JP3821330B2 - Zoom lens - Google Patents
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- JP3821330B2 JP3821330B2 JP23638497A JP23638497A JP3821330B2 JP 3821330 B2 JP3821330 B2 JP 3821330B2 JP 23638497 A JP23638497 A JP 23638497A JP 23638497 A JP23638497 A JP 23638497A JP 3821330 B2 JP3821330 B2 JP 3821330B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、家庭用のビデオカメラ等に好適なズームレンズに関する。特には、ズーム比のさらなる高倍率化を達成することのできるズームレンズに関する。
【０００２】
【従来の技術】
家庭用ビデオカメラのズームレンズを例に採って説明する。この種のズームレンズにおいては、撮像素子の小型化に伴って、次の２つの方向で商品開発がなされてきている。１つは、ズーム比が同じでより小型化を達成する方向であり、他の１つは実用的な大きさの中でより高倍率化する方向である。
【０００３】
後者の高倍率なズームレンズを実現する技術の一例として、特開平８−５９１３号がある。同号のズームレンズは、物体側より順に正、負、正、負、正の屈折力配置の５つのレンズ群からなり、少なくとも第２レンズ群と第４レンズ群を移動させることによりズーミングとフォーカシングを行うことにより、前玉径（物体側のレンズの径）を小型にして約２０倍のズーム比を得るものである。前玉径を小さくできれば、望遠端で使用するときに有効な光学式手振れ補正装置、たとえば可変頂角プリズムなどをレンズの物体側に装着する際、手振れ補正装置を小型にできて、民生用高倍率ズームの実用性を高める上で好都合である。
【０００４】
【発明が解決しようとする課題】
しかしながら、撮像素子のさらなる小型化を活かして、高倍率化をさらに進めて、たとえば５０倍ズームレンズに上記特開平８−５９１３号の技術をそのまま適用すると、次のような問題点が生じていた。すなわち、ズーミングによる収差変動や、望遠端での色収差及び球面収差などが補正できなかった。そのため、従来技術では、レンズの実用的な大きさを維持した上での高倍率化は２０倍くらいが限界であった。
【０００５】
本発明は、このような問題点に鑑みてなされたもので、家庭用のビデオカメラ等に好適なズームレンズであって、特には、ズーム比のさらなる高倍率化を達成することのできるズームレンズを提供することを目的とする。より具体的には、上記従来技術を画面対角線長４．５mmで変倍比約２０倍に適用した場合と同様の大きさで、画面対角線長３mmで約５０倍の変倍比を実現し、撮像素子の小型化を高倍率化に活かすとともに諸収差が良好に補正されたズームレンズを提供することを目的とする。
【０００６】
【課題を解決するための手段】
上記課題を解決するため、本発明のズームレンズは、物体側より順に、固定で正の屈折力の第１レンズ群と、負の屈折力の第２レンズ群と、固定で正の屈折力の第３レンズ群と、負の屈折力の第４レンズ群と、固定で正の屈折力の第５レンズ群とからなり、第２レンズ群及び第４レンズ群を光軸方向に移動させることにより、変倍並びに変倍による像位置の変動補正及びフオーカシングを行うズームレンズであつて、第１レンズ群が、物体側より順に配列された凹レンズ及び凸レンズの接合レンズ並びに凸レンズからなり、少なくとも１面が有効径において近軸球面の深さより浅くなる樹脂の薄い層で形成した複合非球面をもつ非球面形状であり、２枚の凸レンズのうち少なくとも１枚のアツベ数が８０以上であり、第２レンズ群が、物体側より順に配列された凹レンズ並びに凹レンズ及び凸レンズの接合レンズからなり、第３レンズ群が、物体側より順に配列された凸レンズ並びに凸レンズ及び凹レンズの接合レンズからなり、少なくとも１面が、有効径において近軸球面の深さより浅くなる非球面形状であり、第４レンズ群が、物体側より順に配列された凹レンズ並びに凹レンズ及び凸レンズの接合レンズからなり、第５レンズ群が、物体側より順に配列された凸レンズ並びに凸レンズ及び凹レンズの接合レンズからなり、少なくとも１面が、有効径において近軸球面の深さより浅くなる非球面形状であり、広角端における第４レンズ群の横倍率β４Ｗが３＜β４Ｗ＜８であり、焦点距離が広角端の略５０倍に変倍可能に構成されたことを特徴とする。
【０００７】
広角端から望遠端へズーミングするとき、上記第２レンズ群が物体側から像側へ移動し、第２レンズ群の横倍率が高くなって全体の焦点距離を長くする働きをする。このとき上記第４レンズ群が、広角端から第２レンズ群の横倍率が−１になるまでは物体側から像側へ移動して増倍の働きをし、第２レンズ群の横倍率が−１から望遠端までは反転して像側から物体側へ移動して減倍の働きをする。なお、第４レンズ群の移動方向が反転する位置を変曲点と呼ぶこととする。
