JPH04238311A - Internal focusing telephoto lens for automatic focusing camera - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal focusing telephoto lens for autofocus cameras such as single-lens reflex cameras and electronic still cameras.

0002

2. Description of the Related Art Conventionally, in this type of objective lens, when focusing, the focusing group had to move over a very long distance. In other words, as the imaging magnification was increased, the moving distance tended to become longer. This increases the burden on the autofocus drive motor and increases the size of the focusing mechanism.

0003

SUMMARY OF THE INVENTION The present invention provides an internal focusing telephoto lens that is compact and has a short focusing movement while maintaining excellent optical performance.

0004

[Means for Solving the Problem] The first group G1 has a positive refractive power, the second group G2 has a negative refractive power, and the third group G3 has a positive refractive power, in order from the object side. In an internal focusing telephoto lens in which the group G1 and the second group G2 having a negative refractive power form a substantially afocal system, and the second group G2 performs focusing, the first group G1 has a positive refractive power in order from the object side. A front group G11 that has a positive refractive power as a whole and is composed of a first lens component L1, a positive second lens component L2, and a negative third lens component L3, and a rear group that has a weak positive refractive power with respect to the front group. a group G12, and the third group G3 has a positive lens component L7,
An internal focusing telephoto lens characterized by satisfying the following conditions. (1) 0.43<Φ/f1<0.75(2)
0.39<f1 /F<0.55(3) 0<R1
+0.9R2 However, Φ: Effective diameter of the object-side lens surface of the most object-side positive lens component in the first group F: Focal length of the entire system f1: Focal length of the first group R1: Positive lens in the third group Radius of curvature R2 of the object-side lens surface of the component: Radius of curvature of the image-side lens surface of the positive lens component in the third group

[0005]

[Operation] The basic configuration of the photographing optical system of the present invention is that of positive, negative, and positive three.
This is a group configuration, and focusing is performed by movement of the negative second group G2. The focusing method for this configuration is
Near the image point for the subject formed by the first group G1,
The second group G2 is brought into focus. Therefore, the first group G1
An image point by the combined optical system of the second group G2 and the second group G2 is formed at a substantially infinite distance. Therefore, the light beam incident on the third group G3 always becomes a substantially afocal light beam, and the image point of the entire optical system is always at a constant position. From the above, by considering the refractive power arrangement of the thin-walled system, the amount of focusing movement for the thick-walled system can be uniquely determined. Therefore, in order to reduce the amount of focusing movement of the negative group, which is the object of the present invention, it is sufficient to reduce the amount of movement of the image by the first group G1 (focal length f1) relative to the amount of movement of the object point.

If the first group G1 is a thin lens and the focal length is f1 = f1', the object point distance is a, and the image point distance is b, then from the relational expression for lens imaging, 1/a+1/b=1/ f1 → f1
=a/(a/b+1) (A) Next, considering the vertical magnification α, the vertical magnification α is expressed by the following formula. α=(-a/b)2 =a2/b2
→ b=a√α>0 (B) If the object point moves from a specific location and is fixed with respect to the first group,
In other words, when a=constant, in order to reduce the amount of movement of the negative second group for focusing, that is, the amount of movement of the image point by the first group relative to the amount of movement of the object point, the vertical magnification α should be made small. Bye. Now, by substituting equation (B) into equation (A), f1 = a/(1/√α+1)
(C
). Therefore, as α becomes smaller, f1 also becomes smaller. Therefore, by reducing the focal length f1 of the first group G1, the amount of focusing movement can be reduced.

However, if the power of G1 is too strong, the spherical aberration of the first group G1 itself becomes too large, which worsens the aberration of the photographic optical system as a whole. Therefore, in order to reduce the amount of focusing movement and obtain good spherical aberration, f
Equations (1) and (2) regarding 1 and equation (3) regarding residual aberration must be satisfied. Equation (1) is given by the effective diameter Φ of the object-side lens surface of the most object-side positive lens component in the first group with respect to the focal length f1 of the first group.
This is a conditional expression that defines the ratio of . If the upper limit of equation (1) is exceeded, the focal length of the first group G1 is too small relative to the effective diameter, and the spherical aberration of the first group G1 itself becomes too large, causing the second group G2 and the third group G3 to It is difficult to correct this by using a configuration with a small number of lenses. Moreover, the spherical aberration of the secondary color also increases, making it difficult to configure the first group G1 with a small number of lenses. When the lower limit of equation (1) is exceeded,
Since the focal length of the first group G1 becomes longer, the amount of focusing movement becomes larger, which is contrary to the purpose.

