JP3147167B2 - Zoom lens - Google Patents

Description

The present invention relates to a zoom lens mainly used for a video camera.

[Related Art] In recent years, miniaturization, low cost, and high image quality of video cameras have been rapidly progressing. At the same time, miniaturization, cost reduction, and high resolution are also demanded for zoom lenses for video cameras.

Conventionally, a zoom lens having a high zoom ratio of 6 times or more for a video camera has a four-group configuration of positive, negative, negative, and positive from the object side. In most cases, correction was performed. However, recently, the third lens group was omitted, and the fourth lens group was divided into a front lens group and a rear lens group, and one of them was provided with an image position correcting action to reduce the number of lenses and downsize the lens system. Things have been devised. As such conventional examples, JP-A-62-206516 and JP-A-2-53017.
And others described in Japanese Patent Application Publication No.

[Problems to be Solved by the Invention] Among the above conventional examples, the former has a small zoom ratio of about 3 and a large number of members of the third lens group, so that low cost has not been achieved. In the latter, the refractive power of each group is small, and the miniaturization of the lens system is not sufficient.

An object of the present invention is to provide a high-performance zoom lens having a large zoom ratio, a small number, a small number of lenses, and a high performance.

Means for Solving the Problems A zoom lens according to the present invention has, in order from the object side, a first lens unit having a positive refractive power and fixed during zooming, and a movable first zoom lens having a negative refractive power and zooming. A second group having a zooming action, a third group having a positive refractive power and fixed during zooming, and a fourth group having a positive refractive power and movable during zooming and mainly correcting the image position. A third lens unit, wherein the third lens unit includes four or less lenses including a positive lens having a convex surface on the object side closest to the object side and at least one negative lens,
The fourth group is composed of a single positive lens or two positive lenses, and at least one of the lens surfaces of the fourth group is an aspheric surface whose refractive power becomes weaker as the distance from the optical axis increases. It is characterized by:

In the case of the lens system according to the present invention, in order to reduce the size, reduce the cost, and save the extra space, and to smoothly correct the generated aberration, the lens having the least effect is eliminated as much as possible to minimize the necessary number of lenses. It is desirable to configure with. For this purpose, the third, which mainly has an image forming action,
The arrangement of the group and the fourth group requires the most ingenuity.

In order to satisfactorily correct chromatic aberration, it is necessary to use at least one negative lens in the third and fourth units. In the present invention, the axial chromatic aberration and the lateral chromatic aberration are simultaneously corrected by disposing the negative lens in the third unit as described above. Further, the negative lens corrects negative spherical aberration. In order to reduce the size of the lens system, a sufficient refractive power should be given to the third lens unit, and the principal point of the third lens unit should be placed as far as possible. A positive lens having a convex surface on the object side is arranged on the object side,
One or three positive lenses are required. A lens larger than that is not preferable because the cost and the length of the lens system are larger than the effect.

Incidentally, if at least one surface of the positive lens in the third group is made aspherical so as to correct the spherical aberration as in the embodiment described later, it is possible to use only one positive lens.

It is desirable that the most object-side positive lens of the third group satisfies the following condition.

−1.2 <(R ₁ + R ₂ ) / (R ₁ −R ₂ ) <− 0.2 where R ₁ and R ₂ are the radii of curvature of the object-side and image-side surfaces of the positive lens closest to the object in the third group, respectively. When the lens surface is an aspherical surface, the calculation is performed using a paraxial radius of curvature.

If the lower limit of the above condition is exceeded, spherical aberration cannot be corrected, and if the upper limit is exceeded, downsizing of the lens system cannot be achieved.

Further, it is preferable that all the negative lenses in the third group are closer to the image side than all the positive lenses. The reason is preferable for miniaturization of the lens system and correction of chromatic aberration.

This third group is composed of three positive, positive, and negative lenses, or positive, positive, positive,
It is preferable to use a negative four-element configuration because the number of lenses can be reduced.

