JP4109896B2 - Variable magnification optical system having anti-vibration function and imaging apparatus using the same - Google Patents

Variable magnification optical system having anti-vibration function and imaging apparatus using the same Download PDF

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Publication number
JP4109896B2
JP4109896B2 JP2002129531A JP2002129531A JP4109896B2 JP 4109896 B2 JP4109896 B2 JP 4109896B2 JP 2002129531 A JP2002129531 A JP 2002129531A JP 2002129531 A JP2002129531 A JP 2002129531A JP 4109896 B2 JP4109896 B2 JP 4109896B2
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lens group
lens
optical system
image
refractive power
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JP2003322795A (en
JP2003322795A5 (en
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浩 猿渡
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Canon Inc
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Canon Inc
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/64Imaging systems using optical elements for stabilisation of the lateral and angular position of the image
    • G02B27/646Imaging systems using optical elements for stabilisation of the lateral and angular position of the image compensating for small deviations, e.g. due to vibration or shake
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B15/00Optical objectives with means for varying the magnification
    • G02B15/14Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective
    • G02B15/144Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only
    • G02B15/1441Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only the first group being positive
    • G02B15/144113Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only the first group being positive arranged +-++

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Lenses (AREA)
  • Adjustment Of Camera Lenses (AREA)

Description

【0001】
【発明の属する技術分野】
本発明は防振機能を有した変倍光学系に関し、特に変倍光学系の一部のレンズ群を光軸と垂直方向に移動させることにより、該変倍光学系が振動(傾動)した時の撮影画像のぶれを光学的に補正して静止画像を得るようにし、撮影画像の安定化を図ったビデオカメラや電子スチルカメラ、そして3−CCD対応の電子カメラなどに好適な防振機能を有した変倍光学系に関するものである。
【0002】
【従来の技術】
進行中の車や航空機等移動物体上から撮影しようとすると、撮影系に振動が伝わり手振れとなり撮影画像にぶれが生じる。
【0003】
従来よりこのときの撮影画像のぶれを、撮影系のレンズ群の一部を平行偏心させることにより防止する機能を有した防振光学系が種々提案されている。
【0004】
例えば特開平1−116619号公報や特開平2−124521号公報では、加速度センサー等を利用して撮影系の振動を検出し、この時得られる信号に応じ、撮影系の一部のレンズ群を光軸と垂直方向に振動されることにより静止画像を得ている。
【0005】
また特開平7−128619号公報では、正、負、正、正の4群構成の変倍光学系の第3レンズ群を正、負の二つのレンズ群で構成し、正のレンズ群を振動することにより防振を行っている。
【0006】
特開平7−199124号公報では、正、負、正、正の4群構成の変倍光学系の第3レンズ群全体を振動させて防振を行っている。
【0007】
特開平11−237550号広報では、正、負、正、正の4群構成の変倍光学系の第3レンズ群の一部を振動させることにより、3−CCD対応の光学系の小型化と高画質化とを同時に実現させている。
