JP2004317967A - Zoom lens and electronic imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-resolution zoom lens whose zoom ratio is about 3, whose open aperture F value is about F2 at a wide angle end, and whose viewing angle exceeds 70°. <P>SOLUTION: The zoom lens is equipped with a 1st lens group G1 having positive power, a 2nd lens group G2 having positive power, a 3rd lens group G3 having negative power, a 4th lens group G4 having positive power, a 5th lens group G5 having positive power, a variable diaphragm A1 fixed on the object side of the 4th lens group G4 and a fixed diaphragm A2 which is arranged between the 3rd lens group G3 and the variable diaphragm and whose aperture diameter and position are fixed in order from the object side. In the case of varying power from the wide angle end to a telephoto end, the 1st lens group G1 is fixed, the 2nd lens group G2 draws a locus convex to an image side, the 3rd lens group G3 monotonously moves to the image side, and the 4th lens group G4 and the 5th lens group G5 monotonously move to the object side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１２３】
ここで、ｋ_ｉは第ｉ面の円錐定数、Ｄ_ｉ，Ｅ_ｉ，Ｆ_ｉ，Ｇ_ｉはそれぞれ第ｉ面の４次、６次、８次、１０次の非球面係数、ｈは光軸からの高さ、ｚは光軸からの高さがｈの点における非球面上のサグ量である。
【０１２４】
また、ｆは焦点距離、ＦＮＯは開放Ｆ値、２ωは画角、Ｌは光学全長である。
【０１２５】
【表１】

【０１２６】
図１に示したズームレンズの撮影距離が∞で絞り開放時の収差図（球面収差、非点収差、歪曲収差）を図２に示す。図２（ａ）は広角端の場合、図２（ｂ）は中間位置の場合、図２（ｃ）は望遠端の場合である。球面収差図において、実線はｄ線、短破線はＦ線、長破線はＣ線、一点鎖線はｇ線の特性である。非点収差図において、実線はサジタル平面上、破線はメリディオナル平面上の特性である。図２より、３種類のズーム位置において諸収差が良好に補正されていることが分かる。
【０１２７】
図１に示したズームレンズは、固体撮像素子として、記録画素数が水平２８８０×垂直２１６０（約６００万画素）、画素ピッチが水平３．０μｍ×垂直３．０μｍ、記録画面サイズが水平８．６４ｍｍ×垂直６．４８ｍｍのものを用いることができる。また、固体撮像素子として、実効開口率の向上のために画素ごとにマイクロレンズを設けたものを用いることができる。
【０１２８】
第４レンズ群Ｇ４の調心を行う場合、次のようにするとよい。
【０１２９】
第１０レンズＬ１０と、第１１レンズＬ１１と第１２レンズＬ１２とによる接合レンズＬ１１／Ｌ１２とをレンズ群枠に組み込んだ後に、第８レンズＬ８と第９レンズＬ９とによる接合レンズＬ８／Ｌ９を所定の位置に取り付け、偏心測定装置を利用して第４レンズ群Ｇ４全体の偏心が小さくなるように、接合レンズＬ８／Ｌ９の位置を調整し、最後に接着剤によりこの接合レンズＬ８／Ｌ９をレンズ群枠に固定する。このとき、第９レンズＬ９の像側面が凸面の場合には、第９レンズＬ９を移動させようとすると、平行偏心と傾斜偏心との両方を生じるため、調心がやりにくい。これに対して、図１に示したズームレンズでは、第９レンズＬ９の像側面を平面としているので、接合レンズＬ８／Ｌ９を傾斜させることなく平行移動させることができ、調心がやりやすい。なお、第９レンズＬ９の像側面を凹面としても、同一の効果が得られる。
【０１３０】
図１に示した構成では、第２レンズ群Ｇ２は１枚の正レンズ（第３レンズＬ３）で構成されているが、第３レンズＬ３は両面が球面のガラスレンズの少なくとも一方の面に薄い樹脂層を設け、樹脂層の表面を非球面としてもよい。本発明では、このようなレンズ素子も１枚と考えることにする。
【０１３１】
図１に示した構成では、可変絞りＡ１を第４レンズ群Ｇ４の物体側に一体化している。これは、前述のように第４レンズ群Ｇ４の偏心敏感度が高く、他のレンズ群の偏心敏感度も比較的高いことから、鏡筒には高精度が要求され、そのためには鏡筒の構成を少しでも簡単な構成にした方が量産性が有利となるためである。
【０１３２】
以上に説明したように、図１に示したズームレンズは、ズーム比が約３倍で、広角端において開放Ｆ値がＦ２程度、画角が約７６°で、高解像度となっている。
【０１３３】
（実施の形態２）
図３（ａ）は本発明の実施の形態２におけるズームレンズの構成を示したものである。図３（ａ）は広角端におけるレンズ配置を示している。図３（ｂ）は、変倍時の各レンズ群の移動軌跡を示している。縦軸の上端が広角端、下端が望遠端であり、縦軸のスケールはレンズ系全体の焦点距離に比例した量としている。
【０１３４】
図３に示したズームレンズは、実施の形態１に示したズームレンズと同様に、物体側から順に正、正、負、正、正の５つのレンズ群で構成されているが、第４レンズ群Ｇ４は４枚構成であり、第１０レンズＬ１０の物体側面と第１２レンズＬ１２の物体側面が非球面となっている。
【０１３５】
図３に示したズームレンズのレンズデータを以下の表２に示す。各パラメータの定義は実施の形態１の場合と同一である。
【０１３６】
【表２】

【０１３７】
図３に示したズームレンズの撮影距離が∞で絞り開放時の収差図を図４に示す。図４（ａ）は広角端の場合、図４（ｂ）は中間位置の場合、図４（ｃ）は望遠端の場合である。図４よりズーム位置が変化した場合でも諸収差が良好に補正されていることが分かる。
【０１３８】
固体撮像素子としては、実施の形態１で説明したものを用いることができる。
【０１３９】
実施の形態２におけるズームレンズで、より望ましい結像特性を得るには、実施の形態１で説明した条件式（１）〜（７）を満足するように、さらに望ましくは、条件式（１ａ）〜（７ａ）を満足するように構成するとよい。
【０１４０】
第９レンズＬ９の像側面を平面としているので、必要であれば、実施の形態１で説明したのと同様に、第４レンズ群Ｇ４の先頭の接合レンズＬ８／Ｌ９の調心を容易に行うことができる。
【０１４１】
また、第１０レンズＬ１０の物体側面を非球面として、特に非点収差を良好に補正するようにしている。
【０１４２】
以上に説明したように、図５に示したズームレンズは、ズーム比が約３倍、広角端において開放Ｆ値がＦ２程度、画角が約７６°で、高解像度となっている。
【０１４３】
（実施の形態３）
図５（ａ）は本発明の実施の形態３におけるズームレンズの構成を示したものである。図５（ａ）は広角端におけるレンズ配置を示している。図５（ｂ）は、変倍時の各レンズ群の移動軌跡を示している。縦軸の上端が広角端、下端が望遠端であり、縦軸のスケールはレンズ系全体の焦点距離に比例した量としている。
【０１４４】
図５に示したズームレンズは、実施の形態２に示したズームレンズと同様に、物体側から順に正、正、負、正、正の５つのレンズ群で構成され、第４レンズ群が４枚構成であるが、第１０レンズＬ１０の物体側面と第１２レンズＬ１２の両面が非球面となっている。
【０１４５】
図５に示したズームレンズのレンズデータを以下の表３に示す。各パラメータの定義は実施の形態１の場合と同一である。
【０１４６】
【表３】

【０１４７】
図５に示したズームレンズの撮影距離が∞で絞り開放時の収差図を６に示す。図６（ａ）は広角端の場合、図６（ｂ）は中間位置の場合、図６（ｃ）は望遠端の場合であり、いずれも球面収差、非点収差、歪曲収差を示している。図６より諸収差が良好に補正されていることが分かる。
【０１４８】
固体撮像素子としては、実施の形態１で説明したものを用いることができる。
【０１４９】
実施の形態３におけるズームレンズで、より望ましい結像特性を得るには、実施の形態１で説明した条件式（１）〜（７）を満足するように、さらに望ましくは、条件式（１ａ）〜（７ａ）を満足するように構成するとよい。
【０１５０】
以上に説明したように、図５に示したズームレンズは、ズーム比が約３倍で、広角端において開放Ｆ値がＦ２程度、画角が約７６°で、高解像度となっている。
【０１５１】
（実施の形態４）
図７（ａ）は本発明の実施の形態４におけるズームレンズの構成を示したものである。図７（ａ）は広角端におけるレンズ配置を示している。図７（ｂ）は、変倍時の各レンズ群の移動軌跡を示している。縦軸の上端が広角端、下端が望遠端であり、縦軸のスケールはレンズ系全体の焦点距離に比例した量としている。
【０１５２】
図７に示したズームレンズは、実施の形態１に示したズームレンズと同様に５つのレンズ群で構成されているが、第１レンズ群Ｇ１が負パワーであり、第１０レンズＬ１０の両面と第１３レンズＬ１３の両面がいずれも非球面となっている。
【０１５３】
図７に示したズームレンズのレンズデータを以下の表４に示す。各パラメータの定義は実施の形態１の場合と同一である。
【０１５４】
【表４】

【０１５５】
図７に示したズームレンズの撮影距離が∞で絞り開放時の収差図を図８に示す。図８（ａ）は広角端の場合、図８（ｂ）は中間位置の場合、図８（ｃ）は望遠端の場合であり、いずれも球面収差、非点収差、歪曲収差を示している。図８より、諸収差が良好に補正されていることが分かる。
【０１５６】
固体撮像素子としては、実施の形態１で説明したものを用いることができる。
【０１５７】
実施の形態４におけるズームレンズで、より望ましい結像特性を得るには、実施の形態１で説明した条件式（１）〜（７）を満足するように、さらに望ましくは、条件式（１ａ）〜（７ａ）を満足するように構成するとよい。
【０１５８】
以上に説明したように、図７に示したズームレンズは、ズーム比が約３倍で、広角端において開放Ｆ値がＦ２程度、画角が約７６°で、高解像度となっている。
【０１５９】
（実施の形態５）
図９（ａ）は本発明の実施の形態５におけるズームレンズの構成を示したものである。図９（ａ）は広角端におけるレンズ配置を示している。図９（ｂ）は、変倍時の各レンズ群の移動軌跡を示している。縦軸の上端が広角端、下端が望遠端であり、縦軸のスケールはレンズ系全体の焦点距離に比例した量としている。
【０１６０】
図９に示したズームレンズは、実施の形態４に示したズームレンズと同様に、負、正、負、正、正の５つのレンズ群で構成され、第１レンズ群Ｇ１のパワーが負であり、第５レンズＬ５の像側面、第１０レンズＬ１０の両面および第１３レンズＬ１３の両面がいずれも非球面となっている。
【０１６１】
図９に示したズームレンズのレンズデータを以下の表５に示す。各パラメータの定義は実施の形態１の場合と同一である。
【０１６２】
【表５】