Equation (2) is a conditional expression regarding the ratio of the focal length of the first group to the focal length F of the entire system. If the upper limit of equation (2) is exceeded, the focal length of the first group becomes long, which increases the overall length of the optical system and increases the amount of focusing movement, which is not preferable. If the lower limit of equation (2) is exceeded, the first group G1
Since the focal length of the lens is too short, if an attempt is made to increase the aperture with the configuration in which the first group G1 is small, the center thickness of the convex lens must be increased, which is undesirable as it increases the weight of the photographic optical system.

Equation (3) is based on the positive lens component L7 in the third group.
This is a conditional expression that defines an appropriate shape of the positive lens component L7 in the third group with respect to the radius of curvature of the object side lens surface and the image side lens surface of the third group. If formula (3) is not satisfied, the lower coma aberration becomes positively large, which is undesirable. Furthermore, in the present invention, in order to make the optical system compact, when the focal length of the entire system is F and the total length of the optical system is L, it is preferable that 0.68<L/F<0.93 be satisfied. . If the lower limit of the above equation is exceeded, the total length of the lens becomes too short relative to the combined focal length of the entire system, which is undesirable because the coma aberration of the lower color becomes large. If the upper limit is exceeded, the total length will become longer, which is not preferable.

In the basic configuration of the present invention as described above, since the first group G1 has a very short focal length, spherical aberration tends to increase. Therefore, the first lens group G1 includes, in order from the object side, a first lens component L having a positive refractive power and having a convex surface facing the object side.
1. A front group G11 having a positive refractive power as a whole composed of a biconvex positive second lens component L2 and a biconcave negative third lens component L3, and a rear group G12 having a positive refractive power. It is desirable to have a configuration in which

[0011] Now, the peripheral ray from an object point at infinity on the axis will be called a land ray. Even though the land ray that is incident on the first lens of the telephoto lens is a ray that is emitted from a close object point, it is incident on the first incident surface substantially parallel to the optical axis. Therefore, if the first lens is considered as a collection of micro prisms, it needs to have a shape close to the minimum deviation angle, with the object side surface being a convex surface and the image side surface having a gentle curvature. The sign of the radius of curvature on the image side surface may be either positive or negative depending on the aberration structure within the first group G1. Since the land ray becomes a convergent light beam in the first lens component L1, the second lens component L2 also has a biconvex shape with a surface with a stronger curvature facing the object side so as to take the minimum deviation angle so as to further converge this light beam. As a positive lens component, the first group G
The positive refractive power in 1 is almost determined by the first lens component L1 and the second lens component L2. However, since the spherical aberration and chromatic aberration become too large if only the positive lens component is used, a negative third lens component L3 is placed immediately after the positive lens component to perform appropriate correction. Under conditions near the upper limit of equation (1),
Since the refractive power of the first group G1 is very strong, a positive fourth lens component, that is, a rear group, is placed immediately after the front group to distribute the positive refractive power of the first and second lens components L1 and L2. do.

Regarding the rear group G12 in the first group G1, in order to obtain better aberrations, the rear group G12 consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, and a negative meniscus lens with a convex surface facing the object side. It is preferable to configure the lens with a positive meniscus lens with a convex surface facing. Since the rear group is for correcting spherical aberration, it is best to have a meniscus shape with a convex surface facing the object side so as not to affect rays other than the land rays. Furthermore, rear group G
12 may be constructed as a bonded structure in order to simplify the lens barrel structure. Furthermore, in the present invention, in order to better correct aberrations, if the refractive index of the positive meniscus lens in the fourth lens component is Na and the Abbe number is νa, then Na<
1.60 (4) It is desirable to satisfy 65<νa (5).