【0008】
いずれの例においても、充分な絞り前後間隔を確保した上で、全長の短縮と高性能化が達成されているとは、言い難い。
【0009】
【発明が解決しようとする課題】
一般に撮影系の一部のレンズを、光軸に対して垂直方向に平行偏心させて防振を行う光学系においては、防振のために特別に余分な光学系を必要としないという利点はあるが、移動させるレンズのための空間を必要とし、また防振時における偏心収差の発生量が多くなってくるという問題点があった。
【0010】
また、近年民生用ビデオカメラにおいても高画質化のために、3−CCD方式が一部のカメラでは採用されている。3−CCD対応の正負正正の4群構成の変倍光学系において、変倍光学系の一部を構成する比較的小型軽量のレンズ群を光軸と垂直方向に移動させて、該変倍光学系が振動(傾動)したときの画像のぶれを補正するように構成することにより、装置全体の小型化、機構上の簡素化及び駆動手段の負荷の軽減化を図りつつ、該レンズ群を偏心させた時の偏心収差を良好に補正すると共に、偏心レンズ群の防振のための敏感度を大きくして光学系全体の小型化を図った防振機能を有した変倍光学系の提供が可能である。
【0011】
一方、CCDの高密度化とともに求められる解像周波数が高くなると、特に絞り径が小さくなる状態、或いは真円形からかけ離れた絞り開口状態における回折による画像劣化が無視できなくなる。
【0012】
これを解決する方法として、虹彩絞りの採用やNDフィルタの光路内挿入により、回折による影響を最小限に抑制する方法が考えられるが、このときの絞り機構の複雑化、ND挿入に要する軸上間隔の増大により、光学系が大型化しやすくなる欠点がある。
【0013】
本発明は、変倍光学系の一部を構成する比較的小型軽量のレンズ群を光軸と垂直方向に移動させて、該変倍光学系が振動したときの画像のぶれを補正する光学系において、高画質化を実現させるための機構上の要件を満足させた上で、適切な屈折力配置により光学系全体の全長短縮を図った防振機能を有した変倍光学系の提供を目的とする。
【0014】
【課題を解決するための手段】
本発明の防振機能を有した変倍光学系は、物体側より順に変倍及び合焦の際に固定の正の屈折力の第1レンズ群、変倍機能を有する負の屈折力の第2レンズ群、正の屈折力の第3レンズ群、変倍により変動する像面を補正すると共に合焦機能を有する正の屈折力の第4レンズ群を有した変倍光学系であって、該第3レンズ群は少なくとも負の屈折力を持つ第31レンズ群と正の屈折力を持つ第32レンズ群を有し、該第32レンズ群を光軸と垂直方向に移動させて該変倍光学系が振動した時の撮影画像のぶれを補正し該第3レンズ群の最も像側のレンズの物体側曲率半径をr3a、像側曲率半径をr3bとしたとき、
0<(r3a+r3b)/(r3a−r3b)<1.0
なる条件式を満足することを特徴としている。
【0015】
特に前記第3レンズ群は物体側から順に前記第31レンズ群、第32レンズ群の順に配置していることを特徴としている。
【0016】
または前記構成において、第32レンズ群は物体側から順に、正レンズ、負レンズ、正レンズにより構成されている事を特徴としている。
【0017】
または前記構成において、第3レンズ群と第4レンズ群の広角端における光軸上間隔をD34、広角端でのズーム全系の焦点距離をfwとするとき、
1.0 < D34/fw < 1.5
なる条件を満足することを特徴としている。
【0018】
または、前記構成の変倍光学系と、その像面側に色分解光学系と電気的撮像素子を配置することで、撮像装置を形成することを特徴としている。
【0019】
【発明の実施の形態】
次に、本発明の実施例を用いて具体的に説明する。
【0020】
図1〜図3は本発明の防振機能を有した変倍光学系の、後述する数値実施例1〜3のレンズ断面図、図4〜図6は数値実施例1〜3の諸収差図を各々示す。各収差図においてAは広角端における収差図、Bは中間のズーム位置における収差図、Cは望遠端における諸収差図を示す。
【0021】
図1に本発明の数値実施例1の光学系の断面図を示す。図中L1は正の屈折力の第1レンズ群、L2は負の屈折力の第2レンズ群、L3は正の屈折力の第3レンズ群、L4は正の屈折力の第4レンズ群である。SPは開口絞りであり、第3レンズ群L3の直前に配置している。
【0022】
GBは色分解プリズムやCCDのフェースプレートやローパスフィルター等のガラスブロックである。
【0023】
本実施例においては、第3レンズ群L3は負の屈折力の第31レンズ群L31と正の屈折力の第32レンズ群L32より構成されている。
【0024】
撮影時には、第32レンズ群L32を光軸に垂直方向に移動させることにより、光学系全体が振動(傾動)したときの撮影画像のぶれを補正している。
【0025】
本実施例では広角端から望遠端への変倍に際して矢印のように第2レンズ群を像面側へ移動させると共に、変倍に伴う像面変動を第4レンズ群を移動させて補正している。
【0026】
また、第4レンズ群を光軸上移動させてフォーカシングを行うリヤーフォーカス式を採用している。同図に示す第4レンズ群の実線の曲線4aと点線の曲線4bは各々無限遠物体と近距離物体にフォーカスしているときの広角端から望遠端への変倍に伴う際の像面変動を補正するための移動軌跡を示している。尚、第1レンズ群と第3レンズ群は変倍及びフォーカスの際固定である。
【0027】
本実施例においては第4レンズ群を移動させて変倍に伴う像面変動の補正を行うと共に第4レンズ群を移動させてフォーカスを行うようにしている。特に同図の曲線4a、4bに示すように広角端から望遠端への変倍に際して物体側へ凸状の軌跡を有するように移動させている。
【0028】
これにより第3レンズ群と第4レンズ群との空間の有効利用を図りレンズ全長の短縮化を効果的に達成している。
【0029】
本実施例におけるズームレンズは、第1レンズ群と第2レンズ群の合成系で形成した虚像を、第3レンズ群と第4レンズ群で感光面上に結像するズーム方式をとっている。
