JP3582872B2 - Zoom lens and video camera using the same - Google Patents

Description

【００２７】
（表１）において、左から１列目の数は図１に示したＧ１からＧ６までのレンズ群を示す数であり、２列目の数ｊは、同図に示した曲率半径ｒｊ（ｊ＝１から２１）に対応する各面の番号である。また、続く列に示すｒは曲率半径、ｄは面間隔、ｎは各レンズのスペクトルのｄ線に対する屈折率、νは各レンズのｄ線に対するアッベ数である。非球面形状は、次の（数２）で定義され、各非球面に関する円錐定数及び各非球面係数の値を（表２）に示す。なお、（表２）において、左から１列目の数は、（表１）の面番号に対応する非球面の面番号である。
【００２８】
【数２】

【００２９】
【表２】

【００３０】
次に、変倍時における第２レンズ群Ｇ２の移動と、それに伴う第４レンズ群Ｇ４の移動により変化する面間隔について説明する。図１において、各レンズ群の下部に示した曲線は、広角端から望遠端へ変倍するときの各レンズ群の軌跡を表す。第１及び第３レンズ群Ｇ１及びＧ３は固定され、第４レンズ群Ｇ４は最初は第２レンズ群Ｇ２の移動にともない第３レンズ群Ｇ３に近づき、その後に再び離れて行く。
【００３１】
変倍時に変化するこれらの面間隔の具体的な数値と、ズームレンズの焦点距離、Ｆナンバー及び半画角を、物体位置２ｍについて、広角端、標準、望遠端に関して計算したものを（表３）に示す。（表３）から明らかなように、Ｆナンバーは１．６５、ズーム比は１３．８、画角は全画角で６７．１度が得られている。ここで言う標準とは、第２レンズ群による像のリレー倍率が１倍となる第２レンズ群の位置を言う。
【００３２】
【表３】

【００３３】
（第２の実施例）
次に、本発明のズームレンズの好適な第２の実施例の構成を図２に示す。なお、上記第１の実施例と共通する部分の説明は省略し、第１の実施例と異なる点についてのみ、その構成を説明する。また、その動作については、以下に示す各実施例すべて第１の実施例と同様であるため、説明を省略する。
【００３４】
図２において、第３レンズ群Ｇ３は、絞りＳ側から順に、アッベ数５５．２のガラスを用いた凹レンズＧ３ａと、アッベ数３５．９のガラスを用いた凸レンズＧ３ｂで構成され、正の屈折力を持ち、前述の条件（５）を満たすような収束性の色収差を発生する作用を有する。凹レンズＧ３ａは、頂点曲率半径ｒ１２の非球面、曲率半径ｒ１３，中心厚ｄ１２を有する凹メニスカスレンズであり、絞りＳ側に凸面を向けている。凸レンズＧ３ｂは、曲率半径ｒ１３、ｒ１４、中心厚ｄ１３を有する。これら２枚のレンズＧ３ａ及びＧ３ｂは接合されている。ｄ１４は、第３レンズ群Ｇ３と第４レンズ群Ｇ４との間の空気間隔であり、前述の第１の実施例と同様に、変倍時及びフォーカス動作時に変化する。なお、図２において、第４レンズ群Ｇ４の構成は、第１の実施例と同様であるが、各面の面番号は１づつずれている。
【００３５】
第２の実施例の具体的数値に関し、レンズ構成を（表４）に、非球面係数を（表５）に、前述の（表１）及び（表２）と同じ形式で示す。また、変倍時に変化する間隔等を前述の（表３）と同じ形式で（表６）に示す。
【００３６】
【表４】

【００３７】
【表５】

【００３８】
【表６】

【００３９】
（第３の実施例）
次に、本発明のズームレンズの好適な第３の実施例の構成を図３に示す。なお、図３に示す第３の実施例の構成は上記第２の実施例とほぼ同様の構成であるため、その説明を省略する。第３の実施例の具体的数値を（表７）、（表８）及び（表９）に示す。なお、これらの各表は、上記第２の実施例と同様に各々、レンズ構成、非球面係数、変倍時に変化する間隔等を示す。
【００４０】
【表７】

【００４１】
【表８】

【００４２】
【表９】

【００４３】
（第４の実施例）
次に、本発明のズームレンズの好適な第４の実施例を図４に示す。なお、上記第２の実施例の構成と共通する部分についてはその説明を省略し、異なる部分についてのみ、その構成を説明する。
【００４４】
図４において、第３レンズ群Ｇ３は、絞りＳ側から順に、アッベ数３４．０のガラスを用いた凸レンズＧ３ａと、アッベ数５５．５のガラスを用いた凹レンズＧ３ｂとで構成され、正の屈折力を持ち、前述と同様の収束性の色収差を発生する。凸レンズＧ３ａは、頂点曲率半径ｒ１２の非球面、曲率半径ｒ１３、中心厚ｄ１２を有する。凹レンズＧ３ｂは、曲率半径ｒ１３、ｒ１４、中心厚ｄ１３を有する。これら２枚のレンズＧ３ａ及びＧ３ｂは接合されている。
【００４５】
第４の実施例の具体的な数値を（表１０）、（表１１）及び（表１２）に示す。なお、これらの各表は、上記第２の実施例と同様に各々、レンズ構成、非球面係数、変倍時に変化する間隔等を示す。
【００４６】
【表１０】