【０１６３】
図９に示したズームレンズの撮影距離が∞で絞り開放時の収差図を図１０に示す。図１０（ａ）は広角端の場合、図１０（ｂ）は中間位置の場合、図１０（ｃ）は望遠端の場合であり、いずれも球面収差、非点収差、歪曲収差を示している。図１０より、諸収差が良好に補正されていることが分かる。
【０１６４】
固体撮像素子としては、実施の形態１で説明したものを用いることができる。
【０１６５】
図９に示したズームレンズは、第５レンズＬ５の像側面を非球面として、広角端における負の歪曲収差の低減を図っている。撮影距離が∞で広角端の最大像高における歪曲収差について他の実施の形態と比較すると、実施の形態１から実施の形態４ではいずれも−３．５％であるのに対して、本実施の形態では−３．２％と少し小さくなっている。
【０１６６】
実施の形態５におけるズームレンズで、より望ましい結像特性を得るには、実施の形態１で説明した条件式（１）〜（７）を満足するように、さらに望ましくは、条件式（１ａ）〜（７ａ）を満足するように構成するとよい。
【０１６７】
以上に説明したように、図９に示したズームレンズは、ズーム比が約３倍で、広角端において開放Ｆ値がＦ２程度、画角が約７６°で、高解像度となっている。
【０１６８】
以上に説明した実施の形態１〜５におけるズームレンズでは、いずれも、広角端から望遠端への変倍に際して、第３レンズ群は像側に単調に移動しているが、同一の焦点距離の変化に対する第３レンズ群Ｇ３の移動量は、広角端付近では大きく移動し、広角端から離れるにつれて移動量が低下していく。
【０１６９】
広角端から望遠端への変倍に際して、広角端から望遠端の少し手前までは第３レンズ群が像側に単調に移動し、そこから望遠端の間では第３レンズ群が物体側に単調に移動する構成であっても良い。ただし、望遠端における第３レンズ群の位置は広角端における第３レンズ群の位置より像側にあるようにするとよい。
【０１７０】
以上に説明した５つの数値実施例に関して、前述の条件式の数値を以下の表６に示す。
【０１７１】
【表６】

