JP2004233536A - Imaging optical system and image pickup unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging optical system that satisfies high performance and miniaturization concurrently, and copes with wide angle imaging, and also to provide an image pickup unit that uses the system. <P>SOLUTION: The imaging optical system is provided with a brightness diaphragm S, a first positive lens L1, a second negative lens L2, and a third positive lens L3 which are arranged in this order successively from an object side. The system also fulfills the following conditional expression: 1.5<d/(f×tan θ)<3.0 (where d is the distance measured along the optical axis from the brightness diaphragm plane to the image plane of the system, θ is the maximum angle of incidence of the system, and f is the focal length of the entire system). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００９９】

【０１００】

【０１０１】

【０１０２】

【０１０３】
上記実施例１〜５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６〜図１０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。
【０１０４】
次に、上記各実施例における条件（１）〜（１３）の値を示す。
【０１０５】

（注）条件式（７）、（８）の数値は、上が物体側の面の数値、下が像側の面の数値である。
【０１０６】
上記各実施例は小型でありながら、図６〜図１０の収差図に示すように、良好な画像が得られている。
【０１０７】
なお、以上の本発明の実施例において、明るさ絞りＳの直前にカバーガラスを配置するようにしてもよい。
【０１０８】
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）。
【０１０９】
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以外にフレア絞りを配置してもよい。以上の実施例において、明るさ絞りＳから第１レンズＬ１間、第１レンズＬ１と第２レンズＬ２間、第２レンズＬ２と第３レンズＬ３間、第３レンズＬ３と像面Ｉ間の何れの場所にフレア絞りを配置してもよい。また、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、別の部材を用いてフレア絞りを構成してもよい。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。
【０１１０】
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。
【０１１１】
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。
【０１１２】
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。
【０１１３】
図１１は、上記実施例１の結像光学系５とその像面Ｉに配置されるＣＣＤ６とを、樹脂材で一体成形したレンズ枠７に固定する構成例の、結像光学系５の光軸を含みＣＣＤ６の像面Ｉの対角方向に取った断面図であり、明るさ絞りＳは樹脂製のレンズ枠７に一体成形している。このようにすると、結像光学系５を保持するレンズ枠７の製造が容易になる。また、レンズ枠７に明るさ絞りＳの構成を一体化させることで、製造工程を大幅に削減し、また、このレンズ枠７自体に撮像素子のＣＣＤ６の保持機能を備えさせることで、レンズ枠７内へごみ等が進入し難くなる。
【０１１４】
また、図１１から明らかなように、結像光学系５の第１正レンズＬ１、第２負レンズＬ２、第３正レンズＬ３の各々の外周８に、物体側程光軸に近づくよう傾斜させた傾斜面を設け、レンズ枠７にその傾斜面を当接して固定可能にすることにより、レンズ枠７へ像面側からレンズＬ１〜Ｌ３を落とし込んで位置決め固定できるようになる。
【０１１５】
また、図１２に模式的分解斜視図を示すように、プラスチックで成形したレンズ枠７内に保持される結像光学系の第１正レンズＬ１の形状は、第１正レンズＬ１、第２負レンズＬ２は入射側からみて円形、第３正レンズＬ３は円形のレンズを基に、その上部と下部を切削した小判型の形状をしている。そして、各々のレンズＬ１〜Ｌ３のの外周８は絞りＳ側に傾斜している。レンズ枠７の内面もその傾きに対応して傾斜して成形されている。
【０１１６】
このように、第１正レンズＬ１の形状を入射側からみて円形、第３正レンズＬ３の形状を、入射側から見たときに撮像素子のＣＣＤ６の有効撮像領域の短辺方向に対応する方向の長さがその有効撮像領域の長辺方向に対応する長さよりも短いものに構成することにより、結像光学系の第１正レンズＬ１、第２負レンズＬ２、第３正レンズＬ３を有効光束に沿ったレンズ外形にすることができ、ケラレを抑えつつ小型化ができる。なお、この例でも、レンズ枠７内に結像光学系５の第１正レンズＬ１、第２負レンズＬ２、第３正レンズＬ３の各々の外周８の傾斜面を当接して固定させるようにすることで、レンズ枠７内に像面側からレンズＬ１〜Ｌ３を落とし込んで位置決め固定できる。
【０１１７】
また、明るさ絞りＳの開口の周辺面は、図１１の断面図に示すように、レンズＬ１側に傾いて構成することが望ましく、その明るさ絞りＳの開口の周辺面を、有効光束よりも傾斜角が大きく、実質的に最もレンズ側の角部が絞りの役目をするようにすることで、明るさ絞りＳの開口部の外周面で反射した光束が撮像素子のＣＣＤ６に入射し難くなり、フレア、ゴーストの影響を低減することが可能になる。
【０１１８】
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。
【０１１９】
基 板 材質 物理的膜厚（ｎｍ） λ／４
───────────────────────────────
第１層 Ａｌ_２ Ｏ_３ ５８．９６ ０．５０
第２層 ＴｉＯ_２ ８４．１９ １．００
第３層 ＳｉＯ_２ １３４．１４ １．００
第４層 ＴｉＯ_２ ８４．１９ １．００
第５層 ＳｉＯ_２ １３４．１４ １．００
第６層 ＴｉＯ_２ ８４．１９ １．００
第７層 ＳｉＯ_２ １３４．１４ １．００
第８層 ＴｉＯ_２ ８４．１９ １．００
第９層 ＳｉＯ_２ １３４．１４ １．００
第１０層 ＴｉＯ_２ ８４．１９ １．００
第１１層 ＳｉＯ_２ １３４．１４ １．００
第１２層 ＴｉＯ_２ ８４．１９ １．００
第１３層 ＳｉＯ_２ １３４．１４ １．００
第１４層 ＴｉＯ_２ ８４．１９ １．００
第１５層 ＳｉＯ_２ １７８．４１ １．３３
第１６層 ＴｉＯ_２ １０１．０３ １．２１
第１７層 ＳｉＯ_２ １６７．６７ １．２５
第１８層 ＴｉＯ_２ ９６．８２ １．１５
第１９層 ＳｉＯ_２ １４７．５５ １．０５
第２０層 ＴｉＯ_２ ８４．１９ １．００
第２１層 ＳｉＯ_２ １６０．９７ １．２０
第２２層 ＴｉＯ_２ ８４．１９ １．００
第２３層 ＳｉＯ_２ １５４．２６ １．１５
第２４層 ＴｉＯ_２ ９５．１３ １．１３
第２５層 ＳｉＯ_２ １６０．９７ １．２０
第２６層 ＴｉＯ_２ ９９．３４ １．１８
第２７層 ＳｉＯ_２ ８７．１９ ０．６５
───────────────────────────────
空 気 。
【０１２０】
上記の近赤外シャープカットコートの透過率特性は図１３に示す通りである。
【０１２１】
また、ローパスフィルターの射出面側には、図１４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。
【０１２２】
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。
【０１２３】
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。
【０１２４】
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。
【０１２５】
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。
【０１２６】
上記各実施例では、図１４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。
【０１２７】
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。
【０１２８】
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。
【０１２９】
また、ＣＣＤの撮像面Ｉ上には、図１５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。
【０１３０】
補色モザイクフィルターは、具体的には、図１５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。
【０１３１】
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。
【０１３２】
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。
【０１３３】
上記各実施例におけるそれぞれの波長特性の１例を図１６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。
【０１３４】
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。
【０１３５】
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。
【０１３６】
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１７は、開口時絞り形状の例を示す説明図、図１８は、２段絞り時の絞り形状の例を示す説明図である。図１７、図１８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１７）と、所定の条件を満たすＦ値となる絞り値（２段絞り、図１８）の２種類のみとすることができる。
【０１３７】
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。
【０１３８】
この場合の１例の構成を示す斜視図を図１９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。
【０１３９】
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。
【０１４０】
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。
【０１４１】
また、図１９に示すターレット１０に代えて、図２０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。
【０１４２】
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。
【０１４３】
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。
【０１４４】
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２１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。
【０１４５】
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２２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。
【０１４６】
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。
【０１４７】
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。
【０１４８】
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。
【０１４９】
図２３にシャッターの１例を示す。図２３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２３（ａ）は裏面側から見た図、図２３（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。
【０１５０】
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。
【０１５１】
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。
【０１５２】
図２４（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。
【０１５３】
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。
【０１５４】
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２５、図２６によりＣＣＤ撮像の動作を説明しながら説明する。図２５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２５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。
【０１５５】
図２５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。
【０１５６】
図２５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。
【０１５７】
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２５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。
【０１５８】
図２６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２６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。
【０１５９】
図２６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２６の例では、図２５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２５、図２６の何れの方式も採用することができる。
【０１６０】
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。
【０１６１】
図２７〜図２９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２７はデジタルカメラ４０の外観を示す前方斜視図、図２８は同後方斜視図、図２９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。
【０１６２】
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。
【０１６３】
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。
【０１６４】
なお、図２９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。
【０１６５】
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３０〜図３２に示される。図３０はパソコン３００のカバーを開いた前方斜視図、図３１はパソコン３００の撮影光学系３０３の断面図、図３２は図３０の状態の側面図である。図３０〜図３２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。
【０１６６】
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。
【０１６７】
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。
【０１６８】
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３０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。
【０１６９】
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３３に示される。図３３（ａ）は携帯電話４００の正面図、図３３（ｂ）は側面図、図３３（ｃ）は撮影光学系４０５の断面図である。図３３（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。
【０１７０】
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。
【０１７１】
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。
【０１７２】
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。
【０１７３】
なお、本発明において次のように結像光学系を構成することもできる。
【０１７４】
〔１〕 物体側から順に、明るさ絞り、第１正レンズ、第２負レンズ、第３正レンズの順に配置され、少なくとも第１正レンズに非球面を有し、次の条件式を満たすことを特徴とする結像光学系。
【０１７５】
−５．０＜ｆ_２−３ ／ｆ＜−０．５ ・・・（２）
ただし、ｆ_２−３ は第２負レンズと第３正レンズの合成焦点距離、ｆは全系の焦点距離である。
【０１７６】
〔２〕 物体側から順に、明るさ絞り、第１正レンズ、第２負レンズ、第３正レンズの順に配置され、少なくとも第２負レンズに非球面を有し、次の条件式を満たすことを特徴とする結像光学系。
【０１７７】
−５．０＜ｆ_２−３ ／ｆ＜−０．５ ・・・（２）
ただし、ｆ_２−３ は第２負レンズと第３正レンズの合成焦点距離、ｆは全系の焦点距離である。
【０１７８】
〔３〕 物体側から順に、明るさ絞り、像側に凸面を向けた第１正メニスカスレンズ、第２負レンズ、第３正レンズの順に配置され、次の条件式を満たすことを特徴とする結像光学系。
【０１７９】
０．２＜ｆ_１ ／ｆ_３ ＜０．５８ ・・・（３−１）
ただし、ｆ_１ は第１正レンズの焦点距離、ｆ_３ は第３正レンズの焦点距離である。
【０１８０】
【発明の効果】
本発明により、全長が短く高性能な広角化にも耐える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５の結像光学系の図１と同様のレンズ断面図である。
【図６】実施例１の無限遠物点合焦時の収差図である。
【図７】実施例２の無限遠物点合焦時の収差図である。
【図８】実施例３の無限遠物点合焦時の収差図である。
【図９】実施例４の無限遠物点合焦時の収差図である。
【図１０】実施例５の無限遠物点合焦時の収差図である。
【図１１】実施例１の結像光学系とその像面に配置されるＣＣＤとを樹脂材で一体成形したレンズ枠に固定する構成例の断面図である。
【図１２】結像光学系の第３正レンズを小判型の形状にする場合の模式的分解斜視図である。