【０００８】
入射瞳は、広角端では、第２レンズ群が絞りから遠い位置にあるため、第１レンズ群寄りに位置し、広角端の画角と入射瞳位置から前玉を通る主光線の光線高が決まる。第２レンズ群が像側へ移動するにつれて入射瞳は第１レンズ群から遠ざかり、画角は徐々に狭くなるので、その入射瞳位置と画角から決まる主光線の前玉における光線高が変化する。広角端の画角が６０度程度で変倍比が１０倍以上のズームレンズでは、通常、広角端より少し画角が狭いズーム位置で主光線の前玉光線高が最大になることが多い。しかし、上記５群構成のズームレンズでは、入射瞳位置の変化は第２レンズ群の移動のみで決まるのに対して、画角変化は広角端から変曲点までは第４レンズ群も変倍の役割を果たす。そのため、主光線の前玉光線高が最大になるときの画角をより狭くできるので、主光線高で決まる前玉径を小さくできる効果がある。
【０００９】
【発明の実施の形態】
本発明のズームレンズでは、高倍率化により前玉径が大型化するのを抑える効果がさらに顕著になるように、広角端から変曲点までの第４レンズ群の倍率変化が大きくなる屈折力配置に設定することが好ましい。具体的には、広角端における第４レンズ群の横倍率をβ４Ｗとすると、３＜β４Ｗ＜８とすることが好ましい。この値の下限を下回ると、第４レンズ群の移動量が増加して小型化が達成しにくい。一方、上記値の上限を越えると、第４レンズ群でフォーカシングする際の倍率変化が大きくなって不自然になる。特に、オートフォーカスのために第４レンズ群を光軸方向に微小振動させてコントラストの変化を見る動作をさせたときに、画角が周期的に変化するのが顕著に見えて問題となる。
【００１０】
上述の従来例では、第４レンズ群が１枚乃至２枚のレンズで構成されていた。しかし、本発明では、第４レンズ群の倍率変化をより大きくして、収差変動、特にワイド側における球面収差が第３レンズ群と第４レンズ群との間で打ち消しあっていることに起因する球面収差の変動をあまり増大しないように抑えることを重視した。そのために、第４レンズ群に、倍率変化による収差変動の小さい第２レンズ群と同様の構成、すなわち物体側より順に凹レンズ及び凹レンズと凸レンズの接合レンズの３枚構成を適用することで、高倍率化と小型化を両立させた。
【００１１】
次に、望遠端の画角が狭くなることにより顕著になる色収差を良好に補正することと小型化とを両立させるための好ましい構成について説明する。望遠端の２次スペクトルは、第１レンズ群の残存色収差が第２レンズ群以降のレンズ系で拡大されることが支配的要因である。この第１レンズ群の残存色収差を低減するには、第１レンズ群の凸レンズにアッベ数が８０以上のいわゆる超低分散ガラスを用いることが効果的であることを本発明者は見出した。それ以外の設計手段、たとえば第１レンズ群の枚数を増やすなどして異常分散性のある一般的なガラスで色消しを行うような手段も考えられるが、小型化との両立が果たしにくい。
【００１２】
図１は、本発明の１実施例に係るズームレンズの基本的な構成を示すレンズ断面図である。（Ａ）は広角端状態、（Ｂ）はズーム比約３０倍（焦点距離が広角端の３０倍）の状態、（Ｃ）は望遠端状態である。前述のように、本実施例では、絞りＳは固定されており第３レンズ群の直前に配置されている。像面ＩＭ（ＣＣＤ結像面）の前のＦは、フィルターに相当する平行平面ガラスである。
【００１３】
次に望遠端で補正不足になりがちな球面収差の補正について説明する。図１における二点鎖線は、軸上無限遠物点から出た光線の光路を示す。第１レンズ群は補正不足の球面収差が残っており、第２レンズ群は補正過剰の球面収差を発生させるものとする。図１（Ａ）の広角端から望遠方向へズーミングすると、図１（Ｂ）に示すように、軸上無限遠物点から出た光線が第１レンズ群を通る光線高が高くなる。これによって、第１レンズ群で発生する補正不足の球面収差が増大する。また同時に、第２レンズ群を通る光線高も高くなることから、第２レンズ群から発生する補正過剰の球面収差も増大して、第１レンズ群と第２レンズ群が球面収差の変化を打ち消すように働く。したがって、ズーム位置が図１（Ｂ）までは、第１レンズ群と第２レンズ群との間の球面収差の打ち消しの条件が保たれる。
【００１４】
しかしながら、さらに望遠側へズーミングすると、上記光線は第１レンズ群の有効径で制限を受けて第１レンズ群の光線高は一定のままである。しかし、第２レンズ群を通る光線高はズーミングとともに低くなって、第２レンズ群から発生する補正過剰の球面収差が減少に転じるため、望遠端では球面収差が補正不足になる。そこで本実施例では、上記のような第１レンズ群と第２レンズ群の打ち消しにのみ頼るのではなく、第１レンズ群の球面収差の残存量を減少させるために、第１レンズ群の少なくとも１面に非球面を導入し、有効径において近軸球面の深さより浅くなる非球面形状としている。一方、第１レンズ群の枚数を増やして屈折力を分散させることで、発生する球面収差を減少させる設計手段もある。しかし、小型化と両立しにくくなるため、非球面により球面収差の発生を抑えるのが効果的である。
