JPH0921949A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens of small size and with high performance. SOLUTION: This lens comprises the zoom lens consisting of a first group G1 of positive power, a second group G2 of negative power, a third group G3 of positive power and a fourth group G4 of positive power, and which performs focusing by the third group G3 or the fourth group G4 . The first group G1 consists of a negative meniscus lens and a positive lens group, and the second group G2 consists of a lens group including a negative lens with stronger curvature for an object side surface, a negative lens and a positive lens with stronger curvature for the object side surface nearest to an image side. The powers of the first group G1 and the second group G2 , and the shaping factors included in the first group G1 and the second group G2 are decided so as to satisfy a prescribed condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens applied to a video camera, a still video camera and the like, and more particularly to a zoom lens having high optical performance suitable for use in capturing recent high definition images.

[0002]

2. Description of the Related Art In a camera using a solid-state image pickup device as an image pickup means (imager), a zoom lens having an extremely large zoom ratio is generally used as a photographing lens, and the size of the image pickup means is relatively large. Since it is relatively small, a bright and high-performance optical system is required.

As a means for achieving such an optical system,
In order from the object side, a first lens group having a positive power, a second lens group having a negative power having a zooming effect, and a third lens group having a negative power which keeps an image surface constant during zooming. A four-group zoom lens including a lens group and a fourth lens group having a positive power having an image forming action is well known. However, in this type of zoom lens, it is necessary to secure an interval for moving the third lens group. And that the fourth lens group is divided into a front group that makes the divergent light flux emitted from the third lens group substantially parallel and a rear group that forms an image of the light flux, and the like, the overall lens length is large, and in recent years, It is difficult to meet the demand for miniaturization of video cameras.

Therefore, recently, a first lens unit having a positive power in order from the object side, a second lens unit having a negative power having a zooming effect, and a third lens unit having a positive power and fixed during zooming. A four-group zoom lens that has a positive power and a fourth lens group that has a positive power and that corrects a variation in image plane position due to zooming, and that focuses by moving the fourth lens group toward the object side is the mainstream. Is coming.

Known examples of this type of zoom lens include those disclosed in JP-A-62-178917, JP-A-62-215225, and JP-A-63-123009. Further, in recent years, for the purpose of downsizing the image pickup device and shooting so-called high-definition images such as high-definition images, image pickup devices having extremely small individual pixel sizes are being developed. Generally, as the pixel size of the image pickup device becomes smaller, a high resolution is required for the taking lens, and thus the demand for improvement in optical performance is increasing more and more.

As a zoom lens satisfying such requirements, Japanese Patent Laid-Open Nos. 62-153913 and 1-126 have been proposed.
Conventional examples described in Japanese Patent Laid-Open No. 614 and JP-A-6-56453 are known.

[0007]

Generally, in order to obtain high optical performance, a method of achieving it by canceling positive and negative components of the aberrations generated on the respective refracting surfaces well can be used. In the case of a lens, the way a light ray passes is greatly different for each focal length state, and the way aberrations occur on each refracting surface also differs, so it is not possible to cancel the aberrations occurring on each refracting surface for all focal lengths. Very difficult. Particularly in a zoom lens having a relatively simple structure in which the number of lens groups that contribute to zooming is relatively small, it is necessary to increase the refracting power of each lens group in order to shorten the total lens length, and therefore, it occurs on each refracting surface. Since the aberration also becomes large, it is particularly difficult to cancel the aberrations.

Particularly, in the positive / negative / positive type four-group zoom lens described above, the lens group having a negative refracting power is only the second lens group having a magnifying action, and the second lens group is required for size reduction. If the refracting power of the third lens group is increased, it becomes necessary to increase the refracting power of the third lens group or the fourth lens group, which makes it difficult to secure the back focus or to obtain high optical performance.

Therefore, in order to achieve extremely high optical performance for capturing a high-definition image, the number of lenses is increased and the light rays are refracted as little as possible as many times as possible to form an image. It is conceivable to reduce the amount of aberration generated in the above, or to cancel the aberrations by complicating the configuration of the lens group that contributes to zooming, but in both cases there was a drawback that the lens system became large. .

