JP3372420B2 - Compact zoom lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens. 2. Description of the Related Art In recent years, the use of lens shutter cameras has been remarkably widespread among general users, and accordingly, the size of cameras themselves has been rapidly reduced in order to make them easier to use. On the other hand, since a conventional lens shutter camera is equipped with a wide-angle lens having a focal length of about 35 mm, there has been a strong demand for a telephoto lens capable of taking a still further image. [0003] Conventionally, a zoom lens of a type comprising a front group having a negative refractive power and a rear group having a positive refractive power and performing zooming by changing an air gap between the two groups is well known. ing. However, this type of zoom lens has a retrofocus lens system configuration, so the back focus is long, and when used for a single-lens reflex camera, there is an advantage in that a space for disposing a mirror can be secured. However, it is not suitable for shortening the overall length. [0004] On the other hand, as a zoom lens which is so small that it can be incorporated in a lens shutter camera, a zoom lens comprising a front group having a positive refractive power and a rear group having a negative refractive power is known. . This lens system is characterized by having a group configuration of a telephoto type, whereby the total length can be shortened. Japanese Patent Application Laid-Open No. 57-201213 is known as a conventional example of this type. A conventional zoom lens of this type having a zoom ratio of up to 2 is disclosed in JP-A-60-1708.
No. 16 and JP-A-61-15115 are known. Further, as a conventional example having a shape similar to the present invention, a lens system described in JP-A-58-215620 published at the time of filing, or JP-A-63-155113 published at the time of filing is disclosed. Are known. JP-A-58-2156
No. 20 is a three-group positive / negative / positive zoom type. The positive first group includes, in order from the object side, a biconvex positive lens, an aperture, a negative meniscus lens convex to the image side, and a positive meniscus lens convex to the image side. , And a biconvex positive lens. On the other hand, Japanese Patent Application Laid-Open No. 63-155113 discloses a positive / negative two-unit zoom type in which a positive first unit is a positive meniscus lens convex to the object side and a negative meniscus convex to the image side in order from the object side. It is composed of a lens, a positive meniscus lens convex to the image side with a large thickness, and a biconvex cemented positive lens.
There is no description about the aperture position. However, the zoom lenses described in JP-A-57-201213 and JP-A-58-215620 have a small zoom ratio of about 1.5 times. Also, Japanese Patent Application Laid-Open No.
In the zoom lens described in No. 1-15115, the second lens system has a long overall length and a short back focus.
The outer diameter of the lens group became large and compactness was insufficient. In each of the prior arts, the configuration of the first lens group is different from that of the present invention. Therefore, the aberration correction is not sufficient, and the ratio of the aberration variation caused by the eccentricity is large. Required and has the disadvantage of poor productivity. SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a compact zoom lens having a high zoom ratio and a good correction of aberrations. It is an object of the present invention to provide a zoom lens capable of reducing the accuracy of assembly during manufacturing by suppressing the ratio of aberration fluctuations caused by eccentricity, thereby improving productivity. A zoom lens according to the present invention that achieves the above object comprises, in order from the object side, a first lens group having a positive refractive power as a whole and a first lens group having a negative refractive power as a whole. 2
