JPH10104520A - Wide angle zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wide angle zoom lens which has a sufficiently large photographing angle of view at a wide angle end, has a variable power ratio exceeding two times and is well corrected of various aberrations by constituting the zoom lens so as to satisfy specific conditions. SOLUTION: This wide angle zoom lens has a first lens group G1 having negative refracting power, a second lens group G2 having positive refracting power and a third lens group G3 having positive refracting power. The one lens face of the lens faces constituting the first lens group G1 is formed to an aspherical shape. At the time of variable magnification from the wide angle end to the telephoto end, the first lens group G1 to the third lens group G3 move in such a manner that the air spacing between the first lens group G1 and the second lens group G2 decreases and the air spacing between the second lens group G2 and the third lens group G3 decreases. The conditions -1.2<f1/ft<-0.4, 0.5<f2/ft<0.35 are satisfied. In the equations, f1 denotes the focal length of the first lens group G1; f2 denotes the focal length of the second lens group G2 and further, ft denotes the focal length of the entire system at the telephoto end.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wide-angle zoom lens, and more particularly to a wide-angle zoom lens suitable for a single-lens reflex camera, an electronic still camera, and the like.

[0002]

2. Description of the Related Art At present, as a wide-angle zoom lens for a single-lens reflex camera, the angle of view at the wide-angle end is 100 ° to 94 °.
A zoom lens having a zoom ratio (magnification ratio) of about 2 or less has been commercialized. For example, JP-A-5-173071
The publication discloses that the shooting angle of view at the wide-angle end is about 94 °, the zoom ratio is about 1.75 times, and negative, positive, negative,
A four-group zoom lens having a positive refractive power is disclosed. However, recently, there has been an increasing demand for a wide-angle zoom lens having a larger angle of view at the wide-angle end and a zoom ratio of more than twice.

[0003]

Generally, if the power (refractive power) of each lens group in a zoom lens is increased,
The amount of zooming movement of each lens group is reduced, and downsizing and high zooming can be achieved. However, if the power of each lens group is simply increased, the amount of aberration generated in each lens group increases drastically, making it difficult to obtain good optical performance.

The present invention has been made in view of the above-mentioned problem, and has a wide angle of view at a wide-angle end that is sufficiently large, has a zoom ratio of more than twice, and has well-corrected various aberrations. It is an object to provide a zoom lens.

[0005]

In order to solve the above-mentioned problems, according to the present invention, a first lens unit G1 having a negative refractive power and a second lens unit G1 having a positive refractive power are arranged in order from the object side. G2, and a third lens group G3 having a positive refractive power. The first lens group G1 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative lens, and a A positive lens having a convex surface.
The lens group G2 has at least one positive lens with a convex surface facing the object side, the third lens group G3 has at least one negative lens with a concave surface facing the object side, and the first lens group At least one of the lens surfaces constituting G1
The two lens surfaces are formed in an aspherical shape, and at the time of zooming from the wide-angle end to the telephoto end, the air gap between the first lens group G1 and the second lens group G2 decreases, and the second lens group G
The first lens group G1 to the third lens group G3 move so that the air gap between the second lens group G3 and the third lens group G3 decreases, and the focal length of the first lens group G1 is set to f1,
When the focal length of the second lens group G2 is f2 and the focal length of the entire system at the telephoto end is ft, -1.2 <f1 / ft <-0.4 0.5 <f2 / ft <3 And a wide-angle zoom lens satisfying the following condition:

According to a preferred aspect of the present invention, the third
The lens group G3 has at least one positive lens and at least one negative lens, the focal length of the third lens group G3 is f3, and the strongest of the negative lenses constituting the third lens group G3. Assuming that the focal length of the negative lens having a refractive power is f3n, the condition of -1.1 <f3n / f3 <-0.1 is satisfied. Further, the second lens group G2 has at least one cemented lens of a positive lens and a negative lens, the focal length of the second lens group G2 is f2, and the second object of the second lens group G2 is closest to the object. Assuming that the radius of curvature of the lens surface is ra, it is preferable to satisfy the following condition: 0.2 <ra / f2 <1.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wide-angle zoom lens according to the present invention comprises, in order from the object side, a front group having a negative refractive power and a rear group having a positive refractive power.
The basic form is group composition. By dividing the rear group of the positive refractive power and changing the relative position of the divided lens groups, correction of negative distortion, which is a serious drawback in the wide-angle zoom lens, is realized.

