JP2005025229A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which has an F-number of about 2.0 at a variable magnification ratio of about 8 times, is well corrected of various aberrations and is excellent in manufacturability. <P>SOLUTION: The zoom lens is a lens system consisting, successively from an object side, of a first group which has positive refractive power and is fixed at the time of variable magnification, a second group which has negative refractive power and moves back and forth on the optical axis for the purpose of variable magnification, a third group which has positive refractive power and is fixed at the time of variable magnification, a fourth group which has positive refractive power and moves back and forth on the optical axis for the purpose of correcting the movement of a focal position, and a fifth group which has negative refractive power and is fixed at the time of the variable magnification. In the above lens system, the third group or the fifth group which is fixed at the time of the variable magnification is provided with at least one aspherical surface and all the lenses of the fourth group consist of spherical surfaces. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

    The present invention relates to a zoom lens used in a video camera or the like.

    With the miniaturization of solid-state imaging devices such as CCDs, zoom lenses used in video cameras are required to have higher imaging performance. On the other hand, a further reduction in size and weight is desired also in the lens system because of the demand for downsizing of the video camera body. In general, it is known that an aspherical surface is used as a means for achieving high performance and miniaturization in a zoom lens used in a video camera. As a conventional example aiming at high performance and downsizing using an aspherical surface as described above, for example, a lens system described in JP-A-4-301612 is known. The lens system includes a positive first group, a negative second group, a positive third group, a positive fourth group, and a negative fifth group in order from the object side. A zoom lens whose group is movable. However, this conventional example uses an aspherical surface in the fourth lens group that is movable at the time of zooming, which causes high manufacturing costs due to tight tolerances.

    Further, as conventional examples of zoom lenses that do not use an aspherical surface in the group that is movable at the time of zooming, they are described in, for example, Japanese Patent Laid-Open Nos. 4-78809, 4-13109, and 4-60509. Lens systems are known. These conventional examples are composed of a positive first group, a negative second group, a positive third group, a positive fourth group, and a negative fifth group in order from the object side. The zoom lens uses an aspherical surface for the third group or the fifth group which is movable during zooming and which is fixed during zooming. However, each conventional example increases the refractive power of each group in order to reduce the size of the lens system, so various aberrations occur in each group, and these are corrected to a good level in the entire lens system. The high-performance imaging performance required with the miniaturization of a solid-state imaging device such as a CCD is not achieved.

    An object of the present invention is to achieve a zoom lens that is excellent in manufacturability with various aberrations corrected satisfactorily when the zoom ratio is about 8 times and the F number is about 2.0.

    The zoom lens of the present invention includes, in order from the object side, a first lens unit having a positive refractive power and fixed at the time of zooming, and a first lens unit having a negative refractive power and moving back and forth on the optical axis for zooming. A second group having a positive refracting power and fixed at the time of zooming, and a second group having a positive refracting power and moving back and forth on the optical axis in order to correct the movement of the focal position accompanying zooming. 4 groups and a fifth group having a negative refractive power and fixed at the time of zooming, and using at least one lens having an aspherical surface in the third group or the fifth group fixed at the time of zooming, All of the lenses constituting the fourth group that are movable at the time of zooming are spherical, and satisfy the following condition (1).

(1) −0.85 <f _W / f ₂ <−0.25
Here, f _W is the focal length of the entire lens system at the wide angle end, and f ₂ is the focal length of the second group.

    In order to achieve a compact, high-performance and highly manufacturable lens system for a zoom lens used in a video camera, in order from the object side, a first lens unit having positive refractive power and fixed at the time of zooming, and negative refraction A second group that has force and moves back and forth on the optical axis for zooming, a third group that has positive refractive power and is fixed at the time of zooming, and has positive refractive power and accompanies zooming In order to correct the movement of the focal position, the fourth group moves back and forth on the optical axis, and the fifth group has negative refractive power and is fixed at the time of zooming. The second group satisfies the condition (1). It is desirable to use at least one lens having at least one aspherical surface in the third group or the fifth group which is fixed at the time of zooming.

    In general, in order to reduce the size of the 5-group zoom lens having the above configuration, the refractive power of the second group that contributes most to zooming is increased to shorten the moving distance of the second group during zooming, or the third group. A method of enlarging the refractive power of each group thereafter to narrow the lens interval between these groups can be considered. However, when the former method, that is, when the refractive power of the second group is increased, the amount of various aberrations generated in the negative group becomes large, and it becomes difficult to achieve a high-performance lens system.

    The lens system of the present invention will be described in more detail. First, in order to achieve a compact and high-performance lens system, the first configuration of the present invention increases the negative refractive power of the second group to such an extent that various aberrations are not deteriorated, and further the refraction of each group after the third group. We thought about increasing the power and shortening the overall lens length. Condition (1) defines the range of the refractive power of the second group that can satisfactorily correct various aberrations and achieve a high-performance lens system in the lens system of the present invention. If the lower limit of −0.85 of the condition (1) is exceeded, various aberrations generated in the second group become large, and it becomes difficult to achieve a high-performance lens system. If the upper limit of −0.25 is exceeded, the refractive power of the second lens unit becomes weak and the amount of movement during zooming becomes large, making it difficult to reduce the size of the entire lens system. .

