JP2004085603A

JP2004085603A - Zoom lens and photographic system

Info

Publication number: JP2004085603A
Application number: JP2002242370A
Authority: JP
Inventors: Hatayuki Tomita; 富田　秦行; Shinichiro Yakita; 矢北　真一郎
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2002-08-22
Filing date: 2002-08-22
Publication date: 2004-03-18
Anticipated expiration: 2022-08-22
Also published as: JP4298237B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens of a rear focus system which permits simple adjustment of a flange back with high accuracy. <P>SOLUTION: The zoom lens having a first lens group for at least variable power, a diaphragm for adjusting a light quantity nearer an imaging surface side than the first lens group, and a second lens group for focusing is constituted to have a means for correcting the second lens group at a wide angle end in accordance with the storage information judged from a focusing position at a telephoto end relating to the dormant subject existing at an arbitrary distance focusable in the entire area of zooming in the flange back adjustment for the purpose of determining the reference position of the second lens group, for determining the same as the reference position and for storing the position. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、放送用あるいはビデオカメラ用に好適な交換式ズームレンズ及び撮影システムに関するものである。
【０００２】
【従来の技術】
テレビカメラに脱着可能な撮影光学系を装着した場合には、レンズの結像面と撮像素子（ＣＣＤ等）の位置を合致させるように、レンズの取付け面（フランジ面）から結像面までの距離（フランジバック）を調整する必要がある。従来の前玉マニュアルフォーカスレンズにおけるフランジバック調整の手順を図２を用いて説明する。
【０００３】
図２において、２１０はカメラ本体にレンズを装着した撮影システム本体、２０１は撮影光学系、２０２はフォーカスの為のレンズ群、２０３は変倍のためのレンズ群、２０４は絞り、２０５は撮影光学系レンズ最終面から撮像面までの距離（バックフォーカス）を調整可能なレンズ群、２０６はフィルターや色分解プリズムに相当するガラスブロック、２０７は撮影光学系２０１によって形成される被写体像を受光するＣＣＤ等の撮像素子、２０８、２０９は撮影装置及びレンズの制御を行うＣＰＵである。
【０００４】
先ず、▲１▼絞り２０４を開放にする。▲２▼レンズ群２０３にてズームを望遠端にしてレンズ群２０２にて合焦させる。▲３▼レンズ群２０３にてズームを広角端にして、レンズ群２０５にて合焦させる。上記▲２▼、▲３▼の工程を数回繰り返してフランジバックを調整する。
【０００５】
このフランジバックを調整により、ズーミングに際して結像位置を所定の位置に一定にする。
【０００６】
特開平１１−１２７３７６では、絞り２０４、及びレンズ群２０２、２０５各々に電気的に駆動する手段を設け、自動合焦手段にて上記▲１▼〜▲３▼の作業を自動化している。
【０００７】
また、図２において、レンズ群２０２が固定され、レンズ群２０３より結像面側のレンズ群２０５にて合焦するというリアフォーカスタイプの撮影光学系が数多く提案されている。この種の撮影光学系は、上記のフランジバック調整工程▲２▼の作業が行えない為、レンズ群２０５のズームに連動した移動軌跡（ズームトラッキング曲線）を利用してフランジバック調整を行う方法が提案されている。
【０００８】
特開平７−１５４６６７では、上記ズームトラッキング曲線の変曲点を見つけ、その後、広角端及び望遠端位置を決定してフランジバックを調整する方法が提案されている。
【０００９】
特開２０００−１２１９１１では、上記ズームトラッキング曲線が変曲点を持たないタイプのレンズ系におけるフランジバック調整方法が提案されている。それは、変倍光学群が設計広角端と設計望遠端の位置にある時に、自動合焦にてそれぞれのズーム位置でのフォーカス位置を把握し、予め用意されたテーブルから実際のズーム方向の調整値とフォーカス方向の調整値を求めるものである。
【００１０】
【発明が解決しようとする課題】
上述したように、撮影システムによって様々なフランジバック調整法が存在するが、テレビカメラの交換レンズ装置の観点から必ずしも適切ではない。
【００１１】
具体的には、上記特開平１１−１２７３７６では、図１におけるレンズ群１０２、１０５各々に自動駆動装置を設けると共に双方のレンズ群に対して自動焦点検出が可能なシステムを構築しなければならないため、システムとして複雑な構成となってしまう。
【００１２】
また、上記特開平７−１５４６６７、及び特開２０００−１２１９１１では、フランジバック調整に適当な被写体を所定の距離に設置しなければならない。これは撮影者が撮影現場でフランジバックを調整することを考慮した時、制約となるばかりでなく、被写体距離のズレがフランジバック調整精度の劣化の原因となる。
【００１３】
そこで、本発明は、リアフォーカスタイプの撮影光学系において、自動合焦手段を利用して、任意の距離にある不動の被写体にてフランジバック調整を行うことを可能にすると共に、演算が簡潔で、高速、高精度なフランジバック調整機能を有するズームレンズ及び撮影システムの提供を目的とする。
【００１４】
【課題を解決するための手段】
上記の目的を達成するために、本発明では、少なくとも変倍の為の第１レンズ群と、前記第１レンズ群より結像面側に光量を調節する為の絞りと、フォーカスの為の第２レンズ群とを有して構成されているズームレンズにおいて、前記第２レンズ群の基準位置を決定する為のフランジバック調整において、ズーム全域に渡って合焦可能な任意の距離にある不動の被写体に対して、望遠端にて合焦の可否及び位置を判断、記憶するとともに、
【数５】

