JPH10307257A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zoom lens drastically reduced in cost while having a large aperture and high variable power ratio by providing four groups which are positive, negative, positive and positive in order from an object side and using plastic lens multiply. SOLUTION: This lens is provided with the 1st lens group having positive refractive power, the 2nd lens group having negative refractive power and moving for the purpose of variable power, the 3rd lens group having the positive refractive power and fixed, and the 4th lens group having the positive refractive power and correcting the positional change of an image formation surface at the time of variable power in order from the object side. In the 1st lens group, one positive lens is formed of inorganic glass and other lenses are all formed of plastic. In the 2nd lens group, one negative lens is formed of inorganic glass and other lenses are all formed of plastic. Then, all the lenses are formed of plastic in the 3rd lens group, and one positive lens is formed of inorganic glass and other lenses are all formed of plastic in the 4th lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-cost zoom lens having a large diameter and a high zoom ratio suitable for a still camera or a video camera.

[0002]

2. Description of the Related Art Conventionally, positive, negative, positive, positive
A zoom lens having two groups, a second lens group having a zooming function, and a fourth lens group having a function of correcting image plane movement accompanying zooming is well known, and many applications have been filed. ing. Japanese Patent Application Laid-Open No. 5-264902 discloses a zoom lens which achieves a high zoom ratio of 10 to 12 times while reducing the cost by using three of the 12 lenses as plastic lenses. Also, JP-A-8-1060
In the 46th publication, the cost is further reduced.
While 4 out of 10 lenses are plastic lenses, 1
A zoom lens achieving a double magnification ratio is disclosed.

[0003]

However, in each of the embodiments, more than half of the number of components is a glass lens, leaving room for further cost reduction.

[0004] The present invention has been made to solve the above problems. In other words, an object of the present invention is to provide a zoom lens which is suitable for a still camera or a video camera, has a large aperture, and has a high zoom ratio, but uses a large amount of plastic lenses, thereby significantly reducing the cost compared to the related art. Things.

[0005]

The above object is achieved by the following means.

That is, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power and moving for zooming, and having a positive refractive power and fixed. A third lens group, a fourth lens group having a positive refractive power and correcting a change in the position of an image forming surface during zooming, and one positive lens among the lenses constituting the first lens group; Is formed of inorganic glass, and all other lenses are formed of plastic. Of the lenses constituting the second lens group, one negative lens is formed of inorganic glass, and all other lenses are formed of plastic. The lenses constituting the third lens group are all formed of plastic, one of the lenses constituting the fourth lens group is formed of inorganic glass, and the other lenses are all formed of plastic. Characterized by the fact that Zoom lens.

A zoom lens characterized by satisfying the following conditional expression.

| Fw · {1 / fp ₍₁₎ } | <0.10 ... 1 equation | fw · {1 / fp ₍₂₎ } | <0.25 ... 2 equation | fw · Σ ｛ 1 / fp ₍₃ , ₄₎ ｝ | <0.10 _{(3 )} where fw is the focal length at the wide-angle end of the entire system {1 / fp ₍₁₎ } is each plastic in the first lens group. The sum of the reciprocals of the focal lengths of the lenses {1 / fp ₍₂₎ } is the sum of the reciprocals of the focal lengths of the plastic lenses in the second lens group {1 / fp ₍ 3,4 ₎ } is the third The sum of the reciprocals of the focal lengths of the plastic lenses in the four lens groups. The first lens group is composed of two positive lenses and one negative lens, and constitutes the first lens group. A zoom lens, wherein one positive lens and one negative lens are formed of plastic, and the remaining one positive lens is formed of inorganic glass.

The second lens group includes a negative single lens having a concave surface having a curvature larger than the curvature of the object side toward the image side in order from the object side, and a negative and positive cemented lens. A zoom lens, wherein the single lens is formed of inorganic glass, and the two lenses forming the bonded lens are both formed of plastic.

The third lens group is a positive lens formed of one piece of plastic.

The fourth lens group includes a positive and negative or negative and positive cemented lens, and a positive single lens,
A zoom lens, wherein the two lenses constituting the cemented lens are both formed of plastic, and the positive single lens is formed of inorganic glass.

Here, the operation of the zoom lens according to the present invention will be described.

In general, when a plastic lens is used as a zoom lens, if temperature compensation is strictly performed over the entire zoom range, it is necessary to perform temperature compensation for each zoom group.
That is, each group requires at least one glass lens.

