JP3597692B2

JP3597692B2 - Imaging device

Info

Publication number: JP3597692B2
Application number: JP4975798A
Authority: JP
Inventors: 昌之西川; 英生岡田
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 1998-03-02
Filing date: 1998-03-02
Publication date: 2004-12-08
Anticipated expiration: 2018-03-02
Also published as: JPH11252467A

Description

【０００１】
【発明が属する技術分野】
本発明は、撮像素子の解像度よりも高い解像度の画像を得ることができる撮像装置に関する。
【０００２】
【従来の技術】
近年、電子スチルカメラ等の撮像装置において、該撮像装置で得られる画像の高解像度化が求められている。前記画像を高解像度化する第１の手法としては、前記撮像素子内に備えられる撮像素子の受光領域、いわゆる撮像素子の画素の数を、従来の撮像素子の画素の数よりも多くすることが考えられる。しかしながら、画素の数を多くした撮像素子は、生産性が乏しいために高価になりやすい。
【０００３】
前記画像を高解像度化する第２の手法として、前記従来の撮像素子を用い、かつ、いわゆるイメージシフトを行うことが考えられる。前記イメージシフトに関する従来技術は、特開平９−９１１５号公報と特開平３−１３９９９０号公報とに開示される。
【０００４】
図２６は、特開平９−９１１５号公報に開示される撮像装置１の被写体からの光の処理に関する部分の構成を示す図である。前記部分は、レンズ群３と、撮像素子４と、イメージシフト部５と、空間フィルタ部６とを含む。イメージシフト部５および空間フィルタ部６は、レンズ群３と撮像素子４との間に、この順で介在される。空間フィルタ部６は、光学ローパスフィルタ７と、光学ローパスフィルタ回転機構部８とを含む。イメージシフト手段は、平行平板ガラス９と、平行平板ガラス駆動部１０とを含む。平行平板ガラス９と光学ローパスフィルタ７とが、レンズ群３の光軸１１上に、この順で配置される。平行平板ガラス９は、光軸１１にそれぞれ直交し、かつ、相互に直交する２本の中心軸線を備える。平行平板ガラス駆動部１０は、２本の前記中心軸線をそれぞれ中心として、平行平板ガラス９を角変位させる。これによって、被写体からの光の光路が、光軸１１から平行移動される。
【０００５】
上述の撮像装置１では、平行平板ガラス９と光学ローパスフィルタ７とが、それぞれ光軸１１上に並べられているので、撮像装置１の前記部分の光軸１１に平行な方向の長さが、長くなり易い。この結果、撮像装置１の小型化が困難になる。また、イメージシフト部５と空間フィルタ部６とが別々に設けられているので、イメージシフトを行わない従来の撮像装置よりも部品点数が増加する。この結果、撮像装置１の製造コストが増加しやすい。
【０００６】
また、特開平３−１３９９９０号公報に開示される撮像装置の被写体からの光の処理に関する部分の構成は、以下のとおりである。前記部分は、撮影レンズと、撮像素子と、回転フィルタとを含む。前記回転フィルタは、無色透明で厚みのある平行平板であり、屈折率が空気の屈折率とは異なる。前記回転フィルタは、前記撮影レンズと前記撮像素子との間に介在され、予め定める回転軸を中心に、角変位される。前記回転軸は、前記撮像素子の撮像面に垂直であり、かつ前記回転フィルタの平面と９０度未満の角度で交わる。この結果、前記回転フィルタが角変位されることに伴い、被写体からの光の光路が、前記撮影レンズの光軸から平行移動される。
【０００７】
【発明が解決しようとする課題】
特開平３−１３９９９０号公報の前記撮像装置は空間フィルタを含んでいない。前記撮像装置に空間フィルタを付加える場合、特開平９−９１１５号公報の撮像装置１と同様に、前記撮像装置の小型化が困難になり、また、前記撮像装置の部品点数が増加しやすい。また、前記回転フィルタを角変位させることに伴って、該回転フィルタの空間周波数特性が変化することがあると予想されるが、前記回転フィルタは前記空間周波数特性の変化を考慮していないので、前記回転フィルタの角変位に拘わらず前記撮像装置に最適の空間周波数特性を保つことの実現性は、乏しい。
【０００８】
本発明の目的は、従来の撮像装置よりも高解像度の画像を撮像する撮像装置であって、前記高解像度の画像に応じた空間周波数特性をイメージシフトを行う際にも保つことができ、かつ、小型化と薄型化と組立てコストの低減化とが可能な撮像装置を提供することである。
【０００９】
【課題を解決するための手段】
本発明は、被写体からの光を集光する光学系と、
前記光学系によって集光された光が結像される結像面を有する撮像素子と、
前記光学系と前記撮像素子との間に介在される少なくとも１枚の複屈折板を、含む空間フィルタと、
前記撮像素子へ入射される光の光路をずらすために、前記空間フィルタ内の全ての複屈折板のうちの少なくとも１枚の複屈折板と前記光学系の光軸との角変位による位置関係を変化させるイメージシフト手段と、
前記イメージシフト手段が前記位置関係を変化させるたびに、前記撮像素子に、画像を表す画像信号を生成させる撮像制御手段と、
複数の前記画像信号を合成する合成手段とを含み、
前記位置関係は、前記位置関係が変化される前後で、前記空間フィルタを通過した常光線Ｌｅｏｏ，Ｌｏｅｏと、異常光線Ｌｅｏｅ，Ｌｏｅｅとの分離幅ｄ３と、常光線Ｌｅｏｏ，Ｌｏｅｏから異常光線Ｌｅｏｅ，Ｌｏｅｅへ向かう方向とを等しく保たせて、変化されることを特徴とする撮像装置である。
【００１０】
本発明に従えば、前記撮像装置は、前記空間フィルタの一部と前記イメージシフト手段とが上述のように動作することによって、いわゆるイメージシフトの効果を得る。これによって、被写体からの光の光路のうちの前記光学系と前記撮像素子との間の部分には、前記空間フィルタ内の全ての複屈折板だけが介在され、前記部分に従来介在されていたイメージシフト用の屈折板が、省略される。したがって、前記光学系と前記撮像素子との間の間隔を、前記イメージシフト用の屈折板の分だけ、従来技術の撮像装置内の光学系と撮像素子との間の間隔よりも短くすることができる。ゆえに、いわゆるバックフォーカスが、従来技術の撮像装置よりも短くなるので、本発明の撮像装置は、従来技術の撮像装置よりも、小型化することができる。また、前記イメージシフト用の屈折板が除かれたことによって、本発明の撮像装置の部品点数が従来技術の撮像装置よりも減少する。ゆえに、本発明の前記撮像装置は、従来技術の撮像装置よりも、軽量化することができ、かつ、組立てコストを低減化することができる。
【００１２】
また前記撮像装置の前記空間フィルタは、前記位置関係の変化に拘わらず、常に予め定める空間周波数特性を保つことができる。ゆえに、前記予め定める空間周波数特性を、前記撮像装置で生成される画像信号が表す画像の解像度に対して適正な空間周波数特性に予めしておけば、前記撮像素子は、前記位置関係の変化に拘わらず、前記適性な空間周波数特性の空間フィルタを通して、被写体を常に撮像することができる。
イメージシフト手段は、空間フィルタ内の全ての複屈折板のうちの少なくとも１枚の複屈折板と光学系の光軸との角変位による位置関係を変化させる。この位置関係は、前記位置関係が変化される前後で、前記空間フィルタを通過した常光線Ｌｅｏｏ，Ｌｏｅｏと、異常光線Ｌｅｏｅ，Ｌｏｅｅとの分離幅ｄ３と、常光線Ｌｅｏｏ，Ｌｏｅｏから異常光線Ｌｅｏｅ，Ｌｏｅｅへ向かう方向とを等しく保たせて、変化される。
【００１３】
また本発明は、被写体からの光を集光する光学系と、
前記光学系によって集光された光が結像される結像面を有する撮像素子と、
前記光学系と前記撮像素子との間に介在される少なくとも１枚の複屈折板を、含む空間フィルタと、
前記撮像素子へ入射される光の光路をずらすために、前記空間フィルタ内の全ての複屈折板のうちの少なくとも１枚の複屈折板と前記光学系の光軸との位置関係を変化させるイメージシフト手段と、
前記イメージシフト手段が前記位置関係を変化させるたびに、前記撮像素子に、画像を表す画像信号を生成させる撮像制御手段と、
複数の前記画像信号を合成する合成手段とを含み、
前記少なくとも１枚の複屈折板のうちの少なくとも１枚の複屈折板は、前記光軸に垂直な基準平面に対して傾斜しており、
前記イメージシフト手段は、前記少なくとも１枚の複屈折板を、前記光軸に平行な基準軸線を中心に角変位させることを特徴とする撮像装置である。
【００１４】
本発明に従えば、前記撮像装置の前記少なくとも１枚の複屈折板は、前記光路をずらすために、前記基準平面に対して予め傾斜されてあり、前記イメージシフト手段は上述の動作を行う。これによって、傾斜された前記複屈折板と前記光軸との位置関係、たとえば傾斜された前記複屈折板の入射面と光軸との成す角度が変化するので、前記イメージシフトの効果を得ることができる。したがって、前記イメージシフト手段の構成が、屈折板を光軸に垂直な基準軸線を中心に角変位させる従来技術のイメージシフト手段と比較して、簡単になる。また、傾斜された前記複屈折板と前記基準平面とのなす角度は、前記撮像装置の組立て工程で精密に調整することが容易にでき、かつ、傾斜された前記複屈折板は前記基準軸線回りに角変位されるだけなので、前記位置関係を精密に変化させることが容易にできる。したがって、前記撮像装置のイメージシフトの精度を向上させることができる。
【００１５】
また本発明は、前記撮像素子の結像面には、複数の矩形の受光領域が、行列状に配置されており、
傾斜された前記複屈折板は、角変位させるべき前記複屈折板が角変位される前の前記空間フィルタを通過した光の光路から、角変位させるべき前記複屈折板が角変位された後の前記空間フィルタを通過した光の光路が、前記受光領域の対角線に平行な方向にずれるように、傾斜されており、
傾斜された前記複屈折板と前記基準平面とのなす角度は、２つの前記光路間の距離が、画素の対角線に平行な方向に並ぶ２つの画素の中心間の距離の半分になるように、設定されることを特徴とする。
【００１６】
本発明に従えば、前記撮像装置内の傾斜された前記複屈折板と前記基準平面とのなす角度と、該複屈折板の傾斜する方向とは、上述のように定められる。この結果、前記２つの光路は、前記画素の対角線に平行な方向に前記２つの画素間の距離の半分の距離だけ、相互にずれる。前記合成手段は、角変位させるべき前記複屈折板が角変位される前に前記撮像素子が生成した画像信号と、前記角変位させるべき複屈折板が角変位された後に前記撮像素子が生成した画像信号とを、合成する。この結果、合成された画像信号が表す画像の解像度は、前記撮像素子の解像度よりも高くなる。ゆえに、前記撮像素子の解像度よりも高解像度の画像を得るために必要な画像信号が２つで良いので、撮像素子が被写体を撮像するために要する時間を最短にすることができるため、前記撮像装置の利便性が向上される。
【００１７】
また本発明は、前記イメージシフト手段が角変位させるべき前記複屈折板を角変位させる角度は、１８０度であることを特徴とする。
【００１８】
本発明に従えば、前記イメージシフト手段は、角変位させるべき前記複屈折板を、１８０度角変位させることが好ましい。これの第１の理由は、前記複屈折板の角変位の角度が１８０度であるときが、前記複屈折板と前記基準平面とのなす角度を最も小さくすることができるので、前記複屈折板の傾斜に拘わる画像の画質の低下を、最も小さくすることができるからである。第２の理由は、以下のとおりである。前記角変位させるべき複屈折板は前記基準軸線まわりに１８０度角変位されるので、前記角変位させるべき複屈折板の形状は、前記基準軸線を対称中心として、点対称にすることができる。したがって、現行の撮像装置で用いられている略長方形の複屈折板を、本発明の撮像装置の空間フィルタに流用することができる。ゆえに、複屈折板の角変位の角度が１８０度であるならば、前記撮像装置の製造コストの増加を、抑えることができるのである。
【００１９】
また本発明は、全ての角変位させるべき前記複屈折板のうちの複数の複屈折板が、前記基準平面に対して傾斜している場合、前記複数の複屈折板それぞれと前記基準平面とのなす角度は、相互に等しいことを特徴とする。
【００２０】
本発明に従えば、上記場合、前記複数の複屈折板それぞれと前記基準平面がなす角度は、相互に等しい。これによって、前記撮像装置の組立て時の前記傾斜させるべき複数の複屈折板の角度調整が、容易になる。また、同じ角度で傾斜する複屈折板の枚数が増加するほど、傾斜する全ての複屈折板の前記光軸に平行な方向の厚みの和が、増加する。これによって、傾斜するべき複数の複屈折板それぞれと前記基準平面とがなす角度を、前記同じ角度で傾斜する複屈折板の枚数が増加するほど、小さくすることができる。したがって、たとえば収差に起因する前記画像の画質の低下を、小さくすることができる。
【００２１】
また本発明は、角変位されるべき前記複屈折板が角変位される前の前記空間フィルタの空間周波数特性と、角変位されるべき前記複屈折板が角変位された後の前記空間フィルタの空間周波数特性とが、等しいことを特徴とする。
【００２２】
本発明に従えば、前記空間フィルタは、傾斜された前記複屈折板が角変位されたか否かに拘わらず、常に予め定める空間周波数特性を保つことができる。ゆえに、前記予め定める空間周波数特性を、前記撮像装置で生成される画像信号が表す画像の解像度に対して適正な空間周波数特性に予めしておけば、前記撮像素子は、傾斜された前記複屈折板が角変位されたか否かに拘わらず、前記適性な空間周波数特性の空間フィルタを通して、被写体を常に撮像することができる。
【００２３】
【発明の実施の形態】
図１は、本発明の第１実施形態である撮像装置２０の全体の構成を示すブロック図である。撮像装置２０は、レンズ群２３、第１空間フィルタ２４、複屈折板駆動部２５、撮像素子２６、制御装置２７、メモリ装置２８、および合成装置２９を含む。
【００２４】
レンズ群２３は１または複数のレンズから構成されて、単一の光軸２２を有する。第１空間フィルタ２４は、レンズ群２３と撮像素子２６との間に介在される。第１空間フィルタ２４は、予め定める空間周波数特性を有し、被写体２１からの光の空間周波数成分の一部を制限する。前記光は、レンズ群２３によって集光され、第１空間フィルタ２４を通過して、撮像素子２６の撮像面４１上に結像される。
【００２５】
第１空間フィルタ２４は、１枚の複屈折板、または光軸２２に沿って順次的に配置される複数の複屈折板を有する。本実施形態では、第１空間フィルタ２４は、第１〜第３複屈折板３３〜３５を有する。第１〜第３複屈折板３３〜３５はいずれも、平行な２つの表面を有する平板である。前記１または複数の複屈折板のうちの少なくとも１枚は、前記光軸に垂直な基準平面３７に対して、傾斜されている。本実施形態では、第１および第２複屈折板３３，３４は、基準平面３７に対して平行であり、第３複屈折板３５が、その表面と基準平面３７とが傾斜角度θ１をなすように、傾斜されている。
【００２６】
複屈折板駆動部２５は、制御装置２７によって制御され、全ての複屈折板のうちの傾斜された前記少なくとも１枚の複屈折板を含む１または複数の複屈折板を、光軸２２に平行な基準軸線まわりに、予め定める基準角度だけ、角変位させる。本実施形態では、複屈折板駆動部２５は、第１〜第３複屈折板３３〜３５の全てを角変位させ、前記基準軸線は光軸２２と一致しており、前記基準角度は１８０度である。すなわち、複屈折板駆動部２５は、イメージシフトのために、第１空間フィルタ２４内の少なくとも１枚の角変位させるべき複屈折板と光軸２２との位置関係を変化させるための、イメージシフト部に相当する。また、前記角変位させるべき複屈折板と複屈折板駆動部２５とが、従来技術のイメージシフト部と同じ働きをする。
【００２７】
撮像素子２６は、撮像面に結像された前記光を光電変換して画像信号を生成し、前記画像信号をメモリ装置２８に記憶させる。撮像素子２６は、いわゆる白黒単板の構造、いわゆるカラー３板の構造、およびいわゆる単板カラーの構造のいずれかの構造を有し、本実施形態では、ベイヤ配列単板カラーの構造であると仮定して説明する。
【００２８】
制御装置２７は、撮像素子２６と複屈折板駆動部２５とを制御して、複屈折板駆動部２５が角変位させるべき複屈折板、すなわち第１〜第３複屈折板３３〜３５を角変位させるたびに、撮像素子２６に光電変換を行わせ、この結果得られる前記画像信号をメモリ装置２８に記憶させる。さらに制御装置２７は、メモリ装置２８に記憶された複数の画像信号のうちで、撮像素子２６で続けて生成された２つの画像信号を、合成装置２９に与えさせる。合成装置２９は、前記２つの画像信号を合成する。さらに合成装置２９は、前記合成の結果得られる単一の合成画像信号に予め定める補間処理を施して、撮像素子２６の解像度よりも高い解像度の画像を表す出力画像信号を生成する。前記出力画像信号は、メモリ装置２８に記憶されると共に、撮像装置２０の外部に出力される。制御装置２７と合成装置２９とは、たとえばマイクロコンピュータによって実現され、メモリ装置２８はたとえばランダムアクセスメモリによって実現される。
【００２９】
上述したように、本実施形態の撮像装置２０では、また、第１空間フィルタ２４内の全ての複屈折板３３〜３５のうちの少なくとも１枚の傾斜された複屈折板、本実施形態では第３複屈折板３５が、イメージシフトのための屈折板を兼ねる。ゆえに、レンズ群２３と撮像素子２６との間には、第１空間フィルタ２４だけが介在され、前記屈折板が介在されない。これによって、イメージシフトを行う従来技術の撮像装置と比較して、レンズ群２３と撮像素子６との間の間隔を、短くすることができる。したがって、撮像装置２０のバックフォーカスが前記従来技術の撮像装置のそれよりも短くなるので、撮像装置２０を前記従来技術の撮像装置よりも小型化しかつ薄型化することができる。また、撮像装置２０の部品点数が前記従来技術の撮像装置のそれよりも少なくなるので、撮像装置２０の製造コストを前記従来技術の撮像装置のそれよりも減少させることができる。
【００３０】
図２は、撮像素子２６の撮像面４１の正面図である。撮像素子２６は、ＣＣＤ（電荷結合素子）イメージセンサによって実現される。撮像素子２６の撮像面４１には複数の画素４２、すなわち複数の受光領域が、水平方向ｘに予め定める第１のピッチＰｘをあけて、かつ、垂直方向ｙに予め定める第２のピッチＰｙをあけて、行列状に配置される。図２では、画素を矩形で示す。水平方向ｘは図１では紙面に垂直な方向であってかつ図２では紙面の左右方向であり、垂直方向ｙは図１および図２のどちらでも紙面の上下方向であると仮定する。また、光軸２２に平行な方向を、Ｚ方向または光軸方向と称することがある。本実施形態では、撮像面４１は、いわゆるベイヤ配列の単板カラーの構成を有するものと仮定する。本実施形態では、第１および第２のピッチＰｘ，Ｐｙは等しいと仮定し、第１および第２のピッチＰｘ，ＰｙをピッチＰと総称する。また、行列状に画素４２が配置された状態において、水平方向ｘに平行に並ぶ画素の一群を行と称し、垂直方向ｙに並ぶ画素の一群を列と称する。
【００３１】
一般的な単板カラーの構造の撮像素子の各画素は、光の３原色のうちの予め定めるいずれか１つの色の輝度を検出し、かつ各画素が検出するべき色の輝度は各画素毎に異なる。ベイヤ配列は、カラー光の３原色の各色の輝度をそれぞれ検出する３種類の画素の配列の１つであり、全ての画素を、赤の輝度を検出する画素と青の輝度を検出する画素と緑の画素を検出する画素との３種類に区分し、各色の輝度を検出する画素を２行２列の４つの画素単位で並べる配列である。図面では、赤、緑、青の輝度を検出する画素を表す矩形内に、「Ｒ」，「Ｇ」，「Ｂ」をそれぞれ記載して示す。
【００３２】
ベイヤ配列における各色の輝度を検出する画素４２Ｒ，４２Ｂ，４２Ｇの具体的な配置を、単板カラーの撮像素子の撮像面４１内に行列状に並べられた全ての画素のうちの、任意の隣合う一対の行４５，４６を例に説明する。一対の行のうちの一方の行４５内では、緑の輝度を検出する画素４２Ｇと青の輝度を検出する画素４２Ｂとが、交互に並ぶ。一対の行のうちの他方の行４６内では、赤の輝度を検出する画素４２Ｒと緑の輝度を検出する画素４２Ｇとが、交互に並ぶ。かつ、一方の行４５内の緑の輝度を検出する画素４２Ｇと他方の行４６内の緑の輝度を検出する画素４２Ｇとは、水平方向ｘにピッチＰだけずれている。撮像面４１全体では、上述の一対の行４５，４６と同じ構成の行が周期的に配置される。
【００３３】
図３は、第１〜第３複屈折板３３〜３５が角変位される前後の第１空間フィルタ２４とを示す図である。以後の説明のために、第１〜第３複屈折板３３〜３５が角変位させる前の第１空間フィルタの状態を、第１状態、第１〜第３複屈折板３３〜３５が予め定める基準角度だけ角変位された後の第１空間フィルタの状態を、第２状態と定義する。また、第１および第２状態の第１空間フィルタ２４を通過する前の被写体２１からの光の光路５１，５２は、どちらもレンズ群２３の光軸２２と一致していると仮定する。また、第１〜第３複屈折板３３〜３５の２つの表面のうちで、前記光が入射する側の表面を、入射面と称する。
