JP3771993B2 - Imaging optical system and imaging apparatus using the same - Google Patents

Description

ただし、Ｃ_m （ｍは２以上の整数）は係数である。
【００４９】
上記自由曲面は、一般的には、Ｘ−Ｚ面、Ｙ−Ｚ面共に対称面を持つことはないが、本発明ではｘの奇数次項を全て０にすることによって、Ｙ−Ｚ面と平行な対称面が１つだけ存在する自由曲面となる。例えば、上記定義式（ａ）においては、Ｃ₄ ，Ｃ₆ ，Ｃ₉ ，Ｃ₁₁，Ｃ₁₃，Ｃ₁₅，Ｃ₁₈，Ｃ₂₀，Ｃ₂₂，Ｃ₂₄，Ｃ₂₆，Ｃ₂₈，Ｃ₃₁，Ｃ₃₃，Ｃ₃₅，Ｃ₃₇，・・・の各項の係数を０にすることによって可能である。
【００５０】
また、ｙの奇数次項を全て０にすることによって、Ｘ−Ｚ面と平行な対称面が１つだけ存在する自由曲面となる。例えば、上記定義式（ａ）においては、Ｃ₃ ，Ｃ₆ ，Ｃ₈ ，Ｃ₁₀，Ｃ₁₃，Ｃ₁₅，Ｃ₁₇，Ｃ₁₉，Ｃ₂₁，Ｃ₂₄，Ｃ₂₆，Ｃ₂₈，Ｃ₃₀，Ｃ₃₂，Ｃ₃₄，Ｃ₃₆，・・・の各項の係数を０にすることによって可能であり、また、以上のような対称面を持つことにより製作性を向上することが可能となる。
【００５１】
上記Ｙ−Ｚ面と平行な対称面、Ｘ−Ｚ面と平行な対称面の何れか一方を対称面とすることにより、偏心により発生する回転非対称な収差を効果的に補正することが可能となる。
【００５２】
上記定義式は、１つの例として示したものであり、本発明の特徴は対称面を１面のみ有する回転非対称面で偏心により発生する回転非対称な収差を補正することが特徴であり、他のいかなる定義式に対しても同じ効果が得られることは言うまでもない。
【００５３】
さて、一般に、偏心した回転非対称反射面を有する光学系構成要素（偏心プリズム光学系）は研磨により製作することは難しく、研削により１面ずつ形成するか、プラスチックの射出成形又はガラスモールド成形により作製することになる。このとき、偏心プリズム光学系の面が所定の形状に作製されているかどうかを確認する必要がある。このような３次元の回転非対称な形状の測定には、一般的に３次元座標測定器が使用されるが、測定時間がかかり、現実的ではない。
【００５４】
本発明では、偏心プリズム光学系４を構成する少なくとも３つの面の中、少なくとも１面を回転対称面で構成することが重要である。
【００５５】
さらに好ましくは、最も有効面積が広く、比較的収差の劣化が大きい瞳に近い側の透過作用と内部反射作用を有する面を回転対称面として構成することにより、面形状の出来上がり具合を簡単に短時間で評価することが可能な偏心プリズム光学系を構成することに成功したものである。
【００５６】
また、後側光学群の偏心プリズム光学系が、第１の透過作用面と、第１の反射作用面と、第２の反射作用面と、第２の透過作用面とを有し、第２の反射作用面が回転非対称面形状を有し、対称面を１つのみ有する面対称自由曲面からなっており、かつ、第１の反射作用面は第２の透過作用面と共通の面からなる場合、この面に強いパワーを持たせると、色収差の発生が大となる。また、第１の反射作用面と第２の透過作用面として利用する領域がほぼ分離できればよいが、そうすると後側光学群を構成するプリズムブロックの大型化を招くため、第１の反射作用面と第２の透過作用面との重なりあう領域が増える。そこで、第１の反射作用面での作用と第２の透過作用面での作用を両立させるためには、強いパワーを持たせない方が、制御が容易である。すなわち、面対称自由曲面の唯一の対称面をＹ−Ｚ面とし、その面に直交する方向をＸ軸とし、軸上主光線の第１の反射作用面、第２の反射作用面との交点近傍のＸ方向のパワーをそれぞれＰｘ１、Ｐｘ２とするとき、
｜Ｐｘ１｜＜｜Ｐｘ２｜ ・・・（５）
であることが望ましい。
【００５７】
さらには、
１＜｜Ｐｘ２／Ｐｘ１｜＜２０ ・・・（６）
を満足することが望ましい。この条件の上限値２０を越えると、極度に第２の反射作用面のパワーが強くなり、バックフォーカスが確保できなくなると共に、収差補正のために面形状の複雑さが増し、好ましくない。さらには、
１．１＜｜Ｐｘ２／Ｐｘ１｜＜１０ ・・・（６）’
を満足するとなおよい。
【００５８】
さらには、
２．０＜｜Ｐｘ２／Ｐｘ１｜＜５ ・・・（６）”
を満足するとさらによい。
【００５９】
また、軸上主光線の第２の透過作用面との交点近傍のＸ方向のパワーをＰｘ３とするとき、
｜Ｐｘ３／Ｐｘ２｜＜０．５ ・・・（７）
であることが望ましい。すなわち、第２の透過作用面に強いパワーを持たせると、歪曲収差と色収差の発生が大となり、好ましくない。そこで、条件（７）を満足することが望ましい。
【００６０】
さらには、
｜Ｐｘ３／Ｐｘ２｜＜０．２ ・・・（７）’
を満足するとなおよい。
【００６１】
また、以上において、面対称自由曲面の唯一の対称面をＹ−Ｚ面とし、その面に直交する方向をＸ軸とし、その面のＸ方向の最大画角主光線が当たる位置での面の法線のＹ−Ｚ面内でのｔａｎの値と、軸上主光線が前記面に当たる位置でのその面の法線のＹ−Ｚ面内でのｔａｎの値との差をＤＹとするとき、
０≦｜ＤＹ｜＜０．１ ・・・（８）
なる条件を満足することが望ましい。
【００６２】
この条件式は、例えば水平線を写したときに弓なりに湾曲してしまう弓なりな回転非対称な像歪みに関するものである。図１０（ａ）の斜視図、同図（ｂ）のＹ−Ｚ面への投影図に示すように、Ｘ方向の最大画角の主光線が回転非対称面Ａと交差する点におけるその回転非対称面の法線ｎ’のＹ−Ｚ面内でのｔａｎの値と、軸上主光線がその回転非対称面Ａと交差する点における回転非対称面の法線ｎのＹ−Ｚ面内でのｔａｎの値との差をＤＹとするとき、（８）の条件を満足することが重要である。上記条件式の下限の０を越えると、弓なりな像歪みを補正することができなくなる。また、上限の０．１を越えると、弓なりな像歪みが補正過剰となり、どちらの場合も像が弓なりに歪んでしまう。
【００６３】
さらに好ましくは、
０≦｜ＤＹ｜＜０．０１ ・・・（８）’
なる条件を満足することが好ましい。
【００６４】
また、軸上主光線が光学系の第１面に到るまでの方向をＺ軸方向、面対称自由曲面の唯一の対称面をＹ−Ｚ面とし、その面に直交する方向をＸ軸とし、Ｙ正方向の最大画角の主光線とＹ負方向の最大画角の主光線とがその面と当たる部分のＸ方向の曲率の差をＣｘｎ、軸上主光線がその面と当たる部分のＸ方向のパワーをＰｘｎとするとき、
０≦｜Ｃｘｎ／Ｐｘｎ｜＜１０ ・・・（９）
の条件を満足することが重要である。この条件式は、台形に発生する像歪みに関するものである。上記条件式の上限１０を越えると、台形歪みが大きく発生し、他の面で補正することがが難しくなる。
【００６５】
さらに好ましくは、
０≦｜Ｃｘｎ／Ｐｘｎ｜＜１ ・・・（９）’
なる条件式を満足することが好ましい。
【００６６】
また、回転非対称面は偏心して構成された光学系に配置され、偏心して配置された各面の偏心面と略同一の面が対称面となるような面対称自由曲面とすることで、対称面を挟んで左右両側を対称にすることができ、収差補正と製作性を大幅に向上させることができる。
【００６７】
次に、Ｘ方向の光学系全体のパワーをＰｘとし、回転非対称な面の軸上主光線が当たる部分のＸ方向のパワーをＰｘｎとするとき、
０＜｜Ｐｘｎ／Ｐｘ｜＜１００ ・・・（１０）
なる条件式を満足することが、収差補正上好ましい。上記条件式の上限１００を越えると、回転非対称面のパワーが光学系全体のパワーに比べて強くなりすぎ、強い屈折力を回転非対称面が持ちすぎてしまい、この回転非対称な面で発生する収差を他の面で補正できなくなる。また、下限の０を越えると、回転非対称面のＸ軸方向のパワーがなくなり、別の面としてＸ軸方向のパワーを配置しなければならなくなり、必要な面数が増え、本発明で回転非対称面を用いることによって光学系の小型化を図ろうとする目的に反する。
【００６８】
さらに好ましくは、
０．０５＜｜Ｐｘｎ／Ｐｘ｜＜１０ ・・・（１０）’
なる条件を満足すると、回転非対称な収差を良好に補正でき、収差補正上好ましい。
【００６９】
また、Ｙ方向の光学系全体のパワーをＰｙとし、回転非対称な面の軸上主光線が当たる部分のＹ方向のパワーＰｙｎとするとき、
０＜｜Ｐｙｎ／Ｐｙ｜＜１００ ・・・（１１）
なる条件式を満足することが、収差補正上好ましい。上記条件式の下限０と上限１００のの意味は条件式（１０）の場合と同様である。
【００７０】
さらに好ましくは、
０＜｜Ｐｙｎ／Ｐｙ｜＜１０ ・・・（１１）’
なる条件を満足すると、回転非対称な収差を良好に補正でき、収差補正上好ましい。
【００７１】
次に、上記光学系全体のＸ方向、Ｙ方向のパワーをＰｘ、Ｐｙとするとき、
０．３＜｜Ｐｘ／Ｐｙ｜＜２ ・・・（１２）
なる条件式を満足することが、収差補正上好ましい。上記条件式の下限０．３と上限２を越えると、光学系全体の焦点距離がＸ方向とＹ方向で異なりすぎ、良好な像歪みを得ることが難しくなり、像が歪んでしまう。
【００７２】
さらに好ましくは、
０．８＜｜Ｐｘ／Ｐｙ｜＜１．２ ・・・（１２）’
なる条件を満足すると、回転非対称な収差を良好に補正でき、収差補正上好ましい。
【００７３】
また、本発明の撮像光学系において、光学系の横収差が２００μｍ以下であることが望ましい。本発明に光学系の横収差が２００μｍ以下であると、収差を十分に無視することができ、良好な結像性能を得られる
また、本発明の撮像光学系の像歪みは２０％以下であることが望ましい。本発明に光学系の像歪みが２０％以下だと、収差を十分に無視することができ、良好な結像性能を得られる
なお、さらに好ましくは、第１の透過作用面が透過光に対して正のパワーを持つレンズである場合には、第１の反射作用面の光線の広がりを抑えることが可能となり、第１の反射面を小型にすることが可能である。
【００７４】
また、光線を第１の透過作用面、第１の反射作用面、第２の透過作用面の順番に進むように構成することによって、第１の反射作用面を裏面鏡として構成することが可能となる。第１の反射作用面を裏面鏡で構成すると、表面鏡で構成するよりもさらに像面湾曲収差に対して良い結果を得られる。
【００７５】
さらに、第１の透過作用面と第２の透過作用面のどちらか又は両方に第１の反射作用面と同じ符号のパワーを持たせることにより、像面湾曲はほぼ完全に補正することが可能となる。
【００７６】
一方、第１の透過作用面と第２の透過作用面のパワーを略０にすることにより、色収差に対して良い結果を得られる。これは、第１の反射作用面では、原理上色収差の発生がないため、色収差を他の面と補正し合う必要がない。そこで、第１の透過作用面と第２の透過作用面でも色収差が発生しないようにパワーをほぼ０にすることで、全体の光学系で色収差の少ない光学系を構成することが可能となる。
【００７７】