In the present invention, one glass lens having a positive refractive power is disposed in the first lens group having a positive refractive power, and the other lens in the first lens group is used as a plastic lens. The refractive power of the lens group is mainly applied to one glass lens to compensate for the temperature of the first lens group, and the second lens group having a negative refractive power is provided with one glass of negative refractive power. A lens is disposed, and the other lens in the second lens group is made of a plastic lens, and the refractive power of the second lens group is mainly borne by one glass lens to compensate for the temperature of the second lens group. .

In the third and fourth lens groups, since the fluctuation of magnification due to zooming is small, sufficient temperature compensation can be performed by the combined system of the third and fourth lens groups without temperature compensation for each group. It is. Therefore, the third lens group is composed of only plastic lenses, and the fourth lens group has a positive refractive power of one.
Two glass lenses are arranged, and the other lenses in the fourth lens group are plastic lenses, and these and the plastic lenses in the third lens group perform temperature compensation.

A more specific structure of the zoom lens according to the present invention will be described.

The first lens group preferably comprises a positive and negative lens or a negative and positive lens formed of plastic and a positive single lens formed of inorganic glass. The chromatic aberration can be favorably corrected by the positive lens and the negative lens of the plastic lens, and when the positive single lens is used as the glass lens and the main refractive power of the first lens group is borne by this lens, Temperature compensation can be performed satisfactorily.

The second lens group is preferably composed of a single negative lens made of inorganic glass and a negative and positive cemented lens made of a plastic lens. Since the cemented lens has a negative lens and a positive lens, chromatic aberration can be satisfactorily corrected. In addition, when a negative single lens is used as a glass lens and the main refractive power of the second lens group is borne by this lens, the second lens becomes The temperature compensation in the lens group can be favorably performed. By attaching a plastic lens, eccentricity sensitivity can be suppressed, and the number of lens surfaces can be reduced to improve transmittance.

The third lens group is preferably composed of one positive plastic lens in order to minimize the number of glass lens groups. The third and fourth lens groups only need to have a single glass lens in the third and fourth lens groups, since the temperature should be compensated by a combining system. However, the third lens group should have a minimum number of one. If a glass lens is used for the third lens group when trying to compose, the temperature compensation becomes impossible if the fourth lens group is entirely made of a plastic lens, so that a glass lens is also required for the fourth lens group. Because. If the third lens group is a single positive plastic lens, temperature compensation can be achieved by arranging a positive glass lens in the fourth lens group and making the combined refractive power of the plastic lenses in the fourth lens group negative. It becomes possible.

The fourth lens group preferably comprises a positive and negative or negative and positive cemented lens made of a plastic lens and a single positive lens made of inorganic glass. The combined refractive power of the plastic lens of the fourth lens group is assumed to be negative in order to correct the chromatic aberration by the cemented lens and to cancel the change in the refractive power at the time of temperature change occurring in the positive plastic lens of the third lens group. Therefore, a positive glass lens is required in the fourth lens group. Similarly to the second lens group, by attaching a plastic lens, eccentric sensitivity can be suppressed, and the number of lens surfaces can be reduced to improve transmittance.

Hereinafter, conditional expressions 1 to 3 will be described.

Equation 1 relates to the refractive power of the plastic lens in the first lens group. The first lens group negates a change in refractive power due to a temperature change by using one plastic lens as one positive lens and one negative lens among the three lens elements that constitute the first lens group. Within the range of this expression, it is possible to sufficiently cancel the change in the refractive power due to the temperature change, and to further reduce the amount of change in the focal position.

It is more desirable that Equation 1 takes the value of Equation 1-1 below.

| Fw · {1 / fp ₍₁₎ } | <0.05 Expression 1-1 Expression 2 relates to the refractive power of the plastic lens in the second lens group. In the second lens group, a change in refractive power due to a change in temperature is canceled by using one plastic lens as one negative lens and one positive lens among the three lenses that constitute the second lens group. If it is within the range of this equation, the refractive power change due to the temperature change is sufficiently canceled,
It is possible to further reduce the change amount of the focal position.

It is more desirable that the two equations take the values of the following equation 2-1.

| Fw · {1 / fp ₍₂₎ } | <0.22 Equation 2-1 Equation 3 relates to the refractive power of the plastic lens in the third and fourth lens groups. In the lens system of the present invention, since the lens system is composed of only the plastic lens of the third lens group, the combined refractive power of the plastic lenses in the fourth lens group is made negative to cancel the change in refractive power due to the temperature change. Within the range of Expression 3, it is possible to further reduce the amount of change in the focal position.