【００３４】
第１状態の第１空間フィルタ２４内の第１および第２複屈折板３３，３４の入射面は光軸２２に垂直なので、第１および第２複屈折板３３，３４を角変位させた後も、前記入射面は光軸２２に垂直である。すなわち、前記第１状態の第１空間フィルタ２４内の第１および第２複屈折板３３，３４の入射面と前記光路５１とが成す角度は、前記第２状態の第１空間フィルタ２４内の第１および第２複屈折板３３，３４の入射面と前記光路５２とが成す角度と、等しい。
【００３５】
第１状態の第１空間フィルタ２４の第３複屈折板３５は基準平面３７に対して傾斜角度θ１で傾斜している。ゆえに、たとえば、前記光路５１，５２と第３複屈折板３５の入射面との成す角度を前記光路５１，５２と前記入射面との交点を中心に時計まわりに計測する場合、第１状態の第１空間フィルタ２４内の第３複屈折板３５の入射面と前記光路５１との成す角度θａ１は、第２状態の第１空間フィルタ２４内の第３複屈折板３５の入射面と前記光路５２との成す角度θａ２と、異なる。前記角度θａ２は、たとえば、１８０度から角度θａ１を減算した角度である。
【００３６】
このように、傾斜された複屈折板が角変位されることに応じて、前記傾斜された複屈折板の入射面と第１空間フィルタ２４通過前の前記光の光路との成す角度が変化するので、前記角度の変化に伴い、第１空間フィルタ２４を通過した後の被写体２１からの光の光路の位置が、変化する。前記第１状態の第１空間フィルタ２４通過後の前記光の光路、すなわち第１光路５３と、前記第２状態の第１空間フィルタ２４通過後の前記光の光路、すなわち第２光路５４の位置関係は、具体的には、以下のとおりである。
【００３７】
第１光路５３は、光軸２２から、予め定める第１の方向ａ１に、予め定める第１の距離Ｄ１だけ、光軸２２と平行にずれる。第２光路５４は、光軸２２から、第１の方向ａ１と反対の第２の方向ａ２に、第１の距離Ｄ１だけ、光軸２２と平行にずれる。第１の方向ａ１は光軸２２と垂直であるので、第１および第２の方向ａ１，ａ２は、どちらも、基準平面３７に平行である。さらに、第２の方向ａ２は垂直方向ｙと予め定める角度φを成す。この結果、第２光路５４は、第１光路５３から、第２の方向ａ２に、第１の距離Ｄ１の２倍の距離Ｄ３だけ離れる。
【００３８】
２つの前記光路５３，５４間の距離Ｄ３は、角変位するべき全ての複屈折板のうちの傾斜した複屈折板の傾斜角度と、前記傾斜した複屈折板の厚みとに応じて定まる。第３複屈折板３５の傾斜角度θ１は、前記傾斜した複屈折板の厚みを考慮し、距離Ｄ３が、前述したピッチＰの√２分の１（Ｐ／√２）倍の長さになるように、設定されている。前記長さは、撮像面４１の画素４２の対角線に平行な方向Ｕに並ぶ２つの画素４２の中心間の距離の半分に相当する。また、第１光路５３から第２光路５４へ向かう方向、すなわち第２の方向ａ２は、前記傾斜した複屈折板の傾斜方向によって定まる。前記傾斜方向は、前記傾斜した複屈折板の表面の法線と光軸２２とを含む前記仮想平面に平行な方向であり、前記傾斜方向は垂直方向ｙと前記角度φを成す。第３複屈折板３５の前記傾斜方向は、第２の方向ａ２が、前述した撮像面４１の画素４２の対角線に平行な方向Ｕになるように、調整されている。
【００３９】
図４は、複屈折板駆動部２５の具体的構成を示す図である。複屈折板駆動部２５は、円筒状の保持部材６１と、ウォーム６２と、モータ６３と、複数の回転ローラ６４と、カウンタ６５とを含む。
【００４０】
保持部材６１には、その中心軸線６８に平行な方向に貫通する保持孔６６が設けられる。保持孔６６には、第１空間フィルタ２４内の角変位させるべき複屈折板、本実施形態では第１〜第３複屈折板３３〜３５が、嵌め込まれる。複屈折板駆動部２５が撮像装置２０に組込まれた場合、光軸２２は保持孔６６を貫通する。保持部材６１は、たとえば、保持部材６１の外周端の円の中心軸線６８が光軸２２と一致しており、光軸２２を中心に角変位することができる。第１〜第３複屈折板３３〜３５は、複屈折板駆動部２５が撮像装置２０に組込まれた時点で、第１および第２複屈折板３３，３４が光軸２２に垂直であり、かつ、第３複屈折板３５が基準平面３７に対して傾斜角度θ１だけ傾斜され、さらに、第１〜第３複屈折板の光学軸方向が第１または第２状態における後述する位置関係を保つように、保持部材６１に嵌め込まれる。
【００４１】
保持部材６１の外周部６７には歯車の歯が形成されて、保持部材６１がウォーム歯車、すなわちウォームホイールになっている。外周部６７の歯車の歯は、ウォーム６２に噛み合わされる。ウォーム６２はモータ６３の回転軸に取付けられる。複数の回転ローラ６４は、少なくとも３つあり、保持部材６１の周囲に配置される。前記各回転ローラ６４は、外周部６７の歯車の歯にそれぞれ噛み合わされる。これによって保持部材６１の外周部６７の少なくとも３点が、支持される。モータ６３が駆動されると、モータ６３の回転力がウォーム６２に伝達され、ウォーム６２の回転に伴って、保持部材６１は光軸２２を中心に角変位する。カウンタ６５はモータ６３の回転数を計数しており、計数した回転数を制御装置２７に与える。
【００４２】
制御装置２７は、モータ６３の回転数と第１〜第３複屈折板３３〜３５の角変位量との関係、すなわち、たとえばモータ６３の予め定める回転数あたりに保持部材６１が角変位する角度を、予め備えている。制御装置２７は、前記関係とカウンタ６５から与えられたモータ６３の回転数とに基づいて、モータ６３が回転し始めた時点からカウンタ６５が前記回転数を計数した時点までに第１〜第３複屈折板３３〜３５が角変位した角度を求めることができる。したがって、制御装置２７は、求められた前記角度に基づいて、モータ６３をさらに駆動させまたは停止させて、第１〜第３複屈折板３３〜３５の角度を、所望の角度にすることができる。
【００４３】
このように、複屈折板駆動部２５は極めて簡単な構成の機構なので、小型化が容易である。また、極めて簡単な構成の複屈折板駆動部２５によって、前記角変位させるべき複屈折板を、確実に所望の角度だけ角変位させることができる。また、傾斜させるべき複屈折板、本実施形態では第３複屈折板３５の傾斜角度θ１は、第３複屈折板３５を保持部材６１に取付ける際に定められるので、傾斜角度を精密に調整することができる。かつ、実際に撮像素子２６が被写体を撮像する際には、第３複屈折板３５の角変位する角度を定めるだけで、第１空間フィルタ２４通過後の光の光路を、上述のように平行移動させることができる。したがって、簡単な構成の複屈折板駆動部２５を用いる場合でも、イメージシフトの精度を良くすることができる。
【００４４】
以下に、撮像装置２０が被写体２１を撮像して前記出力画像信号を出力するまでの挙動を、概略的に説明する。
【００４５】
撮像素子２６は、予め定める周期で光電変換を２回行い、各回の光電変換終了後に、それぞれ画像信号を出力する。複屈折板駆動部２５は、撮像素子２６が１回目の光電変換を行なう間、角変位させるべき複屈折板、本実施形態では第１〜第３複屈折板３３〜３５を固定して、第１空間フィルタ２４に前記第１状態を保たせる。第１〜第３複屈折板３３〜３５は、１回目の光電変換が終了した時点から２回目の光電変換が始まる時点までの間に、前記基準角度だけ角変位され、この結果、第１空間フィルタ２４は前記第１状態から前記第２状態へ移る。第２状態の第１空間フィルタ２４の空間周波数特性と、第１状態の第１空間フィルタ２４の空間周波数特性とは、等しい。複屈折板駆動部２５は、撮像素子２６が２回目の光電変換を行なう間、第１〜第３複屈折板３３〜３５を固定して、第１空間フィルタ２４に前記第２状態を保たせる。また、第１空間フィルタ２４は、１回目の光電変換の間に前記第２状態を保ち、２回目の光電変換の間に前記第１状態を保っても良い。
【００４６】
これによって、２回目の光電変換の間にレンズ群２３および第１空間フィルタ２４を通過した光の光路は、１回目の光電変換の間にレンズ群２３および第１空間フィルタ２４を通過した光の光路から、撮像面４１の画素４２の対角線に平行な方向Ｕに、画素４２の配列のピッチＰの√２分の１倍の長さだけ、ずれる。このため、図５に示すように、撮像面４１上に結像される被写体像のうちの、１回目の光電変換の間に各画素４２上に結像されていた部分は、２回目の光電変換の間には、それぞれ、点線の矩形で示す位置４２ａに結像される。図５では、画素４２の行列内のｎ行ｍ列に属する画素に付加される参照符「４２」に、符号「（ｎ，ｍ）」がさらに付加される。また、１回目の光電変換の間にｎ行ｍ列の画素４２（ｎ，ｍ）に結像されていた前記部分が２回目の光電変換の間に結像される位置に付加される参照符「４２ａ」にも、符号「（ｎ，ｍ）」がさらに付加されている。ｎおよびｍは、それぞれ、任意の自然数である。図５から、複屈折板駆動部２５と第３複屈折板３５によって行われたイメージシフトのシフト量が、水平方向ｘに第１のピッチＰｘの半分であり、かつ、垂直方向ｙに第２のピッチＰｙの半分であることが分かる。すなわち前記シフト量は、画素４２の対角線に平行な方向Ｕに、画素の配列のピッチＰの√２分の１倍の長さである。
【００４７】
この結果、撮像素子２６は、２つの画像信号を出力する。各画像信号が表す画像は、撮像面４１の画素４２と同数の画素が、撮像面４１の画素４２の配列と相似の配列で、並べられて構成される。前記画像を構成する複数の画素は、撮像面４１の複数の画素４２と、１対１で対応している。前記画像の各画素の色相や明度等を示す画素データは、前記被写体像内の該各画素に対応する画素４２に結像された部分の色相や明度等に応じて、定められる。合成装置２９は、１回目および２回目の光電変換によって生成された２つの画像信号を合成して、合成画像信号を生成する。合成装置２９は、さらに、前記合成画像信号に予め定める補間処理を施す。この結果、前記出力画像信号が得られる。
【００４８】
図６は、前記出力画像信号を仮想的に目視表示した出力画像の一部分を示す図である。黒枠の矩形それぞれが、前記出力画像の画素を示す。前記出力画像の画素のうちで、参照符「ａ（ｎ，ｍ）」が描かれた画素は、１回目の光電変換によって生成された画像信号が表す画像のｎ行ｍ列の画素に相当し、該ｎ行ｍ列の画素の画素データが当て嵌められる。前記出力画像の画素のうちで、参照符「ｂ（ｎ，ｍ）」が描かれた画素は、２回目の光電変換によって生成された画像信号が表す画像のｎ行ｍ列の画素に相当し、該ｎ行ｍ列の画素の画素データが当て嵌められる。前記出力画像の画素のうちで、「○」が描かれた画素は、前記２つの画像信号が表す画像内のいずれの画素にも相当しない仮想画素であり、画素データは、補間処理によって決定される。前述したように、第２光路５４は、第１光路５３から、前記対角線に平行な方向Ｕに、ピッチＰの√２分の１倍の長さだけ平行移動しているので、参照符ｂ（ｎ，ｍ）が付された画素は、参照符ａ（ｎ，ｍ），ａ（ｎ＋１，ｍ＋１）が付された画素の間に挿入されている。前記仮想画素は、前記出力画像内に、市松状に配置されている。
【００４９】
この結果、前記出力画像は、前記画像信号が表す画像と比較して、画素の数が４倍であり、画素の行および列の数が、それぞれ２倍になっている。この結果、前記出力画像の水平方向ｘおよび垂直方向ｙの解像度は、撮像素子２６の水平方向ｘおよび垂直方向ｙの解像度の２倍にそれぞれなっている。すなわち、１回目および２回目の光電変換の間に第１空間フィルタ２４を通過した光の光路５３，５４を、画素４２の対角線に平行な方向にピッチＰの√２分の１倍の長さだけずらす場合、前記光路５３，５４の位置が、前記出力画像の解像度を撮像素子２６の解像度よりも向上させるための適正なシフトポジションになる。
【００５０】
また前記場合には、上述したように、２つの画像信号を用いて、前記出力画像の水平方向ｘおよび垂直方向ｙの解像度を、両方とも向上させることができる。第１および第２光路５３，５４のずれる方向やずれる間隔を、上述のように設定しない場合、前記出力画像の水平方向ｘおよび垂直方向ｙの解像度を両方とも向上させるには、３つ以上の画像信号が必要になると予想される。これらのことから、第１および第２光路５３，５４の関係を上述した関係にした場合が、１枚の前記出力画像を得るために撮像素子２６が生成するべき画像信号の数を、最も少なくすることができる。ゆえに、１枚の前記出力画像を得るために撮像素子２６が被写体を撮像するために要する時間を、最も短くすることができる。したがって、撮像装置２０の利便性を向上させることができる。
【００５１】
図７（Ａ）〜（Ｃ）は、前記第１状態の第１空間フィルタ２４の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の方向を示す図である。第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３は、光軸２２に対して約４５度にそれぞれ切出されており、かつ投影方向がそれぞれ異なる。投影方向とは、光学軸方向ｑ１〜ｑ３をｘｙ平面、すなわち基準平面３７に投影した場合の投影像の方向であり、水平方向ｘに平行な座標軸と平行な該投影像の方向を基準の０度と定義する。第１複屈折板３３の光学軸方向ｑ１の前記投影方向は、水平方向ｘから反時計まわりに９０度である。第２複屈折板３４の光学軸方向ｑ２の前記投影方向は、水平方向ｘから時計まわりに０度である。第３複屈折板３５の光学軸方向ｑ３の前記投影方向は、水平方向ｘから反時計まわりに４５度である。
【００５２】
以下に、第１および第２状態の第１空間フィルタ２４の空間周波数特性を説明する。前記空間周波数特性は、第１空間フィルタ２４通過後の光の分離状態に応じて、定まる。一般的に、単一枚の複屈折板に入射した光は、前記複屈折板内部を通過する間に、常光線と異常光線とに分離され、常光線は前記入射した光の入射前の光路の延長線上に出射され、異常光線は前記入射前の光路から、該複屈折板の厚みに応じて定まる分離幅だけ、該複屈折板の光学軸方向の投影方向に、平行移動して出射する。常光線の振動面は、前記複屈折板の光学軸方向に垂直であり、異常光線の振動面は前記複屈折板の光学軸方向に平行である。第１〜第３複屈折板３３〜３５の厚さは、その分離幅ｄ１〜ｄ３が、それぞれ、前述したピッチＰの半分（Ｐ／２）、ピッチＰの半分、ピッチＰの√２分の１になるように、調整されている。
【００５３】
図８（Ａ）〜（Ｃ）は、前記第１状態の第１空間フィルタ２４における第１〜第３複屈折板３３〜３５の分離光像を説明するための図である。
【００５４】
レンズ群２３を通過した光は、まず第１複屈折板３３に入射する。前記光は、第１複屈折板３３を通過する間に、図８（Ａ）に示すように、常光線Ｌｏと異常光線Ｌｅとに分離されて出射する。第１複屈折板３３の常光線Ｌｏから第１複屈折板３３の異常光線Ｌｅへ向かう方向は、前記第１状態の第１複屈折板３３の光学軸方向ｑ１の投影方向、すなわち垂直方向ｙと、等しい。第１複屈折板３３の常光線Ｌｏと第１複屈折板３３の異常光線Ｌｅとは分離幅ｄ１だけ離れている。
【００５５】
次に、第２複屈折板３４に、第１複屈折板３３の常光線Ｌｏおよび異常光線Ｌｅが入射する。図８（Ｂ）に示すように、第１複屈折板３３の常光線Ｌｏは、第２複屈折板の異常光線Ｌｏｅとして、第２複屈折板３４を通過する間に、元の位置から分離幅ｄ２だけ、前記第１状態の第２複屈折板３４の光学軸方向ｑ２の投影方向、すなわち水平方向ｘにシフトして出射される。また第１複屈折板３３の異常光線Ｌｅは、図８（Ｂ）に示すように、第２複屈折板２４の常光線Ｌｅｏとして、第２複屈折板３４を通過する間も位置を変えずにそのまま出射される。第２複屈折板３３の常光線Ｌｏの振動面は光学軸方向ｑ２に平行なので、第１複屈折板３３の常光線Ｌｏに対応する第２複屈折板３４の常光線は存在しない。第１複屈折板３３の異常光線Ｌｅの振動面は光学軸方向ｑ２に垂直なので、第１複屈折板３４の異常光線Ｌｅに対応する第２複屈折板２４の異常光線は存在しない。
【００５６】
続いて、第３複屈折板３５に、第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅが入射する。第２複屈折板３４の異常光線Ｌｏｅは、第３複屈折板３５を通過する間に、図８（Ｃ）に示すように、第３複屈折板３５の常光線Ｌｏｅｏと第３複屈折板の異常光線Ｌｏｅｅとに分離されて、出射する。第２複屈折板３４の常光線Ｌｅｏは、第３複屈折板３５を通過する間に、図８（Ｃ）に示すように、第３複屈折板３５の常光線Ｌｅｏｏと第３複屈折板の異常光線Ｌｅｏｅとに分離されて、出射する。第３複屈折板３５の常光線Ｌｏｅｏから第３複屈折板の異常光線Ｌｏｅｅへ向かう方向、および第３複屈折板３５の常光線Ｌｅｏｏから第３複屈折板の異常光線Ｌｅｏｅへ向かう方向は、前記第１状態の第３複屈折板３５の光学軸方向ｑ３の投影方向、すなわち水平方向ｘから反時計まわりに４５度の方向と、それぞれ等しい。第３複屈折板３５の常光線Ｌｏｅｏと第３複屈折板の異常光線Ｌｏｅｅとは分離幅ｄ３だけ離れ、かつ第３複屈折板３５の常光線Ｌｅｏｏと第３複屈折板の異常光線Ｌｅｏｅとは分離幅ｄ３だけ離れている。
【００５７】
したがって、前記第１状態の第１空間フィルタ２４において最終的に得られる光の分離状態は、図８（Ｃ）の分離状態、すなわち図９で示す分離状態になる。前記分離状態は、具体的には、第３複屈折板３５の常光線Ｌｅｏｏと第３複屈折板３５の異常光線Ｌｏｅｅとが、水平方向ｘに平行に、前述のピッチＰと同じ間隔を空けて並び、かつ、第３複屈折板３５の常光線Ｌｏｅｏと第３複屈折板３５の異常光線Ｌｅｏｅとが、垂直方向ｙに平行に、前述のピッチＰと同じ間隔を空けて並んでいる。
【００５８】
図１０（Ａ）〜（Ｃ）は、前記第２状態の第１空間フィルタ２４の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の投影方向を示す図である。前記第２状態の第１空間フィルタ２４の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の投影方向は、前記第１状態の第１空間フィルタ２４の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の投影方向を、光軸２２と平行な軸線まわりに１８０度角変位させた方向になっている。具体的には、第１複屈折板３３の光学軸方向ｑ１の前記投影方向は、水平方向ｘから時計まわりに９０度である。第２複屈折板３４の光学軸方向ｑ２の前記投影方向は、水平方向ｘから時計まわりに１８０度である。第３複屈折板３５の光学軸方向ｑ３の前記投影方向は、水平方向ｘから時計まわりに１３５度である。
【００５９】
図１１（Ａ）〜（Ｃ）は、前記第２状態の第１空間フィルタ２４における第１〜第３複屈折板３３〜３５の分離光像を説明するための図である。図１１は、図８と比較して、常光線の位置と異常光線の位置とがそれぞれ入代わっている点が異なり、他は等しい。以下に、詳しく説明する。
【００６０】
レンズ群２３を通過した光は、まず第１複屈折板３３に入射する。前記光は、第１複屈折板３３を通過する間に、図１１（Ａ）に示すように、常光線Ｌｏと異常光線Ｌｅとに分離されて出射する。第１複屈折板３３の常光線Ｌｏから第１複屈折板３３の異常光線Ｌｅへ向かう方向は、前記第２状態の第１複屈折板３３の光学軸方向ｑ１の投影方向、すなわち水平方向ｘから時計まわりに９０度の方向と等しい。第１複屈折板３３の常光線Ｌｏと第１複屈折板３３の異常光線Ｌｅとは、分離幅ｄ１だけ離れている。
【００６１】
次に、第２複屈折板３４に、第１複屈折板３３の常光線Ｌｏおよび異常光線Ｌｅが入射する。図１１（Ｂ）に示すように、第１複屈折板３３の常光線Ｌｏは、第２複屈折板の異常光線Ｌｏｅとして、第２複屈折板３４を通過する間に、元の位置から分離幅ｄ２だけ、前記第２状態の第２複屈折板３４の光学軸方向ｑ２の投影方向、すなわち水平方向ｘから時計まわりに１８０度の方向にシフトして出射される。また第１複屈折板３３の異常光線Ｌｅは、図１１（Ｂ）に示すように、第２複屈折板２４の常光線Ｌｅｏとして、第２複屈折板３４を通過する間も位置を変えずにそのまま出射される。第１複屈折板３３の常光線Ｌｏに対応する第２複屈折板３４の常光線と、第１複屈折板３４の異常光線Ｌｅに対応する第２複屈折板２４の異常光線とは、図８と同じ理由から、存在しない。
【００６２】