の時、
上記第２レンズ群に関して、広角端にて合焦後に望遠端での合焦位置を基に合焦位置を補正して基準位置として記憶するようにしている。
【００１５】
カム等を用いた機構式によって広角端での上記第１レンズ群の光軸上の位置が確定しているズームレンズにおいて、広角端で上記第２レンズ群にて自動合焦することによって、ズームトラッキング曲線の広角端における端点を明確にすることができる。また、無限遠の被写体に対する合焦位置と、全ズーム領域にわたって合焦可能な最至近距離の被写体に対する合焦位置との差の絶対値は、一般的に概ね焦点距離の自乗に比例することが知られており、広角端にて最も小さい。従って、全ズーム領域で合焦可能な被写体距離範囲内において任意の距離にある不動の被写体に対して、広角端での上記第２レンズ群の合焦位置近傍に必ず基準位置が存在する。
【００１６】
上記発明において好ましくは、上記第２レンズ群に関して、望遠端にて上記フランジバック調整時に用いる被写体に対して合焦の可否を判断する手段を有するのがよい。すなわち、合焦が不可能と判断された場合、全ズーム領域で合焦可能な被写体距離範囲外に被写体が存在する事を表す。この被写体を用いて上記に記載のフランジバック調整を行うと、その精度は悪化する。あるいは、この被写体にて精度良くフランジバック調整を行うには、その方法は複雑化してしまう。つまり、合焦の可否を判断する事により、上記に記載のフランジバック調整を高精度に行うことが可能となる。
【００１７】
また、Ｆナンバーが明るい、撮像素子の画素が細かいなど焦点深度が浅い撮影システムにおいては、望遠端における前記第２群の無限遠の被写体距離に対する合焦位置とズーム全域において合焦可能な最も近距離の被写体Ｌに対する合焦位置との差をＭｔ、広角端における無限遠の被写体に対する合焦位置と前記被写体距離Ｌに対する合焦位置との差をＭｗ、撮影システムの焦点深度をδ、前記第２レンズ群の最小移動量をｄ、また、前記第２レンズ群によって焦点深度に相当するバックフォーカスを変化させるのに必要な移動量をｌとしたとき、分割数ｍを以下の式で定義するとともに、
【００１８】
【数６】