【図１３】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１４】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１５】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１６】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１７】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１８】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１９】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２０】図１９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２１】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２２】光量ムラを抑えるフィルターの例を示す図である。
【図２３】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２４】図２３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２５】インターレース式ＣＣＤ撮像の動作説明図である。
【図２６】プログレッシブ式ＣＣＤ撮像の動作説明図である
【図２７】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２８】図２７のデジタルカメラの後方斜視図である。
【図２９】図２７のデジタルカメラの断面図である。
【図３０】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３１】パソコンの撮影光学系の断面図である。
【図３２】図３０の状態の側面図である。
【図３３】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
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
５…結像光学系
６…ＣＣＤ
７…レンズ枠
８…レンズ外周
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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging optical system and an imaging apparatus using the same, and more particularly, to a digital still camera, a digital video camera, a mobile 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 device such as a small camera and a surveillance camera.
[0002]
[Prior art]
2. Description of the Related Art In recent years, electronic cameras that take an image of a subject using a solid-state imaging device such as a CCD or a CMOS instead of a silver halide film have become widespread. Among such electronic cameras, imaging devices mounted on portable computers, mobile phones, and the like are particularly required to be small and light.
[0003]
As an image forming optical system used in such an image pickup apparatus, there is an image forming optical system having one or two lenses conventionally. However, it is already known that these cannot correct the field curvature and cannot expect high performance, as is clear from the theory of aberration. Therefore, in order to satisfy the high performance, it is necessary to be configured with three or more lenses.
[0004]
On the other hand, in the case of a CCD, if the off-axis light flux emitted from the imaging lens system enters the image plane at an excessively large angle, the light-collecting performance of the micro lens is not sufficiently exhibited, and the brightness of the image is reduced in the center of the image. There is a problem that the image is extremely changed between the portion and the peripheral portion of the image. Therefore, the angle of incidence of the light beam on the CCD, that is, the position of the exit pupil is important in design. In the case of an optical system with a small number, the position of the aperture stop becomes important.
[0005]
In consideration of 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]
JP-A-5-188284
[0010]
[Patent Document 5]
JP-A-9-288235
[0011]
[Patent Document 6]
JP 2001-75006 A
[0012]
[Problems to be solved by the invention]
However, these prior examples have various problems as described below.
[0013]
In general, when the total length of the optical system is shortened, the exit pupil position must also be arranged on the image side accordingly, so that the light incident angle on the image plane becomes tight. Conversely, if the exit pupil position is located on the object side, the angle of incidence of the light beam on the image plane is reduced, but the overall length is increased.
[0014]
None of Patent Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 5 has a long overall length and cannot be said to achieve miniaturization. In addition, the half angle of view is about 25, and further widening the angle of view has a limit in performance. The angle of incidence of the light beam on the image plane was not small for the angle of view.
[0015]
Patent Literatures 4 and 5 consider the incident angle of a light beam on an image plane, but similarly cannot say that the entire length is short.
[0016]
As described above, none of the prior arts had a balance between the size of the optical system and the angle of incidence of the light beam on the image plane. Further, when the angle of view is widened to a half angle of view of about 35 °, the angle of incidence on the optical system is further increased. Therefore, the angle of emergence, that is, the angle of incidence on the image plane is also increased. There was no.
[0017]
The present invention has been made in view of such problems of the related art, and an object of the present invention is to provide an imaging optical system that can simultaneously achieve high performance and miniaturization and endure a wide angle, and an imaging apparatus using the same. To provide.
[0018]
[Means for Solving the Problems]
The image forming optical system of the present invention that achieves the above object is arranged in the order of the aperture stop, the first positive lens, the second negative lens, and the third positive lens from the object side, and satisfies the following conditional expression. It is a feature.
[0019]
1.5 <d / (f · tan θ) <3.0 (1)
Here, d is the distance measured along the optical axis from the brightness stop surface of the imaging optical system to the image plane, θ is the maximum incident angle of the imaging optical system, and f is the focal length of the entire system.
[0020]
Another imaging optical system according to the present invention is arranged from the object side in the following order: an aperture stop, a first positive meniscus lens having a convex surface facing the image side, a second negative lens, and a third positive lens. It is characterized by satisfying the expression.
[0021]
−5.0 <f_2-3/F<-0.5 (2)
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.
[0022]
Hereinafter, the reason and operation of the above configuration in the present invention will be described.
[0023]
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 can be further improved by increasing the number of lenses to four or more. However, increasing the number of single lenses increases the thickness of the lenses, the distance between the lenses, and the space of the frame, thereby increasing the size. Is inevitable. Further, as described in the section of the related art, if the number of sheets is two or less, the curvature of field is not reduced and the peripheral performance is considerably deteriorated. Optimum performance and size are achieved with three components.
[0024]
Next, in order to reduce the angle of incidence of light rays on the CCD, which is an image pickup device, the aperture stop was disposed closest to the object. The power of the lens may be configured so that the position of the exit pupil is farther to the object side. However, since the number of lenses is small, it is most effective to arrange the position of the aperture stop on the object side.
[0025]
Here, if the aperture stop is arranged closest to the object, there is only one lens with respect to the stop, and it is difficult to correct distortion and chromatic aberration of magnification, which are peripheral performances, in optical design. Therefore, by arranging the positive lens, the negative lens, and the positive lens from the object side, the power of the opposite sign is arranged on the second lens and the third lens whose ray height becomes large, and the correction is performed. The central performance is such that spherical aberration and axial chromatic aberration generated by the first positive lens are corrected by the second negative lens, thereby achieving high performance of the entire screen.
[0026]
By doing so, it is basically possible to reduce the overall length and the incident angle of the light beam on the image plane, but since the number of lenses is small, the focal length and the angle of view must be sufficiently considered. The size cannot be reduced unless the surface spacing, wall thickness, and back focus are set appropriately. Therefore, it is necessary to satisfy the following conditional expression.
[0027]
1.5 <d / (f · tan θ) <3.0 (1)
Here, d is the distance measured along the optical axis from the brightness stop surface of the imaging optical system to the image plane, θ is the maximum incident angle of the imaging optical system, and f is the focal length of the entire system.
[0028]
If the upper limit of 3.0 of conditional expression (1) is exceeded, the overall length will be too large to achieve miniaturization. If the lower limit of 1.5 is exceeded, the power of each lens will be too strong and the performance will deteriorate. Or the wall thickness and surface spacing are too narrow, making it difficult to process and assemble.
[0029]
It is more preferable to satisfy the following conditional expression.
[0030]
1.8 <d / (f · tan θ) <2.8 (1-1)
Next, a power configuration for more effectively achieving downsizing and high performance of the imaging optical system will be described. Generally, in order to shorten the total length with respect to the focal length, it is conceivable to arrange power in the order of positive and negative telephoto types. However, since the negative light has a diverging effect, the angle of incidence on the image plane tends to be sharp if the structure is used as it is. On the other hand, when a wide-angle optical system is configured, it is known that arranging a group having a negative divergence on the most object side is advantageous in optical performance.