【０１７２】
（実施の形態６）
図１１は本発明の実施の形態６における電子スチルカメラの概略構成を示した断面図である。図１１において、１２はズームレンズ、１４は固体撮像素子、１５は電子ビューファインダ、１６は液晶モニタ、２１は第１レンズ群、２２は第２レンズ群、２３は第３レンズ群、２４は第４レンズ群、２５は第５レンズ群、２６は可変絞り、２７は固定絞りである。
【０１７３】
筐体１１の前側にズームレンズ１２が配置され、ズームレンズ１２の後側には、物体側から順に、光学ローパスフィルタ１３、固体撮像素子１４が配置されている（固体撮像素子１４の物体側にはカバーガラスが取り付けられているが、図を見やすくするためカバーガラスは省略している）。筐体１１の上部には電子ビューファインダ１５が配置され、筐体１１の後側には液晶モニタ１６が配置されている。
【０１７４】
光学ローパスフィルタ１３は、物体側から順に、第１水晶板、赤外吸収ガラス板、第２水晶板、第３水晶板を透明接着剤により互いに接合したものである。光学ローパスフィルタ１３は、固体撮像素子１４の画素構造に起因するモアレなどの誤信号の発生を防ぐとともに、不要な赤外光が固体撮像素子に入射して誤信号を発生するのを防いでいる。光学ローパスフィルタ１３の物体側面と像側面には反射防止膜が蒸着されている。
【０１７５】
固体撮像素子１４は、有効画素数が水平２８８０×垂直２１６０（約６００万画素）、画素ピッチが水平３．０μｍ×垂直３．０μｍ、有効画面サイズが水平８．６４ｍｍ×垂直６．４８ｍｍであり、各画素に微小正レンズが設けられている。ズームレンズ１２による被写体の像が固体撮像素子１４の撮像面１８に形成される。
【０１７６】
ズームレンズ１２として、図１に示したズームレンズが用いられている。ズームレンズ１２は、物体側から順に、第１レンズ群２１、第２レンズ群２２、第３レンズ群２３、第４レンズ群２４、第５レンズ群２５で構成され、第３レンズ群２３と第４レンズ群の間には、可変絞り２６、固定絞り２７が設けられている。
【０１７７】
第２レンズ群２２を構成する第３レンズ２８は、図１２に示すように、周辺部の一部が切除され、切除後の端面２９は光軸と平行な平面となっている。他のレンズはすべて外周が円形となっている。詳細は後述する。
【０１７８】
第４レンズ群２４の物体側には開口径が可変の可変絞り２６が取り付けられ、第３レンズ群と可変絞り２６との間には開口径と位置とが固定の固定絞り２７が配置されている。
【０１７９】
鏡筒は、主鏡筒３１、裏板３２、円筒カム３３、５つのレンズ群枠、４本のガイドポール３４，３５，３６，３７、ズームリング３９で構成されている。
【０１８０】
光学ローパスフィルタ１３と固体撮像素子１４は裏板３２に取り付けられ、裏板３２は主鏡筒３１の像側端に取り付けられている。２本のガイドポール３４，３５は、光軸３８と平行に、固体撮像素子１４の記録画面の上側中央部、下側中央部に配置されている。また、２本のガイドポール３６，３７は、光軸３８と平行に、固体撮像素子１４から離れた位置に配置されている。
【０１８１】
５つのレンズ群２１〜２５はそれぞれ対応するレンズ群枠に取り付けられている（図の見やすくするためにレンズ群枠は図示を省略）。
【０１８２】
第１レンズ群枠は主鏡筒３１の物体側端に取り付けられている。第４レンズ群枠の物体側には可変絞り２６が取付けられている。固定絞り２７は、第３レンズ群２３と第４レンズ群２４との間の所定の位置に配置されるように、２本のガイドポール３６，３７に固定されている。
【０１８３】
円筒カム３３には所定のカム溝が設けられている。第２レンズ群枠、第３レンズ群枠、第４レンズ群枠には、ガイドポール３４，３５が貫通する穴と、円筒カム３３のカム溝にはまる突起が設けられている。主鏡筒３１の外側にはズームリング３９が取り付けられ、ズームリング３９は円筒カム３３と結合されており、ズームリング３９を回転させると円筒カム３３が回転するようになっている。ズームリング３９を回転させると、第２レンズ群枠、第３レンズ群枠および第４レンズ群枠が光軸３８に沿って移動し、第２レンズ群２２、第３レンズ群２３および第４レンズ群２４が固体撮像素子１４を基準にした所定の位置に移動するので、広角端から望遠端までの変倍を行うことができる。また、可動レンズ群２２，２３，２４を２本のガイドポール３４，３５により保持するため、変倍時の可動レンズ群２２，２３，２４の偏心を非常に小さくすることができる。
【０１８４】
第５レンズ群枠にはガイドポール３６，３７が貫通する穴が設けられている。第５レンズ群枠はステッピングモータにより光軸３８に沿って移動可能である。モータにより第５レンズ群２５を光軸方向に移動させながら撮影画像の高周波成分がピークとなる位置を検出して、その位置に第５レンズ群２５を移動させれば、オートフォーカスを行うことができる。
【０１８５】
第１レンズ群枠の物体側にはフィルタ装着用のめねじを設けるとよい。図１１に示した構成では、変倍時に第１レンズ群枠が移動しないので、重いフィルタを装着しても第１レンズ群２１が偏心することはなく、結像特性の劣化はない。
【０１８６】
第３レンズ２８を図１２に示すような形状とすることについて説明する。
【０１８７】
第３レンズ２８の物体側面の有効領域４１を図１３に示す。図１３は第３レンズ２８を光軸３８に沿って見たものである。ここで、有効領域とは有効光束が通過する領域で、その面積が最大となる場合の領域である。有効光束が通過する領域の面積はズーム位置により変化するが、その面積は広角中間位置の付近で最大となる。有効領域４１の境界４２を光軸３８と垂直な平面に射影した形状は、固体撮像素子１４の記録画面と相似で四隅が円弧状の長方形状となる。この長方形状の形状の対称軸は２つ存在し、２つの対称軸４３，４４はそれぞれ固体撮像素子の画面水平方向、画面垂直方向と平行となる。
【０１８８】
図１３から分かるように、第３レンズ２８の外周４７が円形の場合、外周４７の内側にあって、長方形状の有効領域４１の上側と下側に有効光束が通過しない領域が存在する。この有効光束が通過しない領域は除去してもかまわない。従って、図１１に示したズームレンズの第３レンズ２８を、物体側面の有効領域４１が削られない範囲で周辺部の一部を切除して図１２に示した形状にすることができる。この場合、変倍時に第３レンズ２８が回転しないように光軸に沿って移動させる必要があるが、第３レンズ２８はガイドポール３４，３５に沿って移動させるので全く問題はない。
【０１８９】
図１２に示したように第３レンズ２８の有効領域の上側と下側を切除すると、図１１から分かるように、２本のガイドポール３４、３５の間隔を狭くすることができ、その結果、鏡筒の中間部の外径を小さくすることができる。第３レンズ２８の垂直方向の寸法は第４レンズ４８の外径とほぼ同じにするとよい。第３レンズ２８の周辺部の一部を切除して鏡筒の中間部の外径を小さくする場合、広角端の画角が小さい場合にはそれほどの効果が得られないが、広角端の画角が７０°を超えるような広角の場合には非常に有効である。
【０１９０】
第３レンズ２８の周辺部を切除する他の例を図１４に示す。図１４（ａ）は第３レンズ２８の周辺部の２箇所を端面５１，５２が円筒面の一部になるように切除した例であり、図１４（ｂ）は第３レンズ２８の周辺部の２箇所に貫通穴５３，５４を設けた例である。いずれも、光軸に沿って見たものであり、２つの切除部は物体側面の有効領域が削られないように設定されている。
【０１９１】
以上の説明では、実施の形態１におけるズームレンズを例にしたが、実施の形態２〜５におけるズームレンズの場合も同じように構成することができ、鏡筒の中間部の外径を小さくすることができる。
【０１９２】
また、図１２、図１４では、第３レンズ２８の切除部が有効領域の上側中央部と下側の中央部に配置されているが、物体側面の有効領域が削られなければ、切除部の位置を上側中央部あるいは下側中央部からずらしてもよい。
【０１９３】
以上に説明したように、第３レンズ２８の周辺部の一部を切除すると、鏡筒の中間部の外径を小さくすることができる。鏡筒の中間部の外径が多少大きくてもよければ、第３レンズ２８の周辺部の一部を切除する必要はない。
【０１９４】
こうして、ズーム比が約３倍、広角端において開放Ｆ値がＦ２程度、画角が７０°を超え、高解像度の電子スチルカメラを提供することができる。
【０１９５】
なお、図１１に示した電子スチルカメラには、実施の形態１のズームレンズの代わりに実施の形態２〜実施の形態５のいずれかのズームレンズを用いてもよい。また、図１１に示した電子スチルカメラの光学系は、動画を対象とするビデオカメラに用いることもできる。この場合、動画だけでなく、解像度の高い静止画を撮影することができる。
【０１９６】
以上の説明では、６００万画素の固体撮像素子を用いる場合について説明したが、記録画面サイズがほぼ同じで画素数の少ない固体撮像素子を用いることもできる。例えば、記録画面の対角長が約１１ｍｍで、記録画素数が水平２５６０×垂直１９２０（約５００万画素）、画素ピッチが水平３．４μｍ×垂直３．４μｍの固体撮像素子を用いることができる。この場合、光学ローパスフィルタ１３の分離幅は画素ピッチとほぼ等しくなるように決める必要がある。
【０１９７】
【発明の効果】
以上のように本発明によれば、ズーム比が２．５倍〜３．２倍で、広角端において開放Ｆ値がＦ２程度、画角が７０°を超え、高解像度のズームレンズを提供することができる。このズームレンズを用いることにより、広角で明るく、高解像度の電子スチルカメラを提供することができる。
【図面の簡単な説明】
【図１】図１（ａ）：本発明の実施の形態１におけるズームレンズの広角端での構成を示した側面図
図１（ｂ）：本発明の実施の形態１におけるズームレンズを構成する各レンズ群の変倍時の移動軌跡を示した図
【図２】本発明の実施の形態１におけるズームレンズの撮影距離が∞の場合の収差図
【図３】図３（ａ）：本発明の実施の形態２におけるズームレンズの広角端での構成を示した側面図
図３（ｂ）：本発明の実施の形態２におけるズームレンズを構成する各レンズ群の変倍時の移動軌跡を示した図
【図４】本発明の実施の形態２におけるズームレンズの撮影距離が∞の場合の収差図
【図５】図５（ａ）：本発明の実施の形態３におけるズームレンズの広角端での構成を示した側面図
図５（ｂ）：本発明の実施の形態３におけるズームレンズを構成する各レンズ群の変倍時の移動軌跡を示した図
【図６】本発明の実施の形態３におけるズームレンズの撮影距離が∞の場合の収差図
【図７】図７（ａ）：本発明の実施の形態４におけるズームレンズの広角端での構成を示した側面図
図７（ｂ）：本発明の実施の形態４におけるズームレンズを構成する各レンズ群の変倍時の移動軌跡を示した図
【図８】本発明の実施の形態４におけるズームレンズの撮影距離が∞の場合の収差図
【図９】図９（ａ）：本発明の実施の形態５におけるズームレンズの広角端での構成を示した側面図
図９（ｂ）：本発明の実施の形態５におけるズームレンズを構成する各レンズ群の変倍時の移動軌跡を示した図
【図１０】本発明の実施の形態５におけるズームレンズの撮影距離が∞の場合の収差図
【図１１】本発明の実施の形態６における電子スチルカメラの概略構成を示す側断面図
【図１２】図１１に示したズームレンズの第３レンズの形状を示す斜視図
【図１３】図１２に示した第３レンズの物体側面の有効領域を示す正面図
【図１４】図１１に示したズームレンズの第３レンズの形状に関する他の例を示す正面図
【符号の説明】
Ｇ１，２１ 第１レンズ群
Ｇ２，２２ 第２レンズ群
Ｇ３，２３ 第３レンズ群
Ｇ４，２４ 第４レンズ群
Ｇ５，２５ 第５レンズ群
Ａ１，２６ 可変絞り
Ａ２，２７ 固定絞り
Ｐ 平行平面素子
Ｓ 像面
Ｌ１ 第１レンズ
Ｌ２ 第２レンズ
Ｌ３ 第３レンズ
Ｌ４ 第４レンズ
Ｌ５ 第５レンズ
Ｌ６ 第６レンズ
Ｌ７ 第７レンズ
Ｌ８ 第８レンズ
Ｌ９ 第９レンズ
Ｌ１０ 第１０レンズ
Ｌ１１ 第１１レンズ
Ｌ１２ 第１２レンズ
Ｌ１３ 第１３レンズ
１２ ズームレンズ
１４ 固体撮像素子
１５ 電子ビューファインダ
１６ 液晶モニタ
２８ 第３レンズ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-resolution zoom lens suitable for an electronic still camera, and an electronic imaging device such as an electronic still camera or a video camera using the zoom lens.
[0002]
[Prior art]
2. Description of the Related Art With the progress and spread of personal computers, electronic still cameras have rapidly spread as image input devices.
[0003]
Recent electronic still cameras have a solid-state image sensor of about 2 million pixels or about 3 million pixels, a zoom ratio of 2 to 3 times, an open F value of about F2.8 at the wide angle end, and an angle of view of about 63 °. The mainstream is equipped with a zoom lens. This type of zoom lens includes, in order from the object side, a first lens unit having a negative power, a second lens unit having a positive power, and a third lens unit having a positive power. When zooming from the wide-angle end to the telephoto end, The first lens group draws a locus convex toward the image side, the second lens group moves toward the object side, the third lens group also moves, and focus adjustment is performed by moving the third lens group. In addition, in order to reduce the total optical length when not in use (the distance from the object-side vertex of the lens closest to the object side to the imaging surface), a copper-clad configuration is adopted in which all lens groups are moved toward the solid-state image sensor.
[0004]
The zoom lens is composed of four lens units having positive, negative, positive, and positive power in order from the object side. The zoom ratio is about three times, the open F value is about F2 at the wide angle end, and the angle of view is about 63 °. A zoom lens has been proposed in Patent Document 1.
[0005]
[Patent Document 1]
JP 2001-42215 A
[0006]
As for solid-state image sensors for electronic still cameras, technological developments such as miniaturization of pixel pitch and improvement of light receiving sensitivity have been promoted to increase the number of pixels, and already 5 million pixels with a recording screen diagonal length of about 11 mm are already available. It has been commercialized. At present, zoom lenses for electronic still cameras are required to have higher resolution, higher zoom ratio, larger aperture, and wider angle. Although it is not easy to realize a zoom lens that satisfies all of these demands, many zoom lenses that satisfy some of the demands have been proposed as described below.
[0007]
Patent Literatures 2, 3, and 4 propose zoom lenses having a zoom ratio of 2.4 to 3 times, an open F value of about F2 at the wide angle end, and an angle of view exceeding 70 °.
[0008]
[Patent Document 2]
JP-A-9-203861
[0009]
[Patent Document 3]
JP 2001-174704 A
[0010]
[Patent Document 4]
JP 2001-343588 A
[0011]
The zoom lens disclosed in Patent Literature 2 includes five lens units having negative, positive, negative, positive, and positive power in order from the object side. When zooming from the wide-angle end to the telephoto end, the third lens unit and the third lens unit are used. The position of the fifth lens group is fixed, the first lens group moves monotonously to the image side, and the second lens group and the fourth lens group move monotonously to the image side.
[0012]
The zoom lens disclosed in Patent Document 3 is composed of five lens units having negative, positive, negative, positive, and positive power in order from the object side. When zooming from the wide-angle end to the telephoto end, a third lens unit is used. The lens groups are fixed in position, the first lens group moves monotonically to the image side, and the second lens group, the fourth lens group, and the fifth lens group move monotonously to the object side.
[0013]
The zoom lens disclosed in Patent Document 4 is composed of four lens groups having negative, negative, positive, and positive power in order from the object side. When zooming from the wide-angle end to the telephoto end, the first lens group is used. Is fixed, the second lens group draws a locus convex toward the image side, the third lens group moves monotonously to the object side, and the fourth lens group moves fixedly or moves monotonically to the image side.
[0014]
Patent Documents 5 and 6 propose zoom lenses having a zoom ratio of 6.85 to 11.5 times, an open F value of F2 to F2.8 at the wide-angle end, and an angle of view exceeding 70 °. .
[0015]
[Patent Document 5]
JP 2001-350093 A
[0016]
[Patent Document 6]
JP-A-2002-62478
[0017]
The zoom lens disclosed in Patent Literature 5 includes five lens groups having positive, negative, positive, negative, and positive power in order from the object side. When zooming from the wide-angle end to the telephoto end, the first lens group is used. The lens group moves to the object side, the second lens group first moves to the image side, moves halfway to the object side, and the third lens group and the fourth lens group move to the object side.
[0018]
Patent Document 6 discloses 25 examples. In Example 19, Example 20 includes four lens groups having positive, negative, positive, and positive power in order from the object side. In the twenty-first embodiment, the positive, negative, negative, positive, negative, and positive powers are sequentially arranged from the object side in the order from the object side. Are constituted by six lens groups having the following. In all of the twenty-five embodiments, upon zooming from the wide-angle end to the telephoto end, the first lens unit first moves to the image side, moves halfway to the object side, and the second lens unit moves to the image side.
[0019]
[Problems to be solved by the invention]
A zoom lens for a single-lens reflex camera using a 35 mm film has a focal length of 28 mm to 70 mm (angle of view is about 75 ° to about 29 °), and an open F value of F2.8 over the entire zoom range. Lens ”has been commercialized. There is a demand for an electronic still camera capable of obtaining a captured image close to that of a single-lens reflex camera equipped with a “large-diameter standard zoom lens” and realizing a compact model.
[0020]
The present invention has a resolution corresponding to a 6 million pixel solid-state imaging device approaching a "large aperture standard zoom lens", a zoom ratio of about 3 times, an open F value of about F2 at the wide angle end, and an angle of view of about 70 at the wide angle end. The aim is to realize a zoom lens that is more compact and lighter than a single-lens reflex camera zoom lens using a 35 mm film that exceeds 35 °. For example, a solid-state image sensor having a recording screen with a diagonal length of about 11 mm, a recording pixel number of 2880 horizontal × 2160 vertical (about 6 million pixels), and a pixel pitch of 3.0 μm horizontal × 3.0 μm vertical is used. It is assumed to be used.
[0021]
When the pixel pitch is small as described above, when the F-number of the zoom lens becomes dark, the resolution of the captured image is reduced due to the influence of diffraction. Since the aperture range should be widened, the open F-number of the zoom lens should be bright over the entire zoom range. Therefore, in the present invention, the open F value is aimed at F2 at the wide angle end and at F2.5 at the telephoto end.
[0022]
The zoom lens disclosed in Example 1 of Patent Literature 1 has an open F-number as bright as F2.06 at the wide-angle end and F2.7 at the telephoto end, and has a short overall optical length. However, the angle of view at the wide-angle end is as narrow as 65.1 °.
[0023]
The zoom lens shown in Patent Literatures 5 and 6 has a variable magnification ratio much larger than three times, but has a considerably large optical total length ratio (the ratio of the optical total length to the diagonal length of the recording screen of the solid-state imaging device). The zoom ratio may be about three times, and instead, it is desired to shorten the entire optical length.
[0024]
The zoom lenses disclosed in Patent Literatures 1 to 3, Patent Literature 5, and Patent Literature 6 need to have a complicated and robust lens barrel in order to stably move the large and heavy first lens group during zooming. However, there is a problem that the maximum diameter of the lens barrel becomes large.
[0025]
In the zoom lens disclosed in Patent Literature 4, the zoom ratio and the angle of view at the wide-angle end match the aims of the present invention, and the first lens group is fixed in position during zooming. It is simple, the maximum diameter of the lens barrel is small, and the total optical length is short. However, considering that the open F value is insufficient and the effective image circle diameter is small, there is a problem that the astigmatic difference is considerably large and a high-resolution image cannot be obtained in a well-balanced manner on the entire imaging surface.
[0026]
The present invention has a high resolution that can correspond to a solid-state imaging device having a total number of pixels of about 6 million pixels, a zoom ratio of about 3 times, an open F value at the wide angle end is as bright as about F2, an angle of view exceeds 70 °, It is an object to provide a compact zoom lens and to provide an electronic imaging device such as an electronic still camera or a video camera using the zoom lens.
[0027]
[Means for Solving the Problems]
In order to achieve the above object, a zoom lens and an electronic imaging device according to the present invention are configured as follows.
[0028]
The first zoom lens according to the present invention includes, in order from the object side, a first lens group, a second lens group having a positive power, a third lens group having a negative power, and at least one lens group having a positive power. And a rear lens unit having a positive power, wherein the first lens unit is fixed in position during zooming, and the second lens unit and the third lens unit are movable along an optical axis. And
[0029]
The second zoom lens according to the present invention includes, in order from the object side, a first lens group, a second lens group having a positive power, a third lens group having a negative power, a fixed aperture having a fixed aperture, and at least one lens. A rear lens group having a positive power lens group, wherein at the time of zooming, the first lens group and the fixed stop are fixed in position, and the third lens group moves along the optical axis. And
[0030]
A third zoom lens according to the present invention includes, in order from the object side, a first lens group including a negative lens and a positive lens, a second lens group having positive power, a third lens group having negative power, and a third lens group having negative power. A fourth lens group and a fifth lens group having a positive power, wherein the first lens group has a fixed position and the second lens group has a convex shape on the image side when zooming from the wide-angle end to the telephoto end. Draw a trajectory, the third lens group moves monotonically to the image side, or moves monotonously to the image side halfway, then moves monotonically to the object side, and the fourth lens group moves monotonically to the object side. It is characterized by moving to.
[0031]
Further, the fourth zoom lens according to the present invention includes, in order from the object side, a first lens group, a second lens group including one positive lens, and a rear lens group including a plurality of lens groups. The positive lens that constitutes the second lens group is partially cut off at the periphery, the first lens group is fixed in position during zooming, and the second lens group does not rotate along the optical axis. It is characterized by moving along.
[0032]
Further, an electronic imaging device according to the present invention includes a zoom lens and a solid-state imaging device, and uses the zoom lens according to any one of the first to fourth aspects of the present invention as the zoom lens.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the above-described first to fourth zoom lenses of the present invention, the zoom ratio is 2.5 to 3.2 times, the open F value is about F2 at the wide angle end, the angle of view exceeds 70 °, and the zoom ratio is high. A resolution zoom lens can be provided.
[0034]
According to the electronic imaging device of the present invention, a wide-angle, bright, high-resolution electronic imaging device can be provided by using the zoom lens of the present invention.
[0035]
The first zoom lens according to the present invention includes, in order from the object side, a first lens group, a second lens group having a positive power, a third lens group having a negative power, and at least one lens group having a positive power. And a rear lens unit having a positive power. During zooming, the first lens group is fixed in position, and the second lens group and the third lens group are movable along the optical axis.
[0036]
The second zoom lens according to the present invention includes, in order from the object side, a first lens group, a second lens group having a positive power, a third lens group having a negative power, and a fixed stop having a fixed aperture. And a rear lens group including one positive power lens group. During zooming, the position of the first lens group and the fixed stop is fixed, and the third lens group moves along the optical axis.
[0037]
In the first and second zoom lenses according to the present invention, it is preferable that the first lens group includes a negative lens and a positive lens.
[0038]
In the first and second zoom lenses of the present invention, a lens group closest to the object side in the rear lens group may have a variable aperture with a variable aperture diameter integrated on the object side. .
[0039]
In the first and second zoom lenses of the present invention, it is preferable that a combined lens group of the first lens group and the second lens group has a positive power in the entire zoom range.
[0040]
In the first and second zoom lenses according to the present invention, it is preferable that the second lens group includes one positive lens.
[0041]
In the first and second zoom lenses of the present invention, the focal length of the entire lens system at the wide-angle end is f._W, The focal length of the entire lens system at the telephoto end is represented by f_TAnd the focal length is f_W ^3/4f_T ^1/4When the variable power position is referred to as a wide-angle intermediate position, it is preferable that the second lens group monotonously moves to the image side when changing the power from the wide-angle end to the wide-angle intermediate position.
[0042]
A third zoom lens according to the present invention includes, in order from the object side, a first lens group including a negative lens and a positive lens, a second lens group having positive power, a third lens group having negative power, and a third lens group having negative power. A fourth lens group and a fifth lens group having a positive power are provided. When zooming from the wide-angle end to the telephoto end, the first lens group has a fixed position, the second lens group has a locus convex on the image side, and the third lens group has a monotonous position on the image side. It moves or moves monotonically to the image side partway, then moves monotonically to the object side, and the fourth lens group moves monotonically to the object side.
[0043]
The third zoom lens according to the present invention may further include a fixed stop having a fixed aperture diameter and a fixed position during zooming, between the third lens group and the fourth lens group.
[0044]
In the third zoom lens of the present invention, the fourth lens group may have a variable aperture having a variable aperture diameter integrated on the object side.
[0045]
In the third zoom lens of the present invention, it is preferable that the focus adjustment is performed by moving the fifth lens group on the optical axis.
[0046]
In the third zoom lens according to the present invention, the focal length of the first lens group is f._G1, The focal length of the second lens group is f_G2And the combined focal length of the first lens group and the second lens group at the wide-angle end is f_FW, The focal length of the entire lens system at the wide-angle end is represented by f_WIt is preferable that the following condition is satisfied.
[0047]
−0.02 <f_G2/ F_G1<0.15 ‥‥‥ (1)
0.05 <f_W/ F_FW<0.2 ‥‥‥ (2)
[0048]
In the third zoom lens of the present invention, the air gap between the first lens group and the second lens group at the wide-angle end is d._AWThe air distance between the first lens group and the second lens group at a variable power position where the focal length is a geometric mean of the focal length at the wide-angle end and the focal length at the telephoto end is d._AN, The focal length of the entire lens system at the wide-angle end is represented by f_WIt is preferable that the following condition is satisfied.
[0049]
0.1 <(d_AN-D_AW) / F_W<0.5 ‥‥‥ (3)
[0050]
In the third zoom lens of the present invention, the air gap between the first lens group and the second lens group at the wide-angle end is d._AW, The air gap between the first lens group and the second lens group at the telephoto end is d_AT, The focal length of the entire lens system at the wide-angle end is represented by f_WIt is preferable that the following condition is satisfied.
[0051]
| D_AW-D_AT| / F_W<0.2 ‥‥‥ (4)
[0052]
In the third zoom lens according to the present invention, the focal length of the third lens group is f._G3, The focal length of the fourth lens group is f_G4, The focal length of the entire lens system at the wide-angle end is represented by f_WIt is preferable that the following condition is satisfied.
[0053]
0.4 <f_W/ | F_G3| <0.7 ‥‥‥ (5)
0.25 <f_W/ F_G4<0.5 ‥‥‥ (6)
[0054]
In the third zoom lens of the present invention, the third lens group includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, It is preferable to include a biconcave lens and a positive lens having a convex surface facing the object side.
[0055]
In the third zoom lens of the present invention, the fourth lens group includes a cemented lens including a biconvex lens closest to the object side and a negative lens having a concave surface facing the object side, and an object closest to the image side. It is preferable to provide a cemented lens composed of a positive lens having a convex surface on the side and a negative lens having a concave surface on the object side.
[0056]
Alternatively, in the third zoom lens of the present invention, the fourth lens group includes, in order from the object side, a cemented lens including a biconvex lens and a negative lens having a concave surface facing the object side, and a convex surface facing the object side. It is preferable to include a negative meniscus lens directed toward the lens, and a cemented lens including a biconvex lens and a biconcave lens.
[0057]
Further, in the third zoom lens according to the present invention, the focal length of the fifth lens group is f._G5, The focal length of the entire lens system at the wide-angle end is represented by f_WIt is preferable that the following condition is satisfied.
[0058]
0.3 <f_W/ F_G5<0.5 ‥‥‥ (7)
[0059]
A fourth zoom lens according to the present invention includes, in order from the object side, a first lens group, a second lens group including one positive lens, and a rear lens group including a plurality of lens groups. . A part of the positive lens constituting the second lens group is partially cut off, and the first lens group is fixed in position during zooming, and the second lens group does not rotate along the optical axis. Move.
[0060]
In the fourth zoom lens of the present invention, it is preferable that the first lens group includes a negative lens and a positive lens.
[0061]
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings and tables.
[0062]
In the present invention, the focal length of the entire lens system at the wide-angle end is represented by f_W, The focal length of the entire lens system at the telephoto end is represented by f_TAnd the focal length is
f_N= (F_Wf_T)^1/2
Is the middle position and the focal length is
f_WN= (F_Wf_N)^1/2
Is called a wide-angle intermediate position.
[0063]
(Embodiment 1)
FIG. 1A shows a configuration of a zoom lens according to Embodiment 1 of the present invention. FIG. 1A shows the lens arrangement at the wide-angle end. FIG. 1B shows the movement locus of each lens group during zooming. The upper end of the vertical axis is the wide-angle end, the lower end is the telephoto end, and the scale of the vertical axis is an amount proportional to the focal length of the entire lens system.
