JPH10104516A - Compact variable power optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small-sized variable power optical system which has a zoom ratio exceeding twice, is simple in constitution and has high performance by changing the focal length over the entire system of optical system by changing the air spacing between a positive lens group and a negative lens group so as to satisfy specific conditions. SOLUTION: This optical system comprises the positive lens group G1 and the negative lens group G2 disposed on their image side and an aperture-stop S is arranged between the positive lens group G1 and the negative lens group G2. The positive lens group G1 comprises, successively from an object side, a negative lens L1, a negative L2 and a positive lens L3. The focal length over the entire part of the optical system is changed by changing the air spacing between the positive lens group G1 and the negative lens group G2 of such constitution, by which the conditions 0.5<r22/D<4 are satisfied. In the equation, r22 denotes the radius of curvature on the image side of the second lens L2 and D denotes the distance along the optical axis between the image side face of the second lens L2 and the aperture-stop S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small zoom optical system, and more particularly to a small zoom optical system suitable for a lens shutter type camera.

[0002]

2. Description of the Related Art Recently, a zoom lens has become a mainstream photographing lens for a lens shutter type camera, and various proposals have been made regarding a positive / negative two-unit zoom lens having a simple lens system. The positive / negative two-group zoom lens includes a positive lens group and a negative lens group disposed on the image side thereof, and changes the focal length of the entire lens system by changing the distance between the positive lens group and the negative lens group ( Variable magnification). Such a two-group positive / negative zoom lens
For example, it is disclosed in Japanese Patent Application Laid-Open No. 2-73322.

[0003] As zoom lenses have become popular, various proposals have been made regarding zoom lenses that have been reduced in size and cost. For example, JP-A-3-12700
No. 9 and Japanese Patent Laid-Open Publication No. H5-257063 disclose a lens system in which a predetermined zoom ratio is secured and cost is reduced. In the lens systems disclosed in these publications, cost reduction is achieved by reducing the number of lens components and using a plastic material. Generally, since a plastic material has a lower melting point than a glass material, molding is easy, and manufacturing costs can be reduced.

In the lens system disclosed in Japanese Patent Application Laid-Open No. 3-127909, the positive lens group is composed of two lenses, a negative lens and a positive lens. The object-side surface of the negative lens has a convergence effect and the image-side surface has a divergence effect, and both surfaces of the negative lens are formed as aspherical surfaces to correct axial and off-axis aberrations. I have. In addition, the number of lens components is reduced by configuring the negative sub-unit with one lens. On the other hand, in the lens system disclosed in Japanese Patent Application Laid-Open No. H5-257063, the cost is reduced by using one plastic lens for each of the positive lens group and the negative lens group.

[0005]

However, in the lens system disclosed in Japanese Patent Application Laid-Open No. 3-127,093, the negative lens in the positive lens group has a strong positive refractive power on the object-side surface and a strong negative refractive power on the image-side surface. Since both surfaces were aspherical, the performance degradation caused by the eccentricity occurring during manufacturing was remarkable. In the lens system disclosed in JP-A-5-257063, cost reduction is achieved by introducing a plastic lens. However, since the positive lens group is composed of four lenses, the number of lens components is not sufficiently reduced. In addition, since the lens closest to the object has the convex surface facing the object, correction of positive distortion at the wide-angle end cannot be said to be sufficient.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems, and has as its object to provide a high-performance, compact, variable-power optical system having a simple configuration with a zoom ratio of more than twice.

[0007]

According to a first aspect of the present invention, there is provided a positive lens group G1 having a positive refractive power, and a negative lens group G1 disposed on the image side of the positive lens group G1. A negative lens group G2 having a refractive power, an aperture stop S is disposed in an optical path between the positive lens group G1 and the negative lens group G2, and the positive lens group G1 is sequentially arranged from the object side. , A first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, and a third lens L3 having a positive refractive power. The air gap between the positive lens group G1 and the negative lens group G2 is The focal length of the entire optical system is changed by changing the radius, the radius of curvature of the image-side surface of the second lens L2 is set to r22, and the distance between the image-side surface of the second lens L2 and the aperture stop S is changed. When the distance along the optical axis is D, 1.5 <r22 / D <4 To provide a compact zoom optical system that satisfies the conditions 1).