It is more desirable that Equation 3 takes the value of Equation 3-1 below.

[0028] | fw · Σ {1 / f p (3, 4)} | <0.05 ... 3-1 formula

[0029]

An embodiment satisfying the above conditions will be described below.

Here, r is the radius of curvature of each lens surface, d is the lens thickness or lens interval, n _d is the refractive index, and ν _d is the Abbe number. * Indicates a plastic lens.

The shape of the aspheric surface has an x-axis in the optical axis direction and a y-axis in a direction perpendicular to the optical axis, and κ, A ₂ , A ₄ , A ₆ , A ₈ ,
When A ₁₀ and A ₁₂ are aspheric coefficients, they are expressed by the following equations.

[0032]

(Equation 1)

* 1 to * 4 represent plastic lenses, and the change in the refractive index due to each temperature change is as follows.

[0034]

[Table 1]

FIG. 1 is a sectional view of the lens of the first embodiment.
2A and 2B are aberration diagrams of the lens according to the first embodiment. FIG.
(B) is an aberration diagram at an intermediate region, and (c) is an aberration diagram at a telephoto end. FIG.
6 is a sectional view of a lens according to Example 2. FIG. 4A and 4B are aberration diagrams of the lens according to the second embodiment, in which FIG. 4A is the wide-angle end, FIG.
(C) is an aberration diagram at the telephoto end. FIG. 5 is a sectional view of the lens of the third embodiment. 6A and 6B are aberration diagrams of the lens according to the third embodiment. FIG. 6A is an aberration diagram at the wide angle end, FIG. 6B is an aberration diagram at the intermediate range, and FIG. FIG. 7 is a sectional view of the lens of the fourth embodiment. 8A and 8B are aberration diagrams of the lens according to the fourth embodiment. FIG. 8A is an aberration diagram at the wide-angle end, FIG. 8B is an aberration diagram at an intermediate range, and FIG.
FIG. 9 is a sectional view of the lens of the fifth embodiment. FIGS. 10A and 10B are aberration diagrams of the lens according to the fifth embodiment. FIG. 10A is an aberration diagram at the wide-angle end, FIG. 10B is an aberration diagram at the intermediate range, and FIG. FIG. 11 is a sectional view of the lens of the sixth embodiment. 12A and 12B are aberration diagrams of the lens according to the sixth embodiment. FIG. 12A is the wide-angle end, FIG.
9 is an aberration diagram at a telephoto end.

Example 1 Focal length: f = 4.59 to 52.92 F number: F1.66 to 2.92 Angle of view: 2ω = 56.2 ° to 5.0 °

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

| Fw · Σ ｛1 / fp ₍₁₎ ｝ | = 0.00 | fw · Σ ｛1 / fp ₍₂₎ ｝ | = 0.16 | fw · Σ ｛1 / fp ₍₃ , ₄₎ ｝ | = 0.01 Example 2 Focal length: f = 4.59 to 52.92 F number: F1.66 to 2.76 Angle of view: 2ω = 56.0 ° to 5.0 °

[0042]

[Table 6]

[0043]

[Table 7]

[0044]

[Table 8]

[0045]

[Table 9]

| Fw · Σ ｛1 / fp ₍₁₎ ｝ | = 0.00 | fw · Σ ｛1 / fp ₍₂₎ ｝ | = 0.21 | fw · Σ ｛1 / fp ₍₃₎ , ₄₎ ｝ | = 0.01 Example 3 Focal Length: f = 4.28 to 49.42 F-Number: F1.66 to 2.53 Angle of View: 2ω = 59.8 ° to 5.4 °

[0047]

[Table 10]

[0048]

[Table 11]

[0049]

[Table 12]

[0050]

[Table 13]

| Fw · Σ ｛1 / fp ₍₁₎ ｝ | = 0.01 | fw · Σ ｛1 / fp ₍₂₎ ｝ | = 0.15 | fw · Σ ｛1 / fp ₍₃ , ₄₎ ｝ | = 0.01 Example 4 Focal length: f = 4.28 to 49.42 F number: F1.66 to 2.53 Angle of view: 2ω = 59.8 ° to 5.4 °

[0052]

[Table 14]

[0053]

[Table 15]

[0054]

[Table 16]

[0055]

