JP3715735B2 - telescope lens - Google Patents

Description

【００２６】
【表２】

【００２７】
【表３】

【００２８】
【発明の効果】
以上述べたように、この発明によれば、望遠レンズの合焦群である第２レンズ群の形状を比較的小さく構成することができ、無限遠から焦点距離の７倍程度の近距離までの合焦時の諸収差の変動を小さく抑えることが可能になる。また、近距離での球面収差の倒れと像面の倒れを合致させることにより、近距離においても画面の中心から周辺まで鮮鋭な像を得ることができ、さらに他の収差及びその合焦による変動も充分に小さく良好な性能を達成できた。これによってこの発明による望遠レンズは焦点距離の６倍程度まで最短撮影距離を短くすることが可能になった。
【図面の簡単な説明】
【図１】この発明による望遠レンズの光学系を無限遠に合焦した状態を示す構成図である。
【図２】同じく近距離に合焦した状態を示す構成図である。
【図３】この発明の実施例１における無限遠合焦時の縦の諸収差図である。
【図４】同じくその近距離合焦時の縦の諸収差図である。
【図５】この発明の実施例２における無限遠合焦時の縦の諸収差図である。
【図６】同じくその近距離合焦時の縦の諸収差図である。
【図７】この発明の実施例３における無限遠合焦時の縦の諸収差図である。
【図８】同じくその近距離合焦時の縦の諸収差図である。
【図９】この発明の実施例１のベスト像面における最大像高の７割の像高での横収差図であり、（Ａ）は無限遠合焦時、（Ｂ）は近距離合焦時をそれぞれ示す。
【図１０】この発明の実施例２のベスト像面における最大像高の７割の像高での横収差図であり、（Ａ）は無限遠合焦時、（Ｂ）は近距離合焦時をそれぞれ示す。
【図１１】この発明の実施例３のベスト像面における最大像高の７割の像高での横収差図であり、（Ａ）は無限遠合焦時、（Ｂ）は近距離合焦時をそれぞれ示す。
【符号の説明】
Ｇ１：第１レンズ群 Ｇ２：第２レンズ群
Ｇ３：第３レンズ群 Ｌ１〜Ｌ８：第１〜第８レンズ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inner focus type telephoto lens.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an inner focus type telephoto lens that performs focusing by moving a lens group inside a lens system on an optical axis is known. In such a focusing type lens system, the entire length of the lens does not change during focusing, and a relatively light focusing group with respect to the total weight of the lens only needs to be moved in the optical axis direction by a small amount. However, there is a problem that it is difficult to correct the aberration variation due to the movement of the focusing group.
[0003]
An example of this type of inner focus type telephoto lens is shown in Japanese Patent Publication No. 61-32651. In this system, the optical system is composed of three groups of positive, negative, and negative from the object side, and the second negative lens group is moved on the optical axis for focusing, but the negative lens system is closest to the image side. In addition, the angle of view 2ω is 6.3 °, and it is 8.5 ° at most. It was impossible because of the large aberration.
[0004]
[Problems to be solved by the invention]
A telephoto lens described in Japanese Patent Application Laid-Open No. 61-51117 proposed to solve such problems is composed of three groups of positive, negative, and positive functions from the object side. By configuring the three groups with three lenses, aberration correction with a higher degree of freedom is performed, and the angle of view 2ω is expanded to about 17.0 °.
[0005]
At the same time, in Example 3, a lens system in which the third lens group is composed of a biconvex positive lens and a biconcave negative lens from the object side and the angle of view 2ω is about 12.7 ° is also shown. However, the effective diameter of the second lens group which is a moving lens group is large, which is disadvantageous in terms of mechanism.
In addition, for example, when focusing on a short distance of about 7 times the focal length, the variation of spherical aberration and coma aberration becomes relatively large, and the tilt of the image plane does not match the tilt of the spherical aberration. There is a problem that a sharp image cannot be obtained from the center to the periphery, and the shortest shooting distance cannot be made shorter than about seven times the focal length.
The present invention has been made in view of the above points, and an object of the present invention is to provide a telephoto lens in which aberrations are favorably corrected from infinity to a short distance and aberration fluctuation due to focusing is small.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises, in order from the object side, a converging first lens group, a diverging second lens group, and a converging third lens group. In a telephoto lens that focuses on an object at a shorter distance by moving to the upper image side, the first lens group includes positive, positive, negative, positive first, second, and second in order from the object side. The second lens group includes a negative fifth lens that is biconcave from the object side, and a sixth meniscus positive lens that is convex on the object side on both sides, and the third lens group. Provides a telephoto lens that is composed of a positive seventh lens from the object side and a negative meniscus eighth lens having both surfaces convex toward the image side, and satisfies the following conditions.
(1) 0.05 <d10 / d8 <0.7
(2) r12> 0
Where d8: the distance between the fourth lens and the fifth lens d10: the distance between the fifth lens and the sixth lens r12: the radius of curvature of the image side surface of the sixth lens
DETAILED DESCRIPTION OF THE INVENTION
Embodiments and examples of the present invention will be specifically described below with reference to the drawings. As shown in FIG. 1, the telephoto lens according to the present invention includes a first lens group G1, a divergent second lens group G2, and a third lens group G3 that are convergent in order from the object side.
[0008]
The first lens group G1 includes positive, positive, negative, positive first, second, third, and fourth lenses L1, L2, L3, and L4 in order from the object side, and the second lens group G2 includes: A negative fifth lens L5 that is biconcave in order from the object side and a sixth meniscus positive lens L6 that is convex on both sides toward the object side. The third lens group G3 includes a positive seventh lens L7 in order from the object side. A double-sided meniscus eighth lens L8 is convex on the image side, and the second lens group G2 is moved to the image side on the optical axis to focus an object at a shorter distance.