さらに好ましくは、後側光学群を、物体側から像側に向かって、少なくとも第１の透過作用面と、第１の反射作用面と、第２の反射作用面と、第２の透過作用面とで構成し、第２の反射作用面を回転非対称面形状にて構成する場合、２つの反射作用面のパワーを変えることが可能となり、正負又は負正の組み合わせにして、主点位置を光学系の前に出したり後ろに出したりすることができる。これは像面湾曲にも良い結果を与えることができる。
【００７８】
さらに、２つの反射作用面を裏面鏡にすることで、像面湾曲をほとんどなくすことも可能である。特に、焦点距離に比較して大きなバックフォーカスが必要な電子撮像光学系の場合には、物体側に負のパワーを配置するか、第１反射作用面を負のパワーとするのがよい。しかし、後者でパワーを強くすると、歪曲収差の悪化を招く。さらに、そのとき、第１反射作用面と第２透過作用面が同一である場合には、透過作用面も負のパワーが強くなり、色収差の悪化を招く。したがって、第１反射作用面は、反射作用面として利用する領域は負、第２透過作用面として利用する領域に近づく程パワーが弱くなり、第２透過作用面としては弱いパワーになるような形状が好ましい。なお、前者のように、物体側に負のパワーを配置する場合には、第１反射作用面は弱い正若しくは負のパワーで構成すればよい。
【００７９】
また、本発明の撮像光学系を電子撮像素子上に結像させる電子撮像装置の撮影レンズとして用いる場合には、撮像装置の処理部において、光学系の歪曲収差や倍率色収差の情報をメモリ等に予め保持しておき、その情報をもとにデジタル画像処理技術を用いて補正する機能を備え、光学系で発生する歪曲収差や倍率色収差を補正せしめると、光学系で補正すべき収差の許容量が大きくなり、光学系に対する負担が軽減され、特に本発明のような、少ないレンズ構成要素の数で光学性能を満足する小型の撮影レンズを構成する際には、効果的である。さらには、カメラの処理部として情報を保持しなくても、画像処理ソフトのデータとして、パソコン等の処理装置にインストールし、装置上で画像処理を施すように構成しても、同様の機能を持つことができることは言うまでもない。
【００８０】
なお、本発明は、以上のような撮像光学系によって形成される物体像を受光するために配置された撮像素子を有する撮像装置を含むものである。この場合、その撮像素子は、撮像素子が受光した光を電気情報に変換する作用を有する電子撮像素子にて形成することが望ましく、その電子撮像素子により受光した物体像を観察するための観察手段を備えていることが望ましい。
【００８１】
【発明の実施の形態】
以下に、本発明の撮像光学系の実施例１について説明する。実施例１の構成パラメータは後記するが、その構成パラメータにおいては、図１に示すように、絞り１の面を偏心面の原点として、軸上主光線２を物体中心（図では省略）を出て、絞り１の中心を通る光線で定義し、物体中心から光学系の第１面まで軸上主光線２に沿って進む方向をＺ軸、このＺ軸と像面８中心を含む平面をＹ−Ｚ平面とし、Ｙ軸をＹ−Ｚ平面内のＺ軸に直交する方向に取り、物点から光学系第１面に向かう方向をＺ軸の正方向とし、Ｙ軸の正方向を図の上方向（第１反射面６で反射する方向）とする。そして、Ｙ軸、Ｚ軸と右手直交座標系を構成する軸をＸ軸とする。
【００８２】
図１の実施例１では、このＹ−Ｚ平面内で各面の偏心を行っており、また、各回転非対称自由曲面の唯一の対称面をＹ−Ｚ面として構成している。
そして、偏心面については、その面の面頂位置の光学系の原点の中心からのＸ軸方向、Ｙ軸方向、Ｚ軸方向の偏心量（それぞれｘ、ｙ、ｚ）と、その面の中心軸（自由曲面については、前記の（ａ）式のＺ軸）のＸ軸、Ｙ軸、Ｚ軸それぞれを中心とする傾き角（°）（それぞれα、β、γ）とが与えられている。なお、その場合、αとβの正はそれぞれの軸の正方向に対しての反時計回りを、γの正はＺ軸の正方向に対しての時計回りを意味する。
【００８３】
また、実施例１の光学系を構成する光学面の中、球面は曲率半径が与えられており、また、特定の面とそれに続く面が同軸系を構成する場合には面間隔が与えられており、その他、媒質の屈折率、アッベ数が慣用法に従って与えられている。
【００８４】
また、自由曲面の面の形状は前記の式（ａ）により定義し、その定義式のＺ軸が自由曲面の軸となる。
なお、データの記載されていない非球面に関する項は０である。屈折率については、ｄ線（波長５８７．５６ｎｍ）に対するものを表記してある。長さの単位はｍｍである。
【００８５】
なお、自由曲面の他の定義式としてＺｅｒｎｉｋｅ多項式がある。この面の形状は以下の式（ｂ）により定義する。その定義式のＺ軸がＺｅｒｎｉｋｅ多項式の軸となる。

実施例１の軸上主光線２を含むＹ−Ｚ断面図を図１に示す。図中、１は絞り、２は軸上主光線、４は絞り１より像側の後群を構成する偏心プリズム光学系、５は偏心プリズム光学系の第１面、６は第２面、７は第３面であり、８は像面、９は赤外線カットフィルター、光学ローパスフィルター、カバーガラス等のフィルター類である。なお、偏心プリズム光学系４の第１面５は後群の第１の透過（作用）面、第２面６は第１の反射（作用）面と第２の透過（作用）面、第３面７は第２の反射（作用）面を構成している。なお、実施例１においては、絞り１より物体側に前群は配置していない構成である。
【００８６】
そして、図示しない物体から出た光線は、絞り１の開口を通り、後群の偏心プリズム光学系４の第１面５を透過して内部に入り、第２面６で反射され、次いで第３面７で反射され、今度は第２面６透過して偏心プリズム光学系４の外へ出て、フィルター類９を介して像面８に物体像を結像する。
【００８７】
なお、像の大きさは約４×３ｍｍの１／４インチサイズを想定して最適化したものであるが、もちろんその他のサイズ等の場合も、全体を係数倍することにより適用できることは言うまでもない。
また、本発明は撮像光学系のみならず、その光学系を組み込んだ撮像装置も含むものである。
【００８８】
実施例１の仕様は、水平半画角２１．３２°、垂直半画角１６．３１°、入射瞳径２．０６１ｍｍ、像の大きさ３．９０×２．９３ｍｍである。この実施例は、絞り１より物体側に前群を有せず、撮像光学系を偏心プリズム光学系４だけで構成した実施例である。
【００８９】
本実施例は、１つの対称面を有する回転非対称自由曲面を２面使用して構成した例であり、物体側から、絞り１と、第１透過面５、第１反射面６、第２反射面７、第２透過面６からなり、第１反射面と第２透過面は同一の面６でなり、第１反射面は全反射を利用しているため、全体が３面と少ない面で構成されている。そして、この実施例において、第１反射面６（第２透過面６）に回転対称な球面を用いており、他に回転対称非球面を用いて構成することも可能である。
【００９０】
なお、構成パラメータは後記するが、偏心量は、第１面からの偏心量として表しており、また、第６面は仮想面である。第７面以降は赤外線カットフィルターや光学ローパスフィルター、カバーガラス等の各種光学部材（フィルター類９）を表している。
【００９１】
本実施例の各画角に対する横収差状況を図２に、歪曲収差の状況を図３に示す。横収差を表す図２において、括弧内に示された数字は（水平（Ｘ方向）画角，垂直（Ｙ方向）画角）を表し、その画角における横収差図を示す。
以下、上記実施例１の構成パラメータを示す。
【００９２】

【００９３】
なお、上記実施例の各条件式（１）、（５）〜（１２）に関する値は以下の表の通りである。だだし、球面である第１反射面６に関する値も一部示してある。ここで、ＤＹ１、ＤＹ２は第１反射面６、第２反射面７のＤＹ、Ｐｘ１、Ｐｘ２は第１反射面６、第２反射面７のＰｘｎ、Ｐｙ１、Ｐｙ２は第１反射面６、第２反射面７のＰｙｎ、Ｃｘ１、Ｃｘ２は第１反射面６、第２反射面７のＣｘｎである。また、ＤＴｘ、ＤＴｙはそれぞれＸ方向、Ｙ方向の歪曲収差の最大値（％）である。
【００９４】

【００９５】
さて、以上のような本発明の撮像光学系は、例えばＣＣＤを撮像素子とする小型ＴＶカメラのような撮像装置に用いられる。図４に本発明の撮像光学系１０を、電子撮像素子としてＣＣＤ１１を用いた撮像装置に組み込んだ構成の概念図を示す。この撮像装置において、物体像は撮像光学系１０により赤外線カットフィルター、光学ローパスフィルター等のフィルター類９を介して像面に配置されたＣＣＤ１１上に結像され、その物体像はＣＣＤ１１によって映像信号に変換され、その映像信号は処理手段１２により電子ファインダーとして作用するＣＲＴ１３上に直接表示されると共に、撮像装置に内蔵した記録媒体１４中に記録される。また、撮像装置はマイク１５を備え、映像信号記録と同時に音声情報記録も同様に行う。また、前記したように、処理手段１２において、撮像光学系１０の歪曲収差や倍率色収差の情報を記録媒体１４あるいは処理手段１２に付属したメモリ等に予め保持しておき、その情報をもとにデジタル画像処理技術を用いて光学系１０で発生する歪曲収差や倍率色収差を補正するようにするともできる。
【００９６】
このような撮像装置において、本発明に基づき撮像光学系１０の構成要素数の低減、小型化により、装置としての小型化やコストダウンが達成できる。
【００９７】
以上の本発明の撮像光学系及びそれを用いた撮像装置は例えば次のように構成することができる。
〔１〕 撮像素子面上に物体像を形成するための撮像光学系において、
少なくとも瞳面よりも像側に後側光学群を有し、
前記後側光学群は、物体中心を射出して瞳中心を通り像中心に到達する光線を軸上主光線とするとき、前記主光線に対して面全体が傾くように偏心配置された少なくとも３つの面を備えたプリズム部材を有し、
前記の少なくとも３つの面は、透過作用を有する面と、反射作用と透過作用とを共有し回転対称面形状の曲面と、反射作用を有し偏心により発生する回転非対称な偏心収差を補正する回転非対称面形状の曲面とからなることを特徴とする撮像光学系。
【００９８】
〔２〕 上記〔１〕において、前記反射作用と透過作用とを共有する回転対称面形状の曲面が、全反射面又は半透過反射面にて形成されていることを特徴とする撮像光学系。
【００９９】
〔３〕 上記〔１〕において、前記反射作用面がコーティングされたミラー面にて形成されていることを特徴とする撮像光学系。
【０１００】
〔４〕 上記〔１〕において、前記反射作用を有する面が、前記反射作用と透過作用とを共有する面と対向配置され、かつ、前記軸上主光線が前記光学系の入射面に到るまでの方向をＺ軸方向、面の偏心面内をＹ軸方向、Ｙ軸、Ｚ軸と直交座標系を構成する軸をＸ軸とするとき、前記光学系の入射面側から前記軸上主光線とＹ方向に微少量ｄ離れた平行光束を入射させ、前記光学系から射出する側でその２つの光線のＹ−Ｚ面内でなす角のｓｉｎをＮＡ’ｙｉ、前記ＮＡ’ｙｉを前記平行光束の幅ｄで割った値ＮＡ’ｙｉ／ｄを前記光学系のＹ方向のパワーＰｙとし、前記プリズム部材の入射面から前記プリズム部材の射出面までの前記軸上主光線の光路長をｐとするとき、