[Table 17]

| Fw · Σ ｛1 / fp ₍₁₎ ｝ | = 0.01 | fw · Σ ｛1 / fp ₍₂₎ ｝ | = 0.15 | fw · Σ ｛1 / fp ₍₃₎ , ₄₎ ｝ | = 0.01 Example 5 Focal length: f = 4.28 to 49.46 F number: F1.66 to 2.53 Angle of view: 2ω = 59.2 ° to 5.4 °

[0057]

[Table 18]

[0058]

[Table 19]

[0059]

[Table 20]

[0060]

[Table 21]

| Fw · Σ ｛1 / fp ₍₁₎ ｝ | = 0.01 | fw · Σ ｛1 / fp ₍₂₎ ｝ | = 0.15 | fw · Σ ｛1 / fp ₍₃ , ₄₎ ｝ | = 0.01 Example 6 Focal length: f = 4.28 to 49.47 F number: F1.66 to 2.39 Angle of view: 2ω = 59.8 ° to 5.4 °

[0062]

[Table 22]

[0063]

[Table 23]

[0064]

[Table 24]

[0065]

[Table 25]

| Fw · Σ ｛1 / fp ₍₁₎ ｝ | = 0.01 | fw · Σ ｛1 / fp ₍₂₎ ｝ | = 0.15 | fw · Σ ｛1 / fp ₍₃₎ , ₄₎ ｝ | = 0.01

[0067]

According to the present invention, a zoom lens which is suitable for a still camera or a video camera and which has a large aperture and a high zoom ratio and which uses a large number of plastic lenses can greatly reduce the cost as compared with the conventional one. Will be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a first embodiment.

FIG. 2 is an aberration diagram of the lens according to the first embodiment.

FIG. 3 is a sectional view of a lens according to a second embodiment.

FIG. 4 is an aberration diagram of a lens according to a second embodiment.

FIG. 5 is a sectional view of a lens according to a third embodiment.

FIG. 6 is an aberration diagram of the lens of the third embodiment.

FIG. 7 is a sectional view of a lens according to a fourth embodiment.

FIG. 8 is an aberration diagram of the lens of the fourth embodiment.

FIG. 9 is a sectional view of a lens according to a fifth embodiment.

FIG. 10 is an aberration diagram of the lens of the fifth embodiment.

FIG. 11 is a sectional view of a lens according to a sixth embodiment.

FIG. 12 is an aberration diagram of the lens of the sixth embodiment.

Claims (6)

[Claims] 1. A first lens unit having a positive refractive power and a second lens unit having a negative refractive power and moving for zooming in order from the object side.
A lens group, a fixed third lens group having a positive refractive power,
A fourth lens group that has a positive refractive power and corrects a change in the position of the imaging surface during zooming, wherein one of the lenses constituting the first lens group is made of inorganic glass The other lenses are all formed of plastic, one of the lenses constituting the second lens group is formed of inorganic glass, the other lens is formed of plastic, and the third lens is formed of the third lens. The lenses constituting the group are all formed of plastic, and among the lenses constituting the fourth lens group, one positive lens is formed of inorganic glass and the other lenses are all formed of plastic. Zoom lens. 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied. | Fw · Σ {1 / f p (1)} | <0.10 | fw · Σ {1 / f p (2)} | <0.25 | fw · Σ {1 / f p (3, 4) ｝ | <0.10 where fw is the focal length at the wide-angle end of the entire system {1 / fp ₍₁₎ } is the sum of the reciprocals of the focal length of each plastic lens in the first lens group. fp ₍₂₎ is the sum of the reciprocals of the focal lengths of the plastic lenses in the second lens group. {1 / fp ₍ 3,4 ₎ } is the focal length of each plastic lens in the third and fourth lens groups. Sum of reciprocals of 3. The first lens group includes two positive lenses and one negative lens, and among the lenses constituting the first lens group, one positive lens and one negative lens The negative lens is formed of plastic, and the remaining one positive lens is formed of inorganic glass.
Or the zoom lens according to 2. 4. The second lens group includes a negative single lens having a concave surface having a curvature larger than the curvature of the object side toward the image side in order from the object side, and a negative and positive cemented lens. The zoom lens according to any one of claims 1 to 3, wherein the single lens is formed of inorganic glass, and the two lenses forming the bonded lens are both formed of plastic. 5. The zoom lens according to claim 1, wherein the third lens group is a positive lens formed of one piece of plastic. 6. The fourth lens group includes a positive and negative or negative and positive cemented lens and a positive single lens, and the two lenses constituting the cemented lens are both formed of plastic. The zoom lens according to any one of claims 1 to 5, wherein the positive single lens is formed of inorganic glass.