【００１５】
この第１レンズ群に非球面を導入する手段として、ガラスモールド非球面、精研削非球面、プラスチック非球面、複合非球面が考えられる。しかし、第１レンズ群の外径が大きため、ガラスモールド非球面と精研削非球面はコストが高いので、本発明の主なターゲットである家庭用ビデオカメラにはあまり適当でない。一方、プラスチック非球面は、温度変化、湿度変化などの環境条件によって屈折力や収差が変化して、設計性能を常に維持することができず、高倍率ズームにはあまり適当とはいえない。しかし複合非球面、すなわちガラスレンズの表面に樹脂の薄い非球面層を形成することで、安いコストで目標性能を満足できる。
【００１６】
次に広角端における球面収差とコマ収差の補正について説明する。軸上無限遠物点から出た光線は第３レンズ群で光線高が最大となるので、球面収差とコマ収差は第３レンズ群で発生する量が大きい。良好な収差補正を得るには、収差の発生の支配的な構成要素に対して、収差の発生しにくい構成要素として非球面を導入して、有効径において近軸球面の深さより浅くなる非球面形状にすることで球面収差とコマ収差の発生を小さく抑えることができる。第３レンズ群から発生する球面収差とコマ収差を球面のみの構成で抑えるには枚数の増加が避けられず、小型化と両立しにくい。
【００１７】
次に、第５レンズ群の構成について説明する。高倍率化のために第４レンズ群の移動量が大きくなるので、第５レンズ群は絞りＳから遠い位置に配置することになる。そのため主光線が第５レンズ群を通る光線高が高くなり射出瞳が像面の後方に位置するようになる。主光線は第５レンズ群で大きな偏角で屈折するので、第５レンズ群の正の屈折力の影響で像面湾曲がアンダーになりやすく、広角端の歪曲収差は樽型で大きくなりやすい。この第５レンズ群で発生する収差を軽減するためには、正の屈折力を２つのレンズ群に分担させるとともに、負の屈折力を持つ接合面を配置し、さらに少なくとも１面を非球面とし、有効径において近軸球面の深さより浅くなる非球面形状とすることで、少ない枚数で良好な収差補正と小型化を両立させることができる。
【００１８】
【実施例】
次に本実施例の数値例を以下に示す。
数値例において各符号の意味は以下のとおりである。
ｆ：焦点距離（mm）
Ｆ：Ｆナンバー
２ω：画角
ｒｉ：第ｉ番目の面の曲率半径（mm）
ｄｉ：第ｉ番目の面間隔（mm）
ｎｉ：第ｉ番目のレンズのｄ線の屈折率
νｉ：第ｉ番目のレンズのアッベ数
非球面の定義：非球面の深さをｘｉ、光軸からの高さをＨとして、
ｘｉ＝Ｈ2 ／ｒｉ｛１＋（１−Ｈ2 ／ｒｉ2)1/2 ｝＋ΣＡｊＨj
である。ただし、ｉａは第ｉ番目の面に付けた複合非球面にかかわる数値を示す。
【００１９】
【外１】
【外２】
図２及び図３は、本発明の第１実施例及び第２実施例の諸収差図を示す。図中の各図は、それぞれ広角端状態、ズーム比３０倍の状態、望遠端状態での無限遠合焦状態における諸収差図を表す。
各収差図において、球面収差図中の実線はｄ線についての球面収差、破線はｇ線についての球面収差、一点鎖線はｃ線についての球面収差である。非点収差図中の実線はサジタル像面、破線はメリディオナル像面を示す。
各収差図から、本実施例は諸収差が良好に補正され、優れた結像性能を有していることは明らかである。
【００２２】
【発明の効果】
以上記載したところから明らかなように、本発明のズームレンズは、焦点距離の広角端に対する倍率、すなわちズーム比が、３０倍程度までは第１レンズ群の球面収差の変化を第２レンズ群から発生する補正過剰の球面収差を増大して、第１レンズ群と第２レンズ群が球面収差の変化を打ち消すように働くことにより対応し、さらに望遠側へズーミングすることに対応するために、第１レンズ群を少なくとも１面が有効径において近軸球面の深さより浅くなる樹脂の薄い層で形成した複合非球面をもつ非球面形状とすることにより、安いコストで目標性能を満足させることができる。
【図面の簡単な説明】
【図１】本発明の１実施例に係るズームレンズの基本的な構成を示すレンズ断面図である。（Ａ）は広角端状態、（Ｂ）はズーム比約３０倍の状態、（Ｃ）は望遠端状態である。
【図２】本発明の第１実施例のズームレンズの諸収差図を示す。図中の各図はそれぞれ広角端状態、ズーム比３０倍の状態、望遠端状態での無限遠合焦状態における諸収差図を表す。
【図３】本発明の第２実施例のズームレンズの諸収差図を示す。図中の各図はそれぞれ広角端状態、ズーム比３０倍の状態、望遠端状態での無限遠合焦状態における諸収差図を表す。