Furthermore, if the two lenses closest to the image side in the third group are composed of a positive lens with a strong convex surface facing the object side and a negative lens with a strong concave surface facing the image side, the number of lenses can be reduced.

As described above, the three groups are positive, positive, negative or positive, positive, positive, negative, and the two lenses closest to the image side have a positive lens with a strong convex surface facing the object side and a strong concave surface with a strong concave surface facing the image side. It is more desirable to use a negative lens.

In the zoom lens of the present invention, since the axial chromatic aberration and the chromatic aberration of magnification are simultaneously corrected by the negative lenses in the third group as described above, the fourth group is constituted by only the positive lens without the negative lens. Is preferred. In the present invention, in order to correct astigmatism, coma, and negative distortion generated at the wide-angle end, at least one surface in the fourth lens unit has an aspheric surface whose refractive power decreases from the optical axis toward the lens periphery. I made it. This successfully corrected various aberrations with a minimum number of lenses, and achieved downsizing of the lens system.

In the zoom lens of the present invention, if the fourth group is a focusing group, it is not necessary to provide a new movable group for focusing, and the closest shooting distance can be shortened as compared with focusing by the first group. .

EXAMPLES Next, examples of the zoom lens according to the present invention will be described.

Example 1 f = 8.76 to 65.96, F / 2.0 to F / 2.6 2ω = 50.2 ゜ to 7.2 ゜ r ₁ = 51.4795 d ₁ = 1.0000 n ₁ = 1.80518 ν ₁ = 25.43 r ₂ = 23.9639 d ₂ = 5.6000 n ₂ = 1.60311 ν ₂ = 60.70 r ₃ = -71.1147 d ₃ = 0.1500 r ₄ = 17.8414 d ₄ = 3.8000 n ₃ = 1.60311 ν ₃ = 60.70 r ₅ = 33.3216 d ₅ = D ₁ (variable) r ₆ = 37.2001 d ₆ = 1.1026 n ₄ = 1.69680 ν ₄ = 55.52 r ₇ = 7.3340 d ₇ = 2.0000 r ₈ = -10.3299 d ₈ = 1.0000 