JP2004212920A

JP2004212920A - Objective lens for microscope

Info

Publication number: JP2004212920A
Application number: JP2003067613A
Authority: JP
Inventors: Koichi Hiraga; 康一平賀; Kotaro Yamaguchi; 弘太郎山口
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2002-11-15
Filing date: 2003-03-13
Publication date: 2004-07-29
Anticipated expiration: 2023-03-13
Also published as: JP4352374B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens for a microscope constituted only of a single lens not using a doublet, excellent in the performance of aberration correction and effectiveness to eccentric tolerance, having high magnification (≥ about 40) and such numerical aperture as about 0.9 and used in a deep ultraviolet wavelength region. <P>SOLUTION: The objective lens OL for a microscope is constituted of a first lens group G1 providing a meniscus lens turning its concave surface toward an object side and having positive refractive power, a second lens group G2 consisting of one lens having positive refractive power, a third lens group G3 constituted by arranging at least two or more pairs of lenses when two adjacent lenses having positive and negative refractive power and having the same sign of the radius of curvature of their adjacent surfaces are set as a pair of lenses, and having positive refractive power as a whole, and a fourth lens group G4 having negative refractive power as a whole in order from the object side, and the pair of lenses satisfies a specified condition. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、高倍率（４０倍程度以上）で、開口数が０．９程度に達し、深紫外波長領域で使用することを目的とした顕微鏡用対物レンズに関する。
【０００２】
【従来の技術】
高倍率（４０倍程度以上）で、開口数が０．９程度に達し、深紫外波長領域で使用することを目的とした顕微鏡用対物レンズとしては、例えば特許文献１に開示されたもの等が知られている。
【０００３】
【特許文献１】
特開２００１−３１８３１７号公報
【０００４】
【発明が解決しようとする課題】
特許文献１に開示されている顕微鏡用対物レンズは、接着による接合レンズを含んでおらず、接着剤に深紫外光が照射されることによって発生する諸問題を回避している。しかしながら、接合レンズが無いことによりレンズ形状や配置位置の誤差等が偏心公差を大きくしやすく（このような、レンズ形状や配置位置の誤差等が偏心公差に与える影響を以降の説明では「偏心公差への効き」と呼ぶ）、製造に負担が掛るレンズ構成となっているという課題があった。
【０００５】
本発明は以上のような課題に鑑みなされたものであり、接合レンズを用いなくても偏心公差への効きを緩くすることができる、高倍率（４０倍程度以上）で、開口数が０．９程度に達し、深紫外波長領域で使用することを目的とした顕微鏡用対物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】
前記課題を解決するために、本発明に係る顕微鏡用対物レンズは、隣接したレンズ同士が全て空気間隔を有して配置され、レンズの構成が物体側から順に、物体側に凹面を向けた正の屈折力を有するメニスカスレンズを有してなる第１レンズ群と、正の屈折力を有する１枚のレンズからなる第２レンズ群と、隣接した２枚のレンズが正と負の屈折力を有し、且つ、隣接する面の曲率半径の符号が同一であるこの隣接した２枚のレンズを１組のレンズ組としたとき、このレンズ組を少なくとも５組以上配置してなり、全体として正の屈折力を有する第３レンズ群と、全体として負の屈折力を有する第４レンズ群とから構成される。このとき、第３レンズ群中のレンズ組を構成する２枚のレンズのうち正の屈折力を有するレンズのアッベ数をν３Ｐ、負の屈折力を有するレンズのアッベ数をν３Ｎとしたとき、式ν３Ｐ＞ν３Ｎで表される条件を満足し、第３レンズ群を構成するレンズのうち最も中心厚の薄いレンズの中心厚をｄｍｉｎとし、レンズ組を構成する２枚のレンズの隣接面におけるレンズ間隔をｄｃｅｎｔｅｒ、エッジ空気間隔をｄｅｄｇｅとしたとき、式２×ｄｍｉｎ＞ｄｃｅｎｔｅｒ＋ｄｅｄｇｅで表される条件を満足し、第３レンズ群を構成するレンズのうち、最も物体側のレンズから最大有効径を有するレンズに至る区間に配置された凹レンズの物体側の曲率半径をｒ１ａ、像側の曲率半径をｒ２ａとし、最大有効径を有するレンズから第４レンズ群に至る区間に配置された凹レンズの物体側の曲率半径をｒ１ｂ、像側の曲率半径をｒ２ｂとしたとき、式｜ｒ１ａ｜＜｜ｒ２ａ｜，｜ｒ１ｂ｜＞｜ｒ２ｂ｜で表される条件を満足し、前記第３レンズ群と第４レンズ群はレンズ全長（物体面から対物レンズ最終面までの距離）、若しくは同焦点距離のいずれか短い方の距離の１／６以上の距離の空気間隔を隔てて配置するように構成される。
【０００７】
なお、第３レンズ群において、最大有効径を有するレンズを挟んで物体側と像側にレンズ組が配置され、最も物体側のレンズから最大有効径を有するレンズに至る区間に配置されたレンズ組を構成する２枚のレンズの隣接面は負の曲率半径を有する面若しくは平面で構成され、最大有効径を有するレンズから第４レンズ群至る区間に配置されたレンズ組を構成する２枚のレンズの隣接面は正の曲率半径を有する面若しくは平面で構成されることが好ましい。
【０００８】
このとき、第３レンズ群において、最も物体側のレンズから最大有効径を有するレンズに至る区間に配置されたレンズ組は物体側が正の屈折力を有するレンズで構成され、最大有効径を有するレンズから第４レンズ群に至る区間に配置されたレンズ組は物体側が負の屈折力を有するレンズで構成されることが好ましい。
【０００９】
また、第３レンズ群中に正負正あるいは負正負の屈折力を有する３枚のレンズからなるレンズ組を１組以上有し、この３枚のレンズからなるレンズ組を構成するレンズ同士の隣接面が式２×ｄｍｉｎ＞ｄｃｅｎｔｅｒ＋ｄｅｄｇｅで表される条件を満足するように構成されることが好ましい。
【００１０】
また、物体面において光軸と交わる点から発する光束の主光線と最大開口数の光線、及び、物体面の最大物高から発する光束の主光線と上側及び下側コマ光線中の最大開口数の光線が、第２〜４レンズ群に入射及び出射するときの入射角及び出射角が５０度以下であるように構成されることが好ましく、この角度が４５度以下であるとさらに好ましい。
【００１１】
また、第３レンズ群を構成するレンズのうち、正の屈折力を有するレンズの有効径に対する焦点距離の割合の最大値をＡｍａｘ、最小値をＡｍｉｎとしたとき、式Ａｍａｘ／Ａｍｉｎ＜２で表される条件を満足するように構成されることが好ましい。
【００１２】
また、第３レンズ群を構成するレンズのうち、負の屈折力を有するレンズの有効径に対する焦点距離の割合の最大値をＢｍａｘ、最小値をＢｍｉｎとしたとき、式Ｂｍａｘ／Ｂｍｉｎ＜２で表される条件を満足するように構成されることが好ましい。
【００１３】
また、第３レンズ群中の凸レンズの焦点距離をｆ３Ｐとし、第１〜４レンズ群で構成される全体の焦点距離をｆａｌｌとしたとき、式ｆ３Ｐ／ｆａｌｌ＞６で表される条件を満足するように構成させることが好ましい。
【００１４】
さらに、観察光である深紫外領域波長と自動焦点合わせに用いる可視領域若しくは赤外領域の単波長光線とが軸上色消しされるように第１〜４レンズ群が構成されることが好ましい。
【００１５】
【発明の実施の形態】
以下、本発明の好ましい実施形態について図面を参照して説明する。図１、図３及び図５はそれぞれ本発明の第１〜３の実施形態に対応する顕微鏡用対物レンズＯＬの構成図であり、隣接したレンズ同士が全て空気間隔を有して配置されている。いずれの実施例においても、物体側から順に、物体側に凹面を向けた正の屈折力を有する第１レンズ群Ｇ１と、正の屈折力を有する１枚のレンズからなる第２レンズ群Ｇ２と、隣接した２枚のレンズが正と負の屈折力を有するレンズで構成され、且つ、隣接する面の曲率半径の符号が同一である２枚のレンズを１組のレンズ組としたときこのレンズ組を少なくとも５組以上配置してなり、全体として正の屈折力を有する第３レンズ群Ｇ３と、全体として負の屈折力を有する第４レンズ群Ｇ４とから構成される。
【００１６】
図１に示す第１の実施形態に係る顕微鏡用対物レンズＯＬでは、物体側から順に、第１レンズ群Ｇ１は物体側に凹面を向けた正メニスカスレンズＬ１から構成され、第２レンズ群Ｇ２は物体側に凹面を向けた正メニスカスレンズＬ２から構成され、第３レンズ群Ｇ３は、両凸レンズＬ３と物体側に凹面を向けた負メニスカスレンズＬ４の２枚のレンズからなるレンズ組と、両凸レンズＬ５と物体側に凹面を向けた負メニスカスレンズＬ６の２枚のレンズからなるレンズ組と、両凸レンズＬ７と物体側に凹面を向けた負メニスカスレンズＬ８の２枚のレンズからなるレンズ組と、両凸レンズＬ９と両凹レンズＬ１０と両凸レンズＬ１１の３枚のレンズからなるレンズ組と、両凹レンズＬ１２と両凸レンズＬ１３の２枚のレンズからなるレンズ組と、物体側に凸面を向けた負メニスカスレンズＬ１４と両凸レンズＬ１５の２枚のレンズからなるレンズ組と、物体側に凸面を向けた負メニスカスレンズＬ１６と両凸レンズＬ１７の２枚のレンズからなるレンズ組とから構成され、第４レンズ群Ｇ４は物体側に凸面を向けた正メニスカスレンズＬ１８と両凹レンズＬ１９とから構成される。
【００１７】
図３に示す第２の実施形態に係る顕微鏡用対物レンズＯＬでは、物体側から順に、第１レンズ群Ｇ１は物体側に凹面を向けた正メニスカスレンズＬ２１から構成され、第２レンズ群Ｇ２は物体側に凹面を向けた正メニスカスレンズＬ２２から構成され、第３レンズ群Ｇ３は両凸レンズＬ２３と物体側に凹面を向けた負メニスカスレンズＬ２４の２枚のレンズからなるレンズ組と、両凸レンズＬ２５と物体側に凹面を向けた負メニスカスレンズＬ２６の２枚のレンズからなるレンズ組と、両凸レンズＬ２７と物体側に凹面を向けた負メニスカスレンズＬ２８の２枚のレンズからなるレンズ組と、両凸レンズＬ２９と両凹レンズＬ３０と両凸レンズＬ３１の３枚のレンズからなるレンズ組と、両凹レンズＬ３２と両凸レンズＬ３３の２枚のレンズからなるレンズ組と、物体側に凸面を向けた負メニスカスレンズＬ３４と両凸レンズＬ３５の２枚のレンズからなるレンズ組と、物体側に凸面を向けた負メニスカスレンズＬ３６と両凸レンズＬ３７の２枚のレンズからなるレンズ組とから構成され、第４レンズ群Ｇ４は物体側に凸面を向けた正メニスカスレンズＬ３８と両凹レンズＬ３９とから構成される。
【００１８】
図５に示す第３の実施形態に係る顕微鏡用対物レンズＯＬでは、物体側から順に、第１レンズ群Ｇ１は物体側に凹面を向けた正メニスカスレンズＬ４１から構成され、第２レンズ群Ｇ２は物体側に凹面を向けた正メニスカスレンズＬ４２から構成され、第３レンズ群Ｇ３は両凸レンズＬ４３と両凹レンズＬ４４の２枚のレンズからなるレンズ組と、物体側に凹面を向けた正メニスカスレンズＬ４５と、両凸レンズＬ４６と両凹レンズＬ４７と両凸レンズＬ４８の３枚のレンズからなるレンズ組と、両凸レンズＬ４９と両凹レンズＬ５０と両凸レンズＬ５１の３枚のレンズからなるレンズ組と、両凸レンズＬ５２と両凹レンズＬ５３と両凸レンズＬ５４の３枚のレンズからなるレンズ組と、物体側に凸面を向けた負メニスカスレンズＬ５５と両凸レンズＬ５６の２枚のレンズからなるレンズ組とから構成され、第４レンズ群Ｇ４は物体側に凸面を向けた正メニスカスレンズＬ５７と両凹レンズＬ５８とから構成される。
【００１９】
一般に、本発明に係る顕微鏡用対物レンズＯＬのように、４０倍程度より大きな倍率を有し、高開口数の対物レンズにおいては、最も物体寄りのレンズ群の像側の曲率を不遊条件を満たすようにすることで、球面収差について無収差で正の屈折力を得る構成となっている。この構成のレンズで得られる正の屈折力は非常に大きく、無収差で効率良く倍率を稼ぐのには不可欠な構成である。
【００２０】
本発明に係る顕微鏡用対物レンズＯＬの第１レンズ群Ｇ１は、物体側に凹面を向けた正の屈折力を有するメニスカスレンズとし、像側の面の曲率を不遊条件かそれに近い条件とすることで、球面収差の発生を抑えつつ正の屈折力を稼ぎ、物体側の凹面によってペッツヴァル和を小さくして、像面湾曲の補正に寄与する。
【００２１】
第２レンズ群Ｇ２は、第１レンズ群Ｇ１から続いて正の屈折力を有する単レンズを配置することにより、正の屈折力を稼ぐ構造とする。
【００２２】
第３レンズ群Ｇ３は全体として正の屈折力を有し、第２レンズ群Ｇ２から出射した発散光を収束光に変換するが、このとき、観察光（本発明の実施例では２４８±３ｎｍの光を使用）と自動焦点合わせ機構等に使用する光との色消しを行う為に下に示す条件式（１）を満たし、且つ、隣接したレンズの隣接面の曲率半径の符号が同じで、下に示す条件式（２）及び（３）を満たすような正と負の屈折力を有する２枚のレンズよりなるレンズ組を少なくとも５組以上配置する。この構成は、色消しと同時に凹面による収差補正効果を持たせる上でも必要となる。
【００２３】
【数１】
ν３Ｐ＞ ν３Ｎ（１）
２×ｄｍｉｎ＞ｄｃｅｎｔｅｒ＋ｄｅｄｇｅ（２）
｜ｒ１ａ｜＜｜ｒ２ａ｜，｜ｒ１ｂ｜＞｜ｒ２ｂ｜（３）
但し、
ν３Ｐ：第３レンズ群Ｇ３中のレンズ組を構成する２つのレンズのうち正の屈折力を有するレンズのアッベ数
ν３Ｎ：第３レンズ群Ｇ３中のレンズ組を構成する２つのレンズのうち負の屈折力を有するレンズのアッベ数
ｄｍｉｎ：第３レンズ群Ｇ３を構成するレンズのうち最も中心厚の薄いレンズの中心厚
ｄｃｅｎｔｅｒ：第３レンズ群Ｇ３中のレンズ組を構成する２つのレンズのレンズ間隔
ｄｅｄｇｅ：第３レンズ群Ｇ３中のレンズ組を構成する２つのレンズのエッジ空気間隔
ｒ１ａ：第３レンズ群Ｇ３を構成するレンズのうち、最も物体側のレンズから最大有効径を有するレンズに至る区間に配置された凹レンズの物体側の曲率半径
ｒ２ａ：第３レンズ群Ｇ３を構成するレンズのうち、最も物体側のレンズから最大有効径を有するレンズに至る区間に配置された凹レンズの像側の曲率半径
ｒ１ｂ：第３レンズ群Ｇ３を構成するレンズのうち、最大有効径を有するレンズから第４レンズ群Ｇ４に至る区間に配置された凹レンズの物体側の曲率半径
ｒ２ｂ：第３レンズ群Ｇ３を構成するレンズのうち、最大有効径を有するレンズから第４レンズ群Ｇ４に至る区間に配置された凹レンズの像側の曲率半径
【００２４】
上記のレンズ組は、接合レンズが使える構成では、接合レンズとして構成した方が都合が良い場合も多いが、本発明に係る顕微鏡用対物レンズＯＬでは、接合レンズを形成するために必要な接着剤に深紫外光が照射されることによって発生する諸問題に対応するために接合レンズは用いていない。しかし、上記のレンズ組は、収差補正上では接合レンズと近い効果を持ち、形状的にも接合レンズと近い形状となっていることから、以降の説明では「疑似接合レンズ」と呼ぶことにする。
【００２５】
第４レンズ群Ｇ４は全体として負の屈折力を有し、第３レンズ群Ｇ３から出射した収束光を平行光束に変換し、同時に主に上側コマ光束の収差補正に寄与する。また、この第４レンズ群Ｇ４は第３レンズ群Ｇ３とレンズ全長（物体面から顕微鏡用対物レンズＯＬの最終面までの距離）、若しくは同焦点距離のいずれか短い方の距離の１／６以上の距離の空気間隔を隔てて配置する。本対物レンズのような紫外領域で使用される対物レンズは、硝材の吸収による光量低下が大きいため、上記のような空気間隔を隔てることで硝材の吸収による光量低下を抑えることができる。
【００２６】
ところで、接合レンズを上述の疑似接合レンズで代用した場合、この疑似接合レンズの隣接面を単純に接合レンズを接合するための接着剤を剥いだ様な構成にすると、光線の入射角及び出射角が大きくなる傾向にあり、これにより偏心公差への効きが敏感になるという問題があった。このため、疑似接合レンズを用いた場合には、第２〜４レンズ群Ｇ２〜Ｇ４を構成するレンズを透過する光線の入射角及び出射角を５０度以下に抑えることで、収差補正の性能を維持しつつ、偏心公差への効きを緩くすることができる。なお、第２〜第４レンズ群Ｇ２〜Ｇ４を構成するレンズを透過する光線としては、物体面においてこの顕微鏡用対物レンズＯＬの光軸と交わる点から発する光束の主光線と最大開口数の光線、及び、物体面の最大物高から発する光束の主光線と上側及び下側コマ光線中の最大開口数の光線を対象とし、この光線の入射角及び出射角を５０度以下に抑えるように構成されている。
【００２７】
比較的大きな入射角及び出射角となる面を有したレンズが、設計上では収差が良好に補正される場合があることは知られているが、反面、このような面を有したレンズは偏心公差への効きが敏感になり、製造面の負担が大きくなる。そのため、接合レンズを使わない顕微鏡用対物レンズＯＬでは、上述のように、レンズ面の入射角及び出射角が大きくならないように構成する方が収差補正の性能及び偏心公差への効きが良好になる場合が多い。
【００２８】
例えば、発散光束中ではレンズの曲率を負にした方がレンズ面に対する入射角及び出射角を小さくすることができる。また、逆に収束光束中ではレンズの曲率を正にした方がレンズ面に対する入射角及び出射角を小さくすることができる。このため、第３レンズ群Ｇ３中のレンズ組を構成する疑似接合レンズの隣接面を、上述のように、発散光束中では曲率を負にし、収束光束中では曲率を正にするように構成することにより、第２〜４レンズ群Ｇ２〜Ｇ４を構成するレンズを透過する光線の入射角及び出射角を５０度以下に抑えることができ、偏心公差への効きを緩くすることができる。
【００２９】
第３レンズ群Ｇ３を以上のような構成とするためには、第２レンズ群Ｇ２から出射された発散光束を第３レンズ群Ｇ３で収束光に変換する際に、第３レンズ群Ｇ３を構成するレンズで徐々に変換するように構成する。そのため、第３レンズ群Ｇ３を構成する凹レンズが条件式（３）満たすようにするとともに、第３レンズ群Ｇ３の最大有効径を有するレンズを挟んで物体側と像側にそれぞれレンズ組を配置し、最大有効径を有するレンズの物体側が概ね発散光束となるようにし、像側が概ね収束光束となるようにし、この最大有効径を有するレンズで光束が最大となるように構成する。そして、上述のように、概ね発散光束である光線が透過する最大有効径を有するレンズより物体側に配置された疑似接合レンズで構成されたレンズ組の隣接面の曲率を負とし、概ね収束光束である光線が透過する最大有効径を有するレンズより像側に配置された疑似接合レンズで構成されたレンズ組の隣接面の曲率を正とする。
【００３０】
このとき、第３レンズ群Ｇ３において、最大有効径を有するレンズより物体側に配置されたレンズ組の隣接面は負の曲率となるため、このレンズ組を構成する２つのレンズのうち物体側に配置されたレンズの隣接面は正の屈折力を有し、像側に配置されたレンズの隣接面は負の屈折力を有する。よって、最大有効径を有するレンズより物体側に配置されたレンズ組は、物体側から順に正の屈折力を有するレンズと負の屈折力を有するレンズを順に配置した疑似接合レンズとする方が都合がよい。同様に、最大有効径を有するレンズより像側に配置されたレンズ組の隣接面は正の曲率となるため、このレンズ組を構成する２つのレンズのうち物体側に配置されたレンズの隣接面は負の屈折力を有し、像側に配置されたレンズの隣接面は正の屈折力を有する。そのため、最大有効径を有するレンズより像側に配置されたレンズ組は、物体側から順に負の屈折力を有するレンズと正の屈折力を有するレンズを順に配置した疑似接合レンズとする方が都合が良い。
【００３１】
なお、色消しが必要な光学系では条件式（１）を満たすような正負の屈折力を有するレンズの屈折力を適度に強くして組み合わせることにより、色消しを行っている。そのため、第３レンズ群Ｇ３中のレンズ組を構成する２枚の正及び負の屈折力を有するレンズの配置を上述のように構成すると、両凸レンズや両凹レンズを用いたレンズ組を構成することができるため屈折力を上げることが容易である。一方、レンズ組を構成する正及び負の屈折力を有するレンズの配置を逆にして第３レンズ群Ｇ３を構成することも可能であるが、上述のように最大有効径を有するレンズより物体側に配置されたレンズ組の隣接面を負の曲率とし、最大有効径を有するレンズより像側に配置されたレンズ組の隣接面を正の曲率とした場合、レンズ組を構成する２枚のレンズは両方ともメニスカスレンズで構成する必要があり、レンズの屈折力を上げるのが難しくなる場合がある。
【００３２】
色消しという観点からすると、一般に接合レンズでは３枚接合レンズの方が２枚接合レンズより２次分散性の向上に寄与する。そのため、第３レンズ群Ｇ３に、正負正あるいは負正負の屈折力を有する３枚のレンズからなり、この３枚のレンズが条件式（２）を満たすような疑似接合レンズであるレンズ組を有するように構成することが好ましい。このとき、３枚のレンズからなる疑似接合レンズを用いると、凹レンズの曲率が物体側と像側で符号が逆になる両凹レンズで構成される場合がある。この場合にも条件式（３）を満たすような構成にすると、この凹レンズを透過する光線の入射角及び出射角を極力小さくすることができるため、偏心公差への効きを抑えることができる。
【００３３】
また、レンズ系内の少数のレンズが大きな屈折力を有するような構成とすると、その大きな屈折力を有するレンズが特に偏心公差に対して効きが大きくなる場合が多く、偏心公差への効きを緩めるという観点からは避けたい構成である。しかしながら、一方で適当な場所に大きな屈折力を有するレンズを配置すると、収差補正上有利な場合もある。このため、第３レンズ群Ｇ３を下記に示す条件式（４），（５）を満たすようなレンズの構成にすると、収差補正の性能と偏心公差への効きの両方が良好となり、バランスの良いレンズ系とすることができる。逆に、この条件式（４），（５）で表される条件を超えると、偏心公差への効きが厳しくなり、製造面の負担が増大して設計値通りの性能を出すことが難しくなる。
【００３４】
【数２】
Ａｍａｘ／Ａｍｉｎ＜２（４）
Ｂｍａｘ／Ｂｍｉｎ＜２（５）
但し、
Ａｍａｘ：第３レンズ群Ｇ３中の正の屈折力を有するレンズの有効径（Ｄ）に対する焦点距離（ｆ）の割合（ｆ／Ｄ）の最大値
Ａｍｉｎ：第３レンズ群Ｇ３中の正の屈折力を有するレンズの有効径（Ｄ）に対する焦点距離（ｆ）の割合（ｆ／Ｄ）の最小値
Ｂｍａｘ：第３レンズ群Ｇ３中の負の屈折力を有するレンズの有効径（Ｄ）に対する焦点距離（ｆ）の割合（ｆ／Ｄ）の最大値
Ｂｍｉｎ：第３レンズ群Ｇ３中の負の屈折力を有するレンズの有効径（Ｄ）に対する焦点距離（ｆ）の割合（ｆ／Ｄ）の最小値
【００３５】
また、同様の理由から、下記に示す条件式（６）を満たすように、第３レンズ群Ｇ３を構成する凸レンズの焦点距離を制限して正の屈折力を分散させることにより、偏心公差への効きを緩くするとともに、収差補正の性能にも悪影響が出ない構成することが可能となる。
【００３６】
【数３】
ｆ３Ｐ／ｆａｌｌ＞６（６）
但し、
ｆ３Ｐ：第３レンズ群Ｇ３中の凸レンズの焦点距離
ｆａｌｌ：顕微鏡用対物レンズＯＬの全体の焦点距離
【００３７】
さらに、可視領域や赤外領域の特定の単波長光線と観察光との軸上色消しを実現すると、この単波長を使用した自動焦点合わせ機構をフォーカスのオフセットをすることなく実現できる為、装置構成上有利である。
【００３８】
以上説明したような諸条件を満たすように本発明に係る顕微鏡用対物レンズＯＬを構成することにより、接合レンズを用いない単レンズのみの構成でも、収差補正の性能と偏心公差への効きを良好にすることができ、高倍率（４０倍程度以上）で開口数が０．９程度に達し、深紫外波長領域で使用することを目的とした顕微鏡用対物レンズＯＬを得ることができる。
【００３９】
【実施例】
以下、本発明に係る顕微鏡用対物レンズの具体的な実施例について説明する。下に示す３つの実施例では、上述した第１〜３の実施形態に係る顕微鏡用対物レンズＯＬそれぞれに対応しており、従って、第１〜３の実施形態についてのレンズ構成図（図１、図３及び図５）はそれぞれ、下の第１〜３の実施例のレンズ構成を示している。
【００４０】
（第１実施例）
下の表１に、本第１実施例における各レンズの諸元を示す。表１における面番号１〜３９は本第１実施例に係る顕微鏡用対物レンズＯＬに関するものであり、それぞれ図１における符号１〜３９に対応する。また、表１におけるｆａｌｌは顕微鏡用対物レンズＯＬの焦点距離を、Ｎ．Ａ．は開口数を、βは倍率を、ｒはレンズの曲率半径を、ｄはレンズの面の間隔を、νはアッベ数を、ｎは基準光線（２４８ｎｍ）に対する屈折率を示しており、他の実施例においても同様である。また、以下の全ての諸元値において掲載されている焦点距離ｆａｌｌ、曲率半径ｒ、面間隔ｄその他の長さの単位は、特記の無い場合、一般に「ｍｍ」が使われるが、光学系は比例拡大または比例縮小しても同等の光学性能が得られるので、単位は「ｍｍ」に限定されることなく、他の適当な単位を用いることができる。
【００４１】
【表１】

【００４２】
このように第１実施例では、上記条件式（１）〜（６）は全て満たされていることが分かる。また、対物レンズの全長の１／６が１０．６９、第３レンズ群Ｇ３と第４レンズ群Ｇ４との間隔が１４．１０であるので、Ｇ３とＧ４の間隔に関する条件も満たしている。
【００４３】
図２は、第１実施例における諸収差図を示している。各収差図において、ＮＡは開口数を、ｙは像高を、Ｌは２４８ｎｍの光線を、Ｋは２５１ｎｍの光線を、Ｍは２４５ｎｍの光線をそれぞれ示している。また、非点収差では、実線はサジタル像面を示し、破線はメリジオナル像面を示している。以上の収差図の説明は、他の実施例においても同様である。
【００４４】
以上の各収差図から明らかなように、本実施例では諸収差が良好に補正されていることがわかる。
【００４５】
（第２実施例）
下の表２に、本第２実施例における各レンズの諸元を示す。表２における面番号１〜３９は本第２実施例に係る顕微鏡用対物レンズＯＬに関するものであり、それぞれ図３における符号１〜３９に対応する。
【００４６】
【表２】

【００４７】
このように第２実施例では、上記条件式（１）〜（６）は全て満たされていることが分かる。また、対物レンズの全長の１／６が１０．６５、第３レンズ群Ｇ３と第４レンズ群Ｇ４との間隔が１４．４５であるので、Ｇ３とＧ４の間隔に関する条件も満たしている。
【００４８】
図４は、第２実施例における諸収差図を示している。以上の各収差図から明らかなように、本実施例では諸収差が良好に補正されていることがわかる。
【００４９】
（第３実施例）
下の表３に、本第３実施例における各レンズの諸元を示す。表３における面番号１〜３７は本第３実施例に係る顕微鏡用対物レンズＯＬに関するものであり、それぞれ図５における符号１〜３７に対応する。
【００５０】
【表３】

【００５１】
このように第３実施例では、上記条件式（１）〜（６）は全て満たされていることが分かる。また、対物レンズの全長の１／６が１０．６７、第３レンズ群Ｇ３と第４レンズ群Ｇ４との間隔が１２．９６であるので、Ｇ３とＧ４の間隔に関する条件も満たしている。
【００５２】
図６は、第３実施例における諸収差図を示している。以上の各収差図から明らかなように、本実施例では諸収差が良好に補正されていることがわかる。なお、第１〜３の実施例のいずれにおいても、自動焦点合わせ機構等に使用する光線（７７０ｎｍ）に対しても軸上色消しがなされている。
【００５３】
なお、上述の第１〜３実施例において示した顕微鏡用対物レンズは無限遠補正型であるため、例えば、図７に示す結像レンズＩＬとともに使用される。この結像レンズＩＬは、物体側から順に、両凸レンズＬ６１と両凹レンズＬ６２との接合レンズと、物体側に凹面を向けた負メニスカスレンズＬ６３と物体側に凹面を向けた正メニスカスレンズＬ６４との接合レンズとから構成される。この結像レンズＩＬを構成する各レンズの諸元を下の表４に示す。なお、表４における面番号１〜６は結像レンズＩＬに関するものであり、それぞれ図７における符号１〜６に対応する。
【００５４】
【表４】

【００５５】
【発明の効果】
以上の説明から明らかなように、本発明に係る顕微鏡用対物レンズによれば、接合レンズを用いない単レンズのみの構成でも、収差補正の性能と偏心公差への効きを良好にすることができ、高倍率（４０倍程度以上）で開口数が０．９程度に達し、深紫外波長領域で使用することを目的とした顕微鏡用対物レンズを得ることができる。
【図面の簡単な説明】
【図１】本発明の第１の実施例に係る顕微鏡用対物レンズの構成を示す断面図である。
【図２】本発明の第１の実施例に係る顕微鏡用対物レンズの諸収差図である。
【図３】本発明の第２の実施例に係る顕微鏡用対物レンズの構成を示す断面図である。
【図４】本発明の第２の実施例に係る顕微鏡用対物レンズの諸収差図である。
【図５】本発明の第３の実施例に係る顕微鏡用対物レンズの構成を示す断面図である。
【図６】本発明の第３の実施例に係る顕微鏡用対物レンズの諸収差図である。
【図７】本発明に係る顕微鏡用対物レンズと組み合わせて使われる結像レンズの構成を示す断面図である。
【符号の説明】
ＯＬ顕微鏡用対物レンズ
Ｇ１第１レンズ群
Ｇ２第２レンズ群
Ｇ３第３レンズ群
Ｇ４第４レンズ群[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a microscope objective lens having a high magnification (about 40 times or more), a numerical aperture of about 0.9, and intended to be used in a deep ultraviolet wavelength region.
[0002]
[Prior art]
As an objective lens for a microscope intended to be used in a deep ultraviolet wavelength region at a high magnification (about 40 times or more) and a numerical aperture of about 0.9, for example, those disclosed in Patent Document 1 and the like are known. Are known.
[0003]
[Patent Document 1]
JP 2001-318317 A
[0004]
[Problems to be solved by the invention]
The microscope objective lens disclosed in Patent Literature 1 does not include a cemented lens by adhesion, and avoids various problems caused by irradiating the adhesive with deep ultraviolet light. However, due to the absence of the cemented lens, errors in the lens shape and arrangement position and the like tend to increase the eccentricity tolerance (the effects of such lens shape and arrangement position errors and the like on the eccentricity tolerance will be described in the following description as “eccentricity tolerance This has a problem that the lens configuration has a burden on manufacturing.
[0005]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a high magnification (about 40 times or more) and a numerical aperture of 0. 0, which can reduce the effect on eccentricity tolerance without using a cemented lens. It is an object of the present invention to provide an objective lens for a microscope which reaches about 9 and is intended to be used in a deep ultraviolet wavelength region.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, in a microscope objective lens according to the present invention, adjacent lenses are all arranged with an air gap, and the lens configuration is such that a concave surface faces the object side in order from the object side. A first lens group having a meniscus lens having a positive refractive power, a second lens group including one lens having a positive refractive power, and two adjacent lenses having positive and negative refractive powers. When two adjacent lenses having the same sign of the radius of curvature of adjacent surfaces are formed as one lens set, at least five or more lens sets are arranged, and the positive And a fourth lens group having a negative refractive power as a whole. At this time, when the Abbe number of the lens having a positive refractive power among the two lenses constituting the lens group in the third lens group is ν3P, and the Abbe number of the lens having a negative refractive power is ν3N, the following equation is obtained. The condition expressed by ν3P> ν3N is satisfied, the center thickness of the lens having the smallest center thickness among the lenses constituting the third lens group is dmin, and the lens distance between the adjacent surfaces of the two lenses constituting the lens set Where d is the center and edge air interval is the edge, the lens satisfying the condition expressed by the formula 2 × dmin> dcenter + dedge and having the largest effective diameter from the lens closest to the object side among the lenses constituting the third lens group The radius of curvature on the object side of the concave lens disposed in the section leading to is defined as r1a, and the radius of curvature on the image side is defined as r2a. From the lens having the largest effective diameter to the fourth lens group, When the radius of curvature on the object side of the concave lens arranged in the section is r1b and the radius of curvature on the image side is r2b, the condition represented by the expression | r1a | <| r2a |, | r1b |> | r2b | is satisfied. The third lens group and the fourth lens group have an air gap of a distance equal to or more than 1/6 of the shorter of the total lens length (the distance from the object surface to the final surface of the objective lens) or the parfocal distance. It is configured to be spaced apart.
[0007]
In the third lens group, a lens set is disposed on the object side and the image side with the lens having the maximum effective diameter therebetween, and the lens set disposed in a section from the lens closest to the object to the lens having the maximum effective diameter. The two adjacent lenses of the two lenses are a surface or a flat surface having a negative radius of curvature, and the two lenses constituting a lens set disposed in a section from the lens having the largest effective diameter to the fourth lens group Is preferably formed of a surface or a plane having a positive radius of curvature.
[0008]
At this time, in the third lens group, the lens set disposed in a section from the lens closest to the object side to the lens having the maximum effective diameter is a lens having a positive refractive power on the object side and a lens having the maximum effective diameter. It is preferable that the lens set disposed in the section from to the fourth lens group is constituted by a lens having a negative refractive power on the object side.
[0009]
Further, the third lens group includes at least one lens set including three lenses having positive, negative, positive, negative, positive, and negative refractive powers, and adjacent surfaces of lenses constituting the lens set including the three lenses. Preferably satisfies the condition represented by the formula 2 × dmin> dcenter + dedge.
[0010]
Also, the principal ray of the light beam emitted from a point intersecting with the optical axis on the object plane and the ray of the maximum numerical aperture, and the principal ray of the light ray emitted from the maximum object height of the object plane and the maximum numerical aperture of the upper and lower coma rays. It is preferable that the incident angle and the outgoing angle when the light beam enters and exits the second to fourth lens groups are 50 degrees or less, and more preferably 45 degrees or less.
[0011]
When the maximum value of the ratio of the focal length to the effective diameter of the lens having a positive refractive power among the lenses constituting the third lens group is Amax, and the minimum value is Amin, the expression is expressed as Amax / Amin <2. It is preferable to be configured so as to satisfy the following conditions.
[0012]
Also, when the maximum value of the ratio of the focal length to the effective diameter of the lens having a negative refractive power among the lenses constituting the third lens group is Bmax, and the minimum value is Bmin, it is expressed by the formula Bmax / Bmin <2. It is preferable to be configured so as to satisfy the following conditions.
[0013]
When the focal length of the convex lens in the third lens group is f3P and the entire focal length of the first to fourth lens groups is fall, the condition represented by the equation f3P / fall> 6 is satisfied. It is preferable to make such a configuration.
[0014]
Further, it is preferable that the first to fourth lens groups are configured such that the deep ultraviolet region wavelength as the observation light and the single wavelength light beam in the visible region or the infrared region used for automatic focusing are achromatic on the axis.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIGS. 1, 3, and 5 are configuration diagrams of a microscope objective lens OL corresponding to the first to third embodiments of the present invention, in which adjacent lenses are all arranged with an air gap. . In any of the embodiments, in order from the object side, a first lens group G1 having a positive refractive power with a concave surface facing the object side, and a second lens group G2 including one lens having a positive refractive power. When two adjacent lenses are constituted by lenses having positive and negative refractive powers, and two lenses having the same sign of the radius of curvature of the adjacent surfaces are set as one lens set, At least five or more sets are arranged, and are composed of a third lens group G3 having a positive refractive power as a whole and a fourth lens group G4 having a negative refractive power as a whole.
[0016]
In the microscope objective lens OL according to the first embodiment shown in FIG. 1, the first lens group G1 includes a positive meniscus lens L1 having a concave surface facing the object side, and the second lens group G2 includes, in order from the object side. The third lens group G3 is composed of a biconvex lens L3, a negative meniscus lens L4 having a concave surface facing the object side, and a biconvex lens. The third lens group G3 includes a positive meniscus lens L2 having a concave surface facing the object side. A lens set including two lenses L5 and a negative meniscus lens L6 having a concave surface facing the object side, and a lens set including a biconvex lens L7 and a negative meniscus lens L8 having a concave surface facing the object side. A lens set including three lenses, a biconvex lens L9, a biconcave lens L10, and a biconvex lens L11, and a lens set including two lenses, a biconcave lens L12 and a biconvex lens L13 A lens set composed of two lenses, a negative meniscus lens L14 and a biconvex lens L15 with the convex surface facing the object side, and a lens composed of two lenses, a negative meniscus lens L16 and a biconvex lens L17 with the convex surface facing the object side The fourth lens group G4 includes a positive meniscus lens L18 having a convex surface facing the object side and a biconcave lens L19.
[0017]
In the objective lens OL for a microscope according to the second embodiment shown in FIG. 3, in order from the object side, the first lens group G1 includes a positive meniscus lens L21 having a concave surface facing the object side, and the second lens group G2 includes The third lens group G3 includes a biconvex lens L23, a negative meniscus lens L24 having a concave surface facing the object side, and a biconvex lens L25. The third lens group G3 includes a positive meniscus lens L22 having a concave surface facing the object side. A lens set consisting of two lenses of a negative meniscus lens L26 having a concave surface facing the object side, a lens set consisting of two lenses of a biconvex lens L27 and a negative meniscus lens L28 having a concave surface facing the object side, A lens set including three lenses of a convex lens L29, a biconcave lens L30, and a biconvex lens L31, and two lenses of a biconcave lens L32 and a biconvex lens L33 A lens set composed of two lenses, a negative meniscus lens L34 and a biconvex lens L35 having a convex surface facing the object side, and a negative meniscus lens L36 and a biconvex lens L37 having a convex surface facing the object side The fourth lens unit G4 includes a positive meniscus lens L38 having a convex surface facing the object side and a biconcave lens L39.
[0018]
In the microscope objective lens OL according to the third embodiment shown in FIG. 5, in order from the object side, the first lens group G1 includes a positive meniscus lens L41 having a concave surface facing the object side, and the second lens group G2 includes The third lens group G3 is composed of a biconvex lens L43 and a biconcave lens L44, and a positive meniscus lens L45 having a concave surface facing the object side. A lens set including three lenses of a biconvex lens L46, a biconcave lens L47, and a biconvex lens L48, a lens set including three lenses of a biconvex lens L49, a biconcave lens L50, and a biconvex lens L51, and a biconvex lens L52. A lens set consisting of three lenses, a biconcave lens L53 and a biconvex lens L54, and a negative meniscus lens L55 having a convex surface facing the object side; It consists lens group and consisting of two lenses of a lens L56, the fourth lens group G4 is composed of a positive meniscus lens L57 having a convex surface directed toward the object side biconcave lens L58 Prefecture.
[0019]
In general, in an objective lens having a magnification higher than about 40 times and having a high numerical aperture, such as the objective lens OL for a microscope according to the present invention, the curvature of the image side of the lens group closest to the object is adjusted to the aplanation condition. By satisfying the condition, a positive refractive power is obtained with no spherical aberration. The positive refracting power obtained by the lens having this configuration is extremely large, and is an essential configuration for efficiently obtaining magnification without aberrations.
[0020]
The first lens group G1 of the microscope objective lens OL according to the present invention is a meniscus lens having a positive refractive power with the concave surface facing the object side, and the curvature of the image-side surface is set to an aplanation condition or a condition close thereto. Thus, a positive refractive power is obtained while suppressing the occurrence of spherical aberration, and the Petzval sum is reduced by the concave surface on the object side, thereby contributing to correction of field curvature.
[0021]
The second lens group G2 has a structure in which a single lens having a positive refractive power is arranged subsequently to the first lens group G1 to obtain a positive refractive power.
[0022]
The third lens group G3 has a positive refractive power as a whole, and converts divergent light emitted from the second lens group G2 into convergent light. At this time, observation light (in the embodiment of the present invention, 248 ± 3 nm In order to achromatize the light used for the automatic focusing mechanism and the like, the following conditional expression (1) is satisfied, and the sign of the radius of curvature of the adjacent surface of the adjacent lens is the same. At least five or more lens sets composed of two lenses having positive and negative refractive powers that satisfy the following conditional expressions (2) and (3) are arranged. This configuration is also necessary for providing the aberration correction effect by the concave surface at the same time as the achromatism.
[0023]
(Equation 1)
ν3P> ν3N (1)
2 × dmin> dcenter + dedge (2)
| R1a | <| r2a |, | r1b |> | r2b | (3)
However,
ν3P: Abbe number of a lens having a positive refractive power among two lenses constituting a lens group in the third lens group G3
ν3N: Abbe number of a lens having a negative refractive power among two lenses constituting a lens group in the third lens group G3.
dmin: the center thickness of the lens having the smallest center thickness among the lenses constituting the third lens group G3.
dcenter: the distance between the two lenses constituting the lens set in the third lens group G3
edge: Edge air gap between two lenses constituting a lens set in the third lens group G3.
r1a: Object-side radius of curvature of the concave lens arranged in a section from the lens closest to the object to the lens having the largest effective diameter among the lenses constituting the third lens group G3
r2a: radius of curvature on the image side of a concave lens arranged in a section from the lens closest to the object to the lens having the largest effective diameter among the lenses constituting the third lens group G3
r1b: Object-side radius of curvature of the concave lens disposed in the section from the lens having the largest effective diameter to the fourth lens group G4 among the lenses constituting the third lens group G3
r2b: radius of curvature on the image side of the concave lens disposed in the section from the lens having the largest effective diameter to the fourth lens group G4 among the lenses constituting the third lens group G3
[0024]
In a configuration in which a cemented lens can be used, it is often more convenient to constitute the lens set as a cemented lens. However, in the microscope objective lens OL according to the present invention, an adhesive necessary for forming a cemented lens is used. No cemented lens is used in order to cope with various problems caused by irradiating deep ultraviolet light to the lens. However, since the above-described lens group has an effect similar to that of a cemented lens on aberration correction and has a shape similar to that of a cemented lens, it will be referred to as a “pseudo-joint lens” in the following description. .
[0025]
The fourth lens group G4 has a negative refractive power as a whole, converts the convergent light emitted from the third lens group G3 into a parallel light flux, and at the same time mainly contributes to the aberration correction of the upper coma light flux. The fourth lens group G4 is equal to or longer than the third lens group G3 by one-sixth of the shorter of the shorter of the total lens length (the distance from the object plane to the final plane of the microscope objective lens OL) or the parfocal distance. At a distance of air. Since the objective lens used in the ultraviolet region, such as the present objective lens, has a large decrease in light quantity due to absorption of the glass material, the above-mentioned air gap can suppress the decrease in light quantity due to absorption of the glass material.
[0026]
By the way, when the cemented lens is substituted by the above-described pseudo-joint lens, if the adjacent surface of the pseudo-joint lens is simply stripped of an adhesive for joining the cemented lens, the incident angle and the emission angle of the light beam Has a tendency to be large, which causes a problem that the effect on the eccentricity tolerance becomes sensitive. For this reason, when the pseudo cemented lens is used, the aberration correction performance is reduced by suppressing the incident angle and the outgoing angle of the light beam transmitted through the lenses constituting the second to fourth lens groups G2 to G4 to 50 degrees or less. The effect on the eccentricity tolerance can be reduced while maintaining. The rays that pass through the lenses that constitute the second to fourth lens groups G2 to G4 are the principal ray of the light beam emitted from a point intersecting with the optical axis of the objective lens OL for a microscope on the object plane and the ray of the maximum numerical aperture. , And the main ray of the luminous flux emitted from the maximum object height of the object plane and the ray of the maximum numerical aperture in the upper and lower coma rays, and the incident angle and the exit angle of this ray are suppressed to 50 degrees or less. Have been.
[0027]
It is known that a lens having a surface having a relatively large angle of incidence and an angle of emergence can correct aberration well in design, but a lens having such a surface is eccentric. The effect on tolerance becomes sensitive, and the burden on the manufacturing side increases. Therefore, in the microscope objective lens OL that does not use a cemented lens, as described above, when the incident angle and the exit angle of the lens surface are not increased, the performance of aberration correction and the effect on the eccentricity tolerance are better. Often.
[0028]
For example, in a divergent light beam, making the curvature of the lens negative can reduce the incident angle and the outgoing angle with respect to the lens surface. Conversely, when the curvature of the lens is positive in the convergent light beam, the angle of incidence and the angle of emission with respect to the lens surface can be reduced. For this reason, as described above, the adjacent surface of the pseudo cemented lens constituting the lens group in the third lens group G3 is configured to have a negative curvature in a divergent light beam and a positive curvature in a convergent light beam. Accordingly, the incident angle and the outgoing angle of the light beam transmitted through the lenses constituting the second to fourth lens groups G2 to G4 can be suppressed to 50 degrees or less, and the effect on the eccentricity tolerance can be reduced.
[0029]
In order for the third lens group G3 to be configured as described above, the third lens group G3 must be configured when the divergent light beam emitted from the second lens group G2 is converted into convergent light by the third lens group G3. The lens is configured to be gradually converted. Therefore, the concave lens constituting the third lens group G3 is configured to satisfy the conditional expression (3), and the lens groups are arranged on the object side and the image side with the lens having the maximum effective diameter of the third lens group G3 interposed therebetween. The object side of the lens having the maximum effective diameter is substantially divergent, the image side is substantially convergent light, and the lens having the maximum effective diameter is maximized. Then, as described above, the curvature of the adjacent surface of the lens set constituted by the pseudo-joint lens disposed on the object side with respect to the lens having the maximum effective diameter through which the light beam which is a substantially divergent light beam passes is set to be negative, and the convergent light beam is substantially The curvature of the adjacent surface of a lens set composed of a pseudo-joint lens arranged on the image side of the lens having the maximum effective diameter through which the light beam passes is defined as positive.
[0030]
At this time, in the third lens group G3, the adjacent surface of the lens set disposed closer to the object side than the lens having the largest effective diameter has a negative curvature. The adjacent surface of the disposed lens has a positive refractive power, and the adjacent surface of the lens disposed on the image side has a negative refractive power. Therefore, it is more convenient for the lens set arranged on the object side than the lens having the largest effective diameter to be a pseudo cemented lens in which a lens having a positive refractive power and a lens having a negative refractive power are arranged in order from the object side. Is good. Similarly, since the adjacent surface of the lens set disposed on the image side of the lens having the largest effective diameter has a positive curvature, the adjacent surface of the lens disposed on the object side of the two lenses constituting this lens set Has a negative refractive power, and the adjacent surface of the lens arranged on the image side has a positive refractive power. Therefore, it is more convenient for the lens set arranged on the image side than the lens having the largest effective diameter to be a pseudo cemented lens in which a lens having a negative refractive power and a lens having a positive refractive power are arranged in order from the object side. Is good.
[0031]
In an optical system that requires achromatization, achromatization is performed by appropriately increasing the refractive power of lenses having positive and negative refractive powers that satisfy conditional expression (1) and combining them. Therefore, if the arrangement of the two lenses having the positive and negative refractive powers constituting the lens group in the third lens group G3 is configured as described above, a lens group using a biconvex lens or a biconcave lens can be configured. It is easy to increase the refractive power. On the other hand, it is possible to constitute the third lens group G3 by reversing the arrangement of the lenses having positive and negative refractive powers constituting the lens set, but as described above, the third lens group G3 is located closer to the object side than the lens having the largest effective diameter. In the case where the adjacent surface of the lens set disposed on the image side has a negative curvature and the adjacent surface of the lens set disposed on the image side of the lens having the largest effective diameter has a positive curvature, the two lenses constituting the lens set Need to be constituted by meniscus lenses, it may be difficult to increase the refractive power of the lens.
[0032]
From the viewpoint of achromatism, generally, in a cemented lens, a three-element cemented lens contributes to an improvement in secondary dispersibility than a two-element cemented lens. Therefore, the third lens group G3 includes a lens group that is a pseudo cemented lens including three lenses having positive, negative, positive, negative, positive, and negative refractive powers, and the three lenses satisfy the conditional expression (2). It is preferable to configure as follows. At this time, if a pseudo cemented lens composed of three lenses is used, the concave lens may be constituted by a biconcave lens in which the curvature is opposite between the object side and the image side. Also in this case, if the configuration is such that the conditional expression (3) is satisfied, the incident angle and the output angle of the light beam transmitted through the concave lens can be made as small as possible, so that the effect on the eccentricity tolerance can be suppressed.
[0033]
Further, when a configuration is adopted in which a small number of lenses in the lens system have a large refractive power, the lens having the large refractive power often has a large effect particularly on the eccentricity tolerance, and the effect on the eccentricity tolerance is relaxed. This is a configuration that we want to avoid from the viewpoint of. However, on the other hand, if a lens having a large refractive power is arranged at an appropriate place, it may be advantageous for aberration correction. Therefore, when the third lens group G3 is configured to satisfy the following conditional expressions (4) and (5), both the performance of aberration correction and the effect on the eccentricity tolerance become good, and the balance is good. It can be a lens system. On the other hand, if the conditions expressed by the conditional expressions (4) and (5) are exceeded, the effect on the eccentricity tolerance becomes severe, the load on the manufacturing increases, and it becomes difficult to obtain the performance as designed. .
[0034]
(Equation 2)
Amax / Amin <2 (4)
Bmax / Bmin <2 (5)
However,
Amax: the maximum value of the ratio (f / D) of the focal length (f) to the effective diameter (D) of the lens having a positive refractive power in the third lens group G3.
Amin: the minimum value of the ratio (f / D) of the focal length (f) to the effective diameter (D) of the lens having a positive refractive power in the third lens group G3.
Bmax: the maximum value of the ratio (f / D) of the focal length (f) to the effective diameter (D) of the lens having a negative refractive power in the third lens group G3.
Bmin: the minimum value of the ratio (f / D) of the focal length (f) to the effective diameter (D) of the lens having negative refractive power in the third lens group G3.
[0035]
For the same reason, by limiting the focal length of the convex lens constituting the third lens group G3 and dispersing the positive refractive power so as to satisfy the following conditional expression (6), the eccentricity tolerance is reduced. It is possible to provide a configuration in which the effect is reduced and the performance of aberration correction is not adversely affected.
[0036]
[Equation 3]
f3P / fall> 6 (6)
However,
f3P: focal length of the convex lens in the third lens group G3
fall: the overall focal length of the microscope objective lens OL
[0037]
Furthermore, by realizing on-axis achromatism between a specific single-wavelength light beam in the visible or infrared region and the observation light, an automatic focusing mechanism using this single wavelength can be realized without offsetting the focus. This is advantageous in configuration.
[0038]
By configuring the objective lens OL for a microscope according to the present invention so as to satisfy the above-described conditions, the aberration correction performance and the effect on the eccentricity tolerance can be improved even with the configuration using only a single lens without using a cemented lens. With a high magnification (about 40 times or more), the numerical aperture reaches about 0.9, and a microscope objective lens OL intended for use in the deep ultraviolet wavelength region can be obtained.
[0039]
【Example】
Hereinafter, specific examples of the microscope objective lens according to the present invention will be described. The following three examples correspond to the microscope objective lenses OL according to the above-described first to third embodiments, respectively. Therefore, the lens configuration diagrams of the first to third embodiments (FIG. 1, FIG. 3 and 5) show the lens configurations of the first to third embodiments below, respectively.
[0040]
(First embodiment)
Table 1 below shows data of each lens in the first example. The surface numbers 1 to 39 in Table 1 relate to the microscope objective lens OL according to the first embodiment, and correspond to reference numerals 1 to 39 in FIG. 1, respectively. Further, “fall” in Table 1 indicates the focal length of the microscope objective lens OL. A. Is the numerical aperture, β is the magnification, r is the radius of curvature of the lens, d is the distance between the surfaces of the lens, ν is the Abbe number, n is the refractive index with respect to the reference light beam (248 nm). The same applies to the embodiment. The units of the focal length fall, the radius of curvature r, the surface distance d, and other lengths described in all the following specification values are generally “mm” unless otherwise specified. Since the same optical performance can be obtained even if the magnification is proportionally enlarged or reduced, the unit is not limited to “mm” and another appropriate unit can be used.
[0041]
[Table 1]

[0042]
Thus, in the first embodiment, it can be seen that all of the conditional expressions (1) to (6) are satisfied. In addition, since 1/6 of the total length of the objective lens is 10.69, and the distance between the third lens group G3 and the fourth lens group G4 is 14.10, the condition regarding the distance between G3 and G4 is satisfied.
[0043]
FIG. 2 shows various aberration diagrams in the first example. In each aberration diagram, NA indicates a numerical aperture, y indicates an image height, L indicates a 248 nm ray, K indicates a 251 nm ray, and M indicates a 245 nm ray. In the astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. The above description of the aberration diagrams is the same in the other embodiments.
[0044]
As is clear from the aberration diagrams described above, it is understood that various aberrations are satisfactorily corrected in the present embodiment.
[0045]
(Second embodiment)
Table 2 below shows the data of each lens in the second example. Surface numbers 1 to 39 in Table 2 relate to the objective lens OL for a microscope according to the second embodiment, and correspond to reference numerals 1 to 39 in FIG.
[0046]
[Table 2]

[0047]
Thus, in the second embodiment, it can be seen that all of the conditional expressions (1) to (6) are satisfied. In addition, since 1/6 of the total length of the objective lens is 10.65, and the distance between the third lens group G3 and the fourth lens group G4 is 14.45, the condition regarding the distance between G3 and G4 is also satisfied.
[0048]
FIG. 4 shows various aberration diagrams in the second example. As is clear from the aberration diagrams described above, it is understood that various aberrations are satisfactorily corrected in the present embodiment.
[0049]
(Third embodiment)
Table 3 below shows the specifications of each lens in the third example. Surface numbers 1 to 37 in Table 3 relate to the microscope objective lens OL according to the third embodiment, and correspond to reference numerals 1 to 37 in FIG. 5, respectively.
[0050]
[Table 3]

[0051]
Thus, in the third embodiment, it can be seen that all of the conditional expressions (1) to (6) are satisfied. In addition, since 1/6 of the total length of the objective lens is 10.67, and the distance between the third lens group G3 and the fourth lens group G4 is 12.96, the condition regarding the distance between G3 and G4 is also satisfied.
[0052]
FIG. 6 shows various aberration diagrams in the third example. As is clear from the aberration diagrams described above, it is understood that various aberrations are satisfactorily corrected in the present embodiment. In each of the first to third embodiments, axial achromatism is also performed on a light beam (770 nm) used for an automatic focusing mechanism or the like.
[0053]
Note that the microscope objective lens shown in the first to third embodiments is an infinity-correction type, and thus is used, for example, together with the imaging lens IL shown in FIG. The imaging lens IL includes, in order from the object side, a cemented lens of a biconvex lens L61 and a biconcave lens L62, a negative meniscus lens L63 having a concave surface facing the object side, and a positive meniscus lens L64 having a concave surface facing the object side. And a cemented lens. Table 4 below shows the specifications of each lens constituting the imaging lens IL. The surface numbers 1 to 6 in Table 4 relate to the imaging lens IL, and correspond to reference numerals 1 to 6 in FIG.
[0054]
[Table 4]

[0055]
【The invention's effect】
As is clear from the above description, according to the objective lens for a microscope according to the present invention, it is possible to improve the aberration correction performance and the effect on the eccentricity tolerance even with the configuration of only the single lens without using the cemented lens. At a high magnification (about 40 times or more), the numerical aperture reaches about 0.9, and a microscope objective lens intended for use in the deep ultraviolet wavelength region can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a microscope objective lens according to a first example of the present invention.
FIG. 2 is a diagram illustrating various aberrations of the microscope objective lens according to the first example of the present invention.
FIG. 3 is a cross-sectional view illustrating a configuration of a microscope objective lens according to a second example of the present invention.
FIG. 4 is a diagram illustrating various aberrations of the microscope objective lens according to the second example of the present invention.
FIG. 5 is a cross-sectional view illustrating a configuration of a microscope objective lens according to a third example of the present invention.
FIG. 6 is a diagram illustrating various aberrations of the microscope objective lens according to the third example of the present invention.
FIG. 7 is a cross-sectional view showing a configuration of an imaging lens used in combination with the microscope objective lens according to the present invention.
[Explanation of symbols]
OL Objective lens for microscope
G1 First lens group
G2 Second lens group
G3 Third lens group
G4 4th lens group

Claims

Adjacent lenses are all arranged with an air gap, and the configuration of the lenses is in order from the object side,
A first lens group having a meniscus lens having a positive refractive power with the concave surface facing the object side,
A second lens group including one lens having a positive refractive power;
When the two adjacent lenses having positive and negative refractive powers and the same sign of the radius of curvature of the adjacent surfaces are the same lens set, A third lens group including at least five or more pairs and having a positive refractive power as a whole;
A fourth lens group having a negative refractive power as a whole,
When the Abbe number of a lens having a positive refractive power is ν3P and the Abbe number of a lens having a negative refractive power is ν3N among the two lenses constituting the lens group in the third lens group, the following expression is used. ν3P> ν3N (1)
Satisfies the condition represented by
The center thickness of the lens having the smallest center thickness among the lenses that form the third lens group is dmin, the distance between adjacent lenses of the two lenses that form the lens set is dcenter, and the distance between the edges is edge. Then, the following equation 2 × dmin> dcenter + dedge (2)
Satisfies the condition represented by
Of the lenses constituting the third lens group, the object-side radius of curvature of the concave lens disposed in a section from the lens closest to the object side to the lens having the largest effective diameter is r1a, and the radius of curvature on the image side is r2a; When the radius of curvature on the object side of the concave lens disposed in the section from the lens having the maximum effective diameter to the fourth lens group is r1b, and the radius of curvature on the image side is r2b, the following equation | r1a | <| r2a | , | R1b |> | r2b | (3)
Satisfies the condition represented by
The third lens group and the fourth lens group are separated by an air distance of at least 距離 of the total length of the lens (the distance from the object surface to the final surface of the objective lens) or the shorter of the parfocal distance. An objective lens for a microscope, which is arranged.

In the third lens group,
The lens set is disposed on the object side and the image side with the lens having the maximum effective diameter interposed therebetween,
The adjacent surface of the two lenses constituting the lens set arranged in the section from the lens closest to the object to the lens having the maximum effective diameter is formed of a surface or a plane having a negative radius of curvature,
An adjacent surface of the two lenses constituting the lens set disposed in a section from the lens having the maximum effective diameter to the fourth lens group is formed of a surface or a plane having a positive radius of curvature. The microscope objective lens according to claim 1.

In the third lens group,
The lens set disposed in a section from the lens closest to the object side to the lens having the maximum effective diameter is configured by a lens having a positive refractive power on the object side,
3. The microscope according to claim 2, wherein the lens set disposed in a section from the lens having the maximum effective diameter to the fourth lens group includes a lens having a negative refractive power on the object side. 4. Objective lens.

The third lens group includes at least one lens set including three lenses having positive / negative positive or negative / positive / negative refractive power, and an adjacent surface of the lenses constituting the lens set including the three lenses has The microscope objective lens according to any one of claims 1 to 3, wherein the objective lens satisfies the condition represented by the expression (2) according to claim 1.

The principal ray of the light beam emitted from a point intersecting with the optical axis on the object plane and the ray of the maximum numerical aperture, and the principal ray of the light ray emitted from the maximum object height of the object plane and the ray of the maximum numerical aperture in the upper and lower coma rays The objective lens for a microscope according to any one of claims 1 to 4, wherein an incident angle and an outgoing angle when transmitted through the second to fourth lens groups are 50 degrees or less.

When the maximum value of the ratio of the focal length to the effective diameter of the lens having the positive refractive power among the lenses constituting the third lens group is Amax, and the minimum value is Amin, the following expression is used: Amax / Amin <2 (4) )
The objective lens for a microscope according to any one of claims 1 to 5, which satisfies a condition represented by:

Assuming that the maximum value of the ratio of the focal length to the effective diameter of the lens having a negative refractive power among the lenses constituting the third lens group is Bmax, and the minimum value is Bmin, the following equation Bmax / Bmin <2 (5) )
The objective lens for a microscope according to any one of claims 1 to 6, which satisfies a condition represented by:

Assuming that the focal length of the convex lens in the third lens group is f3P and the overall focal length of the first to fourth lens groups is fall, the following equation is satisfied: f3P / fall> 6 (6)
The objective lens for a microscope according to any one of claims 1 to 7, which satisfies a condition represented by:

The first to fourth lens groups are configured such that a wavelength in a deep ultraviolet region, which is observation light, and a single wavelength light beam in a visible region or an infrared region used for automatic focusing are achromatic on the axis. The microscope objective lens according to claim 1.