JP3365835B2 - Compact 3-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 suitable for a lens shutter camera or the like, and in particular, it has a variable magnification ratio of more than 2 in spite of its small number of constituent lenses, small size and low cost. The present invention relates to a compact 3-group zoom lens having good performance.

[0002]

2. Description of the Related Art Conventionally, a positive / negative two-group zoom type is known as a type suitable for a compact and low-cost zoom lens. However, if the number of constituent lenses is reduced in order to further reduce the size and cost, it becomes impossible to sufficiently correct the aberrations in each group, and the aberration variation due to zooming increases. Therefore, if the aberrations on the wide-angle side and the telephoto side are properly corrected, the aberrations at the intermediate focal length become large.
This tendency becomes worse as the zoom ratio becomes larger, and the field curvature at the intermediate focal length is insufficiently corrected.

Therefore, as disclosed in Japanese Patent Laid-Open No. 2-34812, the positive lens group of the first group is divided into a front group having a weak refracting power and a rear group having a positive refracting power, and is linked with zooming. A zoom type is known in which the field curvature at the intermediate focal length is improved by changing the front-rear group spacing.

It is well known that the cost can be significantly reduced by using a plastic lens instead of a glass lens. However, the plastic lens has a large change in the refractive index and the lens shape due to temperature and humidity, which leads to an image forming performance. Is a problem. As a countermeasure, Japanese Patent Laid-Open No. 5-11
As shown in No. 3537, there is known a method of making the refractive power of a plastic lens extremely weak. Furthermore, in recent years, there is a proposal that all the lenses are made of plastic, as in Japanese Patent Laid-Open No. 5-224122.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The No. 12 lens has an achromatizing action by combining a positive lens and a negative lens, thereby reducing the chromatic aberration in each group and correcting the chromatic aberration of the entire lens system. Therefore, each group requires two or more lenses, a positive lens and a negative lens,
It is difficult to reduce the number of components. Further, when a plastic lens is used for cost reduction, its refractive power is strong, so that the performance change due to temperature and humidity becomes large. Therefore, the embodiment is composed of 8 elements in 7 groups and is made of glass lenses, which is not cost effective.

Further, in the case of Japanese Patent Laid-Open No. 5-113537, when the zoom ratio becomes large, the curvature of field variation accompanying the zoom becomes large, making it difficult to obtain good performance in the entire focal length range. Become.

Further, in Japanese Unexamined Patent Publication No. 5-224122, all the lenses are made of plastic, which is advantageous in terms of cost, but the performance changes greatly depending on temperature and humidity. Also,
Since there is only a lens having a weak refractive power before the stop, it is difficult to cancel chromatic aberration before and after the stop. In particular, when the zoom ratio is large, variation in chromatic aberration due to zooming becomes large.

The present invention has been made in view of the above problems of the prior art, and its object is to reduce the number of constituent lenses, reduce the size and cost, and improve the performance while the zoom ratio exceeds 2. Is to provide a good zoom lens.

[0009]

A compact three-group zoom lens according to the present invention that achieves the above object has, in order from the object side, a first lens group, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. In a zoom lens composed of lens groups for changing the magnification by changing the distance between the lens groups, the first lens group includes at least one aspherical surface, and all the lenses included in the first lens group have the following conditional expressions: It is characterized by comprising a lens satisfying the condition (3) and satisfying the following conditional expression (1). 1.65 <n _N <1.90 (1) | f _T / f ₁ | <0.1 (3) where n _N is the average of the refractive indices of the negative lenses of the third lens group. The value, f _T is the focal length of the entire system at the telephoto end, and f ₁ is the focal length of each lens in the first lens group.

In this case, it is desirable that the first lens group consists of a single lens. Further, it is desirable that the second lens group includes at least a negative lens and a positive lens, and that the following conditional expression is satisfied. _{1.65 <n N '<1.90 ···} (1') , however, n _N 'is the average value of the refractive index of the negative lens in the second lens group and the third lens group.