【００１９】
望遠端における前記第２レンズ群の移動範囲Ｍｔを分割数ｍで等分割し記憶すると共に、望遠端における合焦判定時に前記第２レンズ群がどの領域に位置したかを記憶すると共に、広角端にて自動合焦後に望遠端での記憶情報を基に補正し基準位置として記憶する手段を有するのがよい。これにより、簡潔な演算処理を実現すると共に、より高精度なフランジバック調整を行うことが可能となる。
【００２０】
また、上記フランジバック調整時に上記絞りを開放状態にするのがよい。
【００２１】
これにより焦点深度が浅くなり自動合焦の精度が上がる為、高精度なフランジバック調整が可能となる。
【００２２】
また、上記フランジバック調整を行うことを指示する部材を有するのがよい。
【００２３】
なお、上記第１レンズ群より物体側に手動操作により合焦可能な第０レンズ群を有して構成されているズームレンズにおいて、上記フランジバック調整時に上記第０レンズ群を所定の位置に固定するのがよい。
【００２４】
これにより、望遠端で上記第０レンズ群による合焦作業と広角端で上記第２レンズ群による合焦作業とを数回繰り返して行われる上記記載の従来のフランジバック調整に比して、操作が簡潔で撮影者の負担が少なく、且つ高速なフランジバック調整が可能となる。
【００２５】
【発明の実施の形態】
本発明の実施の形態を図１を用いて説明する。図１において、１１０はカメラ本体にレンズを装着した撮影システム本体、１０１は撮影光学系、１０２は固定もしくは手動による合焦の為に可動なレンズ群、１０３は変倍のためのレンズ群、１０４は絞り、１０５は自動合焦のためのフォーカス群、１０６はフィルターや色分解プリズムに相当するガラスブロック、１０７は撮影光学系１０１によって形成される被写体像を受光するＣＣＤ等の撮像素子、１０８、１０９は撮影システム及びレンズの制御を行うＣＰＵ及びレンズ群の光軸上の位置を記憶するための記憶装置、１１１はフランジバック調整を行う事を指示する部材である。レンズ群１０３はカム方式によってズーム全域に渡って光軸上の位置が決められている。
【００２６】
この撮影システム１１０におけるフランジバックの調整は以下の手順で行う。▲１▼例えばジーメンススターチャートのようにコントラストのはっきりした被写体を撮影システム１１０と正対するように任意の距離に固定して設置する。▲２▼絞り１０４を開放状態にするとともに、レンズ群１０２が手動による合焦の為に可動な場合には所定の位置に固定する。▲３▼レンズ群１０２を望遠端に配置し合焦の可否を判断すると共に、位置を記憶する。▲４▼次に、レンズ群１０２を広角端に配置し自動合焦後に、レンズ群１０５の位置に対して▲３▼で記憶した望遠端での合焦位置の情報を基に補正を掛け基準位置と決定し、その位置を記憶する事でフランジバック調整を終了する。
【００２７】
このとき、部材１１１にて▲２▼、▲３▼及び▲４▼の一連の作業を自動で行うようにしても良いし、▲２▼、▲３▼の作業後に部材１１１によって▲４▼の作業だけ行うようにしてもよい。
【００２８】
本発明の実施の形態をズームレンズの光学的構成から説明する。図３において、物体側から順に、１は合焦の為の第１レンズ群、２は変倍時に移動可能な第２レンズ群、３は変倍時の結像位置の移動を補正するための第３レンズ群、４は固定の第４レンズ群、５は自動合焦の為の第５レンズ群、１２は色分解プリズムなどのガラスブロック、１１は絞りである。第１レンズ群１、第４レンズ群４及び第５レンズ群５は変倍の際に固定である。また、第５レンズ群５にて合焦させる事でフランジバックを調整する。
【００２９】
下記の表１は、図３のズームレンズに対応するものである。
【００３０】
【表１】

【００３１】
図４に無限遠と最至近距離の各々の被写体に対するズームトラッキング曲線を示す。なお、図３のズームレンズにおいて、全ズーム域に渡って合焦可能な最至近距離はズームレンズ最前面から４３２ｍｍである。
【００３２】
図４よりフォーカスの移動範囲は、広角端にて最も小さく、望遠端にて最も大きい。つまり、望遠端にて合焦可能な被写体距離であれば、全ズーム領域で合焦可能な被写体距離と言える。全ズーム領域にわたって合焦可能な最も近い被写体距離を至近距離Ｌとした時、本発明は、図４の無限遠と至近距離Ｌの両ズームトラッキング曲線間の距離範囲内の被写体に対して効果的であり、上記範囲外の被写体距離に関してはフランジバック調整の精度が悪化する。そのため、任意の距離に設置された被写体に対して、望遠端にて合焦の可否を判断し、フランジバック調整の精度を判断するのがよい。更に、合焦不可能の場合はフランジバック調整不可能を表す信号を出力または表示する手段を有するのがよい。
【００３３】
条件式（１）は、本発明のフランジバック調整で記憶した基準位置を補正する必要性を示している。この条件式（１）を満足した時、広角端での合焦位置を補正して基準位置とすることによって、より高精度なフランジバック調整が可能となる。ここで、許容錯乱円径をε、広角端での開放ＦナンバーをＦすると、焦点深度δは概ね、
δ＝εＦ
で表される。また、第５レンズ群５のバックフォーカスに対する敏感度をｓとすると、バックフォー
カスを焦点深度δだけずらすのに必要な第５レンズ群５の移動量ｌは、
【数７】

で表される。
【００３４】
広角端における、第５レンズ群５の無限遠の被写体に対する合焦位置と至近距離Ｌの被写体に対する合焦位置との差をＭ_Ｗとすると、｜Ｍ_Ｗ｜より上記ｌが小さければ、被写体距離によっては基準位置のズレがボケとして画面上で認知され、より高精度なフランジバック調整が必要となる。上記発明で決定した基準位置の補正が必要となる制限条件は、
【数８】