【符号の説明】
Ｉ：第１レンズ群、II：第２レンズ群、III ：第３レンズ群、
IV：第４レンズ群、Ｖ：第５レンズ群、Ｓ：絞り、
Ｆ：フィルターに相当する平行平面ガラス、ＩＭ：ＣＣＤ撮像素子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens suitable for a home video camera or the like. In particular, the present invention relates to a zoom lens that can achieve a higher zoom ratio.
[0002]
[Prior art]
A zoom lens of a home video camera will be described as an example. In this type of zoom lens, product development has been made in the following two directions along with the downsizing of the image sensor. One is a direction in which the zoom ratio is the same to achieve further miniaturization, and the other is a direction in which a higher magnification is achieved in a practical size.
[0003]
As an example of a technique for realizing the latter high-power zoom lens, there is JP-A-8-5913. The zoom lens of the same number is composed of five lens groups of positive, negative, positive, negative, and positive refractive power arrangement in order from the object side, and zooming and focusing are performed by moving at least the second lens group and the fourth lens group. In this way, the front lens diameter (the lens diameter on the object side) is reduced and a zoom ratio of about 20 times is obtained. If the front lens diameter can be reduced, an optical camera shake correction device that is effective when used at the telephoto end, such as a variable apex angle prism, is mounted on the object side of the lens. This is advantageous in increasing the practicality of magnification zoom.
[0004]
[Problems to be solved by the invention]
However, taking advantage of further downsizing of the image sensor and further increasing the magnification, for example, when the technique of the above-mentioned JP-A-8-5913 is applied as it is to a 50 × zoom lens, the following problems have occurred. . That is, aberration variations due to zooming, chromatic aberration and spherical aberration at the telephoto end, etc. could not be corrected. For this reason, in the prior art, the increase in magnification while maintaining the practical size of the lens is limited to about 20 times.
