JPH0536765B2

JPH0536765B2 -

Info

Publication number: JPH0536765B2
Application number: JP55129838A
Authority: JP
Inventors: Hisayuki Masumoto; Shuji Ogino; Toshihide Doi
Original assignee: Minolta Co Ltd
Current assignee: Minolta Co Ltd
Priority date: 1980-09-17
Filing date: 1980-09-17
Publication date: 1993-05-31
Also published as: JPS5753718A

Description

[Detailed description of the invention]

本発明はズームレンズ系の改良に関する。従来
より、最も物体側に正屈折力の第１レンズ群を有
し、この第１レンズ群との間に可変空気間隔を介
して後続レンズ群が配されるズームレンズ系が知
られている。一般に、この第１レンズ群は後続レ
ンズ群に比べて大きな有効径を有するレンズで構
成され、そのためズームレンズ系全体の重量をか
なり重くしている。ことにTV，８mm等の携帯用
ズームレンズでは、その重量が商品価値を決める
重要な要因となる。本発明の目的は、全体の重量が軽く、かつ、高
性能なズームレンズ系を提供することにある。本発明の特徴は、最も物体側に正屈折力の第１
レンズ群を有し、この第１レンズ群との間に可変
空気間隔を介して後続レンズ群が配されるズーム
レンズ系において、前記第１レンズ群が少なくと
も１枚の像側に強い曲率を有しその像側に非球面
を設けたプラスチツクの負レンズと少なくとも２
枚の物体側に強い曲率を有する正レンズとを含
み、更に、前記負レンズが以下の条件を満足する
ことを特徴とするズームレンズ系。 (1) 0.6＜fI／｜fN｜＜2.2 但し、ここで、fIは前記第１レンズ群の焦点距
離、fNは前記負レンズの焦点距離である。本発明は上記の構成により、従来のガラスレン
ズのみからなるズームレンズ系より軽量でかつそ
れと同等の光学性能を有するズームレンズ系を提
供し得たものである。ところで、プラスチツクの光学材料は種類も比
較的少なく、また屈折率等の光学的特性の選択の
巾もガラスの多種多様さに比べるときわめて狭
い。従つてプラスチツクレンズを用いるとそれだ
けレンズ設計の自由度が制限されることになり、
これはプラスチツクレンズを用いて高性能のレン
ズを設計する上での大きな障害の一つであつた。
本発明では、これに対処するため、上記非球面を
用いており、更に、上記条件式(1)を満足すること
が必要である。上記条件式(1)の下限を越えると軸上色収差の補
正と球面収差の補正を同時に満足することができ
なくなり、一方その上限を越えると非点収差とコ
マ収差の補正が困難となる。更に、本発明においては以下の条件をも満足す
ることが望ましい。 (2) 0.4＜T_L／D_p＜0.6 但し、T_Lは前記第１レンズ群中の正レンズの
芯厚の総和、D_pは前記第１レンズ群中最も物体
側にある正レンズの外径である。上記条件式(2)の下限を越えると、必要最小限の
レンズコバをとつた上で、軸上色収差の補正をす
ることが困難となる。一方条件式(2)の上限を越え
ると、フオーカシングのために第１群を移動させ
たときの収差変動量が大きくなるとともに、本発
明の所望の目的である、ズームレンズ系の軽量化
にそぐわなくなる。以下の表に本発明の実施例を示す。なお、各実
施例は第１レンズ群のみ構成が異なり、後続する
レンズ群は共通であるので、実施例２，３につい
ては実施例１と共通部分は省略する。 The present invention relates to improvements in zoom lens systems. 2. Description of the Related Art Zoom lens systems have conventionally been known in which a first lens group with positive refractive power is provided closest to the object side, and a subsequent lens group is disposed with a variable air gap between the first lens group and the first lens group. Generally, this first lens group is comprised of lenses having a larger effective diameter than the subsequent lens groups, which makes the entire zoom lens system considerably heavier. Particularly in the case of portable zoom lenses such as 8mm for TVs, the weight is an important factor in determining the product value. An object of the present invention is to provide a zoom lens system that is light in overall weight and has high performance. The feature of the present invention is that the first lens with positive refractive power is located closest to the object side.
In a zoom lens system having a lens group and a subsequent lens group disposed with a variable air gap between the first lens group and the first lens group, the first lens group has at least one strong curvature on the image side. A plastic negative lens with an aspherical surface on the image side and at least two
1. A zoom lens system comprising a positive lens having a strong curvature on the object side of the lens, and further characterized in that the negative lens satisfies the following conditions. (1) 0.6<fI/|fN|<2.2 However, here, fI is the focal length of the first lens group, and fN is the focal length of the negative lens. With the above-described structure, the present invention can provide a zoom lens system that is lighter than a conventional zoom lens system consisting only of glass lenses and has optical performance equivalent to that of the zoom lens system. By the way, there are relatively few types of plastic optical materials, and the range of selection of optical properties such as refractive index is extremely narrow compared to the wide variety of glass. Therefore, the use of plastic lenses limits the degree of freedom in lens design.
This has been one of the major obstacles in designing high-performance lenses using plastic lenses.
In order to cope with this problem, the present invention uses the aspherical surface described above, and furthermore, it is necessary to satisfy the above conditional expression (1). If the lower limit of the above conditional expression (1) is exceeded, it becomes impossible to simultaneously satisfy correction of longitudinal chromatic aberration and spherical aberration, while if the upper limit is exceeded, it becomes difficult to correct astigmatism and coma aberration. Furthermore, in the present invention, it is desirable that the following conditions are also satisfied. (2) 0.4<T _L /D _p <0.6 However, T _L is the total core thickness of the positive lenses in the first lens group, and D _p is the outer thickness of the positive lens closest to the object in the first lens group. It is the diameter. If the lower limit of conditional expression (2) is exceeded, it becomes difficult to correct longitudinal chromatic aberration while obtaining the minimum required lens edge. On the other hand, if the upper limit of conditional expression (2) is exceeded, the amount of aberration variation when moving the first lens group for focusing will increase, and this will not meet the desired objective of the present invention, which is to reduce the weight of the zoom lens system. It disappears. The table below shows examples of the invention. Note that in each embodiment, only the first lens group has a different configuration, and the subsequent lens groups are the same, so the parts common to the first embodiment will be omitted for Examples 2 and 3.

【表】【table】

【表】第１図は、本発明による実施例１の最長焦点距
離における構成図で、Ｆは第１レンズ群、Ｒはバ
リエータＶ、コンペンセータＣ、マスターレンズ
Ｍより成る後続レンズ群である。この実施例で
は、第１レンズ群Ｆは、全て、プラスチツクレン
ズで構成され、非球面は、第２、及び第３面に使
用している。実施例２，３でも同様であるが、非
球面の形状は、以下の式で定義している。Ｘ＝Co^-1〔１−（１−C² ₀Y²）^1/2〕＋∽ 〓ｉ＝１CiY²ⁱ Ｘ：平面からの変位置 Co：基準球面の曲率 Ci：非球面係数Ｙ：光軸からの距離第２図は、本発明による実施例２の構成図で、
第２レンズ群以後は、第１図と同じであるので省
略されている。この実施例でも第１レンズ群は、
全てプラスチツクレンズで構成され、非球面は第
２、第３面に用いている。第３図は、本発明による実施例３の構成図で、
第２レンズ群以後は、同様に省略されている。こ
の実施例では、第１レンズ群を物体側より第１の
負レンズ、第１の正レンズ、第２の正レンズの３
枚で構成し、第１の負レンズ、第１の正レンズに
プラスチツクレンズを、第２の正レンズにガラス
レンズを用いて構成している。非球面は、第２、
第３面とである。なお、本実施例のように、負・
正・正の３枚で構成され、全体として正であるレ
ンズ群の、負、正、各レンズ１枚にプラスチツク
レンズを用いることは、光学プラスチツク材が、
ガラスに比べて、温度による屈折率変化や膨張係
数が極めて大きいことから起こるレンズ群の焦点
距離ないしレンズバツクの変動を、負・正レンズ
で互いに打ち消して、温度変化による問題を有効
に軽減するのに効果がある。本発明では、その占める重量比率の大きいズー
ムレンズ系の第１群にプラスチツクレンズを使用
して、ズームレンズ全体の軽量化をはかつたもの
であるが、さらに第２群以後の後続レンズ群に
も、プラスチツクレンズを使用して、いつそう軽
量化をはかることも可能である。次に本発明の効果を具体的に示す。第４図は参
考のために、第１レンズ群Ｆをガラスレンズばか
りで構成した参考例であり、その構成は次表のと
おりである。なお、後続レンズ群は実施例１乃至
３と全く同じにしている。[Table] FIG. 1 is a configuration diagram at the longest focal length of Example 1 according to the present invention, where F is the first lens group and R is the subsequent lens group consisting of the variator V, compensator C, and master lens M. In this embodiment, the first lens group F is entirely composed of plastic lenses, and aspherical surfaces are used for the second and third surfaces. The same applies to Examples 2 and 3, but the shape of the aspherical surface is defined by the following formula. X=Co ^-1 [1-(1-C ² ₀ Y ² ) ^1/2 ] +∽ 〓 i=1CiY ²ⁱ X: Displacement from the plane Co: Curvature of the reference sphere Ci: Aspheric coefficient Y: Optical axis Distance from Figure 2 is a configuration diagram of Embodiment 2 according to the present invention,
The parts after the second lens group are omitted because they are the same as in FIG. 1. In this embodiment as well, the first lens group is
The lens is entirely made of plastic, with aspherical surfaces used for the second and third surfaces. FIG. 3 is a configuration diagram of Embodiment 3 according to the present invention,
The elements after the second lens group are similarly omitted. In this embodiment, the first lens group consists of three lenses, a first negative lens, a first positive lens, and a second positive lens, from the object side.
A plastic lens is used as the first negative lens, a plastic lens is used as the first positive lens, and a glass lens is used as the second positive lens. The aspheric surface is the second,
This is the third page. Note that, as in this example, negative
The use of plastic lenses for each of the negative and positive lenses in a lens group that is composed of three positive and positive lenses means that the optical plastic material is
Compared to glass, changes in the focal length or lens back of the lens group that occur due to extremely large changes in refractive index and expansion coefficient due to temperature can be canceled out using negative and positive lenses, effectively reducing problems caused by temperature changes. effective. In the present invention, a plastic lens is used in the first group of the zoom lens system, which accounts for a large weight ratio, to reduce the weight of the entire zoom lens. However, it is possible to reduce weight by using plastic lenses. Next, the effects of the present invention will be specifically shown. For reference, FIG. 4 shows a reference example in which the first lens group F is composed entirely of glass lenses, and its composition is as shown in the following table. Note that the subsequent lens group is exactly the same as in Examples 1 to 3.

【表】次の表は上記のような参考例と本発明の各実施
例との重量を比較したものである。[Table] The following table compares the weights of the above reference example and each example of the present invention.

【表】また、第５乃至７図はそれぞれ本発明の実施例
１乃至３の（Ｓ），（Ｍ），（Ｌ）各焦点距離におけ
る収差図であり、第８図は上記参考例の収差図で
ある。以上から明らかなように、本発明によれば、ガ
ラスばかりで構成されるレンズに比較して遜色の
ない光学性能を有し、しかもその重量が大巾に削
減された有用性の高いズームレンズ系を提供しう
るものである。[Table] In addition, Figs. 5 to 7 are aberration diagrams at each focal length (S), (M), and (L) of Examples 1 to 3 of the present invention, respectively, and Fig. 8 is an aberration diagram of the above reference example. It is a diagram. As is clear from the above, the present invention provides a highly useful zoom lens system that has optical performance comparable to that of lenses made entirely of glass, and whose weight is significantly reduced. It is possible to provide

[Brief explanation of drawings]

第１図乃至第３図はそれぞれ本発明の実施例１
乃至３のレンズ構成図、第４図は比較のための参
考例のレンズ構成図、第５乃至７図はそれぞれ上
記実施例１乃至３の収差図、第８図は上記参考例
の収差図である。Ｆ…第１レンズ群、Ｒ…後続レンズ群。 Embodiment 1 of the present invention is shown in FIGS. 1 to 3, respectively.
FIG. 4 is a lens configuration diagram of a reference example for comparison, FIGS. 5 to 7 are aberration diagrams of the above Examples 1 to 3, respectively, and FIG. 8 is an aberration diagram of the above reference example. be. F...first lens group, R...subsequent lens group.

Claims

[Claims] 1. A zoom lens system having a first lens group having a positive refractive power closest to the object side, and a subsequent lens group disposed with a variable air gap between the first lens group and the first lens group, The first lens group includes at least one plastic negative lens having a strong curvature on the image side and an aspherical surface on the image side, and at least two positive lenses having a strong curvature on the object side, and further , a zoom lens system characterized in that the negative lens satisfies the following conditions. 0.6<fI/|fN|<2.2 where, fI is the focal length of the first lens group, and fN is the focal length of the negative lens. 2. Claim 1, wherein the first lens group has the negative lens closest to the object side.
Zoom lens system described in section. 3. The zoom lens system according to any one of claims 1 to 2, which satisfies the following conditions: 0.4<T _L /D _O <0.6, where T _L is the first The total core thickness of the positive lenses in the lens group, D _O , is the outer diameter of the positive lens closest to the object in the first lens group. 4. The zoom lens system according to claim 1, wherein at least one of the positive lenses is a plastic lens. However, here, f _I is the focal length of the first lens group, and f _N is the focal length of the negative lens in the first lens group.