[0031]
Therefore, in the present invention, first, in order to shorten the overall length, the basic power configuration is made positive and negative, and the negative power is configured as a negative lens and a positive lens in order from the object side. As a result, while forming a telephoto type, the angle of incidence on the image plane can be reduced by the convergence of the positive lens disposed closest to the image plane. In order to prevent performance degradation even when a wide-angle optical system is configured, the first positive lens is made concave so as to have a diverging effect, and has a meniscus shape with positive power. This makes it possible to sufficiently correct coma and astigmatism of off-axis light rays that are likely to occur when the angle of view is widened.
[0032]
At this time, in order to balance the effect of reducing the overall length and the angle of incidence on the image plane, it is necessary to appropriately set the negative power by the second negative lens and the third positive lens. Therefore, it is necessary to satisfy the following conditional expression.
[0033]
−5.0 <f_2-3/F<-0.5 (2)
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.
[0034]
If the upper limit of -0.5 of conditional expression (2) is exceeded, the telephoto effect becomes too strong and the angle of incidence on the image plane becomes too tight. If the lower limit of -5.0 is exceeded, the telephoto effect becomes weak. Too long and the overall length will be large.
[0035]
It is more preferable to satisfy the following conditional expression.
[0036]
-3.5 <f_2-3/F<-0.8 (2-1)
More preferably, the following conditional expression should be satisfied.
[0037]
−2.0 <f_2-3/F<-0.9 (2-2)
Further, in order to form a telephoto type, it is preferable that the first positive lens of the two positive lenses has stronger positive power. Therefore, it is preferable to satisfy the following conditional expression.
[0038]
0.1 <f₁/ F₃<0.7 ... (3)
Where f₁Is the focal length of the first positive lens, f₃Is the focal length of the third positive lens.
[0039]
If the upper limit of 0.7 to condition (3) is exceeded, the telephoto effect will be reduced and the overall length will be increased, or the power of the second negative lens and the third positive lens will be too strong, leading to coma and astigmatism. Getting worse. If the lower limit of 0.1 is exceeded, the telephoto effect becomes too strong and the amount of aberration generated in the first positive lens becomes large, or the power of the third positive lens becomes too weak and generated in the second negative lens. The chromatic aberration of magnification and distortion cannot be corrected.
[0040]
It is more preferable to satisfy the following conditional expression.
[0041]
0.2 <f₁/ F₃<0.58 (3-1)
Further, the degree of influence of the telephoto effect varies depending on the configuration of the second negative lens and the third positive lens having negative combined power. Further, since the second negative lens and the third positive lens are arranged far from the aperture stop and the off-axis ray height is high, the occurrence of chromatic aberration of magnification and distortion tends to increase. Therefore, it is preferable to satisfy the following conditional expression.
[0042]
−0.6 <f₂/ F₃<-0.1 (4)
Where f₂Is the focal length of the second negative lens, f₃Is the focal length of the third positive lens.
[0043]
If the upper limit of -0.1 of this conditional expression (4) is exceeded, the power of the second negative lens becomes weak or the power of the third positive lens becomes too strong, so that the telephoto effect is reduced and the total length is increased. Become. If the lower limit of -0.6 is exceeded, the power of the second negative lens becomes strong or the power of the third positive lens becomes weak, and the chromatic aberration of magnification and distortion cannot be balanced, resulting in poor performance.
[0044]
It is more preferable to satisfy the following conditional expression.
[0045]
−0.5 <f₂/ F₃<-0.15 (4-1)
The use of a glass having a high refractive index improves the performance, but increases the cost. Therefore, it is preferable to satisfy the following conditional expression.
[0046]
1.45 <n_avg<1.70 (5)
Where n_avgIs the average value of the d-line refractive indices of the first positive lens to the third positive lens.
[0047]
If the upper limit of 1.70 of conditional expression (5) is exceeded, low cost cannot be achieved, and if the lower limit of 1.45 is exceeded, the amount of aberration generation of each lens becomes too large and the performance deteriorates.
[0048]
It is more preferable to satisfy the following conditional expression.
[0049]
1.5 <n_avg<1.65 (5-1)
Further, since the first positive lens is closest to the stop, the light flux from the center to the periphery passes substantially through the same area of the lens. That is, if the aberration of this surface is not properly corrected, it may not be possible to correct the aberration by the second negative lens and the third positive lens, and the performance of the entire screen, in particular, the coma and astigmatism are degraded. Resulting in. Therefore, it is preferable to satisfy the following conditional expression.
[0050]
1.0 <(r_1f+ R_1r) / (R_1f-R_1r) <1.7 (6)
Where r_1fIs the object-side paraxial radius of curvature of the first positive lens, r_1rIs the image-side paraxial radius of curvature of the first positive lens.
[0051]
If the upper limit of 1.7 to condition (6) is exceeded, the power of the image-side surface of the first positive lens will be relatively too strong, and in particular, spherical aberration and coma will worsen. If the value exceeds 1.0, the power of the object-side surface of the first positive lens becomes relatively too weak, and off-axis aberrations, particularly astigmatism and coma aberration, deteriorate.
[0052]
It is more preferable to satisfy the following conditional expression.
[0053]
1.1 <(r_1f+ R_1r) / (R_1f-R_1r) <1.6 (6-1)
Further, in order to achieve a telephoto effect in order to reduce the overall length, the first positive lens requires a strong positive power. Therefore, when at least one surface of the first positive lens is formed of an aspheric surface, aberration can be favorably corrected. Therefore, it is desirable to satisfy the following conditional expression.
[0054]
0.01 <| (r_1s+ R_1a) / (R_1s-R_1a) -1 | <100 (7)
Where r_1sIs the paraxial radius of curvature of the aspheric surface of the first positive lens, r_1aIs the radius of curvature r of the first positive lens in consideration of the aspheric surface defined below._ASPAre the values when the difference from the paraxial radius of curvature changes the most within the optically effective range in.
[0055]
Here, the radius of curvature r considering the aspherical surface_ASPIs defined as f (y), where f (y) is an aspheric definition equation (a function of the shape when the optical axis traveling direction is positive from the tangent plane tangent to the surface vertex). same as below.
[0056]
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).
[0057]
If the upper limit of 100 of the conditional expression (7) is exceeded, the aspherical effect becomes too weak, resulting in insufficient correction, and coma and astigmatism deteriorate. The aspherical effect becomes too strong, resulting in overcorrection, deteriorating performance and making lens processing difficult.
[0058]
It is more preferable to satisfy the following conditional expression.
[0059]
0.05 <| (r_1s+ R_1a) / (R_1s-R_1a) -1 | <10 (7-1)
More preferably, the following conditional expression should be satisfied.
[0060]
0.1 <| (r_1s+ R_1a) / (R_1s-R_1a) -1 | <5 (7-2)
More preferably, the following conditional expression should be satisfied.
[0061]
0.1 <| (r_1s+ R_1a) / (R_1s-R_1a) -1 | <3 (7-3)
Further, in order to produce a telephoto effect in order to reduce the overall length, the second negative lens needs a strong negative power. When at least one surface of the second negative lens is formed of an aspherical surface, aberration can be favorably corrected, and it is desirable that the following conditional expression is satisfied.
[0062]
0.01 <| (r_2s+ R_2a) / (R_2s-R_2a) -1 | <100 (8)
Where r_2sIs the paraxial radius of curvature of the aspheric surface of the second negative lens, r_2aIs the radius of curvature r of the second negative lens taking into account the aspheric surface defined above._ASPAre the values when the difference from the paraxial radius of curvature changes the most within the optically effective range in.
[0063]
If the upper limit of 100 of conditional expression (8) is exceeded, the aspherical effect will be too weak, resulting in insufficient correction, and coma and astigmatism will deteriorate. The aspherical effect becomes too strong, resulting in excessive correction, deteriorating the performance and making the lens processing difficult.
[0064]
It is more preferable to satisfy the following conditional expression.
[0065]
0.1 <| (r_2s+ R_2a) / (R_2s-R_2a) -1 | <5 (8-1)
Also, when a CCD is used as an image sensor, if an off-axis light beam emitted from the imaging optical system enters the image plane at an excessively large angle, the brightness of the image changes at the central portion and the peripheral portion of the image. I will. On the other hand, if the light is incident at a small angle with respect to the image plane, this problem is reduced, but the overall length of the optical system is increased. Therefore, it is preferable to satisfy the following conditional expression.
[0066]
10 ° <α <40 ° (9)
Here, α is the angle of incidence of the principal ray on the image plane at the maximum image height.
[0067]
Exceeding the upper limit of 40 ° in this conditional expression will result in an excessively large incident angle to the CCD, resulting in reduced brightness at the periphery of the image, and exceeding the lower limit of 10 will result in an excessively large overall length.
[0068]
It is more preferable to satisfy the following conditional expression.
[0069]
15 ° <α <35 ° (9-1)
More preferably, the following conditional expression should be satisfied.
[0070]
17.5 ° <α <25 ° (9-2)
The present invention includes an image pickup apparatus having the above-described image forming optical system of the present invention and an image pickup device arranged on the image side thereof.
