JP2000258689A - High variable power zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact zoom lens having a high variable power ratio where aspherical plastic lens is effectively utilized by eliminating trouble such as the positional fluctuation in an image point by the characteristic change (refractive index change or volume change) of plastic material when temperature and humidity are changed. SOLUTION: This zoom lens is constituted of a 1st lens group G1 having positive refractive power, a 2nd lens group G2 having positive refractive power and a 3rd lens group G3 having negative refractive power in order from an object side, and variable power is performed by changing a distance between the respective lens groups. The 3rd lens group G3 is constituted of a 3m-th plastic lens in meniscus shape having an aspherical surface and turning a concave surface to the object side, a 3p-th positive lens turning a convex surface to an image side and a 3n-th negative lens arranged nearest to the image side and turning a concave surface to the object side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens having a high zoom ratio, which is used as a photographing lens for a lens shutter camera.

[0002]

2. Description of the Related Art In a recent lens shutter camera, a positive / negative three-group zoom lens is generally used as a photographing lens having a zoom ratio of 3 times or more. Among them, there are known many examples in which a plastic lens having an aspherical surface is adopted for the purpose of high performance, compactness, and low cost. In particular, when an aspherical surface is employed in the negative third lens group in the three-unit zoom lens, off-axis aberrations such as distortion in the wide-angle end to the intermediate range can be effectively corrected.

Further, since the negative third lens group is constituted by a lens having a relatively large outer diameter, the use of an aspherical lens made of a plastic material is also effective in reducing the weight. For example, Japanese Patent Application Laid-Open No. 6-194573 discloses an invention having a zoom ratio of about 2.8, in which a negative third lens group is composed of a positive aspheric plastic lens and a negative lens.

[0004]

However, the negative third lens group in the positive, negative, positive and negative three-group zoom lens is a lens group having a large refractive power which plays a large part in zooming. Therefore, for example, when a zoom lens having a zoom ratio of 3 times or more is used, the influence of a change in plastic material characteristics (a change in refractive index or a change in volume) due to a change in temperature and humidity cannot be neglected. Point position fluctuations become noticeable.

An object of the present invention is to solve the above-mentioned problems and to provide a compact zoom lens having a high zoom ratio by effectively utilizing an aspherical plastic lens.

[0006]

The object of the present invention is achieved by adopting the following constitution.

That is, in order from the object side, there are a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. In the zoom lens that performs zooming by performing zooming, the third lens group includes a third meniscus-shaped plastic lens having an aspheric surface and a concave surface facing the object side, a third positive lens having a convex surface facing the image side, This is achieved by a high-magnification zoom lens comprising a third negative lens arranged on the image side and having a concave surface facing the object side.

Also, in order from the object side, there are a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. In the zoom lens that performs zooming by performing zooming, the third lens group has an aspheric surface and a third lens group having a concave surface facing the object side.
an m-meniscus lens, a third p-th positive lens having a convex surface facing the image side, and a third n-negative lens having a concave surface facing the object side closest to the image side, and having an aperture stop in the second lens group or the second lens. This is achieved by a high-magnification zoom lens characterized by being arranged on the image side of the group.

Also, in order from the object side, there are a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. In the zoom lens that performs zooming by performing the zooming, the second lens group includes at least one set of a cemented lens,
The third lens group includes a third m meniscus lens having an aspheric surface and having a concave surface facing the object side, and a third p lens having a convex surface facing the image side.
This is achieved by a high-magnification zoom lens comprising a positive lens and a 3n-th negative lens arranged closest to the image side and having a concave surface facing the object side.

Also, in order from the object side, there is a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. At the time of magnification, the distance between the first lens group and the second lens group increases, and the distance between the second lens group and the third lens group decreases, while the zoom lens in which all the lens groups move to the object side. The third lens unit includes a third m meniscus lens having an aspheric surface and a concave surface facing the object side, a third p-positive lens having a convex surface facing the image side, and a third (n) th lens arranged closest to the image side and having a concave surface facing the object side. This is achieved by a high-magnification zoom lens characterized by comprising a negative lens.

Further, the present invention is achieved by a high-magnification zoom lens characterized by satisfying the following conditional expressions.

0.6 <f _W · tan ω _W / | f ₃ | <1.6 (1) | f ₃ / f _3m | <0.2 (2) 15 <ν _3n −ν _3p (3) where, f _W : focal length of the entire system at the wide-angle end tanω _W : tangent of a half angle of view at the wide-angle end f ₃ : focal length of the third lens group f _3m : the third meniscus lens Ν _3n : Abbe number of the 3n negative lens ν _3p : Abbe number of the 3p positive lens Further, the first lens group is a first n negative lens having a concave surface facing the object side in order from the object side. And a high-power zoom lens comprising two positive and negative first p lenses and satisfying the following conditional expression.