    In addition, each group after the third group has a function of a positive lens that forms an image of a divergent light beam from the second group. Therefore, when the refractive power of these groups is increased, the amount of negative spherical aberration generated in particular. It becomes difficult to achieve a high-performance lens system. Therefore, in order to correct negative spherical aberration satisfactorily, it is conceivable to use aspheric surfaces for the third and subsequent groups. If at least one surface of at least one lens of the third and subsequent lenses is aspherical, spherical aberration can be corrected well. However, considering the achievement of high-performance lens systems as in the present invention, and considering the manufacturability, the fourth group that is movable at the time of zooming among the groups after the third group is all a spherical lens without using an aspherical surface. Preferably, at least one surface of at least one lens in at least one of the third group and the fifth group that is configured and fixed during zooming is an aspherical surface. Normally, an aspherical surface has a high aberration correction effect, but the performance deterioration due to decentration increases. For this reason, if an aspherical surface is used for the movable group of the zoom lens in particular, the manufacturing tolerance of this group is affected by the eccentricity of the aspherical shape and the eccentricity of the lens itself when it is incorporated into the lens frame. Therefore, it is necessary to make the process extremely strict, and the manufacturability is remarkably deteriorated due to high cost and increase in production time. Therefore, if an aspherical surface is used for the fixed group at the time of zooming as in the lens system of the present invention, the influence of eccentricity due to the movable mechanism can be eliminated, so that the lens system manufacturing tolerance can be loosened, and the cost and manufacturing time can be reduced. It is possible to improve the manufacturability.

    Further, the lens system of the present invention has a five-group configuration, and the fourth group has a so-called compensator function for correcting a shift of the image plane position at the time of zooming. It is also possible to move the fifth group integrally. However, if the fourth group having a positive refractive power and the fifth group having a negative refractive power are integrated, the positive refractive power of the compensator becomes weaker than that in the case of only the fourth group, so that the image plane position is corrected. The amount of movement of these groups increases, resulting in a disadvantage that the total lens length becomes longer. Further, when the fourth group and the fifth group are integrated, the weight of the lens of the compensator increases, which increases the burden on the lens driving mechanism, which is not desirable for reducing the size and weight of the camera. In other words, like the lens system of the present invention, the five-group configuration instead of the four-group configuration, as described above, reduces the tolerance and improves the manufacturability, as well as reducing the size and weight. Also excellent in terms.

    Further, according to the second configuration of the present invention, in order from the object side, a first lens unit having a positive refractive power and fixed at the time of zooming, and a negative refractive power on the optical axis for zooming. A second group that moves back and forth, a third group that has positive refracting power and is fixed at the time of zooming, and an optical axis for correcting movement of the focal position that accompanies zooming with positive refracting power. A fourth group that moves back and forth, and a fifth group that has negative refractive power and is fixed at the time of zooming, and the third group includes at least one positive lens and at least one negative lens. All of the four groups are constituted by spherical lenses, and the fifth group is constituted by one negative meniscus lens having a concave surface having at least one aspherical shape facing the image side.

    In order to achieve a compact zoom lens with high performance and excellent manufacturability, as described above, it is desirable that the fourth group that is movable at the time of zooming is composed of only a spherical lens. If an aspherical surface is used for the fourth group, it is not preferable because tolerance becomes severe and it becomes difficult to achieve a high-performance lens system with excellent manufacturability.

    Further, when the refractive power of each group after the third group is increased to shorten the total lens length, in addition to the spherical aberration, the value of axial chromatic aberration generated particularly in the third group increases. Therefore, in order to correct this satisfactorily, it is desirable that the third group is composed of at least one positive lens and at least one negative lens. By using a positive lens and a negative lens, it is possible to satisfactorily correct axial chromatic aberration generated in this group. If the third unit is composed of only one positive lens, it is difficult to correct axial chromatic aberration well.

    Furthermore, it is desirable that at least one positive lens and at least one negative lens constituting the third group satisfy the following condition (2).

(2) ν _P / ν _n > 1.1
Where ν _P is the Abbe number of at least one positive lens in the third group, and ν _n is the Abbe number of at least one negative lens in the third group.

    If the condition (2) is satisfied, it is possible to satisfactorily correct the axial chromatic aberration generated in the third group. If the condition (2) is not satisfied, the axial chromatic aberration is insufficiently corrected in the third group, which is not preferable.

    In the lens systems having the above-described configurations (first and second configurations) of the present invention, coma aberration generated in the fourth group or the fifth group close to the image plane side where the off-axis ray height is relatively high. The value tends to increase. In order to satisfactorily correct this, in the lens system of the present invention, coma aberration generated in the fifth group is formed by forming the fifth group with one meniscus negative lens with the concave surface facing the image side. The value was reduced, and coma aberration generated in the fourth group was corrected by using an aspherical surface for this lens. In consideration of only aberration correction, an aspherical surface can be used for the fourth group. However, as described above, in order to loosen the manufacturing tolerance of the lens system, the fixed fifth group should be aspherical at the time of zooming. desirable.

    In order to achieve a lens system having good imaging performance while keeping the entire lens length compact in each of the above-described configurations of the lens system of the present invention, the refractive power of the first group satisfies the condition (3). Is desirable.

(3) 0.05 <f _W / f ₁ <0.22
Here, f ₁ is the focal length of the first group.