【0030】
本実施例では従来の所謂4群ズームレンズにおいて第1群を繰り出してフォーカスを行う場合に比べて、前述のようなリアフォーカス方式を採ることにより、第1レンズ群のレンズ有効径の増大化を効果的に防止している。
【0031】
そして開口絞りを第3レンズ群の直前、または第3レンズ群中または第3レンズ群と第4レンズ群の間に配置することにより、可動レンズ群による収差変動を少なくし、
開口レンズ群の感覚を短くすることにより前玉レンズ径の縮小化を容易に達成している。
【0032】
本発明の数値実施例においては第3レンズ群L3を第31レンズ群L31と第32レンズ群L32より構成し、このうち第32レンズ群L32を防振のために光軸と垂直方向に移動させて光学系全体が振動したときの像ぶれを補正している。これにより可変頂角プリズム等の光学部材や防振のためのレンズ群を新たに付加することなく防振を行っている。
【0033】
今、光軸をθ°補正するために必要なシフトレンズ群の移動量をΔ、光学系全体の焦点距離をf,シフト群Y2の偏心敏感度をTSとするとΔは以下の式で与えられる。
【0034】
Δ=f・tan(θ)/TS
上式より判る通り、シフト群の偏心敏感度TSが小さすぎるとΔは大きな値となり防振に必要なシフト群の移動量が大きくなり過ぎてレンズ径が大きくなってしまう。
【0035】
特に3−CCD対応のビデオカメラ用レンズでは像面側に色分解のためのプリズムを配置するための空間が必要であるため通常の単板式のレンズよりもバックフォーカスが必要となる。このため第3レンズ群の屈折力が第4レンズ群に対して弱くなり、第3レンズ群の光軸に垂直方向の敏感度が小さくなる。従って第3レンズ群全体を光軸方向に対して垂直方向に移動させて防振を行おうとすると第3レンズ群の移動量が大きくなり過ぎてしまう。
【0036】
そこで第3レンズ群を負の屈折力の第31レンズ群と正の屈折力の第32レンズ群に分割することにより第32レンズ群の屈折力を大きくし、その偏心敏感度TSも大きくすることで3−CCD対応でありながらコンパクトな防振光学系が達成できる。
【0037】
本発明のズームタイプにおいては、第2レンズ群と第3レンズ群の間隔が最小となるのは、望遠端においてであり、この際に第3レンズ群の物体側に配置された絞り機構と第2レンズ群とが配置上干渉しないことが重要である。特に画質向上を目的とした撮影系では、多数枚の絞り羽を有する虹彩絞りを採用することで、ボケ味の改善が可能となる。
【0038】
また、光量調整をするためのNDフィルタの光路内への出し入れをするための機構などを追加するために、絞りを挟んだ第2レンズ群と第3レンズ群との間隔を従来以上に広げている。
【0039】
本発明において十分な絞り前後間隔を確保した上で、レンズ全長の短縮するためには、第3レンズ群と第4レンズ群との間隔を削減する必要がある。
【0040】
このとき、高い光学性能を両立するためには、第3レンズ群の最も像側のレンズの物体側曲率半径をr3a、像側曲率半径をr3bとしたとき、
0<(r3a+r3b)/(r3a−r3b)<1.0…(1)
なる条件式を満足することが求められる。
【0041】
条件式(1)は第3レンズ群の最も像側のレンズ形状に関するものである。
【0042】
物体側の面の曲率半径r3aに対し、像側の面の曲率半径r3bが小さくした上で、全長を短縮するために第3レンズ群と第4レンズ群の間隔を短縮すると、周辺像面のコマ収差の悪化する。
【0043】
逆にr3aがr3bに対して小さくなると、第3レンズ群と第4レンズ群の間隔短縮と、充分なバックフォーカスの確保を両立することが、困難になる。
【0044】
また同時に、レンズ全長の短縮のためには、第3レンズ群と第4レンズ群の広角端における光軸上間隔をD34、広角端でのズーム全系の焦点距離をfwとするとき、
1.0 < D34/fw < 1.5 …(2)
なる条件を満足することが求められる。
【0045】
条件式(2)は第3レンズ群と第4レンズ群の間隔に関するものである。条件式(2)の下限を超えて第3レンズ群と第4レンズ群が近接した場合は、ズームの中間状態から、望遠端にかけて、近距離物体に対するフォーカスストロークを充分に確保できなくなる。逆に条件式(2)の上限を超えると、レンズ全長の短縮と言う、所期の目的を得ることが困難になる。
【0046】
本実施例では第3レンズ群を物体側から順に固定の第31レンズ群、防振のために光軸に垂直方向にシフトする第32レンズ群で構成し、第31レンズ群を両凹レンズと正レンズ、第32レンズ群を、物体側に強い凸面を向けた正メニスカスレンズ、像面側に強い凹面を向けた負メニスカスレンズと両凸レンズで構成している。
【0047】
そして第31レンズ群と第32レンズ群の各々少なくとも1面に非球面レンズを設けることにより各レンズ群内で発生する諸収差を小さくし、防振時の光学性能の劣化を抑制している。
【0048】
本実施例では第31レンズ群の最も像面側、第32レンズ群の最も物体側に非球面を導入し、各群内で発生する球面収差、コマ収差を小さくすることにより、防振時に発生する偏心収差特に偏心コマ収差を良好に補正している。
【0049】
本発明における非球面の位置は、各群の異なる面でもよい。
【0050】
また偏心の倍率色収差や偏心による像面湾曲を補正するためには、シフト群単独で出来るだけ色収差が補正されてペッツヴァール和が小さくなっていることが望ましい。従ってシフトレンズ群(第32レンズ群)には少なくとも1枚の負レンズ群を含むように構成するのが、色収差の補正やペッツヴァール和を小さくするのに効果的である。
【0051】
またこの時、全系の色収差を良好に保つためには、第32レンズ群以外に第3レンズ群内に少なくとも1枚の正レンズを有するようにするのが良い。
【0052】
また変倍全域に渡って十分な倍率色収差の補正を行うには第2レンズ群は物体側から順に像面側に強い凹面を向けた負メニスカスレンズ、両凹レンズ、正レンズ、負レンズで構成するのが良い。
【0053】