According to the second aspect of the present invention, there is provided, in order from the object side, a positive lens group G1 having a positive refractive power and a negative lens group G2 having a negative refractive power. The focal length of the entire optical system is changed by changing the air distance between the negative lens group G2 and the negative lens group G2.
2 is f2, the focal length of the entire optical system in the wide-angle end state is fw, and the focal length of the entire optical system in the telephoto end state is ft: 0.5 <(f1 + | f2 |) / ( fw · ft) ^1/2 <1.2 A compact variable-power optical system characterized by satisfying the condition of (5) is provided.

Further, according to the third aspect, in order from the object side, the positive lens group G1 has a positive refractive power and the negative lens group G2 has a negative refractive power. The focal length of the entire optical system is changed by changing the air gap between the zoom lens and the negative lens group G2, the back focus in the wide-angle end state is set to Bfw, the total lens length in the telephoto end state is set to TLt, and the optical length in the wide-angle end state is set. Assuming that the focal length of the entire system is fw and the focal length of the entire optical system in the telephoto end state is ft, the condition of (Bfw / TLt) · (ft / fw) <0.4 (6) is satisfied. A featured compact variable power optical system is provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, in a positive / negative two-group zoom lens, when the lens position changes from a wide-angle end state to a telephoto end state, the distance between the positive and negative lens groups is reduced. Each lens group moves to the object side. The aperture stop is disposed between the positive lens group and the negative lens group, and moves integrally with the positive lens group or independently of each lens group when the lens position changes.

In order to reduce the size of the lens system, it is effective to increase the refractive power of the positive lens group and the refractive power of the negative lens group. However, in this case, since the refractive power arrangement in the wide-angle end state becomes extremely asymmetric, it is difficult to correct the positive distortion. In addition, if the total length of the lens in the telephoto end state is reduced in order to reduce the size of the lens system, a sufficient back focus cannot be obtained in the wide-angle end state. As a result, an off-axis light beam that passes through a lens group located away from the aperture stop is separated from the optical axis, and the lens diameter tends to be large.

In the present invention, the positive lens unit G1 is
By including the positive subgroup G1b disposed on the image side, positive distortion is satisfactorily corrected, and a sufficient back focus is obtained at the wide-angle end.

For example, in the zoom lens disclosed in Japanese Patent Application Laid-Open No. 2-73322, since the negative subgroup is composed of a positive lens component and a negative cemented lens component, the number of lens components is large. As described above, Japanese Unexamined Patent Application Publication No.
In the zoom lens disclosed in Japanese Patent Application Laid-Open Publication No. H11-176, the negative lens unit is composed of a single negative lens. However, since both surfaces of the negative lens are formed in aspherical shape, performance degradation during eccentricity is reduced. There was a manufacturing disadvantage of being very large. In the present invention, the negative subgroup G1a is constituted by the two negative lenses L1 and L2, so that the performance deterioration during eccentricity can be suppressed as much as possible.

When the negative subgroup is composed of a positive lens and a negative lens, the principal point of the negative subgroup is located closer to the image plane, so that the principal point interval between the negative subgroup and the positive subgroup is reduced. . As a result, if an attempt is made to obtain a predetermined refractive power with the positive lens group G1, the refractive power of the negative subgroup and the positive subgroup is increased, and the performance deterioration due to mutual eccentricity is increased. In the present invention, the negative subgroup G1a is constituted by the two negative lenses L1 and L2, so that the principal point of the negative subgroup G1a is moved toward the object, and the refractive power of the negative subgroup G1a and the positive subgroup G1b is changed. , Respectively, can suppress performance degradation due to mutual eccentricity. In particular, in the present invention, by appropriately setting the interval between the negative subgroup G1a and the positive subgroup G1b, the refractive powers of the negative subgroup G1a and the positive subgroup G1b are each reduced to suppress the performance deterioration due to mutual eccentricity. I have.

