JP2003057544A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce manufacturing cost while maintaining high magnification and high image quality in a zoom lens for a video camera for consumer use. SOLUTION: This zoom lens is constituted of a 1st lens group GR1 having a positive refractive index, a 2nd lens group having a negative refractive index, a 3rd lens group GR3 having a positive refractive index and a 4th lens group GR4 having a positive refractive index. Each lens made of plastic is constituted so that at least one surface is an aspherical surface, and a 1st lens having >=1.3 mm thickness is colored. Assuming that f1 is the focal distance of the 1st lens group, f2 is the focal distance of the 2nd lens group, Z is a variable power ratio, D is the diagonal length of an image pickup plane, r5 is the radius of curvature of a 5th lens surface, r8 is the radius of curvature of an 8th lens surface, r9 is the radius of curvature of a 9th lens surface, and r10 is the radius of curvature of a 10th lens surface, they are set to satisfy respective conditions f1/r5<0.25, 0.7<|f2/(0.05Z+1.7)D|<1, 0.7<|r8/r9|<1 and 0.6<|r9/r10|<0.9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for reducing manufacturing cost while maintaining high magnification and high image quality in a zoom lens of a consumer video camera.

[0002]

2. Description of the Related Art Generally, in a zoom lens for a consumer video camera, changing the material of the lens from glass to plastic is an effective method for reducing the manufacturing cost.

As a zoom lens in which a single lens other than the cemented lens is made of plastic for the purpose of reducing the manufacturing cost, for example, Japanese Patent Application Laid-Open No. 6-3 related to the present applicant is disclosed.
There is one described in Japanese Patent No. 4882. In addition, it is a low-power zoom lens in which all the constituent lenses are made of plastic and a filter that blocks ultraviolet rays is arranged on the object side of the lens system to prevent yellowing of the plastic lens. It is described in Kaihei 6-331889. Further, as a high-magnification zoom lens which frequently uses a plastic lens, Japanese Patent Laid-Open No. 8-27 is available.
There is one described in Japanese Patent No. 1787.

The reduction of the manufacturing cost by making the constituent lenses made of plastic has been inadequate effectively because only three lenses of the nine-lens system are made of plastic in the past. . For example, in a high-magnification zoom lens, if all the constituent lenses are glass lenses, the fourth lens group can be composed of two lenses. However, in the case where a large number of plastic lenses are used for the constituent lenses, Since the fourth lens group has a three-lens structure, the effect of reducing the manufacturing cost may not be fully utilized.

By the way, plastic sometimes turns yellow due to aging due to the influence of ultraviolet rays, but when using a plastic lens, this yellowing countermeasure was not sufficient. For example, if the constituent lenses are all plastic lenses having an aspherical surface, an ultraviolet ray cut filter is required for countermeasures against ultraviolet rays, and the number of constituent parts other than the lens increases, and the effect of reducing the manufacturing cost becomes weak. .

Further, when the aspherical surface is used as a means for correcting various aberrations, the aberrational correction load is concentrated on a specific aspherical surface, and the surface is separated from the optical axis due to an assembly error during manufacturing. There was a case where it became too sensitive to the influence on the image forming performance caused by the shift.

Further, in molding a plastic lens, high precision is required, which is the limit of plastic molding. Therefore, when the volume of the lens is large and the error factor sensitively affects the aberration, it may not be known whether it is advantageous to reduce the manufacturing cost unless the mold is actually made to mold the lens. When designing a zoom lens with specific optical characteristics, designing both a large-diameter lens that is difficult to mold with plastic and a large-diameter lens with a glass spherical lens is Takes a long time, costs much for trial production, and causes a lot of waste of the molding die.

[0008]

In view of the above problems, it is an object of the present invention to reduce the manufacturing cost of a zoom lens for a consumer video camera while maintaining high magnification and high image quality.

[0009]

In order to solve the above-mentioned problems, the first configuration of the zoom lens according to the present invention is such that, in order from the object side, the first lens group whose position is always fixed and which has a positive refractive power is imaged. By the cemented lens of the first lens of the concave meniscus lens made of glass with the concave surface facing the side and the second lens of the convex lens made of glass, and the third lens of the convex meniscus lens made of plastic with the convex surface facing the object side The second lens group having a negative refracting power and a fourth concave lens made of plastic with a strong concave surface facing the image side, and a second lens group having negative refractive power The fifth lens, which is a biconcave lens, and the sixth lens, which is a biconvex lens made of plastic, are used as a third lens group which is always fixed in position and has a positive refractive power. The fourth lens group having a positive refracting power is composed of the eighth lens, which is a biconcave lens made of glass, and the plastic lens, which is made of plastic and corrects the fluctuation of the image position and focuses by moving on the optical axis. The ninth lens is a biconvex lens, and each plastic lens has at least one aspherical surface.
The lens has an internal transmittance of 5 mm and a wavelength of 3
It is colored so that it is 45% or less for 70 nm light and has a thickness of 1.3 mm or more. F1 is the focal length of the first lens group, f2 is the focal length of the second lens group, and Z is changed. Multiplication ratio, D is the diagonal length of the imaging screen, r5 is the radius of curvature of the fifth lens surface counting from the object side, r8 is the radius of curvature of the eighth lens surface counting from the object side, and r9 is counting from the object side Assuming that the radius of curvature of the ninth lens surface is r10 and the radius of curvature of the tenth lens surface is r10 counted from the object side, f1 / r5 <0.25, 0.7 <| f2 / (0.0
5Z + 1.7) D | <1, 0.7 <| r8 / r9 | <
1 and 0.6 <| r9 / r10 | <0.9 are satisfied.