【００４７】
【表１１】

【００４８】
【表１２】

【００４９】
（第５の実施例）
次に、本発明のズームレンズの好適な第５の実施例を図５に示す。なお、上記第２の実施例の構成と共通する部分については、その説明を省略し、異なる部分についてのみ、その構成を説明する。
【００５０】
図５において、第３レンズ群Ｇ３は、絞りＳ側から順に、アッベ数５５．２のガラスを用いた凹レンズＧ３ａと、アッベ数３５．９のガラスを用いた凸レンズＧ３ｂとで構成され、これら２枚のレンズＧ３ａとＧ３ｂとが空気間隔を隔てて構成されている点が、第２の実施例と異なる。凹レンズＧ３ａは、頂点曲率半径ｒ１２の非球面、曲率半径ｒ１３、中心厚ｄ１２を有する。ｄ１３はレンズＧ３ａとＧ３ｂの空気間隔である。凸レンズＧ３ｂは、曲率半径ｒ１４、ｒ１５、中心厚ｄ１４を有する。ｄ１５は第３レンズ群Ｇ３と第４レンズ群Ｇ４との間の空気間隔であり、これ以降、結像面Ｉに至る構成は第２の実施例と同様である。なお、図５において、各面の番号は一つずつ増えている。
【００５１】
第５の実施例の具体的な数値を（表１３）、（表１４）及び（表１５）に示す。なお、これらの各表は、上記第２の実施例と同様に各々、レンズ構成、非球面係数、変倍時に変化する間隔等を示す。
【００５２】
【表１３】

【００５３】
【表１４】

【００５４】
【表１５】

【００５５】
以上の５つの実施例について、前記５つの条件を与える各式の値を求めた結果を（表１６）に示す。なお、（表１６）において、左端の列の数は、条件式の番号を示し、その右側の列は、条件式を示す。それに続く列は、各実施例について条件式の値を記したものである。
【００５６】
【表１６】

