JPH0735975A - Wide angle zoom lens - Google Patents

Abstract

PURPOSE:To provide a wide angle zoom lens with wide angle such as photographic angle of field of around 80 deg. at a wide terminal, large aperture with F-number of around 2.0, and variable power ratio 3 and provided with satisfactory optical performance in a full variable power range, and whose diaphragm can be fixed in variable magnification by performing appropriate lens arrangement and utilizing aspherical surface shape. CONSTITUTION:This lens is constituted in such a way that it is comprised of two lens groups of first lens group 1 with negative refracting power and second lens group 2 with positive refracting power and a diaphragm 2 arranged between the first and second lens groups sequentially from an object side, and the lens of the first lens group 1 nearest to the object side and the lens nearest to an image side are provided with negative refracting power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-angle zoom lens for cameras, especially video cameras.

[0002]

2. Description of the Related Art Today's consumer video cameras are required to have a simple operation and a wide angle of view, rather than a conventional high-magnification, high-functionality camera. Further, there is a strong demand for cost reduction, and there is a demand for realization of a wide-angle zoom lens in which the number of constituent elements is reduced while maintaining high performance. Zoom lenses currently used in consumer video cameras have a zoom ratio of 6 to 10 and an F number of 1.4 to
2.0, the so-called 4-group zoom with a shooting angle of view at the wide end of about 55 ° to 50 ° is the mainstream,
For example, JP-A-58-153913 and JP-A-1-1-1
There is one disclosed in Japanese Patent Publication No. 61209 / etc. These zoom lenses include, in order from the object side, a first lens group having a positive refractive power for focusing, a second lens group having a negative refractive power for zooming, and a positive lens group for correcting an image position. And a fourth lens group having a positive refractive power for image formation. With such a configuration, it is relatively easy to increase the aperture ratio and increase the magnification. In addition, since the diaphragm is fixed to the image plane during zooming, the lens barrel can be easily manufactured.
However, these four-group zooms are not suitable for widening the angle of view because the first lens group has a positive refractive power, and the angle of view at the wide end is limited to about 55 °.

In addition to this, there is a two-group zoom lens as a typical one of the zoom lenses achieving a wide angle. This two-group zoom lens generally has a negative refractive power of the first
A so-called negative lead type zoom lens, which is composed of a lens group and a second lens group having a positive refracting power, and which changes the air space between the two lens groups to perform zooming, is the mainstream. With this method, it is relatively easy to widen the angle of view. For example, Japanese Patent Laid-Open Nos. 60-49885 and 6
Japanese Patent Laid-Open No. 0-34734 proposes a photographing field angle at the wide end of 70 ° or more and a zoom ratio of 1.5 to 2.0.

[0004]

However, in these wide-angle zoom lenses, since the diaphragm is in the second lens group,
The aperture also moves as the magnification changes, which increases the cost of creating the lens barrel. Further, in the case of a video camera, a back focus of a certain value or more is required to arrange a crystal filter, cover glass, CCD, etc. behind the lens group. For that purpose, the refractive power of the first group must be increased. However, if this is the case, there is a problem in that the variation in aberration due to zooming becomes large and correction becomes difficult.

The present invention adopts a two-group zoom system in order to solve the problems of a narrow angle of view at the wide end and a large number of lenses in a conventional zoom lens for a video camera, By fixing the aperture between the first and second groups even during zooming, the lens barrel can be easily created, and while maintaining a predetermined back focus, the shooting angle of view at the wide end is about 80 °. With a wide angle of view, while aiming for a large aperture ratio of about F number 2,
It is an object of the present invention to provide a wide-angle zoom lens having good optical performance over the entire zoom range with a zoom ratio of about 3.

