JPH03200909A - Large-aperture intermediate telephoto lens - Google Patents

Abstract

PURPOSE:To obtain the compact, high-performance lens which is put in focus by the movement of only the lens group of the lens rear part and reduced in aberration variation due to the focusing operation by composing the lens of a front group which has positive refracting power on the whole and a rear group which has positive refracting power on the whole and satisfying specific conditions. CONSTITUTION:This lens is equipped with the front group G which consists of at least two lenses having large-curvature convex surfaces on the object side and a negative lens having a large-curvature concave surface on the image side in order from the object side and also has the positive refracting power on the whole. The lens is constituted by providing the rear group GR which consists of at least one positive lens, a concave negative lens having its image-side surface on the image side, and at least one positive lens while the surface closest to the image side is convex to the object side, and also has the positive refracting power on the whole, and the condition shown by an inequality I is satisfied. In the inequality I, (f) is the focal length of the whole system and rR1 is the radius of curvature of the surface which is closest to the object side in the rear group GR. Consequently, the layer-aperture intermediate telephoto lens of compact constitution which has high performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photographing lens for an SLR camera, and particularly to a medium telephoto lens having a large aperture ratio and a relatively wide angle of view.

"Prior Art" Recently, photographing lenses for SLR cameras are required to have high optical performance, a large aperture ratio, and a lens system that can focus easily and quickly.

Conventionally, so-called medium telephoto lenses with a large aperture ratio and a wide angle of view have been developed, for example, in Japanese Patent Application Laid-Open No. 59-48723 and Japanese Patent Laid-Open No. 6
High-performance products are provided in No. 3-205625 and the like.

Furthermore, in recent years, with the shift to autofocus (AF) cameras, inner focus and rear focus cameras have become available, which perform focusing by moving only a part of the lens inside the lens system. For example, JP-A-1
-154111 and Japanese Patent Application Laid-open No. 1-154112 disclose an inner focus type in which a focusing lens group is provided inside a Gauss type lens, and Japanese Patent Laid-Open No. 64-782
No. 08 proposes a rear focus lens that moves the rear group of a Gauss type lens.

"Problem to be Solved by the Invention" However, when using an inner focus type telephoto lens with a large aperture ratio and relatively wide angles, the overall length of the lens is long to provide space within the lens system for the focus lens group to move. Moreover, in order to take in a sufficient amount of peripheral light, the lens diameter must be increased, resulting in a large lens.

On the other hand, in the case of the rear focusing method in which the Gauss type rear group is moved, the size of the lens is relatively compact, but the aberrations fluctuate greatly due to the movement of the focusing group, making it difficult to obtain a high-performance lens. was there.

The present invention was made to solve the above-mentioned problems, and focuses by moving only the lens group at the rear of the lens.
The object of the present invention is to provide a compact, high-performance, large-diameter medium-telephoto lens suitable for AF cameras, with little variation in aberrations caused by focus operations.

"Means for Solving the Problems J" In order to achieve the objects described in item J, the large-diameter medium telephoto lens of the present invention includes, in order from the object side, at least two positive lenses each having a strongly convex surface facing the object side; The front group GP+ consists of a negative lens with a strongly concave surface facing the image side, and has positive refractive power as a whole.
and the surface SR1 closest to the object side is convex toward the object side,
Consisting of a rear group GR that has positive refractive power as a whole, the rear group G
Focus operation is performed by moving only R in the optical axis direction,
and (1) 0.5<f/rRo<3.5, where f: focal length of the entire system rRx: radius of curvature of the surface SRt closest to the object side of the rear group GR.

In order to increase the focus ratio in such a large aperture medium telephoto lens, (2) 0.6 < f R/ f < 1. Starting fR: It is desirable to satisfy the focal length condition of the rear group GR.

In addition, in the above-mentioned large-diameter medium-telephoto lens, the rear group GR is
It consists of at least one positive lens, a negative lens LRn whose image side surface is concave toward the image side, and at least one positive lens, and (3) 0.8 < f / fR4 < 3.0 However, it is desirable to satisfy the condition fR4: radius of curvature of the image side surface of the negative lens LRn.