【００５７】
図６から図２０に示す１５の図は、それぞれ物体距離２ｍについて計算した諸収差を表すものであり、図６から図８は第１の実施例に対応し、図９から図１１は第２の実施例に対応し、図１２から図１４は第３の実施例に対応し、図１５から図１７は第４の実施例に対応し、図１８から図２０は第５の実施例に対応する。各図において、（ａ）は球面収差及び正弦条件、（ｂ）は非点収差、（ｃ）は歪曲収差、（ｄ）は軸上色収差、（ｅ）は倍率色収差を表すグラフである。また、各実施例に対応する３つの図のうち、番号の若い方から順に、広角端、標準、望遠端における諸収差を示す。
【００５８】
各図のグラフ（ａ）において、横軸はガウス像面からのずれ量（ｍｍ）、縦軸は軸上光線の瞳入射高をＦナンバーで表したものである。実線の曲線は、スペクトルのｄ線に関する球面収差を表し、点線の曲線は正弦条件を表す。
【００５９】
各図のグラフ（ｂ）において、横軸はガウス像面からのずれ量（ｍｍ）、縦軸のＷは入射瞳位置での主光線の入射角（度）である。また、実線の曲線はサジタル像面を表し、点線の曲線はメリジオナル像面を表す。
【００６０】
各図のグラフ（ｃ）において、横軸は歪率（パーセント）を表し、縦軸はグラフ（ｂ）と同様に、縦軸のＷは入射瞳位置での主光線の入射角（度）である。
【００６１】
各図のグラフ（ｄ）において、グラフ（ａ）と同様に、横軸はガウス像面からのずれ量（ｍｍ）、縦軸は軸上光線の瞳入射高をＦナンバーで表す。実線の曲線はスペクトルのｄ線について、点線の曲線はＦ線について、破線の曲線はＣ線について、各々軸上色収差を表す。
【００６２】
各図のグラフ（ｅ）において、グラフ（ｂ）と同様に、横軸はガウス像面からのずれ量（ｍｍ）、縦軸のＷは入射瞳位置での主光線の入射角（度）である。各曲線はグラフ（ｄ）と同様に、対応するスペクトル線について、各々倍率色収差を表す。
【００６３】
次に、上記本発明のズームレンズを使用した３板式ビデオカメラの構成を図２１に示す。図２１において、本発明の３板式ビデオカメラは、ズームレンズ１１と、空間周波数フィルター（水晶フィルター等）１２と、３つの色分解プリズム１３ａ，１３ｂ，１３ｃと、３つの撮像素子１４ａ，１４ｂ，１４ｃと、各撮像素子からの信号を処理する信号処理部１５と、映像信号等を記録媒体に記録する信号記録部１６と、ビデオカメラに取り付けられたファインダー等の映像表示部１７を具備する。なお、ズームレンズ１１として上記第１から第５の実施例までのいずれのズームレンズを用いてもよく、小型軽量で、ズーム比が高く、広画角の３板式ビデオカメラが構成できることは言うまでもない。
【００６４】
【発明の効果】
以上のように、本発明によれば、各レンズ群の屈折力を前記（数１）における条件式（１）、（２）、（３）及び（４）を満たすように規定しているので、小型でありながらズーム比の高倍率化、広画角化及び大口径比化（Ｆナンバーを小さくする事）が可能になる。さらに、第３レンズ群をアッベ数が３５以下のガラスを用いた単レンズとし、または、第３レンズ群を２枚のレンズで構成し、各々前記条件式（５）を満たすようにしたので、ズーム比の高倍率化の影響により第１及び第２レンズ群で補正しきれずに残存する倍率色収差を、第４レンズ群で補正することが可能となる。その結果、従来例と同程度のレンズ枚数で構成された、３板式ビデオカメラ等に必要な色分解光学系を挿入できるバックフォーカスの長い高性能なズームレンズ及びそれを用いたビデオカメラを実現することができる。
【００６５】
具体的には、Ｆナンバーが約１．６、広角端の画角が全画角で約６７度、ズーム比が約１４倍といった、従来に比べ高い仕様を満たしながらも、従来と同程度の構成レンズ枚数で、長いバックフォーカスを有する高性能なズームレンズを実現することができる。また、そのような本発明のズームレンズの特徴により、高性能でありながら小型、軽量な３板式ビデオカメラの実現が可能である。
【００６６】
また、絞り位置付近に位置する第３レンズ群を、前記条件式（５）を満たすように、アッベ数が３５以下の高分散ガラスを用いた単レンズによって構成し、または、第３レンズ群を、前記条件式（５）を満たすように、２枚のレンズで構成することにより、第３レンズ群から出射する光束に対して倍率色収差を変化させずに、収束性の軸上色収差を与えることができ、第４レンズ群で発生する発散性の軸上色収差を打ち消し、総合的に倍率色収差を補正することが可能となる。ここで、収束性の軸上色収差とは、凸レンズ単体で生じる色収差と同様の性質、即ち、屈折により短い波長の光の方がより一層収束する性質の軸上色収差を意味する。なお、後者の場合、レンズを２枚使うことにより同じ量の収束性軸上色収差を与えるため、使用できるガラスの種類が増え、非球面の加工方法上での材料に関する制限や収差補正の上で、選択の自由度が広がる。
【図面の簡単な説明】
【図１】本発明のズームレンズの第１の実施例の構成図
【図２】本発明のズームレンズの第２の実施例の構成図
【図３】本発明のズームレンズの第３の実施例の構成図
【図４】本発明のズームレンズの第４の実施例の構成図
【図５】本発明のズームレンズの第５の実施例の構成図
【図６】第１の実施例のズームレンズの広角端における諸収差を示す収差図
【図７】第１の実施例のズームレンズの標準における諸収差を示す収差図
【図８】第１の実施例のズームレンズの望遠端における諸収差を示す収差図
【図９】第２の実施例のズームレンズの広角端における諸収差を示す収差図
【図１０】第２の実施例のズームレンズの標準における諸収差を示す収差図
【図１１】第２の実施例のズームレンズの望遠端における諸収差を示す収差図
【図１２】第３の実施例のズームレンズの広角端における諸収差を示す収差図
【図１３】第３の実施例のズームレンズの標準における諸収差を示す収差図
【図１４】第３の実施例のズームレンズの望遠端における諸収差を示す収差図
【図１５】第４の実施例のズームレンズの広角端における諸収差を示す収差図
【図１６】第４の実施例のズームレンズの標準における諸収差を示す収差図
【図１７】第４の実施例のズームレンズの望遠端における諸収差を示す収差図
【図１８】第５の実施例のズームレンズの広角端における諸収差を示す収差図
【図１９】第５の実施例のズームレンズの標準における諸収差を示す収差図
【図２０】第５の実施例のズームレンズの望遠端における諸収差を示す収差図
【図２１】本発明のズームレンズを使用したビデオカメラの構成図
【図２２】従来のズームレンズの構成図
【符号の説明】
Ｇ１ ：第１レンズ群
Ｇ１ａ〜ｃ ：第１レンズ群を構成するレンズ
Ｇ２ ：第２レンズ群
Ｇ２ａ〜ｃ ：第２レンズ群を構成するレンズ
Ｇ３ ：第３レンズ群
Ｇ３ａ〜ｃ ：第３レンズ群を構成するレンズ
Ｇ４ ：第４レンズ群
Ｇ４ａ〜ｃ ：第４レンズ群を構成するレンズ
Ｇ５、２５ ：色分解光学系に相当するガラス平板
Ｇ６、１２、２６ ：空間周波数フィルター
Ｓ ：絞り
Ｉ、２７ ：結像面
１１ ：ズームレンズ
１３ａ〜ｃ ：色分解用プリズム
１４ａ〜ｃ ：撮像素子
１５ ：信号処理部
１６ ：映像信号記録部
１７ ：映像表示部
２１ ：従来のズームレンズの第１レンズ群
２２ ：従来のズームレンズの第２レンズ群
２３ ：従来のズームレンズの第３レンズ群
２４ ：従来のズームレンズの第４レンズ群[0001]
[Industrial applications]
The present invention relates to a zoom lens having a large zoom ratio and a long back focus used for a three-panel video camera or the like.
[0002]
[Prior art]
With further miniaturization and higher image quality of video cameras, zoom lenses are required to have a smaller size and a larger aperture ratio, as well as a wider angle of view and a higher zoom ratio. FIG. 22 shows a configuration of a zoom lens disclosed in Japanese Patent Application No. 6-138631 as an example of miniaturizing and improving the performance of a zoom lens for a three-panel video camera which is advantageous for high image quality.
[0003]
As shown in FIG. 22, a conventional zoom lens includes a first lens group 21, a second lens group 22, a third lens group 23, a fourth lens group 24, and a glass plate 25 corresponding to the optical path length of a color separation optical system. And a glass plate 26 corresponding to an optical path length such as a quartz filter or a face plate of an image sensor. Reference numeral 27 denotes an image plane. The first lens group 21 is a fixed lens group having a positive refractive power and having an image forming action. The second lens group 22 has a negative refractive power and is movable on the optical axis. The third lens group 23 is a fixed lens group including an aspheric lens having a positive refractive power. The fourth lens group 24 is a lens group having a positive refractive power, including an aspherical surface, and is movable on the optical axis.
[0004]
Next, the operation of the conventional video camera zoom lens configured as described above will be described. The first lens group 21 has an image forming function. The second lens group 22 changes the relay magnification of the image formed by the first lens group by moving on the optical axis to perform zooming. The third lens group 23 has an action of relaying a virtual image generated by the second lens group 22. The fourth lens group 24 has an image forming function, and has a function to correct a change in the image plane position at the time of zooming and a focus function according to a change in the object position by moving on the optical axis. The image plane 27 is kept at a fixed position.
[0005]
[Problems to be solved by the invention]
However, in the conventional zoom lens described above, the angle of view is about 60 degrees at the wide angle end, and the zoom ratio is only about 10 times. Therefore, there has been a problem that the recent demands for a wide angle of view and a high zoom ratio for a video camera zoom lens can no longer be met. Further, if an attempt is made to increase the angle of view and increase the zoom ratio by a conventional zoom lens design method, there has been a problem that the entire lens becomes large and the lens configuration becomes complicated.
[0006]
The present invention has been made to solve the above-described problems of the conventional example, and has a total field angle of about 67 degrees at the wide-angle end, a zoom ratio of about 14 times, and a lens equivalent to the conventional example. It is an object of the present invention to provide a high-performance zoom lens having a long back focus and capable of inserting a necessary color separation optical system into a three-plate video camera or the like constituted by a number of sheets, and a video camera using the same.
[0007]
[Means for Solving the Problems]