[0071]
Further, the first image pickup apparatus of the present invention includes, in order from the object side, a brightness stop, a first positive lens having a convex surface facing the image side, a second negative lens having a concave surface facing the image side, and a third positive lens. An imaging optical system arranged, and an imaging element arranged on the image side thereof, the aperture stop has a fixed aperture shape through which the optical axis passes, and the outer peripheral surface of the aperture is It is characterized in that it is inclined at an inclination angle equal to or greater than the incident angle of the most off-axis light beam so that it approaches the optical axis toward the image plane.
[0072]
Explaining the operation of this configuration, when light reflected on the peripheral surface of the aperture stop enters the image forming optical system, phenomena such as ghost and flare are likely to occur. In particular, as in the present invention, in a small imaging optical system in which the aperture stop, the first positive lens, the second negative lens, and the third positive lens are arranged in this order from the object side, the imaging surface of the imaging element is also small. Therefore, the influence of light reflected on the outer peripheral surface of the aperture stop becomes relatively large.
[0073]
Therefore, in the present invention, by utilizing the fact that the aperture stop is disposed closest to the object side, the incident of the most off-axis light flux is performed so that the outer peripheral surface of the aperture of the aperture stop is closer to the optical axis toward the image plane side. It has a fixed shape inclining at an angle greater than the angle.
[0074]
With such a configuration, it is difficult for the light beam reflected on the outer peripheral surface of the opening to enter the image pickup device, and it is possible to reduce the influence of flare and ghost.
[0075]
Further, the second imaging device of the present invention includes, in order from the object side, a brightness stop, a first positive lens having a convex surface facing the image side, a second negative lens having a concave surface facing the image side, and a third positive lens. A lens frame having an imaging optical system arranged therein, and an imaging device arranged on the image side thereof, holding the imaging optical system and the imaging device, and integrally forming the aperture stop with the same resin material; It is characterized by having.
[0076]
To explain the operation of this configuration, the optical system of the present invention has a configuration in which the aperture stop is located closest to the object side. Become. Therefore, since the lens frame holding these lenses is integrally formed of the same resin that is easy to form, the lens can be positioned by inserting the lens from the image plane side of the frame, thereby facilitating the manufacture.
[0077]
At that time, the structure of the aperture stop is integrated into the lens frame, greatly reducing the manufacturing process, and providing the lens frame itself with the function of holding the image pickup device, so that dust can enter the frame. It is possible to make the configuration hard to enter.
[0078]
Further, the third imaging device of the present invention includes, in order from the object side, a brightness stop, a first positive lens having a convex surface facing the image side, a second negative lens having a concave surface facing the image side, and a third positive lens. An imaging optical system arranged, and an image sensor arranged on the image side thereof, comprising a lens frame for holding the imaging optical system, at least each of the first positive lens and the third positive lens An inclined portion is provided on the outer periphery so as to be closer to the optical axis toward the object side, and the inclined portion is in contact with the lens frame.
[0079]
To explain the operation of this configuration, the optical system of the present invention has a configuration in which the aperture stop is located closest to the object side. Become. This is particularly noticeable with the first positive lens and the third positive lens. Therefore, the above configuration results in a lens outer shape along the off-axis light beam, miniaturization while suppressing vignetting, and lens positioning by inserting the lens from the image plane side of the frame, facilitating manufacture. .
[0080]
Further, an inclined portion may be provided on the outer periphery of all the lenses so as to be closer to the optical axis toward the object side, and the inclined portion may contact the lens frame.
[0081]
Further, the fourth imaging apparatus of the present invention includes, in order from the object side, a brightness stop, a first positive lens having a convex surface facing the image side, a second negative lens having a concave surface facing the image side, and a third positive lens. An imaging optical system arranged, and an imaging element arranged on the image side thereof, comprising a lens frame for holding the imaging optical system, wherein the shape of the first positive lens is viewed from the incident side The third positive lens has a shape whose length in the direction corresponding to the short side direction of the effective imaging region of the imaging element when viewed from the incident side corresponds to the long side direction of the effective imaging region. It is characterized by being shorter than this.
[0082]
To explain the operation of this configuration, the optical system of the present invention has a configuration in which the aperture stop is located closest to the object side. Become. Further, the effective light flux approaches the shape of the effective image pickup area of the image pickup element closer to the image plane. Therefore, with the above-described configuration, the outer shape of the lens follows the effective light beam, and the size can be reduced while suppressing vignetting.
[0083]
Note that, in common with each of the above conditional expressions, only the upper limit value or the lower limit value of the lower conditional expression that further limits each conditional expression range is limited as the upper limit value or the lower limit value of the upper conditional expression. It may be.
[0084]
The effects of the present invention can be further enhanced by combining a plurality of the above conditional expressions arbitrarily.
[0085]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, Examples 1 to 5 of the imaging optical system of the present invention will be described. FIGS. 1 to 5 show lens cross-sectional views of Examples 1 to 5 when focused on an object point at infinity. In the drawing, the aperture stop is denoted by S, the first positive lens is denoted by L1, the second negative lens is denoted by L2, the third positive lens is denoted by L3, the cover glass of the electronic image sensor is denoted by CG, and the image plane is denoted by I. Note that a multilayer film for limiting a wavelength range may be provided on the surface of the cover glass CG. Further, the cover glass CG may have a low-pass filter function.
[0086]
As shown in FIG. 1, the image forming optical system according to the first embodiment includes, in order from the object side, a brightness stop S, a first positive meniscus lens L1 having a double-sided aspheric surface with a convex surface facing the image side, and a biconcave double-sided non-magnifying lens. It comprises a spherical second negative lens L2, a biconvex third aspherical positive lens L3 on both sides, 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-based Zeonex (trade name), and the second lens L2 is made of polycarbonate. I have.
[0087]
The specifications of the present embodiment are a wide-angle optical system having a focal length f = 3.3 mm, an image height 2.4 mm, and a half angle of view ω = 36 °. The optical effective diameter (one side) of each lens is the second surface r₂~ 7th surface r₇In order of 0.647 mm, 0.969 mm, 1.146 mm, 1.241 mm, 1.662 mm, and 1.920 mm.
[0088]
As shown in FIG. 2, the imaging optical system according to the second embodiment includes, in order from the object side, a brightness stop S, a first positive meniscus lens L1 having a double-sided aspheric surface with a convex surface facing the image side, and a convex surface facing the object side. It comprises a second negative meniscus lens L2 having a double-sided aspheric surface, a third positive lens L3 having a biconvex double-sided aspheric surface, and a cover glass CG. In this embodiment, the first lens L1 and 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-based Zeonex.
[0089]
The specifications of this embodiment are a wide-angle optical system having a focal length f = 3.3 mm, an image height 2.4 mm, and a half angle of view ω = 36 °. The optical effective diameter (one side) of each lens is the second surface r₂~ 7th surface r₇In order of 0.656 mm, 1.142 mm, 1.277 mm, 1.344 mm, 1.527 mm, 1.776 mm.
[0090]
As shown in FIG. 3, the image forming optical system according to the third embodiment includes, in order from the object side, a brightness stop S, a first positive meniscus lens L1 having a double-sided aspheric surface with a convex surface facing the image side, It comprises a second negative lens L2 having a spherical surface, a third positive lens 13 having a biconvex double-sided aspheric surface, and a cover glass CG. In this embodiment, the first lens L1 is made of plastic, the second lens L2 and the third lens L3 are made of glass, and the first lens L1 is made of amorphous polyolefin-based Zeonex.
[0091]
The specifications of the present embodiment are a wide-angle optical system having a focal length f = 3.3 mm, an image height 2.4 mm, and a half angle of view ω = 36 °. The optical effective diameter (one side) of each lens is the second surface r₂~ 7th surface r₇In order of 0.674 mm, 1.201 mm, 1.384 mm, 1.692 mm, 1.652 mm, and 1.801 mm.
[0092]
As shown in FIG. 4, the imaging optical system according to the fourth embodiment includes, in order from the object side, a brightness stop S, a first positive meniscus lens L1 having a double-sided aspheric surface with a convex surface facing the image side, and a convex surface facing the object side. It comprises a second negative meniscus lens L2 having a double-sided aspheric surface, a third positive lens L3 having a double-sided aspheric surface with a convex surface facing the image side, 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-based Zeonex, and the second lens L2 is made of polycarbonate.
[0093]
The specifications of the present embodiment are a wide-angle optical system having a focal length f = 3.3 mm, an image height 2.4 mm, and a half angle of view ω = 36 °. The optical effective diameter (one side) of each lens is the second surface r₂~ 7th surface r₇In order of 0.651 mm, 1.109 mm, 1.330 mm, 1.439 mm, 1.445 mm, and 1.717 mm.
[0094]
As shown in FIG. 5, the image forming optical system according to the fifth embodiment includes, in order from the object side, a brightness stop S, a first positive meniscus lens L1 having a double-sided aspheric surface with a convex surface facing the image side, and a convex surface facing the object side. It comprises a second negative meniscus lens L2 having a double-sided aspheric surface, a third positive meniscus lens L3 having a double-sided aspheric surface convex to the object side, and a cover glass CG. In this embodiment, the first lens L1 and 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-based Zeonex.
[0095]
The specifications of the present embodiment are a wide-angle optical system having a focal length f = 3.3 mm, an image height 2.4 mm, and a half angle of view ω = 36 °. The optical effective diameter (one side) of each lens is the second surface r₂~ 7th surface r₇In order of 0.630 mm, 0.942 mm, 1.245 mm, 1.202 mm, 1.350 mm, and 1.599 mm.