[0064]
The zoom lens according to the present embodiment shown in FIG. 1 includes thirteen lenses. The first lens group G1 having positive power, the second lens group G2 having positive power, and the negative power are sequentially arranged from the object side. A third lens group G3 having positive power, a fourth lens group G4 having positive power, and a fifth lens group G5 having positive power. On the object side of the fourth lens group G4, a variable stop A1 having a variable aperture is integrated. A fixed stop A2 having a fixed aperture diameter and a fixed position is disposed between the third lens group G3 and the variable stop A1. The fourth lens unit G4 and the fifth lens unit G5 on the image side of the fixed stop A2 constitute a rear lens unit.
[0065]
As shown in FIG. 1B, when zooming from the wide-angle end to the telephoto end when the shooting distance is infinity (∞), the first lens group G1 and the fixed stop A2 are fixed in position, and the second lens group G1 is fixed in position. The lens group G2 draws a locus convex toward the image side, the third lens group G3 moves monotonously to the image side, and the fourth lens group G4 and the fifth lens group G5 move monotonously to the object side. It should be noted here that, at the wide-angle end, the first lens group G1, the second lens group G2, and the third lens group G3 come closest to each other, and the zoom position changes from the wide-angle end to the wide-angle intermediate position. The second point is that the second lens group G2 is separated from the first lens group G1, and the third lens group G3 is separated from the second lens group G2.
[0066]
Focus adjustment is performed by moving only the fifth lens group G5 in the optical axis direction. As the shooting distance decreases, the fifth lens group G5 moves toward the object side.
[0067]
Since the mutual positional relationship between the second lens group G2, the third lens group G3, and the fourth lens group G4 is independent of the shooting distance, a cylindrical cam provided with a predetermined cam groove is provided. It is preferable to move the three lens groups G2, G3, and G4 by the rotation of. Further, since the position of the fifth lens group G5 depends on the zoom position and the photographing distance, it is preferable that the fifth lens group G5 be movable independently of the cylindrical cam.
[0068]
The first lens group G1 includes, in order from the object side, a first lens L1 of a negative meniscus lens having a convex surface facing the object side, and a second lens L2 of a positive meniscus lens having a convex surface facing the object side. L1 and the second lens L2 are joined.
[0069]
The second lens group G2 includes a positive meniscus lens L3 having a convex surface facing the object side.
[0070]
The third lens group G3 includes, in order from the object side, a fourth lens L4 of a negative meniscus lens having a convex surface facing the object side, a fifth lens L5 of a negative meniscus lens having a convex surface facing the object side, a biconcave lens L6, and an object. The seventh lens L7 is a positive meniscus lens having a convex surface facing the side.
[0071]
The fourth lens group G4 includes, in order from the object side, an eighth lens L8 of a biconvex lens, a ninth lens L9 of a plano-concave lens having a concave surface facing the object side, and a tenth lens L10 of a negative meniscus lens having a convex surface facing the object side , An eleventh lens L11 as a biconvex lens, and a twelfth lens L12 as a biconcave lens, the eighth lens L8 and the ninth lens L9 are joined, and the eleventh lens L11 and the twelfth lens L12 are joined. . The tenth lens L10 has two aspheric surfaces.
[0072]
The fifth lens group G5 includes a bi-convex thirteenth lens L13. The thirteenth lens L13 has two aspheric surfaces.
[0073]
An optical low-pass filter composed of an infrared cut filter and three quartz plates is arranged on the image side of the zoom lens, and a solid-state imaging device is arranged on the image side. A cover glass for protection is attached to the solid-state imaging device. In FIG. 1A, the optical low-pass filter and the cover glass are represented by one equivalent parallel plate element P. The image of the subject is formed on the imaging surface S of the solid-state imaging device by the zoom lens.
[0074]
The basic concept regarding the basic configuration of the zoom lens of the present invention will be described.
[0075]
In order to realize a zoom lens having a high resolution capable of supporting a solid-state imaging device having about 6 million pixels, an open F-number at the wide-angle end of about F2, and a zoom ratio of about 3 times, first, a positive lens and a negative lens in order from the object side , Positive and positive four-group zoom lenses are candidates. As such a four-unit zoom lens, there are a system in which the first lens unit closest to the object side during zooming is fixed, and a system in which the first lens unit moves during zooming.
[0076]
In the method in which the first lens group moves, there is no restriction that the overall optical length does not change at the time of zooming, so that various aberrations can be easily corrected well in the entire zooming range, which is advantageous for the imaging characteristics. However, the method in which the first lens group moves requires a mechanism for stably holding the large and heavy first lens group, and thus has a problem that the outer diameter of the lens barrel increases. On the other hand, in the system in which the first lens group is fixed at the time of zooming, only the first lens group needs to be fixed to the lens barrel, so that the configuration of the lens barrel is simplified. However, since there is a restriction that the total length of the optical system does not change during zooming, it is difficult to satisfactorily correct various aberrations in the entire zooming range, which is disadvantageous for imaging characteristics. That is, the above two types of zoom lenses have advantages and disadvantages.
[0077]
In order to solve this problem, the zoom lens of the present invention shown in FIG. 1 is composed of five lens units, positive, positive, negative, positive, and positive, in that order from the object side. Are fixed, four lens groups from the second lens group G2 to the fifth lens group G5 are moved. The first lens group G1 is composed of a negative lens and a positive lens, the second lens group G2 is composed of one positive lens, and the absolute value of the power of the first lens group G1 is the second lens group. The power of the second lens group G2 is made sufficiently smaller than the power of the second lens group G2 to reduce the moving amount of the second lens group G2 in the entire zoom range. Thereby, the power of the combined lens group composed of the first lens group G1 and the second lens group G2 is made positive, and the positive power is almost determined by the power of the second lens group G2. Thus, axial chromatic aberration and lateral chromatic aberration generated in the third lens group G3 are corrected by the first lens group G1.
[0078]
In this case, since the position of the first lens group G1 is fixed at the time of zooming, the first lens group G1 can be easily held stably, and good imaging performance can be exhibited. Further, since a mechanism for stably moving the large and heavy first lens group G1 is not required, the maximum diameter of the lens barrel can be reduced. Also, at the time of zooming, the four lens groups from the second lens group G2 to the fifth lens group G5 move on the optical axis, and there is little restriction on the position of the second lens group at the time of zooming. Aberration correction can be performed.
[0079]
One of the conditions for shortening the entire optical length of the entire lens system is to shorten the entire length of each lens group. Therefore, in the configuration shown in FIG. 1, the first lens group G1 is configured by the minimum two lenses capable of correcting chromatic aberration, and the second lens group G2 is configured by the minimum one lens capable of realizing positive power. .
[0080]
In the above-described two types of four-group zoom lenses, the stop is generally disposed between the third lens group and a substantially intermediate position between the second lens group and the third lens group. It is formed at a position far away from the lens surface (the surface closest to the object side of the first lens unit) to the image side. When the angle of view at the wide-angle end is increased, the point of incidence of the principal ray on the front lens surface at the maximum image height moves away from the optical axis. Therefore, it is necessary to increase the front lens effective diameter (the effective diameter of the front lens surface). Accordingly, the center lens of the positive lens included in the first lens group needs to have a large thickness in order to secure a required edge thickness. If the center thickness of the positive lens is increased, the distance from the front lens surface to the entrance pupil increases, so that it is necessary to further increase the front lens effective diameter. For this reason, there is a problem that the front lens effective diameter generally increases as the angle of view at the wide-angle end increases.
[0081]
To solve this problem, the five-unit zoom lens of the present invention shown in FIG. 1 can reduce the front lens effective diameter as compared with the four-unit zoom lens described above.
[0082]
The configuration of the present invention shown in FIG. 1, that is, when zooming from the wide-angle end to the wide-angle intermediate position, the first lens group G1 is fixed in position, and the second lens group G2 moves monotonously to the image side; The positions of the first lens group G1 and the second lens group G2 at the wide-angle end are the same as in the configuration shown in FIG. Let's compare the fixed configuration.
[0083]
In any of the configurations, the point at which the lower ray of light having the maximum image height is most distant from the optical axis on each object side surface of the three lenses L1, L2, and L3 is near the wide-angle intermediate position. Comparing the two configurations, in the configuration shown in FIG. 1, the incident point on the object side surface of the second lens L2 is closer to the optical axis. Therefore, in the configuration shown in FIG. 1, the effective diameter of the third lens L3 on the object side surface is small. If the effective diameter is reduced, the center thickness of the third lens L3 can be reduced, the effective diameter of the object side surface of the second lens L2 can be reduced, and the effective surface of the first lens L1 can be reduced. The diameter can also be reduced. Thus, since the outer diameter of the first lens L1 is reduced, the outer diameter of the lens barrel can be reduced.
[0084]
In general, a zoom lens tends to generate negative distortion at the wide-angle end, and this tendency becomes more remarkable as the angle of view at the wide-angle end increases.
[0085]
Accordingly, in the present invention, as shown in FIG. 1, the third lens group G3 has four negative, negative, negative, and positive lenses in order from the object side, and the two negative lenses on the object side are both negative meniscus lenses. The principal ray at the maximum image height at the wide-angle end is bent little by little on both surfaces of the two negative meniscus lenses, thereby suppressing the generation of negative distortion generated in the third lens group G3. In addition, positive distortion is generated by the second lens group G2 having positive power, and the rate of change of distortion to image height near the maximum image height is reduced, thereby reducing negative distortion at the maximum image height. I am planning. Further, the twelfth lens L12 located on the image side of the fourth lens group G4 generates positive distortion, and both surfaces of the thirteenth lens L13, which easily generates negative distortion, are made aspherical, thereby maximizing the image height. Is prevented from being excessively bent, thereby reducing negative distortion at the maximum image height at the wide-angle end of the entire lens system.
[0086]
In order to shorten the total optical length of the zoom lens, the distance between the object and the image of the fourth lens group G4 may be shortened. To this end, the focal length of the fourth lens group G4 may be shortened. In this case, various aberrations generated in the fourth lens group are likely to be large. Further, at the telephoto end where the third lens group G3 and the fourth lens group G4 come closest to each other, it is necessary to secure a space where the variable diaphragm and the fixed diaphragm can be arranged between the third lens group G3 and the fourth lens group G4. There is.
[0087]
Therefore, in the zoom lens of the present invention shown in FIG. 1, the fourth lens group G4 is composed of five positive, negative, negative, positive, and negative lenses in order from the object side, and the positive lens having the strongest positive power on the object side is provided. The negative lens having strong negative power is disposed closest to the image side, and the central tenth lens L10 is a negative meniscus lens having a convex surface facing the object side. In this case, since the object-side principal point of the fourth lens group G4 is deviated toward the object side, a space for disposing a variable stop and a fixed stop between the third lens group G3 and the fourth lens group G4 at the telephoto end is secured. Then, the distance from the image-side principal point of the third lens group G3 to the object-side principal point of the fourth lens group G4 can be shortened, and the focal length of the fourth lens group G4 can be shortened. In this case, the overall optical length becomes shorter. Further, a glass material having a high refractive index is used for the positive lens, thereby suppressing occurrence of various aberrations. Furthermore, both surfaces of the tenth lens L10 are made aspherical, and in particular, astigmatism is favorably corrected.
[0088]
In the zoom lens shown in FIG. 1, all the five lenses from the eighth lens L8 to the twelfth lens L12 constituting the fourth lens group G4 have high eccentric sensitivity. Therefore, the eighth lens L8 and the ninth lens L9 are joined, and the eleventh lens L11 and the twelfth lens L12 are joined. The ninth lens L9 has a flat image side surface, and if necessary, facilitates centering of a cemented lens L8 / L9 formed by the eighth lens L8 and the ninth lens L9 during assembly, as will be described later.
[0089]
The fixed stop A2 determines how the lower ray travels at the maximum image height. The fixed stop A2 can suppress a sharp decrease in image plane illuminance at the periphery of the screen in the range from the wide-angle end to the vicinity of the wide-angle intermediate position.
[0090]
The fifth lens group G5 is composed of one lens, and its moving part including other mechanical parts that move by focus adjustment is light, so that it is possible to move at a high speed even with a small motor having a small power. Can be performed at high speed. Although the chromatic aberration of magnification changes when the fifth lens group G5 moves for the purpose of focus adjustment, the chromatic aberration of magnification is suppressed to such an extent that there is no practical problem.
[0091]
Further, since the fifth lens group G5 has an effect of improving telecentricity, it is convenient when a micro lens is mounted on the solid-state imaging device.
[0092]
In order to realize a desirable zoom lens in the first embodiment, it is preferable that the zoom lens be configured to satisfy the following condition.
[0093]
Let the focal length of the first lens group be f_G1And the focal length of the second lens group is f_G2, The combined focal length of the first lens unit and the second lens unit at the wide angle end is represented by f_FW, The focal length of the entire lens system at the wide-angle end is represented by f_WIn this case, it is preferable that the following condition is satisfied.
[0094]
−0.02 <f_G2/ F_G1<0.15 ‥‥‥ (1)
0.05 <f_W/ F_FW<0.2 ‥‥‥ (2)
[0095]
More preferably, the upper and lower limits of conditional expression (1) and conditional expression (2) may be set as follows.
[0096]
−0.01 <f_G2/ F_G1<0.1 ‥‥‥ (1a)
0.08 <f_W/ F_FW<0.16 ‥‥‥ (2a)
[0097]
The air gap between the first lens group and the second lens group at the wide angle end is represented by d._AWThe air distance between the first lens group and the second lens group at the zooming position where the focal length is a geometric mean of the focal length at the wide-angle end and the focal length at the telephoto end is d._AN, The focal length of the entire lens system at the wide-angle end is represented by f_WIn this case, it is preferable that the following condition is satisfied.
[0098]
0.1 <(d_AN-D_AW) / F_W<0.5 ‥‥‥ (3)
[0099]
More preferably, the upper and lower limits of conditional expression (3) may be set as follows.
[0100]
0.15 <(d_AN-D_AW) / F_W<0.4 ‥‥‥ (3a)
[0101]
The air gap between the first lens group G1 and the second lens group G2 at the wide angle end is represented by d._AWThe air gap between the first lens group G1 and the second lens group G2 at the telephoto end is represented by d._AT, The focal length of the entire lens system at the wide-angle end is represented by f_WThen, the following condition should be satisfied.
[0102]
| D_AW-D_AT| / F_W<0.2 ‥‥‥ (4)
[0103]
More preferably, the upper limit of conditional expression (4) may be set as follows.
[0104]
| D_AW-D_AT| / F_W<0.1 ‥‥‥ (4a)
[0105]
Let the focal length of the third lens group G3 be f_G3And the focal length of the fourth lens group G4 is f_G4, The focal length of the entire lens system at the wide-angle end is represented by f_WThen, the following condition should be satisfied.
[0106]
0.4 <f_W/ | F_G3| <0.7 ‥‥‥ (5)
0.25 <f_W/ F_G4<0.5 ‥‥‥ (6)
[0107]
More preferably, the upper and lower limits of conditional expressions (5) and (6) may be set as follows.
[0108]
0.45 <f_W/ | F_G3| <0.65５ (5a)
0.3 <f_W/ F_G4<0.45 ‥‥‥ (6a)
[0109]
Let the focal length of the fifth lens group G5 be f_G5, The focal length of the entire lens system at the wide-angle end is represented by f_WThen, the following condition should be satisfied.
[0110]
0.3 <f_W/ F_G5<0.5 ‥‥‥ (7)
[0111]
More preferably, the upper and lower limits of conditional expression (7) may be set as follows.
[0112]
0.35 <f_W/ F_G5<0.45 ‥‥‥ (7a)
[0113]
The above conditional expression will be described.
[0114]
Conditional expression (1) defines a desirable power ratio between the first lens group G1 and the second lens group G2. If the upper limit of conditional expression (1) is exceeded, the positive power of the first lens group G1 is too strong, so that various off-axis aberrations generated in the first lens group G1 become excessive. Makes it difficult to correct. On the other hand, when the value goes below the lower limit of the conditional expression (1), the off-axis various aberrations generated in the first lens group G1 are small, but the power of the second lens group G2 becomes excessive. The center thickness of the positive lens must be increased. This means that the effective diameter of each lens surface of the first lens group G1 becomes large near the wide-angle intermediate position, and the front lens effective diameter becomes extremely large.
[0115]
Conditional expression (2) relates to the power of the combined lens group including the first lens group G1 and the second lens group G2. If the upper limit of conditional expression (2) is exceeded, the focal length of the combined lens group composed of the first lens group G1 and the second lens group G2 will be too short, so that the focal length of the third lens group G3 will be shortened. Inevitably, the off-axis aberration generated in the third lens group G3 becomes excessive. As a result, it becomes difficult to satisfactorily correct off-axis aberrations in the subsequent fourth lens group G4 and fifth lens group G5. On the other hand, when the value goes below the lower limit of the conditional expression (2), the focal length of the combined lens unit including the first lens unit G1 and the second lens unit G2 becomes too long, so that the total optical length becomes long.
[0116]
Conditional expression (3) relates to the range of the variable air gap between the first lens group G1 and the second lens group G2 during zooming. If the upper limit of conditional expression (3) is exceeded, the amount of movement of the second lens group G2 is too large. Therefore, if the zoom ratio is set to about 3 and the image plane is not moved during zooming, the third lens group Restrictions on the respective moving ranges of G3 and the fourth lens group G4 become large, and it becomes difficult to correct aberrations in a well-balanced manner over the entire zoom range. On the other hand, when the value goes below the lower limit of the conditional expression (3), the amount of movement of the second lens unit G2 is too small, so that it becomes difficult to satisfactorily correct various aberrations in the entire zoom range.
[0117]
Conditional expression (4) defines a desirable condition regarding the variable air gap between the first lens group G1 and the second lens group G2 at the wide-angle end and the telephoto end. The air gap between the first lens group G1 and the second lens group G2 may be minimized at the wide-angle end or the telephoto end in consideration of manufacturing errors. If the air gap at the wide-angle end is longer than the air gap at the telephoto end beyond the upper limit of conditional expression (4), the effective diameter of the front lens becomes large. If the air gap at the telephoto end is longer than the air gap at the wide-angle end beyond the upper limit of the conditional expression (4), the range of the position change at each magnification of the third lens group G3 to the fifth lens group G5 is restricted. Therefore, it becomes difficult to satisfactorily correct various aberrations near the telephoto end.
[0118]
Conditional expression (5) regulates the power of the third lens group G3. If the upper limit of conditional expression (5) is exceeded, the negative distortion generated in the third lens group G3 at the wide-angle end becomes excessive, and it becomes difficult to correct this negative distortion by another lens group. If the lower limit of conditional expression (5) is exceeded, the overall optical length will increase and the effective diameter of the front lens will increase.
[0119]
Conditional expression (6) is a condition for regulating the power of the fourth lens group G4 so as to minimize the overall optical length and to correct various aberrations in a well-balanced manner. If the upper limit of conditional expression (6) is exceeded, the total optical length will be short, but at the telephoto end, an air gap sufficient to dispose a fixed stop and a variable stop between the third lens group G3 and the fourth lens group G4 can be secured. Disappears. In addition, since various aberrations generated in the fourth lens group G4 become excessive, it becomes difficult to correct these various aberrations with another lens group in a well-balanced manner. On the other hand, when the value goes below the lower limit of the conditional expression (6), the distance between the object and the image of the fourth lens group G4 becomes longer, so that the entire optical length becomes longer. In this case, if the magnification of the fifth lens group G5 is reduced, the total optical length is shortened. However, since the power of the fifth lens group G5 becomes excessive, the field curvature generated in the fifth lens group G5 becomes under. It becomes difficult to correct this field curvature with the first to third lens groups G1 to G3.
[0120]
Conditional expression (7) is a condition for reducing the tilt angle of the principal ray at the maximum image height incident on the solid-state imaging device, that is, for improving the telecentricity, and for reducing the field curvature and astigmatism. If the upper limit of conditional expression (7) is exceeded, the telecentricity will be good, but the curvature of field or astigmatism will be excessive, and it will be difficult to improve the resolution around the screen. On the other hand, when the value goes below the lower limit of the conditional expression (7), the field curvature and astigmatism can be satisfactorily corrected, but the telecentricity becomes insufficient. In the case of using a solid-state imaging device equipped with a microlens, the image signal output from the solid-state imaging device becomes weaker as it approaches the peripheral portion of the screen due to shading by the microlens. It becomes dark. When using a solid-state imaging device in which the lens pitch of the microlens is slightly smaller than the pixel pitch and the exit pupil distance is short, it is not always necessary to satisfy the conditional expression (7).
[0121]
Table 1 below shows lens data of the zoom lens shown in FIG. All units of length in the table are mm. r_iIs the radius of curvature of the i-th surface, d_iIs the surface distance from the i-th surface to the next surface, n_j, Ν_jAre the refractive index and Abbe number of the j-th lens at the d-line, respectively. The surface marked with * is an aspherical surface, and the aspherical shape is defined by the following equation.
[0122]
(Equation 1)

