JPS61129611A - Photographing lens - Google Patents

Abstract

PURPOSE:To eliminate the flare to obtain images of good contrast by using a distributed index lens as a double convex position lens just before a stop of a stop postpositive lens and giving a negative gradient of refractive index to the apex of the image-side surface of the positive lens. CONSTITUTION:The first positive lens which has a convex surface having a high curvature on the object side, the second negative lens which has a concave surface having a high curvature on the image side, the third double convex lens 3, and the stop are arranged in order from the object side, and the third lens is constituted with a distributed index lens whose refractive index is varied in the direction of the optical axis. A gradient dN(x)/dx of the refractive index distribution in the direction of the optical axis at the apex of the image-side surface of the third lens in the case where the focal length of the whole of the system is standardized to one is set to satisfy a formula, thereby compensating aberrations.

Description

【発明の詳細な説明】 本発明は３枚レンズ構成の撮影レンズに関し、更には３
枚レンズの後方に絞りを設けた撮影レンズに関する。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photographic lens having a three-lens configuration, and further relates to a three-lens photographic lens.
This invention relates to a photographic lens having a diaphragm provided at the rear of a lens element.

正、負、正の３枚レンズから成る撮影レンズは最も良く
知られた写真レンズの１つである。A photographic lens consisting of three lenses, positive, negative, and positive, is one of the most well-known photographic lenses.

絞りをレンズの後方に設けたいはゆる後絞り型レンズは
繰り出し時に重たい絞りユニットやシャ９ツタ−ユニッ
トを動かさずに済むので、構造の簡略化を計れ、自動焦
点合わせのための調節の応答性に優れたカメラとするこ
とができもしかしレンズ間に絞りを具えるレンズに比べ
前方のレンズの周辺を軸外光束が通過するため、コマ収
差の発生、特に下線のコマフレアーが大きく、画面の中
間から周辺にかけて像はフレアーを帯びたちのＫなるこ
とが多い。特に全長を縮めて、コンパクト化を進めると
この傾向は大である。If you want to place the diaphragm at the rear of the lens, a rear diaphragm type lens does not require moving the heavy diaphragm unit or shutter unit when it is extended, simplifying the structure and improving the responsiveness of adjustment for automatic focusing. However, compared to a lens with an aperture between the lenses, off-axis light passes around the front lens, causing coma aberration, especially coma flare (underlined), which is large, and the screen From the middle to the periphery, the image often has a flared K shape. This tendency is especially strong when the overall length is shortened and compactness is promoted.

（目的） 本発明は、後絞り型レンズの画面中間から周辺にかけて
発生するフレアーを除去し、コントラストの良い画像を
得ること目的とする。そしてこの目的を達成するため、
複数レンズの像側に両凸の正レンズそして絞りを順置し
、正レンズを光軸方向に屈折率が変化する屈折率分布型
レンズで構成し、全系の焦点距離をＩＫ規格化した時の
正レンズの像側の面頂点における光軸方向の屈折率分布
の傾斜ｄＮ６ｄ　／　ｄｘを下式を満たす様に決定する
。(Objective) An object of the present invention is to remove flare that occurs from the center to the periphery of the screen of a rear aperture type lens, and to obtain an image with good contrast. And to achieve this purpose,
When a biconvex positive lens and a diaphragm are placed on the image side of multiple lenses, the positive lens is a gradient index lens whose refractive index changes in the optical axis direction, and the focal length of the entire system is IK standardized. The slope dN6d/dx of the refractive index distribution in the optical axis direction at the apex of the image side surface of the positive lens is determined so as to satisfy the following formula.

−３＜　ｄＮ６ｃ）　／ｄｘ　＜　−０，２（実施例の
説明） 第１図を使って実施例の光学作用を説明する。-3<dN6c)/dx<-0,2 (Explanation of Example) The optical action of the example will be explained using FIG.

（５）はレンズ中を軸外光線が通過する挙動を示し、（
５）は第３レンズ、中の屈折率分布を示す。Ｎωは屈折
率、Ｘは光軸上の座標で、光線の進行方向が正である。(5) shows the behavior of off-axis rays passing through the lens, and (
5) shows the refractive index distribution inside the third lens. Nω is a refractive index, X is a coordinate on the optical axis, and the traveling direction of the light ray is positive.

第１図（５）で１は物体側に凸の（他面に比して）強い
曲率の面を有する正の第１レンズ、２は像側へ凹の強い
曲率の面を有する負の第２レンズ、３は両凸の第３レン
ズである。In Fig. 1 (5), 1 is a positive first lens that has a surface with a strong curvature that is convex toward the object side (compared to the other surface), and 2 is a negative lens that has a surface with a strong curvature that is concave toward the image side. 2 lens and 3 are biconvex third lenses.

後絞り型レンズの場合軸外光線の下線が第２レンズ２の
物体側曲面で下側へ大きく曲げられコマフレアーの原因
となる。第３レンズ３の像側曲面で多少補正されるもの
の槽圧不足で結果として光線４′の様に７レアーとして
残存する。In the case of a rear aperture type lens, the underline of the off-axis rays is largely bent downward by the object-side curved surface of the second lens 2, causing coma flare. Although it is somewhat corrected by the image-side curved surface of the third lens 3, due to insufficient tank pressure, as a result, 7 rays remain as ray 4'.

本例では、物体側より物体側に凸の強い曲率を有する正
の第２レンズ２、像側に凹の強い曲率を有する負の！２
レンズ２、両凸で正の第３し　　レンズ３で構成し、第
３レンズ３に光軸方向に像側に進むに従って屈折率が減
少する屈折率分布型レンズを使用することによって下線
のコマフレアーを補正する。In this example, the positive second lens 2 has a strongly convex curvature on the object side than the object side, and the negative lens 2 has a strongly concave curvature on the image side. 2
The coma flare (underlined) is achieved by using a gradient index lens whose refractive index decreases as it moves toward the image side in the optical axis direction for the third lens 3. Correct.

すなわち光軸方向に像側に進むに従って屈折率が小さく
なる様な材質の像側面に曲率を付けると曲面の表面の屈
折率は光軸付近に比べ外周部の屈折率が大きく従って同
じ角度で入射した光線でも強く曲げられる。そのため光
［５’の様に下線のコマフレアーが補正される。In other words, if a curvature is added to the image side surface of a material whose refractive index decreases as it moves toward the image side in the optical axis direction, the refractive index of the curved surface will be larger at the outer periphery than near the optical axis, so that the light will be incident at the same angle. Even rays of light can be strongly bent. Therefore, the underlined coma flare as shown in light [5' is corrected.

従って第３レンズ３の像側の面頂点に於ける光軸方向の
屈折率分布の傾斜を負にすれば上記の補正効果は増すが
あまり大きくし過ぎると球面収差がアンダーに発生して
他の面で補正できなくなる。Therefore, if the slope of the refractive index distribution in the optical axis direction at the apex of the image side surface of the third lens 3 is made negative, the above-mentioned correction effect will be increased, but if it is made too large, spherical aberration will occur in an understated manner, and other It will no longer be possible to make corrections on the surface.

従って全系の焦点距離を１に規格化した時の第３レンズ
の像側の面頂点に於ける光軸方向のｄＮ（支）　　　　
　　　　ｄＮ（支）屈折率分布の傾斜□が−３＜　−７
−＜　−０，２ｘ の条件を満たす様に決定する。Therefore, when the focal length of the entire system is normalized to 1, the dN (support) in the optical axis direction at the apex of the image side surface of the third lens
The slope □ of dN (branch) refractive index distribution is -3<-7
Determine so that the condition -< -0, 2x is satisfied.

もし下限値を越えＣＮ（ト）の傾斜が大きくなると軸外
光束の下Ｉａミツレアー正に対しては補正効果があるが
球面収差がアンダ一方向に大きく発生し補正できなくな
る。上限を越えてＮ（支）の傾斜が小さくなると軸外光
束の下線フレアーが補正されないか助長される。If the lower limit value is exceeded and the inclination of CN(g) becomes large, there is a correction effect for the lower Ia Mitsulear positive of the off-axis light beam, but spherical aberration occurs largely in the lower direction and cannot be corrected. If the slope of N (support) becomes small beyond the upper limit, the underline flare of the off-axis light beam will not be corrected or will be promoted.

以上の構成で本願の目的は実現されるわけであるが、更
に画質を洗練させるためには次の条件の１又は２を満足
するのが好ましい。Although the object of the present application is achieved with the above configuration, in order to further refine the image quality, it is preferable to satisfy one or two of the following conditions.

−１＜　Ｒ６＜　−０，３，・・・・・・・・・・・・
・・・・・・（１）Ｒ４十Ｒ３ −０，９＜　−＜　−０，７・・・・−・−＋２７几４
−Ｒ３ 但し、Ｒ６は第３レンズの像側面の曲率半径、Ｒ３は第
２レンズの物体側面の曲率半径、Ｒ４は第２レンズの像
側面の曲率半径。−1<R6< −0,3,・・・・・・・・・・・・
・・・・・・(1) R40R3 −0,9<−< −0,7・・・・−・−+27几4
-R3 However, R6 is the radius of curvature of the image side surface of the third lens, R3 is the radius of curvature of the object side surface of the second lens, and R4 is the radius of curvature of the image side surface of the second lens.

（１）は第３レンズの像側面の曲率を定めるもので上限
を越えてきつくなると球面収差が補正しきれなくなり又
全長の増大を招く。下限値を越えてゆるくなると軸外の
コマフレアーを補正が十分でなくなる。(1) determines the curvature of the image side surface of the third lens, and if the curvature exceeds the upper limit, spherical aberration cannot be corrected completely and the total length increases. If it becomes loose beyond the lower limit, off-axis coma flare will not be corrected enough.

（２）の条件は第２レンズで発生する軸外光束のコマフ
レアー、球面収差、非点収差の補正に関するものであり
、上限を越えてＲ３面が負の値できつくなるとコマフレ
アーがＲ３面で発生する。一方、下限を越えて几４面が
きつくなると非点収差がオーバーに発生する。Condition (2) is related to the correction of coma flare, spherical aberration, and astigmatism of the off-axis light beam generated in the second lens, and if the upper limit is exceeded and the R3 surface becomes tight with a negative value, the coma flare will change to the R3 surface. Occurs in On the other hand, if the lower limit is exceeded and the fourth surface becomes too tight, astigmatism will excessively occur.

以下、レンズデータの実施例を示すが、第１乃至第４実
施゛例の第３レンズは、その物体側レンズ面から像側レ
ンズ面へ屈折率が連続的に減少する特性となっているが
、第５実施例は第３レンズの物体側の面から１．１７ｍ
ｍまでは屈折率が１．８３４であるが１．１７ｍｍから
４．２７ｍｍの間では像側に行くに従い屈折率が低下す
る様な屈折率分布が付いている。Examples of lens data are shown below. The third lenses of the first to fourth embodiments have a characteristic that the refractive index decreases continuously from the object side lens surface to the image side lens surface. , the fifth example is 1.17 m from the object side surface of the third lens.
The refractive index is 1.834 up to m, but between 1.17 mm and 4.27 mm, there is a refractive index distribution in which the refractive index decreases as it goes toward the image side.

この様な分布は、例えば屈折率分布をつけるのにイオン
交換法を用いた場合、一方の面からイオン交換を行ない
所望の深さまで分布がついたところでイオン交換作業を
中断すれば良い。Such a distribution can be obtained, for example, when an ion exchange method is used to create a refractive index distribution, by performing ion exchange from one side and stopping the ion exchange operation when the distribution reaches the desired depth.

この例も第１乃至第４実施例と同等の効果が得られる。This example also provides the same effects as the first to fourth embodiments.

Φ　　　　　哨 ロ　　　ω 呼へ 口 ｌ ロ　　　膿　　　　　　　　　　　　〒−ヘ　　　　　
　　　　　　　ロ ＾　ｌ：ＳＴｌ　ｎ　１１口　＋６ −〇 啼の １１口 ’ＩＩＩ　　　　　　　呻 −　　　へ　　　　　　　　　　　　≧ａ） ６０口 寸　　　　へ　　　　　　　　　　　　　　　　　Ｘｑ
） ｌ　　　　ｌ　　　　　　　　　　　　　　　＠ｍｆｉ
　　　　　　　　　　　　　ｚ ψト リロ （効果） 以上述べた通り、後絞り型レンズの絞り直前の両凸正レ
ンズに光軸方向に屈折率が変化する屈折率分布型レンズ
を使用し、正レンズの像側面の頂点で負の屈折率傾斜を
持たせたことにより、正レンズ直前の発散面に起因する
後絞りレンズ特有の軸外光束下線のコマフレアーを補正
することができ、コンパクトでコントラストの高い画質
が得られる効果がある。Φ Senro ω Call to mouth l Lo Pus 〒-he
＾ l: STl n 11 mouths +6 -〇啼の11口'III groan- ≧a) To 60 mouth size Xq
) l l @mfi
z ψTrillo (Effect) As mentioned above, a gradient index lens whose refractive index changes in the optical axis direction is used for the biconvex positive lens just before the aperture of the rear diaphragm type lens, and the apex of the image side of the positive lens By providing a negative refractive index gradient, it is possible to correct the coma flare of the off-axis light flux underline peculiar to the rear aperture lens caused by the diverging surface just before the positive lens, resulting in a compact image quality with high contrast. There is.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は本発明に係る光学断面図。第２図は実施例１の
レンズ断面図で、第３図は収差図。 第４図は実施例２のレンズ断面図で、第５図は収差図。 第６図は実施例３のレンズ断面図で、第７図は収差図。 第８図は実施例４のレンズ断面図で、第９図は収差図。 第１０図は実施例５のレンズ断面図で、第１１図は収差
図。 第３図 桶！１ 槽収簾 横内４ Ｄｒ　　Ｄｚ　　ρ３Ｄ４１）、ｒ 膓四ｇ−系FIG. 1 is an optical cross-sectional view according to the present invention. FIG. 2 is a cross-sectional view of the lens of Example 1, and FIG. 3 is an aberration diagram. FIG. 4 is a cross-sectional view of the lens of Example 2, and FIG. 5 is an aberration diagram. FIG. 6 is a cross-sectional view of the lens of Example 3, and FIG. 7 is an aberration diagram. FIG. 8 is a cross-sectional view of the lens of Example 4, and FIG. 9 is an aberration diagram. FIG. 10 is a cross-sectional view of the lens of Example 5, and FIG. 11 is an aberration diagram. Figure 3: Oke! 1 tank storage horizontal 4 Dr Dz ρ3D41), r 4g-system

Claims (1)

【特許請求の範囲】[Claims] （１）物体側より物体側に凸の強い曲率の面を有する正
の第１レンズ、像側へ凹の強い曲率の面を有する負の第
２レンズ、両凸の第３レンズそして絞りを順置したレン
ズであつて、第３レンズを光軸方向に屈折率が変化する
屈折率分布型レンズで構成し、全系の焦点距離を１に規
格化した時の第３レンズの像側の面 頂点における光軸方向の屈折率分布の傾斜 ｄＮ（ｘ）／ｄｘを −３＜ｄＮ（ｘ）／ｄｘ＜−０．２ を満たす様にして、収差を補正したことを特徴とする撮
影レンズ。(1) A positive first lens with a highly convex surface of curvature toward the object side, a negative second lens with a strongly concave surface of curvature toward the image side, a biconvex third lens, and an aperture in this order. The image side surface of the third lens when the third lens is a gradient index lens whose refractive index changes in the optical axis direction and the focal length of the entire system is normalized to 1. A photographing lens characterized in that aberrations are corrected by making the slope dN(x)/dx of the refractive index distribution in the optical axis direction at the vertex satisfy -3<dN(x)/dx<-0.2.