    In the lens system of the present invention, when the refractive power of the first lens unit having a positive refractive power is increased in order to shorten the total lens length, the values of off-axis aberration at the wide-angle end and axial chromatic aberration at the telephoto end tend to increase. . Therefore, in order to correct this well, it is desirable that the first group satisfies the condition (3). If the upper limit of 0.22 of the condition (3) is exceeded, the refractive power of the first group becomes large, and it is difficult to satisfactorily correct axial chromatic aberration and the like generated in this group, which is not preferable. . Further, if the lower limit of 0.05 is exceeded, the refractive power of the first group becomes weak, and it becomes difficult to make the entire lens system compact.

    In each of the above configurations of the lens system of the present invention, when an aspheric surface is used for the third group or the fifth group, the positive refractive power of the aspherical shape of at least one surface decreases from the optical axis to the periphery. Alternatively, it is desirable that the negative refractive power be strong. Particularly in each of the second and subsequent groups, negative spherical aberration that occurs due to strong positive refractive power tends to increase. To correct this by using an aspherical surface, the positive refractive power is reduced. It is necessary to make it a simple shape. An aspherical shape that increases the positive refractive power as it goes from the optical axis to the periphery is not preferable because it further promotes negative spherical aberration.

    Further, in the lens system of the present invention, it is desirable to satisfy the condition (1) in order to correct various aberrations satisfactorily. However, especially considering that the Petzval sum and distortion are corrected more satisfactorily, the condition (1) is satisfied. Instead, it is desirable to satisfy the condition (1 ′).

(1 ′) −0.65 <f _W / f ₂ <−0.35
If the upper limit of −0.35 of the condition (1 ′) is exceeded, the negative refractive power of the second group becomes too weak, making it difficult to make the lens system compact. On the other hand, if the lower limit of −0.65 is exceeded, the amount of negative Petzval sum generated in the second group becomes large, the image plane falls in a direction away from the object, and barrel distortion becomes large, which is not preferable.

    Further, in order to achieve high imaging performance in the lens system of the present invention, it is desirable to satisfactorily correct the longitudinal chromatic aberration generated in the third group. For that purpose, it is desirable to satisfy the condition (2). However, in particular, when a high zoom ratio of about 3 times or more is achieved, the condition (2 ′) is satisfied instead of the condition (2). It is desirable to do.

(2 ') ν _P / ν _n > 1.3
If the condition (2 ′) is satisfied, it is possible to satisfactorily correct the axial chromatic aberration generated in the third group and achieve high imaging performance. If the condition (2 ′) is not satisfied, the axial chromatic aberration is insufficiently corrected in the third group, which is not preferable.

    Further, if the refractive power of the first group is increased too much in order to make the lens system of the present invention compact, it is difficult to correct chromatic aberration of magnification that occurs particularly at the wide-angle end. It can be corrected to some extent by satisfying the condition (3). However, when the focal length is extended to the wide-angle end side, it is necessary to correct this more favorably. Therefore, in the lens system of the present invention, it is desirable that the condition (3 ′) is satisfied instead of the condition (3) when the angle of view on the wide angle side is about 2ω = 40 ° or more.

(3 ′) 0.07 <f _W / f ₁ <0.16
If the condition (3 ′) is satisfied, it is possible to satisfactorily correct chromatic aberration of magnification occurring in the first group. If the upper limit of 0.16 of the condition (3 ′) is exceeded, the refractive power of the first group becomes too strong, and it becomes difficult to satisfactorily correct the chromatic aberration of magnification occurring in this group. Exceeding the lower limit of 0.07 to condition (3 ′) is not preferable because the refractive power of the first lens unit becomes too weak and it becomes difficult to make the entire lens length compact.

    Further, in order to improve the manufacturability by loosening the tolerance of the lens system according to the present invention, the fourth group movable at the time of zooming is composed of a homogeneous spherical lens, and the second group movable at the time of zooming is also homogeneous. It is desirable to use a spherical lens.

    Further, in the third group where the divergent light beam from the second group is incident, the amount of negative spherical aberration generated tends to be particularly large. Therefore, it is desirable to satisfy the following condition (4) in order to correct this well.

(4) 0.08 <f _W / f ₃ <0.2
Here, f ₃ is the focal length of the third group.

    If the upper limit of 0.2 of the condition (4) is exceeded, the positive refractive power of the third group becomes too large, and it is difficult to correct negative spherical aberration well, which is not preferable. If the lower limit of 0.08 is exceeded, the refractive power of the third group becomes too weak, making it difficult to make the entire lens length compact.

    In addition, since the fourth group has an effect of imaging the light flux from the third group, it has a relatively strong positive refractive power, and furthermore, since the off-axis ray height is relatively high, the amount of coma aberration generated is large. It tends to be. Therefore, in order to correct this satisfactorily, it is desirable to satisfy the following condition (5).

_{(5) 3.2 <f t /} f 4 <5.0
However, f ₄ is the focal length, f _t of the fourth group is a focal length of the entire system at the telephoto end.

    If the upper limit of 5.0 of the condition (5) is exceeded, the positive refractive power of the fourth group becomes too large, and it is difficult to correct coma well. Further, if the lower limit of 3.2 is exceeded, the refractive power of the fourth group becomes too weak, making it difficult to make the entire lens length compact.

    In addition to increasing the positive refractive power of each of the third and subsequent groups to achieve shortening of the overall lens length, the optical system of the present invention has a negative refractive power of the second group that is not so large. Therefore, the Petzval sum tends to occur in the positive direction and the image plane tends to tilt toward the object side, but this is because the fifth lens unit is composed of one negative lens and satisfies the following condition (6): Is corrected well.

_{(6) -5.0 <f t /} f 5 <-1.0
Here, f ₅ is the focal length of the fifth group.