で表す事ができる。
【００３５】
第５レンズ群は、ステッピング・モーターやＤＣモーター等のアクチュエーターで駆動され最小移動量ｄは概ねｌ／８≦ｄ≦ｌであることが望ましい。ｄ＜ｌ／８の条件では駆動範囲全域を移動させるための移動速度が遅くなりすぎてしまい適切ではない。逆に，δ＜ｌの条件では、画面上ボケとして認められてしまい見苦しいものとなってしまう。
本実施形態ではｄ＝ｌ／２とし、条件式（２）における分割数ｍは、
【数９】

としている。分割数ｍは、小数点第１桁を四捨五入した整数である。
【００３６】
ここで、表１の各パラメータと条件式（１）の関係を表２に示す。
【００３７】
【表２】

【００３８】
表２より、表１は広角端での自動合焦位置を基準位置として記憶するだけでは、被写体距離によって真の基準位置とのズレが上記の理由により画面上で認知されてしまう可能性がある。
【００３９】
次に補正の方法について述べる。上記（２．１）より、望遠端における第２レンズ群の移動範囲を１０分割する。また、無限遠から被写体距離４３２ｍｍまでの第２レンズ群の移動量はＭｔ＝−１３．６ｍｍから、１．３６ｍｍ刻みの１０の領域を記憶しておく。望遠端にて合焦の可否を判断すると共に、基準位置として補正するための補正量を以下に示す。ｍｔは、望遠端におけるレンズの移動量を示す。
【００４０】
【表３】

【００４１】
このように、広角端での合焦位置に補正を加えて基準位置として記憶させる事でより高精度なフランジバック調整が可能となる。本実施形態においてｄ＝ｌ／２としていることにより、フランジバックの精度としては、焦点深度δの１／２、すなわち８μｍ程度という高い精度となる。
【００４２】
望遠端での合焦位置を基に補正量を決定したが、所定のズームポジションにおける合焦位置を基に基準位置を決定しても良い。但し、望遠端以外の所定のズームポジションで行う場合は、そのズームポジションに於ける変倍に関わるレンズ群の光軸上の位置を正確に把握しなければならない為、ズームのどちらかの端点（広角端かあるいは望遠端）との位置関係を予め記憶させておく手段が必要となる等、効率的でない。
【００４３】
【発明の効果】
以上説明したように、本発明によれば、リアフォーカスタイプの撮影光学系において、任意の距離の被写体にて、広角端での上記リアフォーカスレンズ群の合焦位置に望遠端での合焦位置から判断した記憶情報と基に補正し基準位置として決定し、その位置を記憶することで、演算が簡潔で、高速なフランジバック調整を行う事ができる。
【００４４】
また、上記リアフォーカスレンズ群にて、上記の被写体に対して望遠端での合焦の可否を判断する事で、より高精度なフランジバック調整が可能となる。
【００４５】
また、上記フランジバック調整時に上記絞りを開放状態にすることで、焦点深度が浅くなり自動合焦の精度が上がる為、高精度なフランジバック調整が可能となる。
【００４６】
また、上記フランジバック調整を行うことを指示する部材を有する事で、操作が簡潔で撮影者の制約が少なく、且つ高速なフランジバック調整が可能となる。
【００４７】
また、前記第１レンズ群より物体側に合焦可能な第０レンズ群を有して構成されているズームレンズにおいて、前記フランジバック調整時に前記第０レンズ群を所定の位置に固定することによって、前玉フォーカスとリアフォーカス両方の機能を有したズームレンズに於けるフランジバック調整を簡潔にできる。
【図面の簡単な説明】
【図１】本発明の実施形態における撮影システムの模式図。
【図２】前玉マニュアルフォーカスレンズを撮影光学系として用いた撮影システムの模式図。
【図３】本発明の実施形態（表１）のズームレンズの光学的構成を示す図。
【図４】本発明の実施形態（表１）のズームトラッキング曲線を示す図。
【符号の説明】
１　第１レンズ群
２　第２レンズ群
３　第３レンズ群
４　第４レンズ群
５　第５レンズ群
１１　絞り
１２　ガラスブロック[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an interchangeable zoom lens and a photographing system suitable for broadcasting or a video camera.
[0002]
[Prior art]
When a detachable photographic optical system is attached to the TV camera, the distance from the lens mounting surface (flange surface) to the image forming surface is adjusted so that the image plane of the lens and the position of the image sensor (CCD, etc.) match. It is necessary to adjust the distance (flange back). The procedure for adjusting the flange back in the conventional front lens manual focus lens will be described with reference to FIG.
[0003]
In FIG. 2, reference numeral 210 denotes a photographing system main body in which a lens is mounted on a camera main body, 201 denotes a photographing optical system, 202 denotes a lens group for focusing, 203 denotes a lens group for zooming, 204 denotes an aperture, and 205 denotes a photographing optical system. A lens group capable of adjusting the distance (back focus) from the final surface of the system lens to the imaging surface; 206, a glass block corresponding to a filter or a color separation prism; 207, a CCD for receiving a subject image formed by the photographing optical system 201