To achieve the above object, a zoom lens according to the present invention comprises, in order from the object side, a first lens group having a positive refractive power and fixed with respect to a reference image plane position; A second lens group having a zooming action by moving the lens, an aperture stop, a third lens group having a positive refractive power fixed to a reference image plane position and having a condensing action, and the second lens group. A fourth lens group having a positive refractive power, which moves on the optical axis so that the image plane which fluctuates due to the movement of the object and the movement of the object is kept at a fixed position from the reference image plane position, equivalent to a color separation optical system. A three-panel type zoom lens having a glass flat plate, The third lens group is constituted by either a single lens having at least one aspheric surface or a two-lens lens including a concave lens and a convex lens arranged in order from the object side, and fi (i = 1, 2, 3, 4) is the focal length of the i lens group, BF is the distance from the last lens surface to the image plane when the image space is air, and f3d, f3C, and f3F are each the spectrum. On d-line, C-line and F-line Said When the focal length of the third lens group is satisfied, the above (Equation 1) is satisfied.
[0008]
In the above configuration, the third lens group Is a single lens Made of high dispersion glass with Abbe number smaller than 35 And Preferably.
[0009]
Alternatively, in the above configuration, the third lens group Wherein the convex lens is made of glass having an Abbe number smaller than that of the concave lens, and the convex lens or the concave lens is Preferably, at least one of the surfaces of the lens is aspheric.
[0010]
In each of the above configurations, the second lens group and the fourth lens group may be Of the lens surface At least one side But Has an aspheric surface Doing Preferably.
[0011]
On the other hand, a video camera according to the present invention includes a zoom lens having any of the above configurations, a color separation optical system, an image sensor, a signal processing unit, a signal recording unit, and a video display unit.
[0012]
[Action]
According to the zoom lens of the present invention configured as described above, the refractive power of each lens group is set so as to satisfy the conditional expressions (1), (2), (3), and (4) in (Equation 1). Since it is stipulated, it is possible to increase the zoom ratio, widen the angle of view, and increase the aperture ratio (decrease the F-number) while being compact. Further, since the third lens group is a single lens using glass having an Abbe number of 35 or less, or the third lens group is composed of two lenses, each of which satisfies the conditional expression (5). The chromatic aberration of magnification that cannot be completely corrected by the first and second lens groups due to the effect of the higher magnification of the zoom ratio can be corrected by the fourth lens group. As a result, a high-performance zoom lens having a long back focus and capable of inserting a necessary color separation optical system into a three-plate video camera or the like and having the same number of lenses as the conventional example, and a video camera using the same are realized. be able to.
[0013]
The conditional expression (1) defines the ratio between the refractive powers of the first lens group and the second lens group. This is a condition necessary for widening the angle of view at the wide-angle end and for miniaturizing the entire lens while securing the required zoom ratio of 14 times, so as not to make it difficult to correct aberrations throughout the entire system. . When the value exceeds the upper limit, the refractive power of the second lens unit having a negative refractive power becomes too strong, and it becomes difficult to reduce the Petzval sum of the entire system. If the lower limit is exceeded, the movable range of the second lens group becomes narrow, and it becomes difficult to secure a zoom ratio.
[0014]
The conditional expression (2) defines the refractive power of the first lens group. When the focal length f4 of the fourth lens group, which is the imaging lens, is determined based on the conditional expression (4), this is a condition necessary to secure a necessary F-number and shorten the overall length of the lens. . Beyond the upper limit, the overall length of the lens becomes unnecessarily long. If the lower limit is exceeded, the required F-number cannot be secured.
[0015]
The conditional expression (3) defines the refractive power of the third lens group. This is a condition necessary for performing good aberration correction while securing a necessary back focus. When the value exceeds the upper limit, the lens system passing through the first, second, and third lens units becomes a divergent system, so that the effective diameter of the fourth lens unit must be increased. If the lower limit is exceeded, the degree of convergence of the luminous flux emitted from the third lens group increases, and the refractive power of the negative lens of the fourth lens group must be increased in order to secure a necessary back focus. It is difficult to reduce the Petzval sum of the system.
[0016]
The conditional expression (4) defines the focal length of the fourth lens group by the required back focus length. When the value exceeds the upper limit, the refractive power of the negative lens in the fourth lens group must be increased, and it is difficult to reduce the Petzval sum. If the lower limit is exceeded, the total lens length is unnecessarily increased in combination with the conditional expressions (1), (2) and (3).
[0017]
Generally, a lens group that moves greatly during zooming needs to have its chromatic aberration corrected by itself, but it is difficult to completely correct chromatic aberration for each lens group. Therefore, at the telephoto end, the axial chromatic aberration remaining in the first lens group is enlarged by the second lens group, which is a zooming unit. Further, in the variable power range between the telephoto end and the wide-angle end, the luminous flux passes through the peripheral portions of the first and second lens groups, so that chromatic aberration of magnification remains. If the zoom ratio is increased, axial chromatic aberration at the telephoto end must be comprehensively corrected by the first and second lens groups, and it is difficult to sufficiently correct lateral chromatic aberration with these lens groups. . In such a case, it is generally conceivable to arrange the lens groups such that the light beam passes through a place away from the optical axis of the lens group on the opposite side to the aperture stop. That is, the distance between the third lens group and the fourth lens group is sufficiently widened. In this case, the fourth lens group requires a larger effective diameter, which hinders downsizing of the zoom lens. Therefore, in the zoom lens of the present invention, the distance between the third lens unit and the fourth lens unit is not widened, and divergent chromatic aberration is produced by the fourth lens unit, so that the first lens unit and the first lens unit located on opposite sides with respect to the diaphragm are provided. A method for canceling lateral chromatic aberration generated in the second lens group is employed. Here, the divergent chromatic aberration means the same property as the chromatic aberration generated by the concave lens alone, that is, the chromatic aberration in which light of a shorter wavelength is more divergent due to refraction.