[0096]
The numerical data of each of the above embodiments is shown below.₁, 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 d-line refractive index of each lens, ν_d1, Ν_d2... is the Abbe number of each lens. The aspherical shape is represented by the following equation, where x is an optical axis where the traveling direction of light is positive, and y is a direction orthogonal to the optical axis.
[0097]
x = (y²/ R) / [1+ ｛1- (K + 1) (y / r)²｝^1/2]
+ A₄y⁴+ A₆y⁶+ A₈y⁸+ A₁₀y¹⁰
Here, r is the radius of curvature on the optical axis, K is the conic coefficient, A₄, A₆, A₈, A₁₀Are the fourth, sixth, eighth and tenth order aspherical coefficients, respectively.
[0098]

[0099]

[0100]

[0101]

[0102]

[0103]
6 to 10 show aberration diagrams of Examples 1 to 5 when focusing is performed at infinity. In these aberration diagrams, “SA” indicates spherical aberration, “AS” indicates astigmatism, “DT” indicates distortion, and “CC” indicates chromatic aberration of magnification. In each aberration diagram, “ω” indicates a half angle of view.
[0104]
Next, the values of the conditions (1) to (13) in the above embodiments are shown.
[0105]

(Note) The numerical values of the conditional expressions (7) and (8) are the numerical values of the surface on the object side at the top, and the numerical values of the surface on the image side at the bottom.
[0106]
Although each of the above embodiments is small, good images are obtained as shown in the aberration diagrams of FIGS.
[0107]
In the above embodiment of the present invention, a cover glass may be arranged immediately before the aperture stop S.
[0108]
In the above embodiments of the present invention, the lens made of plastic may be made of glass. For example, it goes without saying that higher performance can be achieved by using 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 using a plastic, it is preferable to use a low moisture-absorbing material since performance deterioration due to environmental changes is reduced (for example, ZEONEX (trade name) of Zeon Corporation).
[0109]
In addition, a flare stop other than the brightness stop S may be disposed in order to cut unnecessary light such as ghost and flare. In the above-described embodiment, any one between the aperture 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 between the third lens L3 and the image plane I. A flare stop may be arranged at the location. Further, a flare light beam may be cut by a frame, or a flare stop may be formed by using another member. Further, it may be printed directly on the optical system, painted, or adhered with a seal or the like. Further, the shape may be any shape such as a circle, an ellipse, a rectangle, a polygon, and a range surrounded by a function curve. Further, in addition to cutting harmful light beams, light beams such as coma flare around the screen may be cut.
[0110]
Further, an antireflection coating may be applied to each lens to reduce ghosts and flares. A multi-coat is desirable because ghosts and flares can be effectively reduced. Further, an infrared cut coat may be applied to a lens surface, a cover glass, or the like.
[0111]
In addition, focusing may be performed to perform focus adjustment. Focusing may be performed by extending the entire lens system, or a part of the lens may be extended, or focusing may be performed by being retracted.
[0112]
Further, the decrease in brightness at the periphery 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 reduction amount of the peripheral portion of the image may be corrected by image processing.
[0113]
FIG. 11 shows the light of the imaging optical system 5 in the configuration example in which the imaging optical system 5 of the first embodiment and the CCD 6 arranged on the image plane I are fixed to a lens frame 7 integrally formed of a resin material. FIG. 3 is a sectional view including an axis and taken in a diagonal direction of an image plane I of the CCD 6, and a brightness stop S is integrally formed with a lens frame 7 made of resin. This makes it easy to manufacture the lens frame 7 that holds the imaging optical system 5. In addition, by integrating the configuration of the aperture stop S into the lens frame 7, the manufacturing process is greatly reduced, and by providing the lens frame 7 itself with a function of holding the CCD 6 of the imaging device, It becomes difficult for garbage and the like to enter into the area 7.
[0114]
Also, as is apparent from FIG. 11, the outer periphery 8 of each of the first positive lens L1, the second negative lens L2, and the third positive lens L3 of the imaging optical system 5 is inclined so that the closer to the object, the closer to the optical axis. By providing the inclined surface and fixing the inclined surface to the lens frame 7, the lenses L <b> 1 to L <b> 3 can be dropped and positioned and fixed to the lens frame 7 from the image plane side.
[0115]
As shown in a schematic exploded perspective view of FIG. 12, the shape of the first positive lens L1 of the imaging optical system held in the lens frame 7 formed of plastic is a first positive lens L1 and a second negative lens L1. The lens L2 has a circular shape as viewed from the incident side, and the third positive lens L3 has an oval shape obtained by cutting the upper and lower portions based on a circular lens. The outer periphery 8 of each of the lenses L1 to L3 is inclined toward the stop S. The inner surface of the lens frame 7 is also formed to be inclined corresponding to the inclination.
[0116]
Thus, the shape of the first positive lens L1 is circular when viewed from the incident side, and the shape of the third positive lens L3 is the direction corresponding to the short side direction of the effective imaging area of the CCD 6 of the image sensor when viewed from the incident side. Is shorter than the length corresponding to the long side direction of the effective imaging area, so that the first positive lens L1, the second negative lens L2, and the third positive lens L3 of the imaging optical system are effective. The outer shape of the lens can be made along the light beam, and the size can be reduced while suppressing vignetting. Also in this example, the inclined surfaces of the outer peripheries 8 of the first positive lens L1, the second negative lens L2, and the third positive lens L3 of the imaging optical system 5 are abutted and fixed in the lens frame 7. By doing so, the lenses L1 to L3 can be dropped and positioned and fixed in the lens frame 7 from the image plane side.
[0117]
It is desirable that the peripheral surface of the aperture of the aperture stop S be inclined toward the lens L1 as shown in the sectional view of FIG. Also, the angle of inclination is large, so that the corner most on the lens side substantially serves as a stop, so that the light flux reflected on the outer peripheral surface of the opening of the brightness stop S is less likely to enter the CCD 6 of the image sensor. Thus, the effects of flare and ghost can be reduced.
[0118]
By the way, in each of the above embodiments, a near-infrared sharp cut coat may be applied to the incident surface side of the cover glass CG as described above. The near-infrared sharp cut coat is configured so that the transmittance at a wavelength of 600 nm is 80% or more and the transmittance at a wavelength of 700 nm is 10% or less. Specifically, for example, it is a multilayer film having the following 27 layers. However, the design wavelength is 780 nm.
[0119]
Substrate material Physical thickness (nm) λ / 4
───────────────────────────────
First layer Al₂O₃    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
Fifth 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.
[0120]
The transmittance characteristics of the near-infrared sharp cut coat are as shown in FIG.
[0121]
In addition, a color filter for reducing transmission of colors in a short wavelength range as shown in FIG. 14 or coating is provided on the emission surface side of the low-pass filter to further enhance color reproducibility of an electronic image. I have.
[0122]
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 the ratio of the transmittance of 400 nm to the transmittance of the highest wavelength is not less than 15%. Is preferably 6% or less.
[0123]
As a result, it is possible to reduce the difference between the recognition of the color of the human eye and the color of the captured and reproduced image. In other words, it is possible to prevent the deterioration of the image due to the color on the short wavelength side which is hardly recognized by human eyes to be easily recognized by human eyes.
[0124]
If the ratio of the transmittance at the wavelength of 400 nm exceeds 6%, the short-wavelength castle which is hardly recognized by human eyes is reproduced to a wavelength recognizable, and conversely, the ratio of the transmittance at the wavelength of 420 nm is changed. Is less than 15%, the reproduction of the wavelength castle recognizable by humans is low, and the color balance is poor.
[0125]
Such a means for limiting the wavelength is more effective in an imaging system using a complementary color mosaic filter.
[0126]
In each of the above embodiments, as shown in FIG. 14, the coating is such that the transmittance at a wavelength of 400 nm is 0%, the transmittance at 420 nm is 90%, and the transmittance peak is 100% at 440 nm.
[0127]
By multiplying the action with the near-infrared sharp cut coat described above, the transmittance at a wavelength of 450 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%. , 700 nm is 2%. As a result, more faithful color reproduction is performed.
[0128]
The low-pass filter can use three types of filters having crystal axes in the directions of horizontal (= 0 °) and ± 45 ° in the direction of the optical axis when projected on the image plane. Is shifted horizontally by SQRT (1/2) × a in the a.mu.m and. +-. 45.degree. Directions, thereby suppressing moiré. Here, SQRT is a square route and means a square root.
[0129]
As shown in FIG. 15, a complementary color mosaic filter in which four color filters of cyan, magenta, yellow, and green (green) are provided in a mosaic shape corresponding to the imaging pixels is provided on the imaging surface I of the CCD. ing. These four types of color filters are arranged in a mosaic so that each has substantially the same number and adjacent pixels do not correspond to the same type of color filters. This enables more faithful color reproduction.
[0130]
The complementary color mosaic filter is specifically composed of at least four types of color filters as shown in FIG. 15, and the characteristics of the four types of color filters are preferably as follows.
[0131]
Green color filter G is wavelength G_PHas a spectral intensity peak at
Yellow color filter Y_eIs the wavelength Y_PHas a spectral intensity peak at
Cyan color filter C has wavelength C_PHas a spectral intensity peak at
Magenta color filter M has wavelength M_P1And M_P2And the following conditions are satisfied.