Further, in the present invention, when zooming from the wide-angle end state to the telephoto end state, the distance between the positive lens group G1 and the negative lens group G2 is reduced. For this reason, as the lens approaches the telephoto end state, the axial luminous flux passing through the negative lens group G2 moves away from the optical axis, and the positive spherical aberration tends to increase.
In the present invention, the negative lens group G2 is composed of the positive lens L2P (fourth lens L4) disposed on the object side and the negative lens L2N (fifth lens L5) disposed on the image side. The positive spherical aberration that occurs in the positive lens L
The change in spherical aberration due to zooming from the wide-angle end state to the telephoto end state is suppressed by offsetting by negative spherical aberration generated in 2P. Also, as the magnification changes from the wide-angle end state to the telephoto end state, the height of the off-axis light flux passing through the negative lens group G2 approaches the optical axis, so that the object-side surface of the positive lens L2P is formed in an aspherical shape. By doing so, the fluctuation of coma aberration due to zooming from the wide-angle end state to the telephoto end state is favorably suppressed.

The variable power optical system of the present invention has been made based on the above technical background. In order from the object side, a positive lens group G1 having a positive refractive power and a negative refractive power And a negative lens group G2.
The focal length of the entire optical system is changed by changing the air gap between the lens unit 1 and the negative lens group G2. In the first aspect, the positive lens group G1 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power,
A high-performance variable-power optical system which is composed of a third lens L3 having a positive refractive power and satisfies the predetermined conditional expression (1) achieves downsizing and cost reduction.

Hereinafter, the conditional expressions of the present invention will be described.
In the first invention, the following conditional expression (1) is satisfied. 1.5 <r22 / D <4 (1) where, r22: radius of curvature of the image-side surface of the second lens L2 D: optical axis between the image-side surface of the second lens L2 and the aperture stop S Distance along

Conditional expression (1) defines an appropriate range for the radius of curvature of the image-side lens surface of the negative lens L2.
In the first aspect, the positive lens group G1 includes a negative subgroup G1a including two negative lenses L1 and L2, and a positive subgroup G1b including one positive lens L3 disposed on the image side. Is done. With such a configuration, it is possible to secure a sufficient back focus in the wide-angle end state, reduce the lens diameter, and satisfactorily correct positive distortion. The image-side lens surface of the negative lens L2 is the most image-side lens surface of the negative subgroup G1a, and has a concave surface facing the aperture stop in order to suppress occurrence of off-axis aberration.

If the upper limit of conditional expression (1) is exceeded, the positive spherical aberration generated on the image-side lens surface of the negative lens L2 will be insufficient. It is difficult to make a good correction. vice versa,
If the lower limit value of the conditional expression (1) is not reached, coma aberration for the lower off-axis light beam will be overcorrected in the wide-angle end state, so that good imaging performance cannot be obtained on the entire screen.

In the first aspect of the present invention, it is desirable that the following conditional expression (2) is satisfied in order to achieve a balance between miniaturization and high performance of the lens system. 0.02 <D23 / | f1a | <0.08 (2) Here, D23: On-axis air gap between the second lens L2 and the third lens L3 f1a: Synthesis of the first lens L1 and the second lens L2 Focal length

Conditional expression (2) defines an appropriate range for the focal length f1a of the negative subgroup G1a including the negative lenses L1 and L2 in the positive lens group G1. If the upper limit of conditional expression (2) is exceeded, the diverging effect of the negative subgroup G1a will increase, and it will not be possible to reduce the overall length of the lens in the telephoto end state. On the other hand, conditional expression (2)
When the value is below the lower limit, the diverging action of the negative subgroup G1a is weakened, and it becomes difficult to satisfactorily correct the negative spherical aberration generated in the positive subgroup G1b.