In a second structure of the zoom lens of the present invention, the first lens group having a fixed position and a positive refractive power is arranged in order from the object side, and a concave meniscus made of glass with a concave surface facing the image side. By constructing the cemented lens of the first lens of the lens and the second lens of the convex lens made of glass and the third lens of the convex meniscus lens made of glass with the convex surface facing the object side, by moving on the optical axis Mainly scaling
The second lens group having negative refracting power is a fourth lens of a plastic concave lens with a strong concave surface facing the image side, a fifth lens of a plastic biconcave lens, and a sixth lens of a plastic biconvex lens. The third lens group, which has a fixed position and has a positive refracting power, is composed of a seventh lens, which is a plastic convex lens, and moves on the optical axis to correct the fluctuation of the image position. The fourth lens group that performs focusing and has a positive refractive power is configured by an eighth lens that is a biconcave lens made of glass and a ninth lens that is a biconvex lens made of plastic, and each plastic lens is at least One surface is composed of an aspherical surface, and the first lens has an internal transmittance of 5 m.
m is colored to be 45% or less with respect to light having a wavelength of 370 nm and has a thickness of 1.3 mm or more, f2 is a focal length of the second lens group, Z is a zoom ratio, and D is an imaging screen. Diagonal length, r8 is the radius of curvature of the eighth lens surface counting from the object side, r9 is the radius of curvature of the ninth lens surface counting from the object side, and r10 is the curvature of the tenth lens surface counting from the object side. Radius, F4 is the fourth-order aspherical coefficient of the object-side surface of the ninth lens, R4 is the fourth-order aspherical coefficient of the image-side surface of the ninth lens, and F6 is 6 of the object-side surface of the ninth lens.
Assuming that the next aspherical coefficient is R6 and the sixth-order aspherical coefficient n3 of the image-side surface of the ninth lens is the refractive index of the third lens at the d-line, 0.7 <| f2 / (0.05Z + 1.7). ) D |
1, 0.7 <| r8 / r9 | <1, 0.6 <| r9 / r
10 | <0.9, F4 / R4 <0, F6 / R6 <0,
The condition of 1.69 <n3 is satisfied.

Therefore, by making heavy use of plastic lenses, it is possible to reduce the manufacturing cost while maintaining high image quality and high magnification.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the zoom lens of the present invention will be described below with reference to the accompanying drawings.

First, the outline of the present invention will be described.

An object of the present invention is to significantly reduce the manufacturing cost of a zoom lens, especially a consumer zoom lens. This drastic reduction in manufacturing cost is
This can be achieved by replacing the glass lens with a plastic lens as much as possible. However, as a lens material, plastic has a lower refractive index than glass and has less flexibility in selecting the Abbe number, which tends to make it difficult to correct various aberrations. The solution is to use an aspherical lens for all the plastic lenses and an appropriate refractive power arrangement.

When the aspherical surface of a plastic lens is used as a means for correcting various aberrations, the aberration correction load is concentrated on a specific aspherical surface, and the surface is affected by an assembly error during manufacturing. It may be too sensitive to the influence on the imaging performance that occurs when it is deviated from the optical axis, but this too should be mitigated by appropriate refractive power arrangement, optimization of the curvature shape, and aspherical counting restrictions. I chose

Further, as the material of the plastic lens, it is unavoidable to use a material which does not prevent yellowing due to aging due to ultraviolet rays. By absorbing it, yellowing was prevented.

Next, the structure of the zoom lens of the present invention will be specifically described.

The zoom lens 1 according to the first embodiment of the present invention includes a first lens group GR1 having a positive refractive power.
A second lens group GR2 having a negative refractive power, a third lens group GR3 having a positive refractive power, and a fourth lens group GR4 having a positive refractive power, and the first lens group GR1.
The positions of the third lens group GR3 and the third lens group GR3 are always fixed,
The lens group GR2 is adapted to perform zooming mainly by moving on the optical axis, and the fourth lens group GR4 is adapted to perform correction and focusing of fluctuation of the image position by moving on the optical axis. As shown in FIG. 1, in order from the object side, the first lens group GR1 includes a first lens L1 made of a glass concave meniscus lens having a concave surface facing the image side and a second lens L2 made of a glass convex lens. The cemented lens and the third lens L, which is a plastic convex meniscus lens having a convex surface facing the object side.
The second lens group GR2 includes a fourth lens L4, which is a plastic concave lens with a strong concave surface facing the image side, and a fifth lens L5, which is a biconcave plastic lens.
And a plastic biconvex sixth lens L6, the third lens group GR3 is composed of a plastic convex lens seventh lens L7, and the fourth lens group GR4 is a glass biconcave lens. Eighth lens L8
And a ninth lens L9 which is a biconvex lens made of plastic. A diaphragm IR is provided between the second lens group GR2 and the third lens group GR3, and a filter including an infrared filter, a low-pass filter, or the like is provided between the fourth lens group GR4 and the image plane IMG. FL
Is provided.