続いて、第３複屈折板３５に第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅが入射する。図１１（Ｃ）に示すように、第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５を通過する間に、第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとにそれぞれ分離されて、出射する。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとは、それぞれ分離幅ｄ３だけ離れている。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏから第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅへ向かう方向は、前記第２状態の第３複屈折板３５の光学軸方向ｑ３の投影方向、すなわち、水平方向ｘから反時計まわりに１３５度の方向と、それぞれ等しい。したがって、前記第２状態の第１空間フィルタ２４において最終的に得られる常光線と異常光線との分離状態は、図１１（Ｃ）の分離状態、すなわち図９で示す分離状態になる。
【００６３】
以上のことから、前記第１および第２状態の第１空間フィルタ２４において最終的に得られる光の分離状態は、等しいことが分かる。したがって、前記第１状態の第１空間フィルタ２４の空間周波数特性と、前記第２状態の第１空間フィルタ２４の空間周波数特性とは、等しくなる。したがって、前記空間周波数特性を、前記出力画像の解像度に適した空間周波数特性に予めしておけば、撮像素子２６は、被写体２１を、適正な空間周波数特性の第１空間フィルタ２４を介して撮像することができる。すなわち、イメージシフトのために第１空間フィルタ２４内の少なくとも１枚の複屈折板を角変位させたことに拘わらず、撮像素子２６は、被写体２１を、適正な空間周波数特性の第１空間フィルタ２４を介して常に撮像することができる。
【００６４】
第１〜第３複屈折板３３〜３５は、前記第１状態および第２状態において、光学軸方向方向ｑ１〜ｑ３の相互の位置関係が上述のようになっているならば、並び順を変更しても、最終的な分離状態は図９で示す状態になるので、空間周波数特性は上述したものと等しい。ゆえに、第１〜第３複屈折板３３〜３５の並び順は、上述した並び順から変更してもよい。また、上述の撮像装置２０において、基準平面３７に対して傾斜する複屈折板は、角変位される複屈折板のうちのいずれか１枚であればよいので、第３複屈折板３５の代わりに、第１または第２複屈折板３３，３４が、基準平面３７に対して傾斜されていてもよい。
【００６５】
以下に、本発明の第２実施形態の撮像装置について、説明する。第２実施形態の撮像装置は、第１実施形態の撮像装置２０と比較して、第１空間フィルタ２４が第２空間フィルタ８１に置換えられた点だけが異なり、他は等しい。第２実施形態の撮像装置の構成のうちの、第１実施形態の撮像装置２０と同じ部分に関する説明は、省略する。また、第２実施形態の撮像装置を構成する部品のうちの第１実施形態の撮像装置２０と同じ構成の部品には、同じ参照符を付す。
【００６６】
図１２は、第１状態の第２空間フィルタ８１と、第２状態の第２空間フィルタ８１とを示す図である。第２空間フィルタ８１は、第１複屈折板３３だけが基準平面３７に平行であり、第２および第３複屈折板３４，３５が、基準平面３７に対して予め定める傾斜角度θ２で傾斜している。複屈折板駆動部２５は、イメージシフトのために、実線で示す前記第１状態の第２空間フィルタ８１の第１〜第３複屈折板３３〜３５を、光軸２２に平行な軸線を中心に１８０度、角変位させる。この結果、第２空間フィルタ８１は前記第２状態になる。前記第２状態の空間フィルタの第２および第３複屈折板３４，３５は、基準平面３７に対して、２点破線で示すように、傾斜する。
【００６７】
第２実施形態では、図３で説明したことから類推して、傾斜された複屈折板、第２実施形態では第２および第３複屈折板３５が前記軸線を中心に角変位されることに応じて、第２空間フィルタ８１を通過した後の被写体２１からの光の光路の位置が、変化する。第１および第２状態の第２空間フィルタ８１を通過する前の被写体２１からの光の光路５１，５２は、どちらもレンズ群２３の光軸２２と一致していると仮定する。この場合、前記第２状態の第２空間フィルタ８１通過後の前記光の光路５４が、前記第１状態の第２空間フィルタ８１通過後の前記光の光路５３から、撮像面４１の画素４２の対角線に平行な方向Ｕに、画素４２の配列のピッチＰの√２分の１倍の長さだけずれるように、第２および第３複屈折板３４，３５の傾斜方向と第２および第３複屈折板３４，３５の傾斜角度とが、調整されている。
【００６８】
第２および第３複屈折板３４，３５は、図１２で示すように、第２および第３複屈折板３４，３５の間に間隔を空けて配置されてもよく、第２および第３複屈折板３４，３５を隙間なく接触させて配置されてもよい。また、第１実施形態で説明した理由と同じ理由から、第１〜第３複屈折板３３〜３５の並び順は、上述した並び順から変更してもよい。また、基準平面３７に対して傾斜する複屈折板は、角変位される複屈折板のうちのいずれか２枚であればよいので、第２および第３複屈折板３５の代わりに、第１および第２複屈折板３３，３４が基準平面３７に対して傾斜されていてもよく、第１および第３複屈折板３３，３５が基準平面３７に対して傾斜されていてもよい。
【００６９】
以下に、本発明の第３実施形態の撮像装置について、説明する。第３実施形態の撮像装置は、第１実施形態の撮像装置２０と比較して、第１空間フィルタ２４が第３空間フィルタ８３に置換えられた点だけが異なり、他は等しい。第３実施形態の撮像装置の構成のうちの、第１実施形態の撮像装置２０と同じ部分に関する説明は、省略する。また、第３実施形態の撮像装置を構成する部品のうちの第１実施形態の撮像装置２０と同じ構成の部品には、同じ参照符を付す。
【００７０】
図１３は、第１状態の第３空間フィルタ８３と、第２状態の第３空間フィルタ８３とを示す図である。第３空間フィルタ８３は、第１〜第３複屈折板３４，３５が、基準平面３７に対して予め定める傾斜角度θ３で傾斜している。複屈折板駆動部２５は、イメージシフトのために、実線で示す前記第１状態の第３空間フィルタ８３の第１〜第３複屈折板３３〜３５を、光軸２２に平行な軸線を中心に１８０度、角変位させる。この結果、第３空間フィルタ８３は２点鎖線で示す前記第２状態になる。第１〜第３複屈折板３３〜３５は、図１３で示すように、第１および第２複屈折板３３，３４の間と第２および第３複屈折板３４，３５の間とうちの少なくとも一方に間隔を空けて配置されてもよく、第１〜第３複屈折板３４，３５を隙間なく接触させて配置されてもよい。
【００７１】
第３実施形態では、図３で説明したことから類推して、傾斜された複屈折板、第３実施形態では第１〜第３複屈折板３３〜３５が前記軸線を中心に角変位されることに応じて、第３空間フィルタ８３を通過した後の被写体２１からの光の光路の位置が、変化する。第１および第２状態の第３空間フィルタ８３を通過する前の被写体２１からの光の光路５１，５２は、どちらもレンズ群２３の光軸２２と一致していると仮定する。この場合、前記第２状態の第３空間フィルタ８３通過後の前記光の光路５４が、前記第１状態の第３空間フィルタ８３通過後の前記光の光路５３から、撮像面４１の画素４２の対角線に平行な方向Ｕに、画素４２の配列のピッチＰの√２分の１倍の長さだけずれるように、第１〜第３複屈折板３３〜３５の傾斜方向と第１〜第３複屈折板３３〜３５の傾斜角度θ３が、調整されている。
【００７２】
第１〜第３実施形態において、前記第２状態の第１〜第３空間フィルタ２４，８１，８３通過後の光の光路５４は、どれも、前記第１状態の第１〜第３空間フィルタ２４，８１，８３通過後の光の光路５３から、画素４２の対角線に平行な方向Ｕに、ピッチＰの√２分の１倍の長さだけずれる。ゆえに、第２空間フィルタ８１の第２および第３複屈折板３４，３５の傾斜角度θ２は、第１空間フィルタ２４の第３フィルタ３５の傾斜角度θ１よりも、小さくて良い。また、第３空間フィルタ８３の第１〜第３複屈折板３３〜３５の傾斜角度θ３は、前記傾斜角度θ１，θ２よりも、小さくて良い。これは、傾斜された複屈折板が増える程、前記光の光路のうちの前記傾斜された複屈折板の内部を通る部分の長さが伸びるので、光路のずれの長さが伸びるからである。また、傾斜された複屈折板の傾斜角度が小さくなるほど、空間フィルタを通過する際に光が収差等の影響を受けにくくなるので、撮像素子２６が生成する画像信号が表す画像の画質の劣化を、抑えることができる。
【００７３】
以下に、本発明の第４実施形態の撮像装置について、説明する。第４実施形態の撮像装置は、第１実施形態の撮像装置２０と比較して、第１空間フィルタ２４が第４空間フィルタに置換えられた点だけが異なり、他は等しい。第４実施形態の撮像装置の構成のうちの、第１実施形態の撮像装置２０と同じ部分に関する説明は、省略する。また、第４実施形態の撮像装置を構成する部品のうちの第１実施形態の撮像装置２０と同じ構成の部品には、同じ参照符を付す。
【００７４】
前記第４空間フィルタは、第１〜第３複屈折板３３〜３５を有し、第１および第２複屈折板３３，３４のうちの少なくとも１枚が、基準平面３７に対して傾斜している。すなわち、第１複屈折板３３、あるいは第２複屈折板３４、または、第１および第２複屈折板３３，３４の両方が、基準平面３７に対して傾斜している。第１状態の前記第４空間フィルタにおける第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の相互の位置関係は、前記第１状態の第１空間フィルタ２４のそれと等しい。複屈折板駆動部２５は、第１および第２複屈折板３３，３４だけを１８０度角変位させる。第３複屈折板３５は常に固定されている。このために、たとえば、保持部材６１には、第１および第２複屈折板３３，３４だけが嵌め込まれ、第３複屈折板３５は、別の保持部材に固定されている。この場合、前記第２状態の第４空間フィルタ通過後の前記光の光路が、前記第１状態の第４空間フィルタ通過後の前記光の光路から、撮像面４１の画素４２の対角線に平行な方向Ｕに、画素４２の配列のピッチＰの√２分の１倍の長さだけずれるように、第１および第３複屈折板３３，３５のうちの傾斜されている複屈折板の傾斜方向および傾斜角度が、調整されている。
【００７５】
図１４（Ａ）〜（Ｃ）は、前記第２状態の前記第４空間フィルタの第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の投影方向を示す図である。第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３は、光軸２２に対して約４５度にそれぞれ切出されている。第１複屈折板３３の光学軸方向ｑ１の前記投影方向は、水平方向ｘから時計まわりに９０度である。第２複屈折板３４の光学軸方向ｑ２の前記投影方向は、水平方向ｘから時計まわりに１８０度である。第３複屈折板３５の光学軸方向ｑ３の前記投影方向は、図７（Ｃ）に示す方向と等しく、水平方向ｘから反時計まわりに４５度である。
【００７６】
図１５（Ａ）〜（Ｃ）は、前記第２状態の前記第４空間フィルタにおける第１〜第３複屈折板３３〜３５の分離光像を説明するための図である。図１５を用いて、前記第２状態の前記第４空間フィルタの空間周波数特性を説明する。
【００７７】
レンズ群２３を通過した光は、まず第１複屈折板３３に入射する。第１および第２複屈折板３３，３４を通過する間の前記光の分離状態は、図１５（Ａ）および図１５（Ｂ）に示すように、図１１（Ａ）および図１１（Ｂ）で説明した光の分離状態とそれぞれ等しいので、説明は省略する。
【００７８】
第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５に入射する。図１５（Ｃ）に示すように、第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５を通過する間に、第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとにそれぞれ分離されて、出射する。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとは、分離幅ｄ３だけそれぞれ離れている。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏから第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅへ向かう方向は、前記第２状態の第３複屈折板３５の光学軸方向ｑ３の投影方向、すなわち水平方向ｘから反時計まわりに４５度の方向と、それぞれ等しい。
【００７９】
したがって、前記第２状態の前記第４空間フィルタにおいて最終的に得られる光の分離状態は、図１５（Ｃ）の分離状態、すなわち図９で示す分離状態になる。以上のことから、前記第１および第２状態の前記第４空間フィルタにおいて最終的に得られる光の分離状態は、等しいことが分かる。ゆえに、前記第１状態の前記第４空間フィルタの空間周波数特性と、前記第２状態の第４空間フィルタの空間周波数特性とは、等しくなる。
【００８０】
以下に、本発明の第５実施形態の撮像装置について、説明する。第５実施形態の撮像装置は、第１実施形態の撮像装置２０と比較して、第１空間フィルタ２４が第５空間フィルタに置換えられた点だけが異なり、他は等しい。第５実施形態の撮像装置の構成のうちの、第１実施形態の撮像装置２０と同じ部分に関する説明は、省略する。また、第５実施形態の撮像装置を構成する部品のうちの第１実施形態の撮像装置２０と同じ構成の部品には、同じ参照符を付す。
【００８１】
前記第５空間フィルタは、第１〜第３複屈折板３３〜３５を有し、第３複屈折板３５だけが、基準平面３７に対して傾斜している。第１状態の前記第５空間フィルタにおける第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の相互の位置関係は、前記第１状態の第１空間フィルタ２４のそれと等しい。複屈折板駆動部２５は、第３複屈折板３５だけを、光軸２２に平行な軸線を中心に１８０度角変位させる。第１および第２複屈折板３３，３４は常に固定されている。このために、たとえば、保持部材６１には第３複屈折板３５だけが嵌め込まれ、第１および第２複屈折板３３，３４は、別の保持部材に固定されている。この場合、前記第２状態の第５空間フィルタ通過後の前記光の光路が、前記第１状態の第５空間フィルタ通過後の前記光の光路から、撮像面４１の画素４２の対角線に平行な方向Ｕに、画素４２の配列のピッチＰの√２分の１倍の長さだけずれるように、第３複屈折板３５の傾斜方向および傾斜角度が、調整されている。
【００８２】
図１６（Ａ）〜（Ｃ）は、前記第２状態の前記第５空間フィルタの第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の投影方向を示す図である。第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３は、光軸２２に対して約４５度にそれぞれ切出されている。第１複屈折板３３の光学軸方向ｑ１の前記投影方向は、図７（Ａ）に示す方向と等しく、水平方向ｘから反時計まわりに９０度である。第２複屈折板３４の光学軸方向ｑ２の前記投影方向は、水平方向ｘから時計まわりに０度である。第３複屈折板３５の光学軸方向ｑ３の前記投影方向は、図７（Ｃ）に示す方向と等しく、水平方向ｘから時計まわりに１３５度である。
【００８３】
図１７（Ａ）〜（Ｃ）は、前記第２状態の前記第５空間フィルタにおける第１〜第３複屈折板３３〜３５の分離光像を説明するための図である。図１７を用いて、前記第２状態の前記第５空間フィルタの空間周波数特性を説明する。
【００８４】
レンズ群２３を通過した光は、まず第１複屈折板３３に入射する。第１および第２複屈折板３３，３４を通過する間の前記光の分離状態は、図１７（Ａ）および図１７（Ｂ）に示すように、図８（Ａ）および図８（Ｂ）で説明した光の分離状態とそれぞれ等しいので、説明は省略する。
【００８５】
第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５に入射する。図１７（Ｃ）に示すように、第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５を通過する間に、第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとにそれぞれ分離されて、出射する。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとは、それぞれ分離幅ｄ３だけ離れている。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏから第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅへ向かう方向は、前記第２状態の第３複屈折板３５の光学軸方向ｑ３の投影方向、すなわち水平方向ｘから反時計まわりに１３５度の方向と、それぞれ等しい。
【００８６】
したがって、前記第２状態の前記第５空間フィルタにおいて最終的に得られる光線の分離状態は、図１７（Ｃ）の分離状態、すなわち図９で示す分離状態になる。以上のことから、前記第１および第２状態の前記第５空間フィルタにおいて最終的に得られる光の分離状態は、等しいことが分かる。ゆえに、前記第１状態の前記第５空間フィルタの空間周波数特性と、前記第２状態の第５空間フィルタの空間周波数特性とは、等しくなる。
【００８７】
以下に、本発明の第６実施形態の撮像装置について、説明する。第６実施形態の撮像装置は、第１実施形態の撮像装置２０と比較して、第１空間フィルタ２４が第６空間フィルタに置換えられた点だけが異なり、他は等しい。第６実施形態の撮像装置の構成のうちの、第１実施形態の撮像装置２０と同じ部分に関する説明は、省略する。また、第６実施形態の撮像装置を構成する部品のうちの第１実施形態の撮像装置２０と同じ構成の部品には、同じ参照符を付す。
【００８８】
前記第６空間フィルタは、第１〜第３複屈折板３３〜３５を有し、第１および第３複屈折板３３，３５のうちの少なくとも１枚が、基準平面３７に対して傾斜している。すなわち、第１複屈折板３３あるいは第３複屈折板３５が単体で、または第１および第３複屈折板３３，３５の両方が、基準平面３７に対して傾斜している。第１状態の前記第６空間フィルタにおける第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の相互の位置関係は、前記第１状態の第１空間フィルタ２４のそれと等しい。
【００８９】
複屈折板駆動部２５は、第１複屈折板３３を光軸２２に平行な軸線を中心に１８０度角変位させ、かつ、第３複屈折板３５を前記軸線を中心に反時計まわりに９０度角変位させる。第２複屈折板３４は常に固定されている。このために、たとえば、図４で示す構成の機構が２組備えられて、各機構の保持部材６１に第１および第３複屈折板３３，３５がそれぞれ嵌め込まれ、第２複屈折板３４は、さらに別の保持部材に固定される。この場合、前記第２状態の第６空間フィルタ通過後の前記光の光路が、前記第１状態の第６空間フィルタ通過後の前記光の光路から、撮像面４１の画素４２の対角線に平行な方向Ｕに、画素４２の配列のピッチＰの√２分の１倍の長さだけずれるように、第１および第３複屈折板３３，３５のうちの傾斜されている複屈折板の傾斜方向と第１および第３複屈折板３３，３５の傾斜角度が、調整されている。
【００９０】
図１８（Ａ）〜（Ｃ）は、前記第２状態の前記第６空間フィルタの第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の投影方向を示す図である。第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３は、光軸２２に対して約４５度にそれぞれ切出されている。第１複屈折板３３の光学軸方向ｑ１の前記投影方向は、水平方向ｘから時計まわりに９０度である。第２複屈折板３４の光学軸方向ｑ２の前記投影方向は、図７（Ｂ）に示す方向と等しく、水平方向ｘから時計まわりに０度である。第３複屈折板３５の光学軸方向ｑ３の前記投影方向は、水平方向ｘから反時計まわりに１３５度である。
【００９１】
図１９（Ａ）〜（Ｃ）は、前記第２状態の前記第６空間フィルタにおける第１〜第３複屈折板３３〜３５の分離光像を説明するための図である。図１９を用いて、前記第２状態の前記第６空間フィルタの空間周波数特性を説明する。
【００９２】
レンズ群２３を通過した光は、まず第１複屈折板３３に入射する。第１複屈折板３３を通過する間の前記光の分離状態は、図１９（Ａ）に示すように、図１１（Ａ）で説明した光の分離状態と等しいので、説明は省略する。
【００９３】
第１複屈折板３３の常光線Ｌｏおよび異常光線Ｌｅは、第２複屈折板３４に入射する。図１９（Ｂ）に示すように、第１複屈折板３３の常光線Ｌｏは、第２複屈折板の異常光線Ｌｏｅとして、第２複屈折板３４を通過する間に、元の位置から分離幅ｄ２だけ、前記第１状態の第２複屈折板３４の光学軸方向ｑ２の投影方向、すなわち水平方向ｘから時計まわりに１８０度の方向にシフトして出射される。また第１複屈折板３３の異常光線Ｌｅは、図１９（Ｂ）に示すように、第２複屈折板２４の常光線Ｌｅｏとして、第２複屈折板３４を通過する間も位置を変えずそのまま出射される。第１複屈折板３３の常光線Ｌｏに対応する第２複屈折板３４の常光線と、第１複屈折板３４の異常光線Ｌｅに対応する第２複屈折板２４の異常光線とは、第１実施形態で説明した理由から、存在しない。
