TV broadcast system and the analog video system. If this is used as it is as a DSC (Digital Spectral Compatible) image to form a frame image, in the case of a moving subject, a blur like a double image occurs. Therefore, in this type of CCD imaging, the A and B fields are simultaneously exposed to mix the signals of adjacent fields. Then, after a fluorescent light is emitted at the end of exposure using a mechanical shutter, a method is employed in which the A field and the B field are read out separately to synthesize signals.
[0190]
In the present invention, the mechanical shutter functions only for smear prevention and only the A field is sequentially read out, or the A and B fields are simultaneously mixed readout. The high-speed shutter can be released regardless of the shutter speed (because it can be controlled only with an electronic shutter). In the example of FIG. 23, since the number of CCDs in the vertical transfer unit is half of the number of photodiodes constituting the photosensitive unit, there is an advantage that it is easy to reduce the size.
[0191]
FIG. 24 is a diagram for explaining the operation of CCD imaging in which sequential readout of signals is performed in a progressive manner. In FIG. 24, Pd to Pf are photosensitive portions using photodiodes, Vd to Vf are vertical transfer portions by CCD, and Hb is a horizontal transfer portion by CCD.
[0192]
In FIG. 24, since reading can be performed in the pixel arrangement order, it is possible to electronically control all charge accumulation and reading operations. Therefore, the exposure time can be shortened to about (1/10000 seconds). In the example of FIG. 24, the number of vertical CCDs is larger than in the case of FIG. 23, and there is a disadvantage that downsizing is difficult. However, because of the advantages as described above, in the present invention, FIG. Any of these methods can be employed.
[0193]
The imaging apparatus of the present invention as described above is an imaging apparatus that forms an object image with an imaging optical system and receives the image with an imaging element such as a CCD, and in particular, a digital camera, video camera, information processing It can be used for personal computers, telephones, and especially mobile phones that are convenient to carry. The embodiment is illustrated below.
[0194]
FIGS. 25 to 27 are conceptual diagrams of structures in which the imaging optical system according to the present invention is incorporated in the photographing optical system 41 of a digital camera. 25 is a front perspective view showing the appearance of the digital camera 40, FIG. 26 is a rear perspective view thereof, and FIG. 27 is a cross-sectional view showing the configuration of the digital camera 40. In this example, the digital camera 40 includes a photographic optical system 41 having a photographic optical path 42, a finder optical system 43 having a finder optical path 44, a shutter 45, a flash 46, a liquid crystal display monitor 47, and the like. When the shutter 45 disposed in the position is pressed, photographing is performed through the photographing optical system 41, for example, the imaging optical system of the first embodiment in conjunction therewith. An object image formed by the photographing optical system 41 is formed on the imaging surface of the CCD 49 through a cover glass CG provided with a near-infrared cut coat and having a low-pass filter function. 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.
[0195]
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.
[0196]
The digital camera 40 configured as described above can achieve high performance and downsizing since the photographing optical system 41 is high performance and small.
[0197]
In the example of FIG. 27, a parallel plane plate is disposed as the cover member 50, but a lens having power may be used.
[0198]
Next, a personal computer which is an example of an information processing apparatus in which the imaging optical system of the present invention is incorporated as an objective optical system is shown in FIGS. 28 is a front perspective view with the cover of the personal computer 300 opened, FIG. 29 is a sectional view of the photographing optical system 303 of the personal computer 300, and FIG. 30 is a side view of the state of FIG. As shown in FIGS. 28 to 30, 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.
[0199]
The photographing optical system 303 has an objective lens 112 including an imaging optical system (abbreviated in the drawing) according to the present invention and an image pickup element chip 162 that receives an image on a photographing optical path 304. These are built in the personal computer 300.
[0200]
Here, a cover glass CG having a low-pass filter function is additionally attached on the image pickup element chip 162 to be integrally formed as an image pickup unit 160, and can be touched at the rear end of the lens frame 113 of the objective lens 112 with one touch. Since it can be fitted and attached, it is not necessary to align the center of the objective lens 112 and the image pickup element chip 162 and to adjust the surface interval, and the assembly is simplified. A cover glass 114 for protecting the objective lens 112 is disposed at the tip of the lens frame 113.
[0201]
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 displayed on the monitor 302 as an electronic image. FIG. 28 shows an example of the operator's A captured 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.
[0202]
Next, FIG. 31 shows a telephone which is an example of an information processing apparatus in which the imaging optical system of the present invention is incorporated as a photographing optical system, particularly a portable telephone which is convenient to carry. 31A is a front view of the mobile phone 400, FIG. 31B is a side view, and FIG. 31C is a cross-sectional view of the photographing optical system 405. As shown in FIGS. 31A to 31C, the mobile phone 400 includes a microphone unit 401 that inputs an operator's voice as information, a speaker unit 402 that outputs the voice of the other party, and an operator who receives information. An input dial 403 for inputting information, a monitor 404 for displaying information such as a photographed image of the operator and the other party and a telephone number, 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 an imaging optical system (abbreviated in the drawing) according to the present invention disposed on a photographing optical path 407, and an imaging element chip 162 that receives an object image. These are built in the mobile phone 400.