０．１＜ｐ×Ｐｙ＜８ ・・・（１）
を満たすことを特徴とする撮像光学系。
【０１０１】
〔５〕 上記〔１〕から〔４〕の何れか１項において、前記プリズム部材が、屈折率１よりも大きい媒質を挟んだ透過作用を有する第１面と、反射作用と透過作用とを有する第２面と、反射作用を有する第３面との３つの面からなり、物体からの光が、第１面に入射し、第２面で反射され、第３面で反射され、第２面と透過して射出するように構成されていることを特徴とする撮像光学系。
【０１０２】
〔６〕 上記〔５〕において、前記プリズム部材は一体成形された単体のブロックからなることを特徴とする撮像光学系。
【０１０３】
〔７〕 上記〔１〕から〔６〕の何れか１項において、前記光学系により形成される物体像の赤外線成分をカットする作用を有する赤外線カットフィルターが前記光学系中に配置されていることを特徴とする撮像光学系。
【０１０４】
〔８〕 上記〔１〕から〔６〕の何れか１項において、前記の反射作用を有する面の少なくとも１面は、特定の波長を透過又は遮断する作用を有する波長選択光学部材の裏面鏡にて構成されていることを特徴とする撮像光学系。
【０１０５】
〔９〕 上記〔８〕において、前記波長選択光学部材が赤外線カット作用を備えていることを特徴とする撮像光学系。
【０１０６】
〔１０〕 上記〔６〕において、前記プリズム部材の媒質が赤外線カット作用を備えていることを特徴とする撮像光学系。
【０１０７】
〔１１〕 上記〔１０〕において、前記プリズム部材の媒質が以下の条件（４）を満足することを特徴とする撮像光学系。
ａ＜１ ・・・（４）
ただし、は前記プリズム部材中に含有されるＣｕＯのモル％である。
【０１０８】
〔１２〕 上記〔１１〕において、以下の条件（４）’を満足することを特徴とする撮像光学系。
【０１０９】
１×１０^-5＜ａ＜１ ・・・（４）’
〔１３〕 上記〔１〕から〔１２〕の何れか１項において、前記回転非対称面形状を有する反射作用面は、対称面を１つのみ有する面対称自由曲面からなることを特徴とする撮像光学系。
【０１１０】
〔１４〕 上記〔１３〕において、前記面対称自由曲面の唯一の対称面をＹ−Ｚ面とし、その面に直交する方向をＸ軸とし、前記軸上主光線の前記第１の反射作用面、前記第２の反射作用面との交点近傍のＸ方向のパワーをそれぞれＰｘ１、Ｐｘ２とするとき、
｜Ｐｘ１｜＜｜Ｐｘ２｜ ・・・（５）
であることを特徴とする撮像光学系。
【０１１１】
〔１５〕 上記〔１４〕において、
１＜｜Ｐｘ２／Ｐｘ１｜＜２０ ・・・（６）
であることを特徴とする撮像光学系。
【０１１２】
〔１６〕 上記〔１３〕において、前記面対称自由曲面の唯一の対称面をＹ−Ｚ面とし、その面に直交する方向をＸ軸とし、前記軸上主光線の前記第２の反射作用面との交点近傍のＸ方向のパワーをＰｘ２とし、前記軸上主光線の前記第２の透過作用面との交点近傍のＸ方向のパワーをＰｘ３とするとき、
｜Ｐｘ３／Ｐｘ２｜＜０．５ ・・・（７）
であることを特徴とする撮像光学系。
【０１１３】
〔１７〕 上記〔１３〕において、前記面対称自由曲面の唯一の対称面をＹ−Ｚ面とし、その面に直交する方向をＸ軸とし、前記面のＸ方向の最大画角主光線が当たる位置での面の法線のＹ−Ｚ面内でのｔａｎの値と、前記軸上主光線が前記面に当たる位置での前記面の法線のＹ−Ｚ面内でのｔａｎの値との差をＤＹとするとき、
０≦｜ＤＹ｜＜０．１ ・・・（８）
を満たすことを特徴とする撮像光学系。
【０１１４】
〔１８〕 上記〔１３〕において、前記軸上主光線が前記光学系の第１面に到るまでの方向をＺ軸方向、前記面対称自由曲面の唯一の対称面をＹ−Ｚ面とし、その面に直交する方向をＸ軸とし、Ｙ正方向の最大画角の主光線とＹ負方向の最大画角の主光線とが前記面と当たる部分のＸ方向の曲率の差をＣｘｎ、軸上主光線が前記面と当たる部分のＸ方向のパワーをＰｘｎとするとき、
０≦｜Ｃｘｎ／Ｐｘｎ｜＜１０ ・・・（９）
を満たすことを特徴とする撮像光学系。
【０１１５】
〔１９〕 上記〔１３〕から〔１８〕の何れか１項において、前記プリズム部材の有する偏心面の少なくとも１面は、その偏心方向を含む面が前記対称面と略一致するように偏心配置されていることを特徴とする撮像光学系。
【０１１６】
〔２０〕 上記〔１９〕において、前記プリズム部材の有する全ての偏心面の偏心方向が全て同一面上にあり、かつ、その偏心方向を含む面が前記対称面と略一致するように形成されていることを特徴とする撮像光学系。
【０１１７】
〔２１〕 上記〔１８〕又は〔１９〕において、前記軸上主光線が前記光学系の第１面に到るまでの方向をＺ軸方向、面の偏心面内をＹ軸方向、Ｙ軸、Ｚ軸と直交座標系を構成する軸をＸ軸とするとき、前記光学系の入射面側から前記軸上主光線とＸ方向に微少量ｄ離れた平行光束を入射させ、前記光学系から射出する側でその２つの光線のＹ−Ｚ面に直交し射出した軸上主光線を含む面内でなす角のｓｉｎをＮＡ’ｘｉ、前記ＮＡ’ｘｉを前記平行光束の幅ｄで割った値ＮＡ’ｘｉ／ｄを前記光学系のＸ方向のパワーＰｘとし、前記回転非対称な面の前記軸上主光線が当たる部分のＸ方向のパワーをＰｘｎとするとき、
０＜｜Ｐｘｎ／Ｐｘ｜＜１００ ・・・（１０）
を満たすことを特徴とする撮像光学系。
【０１１８】
〔２２〕 上記〔２１〕において、
０．０５＜｜Ｐｘｎ／Ｐｘ｜＜１０ ・・・（１０）’
を満たすことを特徴とする撮像光学系。
【０１１９】
〔２３〕 上記〔１８〕又は〔１９〕において、前記軸上主光線が前記光学系の第１面に到るまでの方向をＺ軸方向、面の偏心面内をＹ軸方向、Ｙ軸、Ｚ軸と直交座標系を構成する軸をＸ軸とするとき、前記光学系の入射面側から前記軸上主光線とＹ方向に微少量ｄ離れた平行光束を入射させ、前記光学系から射出する側でその２つの光線のＹ−Ｚ面内でなす角のｓｉｎをＮＡ’ｙｉ、前記ＮＡ’ｙｉを前記平行光束の幅ｄで割った値ＮＡ’ｙｉ／ｄを前記光学系のＹ方向のパワーＰｙとし、前記回転非対称な面の前記軸上主光線が当たる部分のＹ方向のパワーをＰｙｎとするとき、
０＜｜Ｐｙｎ／Ｐｙ｜＜１００ ・・・（１１）
を満たすことを特徴とする撮像光学系。
【０１２０】
〔２４〕 上記〔２３〕において、
０＜｜Ｐｙｎ／Ｐｙ｜＜１０ ・・・（１１）’
を満たすことを特徴とする撮像光学系。
【０１２１】
〔２５〕 上記〔１９〕又は〔２０〕において、前記軸上主光線が前記光学系の第１面に到るまでの方向をＺ軸方向、面の偏心面内をＹ軸方向、Ｙ軸、Ｚ軸と直交座標系を構成する軸をＸ軸とするとき、前記光学系の入射面側から前記軸上主光線とＹ方向に微少量ｄ離れた平行光束を入射させ、前記光学系から射出する側でその２つの光線のＹ−Ｚ面内でなす角のｓｉｎをＮＡ’ｙｉ、前記ＮＡ’ｙｉを前記平行光束の幅ｄで割った値ＮＡ’ｙｉ／ｄを前記光学系のＹ方向のパワーＰｙとし、前記軸上主光線が前記光学系の第１面に到るまでの方向をＺ軸方向、面の偏心面内をＹ軸方向、Ｙ軸、Ｚ軸と直交座標系を構成する軸をＸ軸とするとき、前記光学系の入射面側から前記軸上主光線とＸ方向に微少量ｄ離れた平行光束を入射させ、前記光学系から射出する側でその２つの光線のＹ−Ｚ面に直交し射出した軸上主光線を含む面内でなす角のｓｉｎをＮＡ’ｘｉ、前記ＮＡ’ｘｉを前記平行光束の幅ｄで割った値ＮＡ’ｘｉ／ｄを前記光学系のＸ方向のパワーＰｘとするとき、
０．３＜｜Ｐｘ／Ｐｙ｜＜２ ・・・（１２）
を満たすことを特徴とする撮像光学系。
【０１２２】
〔２６〕 上記〔２５〕において、
０．８＜｜Ｐｘ／Ｐｙ｜＜１．２ ・・・（１２）’
を満たすことを特徴とする撮像光学系。
【０１２３】
〔２７〕 上記〔１〕から〔２６〕の何れか１項において、前記光学系の横収差が２００μｍ以下であることを特徴とする撮像光学系。
【０１２４】
〔２８〕 上記〔１〕から〔２６〕の何れか１項において、前記光学系の像歪みが２０％以下であることを特徴とする撮像光学系。
【０１２５】
〔２９〕 上記〔１〕から〔２７〕の何れか１項において、前記光学系によって形成される物体像を受光するために配置された撮像素子を有することを特徴とする撮像装置。
【０１２６】
〔３０〕 上記〔２９〕において、前記撮像素子が受光した光を電気情報に変換する作用を有する電子撮像素子にて形成されていることを特徴とする撮像装置。
【０１２７】
〔３１〕 上記〔３０〕において、前記電子撮像素子により受光した物体像を観察するための観察手段を備えていることを特徴とする撮像装置。
【０１２８】
【発明の効果】
以上の説明から明らかなように、本発明によると、回転対称な透過光学系に比べて小型で収差の発生が少ない撮像光学系を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例１の撮像光学系の光軸を含む断面図である。
【図２】実施例１の横収差図である。
【図３】実施例１の歪曲収差図である。
【図４】本発明の撮像光学系を撮像装置に組み込んだ構成の概念図である。
【図５】本発明における軸上主光線と座標系を説明するための図である。
【図６】偏心した反射面により発生する像面湾曲を説明するための概念図である。
【図７】偏心した反射面により発生する非点収差を説明するための概念図である。
【図８】偏心した反射面により発生するコマ収差を説明するための概念図である。
【図９】本発明の撮像光学系のパワーを説明するための図である。
【図１０】本発明において用いるパラメータＤＹを説明するための図である。
【符号の説明】
１…絞り
２…軸上主光線
３…前群
４…後群（偏心プリズム光学系）
５…偏心プリズム光学系の第１面
６…偏心プリズム光学系の第２面
７…偏心プリズム光学系の第３面
８…像面
９…フィルター類
１０…撮像光学系
１１…ＣＣＤ
１２…処理手段
１３…ＣＲＴ
１４…記録媒体
１５…マイク[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging optical system and an imaging apparatus using the imaging optical system, and in particular, is suitable for an imaging apparatus that forms a relatively small image, and a reflecting surface having at least one imaging power necessary for image formation is arranged eccentrically. The present invention relates to an optical system and an imaging apparatus.