In order to obtain higher imaging performance, it is desirable to introduce an aspherical surface into the negative lens group G2. In this case, it is particularly desirable to form the most object side surface of the negative lens group G2 into an aspherical shape. Since the height difference between the on-axis light beam and the off-axis light beam passing through the negative lens group G2 is large, an aspherical surface is introduced into the negative lens group G2 to achieve higher image formation while widening the angle and reducing the size. Performance can be obtained. Further, as described above, in order to satisfactorily correct the positive spherical aberration generated in the negative lens group G2,
The negative lens group G2 includes a positive lens L2P (fourth lens L4) disposed on the object side and a negative lens L2N (fifth lens L2N) disposed on the image side.
It is desirable to form the lens L5).

In the first invention, the negative lens unit is provided in order to satisfactorily correct axial aberrations generated in the positive lens unit G1 and the negative lens unit G2 to achieve both high performance and high magnification. It is preferable that G2 includes a fourth lens L4 having a positive refractive power and a fifth lens L5 having a negative refractive power in order from the object side, and satisfies the following conditional expression (3). 0.08 <D45 / | f2 | <0.40 (3) where, D45 is an on-axis air gap between the fourth lens L4 and the fifth lens L5. F2 is a focal length of the negative lens group G2.

Conditional expression (3) is satisfied for the fourth lens in the negative lens unit G2.
An appropriate range is defined for the axial air gap D45 between the lens L4 and the fifth lens L5. When the value exceeds the upper limit of conditional expression (3), if an attempt is made to secure a predetermined amount or more of the axial air gap between the positive lens group G1 and the negative lens group G2 in the telephoto end state, the fifth lens L5 is moved in the wide angle end state. Move away from the aperture stop S. As a result, the off-axis light beam passing through the fifth lens L5 is separated from the optical axis, and it becomes impossible to reduce the lens diameter. On the other hand, if the lower limit of conditional expression (3) is not reached, the refractive power of the fourth lens L4 and the refractive power of the fifth lens L5 will increase, making it difficult to correct axial aberration and off-axis aberration simultaneously. Will be.

In the first aspect, the following conditional expression (4) is provided in order to satisfactorily correct the positive distortion generated in the wide-angle end state and to shorten the total lens length in the telephoto end state. It is desirable to satisfy 0.1 <f2 / f1a <0.5 (4) If the lower limit of conditional expression (4) is exceeded, it becomes difficult to satisfactorily correct positive distortion in the wide-angle end state. On the other hand, when the value exceeds the upper limit of conditional expression (4),
The overall length of the lens in the telephoto end state increases.

By the way, in the second aspect according to another aspect of the present invention, conditional expression (5) is satisfied in order to reduce the lens diameter and shorten the overall length of the lens in the telephoto end state. 0.5 <(f1 + | f2 |) / (fw · ft) ^1/2 <1.2 (5) where f1: focal length of the positive lens group G1 fw: focal length of the entire optical system in the wide-angle end state. ft: focal length of the entire optical system in the telephoto end state

Conditional expression (5) defines an appropriate range for the sum of the focal length of the positive lens group G1 and the absolute value of the focal length of the negative lens group G2. When the value exceeds the upper limit of conditional expression (5), the amount of movement of each lens unit when zooming from the wide-angle end state to the telephoto end state becomes extremely large, and especially the entire lens length in the telephoto end state increases. Conversely, if the lower limit value of conditional expression (5) is not reached, the refractive power arrangement across the aperture stop becomes extremely asymmetric in the wide-angle end state, so that positive distortion cannot be satisfactorily corrected. I will.

Further, in accordance with another aspect of the present invention, a third aspect is provided.
In the present invention, the following conditional expression (6) is satisfied in order to simultaneously achieve downsizing of the lens system and high zooming. (Bfw / TLt) · (ft / fw) <0.4 (6) where Bfw: back focus in the wide-angle end state TLt: total length of the lens in the telephoto end state Note that the back focus is the most image side in the optical system. Is the distance on the optical axis between this surface and the image plane, and the total lens length is the distance on the optical axis between the most object side surface and the image plane in the optical system.