[0203]
Here, a cover glass CG having a low-pass filter function is additionally attached on the image pickup element chip 162 to be integrally formed as an image pickup unit 160, and can be touched at the rear end of the lens frame 113 of the objective lens 112 with one touch. Since it can be fitted and attached, it is not necessary to align the center of the objective lens 112 and the image pickup element chip 162 and to adjust the surface interval, and the assembly is simplified. A cover glass 114 for protecting the objective lens 112 is disposed at the tip of the lens frame 113.
[0204]
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.
[0205]
Each of the above embodiments can be variously modified in accordance with the configuration of the claims.
[0206]
【The invention's effect】
According to the present invention, it is possible to obtain a high-performance imaging optical system and a small and high-performance imaging device using the same even if the size is reduced, with little performance degradation due to manufacturing errors.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view of an imaging optical system according to a first embodiment of the present invention when focusing on an object point at infinity.
2 is a lens cross-sectional view similar to FIG. 1 of the imaging optical system of Example 2. FIG.
3 is a lens cross-sectional view similar to FIG. 1 of the imaging optical system of Example 3. FIG.
4 is a lens cross-sectional view similar to FIG. 1 of the imaging optical system of Example 4. FIG.
5 is an aberration diagram for Example 1 upon focusing on an object point at infinity. FIG.
FIG. 6 is an aberration diagram for Example 2 upon focusing on an object point at infinity.
FIG. 7 is an aberration diagram for Example 3 upon focusing on an object point at infinity.
8 is an aberration diagram for Example 4 upon focusing on an object point at infinity. FIG.
FIG. 9 is a diagram for explaining a diagonal length L of an effective imaging surface that defines a maximum image height Ih when imaging is performed with an imaging element.
FIG. 10 is a diagram for explaining a diagonal length L of an effective imaging surface that defines a maximum image height Ih when a field frame is arranged on an imaging surface of an imaging element.
FIG. 11 is a diagram showing transmittance characteristics of an example of a near-infrared sharp cut coat.
FIG. 12 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. 13 is a diagram illustrating a color filter arrangement of a complementary color mosaic filter.
FIG. 14 is a diagram illustrating an example of wavelength characteristics of a complementary color mosaic filter.
FIG. 15 is a diagram showing that the aperture shape of the aperture is in an open state.
FIG. 16 is a diagram showing a state where the aperture shape of the diaphragm is a two-stage diaphragm.
FIG. 17 is a perspective view showing a configuration of an imaging optical system according to the present invention in which a turret provided with a plurality of fixed-shape brightness stops having different shapes and transmittances is disposed.
FIG. 18 is a front view showing another turret replacing the turret shown in FIG. 17;
FIG. 19 is a diagram showing another turret-shaped light amount adjustment filter that can be used in the present invention.
FIG. 20 is a diagram illustrating an example of a filter that suppresses unevenness in the amount of light.
FIG. 21 is a rear view and a front view showing an example of a rotary focal plane shutter.
22 is a diagram illustrating a state in which a rotary shutter curtain of the shutter in FIG. 21 rotates.
FIG. 23 is an explanatory diagram of the operation of interlaced CCD imaging.
FIG. 24 is a diagram illustrating the operation of progressive CCD imaging.
FIG. 25 is a front perspective view showing the external appearance of a digital camera incorporating the imaging optical system according to the present invention.
26 is a rear perspective view of the digital camera of FIG. 25. FIG.
27 is a cross-sectional view of the digital camera of FIG. 25. FIG.
FIG. 28 is a front perspective view in which a cover of a personal computer in which the imaging optical system according to the present invention is incorporated as an objective optical system is opened.
FIG. 29 is a cross-sectional view of a photographing optical system of a personal computer.
30 is a side view of the state of FIG. 28. FIG.
FIG. 31 is a front view, a side view, and a sectional view of a photographing optical system of a mobile phone in which the imaging optical system according to the present invention is incorporated as an objective optical system.
[Explanation of symbols]
S ... Brightness stop
L1 ... 1st positive lens
L2 ... Second negative lens
L3 ... Third positive lens
CG ... Cover glass
I: Image plane
FS ... Flare aperture
OP ... Optical axis
Da ... Aperture plate
Xa, Xb ... opening
Pa to Pf: photosensitive part
Va to Vf: Vertical transfer unit
Ha, Hb ... Horizontal transfer section
E ... Observer eyeball
1A, 1B, 1C, 1D, 1E ... Opening
1A ', 1B', 1C ', 1D', 1E '... opening
1A ", 1B", 1C ", 1D" ... opening
10 ... Turret
10 '... Turret
10 "... Turret
11 ... Rotating shaft
15 ... Shutter substrate
16 ... opening
17 ... Rotary shutter curtain
18 ... Rotating shaft
19, 20 ... Gear
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 (4)

In order from the object side, the imaging optical system is composed of three lenses: an aperture stop, a first positive meniscus lens having a convex surface facing the image side, a biconcave second negative lens, and a third positive lens. An imaging optical system characterized by satisfying the following conditional expression:
−0.6 <f ₂ /Ih<−0.25 (3−1)
Here, f ₂ is the focal length of the second negative lens, and Ih is the maximum image height.   The imaging optical system according to claim 1, wherein the third positive lens is made of plastic.   3. The three air lenses each comprising a single lens, and two air lenses formed by the three lenses are sandwiched between two refracting surfaces having different shapes. The imaging optical system described.   The image pickup apparatus according to claim 1, further comprising an image pickup element disposed on an image side of the three lenses.

Images