JP3310319B2 - Two-group zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens,
In particular, the present invention relates to a two-unit zoom lens which is most suitable for a lens shutter camera or the like having no limitation on the length of the back focus and has a six-group, six-lens configuration and a variable magnification area of about 38 to 70 mm.

[0002]

2. Description of the Related Art Conventionally, as a zoom lens for a lens shutter camera, a positive / negative two-group type or a positive / positive /
Negative or negative / positive / negative three-group types are known as typical configurations.

The above two-group type has a minimum number of groups for zooming, so that the lens frame and the driving mechanism can be simplified and the number of lenses can be reduced. Therefore, many proposals have been made so far. However, the amount of movement of each lens unit tends to increase with zooming, and furthermore, the variation in aberrations with zooming is large (especially, curvature of field at an intermediate focal length). I can't say that.

On the other hand, in the three-group type, since the zoom ratio can be shared by each group, the amount of movement of each group due to zooming can be reduced, and fluctuation of aberration can be corrected well, so that a high zoom ratio can be obtained. Is suitable for However, since the number of groups is large, the lens frame structure and the driving mechanism tend to be complicated, and the number of lenses increases.

As will be described later, the present invention is intended to obtain a low-cost zoom lens using a small number of lenses and using a plastic material. If so, it is possible to achieve a lens system that meets the purpose by taking advantage of the advantages of the two-group type.

Until now, an example in which a two-group type is constituted by about six lenses has been disclosed in JP-A-62-13881.
8, JP-A-63-31224, JP-A-2-733
No. 22, JP-A-2-120714, JP-A-3-116
No. 110 etc. are known.

[0007]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 62-13 / 1987
No. 8818 and JP-A-63-31224,
The glass aspherical lens is used for aberration correction, and the performance is good. However, for glass aspheric lenses,
Although the technological progress in recent years is remarkable, it is still disadvantageous in terms of cost.

Further, Japanese Patent Application Laid-Open No. 2-73322 and
No.-120714 is entirely composed of a glass polished lens, and although the cost is improved as compared with the above-mentioned prior example, the correction of spherical aberration and coma is not sufficient.

Further, in Japanese Patent Application Laid-Open No. 3-116110, the cost is reduced by using a plastic lens in the five-group, six-lens configuration. Because of the configuration of a negative lens and a positive / negative cemented positive lens, correction of spherical aberration and coma is not sufficient. The focal length at the telephoto end is as short as 60 mm.

The present invention has been made in view of such a situation, and an object thereof is to provide an aspheric plastic lens in a two-unit zoom lens having a six-unit and six-unit configuration having a zoom range of about 38 to 70 mm. Use it to reduce costs,
It is also to provide a zoom lens with good performance.

[0011]

A two-unit zoom lens according to the present invention, which achieves the above object, comprises a first unit having a positive refractive power and a second unit having a negative refractive power. In the zoom lens that changes magnification, the first group includes, in order from the object side, a positive meniscus lens convex to the object side, a negative lens, a positive lens, and a positive lens. In order from the side, a positive meniscus lens convex on the image side and a negative meniscus lens convex on the image side are formed, and the positive meniscus lens in the second group is made of a plastic lens having an aspheric surface, and The following conditions, -1,,-
1 is satisfied. _{0.6 <f 1 / f W <} 0.9 ··· 0.6 <| f 2 / f W | <0.81 ··· -1 0.05 <| d 11 / f 2 | <0. _{4 ··· 2.0 <| f 21 /} f 2 | ··· -1 ν d21> 50 ···

In this case, it is desirable that at least one aspheric surface of the positive meniscus lens in the second group has a shape in which the positive power increases (the negative power decreases) as the distance from the optical axis increases. .

In this case, one or both surfaces of the positive meniscus lens in the second lens unit have an aspherical surface, and at least one aspherical surface has a stronger positive power as the distance from the optical axis increases (a negative power decreases). It is desirable to be configured in a shape.

[0014]

The reason and operation of the above configuration will be described below. With the above-described lens configuration, aberration correction can be performed in a well-balanced manner over the entire range from the wide-angle end to the telephoto end. In particular, by arranging two positive lenses on the image side of the negative lens in the front group, it is possible to favorably correct spherical aberration and coma. In addition, it is preferable to use a plastic lens as a convex lens in terms of correction of Petzval's sum. In this case, a plastic lens may be used for any convex lens. Is changed in the second lens unit, the problem of out-of-focus is increased, which is not preferable. Therefore, it is desirable that the positive meniscus lens in the second group be a plastic lens.