    If the upper limit of −1.0 of the condition (6) is exceeded, the refractive power of the fifth group becomes weak, and it becomes difficult to correct the Petzval sum well. On the other hand, if the lower limit of −5.0 is exceeded, the refractive power of the fifth unit becomes too large, and the Petzval sum becomes overcorrected, which is not preferable.

    According to the present invention, it is possible to realize a zoom lens excellent in manufacturability having a small size and high optical performance suitable for a video camera or a still video camera.

Next, embodiments of the zoom lens according to the present invention will be described based on examples. The following is data of each embodiment of the zoom lens of the present invention.
Example 1
f = 8.97-25.03-72.00, F / 2.0-2.0-2.0
2ω = 50.6 ° ～ 17.8 ° ～ 6.2 °
r ₁ = 77.1073 d ₁ = 1.8000 n ₁ = 1.85504 ν ₁ = 23.78
r ₂ = 48.6092 d ₂ = 5.4000 n ₂ = 1.62032 ν ₂ = 63.39
r ₃ = -550.6664 d ₃ = 0.1000
r ₄ = 45.2570 d ₄ = 3.8000 n ₃ = 1.45720 ν ₃ = 90.31
r ₅ = 131.6894 d ₅ = D ₁ (variable)
r ₆ = 529.1017 d ₆ = 1.0000 n ₄ = 1.62032 ν ₄ = 63.39
r ₇ = 14.4314 d ₇ = 5.3395
_{r 8 = -22.5219 d 8 = 1.0000} n 5 = 1.62032 ν 5 = 63.39
r ₉ = 62.6280 d ₉ = 0.2000
r ₁₀ = 33.9831 d ₁₀ = 2.0000 n ₆ = 1.84281 ν ₆ = 21.00
r ₁₁ = 233.4402 d ₁₁ = D ₂ (variable)
r ₁₂ = aperture d ₁₂ = 1.1000
r ₁₃ = 23.0027 (aspherical surface) d ₁₃ = 5.4399 n ₇ = 1.49845 ν ₇ = 81.61
r ₁₄ = -12.8087 d ₁₄ = 1.0000 n ₈ = 1.65425 ν ₈ = 58.52
r ₁₅ = -56.9198 d ₁₅ = D ₃ (variable)
r ₁₆ = 85.7734 d ₁₆ = 3.5883 n ₉ = 1.59446 ν ₉ = 68.30
r ₁₇ = -42.5755 d ₁₇ = 0.1000
r ₁₈ = 21.1073 d ₁₈ = 1.3831 n ₁₀ = 1.81264 ν ₁₀ = 25.43
r ₁₉ = 10.1527 d ₁₉ = 4.0868 n ₁₁ = 1.67340 ν ₁₁ = 47.25
r ₂₀ = -316.4787 d ₂₀ = D ₄ (variable)
r ₂₁ = 9.4073 (aspherical surface) d ₂₁ = 1.5087 n ₁₂ = 1.57366 ν ₁₂ = 50.80
r ₂₂ = 6.5254 d ₂₂ = 3.3484
r ₂₃ = ∞ d ₂₃ = 5.0000 n ₁₃ = 1.51825 ν ₁₃ = 64.15
r ₂₄ = ∞
Aspheric coefficient (13th surface) P = 1, A ₂ = 0, A ₄ = −0.31280 × 10 ⁻⁴
A ₆ = 0.43217 × 10 ^-7 , A ₈ = 0.23724 × 10 ^-9
(21 _{surface) P = 1, A 2 =} 0, A 4 = 0.26769 × 10 -4
A ₆ = 0.37020 × 10 ^-6 , A ₈ = 0.11006 × 10 ^-7
f 8.97 25.03 72.00
D ₁ 1.500 24.957 42.069
D ₂ 42.566 19.116 2.000
D ₃ 4.703 2.891 4.795
D ₄ 0.306 2.132 0.229
f _W / f ₂ = −0.547, ν _P / ν _n = 1.39, f _W / f ₁ = 0.125
f _W / f ₃ = 0.188, f _t / f ₄ = 3.412, f _t / f ₅ = -1.569
Example 2
f = 8.13-25.0-80.0, F / 2.0-2.0-2.0
2ω = 56.9 ° ～ 17.8 ° ～ 5.5 °
r ₁ = 88.2065 d ₁ = 1.8000 n ₁ = 1.85504 ν ₁ = 23.78
r ₂ = 59.7838 d ₂ = 5.8000 n ₂ = 1.57098 ν ₂ = 71.30
r ₃ = -550.2590 d ₃ = 0.1000
r ₄ = 56.1090 d ₄ = 3.8000 n ₃ = 1.45720 ν ₃ = 90.31