[0005]
The present invention has been made in view of such problems, and is a zoom lens suitable for a home video camera or the like, and in particular, a zoom lens capable of achieving a higher zoom ratio. The purpose is to provide. More specifically, it achieves a magnification ratio of about 50 times with a screen diagonal length of 3 mm in the same size as when the above prior art is applied with a screen diagonal length of 4.5 mm and a magnification ratio of about 20 times. An object of the present invention is to provide a zoom lens in which miniaturization of an image pickup element is utilized for high magnification and various aberrations are favorably corrected.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, a zoom lens according to the present invention includes, in order from the object side, a first lens group having a fixed positive refractive power, a second lens group having a negative refractive power, and a fixed positive refractive power. A third lens group, a fourth lens group having a negative refractive power, and a fifth lens group having a fixed positive refractive power, and by moving the second lens group and the fourth lens group in the optical axis direction. A zoom lens that performs zooming and image position variation correction and focusing by zooming, and the first lens group is composed of a cemented lens and a convex lens arranged in order from the object side, and a convex lens, and at least one surface thereof The second lens has an aspherical shape having a composite aspherical surface formed of a thin layer of resin whose effective diameter is shallower than the depth of the paraxial spherical surface, and the at least one of the two convex lenses has an Abbé number of 80 or more. The group is on the object side The third lens group is composed of a convex lens and a convex lens and a cemented lens arranged in order from the object side, and at least one surface is paraxial with an effective diameter. Convex lens having an aspherical shape that becomes shallower than the depth of the spherical surface, the fourth lens group comprising a concave lens arranged in order from the object side, and a cemented lens of a concave lens and a convex lens, and the fifth lens group arranged in order from the object side And a cemented lens of a convex lens and a concave lens, and at least one surface has an aspherical shape that becomes shallower than the depth of the paraxial spherical surface at the effective diameter, and the lateral magnification β4W of the fourth lens group at the wide angle end is 3 <β4W <8. There is a feature that the focal length can be changed to about 50 times the wide-angle end.
[0007]
When zooming from the wide-angle end to the telephoto end, the second lens unit moves from the object side to the image side, and the lateral magnification of the second lens unit increases to increase the overall focal length. At this time, the fourth lens group moves from the object side to the image side until the lateral magnification of the second lens group becomes −1 from the wide-angle end to function as a multiplier, and the lateral magnification of the second lens group is From -1 to the telephoto end, it reverses and moves from the image side to the object side to work for multiplication. A position where the moving direction of the fourth lens group is reversed is called an inflection point.
[0008]
The entrance pupil is located near the first lens group at the wide-angle end because the second lens group is far from the stop, and the ray height of the principal ray passing through the front lens from the angle of view at the wide-angle end and the entrance pupil position is Determined. As the second lens group moves to the image side, the entrance pupil moves away from the first lens group and the angle of view gradually decreases, so that the ray height at the front lens of the principal ray determined from the entrance pupil position and the angle of view changes. . In a zoom lens in which the angle of view at the wide angle end is about 60 degrees and the zoom ratio is 10 times or more, the principal ray height of the principal ray is often maximized at a zoom position where the angle of view is slightly narrower than the wide angle end. However, in the zoom lens having the above five-group configuration, the change in the entrance pupil position is determined only by the movement of the second lens group, while the change in the angle of view is also changed in the fourth lens group from the wide-angle end to the inflection point. To play a role. For this reason, the angle of view when the front beam height of the principal ray is maximized can be narrowed, so that the front lens diameter determined by the principal ray height can be reduced.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the zoom lens of the present invention, the refractive power of the fourth lens unit increases from the wide-angle end to the inflection point so that the effect of suppressing the increase in the front lens diameter due to the higher magnification becomes even more remarkable. It is preferable to set the arrangement. Specifically, when the lateral magnification of the fourth lens group at the wide-angle end is β4W, it is preferable that 3 <β4W <8. Below the lower limit of this value, the amount of movement of the fourth lens group increases and it is difficult to achieve miniaturization. On the other hand, if the upper limit of the above value is exceeded, the change in magnification at the time of focusing with the fourth lens group becomes large and unnatural. In particular, when the fourth lens group is oscillated minutely in the optical axis direction for autofocusing to observe the change in contrast, it is noticeable that the angle of view changes noticeably.
[0010]
In the conventional example described above, the fourth lens group is composed of one or two lenses. However, in the present invention, the change in the magnification of the fourth lens group is further increased, and aberration fluctuations, particularly spherical aberration on the wide side, are canceled out between the third lens group and the fourth lens group. Emphasis was placed on suppressing the variation of spherical aberration so as not to increase so much. Therefore, by applying the same configuration as the second lens group with small aberration fluctuation due to the change in magnification to the fourth lens group, that is, the three-lens configuration of the concave lens and the cemented lens of the concave lens and the convex lens in order from the object side, Both miniaturization and downsizing.
