JP3142353B2 - 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 structure and a zoom ratio of about twice.

[0002]

2. Description of the Related Art Heretofore, as a zoom lens for a lens shutter camera, a positive / negative two-group type, a positive / positive / negative, or a negative / positive / negative three-group type has been represented. Also known as

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. Many proposals have been made before.

However, since the amount of movement of each lens unit tends to increase with zooming, and the aberration variation with zooming is large (especially curvature of field at an intermediate focal length), the zoom ratio is increased. It can be said that it is not suitable for.

On the other hand, in the three-group type, since the zoom ratio can be shared among the groups, the amount of movement of each group due to zooming can be reduced.
In addition, since variation in aberration can be corrected well, it is suitable for increasing the zoom ratio. However, due to the large number of groups, there are disadvantages such as a complicated lens frame structure and a driving mechanism, and a large number of lenses.

As will be described later, the present invention aims to obtain a low-cost zoom lens using a small number of lenses and using a plastic material. If so, a lens system meeting the purpose can be achieved by taking advantage of the advantages of the two-group type.

Japanese Patent Application Laid-Open No. Sho 62 (1987) discloses an example in which the above-mentioned two-group type is constituted by about six lenses.
JP-A-138818, JP-A-63-266413, JP-A-2-73322, JP-A-2-120714 and JP-A-3-116110 are known.

[0008]

SUMMARY OF THE INVENTION
138818 and JP-A-63-266413 use a glass aspherical lens for aberration correction and have good performance. However, with respect to glass aspherical lenses, technical progress has been remarkable in recent years, but they are still disadvantageous in terms of cost.

[0009] Japanese Patent Application Laid-Open No. 2-73322 and
The device of No. -120714 is entirely constituted by 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.

Japanese Patent Application Laid-Open No. 3-116110 discloses a five-group, six-lens configuration in which a plastic lens is used to reduce the cost. 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 of the present invention is to form a zoom lens having a zoom range of about 38 to 70 mm by six groups of six lenses and to use an aspheric plastic lens. Accordingly, it is an object of the present invention to provide a two-unit zoom lens with reduced cost and improved performance.

[0012]

In order to achieve the above object, a two-unit zoom lens according to the present invention comprises: a first lens unit having a positive refractive power;
In a zoom lens configured by a second lens group having a negative refractive power and changing the air gap between each other, the first lens group includes, in order from the object side, a positive meniscus lens convex to the object side and a negative lens. The second lens group includes, in order from the object side, a positive meniscus lens convex on the image side and a negative meniscus lens convex on the image side. Wherein the meniscus lens convex to the image side of the first lens group and the positive meniscus lens convex to the image side of the second lens group are made of a plastic lens having an aspheric surface, and the first lens group and the second lens group Where f ₁ and f ₂ are the focal lengths and f _W is the total focal length of the wide-angle end, respectively, and the following conditional expression is satisfied.

0.6 <f ₁ / f _W <0.9... 0.5 <| f ₂ / f _W | <0.9 In this case, the second lens group has a convex surface on the image side. a positive meniscus lens and the image side air space of a negative meniscus lens convex on when the d _11, it is desirable to satisfy the following conditional expression.

0.08 <| d ₁₁ / f ₂ | <0.4 When the focal length of the meniscus lens convex to the image side of the first lens group is f _L4 , the following conditional expression is satisfied. It is desirable to satisfy.

2.5 <| f _L4 / f ₁ | When the focal length of the positive meniscus lens convex to the image side of the second lens group is f _L5 , the following conditional expression is satisfied. It is desirable to do.

1.5 <| f _L5 / f ₂ |

[0017]

The reason and operation of the above configuration will be described below. By making the lens configuration as above,
Aberration correction can be made with good balance over the entire range from the wide end to the telephoto end.

In particular, by arranging a positive lens and a convex aspheric meniscus lens on the image side on the image side of the negative lens which is the second lens in the first group, it is possible to correct spherical aberration and coma well. It can be carried out.

A point to be noted when using a plastic lens is a focus shift due to a change in temperature and humidity. To keep this defocus small,
It is desired to reduce the power of the plastic lens as much as possible. In the present invention, the last lens of the first group before the stop is made of an aspheric plastic lens, so that spherical aberration and coma are effectively corrected while keeping the power extremely small.

Further, the second lens unit is composed of a plastic aspherical positive meniscus lens convex on the image side and a negative meniscus lens convex on the image side. Aberration and distortion can be corrected well.

In this manner, two of the six groups of six lenses are made of plastic lenses, but the focal shift due to changes in temperature and humidity is very small, and a lens with good performance and low cost is realized.

Although the first object of the present invention is to reduce the cost, it is naturally assumed that the lens system is made compact. The above-mentioned conditional expression is a condition for this compaction. As the contents of the compaction,
Includes (i) shortening the overall length of the lens system, (ii) reducing the amount of movement of each unit due to zooming, and (iii) reducing the lens diameter. Is done.

The shortening of the overall length of the lens system is improved by reducing the number of lens components as described above. On the other hand, to reduce the amount of movement of each group and the lens diameter,
It is necessary to appropriately perform the power arrangement, and the condition for that is the above-mentioned conditional expression.

The focal lengths of the _first and _second lens units are f ₁ , f ₂ ,
The focal length, the back focus, and the imaging magnification of the second group at the wide-angle end are respectively f _W , f _BW , β _2W , the zoom ratio is Z, and the amount of movement of the first and second groups accompanying zooming. Let Δ ₁ and Δ _{1 be} respectively: f _W = f ₁ · β _2W (A) f _BW = f ₁ · (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 upper limit of the above conditional expression is exceeded, β _2W becomes 1
, And the back focus becomes extremely short according to the equation (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 liable 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 unit is weakened beyond the upper limit of the conditional expression, the amount of movement of each lens unit is undesirably increased according to the expressions (C) and (D). On the other hand, if the power of the second lens unit is increased beyond the lower limit of the conditional expression, favorable aberration correction cannot be performed with the lens configuration of the present invention.

Further, the air gap between the positive meniscus lens convex to the image side and the negative meniscus lens convex to the image side in the second group is d.
_When it is set to ₁₁ , it is preferable to satisfy 0.08 <| d ₁₁ / f ₂ | <0.4. The conditional expression relates to the correction of astigmatism. If the interval becomes smaller than the lower limit, the occurrence of astigmatism increases on the wide side. Also, if the interval is widened beyond the upper limit, the overall length of the lens system is undesirably large.

In the present invention, plastic lenses (a meniscus lens convex on the image side of the first group and a positive meniscus lens convex on the image side of the second group) are used in the first and second groups. In order to reduce the influence of temperature, humidity and changes, it is preferable to satisfy the following conditional expressions.

When the focal length of the meniscus lens convex to the image side of the first group is f _L4 , 2.5 <| f _L4 / f ₁ |... The positive meniscus lens convex to the image side of the second group. The focal length of f
_{When L5} , 1.5 <| f _L5 / f ₂ |... Further, the meniscus lens of the first group which is convex on the image side has one or both aspheric surfaces, and at least one surface has light at this time. It is desirable that the aspherical surface be shaped such that the negative power increases as the distance from the axis increases. Further, the positive meniscus lens convex to the image side of the second group has an aspheric surface on one surface or both surfaces, and at this time, it is preferable that at least one surface has an aspheric surface having a positive power that increases as the distance from the optical axis increases.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of a two-unit zoom lens according to the present invention will be described.
4 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 shapes and arrangements of the constituent lenses, in the first and fourth embodiments, the first unit I is composed of a positive meniscus lens L1, a biconcave lens L2, and a biconvex lens L convex on the object side.
3, a positive meniscus lens L4 convex to the image side and a stop, and the second unit II includes a positive meniscus lens L convex to the image side.
5. A negative meniscus lens L6 convex on the image side. Embodiments 2 and 3 are different from Embodiments 1 and 4 in that the fourth lens L4 of the first group I is composed of a negative meniscus lens having a weak convexity on the image side, and the other is the same.

Regarding the aspherical surface, in each of the embodiments, the first
The image-side surface of the fourth lens L4 of the group I and the first lens of the second group II
It is used for a total of two surfaces on the object side of the lens L5.

In the lens data of the following Examples 1 to 4, 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 aspherical 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 + A 10 y 10 where, r is near The radius of curvature of the shaft, P is the conic coefficient, A ₄ , A ₆ ,
A ₈ and A ₁₀ are aspherical coefficients.

[0034] Example 1 f = 39.33 ~ 51.58 ~ 67.55 F NO = 4.66 ~ 6.10 ~ 8.00 2ω = 57.55 ° ~ 45.55 ° ~ 35.46 ° f B = 9.80 ~ 22.74 ~ 39.70 r 1 = 19.4392 d 1 = 2.012 n d1 = _{1.69680 ν d1 = 56.49 r 2 =} 39.7616 d 2 = 1.268 r 3 = -26.9008 d 3 = 1.200 n d2 = 1.83400 ν d2 = 37.16 r 4 = 58.0668 d 4 = 3.518 r 5 = 17.8053 d 5 = 3.790 n d3 = 1.56873 ν _d3 = 63.16 r ₆ = -22.2958 d ₆ = 0.200 r ₇ = -36.0747 d ₇ = 1.854 nd ₄ = 1.49241 ν _d4 = 57.66 r ₈ = -31.9980 (aspherical surface) d ₈ = 0.800 r ₉ = ∞ (aperture) d ₉ = (variable) r ₁₀ = -28.2264 _{(aspherical) d 10 = 2.500 n d5 =} 1.49241 ν d5 = 57.66 r 11 = -24.3908 d 11 = 5.717 r 12 = -8.6864 d 12 = 1.600 n d6 = 1.72916 ν _d6 = 54.68 r ₁₃ = -16.7013 Aspheric coefficient 8th surface P = 7.4100 A ₄ = 0.11309 × 10 ^-3 A ₆ = 0.13273 × 10 ^-5 A ₈ = -0.46037 × 10 ^-7 A ₁₀ = 0.78617 × 10 ^-9 10th surface P = 1.7454 A _{4 ^{= 0.10979 × 10 -3 A 6 =}} 0.51310 × 10 -6 A 8 = 0.17687 × 10 -7 A 10 = -0.13947 × 10 -9 f 1 / f W = 0.704 | f 2 / f W | = 0.746 | d 11 / F ₂ | = 0.195 | f _L4 / f ₁ | = 18.05 | f _L5 / f ₂ | = 10.22
.

[0035] Example 2 f = 39.33 ~ 51.54 ~ 67.55 F NO = 4.66 ~ 6.10 ~ 8.00 2ω = 57.55 ° ~ 45.55 ° ~ 35.46 ° f B = 9.43 ~ 22.36 ~ 39.31 r 1 = 18.0512 d 1 = 2.012 n d1 = _{1.69680 ν d1 = 56.49 r 2 =} 28.1604 d 2 = 1.891 r 3 = -28.0804 d 3 = 1.200 n d2 = 1.83400 ν d2 = 37.16 r 4 = 59.6799 d 4 = 3.924 r 5 = 15.3885 d 5 = 3.862 n d3 = 1.56873 ν _d3 = 63.16 r ₆ = -20.5545 d ₆ = 0.200 r ₇ = -28.3590 d ₇ = 2.007 nd ₄ = 1.49241 ν _d4 = 57.66 r ₈ = -40.7578 (aspheric surface) d ₈ = 0.800 r ₉ = ∞ (aperture) d ₉ = (variable) r ₁₀ = -25.6160 (aspherical surface) d ₁₀ = 2.500 n _d5 = 1.49241 ν _d5 = 57.66 r ₁₁ = -19.6677 d ₁₁ = 5.753 r ₁₂ = -9.5000 d ₁₂ = 1.600 nd ₆ = 1.72916 ν _d6 = 54.68 r ₁₃ = -20.9617 Aspheric surface 8th surface P = -0.5548 A ₄ = 0.12563 x 10 ^-3 A ₆ = 0.30301 x 10 ^-6 A ₈ = -0.14315 x 10 ^-7 A ₁₀ = 0.78487 x 10 ^-9 10th surface P = 4.2708 A ₄ = 0.10494 × 10 ^-3 A ₆ = 0.25702 × 10 ^-6 A ₈ = 0.19256 × 10 ^-7 A ₁₀ = -0.17429 × 10 ^-9 f ₁ / f _W = 0.731 | f ₂ / f _W | = 0.774 | d _{11 / f 2 | = 0.189 |} f L4 / f 1 | = 6.958 | f L5 / f 2 | = 4.964
.

[0036] Example 3 f = 39.33 ~ 51.54 ~ 67.55 F NO = 4.66 ~ 6.10 ~ 8.00 2ω = 57.55 ° ~ 45.55 ° ~ 35.46 ° f B = 9.44 ~ 22.64 ~ 39.93 r 1 = 19.2398 d 1 = 2.0118 n d1 = _{1.69680 ν d1 = 56.49 r 2 =} 33.3467 d 2 = 1.3845 r 3 = -27.3753 d 3 = 1.2000 n d2 = 1.83400 ν d2 = 37.16 r 4 = 72.5840 d 4 = 3.6613 r 5 = 17.0396 d 5 = 3.7994 n d3 = 1.56873 ν _d3 = 63.16 r ₆ = -21.7216 d ₆ = 0.2000 r ₇ = -32.1490 d ₇ = 1.8845 nd ₄ = 1.49241 ν _d4 = 57.66 r ₈ = -36.1417 (aspherical surface) d ₈ = 0.8000 r ₉ = ∞ (aperture) d ₉ = (variable) r ₁₀ = -29.3331 _{(aspherical) d 10 = 2.5000 n d5 =} 1.49241 ν d5 = 57.66 r 11 = -24.4821 d 11 = 5.7268 r 12 = -8.6836 d 12 = 1.6000 n d6 = 1.72916 ν _d6 = 54.68 r ₁₃ = -16.4555 Aspheric surface 8th surface P = 7.9871 A ₄ = 0.12369 × 10 ^-3 A ₆ = 0.25643 × 10 ^-6 A ₈ = -0.12788 × 10 ^-7 A ₁₀ = 0.70669 × 10 ^-9 10th surface P = 1.8131 A _{4 ^{= 0.11014 × 10 -3 A 6 =}} 0.38033 × 10 -6 A 8 = 0.18852 × 10 -7 A 10 = -0.11932 × 10 -9 f 1 / f W = 0.720 | f 2 / f W | = 0.780 | d 11 / F ₂ | = 0.187 | f _L4 / f ₁ | = 24.724 | f _L5 / f ₂ | = 8.400
.

[0037] Example 4 f = 39.33 ~ 55.10 ~ 77.20 F NO = 4.08 ~ 5.71 ~ 8.00 2ω = 57.55 ° ~ 45.83 ° ~ 31.26 ° f B = 10.40 ~ 24.29 ~ 43.76 r 1 = 19.0063 d 1 = 2.0118 n d1 = _{1.64250 ν d1 = 58.37 r 2 =} 38.5640 d 2 = 1.3087 r 3 = -22.9994 d 3 = 1.2000 n d2 = 1.83400 ν d2 = 37.16 r 4 = 107.0105 d 4 = 3.9634 r 5 = 17.3615 d 5 = 4.0000 n d3 = 1.52542 ν _d3 = 64.55 r ₆ = -21.9148 d ₆ = 0.2000 r ₇ = -45.5956 d ₇ = 1.7893 nd ₄ = 1.49241 ν _d4 = 57.66 r ₈ = -31.0525 (aspherical surface) d ₈ = 0.8000 r ₉ = ∞ (aperture) d ₉ = (variable) r ₁₀ = -59.2540 _{(aspherical) d 10 = 2.5000 n d5 =} 1.49241 ν d5 = 57.66 r 11 = -27.6428 d 11 = 5.0940 r 12 = -9.9000 d 12 = 1.6000 n d6 = 1.72916 ν _d6 = 54.68 r ₁₃ = -38.8545 Aspheric surface coefficient 8th surface P = 21.7285 A ₄ = 0.18022 × 10 ^-3 A ₆ = 0.18211 × 10 ^-5 A ₈ = -0.24109 × 10 ^-7 A ₁₀ = 0.13635 × 10 ^-8 10th surface P = 39.2266 A ₄ = 0.98006 × 10 ^-4 A ₆ = 0.47914 × 10 ^-6 A ₈ = 0.16619 × 10 ^-7 A ₁₀ = -0.27174 × 10 ^-9 f ₁ / f _W = 0.685 | f ₂ / f _W | = 0.604 | d ₁₁ / F ₂ | = 0.215 | f _L4 / f ₁ | = 7.048 | f _L5 / f ₂ | = 4.320
.

FIGS. 2A and 2B are aberration diagrams showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end (a), the standard state (b), and the telephoto end (c) of Examples 1 to 4, respectively. As shown in FIG.

[0039]

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.

FIG. 5 is an aberration diagram similar to FIG. 2 of the fourth 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

Claims (4)

(57) [Claims] 1. A zoom lens system comprising a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, wherein a zoom ratio is changed by changing an air gap between the first lens unit and the first lens unit. The second lens 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 meniscus lens convex to the image side. The positive meniscus lens is composed of a positive meniscus lens and a negative meniscus lens convex on the image side. The positive meniscus lens convex on the image side of the first lens group and the positive meniscus lens convex on the image side of the second lens group have an aspherical surface. When the focal lengths of the first lens group and the second lens group are f ₁ and f ₂ , respectively, and the total focal length of the wide-angle end is f _W , the following conditional expression is satisfied. 2 group zoom lens. _{0.6 <f 1 / f W <} 0.9 ··· 0.5 <| f 2 / f W | <0.9 ··· 2. An air gap between a positive meniscus lens convex on the image side of the second lens group and a negative meniscus lens convex on the image side is d.
When the _11, 2-group zoom lens according to claim 1, characterized by satisfying the following conditional expression. 0.08 <| d ₁₁ / f ₂ | <0.4 3. The two-unit zoom lens according to claim 1, wherein the following conditional expression is satisfied when the focal length of the meniscus lens convex on the image side of the first lens unit is f _L4 . 2.5 <| f _L4 / f ₁ | 4. The two-unit zoom lens according to claim 1, wherein the following conditional expression is satisfied when the focal length of the positive meniscus lens convex to the image side of the second lens unit is f _L5 . 1.5 <| f _L5 / f ₂ |