[0018]
The third lens group located near the stop position is constituted by a single lens using high dispersion glass having an Abbe number of 35 or less so as to satisfy the conditional expression (5). By including two lenses so as to satisfy the conditional expression (5), it is possible to impart convergent axial chromatic aberration to the light beam emitted from the third lens group without changing the chromatic aberration of magnification. In addition, it is possible to cancel the divergent axial chromatic aberration generated in the fourth lens group and to comprehensively correct the chromatic aberration of magnification. Here, the convergence axial chromatic aberration means a property similar to the chromatic aberration generated by a single convex lens, that is, an axial chromatic aberration having a property that light having a shorter wavelength is more converged by refraction. In the latter case, since the same amount of convergent axial chromatic aberration is given by using two lenses, the types of glass that can be used are increased, and restrictions on materials in aspherical processing methods and correction of aberrations are required. , The freedom of choice is expanded.
[0019]
【Example】
Hereinafter, preferred first to fifth embodiments of the zoom lens of the present invention will be described in detail with reference to the drawings and tables. Note that the first embodiment is an example in which the third lens group is configured by a single lens using high dispersion glass having an Abbe number of 35 or less, and the second to fifth embodiments use the third lens group. This is an example in which two lenses are used.
[0020]
(First embodiment)
FIG. 1 shows the configuration of a zoom lens according to a first embodiment of the present invention. In FIG. 1, G1 is a first lens group having a positive refractive power and fixed with respect to a reference image plane position, G2 is a second lens group having a negative refractive power and movable on the optical axis, and S is An aperture stop, G3 is a third lens group having a positive refractive power and fixed with respect to a reference image plane position, G4 is a fourth lens group having a positive refractive power and movable on the optical axis, and G5 is A color separation optical system, G6 is a face plate, and I is an image plane. Here, the color separation optical system G5 is an optical system that separates a light beam into three primary colors of red, green, and blue, and is shown as a glass flat plate corresponding to the optical path length of the optical system in FIG. The face plate G6 is a glass plate having an optical path length including a crystal filter, a face plate of an image sensor, and the like.
[0021]
Next, the configuration of each lens group, lens arrangement, and operation of each lens group will be described. In FIG. 1, a first lens group G1 is a lens group including three lenses G1a, G1b, and G1c and having an image forming action. The lens G1a is a concave meniscus lens having radii of curvature r1, r2 and a center thickness d1. The lens G1b is a convex lens having radii of curvature r2 and r3 and a center thickness d2. The lenses G1a and G1b are cemented. d3 is an air gap between the lens G1b and the lens G1c. The lens G1c is a convex meniscus lens having radii of curvature r4 and r5 and a center thickness d4, and is arranged with the convex surface facing the object side. d5 is an air gap between the first lens group G1 and the second lens group G2, and the gap changes during zooming.
[0022]
The second lens group G2 includes three lenses G2a, G2b, and G2c, relays an image formed by the first lens group G1, and has a zooming effect by moving on the optical axis. is there. The lens G2a is a concave meniscus lens having radii of curvature r6 and r7 and a center thickness d6, and has a convex surface facing the first lens group. d7 is an air gap between the lens G2a and the lens G2b. The lens G2b is a concave lens having an aspheric surface having a vertex curvature radius r8, r9, and a center thickness d8. The lens G2c is a convex lens having radii of curvature r9 and r10 and a center thickness d9. The lens G2b and the lens G2c are joined. r11 indicates the surface of the stop S and is a plane. d10 is an air interval between the second lens group G2 and the stop S, and the interval changes at the time of zooming. d11 is an air gap between the stop S and the third lens group G3.
[0023]
The third lens group G3 is a lens group composed of a single lens G3a and having an action of relaying a virtual image generated by the first and second lens groups. The lens G3a has two aspheric surfaces having a vertex radius of curvature r12 and r13 and a center thickness d12. Further, by using glass having an Abbe number of 25.4 for this lens, convergence chromatic aberration as described above is generated, which is useful for correcting lateral chromatic aberration comprehensively. d13 is the air gap between the third lens group G3 and the fourth lens group G4, and the gap changes during the focus operation and during zooming.
[0024]
The fourth lens group G4 includes three lenses G4a, G4b, and G4c, has an image forming function, moves on the optical axis at the time of a focusing operation on an object, and at the time of zooming, and moves the image plane position to a fixed position. Has the effect of keeping The lens G4a is a concave lens having radii of curvature r14 and r15 and a center thickness d14. The lens G4b is a convex lens having an aspheric surface having a curvature radius r15 and a vertex curvature radius r16, and a center thickness d15. The lenses G4a and G4b are joined. d16 is an air gap between the lenses G4b and G4c. The lens G4c is a convex lens having radii of curvature r17 and r18 and a center thickness d17. d18 is an air gap between the fourth lens group G4 and the color separation optical system G5, and changes with the movement of the fourth lens group G4. r19, r20, and r21 indicate respective surfaces of the color separation optical system G5 and the face plate G6, which are flat surfaces. d19 and d20 are the surface intervals of the glass flat plates G5 and G6.
[0025]
Next, specific numerical examples of the first embodiment are shown in (Table 1).
[0026]
[Table 1]