また3−CCD対応でバックフォーカスを伸ばしたとき第4レンズ群の屈折力が強くなると共に、軸上光線が第4レンズ群を通る高さが高くなって球面収差が発生し易くなるので、第4レンズ群は少なくとも1枚の負レンズと2枚の正レンズで構成し、少なくとも1面の非球面を有するようにするのが望ましい。
【0054】
次に本発明の数値実施例を示す。数値実施例においてRiは物体側より順に第i番目のレンズ面の曲率半径、
Diは物体側より順に第i番目のレンズ厚及び空気間隔、
Niとνiは各々物体側より順に第i番目のレンズのガラスの屈折率とアッベ数である。又前述の各条件式と数値実施例の関係を表―1に示す。
【0055】
非球面形状は光軸方向にX軸、光軸と垂直方向にH軸、光の進行方向を正としRを金軸曲率半径、A,B,C,D、Eを各々非球面係数としたとき
【0056】
【数1】
【0057】
なる式で表している。
また例えば「e−0X」の表示は「10−X」を意味する。
【0058】
【外1】
【0059】
【外2】
【0060】
【外3】
【0061】
【表1】
【0062】
【発明の効果】
本発明によれば以上のように、絞り前後間隔を十分に取った光学系において、変倍光学系の一部を構成する比較的小型軽量のレンズ群を光軸と垂直方向に移動させて、該変倍光学系が振動(傾動)したときの画像のぶれを補正するように構成する際のレンズ構成、及び形状を適切にすることで、装置全長の短縮、機構上の簡素化及び駆動手段の負荷の軽減を図りつつ該レンズ群の偏心させたときの偏心収差発生量を少なく抑え、偏心収差を良好に補正した防振機能を有した変倍光学系を達成することが出来る。
【図面の簡単な説明】
【図1】 本発明の数値実施例1の広角端のレンズ断面図
【図2】 本発明の数値実施例2の広角端のレンズ断面図
【図3】 本発明の数値実施例3の広角端のレンズ断面図
【図4A】 本発明の数値実施例1の諸収差図
【図4B】 本発明の数値実施例1の諸収差図
【図4C】 本発明の数値実施例1の諸収差図
【図5A】 本発明の数値実施例2の諸収差図
【図5B】 本発明の数値実施例2の諸収差図
【図5C】 本発明の数値実施例2の諸収差図
【図6A】 本発明の数値実施例3の諸収差図
【図6B】 本発明の数値実施例3の諸収差図
【図6C】 本発明の数値実施例3の諸収差図
【符号の説明】
L1 第1レンズ群
L2 第2レンズ群
L3 第3レンズ群
L4 第4レンズ群
L31 第31レンズ群
L32 第32レンズ群
d d線
g g線
ΔM メリディオナル像面
ΔS サジタル像面
収差図において(A)は広角端、(B)はズーム中間、
(C)は望遠端である。
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable magnification optical system having an anti-vibration function, and in particular, when the variable magnification optical system vibrates (tilts) by moving a part of the lens group of the variable magnification optical system in a direction perpendicular to the optical axis. The image stabilization function is suitable for video cameras, electronic still cameras, and 3-CCD electronic cameras that stabilize the captured images by optically correcting the blur of the captured images. The present invention relates to a variable magnification optical system.
[0002]
[Prior art]
If an attempt is made to shoot from a moving object such as an ongoing car or aircraft, vibrations are transmitted to the photographic system, causing camera shake and blurring of the captured image.
[0003]
Conventionally, various anti-vibration optical systems have been proposed which have a function of preventing a blur of a photographed image at this time by decentering a part of a lens group of the photographing system in parallel.
[0004]
For example, in Japanese Patent Application Laid-Open Nos. 1-116619 and 2-124521, vibration of the photographing system is detected using an acceleration sensor or the like, and a part of the lens group of the photographing system is replaced according to a signal obtained at this time. A still image is obtained by vibrating in the direction perpendicular to the optical axis.
