JP2002228928A - Variable focal distance lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable focal distance lens system consisting of a small number of lenses, made compact and having a high variable power ratio. SOLUTION: This lens system is provided with 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. In the case of changing a lens position state from a wide-angle end state to a telephoto end state, the respective lens groups are moved to the object side so that space between the 1st and the 2nd lens groups G1 and G2 may be increased and space between the 2nd and the 3rd lens groups G2 and G3 may be decreased. Then, an aperture diaphragm S is arranged near the 2nd lens group G2, and is integrally moved with the 2nd lens group G2 in accordance with the change of the lens position state, and the 3rd lens group G3 is composed of a positive lens turning its convex surface to an image side and a negative lens arranged on the image side of the positive lens through air space and turning its concave surface to the object side, and the positive lens is a both-side aspherical lens and also satisfies a specified conditional expression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a variable focal length lens system, and more particularly to a variable focal length lens system suitable for a high zoom ratio.

[0002]

2. Description of the Related Art A demand for a lens shutter type camera is that the camera has excellent portability. In order to achieve a camera excellent in portability, that is, mainly in light weight and miniaturization, it is particularly important to shorten the entire length of the photographing optical system, make each lens thinner, and make the lens diameter smaller.

In general, a lens shutter camera uses a zoom lens as a photographing optical system. The zoom lens uses a so-called telephoto type refractive power arrangement in which a negative lens group is arranged closest to the image plane, and enlarges an image formed by a lens group arranged closer to the object side than the zoom lens. When the lens position state changes from the wide-angle end state to the telephoto end state, a predetermined change is made by moving the negative lens group so that the magnification is small in the wide-angle end state and large in the telephoto end state. Double ratio is realized. At the same time, the distance between the aperture stop and the negative lens group is wide in the wide-angle end state, gradually narrows with the change in the lens position state from the wide-angle end state to the telephoto end state, and becomes the narrowest in the telephoto end state. The aperture stop is arranged as follows. Thereby, the off-axis light beam is separated from the optical axis in the wide-angle end state. In addition, the off-axis light flux approaches the optical axis as approaching the telephoto end state. By configuring the lens system in this manner, the fluctuation of off-axis aberration that occurs with the change in the lens position state is corrected well.

In these photographing optical systems, since the distance between the negative lens unit and the aperture stop is wide in the wide-angle end state, the lens diameter of the negative lens unit tends to increase. Therefore, it is important to reduce the lens diameter of the negative lens group in order to reduce the lens barrel diameter and further reduce the height and width of the camera body.

Generally, a zoom lens having a high zoom ratio has a 3
A so-called multi-group zoom lens having one or more movable lens groups is used. Mainly, a positive / negative three-group type having a relatively small number of movable lens groups is used. This positive / negative three-group type zoom lens includes, in order from the object side, three lens groups of a positive lens group, a positive lens group, and a negative lens group.

For example, a zoom lens disclosed in Japanese Patent Application Laid-Open No. 2000-66100 includes, in order from the object side, a negative lens group having a convex surface facing the image side and a negative lens having a concave surface facing the object side. 3 with a negative lens with a concave surface facing the object side
It is composed of two lenses. Also, Japanese Patent Laid-Open No. 2000-
The lens system disclosed in Japanese Patent No. 56223 includes, in order from the object side, a negative lens group consisting of a positive lens having a convex surface facing the image side and a negative lens having a concave surface facing the object side. . In this lens system, the lens surface on the object side of the positive lens has an aspherical shape. This increases the degree of freedom for aberration correction, and instead reduces the number of lenses by one. Further, in the lens system disclosed in Japanese Patent Laid-Open No. 2000-155263, the positive lens in the negative lens group is an aspherical lens on both sides. Thereby, the degree of freedom of aberration correction is increased, and the performance is improved.

In order to reduce the lens diameter, it is best to make the off-axis light flux reaching the negative lens close to the optical axis by making the positive lens have a strong convergence action. However, when the convergence of the positive lens is increased, a large amount of negative spherical aberration occurs. For this reason, by introducing an aspherical surface, the convergence effect at the peripheral portion is enhanced as compared with the vicinity of the optical axis, that is, the refractive power is increased, and the lens diameter is reduced.