[0011]

The function and operation of the above configuration will be described below. The first group effectively generates aberrations by using an aspherical surface, and in particular, spherical aberrations generated by the second group,
It has a function of canceling coma aberration, field curvature, etc., and reducing the aberration of the entire lens system. Further, by using a powerless lens, it is possible to reduce the occurrence of chromatic aberration in the first group.

Next, there are the second and third groups, which are lens groups having paraxial action (magnification / focus adjustment action) similar to the conventional positive / negative two-group zoom type. In order to shorten the total length of the lens on the telephoto side, it is necessary to strengthen the negative refractive power of the third lens group to enhance the zooming effect and reduce the zoom movement amount. However, in this case, the negative lens in the third lens group needs to satisfy the following condition in order to maintain good image surface characteristics. 1.65 <n _N <1.90 (1) where n _N is the average value of the refractive index of the negative lens of the third lens group.

When the lower limit of 1.65 of the above condition (1) is exceeded, the Petzval sum becomes negatively large, and the upper limit of 1.90 is reached.
When the value exceeds, it becomes positively large, and in both cases, astigmatism becomes large, which is not preferable.

The spherical aberration, coma aberration, curvature of field, etc. are the same as those of the conventional positive / negative two-group zoom type.
It is difficult to make a sufficient correction with only the third lens group, and even if an aspherical surface is used for the second lens group and the third lens group, the correction is not sufficient. Therefore, the aberration of the entire lens system is reduced by the correction effect of the aspherical surface of the first group described above.

By moving to the object side while shortening the distance between the second group and the third group having the above-mentioned paraxial action, the magnification change from the wide-angle end to the telephoto end is performed. If the group and the second group are moved integrally, aberration variation due to zooming will occur as in the conventional two-group zoom type. Therefore,
In the present invention, the distance between the first group and the second group is changed in association with the magnification change to change the aberration balance and improve the aberration fluctuation associated with the magnification change.

Further, since the second group and the third group are lens groups having strong refractive power, if the number of constituent elements is small, it is not possible to sufficiently correct chromatic aberration within each group. However, by installing the diaphragm between these two groups, the chromatic aberrations of magnification that occur in both groups become opposite, cancel each other out, and the overall size can be reduced. Of course, since the generation of chromatic aberration increases in the single lens configuration, it is desirable that both groups include at least a negative lens and a positive lens to correct axial chromatic aberration and lateral chromatic aberration. In particular, when the zoom ratio is large, it is preferable that the chromatic aberration is corrected within each group so that the variation of the chromatic aberration during zooming can be further reduced.

Therefore, it is desirable to satisfy the following conditional expression. _{1.65 <n N '<1.90 ···} (1') | ν dP -ν dN |> 10 ··· (2) However, n _N 'is a negative second lens group and the third lens group Average value of refractive index of lens, ν _dP is average value of Abbe number of positive lens of second lens group or third lens group, and ν _dN is average of Abbe number of negative lens of second lens group or third lens group It is a value.

When the value is out of the range of the conditional expression (2) and becomes 10 or less, the chromatic aberration in the second group or the third group becomes large,
The variation of chromatic aberration associated with zooming becomes large. The conditional expression (1 ′) has the same action as the conditional expression (1) described above.

Further, it is desirable that the first lens group satisfies the following conditional expression. | F _T / f ₁ | <0.1 (3) where f _T is the focal length of the entire system at the telephoto end, and f ₁ is the first
It is the focal length of each lens in the group. If the conditional expression (3) is deviated from and falls to 0.1 or more, chromatic aberration is increased in the first lens group, and the overall chromatic aberration is deteriorated.

Further, when the first lens group is made of a plastic lens which is cheaper than the glass lens, if the conditional expression (3) is satisfied, even if the refractive index and the lens shape change due to temperature and humidity, the lens There is also an advantage that the influence on the imaging performance can be minimized since the refractive power hardly changes. Further, the chromatic aberration of the first group can be made sufficiently small with the one-lens configuration without achromatizing with two or more positive and negative lenses as in the prior art.