Reference numerals

208 and 209 denote CPUs for controlling the imaging device and the lens.
[0004]
First, (1) the aperture 204 is opened. (2) The zoom is set at the telephoto end by the lens group 203, and the lens group 202 focuses. (3) The zoom is set to the wide-angle end by the lens group 203, and the lens group 205 focuses. The steps (2) and (3) are repeated several times to adjust the flange back.
[0005]
By adjusting the flange back, the imaging position is kept at a predetermined position during zooming.
[0006]
In Japanese Patent Application Laid-Open No. H11-127376, means for electrically driving the aperture 204 and the

lens groups

202 and 205 are provided, and the above operations (1) to (3) are automated by automatic focusing means.
[0007]
In FIG. 2, there have been proposed many rear-focus type photographing optical systems in which the lens group 202 is fixed and the lens group 205 on the image plane side of the lens group 203 focuses. Since this type of photographing optical system cannot perform the above-described operation of the flange back adjustment step (2), a method of performing flange back adjustment using a movement locus (zoom tracking curve) interlocked with zooming of the lens group 205 is known. Proposed.
[0008]
Japanese Patent Application Laid-Open No. Hei 7-154667 proposes a method of finding an inflection point of the zoom tracking curve, and thereafter determining the wide-angle end and the telephoto end to adjust the flange back.
[0009]
Japanese Patent Application Laid-Open No. 2000-121911 proposes a flange back adjustment method for a lens system of a type in which the zoom tracking curve has no inflection point. That is, when the variable power optical group is at the design wide-angle end and the design telephoto end, the focus position at each zoom position is grasped by automatic focusing, and the adjustment value in the actual zoom direction is obtained from a table prepared in advance. And the focus direction adjustment value.
[0010]
[Problems to be solved by the invention]
As described above, there are various flange back adjustment methods depending on the photographing system, but they are not always appropriate from the viewpoint of the interchangeable lens device of the television camera.
[0011]
Specifically, in Japanese Patent Application Laid-Open No. H11-127376, it is necessary to provide an automatic driving device for each of the

lens groups

102 and 105 in FIG. 1 and to construct a system capable of automatic focus detection for both lens groups. However, the configuration becomes complicated as a system.
[0012]
In Japanese Patent Application Laid-Open Nos. 7-154667 and 2000-121911, a subject appropriate for flange-back adjustment must be set at a predetermined distance. This is not only a restriction when the photographer considers adjusting the flange back at the photographing site, but also a deviation of the subject distance causes deterioration of the flange back adjustment accuracy.
[0013]
Therefore, the present invention makes it possible to perform flange back adjustment on an immovable subject at an arbitrary distance by using an automatic focusing means in a rear focus type photographing optical system, and the calculation is simple. Another object of the present invention is to provide a zoom lens and a photographing system having a high-speed, high-precision flange-back adjustment function.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, at least a first lens unit for zooming, a stop for adjusting the amount of light from the first lens unit to the image forming surface side, and a first lens unit for focusing. In a zoom lens configured to include two lens groups, in a flange back adjustment for determining a reference position of the second lens group, an immovable lens at an arbitrary distance that can be focused over the entire zoom range. With respect to the subject, while determining and storing whether or not focusing is possible at the telephoto end and the position,
(Equation 5)