The zoom lens 1 includes the third lens L.
3, the image side surface of the fourth lens L4, the object side surface of the fifth lens L6, the image side surface of the sixth lens L6, the seventh lens L7.
The image-side surface and the both surfaces of the ninth lens L9 are aspherical surfaces, and the first lens L1 has an internal transmittance of 45% or less for light having a thickness of 5 mm and a wavelength of 370 nm. It is colored.

As described above, since the plastic material of the lens has a property of yellowing when exposed to ultraviolet rays for a long time, conventionally, the ultraviolet ray cut filter is arranged at the most object side position of the optical system. I tried to prevent yellowing. However, in the zoom lens of the present invention, by using glass colored for absorbing ultraviolet rays as the material of the first lens L1 arranged closest to the object side, the plastic lens is irradiated with ultraviolet rays. The amount is reduced to prevent the yellowing.

As the glass material used for the first lens,
Specifically, FD60, FD110, F manufactured by HOYA
D140, FDS30, FDS90 (these product names) and their equivalents are suitable. When these glass materials are used in a lens having a center thickness of 1.3 mm or more, a sufficient UV blocking effect is obtained, and yellowing of a plastic lens is prevented. Then, the first lens 1 of the zoom lens 1
Then, the center thickness is set to 2 mm.

Incidentally, in the conventional example, there is also an example in which all the constituent lenses are made of plastic by using polycarbonate as the most object side lens. However, as the material of the lens, the glass material has a higher refractive index and a smaller Abbe number than that of polycarbonate. Therefore, in order to obtain the refractive power of the concave lens necessary to make the first lens group GR1 an achromatic lens, the polycarbonate is used. It becomes possible to make the curvature comparatively gentler than that of the lens made of, and it becomes convenient to prevent the Petzval sum from increasing to the negative side and correct the field curvature satisfactorily.

In the zoom lens 1, f1 is the focal length of the first lens group GR1, f2 is the focal length of the second lens group GR2, Z is the zoom ratio, D is the diagonal length of the image pickup screen, and r5 is the object side. From the object side, the radius of curvature of the eighth lens surface counting from the object side, r9 the radius of curvature of the ninth lens surface counting from the object side, r10
Is the radius of curvature of the tenth lens surface counting from the object side, f1 / r5 <0.25 (conditional expression 1), 0.7 <|
f2 / (0.05Z + 1.7) D | <1 (conditional expression 2),
0.7 <| r8 / r9 | <1 (conditional expression 3), 0.6 <|
r9 / r10 | <0.9 (conditional expression 4) is satisfied.

In the zoom lens 1, F4 is a fourth-order aspherical coefficient of the object-side surface of the ninth lens L9, R4 is a fourth-order aspherical coefficient of the image-side surface of the ninth lens L9, and F6 is If a sixth-order aspherical surface coefficient of the object side surface of the ninth lens L9 and a sixth-order aspherical surface coefficient of the image side surface of the ninth lens L9 are F4,
It is preferable that the following conditions are satisfied: / R4 <0 (conditional expression 5) and F6 / R6 <0 (conditional expression 6).

Conditional expression 1 defines a condition for reducing the shape error in molding the third lens L3. When manufacturing plastic lenses by injection molding,
The shrinkage of the resin causes deviation from the shape of the mold. When the concave surface has a strong curvature, the third lens L3, which is a meniscus lens, is easily bent and deformed in a direction in which the concave surface has a stronger curvature due to contraction during molding. If the concave surface of the third lens L3 has a strong curvature, this deformation is likely to be greatly affected as an error from the design value of the aberration. Therefore, in the present invention, the curvature on the concave surface side is constrained by the condition defined in Conditional Expression 1 so that the shape of the third lens L3 is as close as possible to the plano-convex lens or the biconvex lens, and the deformation during molding and the molding The influence on the aberration due to time deformation is reduced.

Conditional expression 2 defines conditions for optimizing the refractive power of the second lens group GR2 with respect to the zoom ratio and the screen size. Compared to glass lenses, plastic lenses have a lower refractive index, so the curvature is stronger,
This causes various aberrations. Further, since the second lens group GR2 has a dominant factor in the aberration variation due to zooming, it is necessary to make the curvature of each surface gentle. Since the curvature of each surface of the second lens group GR2 depends on the refractive power arrangement, it is appropriate that the refractive power of the second lens group GR2 satisfies the above condition.

Further, it is necessary for aberration correction that the absolute value of the focal length of the second lens group GR2 is set to a large value substantially in proportion to the screen size and the zoom ratio. In a glass lens, the value of f2 / (0.05Z + 1.7) D generally exceeds the lower limit of conditional expression 2, but in the present invention, f2 /
When the value of (0.05Z + 1.7) D exceeds the lower limit, the second
The refracting power of the lens group GR2 becomes too strong, and it becomes difficult to suppress variations of various aberrations such as spherical aberration due to zooming. Also, the absolute value of the Petzval sum increases to the negative side, and the image Bending of the surface curve to the over side cannot be corrected. Conversely, f2 / (0.05
If the value of (Z + 1.7) D exceeds the upper limit, it is advantageous for aberration correction, but the whole lens system becomes large and impractical, and the whole lens system becomes large, and the angle plastic lens The volume of the resin increases, and it becomes difficult to perform accurate molding by injection molding.

The rear principal point of the second lens group in the variable power system similar to that of the present invention is generally located forward in the combined thickness of the second lens group GR2. G
It has a function of making the effective diameter of R1 small and making the inclination angle of the chief ray small to make aberration correction advantageous. Therefore, also in the present invention, it is necessary to set the rear principal point of the second lens group GR2 toward the front, as in the above case. The fourth lens L4 is normally a concave meniscus lens with a strong concave surface facing the image side using a glass material having a high refractive index and low dispersion, but a plastic material having a low refractive index cannot be used as the concave meniscus lens. Therefore, the fourth lens L4 of the present invention has a curvature that becomes a biconcave lens as a paraxial spherical surface, has a strong negative refracting power, and has an effect of pulling the rear principal point forward, and at the outer peripheral portion. The shape of the double-sided aspherical surface is close to that of a concave meniscus lens, and the influence of the plastic having a low refractive index is compensated.

Conditional expression 3 defines the distribution of the refracting power between the object-side surface r8 and the image-side surface r9 of the fifth lens L5. Increasing the curvature of the object-side surface r8 of the fifth lens L5 has an effect of moving the rear principal point to the front side, but conditional expression 3
If the value of | r8 / r9 |
When is deviated from the optical axis, the influence on the aberration becomes large and the manufacturing becomes difficult. The value of | r8 / r9 |
By setting the ratio to fall within the range, when the surface r8 and the surface r9 are relatively displaced from each other due to the eccentricity at the time of molding, or when the fifth lens L5 is the fourth lens.
Even if the lens L4 is relatively displaced, the performance close to the design performance can be maintained within the existing range of component accuracy.
If the value of | r8 / r9 | exceeds the upper limit, the rear principal point becomes rearward, and the ray height of the principal ray passing through the fourth lens L4 at the wide-angle end becomes high, which is disadvantageous for aberration correction.

If two or more types of plastic materials are used for achromatization, the selection range is limited. Therefore, the combined refracting power of the fourth lens L4 and the fifth lens L5 and the refracting power of the sixth lens L6 are determined from the negative refracting power required for the second lens group GR2 and the achromatic condition. The shape of the fourth lens L4 and the surface r8 of the fifth lens L5 are the same as those of the fourth lens L4 and the fifth lens L.
Since it is necessary to satisfy the conditions concerning the fifth and sixth lenses L6, the range of the curvature of the remaining surface r9 is also limited.

In consideration of the above, the conditional expression 4 is the fifth lens L5.
And the sixth lens L6 cancel out aberrations with each other, and stipulates conditions relating to assembly accuracy during manufacturing. | R
If the value of 9 / r10 | exceeds the upper limit, the cancellation of spherical aberration and coma at the surfaces r9 and r10 at the telephoto end becomes too strong, and the relative distance between the fifth lens L5 and the sixth lens L6 becomes large. The eccentricity has a strong influence on the aberration, which makes manufacturing difficult. By the way, from the conditional expression 3, the surface r9
It is clear that increasing the radius of curvature of 1 is not a good idea because the load is concentrated on the surface r8, and large spherical aberration and coma will occur from the surface r9 at the telephoto end.
Therefore, in order to cancel the influence of the surface r9, it is necessary to set the curvature of the surface r10 so that the value of | r9 / r10 | does not exceed the lower limit in conditional expression 4.

The seventh lens which is the convex lens of the third lens group GR3.
Since the lens L7 has a high degree of freedom in shape for aberration correction,
It may be a biconvex shape or a meniscus shape, and the aspherical surface may be either one of the object-side surface and the image-side surface, or both. However, considering the eccentricity of the surface due to the manufacturing error, the biconvex shape is more advantageous for reducing the eccentricity.

Since the third lens group GR3 is not achromatic, the fourth lens group GR4 needs to correct even the chromatic aberration generated in the third lens group GR3, and excessive achromatization must be performed. Since the purpose of the present invention is to reduce the manufacturing cost, one convex lens and one concave lens are arranged in the fourth lens group GR4.

However, like the second lens group GR2, if the fourth lens group GR4 is to be achromatized only with a plastic material, the eighth lens L8 of the concave lens must be biconcave and have a strong curvature. . However, if the zoom lens has a zoom ratio of about 15 times and an F number at the wide-angle end of about F2, the concave lens of the fourth lens group GR4 can be designed with a plastic material, but the zoom ratio is about 20. In the case of a zoom lens that is more than double and has an F number that is brighter than F1.8 at the wide-angle end, the curvature of the eighth lens L8 becomes too strong, and the aberration correction and moldability fail.

Therefore, in the present invention, the eighth lens L
No. 8 is a biconcave lens made of a glass material having a high refractive index and a high dispersibility, and the curvature of the surface is made gentle, and the shapes of both surfaces are made symmetrical so that it is not necessary to distinguish between the front and the back at the time of assembly.