[0005]
In Japanese Patent Laid-Open No. 7-128619, the third lens group of the variable power optical system having a positive, negative, positive, and positive four-group configuration is configured by two positive and negative lens groups, and the positive lens group is vibrated. To prevent vibration.
[0006]
In Japanese Patent Application Laid-Open No. 7-199124, the entire third lens group of the variable magnification optical system having a positive, negative, positive, and positive four-group configuration is vibrated to prevent vibration.
[0007]
In JP-A-11-237550, a part of the third lens group of the variable power optical system having a positive, negative, positive, and positive four-group configuration is vibrated, thereby reducing the size of the 3-CCD compatible optical system. High image quality is achieved at the same time.
[0008]
In any of the examples, it is difficult to say that the shortening of the overall length and the enhancement of the performance are achieved while ensuring a sufficient distance between the front and rear of the diaphragm.
[0009]
[Problems to be solved by the invention]
In general, in an optical system that performs image stabilization by decentering a part of a lens of a photographing system in a direction perpendicular to the optical axis, there is an advantage that no extra optical system is required for image stabilization. However, there is a problem that a space for the lens to be moved is required, and the amount of decentration aberrations generated during vibration isolation increases.
[0010]
In recent years, the 3-CCD system has been adopted in some cameras in order to improve image quality in consumer video cameras. In a variable power optical system having a 4-group configuration of positive, negative, positive and positive for 3-CCD, a relatively small and light lens group constituting a part of the variable power optical system is moved in a direction perpendicular to the optical axis, and the power is changed. By configuring the optical system to compensate for image blurring when the optical system vibrates (tilts), the lens group can be formed while reducing the overall size of the apparatus, simplifying the mechanism, and reducing the load on the driving means. Providing a variable magnification optical system with anti-vibration function that corrects decentration aberrations when decentered and increases sensitivity for anti-vibration of the decentered lens group to reduce the size of the entire optical system Is possible.
[0011]
On the other hand, when the resolution frequency required along with the increase in the density of the CCD is increased, image deterioration due to diffraction cannot be ignored particularly in a state where the aperture diameter is reduced or in an aperture opening state far from a true circle.
[0012]
As a method for solving this, there is a method of minimizing the influence of diffraction by adopting an iris diaphragm or inserting an ND filter in the optical path, but the diaphragm mechanism at this time is complicated and the axis required for ND insertion is on the axis. There is a drawback that the optical system is easily increased in size due to the increase in the interval.
[0013]
The present invention relates to an optical system that corrects image blurring when the zoom optical system vibrates by moving a relatively small and light lens group that forms part of the zoom optical system in a direction perpendicular to the optical axis. The objective is to provide a variable magnification optical system with an anti-vibration function that shortens the overall length of the entire optical system by satisfying the mechanical requirements for achieving high image quality in an appropriate refractive power arrangement. And
[0014]
[Means for Solving the Problems]
The variable power optical system having the image stabilization function according to the present invention includes a first lens unit having a fixed positive refractive power and a negative refractive power having a variable power function. A variable power optical system having two lens groups, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power that corrects an image plane fluctuating due to zooming and has a focusing function, The third lens group includes at least a thirty-first lens group having a negative refractive power and a thirty-second lens group having a positive refractive power, and the zoom lens is moved by moving the thirty-second lens group in a direction perpendicular to the optical axis. When the shake of the captured image when the optical system vibrates is corrected and the object-side radius of curvature of the third lens group closest to the image side is r3a and the image-side radius of curvature is r3b,
0 <(r3a + r3b) / (r3a-r3b) <1.0
It satisfies the following conditional expression.
[0015]
In particular, the third lens group is arranged in the order of the 31st lens group and the 32nd lens group in order from the object side.
[0016]
Alternatively, in the above-described configuration, the thirty-second lens group includes a positive lens, a negative lens, and a positive lens in order from the object side.
[0017]
Alternatively, in the above configuration, when the distance on the optical axis at the wide angle end of the third lens group and the fourth lens group is D34, and the focal length of the entire zoom system at the wide angle end is fw,
1.0 <D34 / fw <1.5
It is characterized by satisfying the following conditions.
[0018]
Alternatively, an image pickup apparatus is formed by arranging the variable magnification optical system having the above-described configuration and the color separation optical system and the electric image pickup element on the image plane side.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Next, it demonstrates concretely using the Example of this invention.
[0020]
FIGS. 1 to 3 are sectional views of lenses of numerical examples 1 to 3 to be described later, and FIGS. 4 to 6 are graphs showing various aberrations of numerical examples 1 to 3. FIG. Are shown respectively. In each aberration diagram, A is an aberration diagram at the wide-angle end, B is an aberration diagram at an intermediate zoom position, and C is various aberration diagrams at the telephoto end.