time,
For the second lens group, after focusing at the wide-angle end, the focusing position is corrected based on the focusing position at the telephoto end and stored as a reference position.
[0015]
In a zoom lens in which the position on the optical axis of the first lens group at the wide-angle end is determined by a mechanism using a cam or the like, zooming is performed by automatic focusing by the second lens group at the wide-angle end. The end point at the wide-angle end of the tracking curve can be clarified. In addition, the absolute value of the difference between the in-focus position for an infinitely distant subject and the in-focus position for the closest object that can be focused over the entire zoom area is generally approximately proportional to the square of the focal length. Known and smallest at wide-angle end. Therefore, a reference position always exists near an in-focus position of the second lens group at the wide-angle end for an immovable subject at an arbitrary distance within a subject distance range that can be focused in the entire zoom region.
[0016]
Preferably, in the above invention, the second lens group preferably has means for determining whether or not the subject used at the time of the flange back adjustment at the telephoto end is in focus. That is, when it is determined that focusing cannot be performed, it indicates that the subject exists outside the subject distance range in which focusing can be performed in the entire zoom area. When the above-described flange back adjustment is performed using this subject, the accuracy is deteriorated. Alternatively, in order to accurately perform flange-back adjustment on this subject, the method becomes complicated. That is, by determining whether or not focusing is possible, the above-described flange back adjustment can be performed with high accuracy.
[0017]
In a photographing system having a shallow depth of focus such as a bright F-number or a fine pixel of an image sensor, the focus position with respect to the infinity subject distance of the second group at the telephoto end and the closest focus position in the entire zoom range. Mt is the difference between the in-focus object at the wide-angle end and the difference between the in-focus object at the wide-angle end and the in-focus position with respect to the object distance L. When the minimum movement amount of the two lens groups is d and the movement amount required to change the back focus corresponding to the depth of focus by the second lens group is l, the division number m is defined by the following equation. With
[0018]
(Equation 6)

[0019]
The moving range Mt of the second lens group at the telephoto end is equally divided by the division number m and stored, and at the time of focusing determination at the telephoto end, which area the second lens group is located at is stored. It is preferable to have a means for correcting based on the information stored at the telephoto end after automatic focusing and storing it as a reference position. As a result, it is possible to realize simple arithmetic processing and perform more accurate flange back adjustment.
[0020]
In addition, it is preferable that the aperture be opened when the flange back is adjusted.
[0021]
As a result, the depth of focus becomes shallow, and the accuracy of automatic focusing is increased, so that highly accurate flange back adjustment can be performed.
[0022]
Also, it is preferable to have a member for instructing to perform the flange back adjustment.
[0023]
In the zoom lens having a zero lens group that can be manually focused on the object side with respect to the first lens group, the zero lens group is fixed at a predetermined position during the flange back adjustment. Good to do.
[0024]
As a result, compared to the above-described conventional flange back adjustment in which the focusing operation by the 0th lens group and the focusing operation by the second lens group at the wide-angle end are repeated several times at the telephoto end, However, it is simple, the burden on the photographer is small, and high-speed flange back adjustment can be performed.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 110 denotes a photographing system main body in which a lens is mounted on a camera main body, 101 denotes a photographing optical system, 102 denotes a fixed or manual movable lens group for focusing, 103 denotes a lens group for zooming, 104 Is a diaphragm, 105 is a focus group for automatic focusing, 106 is a glass block corresponding to a filter or a color separation prism, 107 is an image sensor such as a CCD for receiving a subject image formed by the photographing

optical system

101, 108, Reference numeral 109 denotes a CPU for controlling the photographing system and the lens, and a storage device for storing the positions of the lens groups on the optical axis. Reference numeral 111 denotes a member for instructing to perform the flange back adjustment. The position of the lens group 103 on the optical axis is determined over the entire zoom range by the cam method.
[0026]
The adjustment of the flange back in the photographing system 110 is performed in the following procedure. {Circle around (1)} An object having a clear contrast such as a Siemens star chart is fixedly installed at an arbitrary distance so as to face the photographing system 110. {Circle around (2)} The aperture 104 is opened, and when the lens group 102 is movable for manual focusing, it is fixed at a predetermined position. {Circle around (3)} The lens group 102 is arranged at the telephoto end to determine whether or not focusing is possible, and to store the position. (4) Next, the lens group 102 is arranged at the wide-angle end, and after automatic focusing, the position of the lens group 105 is corrected based on the information on the focusing position at the telephoto end stored in (3) and used as a reference. The flange back adjustment is completed by determining the position and storing the position.
[0027]
At this time, a series of operations of (2), (3) and (4) may be automatically performed by the member 111, or the (111) of (4) may be performed by the member 111 after the operations of (2) and (3). Only the work may be performed.
[0028]
An embodiment of the present invention will be described from an optical configuration of a zoom lens. In FIG. 3, in order from the object side, 1 is a first lens group for focusing, 2 is a second lens group movable at the time of zooming, and 3 is a lens for correcting movement of an imaging position at the time of zooming. The third lens group, 4 is a fixed fourth lens group, 5 is a fifth lens group for automatic focusing, 12 is a glass block such as a color separation prism, and 11 is a diaphragm. The first lens group 1, the fourth lens group 4, and the fifth lens group 5 are fixed during zooming. In addition, the focal length is adjusted by the fifth lens group 5 to adjust the flange back.
[0029]
Table 1 below corresponds to the zoom lens of FIG.
[0030]
[Table 1]