[0027]
In Table 1, the numbers in the first column from the left indicate the lens groups G1 to G6 shown in FIG. 1, and the number j in the second column indicates the radius of curvature rj (j shown in FIG. = 1 to 21). In the following columns, r is the radius of curvature, d is the surface interval, n is the refractive index of each lens spectrum for the d-line, and ν is the Abbe number of each lens for the d-line. The aspheric shape is defined by the following (Equation 2), and the conical constant and the value of each aspheric coefficient for each aspheric surface are shown in (Table 2). In (Table 2), the numbers in the first column from the left are the surface numbers of the aspheric surfaces corresponding to the surface numbers in (Table 1).
[0028]
(Equation 2)

[0029]
[Table 2]

[0030]
Next, a description will be given of the surface distance that changes due to the movement of the second lens group G2 during zooming and the accompanying movement of the fourth lens group G4. In FIG. 1, a curve shown below each lens unit represents a locus of each lens unit when zooming from the wide-angle end to the telephoto end. The first and third lens groups G1 and G3 are fixed, and the fourth lens group G4 first approaches the third lens group G3 with the movement of the second lens group G2, and then moves away again.
[0031]
Specific values of these surface intervals that change during zooming, and the focal length, F-number, and half angle of view of the zoom lens calculated for the wide-angle end, the standard, and the telephoto end for the object position of 2 m (Table 3). ). As is clear from (Table 3), the F number is 1.65, the zoom ratio is 13.8, and the angle of view is 67.1 degrees at all angles of view. The standard here refers to the position of the second lens group where the magnification of the image relay by the second lens group becomes 1 ×.
[0032]
[Table 3]

[0033]
(Second embodiment)
Next, the configuration of a second preferred embodiment of the zoom lens according to the present invention is shown in FIG. The description of the parts common to the first embodiment is omitted, and only the configuration different from the first embodiment is described. The operation of each of the following embodiments is the same as that of the first embodiment, and a description thereof will not be repeated.
[0034]
In FIG. 2, the third lens group G3 includes, in order from the stop S side, a concave lens G3a using glass having an Abbe number of 55.2 and a convex lens G3b using glass having an Abbe number of 35.9. It has the power and has the effect of generating convergence chromatic aberration that satisfies the above condition (5). The concave lens G3a is a concave meniscus lens having an aspheric surface having a vertex curvature radius r12, a curvature radius r13, and a center thickness d12, and has a convex surface facing the stop S side. The convex lens G3b has radii of curvature r13 and r14 and a center thickness d13. These two lenses G3a and G3b are joined. d14 is the air gap between the third lens group G3 and the fourth lens group G4, and changes during zooming and during the focusing operation, as in the first embodiment. In FIG. 2, the configuration of the fourth lens group G4 is the same as that of the first embodiment, but the surface numbers of the respective surfaces are shifted by one.
[0035]
Regarding specific numerical values of the second embodiment, the lens configuration is shown in (Table 4), the aspherical surface coefficient is shown in (Table 5), and the same format as in (Table 1) and (Table 2) described above. In addition, (Table 6) shows the intervals and the like that change during zooming in the same format as in (Table 3) described above.
[0036]
[Table 4]

[0037]
[Table 5]

[0038]
[Table 6]

[0039]
(Third embodiment)
Next, the configuration of a third preferred embodiment of the zoom lens of the present invention is shown in FIG. Note that the configuration of the third embodiment shown in FIG. 3 is substantially the same as the configuration of the second embodiment, and a description thereof will be omitted. Specific numerical values of the third embodiment are shown in (Table 7), (Table 8) and (Table 9). Each of these tables shows a lens configuration, an aspherical surface coefficient, an interval that changes at the time of zooming, and the like, as in the second embodiment.
[0040]
[Table 7]

[0041]
[Table 8]

[0042]
[Table 9]

[0043]
(Fourth embodiment)
Next, FIG. 4 shows a fourth preferred embodiment of the zoom lens according to the present invention. The description of the portions common to the configuration of the second embodiment is omitted, and the configuration of only the different portions will be described.
[0044]
In FIG. 4, the third lens group G3 includes, in order from the stop S side, a convex lens G3a using glass with an Abbe number of 34.0 and a concave lens G3b using glass with an Abbe number of 55.5. It has refracting power and generates convergence chromatic aberration similar to that described above. The convex lens G3a has an aspheric surface with a vertex curvature radius r12, a curvature radius r13, and a center thickness d12. The concave lens G3b has radii of curvature r13 and r14 and a center thickness d13. These two lenses G3a and G3b are joined.
[0045]
Specific numerical values of the fourth embodiment are shown in (Table 10), (Table 11) and (Table 12). Each of these tables shows a lens configuration, an aspherical surface coefficient, an interval that changes at the time of zooming, and the like, as in the second embodiment.
[0046]
[Table 10]

[0047]
[Table 11]

[0048]
[Table 12]