n ₅ = 1.69680 ν ₅ = 55.52 r ₉ = 9.5724 d ₉ = 2.0000 n ₆ = 1.80518 ν ₆ = 25.43 r ₁₀ = 469.3178 d ₁₀ = D ₂ (variable) r ₁₁ = ∞ (aperture) d ₁₁ = 1.5000 r ₁₂ = 7.9854 (aspheric surface) d ₁₂ = 3.5000 n ₇ = 1.69680 0 ₇ = 55.52 r ₁₃ = -37.1999 d ₁₃ = 1.8644 r ₁₄ = 42.6275 d ₁₄ = 1.2104 n ₈ = 1.805518 v ₈ = 25.43 r ₁₅ = 6.7517 d ₁₅ = D ₃ (variable) r ₁₆ = 10.1365 (aspherical surface) d ₁₆ = 3.3000 n ₉ = 1.56384 v ₉ = 60.69 r ₁₇ = -33.5763 d ₁₇ = D ₄ (variable) r ₁₈ = ∞ d ₁₈ = 5.1000 n ₁₀ = 1.54771 ν ₁₀ = 62 .83 r ₁₉ = ∞ d ₁₉ = 1.2100 r ₂₀ = ∞ d ₂₀ = 0.6000 n ₁₁ = 1.48749 ν ₁₁ = 70.20 r ₂₁ = ∞ Aspheric coefficient (Twelfth surface) E = −0.25435 × 10 ^-3 , F = − 0.14404 × 10 ⁻⁵ G = −0.46594 × 10 ⁻⁷ (Sixteenth surface) E = −0.22509 × 10 ⁻³ , F = 0.35300 × 10 ⁻⁵ G = −0.91309 × 10 ⁻⁷ f 8.76 24.04 65.96 D ₁ 1.000 9.497 _{15.916 D 2 15.916 7.420 1.000 D 3} 6.391 3.500 11.458 D 4 7.067 9.958 2.000 example 2 f = 6.49~48.90, F / 1.4~F / 2.2 2ω = 51.8 ° ～7.4 ° _{r 1 = 57.3585 d 1 = 1.0000} n 1 = 1.80518 ν ₁ = 25.43 r ₂ = 23.7370 d ₂ = 5.6000 n ₂ = 1.60311 ν ₂ = 60.70 r ₃ = -71.5301 d ₃ = 0.1500 r ₄ = 17.1706 d ₄ = 3.8000 n ₃ = 1.60311 ν ₃ = 60.70 r ₅ = 43.6355 d ₅ = D ₁ (variable) r ₆ = 1140.8303 d ₆ = 1.1026 n ₄ = 1.69680 ν ₄ = 55.52 r ₇ = 6.8647 d ₇ = 2.0000 r ₈ = −9.8125 d ₈ = 1.0000 n ₅ = 1.69680 ν ₅ = 55.52 r ₉ = 8.1232 d ₉ = 2.6000 n ₆ = 1.80518 ν ₆ = 25.43 r ₁₀ = 735.99093 d ₁₀ = D ₂ (variable) r ₁₁ = ∞ (aperture) d _{1 1 = 1.5000 r 12 = 13.4774 d} 12 = 3.4000 n 7 = 1.60311 ν 7 = 60.70 r 13 = -65.0959 d 13 = 0.3000 r 14 = 16.4183 d 14 = 2.5000 n 8 = 1.60311 ν 8 = 60.70 r 15 = 141.9059 d 15 _{= 0.3000 r 16 = 8.6800 d 16} = 2.4000 n 9 = 1.60311 ν 9 = 60.70 r 17 = 17.8996 d 17 = 0.7000 r 18 = -28.6777 d 18 = 1.2104 n 10 = 1.80518 ν 10 = 25.43 r 19 = 8.6110 d 19 = D ₃ (variable) r ₂₀ = 8.9305 (aspherical surface) d ₂₀ = 3.3000 n ₁₁ = 1.56384 ν ₁₁ = 60.69 r ₂₁ = −18.5051 d ₂₁ = D ₄ (variable) r ₂₂ = d ₂₂ = 5.1000 n ₁₂ = 1.54771 ν ₁₂ = 62.83 r ₂₃ = ∞ d ₂₃ = 1.2100 r ₂₄ = ∞ d ₂₄ = 0.6000 n ₁₃ = 1.48749 ν ₁₃ = 70.20 r ₂₅ = ∞ Aspherical coefficient E = −0.37686 × 10 ^-3 , F = −0.16869 × 10 ^-5 G = 0 f 6.49 17.82 48.90 D ₁ 1.000 9.287 14.619 D ₂ 14.619 6.332 1.000 D ₃ 6.351 3.500 6.931 D ₄ 2.580 5.431 2.000 Example 3 f = 6.49-48.90, F / 1.5-F / 2.2 2ω = 51.8 ゜- 7.4 ゜ r ₁ = 49.2800 d ₁ = 1.0000 n ₁ = 1.80518 ν ₁ = 25.43 r ₂ = 23.1 954 d ₂ = 5.2000 n ₂ = 1.60311 ν ₂ = 60.70 r ₃ = -104.9168 d ₃ = 0.1500 r ₄ = 18.4142 d ₄ = 3.7500 n ₃ = 1.60311 ν ₃ = 60.70 r ₅ = 58.6398 d ₅ = D ₁ (variable) r ₆ = 60.7724 d ₆ = 1.1026 n ₄ = 1.69680 ν ₄ = 55.52 r ₇ = 6.6301 d ₇ = 2.0000 r ₈ = −9.8199 d ₈ = 1.0000 n ₅ = 1.69680 ν ₅ = 55.52 r ₉ = 11.1626 d ₉ = 2.4000 n ₆ = 1.80518 ν ₆ = 25.43 r ₁₀ = -73.9440 d ₁₀ = D ₂ (variable) r ₁₁ = ∞ (aperture) d ₁₁ = 1.5000 r ₁₂ = 8.9570 d ₁₂ = 4.2000 n ₇ = 1.69680 ν ₇ = 55.52 r ₁₃ = _{-97.9282 d 13 = 0.8990 r 14 =} -18.4246 d 14 = 1.2000 n 8 = 1.80518 ν 8 = 25.43 r 15 = 9.9456 d 15 = 0.5000 r 16 = 16.4456 d 16 = 2.4000 n 9 = 1.69680 ν 9 = 55.52 r 17 = −31.7035 d ₁₇ = D ₃ (variable) r ₁₈ = 9.9286 (aspherical surface) d ₁₈ = 4.1000 n ₁₀ = 1.56384 ν ₁₀ = 60.69 r ₁₉ = −29.2366 d ₁₉ = D ₄ (variable) r ₂₀ = ∞d ₂₀ = 5.1000 n ₁₁ = 1.54771 ν ₁₁ = 62.83 r ₂₁ = ∞ d ₂₁ = 1.2100 r ₂₂ = ∞ d ₂₂ = 0.600 0 n ₁₂ = 1.48749 ν ₁₂ = 70.20 r ₂₃ = ∞ Aspherical surface coefficient E = −0.22999 × 10 ^-3 , F = −0.97968 × 10 ^-6 G = 0 f 6.49 17.82 48.90 D ₁ 1.300 9.552 14.895 D ₂ 15.095 6.843 1.500 D ₃ 3.764 2.500 7.591 D ₄ 6.264 7.528 2.437 Example 4 f = 6.49 to 48.89, F / 1.5 to F / 2.1 2ω = 51.8 ゜ to 7.4 ゜ r ₁ = 61.1461 d ₁ = 1.0000 n ₁ = 1.80518 ν ₁ = 25.43 r _{2 = 25.5792 d 2 = 5.2000 n} 2 = 1.60311 ν 2 = 60.70 r 3 = -82.8557 d 3 = 0.1500 r 4 = 18.9721 d 4 = 3.7500 n 3 = 1.60311 ν 3 = 60.70 r 5 = 50.8855 d 5 = D 1 ( Variable) r ₆ = 293.8083 d ₆ = 1.1026 n ₄ = 1.69680 ν ₄ = 55.52 r ₇ = 7.3631 d ₇ = 2.0000 r ₈ = -10.8606 d ₈ = 1.0000 n ₅ = 1.69680 ν ₅ = 55.52 r ₉ = 9.0391 d ₉ = _{2.4000 n 6 = 1.80518 ν 6 =} 25.43 r 10 = -479.7696 d 10 = D 2 ( variable) r ₁₁ = ∞ _{(stop) d 11 = 1.5000 r 12 =} 11.1400 d 12 = 4.2000 n 7 = 1.69680 ν 7 = 55.52 r _{13 = -43.8310 d 13 = 0.3000 r} 14 = 8.2915 d 14 = 2.4000 n 8 = 1.69680 ν 8 = 55. 