First, in a wide-angle lens, since it is necessary to secure a back focus at the wide-angle end, a negative lens group of a front group and a positive lens group of a rear group are arranged at a predetermined distance from each other as in a retrofocus type. . In general, an iris diaphragm (aperture stop) is disposed in the rear group or immediately before the rear group (near the object side), and the iris diaphragm is moved integrally with the rear group. Here, since the front group has a strong negative power (refractive power) and is located away from the iris diaphragm, the height of the principal ray incident on the front group becomes large, and negative distortion occurs. Would.

As countermeasures against the negative distortion, the power of the negative lens unit, which is the front unit, is reduced,
It is conceivable to increase the number of lenses in the negative lens group and correct aberrations inside the front group. However, in either case, the size of the entire lens system is undesirably increased. Therefore, either a positive lens group is arranged in front of the iris diaphragm (object side) or a negative lens group is arranged behind the iris diaphragm (image side) to generate positive distortion and correct negative distortion. It is possible to do.

In the present invention, since the rear unit has a positive power as a whole, the positive lens unit is disposed in front of the iris diaphragm. A positive lens group including a lens having a strong negative power is disposed behind the iris diaphragm.
In this way, by arranging the negative lens unit, the positive lens unit, the iris diaphragm, and the positive lens unit in this order from the object side, the entire system is made compact. As described above, the positive lens group disposed behind the iris diaphragm includes a lens having strong negative power. Therefore, in order to generate a positive distortion and correct a negative distortion, it is necessary to make the incident height of the principal ray incident on the positive lens group disposed behind the iris diaphragm as large as possible. Is effective.

Specifically, at the time of zooming from the wide-angle end to the telephoto end, if the zoom movement trajectory is set so that the distance between the iris diaphragm and the positive lens group disposed behind it is reduced,
At the wide-angle end, the incident height of the principal ray incident on the positive lens group disposed behind the iris stop increases, and the effect of correcting distortion aberration increases. Further, it is necessary to have a lens structure in which a positive lens group disposed behind the iris diaphragm generates positive distortion. For example, in a positive lens group disposed behind an iris diaphragm, a lens surface having a strong negative power is necessary, but a surface with a convex surface facing the object side, and the positive power decreases from the center to the periphery. The introduction of such an aspherical surface is also effective.

Therefore, in each embodiment of the present invention, a three-group lens arrangement is employed, and a first lens group G1 having a negative power and a second lens group G2 having a positive power are arranged in order from the object side. Iris diaphragm, and a third lens group G3 having a positive power as a whole including a negative lens having a strong negative power. Then, at the time of zooming from the wide-angle end to the telephoto end, the air gap between the first lens group G1 and the second lens group G2 decreases, and the air gap between the second lens group G2 and the third lens group G3 decreases. As described above, the first lens group G
The first to third lens groups G3 are moved.

In each embodiment of the present invention, the surface of the first lens group G1 having a concave surface facing the image side and having negative power has a shape such that the negative refractive power becomes weaker from the center toward the periphery. Uses an aspheric surface. Even if the center curvature is reduced and negative power is increased toward the periphery, it is possible to reduce distortion on the wide-angle side and spherical aberration on the telephoto side due to the effect of the aspherical surface. Further, the introduction of the aspherical surface can reduce the number of lenses in the first lens group G1, which is useful for reducing the size of the entire lens.

Hereinafter, the conditional expressions of the present invention will be described. In the present invention, the following conditional expressions (1) and (2) are satisfied. −1.2 <f1 / ft <−0.4 (1) 0.5 <f2 / ft <3.5 (2) where f1: focal length of the first lens group G1 f2: second lens group G2 Ft: focal length of the entire system at the telephoto end

Conditional expression (1) defines an appropriate range for the ratio of the focal length f1 of the first lens group G1 to the focal length ft of the entire system at the telephoto end. When the value exceeds the upper limit of conditional expression (1), the power of the first lens group G1 becomes weak. As a result, the outer diameter of the front lens of the first lens group G1 becomes large in order to make the off-axis light beam incident, and the lens system becomes large. Conversely, when the value goes below the lower limit of conditional expression (1), the power of the first lens group G1 increases, which is suitable for miniaturization. However, distortion occurs on the wide-angle side and spherical aberration occurs on the telephoto side, and it becomes difficult to correct the aberration. It is more preferable to set the upper limit of conditional expression (1) to -0.5 and the lower limit to -1.

Conditional expression (2) defines an appropriate range for the ratio of the focal length f2 of the second lens group G2 to the focal length ft of the entire system at the telephoto end. Conditional expression (2) is
This is a condition relating to the zoom movement amount of the second lens group G2. When the value exceeds the upper limit of conditional expression (2), the power of the second lens unit G2 becomes weak, and the second power required for obtaining a predetermined zoom ratio is obtained.
The amount of zoom movement of the lens group G2 increases. as a result,
The overall length of the lens becomes large, and the lens system becomes large.