[0002]
[Prior art]
Japanese Unexamined Patent Publication No. 59-84201 is a well-known conventional small-sized reflective decentering optical system. However, this is an invention of a one-dimensional light receiving lens with a cylindrical reflecting surface, and two-dimensional imaging cannot be performed. Japanese Patent Application Laid-Open No. 62-144127 uses the same cylindrical surface for reflection twice in order to reduce the spherical aberration of the present invention.
[0003]
Japanese Patent Laid-Open No. 62-205547 shows that an aspherical reflecting surface is used as the shape of the reflecting surface, but does not mention the shape of the reflecting surface.
Furthermore, two cases of US Pat. No. 3,810,221 and US Pat. No. 3,836,931 both have a rotationally symmetric aspherical mirror and only one plane of symmetry in the finder optical system of the reflex camera. An example using a lens system having a surface is shown. However, the surface having only one plane of symmetry is used for the purpose of correcting the tilt of the observed virtual image.
[0004]
Japanese Patent Laid-Open No. 1-257834 (US Pat. No. 5,274,406) discloses an example in which a rear-projection television uses a surface having only one plane of symmetry as a reflecting mirror in order to correct image distortion. However, a projection lens system is used for projection onto a screen, and a plane having only one plane of symmetry is used for correcting image distortion. In addition, as an observation optical system, an example of a decentered optical system of a back mirror type using an anamorphic surface and a toric surface is shown. However, correction of aberrations including image distortion is insufficient.
In any of the above prior arts, a surface having only one symmetry plane is used and is not used as a back mirror for a folded optical path.
[0005]
Japanese Patent Application Laid-Open Nos. Hei 8-292368, Hei 8-292371, and Hei 8-292372 all have an imaging optical system (single-focus optical system) using a surface having only one symmetry plane as a reflecting surface. , Zoom optical system). However, the optical path length from the most object-side rotationally asymmetric surface to the most image-side rotationally asymmetric surface is long until it enters and exits an optical component including a rotationally asymmetric surface (example of forming an image once in the middle) Yes), because the optical system is enlarged, there is no merit of using a rotationally asymmetric surface that is difficult to manufacture.
[0006]
[Problems to be solved by the invention]
In a conventional rotationally symmetric optical system, a refracting power is borne by a transmission rotationally symmetric lens having a refractive power, and thus many components are required for aberration correction. However, in these conventional decentered optical systems, the aberration of the image formed is corrected well, and if the rotationally asymmetric distortion is not particularly corrected, the formed figure is distorted. The correct shape could not be recorded.
[0007]
In addition, in a rotationally symmetric optical system in which the refractive lens constituting the optical system has a rotationally symmetric surface with the optical axis as the axis, the entire optical system becomes longer in the optical axis direction because the optical path is a straight line. There was a problem that the apparatus would become large.
[0008]
The present invention has been made in view of such problems of the prior art, and an object of the present invention is a small imaging optical system that provides a clear and less distorted image even at a wide angle of view, and an imaging apparatus using the same. Is to provide.
[0009]
[Means for Solving the Problems]
The imaging optical system of the present invention that achieves the above object is an imaging optical system for forming an object image on the imaging element surface.
Having a rear optical group at least on the image side of the pupil plane,
The rear optical group is at least 3 eccentrically arranged so that the entire surface is inclined with respect to the principal ray when a ray that exits the object center and passes through the pupil center and reaches the image center is used as an axial principal ray. Having a prism member with two surfaces,
The at least three surfaces include a surface having a transmission action, a curved surface having a rotationally symmetric surface sharing the reflection action and the transmission action, and a rotation having a reflection action and correcting rotationally asymmetric decentration aberrations caused by eccentricity. It consists of a curved surface with an asymmetric surface shape,
The surface having the transmitting action is the first surface, the curved surface having the rotationally symmetric surface shape sharing the reflecting action and the transmitting action is the second surface, and the curved surface having the rotationally asymmetric surface shape having the reflecting action is the third surface,
After the light from the object is incident on the first surface, the first surface to the third surface are configured to be reflected by the second surface, reflected by the third surface, and transmitted through the second surface. It is characterized by that.
In this case, the prism member is preferably composed of a single block formed integrally.
[0010]
In addition, it is desirable that a rotationally symmetric curved surface that shares a reflection action and a transmission action be formed by a total reflection surface or a semi-transmission reflection surface.
Further, it is desirable that the mirror surface is coated with a curved surface having a reflecting action.
[0011]
Also has a reflective action Song The surface is arranged opposite to the surface sharing the reflection and transmission functions, and the axial principal ray is Rear optical group The direction to reach the incident surface is the Z-axis direction, the eccentric surface of the surface is the Y-axis direction, the Y-axis, the axis constituting the orthogonal coordinate system with the Z-axis is the X-axis Shi , Rear optical group A collimated light beam that is separated by a small amount d in the Y direction from the axial principal ray from the incident surface side of Rear optical group NA'yi / d, which is obtained by dividing sin of the angle formed in the YZ plane of the two rays by NA'yi and NA'yi by the width d of the parallel light flux on the side exiting from Rear optical group When the optical path length of the axial principal ray from the incident surface of the prism member to the exit surface of the prism member is p,
0.1 <p × Py <8 (1)
It is desirable to satisfy.
[0012]
First, a coordinate system used in the following description will be described.
As shown in FIG. 5, a ray passing through the center of the object point, passing through the center of the aperture stop 1 and reaching the center of the image plane 8 is defined as an axial principal ray 2, and is defined by a straight line extending to the first surface of the optical system. The optical axis to be used is defined as the Z axis, the axis in the eccentric plane of each surface constituting the imaging optical system is defined as the Y axis, and the axis orthogonal to the Z axis and orthogonal to the Y axis The X axis is assumed.
[0013]
In general, in a spherical lens system composed of only spherical lenses, the spherical aberration generated by the spherical surface, coma aberration, curvature of field, and other aberrations are corrected with respect to each other to reduce aberrations as a whole. It has become. On the other hand, an aspherical surface or the like is used to satisfactorily correct aberrations with a small number of surfaces. This is to reduce various aberrations that occur on the spherical surface. However, in a decentered optical system, it is impossible to correct rotationally asymmetric aberration caused by the decentration with a rotationally symmetric optical system.
[0014]
The configuration and operation of the present invention will be described below.
When a rotationally symmetric optical system is decentered, rotationally asymmetric aberration is generated, and this cannot be corrected only by the rotationally symmetric optical system. The rotationally asymmetric aberration generated by this decentration includes image distortion, curvature of field, and astigmatism and coma generated on the axis. 6 is a field curvature generated by the decentered concave mirror M, FIG. 7 is an astigmatism generated by the decentered concave mirror M, and FIG. 8 is an axial coma generated by the decentered concave mirror M. It is a figure which shows an aberration. In the present invention, in order to correct the rotationally asymmetric aberration caused by the eccentricity as described above, a rotationally asymmetric surface is disposed in the optical system to correct the rotationally asymmetric aberration.
[0015]
One example of rotationally asymmetric aberration generated by a decentered concave mirror is rotationally asymmetric field curvature. For example, a light ray incident on a concave mirror decentered from an object point at infinity hits the concave mirror and is reflected and imaged. Halved. Then, as shown in FIG. 6, an image plane inclined with respect to the axial principal ray is formed. It has been impossible to correct such rotationally asymmetric field curvature with a rotationally symmetric optical system. In order to correct this tilted field curvature, the concave mirror M is composed of a rotationally asymmetric surface. In this example, the curvature is increased (refractive power is increased) with respect to the positive Y-axis direction (upward in the figure). This can be corrected by making the curvature weak (refracting power weak) with respect to the negative direction of the Y axis (the downward direction of the figure), and a rotationally asymmetric surface having the same effect as the above configuration is a concave mirror. By arranging it in the optical system separately from M, it is possible to obtain a flat image surface with a small number of components.
[0016]
Next, rotationally asymmetric astigmatism will be described. As in the above description, in the concave mirror M arranged eccentrically, astigmatism as shown in FIG. This astigmatism Correction As in the above description, this can be achieved by appropriately changing the curvature in the X-axis direction and the curvature in the Y-axis direction of the rotationally asymmetric surface.
[0017]
Further, rotationally asymmetric coma will be described. Similar to the above description, in the concave mirror M arranged eccentrically, coma aberration as shown in FIG. This coma aberration Correction Can be achieved by changing the inclination of the surface as it moves away from the origin of the X axis of the rotationally asymmetric surface, and by appropriately changing the inclination of the surface depending on whether the Y axis is positive or negative.