Furthermore, the large-diameter medium-telephoto lens of the present invention consists of, in order from the object side, at least two positive lenses with a strongly convex surface facing the object side, and a negative lens with a strongly concave surface facing the image side, so that the overall lens has a positive The front group GF has a refractive power of , and the surface SR closest to the object side.
□ is convex toward the object side, and consists of at least a 7-lens lens, a negative lens LRn whose image side surface is concave toward the image side, and at least one positive lens, and the overall positive It consists of a rear group GR with refractive power, (]) 0.5 < f / rRl < 3.5 (2
) 0.6 < fR/ f < 1.1 (3) 0.
8<f/rRl<3.0.

"Operation" FIG. 13 is a simple basic configuration diagram of the present invention. (hereinafter referred to only as SRt) is characterized by having a convex surface facing the object side.

On the other hand, as shown in Fig. 4, the Gaussian type rear group G
The type of SRt that moves R is characterized by having a concave surface facing the object side. In other words, a Gauss type lens is
The configuration is characterized by the symmetrical shape of the rear group, which cancels out aberrations and achieves good performance.

However, in a Gauss type lens, when the rear group is moved for focusing, the symmetry between the front and rear groups is broken, and aberrations fluctuate. In particular, as shown in FIG. 14, the height of incidence of the off-axis marginal ray on SR+ changes as the rear group GR moves in focus. That is,
Since SRx is concave toward the object, the angle between the off-axis marginal ray and the normal to the SRI changes greatly, resulting in large aberration fluctuations.When focusing from infinity to a short distance, the off-axis marginal ray The rays now generate inward comas.

In the present invention, since SR□ is convex toward the object side, the angle between the off-axis marginal ray and the normal to SRt is small, so the rear group GR moves with focus. Even if the height of incidence of the off-axis marginal ray on SR□ changes, the change in the angle with respect to the normal line of SR□ is relatively small, and aberration fluctuations due to focus operation can be reduced.

Therefore, condition (1) indicates what radius of curvature of a surface is appropriate for SRt.

When the radius of curvature rRx of SRx is made extremely small, S
Even if Rt is convex toward the object side, when the rear group GR moves with focus and the incident height of the off-axis marginal ray changes, the change in the angle between Sn Aberration fluctuations increase. That is, when focusing from fisheye speed to short distance, the off-axis marginal ray will generate an outer coma. Therefore, r beyond the upper limit of condition (1)
Setting R+ to a small value is not permissible in terms of aberration fluctuations.

Conversely, if the radius of curvature rRx of SR1 is increased to bring it closer to a flat surface, aberration fluctuations due to focusing can be reduced.

However, as the rear group GR needs to have a certain degree of strong positive refractive power, as described in condition (2) below, the SR
If only the radius of curvature rRt of 1 is made loose and the other positive surface bears positive refractive power, the aberration correction will become unbalanced.
Negative spherical aberration is likely to occur. Further, since the rear group GR moves within the lens system to perform focusing, it must be compact by itself in order to secure movement space. Therefore, it is desirable that SRx has strong positive refractive power. Therefore, loosening rRz beyond the lower limit of the fourth condition (1) is not permissible from the viewpoint of aberration correction and compactness of the rear group GR.

Next, condition (2) regarding the positive refractive power of the rear group GR will be explained. Since the rear group GR is a lens group that moves for focusing within the lens system, a space must be provided in the lens system for the rear group GR to move, but the focal length fR of the rear group GR is If the upper limit of condition (2) is exceeded, the closest possible subject distance cannot be reduced due to mechanical constraints in a limited moving space, and the moving space of the rear group GR is reduced in order to shorten the closest subject distance. Increasing the size of the lens system results in an increase in the size of the lens system.

Therefore, increasing the focal length fR of the rear group GR beyond condition (2) is not permissible from the viewpoint of the closest object distance or miniaturization of the entire lens system.

Conversely, making the focal length fR of the rear group GR smaller than the lower limit of condition (2) shortens the closest shooting distance.

Although it is advantageous for downsizing the lens system, in the lens for SLR camera which is the object of the present invention, it is necessary to secure a certain degree of back focus, so the rear group GR must also have a certain focal length in order to secure the back focus. need to be made longer. Therefore, the rear group G exceeds the lower limit of condition (2).
It is not desirable to reduce the focal length fR of R.

Further, it is desirable that the rear group GR of the present invention has a structure in which aberrations are well corrected together with the front group G.