Although the first object of the present invention is to reduce the cost, it is naturally premised that the lens system is made compact. The above conditional expression is a condition for compactness. The miniaturization includes (i) shortening the overall length of the lens system, (ii) reducing the amount of movement of each group due to zooming, (ii)
i) The reduction of the lens diameter is included, and only when these are satisfied, the camera can be downsized. As described above, the overall length of the lens system is reduced by reducing the number of lens components. On the other hand, in order to reduce the moving amount and the lens diameter, it is necessary to appropriately perform the power arrangement, and a conditional expression therefor is as follows.

The focal lengths of the _first and _second units are f ₁ , f ₂ ,
Focal length, back focus,
And the imaging magnifications of the second group are f _W , f _BW , β _2W ,
Assuming that the zoom ratio is z, and the moving amounts of the _first and _second units due to zooming are Δ ₁ and Δ ₂ , respectively, f _W = f ₁ · β _2W (A) f _BW = f ₂ · (1−β _2W ) (B) Δ ₁ = (1-z) f ₂ {β _2W −1 / (z · β _2W )} (C) Δ ₂ = (1-z) f ₂ · β _2W (D)

When the value exceeds the upper limit of the conditional expression, β _2W becomes close to 1, and the back focus becomes extremely short as compared with the expression (B). As a result, not only the lens diameter of the second group becomes large, but also flare or the like due to reflection of the final lens surface and the film surface is likely to occur. If the lower limit of the conditional expression is exceeded, the power of the first lens unit becomes too strong, and the lens configuration of the present invention causes deterioration of aberration.

If the power of the second lens group is weakened beyond the upper limit of the conditional expression, the amount of movement of each lens group is increased from the expressions (C) and (D), which is not preferable. On the other hand, if the power of the second lens unit is increased beyond the lower limit of the conditional expression, good aberration correction cannot be performed with the lens configuration of the present invention.

Furthermore, when the air gap between the positive meniscus lens and the negative meniscus lens of the second group and _{d 11, 0.05 <| d 11} / f 2 | < to meet the 0.4 ... Is desirable. The conditional expression relates to the correction of astigmatism. If the interval becomes smaller than its lower limit, the occurrence of astigmatism increases on the wide side. On the other hand, if the interval exceeds the upper limit, the overall length of the lens system increases, which is not preferable.

Further, in the present invention, the positive meniscus lens in the second group is made of a plastic lens in order to reduce the influence of the change in the focal length of the plastic lens caused by the change in temperature and humidity. When the focal length of the positive meniscus lens with _{f 21, 1.5 <| f 21} / f 2 | by setting so as to satisfy the ... The condition can be further reduced temperature, the effect of humidity Therefore, it is preferable. When the Abbe number of this positive meniscus lens is ν _d21 , it is desirable to satisfy ν _d21 > 50 for chromatic aberration correction. Further, this positive meniscus lens in the second group has a degree of freedom of aberration correction by making one or both surfaces aspherical.
At least one surface is desirably an aspherical surface in which the positive power increases (the negative power decreases) as the distance from the optical axis increases.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of a two-unit zoom lens according to the present invention will be described.
3 will be described. Although lens data of each embodiment will be described later, FIG. 1 shows lens cross-sectional views of the first embodiment at the wide end (a) and the telephoto end (b). The lens cross-sectional views of the other embodiments are almost the same, and therefore will not be described.

Regarding the shape and arrangement of each lens, the first unit I of the first embodiment is composed of a positive meniscus lens L1, a biconcave lens L2, a biconvex lens L3, a biconvex lens L4, and an aperture. Positive meniscus lens L5 with a convex surface facing the negative side, negative meniscus lens L6 with a convex surface facing the image side
Consists of The second embodiment differs from the first embodiment in that the third lens L3 of the first group I is a plano-convex lens.
The third embodiment differs from the first embodiment in that the third lens L3 of the first group I is a positive meniscus lens having a convex surface facing the image side.

With respect to the aspherical surface, Embodiments 1 and 3
This is used for one surface on the object side of the positive meniscus lens L5 of the group II, and the second embodiment is used for one image-side surface of this positive meniscus lens L5.

In each embodiment, the second lens unit I
Plastic is used for the positive meniscus lens L5 of I.