[0021]
FIG. 1 shows a cross-sectional view of an optical system according to Numerical Example 1 of the present invention. In the figure, L1 is a first lens group having a positive refractive power, L2 is a second lens group having a negative refractive power, L3 is a third lens group having a positive refractive power, and L4 is a fourth lens group having a positive refractive power. is there. SP is an aperture stop, which is disposed immediately before the third lens unit L3.
[0022]
GB denotes a glass block such as a color separation prism, a CCD face plate, or a low-pass filter.
[0023]
In the present embodiment, the third lens unit L3 includes a 31st lens unit L31 having a negative refractive power and a 32nd lens unit L32 having a positive refractive power.
[0024]
During shooting, the thirty-second lens unit L32 is moved in the direction perpendicular to the optical axis to correct blurring of the shot image when the entire optical system vibrates (tilts).
[0025]
In this embodiment, when zooming from the wide angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by an arrow, and the image plane variation accompanying zooming is corrected by moving the fourth lens unit. Yes.
[0026]
Further, a rear focus type is employed in which the fourth lens group is moved on the optical axis to perform focusing. The solid line curve 4a and the dotted line curve 4b of the fourth lens group shown in the figure are image plane fluctuations accompanying zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a short-distance object, respectively. The movement locus | trajectory for correct | amending is shown. The first lens group and the third lens group are fixed during zooming and focusing.
[0027]
In the present embodiment, the fourth lens group is moved to correct image plane fluctuations accompanying zooming, and the fourth lens group is moved to perform focusing. In particular, as shown by the curves 4a and 4b in the figure, the zoom lens is moved so as to have a convex locus toward the object side upon zooming from the wide-angle end to the telephoto end.
[0028]
As a result, the space between the third lens group and the fourth lens group is effectively used to effectively shorten the entire lens length.
[0029]
The zoom lens according to the present embodiment employs a zoom system in which a virtual image formed by the combined system of the first lens group and the second lens group is formed on the photosensitive surface by the third lens group and the fourth lens group.
[0030]
In the present embodiment, the effective lens diameter of the first lens group is increased by adopting the rear focus method as described above, compared to the case where the first group is extended and focused in a conventional so-called four-group zoom lens. Effectively prevent.
[0031]
Then, by arranging the aperture stop immediately before the third lens group, or in the third lens group or between the third lens group and the fourth lens group, variation in aberration due to the movable lens group is reduced,
By shortening the sensation of the aperture lens group, the front lens diameter can be easily reduced.
[0032]
In the numerical example of the present invention, the third lens unit L3 includes a thirty-first lens unit L31 and a thirty-second lens unit L32. Among these, the thirty-second lens unit L32 is moved in a direction perpendicular to the optical axis for image stabilization. This corrects the image blur when the entire optical system vibrates. As a result, image stabilization is performed without adding an optical member such as a variable apex angle prism or a lens group for image stabilization.
[0033]
Now, Δ is given by the following equation, where Δ is the amount of movement of the shift lens group necessary to correct the optical axis by θ °, f is the focal length of the entire optical system, and TS is the decentering sensitivity of the shift group Y2. .
[0034]
Δ = f · tan (θ) / TS
As can be seen from the above equation, if the eccentricity sensitivity TS of the shift group is too small, Δ becomes a large value, and the shift group necessary for image stabilization becomes too large and the lens diameter becomes large.
[0035]
In particular, a 3-CCD video camera lens requires a space for disposing a prism for color separation on the image plane side, and therefore requires a back focus as compared with a normal single-plate lens. For this reason, the refractive power of the third lens group is weaker than that of the fourth lens group, and the sensitivity in the direction perpendicular to the optical axis of the third lens group is reduced. Therefore, if the entire third lens group is moved in the direction perpendicular to the optical axis direction to perform image stabilization, the amount of movement of the third lens group becomes too large.
[0036]
Therefore, by dividing the third lens group into a 31st lens group having a negative refractive power and a 32nd lens group having a positive refractive power, the refractive power of the 32nd lens group is increased, and the decentering sensitivity TS is also increased. Thus, a compact anti-vibration optical system can be achieved while being compatible with 3-CCD.
[0037]
In the zoom type of the present invention, the distance between the second lens group and the third lens group is the minimum at the telephoto end. At this time, the aperture mechanism disposed on the object side of the third lens group and the second lens group It is important that the two lens groups do not interfere with each other in arrangement. In particular, in an imaging system aimed at improving the image quality, it is possible to improve the blur by adopting an iris diaphragm having a large number of diaphragm blades.
[0038]
In addition, in order to add a mechanism for moving the ND filter in and out of the optical path for adjusting the amount of light, the distance between the second lens group and the third lens group with the stop interposed therebetween is increased more than before. Yes.
[0039]
In the present invention, it is necessary to reduce the distance between the third lens group and the fourth lens group in order to shorten the total lens length while securing a sufficient front-rear aperture distance.
[0040]
At this time, in order to achieve both high optical performance, when the object-side radius of curvature of the third lens group closest to the image side is r3a and the image-side radius of curvature is r3b,
0 <(r3a + r3b) / (r3a−r3b) <1.0 (1)
It is required to satisfy the following conditional expression.
[0041]
Conditional expression (1) relates to the most image-side lens shape of the third lens group.
[0042]
When the radius of curvature r3b of the image side surface is made smaller than the radius of curvature r3a of the object side surface and the distance between the third lens group and the fourth lens group is shortened in order to shorten the total length, The coma becomes worse.
[0043]
On the other hand, when r3a is smaller than r3b, it becomes difficult to achieve both a reduction in the distance between the third lens group and the fourth lens group and a sufficient back focus.
[0044]
At the same time, in order to shorten the total lens length, when the distance on the optical axis at the wide-angle end of the third lens group and the fourth lens group is D34, and the focal length of the entire zoom system at the wide-angle end is fw,
1.0 <D34 / fw <1.5 (2)
It is required to satisfy the following conditions.
[0045]
Conditional expression (2) relates to the distance between the third lens group and the fourth lens group. When the third lens group and the fourth lens group are close to each other exceeding the lower limit of the conditional expression (2), it is impossible to secure a sufficient focus stroke for a short-distance object from the intermediate zoom state to the telephoto end. Conversely, if the upper limit of conditional expression (2) is exceeded, it will be difficult to achieve the intended purpose of shortening the overall lens length.
[0046]
In this embodiment, the third lens group is composed of a 31st lens group that is fixed in order from the object side, and a 32nd lens group that is shifted in the direction perpendicular to the optical axis for image stabilization. The lens and the 32nd lens group are composed of a positive meniscus lens having a strong convex surface facing the object side, a negative meniscus lens having a strong concave surface facing the image surface side, and a biconvex lens.
[0047]
Further, by providing an aspheric lens on at least one surface of each of the 31st lens group and the 32nd lens group, various aberrations occurring in each lens group are reduced, and deterioration of optical performance during image stabilization is suppressed.
[0048]
In this embodiment, an aspherical surface is introduced closest to the image surface side of the 31st lens group and closest to the object side of the 32nd lens group, and the spherical aberration and coma aberration generated in each group are reduced, thereby occurring during image stabilization. This corrects decentration aberrations, especially decentration coma, well.
[0049]
The position of the aspheric surface in the present invention may be a different surface of each group.
[0050]
In order to correct the decentered lateral chromatic aberration and the curvature of field due to the eccentricity, it is desirable that the shift group alone corrects the chromatic aberration as much as possible to reduce the Petzval sum. Therefore, it is effective for correcting the chromatic aberration and reducing the Petzval sum to include at least one negative lens group in the shift lens group (the 32nd lens group).
[0051]
At this time, in order to keep the chromatic aberration of the entire system favorable, it is preferable to have at least one positive lens in the third lens group in addition to the thirty-second lens group.
[0052]
In addition, in order to sufficiently correct lateral chromatic aberration over the entire zooming range, the second lens unit is composed of a negative meniscus lens, a biconcave lens, a positive lens, and a negative lens with a strong concave surface directed from the object side toward the image surface side. Is good.
[0053]
In addition, when the back focus is extended for 3-CCD, the refractive power of the fourth lens group becomes strong, and the height of the axial ray passing through the fourth lens group becomes high and spherical aberration is likely to occur. It is desirable that the four lens group is composed of at least one negative lens and two positive lenses and has at least one aspherical surface.
[0054]
Next, numerical examples of the present invention will be shown. In numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side,
Di is the i-th lens thickness and air spacing in order from the object side,
Ni and νi are respectively the refractive index and Abbe number of the glass of the i-th lens in order from the object side. Table 1 shows the relationship between the above conditional expressions and numerical examples.
[0055]
The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the radius of curvature of the metal axis, and A, B, C, D, and E are aspherical coefficients, respectively. When [0056]
[Expression 1]
[0057]
It is expressed by the following formula.
For example, the display of “e-0X” means “10 −X ”.
