JPH05232382A - Two-group zoom lens - Google Patents

Abstract

PURPOSE:To reduce cost and to improve even the performance by using an aspherical plastic lens the two-group zoom lens of six-group and six-element constitution which has an about 38-70mm power variation range. CONSTITUTION:The zoom lens consists of a 1st positive group I and a 2nd negative group II and varies in power by varying the air interval between both the group. The 1st group consists of a positive meniscus lens L1 which is convex to the object side, a negative lens L2, a positive lens L3, and a positive lens L4 and the 2nd group consists of a positive meniscus lens L5 which is convex to the image side and a negative meniscus lens L6 which is convex to the image side; and L5 is composed of a plastic lens with an aspherical surface, and 0.6<f1/fW<0.9 and 0.6<¦f2/fW¦<0.9 hold, where f1 and f2 are the focal lengths of the 1st and 2nd groups and fW is the focal length of the whole system at the wide-angle end.

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-group zoom lens, which is most suitable for a lens shutter camera or the like having no limitation on the back focus length, has a lens structure of six groups and six lenses, and has a variable power region of about 38 to 70 mm.

[0002]

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

The above-mentioned two-group type has a minimum number of groups for zooming, so that the lens frame and drive 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 group tends to increase with zooming, and the aberration variation with zooming is large (especially, the field curvature at the intermediate focal length), which is suitable for high zoom ratios. You can say that you haven't.

On the other hand, in the 3-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 fluctuations in aberration can be corrected well, so that a high zoom ratio is achieved. Suitable for However, due to the large number of groups, the lens frame structure and the driving mechanism tend to be complicated, and the number of lenses also increases.

As will be described later, the present invention is intended to obtain a low-cost zoom lens with a small number of lenses and using a plastic material. However, the zoom ratio is about 2 times. If so, it is possible to achieve the objective lens system by taking advantage of the two-group type.

As an example of a two-group type having about six lenses, there has been disclosed in Japanese Patent Laid-Open No. 62-13881.
No. 8, JP-A-63-311224, and JP-A-2-733.
No. 22, JP-A-2-120714, JP-A-3-116.
Things such as 110 are known.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
8818 and JP-A-63-311224,
A glass aspherical lens is used for aberration correction, and the performance is good. However, for glass aspherical lenses,
Although the technological progress in recent years is remarkable, it is still disadvantageous in terms of cost.

Further, JP-A-2-73322 and JP-A-2-73322
No. -120714 is composed of a glass-polished lens, and although the cost is improved as compared with the preceding example, correction of spherical aberration and coma is not sufficient.

Further, in Japanese Patent Laid-Open No. 3-116110, the cost is reduced by using a plastic lens in a 5-group, 6-lens structure. However, the structure of the first group having a positive refractive power is a positive lens, Since it has a negative lens and a positive / negative cemented positive lens, correction of spherical aberration and coma is not sufficient. Moreover, 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 aspherical plastic lens in a two-group zoom lens having a six-group, six-lens structure having a variable power range of about 38 to 70 mm. Use to reduce costs,
The objective is to provide a zoom lens with good performance.

[0011]

A two-group zoom lens of the present invention which achieves the above object is composed of a first group having a positive refracting power and a second group having a negative refracting power. In the zoom lens that changes the magnification by changing, the first group is composed of, 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, and the second group is the object. In order from the side, the positive meniscus lens having a convex surface on the image side and the negative meniscus lens having a convex surface on the image side are formed, and the positive meniscus lens in the second group is made of a plastic lens having an aspherical surface, and When the focal lengths of the first group and the second group are f ₁ and f ₂ , respectively, and the focal length of the entire system at the wide end is f _W , 0.6 <f ₁ / f _W <0.9 ... 0 .6 <| f ₂ / f _W | <0.9 ...

In this case, when the air gap between the positive meniscus lens and the negative meniscus lens in the second group is d ₁₁ , 0.05 <| d ₁₁ / f ₂ | <0.4 ... It is desirable to satisfy

Further, when the focal length of the positive meniscus lens in the second lens unit is f ₂₁ , it is desirable that 1.5 <| f ₂₁ / f ₂ |

[0014]

The function and operation of the above configuration will be described below. With the above lens configuration, it is possible to perform well-balanced aberration correction over the entire range from the wide end to the tele end. In particular, by disposing 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 for the convex lens in terms of Petzval sum correction, and as long as this is the case, any convex lens may be used, but when used in the front group, the plastic lens due to changes in temperature and humidity Since the change in the focal length of No. 2 is magnified in the second lens group, the problem of focus shift becomes large, which is not preferable. Therefore, it is desirable that the positive meniscus lens in the second group is a plastic lens.

