JPH0921950A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens using many plastic lenses for reducing a cost in a zoom lens of wide angle and with zoom ratio of around three times. SOLUTION: This zoom lens comprises three groups consisting of a first lens groups of negative refracting power and that moves on an optical axis during variable magnification, a second lens group of positive refracting power and that moves on the optical axis during the variable magnification, and a third lens group of positive refracting power fixed during the variable magnification arranged sequentially from an object side. In the zoom lens, there are provided with the first lens group consists of one glass of negative refracting power and at least two or more plastic lenses, and the second lens group consists of at least one glass lens of positive refracting power and at least two or more plastic lenses.

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 compact and low-cost wide-angle zoom lens suitable for video cameras and the like.

[0002]

2. Description of the Related Art Recently, a zoom lens for a democratic video camera using a solid-state image pickup device is required to be a high-end model with a high zoom ratio and a large aperture ratio, but at the same time, it is required to have low cost, simplicity, and wide angle. As a popular machine pursued, one with a zoom ratio of about 3 is required.

Conventionally, as a lens type suitable for a wide angle, there is a negative group first two-group zoom used for a still camera. When this type is used for a video camera, an exit pupil position is used for a still camera. Because it's short
This is unsuitable because of the drawbacks such as a decrease in the amount of peripheral light on the focusing surface. In order to solve this problem, a positive lens group provided behind the second lens group is disclosed in JP-A-3-11.
It is disclosed in Japanese Patent No. 653.

It is also known to use a glass mold lens to reduce the number of lenses as one of means for realizing low cost, but it is expensive and the whole lens is expensive. . It is also possible to achieve cost reduction by using a plastic lens, but since the refractive index is generally lower than that of glass lenses and the types are limited, conventional optical performance is maintained and the entire lens is made compact. It was difficult to do.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems. It is a zoom lens with a wide angle and a variable power ratio of about 3 times. The objective is to provide a zoom lens that is cost effective.

[0006]

The above object is achieved by the following means. That is, (1) a first lens group having a negative refractive power in order from the object side and moving on the optical axis during zooming, and a second lens group having a positive refractive power and moving on the optical axis during zooming. In a zoom lens of three groups consisting of a group and a third lens group having a positive refractive power which is fixed during zooming, the first lens group includes one glass lens having a negative refractive power and at least two or more lenses. 2. The zoom lens, wherein the second lens group comprises at least one glass having a positive refractive power and at least two plastic lenses.

(2) A first lens group having a negative refracting power in order from the object side and moving on the optical axis during zooming, and a second lens group having a positive refracting power and moving on the optical axis during zooming. In a zoom lens of three groups consisting of a lens group and a third lens group having a positive refractive power which is fixed during zooming, the first lens group includes one glass lens having a negative refractive power and at least two glass lenses. The second lens group comprises at least one glass having a positive refractive power and at least two plastic lenses. 0.01 <| _FW / ^F1PL | <0.09 ...... However, F1 ^PL; combined focal length F _W of the plastic lenses included in the first lens group; and characterized by being configured so as to satisfy the focal length condition of the wide-angle end (1) The described zoom lens.

(3) The second lens group is composed of at least one glass lens and at least two plastic lenses, and 0 <| F _W / F2 ^PL | <0.09 ... The zoom lens according to (1) or (2) is characterized in that ^PL : a composite focal length of the plastic lens included in the second lens group, _FW ; a focal length at the wide-angle end.

(4) 0.01 <| F _W /F3|<0.25 in the third lens group, where F3; focal length of third lens group F _W ; focal length at wide angle end The zoom lens according to (1), (2) or (3) is characterized in that the zoom lens is configured to satisfy the following condition.

[0010]

FUNCTION Now, the function configured as above will be described.

(1) The zoom lens of the present invention has a negative refractive power as the first lens group in order from the object side, moves on the optical axis during zooming, and has a positive refractive power as the second lens group. It moves on the optical axis during zooming, and as a third lens group,
It has a fixed positive refractive power during zooming. The zoom lens is composed of the first lens group, the second lens group, and the third lens group.
A zoom lens of a group, wherein the first lens group comprises one glass lens having a negative refractive power and at least two plastic lenses, and the second lens group has at least one positive refractive power. A zoom lens comprising a glass having strength and at least two or more plastic lenses.

The first lens group can achieve its purpose even if the number of plastic lenses is an odd number, but the plastic lens is sensitive to environmental changes such as temperature and humidity, and thus the focus position is displaced. Since it has an adverse effect, it is a design problem to suppress the change in temperature and humidity to a level at which there is no practical problem, and it is preferable to use a pair of a positive lens and a negative lens in implementing the present invention.