A zoom lens that has a lens group, and changes a group interval between the first lens group and the second lens group when zooming from a wide-angle end to a telephoto end. A positive meniscus first lens having a convex surface facing the object side, a negative meniscus second lens having a convex surface facing the image side, a positive meniscus third lens having a convex surface facing the image side, and a positive lens And a fourth lens. Hereinafter, the reason and operation of the above configuration in the present invention, and a more preferable configuration will be described. In the zoom lens according to the present invention, in order to simplify the lens frame structure, it is desirable that the stop position is located closest to the image side of the first lens group or in the vicinity thereof. At this time, as the off-axis principal ray approaches the first lens, the ray height increases and the amount of aberration increases. In particular, it is desirable that the first lens has a meniscus shape convex toward the object side in order to correct distortion. It is known that the second lens may be a biconcave lens, the third lens may be a biconvex lens, and the positive fourth lens may be used to correct spherical aberration and coma. However, in this shape, a large aberration of opposite sign occurs on the surface where the second lens and the third lens face each other, and these cancel each other out, so that the relative eccentricity tolerance between the second lens and the third lens is strict. Was. In the present invention, both the second lens and the third lens are formed in a meniscus shape so that the incident angle and the exit angle of the light beam are reduced, so that large aberration does not occur on these lens surfaces. Therefore, a lens system with little deterioration of aberration with respect to the eccentricity of both lenses and good assemblability is obtained. If both the second lens and the third lens have a meniscus shape with the convex surface facing the image side, it is possible to obtain a more remarkable effect of preventing the aberration from decentration. Further, in the present invention, it is desirable to move the aperture together with the first lens group in order to simplify the cam mechanism during zooming. In the present invention, while maintaining a high zoom ratio,
The power of each group is set relatively high in order to prevent the enlargement of the zoom movement amount and the size reduction. As a result, insufficient correction of spherical aberration occurs due to the increase in power from the positive first lens group. Therefore, in the present invention, taking this point into consideration, the third lens group in the first lens group is set.
It has been found that focusing on the lens and the fourth lens and making at least one surface aspherical is effective in correcting spherical aberration. An effective configuration of the aspherical surface at this time is such that the positive refractive power becomes weaker as the distance from the optical axis increases. This is because the power that is increased by the first lens group is largely borne by the third and fourth lenses, and the undercorrected spherical aberration that occurs in the first lens group is also positive by the third and fourth lenses around the lens. This is because it is effective to reduce power and make correction. The second lens group may be formed of a positive meniscus lens having a convex surface facing the image side and a negative meniscus lens having a convex surface facing the image side in order from the object side.
This is desirable in terms of making the zoom lens compact with a small number of lenses. In the second lens group, the curvature of field and distortion cannot be completely corrected by the small number of lenses, and pincushion type distortion is particularly large at the wide-angle end. For this reason, the fluctuation of the curvature of field accompanying zooming becomes large. Therefore, as a solution, it is desirable to provide at least one aspheric surface in the second lens group. The aspherical shape is effective in weakening the negative power that is increased by the negative second lens group around the lens. When the negative meniscus lens is provided on the positive meniscus lens, the positive refractive power increases as the distance from the optical axis increases. When a stronger shape is provided on the negative meniscus lens, a shape in which the negative refractive power becomes weaker as the distance from the optical axis increases is effective. The zoom lens according to the present invention has the following conditions.