[0006]

In order to achieve the above object, a wide-angle zoom lens according to the present invention has a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side. And a diaphragm fixed between the first lens group and the second lens group with respect to the image plane during zooming,
In a wide-angle zoom lens that performs zooming by changing the air space between the first lens group and the second lens group, the first lens group is a meniscus negative lens whose object side faces are convex in order from the object side. No. 11 lens having a negative refracting power whose image side surface is concave toward the image surface side, and a thirteenth lens having a negative refracting power whose object side surface is a convex surface toward the object side. When the composite focal length of the first lens unit is f1 and the air gap between the eleventh lens component and the twelfth lens component is d2, the zoom lens is composed of a fourteenth lens having a negative refracting power. It satisfies the condition of <d2 / | f1 | <0.9.

[0007]

The wide-angle zoom lens of the present invention comprises, from the object side, a first lens unit having a negative refracting power, a second lens unit having a positive refracting power, and an aperture in order from the wide end to the tele end. At the time of zooming, the first group moves from the object side to the image plane side, and the second group moves from the image plane side to the object direction, so that The air space between the second group is changed. At this time, the diaphragm disposed between the first group and the second group is fixed with respect to the image plane even during zooming.

According to the present invention, with the above construction, the lens arrangement is simple and the aspherical shape is utilized, so that the lens construction is simple and the wide-angle photographing field angle is about 80 ° and the F-number is 2.0. It is possible to realize a wide-angle zoom lens having good optical performance in a large aperture ratio of about 3 and a total zoom range of about 3 zoom ratios.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 and 5 are lens cross-sectional views at the wide end of Numerical Embodiments 1 and 2 of the present invention, respectively. 1 and 5, 1 is the first lens group, 2 is a fixed diaphragm,
Reference numeral 3 is a second lens group, 4 is an equivalent glass plate corresponding to a crystal filter or a cover glass, and 5 is an image plane. Also,
f1 is a combined focal length of the first lens group 1.

In this embodiment, the following conditional expression is satisfied. 0.3 <d2 / | f1 | <0.9 (1) The technical meaning of the conditional expression (1) will be described.

Conditional expression (1) has a negative meniscus eleventh lens with the object side surface of the first lens group 1 having a convex surface facing the object side and a positive refractive power with respect to the combined focal length f1 of the first lens group 1. With respect to the ratio with the air distance d2 between the twelfth lens and the twelfth lens, mainly for downsizing of the entire lens system and for securing a back focus above a certain value and reducing various aberrations, particularly the amount of distortion. Is. First lens group 1
If the combined focal length f1 of (1) becomes longer than the lower limit of conditional expression (1), the total lens length at the wide end becomes long, the front lens diameter becomes large, and it is difficult to secure sufficient back focus. Become. If the air gap d2 is shortened and the lower limit value of the conditional expression (1) is exceeded, the amount of various aberrations generated, especially the distortion aberration, increases, which is not preferable.
If the combined focal length of the first lens unit becomes shorter than the upper limit value of the conditional expression (1), aberration variation due to zooming increases and it becomes difficult to correct this in a well-balanced manner, which is not preferable.
Further, by satisfying the conditional expression (1), a compact lens structure can be achieved as a whole, and the distance between lenses of each lens group due to zooming can be reduced. This makes it possible to suppress the change in the F number during zooming to be small, which allows the diaphragm to be fixed to the image plane during zooming.

In addition to this, in the present embodiment, in order to satisfactorily correct the aberration variation due to zooming and obtain good optical performance over the entire zooming range of a zoom ratio of about 3, the object-side curvature of the eleventh lens is Further, it is desirable to have an aspherical surface in which the positive refractive power becomes strong from the lens center to the lens periphery.