[0049]
(Fifth embodiment)
Next, FIG. 5 shows a fifth preferred embodiment of the zoom lens according to the present invention. The description of the same parts as those of the second embodiment is omitted, and the structure of only the different parts will be described.
[0050]
In FIG. 5, the third lens group G3 includes, in order from the stop S side, a concave lens G3a using glass having an Abbe number of 55.2 and a convex lens G3b using glass having an Abbe number of 35.9. The difference from the second embodiment is that the lenses G3a and G3b are configured with an air gap therebetween. The concave lens G3a has an aspheric surface with a vertex curvature radius r12, a curvature radius r13, and a center thickness d12. d13 is the air gap between the lenses G3a and G3b. The convex lens G3b has radii of curvature r14 and r15 and a center thickness d14. d15 is an air gap between the third lens group G3 and the fourth lens group G4, and the configuration up to the image forming plane I thereafter is the same as that of the second embodiment. In FIG. 5, the number of each surface is increased by one.
[0051]
Specific numerical values of the fifth embodiment are shown in (Table 13), (Table 14) and (Table 15). Each of these tables shows a lens configuration, an aspherical surface coefficient, an interval that changes at the time of zooming, and the like, as in the second embodiment.
[0052]
[Table 13]

[0053]
[Table 14]

[0054]
[Table 15]

[0055]
Table 16 shows the results of obtaining the values of the respective equations that give the above five conditions for the above five examples. In Table 16, the number of the leftmost column indicates the number of the conditional expression, and the rightmost column indicates the conditional expression. The subsequent columns indicate the values of the conditional expressions for each embodiment.
[0056]
[Table 16]