【００９４】
第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５に入射する。図１９（Ｃ）に示すように、第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５を通過する間に、第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとにそれぞれ分離されて、出射する。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとは、それぞれ分離幅ｄ３だけ離れている。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏから第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅへ向かう方向は、前記第２状態の第３複屈折板３５の光学軸方向ｑ３の投影方向、すなわち水平方向ｘから反時計まわりに１３５度の方向と、それぞれ等しい。
【００９５】
したがって、前記第２状態の前記第６空間フィルタにおいて最終的に得られる光の分離状態は、図１９（Ｃ）の分離状態、すなわち図９で示す分離状態になる。以上のことから、前記第１および第２状態の前記第６空間フィルタにおいて最終的に得られる光との分離状態は、等しいことが分かる。ゆえに、前記第１状態の前記第６空間フィルタの空間周波数特性と、前記第２状態の第６空間フィルタの空間周波数特性とは、等しくなる。
【００９６】
以下に、本発明の第７実施形態の撮像装置について、説明する。第７実施形態の撮像装置は、第１実施形態の撮像装置２０と比較して、第１空間フィルタ２４が第７空間フィルタに置換えられた点だけが異なり、他は等しい。第７実施形態の撮像装置の構成のうちの、第１実施形態の撮像装置２０と同じ部分に関する説明は、省略する。また、第７実施形態の撮像装置を構成する部品のうちの第１実施形態の撮像装置２０と同じ構成の部品には、同じ参照符を付す。
【００９７】
前記第７空間フィルタは、第１〜第３複屈折板３３〜３５を有し、第２および第３複屈折板３４，３５のうちの少なくとも１枚が、基準平面３７に対して傾斜している。すなわち、第２複屈折板３４あるいは第３複屈折板３５が単独で、または第２および第３複屈折板３４，３５の両方が、基準平面３７に対して傾斜している。第１状態の前記第７空間フィルタにおける第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の相互の位置関係は、前記第１状態の第１空間フィルタ２４のそれと等しい。
【００９８】
複屈折板駆動部２５は、第２複屈折板３４を光軸２２に平行な軸線を中心として１８０度角変位させ、かつ、第３複屈折板３５を前記軸線を中心として時計まわりに９０度角変位させる。第１複屈折板３４は常に固定されている。このために、たとえば、図４で示す構成の機構が２組備えられて、各機構の保持部材６１に第２および第３複屈折板３４，３５がそれぞれ嵌め込まれ、第１複屈折板３３は、さらに別の保持部材に固定される。この場合、前記第２状態の第７空間フィルタ通過後の前記光の光路が、前記第１状態の第７空間フィルタ通過後の前記光の光路から、撮像面４１の画素４２の対角線に平行な方向Ｕに、画素４２の配列のピッチＰの√２分の１倍の長さだけずれるように、第２および第３複屈折板３４，３５のうちの傾斜された複屈折板の傾斜方向および傾斜角度が、調整されている。
【００９９】
図２０（Ａ）〜（Ｃ）は、前記第２状態の前記第７空間フィルタの第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３の投影方向を示す図である。第１〜第３複屈折板３３の光学軸方向ｑ１〜ｑ３は、光軸２２に対して約４５度にそれぞれ切出されている。第１複屈折板３３の光学軸方向ｑ１の前記投影方向は、図７（Ａ）に示す方向と等しく、水平方向ｘから反時計まわりに９０度である。第２複屈折板３４の光学軸方向ｑ２の前記投影方向は、水平方向ｘから時計まわりに１８０度である。第３複屈折板３５の光学軸方向ｑ３の前記投影方向は、水平方向ｘから時計まわりに４５度である。
【０１００】
図２１（Ａ）〜（Ｃ）は、前記第２状態の前記第７空間フィルタにおける第１〜第３複屈折板３３〜３５の分離光像を説明するための図である。図２１を用いて、前記第２状態の前記第７空間フィルタの空間周波数特性を説明する。
【０１０１】
レンズ群２３を通過した光は、まず第１複屈折板３３に入射する。第１複屈折板３３を通過する間の前記光の分離状態は、図２１（Ａ）に示すように、図８（Ａ）で説明した光の分離状態と等しいので、説明は省略する。
【０１０２】
第１複屈折板３３の常光線Ｌｏおよび異常光線Ｌｅは、第２複屈折板３４に入射する。図２１（Ｂ）に示すように、第１複屈折板３３の常光線Ｌｏは、第２複屈折板の異常光線Ｌｏｅとして、第２複屈折板３４を通過する間に、元の位置から分離幅ｄ２だけ、前記第２状態の第２複屈折板３４の光学軸方向ｑ２の投影方向、すなわち水平方向ｘから時計回りに１８０度の方向にシフトして出射される。また第１複屈折板３３の異常光線Ｌｅは、図２１（Ｂ）に示すように、第２複屈折板２４の常光線Ｌｅｏとして、第２複屈折板３４を通過する間も位置を変えずにそのまま出射される。第１複屈折板３３の常光線Ｌｏに対応する第２複屈折板３４の常光線と、第１複屈折板３４の異常光線Ｌｅに対応する第２複屈折板２４の異常光線とは、第１実施形態で説明した理由から、存在しない。
【０１０３】
第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５に入射する。図２１（Ｃ）に示すように、第２複屈折板３４の常光線Ｌｅｏおよび異常光線Ｌｏｅは、第３複屈折板３５を通過する間に、第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとにそれぞれ分離されて、出射する。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏと第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅとは、それぞれ分離幅ｄ３だけ離れている。第３複屈折板３５の常光線Ｌｅｏｏ，Ｌｏｅｏから第３複屈折板の異常光線Ｌｅｏｅ，Ｌｏｅｅへ向かう方向は、前記第２状態の第３複屈折板３５の光学軸方向ｑ３の投影方向、すなわち水平方向ｘから反時計まわりに４５度の方向と、それぞれ等しい。したがって、前記第２状態の前記第７空間フィルタにおいて最終的に得られる常光線と異常光線との分離状態は、図２１（Ｃ）の分離状態、すなわち図９で示す分離状態になる。
【０１０４】
以上のことから、前記第１および第２状態の前記第７空間フィルタにおいて最終的に得られる常光線と異常光線との分離状態は、等しいことが分かる。したがって、前記第１状態の前記第７空間フィルタの空間周波数特性と、前記第２状態の第７空間フィルタの空間周波数特性とは、等しくなる。
【０１０５】
以上のように、第４〜第７実施形態の撮像装置の第４〜第７空間フィルタは、前記第１状態の空間周波数特性と前記第２状態の空間周波数特性とが、等しい。ゆえに、第４〜第７実施形態の撮像装置のいずれにおいても、第１実施形態で説明したように、イメージシフトのために第４〜第７空間フィルタ内の少なくとも１枚の複屈折板を角変位させたことに拘わらず、撮像素子２６は、被写体２１を、適正な空間周波数特性の第４〜第７空間フィルタを介して、常に撮像することができる。
【０１０６】
また、空間フィルタは、第１〜第３複屈折板の光学軸方向が図７，１０，１４，１６，１８，２０でそれぞれ示す位置関係を保つ状態ならば、最終的な光の分離状態がどれも同じである。ゆえに、上述の複数の位置関係のうちから２つの位置関係を選び、第１および第２状態の空間フィルタが保つべき第１〜第３複屈折板３３〜３５の光学軸方向の位置関係を、選ばれた２つの位置関係にしてもよい。たとえば、第１状態の空間フィルタに図１０で示す位置関係を保たせ、第２状態の空間フィルタに図１４で示す位置関係を保たせても良い。また、第１〜第３複屈折板の光学軸方向が上述した複数の位置関係をそれぞれ保つ場合、どの状態でも、第１〜第３複屈折板３３〜３５の順番を入換えても最終的な光の分離状態は等しいので、第１〜第３複屈折板３３〜３５を上述の図で示す順から変更してもよい。
【０１０７】
第１〜第７実施形態の撮像装置は本発明の撮像装置の例示であり、主要な動作が等しければ、他の様々な形で実施することができる。特に各装置の詳細な動作は、同じ出力が得られれば、これに限らず他の動作によって実現されてもよい。また、本発明の撮像装置の空間フィルタは、１または複数の複屈折板を有し、全ての複屈折板のうちの少なくとも１枚が基準軸線を中心に角変位され、かつ、角変位される複屈折板のうちの少なくとも１枚が基準軸線に垂直な基準平面に対して傾斜しているならば、上述の第１〜第７空間フィルタに限らず、他の構成であってもよい。また、２枚以上の複屈折板を前記基準平面に対して傾斜させる場合、各複屈折板と前記基準平面との成す角度は、各複屈折板毎に変えても良いが、傾斜させる全ての複屈折板それぞれと前記基準平面とのなす角度を等しくしておくことが好ましい。これは、傾斜される全ての複屈折板の撮像装置への取付けが容易になるからである。またこれは、各複屈折板と前記基準平面との成す角度が、前記角度を等しくしない場合と比較して、最も小さくすることができるので、複屈折板の傾斜に起因する画像の劣化等を、抑えることができるからである。
【０１０８】
また、本発明の撮像装置では、複屈折板を角変位させる角度、すなわち基準角度は、１８０度であることが好ましい。これは、以下の２つの理由からである。
【０１０９】
第１の理由は以下のとおりである。ＣＣＤイメージセンサが搭載された撮像装置に用いられる複屈折板は、一般的に、水晶を用いている。水晶を用いた複屈折板は高価になり易いので、現在市販されている前記複屈折板の形状は、図２２に示すように、両端が半径ｒの円弧になった略長方形になっている。本発明の撮像装置において複屈折板を９０度角変位させる場合、前記複屈折板の形状は、円形、または、図２３に示すような略十字形にする必要があると考えられる。本発明の撮像装置において複屈折板を１８０度角変位させる場合、前記複屈折板の形状を光軸２２を基準とする左右対称の形状にすることができるので、前記複屈折板の形状は図２２に示す略長方形でも良いと考えられる。したがって、前記基準角度が１８０度である場合、本発明の撮像装置の複屈折板に、前記市販されている複屈折板を流用することができる。また、図２２の複屈折板は、円形の複屈折板および図２３の複屈折板と半径ｒを等しくするならば、前記円形の複屈折板および図２３の複屈折板よりも面積を小さくすることができる。これらのことから、本発明の撮像装置の製造コストの増加を抑えることができるので、前記基準角度は１８０度であることが好ましいのである。
【０１１０】
第２の理由は以下のとおりである。図２４（Ａ），図２５（Ａ）は、複屈折板が角変位される角度、すなわち前記基準角度が１８０度および９０度であり、かつ、角変位される複屈折板の傾斜角度が０度である場合の、複屈折板が角変位される前の空間フィルタ通過後の被写体からの光の光路１００，１０１の位置を、それぞれ示す。前記場合には、複屈折板が角変位された後の空間フィルタ通過後の被写体からの光の光路は、前記光路１００，１０１と等しい。２点鎖線で示す仮想矩形１０２は、１辺の長さが、撮像面４１の画素４２の配列のピッチＰの半分（Ｐ／２）である正方形である。図２４（Ａ），（Ｂ）では、仮想矩形１０２の中心が光路１００と一致させてあり、図２５（Ａ），（Ｂ）では、仮想矩形１０２の右上の頂点が光路１０１と一致させてある。
【０１１１】
前記空間フィルタ内の角変位される複屈折板のうちの少なくとも１枚が、前記基準角度に応じて、複屈折板が角変位される前の空間フィルタ通過後の被写体からの光の光路と、複屈折板が角変位された後の空間フィルタ通過後の被写体からの光の光路との距離が、ピッチＰの√２分の１になるように、傾斜されたと仮定する。基準角度が１８０度である場合、複屈折板が角変位される前の空間フィルタ通過後の被写体からの光の光路１０３と、複屈折板が角変位された後の空間フィルタ通過後の被写体からの光の光路１０４とは、図２４（Ｂ）に示すように、仮想矩形１０２の隣合わない２つの頂点に、位置する。この場合、前記光路１００と光路１０３，１０４との距離は、それぞれピッチＰの４分の√２倍（Ｐ√２／４）である。基準角度が９０度である場合、複屈折板が角変位される前の空間フィルタ通過後の被写体からの光の光路１０５と、複屈折板が角変位された後の空間フィルタ通過後の被写体からの光の光路１０６とは、図２５（Ｂ）に示すように、仮想矩形１０２の隣合わない２つの頂点に、位置する。この場合、前記光路１０１と光路１０５，１０６との距離は、それぞれピッチＰの半分である。
【０１１２】
この結果、基準角度が１８０度である場合の前記光路１０１と光路１０３，１０４との距離は、基準角度が９０度である場合の前記光路１０１と光路１０５，１０６との距離よりも、短くなる。すなわち、基準角度が１８０度である場合のほうが、基準角度が９０度である場合よりも、複屈折板の傾斜に起因する光路のずれが小さい。したがって、基準角度が１８０度である場合の複屈折板の傾斜角度は、基準角度が９０度である場合の複屈折板の傾斜角度よりも小さいと考えられる。以上のことから、複屈折板の角変位の前後の空間フィルタ通過後の光路のずれが予め定められるならば、基準角度が１８０度である場合、複屈折板の傾斜角度を最も小さくすることができると予想される。これによって、基準角度が１８０度である場合、本発明の撮像装置で生成される出力画像信号が表す出力画像において、複屈折板の傾斜に起因する画質の低下を、最も小さくすることができるのである。
【０１１３】
【発明の効果】
以上のように本発明によれば、撮像装置は、空間フィルタ内の少なくとも１枚に複屈折板と光学系の光軸との位置関係が、イメージシフト手段によって変化される。これによって、前記少なくとも１枚の複屈折板は、イメージシフトのための屈折板を兼ねる。これによって、本発明の撮像装置は、従来技術の撮像装置よりも小型化および軽量化することができ、かつ、従来技術の撮像装置よりも組立てコストを低減化することができる。
【０１１４】
また前記空間フィルタは、前記少なくとも１枚の複屈折板と前記光軸との位置関係の変化に拘わらず、常に予め定める空間周波数特性を保つ。ゆえに、前記撮像装置の撮像素子は、常に適性な空間周波数特性の空間フィルタを通して、被写体を撮像することができる。
【０１１５】
さらにまた本発明によれば、前記少なくとも１枚の複屈折板は前記光軸に垂直な基準平面に対して予め傾斜されており、前記イメージシフト手段は、前記少なくとも１枚の複屈折板を光軸に平行な軸線まわりに角変位させる。これによって撮像装置におけるイメージシフトの精度を向上させることができる。
【０１１６】
また本発明によれば、傾斜された前記少なくとも１枚の複屈折板と前記基準平面とのなす角度および方向は、該複屈折板の角変位に伴って、空間フィルタ通過後の光の光路が、撮像素子の画素の配列ピッチの√２分の１だけ、前記画素の対角線に平行な方向にずれるように、定められる。これによって、前記撮像装置の利便性が向上される。
【０１１７】
さらにまた本発明によれば、前記イメージシフト手段は、前記全ての複屈折板のうちの角変位させるべき前記１または複数の複屈折板を、１８０度角変位させる。これによって、前記複屈折板の傾斜に拘わる画像の画質の低下を、最も小さくすることができる。またこれによって、前記撮像装置の製造コストの増加を、抑えることができる。
【０１１８】
また本発明によれば、前記全ての角変位させるべき複屈折板のうちの複数の複屈折板が前記基準平面に対して傾斜している場合、前記複数の複屈折板それぞれと前記基準平面がなす角度は、相互に等しい。これによって、前記撮像装置の組立て時の前記傾斜させるべき複数の複屈折板の角度調整が、容易になる。また、収差に起因する前記画像の画質の低下を、小さくすることができる。
【０１１９】
さらにまた本発明によれば、前記空間フィルタは、傾斜された前記１または複数の複屈折板が角変位されたか否かに拘わらず、常に予め定める空間周波数特性を保つことができる。ゆえに、前記撮像素子は、常に適性な空間周波数特性の空間フィルタを通して、被写体を撮像することができる。
【図面の簡単な説明】
【図１】本発明の第１実施形態である撮像装置２０の構成を示すブロック図である。
【図２】撮像装置２０の撮像素子２６の撮像面４１の構成を示す図である。
【図３】撮像装置２０の第１空間フィルタ２４の第１および第２状態を示す図である。
【図４】撮像装置２０の複屈折板駆動部２５の具体的な構成を示す図である。
【図５】撮像面４１に結像される被写体像の位置を示す図である。
【図６】撮像装置２０で生成される出力画像信号が表す出力画像を示す図である。
【図７】第１状態の第１空間フィルタ２４内の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３のｘｙ平面への投影像の方向の位置関係を示す図である。
【図８】第１状態の第１空間フィルタ２４の光の分離状態を示す図である。
【図９】第１状態の第１空間フィルタ２４の最終的な光の分離状態を示す図である。
【図１０】第２状態の第１空間フィルタ２４内の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３のｘｙ平面への投影像の方向の位置関係を示す図である。
【図１１】第２状態の第１空間フィルタ２４の光の分離状態を示す図である。
【図１２】本発明の第２実施形態である撮像装置内の第２空間フィルタ８１の第１および第２状態を示す図である。
【図１３】本発明の第３実施形態である撮像装置内の第３空間フィルタ８３の第１および第２状態を示す図である。
【図１４】本発明の第４実施形態である撮像装置内の第２状態の第４空間フィルタ内の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３のｘｙ平面への投影像の方向の位置関係を示す図である。
【図１５】第２状態の第４空間フィルタの光の分離状態を示す図である。
【図１６】本発明の第５実施形態である撮像装置内の第２状態の第５空間フィルタ内の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３のｘｙ平面への投影像の方向の位置関係を示す図である。
【図１７】第２状態の第５空間フィルタの光の分離状態を示す図である。
【図１８】本発明の第６実施形態である撮像装置内の第２状態の第６空間フィルタ内の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３のｘｙ平面への投影像の方向の位置関係を示す図である。
【図１９】第２状態の第６空間フィルタの光の分離状態を示す図である。
【図２０】本発明の第７実施形態である撮像装置内の第２状態の第７空間フィルタ内の第１〜第３複屈折板３３〜３５の光学軸方向ｑ１〜ｑ３のｘｙ平面への投影像の方向の位置関係を示す図である。
【図２１】第２状態の第７空間フィルタの光の分離状態を示す図である。
【図２２】本発明の第１〜第７実施形態の撮像装置において、複屈折板を角変位する基準角度が１８０度である場合に使用可能な、現在市販されている複屈折板の形状を示す図である。
【図２３】本発明の第１〜第７実施形態の撮像装置において、複屈折板を角変位する基準角度が９０度である場合に使用される複屈折板の形状を示す図である。
【図２４】本発明の第１〜第７実施形態の撮像装置において、空間フィルタ通過後の光の光路の、複屈折板の傾斜角度に起因するずれを説明するための図である。
【図２５】本発明の第１〜第７実施形態の撮像装置において、空間フィルタ通過後の光の光路の、複屈折板の傾斜角度に起因するずれを説明するための図である。
【図２６】従来技術の撮像装置の構造を説明するための図である。
【符号の説明】
２０撮像装置
２２光軸
２３レンズ
２４第１空間フィルタ
２５複屈折板駆動部
２６撮像素子
３３第１複屈折板
３４第２複屈折板
３５第３複屈折板
３７基準平面
８１第２空間フィルタ
８３第３空間フィルタ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging device capable of obtaining an image with a higher resolution than the resolution of an imaging device.