52 r ₁₅ = 19.0091 d ₁₅ = 0.6044 r ₁₆ = -27.4999 d ₁₆ = 1.2104 n ₉ = 1.80518 ν ₉ = 25.43 r ₁₇ = 7.3325 d ₁₇ = D ₃ (variable) r ₁₈ = 9.6114 (aspherical surface) d ₁₈ = 4.1000 n ₁₀ = 1.56384 ν ₁₀ = 60.69 r ₁₉ = -15.3541 d ₁₉ = D ₄ (variable) r ₂₀ = ∞ d ₂₀ = 5.1000 n ₁₁ = 1.54771 ν ₁₁ = 62.83 r ₂₁ = ₂₁ d ₂₁ = 1.2100 r ₂₂ = ∞ d _{22 = 0.6000 n 12 = 1.48749 ν} 12 = 70.20 r 23 = ∞ aspherical coefficient ^{E = -0.39357 × 10 -3, F} = -0.40862 × 10 -6 G = 0 f 6.49 17.82 48.89 D 1 1.300 10.119 16.488 D 2 16.688 7.869 1.500 D ₃ 4.934 2.472 6.157 D ₄ 3.660 6.123 2.437 Example 5 f = 6.49 to 48.90, F / 1.6 to F / 2.2 2ω = 51.8 ゜ to 7.4 ゜ r ₁ = 62.6591 d ₁ = 1.0000 n ₁ = 1.80518 ν ₁ = ₁ 25.43 r ₂ = 25.66867 d ₂ = 5.2000 n ₂ = 1.60311 ν ₂ = 60.70 r ₃ = −88.1045 d ₃ = 0.1500 r ₄ = 19.1934 d ₄ = 3.7500 n ₃ = 1.60311 ν ₃ = 60.70 r ₅ = 58.7953 d ₅ = D ₁ (variable) r ₆ = -157.6505 d ₆ = 1.1026 n ₄ = 1.69680 ν ₄ = 55.52 r ₇ = 7.6914 d ₇ = 2.000 r ₈ = -13.7250 d ₈ = 1.0000 n ₅ = 1.69680 ν ₅ = 55.52 r ₉ = 8.3 911 d ₉ = 2.4000 n ₆ = 1.80518 ν ₆ = 25.43 r ₁₀ = 204.9580 d ₁₀ = D ₂ (variable) r ₁₁ = ∞ (aperture) d ₁₁ = 1.5000 r ₁₂ = 11.4645 d ₁₂ = 4.2000 n ₇ = 1.69680 ν ₇ = 55.52 r ₁₃ = -41.1109 d ₁₃ = 0.3000 r ₁₄ = 9.3876 d ₁₄ = 2.4000 n ₈ = 1.69680 ν ₈ = 55.52 r ₁₅ = 28.3293 d ₁₅ = 0.4948 r ₁₆ = −24.6734 d ₁₆ = 1.2104 n ₉ = 1.80518 ν ₉ = 25.43 r ₁₇ = 8.40553 d ₁₇ = D ₃ (variable) r ₁₈ = 24.2967 d ₁₈ = 2.0000 n ₁₀ = 1.60311 ν ₁₀ = 60.70 r ₁₉ = -36.3424 d ₁₉ = 0.1000 r ₂₀ = 10.7865 (aspheric surface) d ₂₀ = 2.000 n ₁₁ = 1.60311 ν ₁₁ = 60.70 r ₂₁ = 70.0000 d ₂₁ = D ₄ (variable) r ₂₂ = ∞ d _{22 = 5.1000 n 12 = 1.54771 ν 12} = 62.83 r 23 = ∞ d 23 = 1.2100 r 24 = ∞ d 24 = 0.6000 n 13 = 1.48749 ν 13 = 70.20 r 25 = ∞ aspherical coefficient E = -0.17524 × 10 ^-3, F = 0.70866 × 10 ⁻⁵ G = −0.23328 × 10 ⁻⁶ f 6.49 17.82 48.90 D ₁ 1.300 10.352 16.336 D ₂ 16.536 7.483 1.500 D ₃ 5.837 3.797 7.805 D ₄ 3.467 5.507 1.500 where r ₁ , r ₂ , ... is the radius of curvature of each lens surface, d ₁ , d ₂ ,… is the wall thickness and air space of each lens, n ₁ , n ₂ ,... Are the refractive indexes of the lenses, and v ₁ , v ₂ ,.