The conventional examples described in the above-mentioned JP-A-62-178917, JP-A-62-215225, and JP-A-63-123009 have a relatively simple lens structure, and Although it has been extremely miniaturized, its optical performance is insufficient as a taking lens for taking in high-definition images such as high-definition images.
No. 13, JP-A-1-126614, and JP-A-6-564.
Although the conventional example described in each publication of No. 53 achieves extremely high optical performance, it uses a large number of lenses and complicates the aberrations by complicating the configuration of the zoom unit. It is hard to say that we have achieved a compact lens system.

Therefore, in order to achieve miniaturization while maintaining high optical performance, it is possible to select a zoom type that is advantageous for miniaturization without complicating the lens structure, but excessively increase the refractive power of the lens group. It is desirable to achieve miniaturization by devising the configuration without strengthening. Specifically, it is possible to make the lens configuration and the shape of each lens appropriate without significantly strengthening the refracting power of the second lens group while adopting the so-called positive / negative / positive / positive four-group zoom lens described above. is important.

From this point of view, the present invention provides a compact and high-performance zoom lens by properly selecting the refractive powers of the first lens group and the second lens group, and the shapes of the lens elements constituting them. It is intended to provide a lens.

[0013]

In order to solve the above-mentioned problems, the zoom lens of the present invention has a first lens group having positive power in order from the object side, and a negative lens having a negative power on the optical axis during zooming. The second lens group that has a function of mainly distributing the zooming effect by moving the lens, the third lens group having a positive power, and the third lens group having a positive power, and moving back and forth during zooming to change the magnification. A zoom lens that includes a fourth lens group that corrects a variation in image plane position that accompanies the zoom lens and performs focusing by moving the third lens group, the fourth lens group, or a part of these lens groups. The group is composed of a negative meniscus lens whose convex surface faces the object side in order from the object side, and a positive lens group including at least one positive lens, and the second lens group has a surface having a strong curvature in order from the object side. Image side It consists of a negative lens directed to the lens, a negative lens, and a lens group in which a positive lens with the surface with the strong curvature facing the object side is arranged closest to the image side, and the following conditions are satisfied. There is.

(1) 0.13 <f _W / f ₁ <0.18 (2) −0.83 <f _W / f ₂ <−0.53 (3) 0.20 <1 / SF _1N <0 .30 (4) 0.70 <1 / SF _2N <1.30 (5) −0.80 <1 / SF _2P <−0.25 where f _W , f ₁ , f ₂ , SF _1N , SF _2N , SF _2P are the focal length of the entire lens system at the wide-angle end, the focal length of the first lens group, the focal length of the second lens group, the shaping factor of the negative meniscus lens closest to the object side of the first lens group, and the second lens, respectively. It is the shaping factor of the negative lens closest to the object in the group, and the shaping factor of the positive lens closest to the image in the second lens group.

Here, the shaping factor SF is
When the radii of curvature of the object side surface and the image side surface of the single lens are r ₁ and r ₂ , respectively, they are expressed by the following equations. SF = (r ₁ + r ₂ ) / (r ₁ −r ₂ ) The meaning of each conditional expression will be described below. Conditional expression (1),
(2) is for keeping the refractive powers of the first lens group and the second lens group at appropriate values. If the value is smaller than the lower limit of the conditional expression (1), the light flux is not sufficiently narrowed by the first lens group and is incident on the second lens group. Therefore, a large negative refractive power of the second lens group causes a large aberration. It becomes impossible to correct the large negative distortion that occurs in the second lens group at the wide angle end. If the value of Conditional Expression (1) exceeds the upper limit, it becomes difficult to secure the back focus unless the refractive power of the second lens group is excessively increased, which is not preferable.

If the value of Conditional Expression (2) exceeds the upper limit, the negative refractive power of the second lens group becomes insufficient, so that size reduction and back focus can be ensured even if other lens groups are devised. Will be difficult. If the value is smaller than the lower limit, it is advantageous for downsizing and securing the back focus.
The positive refracting power of the lens unit or the fourth lens unit must also be strengthened, which causes deterioration of various aberrations and makes it impossible to maintain high optical performance.