The second lens group 3 includes a positive 21st lens having an object side surface whose convex surface faces the object side, and a second lens having a positive refractive power.
It is desirable that it is composed of four lenses, two lenses, a twenty-third lens having a negative refracting power, and a twenty-fourth lens having a positive refracting power with the image plane side surface having a convex surface facing the image plane side. This is the number of lenses required to obtain good optical performance over the entire zoom range, and if the number of lenses is less than this, it becomes difficult to correct aberration fluctuations during zooming in a well-balanced manner. Further, if the number of lenses is increased, aberration correction becomes easier, but the total lens length becomes longer and the cost also increases as the number of lenses increases.
Furthermore, in order to simplify the lens configuration and obtain good optical performance over the entire zoom range, the second lens group 3
It is desirable that the object-side curvature of the twenty-first lens and the object-side curvature of the twenty-fourth lens have an aspherical surface having a positive refractive power that increases from the lens center to the periphery.

Under the lens construction and conditions according to the present invention, good optics is obtained in the entire zoom range with a shooting angle of view at the wide-angle end of about 80 °, an F number of 2.0, and a zoom ratio of about 3. A wide-angle zoom lens having performance can be realized.

Numerical examples of the present invention satisfying the above conditional expressions will be shown below. f is the composite focal length of the entire system, F is the F number, and 2ω is the angle of view. In the table, r ₁ , r ₂ , ... Are radii of curvature of the respective lens surfaces counted in order from the object side, d ₁ , d ₂ ,
Is the wall thickness of the surface spacing for each lens surface counted from the object side, or the air spacing, and n _d and ν _d are the refractive index and Abbe number of the lens material, respectively. The surface having an aspherical shape (indicated by *) is specified by the following display.

[0016]

[Equation 1]

Where Z is the distance from the tangent plane of the aspherical vertex of the aspherical surface having a height y from the optical axis, y is the height from the optical axis, c is the curvature of the aspherical vertex, k is the conical constant D, E, F, G: Aspherical surface coefficient (Example 1) f = 3 to 7.8 to 8.7 F = 2 to 3.2 to 3.5 2ω = 75.6 to 32.2
~ 29.8 surface No rdn _d ν _d 1 ^* 27.355 1.58 1.670032 47.2 2 14.310 4.00 3 427.250 1.30 1.696801 55.6 4 5.705 3.00 5 9.958 3.33 1.805179 25.5 6 28.396 1.88 7 -18.021 0.63 1.603 110 60.7 8 -617.772 (variable) 9 (diaphragm) ) (Variable) 10 ^* 8.010 1.50 1.603 110 60.7 11 -2291.344 0.12 12 20.360 1.35 1.772499 49.6 13 -18.400 0.60 14 -11.688 0.63 1.805179 25.5 15 23.000 1.00 16 ^* -21.182 2.00 1.487490 70.4 17 -5.931 (Variable) 18 ∞ 4.50 1.516329 64.1 19 ∞ The surface marked with * is an aspherical surface, and its aspherical coefficient is shown below.

The surface No. 10 face First Face 16 k 0.0 0.0 0.0 D 1.14947 × 10 -04 -2.11781 × 10 -04 -1.34236 × 10 -03 E 2.03216 × 10 -06 -1.03792 × 10 -06 -3.00166 × 10 ^{-06 F -3.86971 × 10 -08 1.66387 ×} 10 -07 -8.12489 × 10 -07 G 2.76728 × 10 -10 -4.48429 × 10 -09 5.43192 × 10 -09 is shown below the variable air space by zooming.

[0019] 2, 3 and 4 are diagrams showing the results of measuring various aberrations in the first embodiment.

Example 2 f = 3 to 7.5 to 8.7 F = 2 to 3.2 to 3.6 2ω = 72.2 to 33.6
~ 30.4 surface No rdn _d ν _d 1 ^* 27.765 1.58 1.802351 46.7 2 14.377 5.00 3 156.137 1.03 1.651601 58.5 4 5.417 3.00 5 11.070 3.33 1.805179 25.5 6 41.897 1.88 7 -15.425 0.63 1.603110 60.7 8 -126.533 (variable) 9 (diaphragm) ) (Variable) 10 ^* 8.010 1.50 1.603 110 60.7 11 -2291.344 0.12 12 20.360 1.35 1.772499 49.6 13 -18.400 0.60 14 -11.688 0.63 1.805179 25.5 15 23.000 1.00 16 ^* -21.182 2.00 1.487490 70.4 17 -5.931 (Variable) 18 ∞ 4.50 1.516329 64.1 19 ∞ The surface marked with * is an aspherical surface, and its aspherical coefficient is shown below.