r ₅ = 155.1498 d ₅ = D ₁ (variable)
r ₆ = 819.7789 d ₆ = 1.0000 n ₄ = 1.62032 ν ₄ = 63.39
r ₇ = 22.0124 d ₇ = 6.3499
r ₈ = -29.6409 d ₈ = 1.0000 n ₅ = 1.69979 ν ₅ = 55.53
r ₉ = 29.6976 d ₉ = 0.2000
_{r 10 = 29.0354 d 10 = 2.0000} n 6 = 1.84281 ν 6 = 21.00
r ₁₁ = 146.0070 d ₁₁ = D ₂ (variable)
r ₁₂ = aperture d ₁₂ = 1.1000
r ₁₃ = 33.5424 (aspherical surface) d ₁₃ = 6.9327 n ₇ = 1.57098 ν ₇ = 71.30
r ₁₄ = -14.2380 d ₁₄ = 1.0000 n ₈ = 1.76651 ν ₈ = 40.10
r ₁₅ = -43.0482 d ₁₅ = D ₃ (variable)
r ₁₆ = 31.0185 d ₁₆ = 5.1700 n ₉ = 1.57098 ν ₉ = 71.30
r ₁₇ = -45.9716 d ₁₇ = 0.1000
r ₁₈ = 15.5957 d ₁₈ = 1.0000 n ₁₀ = 1.88814 ν ₁₀ = 40.78
r ₁₉ = 10.1763 d ₁₉ = 4.5724 n ₁₁ = 1.60520 ν ₁₁ = 65.48
r ₂₀ = 18506.0000 d ₂₀ = D ₄ (variable)
r ₂₁ = 10.7535 (aspherical surface) d ₂₁ = 1.2335 n ₁₂ = 1.88814 ν ₁₂ = 40.78
r ₂₂ = 6.3488 d ₂₂ = 7.3568
r ₂₃ = ∞ d ₂₃ = 5.0000 n ₁₃ = 1.51825 ν ₁₃ = 64.15
r ₂₄ = ∞
Aspheric coefficient (13th surface) P = 1, A ₂ = 0, A ₄ = −0.38676 × 10 ⁻⁴
A ₆ = 0.16576 × 10 ⁻⁷ , A ₈ = −0.40075 × 10 ⁻¹⁰
(21st surface) P = 1, A ₂ = 0, A ₄ = 0.14712 × 10 ⁻⁴
A ₆ = 0.16441 × 10 ^-6 , A ₈ = -0.19954 × 10 ^-9
f 8.13 25.0 80.0
D ₁ 1.500 33.071 54.549
D ₂ 55.052 23.480 2.000
D ₃ 2.707 1.397 1.977
D ₄ 0.100 1.416 0.844
f _W / f ₂ = −0.451, ν _P / ν _n = 1.78, f _W / f ₁ = 0.091
_{f W / f 3 = 0.169,} f t / f 4 = 4.685, f t / f 5 = -3.980
Example 3
f = 7.52 to 20.0 to 60.0, F / 2.0 to 2.0 to 2.0
2ω = 59.1 ° ～ 22.0 ° ～ 7.3 °
r ₁ = 137.6711 d ₁ = 1.8000 n ₁ = 1.84281 ν ₁ = 21.00
r ₂ = 66.4571 d ₂ = 5.6000 n ₂ = 1.57098 ν ₂ = 71.30
r ₃ = -271.6983 d ₃ = 0.1000
r ₄ = 48.4907 d ₄ = 4.0000 n ₃ = 1.75844 ν ₃ = 52.33
r ₅ = 131.0602 d ₅ = D ₁ (variable)
r ₆ = 126.7542 d ₆ = 1.0000 n ₄ = 1.62032 ν ₄ = 63.39
r ₇ = 15.7517 d ₇ = 6.9076
r ₈ = -49.1898 d ₈ = 1.0000 n ₅ = 1.57098 ν ₅ = 71.30
r ₉ = 49.7962 d ₉ = 0.2000
_{r 10 = 25.1187 d 10 = 2.0000} n 6 = 1.85504 ν 6 = 23.78
r ₁₁ = 92.7708 d ₁₁ = 2.9512
r ₁₂ = -31.6994 d ₁₂ = 2.0000 n ₇ = 1.62032 ν ₇ = 63.39
r ₁₃ = 85.3332 d ₁₃ = D ₂ (variable)
r ₁₄ = aperture d ₁₄ = 1.1000
r ₁₅ = 22.2995 (aspherical surface) d ₁₅ = 4.1553 n ₈ = 1.57098 ν ₈ = 71.30
r ₁₆ = −20.1628 (aspherical surface) d ₁₆ = 1.0629
r ₁₇ = -15.8936 d ₁₇ = 1.0000 n ₉ = 1.82017 ν ₉ = 46.62
r ₁₈ = -79.7583 d ₁₈ = D ₃ (variable)
r ₁₉ = 62.6218 d ₁₉ = 3.7459 n ₁₀ = 1.82017 ν ₁₀ = 46.62
r ₂₀ = -31.3011 d ₂₀ = 0.1000
r ₂₁ = 18.4299 d ₂₁ = 1.0000 n ₁₁ = 1.81264 ν ₁₁ = 25.43
r ₂₂ = 10.3448 d ₂₂ = 4.9146 n ₁₂ = 1.62032 ν ₁₂ = 63.39
r ₂₃ = -169.8183 d ₂₃ = D ₄ (variable)
r ₂₄ = 9.5808 (aspherical surface) d ₂₄ = 1.4502 n ₁₃ = 1.69417 ν ₁₃ = 31.08
r ₂₅ = 6.0393 d ₂₅ = 5.3543