[0123]
Where k_iIs the conic constant of the i-th surface, D_i, E_i, F_i, G_iIs the fourth-, sixth-, eighth-, and tenth-order aspherical coefficients of the i-th surface, h is the height from the optical axis, and z is the sag amount on the aspherical surface at the point where the height from the optical axis is h. It is.
[0124]
F is the focal length, FNO is the open F value, 2ω is the angle of view, and L is the total optical length.
[0125]
[Table 1]

[0126]
FIG. 2 shows aberration diagrams (spherical aberration, astigmatism, distortion) when the shooting distance of the zoom lens shown in FIG. 2A shows the case at the wide-angle end, FIG. 2B shows the case at the intermediate position, and FIG. 2C shows the case at the telephoto end. In the spherical aberration diagram, the solid line is the characteristic of the d line, the short dashed line is the F line, the long dashed line is the C line, and the dashed line is the g line. In the astigmatism diagram, a solid line indicates a characteristic on a sagittal plane, and a broken line indicates a characteristic on a meridional plane. FIG. 2 shows that various aberrations are favorably corrected at three types of zoom positions.
[0127]
The zoom lens shown in FIG. 1 has, as a solid-state image sensor, a recording pixel number of 2880 horizontal × 2160 vertical (approximately 6 million pixels), a pixel pitch of 3.0 μm horizontal × 3.0 μm vertical, and a recording screen size of 8.8 horizontal. Those having a size of 64 mm × vertical 6.48 mm can be used. Further, as the solid-state imaging device, a device provided with a microlens for each pixel in order to improve the effective aperture ratio can be used.
[0128]
When the alignment of the fourth lens group G4 is performed, the following may be performed.
[0129]
After the tenth lens L10 and the cemented lens L11 / L12 formed by the eleventh lens L11 and the twelfth lens L12 are assembled in the lens group frame, the cemented lens L8 / L9 formed by the eighth lens L8 and the ninth lens L9 is predetermined. And adjust the position of the cemented lens L8 / L9 using an eccentricity measuring device so that the eccentricity of the entire fourth lens group G4 is reduced. Fix to the group frame. At this time, if the image side surface of the ninth lens L9 is convex, trying to move the ninth lens L9 causes both parallel eccentricity and inclined eccentricity, so that it is difficult to perform alignment. On the other hand, in the zoom lens shown in FIG. 1, since the image side surface of the ninth lens L9 is a flat surface, the cemented lenses L8 / L9 can be moved in parallel without tilting, and alignment is easy. The same effect can be obtained even if the image side surface of the ninth lens L9 is concave.
[0130]
In the configuration shown in FIG. 1, the second lens group G2 is composed of one positive lens (third lens L3), but the third lens L3 is thin on at least one surface of a glass lens having two spherical surfaces. A resin layer may be provided, and the surface of the resin layer may be aspheric. In the present invention, such a lens element is considered to be one.
[0131]
In the configuration shown in FIG. 1, the variable aperture A1 is integrated with the fourth lens group G4 on the object side. This is because the eccentric sensitivity of the fourth lens group G4 is high and the eccentric sensitivity of the other lens groups is relatively high, as described above, so that the lens barrel is required to have high accuracy. This is because mass production is more advantageous if the configuration is as simple as possible.
[0132]
As described above, the zoom lens shown in FIG. 1 has a zoom ratio of about 3 times, an open F-number of about F2 at the wide angle end, an angle of view of about 76 °, and high resolution.
[0133]
(Embodiment 2)
FIG. 3A shows a configuration of a zoom lens according to Embodiment 2 of the present invention. FIG. 3A shows the lens arrangement at the wide-angle end. FIG. 3B shows the movement locus of each lens group during zooming. The upper end of the vertical axis is the wide-angle end, the lower end is the telephoto end, and the scale of the vertical axis is an amount proportional to the focal length of the entire lens system.
[0134]
The zoom lens shown in FIG. 3 includes five lens groups of positive, positive, negative, positive, and positive in order from the object side, similarly to the zoom lens described in the first embodiment. The group G4 includes four lenses, and the object side surface of the tenth lens L10 and the object side surface of the twelfth lens L12 are aspherical.
[0135]
Table 2 below shows lens data of the zoom lens shown in FIG. The definition of each parameter is the same as in the first embodiment.
[0136]
[Table 2]