[0008]

As described above, Japanese Patent Laid-Open No.
In the lens system disclosed in 000-56223, the object side lens surface of the positive lens has an aspherical shape. This aspherical shape has a divergent effect near the optical axis and a convergent effect at the periphery. In the vicinity of the optical axis, the off-axis light beam is smoothly refracted with the concave surface facing the aperture stop. On the other hand, at the peripheral portion, the light beam is sharply refracted with the convex surface facing the aperture stop. For this reason, there is a problem that the performance is rapidly deteriorated even by a minute eccentricity.

As described above, Japanese Patent Application Laid-Open No. 2000-155
In the lens system disclosed in Japanese Patent Publication No. 263, the positive lens is an aspherical lens on both sides. Thereby, the image side lens surface strengthens the convergence action at the peripheral edge. For this reason, performance degradation due to minute eccentricity can be sufficiently suppressed. However, there is a problem that the processing of the aspherical lens is difficult because the radius of curvature at the peripheral edge portion is sharply reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a small variable focal length lens system having a high zoom ratio while having a small number of lenses.

[0011]

In order to achieve the above object, the present invention provides, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a negative refractive power. A third lens group having a force, and when the lens position state changes from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group increases, Each lens group is moved to the object side so that the distance between the lens group and the third lens group is reduced, and an aperture stop is arranged near the second lens group. An aperture stop moves integrally with the second lens group, and the third lens group is disposed with a positive lens having a convex surface facing the image side, and an air gap is disposed on the image side of the positive lens, and the third lens group is disposed on the object side. A negative lens having a concave surface facing the positive lens. Together with a bilateral aspheric lenses, which provide a variable focal length lens system that satisfies the following conditional expression (1). (1) 0.9 <κa (Ya / Ra) ² <1.3, where κa: the conic constant of the image-side lens surface of the aspherical lens on both sides arranged in the third lens group, Ya: screen diagonal Half the length is Ymax, the distance from the image side lens surface to the image plane in the wide-angle end state is DA, and the distance from the aperture stop to the image plane in the wide-angle end state is DS.
Where Ya = Ymax.multidot. (DA / DS), Ra: paraxial radius of curvature of the image-side lens surface.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a general theory regarding an aspheric lens will be described. In general, the positive refractive power of an aspheric lens arranged in a lens group having a positive refractive power gradually decreases from the center of the lens toward the periphery of the lens. This is due to the fact that negative spherical aberration easily occurs in the positive lens group.

On the other hand, an aspheric lens disposed in a lens group having a negative refractive power gradually increases its positive refractive power from the center of the lens toward the periphery of the lens. This is as described in, for example, Japanese Patent Application Laid-Open No. 1-288823. Incidentally, an aspheric lens is generally represented by the following equation.

[0014]

X = cy ² / {1+ (1-κc ² y ² ) ^1/2 } + C
_{^{4 y 4 + C 6 y 6}} + ...

In the present invention, the cone constant κ is appropriately set in order to solve the problem of the radius of curvature described above. As described above, the positive refractive power of the aspherical lens arranged in the negative lens group increases toward the lens periphery. However, in other words, the curvature changes in the positive direction from the center of the lens toward the periphery of the lens, and the conic constant κ tends to be larger than 1.

As the conic constant κ becomes larger than 1,
The curvature at the periphery of the lens changes greatly with respect to the center. Therefore, a larger aspherical surface effect can be obtained. However, if the aspheric effect is too large, the following problem occurs.

1-κc in the above aspherical expression^Twoy^TwoIs negative
When it becomes a value, (1-κc^Twoy^Two) ^1/2Is an imaginary number
That is the problem. The height y from the optical axis is large
1-κc^Twoy^TwoValue approaches 0 and reaches 0
When approaching, the curvature suddenly changes in the positive direction. Soshi
And the 1-κc^Twoy^TwoCurvature is infinite at the position where the value of becomes zero
And there is no solution above that height.

Therefore, in the present invention, the above problem is solved by appropriately setting the conical constant κ.
Specifically, the variable focal length lens system according to the present invention includes, in order from the object side, 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. And When the lens position changes from the wide-angle end state (the shortest focal length) to the telephoto end state (the longest focal length), the distance between the first lens group and the second lens group increases, Each lens group moves toward the object side such that the distance between the lens group and the third lens group is reduced.
The lens system is configured to satisfy the following conditions (A) to (C). As described above, it is possible to achieve an optical system suitable for reducing the lens diameter and shortening the overall length of the lens system.