0.1 <f _W · tanω _W / f ₁ <0.6 (4) 20 <ν _1p −ν _1n (5) where f ₁ : focal point of the first lens group Distance ν _1p : Abbe number of the first p-th positive lens ν _1n : Abbe number of the first n-negative lens Further, at the time of zooming, the first lens group and the third lens group move integrally. Achieved by a high zoom lens.

In addition, the zoom lens system has at least three lens groups including a first lens group having a positive refractive power closest to the object side and a final lens group having a negative refractive power closest to the image side, and has a wide angle. At the time of zooming from the end to the telephoto end, the air gap between the first lens group adjacent to the image side of the first lens group and the first lens group increases, and the lens group adjacent to the object side of the final lens group At least the first lens group and the last lens group move toward the object side so that the air gap between the first lens group and the last lens group decreases. A negative lens having a concave surface is arranged, and the final lens group is a meniscus-shaped plastic lens having an aspheric surface and having a concave surface facing the object side, a positive lens having a convex surface facing the image side, and is arranged closest to the image side. Facing the concave side It is achieved by a high-zoom-ratio zoom lens, characterized in that it is composed of a negative lens.

[0015]

Next, the structure and operation of a zoom lens according to the present invention will be described.

The high-magnification zoom lens according to the present invention includes, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. When zooming from the telephoto end to the telephoto end, all three lens units are positioned such that the distance between the first lens unit and the second lens unit increases and the distance between the second lens unit and the third lens unit decreases. Move to the side.

The aperture stop is arranged in the second lens group or behind the second lens group, so that the lens diameter of each lens group can be reduced in a well-balanced manner.

A first n-th negative lens having a concave surface facing the object side is disposed closest to the object side of the first lens group, and corrects astigmatism and distortion on the wide-angle side.

The second lens group has a configuration in which a sub-group having a negative refractive power is arranged on the object side and a sub-group having a positive refractive power is arranged on the image side, so that the object-side lens diameter of the second lens group is reduced. , Ensuring the back focus at the wide-angle end. Also, by using an aspherical surface on the surface near the aperture stop, spherical aberration, coma aberration, and the like are satisfactorily corrected in the entire zoom range. Further, in order to satisfactorily correct various aberrations including chromatic aberration, it is desirable to use at least one set of cemented lenses in the second lens group.

A characteristic configuration of the present invention resides in the third lens group. The third lens group includes a third m meniscus lens having an aspheric surface with a concave surface facing the object side, and a third meniscus lens with a convex surface facing the image side.
It is composed of a p-positive lens and a 3n-negative lens disposed closest to the image side and having a concave surface facing the object side. The third m meniscus lens satisfactorily corrects off-axis aberrations such as distortion on the wide-angle side by using an aspherical surface, and prevents performance degradation accompanying high zooming and compactness.

Further, by using a plastic material for the material of the third m meniscus lens, which tends to have a relatively large outer diameter, a reduction in weight can be achieved. In addition, a plastic lens manufactured by injection molding can easily add an aspherical surface and has excellent mold durability, so that there is an advantage in terms of cost reduction of a zoom lens. On the other hand, when a plastic lens is used in a high-magnification zoom lens, it is important to suppress image point position fluctuation due to temperature and humidity changes. In the present invention, this is achieved by forming the third m plastic lens into a meniscus shape having a very low refractive power. This minimizes the effects of changes in the surface shape due to changes in the refractive index when the temperature and humidity change and changes in the volume.

As described above, since the 3m plastic lens cannot have a large refractive power, the role of correcting spherical aberration and chromatic aberration in the third lens group is mainly the 3p positive lens and the 3n negative lens. The lens is responsible.
The configuration of the third lens group is divided into a lens responsible for effective off-axis aberration correction by an aspherical surface and a lens responsible for correction of spherical aberration, chromatic aberration, and the like. This is an optimal configuration for a high-magnification zoom lens that has a large degree of power and is well-corrected for aberrations in all zoom ranges while being compact. The present invention does not limit the arrangement order of the third m meniscus lens and the third p positive lens from the object side.

With respect to the movement of each lens unit during zooming, if the first lens unit and the third lens unit are moved integrally, the mechanical structure can be simplified, and the position error of each lens unit can be reduced. The error sensitivity of the image point movement can be reduced.