Conversely, if the lower limit of conditional expression (2) is not reached,
The power of the second lens group G2 is increased, which is suitable for miniaturization. However, since the back focus on the wide-angle side is reduced, the power of the first lens group G1 and the third
The power of the lens group G3 must also be increased.
As a result, aberration occurs in each lens group, and it becomes difficult to correct the aberration. It is more preferable to set the upper limit of conditional expression (2) to 3 and the lower limit to 0.7.

In the present invention, it is desirable that the third lens group G3 has at least one positive lens and at least one negative lens, and satisfies the following conditional expression (3). −1.1 <f3n / f3 <−0.1 (3) where, f3: focal length of the third lens group G3 f3n: negative lens having the strongest refracting power among the negative lenses constituting the third lens group G3 Lens focal length

Conditional expression (3) defines an appropriate range for the ratio of the focal length f3n of the negative lens L3n having the strongest power in the third lens group G3 to the focal length f3 of the third lens group G3. . If the lower limit of conditional expression (3) is not reached,
The power of the negative lens L3n, which has the highest power in the third lens group G3, becomes weak, and the amount of positive distortion generated in the third lens group G3 decreases, which is not preferable. vice versa,
When the value exceeds the upper limit of conditional expression (3), the power of the negative lens L3n having the strongest power in the third lens group G3 increases, and the amount of positive distortion generated in the third lens group G3 increases. Correction of distortion on the wide-angle side is improved. However, a large amount of positive spherical aberration occurs on the telephoto side, which is not preferable. It should be noted that the upper limit of conditional expression (3) is-
More preferably, the lower limit is set to 0.2 and the lower limit to -0.9.

In the present invention, the second lens group G
2 has at least one cemented lens of a positive lens and a negative lens.
It is preferable that the zoom lens satisfies the following conditional expression (4). 0.2 <ra / f2 <1 (4) where, f2: focal length of the second lens group G2, ra: radius of curvature of the lens surface of the second lens group G2 closest to the object

Conditional expression (4) defines an appropriate range for the ratio of the radius of curvature of the lens surface closest to the object in the second lens group G2 to the focal length of the second lens group G2. When the value goes below the lower limit of conditional expression (4), the power of the surface closest to the object side of the second lens unit G2 becomes strong, and a large amount of negative spherical aberration occurs at the telephoto end. Conversely, when the value exceeds the upper limit of conditional expression (4), the power of the surface closest to the object side of the second lens unit G2 becomes weak, and a large amount of inward coma occurs. It is more preferable to set the upper limit of conditional expression (4) to 0.8 and the lower limit to 0.3.

Conventionally, in such a wide-angle zoom lens,
A front lens feeding system in which the first lens group G1 is moved to the object side to perform focusing on a short-distance object has been often used. However, in the front lens feeding method, the peripheral light amount at the wide-angle end is significantly reduced during focusing on a short-distance object. In order to secure sufficient peripheral light, the front lens diameter must be made larger,
As a result, the lens diameter and the filter diameter are undesirably increased. Furthermore, in recent AF lenses, if the moving distance of the focusing lens group is large or the weight of the focusing lens group is large, a heavy load is applied to the motor for driving the autofocus, and the focusing mechanism becomes large. .

Therefore, the present invention employs an inner focus type focusing system in which a focusing lens group constituting a part of the second lens group G2 is moved to perform focusing in the first embodiment described later. In general,
It is known that the power of each lens group can be increased to reduce the amount of movement of the focusing lens group. However, simply increasing the power of each lens group causes excessive aberration in each lens group. Not preferred. In addition, aberration fluctuation due to focusing also occurs.
Therefore, in the present invention, the power arrangement and the shape of each lens group and the lens are determined to optimal values.

In the present invention, when the focusing lens group forming a part of the second lens group G2 is moved to the image side to perform focusing on a short-distance object, the light beam emitted from the on-axis object is focused on the focusing lens. When entering the group, it becomes a divergent light flux. For this reason, the height of incidence on the focusing lens unit increases, and a large amount of negative spherical aberration occurs.