In the lens data of the following Examples 1 to 3, symbols are the above, f is the focal length of the entire system, and F _NO is F
Number, 2ω is angle of view, f _B is back focus,
r _1, r ₂ ... is the radius of curvature, d _1, d ₂ ... the spacing between the lens surfaces, n _d1, n _d2 ... d-line refractive index of each lens of the lens surfaces, ν _d1, ν _d2 ... Is the Abbe number of each lens. The aspheric shape is represented by the following equation, where x is the optical axis direction and y is the direction orthogonal to the optical axis. ^{x = (y 2 / r)} / [1+ {1-P (y 2 / r 2)} 1/2] + A 4 y 4 + A 6 y 6 + A 8 y 8 where, r is a paraxial radius of curvature, P Is the conic coefficient, A ₄ , A ₆ , A ₈
Is an aspheric coefficient.

[0026] Example 1 f = 39.33 ~ 51.54 ~ 67.55 F NO = 4.66 ~ 6.10 ~ 8.00 2ω = 57.55 ° ~ 45.48 ° ~ 35.46 ° f B = 9.77 ~ 22.42 ~ 39.01 r 1 = 16.6160 d 1 = 2.5000 n d1 = _{1.69680 ν d1 = 56.49 r 2 =} 73.1490 d 2 = 1.3000 r 3 = -20.4300 d 3 = 1.2000 n d2 = 1.83400 ν d2 = 37.16 r 4 = 29.2200 d 4 = 1.7900 r 5 = 186.9680 d 5 = 3.9100 n d3 = 1.51633 _{ν d3 = 64.15 r 6 = -14.8230} d 6 = 0.1500 r 7 = 41.4470 d 7 = 2.0000 n d4 = 1.54072 ν d4 = 47.20 r 8 = -42.1360 d 8 = 0.8000 r 9 = ∞ ( stop) d ₉ = (variable ) r ₁₀ = -23.8790 (aspherical surface) d ₁₀ = 2.5000 n _d5 = 1.49241 ν _d5 = 57.66 r ₁₁ = -18.6680 d ₁₁ = 6.3200 r ₁₂ = -11.8220 d ₁₂ = 1.6000 nd ₆ = 1.72916 ν _d6 = 54.68 r ₁₃ = -36.3990 Aspherical coefficients tenth surface _{P = 0.9964 A 4 = 0.34157 ×} 10 -4 A 6 = 0.27370 × 10 -6 A 8 = 0.46638 × 10 -9 f 1 / f W = 0.729 | f 2 / f W | = 0.756 | d ₁₁ / f ₂ | = 0.213 | f ₂₁ / f ₂ | = 5.047 ν _d21 = 57.66
.

[0027]

[0028] Example 2 f = 39.33 ~ 51.54 ~ 67.55 F NO = 4.66 ~ 6.10 ~ 8.00 2ω = 57.55 ° ~ 45.48 ° ~ 35.46 ° f B = 9.86 ~ 22.69 ~ 39.51 r 1 = 16.9290 d 1 = 2.5700 n d1 = _{1.69680 ν d1 = 56.49 r 2 =} 96.5320 d 2 = 1.3000 r 3 = -21.7680 d 3 = 1.2000 n d2 = 1.83400 ν d2 = 37.16 r 4 = 30.1270 d 4 = 2.2800 r 5 = ∞ d 5 = 3.6100 n d3 = 1.48749 ν _d3 = 70.20 r ₆ = -15.0470 d ₆ = 0.1500 r ₇ = 41.4680 d ₇ = 2.0100 nd ₄ = 1.54072 ν _d4 = 47.20 r ₈ = -41.4430 d ₈ = 0.8000 r ₉ = ∞ (aperture) d ₉ = (variable) _{) r 10 = -25.0680 d 10 =} 2.5000 n d5 = 1.49241 ν d5 = 57.66 r 11 = -17.1560 ( _{aspherical) d 11 = 5.6200 r 12 =} -12.7140 d 12 = 1.6000 n d6 = 1.72916 ν d6 = 54.68 r 13 = -54.6230 zoom interval Aspherical surface eleventh surface P = 0.9285 A ₄ = −0.919934 × 10 ⁻⁴ A ₆ = −0.88594 × 10 ⁻⁷ A ₈ = −0.15156 × 10 ⁻⁸ f ₁ / f _W = 0.747 | f ₂ / f _W | _{= 0.785 | d 11 / f 2} | = 0.182 | f 21 / f 2 | = 3.239 ν d21 = 57.66