The conditions (A) to (C) will be described. (A) An aperture stop is arranged near the second lens group. (B) The third lens group includes: a positive lens having a convex surface facing the image side; and a negative lens arranged on the image side of the positive lens and having a concave surface facing the object side. (C) The positive lens disposed in the third lens group is a bilateral aspheric lens, the object-side lens surface has a negative radius of curvature, and the negative refracting power decreases as the distance from the optical axis increases, and the image-side lens surface Has a negative radius of curvature, and the positive refractive power increases with distance from the optical axis.

The condition (A) relates to the arrangement of the aperture stop in the lens system. Generally, in a lens system having a high zoom ratio, it is important to arrange an aperture stop near the center of the lens system. When the lens position changes, it is important that each lens group positively changes the distance from the aperture stop.

In the present invention, the light beam passing through the first lens group passes near the optical axis in the wide-angle end state, and gradually moves away from the optical axis toward the telephoto end state. Conversely, the off-axis light beam passing through the third lens group passes away from the optical axis in the wide-angle end state, and gradually approaches the optical axis toward the telephoto end state. By positively changing the distance between the lens groups in this manner, off-axis aberrations are corrected mainly in the third lens group in the wide-angle end state, and off-axis aberrations are mainly corrected in the first lens group in the telephoto end state. Can be corrected. Therefore, even if the zoom ratio is increased, it is possible to satisfactorily correct the fluctuation of off-axis aberration that occurs with the change in the lens position.

Condition (B) relates to the lens configuration of the third lens group. The third lens group includes a positive lens and a negative lens disposed on the image side of the positive lens. With this configuration, in the wide-angle end state, the off-axis light beam is converged by the positive lens and then diverged by the negative lens. Therefore, the lens diameter can be reduced. In particular, the image-side lens surface of the positive lens is configured to be convex, and the object-side lens surface of the negative lens is configured to be concave. With this configuration, it is possible to satisfactorily correct the on-axis aberration and the off-axis aberration by utilizing the optical path difference generated in the air gap formed between the positive lens and the negative lens.

The condition (C) relates to the shape of the positive lens disposed in the third lens group. The positive lens arranged in the third lens group is an aspherical lens on both sides. The object side lens surface has a negative radius of curvature. The object-side lens surface satisfactorily corrects positive spherical aberration generated in the third lens group by decreasing the radius of curvature from the optical axis toward the peripheral edge. The image side lens surface has a negative radius of curvature. The image-side lens surface satisfactorily corrects coma aberration generated in the wide-angle end state by increasing the radius of curvature as the distance from the optical axis increases.

Hereinafter, the respective conditional expressions will be described. Conditional expression (1) is a conditional expression that defines the shape of the object-side lens surface of the double-sided aspheric lens disposed in the third lens group. When the value exceeds the upper limit of conditional expression (1), the curvature sharply increases at the lens peripheral portion. For this reason, the light beam is sharply bent. As a result, the optical performance is significantly deteriorated even by minute eccentricity that occurs when the lens is incorporated.
Conversely, when the value goes below the lower limit value of the conditional expression (1), the correction of coma in the peripheral portion of the screen becomes insufficient in the wide-angle end state.

In the present invention, the lens disposed closest to the object side in the first lens group is a positive lens cemented with a positive lens having a convex surface facing the object side and a negative lens having a concave surface facing the object side. It is desirable to satisfy the following conditional expression (2). This is to reduce the overall length of the lens in the telephoto end state and to reduce the size of the camera body. (2) 1.5 <| R2 | / D2 <4, where R2 is the radius of curvature (R2 <0) of the cemented surface of the cemented positive lens arranged in the first lens group, and D2 is the first in the telephoto end state. Distance from the cemented surface of the cemented positive lens arranged in the lens group to the aperture stop.

Conventionally known, for example, in JP-A-8-26
The zoom lens disclosed in Japanese Patent No. 2325 has a negative lens disposed closest to the object. For this reason, it is difficult to reduce the overall length of the lens in the telephoto end state.

In the present invention, the positive lens is arranged closest to the object side to shorten the overall length of the lens system. In addition, even if the refractive power of the first lens group is increased by using the cemented lens as the positive lens, the negative spherical aberration generated in the first lens group can be satisfactorily corrected.

Conditional expression (2) defines the radius of curvature of the cemented surface of the cemented lens in the first lens group. When the value exceeds the upper limit of conditional expression (2), negative spherical aberration generated in the first lens group cannot be satisfactorily corrected. For this reason, predetermined optical performance cannot be obtained.
Conversely, when the value goes below the lower limit of conditional expression (2), the off-axis light beam passes through a position distant from the optical axis in the telephoto end state. For this reason, a large amount of off-axis aberration occurs, and a predetermined optical performance cannot be obtained.