[0031]
FIG. 4 shows a zoom tracking curve for each subject at infinity and the closest distance. In the zoom lens shown in FIG. 3, the shortest distance at which focus can be achieved over the entire zoom range is 432 mm from the front surface of the zoom lens.
[0032]
FIG. 4 shows that the focus movement range is the smallest at the wide-angle end and the largest at the telephoto end. In other words, if the object distance can be focused at the telephoto end, it can be said that the object distance can be focused in the entire zoom area. When the closest object distance that can be focused over the entire zoom region is the close distance L, the present invention is effective for an object within the distance range between the zoom tracking curves of infinity and close distance L in FIG. However, for subject distances outside the above range, the accuracy of the flange back adjustment deteriorates. Therefore, it is preferable to determine whether or not to focus on a subject set at an arbitrary distance at the telephoto end, and to determine the accuracy of the flange back adjustment. Further, it is preferable to have a means for outputting or displaying a signal indicating that flange back adjustment is impossible when focusing is impossible.
[0033]
Conditional expression (1) indicates the need to correct the reference position stored in the flange back adjustment of the present invention. When this conditional expression (1) is satisfied, the focus position at the wide-angle end is corrected and used as the reference position, thereby enabling more accurate flange-back adjustment. Here, when the allowable confusion circle diameter is ε and the open F number at the wide-angle end is F, the depth of focus δ is approximately
δ = εF
Is represented by Further, assuming that the sensitivity of the fifth lens group 5 to the back focus is s, the movement amount l of the fifth lens group 5 required to shift the back focus by the depth of focus δ is:
(Equation 7)

Is represented by
[0034]
At the wide angle end, when the difference between the focus position with respect to the subject of the focusing position and a close distance L to an object at infinity of the fifth lens group 5 and M _W, _| M _W | Smaller than the l, object distance In some cases, the deviation of the reference position is recognized as blur on the screen, and a more accurate flange back adjustment is required. The limiting conditions that require correction of the reference position determined in the above invention are as follows:
(Equation 8)

Can be represented by
[0035]
The fifth lens group is driven by an actuator such as a stepping motor or a DC motor, and it is desirable that the minimum movement amount d is approximately 1/8 ≦ d ≦ l. Under the condition of d <l / 8, the moving speed for moving the entire driving range becomes too slow, which is not appropriate. Conversely, under the condition of δ <l, the image is recognized as blur on the screen, making the image unsightly.
In this embodiment, d = 1/2, and the division number m in the conditional expression (2) is
(Equation 9)

And The division number m is an integer obtained by rounding off the first digit of the decimal point.
[0036]
Here, Table 2 shows the relationship between each parameter in Table 1 and conditional expression (1).
[0037]
[Table 2]

[0038]
As can be seen from Table 2, in Table 1, simply storing the autofocus position at the wide-angle end as the reference position may cause the deviation from the true reference position to be recognized on the screen due to the subject distance for the above-described reason. .
[0039]
Next, a correction method will be described. According to (2.1) above, the moving range of the second lens group at the telephoto end is divided into ten. In addition, as for the movement amount of the second lens group from infinity to the object distance of 432 mm, ten areas are stored in increments of 1.36 mm from Mt = 13.6 mm. The correction amount for determining whether or not focusing is possible at the telephoto end and correcting the focus as a reference position is shown below. mt indicates the amount of movement of the lens at the telephoto end.
[0040]
[Table 3]