[0011]
Next, a description will be given of a preferred configuration for achieving good correction of chromatic aberration that becomes noticeable when the angle of view at the telephoto end becomes narrower and miniaturization. The dominant secondary spectrum at the telephoto end is that the residual chromatic aberration of the first lens group is magnified by the lens system after the second lens group. In order to reduce the residual chromatic aberration of the first lens group, the inventors have found that it is effective to use so-called ultra-low dispersion glass having an Abbe number of 80 or more for the convex lens of the first lens group. Other design means, for example, a means of achromatizing with ordinary glass having anomalous dispersion by increasing the number of the first lens group can be considered, but it is difficult to achieve both miniaturization and miniaturization.
[0012]
FIG. 1 is a lens cross-sectional view showing a basic configuration of a zoom lens according to an embodiment of the present invention. (A) is a wide-angle end state, (B) is a zoom ratio of about 30 times (focal length is 30 times that of the wide-angle end), and (C) is a telephoto end state. As described above, in this embodiment, the diaphragm S is fixed and is disposed immediately before the third lens group. F in front of the image plane IM (CCD imaging plane) is parallel plane glass corresponding to a filter.
[0013]
Next, correction of spherical aberration that tends to be insufficiently corrected at the telephoto end will be described. A two-dot chain line in FIG. 1 indicates an optical path of a light beam emitted from an object point on the axis at infinity. It is assumed that the uncorrected spherical aberration remains in the first lens group, and the overcorrected spherical aberration is generated in the second lens group. When zooming from the wide-angle end in FIG. 1A to the telephoto direction, as shown in FIG. 1B, the height of a light beam emitted from an axially infinite object point passes through the first lens group. This increases the undercorrected spherical aberration that occurs in the first lens group. At the same time, since the height of the light beam passing through the second lens group also increases, the overcorrected spherical aberration generated from the second lens group also increases, and the first lens group and the second lens group cancel the change in spherical aberration. Work like so. Therefore, until the zoom position reaches FIG. 1B, the spherical aberration canceling condition between the first lens group and the second lens group is maintained.
[0014]
However, when zooming further to the telephoto side, the light beam is limited by the effective diameter of the first lens group, and the light beam height of the first lens group remains constant. However, the height of the light beam passing through the second lens group decreases with zooming, and the overcorrected spherical aberration generated from the second lens group starts to decrease, so that the spherical aberration is undercorrected at the telephoto end. Therefore, in this embodiment, in order not to rely only on the cancellation of the first lens group and the second lens group as described above, in order to reduce the remaining amount of spherical aberration of the first lens group, at least the first lens group An aspherical surface is introduced into one surface, and the aspherical shape becomes shallower than the depth of the paraxial spherical surface at the effective diameter. On the other hand, there is also a design means for reducing the generated spherical aberration by increasing the number of first lens groups and dispersing the refractive power. However, since it becomes difficult to achieve compatibility with downsizing, it is effective to suppress the occurrence of spherical aberration by an aspherical surface.
[0015]
As a means for introducing an aspheric surface into the first lens group, a glass mold aspheric surface, a fine grinding aspheric surface, a plastic aspheric surface, and a composite aspheric surface are conceivable. However, since the outer diameter of the first lens group is large, the glass mold aspherical surface and the fine grinding aspherical surface are expensive, so that they are not very suitable for the home video camera which is the main target of the present invention. On the other hand, the plastic aspherical surface is not suitable for high-power zoom because the refractive power and aberration change due to environmental conditions such as temperature change and humidity change, and the design performance cannot always be maintained. However, by forming a composite aspherical surface, that is, a thin aspherical layer of resin on the surface of the glass lens, the target performance can be satisfied at a low cost.
[0016]
Next, correction of spherical aberration and coma at the wide angle end will be described. Since the ray height from the object point at infinity on the axis has the maximum ray height in the third lens group, the amount of spherical aberration and coma generated in the third lens group is large. In order to obtain good aberration correction, an aspherical surface is introduced that is less than the depth of the paraxial spherical surface at the effective diameter by introducing an aspherical surface as a component that is less likely to generate aberrations, in contrast to the dominant component that generates aberrations. By making the shape, generation of spherical aberration and coma aberration can be suppressed to a low level. In order to suppress the spherical aberration and coma aberration generated from the third lens group with a configuration of only a spherical surface, an increase in the number of images is inevitable, and it is difficult to achieve a reduction in size.