[0002]
[Prior art]
2. Description of the Related Art In recent years, imaging devices such as electronic still cameras have been required to have higher resolution of images obtained by the imaging devices. As a first method for increasing the resolution of the image, a light receiving area of an image sensor provided in the image sensor, that is, the number of pixels of the image sensor is set to be larger than the number of pixels of the conventional image sensor. Conceivable. However, an image sensor having a large number of pixels tends to be expensive due to poor productivity.
[0003]
As a second technique for increasing the resolution of the image, it is conceivable to use the conventional image sensor and perform so-called image shift. Conventional techniques relating to the image shift are disclosed in Japanese Patent Application Laid-Open Nos. 9-9115 and 3-139990.
[0004]
FIG. 26 is a diagram showing a configuration of a part relating to processing of light from a subject of the imaging apparatus 1 disclosed in Japanese Patent Application Laid-Open No. 9-9115. The portion includes a lens group 3, an image sensor 4, an image shift unit 5, and a spatial filter unit 6. The image shift unit 5 and the spatial filter unit 6 are interposed between the lens group 3 and the image sensor 4 in this order. The spatial filter unit 6 includes an optical low-pass filter 7 and an optical low-pass filter rotation mechanism unit 8. The image shift means includes a parallel flat glass 9 and a parallel flat glass driving unit 10. The parallel plate glass 9 and the optical low-pass filter 7 are arranged on the optical axis 11 of the lens group 3 in this order. The parallel plate glass 9 has two central axes perpendicular to the optical axis 11 and perpendicular to each other. The parallel flat glass driving unit 10 angularly displaces the parallel flat glass 9 around the two central axes. Thereby, the optical path of the light from the subject is translated from the optical axis 11.
[0005]
In the above-described imaging device 1, since the parallel plate glass 9 and the optical low-pass filter 7 are arranged on the optical axis 11, respectively, the length of the portion of the imaging device 1 in the direction parallel to the optical axis 11 is: Easy to be long. As a result, it becomes difficult to reduce the size of the imaging device 1. Further, since the image shift unit 5 and the spatial filter unit 6 are separately provided, the number of components is increased as compared with a conventional imaging device that does not perform image shift. As a result, the manufacturing cost of the imaging device 1 is likely to increase.
[0006]
The configuration of a portion related to processing of light from a subject of the imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 3-139990 is as follows. The part includes a photographing lens, an image sensor, and a rotation filter. The rotating filter is a colorless transparent and thick parallel plate, and has a refractive index different from that of air. The rotation filter is interposed between the imaging lens and the image sensor, and is angularly displaced about a predetermined rotation axis. The rotation axis is perpendicular to the imaging plane of the imaging device and intersects the plane of the rotation filter at an angle of less than 90 degrees. As a result, as the rotary filter is angularly displaced, the optical path of light from the subject is translated from the optical axis of the photographing lens.
[0007]
[Problems to be solved by the invention]
The imaging device disclosed in Japanese Patent Application Laid-Open No. 3-139990 does not include a spatial filter. When a spatial filter is added to the imaging device, it is difficult to reduce the size of the imaging device similarly to the imaging device 1 of Japanese Patent Application Laid-Open No. 9-9115, and the number of components of the imaging device tends to increase. Also, with the angular displacement of the rotary filter, it is expected that the spatial frequency characteristics of the rotary filter may change, but since the rotary filter does not consider changes in the spatial frequency characteristics, Possibility of maintaining an optimal spatial frequency characteristic for the imaging device regardless of the angular displacement of the rotary filter is poor.
[0008]
An object of the present invention is an imaging device that captures a higher resolution image than a conventional imaging device, and can maintain a spatial frequency characteristic according to the high resolution image even when performing an image shift, and Another object of the present invention is to provide an imaging device that can be reduced in size and thickness and that can reduce assembly costs.
[0009]
[Means for Solving the Problems]
The present invention provides an optical system for condensing light from a subject,
An imaging element having an imaging surface on which light condensed by the optical system is imaged;
A spatial filter including at least one birefringent plate interposed between the optical system and the image sensor,
In order to shift the optical path of the light incident on the image sensor, the positional relationship between at least one of the birefringent plates in the spatial filter and the optical axis of the optical system is determined by the angular displacement. Image shifting means for changing;
Each time the image shift means changes the positional relationship, the imaging device, the imaging control means for generating an image signal representing an image,
Combining means for combining a plurality of the image signals,
Before and after the positional relationship is changed, the positional relationship includes a separation width d3 between the ordinary rays Leoo and Loeo passing through the spatial filter and the extraordinary rays Leoe and Loee, and the extraordinary rays Leoe and Loeo from the ordinary rays Leoo and Loeo. An imaging apparatus characterized by being changed while keeping the direction to Loee equal.
[0010]
According to the present invention, in the imaging device, a so-called image shift effect is obtained by operating a part of the spatial filter and the image shift unit as described above. Thereby, in the portion of the optical path of the light from the subject between the optical system and the imaging element, only all the birefringent plates in the spatial filter are interposed, and the portion is conventionally interposed in the portion. The refraction plate for image shift is omitted. Therefore, the distance between the optical system and the imaging device may be shorter than the distance between the optical system and the imaging device in the conventional imaging apparatus by the refraction plate for image shift. it can. Therefore, the so-called back focus is shorter than that of the prior art imaging device, so that the imaging device of the present invention can be made smaller than the prior art imaging device. In addition, since the image shift refraction plate is removed, the number of components of the image pickup device of the present invention is reduced as compared with the conventional image pickup device. Therefore, the imaging device of the present invention can be made lighter than the imaging device of the related art, and the assembly cost can be reduced.
[0012]
Further, the spatial filter of the imaging device can always maintain a predetermined spatial frequency characteristic regardless of a change in the positional relationship. Therefore, if the predetermined spatial frequency characteristic is set in advance to an appropriate spatial frequency characteristic with respect to the resolution of the image represented by the image signal generated by the imaging device, the imaging device can change the positional relationship. Regardless, the subject can always be imaged through the spatial filter having the appropriate spatial frequency characteristics.
The image shifting means changes the positional relationship between at least one of the birefringent plates in the spatial filter and the optical axis of the optical system due to angular displacement. Before and after the positional relationship is changed, the positional relationship is determined by a separation width d3 between the ordinary rays Leoo and Loeo passing through the spatial filter and the extraordinary rays Leoe and Loee, and the extraordinary rays Leeo and Loeo from the ordinary rays Leoo and Loeo. It is changed while keeping the direction toward Loee equal.
[0013]
The present invention also provides an optical system for condensing light from a subject,
An imaging element having an imaging surface on which light condensed by the optical system is imaged;
A spatial filter including at least one birefringent plate interposed between the optical system and the image sensor,
Image of changing the positional relationship between at least one of the birefringent plates in the spatial filter and the optical axis of the optical system in order to shift the optical path of light incident on the image sensor. Shifting means;
Each time the image shift means changes the positional relationship, the imaging device, the imaging control means for generating an image signal representing an image,
Combining means for combining a plurality of the image signals,
At least one of the at least one birefringent plate is inclined with respect to a reference plane perpendicular to the optical axis,
The image shifter is an imaging apparatus, wherein the at least one birefringent plate is angularly displaced around a reference axis parallel to the optical axis.
[0014]
According to the present invention, the at least one birefringent plate of the imaging device is previously inclined with respect to the reference plane to shift the optical path, and the image shift means performs the above-described operation. Thereby, the positional relationship between the tilted birefringent plate and the optical axis, for example, the angle between the incident surface of the tilted birefringent plate and the optical axis changes, so that the effect of the image shift can be obtained. Can be. Therefore, the configuration of the image shifting means is simplified as compared with the prior art image shifting means for angularly displacing the refraction plate about a reference axis perpendicular to the optical axis. Further, the angle between the inclined birefringent plate and the reference plane can be easily adjusted precisely in the assembling process of the imaging device, and the inclined birefringent plate is rotated around the reference axis. Since only the angular displacement is performed, the positional relationship can be easily changed precisely. Therefore, the accuracy of the image shift of the imaging device can be improved.
[0015]
Further, according to the present invention, a plurality of rectangular light receiving areas are arranged in a matrix on an image forming surface of the image sensor,
The birefringent plate that is inclined, from the optical path of the light that has passed through the spatial filter before the birefringent plate to be angularly displaced is angularly displaced, after the birefringent plate to be angularly displaced is angularly displaced. The optical path of the light passing through the spatial filter is inclined so as to be shifted in a direction parallel to a diagonal line of the light receiving area,
The angle between the inclined birefringent plate and the reference plane is such that the distance between the two optical paths is half the distance between the centers of the two pixels arranged in a direction parallel to the diagonal of the pixels. It is characterized by being set.
[0016]
According to the present invention, the angle between the inclined birefringent plate in the imaging device and the reference plane and the direction in which the birefringent plate is inclined are determined as described above. As a result, the two light paths are offset from each other by a distance half the distance between the two pixels in a direction parallel to the diagonal of the pixels. The synthesizing unit generates an image signal generated by the image sensor before the birefringent plate to be angularly displaced is angularly displaced, and an image signal generated by the image sensor after the birefringent plate to be angularly displaced is angularly displaced. The image signal is synthesized. As a result, the resolution of the image represented by the synthesized image signal is higher than the resolution of the image sensor. Therefore, since only two image signals are required to obtain an image having a higher resolution than the resolution of the image sensor, the time required for the image sensor to image a subject can be minimized. The convenience of the device is improved.
[0017]
Further, the invention is characterized in that the angle at which the image shift means angularly displaces the birefringent plate to be angularly displaced is 180 degrees.
[0018]
According to the present invention, it is preferable that the image shift means performs the angular displacement of the birefringent plate to be angularly displaced by 180 degrees. The first reason for this is that when the angle of the angular displacement of the birefringent plate is 180 degrees, the angle between the birefringent plate and the reference plane can be minimized. This is because the degradation of the image quality of the image related to the inclination can be minimized. The second reason is as follows. Since the birefringent plate to be angularly displaced is angularly displaced 180 degrees around the reference axis, the shape of the birefringent plate to be angularly displaced can be point-symmetrical with respect to the reference axis. Therefore, the substantially rectangular birefringent plate used in the current imaging device can be used as the spatial filter of the imaging device of the present invention. Therefore, if the angle of the angular displacement of the birefringent plate is 180 degrees, an increase in the manufacturing cost of the imaging device can be suppressed.
[0019]
Further, according to the present invention, when a plurality of birefringent plates among the birefringent plates to be angularly displaced are inclined with respect to the reference plane, each of the plurality of birefringent plates and the reference plane The angles formed are equal to each other.
[0020]
According to the present invention, in the above case, the angles formed by each of the plurality of birefringent plates and the reference plane are equal to each other. This facilitates angle adjustment of the plurality of birefringent plates to be inclined when assembling the imaging device. Further, as the number of birefringent plates inclined at the same angle increases, the sum of the thicknesses of all the inclined birefringent plates in the direction parallel to the optical axis increases. Thus, the angle formed between each of the plurality of birefringent plates to be inclined and the reference plane can be reduced as the number of birefringent plates inclined at the same angle increases. Therefore, for example, a decrease in the image quality of the image caused by the aberration can be reduced.
[0021]
Further, according to the present invention, a spatial frequency characteristic of the spatial filter before the birefringent plate to be angularly displaced is angularly displaced, and a spatial frequency characteristic of the spatial filter after the birefringent plate to be angularly displaced is angularly displaced. The spatial frequency characteristics are equal.
[0022]
According to the present invention, the spatial filter can always maintain a predetermined spatial frequency characteristic regardless of whether or not the inclined birefringent plate is angularly displaced. Therefore, if the predetermined spatial frequency characteristic is set in advance to an appropriate spatial frequency characteristic with respect to the resolution of the image represented by the image signal generated by the imaging device, the imaging device will have a tilted birefringence. Regardless of whether or not the plate is angularly displaced, the subject can always be imaged through the spatial filter having the appropriate spatial frequency characteristics.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram illustrating an overall configuration of an imaging device 20 according to the first embodiment of the present invention. The imaging device 20 includes a lens group 23, a first spatial filter 24, a birefringent plate driving unit 25, an imaging device 26, a control device 27, a memory device 28, and a combining device 29.
[0024]
The lens group 23 includes one or a plurality of lenses and has a single optical axis 22. The first spatial filter 24 is interposed between the lens group 23 and the image sensor 26. The first spatial filter 24 has a predetermined spatial frequency characteristic, and limits a part of the spatial frequency component of the light from the subject 21. The light is collected by the lens group 23, passes through the first spatial filter 24, and forms an image on the imaging surface 41 of the imaging device 26.
[0025]
The first spatial filter 24 has one birefringent plate or a plurality of birefringent plates sequentially arranged along the optical axis 22. In the present embodiment, the first spatial filter 24 has first to third birefringent plates 33 to 35. Each of the first to third birefringent plates 33 to 35 is a flat plate having two parallel surfaces. At least one of the one or more birefringent plates is inclined with respect to a reference plane 37 perpendicular to the optical axis. In the present embodiment, the first and second birefringent plates 33 and 34 are parallel to the reference plane 37, and the third birefringent plate 35 is configured such that the surface thereof and the reference plane 37 form an inclination angle θ1. In addition, it is inclined.
[0026]
The birefringent plate driving unit 25 is controlled by the control device 27, and controls one or more birefringent plates including the inclined at least one birefringent plate of all the birefringent plates to be parallel to the optical axis 22. A predetermined reference angle is displaced angularly around a suitable reference axis. In the present embodiment, the birefringent plate driving unit 25 angularly displaces all of the first to third birefringent plates 33 to 35, the reference axis coincides with the optical axis 22, and the reference angle is 180 degrees. It is. That is, the birefringent plate driving unit 25 performs image shift for changing the positional relationship between at least one birefringent plate to be angularly displaced in the first spatial filter 24 and the optical axis 22 for image shift. Part. Further, the birefringent plate to be angularly displaced and the birefringent plate driving section 25 have the same function as the conventional image shift section.
[0027]
The imaging element 26 photoelectrically converts the light focused on the imaging surface to generate an image signal, and causes the memory device 28 to store the image signal. The imaging element 26 has one of a so-called black-and-white single-plate structure, a so-called three-color plate structure, and a so-called single-plate color structure. In the present embodiment, the image pickup device 26 has a Bayer array single-plate color structure. Assuming the explanation.
[0028]
The control device 27 controls the image sensor 26 and the birefringent plate driving unit 25 to set the birefringent plates to be angularly displaced by the birefringent plate driving unit 25, that is, the first to third birefringent plates 33 to 35. Each time it is displaced, the imaging device 26 performs photoelectric conversion, and the image signal obtained as a result is stored in the memory device 28. Further, the control device 27 causes the synthesizing device 29 to provide two image signals, which are successively generated by the image sensor 26, among the plurality of image signals stored in the memory device 28. The combining device 29 combines the two image signals. Further, the synthesizing device 29 performs a predetermined interpolation process on a single synthesized image signal obtained as a result of the synthesis to generate an output image signal representing an image having a higher resolution than the resolution of the image sensor 26. The output image signal is stored in the memory device 28 and output to the outside of the imaging device 20. The control device 27 and the synthesizing device 29 are realized by, for example, a microcomputer, and the memory device 28 is realized by, for example, a random access memory.
[0029]
As described above, in the imaging device 20 of the present embodiment, at least one of the birefringent plates 33 to 35 in the first spatial filter 24 is inclined. The three birefringent plates 35 also function as refracting plates for image shift. Therefore, only the first spatial filter 24 is interposed between the lens group 23 and the image sensor 26, and the refraction plate is not interposed. Thus, the distance between the lens group 23 and the image sensor 6 can be reduced as compared with a conventional image pickup apparatus that performs image shift. Therefore, since the back focus of the imaging device 20 is shorter than that of the conventional imaging device, the imaging device 20 can be made smaller and thinner than the conventional imaging device. Further, since the number of components of the imaging device 20 is smaller than that of the conventional imaging device, the manufacturing cost of the imaging device 20 can be reduced more than that of the conventional imaging device.
[0030]
FIG. 2 is a front view of the imaging surface 41 of the imaging element 26. The imaging device 26 is realized by a CCD (charge coupled device) image sensor. A plurality of pixels 42, i.e., a plurality of light receiving regions, are spaced apart by a first pitch Px that is predetermined in the horizontal direction x and a second pitch Py that is predetermined in the vertical direction y on the imaging surface 41 of the imaging element 26. After that, they are arranged in a matrix. In FIG. 2, pixels are indicated by rectangles. The horizontal direction x is a direction perpendicular to the paper surface in FIG. 1 and the left-right direction of the paper surface in FIG. 2, and the vertical direction y is a vertical direction in the paper surface in both FIGS. A direction parallel to the optical axis 22 may be referred to as a Z direction or an optical axis direction. In the present embodiment, it is assumed that the imaging surface 41 has a so-called Bayer array single-plate color configuration. In the present embodiment, the first and second pitches Px and Py are assumed to be equal, and the first and second pitches Px and Py are collectively referred to as a pitch P. In a state where the pixels 42 are arranged in a matrix, a group of pixels arranged in parallel in the horizontal direction x is referred to as a row, and a group of pixels arranged in the vertical direction y is referred to as a column.
[0031]
Each pixel of the image sensor having a general single-plate color structure detects the luminance of any one of the three primary colors of light and determines the luminance of the color to be detected by each pixel. Different. The Bayer array is one of an array of three types of pixels that respectively detect the luminance of each of the three primary colors of color light, and all the pixels include a pixel that detects red luminance and a pixel that detects blue luminance. This is an array in which pixels are classified into three types, that is, pixels for detecting green pixels, and pixels for detecting the luminance of each color are arranged in units of four pixels in two rows and two columns. In the drawing, “R”, “G”, and “B” are respectively shown and shown in a rectangle representing a pixel for detecting red, green, and blue luminances.
[0032]
The specific arrangement of the pixels 42R, 42B, and 42G for detecting the luminance of each color in the Bayer array is determined by arranging the pixels 42R, 42B, and 42G in a matrix on the imaging surface 41 of the single-chip color imaging device. A description will be given of a pair of matching rows 45 and 46 as an example. In one row 45 of the pair of rows, pixels 42G for detecting green luminance and pixels 42B for detecting blue luminance are alternately arranged. In the other row 46 of the pair of rows, pixels 42R for detecting red luminance and pixels 42G for detecting green luminance are alternately arranged. In addition, the pixels 42G for detecting the green luminance in one row 45 and the pixels 42G for detecting the green luminance in the other row 46 are shifted by a pitch P in the horizontal direction x. Rows having the same configuration as the pair of rows 45 and 46 described above are periodically arranged on the entire imaging surface 41.
[0033]
FIG. 3 is a diagram showing the first spatial filter 24 before and after the first to third birefringent plates 33 to 35 are angularly displaced. For the following description, the state of the first spatial filter before the first to third birefringent plates 33 to 35 are angularly displaced is determined in advance by the first state and the first to third birefringent plates 33 to 35. The state of the first spatial filter after being angularly displaced by the reference angle is defined as a second state. Further, it is assumed that the optical paths 51 and 52 of the light from the subject 21 before passing through the first spatial filter 24 in the first and second states coincide with the optical axis 22 of the lens group 23. Also, of the two surfaces of the first to third birefringent plates 33 to 35, the surface on the side where the light is incident is referred to as an incident surface.
[0034]
Since the incident surfaces of the first and second birefringent plates 33 and 34 in the first spatial filter 24 in the first state are perpendicular to the optical axis 22, the first and second birefringent plates 33 and 34 are angularly displaced. Also, the plane of incidence is perpendicular to the optical axis 22. That is, the angle formed between the entrance surfaces of the first and second birefringent plates 33 and 34 in the first spatial filter 24 in the first state and the optical path 51 is equal to the angle in the first spatial filter 24 in the second state. The angle formed between the entrance surfaces of the first and second birefringent plates 33 and 34 and the optical path 52 is equal.
[0035]
The third birefringent plate 35 of the first spatial filter 24 in the first state is inclined with respect to the reference plane 37 at an inclination angle θ1. Therefore, for example, when measuring the angle formed between the optical paths 51 and 52 and the incident surface of the third birefringent plate 35 clockwise around the intersection of the optical paths 51 and 52 and the incident surface, the first state is set. The angle θa1 between the incident surface of the third birefringent plate 35 in the first spatial filter 24 and the optical path 51 is equal to the angle between the incident surface of the third birefringent plate 35 in the first spatial filter 24 in the second state and the optical path. 52 is different from the angle θa2 formed by the angle 52. The angle θa2 is, for example, an angle obtained by subtracting the angle θa1 from 180 degrees.
