JPH0431087B2 - - Google Patents
Info
- Publication number
- JPH0431087B2 JPH0431087B2 JP59087854A JP8785484A JPH0431087B2 JP H0431087 B2 JPH0431087 B2 JP H0431087B2 JP 59087854 A JP59087854 A JP 59087854A JP 8785484 A JP8785484 A JP 8785484A JP H0431087 B2 JPH0431087 B2 JP H0431087B2
- Authority
- JP
- Japan
- Prior art keywords
- lens
- group
- focal length
- condition
- recording
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 230000003287 optical effect Effects 0.000 claims description 6
- 239000002131 composite material Substances 0.000 claims description 2
- 230000004075 alteration Effects 0.000 description 15
- 239000000463 material Substances 0.000 description 3
- 239000006059 cover glass Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000011521 glass Substances 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
Landscapes
- Lenses (AREA)
Description
発明の目的
(産業上の利用分野)
この発明は光デイスクの記録・再生用対物レン
ズ、特に異なる波長で記録・再生を行なうに適し
た対物レンズに関する。
(従来技術)
従来、光デイスク等の情報記録媒体への情報の
記録及びその再生のための対物レンズは、それぞ
れの目的のために開発され、一般に色収差は補正
されていない。
このため、2種類の波長の光を用い、同一の対
物レンズを用い、一方の波長の光で情報を記録
し、他方の波長の光で再生を行なう場合、この2
種類の波長の平行光を同じ焦点位置に集光するこ
とができない。止むを得ず、対物レンズへの入射
光を一方の波長の光ではわずかに発散光とし、他
方の波長の光をわずかに収歛光とすることで、両
光束を同一焦点位置に集歛させていた。
(発明が解決しようとする問題点)
しかし、この方法では、デイスクの面振れに対
応して対物レンズを光軸方向に移動させると、両
光束の収歛位置がずれてくる。このため、デイス
クの面振れに対してフオーカシング制御可能な範
囲が限定されるという問題があつた。
このような問題の解決のためには、対物レンズ
の色収差の補正が必要となる。特開昭58−72114
号公報記載のレンズはその例であるが、これは非
常に屈折力の大きい負レンズを含む3枚接合レン
ズを用いているため、量産に向かないという問題
を含んでいた。
この発明は、簡単な構成を有しながら色収差が
良好に補正され、光デイスク用レンズとして十分
な性能を有するレンズを得ようとするものであ
る。
発明の構成
(問題点を解決するための手段)
この発明の対物レンズは、第1図にその構成を
示すように、各々が正の屈折力を持つ2群構成で
あり、各群が物体側から順に凸レンズと負レンズ
の接合レンズであり、
3f<f〓<5f …(1)
0.35<ν2|f2|/ν1 f1<0.7 …(2)
8<ν3−ν4 …(3)
但し
f:全系の合成焦点距離
f〓:第1群レンズの焦点距離
Fi:第iレンズの焦点距離
νi:第iレンズのアツベ数
(作用)
条件(1)は第1群レンズに配分される屈折力を規
定し、上限をこえて第1群の焦点距離が長くなる
と第2群レンズの屈折力が大きくなり、負の球面
収差の発生が著しい。これを無理に補正しようと
すると、球面収差もしくは正弦条件のふくらみが
大きくなる。逆に下限をこえて第1群レンズの焦
点距離が短かくなると、レンズ系の作動距離が短
かくなり、光デイスク記録・再生用レンズには不
適となる。
条件(2)は第1群レンズにおける色収差の補正状
況を規定するものであり、上限をこえて大となる
と、第1群レンズでの色収差補正が不十分とな
り、第2群レンズに色収差補正の負担がかかる。
この結果、第2群レンズを構成する正レンズ、負
レンズの屈折力をそれぞれ大きくしなければなら
ない。これにより、第2群レンズを構成する各面
の曲率半径が小さくなり量産に向かないものとな
つてしまう。下限をこえて小とすれば、色収差補
正効果は大きくなる。しかし、これを実現するに
はν2/ν1を小ににするか、|f2|/f1を小にする
か、或いはその両方を小にする必要がある。しか
し、現在する硝子材料のアツベ数は正で、その大
きさには限界がありν2/ν1をあまり小にすること
はできない。また、|f2|/f1を小にするにはf1を
大きくし|f2|を小さくする必要があるが、条件
(2)の下限を超える程小さくすると、fIが条件(1)の
上限を超え、前記の問題が生じる。
条件(3)は第1群レンズでは補正しきれなかつた
色収差を補正するための条件であり、下限を超え
て小になると全系の色収差が補正不足となる。
(実施例)
以下この発明の対物レンズの実施例を示す。表
中の記号は以下のものを示す。
fi:物体側からi番目のレンズ面曲率半径
di:物体側からi番目のレンズ面間隔
ni:物体側からi番目のレンズ材料の波長
830nmの光に対する屈折率
νi:物体側からi番目のレンズ材料のd線に対
するアツベ数
M:結像倍率
dc:カバーガラスの軸上厚(830nm光に対する
屈折率は1.50974、d線に対するアツベ数
は64.1である)
W.D.:作動距離
OBJECT OF THE INVENTION (Field of Industrial Application) The present invention relates to an objective lens for recording and reproducing optical disks, and particularly to an objective lens suitable for recording and reproducing at different wavelengths. (Prior Art) Conventionally, objective lenses for recording and reproducing information on information recording media such as optical disks have been developed for each purpose, and generally chromatic aberration has not been corrected. Therefore, when using light of two different wavelengths and using the same objective lens, recording information with light of one wavelength and reproducing with light of the other wavelength, these two wavelengths are used.