[0041]
As described above, by correcting the focus position at the wide-angle end and storing the corrected focus position as the reference position, more accurate flange-back adjustment can be performed. By setting d = l / 2 in the present embodiment, the accuracy of the flange back is as high as の of the depth of focus δ, that is, about 8 μm.
[0042]
Although the correction amount is determined based on the focus position at the telephoto end, the reference position may be determined based on the focus position at a predetermined zoom position. However, when the zoom is performed at a predetermined zoom position other than the telephoto end, the position on the optical axis of the lens group related to zooming at that zoom position must be accurately grasped. This is inefficient because, for example, means for pre-storing the positional relationship with the wide-angle end or the telephoto end is required.
[0043]
【The invention's effect】
As described above, according to the present invention, in a rear-focus type photographing optical system, an in-focus position of the rear focus lens group at the wide-angle end and an in-focus position at the telephoto end are set for a subject at an arbitrary distance. The reference position is corrected based on the stored information determined from the above, and is determined as the reference position, and the position is stored, so that the calculation can be simplified and the flange back adjustment can be performed at high speed.
[0044]
Further, by determining whether or not the subject can be focused at the telephoto end by the rear focus lens group, it is possible to perform more accurate flange-back adjustment.
[0045]
In addition, by setting the aperture to the open state at the time of the flange back adjustment, the depth of focus becomes shallow, and the accuracy of the automatic focusing is increased, so that the flange back can be adjusted with high accuracy.
[0046]
Further, the provision of the member for instructing to perform the above-mentioned flange-back adjustment enables a simple operation, less restrictions on the photographer, and a high-speed flange-back adjustment.
[0047]
Further, in a zoom lens configured to include a zero lens group capable of focusing on the object side with respect to the first lens group, by fixing the zero lens group at a predetermined position during the flange back adjustment. In addition, flange back adjustment in a zoom lens having both front and rear focus functions can be simplified.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an imaging system according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a photographing system using a front lens manual focus lens as a photographing optical system.
FIG. 3 is a diagram showing an optical configuration of a zoom lens according to the embodiment (Table 1) of the present invention.
FIG. 4 is a diagram showing a zoom tracking curve according to the embodiment (Table 1) of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 first lens group 2 second lens group 3 third lens group 4 fourth lens group 5 fifth lens group 11 aperture 12 glass block

Claims

In a zoom lens having at least a first lens group for zooming, an aperture for adjusting the amount of light on the image plane side of the first lens group, and a second lens group for focusing,
In the flange back adjustment for determining the reference position of the second lens group, for an immovable subject at an arbitrary distance that can be focused over the entire zoom range, whether or not to focus at the telephoto end and the position are determined. Judge and remember,

time,
The zoom lens according to claim 2, wherein after focusing at the wide-angle end, the focusing position is corrected based on the focusing position at the telephoto end and stored as a reference position.

Mt is the difference between the in-focus position of the second group at infinity at the telephoto end and the in-focus position of the closest object L that can be focused in the entire zoom range. The difference between the focus position and the focus position with respect to the subject distance L is Mw, the depth of focus of the imaging system is δ, the minimum amount of movement of the second lens group is d, and the back focus equivalent to the depth of focus by the second lens group. Assuming that the amount of movement required to change is 1, the number of divisions m is defined by the following equation,

The moving range Mt of the second lens group at the telephoto end is equally divided by the division number m and stored, and at the time of focusing determination at the telephoto end, which area the second lens group is located at is stored. 2. The zoom lens according to claim 1, wherein after focusing, a correction is made based on information stored at the telephoto end and stored as a reference position.

2. The zoom lens according to claim 1, wherein the aperture is opened when the flange back is adjusted.

The zoom lens according to claim 1, further comprising a member that instructs to perform the flange back adjustment.

In a zoom lens configured to include a zero lens group capable of focusing on the object side with respect to the first lens group, the zero lens group is fixed at a predetermined position during the flange back adjustment. The zoom lens according to claim 1, wherein:

An imaging system including a zoom lens having at least a first lens group for zooming, an aperture for adjusting the amount of light on the image plane side of the first lens group, and a second lens group for focusing. At
In the flange back adjustment for determining the reference position of the second lens group, for an immovable subject at an arbitrary distance that can be focused over the entire zoom range, whether or not to focus at the telephoto end and the position are determined. Judge and remember,

time,
An imaging system, wherein the second lens group is configured to correct a focus position based on a focus position at a telephoto end after focusing at a wide-angle end and store the corrected focus position as a reference position.

Mt is the difference between the in-focus position of the second group at infinity at the telephoto end and the in-focus position of the closest object L that can be focused in the entire zoom range. The difference between the focus position and the focus position with respect to the subject distance L is Mw, the depth of focus of the imaging system is δ, the minimum movement amount of the second lens group is d, and the second lens group corresponds to the depth of focus. Assuming that the amount of movement required to change the back focus is l, the division number m is defined by the following equation,

The moving range Mt of the second lens group at the telephoto end is equally divided by the division number m and stored, and at the time of focusing determination at the telephoto end, which area the second lens group is located at is stored. 7. The photographing system according to claim 6, wherein after focusing, a correction is made based on information stored at the telephoto end and stored as a reference position.

7. The photographing system according to claim 6, wherein the aperture is opened when the flange back is adjusted.

The photographing system according to claim 6, further comprising a member that instructs to perform the flange back adjustment.

In a zoom lens configured to include a zero lens group capable of focusing on the object side with respect to the first lens group, the zero lens group is fixed at a predetermined position during the flange back adjustment. The photographing system according to claim 6.