Therefore, in the present invention, in order to correct negative spherical aberration, the focusing lens unit has a cemented lens of a positive lens and a negative lens, and satisfies the following conditional expressions (5) to (7). It is desirable. 0.1 <rb / f2f <0.3 (5) 0.25 <Nn-Np (6) | βfw / βft | <6 (7)

Where, rb: radius of curvature of the center of the cemented surface of the cemented lens in the focusing lens group f2f: focal length of the focusing lens group Np: refractive index Nn of the positive lens of the cemented lens in the focusing lens group with respect to the d-line Refractive index for the d-line of the negative lens of the cemented lens in the focusing lens group βfw: Use magnification of the focusing lens group at the wide-angle end in the infinity focus state βft: Use of the focusing lens group in the telephoto end in the infinity focus state Use magnification

At the cementing surface of the cemented lens in the focusing lens group, positive high-order spherical aberration occurs due to a change in the incident height during focusing. Conditional expression (5)
Defines the power of the cemented surface of the cemented lens in the focusing lens group to control the amount of positive higher order spherical aberration generated. When the value goes below the lower limit of conditional expression (5), the power of the cemented surface of the cemented lens in the focusing lens unit becomes too strong, and negative spherical aberration is excessively corrected. On the other hand, when the value exceeds the upper limit of the conditional expression (5), the power of the cemented surface of the cemented lens in the focusing lens unit is weak, so that the correction amount for the negative spherical aberration is insufficient.

Conditional expression (6) defines the difference between the refractive index of the positive lens of the cemented lens and the refractive index of the negative lens in the focusing lens group in order to control the amount of generation of positive higher-order spherical aberration. doing. When the value goes below the lower limit of conditional expression (6), the difference in refractive index becomes small, and the amount of generation of positive higher-order spherical aberration decreases, which is not preferable for correction of negative spherical aberration.

Conditional expression (7) is a condition for reducing aberrations generated in the focusing lens unit, and includes a use magnification of the focusing lens unit at the wide-angle end and a focusing lens unit at the telephoto end in an infinity in-focus state. An appropriate range is specified for the ratio to the use magnification. When the value exceeds the upper limit of conditional expression (7), the working magnification of the focusing lens unit differs greatly between the telephoto end and the wide-angle end. As a result, it becomes difficult to reduce short-range fluctuations (aberration fluctuations due to short-distance focusing) over the entire zooming region from the telephoto end to the wide-angle end.

The most important problem in a wide-angle zoom lens is correction of distortion. In the present invention, it is preferable to generate positive distortion by using one positive lens and one negative lens for the fixed fourth lens group G4 at the time of zooming and focusing. In particular, in the first embodiment, the fourth
The lens group G4 includes, in order from the object, a lens component having a concave surface facing the object side and a lens component having a convex surface facing the image side, and the two lens components generate positive distortion. .

[0031]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each embodiment, the wide-angle zoom lens according to the present invention includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.
And a third lens group G3 having a positive refractive power. The first lens group G1 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative lens, and a positive lens having a convex surface facing the object side. The second lens group G2 has at least one positive lens whose convex surface faces the object side. Further, the third lens group G3 has at least one negative lens whose concave surface faces the object side.

In each embodiment, the aspheric surface has a height y in a direction perpendicular to the optical axis, a displacement amount (sag amount) in the optical axis direction at the height y of S (y), and a reference radius of curvature (nearby). Assuming that r is the radius of curvature of the axis, κ is the cone coefficient, and Cn is the n-th order aspherical coefficient, the following equation (a) is used.

[Number 1] ^{S (y) = (y 2} / r) / {1+ (1-κ · y 2 / r 2) 1/2} + C 2 · y 2 + C 4 · y 4 + C 6 · y 6 + C 8 · Y ⁸ + C ₁₀ · y ¹⁰ + ... (a) In each embodiment, the aspherical surface is marked with an asterisk on the right side of the surface number.

[First Embodiment] FIG. 1 is a diagram showing a lens configuration of a wide-angle zoom lens according to a first embodiment of the present invention. The zoom lens of FIG. 1 includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G having a positive refractive power.
3 and a fourth lens group G4 having a negative refractive power. The first lens group G1 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. .

The second lens group G2 includes, in order from the object side, a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. And a positive meniscus lens having a convex surface facing the object side. Further, the third lens group G3 includes, in order from the object side, a cemented negative lens of a negative meniscus lens having a concave surface facing the object side, a positive meniscus lens having a concave surface facing the object side, and a biconvex lens. The third lens group G
On the image side of No. 3, a fourth lens group G4 is provided. 4th
The lens group G4 includes, in order from the object side, a cemented negative lens of a positive meniscus lens having a concave surface facing the object side and a negative meniscus lens having a concave surface facing the object side.