[0029] Example 3 f = 39.33 ~ 51.54 ~ 67.55 F NO = 4.66 ~ 6.10 ~ 8.00 2ω = 57.55 ° ~ 45.48 ° ~ 35.46 ° f B = 10.88 ~ 23.84 ~ 40.83 r 1 = 17.2530 d 1 = 2.4200 n d1 = _{1.69680 ν d1 = 56.49 r 2 =} 70.6770 d 2 = 1.5300 r 3 = -18.1360 d 3 = 1.2000 n d2 = 1.83400 ν d2 = 37.16 r 4 = 38.5580 d 4 = 2.0100 r 5 = -140.6470 d 5 = 2.4700 n d3 = 1.56384 ν _d3 = 60.69 r ₆ = -13.8900 d ₆ = 0.1500 r ₇ = 35.0130 d ₇ = 3.0200 nd ₄ = 1.53358 ν _d4 = 51.56 r ₈ = -43.0570 d ₈ = 0.8000 r ₉ = 絞 り (aperture) d ₉ = ( variable) r ₁₀ = -34.5070 _{(aspherical) d 10 = 3.5000 n d5 =} 1.49241 ν d5 = 57.66 r 11 = -17.2870 d 11 = 3.7400 r 12 = -11.0770 d 12 = 1.6000 n d6 = 1.72916 ν d6 = 54.68 r ₁₃ = -46.5560 zoom interval Aspherical coefficients tenth surface _{P = 1.0105 A 4 = 0.46580 ×} 10 -4 A 6 = 0.18948 × 10 -6 A 8 = 0.23569 × 10 -8 f 1 / f W = 0.723 | f 2 / f W | = 0.768 | d ₁₁ / f ₂ | = 0.124 | f ₂₁ / f ₂ | = 2.183 ν _d21 = 57.66

FIGS. 2A to 2C are diagrams showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at the wide end (a), the standard state (b), and the tele end (c) of Examples 1 to 3, respectively. As shown in FIG.

[0031]

As is clear from the above description, by satisfying the structure of the present invention, a two-unit zoom lens having a six-group, six-lens structure and a good zoom ratio of about twice can be realized at low cost. Can be achieved.

The zoom lens of the present invention is suitable for a lens shutter camera or the like.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of a two-unit zoom lens according to the present invention at a wide end (a) and a telephoto end (b).

FIG. 2 is an aberration diagram showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at a wide end (a), a standard state (b), and a tele end (c) in Example 1.

FIG. 3 is an aberration diagram similar to FIG. 2 of the second embodiment.

FIG. 4 is an aberration diagram similar to FIG. 2 of the third embodiment.

[Explanation of symbols]

 I: first lens group II: second lens group L1: first lens L2: second lens L3: third lens L4: fourth lens L5: fifth lens L6: sixth lens

Continuation of the front page (56) References JP-A-63-311224 (JP, A) JP-A-62-138818 (JP, A) JP-A-3-116110 (JP, A) JP-A-4-124607 (JP) JP-A-4-161914 (JP, A) JP-A-3-267909 (JP, A) JP-A-3-146916 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (2)

(57) [Claims] 1. A zoom lens system comprising a first group having a positive refractive power and a second group having a negative refractive power, wherein a zoom ratio is changed by changing an air gap between the two groups. The second group includes, in order from the object side, a positive meniscus lens convex to the image side and a convex meniscus lens convex to the image side. The positive meniscus lens in the second group is composed of a plastic lens having an aspherical surface , and satisfies the following conditions : -1, -1. 2 group zoom lens. _{0.6 <f 1 / f W <} 0.9 ··· 0.6 <| f 2 / f W | <0.81 ··· -1 0.05 <| d 11 / f 2 | <0. 4... 2.0 <| f ₂₁ / f ₂ |... −1 ν _d21 > 50 where the focal lengths of the first and second groups are f ₁ , f ₂ and wide, respectively. The focal length of the entire system at the end is f _W , the air gap between the positive meniscus lens and the negative meniscus lens in the second group is d ₁₁ , the focal length of the positive meniscus lens in the second group is f ₂₁ , The Abbe number of the positive meniscus lens in the second group is ν _d21 . Wherein the aspherical surface of one side even small <br/> without positive meniscus lens in the second group, a positive power becomes stronger (negative power becomes weak) as the distance from the optical axis constituted by the shape 2. The two-unit zoom lens according to claim 1, wherein: