JP3331011B2 - Small 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 small-sized two-unit zoom lens, and more particularly to a small-sized two-unit zoom lens having a front lens unit having a negative refractive power and a rear lens unit having a positive refractive power. The present invention relates to a zoom lens having a reduced number of components.

[0002]

2. Description of the Related Art Conventionally, such a type of zoom lens has been widely used as a so-called standard zoom lens having a standard angle of view as an interchangeable lens for a single-lens reflex camera. This type of two-unit zoom lens forms a retrofocus paraxial arrangement in which two lens units, a front unit having a negative refractive power and a rear unit having a positive refractive power, are arranged apart from each other. There is an advantage that it is easy to secure the long back focus required for mounting the quick return mirror of the reflex camera, and it is easy to obtain good performance in addition to being compact as a whole.

In such a negative / positive two-unit zoom type, an example in which the number of components is reduced is disclosed in
A lens system described in 64811 is known. This lens system is a zoom lens having a focal length of about 35 to 70 mm. The zoom lens system includes two front groups, two rear groups, and four rear groups, and includes an aspheric surface in the front group. The aberration correction is performed by the provision.

As an example in which the number of components is further reduced, Japanese Patent Application Laid-Open No. 4-46308 is known. In this conventional example, in a zoom lens having a focal length of about 35 to 70 mm, the front group is composed of two groups, and the rear group is composed of two groups or three groups. The aberration correction is performed by frequently using the aspherical surface.

On the other hand, as an example of applying this type of lens system to a lens shutter camera, see Japanese Patent Application Laid-Open No. 62-507.
No. 18 is known. In a lens shutter camera, it is not necessary to lengthen the back focus, which is advantageous for shortening the entire length of the lens. However, in this conventional example, the so-called rear lens unit is arranged with a positive refractive power and a negative refractive power separated from each other. By adopting the telephoto paraxial arrangement,
The overall length is further reduced. This lens system has a focal length of about 35 to 70 mm, the front group is composed of three elements in three groups, the rear group is composed of six elements in four groups, and aberration correction is performed by making the front and rear groups aspherical. It is carried out.

[0006]

Among the above-mentioned prior arts, the lens system disclosed in Japanese Patent Application Laid-Open No. S59-64811 has a small number of six lenses in the entire system. In setting the refractive power distribution to the lens unit, the effective diameter of the front group becomes large, which is not preferable in terms of compactness. Further, since the diameter of the lens of the front group is large, both the material cost and the processing cost are increased, which is not preferable in terms of cost. This tendency becomes more remarkable when the focal length at the wide-angle end is shortened to achieve a wide angle.

The lens system disclosed in Japanese Patent Application Laid-Open No. 4-46308 has a total of four or five lenses.
Since an aspherical surface is frequently used, it is not preferable in terms of cost, and the aberration correction state is not practically usable despite the large number of aspherical surfaces.

Further, the lens system disclosed in Japanese Patent Application Laid-Open No. Sho 62-50718 is miniaturized in both length and effective diameter.
As many as nine lenses are used in the entire system, which is undesirable in terms of cost.

The present invention has been made in view of such problems of the prior art, and has as its object to provide a two-unit zoom lens comprising a front group having a negative refractive power and a rear group having a positive refractive power. An object of the present invention is to provide a zoom lens having a wide angle of view and a high zoom ratio, while maintaining sufficient compactness and high performance while reducing the number of components.

[0010]

According to the present invention, there is provided a compact two-unit zoom lens system comprising a front unit having a negative refractive power and a rear unit having a positive refractive power. In a zoom lens having a two-unit configuration in which the distance between the two units is changed by integrally changing the magnification, the rear unit includes, in order from the object side, a first lens component having a positive refractive power and a first lens component having a positive or negative refractive power. The positive lens component has at least one aspheric surface, and satisfies the following conditional expression. The positive lens component includes at least one aspherical surface, and includes two lenses and a third lens component having a negative refractive power. It is characterized by the following. 1.45 <| f ₁ | / f _W <2.0 (1-1) 0.7 <f ₂ / f _W <1.4 (2) where f ₁ and f the focal length of each of ₂ the front group and rear group, f _W is the focal length at the wide angle end.