[0132]
510 nm <G_P<540 nm
5 nm <Y_P-G_P<35 nm
-100 nm <C_P-G_P<-5 nm
430 nm <M_P1<480 nm
580 nm <M_P2<640 nm
Further, the green, yellow, and cyan color filters have an intensity of 80% or more at a wavelength of 530 nm with respect to their respective spectral intensity peaks, and the magenta color filter has an intensity of 10% at a wavelength of 530 nm with respect to their spectral intensity peaks. From 50 to 50% is more preferable for enhancing color reproducibility.
[0133]
FIG. 16 shows an example of each wavelength characteristic in each of the above embodiments. The green color filter G has a beak of spectral intensity at 525 nm. Yellow color filter Y_eHas a peak of spectral intensity at 555 nm. The cyan color filter C has a peak of the spectral intensity at 510 nm. The magenta color filter M has peaks at 445 nm and 620 nm. In each color filter at 530 nm, G is 99% and Y is Y with respect to the peak of each spectral intensity._eIs 95%, C is 97%, and M is 38%.
[0134]
In the case of such a complementary color filter, a controller (not shown) (or a controller used for a digital camera) electrically performs the following signal processing,
Luminance signal
Y = | G + M + Y_e+ C | × 1/4
Color signal
R−Y = | (M + Y_e)-(G + C) |
BY = | (M + C)-(G + Y_e) ｜
Are converted into R (red), G (green), and B (blue) signals.
[0135]
By the way, the arrangement position of the near-infrared sharp cut coat may be any position on the optical path. Also, the number of low-pass filters may be two or one.
[0136]
In the image pickup apparatus of the present invention, for adjusting the light amount, the aperture stop S may be composed of a plurality of aperture blades, and a variable aperture that is adjusted by making the aperture shape variable may be used. FIG. 17 is an explanatory diagram showing an example of the aperture shape at the time of opening, and FIG. 18 is an explanatory diagram showing an example of the aperture shape at the time of two-stage aperture. 17 and 18, OP indicates an optical axis, Da indicates six aperture plates, and Xa and Xb indicate openings. In the present invention, the aperture shape of the aperture can be only two types: an open state (FIG. 17), and an aperture value (two-step aperture, FIG. 18) which is an F value satisfying a predetermined condition.
[0137]
Or, using a turret provided with a plurality of shape-fixed brightness apertures having different shapes or transmittances, depending on the required brightness, place any brightness aperture on the object-side optical axis of the imaging optical system. With this arrangement, the aperture mechanism can be made thinner. Also, a configuration may be adopted in which a light amount reduction filter having a transmittance lower than the transmittance of the other brightness stops is arranged in the opening that reduces the light amount among the openings of the plurality of brightness stops arranged on the turret. Good. As a result, the aperture diameter of the stop is not excessively reduced, and deterioration of the imaging performance due to diffraction caused by the small aperture diameter of the stop can be suppressed.
[0138]
FIG. 19 is a perspective view showing a configuration of an example in this case. 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, it is possible to adjust the brightness of 0, -1, 2, -3, -4 steps. A turret 10 is arranged.
[0139]
The turret 10 has an opening 1A (a transmittance of 100% for a wavelength of 550 nm) having a circular shape with a maximum aperture diameter and a fixed space, and an opening 1A for correcting by -1 step. An opening 1B made of a transparent parallel flat plate having an opening area of about half of the area and having a fixed opening shape (the transmittance for a wavelength of 550 nm is 99%), a circular opening having the same area as the opening 1B, and -2 steps , -3 steps, and -4 steps are provided with openings 1C, 1D, and 1E provided with ND filters having transmittances of 50%, 25%, and 13% for a wavelength of 550 nm, respectively.
[0140]
Then, the light amount is adjusted by arranging one of the openings at the stop position by turning around the rotation shaft 11 provided on the turret 10.
[0141]
Further, instead of the turret 10 shown in FIG. 19, a turret 10 'shown in the front view of FIG. 20 can be used. 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, it is possible to adjust the brightness of 0, -1, 2, -3, -4 steps. A turret 10 'is arranged.
[0142]
The turret 10 'has an opening 1A' in which the shape of the opening for zero-step adjustment is circular and has the maximum aperture diameter, and an opening area which is about half the opening area of the opening 1A 'in order to perform -1 step correction. An opening 1B 'having a fixed opening shape, and openings 1C', 1D ', and 1E' having fixed shapes for correcting the opening area in order of -2, -3, and -4 steps. Have.
[0143]
Then, the light amount is adjusted by arranging one of the apertures at the stop position by rotating the rotary shaft 11 provided on the turret 10 '.
[0144]
In order to further reduce the thickness, the aperture of the aperture stop S may be a fixed stop in both shape and position, and the light amount adjustment may be performed by electrically adjusting the output signal from the image sensor. Further, the light amount may be adjusted by extracting and inserting an ND filter between other spaces of the lens system, for example, between the third positive lens L3 and the CCD cover glass CG. FIG. 21 is a view showing an example of the turret. The opening 1A "of the turret 10" is a transparent surface or a hollow opening, the opening 1B "is an ND filter having a transmittance of 1/2, and the opening 1C" is a ND filter having a transmittance of 1/4. As the ND filter and the aperture 1D ″, a turret-shaped filter provided with an ND filter and the like having a transmittance of 1/8 is used, and one of the apertures is arranged at any position in the optical path by rotating around a central rotation axis. By doing so, the light amount is adjusted.
[0145]
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. 22, the amount of light is concentrically adjusted so as to make the transmittance uniform for a dark subject with priority given to securing the amount of light at the center, and to compensate for uneven brightness only for a bright subject. It is good also as a structure which arrange | positions the filter which falls gradually.
[0146]
Further, the stop S may be one in which the peripheral portion on the incident surface side of the first positive lens L1 is painted black.
[0147]
Further, when the imaging apparatus according to the present invention is to store a video as a still image like a camera or the like, a shutter for adjusting the amount of light may be arranged in the optical path.
[0148]
Such a shutter may be a focal plane shutter, a rotary shutter, a liquid crystal shutter disposed immediately before the CCD, or the aperture stop itself may be configured as a shutter.
[0149]
FIG. 23 shows an example of the shutter. FIG. 23 shows an example of a rotary focal plane shutter which is one of the focal plane shutters. FIG. 23 (a) is a view from the back side, and FIG. 23 (b) is a view from the front side. is there. Reference numeral 15 denotes a shutter substrate, which is arranged immediately before the image plane or at an arbitrary optical path position. The substrate 15 is provided with an opening 16 for transmitting an effective light beam of the optical system. 17 is a rotary shutter curtain. Reference numeral 18 denotes a rotation axis of the rotary shutter curtain 17. The rotation axis 18 rotates with respect to the substrate 15 and is integrated with the rotary shutter curtain 17. The rotation 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).
[0150]
In such a configuration, the rotary shutter curtain 17 is configured to rotate around the rotation shaft 18 by driving a motor (not shown) via the gears 19 and 20 and the rotation shaft 18.
[0151]
The rotary shutter curtain 17 is formed in a substantially semicircular shape, and shields and retracts the opening 16 of the substrate 15 by rotation, and plays a role of a shutter. The shutter speed is adjusted by changing the rotating speed of the rotary shutter curtain 17.
[0152]
FIGS. 24A to 24D are views showing how the rotary shutter curtain 17 rotates as viewed from the image plane side. It moves in the order of (a), (b), (c), (d), and (a) in the figure with time.
[0153]
As described above, by arranging the aperture stop S having a fixed shape and the filter or shutter for adjusting the light amount at different positions of the lens system, the light amount is adjusted by the filter and the shutter while suppressing the effect of diffraction and maintaining high image quality. And an image pickup apparatus capable of shortening the overall length of the lens system can be obtained.
[0154]
Further, a configuration may be employed in which a part of the electric signal of the CCD is taken out and an electric control is performed to obtain a still image without using a mechanical shutter. An example of such a configuration will be described with reference to FIGS. 25 and 26 while explaining the operation of CCD imaging. FIG. 25 is a view for explaining the operation of CCD imaging in which signals are sequentially read out in an interlace system (interlaced scanning system). In FIG. 25, Pa to Pc are photosensitive sections using photodiodes, Va to Vc are vertical transfer sections using CCDs, and Ha is a horizontal transfer section using CCDs. The A field indicates an odd field, and the B field indicates an even field.
[0155]
In the configuration of FIG. 25, the basic operation is performed as follows. That is, (1) accumulation of signal charges by light in the photosensitive section (photoelectric conversion), (2) shift of signal charges from the photosensitive section to the vertical transfer section (field shift), and (3) signal charge in the vertical transfer section. Transfer (vertical transfer), (4) transfer of signal charge from vertical transfer unit to horizontal transfer unit (line shift), (5) transfer of signal charge in horizontal transfer unit (horizontal transfer), (6) horizontal transfer unit Detection (detection) of signal charge at the output terminal of Such sequential reading can be performed using one of the A field (odd field) and the B field (even field).
[0156]
In the interlaced (interlaced scanning) CCD imaging in FIG. 25, the storage timing of the A field and the storage field of the B field are shifted by 1/60 in the TV broadcasting system and the analog video system. If this is used as it is as a DSC (Digital Spectrum Compatible) image to form a frame image, a moving subject will be blurred like a double image. Therefore, in this type of CCD imaging, the A and B fields are simultaneously exposed to mix signals of adjacent fields. Then, after the exposure is completed by a mechanical shutter at the end of the exposure, the A field and the B field are separately read out and a signal is synthesized.
[0157]
In the present invention, the vertical resolution is reduced by sequentially reading out only the A field or simultaneously reading out the A and B fields by setting the role of the mechanical shutter only to prevent smearing. High-speed shutter can be released without being affected by the driving speed of the shutter (because it can be controlled only by the electronic shutter). In the example of FIG. 25, since the number of CCDs in the vertical transfer unit is half of the number of photodiodes forming the photosensitive unit, there is an advantage that the size can be easily reduced.
[0158]
FIG. 26 is an explanatory diagram of CCD imaging operation in which signals are sequentially read in a progressive manner. In FIG. 26, Pd to Pf are photosensitive sections using photodiodes, Vd to Vf are vertical transfer sections using CCDs, and Hb is a horizontal transfer section using CCDs.
[0159]
In FIG. 26, since the pixels can be read out in the arrangement order of the pixels, it is possible to electronically control all the charge storage and readout operations. Therefore, the exposure time can be shortened to about (1 / 10,000 seconds). In the example of FIG. 26, there are disadvantages that the number of vertical CCDs is larger and the miniaturization is difficult than in the case of FIG. 25. However, because of the advantages described above, in the present invention, FIGS. Any of the methods can be adopted.
[0160]
The above-described imaging apparatus according to the present invention is an imaging apparatus that forms an object image with an imaging optical system and receives the image by an imaging device such as a CCD to perform imaging, and in particular, a digital camera or a video camera, The present invention can be used for a personal computer or a telephone as an example of the apparatus, particularly a portable telephone which is easy to carry. Below, the embodiment is illustrated.
[0161]
FIG. 27 to FIG. 29 are conceptual diagrams of a configuration in which the imaging optical system according to the present invention is incorporated in a photographing optical system 41 of a digital camera. 27 is a front perspective view showing the appearance of the digital camera 40, FIG. 28 is a rear perspective view of the same, and FIG. 29 is a sectional view showing the configuration of the digital camera 40. In this case, 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 at the position is depressed, the photographing is performed through the photographing optical system 41, for example, the image forming optical system of the first embodiment in conjunction therewith. The object image formed by the photographing optical system 41 is formed on the imaging surface of the CCD 49 via 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 a liquid crystal display monitor 47 provided on the back of the camera via the processing means 51. Further, a recording means 52 is connected to the processing means 51 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 record and write electronically using a floppy disk, a memory card, an MO, or the like. Further, the camera may be configured as a silver halide camera in which a silver halide film is arranged instead of the CCD 49.
[0162]
Further, a finder objective optical system 53 is arranged on the finder optical path 44. An object image formed by the finder objective optical system 53 is formed on a field frame 57 of a Porro prism 55 which is an image erecting member. Behind the polyprism 55, an eyepiece optical system 59 for guiding the erect image to the observer's eyeball E is arranged. Note that cover members 50 are arranged on the entrance 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.
[0163]
In the digital camera 40 configured as described above, since the imaging optical system 41 is high-performance and small, high performance and small size can be realized.
[0164]
In the example of FIG. 29, a parallel flat plate is arranged as the cover member 50, but a lens having power may be used.
[0165]
Next, a personal computer as 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. 30 is a front perspective view of the personal computer 300 with the cover opened, FIG. 31 is a cross-sectional view of the photographing optical system 303 of the personal computer 300, and FIG. 32 is a side view of the state of FIG. As shown in FIGS. 30 to 32, the personal computer 300 includes a keyboard 301 for the processor to input information from the outside, information processing means and recording means (not shown), and a monitor for displaying information to the operator. The image processing apparatus includes an image capturing system 302 and an image capturing optical system 303 for capturing an image of the operator or a surrounding image. Here, the monitor 302 may be a transmissive liquid crystal display element that illuminates from the back with a backlight (not shown), a reflective liquid crystal display element that reflects and displays light from the front, a CRT display, or the like. Although the photographing optical system 303 is built in the upper right corner of the monitor 302 in the figure, the photographing optical system 303 is not limited to this location, and may be anywhere around the monitor 302 or around the keyboard 301.
[0166]
The photographing optical system 303 includes, on a photographing optical path 304, an objective lens 112 including an image forming optical system (not shown in the drawing) according to the present invention, and an image sensor chip 162 that receives an image. These are built in the personal computer 300.
[0167]
Here, a cover glass CG having a low-pass filter function is additionally attached on the imaging element chip 162 to be integrally formed as the imaging unit 160, and the rear end of the lens frame 113 of the objective lens 112 is touched with one touch. Since it can be fitted and attached, the centering of the objective lens 112 and the image sensor chip 162 and the adjustment of the surface interval are not required, and the assembling is simplified. Further, a cover glass 114 for protecting the objective lens 112 is disposed at the tip of the lens frame 113.
[0168]
The object image received by the imaging element 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. A photographed image 305 is shown. Further, the image 305 can be displayed on a personal computer of a communication partner from a remote place via the processing means, the Internet or a telephone.
[0169]
Next, FIG. 33 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 easy to carry. 33A is a front view of the mobile phone 400, FIG. 33B is a side view, and FIG. 33C is a cross-sectional view of the photographing optical system 405. As shown in FIGS. 33A to 33C, the mobile phone 400 includes a microphone unit 401 for inputting the voice of the operator as information, a speaker unit 402 for outputting the voice of the other party, and information for the operator. An input dial 403, a monitor 404 for displaying a photographed image of the operator himself / herself and the other party and information such as a telephone number, a photographing optical system 405, an antenna 406 for transmitting and receiving communication radio waves, and an image A processing unit (not shown) for processing information, communication information, input signals, and the like. Here, the monitor 404 is a liquid crystal display element. In addition, in the drawings, the arrangement position of each component is not particularly limited to these. The imaging optical system 405 includes an objective lens 112 including an imaging optical system (abbreviated in the drawing) according to the present invention and an imaging element chip 162 that receives an object image. These are built into the mobile phone 400.
[0170]
Here, a cover glass CG having a low-pass filter function is additionally attached on the imaging element chip 162 to be integrally formed as the imaging unit 160, and the rear end of the lens frame 113 of the objective lens 112 is touched with one touch. Since it can be fitted and attached, the centering of the objective lens 112 and the image sensor chip 162 and the adjustment of the surface interval are not required, and the assembling is simplified. Further, a cover glass 114 for protecting the objective lens 112 is disposed at the tip of the lens frame 113.
[0171]
The object image received by the imaging element chip 162 is input to a processing unit (not shown) via a terminal 166, and is displayed as an electronic image on the monitor 404, a monitor of a communication partner, or both. . When transmitting an image to a communication partner, the processing unit includes a signal processing function of converting information of an object image received by the image sensor chip 162 into a transmittable signal.
[0172]
Each of the above embodiments can be variously modified in accordance with the configuration of the claims.
[0173]
In the present invention, the imaging optical system can be configured as follows.
[0174]
[1] A brightness stop, a first positive lens, a second negative lens, and a third positive lens are arranged in this order from the object side, and at least the first positive lens has an aspheric surface and satisfies the following conditional expression. An imaging optical system characterized by the above.
[0175]
−5.0 <f_2-3/F<-0.5 (2)
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.
[0176]
[2] A brightness stop, a first positive lens, a second negative lens, and a third positive lens are arranged in this order from the object side, and at least the second negative lens has an aspheric surface and satisfies the following conditional expression. An imaging optical system characterized by the above.
[0177]
−5.0 <f_2-3/F<-0.5 (2)
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.
[0178]
[3] A brightness stop, a first positive meniscus lens having a convex surface facing the image side, a second negative lens, and a third positive lens are arranged in this order from the object side, and satisfy the following conditional expression. Imaging optics.
[0179]
0.2 <f₁/ F₃<0.58 (3-1)
Where f₁Is the focal length of the first positive lens, f₃Is the focal length of the third positive lens.
[0180]
【The invention's effect】
According to the present invention, it is possible to obtain an imaging optical system that has a short overall length and withstands high-performance wide-angle shooting, and a small and high-performance imaging apparatus using the same.
[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 focused on an object point at infinity.
FIG. 2 is a lens cross-sectional view of an imaging optical system according to a second embodiment, which is similar to FIG.
FIG. 3 is a lens cross-sectional view of an imaging optical system according to a third embodiment, which is similar to FIG.
FIG. 4 is a lens cross-sectional view of an imaging optical system according to a fourth embodiment, which is similar to FIG.
FIG. 5 is a sectional view of the imaging optical system according to a fifth embodiment, which is similar to FIG.
FIG. 6 is an aberration diagram for Example 1 upon focusing on an object point at infinity.
FIG. 7 is an aberration diagram for Example 2 upon focusing on an object point at infinity.
FIG. 8 is an aberration diagram for Example 3 upon focusing on an object point at infinity.
FIG. 9 is an aberration diagram for Example 4 upon focusing on an object point at infinity.
FIG. 10 is an aberration diagram for Example 5 upon focusing on an object point at infinity.
FIG. 11 is a cross-sectional view of a configuration example in which the imaging optical system of Example 1 and a CCD arranged on the image plane are fixed to a lens frame integrally formed of a resin material.
FIG. 12 is a schematic exploded perspective view when the third positive lens of the imaging optical system has an oval shape.
FIG. 13 is a diagram illustrating transmittance characteristics of an example of a near-infrared sharp cut coat.