[0017]
Next, the configuration of the fifth lens group will be described. Since the amount of movement of the fourth lens group increases for higher magnification, the fifth lens group is arranged at a position far from the stop S. For this reason, the height of the ray at which the principal ray passes through the fifth lens group is increased, and the exit pupil is positioned behind the image plane. Since the principal ray is refracted by the fifth lens group with a large declination, the curvature of field tends to be under due to the positive refractive power of the fifth lens group, and distortion at the wide-angle end tends to be large due to the barrel shape. In order to reduce the aberration generated in the fifth lens group, the positive refractive power is shared between the two lens groups, a cemented surface having a negative refractive power is disposed, and at least one surface is made an aspherical surface. By making the aspherical shape shallower than the depth of the paraxial spherical surface in the effective diameter, it is possible to achieve both good aberration correction and downsizing with a small number of sheets.
[0018]
【Example】
Next, numerical examples of the present embodiment are shown below.
In the numerical examples, the meaning of each symbol is as follows.
f: Focal length (mm)
F: F number 2ω: Angle of view ri: Radius of curvature of i-th surface (mm)
di: i-th surface interval (mm)
ni: Refractive index of d-line of i-th lens νi: Abbe number of i-th lens Definition of aspheric surface: Depth of aspheric surface is xi, height from optical axis is H,
xi = H 2 / ri {1+ (1−H 2 / ri 2 ) 1/2 } + ΣAjH j
It is. Here, ia represents a numerical value related to the composite aspheric surface attached to the i-th surface.
[0019]
[Outside 1]
[Outside 2]
2 and 3 show aberration diagrams of the first and second embodiments of the present invention. Each diagram in the drawing represents various aberration diagrams in the wide-angle end state, the zoom ratio of 30 times, and the infinite focus state in the telephoto end state.
In each aberration diagram, the solid line in the spherical aberration diagram indicates the spherical aberration for the d line, the broken line indicates the spherical aberration for the g line, and the alternate long and short dash line indicates the spherical aberration for the c line. The solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane.
From each aberration diagram, it is clear that the present example has excellent image forming performance with various aberrations corrected well.
[0022]
【The invention's effect】
As is apparent from the above description, the zoom lens of the present invention shows the change of the spherical aberration of the first lens group from the second lens group until the magnification of the focal length with respect to the wide angle end, that is, the zoom ratio is about 30 times. In order to cope with the increase in the overcorrected spherical aberration that occurs, the first lens group and the second lens group work by canceling the change in spherical aberration, and further zooming to the telephoto side. By making one lens group an aspherical shape having a composite aspherical surface formed of a thin resin layer in which at least one surface has an effective diameter that is shallower than the depth of the paraxial spherical surface, the target performance can be satisfied at a low cost. .
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view showing a basic configuration of a zoom lens according to an embodiment of the present invention. (A) is a wide-angle end state, (B) is a state with a zoom ratio of about 30 times, and (C) is a telephoto end state.
FIG. 2 is a diagram illustrating various aberrations of the zoom lens according to the first example of the present invention. Each figure in the drawing represents various aberration diagrams in the wide-angle end state, the zoom ratio of 30 times, and the infinite focus state in the telephoto end state.
FIG. 3 shows various aberrations of the zoom lens according to the second embodiment of the present invention. Each figure in the drawing represents various aberration diagrams in the wide-angle end state, the zoom ratio of 30 times, and the infinite focus state in the telephoto end state.