Regarding the lower limit of equation (4), since there is currently no suitable optical material, the lower limit is essentially 1.42. If the upper limit is exceeded, the Petzval sum becomes negative and undesirable. If the lower limit of equation (5) is exceeded, it is difficult to reduce chromatic aberration in the first group G1, which is not desirable. As for the upper limit, 97 is practically the upper limit because there is currently no suitable optical material.

Further, the positive third group G3 is constructed as a composite lens consisting of a biconvex positive lens and a negative meniscus lens with a concave surface facing the object side in order from the object side, and the refractive index of the convex lens is nb, and the Abbe number is If νb, it is preferable that nb<1.58 (6) 45<νb (7).

If Equation (6) is deviated from, the Petzval sum becomes negative and undesirable. Deviating from equation (7) is not preferable because it is difficult to correct axial chromatic aberration, especially secondary chromatic aberration, with a configuration with a small number of lenses. Also, the simplest configuration is to configure the third group G3 with a single lens, in which case the lens shape is a biconvex positive lens, the refractive index is nc, and the Abbe number is ν.
If c, then it is desirable to satisfy the following conditions: nc<1.55 (8) νc>50 (9).

If the equation (8) is not satisfied, the Petzval sum becomes negative, making it difficult to construct the third group G3 with one lens, which is not preferable. If the equation (9) is not satisfied, axial chromatic aberration, especially secondary chromatic aberration, becomes large, which is not preferable.

[0017]

[Embodiment] In the first embodiment, the rear group G12 in the first group G1 and the third group G3 are composed of one biconvex lens. Focusing is performed by the second group G2. Here, a fixed filter is added to the closest image side. In the second embodiment, the rear group G12 in the first group G1 is composed of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, and a positive meniscus lens with a convex surface facing the object side. They are arranged at intervals. The third group G3 is composed of one biconvex lens. Here, a fixed filter is added to the closest image plane. Focusing is performed by the second group G2.

The rear group G12 in the first group G1 of the third and sixth embodiments is composed of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, and a positive meniscus lens with a convex surface facing the object side. They are constructed and pasted together. Third
Group G3 is composed of, in order from the object side, a biconvex lens and a negative meniscus lens with a concave surface facing the object side, which are bonded together. Focusing is performed by the second group G2. A fixed filter is added to the closest image side.

In the fourth and seventh embodiments, the rear group G12 in the first group G1 includes, in order from the object side, a negative meniscus lens with a convex surface facing the object side, and a positive meniscus lens with a convex surface facing the object side. It is made up of several parts and pasted together. Third
Group G3 is composed of one biconvex lens. Especially R1
:R2 for easy processing. Focusing is performed by the second group G2. A fixed filter is added to the closest image side.

In the fifth embodiment, the rear group G12 in the first group G1
consists of a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side, which are bonded together in order from the object side. The third group G3 is composed of one biconvex lens. Focusing is performed by the second group G2. Fixed filters are added to the closest object plane and the closest image plane.

The values of the specifications of each embodiment of the present invention are listed below. The leftmost number in the specification table of the example represents the order from the object side, r is the radius of curvature of the lens surface, d is the distance between lens surfaces, refractive index n and Abbe number ν are the d-line (λ = 587.6
nm).

[0022]

[Example 1] f=392.0 Fno=3.6 Δx (β=-0.13)=13.0 r d ν n
1 198.577 13.00
82.6 1.49782 2 -5
50.482 1.00 3 1
31.746 16.60 82.6 1.
49782 4 -1037.798
7.56 5 -555.893
5.20 31.6 1.75692 6
304.686 41.13 7
245.724 3.50 82
．． 6 1.49782 8 551
．． 583 37.38 9 -1528.622 5.70 3
2.2 1.67270 10 -1
00.624 2.50 64.1 1.
51680 11 130.475
3.85 12 -200.681
2.50 60.7 1.56384
13 81.646 18.41
14 378.614 5.70
82.6 1.49782 15
-97.258 56.50 16
∞ 2.00 64.1 1
．． 51680 17 ∞
96.50 F 392.0043 -. 1296
D0 ∞ 3207.1651
d 8 37.3781 50.3535
d13 96.4979 96.5008
f1 =197.75 Φ=109.8 Φ/f1 =0.555 f1 /F=0.504 R1 +0.9R2 =291.08