[0137]
FIG. 4 shows aberration diagrams when the shooting distance of the zoom lens shown in FIG. 3 is ∞ and the aperture is opened. 4A shows the case at the wide-angle end, FIG. 4B shows the case at the intermediate position, and FIG. 4C shows the case at the telephoto end. FIG. 4 shows that various aberrations are well corrected even when the zoom position changes.
[0138]
As the solid-state imaging device, those described in Embodiment 1 can be used.
[0139]
In order to obtain more desirable imaging characteristics with the zoom lens according to the second embodiment, it is more preferable to satisfy the conditional expressions (1) to (7) described in the first embodiment, and more desirably, the conditional expression (1a) To (7a).
[0140]
Since the image side surface of the ninth lens L9 is flat, if necessary, centering of the first cemented lens L8 / L9 of the fourth lens group G4 can be easily performed in the same manner as described in the first embodiment. be able to.
[0141]
In addition, the object side surface of the tenth lens L10 is made to be aspherical, so that astigmatism is particularly well corrected.
[0142]
As described above, the zoom lens shown in FIG. 5 has a high resolution with a zoom ratio of about 3 times, an open F value of about F2 at the wide angle end, and an angle of view of about 76 °.
[0143]
(Embodiment 3)
FIG. 5A shows a configuration of a zoom lens according to Embodiment 3 of the present invention. FIG. 5A shows the lens arrangement at the wide-angle end. FIG. 5B shows the movement locus of each lens group during zooming. The upper end of the vertical axis is the wide-angle end, the lower end is the telephoto end, and the scale of the vertical axis is an amount proportional to the focal length of the entire lens system.
[0144]
The zoom lens illustrated in FIG. 5 includes five lens groups of positive, positive, negative, positive, and positive in order from the object side, similarly to the zoom lens described in Embodiment 2, and the fourth lens group includes four lenses. Although it has a sheet configuration, the object side surface of the tenth lens L10 and both surfaces of the twelfth lens L12 are aspherical.
[0145]
Table 3 below shows lens data of the zoom lens shown in FIG. The definition of each parameter is the same as in the first embodiment.
[0146]
[Table 3]

[0147]
FIG. 6 shows aberration diagrams when the shooting distance of the zoom lens shown in FIG. FIG. 6A shows the case at the wide-angle end, FIG. 6B shows the case at the intermediate position, and FIG. 6C shows the case at the telephoto end, all showing spherical aberration, astigmatism, and distortion. . It can be seen from FIG. 6 that the various aberrations are well corrected.
[0148]
As the solid-state imaging device, those described in Embodiment 1 can be used.
[0149]
In order to obtain more desirable imaging characteristics with the zoom lens according to the third embodiment, it is more preferable that the conditional expressions (1a) to (7a) described in the first embodiment be satisfied. To (7a).
[0150]
As described above, the zoom lens shown in FIG. 5 has a zoom ratio of about 3 times, an open F-number of about F2 at the wide-angle end, an angle of view of about 76 °, and high resolution.
[0151]
(Embodiment 4)
FIG. 7A illustrates a configuration of a zoom lens according to Embodiment 4 of the present invention. FIG. 7A shows a lens arrangement at the wide-angle end. FIG. 7B shows the movement locus of each lens group at the time of zooming. The upper end of the vertical axis is the wide-angle end, the lower end is the telephoto end, and the scale of the vertical axis is an amount proportional to the focal length of the entire lens system.
[0152]
The zoom lens shown in FIG. 7 is composed of five lens groups similarly to the zoom lens described in the first embodiment. However, the first lens group G1 has negative power, and the zoom lens shown in FIG. Both surfaces of the thirteenth lens L13 are aspherical.
[0153]
Table 4 below shows the lens data of the zoom lens shown in FIG. The definition of each parameter is the same as in the first embodiment.
[0154]
[Table 4]

[0155]
FIG. 8 is an aberration diagram when the shooting distance of the zoom lens shown in FIG. 7 is ∞ and the aperture is opened. 8A shows the case at the wide-angle end, FIG. 8B shows the case at the intermediate position, and FIG. 8C shows the case at the telephoto end, all showing spherical aberration, astigmatism, and distortion. . From FIG. 8, it can be seen that various aberrations are favorably corrected.
[0156]
As the solid-state imaging device, those described in Embodiment 1 can be used.
[0157]
In order to obtain more desirable imaging characteristics with the zoom lens according to the fourth embodiment, it is more preferable that the conditional expressions (1a) are satisfied so as to satisfy the conditional expressions (1) to (7) described in the first embodiment. To (7a).
[0158]
As described above, the zoom lens shown in FIG. 7 has a zoom ratio of about 3 times, an open F-number of about F2 at the wide-angle end, an angle of view of about 76 °, and high resolution.
[0159]
(Embodiment 5)
FIG. 9A shows a configuration of a zoom lens according to Embodiment 5 of the present invention. FIG. 9A shows the lens arrangement at the wide-angle end. FIG. 9B shows the movement locus of each lens group during zooming. The upper end of the vertical axis is the wide-angle end, the lower end is the telephoto end, and the scale of the vertical axis is an amount proportional to the focal length of the entire lens system.
[0160]
The zoom lens shown in FIG. 9 includes five lens groups, negative, positive, negative, positive, and positive, similarly to the zoom lens described in the fourth embodiment, and the power of the first lens group G1 is negative. The image side surface of the fifth lens L5, both surfaces of the tenth lens L10, and both surfaces of the thirteenth lens L13 are all aspherical.
[0161]
Table 5 below shows the lens data of the zoom lens shown in FIG. The definition of each parameter is the same as in the first embodiment.
[0162]
[Table 5]

[0163]
FIG. 10 shows aberration diagrams when the shooting distance of the zoom lens shown in FIG. 9 is ∞ and the aperture is fully opened. 10A shows the case at the wide-angle end, FIG. 10B shows the case at the intermediate position, and FIG. 10C shows the case at the telephoto end, all showing spherical aberration, astigmatism, and distortion. . From FIG. 10, it can be seen that various aberrations are satisfactorily corrected.
[0164]
As the solid-state imaging device, those described in Embodiment 1 can be used.
[0165]
In the zoom lens shown in FIG. 9, the image side surface of the fifth lens L5 is made aspherical to reduce negative distortion at the wide-angle end. Compared with the other embodiments, the distortion at the maximum image height at the wide-angle end when the shooting distance is ∞ is -3.5% in each of the first to fourth embodiments, whereas the present embodiment is different from the first embodiment. In the embodiment, it is slightly smaller at -3.2%.
[0166]
In order to obtain more desirable imaging characteristics with the zoom lens according to the fifth embodiment, it is more preferable that the conditional expressions (1a) are satisfied so as to satisfy the conditional expressions (1) to (7) described in the first embodiment. To (7a).
[0167]
As described above, the zoom lens shown in FIG. 9 has a zoom ratio of about 3 times, an open F-number of about F2 at the wide-angle end, an angle of view of about 76 °, and high resolution.
[0168]
In each of the zoom lenses according to Embodiments 1 to 5 described above, the third lens group monotonously moves to the image side during zooming from the wide-angle end to the telephoto end, but has the same focal length. The amount of movement of the third lens group G3 with respect to the change largely moves near the wide-angle end, and decreases as the distance from the wide-angle end increases.
[0169]
During zooming from the wide-angle end to the telephoto end, the third lens group moves monotonously to the image side from the wide-angle end to slightly before the telephoto end, and between there and the telephoto end, the third lens group moves monotonously to the object side. It may be configured to move to. However, the position of the third lens group at the telephoto end is preferably closer to the image than the position of the third lens group at the wide-angle end.
[0170]
Table 6 below shows the numerical values of the above-described conditional expressions for the five numerical examples described above.
[0171]
[Table 6]

[0172]
(Embodiment 6)
FIG. 11 is a sectional view showing a schematic configuration of an electronic still camera according to Embodiment 6 of the present invention. 11, 12 is a zoom lens, 14 is a solid-state image sensor, 15 is an electronic viewfinder, 16 is a liquid crystal monitor, 21 is a first lens group, 22 is a second lens group, 23 is a third lens group, and 24 is a third lens group. A fourth lens group, 25 is a fifth lens group, 26 is a variable stop, and 27 is a fixed stop.
[0173]
A zoom lens 12 is arranged on the front side of the housing 11, and an optical low-pass filter 13 and a solid-state imaging device 14 are arranged behind the zoom lens 12 in this order from the object side (on the object side of the solid-state imaging device 14). Has a cover glass attached, but the cover glass has been omitted for clarity). An electronic viewfinder 15 is arranged on the top of the housing 11, and a liquid crystal monitor 16 is arranged on the rear side of the housing 11.
[0174]
The optical low-pass filter 13 is formed by joining a first quartz plate, an infrared absorbing glass plate, a second quartz plate, and a third quartz plate to each other with a transparent adhesive in order from the object side. The optical low-pass filter 13 prevents generation of an erroneous signal such as moire caused by the pixel structure of the solid-state imaging device 14 and also prevents unnecessary infrared light from entering the solid-state imaging device and generating an erroneous signal. . An antireflection film is deposited on the object side surface and the image side surface of the optical low-pass filter 13.
[0175]
The solid-state imaging device 14 has an effective pixel number of 2880 horizontal × 2160 vertical (approximately 6 million pixels), a pixel pitch of 3.0 μm horizontal × 3.0 μm vertical, and an effective screen size of 8.64 mm horizontal × 6.48 mm vertical. Each pixel is provided with a minute positive lens. An image of the subject by the zoom lens 12 is formed on an imaging surface 18 of the solid-state imaging device 14.
[0176]
As the zoom lens 12, the zoom lens shown in FIG. 1 is used. The zoom lens 12 includes, in order from the object side, a first lens group 21, a second lens group 22, a third lens group 23, a fourth lens group 24, and a fifth lens group 25. A variable stop 26 and a fixed stop 27 are provided between the four lens groups.
[0177]
As shown in FIG. 12, a part of the peripheral portion of the third lens 28 constituting the second lens group 22 is cut away, and the cut end surface 29 is a plane parallel to the optical axis. All other lenses have a circular outer circumference. Details will be described later.
[0178]
A variable aperture 26 having a variable aperture is attached to the object side of the fourth lens group 24, and a fixed aperture 27 having a fixed aperture and a fixed position is disposed between the third lens group and the variable aperture 26. I have.
[0179]
The lens barrel includes a main lens barrel 31, a back plate 32, a cylindrical cam 33, five lens group frames, four guide poles 34, 35, 36, and 37, and a zoom ring 39.
[0180]
The optical low-pass filter 13 and the solid-state imaging device 14 are attached to a back plate 32, and the back plate 32 is attached to the image side end of the main lens barrel 31. The two guide poles 34 and 35 are arranged in the upper central part and the lower central part of the recording screen of the solid-state imaging device 14 in parallel with the optical axis 38. Further, the two guide poles 36 and 37 are arranged at a position away from the solid-state imaging device 14 in parallel with the optical axis 38.
[0181]
The five lens groups 21 to 25 are respectively attached to the corresponding lens group frames (the lens group frames are not shown for easy viewing of the drawing).
[0182]
The first lens group frame is attached to the object side end of the main barrel 31. A variable stop 26 is mounted on the object side of the fourth lens group frame. The fixed stop 27 is fixed to two guide poles 36 and 37 so as to be arranged at a predetermined position between the third lens group 23 and the fourth lens group 24.
[0183]
The cylindrical cam 33 has a predetermined cam groove. The second lens group frame, the third lens group frame, and the fourth lens group frame are provided with holes through which the guide poles 34 and 35 penetrate, and projections that fit into the cam grooves of the cylindrical cam 33. A zoom ring 39 is attached to the outside of the main lens barrel 31, and the zoom ring 39 is connected to the cylindrical cam 33. When the zoom ring 39 is rotated, the cylindrical cam 33 rotates. When the zoom ring 39 is rotated, the second lens group frame, the third lens group frame, and the fourth lens group frame move along the optical axis 38, and the second lens group 22, the third lens group 23, and the fourth lens Since the group 24 moves to a predetermined position based on the solid-state imaging device 14, zooming from the wide-angle end to the telephoto end can be performed. Further, since the movable lens groups 22, 23, 24 are held by the two guide poles 34, 35, the eccentricity of the movable lens groups 22, 23, 24 during zooming can be made very small.
[0184]
The fifth lens group frame is provided with a hole through which the guide poles 36 and 37 pass. The fifth lens group frame is movable along the optical axis 38 by a stepping motor. When the fifth lens group 25 is moved in the optical axis direction by a motor, a position where the high frequency component of the captured image has a peak is detected, and if the fifth lens group 25 is moved to that position, autofocusing can be performed. it can.
[0185]
It is preferable to provide a female screw for mounting a filter on the object side of the first lens group frame. In the configuration shown in FIG. 11, since the first lens group frame does not move at the time of zooming, even if a heavy filter is mounted, the first lens group 21 will not be decentered, and the imaging characteristics will not be degraded.
[0186]
The formation of the third lens 28 as shown in FIG. 12 will be described.
[0187]
FIG. 13 shows an effective area 41 on the object side surface of the third lens 28. FIG. 13 shows the third lens 28 viewed along the optical axis 38. Here, the effective area is an area through which an effective light beam passes, and is an area where the area is maximized. Although the area of the area through which the effective light beam passes varies depending on the zoom position, the area becomes maximum near the wide-angle intermediate position. The shape obtained by projecting the boundary 42 of the effective area 41 onto a plane perpendicular to the optical axis 38 is similar to the recording screen of the solid-state imaging device 14 and has a rectangular shape having four arcs at four corners. There are two symmetry axes of this rectangular shape, and the two symmetry axes 43 and 44 are parallel to the screen horizontal direction and the screen vertical direction of the solid-state imaging device, respectively.
[0188]
As can be seen from FIG. 13, when the outer periphery 47 of the third lens 28 is circular, there are regions inside the outer periphery 47 where the effective luminous flux does not pass above and below the rectangular effective region 41. The region through which the effective light beam does not pass may be removed. Accordingly, the third lens 28 of the zoom lens shown in FIG. 11 can be formed into a shape shown in FIG. 12 by cutting off a part of the peripheral portion in a range where the effective area 41 on the object side surface is not cut. In this case, it is necessary to move the third lens 28 along the optical axis so that the third lens 28 does not rotate during zooming, but there is no problem since the third lens 28 is moved along the guide poles 34 and 35.
[0189]
When the upper and lower sides of the effective area of the third lens 28 are cut off as shown in FIG. 12, as can be seen from FIG. 11, the distance between the two guide poles 34 and 35 can be reduced, and as a result, The outer diameter of the intermediate portion of the lens barrel can be reduced. The dimension of the third lens 28 in the vertical direction is preferably substantially the same as the outer diameter of the fourth lens 48. When a part of the periphery of the third lens 28 is cut off to reduce the outer diameter of the middle part of the lens barrel, when the angle of view at the wide-angle end is small, not so much effect is obtained. It is very effective in the case of a wide angle where the angle exceeds 70 °.
[0190]
FIG. 14 shows another example in which the periphery of the third lens 28 is cut off. FIG. 14A is an example in which two portions around the third lens 28 are cut away so that the end surfaces 51 and 52 become a part of a cylindrical surface, and FIG. 14B is a portion around the third lens 28. This is an example in which through holes 53 and 54 are provided at two places. Both are viewed along the optical axis, and the two resections are set so that the effective area on the object side surface is not cut away.
[0191]
In the above description, the zoom lens according to the first embodiment is taken as an example. However, the zoom lenses according to the second to fifth embodiments can be configured in the same manner, and the outer diameter of the intermediate portion of the lens barrel can be reduced. be able to.
[0192]
Further, in FIGS. 12 and 14, the cutout portions of the third lens 28 are arranged at the upper central portion and the lower central portion of the effective area. The position may be shifted from the upper central portion or the lower central portion.
[0193]
As described above, when a part of the peripheral portion of the third lens 28 is cut off, the outer diameter of the intermediate portion of the lens barrel can be reduced. If the outer diameter of the middle part of the lens barrel may be slightly larger, it is not necessary to cut off a part of the peripheral part of the third lens 28.
[0194]
Thus, it is possible to provide a high-resolution electronic still camera with a zoom ratio of about three, an open F-number of about F2 at the wide-angle end, and an angle of view exceeding 70 °.
[0195]
In the electronic still camera shown in FIG. 11, any one of the zoom lenses according to the second to fifth embodiments may be used instead of the zoom lens according to the first embodiment. Further, the optical system of the electronic still camera shown in FIG. 11 can be used for a video camera for moving images. In this case, not only moving images but also high-resolution still images can be shot.
[0196]
In the above description, the case where the solid-state imaging device having 6 million pixels is used has been described. However, a solid-state imaging device having substantially the same recording screen size and a small number of pixels may be used. For example, it is possible to use a solid-state imaging device having a recording screen with a diagonal length of about 11 mm, a number of recording pixels of 2560 horizontal × 1920 vertical (about 5 million pixels), and a pixel pitch of 3.4 μm horizontal × 3.4 μm vertical. . In this case, the separation width of the optical low-pass filter 13 needs to be determined so as to be substantially equal to the pixel pitch.
[0197]
【The invention's effect】
As described above, according to the present invention, a high-resolution zoom lens having a zoom ratio of 2.5 to 3.2 times, an open F value of about F2 at the wide-angle end, and an angle of view exceeding 70 ° is provided. be able to. By using this zoom lens, a wide-angle, bright, high-resolution electronic still camera can be provided.
[Brief description of the drawings]
FIG. 1A is a side view showing a configuration of a zoom lens at a wide-angle end according to a first embodiment of the present invention.
FIG. 1B is a diagram showing a movement locus of each lens group constituting the zoom lens according to Embodiment 1 of the present invention at the time of zooming.
FIG. 2 is an aberration diagram when the shooting distance of the zoom lens according to the first embodiment of the present invention is ∞.
FIG. 3A is a side view showing a configuration of a zoom lens at a wide-angle end according to a second embodiment of the present invention.
FIG. 3B is a diagram illustrating a movement locus of each lens group included in the zoom lens according to Embodiment 2 of the present invention during zooming.
FIG. 4 is an aberration diagram when the shooting distance of the zoom lens according to the second embodiment of the present invention is ∞.
FIG. 5A is a side view showing a configuration of a zoom lens at a wide-angle end according to a third embodiment of the present invention.
FIG. 5B is a diagram showing a movement locus of each lens group constituting the zoom lens according to the third embodiment of the present invention at the time of zooming.
FIG. 6 is an aberration diagram when the shooting distance of the zoom lens is 実 施 according to the third embodiment of the present invention.
FIG. 7A is a side view showing a configuration of a zoom lens according to a fourth embodiment of the present invention at the wide-angle end.
FIG. 7 (b): A diagram showing the movement locus of each lens group constituting the zoom lens according to Embodiment 4 of the present invention during zooming.
FIG. 8 is an aberration diagram when the photographing distance of the zoom lens according to the fourth embodiment of the present invention is ∞.
FIG. 9A is a side view showing a configuration of a zoom lens at a wide-angle end according to a fifth embodiment of the present invention.
FIG. 9 (b): A diagram showing the movement locus of each lens group constituting the zoom lens according to Embodiment 5 of the present invention at the time of zooming.
FIG. 10 is an aberration diagram when the shooting distance of the zoom lens is 実 施 according to the fifth embodiment of the present invention.
FIG. 11 is a side sectional view showing a schematic configuration of an electronic still camera according to Embodiment 6 of the present invention.
FIG. 12 is a perspective view showing a shape of a third lens of the zoom lens shown in FIG. 11;
13 is a front view showing an effective area on the object side surface of the third lens shown in FIG. 12;
14 is a front view showing another example of the shape of the third lens of the zoom lens shown in FIG. 11;
[Explanation of symbols]
G1, 21 First lens group
G2,22 Second lens group
G3,23 3rd lens group
G4,24 4th lens group
G5, 25 Fifth lens group
A1,26 Variable aperture
A2,27 Fixed aperture
P Parallel plane element
S image plane
L1 First lens
L2 Second lens
L3 Third lens
L4 4th lens
L5 5th lens
L6 6th lens
L7 7th lens
L8 8th lens
L9 9th lens
L10 10th lens
L11 11th lens
L12 12th lens
L13 13th lens
12 Zoom lens
14 Solid-state image sensor
15 Electronic viewfinder
16 LCD monitor
28 Third lens

Claims (21)

In order from the object side, a first lens group, a second lens group having a positive power, a third lens group having a negative power, and a rear lens group having at least one positive power lens group are provided. A zoom lens in which, during zooming, the first lens group is fixed in position, and the second lens group and the third lens group are movable along the optical axis. A rear lens group including, in order from the object side, a first lens group, a second lens group having a positive power, a third lens group having a negative power, a fixed stop having a fixed aperture, and at least one lens group having a positive power. A zoom lens, wherein at the time of zooming, the first lens group and the fixed stop have fixed positions, and the third lens group moves along the optical axis. The zoom lens according to claim 1, wherein the first lens group includes a negative lens and a positive lens. The zoom lens according to any one of claims 1 to 3, wherein the most object-side lens group of the rear lens group has a variable aperture with a variable aperture diameter integrated on the object side. The zoom lens according to any one of claims 1 to 4, wherein a combined lens group of the first lens group and the second lens group has positive power in the entire zoom range. The zoom lens according to claim 1, wherein the second lens group includes a single positive lens. The focal length of the entire lens system and f _W at the wide-angle _end, the focal length of the entire lens system at the telephoto end and f _T, and the zooming position of the focal length becomes f _W ^3/4 f _T ^1/4 wide middle position The zoom lens according to any one of claims 1 to 6, wherein the second lens group monotonously moves to the image side when zooming from a wide-angle end to a wide-angle intermediate position. In order from the object side, a first lens group including a negative lens and a positive lens, a second lens group with positive power, a third lens group with negative power, a fourth lens group with positive power, and a fourth lens group with positive power The first lens group has a fixed position, the second lens group has a locus convex toward the image side, and the third lens group has a fifth lens group, when zooming from the wide-angle end to the telephoto end. A zoom lens that moves monotonically to the image side, moves monotonously to the image side halfway, then moves monotonically to the object side, and the fourth lens group moves monotonically to the object side. 9. The zoom lens according to claim 8, further comprising a fixed stop having a fixed aperture diameter and a fixed position at the time of zooming, between the third lens group and the fourth lens group. The zoom lens according to claim 8, wherein the fourth lens group has a variable aperture having a variable aperture diameter integrated with an object side thereof. The zoom lens according to any one of claims 8 to 10, wherein the focus adjustment is performed by moving the fifth lens group on the optical axis. The focal length of the first lens group is f _G1 , the focal length of the second lens group is f _G2 , the combined focal length of the first and second lens groups at the wide-angle end is f _FW , when the focal length of the entire lens system and f _W, zoom lens according to any one of claims 8 to 11 which satisfy the following conditions.
_{-0.02 <f G2 / f G1 <} 0.15 ‥‥‥ (1)
_{0.05 <f W / f FW <} 0.2 ‥‥‥ (2) The air distance between the first lens group and the second lens group at the wide-angle end is d _AW , and the focal length at the zooming position at which the focal length is the geometric mean of the focal length at the wide-angle end and the focal length at the telephoto end is described. the air gap d _aN between the first lens group and the second lens _group, when the focal length of the entire lens system at the wide-angle end and f _W, in any one of claims 8 to 12 which satisfies the following conditions The described zoom lens.
0.1 <(d _AN −d _AW ) / f _W <0.5 ‥‥‥ (3) The air gap between the first lens group and the second lens group at the wide-angle end is d _AW , the air gap between the first lens group and the second lens group at the telephoto end is d _AT , and the wide-angle end when the focal length of the entire lens system and the f _W in the zoom lens according to any one of claims 8 to 13 which satisfy the following conditions.
| D _AW −d _AT | / f _W <0.2 ＜ (4) The following condition is satisfied when the focal length of the third lens group is f _G3 , the focal length of the fourth lens group is f _G4 , and the focal length of the entire lens system at the wide-angle end is f _W. 15. The zoom lens according to any one of 14.
_{0.4 <f W / | f G3} | <0.7 ‥‥‥ (5)
_{0.25 <f W / f G4 <} 0.5 ‥‥‥ (6) The third lens group includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a biconcave lens, and a positive lens having a convex surface facing the object side. The zoom lens according to any one of claims 8 to 15, further comprising: The fourth lens group includes a cemented lens composed of a biconvex lens closest to the object side and a negative lens having a concave surface facing the object side, and a positive lens having a convex surface facing the object side closest to the image side and a concave lens facing the object side. The zoom lens according to any one of claims 8 to 16, further comprising a cemented lens including a negative lens directed toward the zoom lens. The fourth lens group includes, in order from the object side, a cemented lens composed of a biconvex lens and a negative lens having a concave surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a biconvex lens, and a biconcave lens. The zoom lens according to claim 8, further comprising a cemented lens. 19. The zoom lens according to claim 8, wherein the following condition is satisfied, where f _{G5 is} a focal length of the fifth lens group, and f _W is a focal length of the entire lens system at a wide-angle end.
_{0.3 <f W / f G5 <} 0.5 ‥‥‥ (7) A first lens group, a second lens group including one positive lens, and a rear lens group including a plurality of lens groups in order from the object side. A zoom lens in which the periphery of the positive lens is partially cut off, the first lens group is fixed in position during zooming, and the second lens group moves along the optical axis without rotating. 21. An electronic imaging apparatus comprising a zoom lens and a solid-state imaging device, wherein the zoom lens according to claim 1 is used as the zoom lens.

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