The second lens group G2 and the third lens group G
3 is provided with an aperture stop S, and the second stop is used for zooming.
It moves integrally with the lens group G2. FIG. 2 shows a lens arrangement at the wide-angle end. Then, at the time of zooming to the telephoto end, the air gap between the first lens group G1 and the second lens group G2 decreases, and the second lens group G2 and the third lens group G3
The first lens group G1 to the third lens group G3 move so that the air gap between them decreases. However, the fourth lens group G
4 is always fixed during zooming. Also, the second lens group G2
The middle positive meniscus lens and the cemented positive lens on the object side constitute a focusing lens group. And
By moving the focusing lens unit to the image side, focusing on a short-distance object is performed.

Table 1 below summarizes the data values of the first embodiment of the present invention. In Table (1), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, Bf represents the back focus, β represents the photographing magnification, and do represents the distance along the optical axis from the object to the lens surface closest to the object. Further, the surface number indicates the order of the lens surface from the object side along the direction in which the light beam travels, and the refractive index and Abbe number indicate values for the d-line (λ = 587.6 nm).

[0037]

Table 1 f = 18.90 to 28.0 to 43.00 FNO = 3.6 to 3.6 to 3.6 2ω = 97.63 to 75.3 to 53.34 ° Surface number Curvature radius Surface spacing Abbe number Refractive index 1 120.000 2.00 49.5 1.75492 2 * 22.000 9.31 3 144.906 2.00 55.6 1.70551 4 30.000 1.70 5 34.463 3.73 23.0 1.88747 6 61.144 (d6 = variable) 7 27.868 2.45 48.9 1.53932 8 462.243 0.10 9 33.197 2.10 46.5 1.81619 10 15.374 2.6 1.50756 11 34.492 (d11 = variable) 12 22.015 6.03 70.4 1.49227 13 85.086 1.00 14 ∞ (d14 = variable) (Aperture stop S) 15 -20.396 1.50 28.5 1.81481 16 -76.662 1.50 49.5 1.75492 17 * -54.843 1.47 18 619.150 5.13 60.0 1.64739 19 -19.337 (d19 = variable) 20 -35.243 1.60 46.5 1.81619 21 -30.134 1.50 25.4 1.82707 22 * -39.851 Bf (Aspherical data) κ C ₂ C ₄ 2 plane 0.0000 0.0000 2.19330 × 10 ^-6 C ₆ C ₈ C ₁₀ -2.32950 × 10 ^-10 6.31 760 × 10 ^-12 -9.47 200 × 10 ^-15 κ C ₂ C ₄ 17 face 1.0000 0.0000 2.54 230 × 10 ^-5 C ₆ C ₈ C ₁₀ 3.10 650 × 10 ^-8 -2.53650 × 10 ^-11 -2.19650 × 10 ^-13 κ C ₂ C ₄ 22 surface 1.0000 0.0000 5.28570 × 10 ^-6 C ₆ C ₈ C ₁₀ 3.55770 × 10 ^-9 -1.23020 × 10 ^-11 5.58 200 × 10 ^-14 (variable F / β 18.90 28.00 43.00 -0.07 -0.09 -0.15 d0 ∞ ∞ 3.7 253.74 267.69 267.77 d6 38.63 15.90 1.00 41.53 19.09 5.32 d11 5.32 5.32 5.32 2.42 2.13 1.00 d14 13.83 8.41 3.00 13.83 8.41 3.00 d19 1.00 15.16 35.42 1.00 15.16 35.42 Bf 37.937 38.109 37.912 37.895 38.238 38.034 (Conditional value) (1) f1 / ft = -0.63 (2) f2 / ft = 0.94 (3) f3n / f3 = -0.57 ( 4) ra / f2 = 0.69 (5) rb / f2f = 0.16 (6) Nn-Np = 0.30 (7) | βfw / βft | = 2.44

FIGS. 2 to 7 are graphs showing various aberrations of the first embodiment. FIG. 2 is a diagram illustrating various aberrations at the wide-angle end in a focused state at infinity, FIG. 3 is a diagram illustrating various aberrations at an intermediate focal length state in a focused state at infinity, and FIG. FIG. 7 is a diagram illustrating various aberrations at the telephoto end. On the other hand, FIG. 5 is a diagram showing various aberrations at a wide-angle end in a short-range shooting state, FIG. 6 is a diagram showing various aberrations at an intermediate focal length state in a short-range shooting state, and FIG. FIG. 7 is a diagram illustrating various aberrations at an edge.

In each aberration diagram, FNO represents an F number,
NA is the numerical aperture, Y is the image height, and D is the d-line (λ = 587.
G indicates the g-line (λ = 435.8 nm). In the aberration diagram showing astigmatism,
The solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. As is clear from the aberration diagrams, in this embodiment, various aberrations are favorably corrected in each shooting distance state and each focal length state, and excellent imaging performance is secured.

[Second Embodiment] FIG. 8 is a diagram showing a lens configuration of a wide-angle zoom lens according to a second embodiment of the present invention. The zoom lens in FIG. 8 includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G having a positive refractive power.
And 3. The first lens group G1 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side;
It is composed of a biconcave lens and a biconvex lens. The second lens group G2 is composed of, in order from the object side, a cemented positive lens of a biconvex lens and a biconcave lens.

The third lens group G3 includes, in order from the object side, a positive meniscus lens having a convex surface facing the object side, a cemented negative lens of a biconcave lens and a positive meniscus lens having a convex surface facing the object side, and The lens comprises a positive meniscus lens having a concave surface. The second lens group G2
An aperture stop S is provided between the zoom lens and the third lens group G3.
At the time of zooming, it moves integrally with the second lens group G2. FIG. 8 shows a lens arrangement at the wide-angle end. Then, upon zooming to the telephoto end, the first lens group G1 and the second
The air gap with the lens group G2 decreases, and the second lens group G2
The first lens group G1 to the third lens group G3 move so that the air gap between the first lens group G3 and the third lens group G3 decreases.

Table 2 below summarizes data values of the second embodiment of the present invention. In Table (2), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, Bf represents the back focus, β represents the photographing magnification, and do represents the distance along the optical axis from the object to the lens surface closest to the object. Further, the surface number indicates the order of the lens surface from the object side along the direction in which the light beam travels, and the refractive index and Abbe number indicate values for the d-line (λ = 587.6 nm).

[0043]

Table 2 f = 18.90 to 28.0 to 43.00 FNO = 3.6 to 3.6 to 3.6 2ω = 97.63 to 75.3 to 53.34 ° Surface number Curvature radius Surface spacing Abbe number Refractive index 1 120.000 1.80 49.4 1.77278 2 * 22.000 11.92 3 -203.504 1.50 46.5 1.80410 4 57.023 3.79 5 65.107 5.00 25.4 1.80518 6 -249.139 (d6 = variable) 7 39.327 8.89 60.0 1.64000 8 -40.612 1.50 43.3 1.84042 9 329.349 2.00 10 ∞ (d10 = variable) (Aperture stop S) 11 24.004 3.68 69.9 1.51860 12 461.381 10.89 13 -40.509 1.50 28.5 1.79504 14 149.363 1.50 55.6 1.69680 15 * -292.209 2.66 16 -55.378 3.45 69.9 1.51860 17 -20.005 Bf (Aspherical data) κ C ₂ C ₄ 2 side 0.0000 0.0000 3.72060 × 10 ^-6 C ₆ C ₈ C ₁₀ 1.30 230 × 10 ^-9 -3.37 130 × 10 ^-12 4.87300 × 10 ^-15 κ C ₂ C ₄ 15 side 1.0000 0.0000 3.09420 × 10 ^-5 C ₆ C ₈ C ₁₀ 1.77060 × 10 ^-8 -9.65600 × 10 ^-11 8.87960 × 10 ^-14 (variable interval in zooming) f 18.90 28.00 43.00 d0 ∞ ∞ ∞ d6 45.48 19.64 3.44 d 10 16.97 8.53 1.00 Bf 38.006 48.98 65.541 (Conditional value) (1) f1 / ft = -0.82 (2) f2 / ft = 2.46 (3) f3n / f3 = -0.76 (4) ra / f2 = 0.37

FIGS. 9 to 11 show various aberration diagrams of the second embodiment. FIG. 9 is a diagram illustrating various aberrations at the wide-angle end in a focused state at infinity, FIG. 10 is a diagram illustrating various aberrations at an intermediate focal length state in a focused state at infinity, and FIG. FIG. 7 is a diagram illustrating various aberrations at the telephoto end. In each aberration diagram, FNO represents the F number, Y represents the image height, and D represents the d-line (λ =
587.6 nm) and G is the g-line (λ = 435.8 nm).
Are respectively shown. In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. As is clear from each aberration diagram,
In the present embodiment, it can be seen that various aberrations are satisfactorily corrected in each shooting distance state and each focal length state, and excellent imaging performance is secured.

[Third Embodiment] FIG. 12 is a diagram showing a lens configuration of a wide-angle zoom lens according to a third embodiment of the present invention. The zoom lens in FIG. 12 includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. , And a fourth lens group G4 having a positive refractive power. The first lens group G1 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a biconcave lens, and a biconvex lens. The second lens group G2 is composed of, in order from the object side, a cemented positive lens of a biconvex lens and a biconcave lens.

The third lens group G3 includes, in order from the object side, a positive meniscus lens having a convex surface facing the object side, and a cemented negative lens composed of a biconcave lens and a positive meniscus lens having a convex surface facing the object side. ing. A fourth lens group G4 is provided on the image side of the third lens group G3. The fourth lens group G4 includes a positive meniscus lens having a concave surface facing the object side.

The second lens group G2 and the third lens group G
3 is provided with an aperture stop S, and the second stop is used for zooming.
It moves integrally with the lens group G2. FIG. 12 shows a lens arrangement at the wide-angle end. Then, at the time of zooming to the telephoto end, the air gap between the first lens group G1 and the second lens group G2 decreases, and the second lens group G2 and the third lens group G
The first lens group G1 to the fourth lens group G4 move so that the air gap with the third lens group decreases.

Table 3 below summarizes data values of the third embodiment of the present invention. In Table (3), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, Bf represents the back focus, β represents the photographing magnification, and do represents the distance along the optical axis from the object to the lens surface closest to the object. Further, the surface number indicates the order of the lens surface from the object side along the direction in which the light beam travels, and the refractive index and Abbe number indicate values for the d-line (λ = 587.6 nm).

[0049]

Table 3 f = 18.90 to 28.0 to 43.00 FNO = 3.6 to 3.6 to 3.6 2ω = 97.63 to 75.3 to 53.34 ° Surface number Curvature radius Surface spacing Abbe number Refractive index 1 120.000 1.80 52.3 1.74809 2 * 22.000 11.80 3 -356.320 1.50 46.5 1.80410 4 62.428 5.34 5 73.194 5.00 23.0 1.86074 6 -2087.035 (d6 = variable) 7 40.078 6.92 60.0 1.64000 8 -38.912 1.50 43.3 1.84042 9 399.976 2.00 10 ∞ (d10 = variable) (Aperture stop S) 11 24.546 3.73 69.9 1.51860 12 1357.492 11.42 13 -40.506 1.50 31.6 1.75692 14 70.165 1.50 67.8 1.59318 15 * -307.889 (d15 = variable) 16 -66.721 3.53 69.9 1.51860 17 -20.617 Bf ( Aspherical data) κ C ₂ C ₄ 2 surface 0.0000 0.0000 3.71340 × 10 ^-6 C ₆ C ₈ C ₁₀ -5.70220 × 10 ^-11 2.13 180 × 10 ^-12 -3.36050 × 10 ^-16 κ C ₂ C ₄ 15 surface 1.0000 0.0000 3.55830 × 10 ^-5 C ₆ C ₈ C ₁₀ 8.99390 × 10 ^-9 3.03650 × 10 ^-11 -5.23110 × 10 ^-13 (Variable interval in variable magnification) f 18.90 28.00 43.00 d0 ∞ ∞ ∞ d6 44.17 1 9.10 2.94 d10 14.54 8.31 1.00 d15 1.77 2.90 3.19 Bf 38.096 48.755 65.386 (Conditional value) (1) f1 / ft = -0.82 (2) f2 / ft = 2.52 (3) f3n / f3 = -0. 24 (4) ra / f2 = 0.37

FIGS. 13 to 15 show various aberration diagrams of the third embodiment. FIG. 13 is a diagram showing various aberrations at the wide-angle end in a focused state at infinity, FIG. 14 is a diagram showing various aberrations at an intermediate focal length state in a focused state at infinity, and FIG. FIG. 7 is a diagram illustrating various aberrations at the telephoto end. In each aberration diagram, FNO represents the F number, Y represents the image height, and D represents the d-line (λ
= 587.6 nm) and G is the g-line (λ = 435.8 n).
m). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. As is clear from the aberration diagrams, in this embodiment, various aberrations are favorably corrected in each shooting distance state and each focal length state, and excellent imaging performance is secured.

As described above, in each of the embodiments of the present invention, the angle of view at the wide-angle end is about 97.7 °, the open F-number is about 3.6, and the zoom ratio is 2. A zoom lens of about three times is realized.

[0052]

As described above, according to the present invention, a wide-angle zoom lens having a sufficiently large shooting angle of view at the wide-angle end, a zoom ratio exceeding 2 times, and excellent correction of various aberrations is realized. can do.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a lens configuration of a wide-angle zoom lens according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating various aberrations of the first embodiment at a wide-angle end in a focusing state at infinity.

FIG. 3 is a diagram illustrating various aberrations of the first embodiment in an intermediate focal length state in an infinity in-focus state;

FIG. 4 is a diagram of various types of aberration at the telephoto end in a focusing state at infinity according to the first example.