[0023]

[Example 2] f=392.0 Fno=3.6 Δx (β=-0.13)=13.0 r d ν n
1 204.548 11.80 8
2.6 1.49782 2 -93
3.163 1.00 3 13
7.181 16.60 82.6 1.4
9782 4 -741.847
4.10 5 -602.191
5.20 35.2 1.74950 6
378.609 52.18 7
122.943 3.50 46.
8 1.76684 8 68.
550 2.00 9 67.
730 10.40 65.7 1.464
50 10 506.871 27
．． 08 11 -536.039 5.70
32.2 1.67270 12
-89.868 2.50 64.1 1
．． 51680 13 122.103
3.85 14 -216.174
2.50 53.5 1.54739
15 88.049 18.33
16 228.492 5.70
64.1 1.51680 17 -
123.591 56.50 18
∞ 2.00 64.1 1
．． 51680 19 ∞
95.95 F 392.0050 -. 1300
D0 ∞ 3200.9989
d10 27.0818 40.0572
d15 18.3338 5.3584
d19 95.9528 95.952
8 f1 =197.75 Φ=109.8 Φ/f1 =0.555 f1 /F=0.504 R1 +0.9R2 =117.26

[0024]

[Example 3] f=294.0 Fno=2.9 Δx (β=-0.13)=10.9 r d ν n
1 156.233 12.20 8
2.6 1.49782 2 -180
6.226. 10 3 9
8.943 19.30 82.6 1.4
9782 4 -385.600
．． 78 5 -403.319
4.60 35.2 1.74950 6
301.384 39.94 7
83.928 3.10 46.
8 1.76684 8 45.
936 12.50 65.7 1.464
50 9 220.022 3.
98 10 161.322 8.40
32.2 1.67270 11
-90.593 2.30 56.4 1
．． 50137 12 62.128
6.31 13 -104.466
2.30 46.4 1.58267
14 66.096 16.84
15 112.382 8.20
49.0 1.53172 16
-64.652 2.20 33.9 1
．． 80384 17 -98.465
40.40 18 ∞
2.00 64.1 1.51680
19 ∞ 72.88
F 293.9725 -. 1300
D0 ∞ 2423.7514
d 9 3.9816 14.8725
d14 16.8403 5.9493
d19 72.8818 72.881
8 f1 =157.00 Φ=101.9 Φ/f1 =0.649 f1 /F=0.534 R1 +0.9R2 =23.76

[0025]

[Example 4] f=392.0 Fno=3.56 Δx (β=-0.13)=13.0 r d ν n
1 212.720 11.80 8
2.6 1.49782 2 -85
0.437 1.00 3 12
9.181 16.60 82.6 1.4
9782 4 -726.621
4.10 5 -594.328
5.20 35.2 1.74950 6
341.228 60.59 7
123.774 3.50 46.
8 1.76684 8 67.
389 10.40 65.7 1.464
50 9 711.769 19.
51 10 -6991.000 5.70
32.2 1.67270 11
-97.087 2.50 64.1 1
．． 51680 12 110.331
3.85 13 -233.088
2.50 60.7 1.56384
14 80.666 19.59
15 154.427 5.70
82.6 1.49782 16 -
154.427 56.50 17
∞ 2.00 64.1 1
．． 51680 18 ∞
95.36 F 392.0052
−． 1300 D0 ∞ 32
01.7637 d 9 19.5072
32.4826 d14 19.5946
6.6192 d18 95.3650
95.3650 f1 =197.75 Φ=109.8 Φ/f1 =0.555 f1 /F=0.504 R1 +0.9R2 =15.44

[0026]

[Example 5] f=588.0 Fno=4.1 Δx (β=-0.13)=13.3 r d ν n
1 ∞ 5.00 6
4.1 1.51680 2
∞ 1.20 3 201
．． 438 18.00 82.6 1.49
782 4 -1821.902
．． 90 5 201.189 19
．． 00 82.6 1.49782 6
-794.165 6.60 7
-627.182 7.00 31.7
1.75692 8 551.9
55 103.43 9 101.1
70 5.00 54.0 1.7130
0 10 49.452 13.
00 67.9 1.59319 11
145.498 7.21 12 -90000.000 7.00
25.4 1.80518 13 -
122.159 3.30 54.0 1
．． 71300 14 110.402
6.90 15 -1527.933
3.30 53.8 1.69350
16 130.260 17.88
17 218.270 7.00
82.6 1.49782 18 -
187.896 65.20 19
∞ 2.00 64.1 1
．． 51680 20 ∞
135.31 F 588.0001 -. 1300
D0 ∞ 4756.3500
d11 7.2137 20.4845
d16 17.8751 4.6043
d20 93.3069 93.306
9 f1 =197.75 Φ=109.8 Φ/f1 =0.594 f1 /F=0.417 R1 +0.9R2 =49.16

[0027]

[Example 6] f=294.0 Fno=2.9 Δx (β=-0.13)=10.9 r d ν n
1 157.463 12.20 8
2.6 1.49782 2 -168
2.641. 10 3 9
8.632 19.30 82.6 1.4
9782 4 -387.044
1.00 5 -401.055
4.60 35.2 1.74950 6
300.368 39.60 7
84.165 3.10 46.
8 1.76684 8 46.
165 12.50 65.7 1.464
50 9 219.377 3.
88 10 158.047 8.40
32.2 1.67270 11
-91.089 2.30 56.4 1
．． 50137 12 62.149
6.31 13 -103.795
2.30 46.4 1.58267
14 65.621 16.81
15 112.522 8.20
59.0 1.51823 16
-64.444 2.20 49.4 1
．． 77279 17 -96.198
35.00 18 ∞
2.00 64.1 1.51680
19 ∞ 78.31
F 293.9708 -. 1300
D0 ∞ 2423.9264
d 9 3.8820 14.7729
d14 16.8091 5.9181
d27 195.9549 195.954
9 f1 =157.00 Φ=101.9 Φ/f1 =0.649 f1 /F=0.534 R1 +0.9R2 =25.94

[0028]

[Example 7] f=392.0 Fno=3.6 Δx (β=-0.13)=13.0 r d ν n
1 233.537 11.80 8
2.6 1.49782 2 -74
4.832 1.00 3 13
2.172 16.60 82.6 1.4
9782 4 -712.757
2.50 5 -622.601
5.20 35.2 1.74950 6
380.065 65.83 7
130.032 3.50 52.
3 1.74810 8 67.
822 10.40 82.6 1.497
82 9 495.828 18.
24 10 -90000.000 5.70
32.2 1.67270 11
-95.818 2.50 64.1 1
．． 51680 12 110.854
3.85 13 -216.517
2.50 60.7 1.56384
14 81.169 19.67
15 154.427 5.70
82.6 1.49782 16 -
154.427 56.50 17
∞ 2.00 64.1 1
．． 51680 18 ∞
95.36 F 392.0040 -. 1300
D0 ∞ 3198.9257
d 9 18.2409 31.2163
d14 19.6667 6.6913
d18 95.3639 95.363
9 f1 =197.75 Φ=109.8 Φ/f1 =0.555 f1 /F=0.504 R1 +0.9R2 =15.44 Example 1, Example 2, Example 3, Example 4, Implementation Example 5,
Lens cross-sectional views of Example 6 and Example 7 are shown in Figures 1, 3, and 5.
, Fig. 7, Fig. 9, Fig. 11, and Fig. 13, respectively.

In each of the embodiments, an aperture stop is provided immediately before the fixed filter close to the image plane, but it may also be provided immediately before the second group. Furthermore, as shown in each example, the amount of movement of the second group due to close-range photography is very small, moving the optical axis toward the image plane, even though the photographing magnification of each example is β = -0.13. This is achieved by moving in quantity.