(2) The zoom lens of the present invention has a negative refractive power as the first lens group in order from the object side, moves on the optical axis during zooming, and has a positive refractive power as the second lens group. It moves on the optical axis during zooming, and as a third lens group,
It has a fixed positive refractive power during zooming. The zoom lens is composed of the first lens group, the second lens group, and the third lens group.
A zoom lens of a group, wherein the first lens group comprises one glass lens having a negative refractive power and at least two plastic lenses, and the second lens group has at least one positive refractive power. A zoom lens characterized by being composed of glass having strength and at least two or more plastic lenses, which satisfies the following formula.

0.01 <| F _W / F1 ^PL | <0.09 ... F1 ^PL ; composite focal length of plastic lenses included in the first lens group F _W ; focal length at wide angle end If the | _FW / ^F1PL | value in the equation exceeds the upper limit value, the focus shift of temperature and humidity becomes practically unacceptable. On the other hand, if the value of | _FW / ^F1PL | in the equation exceeds the lower limit, it is preferable in that it is hardly affected by temperature and humidity.
The power of the glass lens included in the first lens group becomes too strong, the error sensitivity of the movable first lens group increases, and the productivity deteriorates.

Further, it is preferable to satisfy the following equation.

0.02 <| F _W / F1 ^PL | <0.07 ·································· If the value | F _W / F1 ^PL | It stays within the allowable focus shift. Also'
If the | _FW / ^F1PL | value in the formula is within the lower limit, it is hardly affected by temperature and humidity, and the power of the glass lens included in the first lens group does not become too strong. Better productivity without increasing error sensitivity of the group.

(3) The plastic lens included in the second lens group also satisfies the following conditions with respect to the environment resistance as described above.

0 <| F _W / F2 ^PL | <0.09 ··· F2 ^PL ; synthetic focal length of the plastic contained in the second lens group, | F _W / F2 ^PL | If the upper limit is exceeded, the focus shift of temperature and humidity becomes unacceptable for practical use. Conversely the formula | F _W / F2 ^PL | value although the preferable because not affected little by the temperature and humidity exceeds the lower limit,
The power of the glass lens included in the second lens group becomes too strong, the error sensitivity of the movable second lens group increases, and the productivity deteriorates.

Further, it is preferable to satisfy the following formula.

[0020] ^{_{0.01 <| F W / F2 PL}} | <0.07 ······ '' expression in the | F _W / F2 ^PL | influence the value is if the temperature and humidity it is within the upper limit value is very small It stays within the allowable focus shift. Also'
Expressions | F _W / F2 ^PL | value hardly affected in if the temperature and humidity is within the lower limit, it no power becomes too strong of a glass lens in the second lens group, the second lens movable Better productivity without increasing error sensitivity of the group.

(4) The third lens group satisfies the following conditions.

0.01 <| F _W /F3|<0.25, where F3; injection is performed when the | F _W / F3 | value of the focal length formula of the third lens group exceeds the lower limit value. This is advantageous for the pupil position, but since the back focus becomes long, the total length becomes large. On the other hand, if the | F _W / F3 | value exceeds the upper limit, the exit pupil position cannot be moved to a distant position.

Further, it is preferable to satisfy the following equation.

0.02 <| F _W /F3|<0.15 ································· The value | F _W / F3 | The focus is not long and the total length is shorter. Further, if the | _FW / F3 | value in the equation 'is within the upper limit value, the exit pupil position can be made sufficiently far away.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the lens system configuration diagrams shown in FIGS.

In the lens system according to the present invention, the first lens group having a negative refractive power in order from the object side and moving on the optical axis during zooming, has a positive refractive power, and moves on the optical axis during zooming. Second to move
It is composed of a lens group and a third group zoom lens composed of a third lens group having a positive refractive power which is fixed during zooming.

An embodiment satisfying the above conditional expression will be shown below. Here, each symbol used will be described. R is the radius of curvature of each lens surface, D is the center thickness of the lens or the lens interval, N is the refractive index for the glass material d line, νd is the Abbe number for the d line, 2ω is the angle of view, Fno is the f number, and f is the focus. The distances a and b indicate the lens group intervals at each position. In addition, “*” indicates that the lens is a plastic lens. Further, the shape of the aspherical surface is represented by the following "Equation 1".

[0028]

[Equation 1]

Where X is the origin of the aspherical vertex and the coordinates are from the object side to the image side along the optical axis Y; the aspherical vertex is the origin and the coordinates are perpendicular to the optical axis r; Axial radius of curvature K; surface conical constants A ₄ , A ₆ , A ₈ , A ₁₀ ; aspherical coefficient.

Example 1 The lens data of Example 1 according to the present invention are as shown in "Table 1".

[0031]

[Table 1]

<Embodiment 2> Further, lens data of Embodiment 2 according to the present invention is as shown in "Table 2".

[0033]

[Table 2]

Numerical values relating to the conditional expressions of the examples according to the present invention are shown in "Table 3", and Table 4 shows original lens data.

[0035]

[Table 3]

[0036]

[Table 4]

As shown in Table 3 above, both Example 1 and Example 2 have values satisfying the numerical values of the conditional expressions.

In the zoom lens according to the present invention, when plastic lenses are frequently used and a compact lens design is attempted, it becomes very difficult to correct various aberrations because the degree of freedom of the refractive index is particularly small. Therefore, in the embodiment of the present invention, at least two or more aspherical surfaces are provided in the first lens group and the second lens group. The aspherical surface of the first lens group can perform good correction of distortion especially for an image height of a high angle of view, and the aspherical surface of the second lens group selectively corrects spherical aberration during zooming and high-order coma. Aberration correction is performed.

In the embodiment of the present invention, the plastic lens included in the second lens group is composed of a cemented lens. This is because it is very difficult to apply a highly effective antireflection coating to a plastic lens, and thus the loss of light amount becomes large and the transmittance decreases. Therefore, two plastic lenses are cemented together to reduce the lens surface and reduce the light amount loss.

Next, as shown in the aberration diagrams of each of Examples 1 and 2, any aberration is satisfactorily corrected, and the lens system is excellent.

In Embodiment 1, the wide-angle end is shown in FIG.
Spherical aberration, astigmatism, and distortion aberration of FIG. 4, intermediate focal length as shown in FIG. 3 of spherical aberration, astigmatism, and distortion aberration, and at the telephoto end of FIG. Good results are obtained as shown in the point aberration and the distortion.

Next, in Example 2, as shown in the spherical aberration, astigmatism, and distortion aberration of FIG. 6 at the wide-angle end, and for the intermediate focal length, the spherical aberration, astigmatism, and distortion aberration of FIG. As shown in Fig. 8 and at the telephoto end,
Good results are obtained as shown in the spherical aberration, astigmatism, and distortion.

The present invention is not limited to the above-described embodiments, but various modifications can be made without departing from the scope of the invention.

[0044]

With the above-mentioned structure, it is suitable for use in a small video camera or the like, and the zoom ratio is about 3 times.
It is a zoom lens that uses a lot of plastic lenses as a zoom lens suitable for a wide angle and that has a lower cost than the conventional one.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system of a lens system of Example 1.

FIG. 2 is a characteristic diagram of spherical aberration, astigmatism, and distortion at the wide-angle end according to the first exemplary embodiment.

FIG. 3 is a characteristic diagram of spherical aberration, astigmatism, and distortion at the intermediate focal length of Example 1.

FIG. 4 is a characteristic diagram of spherical aberration, astigmatism, and distortion at the telephoto end according to the first exemplary embodiment.

5 is an optical system configuration diagram of a lens system of Example 2. FIG.

FIG. 6 is a characteristic diagram of spherical aberration, astigmatism, and distortion at the wide-angle end according to the second exemplary embodiment.

FIG. 7 is a characteristic diagram of spherical aberration, astigmatism, and distortion at the intermediate focal length of Example 2.

FIG. 8 is a characteristic diagram of spherical aberration, astigmatism, and distortion at the telephoto end of the second embodiment.

[Explanation of symbols]

 1 1st surface 2 2nd surface 3 3rd surface 4 4th surface 5 5th surface 6 6th surface 7 7th surface 8 8th surface 9 9th surface 10 10th surface 11 11th surface 12 12th surface 13th 13th surface 14 14th surface 15th 15th surface 16 16th surface 17 17th surface

Claims (4)

[Claims] 1. A first lens unit having a negative refracting power and moving along the optical axis during zooming in order from the object side, and a second lens group having a positive refracting power and moving along the optical axis during zooming. In a zoom lens of three groups consisting of a group and a third lens group having a positive refractive power which is fixed during zooming, the first lens group includes one glass lens having a negative refractive power and at least two or more lenses. The second lens group comprises at least one
A zoom lens comprising one glass having a positive refractive power and at least two plastic lenses. 2. The relationship between the combined focal length of the plastic lenses included in the first lens group and the focal length at the wide-angle end is 0.01 <| _FW / ^F1PL | <0.09, where ^F1PL ; The zoom lens according to claim 1, wherein the zoom lens is configured so as to satisfy a condition that a composite focal length F _W of a plastic lens included in the first lens group; a focal length at a wide-angle end. 3. A relationship between the focal length of the composite focal distance and a wide-angle end of the plastic lenses included in the second lens group ^{_{0 <| F W / F2 PL}} | <0.09 where, F2 ^PL; a second The zoom lens according to claim 1, wherein the zoom lens is configured so as to satisfy the following conditions: composite focal length F _W of plastic lens included in lens group; focal length at wide-angle end. 4. The relationship between the focal length of the third lens group and the focal length at the wide-angle end is 0.01 <| F _W /F3|<0.25, where F3; the focal length of the third lens unit F _W The zoom lens according to claim 1, 2 or 3, wherein the zoom lens is configured to satisfy a condition of a focal length at a wide-angle end.