The zoom lens according to the present invention is a three-group zoom lens in terms of the mechanism of the lens frame, but since the first group moves almost integrally with the second group, the lens is different from the conventional three-group zoom type. The frame moving mechanism can be made smaller. for that reason,
It is desirable to satisfy the following conditional expression. | ΔD ₁ / ΔD ₂ | <0.5 (4) where ΔD ₁ is the maximum value of the first group / second group interval change amount,
ΔD ₂ is the maximum value of the second group / third group spacing change amount. If the upper limit of 0.5 to condition (4) is exceeded, the first and second groups
The amount of change in group spacing becomes large, and the lens frame mechanism becomes large.

Further, since the lens construction length is equal to or less than that of the conventional two-group zoom type, the distance from the pupil position to the entrance surface / exit surface of the lens is short. Therefore, the marginal ray heights on the entrance and exit surfaces are low, and the lens diameter does not increase.

[0023]

EXAMPLES Examples 1 to 1 of the zoom lens of the present invention will be described below.
7 will be described. Although the lens data of each example will be described later, FIGS. 1 to 7 show lens cross-sectional views at the wide-angle end (a) and the telephoto end (b) of Examples 1 to 7, respectively.

Regarding the lens arrangement, in Example 1, from the object side, the first group G1 consisting of a plastic lens having a very weak refractive power, the second group G2 consisting of a cemented positive lens of a negative lens and a positive lens, and a positive lens. And a negative lens which has a negative refracting power and is composed of a total of five lenses in the third group G3, and the aspheric surface is the first
One surface is used for each of the group G1 and the third group G3. Since the entrance surface of the first group G1 where the central light flux and the peripheral light flux are separated is an aspherical surface, the field curvature and the coma aberration fluctuation in the peripheral portion are well corrected.

In the second embodiment, from the object side, a first group G1 composed of a plastic lens having a very weak refractive power, a second lens group G2 composed of a powerless plastic lens and a cemented positive lens composed of a negative lens and a positive lens, It is composed of a total of 6 pieces of the 3rd group G3 which has a negative refractive power which consists of a positive lens and a negative lens,
One aspherical surface is used for each group. The plastic lens in the second group G2 is an aspherical lens and is powerless in order to reduce the performance change due to temperature and humidity. Further, due to the aberration correction effect of this aspherical surface, the occurrence of aberration in the second group G2 is much smaller than that in the first embodiment.
Therefore, it is possible to reduce the occurrence of aberration in the first group G1,
The positional accuracy between the group G1 and the second group G2 can be loosened.

The third embodiment comprises, from the object side, a first group G1 consisting of a plastic lens having a very weak refractive power, a second group G2 consisting of a positive lens cemented with a positive lens and a negative lens, a positive lens and a negative lens. It is composed of a total of 5 sheets of the third group G3 having a negative refractive power, and one aspherical surface is used for each group. Since the aspherical surface is used in the second lens group G2 as in the second embodiment, the positional accuracy between the first lens group G1 and the second lens group G2 can be relaxed.

In the fourth embodiment, from the object side, a first lens group G1 made of a plastic lens having a very weak refractive power, a second lens group G2 having a positive refractive power composed of a negative lens and a positive lens, a positive lens and a negative lens. 3rd group G with negative refractive power consisting of 2 sheets
The first lens group G1 has one aspherical surface.

The fifth embodiment comprises, from the object side, a first group G1 consisting of a plastic lens having a very weak refractive power, a second group G2 consisting of a cemented positive lens of a negative lens and a positive lens, a positive lens and a negative lens. It is composed of a total of five third group G3 having negative refracting power, and the aspherical surface is divided into the first group G1 and the third group G3.
Two surfaces are used for the second group G2, one for each surface. Since an aspherical surface is used in the second group G2 as in the second embodiment,
The positional accuracy between the first group G1 and the second group G2 can be loosened.