Example 1 has a lens configuration shown in FIG. 1, in which the third group is composed of a positive lens and a negative lens, or the fourth group is composed of a single positive lens, and the object-side surface (r ₁₆ ) of the fourth group is non-uniform. It is a spherical surface. The most object side surface (r ₁₂ ) of the third lens unit is also aspheric.

The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of the first embodiment are as shown in FIGS. 6, 7, and 8, respectively.

Example 2 has a configuration shown in FIG. 2, in which the third group is composed of three positive lenses and one negative lens, the fourth group is composed of a positive single lens, and the fourth group has an object-side surface (r ₂₀ ) is an aspherical surface.

The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of the second embodiment are as shown in FIGS. 9, 10, and 11, respectively.

The third embodiment has a configuration shown in FIG.
The negative lens, the positive lens, and the fourth unit are formed of a positive single lens, and the object-side surface (r ₁₈ ) of the fourth group is aspheric.

The aberrations at the wide angle end, the intermediate focal length, and the telephoto end of the third embodiment are as shown in FIGS. 12, 13, and 14, respectively.

In the fourth embodiment, the third unit includes two positive lenses and a negative lens, the fourth unit includes a single positive lens, and the fourth unit includes the object side (r _18). ) Is an aspherical surface.

The aberrations at the wide-angle end, the intermediate focal length, and the telephoto end of the fourth embodiment are as shown in FIGS. 15, 18, and 17, respectively.

The fifth embodiment has a configuration shown in FIG. 5, in which the third group is composed of two positive lenses and a negative lens, and the fourth group is composed of two positive lenses. The object-side surface (r ₂₀ ) of the lens is aspheric.

The aberrations of the fifth embodiment at the wide-angle end, at the intermediate focal length, and at the telephoto end are as shown in FIGS. 18, 19, and 20, respectively.

The shape of the aspherical surface used in these embodiments is represented by the following equation when the optical axis direction is the x axis and the direction perpendicular to the optical axis is the y axis.

Here, r is the radius of curvature of the reference spherical surface, and E, F, G,... Are aspherical surface coefficients.

[Effect of the Invention] The zoom lens of the present invention is a small lens system having a high zoom ratio, a large aperture ratio, and a small number of lenses.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 5 are cross-sectional views of Embodiments 1 to 5 of a zoom lens according to the present invention, and FIGS. 6 to 8 are Embodiment 1 respectively.
9 to 11 are aberration curve diagrams of the second embodiment, FIGS. 12 to 14 are aberration curve diagrams of the third embodiment, and FIGS. 15 to 17 are aberration curves of the fourth embodiment. 18 to 20 are graphs showing aberration curves of the fifth embodiment.

Claims (3)

(57) [Claims] 1. A first group having a positive refractive power and fixed during zooming in order from the object side, a second group having a negative refractive power and movable during zooming and having a variable power, and a positive refractive power. A third group fixed during zooming and a fourth group having a positive refractive power and movable during zooming and having the function of correcting the image position, wherein the third group is closest to the object side and has a surface on the object side. Is composed of four or less lenses including a positive lens having a convex surface and at least one negative lens.
And at least one of the lens surfaces of the fourth group is an aspheric surface whose refracting power decreases as the distance from the optical axis increases. Zoom lens that satisfies the conditions of −1.2 <(R ₁ + R ₂ ) / (R ₁ −R ₂ ) <− 0.2 where R ₁ and R ₂ are the curvatures of the object-side and image-side surfaces of the most object-side positive lens of the third lens unit, respectively. Radius (when the lens surface is an aspheric surface, it is calculated by a paraxial radius of curvature). 2. The method according to claim 1, wherein all of the negative lenses in the third group are arranged on the image side of all of the positive lenses, a positive lens, a positive lens, and a negative lens. The rearmost two of the four lenses, a positive lens and a negative lens, are composed of a positive lens with a strong convex surface facing the object side and a negative lens with a strong concave surface facing the image side. Item 1. The zoom lens according to item 1. 3. The zoom lens according to claim 1, wherein said fourth unit has a function as a focusing unit.