FIG. 14 is a diagram illustrating transmittance characteristics of an example of a color filter provided on an emission surface side of a low-pass filter.
FIG. 15 is a diagram showing a color filter arrangement of a complementary color mosaic filter.
FIG. 16 is a diagram illustrating an example of a wavelength characteristic of a complementary color mosaic filter.
FIG. 17 is a diagram showing that the aperture shape of the stop is in an open state.
FIG. 18 is a diagram showing a state in which the aperture shape of the stop is a two-step stop.
FIG. 19 is a perspective view showing a configuration of an imaging optical system of the present invention in which a turret provided with a plurality of shape-fixed aperture stops having different shapes and transmittances is arranged.
FIG. 20 is a front view showing another turret instead of the turret shown in FIG. 19;
FIG. 21 is a diagram showing another turret-shaped light amount adjustment filter usable in the present invention.
FIG. 22 is a diagram illustrating an example of a filter that suppresses light amount unevenness.
FIG. 23 is a back view and a front view showing an example of a rotary focal plane shutter.
24 is a diagram illustrating a state in which a rotary shutter curtain of the shutter in FIG. 23 rotates.
FIG. 25 is a diagram illustrating an operation of interlaced CCD imaging.
FIG. 26 is an explanatory diagram of an operation of progressive CCD imaging.
FIG. 27 is a front perspective view showing the appearance of a digital camera incorporating an imaging optical system according to the present invention.
FIG. 28 is a rear perspective view of the digital camera shown in FIG. 27;
FIG. 29 is a sectional view of the digital camera of FIG. 27;
FIG. 30 is a front perspective view of a personal computer in which an imaging optical system according to the present invention is incorporated as an objective optical system with a cover opened.
FIG. 31 is a sectional view of a photographic optical system of a personal computer.
FIG. 32 is a side view of the state of FIG. 30;
FIG. 33 is a front view, a side view, and a cross-sectional view of a photographing optical system of a mobile phone in which an imaging optical system according to the present invention is incorporated as an objective optical system.
[Explanation of symbols]
S: Brightness aperture
L1: First positive lens
L2: Second negative lens
L3: Third positive lens
CG: Cover glass
I: Image plane
OP: Optical axis
Da ... aperture plate
Xa, Xb ... opening
Pa to Pf: photosensitive section
Va to Vf: vertical transfer unit
Ha, Hb: Horizontal transfer unit
E ... observer's eyeball
1A, 1B, 1C, 1D, 1E ... opening
1A ', 1B', 1C ', 1D', 1E '... opening
1A ", 1B", 1C ", 1D" ... opening
5. Image forming optical system
6 ... CCD
7 ... Lens frame
8: Lens circumference
10 ... Turret
10 '... turret
10 "... turret
11 ... Rotary axis
15 ... Shutter substrate
16 ... Opening
17 ... Rotary shutter curtain
18 ... Rotary axis
19, 20 ... gear
40 ... Digital camera
41 ... Shooting optical system
42 ... Optical path for photography
43 Finder optical system
44 ... Optical path for viewfinder
45 ... Shutter
46 ... Flash
47 ... LCD display monitor
49… CCD
50 ... Cover member
51 Processing means
52 recording means
53 Objective optical system for viewfinder
55 ... Poro prism
57… Field of view
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 photographic optical system
304: Optical path for shooting
305 ... Image
400… mobile phone
401 ... Microphone part
402: speaker unit
403… Input dial
404… Monitor
405 ... Photographing optical system
406 ... antenna
407… Shooting light path

Claims (22)

An imaging optical system comprising: a brightness stop, a first positive lens, a second negative lens, and a third positive lens arranged in this order from the object side, and satisfying the following conditional expression.
1.5 <d / (f · tan θ) <3.0 (1)
Here, d is the distance measured along the optical axis from the brightness stop surface of the imaging optical system to the image plane, θ is the maximum incident angle of the imaging optical system, and f is the focal length of the entire system. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
1.8 <d / (f · tan θ) <2.8 (1-1) An imaging optics, comprising, in order from the object side, an aperture stop, a first positive meniscus lens having a convex surface facing the image side, a second negative lens, and a third positive lens, satisfying the following conditional expression: system.
−5.0 <f _2-3 /f<−0.5 (2)
Here, f _2-3 is the combined focal length of the second negative lens and the third positive lens, and f is the focal length of the entire system. The imaging optical system according to claim 3, wherein the following conditional expression is satisfied.
-3.5 <f _2-3 /f<-0.8 (2-1) The imaging optical system according to any one of claims 1 to 4, wherein the following conditional expression is satisfied.
_{0.1 <f 1 / f 3 <} 0.7 ··· (3)
However, f ₁ is the focal length of the first positive lens, f ₃ is the focal length of the third positive lens. The imaging optical system according to claim 5, wherein the following conditional expression is satisfied.
_{0.2 <f 1 / f 3 <} 0.58 ··· (3-1) The imaging optical system according to any one of claims 1 to 6, wherein the following conditional expression is satisfied.
−0.6 <f ₂ / f ₃ <−0.1 (4)
However, f ₂ is the focal length of the second negative lens, f ₃ is the focal length of the third positive lens. The imaging optical system according to claim 7, wherein the following conditional expression is satisfied.
−0.5 <f ₂ / f ₃ <−0.15 (4-1) 9. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
1.45 <n _avg <1.70 (5)
Here, _navg is the average value of the d-line refractive indices of the first positive lens to the third positive lens. The imaging optical system according to claim 9, wherein the following conditional expression is satisfied.
1.5 <n _avg <1.65 (5-1) The imaging optical system according to any one of claims 1 to 10, wherein the following conditional expression is satisfied.
_{1.0 <(r 1f + r 1r} ) / (r 1f -r 1r) <1.7 ··· (6)
Here, r _1f is an object-side paraxial curvature radius of the first positive lens, and r _1r is an image-side paraxial curvature radius of the first positive lens. The imaging optical system according to claim 11, wherein the following conditional expression is satisfied.
_{1.1 <(r 1f + r 1r} ) / (r 1f -r 1r) <1.6 ··· (6-1) The imaging optical system according to claim 1, wherein the first positive lens has at least one aspherical surface that satisfies the following conditional expression.
0.01 <| (r _1s + r _1a ) / (r _1s −r _1a ) −1 | <100 (7)
Here, r _1s is the paraxial radius of curvature of the aspheric surface of the first positive lens, and r _1a is the difference between the paraxial radius of curvature within the optical effective range within the radius of curvature in consideration of the aspheric surface of the first positive lens. This is the value when it changes. The imaging optical system according to claim 13, wherein the following conditional expression is satisfied.
_{0.05 <| (r 1s + r} 1a) / (r 1s -r 1a) -1 | <10 ··· (7-1) 15. The imaging optical system according to claim 1, wherein the second negative lens has at least one aspherical surface satisfying the following conditional expression.
_{0.01 <| (r 2s + r} 2a) / (r 2s -r 2a) -1 | <100 ··· (8)
Here, r _2s is the paraxial radius of curvature of the aspheric surface of the second negative lens, and r _2a is the difference between the paraxial radius of curvature within the optical effective range within the radius of curvature in consideration of the aspheric surface of the second negative lens. This is the value when it changes. The imaging optical system according to claim 15, wherein the following conditional expression is satisfied.
_{0.1 <| (r 2s + r} 2a) / (r 2s -r 2a) -1 | <5 ··· (8-1) 9. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
10 ° <α <40 ° (9)
Here, α is the angle of incidence of the principal ray on the image plane at the maximum image height. 18. The imaging optical system according to claim 17, wherein the following conditional expression is satisfied.
15 ° <α <35 ° (9-1) From the object side, an aperture stop, a first positive lens with a convex surface facing the image side, a second negative lens with a concave surface facing the image side, an imaging optical system arranged in the order of a third positive lens, and an image thereof The aperture stop has a fixed aperture shape through which the optical axis passes, and the outermost peripheral surface of the aperture is closer to the optical axis toward the image plane. An imaging apparatus characterized by being inclined at an inclination angle equal to or greater than an incident angle of an off-axis light beam. From the object side, an aperture stop, a first positive lens with a convex surface facing the image side, a second negative lens with a concave surface facing the image side, an imaging optical system arranged in the order of a third positive lens, and an image thereof An image pickup apparatus comprising: an image pickup element disposed on a side of the image pickup apparatus; and a lens frame holding the image forming optical system and the image pickup element and integrally forming the aperture stop with the same resin material. From the object side, an aperture stop, a first positive lens with a convex surface facing the image side, a second negative lens with a concave surface facing the image side, an imaging optical system arranged in the order of a third positive lens, and an image thereof A lens frame for holding the imaging optical system, wherein at least an outer periphery of each of the first positive lens and the third positive lens is inclined such that the closer to the object, the closer to the optical axis. An image pickup apparatus comprising: a slanted portion provided with the slanted portion in contact with the lens frame. From the object side, an aperture stop, a first positive lens with a convex surface facing the image side, a second negative lens with a concave surface facing the image side, an imaging optical system arranged in the order of a third positive lens, and an image thereof A lens frame for holding the imaging optical system, wherein the shape of the first positive lens is circular when viewed from the incident side, and the shape of the third positive lens However, when viewed from the incident side, the length of a direction corresponding to the short side direction of the effective imaging region of the imaging element is shorter than the length corresponding to the long side direction of the effective imaging region.

Images