Further, the ninth lens L9 must be made of plastic having a low refractive index and have a strong positive refracting power, so that the curvature of the surface must be strengthened.
Then, by increasing the curvature of the surface, the ninth lens L
In order to alleviate the spherical aberration, the coma aberration and the curvature of field generated from 9, even if only one surface of the ninth lens L9 is aspherical, the effect is insufficient, so it is necessary to make both surfaces aspherical. is there. When both surfaces of the ninth lens L9 are aspherical, an object-side surface r17 and an image-side surface r18 are caused by a molding error.
The eccentricity relative to and may act on coma, and one-sided blurring may appear sensitively. This is not remarkable if the effect of the aberration correction by the aspherical surface is divided into two surfaces, but the coma aberration generated by the aspherical surface term of one surface is canceled by the aspherical surface term of the other surface. This is because when it is made to act, when the canceling relationship is broken due to eccentricity due to an error during molding, it appears remarkably as one-sided blur.

In the ninth lens L9, if the fourth-order and sixth-order terms of the aspherical coefficients have the same sign on both surfaces, the third-order aberration coefficient and the fifth-order aberration coefficient are affected, so that the aberrations on both surfaces are affected. The cancellations become stronger. Therefore, conditional expressions 5 and 6 define the conditions for reducing the sensitivity to the eccentricity. In the ninth lens L9, it is desirable that the conditional expressions 5 and 6 are satisfied and the aspherical terms on both surfaces are symmetrically close to each other. In the zoom lens 1 according to the first embodiment of the present invention, both surfaces of the ninth lens L9 are made completely of symmetrical aspherical surfaces to reduce the sensitivity to decentering.

The zoom lens 2 according to the second embodiment of the present invention has a first lens group G having a positive refractive power.
The first lens group G includes R1, a second lens group GR2 having a negative refractive power, a third lens group GR3 having a positive refractive power, and a fourth lens group GR4 having a positive refractive power.
The positions of R1 and the third lens group GR3 are always fixed,
The second lens group GR2 is adapted to perform zooming mainly by moving on the optical axis, and the fourth lens group GR4 is adapted to perform correction and focusing of a change in image position by moving on the optical axis. As shown in FIG. 5, in order from the object side, the first lens group GR1 is provided with a first lens L1 made of a glass concave meniscus lens having a concave surface facing the image side and a second lens L2 made of a glass convex lens. And a third lens L3, which is a cemented lens of a convex meniscus lens made of glass and having a convex surface facing the object side.
And the second lens group GR2 is a fourth lens L which is a plastic concave lens with a strong concave surface facing the image side.
4 and the fifth lens L5, which is a biconcave lens made of plastic
And a plastic biconvex sixth lens L6, the third lens group GR3 is composed of a plastic convex lens seventh lens L7, and the fourth lens group GR4 is a glass biconcave lens. Eighth lens L8
And a ninth lens L9 which is a biconvex lens made of plastic. A diaphragm IR is provided between the second lens group GR2 and the third lens group GR3, and a filter including an infrared filter, a low-pass filter, or the like is provided between the fourth lens group GR4 and the image plane IMG. FL
Is provided.

The zoom lens 2 includes the third lens L.
3, the image side surface, the both surfaces of the fourth lens L4, and the fifth lens L5.
The object side surface, the image side surface of the sixth lens L6, the image side surface of the seventh lens L7, and the both surfaces of the ninth lens L9 are each formed of an aspherical surface, and the material of the first lens L1 is Is colored to have an internal transmittance of 5 mm or less and 45% or less for light having a wavelength of 370 nm.

Further, in the zoom lens 2, when n3 is the refractive index of the third lens at the d-line, 0.7 <| f2 /
(0.05Z + 1.7) D | <1 (conditional expression 2), 0.7
<| R8 / r9 | <1 (conditional expression 3), 0.6 <| r9 /
r10 | <0.9 (conditional expression 4), F4 / R4 <0 (conditional expression 5), F6 / R6 <0 (conditional expression 6), 1.69 <n3
Each of the conditions (conditional expression 7) is satisfied.

Conditional expression 7 shows that the third lens L3 made of aspherical plastic in the zoom lens 1 is replaced by the third lens L3 made of spherical glass as in the zoom lens 2.
It specifies the conditions necessary to replace with.
That is, in the zoom lens 2, the refractive index of the third lens L3 is set to 1.69 or more to loosen the curvature of the surface, and
Not only the third lens L3 but also the three lenses constituting the first lens group GR3 are aberration-corrected in accordance with the characteristics of the fourth lens L4 and thereafter, so that the zoom lens 1 and the fourth lens
The lenses L4 to ninth lens L9 can be commonly used.

In the zoom lens 1 and the zoom lens 2, the fourth lens L4 to the ninth lens L9 constituting the second lens group GR2 to the fourth lens group GR4 are common, and the first lens group GR1 is constituted. Only the first lens L1 to the third lens L3 are different. That is, the zoom lens 1 and the zoom lens 2 can take either configuration only by exchanging the first lens group GR1.

Next, numerical examples embodying the zoom lenses 1 and 2 will be shown.

In the following description, "ri" is the i-th surface counted from the object side and its radius of curvature, and "d"
i ”is the surface distance between the surface ri and the surface ri + 1, and
“Ni” is the refractive index at the d-line of the material forming the i-th i-th lens Li counted from the object side, and “νi” is the Abbe number of the material forming the i-th lens Li. Similarly, “nFL” and “νFL” are the filter FL.
Is the refractive index and Abbe number at the d-line of the material constituting the.