r ₂₆ = ∞ d ₂₆ = 5.0000 n ₁₄ = 1.51825 ν ₁₄ = 64.15
r ₂₇ = ∞
Aspheric coefficient (fifteenth surface) P = 1, A ₂ = 0, A ₄ = −0.445410 × 10 ⁻⁴
A ₆ = 0.10984 × 10 ⁻⁷ , A ₈ = −0.15415 × 10 ⁻⁸
(Sixteenth surface) P = 0, A ₂ = 0, A ₄ = −0.17051 × 10 ⁻⁴
A ₆ = -0.33448 × 10 ^-10 , A ₈ = -0.21172 × 10 ^-8
(24th surface) P = 1, A ₂ = 0, A ₄ = −0.44752 × 10 ⁻⁷
A ₆ = -0.14270 × 10 ^-7 , A ₈ = -0.39118 × 10 ^-8
f 7.52 20.0 60.0
D ₁ 1.500 22.830 39.341
D ₂ 39.842 18.512 2.000
D ₃ 3.039 1.601 1.713
D ₄ 0.100 1.535 1.423
f _W / f ₂ = −0.523, ν _P / ν _n = 1.53, f _W / f ₁ = 0.106
f _W / f ₃ = 0.118, f _t / f ₄ = 4.009, f _t / f ₅ = -2.122
Example 4
f = 8.16-20.07-56.0, F / 2.8-2.8-2.8
2ω = 55.5 ° to 22.2 ° to 7.9 °
r ₁ = 98.8042 d ₁ = 1.6000 n ₁ = 1.85504 ν ₁ = 23.78
r ₂ = 54.8396 d ₂ = 5.5000 n ₂ = 1.57098 ν ₂ = 71.30
r ₃ = -213.9098 d ₃ = 0.2000
r ₄ = 37.2379 d ₄ = 4.0000 n ₃ = 1.57098 ν ₃ = 71.30
r ₅ = 95.3887 d ₅ = D ₁ (variable)
r ₆ = 148.7751 d ₆ = 1.0000 n ₄ = 1.62032 ν ₄ = 63.39
r ₇ = 15.5841 d ₇ = 5.6681
r ₈ = -55.3588 d ₈ = 1.0000 n ₅ = 1.59446 ν ₅ = 68.30
r ₉ = 49.9381 d ₉ = 0.2000
r ₁₀ = 23.8741 d ₁₀ = 2.0000 n ₆ = 1.85504 ν ₆ = 23.78
r ₁₁ = 92.6110 d ₁₁ = 2.9929
_{r 12 = -27.3377 d 12 = 1.0000} n 7 = 1.62032 ν 7 = 63.39
r ₁₃ = 73.8028 d ₁₃ = D ₂ (variable)
r ₁₄ = diaphragm d ₁₄ = 1.000
r ₁₅ = 19.7703 d ₁₅ = 3.8956 n ₈ = 1.59446 ν ₈ = 68.30
r ₁₆ = -23.0023 (aspherical surface) d ₁₆ = 0.7798
r ₁₇ = -15.3244 d ₁₇ = 1.0000 n ₉ = 1.83945 ν ₉ = 42.72
r ₁₈ = -85.7764 d ₁₈ = D ₃ (variable)
r ₁₉ = 63.9107 d ₁₉ = 3.3787 n ₁₀ = 1.79196 ν ₁₀ = 47.38
r ₂₀ = -25.2681 d ₂₀ = 0.2000
r ₂₁ = 20.3710 d ₂₁ = 3.8509 n ₁₁ = 1.62032 ν ₁₁ = 63.39
r ₂₂ = -12.0220 d ₂₂ = 1.0000 n ₁₂ = 1.70605 ν ₁₂ = 30.11
r ₂₃ = -93.5290 d ₂₃ = D ₄ (variable)
r ₂₄ = 9.8017 (aspherical surface) d ₂₄ = 1.8000 n ₁₃ = 1.67158 ν ₁₃ = 33.04
r ₂₅ = 5.8851 d ₂₅ = 5.1300
r ₂₆ = ∞ d ₂₆ = 5.0000 n ₁₄ = 1.51825 ν ₁₄ = 64.15
r ₂₇ = ∞
Aspheric coefficient (16th surface) P = 1, A ₂ = 0, A ₄ = 0.43220 × 10 ⁻⁴
A ₆ = -0.15285 × 10 ^-7 , A ₈ = -0.35514 × 10 ^-8
(24th surface) P = 1, A ₂ = 0, A ₄ = 0.13948 × 10 ⁻⁴
A ₆ = -0.18048 × 10 ^-6 , A ₈ = 0.11347 × 10 ^-8
f 8.16 20.07 56.0
D ₁ 1.500 18.955 33.529
D ₂ 34.022 16.570 2.000
D ₃ 2.545 1.301 1.662
D ₄ 0.200 1.436 1.065
f _W / f ₂ = −0.592, ν _P / ν _n = 1.60, f _W / f ₁ = 0.127
_{f W / f 3 = 0.116,} f t / f 4 = 4.061, f t / f 5 = -2.082
However r _1, r _2, ··· the radius of curvature of each lens surface, d _1, d _2, ··· wall thickness and lens distance of each lens, n _1, n _2, ··· are of the lenses The refractive index of e-line, ν ₁ , ν ₂ ,... is the Abbe number of each lens.