[0058]
[Outside 1]
[0059]
[Outside 2]
[0060]
[Outside 3]
[0061]
[Table 1]
[0062]
【The invention's effect】
According to the present invention, as described above, in an optical system with a sufficient distance between the front and rear of the stop, a relatively small and lightweight lens group constituting a part of the variable magnification optical system is moved in a direction perpendicular to the optical axis, By optimizing the lens configuration and shape when correcting the image blurring when the variable magnification optical system vibrates (tilts), the overall length of the apparatus is shortened, the mechanism is simplified, and the driving means A variable power optical system having an anti-vibration function in which the amount of decentration aberration when the lens group is decentered can be reduced and the decentering aberration can be corrected well.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view at the wide-angle end of Numerical Example 1 of the present invention. FIG. 2 is a lens cross-sectional view at the wide-angle end of Numerical Example 2 of the present invention. FIG. 4A is an aberration diagram of Numerical Example 1 of the present invention. FIG. 4B is an aberration diagram of Numerical Example 1 of the present invention. FIG. 4C is an aberration diagram of Numerical Example 1 of the present invention. FIG. 5A is an aberration diagram of Numerical Example 2 of the present invention. FIG. 5B is an aberration diagram of Numerical Example 2 of the present invention. FIG. 5C is an aberration diagram of Numerical Example 2 of the present invention. Aberration diagram of Numerical Example 3 of the present invention [FIG. 6B] Aberration diagram of Numerical Example 3 of the present invention [FIG. 6C] Aberration diagram of Numerical Example 3 of the present invention
L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L31 31st lens group L32 32nd lens group d d line g g line ΔM Meridional image surface ΔS In the sagittal image surface aberration diagram (A) Is the wide-angle end, (B) is the middle zoom,
(C) is the telephoto end.

Claims (5)

物体側より順に変倍及び合焦の際に固定の正の屈折力の第1レンズ群、変倍機能を有する負の屈折力の第2レンズ群、正の屈折力の第3レンズ群、変倍により変動する像面を補正すると共に合焦機能を有する正の屈折力の第4レンズ群を有した変倍光学系であって、該第3レンズ群は少なくとも負の屈折力を持つ第31レンズ群と、少なくとも2枚の正レンズを有し正の屈折力を持つ第32レンズ群を有し、該第32レンズ群を光軸と垂直方向に移動させて該変倍光学系が振動した時の撮影画像のぶれを補正し、該第3レンズ群の最も像側のレンズの物体側曲率半径をr3a、像側曲率半径をr3bとしたとき、
0<(r3a+r3b)/(r3a−r3b)<1.0
なる条件式を満足することを特徴とする防振機能を有した変倍光学系。
A first lens unit having a positive refractive power, a second lens unit having a negative refractive power having a variable power function, a third lens group having a positive refractive power, A variable power optical system having a fourth lens unit having a positive refractive power that corrects an image plane fluctuating due to magnification and has a focusing function, wherein the third lens unit has at least a negative refractive power. A lens group and a thirty-second lens group having at least two positive lenses and having a positive refractive power, and the variable-power optical system vibrates by moving the thirty-second lens group in a direction perpendicular to the optical axis. When the blur of the photographed image at the time is corrected, and the object-side radius of curvature of the third lens group closest to the image side is r3a and the image-side radius of curvature is r3b,
0 <(r3a + r3b) / (r3a-r3b) <1.0
A variable magnification optical system having a vibration isolating function characterized by satisfying the following conditional expression:
前記第3レンズ群は物体側より順に負の屈折力の第31レンズ群、正の屈折力の第32レンズ群で構成されている事を特徴とする請求項1記載の防振機能を有した変倍光学系。  2. The anti-vibration function according to claim 1, wherein the third lens group includes a 31st lens group having a negative refractive power and a 32nd lens group having a positive refractive power in order from the object side. Variable magnification optical system. 前記第32レンズ群は物体側から順に、正レンズ、負レンズ、正レンズにより成ることを特徴とする請求項2記載の防振機能を有した変倍光学系。  3. A variable magnification optical system having an image stabilization function according to claim 2, wherein the thirty-second lens group includes a positive lens, a negative lens, and a positive lens in order from the object side. 前記第3レンズ群と第4レンズ群の広角端における光軸上間隔をD34、広角端でのズーム全系の焦点距離をfwとするとき、
1.0 < D34/fw < 1.5
なる条件を満足することを特徴とする請求項1から3記載の防振機能を有した変倍光学系。
When the distance on the optical axis at the wide-angle end of the third lens group and the fourth lens group is D34, and the focal length of the entire zoom system at the wide-angle end is fw,
1.0 <D34 / fw <1.5
4. The variable magnification optical system having a vibration isolating function according to claim 1, wherein the following condition is satisfied.
請求項1から4のいずれか1項記載の防振機能を有した変倍光学系と、その像面側に色分解光学系と電気的撮像素子を有していることを特徴とする撮像装置。  5. An image pickup apparatus comprising: a variable magnification optical system having an image stabilization function according to claim 1; and a color separation optical system and an electric image pickup element on the image plane side. .
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JP4677210B2 (en) * 2004-08-05 2011-04-27 キヤノン株式会社 Zoom lens and image pickup apparatus using the same
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