[0057]
6 to 20 show various aberrations calculated for an object distance of 2 m. FIGS. 6 to 8 correspond to the first embodiment, and FIGS. 9 to 11 correspond to the second embodiment. 12 to 14 correspond to the third embodiment, FIGS. 15 to 17 correspond to the fourth embodiment, and FIGS. 18 to 20 correspond to the fifth embodiment. I do. In each figure, (a) is a graph showing spherical aberration and sine conditions, (b) is astigmatism, (c) is distortion, (d) is axial chromatic aberration, and (e) is a graph showing lateral chromatic aberration. Further, among three figures corresponding to each embodiment, various aberrations at the wide-angle end, the standard, and the telephoto end are shown in ascending order of numbers.
[0058]
In the graph (a) of each figure, the horizontal axis represents the amount of displacement (mm) from the Gaussian image plane, and the vertical axis represents the pupil incident height of the on-axis ray by the F number. The solid curve represents the spherical aberration for the d-line of the spectrum, and the dotted curve represents the sine condition.
[0059]
In the graph (b) of each figure, the horizontal axis represents the amount of deviation (mm) from the Gaussian image plane, and the vertical axis W represents the incident angle (degree) of the principal ray at the entrance pupil position. The solid curve represents the sagittal image plane, and the dotted curve represents the meridional image plane.
[0060]
In the graph (c) of each figure, the horizontal axis represents the distortion rate (percent), and the vertical axis represents W, which is the incident angle (degree) of the principal ray at the entrance pupil position, similarly to the graph (b). is there.
[0061]
In graph (d) of each figure, similarly to graph (a), the horizontal axis represents the amount of deviation (mm) from the Gaussian image plane, and the vertical axis represents the pupil incident height of the on-axis light beam by the F number. The solid curve represents the axial chromatic aberration for the d-line of the spectrum, the dotted curve represents the F-line, and the dashed curve represents the C-line for the C-line.
[0062]
In the graph (e) of each figure, similarly to the graph (b), the horizontal axis is the shift amount (mm) from the Gaussian image plane, and the vertical axis is W, the incident angle (degree) of the principal ray at the entrance pupil position. is there. Each curve represents the chromatic aberration of magnification for the corresponding spectral line, similarly to the graph (d).
[0063]
Next, FIG. 21 shows a configuration of a three-panel video camera using the zoom lens of the present invention. In FIG. 21, a three-panel video camera according to the present invention includes a zoom lens 11, a spatial frequency filter (such as a quartz filter) 12, three color separation prisms 13a, 13b, 13c, and three image sensors 14a, 14b, 14c. A signal processing unit 15 that processes signals from the respective image sensors, a signal recording unit 16 that records video signals and the like on a recording medium, and a video display unit 17 such as a finder attached to a video camera. It should be noted that any of the zoom lenses from the first to fifth embodiments may be used as the zoom lens 11, and it goes without saying that a three-panel video camera having a small size, light weight, a high zoom ratio, and a wide angle of view can be configured. .
[0064]
【The invention's effect】
As described above, according to the present invention, the refractive power of each lens group is defined so as to satisfy the conditional expressions (1), (2), (3) and (4) in (Equation 1). In addition, it is possible to increase the zoom ratio, widen the angle of view, and increase the aperture ratio (decrease the F-number) despite its small size. Further, since the third lens group is a single lens using glass having an Abbe number of 35 or less, or the third lens group is composed of two lenses, each of which satisfies the conditional expression (5). The chromatic aberration of magnification that cannot be completely corrected by the first and second lens groups due to the effect of the higher magnification of the zoom ratio can be corrected by the fourth lens group. As a result, a high-performance zoom lens having a long back focus and capable of inserting a necessary color separation optical system into a three-plate video camera or the like and having the same number of lenses as the conventional example, and a video camera using the same are realized. be able to.
[0065]
More specifically, the F-number is about 1.6, the angle of view at the wide-angle end is about 67 degrees at the full angle of view, and the zoom ratio is about 14 times. With the number of constituent lenses, a high-performance zoom lens having a long back focus can be realized. In addition, with such features of the zoom lens of the present invention, it is possible to realize a compact, lightweight three-panel video camera with high performance.
[0066]
Further, the third lens group located near the stop position is constituted by a single lens using high-dispersion glass having an Abbe number of 35 or less so as to satisfy the conditional expression (5). By providing two lenses so as to satisfy the conditional expression (5), convergent axial chromatic aberration can be given to the light beam emitted from the third lens group without changing the chromatic aberration of magnification. Accordingly, it is possible to cancel the divergent axial chromatic aberration generated in the fourth lens group and to comprehensively correct the lateral chromatic aberration. Here, the convergence axial chromatic aberration means a property similar to the chromatic aberration generated by a single convex lens, that is, an axial chromatic aberration having a property that light having a shorter wavelength is more converged by refraction. In the latter case, since the same amount of convergent axial chromatic aberration is given by using two lenses, the types of glass that can be used are increased, and restrictions on materials in aspherical processing methods and correction of aberrations are required. , The freedom of choice is expanded.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a first embodiment of a zoom lens according to the present invention;
FIG. 2 is a configuration diagram of a second embodiment of the zoom lens according to the present invention;
FIG. 3 is a configuration diagram of a third embodiment of the zoom lens according to the present invention;
FIG. 4 is a configuration diagram of a fourth embodiment of the zoom lens according to the present invention;
FIG. 5 is a configuration diagram of a fifth embodiment of the zoom lens according to the present invention;
FIG. 6 is an aberration diagram showing various aberrations at the wide-angle end of the zoom lens according to the first embodiment.
FIG. 7 is an aberration diagram showing various aberrations in a standard of the zoom lens according to the first embodiment;
FIG. 8 is an aberration diagram showing various aberrations at the telephoto end of the zoom lens according to the first embodiment.
FIG. 9 is an aberration diagram showing various aberrations at the wide-angle end of a zoom lens according to a second embodiment.
FIG. 10 is an aberration diagram showing various aberrations in a standard of the zoom lens according to the second embodiment.
FIG. 11 is an aberration diagram showing various aberrations at a telephoto end of a zoom lens according to a second embodiment.
FIG. 12 is an aberration diagram showing various aberrations at the wide-angle end of a zoom lens according to a third embodiment.
FIG. 13 is an aberration diagram showing various aberrations of the zoom lens according to the third embodiment as a standard.
FIG. 14 is an aberration diagram showing various aberrations at the telephoto end of a zoom lens according to a third embodiment.
FIG. 15 is an aberration diagram showing various aberrations at the wide-angle end of a zoom lens according to a fourth embodiment.
FIG. 16 is an aberration diagram showing various aberrations in a standard of the zoom lens according to the fourth embodiment;
FIG. 17 is an aberration diagram showing various aberrations at the telephoto end of a zoom lens according to a fourth example.
FIG. 18 is an aberration diagram showing various aberrations at the wide-angle end of a zoom lens according to a fifth embodiment.
FIG. 19 is an aberration diagram showing various aberrations in a standard of the zoom lens according to a fifth embodiment;
FIG. 20 is an aberration diagram showing various aberrations at the telephoto end of a zoom lens according to a fifth embodiment.
FIG. 21 is a configuration diagram of a video camera using the zoom lens of the present invention.
FIG. 22 is a configuration diagram of a conventional zoom lens.
[Explanation of symbols]
G1: First lens group
G1a-c: lenses constituting the first lens group
G2: second lens group
G2a-c: lenses constituting the second lens group
G3: Third lens group
G3a-c: lenses constituting the third lens group
G4: fourth lens group
G4a-c: lenses constituting the fourth lens group
G5, 25: glass plate equivalent to color separation optical system
G6, 12, 26: Spatial frequency filter
S: Aperture
I, 27: Image plane
11: Zoom lens
13a-c: prism for color separation
14a-c: Image sensor
15: Signal processing unit
16: Video signal recording unit
17: Video display section
21: First lens group of conventional zoom lens
22: Second lens group of conventional zoom lens
23: Third lens group of conventional zoom lens
24: fourth lens group of conventional zoom lens

Claims (5)

A first lens group having a positive refractive power and fixed with respect to a reference image plane position in order from the object side, and a second lens group having a negative refractive power and having a zooming action by moving on the optical axis. An aperture stop, a third lens group having a positive refracting power fixed to a reference image plane position and having a condensing action, moving the second lens group, and moving an object to move the image plane. A fourth lens group having a positive refractive power, which moves on the optical axis so as to maintain a fixed position from the image plane position of the image plane, and a zoom lens for a three-plate system including a glass plate corresponding to a color separation optical system. The third lens group is constituted by either a single lens having at least one aspherical surface or a two-lens lens composed of a concave lens and a convex lens arranged in order from the object side, and fi (i = 1, 2, 3, 4) is the focal length of the i lens group, B Distance of F from the last lens surface of the case is the image space is air to the image plane, and f3d, F3C and each spectrum of d line F3F, and C-line and the focal length of in the third lens group to the F-line When

A zoom lens that satisfies each of the following. The single lens constituting the third lens group, the zoom lens according to claim 1, wherein the Abbe number is made up of 35 smaller high dispersion glass. In two lenses constituting the third lens group, wherein the convex lens is made of glass having a smaller Abbe number than said concave, and at least one surface of each face of the convex lens or the concave lens is aspherical The zoom lens according to claim 1. The second lens group and the fourth lens group, each of the at least one surface according to claim 2 or 3, wherein the zoom lens that has have a non-spherical of the lens surfaces. A video camera comprising the zoom lens according to claim 1, a color separation optical system, an image sensor, a signal processing unit, a signal recording unit, and a video display unit.

Images