[Explanation of symbols]
I: first lens group, II: second lens group, III: third lens group,
IV: 4th lens group, V: 5th lens group, S: Aperture,
F: Parallel plane glass corresponding to a filter, IM: CCD image sensor
Claims (1)
上記第１レンズ群が、物体側より順に配列された凹レンズ及び凸レンズの接合レンズ並びに凸レンズからなり、少なくとも１面が有効径において近軸球面の深さより浅くなる樹脂の薄い層で形成した複合非球面をもつ非球面形状であり、２枚の凸レンズのうち少なくとも１枚のアツベ数が８０以上であり、
上記第２レンズ群が、物体側より順に配列された凹レンズ並びに凹レンズ及び凸レンズの接合レンズからなり、
上記第３レンズ群が、物体側より順に配列された凸レンズ並びに凸レンズ及び凹レンズの接合レンズからなり、少なくとも１面が、有効径において近軸球面の深さより浅くなる非球面形状であり、
上記第４レンズ群が、物体側より順に配列された凹レンズ並びに凹レンズ及び凸レンズの接合レンズからなり、
上記第５レンズ群が、物体側より順に配列された凸レンズ並びに凸レンズ及び凹レンズの接合レンズからなり、少なくとも１面が、有効径において近軸球面の深さより浅くなる非球面形状であり、
広角端における第４レンズ群の横倍率β４Ｗが
３＜β４Ｗ＜８
であり、
焦点距離が広角端の略５０倍に変倍可能に構成された
ことを特徴とするズームレンズ。In order from the object side, a fixed first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having fixed positive refractive power, and a fourth lens having negative refractive power. And a fifth lens group having a fixed positive refractive power, and moving the second lens group and the fourth lens group in the optical axis direction, zooming, and correction of image position variation due to zooming and focusing A zoom lens that performs
The first lens group includes a cemented lens of a concave lens and a convex lens arranged in order from the object side, and a convex lens, and at least one surface is a composite aspherical surface formed of a thin layer of resin whose effective diameter is shallower than the depth of the paraxial spherical surface An aspherical shape having at least one of the two convex lenses, the number of which is 80 or more,
The second lens group includes a concave lens and a cemented lens of a concave lens and a convex lens arranged in order from the object side,
The third lens group is composed of a convex lens and a cemented lens of a convex lens and a concave lens arranged in order from the object side, and at least one surface has an aspherical shape that becomes shallower than the depth of the paraxial spherical surface at the effective diameter,
The fourth lens group includes a concave lens and a cemented lens of a concave lens and a convex lens arranged in order from the object side,
The fifth lens group is composed of a convex lens and a cemented lens of a convex lens and a concave lens arranged in order from the object side, and at least one surface has an aspherical shape that becomes shallower than the depth of the paraxial spherical surface at the effective diameter,
The lateral magnification β4W of the fourth lens group at the wide angle end is 3 <β4W <8.
And
A zoom lens characterized in that the focal length can be changed to about 50 times the wide-angle end.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23638497A JP3821330B2 (en) | 1997-09-02 | 1997-09-02 | Zoom lens |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23638497A JP3821330B2 (en) | 1997-09-02 | 1997-09-02 | Zoom lens |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2005330692A Division JP2006099130A (en) | 2005-11-15 | 2005-11-15 | Zoom lens |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH1184239A JPH1184239A (en) | 1999-03-26 |
| JP3821330B2 true JP3821330B2 (en) | 2006-09-13 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP23638497A Expired - Fee Related JP3821330B2 (en) | 1997-09-02 | 1997-09-02 | Zoom lens |
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| Country | Link |
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| JP (1) | JP3821330B2 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4510178B2 (en) * | 1999-07-16 | 2010-07-21 | キヤノン株式会社 | Zoom lens |
| JP4447706B2 (en) * | 1999-10-29 | 2010-04-07 | キヤノン株式会社 | Variable magnification optical system having anti-vibration function and optical apparatus including the same |
| JP4257600B2 (en) | 2004-06-14 | 2009-04-22 | ソニー株式会社 | Imaging device and zoom lens |
| JP4617111B2 (en) * | 2004-07-30 | 2011-01-19 | キヤノン株式会社 | Zoom lens and imaging apparatus having the same |
| JP5084312B2 (en) * | 2007-03-16 | 2012-11-28 | オリンパス株式会社 | Imaging optical system and electronic imaging apparatus having the same |
| JP5159398B2 (en) * | 2008-04-07 | 2013-03-06 | キヤノン株式会社 | Zoom lens and imaging apparatus having the same |
| US8736968B2 (en) | 2008-07-28 | 2014-05-27 | Nikon Corporation | Zoom lens, optical apparatus having same, and method of manufacturing zoom lens |
| JP5448028B2 (en) * | 2008-07-28 | 2014-03-19 | 株式会社ニコン | Zoom lens and optical apparatus having the same |
| JP5641680B2 (en) * | 2008-07-28 | 2014-12-17 | 株式会社ニコン | Zoom lens and optical apparatus having the same |
| US8614855B2 (en) | 2009-02-26 | 2013-12-24 | Tamron Co., Ltd. | Zoom lens |
| JP5743810B2 (en) * | 2010-10-07 | 2015-07-01 | キヤノン株式会社 | Zoom lens and imaging apparatus having the same |
-
1997
- 1997-09-02 JP JP23638497A patent/JP3821330B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH1184239A (en) | 1999-03-26 |
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