The surface No. 10 face First Face 16 k 0.0 0.0 0.0 D 9.07513 × 10 -05 -2.11781 × 10 -04 -1.34236 × 10 -03 E 6.56508 × 10 -07 -1.03792 × 10 -06 -3.00166 × 10 ^{-06 F -8.52476 × 10 -09 1.66387 ×} 10 -07 -8.12489 × 10 -07 G 7.30179 × 10 -11 -4.48429 × 10 -09 5.43192 × 10 -09 is shown below the variable air space by zooming.

[0022] 6, 7 and 8 are diagrams showing the results of measuring various aberrations in the second embodiment.

[0023]

As described above, based on the lens construction and the conditional expression of the present invention, a large aperture ratio with a wide angle of view at a wide angle of about 80 ° and an F number of about 2 is obtained. In addition, it is possible to provide a compact wide-angle zoom lens having good optical performance in the entire zoom range of a zoom ratio of about 3.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view at a wide end according to a first exemplary embodiment of the present invention.

FIG. 2 is a diagram of various types of aberration at the wide-angle end of Example 1;

FIG. 3 is a diagram of various types of aberration at the normal position in Example 1;

FIG. 4 is a diagram of various types of aberration at the telephoto end of the first example.

FIG. 5 is a lens cross-sectional view at a wide end according to a second exemplary embodiment of the present invention.

FIG. 6 is a diagram of various types of aberration at the wide-angle end of Example 2;

FIG. 7 is a diagram of various types of aberration at the normal position in Example 2;

FIG. 8 is a diagram of various types of aberration at the telephoto end of Example 2;

[Explanation of symbols]

 1 1st lens group 2 Fixed diaphragm 3 2nd lens group 4 Glass plate 5 Image plane

Claims (5)

[Claims] 1. A two-lens group consisting of a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side, and the first lens group and the second lens group. A wide-angle zoom lens comprising a diaphragm arranged between the two lens groups for changing the magnification by changing the air space between the two lens groups.
The lens group is a wide-angle zoom lens characterized in that the most object-side lens and the most image-side lens are composed of lenses having negative refracting power. 2. The first lens group has, in order from the object side, an eleventh lens having a meniscus-shaped negative refracting power whose object side surface is a convex surface facing the object side, and whose image side surface is a concave surface facing the image surface side. A twelfth lens having a negative refracting power, a thirteenth lens having a positive refracting power in which an object side surface is a convex surface facing the object side, and a fourteenth lens having a negative refracting power, and the first lens group is composed. When the focal length is f1 and the air gap between the eleventh lens component and the twelfth lens component is d2, the condition 0.3 <d2 / | f1 | <0.9 is satisfied. The wide-angle zoom lens according to claim 1. 3. The wide-angle zoom lens according to claim 2, wherein the object-side curvature of the eleventh lens has an aspherical surface whose positive refracting power increases from the lens center to the lens periphery. 4. The wide-angle zoom lens according to claim 1, wherein the diaphragm is fixed with respect to the image plane during zooming. 5. The second lens group is a twenty-first lens having positive refracting power in which the object side surface has a convex surface facing the object side in order from the object side.
22nd lens with positive refractive power, 2nd lens with negative refractive power
The third lens includes a twenty-fourth lens having a positive refracting power whose image side surface is a convex surface facing the image surface side, and the object side curvature of the twenty-first lens and the object side curvature of the twenty-fourth lens from the lens center to the periphery The wide-angle zoom lens according to claim 1, wherein the wide-angle zoom lens has an aspherical surface having a positive refractive power that increases toward the front.