JP2004258571A - Apochromatic telephoto lens - Google Patents
Apochromatic telephoto lens Download PDFInfo
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- JP2004258571A JP2004258571A JP2003052119A JP2003052119A JP2004258571A JP 2004258571 A JP2004258571 A JP 2004258571A JP 2003052119 A JP2003052119 A JP 2003052119A JP 2003052119 A JP2003052119 A JP 2003052119A JP 2004258571 A JP2004258571 A JP 2004258571A
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Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、写真用カメラ、スチルビデオカメラ、ビデオカメラ等に最適なアポクロマート望遠レンズに関するものである。
【0002】
【従来の技術】
従来のアポクロマート望遠レンズは、先頭部に異常分散性の低分散ガラスを使用し、アポクロマートな色収差の補正を行ってきた(特許文献1を参照)。近年、回折複合素子をシステム前部配したコンパクトなアポクロマート望遠レンズも提案されている(特許文献2を参照)。しかし、異常分散性の低分散ガラスは機械的性質等に弱点があって先頭レンズに使用することに問題があり、回折複合素子は加工が困難でありコスト高になる問題点がある。
【0003】
【特許文献1】
特開昭55−147606号公報
【特許文献2】
特開2002−72082号公報
【0004】
【発明が解決しようとする課題】
異常分散性の低分散ガラスを多用、あるいは回折複合素子を使用することなく、通常の硝材を使用して望遠比の小さいアポクロマート望遠レンズを提供することにある。
【0005】
【課題を解決するための手段】
本発明は物体側から順に、第1群正パワー、第2群負パワー、第3群正パワーおよび第4群負パワーからなり、第1群正パワーにアッベ数が35より小さい2種類のガラスで構成されたパワーの小さい素子を有し、当該素子のパワーをφS、第1群正パワーをφ1とするとき
0.2>|φS/φ1|・・・・・・・・・・・・・・・・・・・・(1)
の条件を課して課題を解決した。さらに、当該素子の面を非球面化することにより高い性能を実現し、また、第3群正パワーを負および正レンズの接合レンズとし、両者の屈折率の差が0.01より小さいという条件を課して軸上色収差を良好に補正した。
【0006】
望遠比を小さくするには望遠タイプの構成が必要不可欠である。本発明は正・負・正・負の4群構成、すなわち望遠タイプの構成をダブルにすることによって望遠比を小さくしコンパクト化を実現した。
【0007】
しかし、望遠タイプは正レンズの像を負レンズで拡大する構造であるから、前部正レンズの軸上色収差が小さくないと全系の軸上色収差が大きなものになる。そのため、本発明は望遠タイプ構成の第1、第2群の正パワーにアッベ数が35より小さい2種類のガラスで構成されたパワーの小さい素子を有し、当該素子のパワーをφS、第1群正パワーをφ1とするとき
0.2>|φS/φ1|・・・・・・・・・・・・・・・・・・・・(1)
として軸上色収差の発生を小さくした。
【0008】
2種の重フリント(SF)ガラスと低分散ガラスの3枚によってアポクロマートな対物レンズが実現できることは古くから知られている。本発明は重フリントアポクロマートの思想を継承発展させ、アッベ数が35より小さい2種のガラス、すなわち2種の重フリントガラスで構成した素子を導入し、かつ当該素子のパワーを小さく設定するという条件を課すことによってアポクロマート化、コンパクト化および高性能化を実現した。
【0009】
条件式(1)はアッベ数が35より小さい2種の重フリントガラスで構成された素子の合成パワーが小さい条件を定式化したものである。本条件は2種の重フリントガラスの分散特性の関連によって二次スペクトルを小さくする効果を保証する。当該素子のパワーが条件から外れる場合、望遠タイプを構成する第1、第2群による二次スペクトルが大きくなり、後に続く第3、第4群では二次スペクトルの補正が困難である。
【0010】
しかし、軸上色収差をアポクロマートに補正するのに有効な条件(1)は、当該素子のパワーが小さいことであるから、単色の諸収差の補正にとって好ましいとは言い難い。したがって、当該素子の面を非球面化することはシステムをコンパクト化して軸上色収差および単色収差を良好に補正するのに有効である。非球面化しなければ軸上色収差と単色の諸収差を良好に補正することが困難であり、非球面の導入なしに良好に補正しようとすればレンズシステムが大型化するので好ましくない。
【0011】
第1、第2群の望遠タイプの構成に加え、第3、第4群を正・負パワーの望遠タイプにすることによってシステムのコンパクト化を実現した。本システムの第3群はハイパークロマチックな構成が特徴であるが、屈折率が等しくアッベ数が異なるガラスの接合によるハイパークロマチックなレンズにすることによって軸上色収差の補正、球面収差の波長による差の補正を良好に行うことができる。接合面前後の屈折率差が0.01を越えるときは球面収差の色収差の発生が大きくなり、口径比の大きいアポクロマートな望遠レンズの実現が困難になるので好ましくない。
【0012】
【実施例】
本発明の数値実施例を示す。fは焦点距離、FnoはFナンバー、2ωは画角であり、rはレンズ各面の曲率半径、dはレンズ厚またはレンズの間隔、nは各レンズのd線の屈折率、νはアッベ数を示す。
【0013】
非球面形状は光軸方向にx軸、光軸と垂直方向にH軸、光の進行方向を正とし、Rを曲率半径、円錐係数をAとし、A1、A2、A3、A4、A5を各非球面係数としたとき、
【数1】
【0014】
数値実施例1
f=390.6
Fno=4.4
2ω=6.4°
【0015】
【0016】
非球面データ
r1の非球面係数
A = 0.10623000E+01
A1= 0.00000000E+00
A2= 0.75533904E−07
A3=−0.18245379E−12
A4=−0.41155814E−15
A5=−0.66532626E−18
【0017】
r3の非球面係数
A = 0.14679000E+01
A1= 0.00000000E+00
A2= 0.26308098E−06
A3= 0.25794241E−10
A4= 0.45532006E−14
A5=−0.26911153E−17
【0018】
条件式
|φS/φ1|=0.0820
【0019】
数値実施例2
f=390.6
Fno=4.3
2ω=6.4°
【0020】
【0021】
非球面データ
r1の非球面係数
A = 0.11800000E+01
A1= 0.00000000E+00
A2= 0.20087269E−07
A3=−0.15225299E−10
A4= 0.66421469E−15
A5=−0.23554154E−17
【0022】
r3の非球面係数
A=0.15342000E+01
A1=0.00000000E+00
A2=0.18602701E−06
A3=−0.78816172E−11
A4= 0.13059678E−13
A5=−0.13023977E−16
【0023】
条件式
|φS/φ1|=0.0858
【0024】
【発明の効果】
異常分散を有する低分散ガラスを多用することなく、また回折複合素子のような特殊な素子を使用することなく、極めて小さい望遠比で高性能なアポクロマート望遠レンズを実現することができた。
【図面の簡単な説明】
【図1】本発明の数値実施例1のレンズ断面図である。
【図2】本発明の数値実施例1の収差図である。
【図3】本発明の数値実施例2のレンズ断面図である。
【図4】本発明の数値実施例2の収差図である。
【符号の説明】
r レンズ各面の曲率半径
d レンズ厚またはレンズの間隔
Fno Fナンバー
2ω 画角[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apochromatic telephoto lens most suitable for a photographic camera, a still video camera, a video camera, and the like.
[0002]
[Prior art]
A conventional apochromatic telephoto lens uses anomalous low-dispersion glass at the head and corrects apochromatic chromatic aberration (see Patent Document 1). In recent years, a compact apochromatic telephoto lens in which a diffractive composite element is arranged in front of a system has been proposed (see Patent Document 2). However, low dispersion glass having anomalous dispersion has problems in mechanical properties and the like and has a problem in being used as a leading lens. Diffraction composite elements have a problem that processing is difficult and costs are increased.
[0003]
[Patent Document 1]
JP-A-55-147606 [Patent Document 2]
JP-A-2002-72082
[Problems to be solved by the invention]
An object of the present invention is to provide an apochromatic telephoto lens having a small telephoto ratio by using ordinary glass material without using a lot of low dispersion glass having anomalous dispersion or using a diffraction composite element.
[0005]
[Means for Solving the Problems]
The present invention comprises, in order from the object side, two types of glasses having a first group positive power, a second group negative power, a third group positive power, and a fourth group negative power, wherein the first group positive power has an Abbe number smaller than 35. When the power of the element is φS and the positive power of the first group is φ1, 0.2> | φS / φ1 |・ ・ ・ ・ ・ ・ ・ ・ (1)
The task was solved by imposing the conditions of: Furthermore, a high performance is realized by making the surface of the element aspherical, and the third lens unit has a positive power as a cemented lens of a negative lens and a positive lens, and the difference between the refractive indices of the two is less than 0.01. To correct the longitudinal chromatic aberration well.
[0006]
In order to reduce the telephoto ratio, a telephoto type configuration is indispensable. In the present invention, the telephoto ratio is reduced and the size is reduced by making the four-group configuration of positive, negative, positive, and negative, that is, the double telephoto configuration.
[0007]
However, since the telephoto type has a structure in which the image of the positive lens is enlarged by the negative lens, the axial chromatic aberration of the entire system becomes large unless the axial chromatic aberration of the front positive lens is small. Therefore, the present invention has a low power element composed of two types of glass having an Abbe number smaller than 35 in the positive power of the first and second groups of the telephoto type configuration, and the power of the element is φS and the first power is φS. When the group positive power is φ1, 0.2> | φS / φ1 | (1)
The generation of axial chromatic aberration was reduced.
[0008]
It has long been known that an apochromatic objective lens can be realized by three types of heavy flint (SF) glass and low dispersion glass. The present invention inherits and develops the idea of heavy flint apochromat, and introduces two kinds of glass having an Abbe number smaller than 35, that is, an element constituted by two kinds of heavy flint glass, and a condition that the power of the element is set to be small. Achieved apochromatization, compactness and high performance by imposing.
[0009]
Conditional expression (1) formulates the condition that the combined power of the elements composed of two types of heavy flint glass having an Abbe number smaller than 35 is small. This condition guarantees the effect of reducing the secondary spectrum by relating the dispersion characteristics of the two types of heavy flint glass. If the power of the element deviates from the condition, the secondary spectrum of the first and second units constituting the telephoto type becomes large, and it is difficult to correct the secondary spectrum in the subsequent third and fourth units.
[0010]
However, the condition (1) effective for apochromatic correction of axial chromatic aberration is that the power of the element is small, so it is hard to say that it is preferable for correction of monochromatic aberrations. Therefore, making the surface of the element aspherical is effective for downsizing the system and favorably correcting axial chromatic aberration and monochromatic aberration. It is difficult to satisfactorily correct axial chromatic aberration and monochromatic aberrations without aspherical surface, and it is not preferable to satisfactorily correct it without introducing an aspherical surface, because the lens system becomes large.
[0011]
In addition to the telephoto configuration of the first and second lens units, the third and fourth lens units are of a telephoto type with positive and negative power, thereby realizing a compact system. The third group of this system is characterized by a hyperchromatic configuration, but the correction of axial chromatic aberration and the difference of spherical aberration by wavelength are achieved by forming a hyperchromatic lens by joining glass with the same refractive index and different Abbe numbers. Correction can be performed satisfactorily. If the difference between the refractive indexes before and after the cemented surface exceeds 0.01, chromatic aberration of spherical aberration increases, and it becomes difficult to realize an apochromatic telephoto lens having a large aperture ratio.
[0012]
【Example】
A numerical example of the present invention will be described. f is the focal length, Fno is the F number, 2ω is the angle of view, r is the radius of curvature of each lens surface, d is the lens thickness or lens spacing, n is the d-line refractive index of each lens, and ν is the Abbe number Is shown.
[0013]
The aspherical shape has an x-axis in the optical axis direction, an H-axis in a direction perpendicular to the optical axis, a positive traveling direction of the light, a radius of curvature of R, a conic coefficient of A, and A 1 , A 2 , A 3 , and A 4. , A 5 as each aspheric coefficient,
(Equation 1)
[0014]
Numerical example 1
f = 390.6
Fno = 4.4
2ω = 6.4 °
[0015]
[0016]
Aspherical surface coefficient A of aspherical surface data r 1 = 0.10623000E + 01
A 1 = 0.0000000E + 00
A 2 = 0.7553533904E-07
A 3 = -0.18245379E-12
A 4 = -0.41155814E-15
A 5 = -0.66532626E-18
[0017]
Aspherical coefficient A of r 3 = 0.14679000E + 01
A 1 = 0.0000000E + 00
A 2 = 0.26308098E-06
A 3 = 0.2579424E-10
A 4 = 0.45532006E-14
A 5 = -0.26911153E-17
[0018]
Conditional expression | φS / φ1 | = 0.0820
[0019]
Numerical example 2
f = 390.6
Fno = 4.3
2ω = 6.4 °
[0020]
[0021]
Aspherical surface coefficient A of aspherical surface data r 1 = 0.11800000E + 01
A 1 = 0.0000000E + 00
A 2 = 0.20087269E-07
A 3 = −0.152225E-10
A 4 = 0.66421469E-15
A 5 = -0.23554154E-17
[0022]
aspherical coefficient of r 3 A = 0.15342000E + 01
A 1 = 0.0000000E + 00
A 2 = 0.18602701E-06
A 3 = −0.78816172E-11
A 4 = 0.130596678E-13
A 5 = -0.13023977E-16
[0023]
Conditional expression | φS / φ1 | = 0.0858
[0024]
【The invention's effect】
A high-performance apochromatic telephoto lens with an extremely small telephoto ratio was realized without using much low-dispersion glass having anomalous dispersion and without using a special element such as a diffraction composite element.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.
FIG. 2 is an aberration diagram according to Numerical Example 1 of the present invention.
FIG. 3 is a lens cross-sectional view of Numerical Example 2 of the present invention.
FIG. 4 is an aberration diagram of Numerical Example 2 of the present invention.
[Explanation of symbols]
r Curvature radius of each lens surface d Lens thickness or lens spacing Fno F number 2ω Angle of view
Claims (3)
0.2>|φS/φ1|・・・・・・・・・・・・・・・・・・・・(1)
の条件満足することを特徴とするアポクロマート望遠レンズ。In order from the object side, the first group has positive power, the second group negative power, the third group positive power, and the fourth group negative power. The first group positive power is composed of two types of glass having an Abbe number smaller than 35. When the power of the element is φS and the positive power of the first group is φ1, 0.2> | φS / φ1 |・ ・ ・ ・ ・ (1)
An apochromatic telephoto lens that satisfies the following conditions:
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JP2003052119A JP2004258571A (en) | 2003-02-28 | 2003-02-28 | Apochromatic telephoto lens |
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JP2003052119A JP2004258571A (en) | 2003-02-28 | 2003-02-28 | Apochromatic telephoto lens |
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2013246354A (en) * | 2012-05-28 | 2013-12-09 | Sigma Corp | Imaging optical system |
-
2003
- 2003-02-28 JP JP2003052119A patent/JP2004258571A/en active Pending
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2013246354A (en) * | 2012-05-28 | 2013-12-09 | Sigma Corp | Imaging optical system |
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