[0018]
Further, when the imaging optical system of the present invention is configured to have a bent optical path, it is possible to give power to the reflecting surface and to omit the transmissive lens. Furthermore, the optical system can be made compact by bending the optical path.
[0019]
In addition, the reflection surface can be made highly reflective by being composed of a total reflection surface that is inclined with respect to the light beam so that the light beam is incident beyond the critical angle. It is possible to have both an action and a permeation action. Moreover, it is preferable to comprise a reflective surface in which a metal thin film such as aluminum or silver is formed on the surface constituting the reflective surface, or a reflective surface or a transflective surface formed of a dielectric multilayer film. When the metal thin film has a reflecting action, it is possible to easily obtain a high reflectance. In the case of a dielectric reflection film, it is advantageous when forming a reflection film with little wavelength selectivity and absorption.
[0020]
More preferably, when a rotationally asymmetric surface is used for the reflecting surface, no chromatic aberration is generated as compared with the case of using the transmitting surface. In addition, since the light beam can be bent even when the surface inclination is small, other aberrations are less likely to occur. That is, when the same refractive power is obtained, the reflective surface requires less aberration than the refractive surface.
[0021]
In addition, as the imaging optical system according to the present invention, when the formed image is small, the imaging optical system can be reduced in size in accordance with the so-called principle of coefficient multiplication. It is not preferable to downsize the optical system unnecessarily because the thickness of the edge of the lens and the thickness of the center become thin, or the lens diameter becomes too small. On the other hand, when the optical system is configured while maintaining a manufacturable size, in the optical system using the conventional refractive lens, the optical axis is a straight line, so that there is a waste of space between the power-refracting surfaces. . Therefore, if the optical axis is spatially folded using the reflecting surface, it is possible to effectively use a relatively small space and secure an optical path necessary for imaging. At this time, if the optical path length of the imaging optical system is unnecessarily increased, the optical axis length is deviated not only for the purpose of effectively using the space by the decentering and folding of the optical axis, but also compared with the image to be formed. If the length is too long, there arises a problem that it becomes difficult to secure a back focus necessary for arranging a member for capturing an optical image, such as a film or an image sensor.
[0022]
In the present invention, a compact optical system has been successfully constructed by adopting a bent optical path and simultaneously satisfying the following conditions.
[0023]
That is, in the imaging optical system of the present invention, the rear optical group has at least a second reflecting action surface disposed opposite to the reflecting action surface, and the axial principal ray reaches the first surface of the optical system. When the axis up to the Z axis direction, the Y axis direction in the eccentric plane of the surface, the Y axis, and the axis constituting the orthogonal coordinate system with the Z axis as the X axis, the axial principal ray from the incident surface side of the optical system A parallel light beam separated by a small amount d in the Y direction is incident, and on the side exiting from the optical system, the angle formed by the two rays in the YZ plane is NA'yi, and the NA'yi is the width of the parallel light beam. The value NA′yi / d divided by d is the power Py in the Y direction of the optical system, and the axial principal ray is incident on an optical system component having a rotationally asymmetric surface arranged on the most object side of the optical system. The optical path length from when the optical system component having a rotationally asymmetric surface arranged on the most image side of the optical system to Rutoki,
0.1 <p × Py <8 (1)
It is desirable to satisfy.
[0024]
First, the power of the optical system is defined in the present invention. As shown in FIG. 9, when the eccentric direction of the optical system is taken in the Y-axis direction, a light beam having a minute height d in the YZ plane parallel to the axial principal ray 2 is incident on the optical system from the object side. The angle sin formed in the YZ plane of the two rays on the side exiting from the optical system is NA′yi, NA′yi / d is the power Py of the entire optical system in the Y direction, A light beam having a minute height d in the XZ plane parallel to the axial principal ray 2 is incident on the optical system from the object side, and exits perpendicularly to the YZ plane of the two light beams on the side exiting from the optical system. The sin of the angle formed in the plane including the axial principal ray is NA′xi, and NA′xi / d is the power Px of the entire optical system in the X direction.
[0025]
An optical system having a rotationally asymmetric surface disposed on the most image side of the optical system after the axial principal ray is incident on the optical system component having the rotationally asymmetric surface disposed on the most object side of the optical system. Assuming that the optical path length until the component is emitted is p (in FIG. 9, since both are the same decentered prism optical system 4, the optical path length of the axial principal ray 2 therein), (1 It is desirable that the optical system is configured so as to satisfy the above formula.
[0026]
More preferably,
0.5 <p × Py <5.0 (1) ′
If it is made to satisfy, a small lens system can be achieved.
[0027]
More preferably,
0.5 <p × Py <0.7 (1) ”
If it is satisfied, a smaller lens system can be achieved.
[0028]
Further, when the optical system component having the rotationally asymmetric surface of the imaging optical system of the present invention is constituted by the first and second reflection action surfaces and the first and second transmission action surfaces, the optical axis is set to two reflection action surfaces. The optical system can be miniaturized. Furthermore, since there are two transmission surfaces, better results can be obtained for the principal point position and field curvature.
Furthermore, better aberration performance can be obtained by using two reflecting surfaces as back mirrors.
[0029]
By the way, if the pupil is not projected to the object side, the optical system becomes large and the optical path length p becomes too large. Or, it becomes difficult to ensure the back focus. Furthermore, if the power is relied on the decentered rotationally asymmetric surface too much, it becomes difficult to correct asymmetric aberrations, particularly decentration coma, generated by the decentration. Therefore, it is also an effective means to improve optical performance by arranging an optical system closer to the object side than the rotationally asymmetric surface and sharing power.
[0030]
In addition, when an aperture is disposed on the object side of an optical system component having a rotationally asymmetric surface, an optical member is further disposed on the object side, so that the aperture member is protected and the reflecting surface is configured by a surface mirror. In some cases, it is also useful for measures such as dust prevention.
[0031]
In the imaging optical system of the present invention, the eccentric aberration can be corrected by the eccentric rotationally asymmetric surface. However, an optical member is arranged on the object side, and the total aberration correction is performed together with the eccentric rotationally asymmetric reflecting surface. It is good to do. At that time, it is preferable to decenter the optical member in order to satisfactorily correct the asymmetric aberration because uniform correction is possible.
[0032]
In the imaging optical system of the present invention, if the number of optical system components having a decentered rotationally asymmetric reflective surface is reduced or the optical system component having the reflective surface is configured by a prism block, the diaphragm is brought out to the object side. Otherwise, the optical system becomes large. At that time, all the power is biased to the image side with respect to the stop. In order to correct distortion, both negative and positive powers are required. However, if the negative power is increased too much, the optical system becomes larger and the optical path length increases, which is not preferable. Therefore, it is preferable to correct the distortion by arranging a positive lens on the object side of the stop. In addition, when an optical system component having a decentered rotationally asymmetric reflecting surface is configured by a prism block, it is difficult to correct some chromatic aberration generated on the transmission surface, but it is also effective for correcting chromatic aberration. It is. In particular, it is better to decenter the positive lens in order to correct asymmetric aberrations.
[0033]
In particular, when a wide-angle lens having a wide angle of view is constructed, the focal length is shortened, so that it is difficult to ensure the back focus. In that case, it is preferable to adopt a so-called retrofocus type in which negative and positive powers are arranged in order from the object side. Moreover, it is better to increase the negative power so that the gap between the negative group and the positive group is as much as possible. However, if a negative power is given to a decentered rotationally asymmetric surface, decentration aberrations become too large to be corrected, and it is particularly difficult to correct coma asymmetry.
[0034]
Therefore, it is preferable to arrange a concave lens on the object side, to give a negative power to an ordinary refractive lens, to arrange the negative group and the positive group at an interval, and to fold the optical axis and make it compact.
[0035]
Further, when the optical system component having an eccentric rotationally asymmetric reflecting surface is constituted by a single block and the stop is provided, it is preferable to provide the stop closer to the object side than the block without increasing the size of the block. At this time, it is preferable to dispose an optical member having substantially zero optical power, which also serves as a diaphragm protecting means, on the object side. As another effect, when an electronic image sensor is used, a region within the surface is divided, a slight inclination is given to the surface for each region, and a function of changing the light traveling direction by a small amount is provided. If the method has an optical low-pass filter function, it is effective for shortening the back focus.
[0036]
By the way, when the axial principal ray enters and exits the front optical group arranged on the object side of the optical system component having the eccentric rotationally asymmetric reflecting surface, the displacement amount of the angle is Δθ, and the displacement amount of the position is Δh. And when
0.1 ° <Δθ <45 ° (2)
Or
0 <Δh × Py <1.0 (3)
It is desirable to satisfy at least one of the above. Here, Py is the power in the Y direction of the optical system.
[0037]
If both the above formulas (2) and (3) take a small value beyond the lower limit, there is no point in decentering. If both values exceed the upper limit and take a large value, the decentration aberrations at each part will become too large and correction will be difficult.
[0038]
More preferably,
1 ° <Δθ <30 ° (2) '
Or
0.005 <Δh × Py <0.5 (3) ′
It is desirable to satisfy at least one of the following.
[0039]
By the way, if the first reflection action surface and the second transmission action surface of the optical system component having the eccentric rotationally asymmetric reflection surface are the same surface, the number of surfaces to be formed is three, and the manufacturability is improved.
[0040]
Further, when the total reflection is used for the reflection of the first reflecting surface, the high reflectance can be obtained as described above, the light loss can be minimized, and the reflecting surface and the transmitting surface can be made the same. Manufacturing is facilitated.
[0041]
Further, as described above, the optical system component having an eccentric rotationally asymmetric reflection surface is configured by a single block and the number of components is reduced, so that the optical system can be reduced in size and cost.
[0042]
Further, the rotationally asymmetric reflecting surface is configured as a back mirror of an optical material having the function of wavelength selection means, the wavelength selection means has a so-called infrared cut function, and the mol% a of CuO contained in the optical material is as follows. It is desirable to satisfy the following conditions.
[0043]
a <1 (4)
A so-called infrared cut filter or the like can be manufactured by mixing impurities such as copper. However, if the number of impurities increases, it becomes difficult to control wavelength selectivity. Moreover, in order to improve the resistance of glass containing a large amount of copper or the like, it is common to use a fluorophosphate-based network, but if the content can be reduced, a highly resistant network structure can be adopted. ,It is valid. However, if the impurities are reduced, in order to ensure wavelength selectivity, the thickness of the filter must be increased, and there is a problem that the lens system becomes large in order to ensure space.
[0044]
In an optical system that turns the optical axis as in the present invention, an optical path length longer than the actual thickness can be obtained, so that effective wavelength selection characteristics can be achieved with a small impurity content. The copper content may be adjusted according to the optical path length of the designed optical system, but when the mol% of CuO is particularly a,
a <1 (4)
It is desirable to satisfy
[0045]
Moreover,
1 × 10 ^-Five <A <1 (4) '
It is more preferable that
[0046]
Also,
1 × 10 ^-Five <A <0.5 (4) "
If it is better.