Therefore, in the present invention, as shown in the embodiment, it is desirable that the rear group GR be of the triplet type or its advanced form, and that condition (3) be satisfied in order to obtain even better performance. In rRx defined in the above condition (1),
Because it has positive refractive power, it produces negative spherical aberration.

Therefore, in the rear group GR, this negative spherical aberration is corrected.

It is necessary to provide a surface for maintaining good performance of the rear group G. The condition for this is (3), and if rR4 is made loose beyond the lower limit, negative spherical aberration due to SRt will remain, which is not desirable. On the other hand, tightening rR4 beyond the upper limit is undesirable because it causes higher-order spherical aberration.

In the above explanation, we have talked about using the large-diameter medium-telephoto lens of the present invention with a rear focus type focusing operation. Of course, it is also possible to use it in a method that performs operations.

r Example” Examples 1 to 6 of the present invention are shown below.

Here, f: Focal length of the entire system FNO: Aperture ratio ω: Half angle of view r: Radius of curvature of each lens surface d: Lens thickness or lens spacing n: d-1ine refractive index of each lens V = Each lens The Atsube number f is the second back focus.

Note that in the case of full extension, the distance between the front group G and the rear group GR remains the same.

[Example 1 FNo=1:1.8 FNOr 1 53.523 2 152.039 3 40.942 4 51223 5 74403 6 29884 7 39084 8 89132 9 -87130 10 41858 11 88.669 12 -68. 007f =100.0 7.30 0.18 8.79 4.38 2.11 Variable 7.13 3.12 2.98 7.58 6.75 1.80610 ω=14.3” n v 1.69680 55 .5 1.77250 1.71736 1.77250 1.68893 49.6 29.5 49.6 31.1 40.9 rRl = rt = 39.084 f, :97.15 rR4 = r 1o = 41.858 [Example 2 FNO=1:1.8 FNOr 1 55.558 2 141.167 3 43.158 4 54.420 5 68.388 6 31.079 7 39.8/18 8 105.369 9 -114 .402 10 37.269 11 14Q, 743 12 36.297 13 -82.064 f = 100.O 6,78 0,18 9,60 3,75 2,11 Variable 7.59 2.65 4.70 8 .74 1.76 7.13 ω=14.3' n ν 1.69680 55.5 1.77250 49.6 1.72825 28.5 1.77250 49.6 1.64769 33.8 1.69895 1 .83400 30.1 37.2 [Example 3] FNO=1:1.7 FNOr 1 55.492 2 272.701 3 43, .272 4 69.167 5 134.352 6 31.963 7 55.743 8 149.341 9 -64.353 10 69.176 11 -72.361 12 67.813 13 -53.030 14 86.312 15 -1007.015 ω=14.4' n Ya1.69680 55.5 f=100.0 9.55 0.18 6.22 1.61800 5.86 2.37 Variable 3.85 6.54 5.40 3.63 2.13 8.28 0.12 3.90 1. 78590 1.64769 33.8 1.83400 37.2 1.68893 1.77250 1.67270 63.4 32.1 49.6 31.1 44.2 r Rx :” r t =39.848fR:98.
59 I” R4= r 16 ” 37.269r R,:
r 7 = 55.743 fR = 91.50 r R4 = r 1. = 69.176 [Example 4] FNo”1:1.4 FNOr 1 55.159 2 353.958 3 47.367 4 79.655 5 193.855 6 31.607 7 57.371 8 245.363 9 -61.317 10 74.188 11 -65.690 12 101.428 13 -57.545 14 98.095 15 -160.255 f=100.0 13.94 0.17 7.04 7.20 2. 33 Variable 4.61 6.76 3.19 4.33 2.33 9.28 0.12 5.64 ω=14.1″ ny 1.61800 63.4 1.77250 49.6 1.69895 30 .1 1.77250 49.6 1.66680 33.0 1.67270 1.83400 32.1 37.2 1.78590 44.2 [Example 5 FNo=1:1.4 FNOr 1 55.480 2 246.706 3 46.202 4 74.871 5 163.1B3 6 30.896 7 60.755 8 290.947 9 -59.387 10 80.601 11 -69.419 12 94.667 13 -60.204 14 110.139 15 -133.433 f =100.0 13.15 0.28 7.38 5.88 2.33 Variable 4.56 6.94 3.77 4.04 2.33 9.31 0. 12 5.69 1.80610 ω=14.1” n v 1.72916 54.7 1.72916 1.71736 1.77250 1.68893 1.67270 1.83400 54.7 29.5 49.6 31. 1 32.1 37.2 40.9 r R1:= r , =57.371fR=78.7
4 rR+= r1g=74.188 1'Rt: r7=60.755 fR=79.26 rR4: r,. =80.601 [Example 6] FNo=1:1.4 FNOr 1 59.318 2 142770 3 77863 4 150243 5 49552 6 65025 7 152087 8 33363 9 71275 to 11461308 11 -5 0130 12 82.006 13 -92026 14 55236 15 -52841 16 95443 17 -785494 f=100.0 10.33 0.23 6.05 0.48 6.08 6.11 2.33 Variable 5.66 1.77250 6.94 55 52 33 145 12 74 ω=14.1@n v 1.75700 47.9 1.78470 1.80610 1.69350 1.69350 1.67270 1.67270 32.1 1.83400 37.2 53.2 53.2 26. 2 49.6 32.1 40.9 rR1= r9=71.275 fR=74.17 r R4= r □z =82.006 "Effect of invention"
- As explained above, according to the present invention, the rear focus large aperture ratio medium telephoto lens that performs focusing by moving only the rear group GR is compact and can focus by satisfying predetermined conditions. High performance with little aberration fluctuation due to operation (infinity (A) as shown in the attached various aberration diagrams)
, and short range (B) with good performance. Furthermore, even when the entire lens is extended, a compact, high-performance, large-diameter, medium-telephoto lens can be provided.

[Brief explanation of drawings]

FIG. 1, FIG. 3, FIG. 5, FIG. 7, FIG. 9, and FIG. 11 are lens sectional views of Examples 1, 2, 3, and 4°5.6 of the present invention, respectively. 2, 4, 6, 8, 10, and 12 are various aberration diagrams of Examples 1, 2, 3, and 4°5.6 of the present invention, respectively. ) is an aberration diagram at infinity, and (B) is an aberration diagram at a photographing magnification of 1/1O during rear focus. FIG. 13 is a simple basic configuration diagram of the present invention. FIG. 14 is a simple basic configuration diagram of a conventionally known Gauss type. Figure 1

Claims (1)

[Claims] 1 Consisting of, in order from the object side, at least two positive lenses with a strongly convex surface facing the object side and a negative lens with a strongly concave surface facing the image side, and having a positive refractive power as a whole. The front group G_F and the surface S_R_1 closest to the object side are convex toward the object side, and the rear group G_R has a positive refractive power as a whole. Focus operation is performed by moving only the rear group G_R in the optical axis direction. and (1) 0.5<f/r_R_1<3.5, where f: focal length of the entire system r_R_1: radius of curvature of the surface S_R_1 closest to the object side of the rear group G_R. A large aperture medium telephoto lens. 2. A large-diameter medium telephoto lens according to claim 1, further satisfying the following condition: (2) 0.6<f_R/f<1.1, where f_R: focal length of rear group G_R. 3 In claim 1, the rear group G_R includes at least one positive lens and a negative lens L whose image side surface is concave toward the image side.
_R_n and at least one positive lens, and is characterized by satisfying the following conditions: (3) 0.8<f/r_R_4<3.0 where r_R_4: radius of curvature of the image side surface of the negative lens L_R_n A large aperture medium telephoto lens. 4. In order from the object side, the front group G_F consists of at least two positive lenses with a strongly convex surface facing the object side, a negative lens with a strongly concave surface facing the image side, and has a positive refractive power as a whole, and the most The object side surface S_R_1 is convex toward the object side and consists of at least one positive lens, a negative lens L_R_n whose image side surface is concave toward the image side, and at least one positive lens; Consisting of a rear group G_R with positive refractive power as a whole, (1) 0.5<f/r_R_1<3.5 (2) 0.6<f_R/f<1.1 (3) 0.8<f /r_R_4<3.0 However, f: Focal length of the entire system r_R_1: Radius of curvature of the most object-side surface S_R_1 of the rear group G_R f_R: Focal length of the rear group G_R r_R_4: Curvature of the image-side surface of the negative lens L_R_n A large aperture medium telephoto lens that satisfies various radius conditions.