Further, the constitution of the first lens unit and the third lens unit in the present invention is not limited to the positive / negative three-unit zoom lens. For example, the present invention is also applicable to a positive / negative positive / negative four-unit zoom lens in which the second lens unit is divided into two, a five-unit zoom lens, and the like.

Hereinafter, the conditional expressions of the present invention will be described.

Condition (1) defines the refractive power of the negative third lens group. When the refractive power of the third lens unit is reduced below the lower limit, a large amount of movement is required during zooming, so that it becomes difficult to secure the back focus at the wide-angle end, and further, the outer diameter of the third lens unit. Also become large and impair compactness. If the refractive power of the negative third lens unit is increased beyond the upper limit, it becomes difficult to correct various aberrations generated in the third lens unit on the wide angle side.

Conditional expression (2) defines the refractive power of the third m meniscus lens made of a plastic material. If the refractive power of the third m meniscus lens is increased outside of this condition, the fluctuation of the image point position when the temperature and humidity change is undesirably noticeable.

Condition (3) defines the Abbe number of the third positive lens and the negative third lens for chromatic aberration correction. Deviating from this condition makes it difficult to correct chromatic aberration.

Conditional expression (4) defines the refractive power of the first lens unit having a positive refractive power. If the refractive power of the first lens group is reduced below the lower limit, the amount of movement for zooming is increased, thereby impairing compactness. If the refractive power of the first lens group exceeds the upper limit, it becomes difficult to secure the back focus at the wide-angle end, and it becomes difficult to correct various aberrations generated in the first group.

Condition (5) defines the Abbe number of the first p-th positive lens and the first n-n negative lens for chromatic aberration correction. Deviating from this condition makes it difficult to correct chromatic aberration.

[0031]

Embodiments of the present invention will be described below.

In the high-power zoom lens according to each embodiment of the present invention, the first lens unit G1 having a positive refractive power, the second lens unit G2 having a positive refractive power, and the third lens unit G having a negative refractive power are arranged in order from the object side.
3 for zooming from the wide-angle end to the telephoto end.
The air gap between the lens group G1 and the second lens group G2 increases,
All the lens groups move toward the object side so that the air gap between the second lens group G2 and the third lens group G3 decreases. Further, the first lens group G1 and the third lens group G3 move together during zooming. The aperture stop S is arranged on the image side of the second lens group G2, and moves together with the second lens group during zooming. The third lens group includes, in order from the object, a third m meniscus lens, a third positive lens, and a third negative lens.

In the following symbols, f is the focal length (mm) of the entire system, F is the F number, fB is the back focus (mm), ω is the half angle of view (°), r is the radius of curvature (mm),
d is the axial top surface interval (mm), _nd is the refractive index for d-line,
ν _d is the Abbe number.

* In the surface No represents an aspheric surface. In an orthogonal coordinate system in which the vertex of the surface is the origin and the optical axis direction is the X axis, the vertex curvature is C, the conic constant is K, the aspheric coefficient is A4,
A6, A8, and A10 are represented by the following equations.

[0035]

(Equation 1)

First Embodiment f: 39.45 to 76.01 to 144.39 F: 5.2 to 8.5 to 14.3 ω: 28.8 to 15.5 to 8.4 fB: 9. 53-32.71-74.90

[0037]

[Table 1]

[0038]

[Table 2]

Second Example f: 39.56 to 75.9 to 144.01 F: 4.8 to 8.2 to 14.1 ω: 28.5 to 15.5 to 8.5 fB: 9. 41 to 33.51 to 77.73

[0040]

[Table 3]

[0041]

[Table 4]

Third Embodiment f: 39.55 to 76.0 to 143.90 F: 4.8 to 8.1 to 13.9 ω: 28.7 to 15.5 to 8.5 fB: 9. 03-32.38-75.02

[0043]

[Table 5]

[0044]

[Table 6]

Fourth Embodiment f: 39.55 to 76.0 to 143.90 F: 4.9 to 7.9 to 13.2 ω: 27.9 to 15.5 to 8.5 fB: 9. 41 to 32.69 to 74.75

[0046]

[Table 7]

[0047]

[Table 8]

Table 9 below shows numerical values of each embodiment corresponding to each conditional expression.

[0049]

[Table 9]

[0050]

According to the present invention, a compact and high zoom ratio zoom lens using an aspherical plastic lens effectively is provided.

[Brief description of the drawings]

FIG. 1 is a lens cross-sectional view of a first embodiment at a wide-angle end, an intermediate range, and a telephoto end.

FIG. 2 is an aberration diagram at a wide angle end, a middle range, and a telephoto end in the first embodiment.

FIG. 3 is a sectional view of a lens at a wide angle end, a middle range, and a telephoto end according to a second embodiment.

FIG. 4 is an aberration diagram at a wide-angle end, a middle range, and a telephoto end in the second embodiment.

FIG. 5 is a sectional view of a lens at a wide angle end, an intermediate range, and a telephoto end according to a third embodiment.

FIG. 6 is an aberration diagram at a wide-angle end, a middle range, and a telephoto end in the third embodiment.

FIG. 7 is a sectional view of a lens at a wide angle end, a middle range, and a telephoto end according to a fourth embodiment.

FIG. 8 is an aberration diagram at a wide angle end, an intermediate range, and a telephoto end in the fourth embodiment.

Claims (8)

[Claims] 1. A first lens having a positive refractive power in order from an object side.
A zoom lens, comprising a lens group, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, performing zooming by changing the air spacing of each lens group,
The lens group includes a third meniscus-shaped plastic lens having an aspheric surface and a concave surface facing the object side, a third p-positive lens having a convex surface facing the image side, and a third p-th lens arranged closest to the image side and having a concave surface facing the object side. A high-magnification zoom lens comprising a 3n negative lens. 2. A first lens having a positive refractive power in order from the object side.
A zoom lens, comprising a lens group, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, performing zooming by changing the air spacing of each lens group,
The lens unit has an aspheric surface and a concave surface facing the object side.
A meniscus lens, a third p-positive lens with a convex surface facing the image side, and a third n-negative lens with the concave surface facing the object side closest to the image side, and an aperture stop in the second lens group or the second lens group A high-magnification zoom lens, which is arranged on the image side of. 3. A first lens having a positive refractive power in order from the object side.
A zoom lens, which includes a lens group, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, and performs zooming by changing the air spacing of each lens group;
The lens group has at least one set of cemented lenses, the third lens group is a third m meniscus lens having an aspheric surface and having a concave surface facing the object side, a third p positive lens having a convex surface facing the image side, The third one that is arranged closest to the image side and has a concave surface facing the object side
A high zoom ratio zoom lens comprising an n-negative lens. 4. A first lens having a positive refractive power in order from the object side.
Consisting of a lens group, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, the distance between the first lens group and the second lens group increases when zooming from the wide-angle end to the telephoto end. And
In a zoom lens in which the distance between the second lens group and the third lens group is reduced while all the lens groups move toward the object side, the third lens group has an aspheric surface and a concave surface facing the object side. A high-magnification zoom lens comprising a 3m meniscus lens, a third p-th positive lens having a convex surface facing the image side, and a third n-negative lens having a concave surface facing the object side closest to the image side. 5. The high-magnification zoom lens according to claim 1, wherein the following conditional expression is satisfied. 0.6 <f _W · tanω _W / | f ₃ | <1.6 | f ₃ / f _3m | <0.2 15 <ν _3n −ν _{3p where} , f _W : focal length of the whole system at the wide-angle end tan ω _W : tangent of the half angle of view at the wide-angle end f ₃ : focal length of the third lens group f _3m : focal length of the third m meniscus lens ν _3n : Abbe number of the third negative lens ν _3p : third positive Abbe number of lens 6. The first lens group includes, in order from the object side,
The high zoom ratio zoom lens according to any one of claims 1 to 5, comprising a first n-th negative lens and a first p-th positive lens having a concave surface facing the object side, and satisfying the following conditional expressions. lens. 0.1 <f _W · tanω _W / f ₁ <0.6 20 <v _1p -v _1n where f ₁ : focal length of the first lens unit v _1p : Abbe number of the first p positive lens v _1n : Abbe number of the first n-th negative lens 7. The zoom lens according to claim 1, wherein the first lens group and the third lens group move integrally during zooming. 8. A wide-angle lens having at least three lens groups including a first lens group having a positive refractive power closest to the object side and a final lens group having a negative refractive power closest to the image side. At the time of zooming from the end to the telephoto end, the air gap between the first lens group adjacent to the image side of the first lens group and the first lens group increases, and the lens group adjacent to the object side of the final lens group At least the first lens group and the last lens group move toward the object side so that the air gap between the first lens group and the last lens group decreases. A negative lens having a concave surface is arranged, and the final lens group is a meniscus-shaped plastic lens having an aspheric surface and having a concave surface facing the object side,
A high-magnification zoom lens comprising a positive lens having a convex surface facing the image side and a negative lens having a concave surface facing the object side disposed closest to the image side.