[0047]
In the imaging optical system of the present invention, it is desirable to use a plane-symmetric free-form surface having only one symmetry plane as at least one of the reflecting action surfaces having an eccentric rotationally asymmetric surface shape. Here, the free-form surface used in the present invention is defined by the following equation.
[0048]

However, C _m (M is an integer of 2 or more) is a coefficient.
[0049]
In general, the free-form surface does not have a symmetric surface in both the XZ plane and the YZ plane. However, in the present invention, by setting all odd-order terms of x to 0, the free-form surface is parallel to the YZ plane. This is a free-form surface with only one symmetrical plane. For example, in the above definition (a), C _Four , C ₆ , C ₉ , C ₁₁ , C ₁₃ , C ₁₅ , C ₁₈ , C ₂₀ , C _{twenty two} , C _{twenty four} , C ₂₆ , C ₂₈ , C ₃₁ , C ₃₃ , C ₃₅ , C ₃₇ This is possible by setting the coefficient of each term of.
[0050]
Further, by setting all odd-order terms of y to 0, a free-form surface having only one symmetry plane parallel to the XZ plane is obtained. For example, in the above definition (a), C _Three , C ₆ , C ₈ , C _Ten , C ₁₃ , C ₁₅ , C ₁₇ , C ₁₉ , C _{twenty one} , C _{twenty four} , C ₂₆ , C ₂₈ , C ₃₀ , C ₃₂ , C ₃₄ , C ₃₆ ,... Can be achieved by setting the coefficient of each term to 0, and by having the symmetry plane as described above, the manufacturability can be improved.
[0051]
By using one of the symmetry plane parallel to the YZ plane and the symmetry plane parallel to the XZ plane as a symmetry plane, it is possible to effectively correct rotationally asymmetric aberration caused by decentration. Become.
[0052]
The above definition formula is shown as an example, and the feature of the present invention is to correct rotationally asymmetric aberration caused by decentration on a rotationally asymmetric surface having only one symmetry plane. Needless to say, the same effect can be obtained for any definition formula.
[0053]
Now, in general, it is difficult to manufacture an optical system component (eccentric prism optical system) having an eccentric rotationally asymmetric reflecting surface by polishing. It is formed by grinding one surface at a time, or by plastic injection molding or glass molding. Will do. At this time, it is necessary to confirm whether or not the surface of the decentered prism optical system is formed in a predetermined shape. In such a three-dimensional rotationally asymmetric shape measurement, a three-dimensional coordinate measuring device is generally used, but it takes time to measure and is not practical.
[0054]
In the present invention, it is important that at least one of the at least three surfaces constituting the decentered prism optical system 4 is a rotationally symmetric surface.
[0055]
More preferably, a surface having a transmission effect and an internal reflection effect on the side close to the pupil that has the largest effective area and relatively large aberration deterioration is configured as a rotationally symmetric surface, so that the surface shape can be easily shortened. It has succeeded in constructing a decentered prism optical system that can be evaluated in time.
[0056]
The decentered prism optical system of the rear optical group has a first transmission action surface, a first reflection action surface, a second reflection action surface, and a second transmission action surface. The reflection action surface has a rotationally asymmetric surface shape, is composed of a plane-symmetry free-form surface having only one symmetry surface, and the first reflection action surface is a surface common to the second transmission action surface. In this case, if strong power is given to this surface, the occurrence of chromatic aberration increases. In addition, it is only necessary that the regions used as the first reflecting action surface and the second transmitting action surface can be substantially separated from each other. However, since this causes an increase in the size of the prism block constituting the rear optical group, The area overlapping with the second permeation surface increases. Therefore, in order to achieve both the action on the first reflecting action surface and the action on the second transmitting action surface, it is easier to control without giving strong power. That is, the only symmetry plane of the plane-symmetric free-form surface is the YZ plane, the direction orthogonal to the plane is the X-axis, and the intersection of the axial principal ray with the first reflection action surface and the second reflection action surface When the neighboring X-direction powers are Px1 and Px2, respectively.
| Px1 | <| Px2 | (5)
It is desirable that
[0057]
Moreover,
1 <| Px2 / Px1 | <20 (6)
It is desirable to satisfy Exceeding the upper limit 20 of this condition is not preferable because the power of the second reflecting surface becomes extremely strong, the back focus cannot be secured, and the complexity of the surface shape increases for aberration correction. Moreover,
1.1 <| Px2 / Px1 | <10 (6) ′
It is even better if you satisfy.
[0058]
Moreover,
2.0 <| Px2 / Px1 | <5 (6) "
It is even better if you satisfy.
[0059]
Further, when the power in the X direction in the vicinity of the intersection point of the axial principal ray with the second transmission surface is Px3,
| Px3 / Px2 | <0.5 (7)
It is desirable that That is, it is not preferable to give a strong power to the second transmission surface because distortion and chromatic aberration are greatly generated. Therefore, it is desirable to satisfy the condition (7).
[0060]
Moreover,
| Px3 / Px2 | <0.2 (7) ′
It is even better if you satisfy.
[0061]
In the above description, the only symmetric plane of the plane-symmetry free-form surface is the YZ plane, the direction orthogonal to the plane is the X axis, and the plane at the position where the maximum field angle chief ray in the X direction hits the plane. When the difference between the tan value in the YZ plane of the normal line and the tan value in the YZ plane of the normal line of the surface at the position where the axial principal ray hits the plane is DY ,
0 ≦ | DY | <0.1 (8)
It is desirable to satisfy the following conditions.
[0062]
This conditional expression relates to, for example, a bow-like rotationally asymmetric image distortion that curves like a bow when a horizontal line is copied. As shown in the perspective view of FIG. 10A and the projection onto the YZ plane of FIG. 10B, the rotational asymmetry at the point where the principal ray having the maximum field angle in the X direction intersects the rotationally asymmetric surface A. The tan value in the YZ plane of the normal n ′ of the surface and the tan in the YZ plane of the normal n of the rotationally asymmetric surface at the point where the axial principal ray intersects the rotationally asymmetric surface A When the difference from the value of DY is DY, it is important to satisfy the condition (8). If the lower limit of 0 to the above conditional expression is exceeded, bow-shaped image distortion cannot be corrected. When the upper limit of 0.1 is exceeded, bow-like image distortion becomes overcorrected, and in either case, the image is distorted like a bow.
[0063]
More preferably,
0 ≦ | DY | <0.01 (8) ′
It is preferable to satisfy the following conditions.
[0064]
The direction until the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the only symmetrical surface of the plane-symmetric free-form surface is the YZ plane, and the direction orthogonal to the surface is the X-axis. , The difference in curvature in the X direction between the principal ray with the maximum field angle in the Y positive direction and the principal ray with the maximum field angle in the Y negative direction is Cxn. When the power in the X direction is Pxn,
0 ≦ | Cxn / Pxn | <10 (9)
It is important to satisfy these conditions. This conditional expression relates to image distortion generated in the trapezoid. If the upper limit of 10 is exceeded, trapezoidal distortion will occur and it will be difficult to correct it on other surfaces.
[0065]
More preferably,
0 ≦ | Cxn / Pxn | <1 (9) ′
It is preferable to satisfy the following conditional expression:
[0066]
In addition, the rotationally asymmetric surface is arranged in an optical system configured to be decentered, and is a plane of symmetry free-form surface in which substantially the same plane as the decentered surface of each decentered surface is a symmetric surface. The left and right sides can be made symmetric with respect to each other, and aberration correction and manufacturability can be greatly improved.
[0067]
Next, when the power of the entire optical system in the X direction is Px, and the power in the X direction of the portion where the axial principal ray of the rotationally asymmetric surface hits is Pxn,
0 <| Pxn / Px | <100 (10)
It is preferable for aberration correction to satisfy the following conditional expression. If the upper limit of 100 of the above conditional expression is exceeded, the power of the rotationally asymmetric surface becomes too strong compared to the power of the entire optical system, and the rotationally asymmetric surface has a strong refractive power, and aberrations occur on this rotationally asymmetric surface. Cannot be corrected on other surfaces. If the lower limit of 0 is exceeded, the power in the X-axis direction of the rotationally asymmetric surface disappears, and the power in the X-axis direction must be arranged as another surface, increasing the number of necessary surfaces, and the present invention is rotationally asymmetric. Use of a surface is contrary to the purpose of downsizing the optical system.
[0068]
More preferably,
0.05 <| Pxn / Px | <10 (10) ′
If this condition is satisfied, rotationally asymmetric aberrations can be corrected well, which is preferable for aberration correction.
[0069]
Further, when the power of the entire optical system in the Y direction is Py, and the power Pyn in the Y direction of the portion where the axial principal ray of the rotationally asymmetric surface hits,
0 <| Pyn / Py | <100 (11)
It is preferable for aberration correction to satisfy the following conditional expression. The meanings of the lower limit 0 and the upper limit 100 in the conditional expression are the same as in the conditional expression (10).
[0070]
More preferably,
0 <| Pyn / Py | <10 (11) ′
If this condition is satisfied, rotationally asymmetric aberrations can be corrected well, which is preferable for aberration correction.
[0071]
Next, when the powers in the X direction and Y direction of the entire optical system are Px and Py,
0.3 <| Px / Py | <2 (12)
It is preferable for aberration correction to satisfy the following conditional expression. If the lower limit of 0.3 and the upper limit of 2 are exceeded, the focal length of the entire optical system will be too different in the X and Y directions, making it difficult to obtain good image distortion, and the image will be distorted.
[0072]
More preferably,
0.8 <| Px / Py | <1.2 (12) ′
If this condition is satisfied, rotationally asymmetric aberrations can be corrected well, which is preferable for aberration correction.
[0073]
In the imaging optical system of the present invention, it is desirable that the lateral aberration of the optical system is 200 μm or less. In the present invention, when the lateral aberration of the optical system is 200 μm or less, the aberration can be sufficiently ignored and good imaging performance can be obtained.
The image distortion of the imaging optical system of the present invention is desirably 20% or less. In the present invention, when the image distortion of the optical system is 20% or less, the aberration can be sufficiently ignored, and good imaging performance can be obtained.
More preferably, when the first transmission action surface is a lens having a positive power with respect to the transmitted light, it is possible to suppress the spread of light rays on the first reflection action surface. It is possible to make the reflecting surface small.
[0074]
In addition, the first reflecting action surface can be configured as a back mirror by configuring the light beam to proceed in the order of the first transmitting action surface, the first reflecting action surface, and the second transmitting action surface. It becomes. When the first reflecting surface is constituted by a back mirror, a better result can be obtained with respect to the field curvature aberration than when it is constituted by a front mirror.
[0075]
Furthermore, the curvature of field can be corrected almost completely by giving either or both of the first transmission surface and the second transmission surface the same power as the first reflection surface. It becomes.
[0076]
On the other hand, by setting the powers of the first transmission surface and the second transmission surface to substantially zero, good results can be obtained for chromatic aberration. This is because, in principle, there is no chromatic aberration on the first reflecting surface, so there is no need to correct chromatic aberration with other surfaces. Therefore, by setting the power to almost zero so that chromatic aberration does not occur on the first transmission surface and the second transmission surface, it is possible to configure an optical system with little chromatic aberration in the entire optical system.
[0077]
More preferably, the rear optical group is moved from the object side to the image side at least a first transmission action surface, a first reflection action surface, a second reflection action surface, and a second transmission action surface. And the second reflecting action surface has a rotationally asymmetric surface shape, the power of the two reflecting action surfaces can be changed, and the principal point position can be optically changed by combining positive and negative or negative and positive. It can be put out before or behind the system. This can also give good results for field curvature.
[0078]
Furthermore, it is possible to eliminate almost no curvature of field by using two reflecting surfaces as back mirrors. In particular, in the case of an electronic imaging optical system that requires a large back focus compared to the focal length, it is preferable that negative power is disposed on the object side or the first reflecting surface is negative power. However, if the power is increased in the latter case, distortion will be worsened. Further, at that time, when the first reflection action surface and the second transmission action surface are the same, the transmission action surface also has a strong negative power, leading to deterioration of chromatic aberration. Therefore, the first reflecting surface has a shape in which the region used as the reflecting surface is negative, the power becomes weaker as the region used as the second transmitting surface becomes closer, and the second transmitting surface becomes weak. Is preferred. When the negative power is arranged on the object side as in the former, the first reflecting surface may be configured with a weak positive or negative power.
[0079]
In addition, when the imaging optical system of the present invention is used as a photographing lens of an electronic imaging device that forms an image on an electronic imaging device, information on distortion and lateral chromatic aberration of the optical system is stored in a memory or the like in the processing unit of the imaging device. It has a function to store in advance and correct it using digital image processing technology based on that information. When distortion and lateral chromatic aberration that occur in an optical system are corrected, the amount of aberration that should be corrected in the optical system This reduces the burden on the optical system, and is particularly effective in constructing a small photographic lens that satisfies the optical performance with a small number of lens components as in the present invention. Furthermore, even if the information is not held as a camera processing unit, the same function can be achieved by installing image processing software data in a processing device such as a personal computer and performing image processing on the device. It goes without saying that you can have it.
[0080]
The present invention includes an image pickup apparatus having an image pickup element arranged to receive an object image formed by the image pickup optical system as described above. In this case, it is desirable that the image sensor is formed by an electronic image sensor having a function of converting light received by the image sensor into electrical information, and observation means for observing an object image received by the electronic image sensor It is desirable to have.
[0081]
DETAILED DESCRIPTION OF THE INVENTION
The first embodiment of the imaging optical system according to the present invention will be described below. The configuration parameters of Example 1 will be described later. In the configuration parameters, as shown in FIG. 1, the axial principal ray 2 is emitted from the center of the object (omitted in the figure) with the surface of the stop 1 as the origin of the eccentric surface. Then, a light beam passing through the center of the stop 1 is defined, and a direction along the axial principal ray 2 from the object center to the first surface of the optical system is defined as the Z axis. A plane including the Z axis and the center of the image surface 8 is defined as Y. -Z plane, the Y axis is taken in the direction perpendicular to the Z axis in the YZ plane, the direction from the object point toward the first surface of the optical system is the positive direction of the Z axis, and the positive direction of the Y axis is The upward direction (the direction of reflection by the first reflecting surface 6) is assumed. Then, an axis constituting the Y-axis, Z-axis and the right-handed orthogonal coordinate system is defined as an X-axis.
[0082]
In Example 1 of FIG. 1, each surface is decentered in the YZ plane, and the only symmetric surface of each rotationally asymmetric free-form surface is configured as a YZ plane.
For the eccentric surface, the amount of eccentricity (x, y, z, respectively) in the X-axis direction, Y-axis direction, and Z-axis direction from the center of the optical system origin at the surface top position of the surface, and the center of the surface Tilt angles (°) (α, β, γ, respectively) about the X-axis, Y-axis, and Z-axis of the axis (the Z-axis in equation (a) for the free-form surface) are given. . In this case, positive α and β means counterclockwise rotation with respect to the positive direction of each axis, and positive γ means clockwise rotation with respect to the positive direction of the Z axis.
[0083]
Of the optical surfaces constituting the optical system of Example 1, the spherical surface is given a radius of curvature, and when a specific surface and a subsequent surface constitute a coaxial system, a surface interval is given. In addition, the refractive index and Abbe number of the medium are given in accordance with conventional methods.
[0084]
The shape of the surface of the free-form surface is defined by the above formula (a), and the Z-axis of the definition formula is the axis of the free-form surface.
The term relating to the aspherical surface for which no data is described is zero. The refractive index is shown for d-line (wavelength 587.56 nm). The unit of length is mm.
[0085]
In addition, there is a Zernike polynomial as another defining formula of a free-form surface. The shape of this surface is defined by the following formula (b). The Z axis of the defining formula becomes the axis of the Zernike polynomial.

A YZ sectional view including the axial principal ray 2 of Example 1 is shown in FIG. In the figure, 1 is a stop, 2 is an axial principal ray, 4 is a decentered prism optical system constituting the rear group on the image side of the stop 1, 5 is a first surface of the decentered prism optical system, 6 is a second surface, 7 Is a third surface, 8 is an image surface, 9 is a filter such as an infrared cut filter, an optical low-pass filter, and a cover glass. The first surface 5 of the decentered prism optical system 4 is the first transmission (action) surface of the rear group, the second surface 6 is the first reflection (action) surface, the second transmission (action) surface, and the third. The surface 7 constitutes a second reflection (action) surface. In the first embodiment, the front group is not disposed on the object side of the diaphragm 1.
[0086]
A light beam emitted from an object (not shown) passes through the aperture of the diaphragm 1, passes through the first surface 5 of the decentered prism optical system 4 in the rear group, enters the inside, is reflected by the second surface 6, and then is third. Reflected by the surface 7, this time passes through the second surface 6, goes out of the decentered prism optical system 4, and forms an object image on the image surface 8 through the filters 9.
[0087]
Although the image size is optimized assuming a 1/4 inch size of about 4 × 3 mm, it is needless to say that the image size can be applied by multiplying the whole coefficient. .
The present invention includes not only an imaging optical system but also an imaging apparatus incorporating the optical system.
[0088]
The specifications of Example 1 are a horizontal half field angle of 21.32 °, a vertical half field angle of 16.31 °, an entrance pupil diameter of 2.061 mm, and an image size of 3.90 × 2.93 mm. In this embodiment, there is no front group on the object side with respect to the stop 1, and the imaging optical system is configured by only the decentered prism optical system 4.
[0089]
The present embodiment is an example in which two rotationally asymmetric free-form surfaces having one symmetric surface are used. From the object side, the diaphragm 1, the first transmitting surface 5, the first reflecting surface 6, and the second reflecting surface. The first reflection surface and the second transmission surface are the same surface 6, and the first reflection surface uses total reflection, so the total number of surfaces is as few as three. It is configured. In this embodiment, a rotationally symmetric spherical surface is used for the first reflecting surface 6 (second transmitting surface 6), and a rotationally symmetric aspherical surface can also be used.
[0090]
Although the configuration parameters will be described later, the amount of eccentricity is expressed as the amount of eccentricity from the first surface, and the sixth surface is a virtual surface. The seventh and subsequent surfaces represent various optical members (filters 9) such as an infrared cut filter, an optical low-pass filter, and a cover glass.
[0091]
FIG. 2 shows the state of lateral aberration for each angle of view in this embodiment, and FIG. 3 shows the state of distortion. In FIG. 2 showing transverse aberration, the numbers shown in parentheses represent (horizontal (X direction) field angle, vertical (Y direction) field angle), and a lateral aberration diagram at that field angle is shown.
The configuration parameters of Example 1 will be shown below.
[0092]

[0093]
In addition, the value regarding each conditional expression (1), (5)-(12) of the said Example is as the following tables. However, some values related to the first reflecting surface 6 which is a spherical surface are also shown. Here, DY1 and DY2 are the first reflection surface 6, DY of the second reflection surface 7, Px1 and Px2 are the first reflection surface 6, Pxn, Py1, and Py2 of the second reflection surface 7 are the first reflection surface 6, and Pyn, Cx1, and Cx2 of the second reflecting surface 7 are Cxn of the first reflecting surface 6 and the second reflecting surface 7, respectively. DTx and DTy are maximum values (%) of distortion in the X direction and Y direction, respectively.
[0094]

[0095]
The imaging optical system of the present invention as described above is used in an imaging apparatus such as a small TV camera using a CCD as an imaging element. FIG. 4 shows a conceptual diagram of a configuration in which the image pickup optical system 10 of the present invention is incorporated in an image pickup apparatus using a CCD 11 as an electronic image pickup element. In this imaging apparatus, an object image is formed on a CCD 11 disposed on the image plane by an imaging optical system 10 via filters 9 such as an infrared cut filter and an optical low-pass filter, and the object image is converted into a video signal by the CCD 11. The converted video signal is directly displayed on the CRT 13 acting as an electronic viewfinder by the processing means 12 and is recorded in the recording medium 14 incorporated in the imaging apparatus. In addition, the imaging apparatus includes a microphone 15 and performs audio information recording at the same time as video signal recording. Further, as described above, in the processing unit 12, information on distortion aberration and lateral chromatic aberration of the imaging optical system 10 is stored in advance in the recording medium 14 or a memory attached to the processing unit 12, and based on the information. It is also possible to correct distortion aberration and lateral chromatic aberration that occur in the optical system 10 using a digital image processing technique.
[0096]
In such an image pickup apparatus, the reduction in the number of constituent elements of the image pickup optical system 10 and the downsizing of the image pickup optical system 10 according to the present invention can achieve downsizing and cost reduction as the apparatus.
[0097]
The imaging optical system of the present invention and the imaging apparatus using the imaging optical system can be configured as follows, for example.
[1] In an imaging optical system for forming an object image on the imaging element surface,
Having a rear optical group at least on the image side of the pupil plane,
The rear optical group is at least 3 eccentrically arranged so that the entire surface is inclined with respect to the principal ray when a ray that exits the object center and passes through the pupil center and reaches the image center is used as an axial principal ray. Having a prism member with two surfaces,
The at least three surfaces include a surface having a transmission action, a curved surface having a rotationally symmetric surface sharing the reflection action and the transmission action, and a rotation having a reflection action and correcting rotationally asymmetric decentration aberrations caused by eccentricity. An imaging optical system comprising an asymmetrical curved surface.
[0098]
[2] The imaging optical system according to [1], wherein the rotationally symmetric curved surface sharing the reflection action and the transmission action is formed by a total reflection surface or a semi-transmission reflection surface.
[0099]
[3] The imaging optical system according to [1], wherein the reflecting surface is formed by a coated mirror surface.
[0100]
[4] In the above [1], the surface having the reflecting action is disposed opposite to the face sharing the reflecting action and the transmitting action, and the axial principal ray reaches the incident surface of the optical system. Is the Z-axis direction, the Y-axis direction is in the eccentric plane of the surface, the Y-axis, and the axis constituting the orthogonal coordinate system with the Z-axis is the X-axis, the main axis on the axis from the incident surface side of the optical system A parallel light beam separated by a slight amount d in the Y direction is made incident on the light beam, and the sin formed at the angle formed in the YZ plane of the two light beams on the side exiting from the optical system is NA'yi, and the NA'yi is A value NA′yi / d divided by the width d of the parallel light flux is defined as the power Py in the Y direction of the optical system, and the optical path length of the axial principal ray from the incident surface of the prism member to the exit surface of the prism member is When p is
0.1 <p × Py <8 (1)
An imaging optical system characterized by satisfying the above.
[0101]
[5] In any one of the above [1] to [4], the prism member has a first surface having a transmission function sandwiching a medium having a refractive index of 1 and a reflection function and a transmission function. It consists of three surfaces, a second surface and a third surface having a reflecting action, and light from the object is incident on the first surface, reflected by the second surface, reflected by the third surface, and second surface. An imaging optical system characterized by being configured to pass through and exit.
[0102]
[6] The imaging optical system according to [5], wherein the prism member is a single block formed integrally.
[0103]
[7] In any one of [1] to [6], an infrared cut filter having an action of cutting an infrared component of an object image formed by the optical system is disposed in the optical system. An imaging optical system characterized by the above.
[0104]
[8] In any one of the above [1] to [6], at least one of the surfaces having the reflecting action is a back mirror of the wavelength selecting optical member having an action of transmitting or blocking a specific wavelength. An imaging optical system characterized by being configured.
[0105]
[9] The imaging optical system as set forth in [8], wherein the wavelength selecting optical member has an infrared cut function.
[0106]
[10] The imaging optical system according to [6], wherein the medium of the prism member has an infrared cut function.
[0107]
[11] The imaging optical system according to [10], wherein the medium of the prism member satisfies the following condition (4).
a <1 (4)
However, is mol% of CuO contained in the said prism member.
[0108]
[12] An imaging optical system according to [11], wherein the following condition (4) ′ is satisfied.
[0109]
1 × 10 ^-Five <A <1 (4) '
[13] The imaging optical system according to any one of [1] to [12], wherein the reflection action surface having a rotationally asymmetric surface shape is a plane-symmetric free-form surface having only one symmetry surface. system.
[0110]
[14] In the above [13], the only symmetric plane of the plane-symmetry free-form surface is the YZ plane, the direction orthogonal to the plane is the X-axis, and the first reflection working surface of the axial principal ray , When the power in the X direction in the vicinity of the intersection with the second reflecting surface is Px1 and Px2, respectively.
| Px1 | <| Px2 | (5)
An imaging optical system characterized by the above.
[0111]
[15] In the above [14],
1 <| Px2 / Px1 | <20 (6)
An imaging optical system characterized by the above.
[0112]
[16] In the above [13], the only symmetric plane of the plane-symmetry free-form surface is the YZ plane, the direction orthogonal to the plane is the X-axis, and the second reflecting action surface of the axial principal ray Px2 is the power in the X direction in the vicinity of the intersection with Px3, and Px3 is the power in the X direction in the vicinity of the intersection with the second transmission surface of the axial principal ray.
| Px3 / Px2 | <0.5 (7)
An imaging optical system characterized by the above.
[0113]
[17] In the above [13], the only symmetric plane of the plane-symmetry free-form surface is the YZ plane, the direction orthogonal to the plane is the X axis, and the maximum principal field angle ray in the X direction of the plane hits The value of tan in the YZ plane of the surface normal at the position and the value of tan in the YZ plane of the surface normal at the position where the axial principal ray hits the surface When the difference is DY,
0 ≦ | DY | <0.1 (8)
An imaging optical system characterized by satisfying the above.
[0114]
[18] In the above [13], the direction until the axial principal ray reaches the first surface of the optical system is the Z-axis direction, and the only symmetry plane of the plane-symmetry free-form surface is the YZ plane, The direction orthogonal to the surface is defined as the X axis, and the difference in curvature in the X direction between the principal ray with the maximum field angle in the Y positive direction and the principal ray with the maximum field angle in the Y negative direction is Cxn. When the power in the X direction of the portion where the upper principal ray hits the surface is Pxn,
0 ≦ | Cxn / Pxn | <10 (9)
An imaging optical system characterized by satisfying the above.
[0115]
[19] In any one of [13] to [18] above, at least one of the eccentric surfaces of the prism member is eccentrically arranged such that a plane including the eccentric direction substantially coincides with the symmetry plane. An imaging optical system characterized by that.
[0116]
[20] In the above [19], the eccentric directions of all the eccentric surfaces of the prism member are all on the same plane, and the plane including the eccentric direction is substantially coincident with the symmetry plane. An imaging optical system characterized by comprising:
[0117]
[21] In the above [18] or [19], the direction until the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the decentered plane of the surface is the Y-axis direction, the Y-axis, When the axis constituting the orthogonal coordinate system with the Z axis is the X axis, a parallel light beam that is separated by a small amount d in the X direction from the incident surface side of the optical system is incident and emitted from the optical system. A value obtained by dividing sin of the angle formed in the plane including the axial principal ray emitted perpendicular to the YZ plane of the two rays by NA′xi and NA′xi by the width d of the parallel light flux When NA′xi / d is the power Px in the X direction of the optical system, and the power in the X direction of the portion of the rotationally asymmetric surface where the axial principal ray hits is Pxn,
0 <| Pxn / Px | <100 (10)
An imaging optical system characterized by satisfying the above.
[0118]
[22] In the above [21],
0.05 <| Pxn / Px | <10 (10) ′
An imaging optical system characterized by satisfying the above.
[0119]
[23] In the above [18] or [19], the direction until the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the decentered plane of the surface is the Y-axis direction, the Y-axis, When the axis constituting the orthogonal coordinate system with respect to the Z axis is the X axis, a parallel light beam separated by a slight amount d in the Y direction from the incident surface side of the optical system is incident and exits from the optical system. NA′yi, which is the angle between the two rays in the YZ plane, NA′yi, and NA′yi divided by the width d of the parallel light flux, NA′yi / d, is the Y direction of the optical system. When the power in the Y direction of the portion of the rotationally asymmetric surface where the axial principal ray strikes is Pyn,
0 <| Pyn / Py | <100 (11)
An imaging optical system characterized by satisfying the above.
[0120]
[24] In the above [23],
0 <| Pyn / Py | <10 (11) ′
An imaging optical system characterized by satisfying the above.
[0121]
[25] In the above [19] or [20], the direction until the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the decentered plane of the surface is the Y-axis direction, the Y-axis, When the axis constituting the orthogonal coordinate system with respect to the Z axis is the X axis, a parallel light beam separated by a slight amount d in the Y direction from the incident surface side of the optical system is incident and exits from the optical system. NA′yi, which is the angle between the two rays in the YZ plane, NA′yi, and NA′yi divided by the width d of the parallel light flux, NA′yi / d, is the Y direction of the optical system. The direction until the axial principal ray reaches the first surface of the optical system is the Z-axis direction, the decentered plane of the surface is the Y-axis direction, the Y-axis, and the Z-axis constitute an orthogonal coordinate system When the axis to be operated is the X-axis, a parallel light beam separated by a small amount d in the X direction from the incident surface side of the optical system is incident on the optical system. The angle sin formed in the plane including the axial principal ray emitted perpendicularly to the YZ plane of the two rays on the side exiting from NA ′ is divided by NA′xi, and NA′xi is divided by the width d of the parallel beam. When the value NA′xi / d is the power Px in the X direction of the optical system,
0.3 <| Px / Py | <2 (12)
An imaging optical system characterized by satisfying the above.
[0122]
[26] In the above [25],
0.8 <| Px / Py | <1.2 (12) ′
An imaging optical system characterized by satisfying the above.
[0123]
[27] The imaging optical system according to any one of [1] to [26], wherein the lateral aberration of the optical system is 200 μm or less.
[0124]
[28] The imaging optical system according to any one of [1] to [26], wherein an image distortion of the optical system is 20% or less.
[0125]
[29] The imaging apparatus according to any one of [1] to [27], further including an imaging device arranged to receive an object image formed by the optical system.
[0126]
[30] The image pickup apparatus according to [29], wherein the image pickup device is formed of an electronic image pickup device having a function of converting light received by the image pickup device into electrical information.
[0127]
[31] The imaging apparatus according to [30], further comprising observation means for observing the object image received by the electronic imaging element.
[0128]
【The invention's effect】
As is clear from the above description, according to the present invention, it is possible to provide an imaging optical system that is small and generates less aberration than a rotationally symmetric transmission optical system.
[Brief description of the drawings]
FIG. 1 is a sectional view including an optical axis of an imaging optical system according to a first embodiment of the present invention.
2 is a lateral aberration diagram of Example 1. FIG.
3 is a distortion aberration diagram of Example 1. FIG.
FIG. 4 is a conceptual diagram of a configuration in which the imaging optical system of the present invention is incorporated in an imaging apparatus.
FIG. 5 is a diagram for explaining an axial principal ray and a coordinate system in the present invention.
FIG. 6 is a conceptual diagram for explaining curvature of field generated by an eccentric reflecting surface.
FIG. 7 is a conceptual diagram for explaining astigmatism generated by a decentered reflecting surface.
FIG. 8 is a conceptual diagram for explaining coma aberration generated by a decentered reflecting surface.
FIG. 9 is a diagram for explaining the power of the imaging optical system of the present invention.
FIG. 10 is a diagram for explaining a parameter DY used in the present invention.
[Explanation of symbols]
1 ... Aperture
2 ... Axial chief ray
3 ... front group
4 ... Rear group (Eccentric prism optical system)
5. First surface of decentered prism optical system
6 ... Second surface of decentered prism optical system
7 ... Third surface of decentered prism optical system
8. Image plane
9 ... Filters
10. Imaging optical system
11 ... CCD
12 ... Processing means
13 ... CRT
14 ... Recording medium
15 ... Microphone

Claims (2)

In an imaging optical system for forming an object image on the imaging element surface,
Having a rear optical group at least on the image side of the pupil plane,
The rear optical group is at least 3 eccentrically arranged so that the entire surface is inclined with respect to the principal ray when a ray that exits the object center and passes through the pupil center and reaches the image center is used as an axial principal ray. Having a prism member with two surfaces,
The at least three surfaces include a surface having a transmission action, a curved surface having a rotationally symmetric surface sharing the reflection action and the transmission action, and a rotation having a reflection action and correcting rotationally asymmetric decentration aberrations caused by eccentricity. It consists of a curved surface with an asymmetric surface shape,
The surface having the transmitting action is the first surface, the curved surface having the rotationally symmetric surface shape sharing the reflecting action and the transmitting action is the second surface, and the curved surface having the rotationally asymmetric surface shape having the reflecting action is the third surface,
After the light from the object is incident on the first surface, the first surface to the third surface are configured to be reflected by the second surface, reflected by the third surface, and transmitted through the second surface. An imaging optical system characterized by that. 2. The imaging optical system according to claim 1 , wherein the prism member is composed of a single block formed integrally.

Images