【発明の詳細な説明】[Detailed description of the invention]
本発明は１眼レフカメラ用の望遠ズームレンズ
に関するものである。一般にテレ側の画角が
11.7゜〜12.5゜、ズーム比が2.3〜2.9倍程度のズーム
レンズのテレ比は0.9以上であつたが、本発明の
ズームレンズは物体側から順に各レンズ群を正、
負、正の３群のパワーで構成し上記条件の如く各
群のパワーを設定することによりテレ比0.75以下
とコンパクトなズームレンズを可能とする。
従来の望遠ズームレンズは一般にフオーカシン
グ機能を有する第１正レンズ群、変倍機能を有す
る第２負レンズ群、ズーミングに際し像面を一定
位置に補正させる機能を有する第３正レンズ群、
結像のための第４正レンズ群で構成され、第１正
レンズ群と第４正レンズ群はズーミングに際し固
定であり全長変化はない。このためこの種のズー
ムレンズの全長は変倍系の移動量と第４群結像系
の望遠比によつてほぼ決められてしまう。したが
つてコンバクト化するためには、第４群結像系の
望遠比を小さくするか、ズーム部のパワーを強め
移動群の移動量を小さくするしかない。前者の場
合、過度のコンパクト化により結像系自体の収差
補正が困難になり少ないレンズ枚数では球面収差
や非対称性コマ収差などの補正ができなくなる。
また後者の場合、過度に強くなつた負レンズ群の
ためペツツバール和が負に増大し非点収差補正が
ズーム全域では困難になる。
本発明ではコンパクト化に重要な役割を持つ第
２群変倍系の変倍比を小さくし、そのため損なわ
れた変倍量を従来変倍作用がなかつた第４群結像
系を移動させることにより、変倍作用を持たせ、
なおかつ像位置補正の役割を持つ第３群と結合す
ることによりレンズ群を３群で構成しコンパクト
化に成功した。
本発明のレンズ系は物体側から順に正の屈折力
を有する第１レンズ群f1、負の屈折力を有する第
２レンズ群f2、正の屈折力を有する第３レンズ群
f3の３群で構成され、各レンズ群がそれぞれ独立
に機械的に移動することを特徴とし、以下の条件
を満たした極めてコンパクトな望遠ズームレンズ
である。
(1) 0.4＜f1＜fT＜0.6
(2) 0.1＜｜f2／fT｜＜0.17
(3) 0.85＜｜１／β2W−１／β2T｜1.3
(4) 0.4＜β2W／β2T＜0.6
(5) 0.1＜f3／fT＜0.2
(6) 0.1＜｜１／β3W−１／β3T｜＜0.3
(7) 0.6＜β3W／β3T＜0.8
(8) 0.8＜f3F／f3＜1.3
(9) 4.5＜｜f3R／f3｜＜8.5
但し
fT：テル時の焦点距離
f1：第１群の焦点距離
f2：第２群の焦点距離
f3：第３群の焦点距離
f3F：第３群前部正レンズ群の焦点距離
f3R：第３群後部負レンズ群の焦点距離
β2W：第２群ワイド時の結像倍率
β2T：第２群テレ時の結像倍率
β3W：第３群ワイド時の結像倍率
β3T：第３群テレ時の結像倍率
次に各条件式について説明を行なうと条件式(1)
は１群の屈折力を視定するものである。上限を越
えると収差補正は楽になるが、レンズ全長の増大
を招き下限を越えると長焦点側での球面収差の補
正を困難とし、フオーカシングの際の球面収差の
変化を押さえることが困難になる。条件式(2)，
(3)，(4)、は２群の屈折力及び移動量を規定する。
(2)式の上限を越えると収差補正は楽になるが移動
量が大きくなりコンパクト化ができない。下限を
越えるとペツツバール和が過度に負になり非点収
差の補正がズーム全域では困難になる。これを補
正するためには３群の負レンズ成分を弱くしなけ
ればらず条件式(8)，(9)と相まつてテレフオトタイ
プを崩すことになりコンパクト化を実現できなく
なる。また長焦点側での球面の補正過剰及び軸外
光束の下光線の色コマ補正が困難になる。また(3)
式及び(4)式の上限を越えると２群における物点が
大きく移動し、この群での収差補正を困難にす
る。また２群の変倍比が大きくなるほど歪曲収差
の発生につながるため好ましくない。(3)式及び(4)
式の下限を越えると歪曲収差などの補正は楽にな
るが全としてのズーム比がかせげなくなり第３群
のズーム比負担が大きくなる。条件式(5)，(6)，(7)
は３群の屈折力及び移動量を規定する。(5)式の下
限を越えるとコンパクト化には有利であるが長焦
点側での球面収差の補正が困難になる。また上限
を越えると収差補正は楽になるが、移動量が大き
くなりコンパクト化できない。(6)式及び(7)式の上
限を越えると３群における物点が大きく移動し、
この群での収差補正を困難とする。また(6)式及び
(7)式の下限を越えると収差補正は楽になるが全系
としてのズーム比がかせげなくなり、これを解消
するならば２群のズーム比負担を大きくしなけれ
ばならず結果的に良好な収差補正をすることがで
きない。条件式(8)は３群における正レンズ群に関
するものである。下限を越えるとコンパクト化に
は有利であるが、正レンズ群自身の口径比が大き
くなりすぎて球面収差の補正を困難にする。上限
を越えると３群自身のテレ比が大きくなりコンパ
クト化できない。条件式(9)は３群における負レン
ズ群に関するものである。下限を越えるとコンパ
クト化には有利であるが、ペツツバール和が過度
に負になり非点収差の補正が困難になる。上限を
越えるとレンズ全長が長くなりコンパクト化でき
ない。
以降に本発明の実施例を示す。但しri，di，
ni，νiはそれぞれ物体側から順に数えた曲率半
径、レンズ面間隔、ｄ線に対する屈折率、アツベ
数である。
The present invention relates to a telephoto zoom lens for a single-lens reflex camera. Generally, the angle of view on the tele side is
A zoom lens with a zoom ratio of 11.7° to 12.5° and a zoom ratio of about 2.3 to 2.9 times had a telephoto ratio of 0.9 or more, but the zoom lens of the present invention has a zoom ratio of 11.7° to 12.5° and a zoom ratio of about 2.3 to 2.9 times.
By configuring the power of three groups, negative and positive, and setting the power of each group according to the above conditions, it is possible to create a compact zoom lens with a telephoto ratio of 0.75 or less. Conventional telephoto zoom lenses generally include a first positive lens group with a focusing function, a second negative lens group with a variable power function, a third positive lens group with a function of correcting the image plane to a fixed position during zooming,
It is composed of a fourth positive lens group for image formation, and the first positive lens group and the fourth positive lens group are fixed during zooming and do not change in overall length. Therefore, the total length of this type of zoom lens is almost determined by the amount of movement of the variable power system and the telephoto ratio of the fourth group imaging system. Therefore, in order to make the lens compact, the only option is to reduce the telephoto ratio of the fourth group imaging system, or increase the power of the zoom section and reduce the amount of movement of the movable group. In the former case, excessive compactness makes it difficult to correct aberrations in the imaging system itself, making it impossible to correct spherical aberrations, asymmetric coma, etc. with a small number of lenses.
In the latter case, the Petzval sum becomes negative due to the excessively strong negative lens group, making it difficult to correct astigmatism over the entire zoom range. In the present invention, the magnification ratio of the second group magnification system, which plays an important role in compactness, is reduced, and the lost magnification amount is replaced by moving the fourth group imaging system, which conventionally had no magnification change effect. By this, it has a magnifying effect,
In addition, by combining the lens with the third group, which plays the role of correcting the image position, the lens group is composed of three groups and has been successfully made compact. The lens system of the present invention includes, in order from the object side, a first lens group f 1 having a positive refractive power, a second lens group f 2 having a negative refractive power, and a third lens group having a positive refractive power.
It is an extremely compact telephoto zoom lens that is composed of three f/3 groups, each of which moves mechanically independently, and satisfies the following conditions. (1) 0.4＜f 1 ＜f T ＜0.6 (2) 0.1＜｜f 2 /f T ｜＜0.17 (3) 0.85＜｜1/β 2W −1/β 2T ｜1.3 (4) 0.4＜β 2W /β 2T ＜0.6 (5) 0.1＜f 3 /f T ＜0.2 (6) 0.1＜｜1/β 3W −1/β 3T ｜＜0.3 (7) 0.6＜β 3W /β 3T ＜0.8 (8) 0.8＜f 3F ／f 3 ＜1.3 (9) 4.5＜｜f 3R ／f 3 ｜＜8.5 However, f T : Focal length at tell time f 1 : Focal length of 1st group f 2 : Focal length of 2nd group f 3 : Focal length of the 3rd group f 3F : Focal length of the front positive lens group of the 3rd group f 3R : Focal length β 2W of the rear negative lens group of the 3rd group : Imaging magnification β 2T when the 2nd group is wide : Imaging magnification β when the 2nd group is telephoto 3W : Imaging magnification β when the 3rd group is wide 3T : Imaging magnification when the 3rd group is telephoto Next, we will explain each conditional expression.Conditional expression (1)
is for visualizing the refractive power of the first group. Exceeding the upper limit makes it easier to correct aberrations, but exceeding the lower limit increases the overall length of the lens, making it difficult to correct spherical aberrations on the long focal length side, making it difficult to suppress changes in spherical aberrations during focusing. Conditional expression (2),
(3) and (4) define the refractive power and amount of movement of the second group.
If the upper limit of equation (2) is exceeded, aberration correction becomes easier, but the amount of movement increases, making it impossible to make the lens compact. If the lower limit is exceeded, the Petzval sum becomes excessively negative, making it difficult to correct astigmatism over the entire zoom range. In order to correct this, the negative lens component of the third group must be weakened, which, together with conditional expressions (8) and (9), destroys the telephoto type, making it impossible to achieve compactness. In addition, it becomes difficult to overcorrect the spherical surface on the long focal point side and to correct the color coma of the lower ray of the off-axis light beam. Also (3)
If the upper limits of equations and (4) are exceeded, the object point in the second group will move significantly, making it difficult to correct aberrations in this group. Further, the larger the zoom ratio of the second lens group, the more distortion aberration occurs, which is not preferable. Equation (3) and (4)
If the lower limit of the formula is exceeded, it becomes easier to correct distortion and other aberrations, but the overall zoom ratio becomes unsatisfactory, and the burden on the zoom ratio of the third group increases. Conditional expressions (5), (6), (7)
defines the refractive power and movement amount of the three groups. If the lower limit of equation (5) is exceeded, it is advantageous for compactness, but it becomes difficult to correct spherical aberration on the long focal point side. Furthermore, if the upper limit is exceeded, aberration correction becomes easier, but the amount of movement becomes large, making it impossible to make the lens compact. When the upper limits of equations (6) and (7) are exceeded, the object point in the third group moves significantly,
This makes it difficult to correct aberrations in this group. Also, equation (6) and
If the lower limit of equation (7) is exceeded, aberration correction becomes easier, but the zoom ratio of the entire system becomes unsatisfactory, and if this is to be solved, the zoom ratio burden on the second group must be increased, resulting in good aberrations. Cannot be corrected. Conditional expression (8) relates to the positive lens group in the third group. If the lower limit is exceeded, it is advantageous for compactness, but the aperture ratio of the positive lens group itself becomes too large, making it difficult to correct spherical aberration. If the upper limit is exceeded, the telephoto ratio of the third group itself becomes too large, making it impossible to make it compact. Conditional expression (9) relates to the negative lens group in the third group. If the lower limit is exceeded, it is advantageous for compactness, but the Petzval sum becomes excessively negative, making it difficult to correct astigmatism. If the upper limit is exceeded, the overall length of the lens becomes long and cannot be made compact. Examples of the present invention will be shown below. However, ri, di,
ni and νi are the radius of curvature, the distance between lens surfaces, the refractive index for the d-line, and the Atsube number, respectively, counted in order from the object side.
【表】【table】
【表】【table】
【図面の簡単な説明】[Brief explanation of drawings]
第１図は実施例の広角時の全レンズ構成図であ
る。第２図、第３図、第４図はそれぞれ実施例の
物体距離無限大における広角、中間、望遠時の収
差図である。
FIG. 1 is a diagram illustrating the entire lens configuration at wide-angle according to the embodiment. FIG. 2, FIG. 3, and FIG. 4 are aberration diagrams of the embodiment at wide-angle, intermediate, and telephoto positions at infinite object distance, respectively.