The sixth embodiment comprises, from the object side, a first group G1 consisting of a plastic lens having a very weak refractive power, a second group G2 consisting of a positive lens cemented with a positive lens and a negative lens, a positive lens and a negative lens. It is composed of a total of 5 pieces of the third lens group G3 having a negative refracting power, and the aspheric surface has two surfaces in the first lens group G1 and the third lens group G3.
One side is used every three. The first group G1 is a double-sided aspherical lens, but there are differences in the marginal ray heights on both sides, and the generated aberrations are different. Therefore, the degree of freedom in correction balance in the central portion (spherical aberration) and the peripheral portion (field curvature, etc.) is increased, and more favorable aberration correction is possible.

Although the incident surface of this embodiment has a shape in which a concave surface is directed toward the object, the distance on the optical axis from the stop becomes large, so that the marginal ray height becomes high and the lens diameter becomes large. . Therefore, although there is no problem in imaging performance,
There is a slight disadvantage in terms of size.

In the seventh embodiment, from the object side, a first group G1 composed of two plastic lenses having very weak refractive power, a second group G2 composed of a cemented positive lens of a negative lens and a positive lens, a positive lens and a negative lens. G3, which has negative refractive power and consists of
It is composed of a total of 6 aspherical surfaces, and the aspherical surface has two surfaces in the first group G1 and a third surface
One side is used for group G3. Similar to the sixth embodiment, the first
There is a difference in the marginal ray heights on the two aspherical surfaces of the group G1, and it becomes possible to perform better aberration correction. The first group G1 has a double-lens structure, but both of them are plastic lenses, which is still advantageous in terms of cost.

In all the above embodiments, the first group G1
Is a plastic lens for cost reduction, but
Even if the group G1 is composed of a glass lens, there is no problem in performance.

The lens data of each embodiment will be shown below. In addition to the above, the symbols are f, the focal length of the entire system, F _NO is the F number, 2ω is the angle of view, f _B is the back focus, r ₁ and
r ₂ ... curvature radius of each lens surface, d _1, d ₂ ... the spacing between the lens surfaces, n _d1, n _d2 ... d-line refractive index of each lens, ν _d1, ν _d2 ... Each lens Is the Abbe number. In addition,
The aspherical shape is x in the optical axis direction and y in the direction orthogonal to the optical axis.
Then, it is expressed by the following equation. x = (y ² / r) / [1+ {1-P (y /
r) ² } ^1/2 ] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ However, r is a paraxial radius of curvature, P is a conic coefficient, A ₄ , A ₆ ,
A ₈ and A ₁₀ are aspherical coefficients.

Example 1 f = 39.2 to 58.6 to 87.1 F _NO = 4.66 to 6.21 to 8.28 2ω = 56.4 ° to 40.0 ° to 27.7 ° f _B = 9.51 to 28.13 to 55.49 r ₁ = 25.4210 (aspherical surface) d ₁ = _{3.000 n d1 = 1.49241 ν d1 =} 57.66 r 2 = 24.5490 d 2 = ( _{variable) r 3 = 157.8680 d 3 =} 1.500 n d2 = 1.83400 ν d2 = 37.16 r 4 = 13.6650 d 4 = 9.980 n d3 = 1.69680 ν d3 = 55.52 r ₅ = -17.5900 d ₅ = 1.000 r ₆ = ∞ (aperture) d ₆ = (variable) r ₇ = -29.8590 d ₇ = 3.000 n _d4 = 1.57501 ν _d4 = 41.49 r ₈ = -16.2750 d ₈ = 3.660 r ₉ = -13.0430 (aspherical surface) d ₉ = 1.800 n _d5 = 1.72916 ν _d5 = 54.68 r ₁₀ = -640.3870 Aspheric coefficient Coefficient 1st surface P = 0.2454 A ₄ = -0.49968 × 10 ^-4 A ₆ = -0.28262 × 10 ^-6 A ₈ = -0.12628 × 10 ^-8 A ₁₀ = -0.47657 × 10 ^-11 9th surface P = 0.2409 A ₄ = -0.19743 x 10 ^-4 A ₆ = 0.55883 x 10 ^-8 A ₈ = -0.12032 x 10 ^-8 A ₁₀ = 0.59178 x 10 ^-11
.

Example 2 f = 39.1 to 59.1 to 87.0 F _NO = 4.64 to 6.15 to 8.28 2ω = 56.8 ° to 39.8 ° to 27.8 ° f _B = 9.28 to 29.66 to 57.96 r ₁ = 129.4710 (aspherical surface) d ₁ = _{2.000 n d1 = 1.49241 ν d1 =} 57.66 r 2 = 137.4900 d 2 = ( variable) r ₃ = 37.7490 _{(aspherical) d 3 = 2.000 n d2 =} 1.49241 ν d2 = 57.66 r 4 = 36.6790 d 4 = 1.420 r 5 = -119.5760 d ₅ = 9.020 n _d3 = 1.67270 ν _d3 = 32.10 r ₆ = 25.8550 d ₆ = 3.830 nd ₄ = 1.62041 ν _d4 = 60.27 r ₇ = -15.3280 d ₇ = 1.000 r ₈ = ∞ (aperture) d ₈ = ( Variable) r ₉ = -30.1720 d ₉ = 4.100 n _d5 = 1.62004 ν _d5 = 36.25 r ₁₀ = -15.3450 d ₁₀ = 3.290 r ₁₁ = -11.3270 (aspherical) d ₁₁ = 1.800 n _d6 = 1.69680 ν _d6 = 55.52 r ₁₂ = -142.9020 Aspherical coefficient 1st surface P = 1.0000 A ₄ = 0.47463 × 10 ^-6 A ₆ = 0.72872 × 10 ^-7 A ₈ = -0.36425 × 10 ^-9 A ₁₀ = 0 3rd surface P = 7.1963 A ₄ = -0.99201 × 10 ^-4 A ₆ = -0.10089 × 10 ^-5 A ₈ = 0.53956 × 10 ^-8 A ₁₀ = -0.64608 × 10 ^-10 11th surface P = -1.7719 A ₄ = -0.20403 × 10 ^-3 A ₆ = 0.81619 × 10 ^-6 A ₈ = -0.43485 × 10 ^-8 A ₁₀ = 0.95073 × 10 ^-11
.

Example 3 f = 36.0 to 55.8 to 76.5 F _NO = 4.63 to 6.19 to 8.26 2ω = 60.8 ° to 42.1 ° to 31.5 ° f _B = 10.48 to 31.73 to 53.93 r ₁ = 67.6840 (aspherical surface) d ₁ = _{2.000 n d1 = 1.49241 ν d1 =} 57.66 r 2 = 61.6270 d 2 = ( variable) r ₃ = -34.8290 _{(aspherical) d 3 = 8.150 n d2 =} 1.56883 ν d2 = 56.34 r 4 = -7.2930 d 4 = 2.380 n _d3 = 1.76182 ν _d3 = 26.52 r ₅ = -10.5950 d ₅ = 1.000 r ₆ = ∞ (aperture) d ₆ = (variable) r ₇ = -164.3180 d ₇ = 2.320 n _d4 = 1.59551 ν _d4 = 39.21 r ₈ =- 34.2860 (aspherical surface) d ₈ = 5.580 r ₉ = -13.4330 d ₉ = 1.800 n _d4 = 1.69350 ν _d4 = 53.23 r ₁₀ = 44509.3797 Aspheric surface Coefficient 1st surface P = 1.0000 A ₄ = -0.13489 × 10 ^-4 A ₆ = 0.640 43 × 10 ^-7 A ₈ = 0.19443 × 10 ^-8 A ₁₀ = 0 3rd surface P = -0.6780 A ₄ = -0.17571 × 10 ^-3 A ₆ = -0.13611 × 10 ^-5 A ₈ = -0.36953 × 10 ^-7 A ₁₀ = 0.45263 × 10 ^-9 8th surface P = -14.4239 A ₄ = -0.78313 × 10 ^-4 A ₆ = 0.13324 × 10 ^-6 A ₈ = -0.14315 × 10 ^-8 A ₁₀ = 0.67894 × 10 ^-11
.