Another small two-unit zoom lens according to the present invention comprises a front unit having negative refracting power and a rear unit having positive refracting power. In a two-group zoom lens that changes magnification by changing
The rear unit includes, in order from the object side, a fourth lens unit including a first lens component having a positive refractive power, a second lens component having a positive or negative refractive power, and a third lens component having a negative refractive power. Wherein the positive lens component has at least one aspheric surface and satisfies the following conditional expression. 1.0 <| f ₁ | / f _W <2.0 (1) 0.95 <f ₂ / f _W <1.4 (2-1) where f ₁ and f the focal length of each of ₂ the front group and rear group, f _W is the focal length at the wide angle end.

Still another small two-unit zoom lens according to the present invention comprises a front unit having negative refracting power and a rear unit having positive refracting power. In a two-unit zoom lens that changes magnification by changing the distance, the rear unit includes, in order from the object side, a first lens component having a positive refractive power, a second lens component having a negative refractive power, and a negative lens having a negative refractive power. A third lens component composed of four lenses in three groups, wherein the positive lens component has at least one aspheric surface, and the positive lens component of the rear group which is closest to the object and has the positive refractive power. When the focal length of the first lens component is f _R1 , the following conditional expression is satisfied. 0.5 <f _R1 / f ₂ <1.0 (6) where f ₂ is the focal length of the rear group.

Another small two-unit zoom lens according to the present invention comprises a front unit having a negative refractive power and a rear unit having a positive refractive power. In the zoom lens having a two-group configuration in which the magnification is changed by changing the distance between the first lens component having the positive refractive power, the second lens component having the positive refractive power, and the negative refractive power, in order from the object side. The third lens component is composed of four lenses in three groups, has at least one aspheric surface in the positive lens component, and the second lens component in the rear group is a positive lens component. The first of the positive refractive power closest to the object side in the rear group
When the focal length of the lens component is f _R1 , the following conditional expression is satisfied. _{0.5 <f R1 / f 2 <} 1.25 ···· (7-1) , however, f ₂ is the focal length of the rear group.

[0014]

The reason why the above configuration is adopted and the operation thereof will be described below. The present invention has a main object of reducing the number of lens components as much as possible. However, simply reducing the number of lenses only causes deterioration of aberrations, and also impairs the degree of freedom of aberration correction. Therefore, the problem is how to reduce the number of lenses while maintaining high performance.

Therefore, in the present invention, the rear lens unit is provided with the positive lens component closest to the object side and the negative lens component closest to the image side. This positive lens component converges the divergent light beam incident on the rear group, and enables aberration correction together with the negative lens component.However, in order to satisfactorily correct spherical aberration and coma, at least the positive lens component includes It is necessary to provide one aspheric surface. Basically, it is advantageous in terms of cost if the rear group is composed of two components, a positive lens component and a negative lens component. However, in order to achieve sufficient aberration correction in practical use, Is composed of three components of a positive lens component, a positive lens component, a negative lens component, or a positive lens component,
It is necessary to include three components, a negative lens component and a negative lens component.

On the other hand, even if the cost is reduced by reducing the number of lens components, the value is small if the lens system is huge. In order to achieve sufficient compactness and high performance in the above-described lens configuration, it is necessary to provide an appropriate refractive power distribution to the front and rear units, and the following conditional expressions (1) and (2) ) Must be satisfied. 1.0 <| f ₁ | / f _W <2.0 (1) 0.7 <f ₂ / f _W <1.4 (2) where f ₁ and f ₂ are the focal length of the front group and rear group respectively, f _W is the focal length at the wide angle end.

As is well known, a two-unit zoom type lens system including a negative lens unit and a positive lens unit has an intermediate focal length f _S (f _S = (f _W · f _T ) ^1/2 ). , F
_W, f _T is the focal length at the wide-angle end, the telephoto end, respectively. In ()), when the rear unit forms an image at the same magnification, the amount of movement of the front unit due to zooming is minimized. In the present invention, in consideration of reducing the amount of movement of the front group and the possibility of aberration correction, the conditional expression (1) is set so that the same-magnification imaging position of the rear group comes between the vicinity of the intermediate focal length and the telephoto end. 1) is set. Therefore, when the value exceeds the upper limit of 2.0 in the conditional expression (1), the moving amount of the front group becomes large, and the interval between the front and rear groups becomes large.
The effective diameter of the front group is undesirably large. On the other hand, when the lower limit of 1.0 to condition (1) is exceeded, sufficient aberration correction cannot be achieved with a small number of lens elements as in the present invention.

Similarly, conditional expression (2) is set based on the amount of movement associated with zooming of the rear unit and the possibility of aberration correction.
As the refractive power of the rear unit increases, the amount of movement can be reduced. However, if the lower limit of 0.7 of conditional expression (2) is exceeded and the refractive power of the rear unit increases, sufficient aberration correction can be achieved with the lens configuration of the present invention. become unable. On the other hand, if the upper limit of conditional expression (2) exceeds the upper limit of 1.4, and the refractive power of the rear unit becomes weak, the amount of movement increases, and
At the wide-angle end, the distance between the front and rear groups widens, so that the effective diameter of the front group increases, which is not preferable.

Furthermore, it is desirable that the positive lens component in the rear group satisfies the following conditional expression (3). 75 <ν _RP (3) where ν _RP is the sum of Abbe numbers of all positive lenses included in the first lens component and the second lens component in the rear group.

Although the refractive power of the rear group is borne by the positive lens component, it is desirable to cancel out the aberrations of the positive lens component and the negative lens component for chromatic aberration correction. However, as in the embodiments described later, since the refractive power of the negative lens component does not necessarily have to be strong, in order to suppress the fluctuation of chromatic aberration due to zooming, the occurrence of chromatic aberration is suppressed by the positive lens component itself. It is desirable to keep. The condition for this is conditional expression (3). If this condition is satisfied, better chromatic aberration correction becomes possible even if the refractive power of the negative lens component is strong.

It is preferable that at least one of the aspheric surfaces of the positive lens component in the rear group satisfies the following conditional expression (4). | Δ _RP / φ _RP | <2 (4) where φ _RP = (n _RP ′ −n _RP ) / r _RP , where r _RP is the paraxial radius of curvature of the aspheric surface, n _RP and n _RP ′ are the refractive indices of the medium before and after the aspheric surface, and _ΔRP is the amount of aspheric surface at the effective radius.

Conditional expression (4) defines an aspherical surface. If the amount of aspherical surface is larger than this range, a higher-order bend easily occurs in spherical aberration and coma, and good aberration correction is achieved. It becomes difficult.

On the other hand, in the lens system of the present invention, it is desirable that the front group is composed of a negative lens component and a positive lens component in order from the object side, and has at least one aspheric surface. At this time, it is desirable that the aspheric surface satisfies the following conditional expression (5).

0 <Δ _F / φ _F (5) where φ _F = (n _F ′ −n _F ) / r _F , where r _F is the paraxial radius of curvature of the aspheric surface. , n _F, n _F 'represents the refractive index of the front and rear of the medium of the aspherical surface, the delta _F are aspherical amount in the effective radius.

Conditional expression (5) defines the shape of the aspherical surface. It is required that the negative refractive index is gradually increased or the positive refractive index is weakened as the distance from the optical axis increases. Is shown. By satisfying conditional expression (5), astigmatism and distortion can be corrected even better.

If the focal length of the positive lens component closest to the object side in the rear group is f _R1 , the following conditional expression (6) is satisfied.
Alternatively, it is desirable to satisfy (7). 0.5 <f _R1 / f ₂ <1.0 (6) 0.5 <f _R1 / f ₂ <1.5 (7) In the lens system of the present invention, After the emitted light beam becomes a divergent light beam and enters the rear lens unit, it is converged on the image surface by the positive refracting power of the rear lens unit. All of the converging action is borne by the positive lens component in the rear lens unit. When the rear group includes a positive lens component, a negative lens component, and a negative lens component, it is preferable to satisfy the conditional expression (6). At this time,
Since there is only one positive lens component in the rear group, the upper limit of 1.0 to condition (6) is not exceeded. On the other hand, when the lower limit of 0.5 to condition (6) is exceeded, the refracting power of the positive lens component in the rear group becomes too strong, making it impossible to perform sufficient aberration correction.

Next, when the rear unit is composed of a positive lens component, a positive lens component, and a negative lens component, conditional expression (7)
It is preferable to satisfy the following. At this time, it is desirable that most of the positive refracting power of the rear group is borne by the positive lens component closest to the object side in the rear group. If the upper limit of 1.5 to condition (7) is exceeded, spherical aberration will be over-corrected. If the lower limit of 0.5 is exceeded, spherical aberration will be under-corrected. Can not.

Furthermore, it is desirable that the following conditional expression (8) is satisfied. 0.1 <d _RP / f ₂ <0.6 (8) where d _RP is the total thickness of the positive lens component included in the first lens component and the second lens component in the rear group. . This is a condition for correcting astigmatism. When the value goes below the lower limit of 0.1 in conditional expression (8), the correction of astigmatism becomes insufficient, and the upper limit of 0. Thickness exceeding 6 is advantageous for aberration correction, but undesirably increases the total length of the lens system.

Further, in order to make the overall length of the lens system compact, it is desirable to satisfy the conditional expression (9). 0.2 <f _BW /IH<1.0 (9) where f _BW is the back focus at the wide angle end and IH
Is the screen diagonal length.

When the back focus exceeds 1.0 which is the upper limit of 1.0 to condition (9), the overall length of the lens system also increases, and as a result, the thickness of the camera tends to increase, which is not preferable. If the back focus is short beyond the lower limit of 0.2 of conditional expression (9), it is advantageous for shortening the overall length.
The effective diameter of the rear lens group is increased, which is not preferable in terms of compactness and cost.

[0031]

Next, embodiments 1 to 5 of a small two-unit zoom lens according to the present invention will be described. 1 to 5 show lens cross-sectional views of Examples 1 to 5 at the wide-angle end (a) and the telephoto end (b), respectively. The front unit F of any of the embodiments includes a negative meniscus lens having a convex surface facing the object side and a positive meniscus lens having a convex surface facing the object side, and the rear unit R has a biconvex lens in the first embodiment. A first lens component having a positive refractive power and a cemented lens of a negative meniscus lens, a second lens component having a convex surface facing the image side having a positive refractive power, and a convex surface facing the image side having a negative refractive power. In the second embodiment, the third lens component of the meniscus lens is composed of four lenses, and in the second embodiment, the first lens component having a positive refractive power, which is a cemented lens of a biconvex lens and a biconcave lens, In the third embodiment, two lens components and a third lens component of a biconcave lens having a negative refractive power are provided. In Example 3, the first lens component of the meniscus lens having a convex surface facing the object side having a positive refractive power is provided. , Biconvex lens and biconcave lens In the fourth embodiment, a cemented lens composed of a biconvex lens and a negative meniscus lens is composed of three groups of a second lens component having a positive refractive power and a third lens component of a biconcave lens having a negative refractive power. A first lens component having a positive refractive power and a second lens component of a meniscus lens having a convex surface facing the image side having a negative refractive power,
The third lens component of the biconcave lens having a negative refractive power is composed of four lenses in three groups. And a third lens component of a meniscus lens having a convex surface facing the image side having negative refracting power.

With respect to the aspherical surface, the first embodiment has three surfaces of the second surface of the negative meniscus lens of the front unit F, the first surface of the first lens component of the rear unit R, and the second surface of the second lens component. Embodiment 2 is the second embodiment of the negative meniscus lens of the front unit F.
The third embodiment uses the first lens component of the rear lens unit R, and the first lens component of the third lens component.
The first surface of the negative meniscus lens, the second surface of the positive meniscus lens, the first surface of the first lens component of the rear unit R, and the third surface
Fourth lens surface is used for the first surface of the lens component.
The second surface of the negative meniscus lens of the front group F and the first surface of the rear group R
The fifth embodiment uses the first surface of the lens component and the fourth surface of both surfaces of the third lens component. In the fifth embodiment, the second surface of the negative meniscus lens of the front unit F and the first surface of the first lens component of the rear unit R are used. One side and the second
It is used for four surfaces, the first surface of the lens component and the second surface of the third lens component.

In the case of a cemented lens, it is possible to arrange the cemented positive lens and the cemented lens slightly apart from each other,
Joining of a single lens and the like can be appropriately employed in constituting the present invention. Further, a glass material or a plastic material is used for the lens glass material of each embodiment. In particular, when a plastic material is used for a lens having a low refractive power as in the fourth embodiment, the influence of temperature and humidity changes is extremely large. The plastic material can be used without receiving it.

The lens data of each embodiment will be shown below. Symbols other than the above, f is the focal length of the entire system, F _NO is the F number, 2ω is the field angle, f _B is the back focus, r ₁ ,
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 of In addition,
In the aspherical shape, the optical axis direction is x, and the direction orthogonal to the optical axis is y
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 where, r is the paraxial radius of curvature, P is a conical coefficient, A _4, A _6,
A ₈ and A ₁₀ are aspherical coefficients.

[0035] Example 1 f = 35 ~ 49.5 ~ 70 F NO = 4.60 ~ 5.42 ~ 6.58 2ω = 63.36 ~ 47.15 ~ 34.30 ° f B = 34.89 ~ 44.04 ~ 56.99 r 1 = 68.4990 d 1 = 1.8000 n d1 = 1.78800 ν _d1 = 47.38 r ₂ = 18.9060 _{(aspherical) d 2 = 7.8900 r 3 =} 23.7030 d 3 = 4.5000 n d2 = 1.78472 ν d2 = 25.68 r 4 = 32.8840 d 4 = ( variable) r ₅ = ∞ (stop) d ₅ = 1.0000 r ₆ = 17.1050 _{(aspherical) d 6 = 6.4400 n d3 =} 1.65160 ν d3 = 58.52 r 7 = -26.5760 d 7 = 1.8000 n d4 = 1.76182 ν d4 = 26.55 r 8 = -143.2890 d 8 = 3.6600 r 9 _{= -27.0260 d 9 = 8.5000 n d5} = 1.60323 ν d5 = 42.32 r 10 = -28.9280 ( _{aspherical) d 10 = 4.5000 r 11 =} -38.2870 d 11 = 1.8000 n d6 = 1.72916 ν d6 = 54.68 r 12 = -1155.1900 Aspheric coefficient Second surface P = 0.9649 A ₄ = -0.24225 × 10 ^-5 A ₆ = 0.33789 × 10 ^-8 A ₈ = -0.68451 × 10 ^-10 A ₁₀ = 0 Sixth surface P = 1.0000 A ₄ = 0.21653 × 10 ^-5 A ₆ = 0.55346 × 10 ^-7 A ₈ = -0.69816 × 10 ^-9 A ₁₀ = 0.97330 × 10 ^-11 Surface 10 P = 1.0000 A ₄ = 0.60291 × 10 ^-4 A ₆ = 0.26055 × 10 ^-6 A ₈ = 0.12963 × 10 ^-8 A ₁₀ = 0
.

[0036] Example 2 f = 28 ~ 44.3 ~ 70 F NO = 4.6 ~ 5.91 ~ 7.97 2ω = 75.30 ~ 51.99 ~ 34.30 ° f B = 25.49 ~ 35.61 ~ 51.57 r 1 = 138.8200 d 1 = 1.8000 n d1 = 1.83481 ν _d1 = 42.72 r ₂ = 17.2270 _{(aspherical) d 2 = 5.8100 r 3 =} 24.9720 d 3 = 3.8000 n d2 = 1.80518 ν d2 = 25.43 r 4 = 49.7390 d 4 = ( variable) r ₅ = ∞ (stop) d ₅ = 1.0000 r ₆ = 11.4130 (aspheric surface) d ₆ = 6.3500 n _d3 = 1.51633 ν _d3 = 64.15 r ₇ = -24.4200 d ₇ = 1.5000 nd ₄ = 1.80518 ν _d4 = 25.43 r ₈ = 1760.5200 d ₈ = 6.0600 r ₉ = _{23.0540 d 9 = 3.2900 n d5 =} 1.59551 ν d5 = 39.21 r 10 = -23.1270 d 10 = 2.1800 r 11 = -10.7390 ( _{aspherical) d 11 = 1.8000 n d6 =} 1.80400 ν d6 = 46.57 r 12 = 185.9930 Aspheric coefficient Second surface P = 0.9025 A ₄ = -0.55651 × 10 ^-5 A ₆ = 0.29336 × 10 ^-8 A ₈ = -0.15492 × 10 ^-9 A ₁₀ = 0 Sixth surface P = 1.0000 A ₄ = -0.25480 × 10 ^-4 A ₆ = -0.12811 × 10 ^-6 A ₈ = -0.11762 × 10 ^-8 A ₁₀ = -0.69714 × 10 ^-11 Surface 11 P = 1.0242 A ₄ = -0.51143 × 10 ^-4 A ₆ =- 0.20170 × 10 ^-6 A ₈ = 0.44978 × 10 ^-8 A ₁₀ = 0
.

[0037] Example 3 f = 28 ~ 44.3 ~ 70 F NO = 4.6 ~ 5.78 ~ 7.65 2ω = 75.30 ~ 51.99 ~ 34.30 ° f B = 38.61 ~ 51.46 ~ 71.74 r 1 = 145.3690 ( aspherical) d ₁ = 1.8000 n _d1 = 1.78590 ν _d1 = 44.18 r ₂ = 16.0840 d ₂ = 7.1100 r ₃ = 32.9610 d ₃ = 3.8000 nd ₂ = 1.80518 ν _d2 = 25.43 r ₄ = 84.3510 (aspherical surface) d ₄ = (variable) r ₅ = ∞ ( _{stop) d 5 = 1.0000 r 6 =} 13.6480 ( _{aspherical) d 6 = 3.2400 n d3 =} 1.49700 ν d3 = 81.61 r 7 = 39.7020 d 7 = 0.8100 r 8 = 28.9790 d 8 = 5.0300 n d4 = 1.58904 ν d4 = 53.20 _{r 9 = -34.5580 d 9 = 1.5000} n d5 = 1.78472 ν d5 = 25.68 r 10 = 516.1740 d 10 = 5.1900 r 11 = -53.5800 ( _{aspherical) d 11 = 1.8000 n d6 =} 1.72000 ν d6 = 50.25 r 12 = 4857.6410 Aspheric surface 1st surface P = 1.0000 A ₄ = 0.78586 × 10 ^-5 A ₆ = -0.17455 × 10 ^-7 A ₈ = 0.22810 × 10 ^-10 A ₁₀ = 0 4th surface P = 1.0000 A ₄ = -0.47697 × 10 ^-5 A ₆ = -0.36401 × 10 ^-7 A ₈ = -0.49533 × 10 ^-10 A ₁₀ = 0 Surface 6 P = 1.0000 A ₄ = -0.19816 × 10 ^-5 A ₆ = -0.32131 × 10 ^-7 A ₈ = 0.40585 × 10 ^-9 A ₁₀ = 0 Surface 11 P = 1.0000 A ₄ = -0.95797 × 10 ^-4 A ₆ = -0.46 194 × 10 ^-6 A ₈ = -0.76050 × 10 ^-8 A ₁₀ = 0
.

[0038] Example 4 f = 35 ~ 49.5 ~ 70 F NO = 4.6 ~ 5.42 ~ 6.58 2ω = 63.36 ~ 47.15 ~ 34.30 ° f B = 36.49 ~ 45.58 ~ 58.42 r 1 = 240.6810 d 1 = 1.8000 n d1 = 1.80610 ν _d1 = 40.95 r ₂ = 21.5360 _{(aspherical) d 2 = 6.9200 r 3 =} 31.2160 d 3 = 3.9200 n d2 = 1.80518 ν d2 = 25.43 r 4 = 65.5500 d 4 = ( variable) r ₅ = ∞ (stop) d ₅ = 1.0000 r ₆ = 15.0920 _{(aspherical) d 6 = 6.0700 n d3 =} 1.58313 ν d3 = 59.36 r 7 = -24.3260 d 7 = 1.5000 n d4 = 1.74077 ν d4 = 27.79 r 8 = -168.6280 d 8 = 5.6800 r 9 _{= -53.2690 d 9 = 1.8000 n d5} = 1.72916 ν d5 = 54.68 r 10 = -120.3020 d 10 = 4.5600 r 11 = -113.6740 ( _{aspherical) d 11 = 1.8000 n d6 =} 1.49241 ν d6 = 57.66 r 12 = 88.9710 ( Aspherical surface) Aspheric coefficient Second surface P = 0.7823 A ₄ = -0.12430 × 10 ^-5 A ₆ = 0.20857 × 10 ^-8 A ₈ = -0.19934 × 10 ^-10 A ₁₀ = 0 Sixth surface P = 1.0000 A ₄ = -0.22122 × 10 ^-5 A ₆ = -0.74253 × 10 ^-8 A ₈ = 0.24774 × 10 ^-9 A ₁₀ = 0 Surface 11 P = 1.0000 A ₄ = -0.37379 × 10 ^-3 A ₆ = -0.33626 × 10 ^-6 A ₈ = -0.47026 × 10 ^-8 A ₁₀ = 0 Surface 12 P = 1.0000 A ₄ = -0.26163 × 10 ^-3 A ₆ = 0.57877 × 10 ^-6 A ₈ = 0.35854 × 10 ^-8 A ₁₀ = 0
.

[0039] Example 5 f = 28 ~ 44.3 ~ 70 F NO = 4.6 ~ 5.78 ~ 7.65 2ω = 75.3 ~ 51.99 ~ 34.30 ° f B = 28.00 ~ 39.37 ~ 57.31 r 1 = 102.0380 d 1 = 1.8000 n d1 = 1.80610 ν _d1 = 40.95 r ₂ = 15.4510 _{(aspherical) d 2 = 5.5100 r 3 =} 22.9950 d 3 = 4.1000 n d2 = 1.80518 ν d2 = 25.43 r 4 = 45.5240 d 4 = ( variable) r ₅ = ∞ (stop) d ₅ = 1.0000 r ₆ = 12.5750 _{(aspherical) d 6 = 5.5000 n d3 =} 1.58313 ν d3 = 59.36 r 7 = -23.9680 d 7 = 1.5000 n d4 = 1.74077 ν d4 = 27.79 r 8 = ∞ d 8 = 7.5700 r 9 = -56.8360 _{(aspherical) d 9 = 1.8000 n d5 =} 1.72916 ν d5 = 54.68 r 10 = 635.4610 d 10 = 4.5600 r 11 = -41.4020 d 11 = 1.8000 n d6 = 1.69680 ν d6 = 55.52 r 12 = -56.3110 ( non Spherical surface) Aspheric surface second surface P = 0.6289 A ₄ = 0.27458 × 10 ^-6 A ₆ = 0.89015 × 10 ^-8 A ₈ = -0.71846 × 10 ^-10 A ₁₀ = 0 0 sixth surface P = 1.0000 A ₄ = -0.44084 × 10 ^-5 A ₆ = -0.43704 × 10 ^-7 A ₈ = 0.75813 × 10 ^-9 A ₁₀ = 0 9th page P = 0.9982 A ₄ = -0.15417 × 10 ^-3 A ₆ = -0.86017 × 10 ^-6 A ₈ = -0.21284 × 10 ^-7 A ₁₀ = 0 Surface 12 P = 1.0000 A ₄ = -0.18827 × 10 ^-4 A ₆ = -0.13806 × 10 ^-6 A ₈ = 0.21554 × 10 ^-9 A ₁₀ = 0
.

FIG. 6 is a 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 5, respectively.
10 to FIG.

The following table shows numerical values of the conditional expressions (1) to (9) in each embodiment. In the table, Ri the lens surface number, Y denotes an effective radius when calculating the aspherical amount Δ _RP, Δ _F. .

[0042]

According to the structure of the present invention, a compact and high-performance zoom lens can be obtained with a small number of lenses in a negative / positive two-unit zoom type.

[Brief description of the drawings]

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

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

FIG. 3 is a sectional view similar to FIG. 1 of Example 3;

FIG. 4 is a sectional view similar to FIG. 1 of Example 4;

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

FIG. 6 shows a wide-angle end (a), an intermediate focal length (b) of the first embodiment,
Spherical aberration, astigmatism, distortion at the telephoto end (c),
FIG. 4 is an aberration diagram illustrating a lateral chromatic aberration.

FIG. 7 is an aberration diagram similar to FIG. 6 of the second embodiment.

FIG. 8 is an aberration diagram similar to FIG. 6 of the third embodiment.

FIG. 9 is an aberration diagram similar to FIG. 6 of the fourth embodiment.

FIG. 10 is an aberration diagram similar to FIG. 6 of the fifth embodiment.

[Explanation of symbols]

 F: front group R: rear group

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-93858 (JP, A) JP-A-4-163512 (JP, A) JP-A-3-196110 (JP, A) JP-A-4-193 218013 (JP, A) JP-A-5-27166 (JP, A) JP-A-5-333266 (JP, A) JP-A-5-346542 (JP, A) JP-A-61-87117 (JP, A) JP-A-61-138227 (JP, A) JP-A-63-32512 (JP, A) JP-A-63-223720 (JP, A) JP-A-3-500582 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 15/16

Claims (13)

(57) [Claims] 1. A two-group zoom system comprising a front group having a negative refractive power and a rear group having a positive refractive power, wherein the front group and the rear group are integrally changed in magnification by changing the distance between the two groups. in the lens, the rear group includes, in order from the object side, a first lens component having a positive refractive power, a second lens component having a positive or negative refractive power, which is constituted by the third lens component having a negative refractive power 3 From 4 lenses in a group
Becomes, the have at least one aspherical surface in the positive lens component, a compact two-group zoom lens to satisfy the following condition. 1.45 <| f ₁ | / f _W <2.0 (1-1) 0.7 <f ₂ / f _W <1.4 (2) where f ₁ and f the focal length of each of ₂ the front group and rear group, f _W is the focal length at the wide angle end. 2. A two-group zoom system comprising a front group having a negative refractive power and a rear group having a positive refractive power, wherein the front group and the rear group are integrally changed in magnification by changing the distance between the two groups. in the lens, the rear group includes, in order from the object side, a first lens component having a positive refractive power, a second lens component having a positive or negative refractive power, which is constituted by the third lens component having a negative refractive power 3 From 4 lenses in a group
Becomes, the have at least one aspherical surface in the positive lens component, a compact two-group zoom lens to satisfy the following condition. 1.0 <| f ₁ | / f _W <2.0 (1) 0.95 <f ₂ / f _W <1.4 (2-1) where f ₁ and f the focal length of each of ₂ the front group and rear group, f _W is the focal length at the wide angle end. 3. A two-group zoom system comprising a front group having a negative refractive power and a rear group having a positive refractive power, wherein the front group and the rear group are integrally changed in magnification by changing the distance between the two groups. in the lens, the rear group includes, in order from the object side, a first lens component having a positive refractive power, a second lens component having a negative refractive power, the third group is constituted by the third lens component having a negative refractive power 4 Consisting of two lenses ,
When the positive lens component has at least one aspheric surface, and the focal length of the first lens component having the positive refractive power closest to the object side in the rear group is f _R1 , the following conditional expression is satisfied: A small two-group zoom lens characterized in that: 0.5 <f _R1 / f ₂ <1.0 (6) where f ₂ is the focal length of the rear group. 4. A two-group zoom system comprising a front group having a negative refractive power and a rear group having a positive refractive power, wherein the front group and the rear group are integrally changed in magnification by changing the distance between the two groups. in the lens, the rear group includes, in order from the object side, a first lens component having a positive refractive power, a second lens component having positive refractive power, the third group is constituted by the third lens component having a negative refractive power 4 Consisting of two lenses ,
The positive lens component has at least one aspheric surface, and the second lens component in the rear group is a positive lens component;
A compact two-unit zoom lens, wherein the following conditional expression is satisfied, where f _R1 is a focal length of the first lens component having the positive refractive power closest to the object side in the rear group. _{0.5 <f R1 / f 2 <} 1.25 ···· (7-1) , however, f ₂ is the focal length of the rear group. 5. The compact two-unit zoom lens according to claim 3, wherein the following conditional expression is satisfied. 1.0 <| f ₁ | / f _W <2.0 (1) 0.7 <f ₂ / f _W <1.4 (2) where f ₁ and f ₂ are focal length of each of the front group and rear group, f _W is the focal length at the wide angle end. 6. In any one of claims 1 to 4,
A compact two-unit zoom lens, characterized by satisfying the following conditional expression. 75 <ν _RP (3) where ν _RP is the sum of Abbe numbers of all the positive lenses included in the first lens component and the second lens component in the rear group. 7. The method according to claim 1, wherein:
At least one of the aspherical surfaces included in the positive lens component in the rear group satisfies the following conditional expression. | Δ _RP / φ _RP | <2 (4) where φ _RP = (n _RP ′ −n _RP ) / r _RP , where r _RP is the paraxial radius of curvature of the aspheric surface, n _RP and n _RP ′ are the refractive indices of the medium before and after the aspheric surface, and _ΔRP is the amount of aspheric surface at the effective radius. 8. The front unit according to claim 1, wherein the front group includes a negative lens component and a positive lens component in order from the object side, and has at least one aspheric surface. A small two-group zoom lens as described. 9. The at least one aspherical surface of the front group,
The compact two-unit zoom lens according to claim 8, wherein the following conditional expression is satisfied. 0 <Δ _F / φ _F (5) where φ _F = (n _F ′ −n _F ) / r _F , where r _F is the paraxial radius of curvature of the aspheric surface, n _F , n _F 'represents the refractive index of the front and rear of the medium of the aspherical surface, the delta _F are aspherical amount in the effective radius. 10. When the second lens component of the rear group is a negative lens component and the focal length of the first lens component having the positive refractive power closest to the object side in the rear group is f _R1 ,
3. The optical system according to claim 1, wherein the following conditional expression is satisfied.
A small two-group zoom lens as described. 0.5 <f _R1 / f ₂ <1.0 (6) where f ₂ is the focal length of the rear group. 11. The second lens component of the rear group is a positive lens component, and the focal length of the first lens component having the positive refractive power closest to the object side in the rear group is f _R1 .
3. The optical system according to claim 1, wherein the following conditional expression is satisfied.
A small two-group zoom lens as described. 0.5 <f _R1 / f ₂ <1.5 (7) where f ₂ is the focal length of the rear group. 12. The small two-unit zoom lens according to claim 3, wherein the following conditional expression is satisfied. 0.1 <d _RP / f ₂ <0.6 (8) where d _RP is included in the first lens component and the second lens component in the rear group. 13. The compact two-unit zoom lens according to claim 12, wherein the following conditional expression is satisfied. 0.2 <f _BW /IH<1.0 (9) where f _BW is the back focus at the wide angle end and IH
Is the screen diagonal length.