[0009]
The telephoto lens having the above-described configuration suppresses the amount of aberration generated in each lens group by disposing a relatively large number of relatively concentric surfaces with respect to the stop D, and in particular the second focusing lens group. Aberration fluctuation due to movement of the lens group G2 is reduced.
As described above, the second lens group G2 has a role of focusing on the short distance side by moving the optical axis to the image side, and only requires a small amount of movement of the relatively light lens group. It becomes possible to focus.
[0010]
However, if the refractive index of the second lens group G2 becomes too strong, the amount of movement for focusing can be reduced, but the variation in aberration increases. Also, if the refractive index of the second lens group G2 becomes too weak, the aberration fluctuation per unit moving amount becomes small, but the moving amount for obtaining the required shortest shooting distance becomes large, which is subject to mechanical limitations. become. Therefore, in this embodiment, when the focal length of the second lens group G2 is f2, and the focal length of the entire telephoto lens system is f,
0.55 <| f2 | / f <0.8 (f2 <0)
It is desirable to satisfy.
[0011]
Next, in FIG. 1, the second lens group G2 is moved closer to the first lens group G1 while keeping the telephoto ratio, that is, the total lens length with respect to the focal length (distance from the first lens surface to the image plane) constant. The refractive index of the second lens group G2 becomes weak, and as a result, the surface distance d10 between the fifth lens L5 and the sixth lens L6 increases. That is, the mechanical problem that the second lens group G2 including the effective diameter becomes large, and the surface distance d10 between the fifth lens L5 and the sixth lens L6 increases, so that the fifth lens L5 to the sixth lens L6. D10 / d8 cannot exceed the upper limit of 0.7 because the change in the height of the light ray incident on the light beam increases and aberration fluctuations occur.
[0012]
Similarly, when the second lens group G2 is moved away from the first lens group G1 while keeping the telephoto ratio constant, the refractive power of the second lens group G2 increases, and as a result, the fifth lens L5 and the sixth lens The surface distance d10 of L6 is increased. That is, the second lens group itself can be reduced and the driving amount for focusing can be reduced, which is advantageous in terms of mechanism. However, as the refractive power of the second lens group G2 is increased, focusing is performed as described above. Since the aberration fluctuation at this time becomes large, d10 / d8 cannot exceed the lower limit of 0.05. In addition,
0.1 <d10 / d8 <0.35
If it is in the range, better performance can be obtained.
[0013]
Further, in the second lens group G2, which is the focusing lens group, increasing the radius of curvature r9 of the surface having a large effective diameter and having the negative refractive power of the fifth lens L5 closest to the object side is various on this surface. This not only causes aberrations, but also causes aberration fluctuations during focusing. Therefore, in order to reduce the radius of curvature r9 of the object side surface of the fifth lens L5 and reduce the negative action of this surface, the negative action of the second lens group G2 as a whole is reduced. The negative-acting image-side curvature radius surface r10 and the negative-acting sixth lens L6 on the image-side curvature radius surface r12 were loaded, and r12> 0.
[0014]
Further, by giving each surface of the second lens group G2 other than the object-side curvature radius r9 surface of the fifth lens L5 to a concentric shape with respect to the stop D, the principal ray of the light beam on each surface abruptly increases. As much as possible, the amount of aberrations is reduced by minimizing the bending, and the fluctuations of various aberrations caused by the movement of the second lens group G2 during focusing, particularly the fluctuations of spherical aberration and coma aberration, are reduced. In addition, aberration cancellation is achieved between the image side surface of the fifth lens L5 and the object side surface of the sixth lens L6.
[0015]
From the viewpoint as described above, the configuration of r12> 0 in particular makes it possible to reduce the change in the emission angle due to focusing with respect to the light beam emitted from the second lens group G2, and thus the fluctuation of various aberrations. It becomes possible to reduce. In addition, by setting r12> 0, when focusing from infinity to a short distance, the ray height of the light beam passing through the surface with the radius of curvature r12 becomes low, so that the negative refraction action on this surface becomes weak and the spherical surface Although the aberration is tilted in the minus direction, the image plane is also tilted in the minus direction for the same reason, and the both tilts coincide with each other, so that a sharp image can be obtained uniformly from the center to the periphery of the screen.
[0016]
Next, in the first lens group G1, positive, positive, negative, positive first, second, third, and fourth lenses L1, L2, L3, and L4 are arranged in order from the object side, thereby making negative. As in the case where the lens is arranged closest to the image side, the light incident on the negative lens from the positive lens group on the front side is prevented from being subjected to a strong refraction and causing high-order aberrations, coma aberration, and the like.
[0017]
In the embodiment of the present invention, the focal length f1 of the first lens group G1 is set so that the focal length of the entire system is f.
0.5 <f1 / f <0.7
It is desirable to be within the range. If this lower limit is exceeded, the refractive power of the first lens group G1 will become stronger and the telephoto ratio can be reduced, but this will cause the spherical aberration and coma aberration to deteriorate, and if the upper limit is exceeded, the refractive power of the first lens group G1 will become smaller. Although it is convenient in terms of aberration correction, the telephoto ratio increases and the total lens length increases.
[0018]
In general, in a telephoto lens, a light ray such as a surface having a radius of curvature r4 on the image side of the second lens L2 of the first lens group G1 and a surface having a radius of curvature r5 on the object side of the third lens L3 shown in FIG. Is incident on the negative lens from the positive lens, the amount of various aberrations including high-order aberrations on both sides increases. Therefore, in this embodiment, the surfaces of these radii of curvature r4 and r5 are formed in a relatively concentric shape with respect to the stop D to reduce the amount of aberration generated on these surfaces, and the first lens. The aberration correction function of the entire group G1 is also provided.
[0019]
Here, when the refractive power of the surface of the third lens L3 having the radius of curvature r5 on the object side is φ5 and the focal length of the first lens group G1 is f1,
0.06 <φ5 · f1 <0.23
If the lower limit is exceeded, the concentric shape on each surface of the first lens group G1 is greatly broken, and the surface from the image side surface of the second lens L2 to the object side surface of the fourth lens L4. The balance of spherical aberration, coma aberration, and astigmatism correction on the image side surface of the second lens L2 and the object side surface of the third lens L3 is also lost. If the upper limit is exceeded, the negative power burden of the third lens L3 in the first lens group G1 largely depends on the image-side surface of the third lens L3, and various aberrations occur on this surface. Cause.
[0020]
In the first lens group G1, the positive second lens L2 and the fourth lens L4 have a partial dispersion ratio θ with respect to the g-line and d-line of 1.22 to 1.24, and an Abbe number νd of 80 to 96. By using an optical material having anomalous dispersion, the secondary spectrum is corrected to be small. At the same time, such an anomalous dispersion optical material is likely to cause a refractive index change or thermal expansion due to a temperature change, and is soft and easily damaged. Therefore, the positive first lens L1 on the object side that directly touches the outside air. Uses optical materials that are resistant to temperature changes, are relatively hard, and are not easily damaged.
[0021]
Since the third lens group G3 has a positive action, the pincushion distortion that is usually a problem in the telephoto lens is not particularly problematic. However, by arranging the eighth lens L8 having a negative action on the image side, the pincushion can be obtained. In consideration of the possibility of mold distortion, the curvature radius r16 of the image side surface of the eighth lens L8 is set to r16 <0.
In other words, the pincushion distortion is prevented from increasing by providing a positive refractive power convex toward the image side. In fact, there is no problem in practical use if the distortion is as large as this embodiment.
[0022]
Further, if the lens distance d14 between the seventh lens L7 and the eighth lens L8 of the third lens group G3 is made too small, the refractive power of each lens becomes large, so that the pincushion distortion due to the negative eighth lens L8 is particularly large. It occurs greatly. Conversely, if the lens interval d14 is too large, the balance of chromatic aberration correction for the g-line will be lost.
0.09 <d14 <0.16
It is desirable to be in the range.
[0023]
【Example】
Next, each embodiment of the telephoto lens according to the present invention will be shown. Where f: focal length of the entire system fb: back focus 2ω: angle of view r: radius of curvature d: surface spacing n: refractive index for d-line ν: Abbe number for d-line M: meridional image plane S: sagittal image plane Table 1, Table 2, and Table 3 below show the parameter values of Example 1, Example 2, and Example 3, respectively.
[0024]
Note that the short distance in each of the following embodiments means a distance in which the distance from the subject to the image plane is approximately seven times the focal length.
[0025]
[Table 1]

[0026]
[Table 2]

[0027]
[Table 3]

[0028]
【The invention's effect】
As described above, according to the present invention, the shape of the second lens group, which is the focusing group of the telephoto lens, can be configured to be relatively small. It becomes possible to suppress fluctuations of various aberrations during the focusing. Also, by matching the fall of spherical aberration at the short distance with the fall of the image plane, a sharp image can be obtained from the center to the periphery of the screen even at a short distance, and other aberrations and fluctuations due to focusing It was small enough to achieve good performance. As a result, the telephoto lens according to the present invention can shorten the shortest shooting distance to about six times the focal length.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a state where an optical system of a telephoto lens according to the present invention is focused at infinity.
FIG. 2 is a configuration diagram showing a state in which the camera is focused on a short distance.
FIG. 3 is a diagram showing various aberrations when focusing on infinity in Example 1 of the present invention.
FIG. 4 is also a vertical aberration diagram when focusing on the short distance.
FIG. 5 is a diagram showing various aberrations when focusing on infinity in Example 2 of the present invention.
FIG. 6 is a diagram showing various aberrations when focusing at a short distance.
FIG. 7 is a diagram showing various aberrations when focusing on infinity in Example 3 of the present invention.
FIG. 8 is a graph showing various aberrations when focusing at a short distance.
FIGS. 9A and 9B are lateral aberration diagrams at an image height that is 70% of the maximum image height in the best image plane according to Example 1 of the present invention, in which FIG. Show each time.
FIGS. 10A and 10B are lateral aberration diagrams at an image height that is 70% of the maximum image height on the best image plane according to Example 2 of the present invention, in which FIG. Show each time.
FIGS. 11A and 11B are lateral aberration diagrams at an image height that is 70% of the maximum image height on the best image plane according to the third embodiment of the present invention, in which FIG. Show each time.
[Explanation of symbols]
G1: First lens group G2: Second lens group G3: Third lens group L1 to L8: First to eighth lenses

Claims (1)

The first lens group that is convergent, the second lens group that is divergent, and the third lens group that is convergent in order from the object side, and by moving the second lens group toward the image side on the optical axis, In a telephoto lens that focuses on an object at a distance,
The first lens group includes positive, positive, negative, positive first, second, third, and fourth lenses in order from the object side.
The second lens group includes a negative fifth lens that is biconcave from the object side, and a sixth meniscus positive lens that is convex on both sides of the object side,
The third lens group includes a positive seventh lens from the object side and a negative meniscus eighth lens whose both surfaces are convex on the image side.
A telephoto lens characterized by satisfying the following conditions.
(1) 0.05 <d10 / d8 <0.7
(2) r12> 0
Where d8: the distance between the fourth lens and the fifth lens d10: the distance between the fifth lens and the sixth lens r12: the radius of curvature of the image side surface of the sixth lens

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