The first object of the present invention is to reduce the cost, but it goes without saying that the lens system is made compact. The above conditional expression is a condition for compactification. The contents of the compactness are (i) shortening the total 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 the miniaturization of the camera is achieved only when these are satisfied. The shortening of the total length of the lens system is improved by reducing the number of lens components as described above. On the other hand, in order to reduce the movement amount and reduce the lens diameter, it is necessary to properly perform power allocation, and the conditional expressions therefor are and.

The focal lengths of the _first and _second lens units are f ₁ , f ₂ ,
The focal length of the entire system at the wide end, back focus,
And the image forming magnifications of the second group are f _W , f _BW , β _2W , and
Assuming that the zoom ratio is z and the movement amounts of the first group and the second group 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 The relationship is ₂ · β _2W (D).

When the upper limit of the conditional expression is exceeded, β _2W becomes close to 1, and the back focus becomes extremely shorter than the expression (B). As a result, not only the lens diameter of the second lens group becomes large, but also flare and the like due to the reflection of the final lens surface and the film surface are likely to occur. On the other hand, if the lower limit of the conditional expression is not reached, the power of the first lens unit will become too strong, and the lens configuration of the present invention will lead to deterioration of aberration.

Further, if the power of the second lens unit becomes weaker than the upper limit of the conditional expression, the amount of movement of each lens group becomes large according to the expressions (C) and (D), which is not preferable. On the other hand, if the power of the second lens unit becomes strong beyond the lower limit of the conditional expression, the aberration of the lens of the present invention cannot be corrected well.

Further, when the air gap between the positive meniscus lens and the negative meniscus lens in the second lens unit is d ₁₁ , 0.05 <| d ₁₁ / f ₂ | <0.4 ... Is desirable. The conditional expression relates to the correction of astigmatism, and if the interval becomes narrower than its lower limit, the generation of astigmatism becomes large on the wide side. If the distance exceeds the upper limit and the distance becomes wide, the total length of the lens system becomes large, which is not preferable.

Further, in the present invention, the positive meniscus lens in the second group is made into a plastic lens in order to reduce the influence of the change in the focal length of the plastic lens due to the change in temperature and humidity. When the focal length of this positive meniscus lens is f ₂₁ , it is possible to further reduce the influence of temperature and humidity by setting the conditional expression 1.5 <| f ₂₁ / f ₂ | Therefore, it is preferable. Further, when the Abbe number of this positive meniscus lens is ν _d21 , it is desirable to satisfy ν _d21 > 50 ... In terms of chromatic aberration correction. Further, the positive meniscus lens in the second group has a degree of freedom of aberration correction by making one surface or both surfaces aspherical. At this time,
At least one surface is preferably an aspherical surface having a shape in which the positive power becomes stronger (the negative power becomes weaker) with distance from the optical axis.

[0021]

EXAMPLES Example 1 of the second group zoom lens according to the present invention will be described below.
4 will be described. Although the lens data of each embodiment will be described later, FIG. 1 shows a lens cross-sectional view at the wide end (a) and the tele end (b) of the first embodiment. The lens cross-sectional views of the other examples are substantially the same, and therefore omitted.

Regarding the shape and arrangement of each lens, the first group 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 a diaphragm, and a second group II is an image. Positive meniscus lens L5 with the convex surface facing the image side, negative meniscus lens L6 with the convex surface facing the image side
Consists of. Examples 2 and 3 are the third lens L3 of the first group I.
Differs from Example 1 in that is composed of a plano-convex lens, and Example 4
Differs from Example 1 in that the third lens L3 of the first group I is a positive meniscus lens having a convex surface facing the image side.

As for the aspherical surface, the first and fourth embodiments are the second one.
The positive meniscus lens L5 of the group II is used for one surface on the object side, the second embodiment is used for two surfaces on both sides of the positive meniscus lens L5, and the third embodiment is for the positive meniscus. It is used for the first surface on the image side of the lens L5.

In any embodiment, the second group I
The positive meniscus lens L5 of I is made of plastic.

In the following lens data of Examples 1 to 4, the 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 ... Radius of curvature of each lens surface, d ₁ , d ₂ ... Spacing between lens surfaces, n _d1 , n _d2 ..., Refractive index of d-line of each lens, v _d1 , v _d2 . Is the Abbe number of each lens. Further, the aspherical shape is expressed by the following formula, 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 the paraxial radius of curvature, P is the conic coefficient, A ₄ , A ₆ , and A ₈
Is an aspherical coefficient.

Example 1 f = 39.33 to 51.54 to 67.55 F _NO = 4.66 to 6.10 to 8.00 2ω = 57.55 ° to 45.48 ° to 35.46 ° f _B = 9.77 to 22.42 to 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 = ∞ (aperture) 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 n _d6 = 1.72916 ν _d6 = 54.68 r ₁₃ = -36.3990 Aspherical coefficient 10th 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
.

Example 2 f = 39.33 to 51.54 to 67.55 F _NO = 4.66 to 6.10 to 8.00 2ω = 57.55 ° to 45.48 ° to 35.46 ° f _B = 10.06 to 22.94 to 39.83 r ₁ = 16.7830 d ₁ = 2.7800 nd ₁ = 1.69680 ν _d1 = 56.49 r ₂ = 103.2480 d ₂ = 1.3100 r ₃ = -22.0920 d ₃ = 1.2000 n _d2 = 1.83400 ν _d2 = 37.16 r ₄ = 29.1640 d ₄ = 2.3500 r ₅ = ∞ d ₅ = 3.4800 n _d3 = 1.51633 ν _d3 = 64.15 r ₆ = -14.9760 d ₆ = 0.1500 r ₇ = 39.5820 d ₇ = 2.5700 n _d4 = 1.53172 ν _d4 = 48.90 r ₈ = -54.4780 d ₈ = 0.8000 r ₉ = ∞ (aperture) d ₉ = (variable) ) r ₁₀ = -45.2930 (aspherical surface) d ₁₀ = 3.1800 nd _d5 = 1.49241 ν _d5 = 57.66 r ₁₁ = -17.9690 (aspherical surface) d ₁₁ = 3.8200 r ₁₂ = -12.2210 d ₁₂ = 1.6000 nd _d6 = 1.72916 ν _d6 = 54.68 r ₁₃ = -86.9650 Aspheric coefficient 10th surface P = 1.0000 A ₄ ＝ -0.21944 × 10 ^-5 A ₆ ＝ 0.37635 × 10 ^-6 A ₈ ＝ -0.67 287 × 10 ^-8 11th surface P ＝ 0.9895 A ₄ ＝ -0.33747 × 10 ^-4 A ₆ = 0.30389 x 10 ^-6 A ₈ = -0.79252 x 10 ^-8 f ₁ / f _W = 0.762 ｜ f ₂ / f _W ｜ ＝ 0.804 ｜ d ₁₁ / f ₂ ｜ ＝ 0.121 ｜ f ₂₁ / f ₂ ｜ ＝ 1.842 ν _d21 = 57.66
.

Example 3 f = 39.33 to 51.54 to 67.55 F _NO = 4.66 to 6.10 to 8.00 2ω = 57.55 ° to 45.48 ° to 35.46 ° f _B = 9.86 to 22.69 to 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 n _d4 = 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 Aspheric surface coefficient 11th surface P = 0.9285 A ₄ = -0.19934 × 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
.

Example 4 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 n _d4 = 1.53358 ν _d4 = 51.56 r ₈ = -43.0570 d ₈ = 0.8000 r ₉ = ∞ (aperture) d ₉ = ( Variable) r ₁₀ = -34.5070 (aspherical surface) 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 Aspherical surface No. 10 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
.

2 to 3 are spherical aberration diagrams, astigmatism aberrations, distortion aberrations, and lateral chromatic aberrations at the wide end (a), the standard state (b), and the tele end (c) of Examples 1 to 4, respectively. As shown in FIG.

[0031]

As is apparent from the above description, by satisfying the constitution of the present invention, a two-group zoom lens having excellent performance with a zoom ratio of about 2 times can be obtained at a low cost with a lens constitution of 6 groups and 6 elements. Can be achieved.

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

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view at a wide end (a) and a tele end (b) of Example 1 of a two-group zoom lens according to the present invention.

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

FIG. 3 is an aberration diagram similar to FIG. 2 of Example 2.

FIG. 4 is an aberration diagram similar to FIG. 2 of Example 3.

FIG. 5 is an aberration diagram similar to FIG. 2 of Example 4.

[Explanation of symbols]

 I ... 1st lens group II ... 2nd lens group L1 ... 1st lens L2 ... 2nd lens L3 ... 3rd lens L4 ... 4th lens L5 ... 5th lens L6 ... 6th lens

Claims (1)

[Claims] 1. A zoom lens comprising a first group having a positive refracting power and a second group having a negative refracting power, in which zooming is performed by changing an air space between the two groups, the first group is arranged in order from an object side. , A positive meniscus lens having a convex surface on the object side, a negative lens, a positive lens, and a positive lens. The second group includes, in order from the object side, a positive meniscus lens having a convex surface on the image side and a convex lens on the image side. The positive meniscus lens in the second group is composed of two negative meniscus lenses. The positive meniscus lens is made of a plastic lens having an aspherical surface, and the focal lengths of the first group and the second group are f ₁ and f ₂ , respectively. When the focal length of the entire system at the wide end is f _W , 0.6 <f ₁ / f _W <0.9 ... 0.6 <| f ₂ / f _W | <0.9 ... A two-group zoom lens characterized by satisfaction.