FIG. 5 is a diagram illustrating various aberrations at a wide-angle end in a close-up shooting state according to the first example.

FIG. 6 is a diagram illustrating various aberrations of the first example in an intermediate focal length state in a close-up shooting state;

FIG. 7 is a diagram illustrating various aberrations at a telephoto end in a close-up shooting state according to the first example.

FIG. 8 is a diagram showing a lens configuration of a wide-angle zoom lens according to Example 2 of the present invention.

FIG. 9 is a diagram illustrating various aberrations at a wide-angle end in a focusing state at infinity according to a second example.

FIG. 10 is a diagram illustrating various aberrations of the second example in an intermediate focal length state in an infinity in-focus state;

FIG. 11 is a diagram of various types of aberration at the telephoto end in a focusing state at infinity according to a second example.

FIG. 12 is a diagram illustrating a lens configuration of a wide-angle zoom lens according to Example 3 of the present invention.

FIG. 13 is a diagram illustrating various aberrations at a wide-angle end in a focusing state at infinity according to a third example.

FIG. 14 is a diagram illustrating various aberrations of the third example in an intermediate focal length state in an infinity in-focus state.

FIG. 15 is a diagram of various types of aberration at the telephoto end in a focusing state at infinity according to a third example.

[Explanation of symbols]

 G1 first lens group G2 second lens group G3 third lens group G4 fourth lens group S aperture stop

Claims (5)

[Claims] 1. A first lens group G1 having a negative refractive power and a second lens group G having a positive refractive power in order from the object side.
2 and a third lens group G3 having a positive refractive power. The first lens group G1 includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative lens, and a The second lens group G2 has at least one positive lens with a convex surface facing the object side, and the third lens group G3 has a concave surface with at least one object side. At least one lens surface among the lens surfaces constituting the first lens group G1 is formed in an aspherical shape, and the first lens unit is used for zooming from a wide-angle end to a telephoto end. The first lens group G1 to the third lens group G3 are configured such that the air gap between the group G1 and the second lens group G2 decreases and the air gap between the second lens group G2 and the third lens group G3 decreases. The lens group G3 moves, and the first lens The focal length of the G1 and f1, the second
When the focal length of the lens group G2 is f2 and the focal length of the entire system at the telephoto end is ft, -1.2 <f1 / ft <-0.4 0.5 <f2 / ft <3.5 A wide-angle zoom lens that satisfies the conditions. 2. The third lens group G3 includes at least one
Three positive lenses and at least one negative lens, wherein the focal length of the third lens group G3 is f3,
When the focal length of the negative lens having the strongest refractive power among the negative lenses constituting the lens group G3 is f3n, the condition of -1.1 <f3n / f3 <-0.1 is satisfied. The wide-angle zoom lens according to claim 1. 3. The second lens group G2 has at least one cemented lens of a positive lens and a negative lens, the focal length of the second lens group G2 is f2, and the second lens group G2 is
Let the radius of curvature of the lens surface of the lens group G2 closest to the object be ra
3. The wide-angle zoom lens according to claim 1, wherein the following condition is satisfied: 0.2 <ra / f2 <1. 4. A fourth lens group G4 arranged on the image side of the third lens group G3 and fixed at the time of zooming and focusing, at least one of the lens surfaces constituting the third lens group G3. The two lens surfaces are formed in an aspherical shape, and the focusing lens group that forms a part of the second lens group G2 is moved to perform focusing from a long-distance object to a short-distance object. Has a cemented lens of a positive lens and a negative lens, the center radius of curvature of the cemented surface of the cemented lens in the focusing lens group is rb, the focal length of the focusing lens group is f2f, and the focusing lens group is The refractive index of the positive cemented lens of the cemented lens with respect to the d-line is denoted by Np, and the d-line of the negative lens of the cemented lens in the focusing lens group The refractive index and Nn, the lateral magnification of the focusing lens group in a wide angle end in an infinity in-focus state and Betafw, the lateral magnification of the focusing lens group at the telephoto end in the infinity in-focus condition β against
4. The method according to claim 1, wherein when ft is satisfied, the following condition is satisfied: 0.1 <rb / f2f <0.3 0.25 <Nn-Np | .beta.fw / .beta.ft | <6. The wide-angle zoom lens according to 1. 5. A lens system comprising only the first lens group G1, the second lens group G2, and the third lens group G3, wherein at least one of the lens surfaces constituting the third lens group G3 is 4. The lens according to claim 1, wherein the first lens group G <b> 1 is formed in an aspherical shape, and focusing is performed from a long-distance object to a short-distance object by moving the first lens group G <b> 1. 5. Wide-angle zoom lens.