In the present invention, in order to further reduce the size, it is desirable to satisfy the following conditional expression (3). (3) 0.25 <f1 / ft <0.4, where f1: focal length of the first lens group, ft: focal length of the entire variable focal length lens system in the telephoto end state.

Conditional expression (3) is a conditional expression for defining the focal length of the first lens group. When the value exceeds the upper limit of conditional expression (3), it becomes difficult to further reduce the total length of the lens system in the telephoto end state. Conversely, when the value goes below the lower limit value of conditional expression (3), the principal ray passing through the first lens group in the telephoto end state is far away from the optical axis. For this reason, the lens diameter increases.

In the present invention, the second lens group includes, in order from the object side, a cemented negative lens of a negative lens having a concave surface facing the object side and a positive lens, an aperture stop, and a positive lens having a convex surface facing the image side. It consists of. Thus, the lens system can be simplified.

Generally, when the number of lenses is reduced, the refractive power of each lens constituting the lens system increases. However, in the present invention, it is possible to weaken each other's refractive power by disposing an aperture stop between the cemented negative lens having negative refractive power and the positive lens having positive refractive power.
As a result, a simple configuration can be achieved.

In particular, in the present invention, by satisfying the following conditional expression (4), stable optical quality can be obtained even during manufacturing. (4) 0.75 <(│r21│ + │r22│) / f2 <0.9, where r21 is the radius of curvature of the lens surface closest to the object side of the cemented negative lens arranged in the second lens group, r22 : Radius of curvature of the image side lens surface of the positive lens arranged in the second lens group, f2: focal length of the second lens group.

Conditional expression (4) defines the ratio of the radius of curvature of the object-side lens surface of the cemented negative lens disposed in the second lens unit to the radius of curvature of the image-side lens surface of the positive lens. . When the value exceeds the upper limit of conditional expression (4), the refractive powers of the cemented negative lens and the positive lens are weakened with each other. For this reason, it becomes impossible to satisfactorily correct positive distortion generated in the wide-angle end state. Conversely, when the value goes below the lower limit of conditional expression (4), the performance deterioration due to the mutual eccentricity of the cemented negative lens and the positive lens becomes large. For this reason, it is difficult to ensure stable optical quality during manufacturing.

In each embodiment of the present invention, an aspheric lens is disposed in the third lens group. In the wide-angle end state, an off-axis light beam passing through the third lens group located away from the aperture stop passes through the aspheric lens away from the optical axis. Therefore, the aspherical surface of the aspherical lens is particularly effective for correcting off-axis aberrations.

Although each of the following embodiments is constituted by three movable lens groups, it is easy to add another lens group between the lens groups or on the adjacent image side or object side.

According to another aspect of the present invention, the following configuration is provided in order to prevent a failure in photographing due to image blur due to hand shake or the like which tends to occur in a high-magnification zoom lens when photographing. You can also The lens system is combined with a shake detection system and a driving unit. The blur detection system detects a blur of the lens system. The driving means is
A part or the whole of one lens group among the lens groups constituting the lens system is decentered as an eccentric lens group. With this configuration, first, the shake of the lens system is detected by the shake detection system. Then, the eccentric lens group is decentered by the driving unit so as to correct the image blur (fluctuation in the image plane position) caused by the blur. The image shifts due to the eccentricity of the eccentric lens group, and the image blur can be corrected. As described above, the variable focal length lens system of the present invention can be a so-called anti-vibration optical system.

[0038]

Embodiments of the present invention will be described below with reference to the drawings. In each embodiment, the aspheric surface is represented by the following equation.

[0039]

## EQU2 ## x = cy^Two/ ｛1+ (1-κc^Twoy^Two)^1/2｝ + C
_Foury^Four+ C₆y⁶+ ... Here, y is the height from the optical axis, x is the amount of sag, and c is the vertex
Rate, κ is the conic constant, C _Four, C₆,... Are aspherical coefficients.
Further, the aspherical surface has an asterisk (*) to the right of the surface number.
You.

FIG. 1 shows the refractive power arrangement of the variable focal length lens system according to each embodiment of the present invention and the change of the focal length state from the wide-angle end state (W) to the telephoto end state (T). It is a figure showing a situation of movement. As shown in FIG. 1, the variable focal length lens system according to each embodiment of the present invention includes:
First lens group G1 having positive refractive power in order from the object side
, A second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power. When the focal length changes from the wide-angle end state to the telephoto end state, the first lens group G1 and the second lens group G
All the lens units move toward the object side such that the distance between the second lens unit and the second lens unit G2 increases and the distance between the second lens unit G2 and the third lens unit G3 decreases.

(First Embodiment) FIG. 2 is a diagram showing a configuration of a variable focal length lens system according to a first embodiment of the present invention.
In the variable focal length lens system shown in FIG.
Reference numeral 1 denotes a cemented positive lens L1 composed of a biconvex positive lens and a meniscus negative lens having a concave surface facing the object side in order from the object side. The second lens group G2 includes, in order from the object side, a cemented negative lens L21 formed of a biconcave negative lens and a convex lens and a biconvex positive lens L22. Further, the third lens group G3 includes a positive lens L31 having a convex surface facing the image side, and a negative lens L32 having a concave surface facing the object side, which is disposed at an image distance from the image side of the positive lens L31. Have been.

As described above, in the first embodiment, the cemented negative lens L21 forms a negative subgroup, and the positive lens L22 forms a positive subgroup. An aperture stop is disposed between the cemented negative lens L21 and the positive lens L22.

Table 1 below shows data values of the first embodiment of the present invention. In the specification table, f represents the focal length, FNO represents the F number, 2ω represents the angle of view, and Bf represents the back focus. The surface number indicates the order of the lens surface from the object side along the direction in which the light beam travels. Further, the refractive index and Abbe number are respectively d-line (λ
= 587.6 nm). Also, the radius of curvature is 0.
0000 indicates a plane.

Note that the same reference numerals as those of the present embodiment are used in the specification values of all the following embodiments. Here, the focal length f, the radius of curvature r, and the
The unit of the surface distance d and other lengths is generally “mm”, but the optical system is not limited to this, since the same optical performance can be obtained even if the optical system is proportionally enlarged or reduced.

[0045]

[Table 1] (Overall specifications) Wide-angle end state Intermediate focal length state Telephoto end state f 39.90-75.15-142.50 FNO 5.92-9.72-13.55 2ω 55.15-31.24-16.92 ° (lens data) Abbe number 1 24.0681 3.15 1.49700 81.61 2 -61.4150 0.80 1.79504 28.39 3 -164.9100 (D3) 1.0 4 -15.2863 1.20 1.83400 37.17 5 34.1970 3.90 1.76182 26.52 6 -121.8747 1.00 1.0 7 0.0000 0.95 1.0 (aperture stop) 8 23.4343 2.10 1.51450 63.05 9 * -13.2664 (D10) 1.0 10 * -39.0983 2.20 1.68893 31.16 11 * -22.2285 3.70 1.0 12 -9.2035 1.00 1.75500 52.32 13 -44.6504 (Bf) 1.0 (Aspheric coefficient) In this embodiment, the ninth and tenth surfaces , The eleventh surface is aspheric. The aspheric coefficients are as shown below. [9th surface] κ = 1.4723 C ₄ = + 1.3090 × 10 ^-4 C ₆ = + 3.7192 × 10 ^-7 C ₈ = −7.4944 × 10 ^-9 C ₁₀ = + 3.2574 × 10 ^-10 [10th surface] κ = 5.6917 C ₄ = + 9.6941 × 10 ^-5 C ₆ = + 5.2325 × 10 ^-8 C ₈ = + 1.6179 × 10 ^-8 C ₁₀ = -2.0236 × 10 ^-10 [Seventh surface] κ = 6.5000 C ₄ = + 5.6189 × 10 ^-5 C ₆ = + 9.8677 × 10 ^-7 C ₈ = -5.3246 × 10 ^-9 C ₁₀ = + 4.5028 × 10 ^-11 (Variable interval data) The variable intervals when the focal length is changed are shown below. . Wide-angle end state Intermediate focal length Telephoto end state f 39.8980 75.1461 142.5002 D3 1.6294 6.9543 16.0671 D10 14.2924 7.0722 0.6500 BF 11.2992 34.8735 69.2829 (Values corresponding to the conditional expressions) The values corresponding to the conditional expressions of this embodiment are shown below. DA = 15.99992, DS = 35.5416 f1 = 48.5793, f2 = 35.6049 (1) κa (Ya / Ra) ² = 1.244 (κa = κ on the eleventh surface) (2) │R2│ / D2 = 2.674 ( 3) f1 / ft = 0.341 (4) (│r21│ + │r22│) /f2=0.802

FIGS. 3A to 3C show various aberration diagrams of the first embodiment of the present invention in an infinity in-focus condition, respectively, at a wide-angle end condition (f = 39.90 mm) and an intermediate focus. Distance state (f = 75.15 mm), telephoto end state (f = 142.5)
0mm).

In each of the aberration diagrams of FIGS. 3A to 3C, a solid line in the spherical aberration diagram indicates a spherical aberration, a dotted line indicates a sine condition, and Y indicates an image height. Also,
In the astigmatism diagram, a solid line indicates a sagittal image plane, a broken line indicates a meridional image plane, and d indicates an aberration with respect to d-line. In the coma diagram, the image height Y = 0, 10.8, 15.12, 1
Coma at 8.34 and 21.6, and A indicates the angle of view. In the various aberration diagrams of all of the following embodiments, the same reference numerals as those of the present embodiment are used.

From each aberration diagram, it is clear that in this embodiment, various aberrations are satisfactorily corrected and have excellent imaging performance.

(Second Embodiment) FIG. 4 is a diagram showing the configuration of a variable focal length lens system according to a second embodiment of the present invention.
In the variable focal length lens system shown in FIG.
Reference numeral 1 denotes a cemented positive lens L1 including a biconvex positive lens and a meniscus negative lens having a concave surface facing the object side. The second lens group G2 is arranged in order from the object side.
A cemented negative lens L21 of a biconcave negative lens and a convex lens
And a biconvex positive lens L22.
Further, the third lens group G3 includes a positive lens L31 having a convex surface facing the image side, and a negative lens L32 having a concave surface facing the object side, which is disposed at an image distance from the image side of the positive lens L31. Have been.

As described above, in the second embodiment, the cemented negative lens L21 forms a negative subgroup, and the positive lens L22 forms a positive subgroup. An aperture stop is disposed between the cemented negative lens L21 and the positive lens L22. Table 2 below shows values of specifications of the second embodiment of the present invention.

[0051]

[Table 2] (Overall specifications) Wide-angle end state Intermediate focal length state Telephoto end state f 39.90-69.39-123.50 FNO 5.75-8.83-11.97 2ω 55.20-33.46-19.37 ° (Lens data) Abbe number 1 23.1391 2.90 1.49700 81.61 2 -42.5480 0.80 1.67270 32.11 3 -146.3675 (D3) 1.0 4 -16.2509 1.35 1.83481 42.72 5 33.0140 1.65 1.62004 36.26 6 -45.8980 2.85 1.0 7 0.0000 1.00 1.0 (aperture stop) 8 26.6530 2.10 1.51450 63.05 9 * -14.3813 (D10) 1.0 10 * -91.5327 2.30 1.68893 31.16 11 * -27.0000 3.55 1.0 12 -9.3994 1.00 1.80400 46.58 13 -63.6912 (Bf) 1.0 (Aspheric coefficient) In this embodiment, the ninth and tenth surfaces , The eleventh surface is aspheric. The aspheric coefficients are as shown below. [9th surface] κ = -4.000 C ₄ = -1.3843 × 10 ^-4 C ₆ = + 3.5389 × 10 ^-6 C ₈ = -1.8648 × 10 ^-7 C ₁₀ = + 4.8390 × 10 ^-9 [10th surface] κ = + 7.8116 C ₄ = + 5.2068 × 10 ^-5 C ₆ = + 6.4858 × 10 ^-7 C ₈ = -2.1377 × 10 ^-8 C ₁₀ = + 1.8295 × 10 ^-10 [Seventh surface] κ = + 7.6000 C ₄ = -4.3957 × 10 ^-6 C ₆ = + 1.1262 × 10 ^-6 C ₈ = -3.0775 × 10 ^-8 C ₁₀ = + 1.4259 × 10 ^-10 (Variable interval data) The variable interval when changing the focal length is It is shown below. Wide-angle end state Intermediate focal length Telephoto end state f 39.9006 69.3874 123.5027 D3 1.8284 6.3386 14.0438 D10 13.5003 7.0141 0.9000 BF 11.1740 30.1340 57.5576 (Values for conditional expressions) The values corresponding to the conditional expressions in this embodiment are shown below. DA = 15.7240, DS = 34.6243 f1 = 45.6884, f2 = 36.7109 (1) κa (Ya / Ra) ² = 1.003 (κa = κ on the eleventh surface) (2) │R2│ / D2 = 2.112 ( 3) f1 / ft = 0.370 (4) (│r21│ + │r22│) /f2=0.834

FIGS. 5 (a) to 5 (c) show various aberrations of the second embodiment of the present invention in the state of focusing on infinity, and are in the wide-angle end state (f = 39.90 mm) and the intermediate focal point, respectively. Distance state (f = 69.39 mm), telephoto end state (f = 123.5)
0mm).

From each aberration diagram, it is clear that in this embodiment, various aberrations are satisfactorily corrected, and that the present embodiment has excellent imaging performance.

(Third Embodiment) FIG. 6 is a diagram showing the configuration of a variable focal length lens system according to a third embodiment of the present invention.
In the variable focal length lens system shown in FIG.
Reference numeral 1 denotes a cemented positive lens L1 including a biconvex positive lens and a meniscus negative lens having a concave surface facing the object side. The second lens group G2 is arranged in order from the object side.
A cemented negative lens L21 of a biconcave negative lens and a convex lens
And a biconvex positive lens L22.
Further, the third lens group G3 includes a positive lens L31 having a convex surface facing the image side, and a negative lens L32 having a concave surface facing the object side, which is disposed at an image distance from the image side of the positive lens L31. Have been.

As described above, in the third embodiment, the cemented negative lens L21 forms a negative subgroup, and the positive lens L22 forms a positive subgroup. An aperture stop is disposed between the cemented negative lens L21 and the positive lens L22. Table 3 below shows values of specifications of the third embodiment of the present invention.

[0056]

[Table 3] (Overall specifications) Wide-angle end state Intermediate focal length state Telephoto end state f 39.90-74.99-142.50 FNO 5.86-9.61-13.56 2ω 55.20-31.33-16.95 ° (Lens data) Abbe number 1 23.9451 3.15 1.49700 81.61 2 -72.4270 0.80 1.79504 28.39 3 -264.0005 (D3) 1.0 4 -15.6751 1.20 1.83481 42.72 5 75.6270 3.90 1.67270 32.11 6 -101.0923 1.00 1.0 7 0.0000 0.95 1.0 (aperture stop) 8 22.4174 2.10 1.51450 63.05 9 * -13.8917 (D10) 1.0 10 * -52.6837 2.20 1.68893 31.16 11 * -26.2400 3.80 1.0 12 -9.2997 1.00 1.75500 52.32 13 -46.8296 (Bf) 1.0 (Aspheric coefficient) In this embodiment, the ninth and tenth surfaces , The eleventh surface is aspheric. The aspheric coefficients are as shown below. [9th surface] κ = + 3.2420 C ₄ = + 2.0325 × 10 ^-4 C ₆ = + 1.6085 × 10 ^-6 C ₈ = -5.5776 × 10 ^-9 C ₁₀ = + 4.9353 × 10 ^-10 [10th surface] κ = + 5.3324 C ₄ = + 6.1457 × 10 ^-5 C ₆ = + 2.9325 × 10 ^-6 C ₈ = -6.5818 × 10 ^-8 C ₁₀ = + 4.6523 × 10 ^-10 [Seventh] κ = + 7.0000 C ₄ = + 4.3238 × 10 ^-6 C ₆ = + 3.4855 × 10 ^-6 C ₈ = -6.6017 × 10 ^-8 C ₁₀ = + 3.2782 × 10 ^-10 (Variable interval data) The variable interval for changing the focal length It is shown below. Wide-angle end state Intermediate focal length Telephoto end state f 39.9005 74.9923 142.5030 D3 1.6584 7.2400 16.7920 D10 14.1127 9.6223 0.6500 BF 11.3260 34.5698 68.4594 (Values corresponding to conditional expressions) The values corresponding to the conditional expressions of the present embodiment are shown below. DA = 16.1260, DS = 35.4886 f1 = 50.8185, f2 = 34.8921 (1) κa (Ya / Ra) ² = 0.979 (κa = κ on the eleventh surface) (2) │R2│ / D2 = 3.057 ( 3) f1 / ft = 0.357 (4) (│r21│ + │r22│) /f2=0.847

FIGS. 7 (a) to 7 (c) show various aberration diagrams of the third embodiment of the present invention in the state of focusing on infinity, and are in the wide-angle end state (f = 39.90 mm) and the intermediate focal point, respectively. Distance state (f = 74.99 mm), telephoto end state (f = 142.5)
0mm).

From each aberration diagram, it is clear that in this embodiment, various aberrations are satisfactorily corrected, and that the present embodiment has excellent imaging performance.

[0059]

According to the present invention, a small-sized variable focal length lens system having a high zoom ratio can be achieved with a small number of components.

[Brief description of the drawings]

FIG. 1 shows how the variable focal length lens system according to each embodiment of the present invention moves in the refractive power arrangement and changes in the focal length state from the wide-angle end state (W) to the telephoto end state (T). FIG.

FIG. 2 is a cross-sectional view illustrating a configuration of a variable focal length lens system according to a first example.

FIGS. 3A, 3B, and 3C are aberration diagrams in a wide-angle end state, an intermediate focal length state, and a telephoto end state in the infinity in-focus state of the first embodiment, respectively.

FIG. 4 is a sectional view showing a configuration of a variable focal length lens system according to Example 2.

FIGS. 5A, 5B, and 5C show aberration diagrams in a wide-angle end state, an intermediate focal length state, and a telephoto end state in an infinity in-focus state according to the second embodiment, respectively.

FIG. 6 is a sectional view showing a configuration of a variable focal length lens system according to Example 3.

FIGS. 7A, 7B, and 7C show aberration diagrams of the third embodiment in a wide-angle end state, an intermediate focal length state, and a telephoto end state in an infinity in-focus state, respectively.

[Explanation of symbols]

 G1: first lens group G2: second lens group G3: third lens group S: aperture stop

Continued on the front page F term (reference) 2H087 KA02 NA07 PA05 PA19 PB07 QA02 QA07 QA14 QA22 QA26 QA37 QA41 QA45 RA05 RA13 RA36 SA13 SA16 SA20 SA62 SA63 SA64 SB03 SB14 SB23

Claims (4)

[Claims] 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. When the lens position state changes to the telephoto end state, 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. Each lens group moves to the object side, and an aperture stop is arranged near the second lens group, and the aperture stop moves integrally with the second lens group according to a change in the lens position state, The third lens group includes a positive lens having a convex surface facing the image side, and a negative lens having a concave surface facing the object side, which is disposed on the image side of the positive lens with an air gap therebetween. A double-sided aspheric lens and the following conditional expression (1) A variable focal length lens system characterized by satisfying (1). (1) 0.9 <κa (Ya / Ra) ² <1.3, where κa: the conic constant of the image-side lens surface of the aspherical lens on both sides arranged in the third lens group, Ya: screen pair Half the angular length is Ymax, the distance from the image-side lens surface to the image plane in the wide-angle end state is DA, and the distance from the aperture stop to the image plane in the wide-angle end state is DS.
Where: Ya = Ymax · (DA / DS), Ra: paraxial radius of curvature of the image-side lens surface. 2. The variable focal length lens system according to claim 1, wherein the first lens group is composed of a positive lens having a biconvex shape closest to the object side and a negative lens having a concave surface facing the object side. A variable focal length lens system comprising a positive lens and satisfying the following conditional expression (2). (2) 1.5 <│R2│ / D2 <4, where R2 is the radius of curvature (R2 <0) of the cemented surface of the cemented positive lens disposed in the first lens group, and D2 is in the telephoto end state. The distance from the cemented surface of the cemented positive lens disposed in the first lens group to the aperture stop. 3. The variable focal length lens system according to claim 2, wherein the following conditional expression (3) is satisfied. (3) 0.25 <f1 / ft <0.4, where f1: focal length of the first lens group, ft: focal length of the entire variable focal length lens system in the telephoto end state. 4. The variable focal length lens system according to claim 1, wherein the second lens group includes, in order from the object side, a negative lens having a concave surface facing the object side and a positive lens. A negative lens having a convex surface facing the image side, wherein the aperture stop is disposed between the negative cemented lens and the positive lens, and satisfies the following conditional expression (4). A variable focal length lens system. (4) 0.75 <(│r21│ + │r22│) / f2 <
0.9 where r21: radius of curvature of the lens surface closest to the object side of the cemented negative lens disposed in the second lens group, r22: image side of the positive lens disposed in the second lens group Radius of curvature of the lens surface, f2: focal length of the second lens group.