Example 4 f = 36.2 to 55.3 to 76.4 F _NO = 4.70 to 6.13 to 8.24 2ω = 60.4 ° to 42.3 ° to 31.5 ° f _B = 8.97 to 28.37 to 49.87 r ₁ = 21.6080 (aspherical surface) d ₁ = _{2.000 n d1 = 1.49241 ν d1 =} 57.66 r 2 = 21.2590 d 2 = ( _{variable) r 3 = 1007.2180 d 3 =} 4.960 n d2 = 1.69895 ν d2 = 30.12 r 4 = 20.2030 d 4 = 1.070 r 5 = 25.5950 d 5 = _{5.230 n d3 = 1.67000 ν d3 =} 57.33 r 6 = -15.3610 d 6 = 1.000 r 7 = ∞ ( stop) d ₇ = _{(variable) r 8 = -37.6030 d 8 =} 2.880 n d4 = 1.62004 ν d4 = 36.25 r 9 = -16.9550 d ₉ = 0.110 r ₁₀ = -28.1660 d ₁₀ = 1.200 n _d5 = 1.77250 ν _d5 = 49.66 r ₁₁ = -56.9180 d ₁₁ = 3.750 r ₁₂ = -14.6170 d ₁₂ = 1.800 n _d6 = 1.69680 ν _d6 = 55.52 r ₁₃ = -215.5420 Aspherical coefficient 1st surface P = 1.5313 A ₄ = -0.92894 × 10 ^-4 A ₆ = -0.70841 × 10 ^-6 A ₈ = -0.73431 × 10 ^-9 A ₁₀ = -0.22903 × 10 ^-10
.

Example 5 f = 29.0 to 45.6 to 67.7 F _NO = 4.69 to 6.18 to 8.26 2ω = 72.7 ° to 50.9 ° to 35.5 ° f _B = 6.44 to 22.71 to 44.51 r ₁ = -19.0410 (aspherical surface) d _{1 = 2.000 n d1 = 1.49241 ν d1} = 57.66 r 2 = -20.1480 d 2 = ( variable) r ₃ = -96.7730 _{(aspherical) d 3 = 5.850 n d2 =} 1.75520 ν d2 = 27.51 r 4 = 47.5540 d 4 = 7.390 n _d3 = 1.58913 ν _d3 = 61.18 r ₅ = -11.4450 (aspherical surface) d ₅ = 1.000 r ₆ = ∞ (aperture) d ₆ = (variable) r ₇ = -37.2850 d ₇ = 2.400 n _d4 = 1.63980 ν _d4 = 34.48 r ₈ = -21.3830 (aspherical surface) d ₈ = 4.580 r ₉ = -10.7740 d ₉ = 1.800 n _d5 = 1.78650 ν _d5 = 50.00 r ₁₀ = -75.1320 Aspherical coefficient 1st surface P = 1.0000 A ₄ = 0.24151 × 10 ^-5 A ₆ = 0.68851 × 10 ^-6 A ₈ = -0.48859 × 10 ^-8 A ₁₀ = 0 3rd surface P = 41.0051 A ₄ = -0.13598 × _{^{10 -3 A 6 = -0.21459 × 10}} -5 A 8 = 0.16093 × 10 -7 A 10 = -0.24295 × 10 -9 fifth surface _{P = 1.0000 A 4 = 0.13462 ×} 10 -4 A 6 = 0.24192 × 10 - ⁶ A ₈ = -0.775276 x 10 ^-9 A ₁₀ = 0 8th surface P = -5.3465 A ₄ = -0.13278 x 10 ^-3 A ₆ = -0.37666 x 10 ^-6 A ₈ = 0.13005 x 10 ^-7 A ₁₀ = -0.15651 x 10 ^-9
.

Example 6 f = 38.9 to 70.2 to 101.9 F _NO = 4.61 to 7.52 to 9.99 2ω = 57.3 ° to 34.3 ° to 24.0 ° f _B = 1.60 to 42.09 to 74.02 r ₁ = -34.6220 (aspherical surface) d _{1 = 5.000 n d1 = 1.49241 ν d1} = 57.66 r 2 = -37.2550 ( aspherical) d ₂ = _{(variable) r 3 = -59.6620 d 3 =} 8.010 n d2 = 1.51633 ν d2 = 64.15 r 4 = -9.2970 d 4 = 1.130 n _d3 = 1.84666 ν _d3 = 23.78 r ₅ = -11.5560 d ₅ = 1.000 r ₆ = ∞ (aperture) d ₆ = (variable) r ₇ = -57.1080 d ₇ = 3.760 nd ₄ = 1.61293 ν _d4 = 37.00 r ₈ = -19.1090 d ₈ = 4.160 r ₉ = -12.0390 (aspherical surface) d ₉ = 1.800 n _d5 = 1.75500 ν _d5 = 52.33 r ₁₀ = -304.1050 Aspheric surface Coefficient 1st surface P = 1.0000 A ₄ = 0.65037 × 10 ^-5 A ₆ = 0.67721 × 10 ^-6 A ₈ = -0.11970 × 10 ^-8 A ₁₀ = 0 2nd surface P = 1.0000 A ₄ = 0.13326 × 10 ^-3 A ₆ = 0.13112 × 10 ^-5 A ₈ = 0.12946 × 10 ^-7 A ₁₀ = 0 9th surface P = 0.7782 A ₄ = 0.25048 × 10 ^-4 A ₆ = 0.11094 × 10 ^-6 A ₈ = 0.12981 × 10 ^-8 A ₁₀ = -0.695 10 × 10 ^-11
.

Example 7 f = 39.1 to 58.8 to 86.7 F _NO = 3.74 to 5.61 to 8.24 2ω = 57.0 ° to 40.1 ° to 27.9 ° f _B = 9.41 to 29.21 to 57.26 r ₁ = 35.3740 (aspherical surface) d ₁ = _{2.000 n d1 = 1.49241 ν d1 =} 57.66 r 2 = 34.0270 d 2 = 3.190 r 3 = -24.8730 d 3 = 2.000 n d2 = 1.49241 ν d2 = 57.66 r 4 = -24.7720 ( aspherical) d ₄ = (variable) r ₅ = -146.7040 d ₅ = 4.120 n _d3 = 1.80518 ν _d3 = 25.43 r ₆ = 51.1930 d ₆ = 5.130 n _d4 = 1.65830 ν _d4 = 57.33 r ₇ = -16.5940 d ₇ = 1.000 r ₈ = ∞ (aperture) d ₈ = (Variable) r ₉ = -44.4300 d ₉ = 3.900 n _d5 = 1.62606 ν _d5 = 39.21 r ₁₀ = -19.3240 d ₁₀ = 4.000 r ₁₁ = -13.1620 (aspherical surface) d ₁₁ = 1.800 n _d6 = 1.69680 ν _d6 = 55.52 r ₁₂ = 342.7680 Aspheric coefficient Coefficient 1st surface P = -2.5291 A ₄ = -0.53535 × 10 ^-4 A ₆ = -0.36823 × 10 ^-6 A ₈ = 0.18007 × 10 ^-8 A ₁₀ = -0.39 220 × 10 ^-10 4th surface P = 1.0000 A ₄ = 0.16946 × 10 ^-4 A ₆ = 0.44124 × 10 ^-6 A ₈ = -0.10783 × 10 ^-7 A ₁₀ = 0.11085 × 10 ^-9 11th surface P = -0.3296 A ₄ = -0.39311 × 10 ^-4 A ₆ = -0.763 313 x 10 ^-7 A ₈ = 0.11467 x 10 ^-8 A ₁₀ = -0.75329 x 10 ^-11
.

FIG. 8 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) of Examples 1 to 7, respectively.
~ Shown in FIG. Further, the conditional expression (1) of each embodiment,
The values of (1 '), (2), (3), and (4) are shown in the following table (EX. Indicates an example, L1 and L2 are lenses on the object side in the first group G1, respectively. Shows the lens on the image side).

[0042] .