    Among the above-described embodiments, the first embodiment is configured as shown in FIG. 1 and has a first group G1 having a positive refractive power which is fixed at the time of zooming, and has a negative refractive power on the optical axis at the time of zooming. The second group G2 having a zooming action by moving to the third group, the third group G3 having a positive refractive power that is fixed at the time of zooming, and an image that has a positive refractive power and is movable at the time of zooming and is accompanied by the zooming The fourth group G4 has an effect of correcting the displacement of the surface position, and the fifth group G5 has a negative refractive power and is fixed at the time of zooming.

    The first group G1 includes, in order from the object side, a negative lens, a positive lens, and a positive lens. The first group G1 has an action of narrowing the light beam on the on-axis object point and an action of guiding the light beam emitted from the off-axis object point to the second group G2. The second group G2 includes a negative lens, a negative lens, and a positive lens in order from the object side, and has a zooming action by moving from the object side to the image side when zooming from the wide-angle end to the telephoto end. The third group G3 includes a positive lens and a negative lens in order from the object side, and has a function of fixing a divergent light beam from the second group to a substantially afocal light beam at the time of zooming. The fourth group G4 includes a positive lens, a negative lens, and a positive lens in order from the object side. The fourth group G4 is movable at the time of zooming and has an effect of correcting a focal position shift caused by zooming. The fifth group G5 is composed of one negative meniscus lens that is fixed at the time of zooming and has a concave surface directed toward the image side.

    Further, by using a cemented lens of a negative lens and a positive lens in the first group G1, the lateral chromatic aberration at the wide-angle end and the axial chromatic aberration at the telephoto end are corrected well.

    Further, by using a cemented lens of a positive lens and a negative lens that satisfies the condition (2) in the third group G3, axial chromatic aberration generated in this group is corrected well.

    Also generated in this group by using an aspherical surface whose positive refractive power becomes weaker from the optical axis toward the periphery on the object side surface of the lens closest to the object side of the third lens group G3 fixed at the time of zooming This makes it possible to satisfactorily correct negative spherical aberration. Further, the fourth group G4 is composed entirely of spherical lenses, which is advantageous in that performance degradation due to group eccentricity during zooming is reduced. Further, the object side surface of the fifth group G5 which is fixed at the time of zooming and whose ray height of the off-axis light beam is relatively high is made an aspherical shape, and in particular, off-axis aberrations can be favorably corrected.

The aspheric shape used in each example is represented by the following formula.

In the above equation, the x axis is taken in the optical axis direction, the y axis is taken in the direction perpendicular to the optical axis, r is the radius of curvature on the optical axis, A _2i is the aspheric coefficient, and p is the conic constant.

    In the zoom lens of Example 1, it is desirable to move the fourth group G4 when focusing on an object point at a close distance. In the lens system of the present invention, the fourth group G4 is movable at the time of zooming and does not use an aspherical surface in order to prevent performance deterioration due to decentration. If this group is a focusing group, performance degradation due to group eccentricity during focusing can be reduced. Furthermore, since it is not necessary to provide a new drive mechanism, the configuration is advantageous in terms of reduction in size and weight.

    The aberration status of Example 1 is as shown in FIGS. 5, 6, and 7. It can be seen that the lens system of the present invention achieves very high optical performance.

    Example 2 is a lens system configured as shown in FIG. 2, and in order from the object side is a positive first group G1, a negative second group G2, a positive third group G3, a positive fourth group G4, It consists of a negative fifth group G5, and the second group G2 and the fourth group G4 are movable at the time of zooming, and the operation of each group is almost the same as in the first embodiment. Example 2 is an example in which the zoom ratio is 10 times, which is higher than that of Example 1.

    The first group G1 is composed of a negative lens, a positive lens, and a positive lens in order from the object side, the second group G2 is composed of a negative lens, a negative lens, and a positive lens in order from the object side, and the third group G3 is from the object side. The fourth group G4 is composed of a positive lens and a negative lens in this order. The fourth group G4 is composed of a positive lens, a negative lens, and a positive lens in order from the object side. The fifth group G5 is a negative meniscus lens that is fixed and has a concave surface facing the image side during zooming. It consists of one sheet. The aspherical surface is used for the third group G3 and the fifth group G5 which are fixed at the time of zooming.

    In Example 2, although the zoom ratio is 10 times and the high zoom ratio, various aberrations can be favorably corrected by satisfying the respective conditions of the present invention.

    The aberration status of Example 2 is as shown in FIGS. 8, 9, and 10. It can be seen that the lens system of the present invention achieves very high optical performance.

    FIG. 3 is a lens sectional view of a third embodiment of the zoom lens according to the present invention. The third embodiment is configured as shown in FIG. 3, and in order from the object side is a positive first group G1, a negative second group G2, a positive third group G3, a positive fourth group G4, a negative The second group G2 and the fourth group G4 are movable at the time of zooming, and the operation of each group is substantially the same as in the first embodiment. The third embodiment is an example in which a wider angle of view is achieved by further shortening the focal length at the wide-angle end as compared with the first and second embodiments.

    The first group G1 is composed of a negative lens, a positive lens, and a positive lens in order from the object side, the second group G2 is composed of a negative lens, a negative lens, a positive lens, and a negative lens in order from the object side, and the third group G3 is The fourth group G4 consists of a positive lens, a negative lens, and a positive lens in order from the object side, and the fifth group G5 is fixed at the time of zooming and has a concave surface facing the image side. This is composed of one meniscus lens. When the focal length at the wide-angle end is shortened, negative distortion that occurs particularly at the wide-angle end becomes a problem. In the third embodiment, since the second group G2 includes three negative lenses, the negative refracting power can be distributed to each lens and the negative distortion generated in this group can be corrected well. It is said. In addition, the aspherical surface is used for the third group G3 and the fifth group G5 which are fixed at the time of zooming. Unlike the first embodiment, the third group G3 separates the positive lens and the negative lens without using a cemented lens. Further, it is possible to correct various aberrations more favorably by making both surfaces aspherical.

    The aberration situation of Example 3 is as shown in FIGS. 11, 12, and 13. It can be seen that the lens system of the present invention achieves very high optical performance.

    Example 4 is a lens system as shown in FIG. 4, and in order from the object side is a positive first group G1, a negative second group G2, a positive third group G3, a positive fourth group G4, It consists of a negative fifth group G5, and the second group G2 and the fourth group G4 are movable at the time of zooming, and the operation of each group is almost the same as in the first embodiment. Example 4 is an example in which the refractive power of each group is strengthened to reduce the total length of the lens.

    The first group G1 is composed of a negative lens, a positive lens, and a positive lens in order from the object side, the second group G2 is composed of a negative lens, a negative lens, a positive lens, and a negative lens in order from the object side, and the third group G3 is The fourth group G4 consists of a positive lens, a positive lens and a negative lens in order from the object side, and the fifth group G5 is fixed at the time of zooming and has a concave surface facing the image side. This is composed of one meniscus lens. Further, aspheric surfaces are used for the third group G3 and the fifth group G5 which are fixed during zooming.

    The amount of aberration in each group increases because the refractive power of each group is increased to shorten the overall lens length, but various aberrations can be corrected satisfactorily by satisfying the conditions of the present invention. It is said.

    The aberration status of Example 4 is as shown in FIGS. 14, 15, and 16, and it can be seen that the lens system of the present invention achieves very high optical performance.

    In the present invention, the zoom lens described in each of the following items in addition to the zoom lens described in the claims achieves the object of the present invention.

  (1) A zoom lens satisfying the following condition (1) in the lens system according to claim 2 of the claims.

(1) -0.85 <f _W / f ₂ <-0.25
(2) A zoom lens system that satisfies the following condition (2) in the lens system described in claim 1 or 2 of the claims or the item (1).

(2) ν _p / ν _n > 1.1
(3) A zoom lens satisfying the following condition (3) in the lens system described in the first or second aspect of the claims or the (1) or (2).

(3) 0.05 <f _W / f ₁ <0.22
(4) In the lens system described in the first or second item of the claims or the item (1), (2) or (2), the following condition (1) is used instead of the condition (1): Zoom lens that satisfies').

(1 ′) −0.65 <f _W / f ₂ <−0.35
(5) A zoom lens that satisfies the following condition (2 ′) in place of condition (2) in the lens system described in (2) above.

(2 ′) ν _p / ν _n > 1.3
(6) A zoom lens that satisfies the condition (3 ′) in place of the condition (3) in the lens system described in the item (3).

(3 ′) 0.07 <f _W / f ₁ <0.16
(7) A zoom lens system that satisfies the following condition (4) in the lens system described in (3) above.

(4) 0.08 <f _W / f ₃ <0.2
(8) A zoom lens system that satisfies the following condition (5) in the lens system described in (7) above.

_{(5) 3.2 <f t /} f 4 <5.0
(9) A zoom lens satisfying the following condition (6) in the lens system described in the item (8).

_{(6) -5.0 <f t /} f 5 <-1.0

The figure which shows the lens structure of Example 1 of this invention. The figure which shows the lens structure of Example 2 of this invention. The figure which shows the lens structure of Example 3 of this invention. The figure which shows the lens structure of Example 4 of this invention. Aberration diagram at the wide-angle end of Example 1 of the present invention Aberration diagram at intermediate focal length in Example 1 of the present invention Aberration diagram at the telephoto end according to the first embodiment of the present invention. Aberration diagram at the wide-angle end of Example 2 of the present invention Aberration diagram at intermediate focal length in Example 2 of the present invention Aberration diagram at the telephoto end according to the second embodiment of the present invention. Aberration diagram at the wide-angle end of Example 3 of the present invention Aberration diagram at intermediate focal length in Example 3 of the present invention Aberration diagram at telephoto end of Embodiment 3 of the present invention Aberration diagram at the wide-angle end of Example 4 of the present invention Aberration diagram at intermediate focal length in Example 4 of the present invention Aberration diagram at the telephoto end according to the fourth embodiment of the present invention.

Claims (2)

In order from the object side, a first group having positive refractive power and fixed at the time of zooming, a second group having negative refractive power and moving back and forth on the optical axis for zooming, and positive refraction A third group that has power and is fixed at the time of zooming, a fourth group that has positive refractive power and moves back and forth on the optical axis in order to correct the movement of the focal position accompanying zooming, and negative refraction A fifth lens group having a force and fixed at the time of zooming is used, and at least one lens having at least one aspherical surface is used in the third group or the fifth lens group fixed at the time of zooming. A zoom lens characterized in that the lenses constituting the four groups are all spherical and satisfy the following condition (1).
(1) −0.85 <f _W / f ₂ <−0.25
Here, f _W is the focal length of the entire lens system at the wide angle end, and f ₂ is the focal length of the second group. In order from the object side, a first group having positive refractive power and fixed at the time of zooming, a second group having negative refractive power and moving back and forth on the optical axis for zooming, and positive refraction A third group that has power and is fixed at the time of zooming, a fourth group that has positive refractive power and moves back and forth on the optical axis in order to correct the movement of the focal position accompanying zooming, and negative refraction The third group is composed of at least one positive lens and at least one negative lens, the fourth group is composed entirely of a spherical surface, A zoom lens comprising at least one negative meniscus lens having an aspheric concave surface facing the image side.

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