A configuration that satisfies (1) and (2) is desirable. 0.6 <f _F / f _W <1.0 (1) 0.7 <| f _R | / f _W <1.1 (2) where f _F and f _R are the focal points of the first and second lens groups, respectively. distance, f _W is the focal length of the entire system at the wide-angle end. The conditions (1) and (2) show the balance between aberration performance and compactness in the first and second lens units, respectively. Exceeding the upper limit of each condition is advantageous for aberration correction, but disadvantageous for compactness. If the lower limit of each condition is exceeded, it is advantageous for downsizing, but on the contrary, it causes deterioration of aberration. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 and 2 of a zoom lens according to the present invention will be described below. Embodiment 1 has a configuration shown in FIG. 1 and is a first lens of a positive meniscus lens convex on the object side from the object side, a second lens of a negative meniscus lens convex on the image side, and a positive lens on the image side. A front group consisting of a third meniscus lens and a fourth biconvex lens, a fifth lens of a positive meniscus lens convex on the image side, and a sixth lens of a negative meniscus lens convex on the image side The fourth lens image side surface and the sixth lens object side surface are aspherical. The embodiment 2 has the structure shown in FIG. 2 and is a first lens of a positive meniscus lens convex on the object side from the object side, a second lens of a negative meniscus lens convex on the image side, and the image side. A front lens group consisting of a third positive meniscus lens and a fourth biconvex lens, a fifth positive meniscus lens convex on the image side, and a sixth negative meniscus lens convex on the image side. The fourth lens image side surface and the fifth lens object side surface are aspherical. Numerical data of each embodiment are shown below, where the symbols are r ₁ , r ₂ ... Are the radii of curvature of each lens surface, d ₁ ,
d ₂ ...... spacing between the lens surfaces, n _1, n ₂ ...... d-line refractive index of each lens, ν _1, ν ₂ ...... the Abbe number of each lens, f is the focal length of the entire system , F are F numbers and 2ω is the angle of view. The aspherical surface used in each of the above embodiments has the following formula, where Z is the optical axis direction (positive is the direction in which light travels), Y is the ray height direction, and R is the paraxial radius of curvature. Is represented by [0020] Here, K is a conical coefficient, and A, B, C, D, and E are aspherical coefficients. Example 1 f = 35 mm to 70 mm, F / 4.5 to 5.6, 2ω = 63.4 ° to 34.3 ° r ₁ = 17.237 d ₁ = 3.050 n ₁ = 1.76200 ν ₁ = 40.10 r ₂ = 21.798 d ₂ = 2.000 r ₃ = -16.868 d ₃ = 1.200 n ₂ = 1.80518 ν ₂ = 25.43 r ₄ = -97.444 d ₄ = 1.540 r ₅ = -64.823 d ₅ = 2.360 n ₃ = 1.60342 ν ₃ = 38.01 r ₆ = -32.692 d _{6 = 0.150 r 7 = 33.202 d} 7 = 3.310 n 4 = 1.57099 ν 4 = 50.80 r 8 = -18.640 ( aspheric _{surface) d 8 = 1.500 r 9 =} ∞ ( stop) d ₉ = D ₉ (variable) r ₁₀ = _{-42.314 d 10 = 3.680 n 5 =} 1.65844 ν 5 = 50.86 r 11 = -18.266 d 11 = 3.230 r 12 = -13.636 ( _{aspherical) d 12 = 1.550 n 6 =} 1.77250 ν 6 = 49.66 r 13 = -178.240 non Spherical coefficient r ₈ plane r ₁₂ plane K = -2.8245 K = -0.1497 A = 0 A = 0 B = -0.85829 × 10 ^-5 B = 0.77385 × 10 ^-5 C = 0.125565 × 10 ^-6 C = -0.79455 × 10 ^-7 D = 0.20809 x 10 ^-9 D = 0.10995 x 10 ^-8 E = -0.40616 x 10 ^-11 E = -0.13464 x 1 0 ^-11 f 35 50 70 D ₉ 15.574 6.784 0.924 f _F / f _W = 0.838, | f _R | / f _W = 0.999 | ΔF | / f _T | ΔR | / f _W = 1.232 × 10 ^-3 = 5.949 × 10 ^-3 [0022] example 2 f = 35mm~70mm, F / 4.5 ~5.6 , 2ω = 63.4 ° ~34.3 ° r 1 = 15.588 d 1 = 2.490 n 1 = 1.72000 ν 1 = 50.25 r 2 = 21.341 d ₂ = 2.200 r ₃ = -17.934 d ₃ = 1.160 n ₂ = 1.74000 ν ₂ = 28.29 r ₄ = -269.719 d ₄ = 1.560 r ₅ = -78.041 d ₅ = 2.340 n ₃ = 1.59270 ν ₃ = 35.29 r _{6 = -28.521 d 6 = 0.150 r} 7 = 34.212 d 7 = 3.280 n 4 = 1.55963 ν 4 = 61.17 r 8 = -21.168 ( aspheric _{surface) d 8 = 0.500 r 9 =} ∞ ( stop) d ₉ = D ₉ ( (Variable) r ₁₀ = -44.311 (aspherical surface) d ₁₀ = 4.200 n ₅ = 1.57135 v ₅ = 52.92 r ₁₁ = -20.542 d ₁₁ = 3.730 r ₁₂ = -12.273 d ₁₂ = 1.560 n ₆ = 1.72916 v ₆ = 54.68 r ₁₃ = -65.497 Aspherical surface coefficient r ₈ plane r ₁₀ plane K = 0 K = 0 A = 0 A = 0 B = 0.3 8523 x 10 ^-4 B = 0.29796 x 10 ^-4 C = 0.71257 x 10 ^-7 C = 0.13406 x 10 ^-6 D = 0.24412 x 10 ^-8 D = 0.19599 x 10 ^-8 E = -0.26616 x 10 ^-10 E = -0.12313 × 10 ^-10 f 35 50 70 D ₉ 14.245 6.314 1.026 f _F / f _W = 0.814, | f _R | / f _W = 0.928 | ΔF | / f _T | ΔR | / f _W = 9.529 × 10 ^-4 = 4.718 × 10 ^-3 [0023] as apparent from the above description, according to the present invention, a positive negative second lens in the first lens group and the positive third lens Are made of meniscus-shaped lenses, the tolerance for eccentricity during manufacturing can be relaxed, and manufacturing becomes easy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of Embodiment 1 of the present invention. FIG. 2 is a sectional view of a second embodiment of the present invention. FIG. 3 is a diagram illustrating spherical aberration (a), astigmatism (b), and distortion (c) at the wide-angle end according to the first embodiment of the present invention. FIG. 4 is a diagram showing spherical aberration (a), astigmatism (b), and distortion (c) at an intermediate focal length in Example 1 of the present invention. FIG. 5 is a diagram illustrating spherical aberration (a), astigmatism (b), and distortion (c) at the telephoto end according to the first embodiment of the present invention. FIG. 6 is a diagram illustrating spherical aberration (a), astigmatism (b), and distortion (c) at the wide-angle end according to the second embodiment of the present invention. FIG. 7 is a diagram showing spherical aberration (a), astigmatism (b), and distortion (c) at an intermediate focal length in Example 2 of the present invention. FIG. 8 is a diagram showing spherical aberration (a), astigmatism (b), and distortion (c) at the telephoto end in Example 2 of the present invention.

Claims (1)

(57) [Claims] In order from the object side, the zoom lens has a first lens group having a positive refractive power as a whole and a second lens group having a negative refractive power as a whole, and the first lens group and the first lens group when zooming from a wide-angle end to a telephoto end. In a zoom lens that changes a group interval with the second lens group, the first lens group sequentially has, from the object side, a positive meniscus first lens having a convex surface facing the object side, and a convex surface facing the image side.
A negative meniscus second lens with a convex surface facing the image side
A third lens having a positive meniscus shape, and a fourth lens having a positive meniscus shape.
Compact zoom lens composed of lens and lens. 2. 2. The compact zoom according to claim 1, wherein a stop is provided between the first lens group and the second lens group, and the stop moves together with the first lens group when zooming from a wide-angle end to a telephoto end. lens. 3. 3. The compact zoom lens according to claim 1, wherein at least one of the third lens and the fourth lens has an aspheric surface having a shape whose positive refractive power becomes weaker as the distance from the optical axis increases. 4. Wherein in order from the second lens group is an object side, a positive meniscus lens having a convex surface directed toward the image side, compact zoom according to claim 1, wherein composed of a negative meniscus lens having a convex surface directed toward the image side lens. 5. 5. The compact zoom lens according to claim 4, wherein the second lens group has at least one aspheric surface. 6. The zoom lens may satisfy the following conditions (1) and (2).
Claim 1 or 4 compact zoom lens according to satisfy. 0.6 <f _F / f _W <1.0 (1) 0.7 <| f _R | / f _W <1.1 (2) where f _F and f _R are the first lens group and the second lens, respectively. the focal length of the group, f _W is the focal length of the entire system at the wide-angle end.