Further, it is desirable that the negative lens closest to the object in the first lens group satisfies conditional expression (3). Conditional expression (3) is a condition that regulates the shape of the negative lens, and if the value exceeds the upper limit, the positive astigmatism and the negative distortion become large at the wide-angle end, and the positive astigmatism becomes positive at the telephoto end. Spherical aberration and positive astigmatism are aggravated. If the value is smaller than the lower limit, the negative spherical aberration at the telephoto end becomes worse, which is not preferable.

The negative lens closest to the object side of the second lens group is conditional expression (4), and the positive lens closest to the image side is conditional expression (5).
It is desirable to satisfy Conditional expression (4) is a condition that defines the shape of the negative lens. If the value exceeds the upper limit of conditional expression (4) and has a large value, negative distortion and positive astigmatism at the wide-angle end increase, At the telephoto end, the positive astigmatism increases and the spherical aberration fluctuates greatly, which makes it difficult to correct even if another lens is used. If the value is below the lower limit of the conditional expression (4), the positive astigmatism and negative distortion at the wide-angle end, the positive spherical aberration and negative astigmatism at the telephoto end are deteriorated, which is not preferable.

Conditional expression (5) is a condition for defining the shape of the positive lens. If the value exceeds the upper limit of conditional expression (5) and has a large value, negative astigmatism at the wide-angle end and negative astigmatism at the telephoto end. It becomes difficult to correct the spherical aberration. If the value is less than the lower limit of conditional expression (5), the positive astigmatism at the wide-angle end and the positive spherical aberration at the telephoto end are deteriorated, which is not preferable. In order to keep the optical performance of the zoom lens of the present invention high, it is desirable that the following conditional expressions (1) ′ to (5) ′ are satisfied instead of the conditional expressions (1) to (5).

(1) ′ 0.13 <f _W / f ₁ <0.17 (2) ′ −0.77 <f _W / f ₂ <−0.56 (3) ′ 0.23 <1 / SF _1N <0.28 (4) '0.80 <1 / SF _2N <1.10 (5)'-0.65 <1 / SF _2P <-0.40

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) f = 9.126 to 25.454 to 71.982 F = 2.0 2ω = 49.84 ° to 17.95 ° to 6.25 ° k rd n ν 1 69.7910 2.0000 1.81264 25.43 2 41.0696 7.8005 1.57098 71.30 3 -402.1761 0.1000 4 35.8895 5.3665 1.57098 71.30 5 119.1882 (variable) 6 308.9133 1.2000 1.73234 54.68 750001.41 1.9238 591 34.269 1.500 103.81 1.56 10 23.8169 1.2000 1.51905. 11 103.2619 (variable) 12 ∞ (aperture) 1.0000 13 431.8399 12.5000 1.67279 57.33 14 -50.3196 0.1500 15 18.6805 9.8589 1.43985 94.97 16 847.0418 3.1334 17 -25.0553 1.5000 1.85504 23.78 18 -41.4964 (variable) 19 48.2049 1.5000 1.81675 22.62 20 19.111 1.7705 21 61 2.5000 1.67279 57.33 22 -49.5960 0.1500 23 17.4781 12.5000 1.69979 55.52 24 221.9526 2.0000 25 ∞ 5.0000 1.51825 64.15 26 ∞ f 9.1259 25.4540 71.9821 d5 1.5000 19.9170 30.5474 d11 30.5474 12.1320 1.5000 d18 9.6562 6.2532 10.3792 where r, d, n, and ν are the radius of curvature of each surface of the lens, the surface spacing, and The refractive index of the e-line and the Abbe number of the d-line of each lens are shown, and k is the number counted from the object side. Also, f is the focal length of the entire system, 2ω is the angle of view, and F is
Is an F number.

In this embodiment, as shown in FIG.
A first lens group G1 having a positive refractive power in order from the object side;
The second lens group G2 having a negative refracting power and monotonically moving on the optical axis during zooming and having a zooming effect, the third lens group G3 having a positive refracting power, and a positive refracting power during zooming. It is composed of a fourth lens group G4 which moves back and forth on the optical axis to correct the image plane position. Further, the first lens group G1 is composed of a negative meniscus lens having a convex surface facing the object side in order from the object side, and a positive lens group G11 consisting of two positive lenses having a surface having a strong curvature facing the object side. The second lens group G2 is composed of, in order from the object side, a negative lens having a surface having a strong curvature facing the image side, a negative lens, and a positive lens having a surface having a strong curvature facing the object side. It is composed of G21. Third lens group G3
Consists of two positive and negative lenses in order from the object side,
The fourth lens group G4 includes, in order from the object side, a negative lens and two positive lenses.