[0036]
As described above, in accordance with the angular displacement of the inclined birefringent plate, the angle between the incident surface of the inclined birefringent plate and the optical path of the light before passing through the first spatial filter 24 changes. Therefore, with the change in the angle, the position of the optical path of the light from the subject 21 after passing through the first spatial filter 24 changes. The optical path of the light after passing through the first spatial filter 24 in the first state, that is, the first optical path 53, and the optical path of the light after passing through the first spatial filter 24 in the second state, that is, the position of the second optical path 54 The relationship is specifically as follows.
[0037]
The first optical path 53 is displaced from the optical axis 22 in a first predetermined direction a1 in parallel with the optical axis 22 by a predetermined first distance D1. The second optical path 54 is shifted from the optical axis 22 in a second direction a2 opposite to the first direction a1 by a first distance D1 in parallel with the optical axis 22. Since the first direction a1 is perpendicular to the optical axis 22, both the first and second directions a1 and a2 are parallel to the reference plane 37. Further, the second direction a2 forms a predetermined angle φ with the vertical direction y. As a result, the second optical path 54 is separated from the first optical path 53 in the second direction a2 by a distance D3 that is twice the first distance D1.
[0038]
The distance D3 between the two optical paths 53 and 54 is determined according to the inclination angle of the inclined birefringent plate of all the birefringent plates to be angularly displaced and the thickness of the inclined birefringent plate. In consideration of the thickness of the inclined birefringent plate, the inclination angle θ1 of the third birefringent plate 35 is such that the distance D3 is √ (P / √2) times the pitch P described above. And so on. The length corresponds to half the distance between the centers of two pixels 42 arranged in a direction U parallel to the diagonal line of the pixels 42 on the imaging surface 41. The direction from the first optical path 53 to the second optical path 54, that is, the second direction a2 is determined by the inclination direction of the inclined birefringent plate. The tilt direction is a direction parallel to the virtual plane including the normal to the surface of the tilted birefringent plate and the optical axis 22, and the tilt direction forms the angle φ with the vertical direction y. The inclination direction of the third birefringent plate 35 is adjusted such that the second direction a2 is the direction U parallel to the diagonal line of the pixel 42 on the imaging surface 41 described above.
[0039]
FIG. 4 is a diagram showing a specific configuration of the birefringent plate driving unit 25. The birefringent plate driving section 25 includes a cylindrical holding member 61, a worm 62, a motor 63, a plurality of rotating rollers 64, and a counter 65.
[0040]
The holding member 61 is provided with a holding hole 66 that penetrates in a direction parallel to the central axis 68. In the holding hole 66, a birefringent plate to be angularly displaced in the first spatial filter 24, in this embodiment, first to third birefringent plates 33 to 35 is fitted. When the birefringent plate driving unit 25 is incorporated in the imaging device 20, the optical axis 22 passes through the holding hole 66. The holding member 61 has, for example, a center axis 68 of a circle at the outer peripheral end of the holding member 61 coinciding with the optical axis 22, and can be angularly displaced about the optical axis 22. The first to third birefringent plates 33 to 35 are such that the first and second birefringent plates 33 and 34 are perpendicular to the optical axis 22 when the birefringent plate driving unit 25 is incorporated in the imaging device 20; In addition, the third birefringent plate 35 is tilted with respect to the reference plane 37 by the tilt angle θ1, and the optical axis directions of the first to third birefringent plates maintain the positional relationship described later in the first or second state. As described above, it is fitted into the holding member 61.
[0041]
Gear teeth are formed on the outer peripheral portion 67 of the holding member 61, and the holding member 61 is a worm gear, that is, a worm wheel. The gear teeth of the outer peripheral portion 67 mesh with the worm 62. The worm 62 is attached to a rotating shaft of a motor 63. There are at least three rotating rollers 64, which are arranged around the holding member 61. Each of the rotating rollers 64 is meshed with a gear tooth of the outer peripheral portion 67. Thus, at least three points on the outer peripheral portion 67 of the holding member 61 are supported. When the motor 63 is driven, the rotational force of the motor 63 is transmitted to the worm 62, and the holding member 61 is angularly displaced about the optical axis 22 with the rotation of the worm 62. The counter 65 counts the number of rotations of the motor 63, and supplies the counted number of rotations to the control device 27.
[0042]
The control device 27 determines the relationship between the number of rotations of the motor 63 and the amount of angular displacement of the first to third birefringent plates 33 to 35, that is, the angle at which the holding member 61 is angularly displaced per predetermined number of rotations of the motor 63, for example. Is provided in advance. Based on the relationship and the number of rotations of the motor 63 given from the counter 65, the control device 27 controls the first to third times from when the motor 63 starts rotating to when the counter 65 counts the number of rotations. The angle at which the birefringent plates 33 to 35 are angularly displaced can be obtained. Therefore, the control device 27 can further drive or stop the motor 63 based on the obtained angle to set the angles of the first to third birefringent plates 33 to 35 to a desired angle. .
[0043]
As described above, since the birefringent plate driving unit 25 has a very simple structure, it is easy to reduce the size. Further, the birefringent plate driving section 25 having an extremely simple configuration can surely angularly displace the birefringent plate to be angularly displaced by a desired angle. In addition, since the inclination angle θ1 of the birefringent plate to be inclined, in this embodiment, the third birefringent plate 35 is determined when the third birefringent plate 35 is attached to the holding member 61, the inclination angle is precisely adjusted. be able to. In addition, when the image sensor 26 actually captures an image of a subject, the optical path of the light after passing through the first spatial filter 24 is parallelized as described above only by determining the angle at which the third birefringent plate 35 is angularly displaced. Can be moved. Therefore, even when the birefringent plate driving unit 25 having a simple configuration is used, the accuracy of the image shift can be improved.
[0044]
Hereinafter, a behavior from when the imaging device 20 images the subject 21 to when the output image signal is output will be schematically described.
[0045]
The image sensor 26 performs photoelectric conversion twice at a predetermined cycle, and outputs an image signal after each photoelectric conversion. The birefringent plate driving section 25 fixes the birefringent plate to be angularly displaced while the imaging device 26 performs the first photoelectric conversion, in this embodiment, the first to third birefringent plates 33 to 35, and The first spatial filter 24 is kept in the first state. The first to third birefringent plates 33 to 35 are angularly displaced by the reference angle between the time when the first photoelectric conversion ends and the time when the second photoelectric conversion starts, and as a result, the first space Filter 24 transitions from the first state to the second state. The spatial frequency characteristic of the first spatial filter 24 in the second state is equal to the spatial frequency characteristic of the first spatial filter 24 in the first state. The birefringent plate driving unit 25 fixes the first to third birefringent plates 33 to 35 and causes the first spatial filter 24 to maintain the second state while the imaging element 26 performs the second photoelectric conversion. . Further, the first spatial filter 24 may maintain the second state during the first photoelectric conversion, and may maintain the first state during the second photoelectric conversion.
[0046]
Thus, the optical path of the light that has passed through the lens group 23 and the first spatial filter 24 during the second photoelectric conversion is the light path of the light that has passed through the lens group 23 and the first spatial filter 24 during the first photoelectric conversion. It is shifted from the optical path in a direction U parallel to the diagonal line of the pixels 42 on the imaging surface 41 by a length of √ times the pitch P of the array of the pixels 42. For this reason, as shown in FIG. 5, of the subject image formed on the imaging surface 41, the portion formed on each pixel 42 during the first photoelectric conversion is the second photoelectric conversion. During the conversion, each image is formed at a position 42a indicated by a dotted rectangle. In FIG. 5, a reference sign “(n, m)” is further added to a reference sign “42” added to a pixel belonging to n rows and m columns in the matrix of pixels 42. Further, a reference numeral added to a position where the portion formed on the pixel 42 (n, m) of n rows and m columns during the first photoelectric conversion is formed during the second photoelectric conversion. The code “(n, m)” is further added to “42a”. n and m are arbitrary natural numbers, respectively. From FIG. 5, the shift amount of the image shift performed by the birefringent plate driving unit 25 and the third birefringent plate 35 is half of the first pitch Px in the horizontal direction x and the second amount in the vertical direction y. It is understood that the pitch Py is half of the pitch Py. That is, the shift amount is a length of √ times the pitch P of the pixel array in the direction U parallel to the diagonal line of the pixel 42.
[0047]
As a result, the image sensor 26 outputs two image signals. The image represented by each image signal is configured by arranging the same number of pixels as the pixels 42 on the imaging surface 41 in an array similar to the array of the pixels 42 on the imaging surface 41. The plurality of pixels constituting the image correspond one-to-one with the plurality of pixels 42 on the imaging surface 41. Pixel data indicating the hue, brightness, and the like of each pixel of the image are determined according to the hue, brightness, and the like of a portion of the subject image formed on the pixel 42 corresponding to the pixel. The combining device 29 combines two image signals generated by the first and second photoelectric conversions to generate a combined image signal. The synthesizing device 29 further performs a predetermined interpolation process on the synthesized image signal. As a result, the output image signal is obtained.
[0048]
FIG. 6 is a diagram showing a part of an output image in which the output image signal is virtually visually displayed. Each of the black frame rectangles indicates a pixel of the output image. Among the pixels of the output image, the pixels on which the reference symbol “a (n, m)” is drawn correspond to the pixels on the n-th row and the m-th column of the image represented by the image signal generated by the first photoelectric conversion. , The pixel data of the pixel in the n-th row and the m-th column is applied. Among the pixels of the output image, the pixel on which the reference symbol “b (n, m)” is drawn corresponds to the pixel at n rows and m columns of the image represented by the image signal generated by the second photoelectric conversion. , The pixel data of the pixel in the n-th row and the m-th column is applied. Among the pixels of the output image, the pixels marked with “」 ”are virtual pixels that do not correspond to any pixels in the image represented by the two image signals, and the pixel data is determined by an interpolation process. You. As described above, since the second optical path 54 is translated from the first optical path 53 in the direction U parallel to the diagonal line by a length of √ the pitch P, the reference numeral b ( The pixels marked with (n, m) are inserted between the pixels marked with reference signs a (n, m) and a (n + 1, m + 1). The virtual pixels are arranged in a checkered pattern in the output image.
[0049]
As a result, the output image has four times the number of pixels and twice the number of rows and columns of pixels as compared to the image represented by the image signal. As a result, the resolution of the output image in the horizontal direction x and the vertical direction y is twice the resolution of the image sensor 26 in the horizontal direction x and the vertical direction y, respectively. That is, the optical paths 53 and 54 of the light that has passed through the first spatial filter 24 during the first and second photoelectric conversions have a length of √ times the pitch P in a direction parallel to the diagonal line of the pixel 42. In the case of only shifting, the positions of the optical paths 53 and 54 are appropriate shift positions for improving the resolution of the output image over the resolution of the image sensor 26.
[0050]
In this case, as described above, the resolution of the output image in both the horizontal direction x and the vertical direction y can be improved using two image signals. If the shift directions and the shift intervals of the first and second optical paths 53 and 54 are not set as described above, in order to improve both the resolution in the horizontal direction x and the vertical direction y of the output image, three or more shifts are required. It is expected that an image signal will be required. For these reasons, when the relationship between the first and second optical paths 53 and 54 is set as described above, the number of image signals to be generated by the image sensor 26 to obtain one output image is minimized. can do. Therefore, the time required for the image sensor 26 to image a subject in order to obtain one output image can be minimized. Therefore, the convenience of the imaging device 20 can be improved.
[0051]
FIGS. 7A to 7C are diagrams showing the optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 of the first spatial filter 24 in the first state. The optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 are respectively cut out at about 45 degrees with respect to the optical axis 22 and have different projection directions. The projection direction is the direction of the projected image when the optical axis directions q1 to q3 are projected on the xy plane, that is, the reference plane 37, and the direction of the projected image parallel to the coordinate axis parallel to the horizontal direction x is defined as 0 as a reference. Defined as degrees. The projection direction of the first birefringent plate 33 in the optical axis direction q1 is 90 degrees counterclockwise from the horizontal direction x. The projection direction in the optical axis direction q2 of the second birefringent plate 34 is 0 degrees clockwise from the horizontal direction x. The projection direction of the third birefringent plate 35 in the optical axis direction q3 is 45 degrees counterclockwise from the horizontal direction x.
[0052]
Hereinafter, the spatial frequency characteristics of the first spatial filter 24 in the first and second states will be described. The spatial frequency characteristic is determined according to the state of light separation after passing through the first spatial filter 24. Generally, light incident on a single birefringent plate is separated into an ordinary ray and an extraordinary ray while passing through the inside of the birefringent plate, and the ordinary ray is an optical path before incidence of the incident light. The extraordinary ray is translated from the optical path before the incidence by a separation width determined according to the thickness of the birefringent plate in the projection direction in the optical axis direction of the birefringent plate, and is emitted. . The vibrating surface of the ordinary ray is perpendicular to the optical axis direction of the birefringent plate, and the vibrating surface of the extraordinary ray is parallel to the optical axis direction of the birefringent plate. The thickness of the first to third birefringent plates 33 to 35 is such that the separation widths d1 to d3 are respectively half of the pitch P (P / 2), half of the pitch P, and √ of the pitch P. It is adjusted to be 1.
[0053]
FIGS. 8A to 8C are diagrams for explaining separated light images of the first to third birefringent plates 33 to 35 in the first spatial filter 24 in the first state.
[0054]
The light that has passed through the lens group 23 first enters the first birefringent plate 33. While passing through the first birefringent plate 33, the light is separated into an ordinary ray Lo and an extraordinary ray Le, as shown in FIG. The direction from the ordinary ray Lo of the first birefringent plate 33 to the extraordinary ray Le of the first birefringent plate 33 is the projection direction of the first birefringent plate 33 in the first state in the optical axis direction q1, that is, the vertical direction y. And equal. The ordinary ray Lo of the first birefringent plate 33 and the extraordinary ray Le of the first birefringent plate 33 are separated by a separation width d1.
[0055]
Next, the ordinary ray Lo and the extraordinary ray Le of the first birefringent plate 33 enter the second birefringent plate 34. As shown in FIG. 8B, the ordinary ray Lo of the first birefringent plate 33 is separated from the original position while passing through the second birefringent plate 34 as the extraordinary ray Loe of the second birefringent plate. The light is emitted shifted by the width d2 in the projection direction of the second birefringent plate 34 in the first state in the optical axis direction q2, that is, the horizontal direction x. Also, as shown in FIG. 8B, the position of the extraordinary ray Le of the first birefringent plate 33 is not changed while passing through the second birefringent plate 34 as the ordinary ray Leo of the second birefringent plate 24. Is emitted as it is. Since the vibration surface of the ordinary ray Lo of the second birefringent plate 33 is parallel to the optical axis direction q2, there is no ordinary ray of the second birefringent plate 34 corresponding to the ordinary ray Lo of the first birefringent plate 33. Since the vibration surface of the extraordinary ray Le of the first birefringent plate 33 is perpendicular to the optical axis direction q2, there is no extraordinary ray of the second birefringent plate 24 corresponding to the extraordinary ray Le of the first birefringent plate 34.
[0056]
Subsequently, the ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 enter the third birefringent plate 35. While passing through the third birefringent plate 35, the extraordinary ray Loe of the second birefringent plate 34 and the ordinary ray Loeo of the third birefringent plate 35 and the third birefringent plate 35 as shown in FIG. Are separated into the extraordinary ray Loee and emit. While passing through the third birefringent plate 35, the ordinary ray Leo of the second birefringent plate 34 and the ordinary ray Leoo of the third birefringent plate 35 and the third birefringent plate 35 as shown in FIG. Is separated from the extraordinary ray Leoe. The direction from the ordinary ray Loeo of the third birefringent plate 35 to the extraordinary ray Loee of the third birefringent plate, and the direction from the ordinary ray Leoo of the third birefringent plate 35 to the extraordinary ray Leoe of the third birefringent plate are: The projection direction of the third birefringent plate 35 in the first state in the optical axis direction q3, that is, the direction of 45 degrees counterclockwise from the horizontal direction x is equal to each other. The ordinary ray Loeo of the third birefringent plate 35 and the extraordinary ray Loee of the third birefringent plate are separated by a separation width d3, and the ordinary ray Leoo of the third birefringent plate 35 and the extraordinary ray Leoe of the third birefringent plate are different from each other. Are separated by a separation width d3.
[0057]
Therefore, the separated state of the light finally obtained by the first spatial filter 24 in the first state is the separated state shown in FIG. 8C, that is, the separated state shown in FIG. Specifically, the separated state is such that the ordinary ray Leoo of the third birefringent plate 35 and the extraordinary ray Loee of the third birefringent plate 35 are spaced parallel to the horizontal direction x at the same interval as the pitch P described above. The ordinary ray Loeo of the third birefringent plate 35 and the extraordinary ray Leoe of the third birefringent plate 35 are arranged in parallel with the vertical direction y at the same interval as the pitch P described above.
[0058]
FIGS. 10A to 10C are diagrams showing the projection directions of the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 of the first spatial filter 24 in the second state. The projection directions of the optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 of the first spatial filter 24 in the second state are the first to third directions of the first spatial filter 24 in the first state. The projection direction of the optical axis directions q1 to q3 of the birefringent plates 33 to 35 is a direction which is displaced by 180 degrees around an axis parallel to the optical axis 22. Specifically, the projection direction of the first birefringent plate 33 in the optical axis direction q1 is 90 degrees clockwise from the horizontal direction x. The projection direction in the optical axis direction q2 of the second birefringent plate 34 is 180 degrees clockwise from the horizontal direction x. The projection direction in the optical axis direction q3 of the third birefringent plate 35 is 135 degrees clockwise from the horizontal direction x.
[0059]
FIGS. 11A to 11C are diagrams for explaining separated light images of the first to third birefringent plates 33 to 35 in the first spatial filter 24 in the second state. FIG. 11 is different from FIG. 8 in that the position of the ordinary ray and the position of the extraordinary ray are replaced, respectively, and the others are equal. The details will be described below.
[0060]
The light that has passed through the lens group 23 first enters the first birefringent plate 33. While passing through the first birefringent plate 33, the light is separated into an ordinary ray Lo and an extraordinary ray Le, as shown in FIG. The direction from the ordinary ray Lo of the first birefringent plate 33 to the extraordinary ray Le of the first birefringent plate 33 is the projection direction of the first birefringent plate 33 in the second state in the optical axis direction q1, that is, the horizontal direction x. Equivalent to 90 degrees clockwise from. The ordinary ray Lo of the first birefringent plate 33 and the extraordinary ray Le of the first birefringent plate 33 are separated by a separation width d1.
[0061]
Next, the ordinary ray Lo and the extraordinary ray Le of the first birefringent plate 33 enter the second birefringent plate 34. As shown in FIG. 11B, the ordinary ray Lo of the first birefringent plate 33 is separated from the original position while passing through the second birefringent plate 34 as an extraordinary ray Loe of the second birefringent plate. The second birefringent plate 34 in the second state is emitted with a shift of 180 degrees clockwise from the projection direction in the optical axis direction q2, that is, the horizontal direction x by the width d2. As shown in FIG. 11B, the position of the extraordinary ray Le of the first birefringent plate 33 is not changed while passing through the second birefringent plate 34 as the ordinary ray Leo of the second birefringent plate 24. Is emitted as it is. The ordinary ray of the second birefringent plate 34 corresponding to the ordinary ray Lo of the first birefringent plate 33 and the extraordinary ray of the second birefringent plate 24 corresponding to the extraordinary ray Le of the first birefringent plate 34 are shown in FIG. No, for the same reason as 8.
[0062]
Subsequently, the ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 enter the third birefringent plate 35. As shown in FIG. 11C, while the ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 pass through the third birefringent plate 35, the ordinary rays Leoo, Loeo of the third birefringent plate 35. And extraordinary rays Leoe and Loee of the third birefringent plate, respectively, and exit. The ordinary rays Leoo and Loeo of the third birefringent plate 35 are separated from the extraordinary rays Leoe and Loee of the third birefringent plate by a separation width d3. The direction from the ordinary rays Leoo, Loeo of the third birefringent plate 35 to the extraordinary rays Leoe, Loee of the third birefringent plate 35 is the projection direction of the third birefringent plate 35 in the second state in the optical axis direction q3 of the third birefringent plate 35, that is, , 135 degrees counterclockwise from the horizontal direction x. Therefore, the separated state of the ordinary ray and the extraordinary ray finally obtained in the first spatial filter 24 in the second state is the separated state shown in FIG. 11C, that is, the separated state shown in FIG.