By bringing the second lens group in as far as the air distance between the second lens group and the third lens group allows, it is possible to focus on an even closer object point. The aberration diagram of Example 1 is shown in Figure 2, the aberration diagram of Example 2 is shown in Figure 4, and the aberration diagram of Example 3 is shown in Figure 6.
, the aberration diagram of Example 4 is shown in Figure 8, and the aberration diagram of Example 5 is shown in Figure 10.
, the aberration diagram of Example 6 is shown in Figure 12, and the aberration diagram of Example 7 is shown in Figure 1.
4.

As shown in each aberration diagram, it is clear that all examples have excellent imaging performance. Incidentally, by moving the third lens group in a direction perpendicular to the optical axis, an anti-vibration effect can be obtained.

[0032]

According to the present invention, it is possible to provide a more compact internal focusing telephoto lens while maintaining excellent performance.

[Brief explanation of the drawing]

FIG. 1: Lens configuration diagram of Example 1 of the present invention

[Fig. 2] Lens aberration diagram of Example 1 of the present invention

[Figure 3] Example 2 of the present invention
lens configuration diagram

[Fig. 4] Lens aberration diagram of Example 2 of the present invention

FIG. 5: Lens configuration diagram of Example 3 of the present invention

[Fig. 6] Lens aberration diagram of Example 3 of the present invention

FIG. 7: Lens configuration diagram of Example 4 of the present invention

[Fig. 8] Lens aberration diagram of Example 4 of the present invention

FIG. 9: Lens configuration diagram of Example 5 of the present invention

[Figure 10
] Lens aberration diagram of Example 5 of the present invention

FIG. 11: Lens configuration diagram of Example 6 of the present invention

FIG. 12: Lens aberration diagram of Example 6 of the present invention

FIG. 13: Lens configuration diagram of Example 7 of the present invention

FIG. 14: Lens aberration diagram of Example 7 of the present invention

[Explanation of symbols of main parts] S... Aperture F... Filter

Claims (7)

[Claims] 1. Consisting of, in order from the object side, a first group G1 with positive refractive power, a second group G2 with negative refractive power, and a third group G3 with positive refractive power, the first group G1 with positive refractive power and the third group G3 with positive refractive power. Second group G with negative refractive power
2 to form a substantially afocal system, and the second group G2 performs focusing, in which the first group G1 includes, in order from the object side, a positive first lens component L1, a positive second lens component L1, and a positive second lens component L1. It has a front group G11 having a positive refractive power as a whole composed of a component L2 and a negative third lens component L3, and a rear group G12 having a weak positive refractive power with respect to the front group, and the third lens component Group G3 is an internal focusing telephoto lens having a positive lens component L7 and satisfying the following conditions. (1) 0.43<Φ/f1<0.75(2)
0.39<f1 /F<0.55(3) 0<R1
+0.9R2 However, Φ: Effective diameter of the object-side lens surface of the most object-side positive lens component in the first group F: Focal length of the entire system f1: Focal length of the first group R1: Positive lens in the third group Radius of curvature R2 of the object-side lens surface of the component: Radius of curvature of the image-side lens surface of the positive lens component in the third group 2. The rear group G12 in the first group G1 is composed of, in order from the object side, a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side. The internal focusing telephoto lens according to claim 1. 3. The internal focusing telephoto lens according to claim 1, wherein the rear group G12 is laminated. 4. The internal focusing telephoto lens according to claim 3, wherein the positive meniscus lens in the rear group G12 having a convex surface facing the object side satisfies the following conditions. (4) Na<1.6 (5) 65<νa Na: refractive index νa: Abbe number 5. The rear group G12 is a single convex lens component, and the object side surface is a convex surface.
The internal focusing telephoto lens described in 4 to 4. 6. The third group G3 is configured by laminating, in order from the object side, a biconvex lens and a negative meniscus lens with a concave surface facing the object side, and satisfies the following conditions. 6. The internal focus telephoto lens described in 5 to 5. (6) Nb<1.58 (7) 45<νb Nb: refractive index of convex lens νb: Abbe number 7. The internal focus telephoto lens according to claim 1, wherein the third group G3 is a single biconvex lens and satisfies the following conditions. (8) Nc<1.55 (9) 50<νc Nc: refractive index νc: Abbe number