Parallel light of different wavelengths cannot be focused at the same focal point. Unavoidably, by making the light incident on the objective lens slightly divergent for one wavelength and slightly converging for the other wavelength, both beams are converged at the same focal point. was. (Problems to be Solved by the Invention) However, in this method, when the objective lens is moved in the optical axis direction in response to surface wobbling of the disk, the convergence positions of both light beams are shifted. For this reason, there has been a problem in that the range in which focusing can be controlled against surface runout of the disk is limited. In order to solve such problems, it is necessary to correct the chromatic aberration of the objective lens. Japanese Patent Publication No. 58-72114
The lens described in the above publication is an example of this, but since it uses a three-lens cemented lens including a negative lens with a very large refractive power, it has the problem of not being suitable for mass production. The present invention aims to provide a lens that has a simple configuration, has chromatic aberrations well corrected, and has sufficient performance as an optical disk lens. Structure of the Invention (Means for Solving Problems) As shown in FIG. These are cemented lenses of a convex lens and a negative lens in order from 3f<f〓<5f …(1) 0.35<ν 2 |f 2 |/ν 1 f 1 <0.7 …(2) 8<ν 3 −ν 4 …( 3) However, f: Composite focal length of the entire system f〓: Focal length of the first group lens F i : Focal length of the i-th lens v i : Atsube number (action) of the i-th lens Condition (1) applies to the first group It defines the refractive power distributed to the lens, and when the focal length of the first group exceeds the upper limit, the refractive power of the second group lens increases, and negative spherical aberration occurs significantly. If you try to forcefully correct this, the spherical aberration or the bulge in the sine condition will increase. On the other hand, if the lower limit is exceeded and the focal length of the first group lens becomes short, the working distance of the lens system becomes short, making it unsuitable for use as an optical disk recording/reproducing lens. Condition (2) defines the state of correction of chromatic aberration in the first group lens, and if it exceeds the upper limit, the chromatic aberration correction in the first group lens will be insufficient, and the second group lens will be required to correct chromatic aberration. It's a burden.
As a result, it is necessary to increase the refractive powers of the positive lens and the negative lens constituting the second lens group. As a result, the radius of curvature of each surface constituting the second group lens becomes small, making it unsuitable for mass production. If the value is smaller than the lower limit, the chromatic aberration correction effect becomes greater. However, in order to achieve this, it is necessary to make ν 2 /ν 1 small, |f 2 |/f 1 small, or both. However, the Atsbe number of current glass materials is positive, and there is a limit to its size, so ν 2 /ν 1 cannot be made very small. Also, to reduce |f 2 |/f 1 , it is necessary to increase f 1 and decrease |f 2 |, but the condition
If it is made so small that it exceeds the lower limit of condition (2), f I will exceed the upper limit of condition (1) and the above problem will occur. Condition (3) is a condition for correcting chromatic aberrations that cannot be completely corrected by the first group lens, and when the lower limit is exceeded, the chromatic aberrations of the entire system become undercorrected. (Example) Examples of the objective lens of the present invention will be shown below. The symbols in the table indicate the following. f i : Radius of curvature of the i-th lens surface from the object side d i : Distance between the i-th lens surfaces from the object side n i : Wavelength of the i-th lens material from the object side
Refractive index for 830 nm light ν i : Atsube number for d-line of the i-th lens material from the object side M: Imaging magnification dc: Axial thickness of cover glass (refractive index for 830 nm light is 1.50974, Atsube number for d-line is 64.1) WD: Working distance
【表】【table】
【表】【table】
【表】【table】
【表】【table】
【表】
発明の効果
この発明の対物レンズは、第1図にその断面を
示すように非常に簡単な構成にもかかわらず、第
2図ないし第5図に示す収差図から明らかなよう
に、球面収差、正弦条件を良好に保ちながら色収
差を良好に補正し、830nmの光束と780nmの光束
を同一点に集束することができる。[Table] Effects of the Invention Although the objective lens of the present invention has a very simple configuration as shown in the cross section of FIG. 1, as is clear from the aberration diagrams shown in FIGS. 2 to 5, It is possible to satisfactorily correct chromatic aberration while maintaining good spherical aberration and sine conditions, and to focus 830nm and 780nm beams to the same point.
第1図はこの発明の対物レンズの1実施例のカ
バーガラスを含めた断面図、第2図ないし第5図
はそれぞれ第1実施例ないし第4実施例の収差図
である。
FIG. 1 is a sectional view including a cover glass of one embodiment of the objective lens of the present invention, and FIGS. 2 to 5 are aberration diagrams of the first to fourth embodiments, respectively.
Claims (1)
群は物体側から順に凸レンズと負レンズの接合レ
ンズであつて 3f<f1<5f 0.35<ν2|f2|/ν1f1<0.7 8<ν3−ν4 ただし f:全系の合成焦点距離 f1:第1群レンズの焦点距離 fi:第iレンズの焦点距離 νi:第iレンズのアツベ数 の各条件を満足することを特徴とする光情報記
録・再生用対物レンズ。[Claims] 1. It has a two-group structure, each having a positive refractive power, and each group is a cemented lens consisting of a convex lens and a negative lens in order from the object side, and 3f<f 1 <5f 0.35<ν 2 |f 2 |/ν 1 f 1 < 0.7 8 < ν 3 − ν 4 where f: Composite focal length of the entire system f 1 : Focal length of the first group lens fi : Focal length of the i-th lens v i : I-th lens An objective lens for recording and reproducing optical information, characterized in that it satisfies each condition of Atsube's number.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP8785484A JPS60232519A (en) | 1984-05-02 | 1984-05-02 | Objective lens for optical information recording and reproduction |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP8785484A JPS60232519A (en) | 1984-05-02 | 1984-05-02 | Objective lens for optical information recording and reproduction |
Publications (2)
Publication Number | Publication Date |
---|---|
JPS60232519A JPS60232519A (en) | 1985-11-19 |
JPH0431087B2 true JPH0431087B2 (en) | 1992-05-25 |
Family
ID=13926468
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP8785484A Granted JPS60232519A (en) | 1984-05-02 | 1984-05-02 | Objective lens for optical information recording and reproduction |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPS60232519A (en) |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4927247A (en) * | 1988-05-13 | 1990-05-22 | Matsushita Electric Industrial Co., Ltd. | Objective lens for optical disk system and optical head using the same |
FR2642883B1 (en) * | 1989-02-09 | 1995-06-02 | Asahi Optical Co Ltd | |
US5491587A (en) * | 1989-02-28 | 1996-02-13 | Asahi Kogaku Kogyo Kabushiki Kaisha | Collimating lens for optical system using semiconductor laser |
JPH02269303A (en) * | 1989-04-11 | 1990-11-02 | Asahi Optical Co Ltd | Chromatic aberration correction lens for optical disk |
JP2784041B2 (en) * | 1989-05-31 | 1998-08-06 | 株式会社リコー | Objective lens for optical disc |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS4919087U (en) * | 1972-05-27 | 1974-02-18 | ||
JPS5334522A (en) * | 1976-09-10 | 1978-03-31 | Minolta Camera Co Ltd | Soft focus lens |
-
1984
- 1984-05-02 JP JP8785484A patent/JPS60232519A/en active Granted
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS4919087U (en) * | 1972-05-27 | 1974-02-18 | ||
JPS5334522A (en) * | 1976-09-10 | 1978-03-31 | Minolta Camera Co Ltd | Soft focus lens |
Also Published As
Publication number | Publication date |
---|---|
JPS60232519A (en) | 1985-11-19 |
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