[0063]
From the above, it can be seen that the separated state of the light finally obtained in the first spatial filter 24 in the first and second states is equal. Therefore, the spatial frequency characteristic of the first spatial filter 24 in the first state is equal to the spatial frequency characteristic of the first spatial filter 24 in the second state. Therefore, if the spatial frequency characteristic is set in advance to a spatial frequency characteristic suitable for the resolution of the output image, the image sensor 26 captures the subject 21 via the first spatial filter 24 having an appropriate spatial frequency characteristic. can do. That is, regardless of the fact that at least one birefringent plate in the first spatial filter 24 is angularly displaced for image shift, the image sensor 26 converts the subject 21 into a first spatial filter having an appropriate spatial frequency characteristic. It is possible to always take an image via the.
[0064]
The first to third birefringent plates 33 to 35 change the arrangement order in the first state and the second state if the mutual positional relationship in the optical axis direction q1 to q3 is as described above. However, since the final separation state is as shown in FIG. 9, the spatial frequency characteristics are the same as those described above. Therefore, the arrangement order of the first to third birefringent plates 33 to 35 may be changed from the above-described arrangement order. Further, in the above-described imaging device 20, the birefringent plate inclined with respect to the reference plane 37 may be any one of the birefringent plates that are angularly displaced. Alternatively, the first or second birefringent plates 33, 34 may be inclined with respect to the reference plane 37.
[0065]
Hereinafter, an imaging device according to a second embodiment of the present invention will be described. The imaging device according to the second embodiment differs from the imaging device 20 according to the first embodiment only in that the first spatial filter 24 is replaced by a second spatial filter 81, and is otherwise equal. In the configuration of the imaging device according to the second embodiment, description of the same portions as those of the imaging device 20 according to the first embodiment will be omitted. In addition, among components constituting the imaging device of the second embodiment, components having the same configuration as the imaging device 20 of the first embodiment are denoted by the same reference numerals.
[0066]
FIG. 12 is a diagram illustrating the second spatial filter 81 in the first state and the second spatial filter 81 in the second state. In the second spatial filter 81, only the first birefringent plate 33 is parallel to the reference plane 37, and the second and third birefringent plates 34 and 35 are inclined at a predetermined inclination angle θ2 with respect to the reference plane 37. ing. The birefringent plate driving unit 25 moves the first to third birefringent plates 33 to 35 of the second spatial filter 81 in the first state indicated by solid lines around an axis parallel to the optical axis 22 for image shift. At 180 degrees. As a result, the second spatial filter 81 enters the second state. The second and third birefringent plates 34 and 35 of the spatial filter in the second state are inclined with respect to the reference plane 37 as shown by two-dot broken lines.
[0067]
In the second embodiment, by analogy with the description of FIG. 3, the inclined birefringent plate is used. In the second embodiment, the second and third birefringent plates 35 are angularly displaced about the axis. Accordingly, the position of the optical path of the light from the subject 21 after passing through the second spatial filter 81 changes. It is assumed that the optical paths 51 and 52 of the light from the subject 21 before passing through the second spatial filter 81 in the first and second states coincide with the optical axis 22 of the lens group 23. In this case, the optical path 54 of the light after passing through the second spatial filter 81 in the second state is moved from the optical path 53 of the light after passing through the second spatial filter 81 in the first state to the pixel 42 of the imaging surface 41. The inclination directions of the second and third birefringent plates 34 and 35 and the second and third birefringent plates 34 and 35 are shifted in a direction U parallel to the diagonal line by a length of √ the pitch P of the array of the pixels 42. The inclination angles of the birefringent plates 34 and 35 are adjusted.
[0068]
As shown in FIG. 12, the second and third birefringent plates 34, 35 may be arranged with a space between the second and third birefringent plates 34, 35, and the second and third birefringent plates 34, 35 may be arranged. The refraction plates 34 and 35 may be arranged so as to contact each other without any gap. Further, for the same reason as described in the first embodiment, the arrangement order of the first to third birefringent plates 33 to 35 may be changed from the above-described arrangement order. The birefringent plate inclined with respect to the reference plane 37 may be any two of the birefringent plates that are angularly displaced. The second and third birefringent plates 33, 34 may be inclined with respect to the reference plane 37, and the first and third birefringent plates 33, 35 may be inclined with respect to the reference plane 37.
[0069]
Hereinafter, an imaging device according to a third embodiment of the present invention will be described. The imaging device according to the third embodiment differs from the imaging device 20 according to the first embodiment only in that the first spatial filter 24 is replaced with a third spatial filter 83, and is otherwise equal. In the configuration of the imaging device according to the third embodiment, description of the same portions as those of the imaging device 20 according to the first embodiment will be omitted. Further, among the components constituting the imaging device of the third embodiment, components having the same configuration as the imaging device 20 of the first embodiment are denoted by the same reference numerals.
[0070]
FIG. 13 is a diagram illustrating the third spatial filter 83 in the first state and the third spatial filter 83 in the second state. In the third spatial filter 83, the first to third birefringent plates 34 and 35 are inclined at a predetermined inclination angle θ3 with respect to the reference plane 37. The birefringent plate driving unit 25 moves the first to third birefringent plates 33 to 35 of the third spatial filter 83 in the first state indicated by solid lines around an axis parallel to the optical axis 22 for image shift. At 180 degrees. As a result, the third spatial filter 83 enters the second state indicated by the two-dot chain line. As shown in FIG. 13, the first to third birefringent plates 33 to 35 are formed between the first and second birefringent plates 33 and 34 and between the second and third birefringent plates 34 and 35. At least one of them may be arranged with an interval, and the first to third birefringent plates 34 and 35 may be arranged in contact with no gap.
[0071]
In the third embodiment, the birefringent plate is inclined by analogy with the description of FIG. 3, and in the third embodiment, the first to third birefringent plates 33 to 35 are angularly displaced about the axis. Accordingly, the position of the optical path of the light from the subject 21 after passing through the third spatial filter 83 changes. It is assumed that both the optical paths 51 and 52 of the light from the subject 21 before passing through the third spatial filter 83 in the first and second states coincide with the optical axis 22 of the lens group 23. In this case, the optical path 54 of the light after passing through the third spatial filter 83 in the second state is moved from the optical path 53 of the light after passing through the third spatial filter 83 in the first state to the pixel 42 of the imaging surface 41. The inclination directions of the first to third birefringent plates 33 to 35 and the first to third directions are shifted in a direction U parallel to the diagonal line by a length of √ the pitch P of the arrangement of the pixels 42. The inclination angle θ3 of the birefringent plates 33 to 35 is adjusted.
[0072]
In the first to third embodiments, the optical path 54 of the light after passing through the first to third spatial filters 24, 81, and 83 in the second state is all the first to third spatial filters in the first state. The light is shifted from the optical path 53 of the light after passing through 24, 81, 83 in the direction U parallel to the diagonal line of the pixel 42 by a length of √ the pitch P. Therefore, the inclination angle θ2 of the second and third birefringent plates 34 and 35 of the second spatial filter 81 may be smaller than the inclination angle θ1 of the third filter 35 of the first spatial filter 24. Further, the inclination angle θ3 of the first to third birefringent plates 33 to 35 of the third spatial filter 83 may be smaller than the inclination angles θ1 and θ2. This is because, as the number of inclined birefringent plates increases, the length of a portion of the optical path of the light that passes through the inside of the inclined birefringent plate increases, so that the length of the optical path shift increases. . Also, as the angle of inclination of the birefringent plate becomes smaller, the light is less affected by aberrations and the like when passing through the spatial filter, so that the image quality of the image represented by the image signal generated by the image sensor 26 is degraded. , Can be suppressed.
[0073]
Hereinafter, an imaging device according to a fourth embodiment of the present invention will be described. The imaging device according to the fourth embodiment differs from the imaging device 20 according to the first embodiment only in that the first spatial filter 24 is replaced with a fourth spatial filter, and is otherwise the same. In the configuration of the imaging device according to the fourth embodiment, description of the same portions as those of the imaging device 20 according to the first embodiment will be omitted. In addition, among components constituting the imaging device of the fourth embodiment, components having the same configuration as the imaging device 20 of the first embodiment are denoted by the same reference numerals.
[0074]
The fourth spatial filter has first to third birefringent plates 33 to 35, and at least one of the first and second birefringent plates 33 and 34 is inclined with respect to the reference plane 37. I have. That is, the first birefringent plate 33, the second birefringent plate 34, or both the first and second birefringent plates 33, 34 are inclined with respect to the reference plane 37. The mutual positional relationship of the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 in the fourth spatial filter in the first state is equal to that of the first spatial filter 24 in the first state. The birefringent plate driving unit 25 displaces only the first and second birefringent plates 33 and 34 by 180 degrees. The third birefringent plate 35 is always fixed. For this purpose, for example, only the first and second birefringent plates 33 and 34 are fitted into the holding member 61, and the third birefringent plate 35 is fixed to another holding member. In this case, the optical path of the light after passing through the fourth spatial filter in the second state is parallel to the diagonal line of the pixel 42 on the imaging surface 41 from the optical path of the light after passing through the fourth spatial filter in the first state. The inclination direction of the inclined birefringent plate of the first and third birefringent plates 33 and 35 so as to be shifted in the direction U by a length of √ half of the pitch P of the arrangement of the pixels 42. And the tilt angle has been adjusted.
[0075]
FIGS. 14A to 14C are views showing the projection directions of the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 of the fourth spatial filter in the second state. The optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 are cut out at about 45 degrees with respect to the optical axis 22. The projection direction in the optical axis direction q1 of the first birefringent plate 33 is 90 degrees clockwise from the horizontal direction x. The projection direction in the optical axis direction q2 of the second birefringent plate 34 is 180 degrees clockwise from the horizontal direction x. The projection direction of the third birefringent plate 35 in the optical axis direction q3 is equal to the direction shown in FIG. 7C, and is 45 degrees counterclockwise from the horizontal direction x.
[0076]
FIGS. 15A to 15C are diagrams for explaining separated light images of the first to third birefringent plates 33 to 35 in the fourth spatial filter in the second state. The spatial frequency characteristics of the fourth spatial filter in the second state will be described with reference to FIG.
[0077]
The light that has passed through the lens group 23 first enters the first birefringent plate 33. The separation state of the light while passing through the first and second birefringent plates 33 and 34 is shown in FIGS. 11A and 11B as shown in FIGS. Since they are the same as the light separation states described in the above, the description is omitted.
[0078]
The ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 enter the third birefringent plate 35. As shown in FIG. 15C, while the ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 pass through the third birefringent plate 35, the ordinary rays Leoo, Loeo of the third birefringent plate 35. And extraordinary rays Leoe and Loee of the third birefringent plate, respectively, and exit. The ordinary rays Leoo and Loeo of the third birefringent plate 35 are separated from the extraordinary rays Leoe and Loee of the third birefringent plate by a separation width d3. The direction from the ordinary rays Leoo, Loeo of the third birefringent plate 35 to the extraordinary rays Leoe, Loee of the third birefringent plate 35 is the projection direction of the third birefringent plate 35 in the second state in the optical axis direction q3 of the third birefringent plate 35, that is, Each direction is equal to 45 degrees counterclockwise from the horizontal direction x.
[0079]
Therefore, the separated state of the light finally obtained in the fourth spatial filter in the second state is the separated state shown in FIG. 15C, that is, the separated state shown in FIG. From the above, it can be seen that the separated states of the light finally obtained in the fourth spatial filter in the first and second states are equal. Therefore, the spatial frequency characteristic of the fourth spatial filter in the first state is equal to the spatial frequency characteristic of the fourth spatial filter in the second state.
[0080]
Hereinafter, an imaging device according to a fifth embodiment of the present invention will be described. The imaging device according to the fifth embodiment differs from the imaging device 20 according to the first embodiment only in that the first spatial filter 24 is replaced with a fifth spatial filter, and is otherwise the same. In the configuration of the imaging device according to the fifth embodiment, description of the same portions as those of the imaging device 20 according to the first embodiment will be omitted. Further, among the components configuring the imaging device of the fifth embodiment, components having the same configuration as the imaging device 20 of the first embodiment are denoted by the same reference numerals.
[0081]
The fifth spatial filter has first to third birefringent plates 33 to 35, and only the third birefringent plate 35 is inclined with respect to the reference plane 37. The positional relationship between the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 in the fifth spatial filter in the first state is equal to that of the first spatial filter 24 in the first state. The birefringent plate drive unit 25 displaces only the third birefringent plate 35 by 180 degrees around an axis parallel to the optical axis 22. The first and second birefringent plates 33, 34 are always fixed. For this purpose, for example, only the third birefringent plate 35 is fitted into the holding member 61, and the first and second birefringent plates 33 and 34 are fixed to another holding member. In this case, the optical path of the light after passing through the fifth spatial filter in the second state is parallel to the diagonal line of the pixel 42 on the imaging surface 41 from the optical path of the light after passing through the fifth spatial filter in the first state. The inclination direction and the inclination angle of the third birefringent plate 35 are adjusted so as to be shifted in the direction U by a length of √ half of the pitch P of the arrangement of the pixels 42.
[0082]
FIGS. 16A to 16C are diagrams showing the projection directions of the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 of the fifth spatial filter in the second state. The optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 are cut out at about 45 degrees with respect to the optical axis 22. The projection direction in the optical axis direction q1 of the first birefringent plate 33 is equal to the direction shown in FIG. 7A, and is 90 degrees counterclockwise from the horizontal direction x. The projection direction in the optical axis direction q2 of the second birefringent plate 34 is 0 degrees clockwise from the horizontal direction x. The projection direction in the optical axis direction q3 of the third birefringent plate 35 is equal to the direction shown in FIG. 7C, and is 135 degrees clockwise from the horizontal direction x.
[0083]
FIGS. 17A to 17C are diagrams for explaining separated light images of the first to third birefringent plates 33 to 35 in the fifth spatial filter in the second state. The spatial frequency characteristics of the fifth spatial filter in the second state will be described with reference to FIG.
[0084]
The light that has passed through the lens group 23 first enters the first birefringent plate 33. As shown in FIGS. 17A and 17B, the separated state of the light while passing through the first and second birefringent plates 33 and 34 is shown in FIGS. 8A and 8B. Since they are the same as the light separation states described in the above, the description is omitted.
[0085]
The ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 enter the third birefringent plate 35. As shown in FIG. 17C, the ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 pass through the third birefringent plate 35, while the ordinary rays Leoo and Loeo of the third birefringent plate 35 pass. And extraordinary rays Leoe and Loee of the third birefringent plate, respectively, and exit. The ordinary rays Leoo and Loeo of the third birefringent plate 35 are separated from the extraordinary rays Leoe and Loee of the third birefringent plate by a separation width d3. The direction from the ordinary rays Leoo, Loeo of the third birefringent plate 35 to the extraordinary rays Leoe, Loee of the third birefringent plate 35 is the projection direction of the third birefringent plate 35 in the second state in the optical axis direction q3 of the third birefringent plate 35, that is, It is equal to a direction of 135 degrees counterclockwise from the horizontal direction x.
[0086]
Therefore, the separated state of the light beam finally obtained in the fifth spatial filter in the second state is the separated state shown in FIG. 17C, that is, the separated state shown in FIG. From the above, it can be seen that the separated state of light finally obtained in the fifth spatial filter in the first and second states is equal. Therefore, the spatial frequency characteristic of the fifth spatial filter in the first state is equal to the spatial frequency characteristic of the fifth spatial filter in the second state.
[0087]
Hereinafter, an imaging device according to a sixth embodiment of the present invention will be described. The imaging device according to the sixth embodiment differs from the imaging device 20 according to the first embodiment only in that the first spatial filter 24 is replaced with a sixth spatial filter, and is otherwise the same. In the configuration of the imaging device according to the sixth embodiment, description of the same portions as those of the imaging device 20 according to the first embodiment will be omitted. Further, among the components constituting the imaging device of the sixth embodiment, components having the same configuration as the imaging device 20 of the first embodiment are denoted by the same reference numerals.
[0088]
The sixth spatial filter has first to third birefringent plates 33 to 35, and at least one of the first and third birefringent plates 33 and 35 is inclined with respect to the reference plane 37. I have. That is, the first birefringent plate 33 or the third birefringent plate 35 is used alone, or both the first and third birefringent plates 33 and 35 are inclined with respect to the reference plane 37. The mutual positional relationship of the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 in the sixth spatial filter in the first state is equal to that of the first spatial filter 24 in the first state.
[0089]
The birefringent plate driving section 25 displaces the first birefringent plate 33 by 180 degrees around an axis parallel to the optical axis 22, and moves the third birefringent plate 35 by 90 degrees counterclockwise around the axis. Perform angular displacement. The second birefringent plate 34 is always fixed. For this purpose, for example, two sets of mechanisms having the configuration shown in FIG. 4 are provided, and the first and third birefringent plates 33 and 35 are fitted into the holding members 61 of each mechanism, respectively. Is fixed to another holding member. In this case, the optical path of the light after passing through the sixth spatial filter in the second state is parallel to the diagonal line of the pixel 42 on the imaging surface 41 from the optical path of the light after passing through the sixth spatial filter in the first state. The inclination direction of the inclined birefringent plate of the first and third birefringent plates 33 and 35 so as to be shifted in the direction U by a length of √ half of the pitch P of the arrangement of the pixels 42. And the inclination angles of the first and third birefringent plates 33 and 35 are adjusted.
[0090]
FIGS. 18A to 18C are diagrams showing the projection directions of the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 of the sixth spatial filter in the second state. The optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 are cut out at about 45 degrees with respect to the optical axis 22. The projection direction in the optical axis direction q1 of the first birefringent plate 33 is 90 degrees clockwise from the horizontal direction x. The projection direction in the optical axis direction q2 of the second birefringent plate 34 is equal to the direction shown in FIG. 7B, and is 0 degrees clockwise from the horizontal direction x. The projection direction of the third birefringent plate 35 in the optical axis direction q3 is 135 degrees counterclockwise from the horizontal direction x.
[0091]
FIGS. 19A to 19C are diagrams for explaining separated light images of the first to third birefringent plates 33 to 35 in the sixth spatial filter in the second state. The spatial frequency characteristic of the sixth spatial filter in the second state will be described with reference to FIG.
[0092]
The light that has passed through the lens group 23 first enters the first birefringent plate 33. As shown in FIG. 19A, the state of separation of the light while passing through the first birefringent plate 33 is the same as the state of separation of light described with reference to FIG.
[0093]
The ordinary ray Lo and the extraordinary ray Le of the first birefringent plate 33 enter the second birefringent plate 34. As shown in FIG. 19B, the ordinary ray Lo of the first birefringent plate 33 is separated from the original position while passing through the second birefringent plate 34 as the extraordinary ray Loe of the second birefringent plate. The light is emitted with a shift of 180 degrees clockwise from the projection direction of the second birefringent plate 34 in the first state in the optical axis direction q2, that is, the horizontal direction x, by the width d2. Further, as shown in FIG. 19B, the position of the extraordinary ray Le of the first birefringent plate 33 is not changed while passing through the second birefringent plate 34 as the ordinary ray Leo of the second birefringent plate 24. It is emitted as it is. The ordinary ray of the second birefringent plate 34 corresponding to the ordinary ray Lo of the first birefringent plate 33 and the extraordinary ray of the second birefringent plate 24 corresponding to the extraordinary ray Le of the first birefringent plate 34 are: It does not exist for the reason described in the first embodiment.
[0094]
The ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 enter the third birefringent plate 35. As shown in FIG. 19C, while the ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 pass through the third birefringent plate 35, the ordinary rays Leoo, Loeo of the third birefringent plate 35. And extraordinary rays Leoe and Loee of the third birefringent plate, respectively, and exit. The ordinary rays Leoo and Loeo of the third birefringent plate 35 are separated from the extraordinary rays Leoe and Loee of the third birefringent plate by a separation width d3. The direction from the ordinary rays Leoo, Loeo of the third birefringent plate 35 to the extraordinary rays Leoe, Loee of the third birefringent plate 35 is the projection direction of the third birefringent plate 35 in the second state in the optical axis direction q3 of the third birefringent plate 35, that is, It is equal to a direction of 135 degrees counterclockwise from the horizontal direction x.
[0095]
Therefore, the separated state of the light finally obtained in the sixth spatial filter in the second state is the separated state shown in FIG. 19C, that is, the separated state shown in FIG. From the above, it can be seen that the separated state from the light finally obtained in the sixth spatial filter in the first and second states is equal. Therefore, the spatial frequency characteristic of the sixth spatial filter in the first state is equal to the spatial frequency characteristic of the sixth spatial filter in the second state.
[0096]
Hereinafter, an imaging device according to a seventh embodiment of the present invention will be described. The imaging device according to the seventh embodiment differs from the imaging device 20 according to the first embodiment only in that the first spatial filter 24 is replaced with a seventh spatial filter, and is otherwise the same. In the configuration of the imaging device according to the seventh embodiment, a description of the same portions as those of the imaging device 20 according to the first embodiment will be omitted. Further, among the components constituting the imaging device of the seventh embodiment, components having the same configuration as the imaging device 20 of the first embodiment are denoted by the same reference numerals.
[0097]
The seventh spatial filter has first to third birefringent plates 33 to 35, and at least one of the second and third birefringent plates 34 and 35 is inclined with respect to the reference plane 37. I have. That is, the second birefringent plate 34 or the third birefringent plate 35 alone, or both the second and third birefringent plates 34 and 35 are inclined with respect to the reference plane 37. The mutual positional relationship of the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 in the seventh spatial filter in the first state is equal to that of the first spatial filter 24 in the first state.
[0098]
The birefringent plate drive unit 25 displaces the second birefringent plate 34 by 180 degrees around an axis parallel to the optical axis 22 and shifts the third birefringent plate 35 by 90 degrees clockwise around the axis. Make angular displacement. The first birefringent plate 34 is always fixed. For this purpose, for example, two sets of mechanisms having the configuration shown in FIG. 4 are provided, and the second and third birefringent plates 34 and 35 are fitted into the holding members 61 of each mechanism, respectively. Is fixed to another holding member. In this case, the optical path of the light after passing through the seventh spatial filter in the second state is parallel to the diagonal line of the pixel 42 on the imaging surface 41 from the optical path of the light after passing through the seventh spatial filter in the first state. The direction of inclination of the inclined birefringent plate of the second and third birefringent plates 34 and 35 is shifted in the direction U by a length of √ half of the pitch P of the arrangement of the pixels 42. The tilt angle has been adjusted.
[0099]
FIGS. 20A to 20C are diagrams showing the projection directions of the first to third birefringent plates 33 to 35 in the optical axis directions q1 to q3 of the seventh spatial filter in the second state. The optical axis directions q1 to q3 of the first to third birefringent plates 33 are respectively cut out at about 45 degrees with respect to the optical axis 22. The projection direction in the optical axis direction q1 of the first birefringent plate 33 is equal to the direction shown in FIG. 7A, and is 90 degrees counterclockwise from the horizontal direction x. The projection direction in the optical axis direction q2 of the second birefringent plate 34 is 180 degrees clockwise from the horizontal direction x. The projection direction of the third birefringent plate 35 in the optical axis direction q3 is 45 degrees clockwise from the horizontal direction x.
[0100]
FIGS. 21A to 21C are views for explaining separated light images of the first to third birefringent plates 33 to 35 in the seventh spatial filter in the second state. The spatial frequency characteristics of the seventh spatial filter in the second state will be described with reference to FIG.
[0101]
The light that has passed through the lens group 23 first enters the first birefringent plate 33. The light separation state while passing through the first birefringent plate 33 is the same as the light separation state described in FIG. 8A as shown in FIG.
[0102]
The ordinary ray Lo and the extraordinary ray Le of the first birefringent plate 33 enter the second birefringent plate 34. As shown in FIG. 21B, the ordinary ray Lo of the first birefringent plate 33 is separated from the original position while passing through the second birefringent plate 34 as the extraordinary ray Loe of the second birefringent plate. The second birefringent plate 34 in the second state is emitted with a shift of 180 degrees clockwise from the projection direction in the optical axis direction q2, that is, the horizontal direction x by the width d2. Further, as shown in FIG. 21B, the position of the extraordinary ray Le of the first birefringent plate 33 is not changed while passing through the second birefringent plate 34 as the ordinary ray Leo of the second birefringent plate 24. Is emitted as it is. The ordinary ray of the second birefringent plate 34 corresponding to the ordinary ray Lo of the first birefringent plate 33 and the extraordinary ray of the second birefringent plate 24 corresponding to the extraordinary ray Le of the first birefringent plate 34 are: It does not exist for the reason described in the first embodiment.
[0103]
The ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 enter the third birefringent plate 35. As shown in FIG. 21C, while the ordinary ray Leo and the extraordinary ray Loe of the second birefringent plate 34 pass through the third birefringent plate 35, the ordinary rays Leoo and Loeo of the third birefringent plate 35. And extraordinary rays Leoe and Loee of the third birefringent plate, respectively, and exit. The ordinary rays Leoo and Loeo of the third birefringent plate 35 are separated from the extraordinary rays Leoe and Loee of the third birefringent plate by a separation width d3. The direction from the ordinary rays Leoo, Loeo of the third birefringent plate 35 to the extraordinary rays Leoe, Loee of the third birefringent plate 35 is the projection direction in the optical axis direction q3 of the third birefringent plate 35 in the second state, that is, Each direction is equal to 45 degrees counterclockwise from the horizontal direction x. Accordingly, the separated state of the ordinary ray and the extraordinary ray finally obtained in the seventh spatial filter in the second state is the separated state shown in FIG. 21C, that is, the separated state shown in FIG.
[0104]
From the above, it can be seen that the separated state of the ordinary ray and the extraordinary ray finally obtained in the seventh spatial filter in the first and second states is equal. Therefore, the spatial frequency characteristic of the seventh spatial filter in the first state is equal to the spatial frequency characteristic of the seventh spatial filter in the second state.
[0105]
As described above, in the fourth to seventh spatial filters of the imaging devices of the fourth to seventh embodiments, the spatial frequency characteristics in the first state and the spatial frequency characteristics in the second state are equal. Therefore, in any of the imaging devices of the fourth to seventh embodiments, as described in the first embodiment, at least one birefringent plate in the fourth to seventh spatial filters is angularly shifted for image shift. Irrespective of the displacement, the image sensor 26 can always image the subject 21 via the fourth to seventh spatial filters having appropriate spatial frequency characteristics.
[0106]
Further, if the spatial filter maintains the positional relationship shown in FIGS. 7, 10, 14, 16, 18, and 20 in the optical axis directions of the first to third birefringent plates, the final light separation state is changed. All are the same. Therefore, two positional relationships are selected from the plurality of positional relationships described above, and the positional relationships in the optical axis direction of the first to third birefringent plates 33 to 35 that the spatial filters in the first and second states should maintain. Two selected positional relationships may be used. For example, the spatial filter in the first state may have the positional relationship shown in FIG. 10, and the spatial filter in the second state may have the positional relationship shown in FIG. In addition, when the optical axis directions of the first to third birefringent plates maintain the above-described plurality of positional relationships, in any state, even if the order of the first to third birefringent plates 33 to 35 is changed, the final order is obtained. Since the light separation states are the same, the first to third birefringent plates 33 to 35 may be changed from the order shown in the above-described drawings.
[0107]
The imaging devices of the first to seventh embodiments are examples of the imaging device of the present invention, and can be implemented in other various forms as long as the main operations are the same. In particular, the detailed operation of each device is not limited to this as long as the same output is obtained, and may be realized by another operation. Further, the spatial filter of the imaging device of the present invention has one or a plurality of birefringent plates, and at least one of all birefringent plates is angularly displaced about the reference axis and is angularly displaced. If at least one of the birefringent plates is inclined with respect to a reference plane perpendicular to the reference axis, the present invention is not limited to the above-described first to seventh spatial filters, and may have another configuration. When two or more birefringent plates are inclined with respect to the reference plane, the angle formed between each birefringent plate and the reference plane may be changed for each birefringent plate. It is preferable to make the angle between each of the birefringent plates and the reference plane equal. This is because it becomes easy to attach all the birefringent plates that are inclined to the imaging device. Further, since the angle formed between each birefringent plate and the reference plane can be minimized as compared with the case where the angles are not equal, deterioration of an image due to the inclination of the birefringent plate and the like can be prevented. Because it can be suppressed.
[0108]
In the imaging device of the present invention, the angle at which the birefringent plate is angularly displaced, that is, the reference angle is preferably 180 degrees. This is for the following two reasons.
[0109]
The first reason is as follows. A birefringent plate used in an image pickup device equipped with a CCD image sensor generally uses quartz. Since a birefringent plate using quartz tends to be expensive, the shape of the birefringent plate currently on the market is, as shown in FIG. 22, substantially rectangular with both ends being arcs with a radius r. When the birefringent plate is angularly displaced by 90 degrees in the imaging apparatus of the present invention, it is considered that the shape of the birefringent plate needs to be circular or substantially cross-shaped as shown in FIG. When the birefringent plate is displaced by 180 degrees in the imaging apparatus of the present invention, the shape of the birefringent plate can be symmetrical with respect to the optical axis 22. It is considered that a substantially rectangular shape shown in FIG. Therefore, when the reference angle is 180 degrees, the commercially available birefringent plate can be used as the birefringent plate of the imaging device of the present invention. Further, if the radius r of the birefringent plate of FIG. 22 is equal to that of the circular birefringent plate and the birefringent plate of FIG. 23, the area is smaller than that of the circular birefringent plate and the birefringent plate of FIG. be able to. From these facts, it is possible to suppress an increase in the manufacturing cost of the imaging device of the present invention, so that the reference angle is preferably 180 degrees.
[0110]
The second reason is as follows. FIGS. 24A and 25A show the angles at which the birefringent plate is angularly displaced, that is, the reference angles are 180 degrees and 90 degrees, and the inclination angle of the birefringent plate that is angularly displaced is 0. In the case of degrees, the positions of the optical paths 100 and 101 of the light from the subject after passing through the spatial filter before the birefringent plate is angularly displaced are shown, respectively. In this case, the optical path of light from the subject after passing through the spatial filter after the birefringent plate has been angularly displaced is equal to the optical paths 100 and 101. The virtual rectangle 102 indicated by the two-dot chain line is a square whose one side length is half (P / 2) of the pitch P of the array of the pixels 42 on the imaging surface 41. In FIGS. 24A and 24B, the center of the virtual rectangle 102 matches the optical path 100, and in FIGS. 25A and 25B, the upper right vertex of the virtual rectangle 102 matches the optical path 101. is there.
[0111]
At least one of the birefringent plates that are angularly displaced in the spatial filter is, according to the reference angle, an optical path of light from a subject after passing through the spatial filter before the birefringent plate is angularly displaced, It is assumed that the birefringent plate is inclined so that the distance from the optical path of light from the subject after passing through the spatial filter after the birefringent plate is angularly displaced is √ of the pitch P. When the reference angle is 180 degrees, the optical path 103 of light from the subject after passing through the spatial filter before the birefringent plate is angularly displaced, and the subject after passing through the spatial filter after the birefringent plate is angularly displaced. As shown in FIG. 24B, the optical path 104 of the light is located at two non-adjacent vertices of the virtual rectangle 102. In this case, the distance between the optical path 100 and the optical paths 103 and 104 is √ of the pitch P (P√2 / 4). When the reference angle is 90 degrees, the optical path 105 of the light from the subject after passing through the spatial filter before the birefringent plate is angularly displaced, and the subject after passing through the spatial filter after the birefringent plate is angularly displaced. As shown in FIG. 25B, the optical path 106 of the light is located at two non-adjacent vertices of the virtual rectangle 102. In this case, the distance between the optical path 101 and the optical paths 105 and 106 is half the pitch P.
[0112]
As a result, the distance between the optical path 101 and the optical paths 103 and 104 when the reference angle is 180 degrees is shorter than the distance between the optical path 101 and the optical paths 105 and 106 when the reference angle is 90 degrees. . That is, the deviation of the optical path due to the inclination of the birefringent plate is smaller when the reference angle is 180 degrees than when the reference angle is 90 degrees. Therefore, it is considered that the inclination angle of the birefringent plate when the reference angle is 180 degrees is smaller than the inclination angle of the birefringent plate when the reference angle is 90 degrees. From the above, if the deviation of the optical path after passing through the spatial filter before and after the angular displacement of the birefringent plate is predetermined, the inclination angle of the birefringent plate can be minimized when the reference angle is 180 degrees. It is expected to be possible. Thereby, when the reference angle is 180 degrees, in the output image represented by the output image signal generated by the imaging device of the present invention, the deterioration of the image quality due to the inclination of the birefringent plate can be minimized. is there.
[0113]
【The invention's effect】
As described above, according to the present invention, in the imaging apparatus, the positional relationship between at least one of the birefringent plates in the spatial filter and the optical axis of the optical system is changed by the image shift unit. Thus, the at least one birefringent plate doubles as a refracting plate for image shift. Thereby, the imaging device of the present invention can be made smaller and lighter than the imaging device of the related art, and the assembly cost can be lower than that of the imaging device of the related art.
[0114]
The spatial filter always keeps a predetermined spatial frequency characteristic regardless of a change in a positional relationship between the at least one birefringent plate and the optical axis. Therefore, the imaging device of the imaging device can always capture an image of a subject through a spatial filter having an appropriate spatial frequency characteristic.
[0115]
Still further, according to the invention, the at least one birefringent plate is pre-tilted with respect to a reference plane perpendicular to the optical axis, and the image shift means shifts the at least one birefringent plate to light. Angular displacement about an axis parallel to the axis. Thereby, the accuracy of the image shift in the imaging device can be improved.
[0116]
Further, according to the present invention, the angle and direction between the inclined at least one birefringent plate and the reference plane are changed according to the angular displacement of the birefringent plate. , Which are shifted in a direction parallel to a diagonal line of the pixel by √ of the array pitch of the pixel of the image sensor. Thereby, the convenience of the imaging device is improved.
[0117]
Furthermore, according to the present invention, the image shift means causes the one or more birefringent plates of all the birefringent plates to be angularly displaced by 180 degrees. Thereby, it is possible to minimize the decrease in the image quality of the image due to the inclination of the birefringent plate. Thus, an increase in the manufacturing cost of the imaging device can be suppressed.
[0118]
According to the present invention, when a plurality of birefringent plates among all the birefringent plates to be angularly displaced are inclined with respect to the reference plane, each of the plurality of birefringent plates and the reference plane are The angles made are equal to each other. This facilitates angle adjustment of the plurality of birefringent plates to be inclined when assembling the imaging device. Further, it is possible to reduce a decrease in image quality of the image caused by the aberration.
[0119]
Furthermore, according to the present invention, the spatial filter can always maintain a predetermined spatial frequency characteristic regardless of whether or not the inclined birefringent plate or the birefringent plates are angularly displaced. Therefore, the imaging device can always image a subject through a spatial filter having an appropriate spatial frequency characteristic.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an imaging device 20 according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration of an imaging surface 41 of an imaging element 26 of the imaging device 20.
FIG. 3 is a diagram showing first and second states of a first spatial filter 24 of the imaging device 20.
FIG. 4 is a diagram showing a specific configuration of a birefringent plate driving unit 25 of the imaging device 20.
FIG. 5 is a diagram showing a position of a subject image formed on an imaging surface 41;
FIG. 6 is a diagram illustrating an output image represented by an output image signal generated by the imaging device.
FIG. 7 is a diagram showing a positional relationship of the first to third birefringent plates 33 to 35 in the first spatial filter 24 in the first state in the directions of the projected images on the xy plane in the optical axis directions q1 to q3. .
FIG. 8 is a diagram illustrating a light separation state of the first spatial filter 24 in the first state.
FIG. 9 is a diagram showing a final light separation state of the first spatial filter 24 in the first state.
FIG. 10 is a diagram showing a positional relationship between first to third birefringent plates 33 to 35 in the first spatial filter 24 in the second state and the direction of an image projected on the xy plane in the optical axis directions q1 to q3. .
FIG. 11 is a diagram illustrating a light separation state of a first spatial filter 24 in a second state.
FIG. 12 is a diagram illustrating first and second states of a second spatial filter 81 in an imaging device according to a second embodiment of the present invention.
FIG. 13 is a diagram illustrating first and second states of a third spatial filter 83 in an imaging device according to a third embodiment of the present invention.
FIG. 14 is a view showing the relationship between the optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 in the fourth spatial filter in the second state in the imaging device according to the fourth embodiment of the present invention on the xy plane. FIG. 3 is a diagram illustrating a positional relationship in a direction of a projected image.
FIG. 15 is a diagram illustrating a light separation state of a fourth spatial filter in a second state.
FIG. 16 is a view showing the optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 in the fifth spatial filter in the second state in the imaging apparatus according to the fifth embodiment of the present invention, taken along the xy plane. FIG. 3 is a diagram illustrating a positional relationship in a direction of a projected image.
FIG. 17 is a diagram illustrating a light separation state of a fifth spatial filter in a second state.
FIG. 18 is a view showing the relationship between the optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 in the sixth spatial filter in the second state in the imaging device according to the sixth embodiment of the present invention, taken along the xy plane. FIG. 3 is a diagram illustrating a positional relationship in a direction of a projected image.
FIG. 19 is a diagram illustrating a light separation state of a sixth spatial filter in a second state.
FIG. 20 is a view showing the optical axis directions q1 to q3 of the first to third birefringent plates 33 to 35 in the seventh spatial filter in the second state in the imaging device according to the seventh embodiment of the present invention, taken along the xy plane. FIG. 3 is a diagram illustrating a positional relationship in a direction of a projected image.
FIG. 21 is a diagram illustrating a light separation state of a seventh spatial filter in a second state.
FIG. 22 shows the shapes of currently commercially available birefringent plates that can be used when the reference angle at which the birefringent plate is angularly displaced is 180 degrees in the imaging apparatus according to the first to seventh embodiments of the present invention. FIG.
FIG. 23 is a diagram illustrating a shape of a birefringent plate used when the reference angle at which the birefringent plate is angularly displaced is 90 degrees in the imaging devices according to the first to seventh embodiments of the present invention.
FIG. 24 is a diagram for explaining a shift of an optical path of light after passing through a spatial filter due to an inclination angle of a birefringent plate in the imaging devices according to the first to seventh embodiments of the present invention.
FIG. 25 is a diagram for explaining a shift of an optical path of light after passing through a spatial filter due to an inclination angle of a birefringent plate in the imaging devices of the first to seventh embodiments of the present invention.
FIG. 26 is a diagram for explaining the structure of a conventional imaging device.
[Explanation of symbols]
20 Imaging device
22 Optical axis
23 lenses
24 1st spatial filter
25 Birefringent plate driver
26 Image sensor
33 1st birefringent plate
34 Second birefringent plate
35 Third birefringent plate
37 Reference plane
81 Second spatial filter
83 Third spatial filter

Claims

An optical system that collects light from the subject,
An imaging element having an imaging surface on which light condensed by the optical system is imaged;
A spatial filter including at least one birefringent plate interposed between the optical system and the image sensor,
In order to shift the optical path of the light incident on the image sensor, the positional relationship between at least one of the birefringent plates in the spatial filter and the optical axis of the optical system is determined by the angular displacement. Image shifting means for changing;
Each time the image shift means changes the positional relationship, the imaging device, the imaging control means for generating an image signal representing an image,
Combining means for combining a plurality of the image signals,
Before and after the positional relationship is changed, the positional relationship includes a separation width d3 between the ordinary rays Leoo and Loeo passing through the spatial filter and the extraordinary rays Leoe and Loee, and the extraordinary rays Leoe and Loeo from the ordinary rays Leoo and Loeo. An imaging apparatus characterized by being changed while keeping the direction to Loee equal.

An optical system that collects light from the subject,
An imaging element having an imaging surface on which light condensed by the optical system is imaged;
A spatial filter including at least one birefringent plate interposed between the optical system and the image sensor,
Image of changing the positional relationship between at least one of the birefringent plates in the spatial filter and the optical axis of the optical system in order to shift the optical path of light incident on the image sensor. Shifting means;
Each time the image shift means changes the positional relationship, the imaging device, the imaging control means for generating an image signal representing an image,
Combining means for combining a plurality of the image signals,
At least one of the at least one birefringent plate is inclined with respect to a reference plane perpendicular to the optical axis,
The image pickup apparatus according to claim 1, wherein the image shift unit angularly displaces the at least one birefringent plate around a reference axis parallel to the optical axis.

A plurality of rectangular light receiving areas are arranged in a matrix on the imaging surface of the image sensor,
The birefringent plate that is inclined, from the optical path of the light that has passed through the spatial filter before the birefringent plate to be angularly displaced is angularly displaced, after the birefringent plate to be angularly displaced is angularly displaced. The optical path of the light passing through the spatial filter is inclined so as to be shifted in a direction parallel to a diagonal line of the light receiving area,
The angle between the inclined birefringent plate and the reference plane is such that the distance between the two optical paths is half the distance between the centers of the two pixels arranged in a direction parallel to the diagonal of the pixels. The imaging apparatus according to claim 2, wherein the setting is performed.

3. The image pickup apparatus according to claim 2, wherein the angle at which the image shift means angularly displaces the birefringent plate to be angularly displaced is 180 degrees.

When a plurality of birefringent plates among all the birefringent plates to be angularly displaced are inclined with respect to the reference plane, angles formed by each of the plurality of birefringent plates and the reference plane are mutually different. 3. The imaging device according to claim 2, wherein:

The spatial frequency characteristics of the spatial filter before the birefringent plate to be angularly displaced are angularly displaced, and the spatial frequency characteristics of the spatial filter after the birefringent plate to be angularly displaced are angularly displaced. The imaging apparatus according to claim 2, wherein: