JP2503665C

JP2503665C -

Info

Publication number: JP2503665C
Authority: JP
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Publication date: 1997-12-17

Description

【発明の詳細な説明】【産業上の利用分野】本発明は、眼の調節力の補助として使用する累進焦点レンズに関する。【従来技術】眼の調節力が衰退して近方視が困難になつた場合の調節力の補助用眼鏡レンズ
として、上方の遠用視矯正領域（以下遠用部という）と下方の近用視矯正領域（
以下近用部という）と両者の中間において連続的に屈折力が変化する累進領域（
以下中間部という）を有する累進焦点レンズが種々知られている。累進焦点レンズにおいて、一般には遠用部と近用部との明視域を広く確保し、
その間を累進帯で結ぶと、その累進帯の側方領域にレンズ収差が集中するように
なり、この領域の存在か像のボケをはじめとして、像のゆがみを引き起こし、視
線を移動したときのゆれとして、装用者に悪い印象を与える。このような視覚特性の問題を解決するために、公知の累進焦点レンズにおいて
は様々な観点での設計、評価がなされている。そして、レンズ面の形状に関して
、レンズ面のほぼ中央に垂直に走る子午線に沿う断面と物体側レンズ面との交線
が、レンズの加入度などの仕様を表すための基準線として用いられ、レンズの設
計においても重要な基準線として用いられている。また、レンズの装用状態にお
いて近用部が鼻側に寄ることを考慮して近用部を非対称な配置とした累進焦点レ
ンズにおいても、遠用中心と近用中心とを縦に通る１本の中心線が基準線として
扱われている。本発明においては、これらの基準線を主子午線曲線という。従来の累進焦点レンズとしては、例えば特公昭４９−３５９５号公報に開示さ
れたものや、特公昭５９−４２２８５号公報に開示されたものが知られている。【発明の解決しようとする課題】上記の公知技術においては一応の視覚性能の向上を図ることが可能ではあるが
、実用上では未だ不十分なものであった。すなわち、前者は主子午線曲線と直角
な平面と屈折面との成す交線の形状について、中間部のほぼ中央に相当する点に
おける交線のみを円形形状とし、それより上部では主子午線曲線から遠ざかるに
従って交線の曲率半径は減少し下部では増加するような、いずれも非円形形状と
するものであり、このように中央部のみを円形形状とし他の領域において単純な
非円形形状としているため、近用部及び遠用部の明視域（非点隔差が０．５ディ
オプター以下の範囲）が狭く、また急激な収差変化を伴うため視野が狭くなり、
像のゆがみ、ゆれが著しいものであった。また後者のものでは、同様に主子午線曲線と直角な平面と屈折力面との成す交線の形状について、遠用部上方では、主子午線曲線より遠ざかるにつれて曲率半
径が減少し、遠用部の上方にいくに従ってその減少率が０に近づき上方周辺部で
は一定の曲率半径とし、遠用部の下部では曲率半径が単調に減少する非円形形状
とし、さらに中間部では遠用部との接続部を除いて主子午線曲線から遠ざかるに
従って、曲率半径が増加し減少する非円形形状とし、近用部では主子午線曲線よ
り遠ざかるにつれて曲率半径が増加して減少する構成としている。このものでは
、前者のものよりはある程度の視覚特性の改良がなされ得るものの、遠用部の周
辺領域、特に遠用部の中央から下方にかけての側方領域における残存非点隔差が
依然著しく、また中間部及び近用部の側方領域においても像のひずみ、ゆれが大
きく、末だ十分広い視野を得ることが難しいものであった。一般に累進帯としての中間部を短くすると屈折力変化が急激になるため、収差
が急激に増大する。ミンクウィッツの法則からもわかるように、特に主子午線曲
線の近傍においては収差が急激に増大し、累進帯の幅が狭くなりがちになるばか
りではなく、像のゆれ、ゆがみが急激に増大する。一方、累進帯が比較的長い場
合には、屈折力変化が比較的穏やかなため非点収差や、ゆれ、ゆがみを低減しや
すい。しかしながら、累進帯が長すぎると装用時において目線を十分下げないと
所望の加入度が得られないため、使用しにくい等の問題があった。本発明は、上述の如き従来の欠点を解消し、累進帯としての中間部が短くなっ
た場合においても、収差的にバランスのとれた累進焦点レンズを提供しようとす
るものであり、具体的には遠用部の下方においても広い視野を有し、実用上不便
のない広さの明視域を有する中間部及び近用部を有し、その周辺においても像の
ゆがみ、ゆれを極力低減し側方視においても不快感を感ずることのない累進焦点
レンズを提供することを目的としている。【課題を解決するための手段】本発明は主子午線曲線に沿って遠景に対応する屈折力を有する遠用部Ｆと、近
景に対応する屈折力を有する近用部Ｎと、前記遠用部と前記近用部との間におい
て両部の屈折刀を連続的になめらかに接続する中間部Ｐとを有する図１の如き累
進焦点レンズにおいて、累進帯としての中間部が短くなった場合、屈折表面の横
断面形状について、各部の最適形状を見出し、屈折面全域における収差バランスの最適化を図ったものである。具体的には、遠用部の下部において屈折表面の横断面形状は、横断面曲線に沿
って該主子午線曲線との交点から遠ざかるに従って横曲率半径の値が減少しその
後増加する非円形曲線であり、該遠用部の上部において屈折表面の横断面形状は
、横断面曲線に沿って該主子午線曲線との交点から遠ざかるに従って横曲率半径
の値が増加しその後減少する非円形曲線であり、該遠用部のほぼ中央部分におい
て横断面曲線に沿って屈折表面の横断面形状がほぼ円形曲線であり、前記中間部
の中央から近用部上方にかけて屈折表面の横断面形状は、横断面曲線に沿って主
子午線曲線との交点から遠ざかるに従って曲率半径の値が増加しその後ほぼ一定
になる非円形曲線である構成としたものである。また、中間部Ｐの上部において、屈折表面の横断面形状は、主子午線曲線との
交点から遠ざかるに従って曲率半径の値が増加する非円形曲線であり、その増加
率は近用部に近づくに従って増大する構成とすることが有効である。そして、中間部の下方から近用部の上方において、屈折表面の横断面形状は、
該主子午線曲線との交点から遠ざかるに従って曲率半径の値が増加しその後ほぼ
一定となる位置が、該累進焦点レンズの半径をＷとするとき、前記主子午線曲線
から垂直方向に１／４Ｗ〜３／４Ｗだけ離れた領域内に存在することを構成とす
ることが有効である。さらに、中間部Ｐ及び近用部Ｎにかけての屈折表面のうち少なくとも近用部の
中間において、累進焦点レンズの半径をＷとするとき、主子午線曲線から垂直方
向に１／２Ｗ以上離れた領域での屈折表面の横断面に沿う方向の面屈折力は、遠
用中心の表面屈折力に対して、加入度をＡ（ディオプター）とするとき、±Ａ／
２ディオプター以内の範囲とすることが有効である。【作用】上記の如き本発明による構成においては、まず遠用部の上方において、屈折表
面の横断面形状が主子午線曲線から遠ざかるに従って増加減少し、一方遠用部の
下方においてはこの逆の傾向をもち、遠用部のほぼ中央においてほぼ円形状とな
るため、遠用部Ｆを極めて広く確保しつつ、中間部とのなめらかな接続を可能と
して、中間部Ｐの側方部での非点隔差の集中を弱めることを可能とし、中間部Ｐでの明視域をより広く、かつ周辺での像のゆがみ、ゆれの軽減を達成したもので
ある。また、中間部Ｐの下部及び近用部Ｎの上方において、屈折表面の横断面形状が
、該主子午線曲線との交点から遠ざかるに従って曲率半径の値が増加し、その後
ほぼ一定になる非円形曲線となっているため、上記の如き遠用部の形状による広
い遠用明視域を有するにもかかわらず、中間部及び近用部での非点隔差の集中を
バランス良く軽減し、側方領域での像のゆれ、ゆがみ等をやわらげ、視覚の改良
を可能としている。【実施例】以下に本発明の実施例について述べるが、まず本発明における横断面及び縦断
面について説明する。図２（Ａ）及び（Ｂ）はレンズの屈折表面σについての横断面及び縦断面を説
明するための斜視図である。レンズの幾何中心Ｏ_Gに光軸をとりこれをＸ軸とし
、幾何中心Ｏ_Gにおける屈折表面の曲率中心位置を中心Ｏ_Oとし、幾何中心Ｏ_Gに
おける屈折表面σの曲率半径Ｒ_Oを半径とする球面を基準球面としている。従っ
て、基準球面はレンズの屈折表面σと幾何中心Ｏ_Gにおいて接している。基準球
面の中心Ｏ_Oを原点として、垂直方向にｙ軸を、水平方向にｚ軸をとっている。本発明における横断面とは、図２（Ａ）に示す如く、基準球の中心Ｏ_Oを通り
主子午線曲線ＭＭ’を含む面（ｘ−ｙ平面）に直交する平面π_jによる屈折表面
σの横断面のことであり、横断面交線Φ_jとして示している。また、本発明にお
ける縦断面とは、図２（Ｂ）に示す如く、基準球の中心Ｏ_Oを通りｙ軸を含む平
面χ_jによる屈折表面σの縦断面のことであり、縦断面交線Σ_jとして示している
。このような横断面交線Φ_j及び縦断面交線Σ_jのレンズ屈折表面上での平面的位
置の様子を示す平面図が図３である。図３に示した各横断面交線（Φ₃，Φ₂，Φ
₁…）に沿って、横方向の曲束半径の値を、主子午線曲線ＭＭ’上の横方向の曲
率半径を基準として屈折表面σの右半分についての変化を示したのが図４である
。尚、ここに説明した横断面交線Φ_j，及び縦断面交線Σ_jとは、それぞれ、本発
明における横断面曲線及び縦断面曲線を意味することは言うまでもない。より具体的に説明すれば、図４は、主子午線曲線ＭＭ’と交差する７つの代表
的横断面での、各横断面交線に沿って縦方向の曲率半径の値を、主子午線曲線Ｍ
Ｍ’上の横方向の曲率半径を基準として、主子午線曲線ＭＭ’の右側半分につい
てプロットしたものである。ここで、プロットした各曲率半径の値は、図２（Ａ
）（Ｂ）において、基準球の中心Ｏ_Oを通り主子午線曲線ＭＭ’を含む面（ｘ−
ｙ平面）に直交する平面π_jによる屈折表面σの横断面交線Φ_jに沿って、ｙ軸を
含む垂直面（χ_j）による縦交線曲線Σ_jが交差する点Ｍ_jにおける横方向の曲率
半径である。そして、基準球の中心を通り主子午線曲線ＭＭ’を含む面（ｘ−ｙ平面）に直
交する平面π_jが光軸（ｘ軸）となす角度Ｖｙを、５．６°毎に変えた７つの面
（π₃，π₂，π₁，π₀，π_-1,π_-2,π_-3）による、７つの横断面交線（Φ₃，Φ₂
，Φ₁，Φ₀，Φ_-1,Φ_-2,Φ_-3）に沿って、それぞれの横断面上で、ｙ軸を含む垂
直面（χ_j）と主子午線曲線ＭＭ’を含む平面（ｘ−ｙ平面）との成す横方向の
角度Ｖｚを、５．６°毎にとった場合の主子午線曲線ＭＭ’上の横方向の曲率半
径を基準として、横方向曲率半径の値を結んだのが図４である。図４に示した如く、本実施例においては、遠用部Ｆの下部（５．６°）におい
て屈折表面の横断面形状は、該主子午線曲線ＭＭ’との交点から遠ざかるに従っ
て曲率半径の値が減少しその後増加する非円形曲線であり、該遠用部Ｆの上部（
１６．８°）において屈折表面の横断面形状は、主子午線曲線ＭＭ’との交点か
ら遠ざかるに従って曲率半径の値が増加しその後減少する非円形曲線であり、遠
用部Ｆのほぼ中央部分（１１．２°）において屈折表面の横断面での曲率半径が
ほぼ一定となり、この横断面形状がほぼ円形曲線となっている。また、中間部Ｐ（−５．６°）において、屈折表面の横断面形状は、該主子午
線曲線との交点から遠ざかるに従って曲率半径の値が増加しその後ほぼ一定にな
る非円形曲線であり、その増加率及び減少率は近用部に近づくに従って増大して
おり、この傾向は近用部Ｎにおける横断面形状（−１１．２°）との比較から明
らかである。そして、近用部Ｎ（−１１．２°の上部、−１６．８°の下部）において、屈
折表面の横断面形状は、近用部の上部では該主子午線曲線ＭＭ’との交点から遠ざかるに従って曲率半径の値が増加しその後ほぼ一定になる非円形曲線である。
ここで曲率半径の増加からほぼ一定になる位置は、該累進焦点レンズの半径をＷ
と丁るとき、Ｗの約半分の位置にあり、実用的には主子午線曲線から横方向にＷ
／４〜３Ｗ／４だけ離れた領域内に存在する構成とすることが有効である。上記の如き横断面に沿って横方向曲率半径の変化について、遠用部Ｆ上方にお
ける側方領域での曲率半径の増加は、その横断面と主子午線曲線との交点におけ
る曲率半径に対して、約７％の増加であり、遠用部Ｆ下方における曲率半径の減
少量は、その横断面と主子午線曲線との交点における曲率半径に対して、約８％
の減少である。また、中間部Ｐの下部における横方向曲率半径の増加からほぼ一
定となるが、その増加の最大値はその横断面と主子午線曲線との交点における曲
率半径に対して、約６０％の増加である。近用部Ｎにおける横方向曲率半径の増
加減少において、最大値はその横断面と主子午線曲線との交点における曲率半径
に対して約８４％の増加であり、近用中心Ｏ_Nの側方領域における横方向曲率半
径の最大値は、その横断面と主子午線曲線との交点における曲率半径に対して、
５０％〜１００％増加した値であることが有効である。ところで、図５は横方向の曲率半径に対応する横方向の屈折力について、縦交
線に沿った変化を示すものである。即ち、屈折表面σでの前述したｙ軸を含む垂
直面（ｘ_j）による縦交線Σ_jに沿って、各点での横方向の屈折力をプロットした
図であり、屈折表面σの横方向曲率半径の縦の変化を示すものでもある。これら
の曲線は、種々の縦交線に沿った加入度曲線でもある。ここで、曲率半径と屈折
力とは密接な関係にあり、曲率半径をＲとし、レンズの屈折率をｎとするとき、
曲率ρは、 ρ＝１／Ｒで表され、屈折力Ｄは、Ｄ＝（ｎ−１）／Ｒ＝（ｎ−１）ρ の関係になる。そして、曲率半径Ｒをメートル単位とする場合に、屈折力Ｄはデ
ィオプター単位で表される。図５におけるΣ₀は主子午線曲線ＭＭ'(Ｖｚ＝０°)に相当し、この主子午線曲
線に沿った横方向の屈折力の変化を曲線ｅ₀で示す。そして、Σ₁，Σ₂，Σ ₃ はそれぞれ、Ｖｚ＝５．６°，１１．２°，１６．８°に対応し、それぞれの
縦交線に沿った横方向屈折力の変化を曲線ｅ₁，ｅ₂，ｅ₃で示している。ここで
、Ｖｚ＝１６．８°が累進焦点レンズとしての最大有効口径にほぼ対応するもの
とすれば、Σ₁，Σ₂，Σ₃はそれそれ、レンズの半径Ｗに対して、Ｗ／３，２Ｗ
／３，Ｗに対応することになる。図５のｅ₃に示される如く、遠用部Ｆの上方においては、主子午線曲線上の屈
折力(ｅ₀)に対して、レンズの側縁部(Σ₃)における屈折力がより大きく、レンズ
側方中間部(Σ₁，Σ₂)における屈折力(ｅ₁，ｅ₂)がより小さくなっており、遠用
部Ｆの中間でこれらがほぼ等しい屈折力となっている。中間部Ｐの上部において
は、最も大きな屈折力となる主子午線曲線上の屈折力(ｅ₀)に対して、レンズ側
方中間部(Σ₁，Σ₂)における屈折力(ｅ₁，ｅ₂)よりも、レンズの側縁部(Σ₃)に
おける屈折力が小さくなっている。そして、中間部の下部から近用部Ｎにおいては、主子午線曲線上の屈折力(ｅ₀
)は最も大きく、所定の加入度をもって増大したのち近用部の下方で減少傾向と
なる。近用部Ｎにおける側方領域の横方向屈折力については、レンズ側方中間部
(Σ₁，Σ₂)において屈折力(ｅ₁，ｅ₂)が減少し、ｅ₂が最も小さく、これより側
方部(Σ₃)の屈折力(ｅ₃)が少し上昇しているが、ほとんど同一の屈折力となって
いる。即ち、レンズの有効径をＷとするとき、近用部Ｎの中間において、主子午
線曲線から垂直方向に２／３Ｗ以上離れた領域(Σ₂)での横方向の面屈折力は、
遠用中心Ｏ_Fでの表面屈折力（５ディオプター）に対して、若干の変動を有する
ものであり、本実施例の如く加入度をＡ（ディオプター）と丁るとき、±Ａ／２
ディオプター以内の範囲とすることが有効である。尚、本実施例では近用部Ｎの
中間において、主子午線曲線から垂直方向に２／３Ｗ離れた領域となっているが
、１／２Ｗ以上離れた領域であれば実質的に有効である。ところで、上記の如き実施例において、主子午線曲線に沿った平均屈折力の分
布の状態は、図６に示すごとくである。本実施例は遠用部Ｆの平均屈折度数（ベ
ースカーブ）が、４．０ディオプターで、加入度２．５ディオプターの累進焦点
レンズであるから、遠用中心Ｏ_Fにおいてほぼ４．０ディオプターであり、近用
中心Ｏ_Nにおいて平均屈折度数はほぼ６．５ディオプターとなっている。このような加入度曲線を有するレンズ面の設計においては、レンズとしての円
形形状の範囲内のみにおいて面形状を設計評価するのではなく、レンズ面の円形
形状を含む図３に示した如き四角形を想定し、この四角形内での面形状の設計と
評価を行った。このように、レンズの円形形状を覆うより大きな面での曲面を最
適化することによって、実用的レンズ面をよりなめらかな優れた形状とすること
が可能となるのである。上記の如き実施例の面形状を有する累進焦点レンズについて、性能評価を行っ
た結果を示したのが、図７の等非点隔差曲線図である。この図において、等非点
隔差曲線は０．５ディオプターごとの値としている。本実施例との比較のために、図８に従来の累進焦点レンズについての等非点隔
差曲線図及び主子午線曲線上の屈折力分布曲線図の概要を示した。この図におい
ても、等非点隔差曲線は０．５ディオプターごとの値としている。従来の累進焦点レンズにおいてば、不発明による上記の如き構成ではないため
、図８に示す如く、非点隔差の密度が高くなり、非点隔差量及び非点隔差の勾配
が急激なものとなり、結果として像のゆがみが大きくなり、視線を移動したとき
に像のゆれを感ずることになる。また、遠用部下方の側方領域には、中間部の側
方領域からの非点隔差の収差がしみ出して、この領域へ眼を向けた場合には、像
のボケばかりではなく、像のゆがみ、ゆれが著しくなっている。これに対し、本実施例においては図７に示す如く、累進帯が短くなったにもか
かわらず表面屈折力の非点隔差の密度も低下し、非点隔差の勾配もゆるやかにな
り、像のゆがみもゆれも軽減されていることが明らかである。ここで、上記実施例の加入度曲線を示した図６を用いて、本発明による累進焦
点レンズの主要な点について説明しておく。遠用中心Ｏ_Fとは、遠用部での所定の表面屈折平均度数を有する主子午線曲線
上の位置であり、実用上は遠用部の測定基準点とされる点である。また、近用中
心Ｏ_Nとは、近用部での所定の表面屈折平均度数を有する主子午線曲線上の位置
であり、実用上は近用部の測定基準点とされる点である。そして、遠用アイポイントＥは、レンズを眼鏡フレームに枠入れする際の基準
とされる位置であり、眼鏡フレームを装用した状態において遠用視線通過位置と合致する遠用基準点となる。このような遠用アイポイントＥの位置は、図６の主
子午線曲線上の平均屈折力分布曲線に示す如く、レンズの幾何中心とは独立に定
められており、本発明においては以下のように定義する。すなわち、主子午線曲
線上の表面屈折力の平均度数を主子午線曲線上の各位置ごとにプロットした図６
の如き加入度曲線において、遠用部Ｆの遠用中心Ｏ_Fと近用部Ｎの近用中心Ｏ_Nと
を結ぶ直線ａと平行で、加入度曲線と遠用部Ｆ側で接する直線ｂが、遠用中心Ｏ
_Fでの平均屈折力を表す直線ｃとの交点Ｅを遠用アイポイントとする。尚、一般の累進焦点レンズでは、主子午線曲線に沿って、全線を微視的な球面
の連続とする所謂臍点曲線としたものや、主子午線曲線上の一部の領域において
臍点ではなく、互いに直交する方向での曲率半径が異なる面形状とするものが提
案されており、主子午線曲線上の面形状についてみれば主子午線曲線の全線にわ
たって臍点状としたものと、主子午線曲線上の少なくとも一部において臍点では
なくして、主子午線曲線に沿う方向の曲室半径とそれに直角な方向での曲率半径
とを異なる値としたものとに２大別されるが、本発明においてはこれらの何れの
場合にも有効である。まだ、一般に累進焦点レンズは眼鏡フレームに合わせて加工されるため、遠用
部、中間部及び近用部の各領域、特に周辺部を含む遠用部と近用部の領域は、フ
レームの形状によって異なることとなるが、加工前の累進焦点レンズは一般に直
径６０ｍｍ程度以上の円形レンズであり、この円形形状のまま眼鏡小売店に供給
され、小売店において所望の眼鏡フレーム形状に合わせて加工されている。従っ
て、本発明における累進焦点レンズの面形状の規定においてはこのような加工前
の形状を基準とするものである。そして、累進焦点レンズの最適面形状の設計に
おいては、使用頻度の高い中心領域のみではなく使用される有効領域を含むより
広い領域における面形状をも考慮して収差バランスを図ることが肝要である。【発明の効果】以上の如き本発明によれば、累進帯としての中間部を短くしても、遠用部の下
方においても広い視野を有し、実用上不便のない広さの明視域を有する中間部及
び近用部を有し、そめ周辺においても像のゆがみ、ゆれを極力低減し側方視にお
いても不快感を感ずることがなく、収差的にバランスのとれた累進焦点レンズを実現することが可能となり、この種のレンズを初めて用いる人にも違和感なく装
用し得る累進焦点レンズを達成することができる。【図面の簡単な説明】第１図本発明の累進焦点レンズの領域区分の概要を示す平面図であり、第２図
（Ａ）及び（Ｂ）は本発明による屈折表面の横断面及び縦断面を説明するための
斜視図、第３図は本発明による横断面を説明するための平面図、第４図は本発明
による実施例の横断面に沿った横方向曲率半径の変化を示す図、第５図は横方向
の屈折力について縦交線に沿った変化を示す図、第６図は実施例における主子午
線曲線に沿う平均屈折力の分布を示す図、第７図は本発明による実施例について
の等非点隔差曲線図、第８図は従来の累進焦点レンズについての等非点隔差曲線
図である。【主要部分の符号の説明】Ｆ・・・遠用部、Ｏ_F・・・遠用中心Ｐ・・・中間部、Ｏ_N・・・近用中心Ｎ・・・近用部、Ｅ・・・遠用アイポイントDescription: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a progressive lens used for assisting accommodation of an eye. 2. Description of the Related Art As an auxiliary spectacle lens for accommodation power when the accommodation power of the eye is reduced and near vision becomes difficult, an upper far vision correction area (hereinafter referred to as a distance section) and a lower near vision are used. Vision correction area (
The progressive zone (where the refractive power changes continuously between the near portion)
Various progressive lenses having an intermediate portion are hereinafter known. In progressive lenses, generally, a clear vision area between the distance portion and the near portion is widely secured,
If the area is connected by a corridor, lens aberrations will be concentrated in the lateral area of the corridor, causing the image to be distorted due to the existence of this area or blurring of the image, and the fluctuation when moving the line of sight. Gives a bad impression to the wearer. In order to solve such a problem of visual characteristics, known progressive lenses have been designed and evaluated from various viewpoints. Then, regarding the shape of the lens surface, an intersection line between a cross section along a meridian running substantially perpendicular to the center of the lens surface and the object side lens surface is used as a reference line for representing specifications such as addition of the lens, It is also used as an important reference line in the design. In addition, even in a progressive lens in which the near portion is asymmetrically arranged in consideration of the near portion approaching the nose side in the wearing state of the lens, one lens that passes vertically through the distance center and the near center is also used. The center line is treated as the reference line. In the present invention, these reference lines are called main meridian curves. As a conventional progressive lens, for example, a lens disclosed in JP-B-49-3595 and a lens disclosed in JP-B-59-42285 are known. The above-mentioned known techniques can improve visual performance to a certain extent, but are still insufficient in practical use. That is, in the former, regarding the shape of the intersection line formed by the plane perpendicular to the main meridian curve and the refraction surface, only the intersection line at a point substantially corresponding to the center of the middle part is circular, and the upper part is far from the main meridian curve As the radius of curvature of the intersection line decreases and increases in the lower part according to the above, all are non-circular shapes.Since only the central portion is circular and the other region is a simple non-circular shape, The clear vision area (range in which the astigmatism is 0.5 diopter or less) of the near portion and the far portion is narrow, and the field of view becomes narrow due to a sudden change in aberration.
The image was significantly distorted and distorted. In the latter case, the radius of curvature of the intersection line between the plane perpendicular to the main meridian curve and the refractive power surface similarly decreases as the distance from the main meridian curve increases, and the radius of curvature decreases. The decreasing rate approaches 0 as it goes upward, and the radius of curvature is constant at the upper peripheral part, the radius of curvature is monotonically reduced at the lower part of the distance part, and the connecting part with the distance part at the middle part. Except for, the radius of curvature increases and decreases as the distance from the main meridian curve increases, and in the near portion, the radius of curvature increases and decreases as the distance from the main meridian curve increases. In this device, although the visual characteristics can be improved to some extent than the former, the residual astigmatic difference in the peripheral region of the distance portion, particularly in the side region from the center to the lower portion of the distance portion is still remarkable, and Even in the side regions of the intermediate portion and the near portion, image distortion and fluctuation are large, and it is difficult to obtain a sufficiently wide field of view. In general, when the intermediate portion as the progressive zone is shortened, the change in refractive power becomes sharp, and thus the aberration increases sharply. As can be seen from Minkwitz's law, especially near the main meridian curve, the aberration increases rapidly, and not only the width of the corridor tends to be narrowed, but also the image distortion and distortion increase rapidly. On the other hand, when the corridor is relatively long, the change in refractive power is relatively gentle, so that astigmatism, shaking, and distortion are easily reduced. However, if the corridor is too long, a desired addition degree cannot be obtained unless the line of sight is lowered sufficiently at the time of wearing. The present invention is intended to solve the above-described conventional disadvantages and to provide a progressive-focus lens that is aberrationally balanced even when the intermediate portion as a progressive zone is shortened. Has a wide field of view even below the far vision part, has a middle part and a near vision part with a clear vision area of a size that is practically inconvenient, and also minimizes image distortion and distortion in the surrounding area. It is an object of the present invention to provide a progressive power lens that does not cause any discomfort even in a side view. The present invention provides a distance section F having a refractive power corresponding to a distant view along a main meridian curve, a near section N having a refractive power corresponding to a near view, and the distance section. In the progressive lens as shown in FIG. 1 having an intermediate portion P which continuously and smoothly connects the refractive swords of the two portions between the intermediate portion and the near portion, if the intermediate portion as a progressive zone becomes shorter, With respect to the cross-sectional shape of the surface, the optimum shape of each part was found, and the aberration balance was optimized over the entire refractive surface. Specifically, the cross-sectional shape of the refractive surface at the lower part of the distance portion is a non-circular curve in which the value of the radius of curvature decreases and then increases as the distance from the intersection with the main meridian curve increases along the cross-sectional curve. In the upper part of the distance portion, the cross-sectional shape of the refractive surface is a non-circular curve in which the value of the radius of curvature increases as the distance from the intersection with the main meridian curve increases along the cross-sectional curve, and then decreases, The cross-sectional shape of the refracting surface is substantially circular along the cross-sectional curve at a substantially central portion of the distance portion, and the cross-sectional shape of the refracting surface from the center of the intermediate portion to the upper portion of the near portion is a cross-sectional curve. , The radius of curvature increases as the distance from the intersection with the main meridian curve increases, and then becomes a substantially non-circular curve. Further, in the upper part of the intermediate portion P, the cross-sectional shape of the refraction surface is a non-circular curve in which the value of the radius of curvature increases as the distance from the intersection with the main meridian curve increases, and the increase rate increases as the distance to the near portion increases. It is effective to adopt a configuration in which: And, from below the middle portion to above the near portion, the cross-sectional shape of the refractive surface is:
The position where the value of the radius of curvature increases as the distance from the intersection with the main meridian curve increases and then becomes substantially constant is, when the radius of the progressive lens is W, 1/4 W to 3 in the vertical direction from the main meridian curve. It is effective to have a configuration in which it exists in a region separated by / 4 W. Further, when the radius of the progressive power lens is W at least in the middle of the near portion of the refractive surface extending to the intermediate portion P and the near portion N, in a region away from the principal meridian curve by Ｗ W or more in the vertical direction when the radius is W. The surface refracting power in the direction along the cross section of the refracting surface of the refracting surface is ± A /
It is effective to set the range within 2 diopters. In the structure according to the present invention as described above, the cross-sectional shape of the refracting surface increases and decreases as the distance from the main meridian curve increases, first, and the opposite tendency is observed below the distance portion. The distance portion F has a substantially circular shape substantially at the center thereof, so that the distance portion F can be secured at an extremely large width and can be smoothly connected to the intermediate portion. This makes it possible to weaken the concentration of the difference, achieve a wider clear vision area at the intermediate portion P 1, and reduce image distortion and fluctuation in the periphery. In addition, a non-circular curve in which the cross-sectional shape of the refracting surface has a value of the radius of curvature that increases as the distance from the intersection with the main meridian curve increases above the intermediate portion P and above the near portion N, and becomes substantially constant thereafter Therefore, despite having a wide distance vision zone due to the shape of the distance portion as described above, the concentration of the astigmatic difference in the intermediate portion and the near portion is reduced in a well-balanced manner, and the lateral region The image can be shaken, distorted, etc., and the vision can be improved. EXAMPLES Hereinafter, examples of the present invention will be described. First, a horizontal section and a vertical section of the present invention will be described. FIGS. 2A and 2B are perspective views for explaining a horizontal section and a vertical section of the refractive surface σ of the lens. This takes the optical axis is the X axis in the geometric center O _G of the lens, the curvature center positions of the refractive surface in the geometric center O _G as the center O _O, and the radius of curvature radius R _O of the refractive surface σ at the geometric center O _G The sphere to be set is the reference sphere. Therefore, the reference spherical surface is in contact with the refracting surface σ and the geometric center O _G of the lens. With the center O _{O of the} reference spherical surface as the origin, the y axis is set in the vertical direction and the z axis is set in the horizontal direction. As shown in FIG. 2A, the cross section in the present invention refers to the refraction surface σ determined by a plane π _j passing through the center O _{O of the} reference sphere and orthogonal to a plane (xy plane) including the principal meridian curve MM ′. It is a cross section and is shown as a cross section intersection line Φ _j . The longitudinal section in the present invention is a longitudinal section of the refraction surface σ by a plane χ _j passing through the center O _{O of the} reference sphere and including the y-axis, as shown in FIG. Σ _j is shown. FIG. 3 is a plan view showing the state of such a plane crossing line Φ _j and a vertical crossing line Σ _{j on} the lens refracting surface. Each cross-section intersection line (Φ ₃ , Φ ₂ , Φ