The definition of the aspherical surface is defined by the depth of the aspherical surface x
i, and the height from the optical axis is H, xi = H ² / ri {1+ (1-H ² / ri ² ) ^1/2 } + ΣA
Let be represented by jH ^j .

Table 1 shows each numerical value of the zoom lens 1.

[0047]

[Table 1]

Table 2 shows the focal lengths of the zoom lens 1 at the wide-angle end, the intermediate focal position and the telephoto end, the F-number, the angle of view (2ω), and the surface distance d5 at which the surface distance changes with zooming and focusing. The numerical values of d11, d14 and d18 are shown.

[0049]

[Table 2]

In Table 3, the image side surface r5 of the third lens L3 formed by the aspherical surface of the zoom lens 1, both surfaces r6 and r7 of the fourth lens L4, and the object side surface r8 of the fifth lens,
The image-side surface r11 of the sixth lens L6, the image-side surface r14 of the seventh lens L7, and both surfaces r17 and r18 of the ninth lens L9.
4th, 6th and 8th aspherical coefficients A4, A8 and A1 of
Indicates 0.

[0051]

[Table 3]

Table 4 shows numerical values relating to the conditional expressions 1 to 6 of the zoom lens 1.

[0053]

[Table 4]

2 to 4, the wide-angle end of the zoom lens 1,
A spherical aberration diagram, an astigmatism diagram, and a distortion diagram at the intermediate focus position and at the telephoto end are shown, respectively. In the spherical aberration diagram, the solid line shows the value at the d line (wavelength 587.6 nm), the broken line shows the value at the g line (wavelength 435.8 nm), and the chain line shows the value at the C line (wavelength 656.3 nm). The solid line indicates sagittal field curvature, and the broken line indicates meridional field curvature. (The same applies to FIGS. 6 to 8 described later).

Table 5 shows each numerical value of the zoom lens 2.

[0056]

[Table 5]

Table 6 Focal length at the wide-angle end, intermediate focal position and telephoto end of the zoom lens 2, F-number, angle of view (2
ω) and the numerical values of the surface distances d5, d11, d14, and d18 in which the surface distance changes with zooming and focusing.

[0058]

[Table 6]

Table 7 shows both surfaces r6 and r7 of the fourth lens L4 formed by the aspherical surface of the zoom lens 2, the object-side surface r8 of the fifth lens, and the image-side surface r11 of the sixth lens L6.
The fourth-order, sixth-order, and eighth-order aspherical surface coefficients A4, A8, and A10 of the image-side surface r14 of the seventh lens L7 and both surfaces r17, r18 of the ninth lens L9 are shown.

[0060]

[Table 7]

Table 8 shows numerical values relating to the conditional expressions 2 to 6 of the zoom lens 2.

[0062]

[Table 8]

6 to 8 show the wide-angle end of the zoom lens 2,
A spherical aberration diagram, an astigmatism diagram, and a distortion diagram at the intermediate focus position and at the telephoto end are shown, respectively.

Thus, in the zoom lenses 1 and 2, as is clear from the aberration diagrams of FIGS. 2 to 4 and FIGS. 6 to 8, each aberration is well corrected over the entire zoom range, Moreover, since the F number is about F1.6 while having a zoom ratio of about 20 times, it is possible to manufacture a bright and high-performance zoom lens at low cost.

Further, since the zoom lenses 1 and 2 use the second lens group GR2 to the fourth lens group GR4 as a common lens system, the cost reduction due to the mass production effect of parts can be further received. It is possible.

As described above, according to the present invention, the zoom lens is composed of the lenses of 9 elements in 4 groups, and 5 or 6 out of the 9 lenses are made of plastic including the aspherical surface. The lens that cannot contribute to the reduction of the manufacturing cost due to the difficulty of molding if it is made of plastic is made of a glass of an appropriate shape by trying to improve the performance while reducing the manufacturing cost of the entire system. By using a spherical lens, we have pursued a balance between maintaining optical performance and cost, thus achieving a high-performance, bright zoom lens that has an F / # of approximately F1.6 while having a zoom ratio of approximately 20x. It will be possible.

Further, according to the present invention, the glass lens located closest to the object side is made of a glass material having a large absorptivity for short-wavelength light, particularly ultraviolet rays, so that the glass lens is positioned closer to the image side than the glass lens. It is also possible to prevent yellowing of the plastic lens due to aging.

It should be noted that the specific shapes and structures of the respective portions shown in the above-mentioned embodiments are merely examples of specific embodiments for carrying out the present invention, and the technical features of the present invention are thereby obtained. The scope should not be limitedly interpreted.