[0043]

As is apparent from the above description, according to the three-group zoom lens of the present invention, the zoom ratio exceeds 2, the number of constituent lenses is small, the size and cost are low, and the performance is good. You can get a nice zoom lens.

[Brief description of drawings]

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

2 is a lens cross-sectional view similar to FIG. 1 of Example 2. FIG.

FIG. 3 is a lens cross-sectional view similar to FIG. 1 of Example 3.

FIG. 4 is a lens cross-sectional view similar to FIG. 1 of Example 4.

5 is a lens cross-sectional view similar to FIG. 1 of Example 5. FIG.

FIG. 6 is a lens cross-sectional view similar to FIG. 1 of Example 6;

7 is a lens cross-sectional view similar to FIG. 1 of Example 7. FIG.

FIG. 8 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) in the first example.

FIG. 9 is an aberration diagram similar to FIG. 8 of Example 2.

FIG. 10 is an aberration diagram similar to FIG. 8 of Example 3.

FIG. 11 is an aberration diagram similar to FIG. 8 of Example 4.

FIG. 12 is an aberration diagram similar to FIG. 8 of Example 5.

FIG. 13 is an aberration diagram similar to FIG. 8 of Example 6.

FIG. 14 is an aberration diagram similar to FIG. 8 of Example 7.

[Explanation of symbols]

G1 ... First lens group G2: Second lens group G3 ... Third lens group

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-10307 (JP, A) JP-A-2-48622 (JP, A) JP-A-3-127010 (JP, A) JP-A-3- 150518 (JP, A) JP 4-78814 (JP, A) JP 4-153613 (JP, A) JP 5-134180 (JP, A) JP 6-67092 (JP, A) International Publication 92/21048 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (10)

(57) [Claims] From 1. A object side, a first lens group, a positive refractive power second lens group, a third lens unit having a negative refractive power,
In a zoom lens that performs zooming by changing the distance between each lens group, the first lens group includes at least one aspherical surface, and
All the lenses of the first lens group have the following conditional expression (3).
Consists lens that satisfies a and compact zoom lens, characterized by satisfying the following conditional expression (1). 1.65 <n _N <1.90 (1) | f _T / f ₁ | <0.1 (3) where n _N is the average refractive index of the negative lenses of the third lens group. Value , f _T is the focal length of the entire system at the telephoto end, f ₁ is the first lens
The focal length of each lens in the lens group . 2. The compact three-group zoom lens according to claim 1, wherein the first lens group comprises a single lens. 3. The second lens group includes at least a negative lens and a positive lens, and satisfies the following conditional expression.
The compact 3-group zoom lens described. _{1.65 <n N '<1.90 ···} (1') , however, n _N 'is the average value of the refractive index of the negative lens in the second lens group and the third lens group. 4. A compact three-group zoom lens according to claim 1, further comprising an aperture provided between the second lens group and the third lens group. 5. The compact three-group zoom lens according to claim 4, wherein both the second lens group and the third lens group have a negative lens and a positive lens. 6. The compact three-group zoom lens according to claim 5, wherein the following conditional expression is satisfied. _{1.65 <n N '<1.90 ···} (1') | ν dP -ν dN |> 10 ··· (2) However, n _N 'is a negative second lens group and the third lens group Average refractive index of the lens, ν _dP is the average Abbe number of the positive lens of the second lens group or the third lens group, ν _dN is the average Abbe number of the negative lens of the second lens group or the third lens group It is a value. 7. A compact zoom lens of claim 1, wherein the said first lens group is constituted by a plastic lens. 8. The compact three-group zoom lens according to claim 1, wherein the first lens group is composed of one lens. 9. The compact three-group zoom lens according to claim 1, wherein the following conditional expression is satisfied. | ΔD ₁ / ΔD ₂ | <0.5 (4) where ΔD ₁ is the maximum value of the amount of change between the first lens group and the second lens group, and ΔD ₂ is the second lens group and the third lens group. It is the maximum value of the interval change amount. 10. A compact zoom lens according to any one of claims 1 zoom ratio is equal to or exceeds twice 9.