Along _one ...), the value of Kyokutaba radial transverse, is a 4 to show changes in the right half of the refractive surface σ relative to the transverse direction of the radius of curvature on the principal meridional curve MM ' . It is needless to say that the cross section intersection line Φ _j and the vertical cross section line Σ _j described here mean the cross section curve and the vertical section curve in the present invention, respectively. More specifically, FIG. 4 shows the value of the radius of curvature in the vertical direction along each cross-section intersection line at seven representative cross-sections that intersect with the main meridian curve MM ′.
This is a plot of the right half of the main meridian curve MM 'based on the radius of curvature in the horizontal direction on M'. Here, the values of the respective radii of curvature plotted are shown in FIG.
) (B), the plane (x−x) passing through the center O _O of the reference sphere and including the principal meridian curve MM ′.
along the y plane) cross-section line of intersection [Phi _j refractive surface σ a plane [pi _j orthogonal to the horizontal direction in the vertical intersection line curve sigma _j points intersect M _j by vertical surfaces (chi _j) including y-axis Is the radius of curvature of The angle Vy formed by the plane π _j passing through the center of the reference sphere and orthogonal to the plane (xy plane) including the principal meridian curve MM ′ and the optical axis (x-axis) was changed every 5.6 °. Seven cross-section lines (Φ ₃ , Φ ₂ ) by one plane (π ₃ , π ₂ , π ₁ , π ₀ , π ₋₁ , π _-2 , π _-3 )
, Φ ₁ , Φ ₀ , Φ _-1 , Φ _-2 , Φ _-3 ), on each cross section, a plane (χ _j ) including the y-axis and a plane including the principal meridian curve MM ′ ( The values of the lateral radii of curvature were formed based on the lateral radii of curvature on the main meridian curve MM ′ when the horizontal angle Vz with the xy plane) was taken every 5.6 °. FIG. As shown in FIG. 4, in the present embodiment, the cross-sectional shape of the refracting surface at the lower portion (5.6 °) of the distance portion F has a radius of curvature as the distance from the intersection with the main meridian curve MM ′ increases. Is a non-circular curve that decreases and then increases.
16.8 °), the cross-sectional shape of the refractive surface is a non-circular curve in which the value of the radius of curvature increases and then decreases as the distance from the intersection with the main meridian curve MM ′ decreases, and is substantially the central portion of the distance portion F ( (11.2 °), the radius of curvature in the cross section of the refraction surface becomes substantially constant, and this cross section has a substantially circular curve. Further, at the intermediate portion P (−5.6 °), the cross-sectional shape of the refraction surface is a non-circular curve in which the value of the radius of curvature increases as the distance from the intersection with the main meridian curve increases, and then becomes substantially constant; The increasing rate and the decreasing rate increase as approaching the near portion, and this tendency is apparent from comparison with the cross-sectional shape (-11.2 °) in the near portion N. Then, in the near portion N (upper portion of -11.2 °, lower portion of -16.8 °), the cross-sectional shape of the refractive surface is farther from the intersection with the main meridian curve MM 'in the upper portion of the near portion. Is a non-circular curve in which the value of the radius of curvature increases and becomes substantially constant thereafter.
Here, the position where the radius of curvature becomes substantially constant from the increase in the radius of curvature is determined by setting the radius of the progressive lens to W.
Is located at about half of W, and practically W from the main meridian curve
It is effective to adopt a configuration that exists in a region separated by / 4 to 3W / 4. With respect to the change in the radius of curvature along the cross section as described above, the increase in the radius of curvature in the lateral region above the distance portion F is determined by the change in the radius of curvature at the intersection of the cross section and the main meridian curve. This is an increase of about 7%, and the amount of decrease in the radius of curvature below the distance portion F is about 8% with respect to the radius of curvature at the intersection of the cross section and the main meridian curve.
Is the decrease. Further, it becomes almost constant from the increase in the lateral radius of curvature at the lower part of the intermediate portion P, but the maximum value of the increase is about 60% increase with respect to the radius of curvature at the intersection of the cross section and the main meridian curve. is there. In the increase and decrease of the lateral radius of curvature at the near portion N, the maximum value is about 84% increase with respect to the radius of curvature at the intersection of the cross section and the principal meridian curve, and the lateral region of the near center O _N The maximum value of the lateral curvature radius at is the radius of curvature at the intersection of the cross section and the principal meridian curve,
It is effective that the value is increased by 50% to 100%. Incidentally, FIG. 5 shows a change along the vertical intersection line in the horizontal refractive power corresponding to the horizontal radius of curvature. That is, it is a diagram in which the refractive power in the horizontal direction at each point is plotted along the vertical intersection line Σ _j on the vertical plane (x _j ) including the above-mentioned y axis on the refractive surface σ. It also indicates the vertical change in the directional radius of curvature. These curves are also addition curves along various vertical lines. Here, the radius of curvature and the refractive power are closely related. When the radius of curvature is R and the refractive index of the lens is n,
The curvature ρ is represented by ρ = 1 / R, and the refractive power D has a relationship of D = (n−1) / R = (n−1) ρ. When the radius of curvature R is in units of meters, the refractive power D is expressed in units of diopters. In FIG. 5, Σ ₀ corresponds to the main meridian curve MM ′ (Vz = 0 °), and a change in refractive power in the horizontal direction along the main meridian curve is indicated by a curve e ₀ . Σ ₁ , Σ ₂ , and Σ ₃ correspond to Vz = 5.6 °, 11.2 °, and 16.8 °, respectively, and the change of the lateral refractive power along each vertical line is represented by a curve e. It is indicated by _1, e _2, e _3. Here, assuming that Vz = 16.8 ° substantially corresponds to the maximum effective aperture of the progressive lens, Σ ₁ , Σ ₂ , and Σ ₃ are respectively W / 3 of the lens radius W. , 2W
/ 3, W. As shown at e ₃ in FIG. 5, above the distance portion F, the refractive power at the side edge (Σ ₃ ) of the lens is larger than the refractive power (e ₀ ) on the main meridian curve, The refractive power (e ₁ , e ₂ ) at the lens side intermediate portion (Σ ₁ , Σ ₂ ) is smaller, and they are almost equal in the middle of the distance portion F. In the upper part of the middle part P, the refractive power (e ₁ , e ₂ ) at the lens side middle part (Σ ₁ , Σ ₂ ) is larger than the refractive power (e ₀ ) on the main meridian curve which is the largest refractive power. ), The refractive power at the side edges (縁₃ ) of the lens is smaller. From the lower portion of the intermediate portion to the near portion N, the refractive power (e ₀ on the main meridian curve)
) Is the largest, increases with a predetermined addition, and then decreases below the near portion. Regarding the lateral refractive power of the lateral region in the near portion N, the lens lateral intermediate portion
At (Σ ₁ , ｅ ₂ ), the refractive power (e ₁ , e ₂ ) decreases, e ₂ is the smallest, and the refractive power (e ₃ ) at the side (Σ ₃ ) slightly increases. Have almost the same refractive power. That is, when the effective diameter of the lens is W, the surface power in the lateral direction in a region (領域₂ ) vertically separated from the main meridian curve by 以上 W or more in the middle of the near portion N is as follows:
To the surface refracting power of the far viewing center O _F (5 diopter), those having a slight variation, when the additional power as in the present embodiment A (diopter) Hinotoru, ± A / 2
It is effective to set the range within diopters. In the present embodiment, the area is 垂直 W apart in the vertical direction from the main meridian curve in the middle of the near portion N, but it is practically effective if it is Ｗ W or more. By the way, in the embodiment as described above, the state of the distribution of the average refractive power along the main meridian curve is as shown in FIG. This embodiment is an average refractive power of the distance portion F (base curve), in 4.0 diopter, because it is progressive lens addition power 2.5 diopters, at approximately 4.0 diopter in the far viewing center O _F There, the average refractive power in the near center O _N is almost 6.5 diopter. In the design of a lens surface having such an addition curve, the surface shape is not designed and evaluated only within the range of the circular shape as a lens, but a square as shown in FIG. Assuming, the design and evaluation of the surface shape within this rectangle were performed. Thus, by optimizing the curved surface on a larger surface covering the circular shape of the lens, it becomes possible to make the practical lens surface smoother and superior. FIG. 7 is an equi-astigmatic curve diagram showing the result of performance evaluation of the progressive lens having the surface shape of the embodiment as described above. In this figure, the equi-astigmatic difference curve is a value for each 0.5 diopter. For comparison with the present embodiment, FIG. 8 shows an outline of an equi-astigmatic difference curve diagram and a refractive power distribution curve diagram on a principal meridian curve of a conventional progressive lens. Also in this figure, the equi-astigmatic difference curve is a value for each 0.5 diopter. In the conventional progressive lens, since the configuration is not as described above due to the invention, as shown in FIG. 8, the density of astigmatism increases, and the amount of astigmatism and the gradient of astigmatism become steep. As a result, the distortion of the image becomes large, and when the user moves his / her line of sight, the user feels the image distortion. Also, in the side region below the distance portion, astigmatic aberration from the side region in the middle portion exudes, and when eyes are turned to this region, not only the blur of the image but also the image Distortion and shaking are significant. On the other hand, in the present embodiment, as shown in FIG. 7, the density of the astigmatic difference of the surface refractive power is reduced, and the gradient of the astigmatic difference becomes gentle even though the corridor is shortened. It is clear that both distortion and sway are reduced. Here, the main points of the progressive lens according to the present invention will be described with reference to FIG. 6 showing the addition curve of the above embodiment. The distance center O _F, a position on the principal meridional curve having a predetermined surface refractive average power in the distance portion, practically is that it is a reference point of the distance portion. Further, the near center O _N is a position on the main meridian curve having a predetermined average surface refraction power at the near portion, and is a point practically used as a measurement reference point of the near portion. The distance eye point E is a position used as a reference when the lens is framed in the spectacle frame, and is a distance reference point that matches the distance line of sight passage position when the spectacle frame is worn. The position of such a distance eye point E is determined independently of the geometric center of the lens as shown in the average refractive power distribution curve on the main meridian curve in FIG. 6, and in the present invention, Define. That is, FIG. 6 in which the average power of the surface refractive power on the main meridian curve is plotted for each position on the main meridian curve.
In such diopter curve of, parallel to the line a connecting the near center O _N of the distance the center of the distance portion F O _F and the near portion N, line b in contact with additional power curve and the distance portion F side But the distance O
An intersection point E with a straight line c representing the average refractive power at _F is defined as a distance eye point. Incidentally, in a general progressive lens, along the main meridian curve, a so-called umbilical point curve in which the whole line is a series of microscopic spheres, or in some areas on the main meridian curve, It has been proposed that the surface shape has a different radius of curvature in the direction orthogonal to each other.The surface shape on the main meridian curve is the same as the navel point shape over the entire main meridian curve, and At least in part, instead of the navel point, the radius of curvature in the direction along the main meridian curve and the radius of curvature in the direction perpendicular to the radius of curvature are differently classified into two types. It is effective in any of these cases. Still, since progressive lenses are generally processed according to the spectacle frame, the distance, intermediate, and near portions, and particularly the distance and near portions including the peripheral portion, have the shape of the frame. The progressive lens before processing is generally a circular lens having a diameter of about 60 mm or more, and is supplied to an eyeglass retailer as it is in this circular shape, and is processed at the retailer according to a desired eyeglass frame shape. ing. Therefore, the definition of the surface shape of the progressive lens in the present invention is based on such a shape before processing. In designing the optimal surface shape of the progressive-focus lens, it is important to balance aberrations by considering not only the central region that is frequently used but also the surface shape in a wider region including an effective region to be used. . According to the present invention as described above, even if the intermediate portion as the progressive zone is shortened, the wide visual field has a wide field of view even below the distance portion, and has a practically inconvenient clear visual field. A progressive lens with balanced aberrations, with an intermediate part and near-vision part, which minimizes image distortion and fluctuation even around the dome and does not cause discomfort even when viewed from the side. This makes it possible to achieve a progressive lens that can be worn without discomfort even by a person using this kind of lens for the first time. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing the outline of the area division of the progressive lens according to the present invention, and FIGS. 2 (A) and (B) are cross-sectional views and longitudinal cross-sectional views of a refractive surface according to the present invention. FIG. 3 is a plan view for explaining a cross section according to the present invention, FIG. 4 is a diagram showing a change in a radius of curvature along a cross section of an embodiment according to the present invention, FIG. 5 is a diagram showing the change of the refractive power in the horizontal direction along the vertical line, FIG. 6 is a diagram showing the distribution of the average refractive power along the principal meridian curve in the embodiment, and FIG. FIG. 8 is an isoastigmatic difference curve for an example, and FIG. 8 is an isoastigmatic difference curve for a conventional progressive power lens. [Description of reference numerals of main parts] F · · · distance portion, O _F · · · distance center P · · · intermediate portion, O _N · · · near the center N · · · near portion, E · ·・ Distance eye point

Claims

Claims 1. A distance section having a refractive power corresponding to a distant view along a main meridian curve, a near section having a refractive power corresponding to a near view, and the near section and the near section. A progressive portion having an intermediate portion that continuously and smoothly connects the refractive powers of the two portions to the intermediate portion, wherein the cross-sectional shape of the refractive surface at the lower portion of the far portion is along a cross-sectional curve. This is a non-circular curve in which the value of the radius of curvature decreases and then increases as the distance from the intersection with the main meridian curve increases, and the cross-sectional shape of the refraction surface at the upper part of the distance portion is such that the main shape follows the cross-sectional curve. A non-circular curve in which the value of the radius of curvature increases and then decreases as the distance from the intersection with the meridian curve increases, and the cross-sectional shape of the refraction surface is substantially circular along the cross-sectional curve at a substantially central portion of the distance portion. And the intermediate part The cross-sectional shape of the refractive surface from the center to the upper part of the near portion is a non-circular curve in which the value of the radius of curvature increases as the distance from the intersection with the principal meridian curve increases along the cross-sectional curve, and then becomes substantially constant. Progressive lens. 2. A position where the value of the radius of curvature is substantially constant with respect to the cross-sectional shape of the refracting surface from the center of the intermediate portion to above the near portion is, when the radius of the progressive lens is W, a principal meridian. The progressive lens according to claim 1, wherein the progressive lens is located in a region vertically separated from the curve by １／ W to ／ W. 3. When the radius of the progressive power lens is W at least in the middle of the refractive surface between the intermediate portion and the near portion, the lens is separated from the principal meridian curve by at least Ｗ W or more in the vertical direction. Power in the direction along the cross section of the refracting surface in the region where the addition is A (diopter) with respect to the surface refracting power at the distance center
2. The progressive lens according to claim 1, wherein the range is within 1/2 diopter.