[0069]

As is apparent from the above description, in the zoom lens according to the present invention, the first lens unit having a fixed position and a positive refractive power is arranged in order from the object side, and the concave surface is directed to the image side. On the optical axis, it is composed of a cemented lens of a first lens of a concave meniscus lens made of glass and a second lens of a convex lens of glass and a third lens of a convex meniscus lens made of plastic with a convex surface facing the object side. The second lens group having negative refracting power is moved mainly by moving the second lens group of the plastic concave lens with the strong concave surface facing the image side, and the fifth lens of the plastic biconcave lens. The third lens group, which is composed of a lens and a sixth biconvex lens made of plastic, is always fixed in position and has a positive refractive power,
The fourth lens group having a positive refracting power is composed of a glass biconcave lens eighth lens and a plastic lens. And a plastic lens having at least one aspherical surface, and the first lens has a material having an internal transmittance of 5 mm and a wavelength of 370 nm. To 45% or less and 1.3
With a thickness of mm or more, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, Z is the zoom ratio, D is the diagonal length of the image pickup screen, and r5 is counted from the object side. The radius of curvature of the fifth lens surface, the radius of curvature of the eighth lens surface counting r8 from the object side, the radius of curvature of the ninth lens surface counting r9 from the object side, and the tenth radius counting r10 from the object side. If the radius of curvature of the lens surface is f1 / r5
<0.25, 0.7 <| f2 / (0.05Z + 1.7)
D | <1, 0.7 <| r8 / r9 | <1, 0.6 <| r
Since the condition 9 / r10 | <0.9 is satisfied, it is possible to manufacture a bright and high-performance zoom lens with a high zoom ratio at a low cost, and at the same time, to manufacture it with a plastic made by the influence of ultraviolet rays. Yellowing of the lens can also be prevented.

In the invention described in claim 2, the fourth aspect
Both surfaces of the ninth lens, which is a biconvex lens in the lens group, are formed by aspherical surfaces, F4 is a fourth-order aspherical coefficient of the object-side surface of the ninth lens, and R4 is 4 of the image-side surface of the ninth lens. The next aspherical coefficient, F6, is set to 6 on the object side surface of the ninth lens
If the next aspherical coefficient, R6, is a sixth-order aspherical coefficient of the image-side surface of the ninth lens, F4 / R4 <0, F6 / R6 <0
Since each condition is satisfied, each aberration is satisfactorily corrected over the entire zoom range, has a high zoom ratio of about 20 times, has an F number of about 1.6, is bright, It is possible to obtain a higher performance zoom lens.

Another embodiment of the zoom lens of the present invention is
In order from the object side, the first lens group, which is always fixed in position and has a positive refracting power, is used as a first lens of a concave meniscus lens made of glass with a concave surface facing the image side and a second lens of a convex lens made of glass.
It is composed of a cemented lens with a lens and a third lens which is a convex meniscus lens made of glass with a convex surface facing the object side, and mainly has a negative refractive power by moving on the optical axis to carry out zooming. The second lens group is configured by a fourth lens which is a plastic concave lens with a strong concave surface facing the image side, a fifth lens which is a plastic biconcave lens, and a sixth lens which is a plastic biconvex lens. The third lens group, which is always fixed and has a positive refracting power, is composed of the seventh lens, which is a convex lens made of plastic, and is moved on the optical axis to correct the fluctuation of the image position and focus, The fourth lens group having refractive power is composed of an eighth lens, which is a biconcave lens made of glass, and a ninth lens, which is a biconvex lens made of plastic. The Kutomo one surface constituted by an aspheric, the first lens, 5mm thick internal transmittance of the material
At a wavelength of 370 nm with a coloring of 45% or less and a thickness of 1.3 mm or more, f2 is the focal length of the second lens group, Z is the zoom ratio, and D is the image pickup screen. Diagonal length, r8 is the radius of curvature of the eighth lens surface counting from the object side, r9 is the radius of curvature of the ninth lens surface counting from the object side, and r10 is the radius of curvature of the tenth lens surface counting from the object side. , F4 is a fourth-order aspherical coefficient of the object-side surface of the ninth lens, R4 is a fourth-order aspherical coefficient of the image-side surface of the ninth lens, and F6 is 6 of the object-side surface of the ninth lens.
Assuming that the next aspherical coefficient is R6 and the sixth-order aspherical coefficient n3 of the image-side surface of the ninth lens is the refractive index of the third lens at the d-line, 0.7 <| f2 / (0.05Z + 1.7). ) D |
1, 0.7 <| r8 / r9 | <1, 0.6 <| r9 / r
10 | <0.9, F4 / R4 <0, F6 / R6 <0,
Since each condition of 1.69 <n3 is satisfied, each aberration is satisfactorily corrected over the entire zoom range, a high zoom ratio of about 20 times and an F number of about 1.6 are provided. It is possible to manufacture a bright and high-performance zoom lens having a low cost at a low cost and prevent yellowing of a plastic lens due to the influence of ultraviolet rays.

[Brief description of drawings]

1 shows a first embodiment of a zoom lens according to the present invention, together with FIGS. 2 to 4, and this figure is a diagram schematically showing a lens configuration.

FIG. 2 is a diagram showing various aberrations at the wide-angle end.

FIG. 3 is a diagram showing various aberrations at an intermediate focal length.

FIG. 4 is a diagram showing various aberrations at the telephoto end.

FIG. 5 shows a second embodiment of the zoom lens according to the present invention, together with FIGS. 6 to 8, and this figure is a diagram schematically showing a lens configuration.

FIG. 6 is a diagram showing various aberrations at the wide-angle end.

FIG. 7 is a diagram showing various aberrations at an intermediate focal length.

FIG. 8 is a diagram showing various aberrations at the telephoto end.

[Explanation of symbols]

1 ... Zoom lens, 2 ... Zoom lens, GR1 ... 1st lens group, GR2 ... 2nd lens group, GR3 ... 3rd lens group, GR4 ... 4th lens group, L1 ... 1st lens, L2 ...
Second lens, L3 ... Third lens, L4 ... Fourth lens, L
5 ... 5th lens, L6 ... 6th lens, L7 ... 7th lens, L8 ... 8th lens, L9 ... 9th lens

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA03 MA15 PA08 PA18 PB09                       QA02 QA07 QA17 QA21 QA25                       QA33 QA42 QA45 RA05 RA12                       RA13 RA32 RA43 SA23 SA27                       SA29 SA32 SA64 SA65 SA72                       SA73 SB04 SB14 SB22 SB33

Claims (3)

[Claims] 1. A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power in order from the object side. And a fourth lens group having a second lens group, the positions of the first lens group and the third lens group are fixed at all times, and the second lens group moves mainly on the optical axis to perform zooming. Is
In the zoom lens in which the fourth lens group moves on the optical axis to correct the variation in the image position and to perform focusing, the first lens group has a concave surface on the image side in order from the object side. And a cemented lens of a first lens of a concave meniscus lens made of glass and a second lens of a convex lens made of glass, and a third lens of a convex meniscus lens made of plastic with a convex surface facing the object side. The second lens group includes, in order from the object side, a fourth lens which is a plastic concave lens with a strong concave surface facing the image side, a fifth lens which is a plastic biconcave lens, and a sixth lens which is a plastic biconvex lens. The third lens group is made up of a plastic convex lens
The fourth lens group is composed of, in order from the object side, an eighth lens which is a biconcave lens made of glass and a ninth lens which is a biconvex lens made of plastic, and each of the plastic lenses is At least one surface is formed of an aspherical surface, and the first lens has a material having an internal transmittance of 5 mm.
The zoom lens is characterized in that it is colored with a light having a wavelength of 370 nm to be 45% or less, has a thickness of 1.3 mm or more, and satisfies the following conditions. f1 / r5 <0.25 0.7 <| f2 / (0.05Z + 1.7) D | <1 0.7 <| r8 / r9 | <1 0.6 <| r9 / r10 | <0.9 , F1: focal length of the first lens group, f2: focal length of the second lens group, Z: zoom ratio, D: diagonal length of the image pickup screen, r5: radius of curvature of the fifth lens surface counted from the object side , R8: the radius of curvature of the eighth lens surface counted from the object side, r9: the radius of curvature of the ninth lens surface counted from the object side, r10: the radius of curvature of the tenth lens surface counted from the object side . 2. The ninth lens, which is a biconvex lens in the fourth lens group, has both surfaces formed of aspherical surfaces, and further satisfies the following conditions. Zoom lens. F4 / R4 <0 F6 / R6 <0, where F4: fourth-order aspherical coefficient of the object-side surface of the ninth lens, R4: fourth-order aspherical coefficient of the image-side surface of the ninth lens, F6: A sixth-order aspherical coefficient of the object-side surface of the ninth lens, R6: a sixth-order aspherical coefficient of the image-side surface of the ninth lens. 3. A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power in order from the object side. And a fourth lens group having a second lens group, the positions of the first lens group and the third lens group are fixed at all times, and the second lens group moves mainly on the optical axis to perform zooming. Is
In the zoom lens in which the fourth lens group moves on the optical axis to correct the variation in the image position and to perform focusing, the first lens group has a concave surface on the image side in order from the object side. And a third lens which is a convex meniscus lens made of glass and has a convex surface facing the object side. The second lens group includes, in order from the object side, a fourth lens which is a plastic concave lens with a strong concave surface facing the image side, a fifth lens which is a plastic biconcave lens, and a sixth lens which is a plastic biconvex lens. The third lens group is made up of a plastic convex lens
The fourth lens group is composed of, in order from the object side, an eighth lens which is a biconcave lens made of glass and a ninth lens which is a biconvex lens made of plastic, and each of the plastic lenses is At least one surface is formed of an aspherical surface, and the first lens has a material having an internal transmittance of 5 mm.
The zoom lens is characterized in that it is colored with a light having a wavelength of 370 nm to be 45% or less, has a thickness of 1.3 mm or more, and satisfies the following conditions. 0.7 <| f2 / (0.05Z + 1.7) D | <1 0.7 <| r8 / r9 | <1 0.6 <| r9 / r10 | <0.9 F4 / R4 <0 F6 / R6 <0 1.69 <n3 However, f2: focal length of the second lens group, Z: variable power ratio, D: diagonal length of the image pickup screen, r8: radius of curvature of the eighth lens surface counted from the object side, r9 : Radius of curvature of ninth lens surface counted from object side, r10: radius of curvature of tenth lens surface counted from object side, F4: fourth-order aspherical coefficient of object-side surface of ninth lens, R4 : A fourth-order aspherical coefficient of the image-side surface of the ninth lens, F6: sixth-order aspherical coefficient of the object-side surface of the ninth lens, R6: sixth-order aspherical coefficient of the image-side surface of the ninth lens Spherical coefficient n3: Refractive index of the third lens at the d-line.