Further, in this embodiment, the fourth lens group G
4 is moved to the object side to perform focusing. By appropriately configuring the first lens group G1 and the second lens group G2, the third lens group G3 and the fourth lens group G4 have excessive aberration correction. Is not burdened with
As can be seen from the aberration diagrams shown in FIGS. 5 to 8, the performance deterioration due to focusing can be kept small.

Second Embodiment f = 9.114 to 25.428 to 71.949 F = 2.0 2ω = 49.72 ° to 17.83 ° to 6.26 ° kr d n ν 1 85.9670 2.0000 1.81264 25.43 2 48.7508 7.1493 1.57098 71.30 3 -499.7847 0.1000 4 43.3093 4.9822 1.59446 68.30 5 149.3725 (Variable) 6 417.8876 1.2000 1.73234 54.68 7 13.0492 5.1370 8 0.72 241. ) 12 ∞ (aperture) 1.0000 13 46.3648 10.3139 1.82017 46.62 14 -80.7457 6.6521 15 -13.5421 1.5000 1.59667 35.29 16 60.8714 0.1500 17 31.9859 8.0330 1.49845 81.61 18 -18.0958 (variable) 19 75.8589 2.5000 1.57098 71.30 20 -47.3959 0.1500 21 32.789230 50005000 22 -65.0876 1.4258 23 -23.7784 1.5000 1.65258 31.23 24 -47.6853 2.0000 25 ∞ 5.0000 1.51825 64.15 26 ∞ f 9.1141 25.4275 71.9494 d5 1.5000 23.6 92 37.8580 d11 37.8580 15.7186 1.5000 d18 4.3600 1.6631 5.7098 In this embodiment, as shown in FIG. 2, the third lens is different from the first embodiment. The difference is that the group includes a positive lens, a negative lens, and a positive lens in order from the object side, and the fourth lens group includes two positive lenses and a negative lens in order from the object side.

(Third Embodiment) f = 9.088 to 25.454 to 71.944 F = 2.0 2ω = 49.97 ° to 17.81 ° to 6.21 ° kr d n ν 1 85.3064 2.0000 1.81264 25.43 2 49.4318 6.9893 1.57098 71.30 3 -493.3354 0.1000 4 44.4729 5.0402 1.57098 71.30 5 159.9973 (variable) 6 534.2111 1.2000 1.60548 60.70 7 13.2125 5.5523 8 8-24.0097 1.2000 1.60548 60.70 128.2 111.00 2.5 ) 12 ∞ (aperture) 1.0000 13 -161.4478 3.5017 1.88814 40.78 14 -42.4520 9.0158 15 15.5014 2.4985 1.43985 94.97 16 2063.2815 1.3557 17 -29.4506 1.0000 1.85649 32.28 18 92.3301 (variable) 19 73.9904 6.9228 1.59446 68.30 20 -22.6637 0.1475 21 26.714662984 1.82017 22 -428.2264 1.7902 23 -29.2516 1.5000 1.85504 23.78 24 -147.2140 2.0000 25 ∞ 5.0000 1.51825 64.15 26 ∞ f 9.0879 25.4541 71.9443 d5 1.5000 23. 4931 38.4571 d11 38.4571 164634 1.5000 d18 11.0525 8.3227 12.3498 This embodiment is different from the first embodiment in the third lens as shown in FIG. The difference is that the group is composed of two positive lenses and a negative lens in order from the object side, and the fourth lens group is composed of two positive lenses and a negative lens in order from the object side. By satisfying each conditional expression also in this embodiment, it is possible to maintain high optical performance and to keep the aberration variation during focusing small.
It can be seen from the aberration diagrams shown in FIGS.

Fourth Embodiment f = 9.211 to 25.386 to 71.921 F = 2.0 2ω = 49.82 ° to 17.86 ° to 6.25 ° kr d n ν 1 74.3743 2.0000 1.81264 25.43 2 45.0025 7.4886 1.59446 68.30 3 -340.0089 0.1000 4 40.8856 4.8883 1.49845 81.61 5 120.1895 (variable) 6 286.5521 1.2000 1.57098 71.30 7 13.0951 5.6711 8418220.6424 1.2000 1.53316 62.44 114.21 329 233 0.14 ) 12 ∞ (Aperture) 1.0000 13 29.3495 10.2289 1.85649 32.28 14 -73.8500 3.4469 15 -13.7871 1.5000 1.73429 28.46 16 45.4840 0.3934 17 36.3656 5.1622 1.45720 90.31 18 -13.0126 (variable) 19 95.1415 2.5000 1.79025 50.00 20 -45.4224 1.7826 21428-17.8303 1.5000 21.00 22 -23.3514 0.1500 23 28.7447 12.5002 1.74435 52.68 24 155.6295 2.0000 25 ∞ 5.0000 1.51825 64.15 26 ∞ f 9.2105 25.3861 71.9205 d5 1.5000 21.7 37 35.2710 d11 35.2710 14.9705 1.5000 d18 5.4748 2.8562 7.0388 In this embodiment, as shown in FIG. 4, the third lens is compared with the first lens. The difference is that the group includes a positive lens, a negative lens, and a positive lens in order from the object side, and the fourth lens group includes a positive lens, a negative lens, and a positive lens in order from the object side.

It can be seen from the aberration diagrams shown in FIGS. 16 to 20 that this embodiment also maintains high optical performance by satisfying each conditional expression, and also keeps the aberration variation during focusing small. . In each of the embodiments, the flat glass arranged on the image side of the lens system is a protective glass for the image pickup surface of the solid-state image pickup device, a low-pass filter for preventing moire when photographing with an electronic image pickup device, an infrared cut filter, or the like. Is represented.

In addition to the focusing method using the fourth lens group shown in the embodiment, a focusing method of moving the third lens group along the optical axis, or a third method
A focusing method of moving only a part of the lens group or the fourth lens group can be adopted. In each embodiment, only the spherical lens is used.
If an aspherical lens is used, the configurations of the third lens group and the fourth lens group can be made simpler. Furthermore, it is clear that the optical element can be constructed by using a gradient index optical material.

[0029]

As described in detail above, according to the present invention, in a so-called positive / negative / positive / four-group zoom lens,
A video camera or a still video camera, regardless of the type of refractive power distribution of the third lens group and the fourth lens group,
In particular, it is suitable for an electronic camera using an image pickup device having a large number of pixels, which is suitable for use in capturing high-definition images in recent years, and it is possible to realize a compact and simple zoom lens.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

FIG. 5 is an aberration curve diagram at the wide-angle end according to the first embodiment of the present invention.

FIG. 6 is an aberration curve diagram at an intermediate focal length according to the first embodiment of the present invention.

FIG. 7 is an aberration curve diagram at the telephoto end according to the first embodiment of the present invention.

FIG. 8 is an aberration curve diagram for an object point distance of 1 m at the telephoto end according to the first embodiment of the present invention.

FIG. 9 is an aberration curve diagram at the wide-angle end according to the second embodiment of the present invention.

FIG. 10 is an aberration curve diagram at an intermediate focal length according to the second embodiment of the present invention.

FIG. 11 is an aberration curve diagram at the telephoto end according to the second embodiment of the present invention.

FIG. 12 is an aberration curve diagram for an object point distance of 1 m at the telephoto end according to the second embodiment of the present invention.

FIG. 13 is an aberration curve diagram at the wide-angle end according to the third embodiment of the present invention.

FIG. 14 is an aberration curve diagram at an intermediate focal length according to the third embodiment of the present invention.

FIG. 15 is an aberration curve diagram at a telephoto end according to a third embodiment of the present invention.

FIG. 16 is an aberration curve diagram for an object point distance of 1 m at the telephoto end according to the third embodiment of the present invention.

FIG. 17 is an aberration curve diagram at the wide-angle end according to the fourth embodiment of the present invention.

FIG. 18 is an aberration curve diagram at an intermediate focal length according to the fourth embodiment of the present invention.

FIG. 19 is an aberration curve diagram at a telephoto end according to a fourth embodiment of the present invention.

FIG. 20 is an aberration curve diagram for an object point distance of 1 m at the telephoto end according to the fourth embodiment of the present invention.

Claims (12)

[Claims] 1. A first lens group having a positive power in order from the object side, and a second lens having a negative power and having a function of monotonically moving along the optical axis during zooming to mainly share a zooming effect. And a third lens group having a positive power, and a fourth lens group having a positive power and moving back and forth during zooming to correct a change in image plane position due to zooming. Alternatively, in the zoom lens for performing focusing by moving the fourth lens group or a part of them, the first lens group includes a negative meniscus lens whose convex surface faces the object side in order from the object side, and at least 1 The second lens group is composed of a positive lens group consisting of one positive lens, and the second lens group has a negative lens in which the surface having a stronger curvature is directed toward the image side in order from the object side, a negative lens, and the subsequent most image side. One with a strong curvature A zoom lens comprising a lens group in which a positive lens is arranged with its surface facing the object side, and the following conditions are satisfied. _{(1) 0.13 <f W /} f 1 <0.18 (2) -0.83 <f W / f 2 <-0.53 (3) 0.20 <1 / SF 1N <0.30 ( _{4) 0.70 <1 / SF 2N} <1.30 (5) -0.80 <1 / SF 2P <-0.25 _{where, f W, f 1, f} 2, SF 1N, SF 2N, SF2P is The focal length of the entire lens system at the wide-angle end, the focal length of the first lens unit, the focal length of the second lens unit, the shaping factor of the negative meniscus lens closest to the object side of the first lens unit, and the most object of the second lens unit Is the shaping factor of the negative lens on the side of the second lens group, and the shaping factor of the positive lens on the most image side of the second lens group. Here, the shaping factor means the SF represented by the following formula, where r1 and r2 are the radii of curvature of the object-side surface and the image-side surface of the single lens, respectively. _{SF = (r 1 + r 2} ) / (r 1 -r 2) 2. The zoom lens according to claim 1, which satisfies the following condition. (1) '0.13 <f _W / f ₁ <0.17 3. A zoom lens according to claim 1, wherein the following condition is satisfied. (2) '- 0.77 <f W / f 2 <-0.56 4. The method according to claim 1, wherein
A zoom lens characterized by satisfying the following conditions. (3) '0.23 <1 / SF _1N <0.28 5. The method according to claim 1, wherein
A zoom lens characterized by satisfying the following conditions. (4) '0.80 <1 / SF _2N <1.10 6. The method according to any one of claims 1 to 5,
A zoom lens characterized by satisfying the following conditions. (5) '- 0.65 <1 / SF 2P <-0.40 7. The negative lens according to claim 6, wherein the first lens group has, in order from the object side, a negative meniscus lens having a convex surface facing the object side and two positive lenses having a surface having a strong curvature facing the object side. The second lens group comprises, in order from the object side, a negative lens having a surface having a strong curvature facing the image side, a negative lens, and a surface having a strong curvature facing the object side. A zoom lens characterized in that it is composed of a positive lens group and a lens group. 8. The third lens group according to claim 7, wherein the third lens group comprises two positive lenses and a negative lens in order from the object side,
The zoom lens, wherein the fourth lens group comprises a negative lens and two positive lenses in order from the object side. 9. The lens system according to claim 7, wherein the third lens group comprises a positive lens, a negative lens and a positive lens in order from the object side, and the fourth lens group comprises two positive lenses and a negative lens in order from the object side. A zoom lens characterized by consisting of. 10. The third lens group comprises, in order from the object side, two positive lenses and a negative lens, and the fourth lens group comprises, in order from the object side, two positive lenses and a negative lens. The zoom lens is characterized by different points. 11. The third lens group according to claim 7, comprising a positive lens, a negative lens and a positive lens in order from the object side, and the fourth lens group comprises a positive lens, a negative lens and a positive lens in order from the object side. A zoom lens characterized by consisting of. 12. The zoom lens according to claim 1, wherein focusing is performed by moving the fourth lens group toward the object side.