As described above, when the back focus in the wide-angle end state is reduced, the off-axis light beam passing through the negative lens group G2 is separated from the optical axis, and the lens diameter is increased. Therefore, it is desirable to increase the ratio of the back focus to the focal length of the entire optical system in the wide-angle end state.
In the telephoto end state, reducing the telephoto ratio (the ratio of the total length of the lens to the focal length of the entire optical system) directly leads to the miniaturization of the entire optical system. The value of the conditional expression (6) can be modified to (Bfw / fw) / (TLt / ft). Therefore, when the value of the conditional expression (6) is large, the back focus in the wide-angle end state is large,
This means that the overall length of the lens in the telephoto end state is short.
The upper limit of conditional expression (6) is a value set in order to balance with the optical performance.

When the value exceeds the upper limit of conditional expression (6), the back focus in the wide-angle end state becomes too large, and it becomes difficult to correct the on-axis aberration and the off-axis aberration independently. In order to further reduce the size of the optical system, it is desirable to set the lower limit of conditional expression (6) to 0.15. Below this lower limit, the optical system becomes extremely large.

In the first to third aspects of the present invention, the following conditions must be satisfied in order to satisfactorily correct the positive distortion generated in the wide-angle end state and to shorten the total lens length in the telephoto end state. It is preferable that the formula (7) is satisfied. 1 <| f1a | / (fw · ft) ^1/2 <4 (7) Conditional expression (7) satisfies the negative subgroup G constituting the positive lens group G1.
An appropriate range is defined for the focal length of 1a. If the value exceeds the upper limit of conditional expression (7), it becomes impossible to satisfactorily correct positive distortion generated in the wide-angle end state. On the other hand, when the value goes below the lower limit value of conditional expression (7), the entire lens length becomes extremely large in the telephoto end state.

As described above, in the present invention, by introducing a plastic lens, it is possible to reduce the cost and weight during mass production. Since the plastic material has a lower molding temperature than the glass material, it is suitable for cost reduction, and an aspherical surface can be introduced at low cost. When using a plastic material for the taking lens, the plastic lens has the following problems. Since the change in the refractive index with respect to the temperature change is larger than that of the glass, the image plane position is likely to change with the temperature change. Since the shape change with respect to the temperature change is larger than that of the glass, the aberration tends to fluctuate with the temperature change.

In the present invention, one plastic lens having a relatively low refractive power and one plastic lens having a negative refractive power are introduced one by one, and the refractive power ratio between them is set to an appropriate value. The accompanying fluctuation of the image plane position is minimized. That is, the negative plastic lens (second lens L2) is disposed in the positive lens group G1, and the positive plastic lens (fourth lens L4) is disposed in the negative lens group G2. When the plastic lens has a biconvex lens shape or a biconcave lens shape, a change in refractive power of the lens surfaces on both sides due to a temperature change is in the same direction.
On the other hand, when the plastic lens has a meniscus shape, the change in the refractive power of the lens surfaces on both sides due to the temperature change is reversed. As a result, aberration fluctuations occurring at the time of temperature change also become opposite on the lens surfaces on both sides, and it is possible to suppress aberration fluctuations due to temperature change. In the present invention, by making the plastic lens have a meniscus shape, it is possible to suppress the fluctuation of aberration due to the temperature change.

Further, when a lens surface having a small difference in the height at which an on-axis light beam and an off-axis light beam pass is formed in an aspherical shape,
It is known that it is effective for correcting axial aberration. Conversely, it is known that when the lens surface through which the off-axis light beam passes away from the on-axis light beam is formed in an aspherical shape, it is effective in correcting the off-axis aberration. In the present invention, by introducing one plastic lens into each of the positive lens group G1 and the negative lens group G2, the number of lenses constituting each of the positive lens group G1 and the negative lens group G2 is reduced, and cost reduction is achieved. Lightening can be achieved.

By introducing more aspherical surfaces into the lens system, it is possible to satisfactorily correct the spherical aberration generated in each lens group and to make the lens system larger in diameter. It is also possible to shift the image by decentering any or all of the lens groups with respect to the optical axis. In this case, for example, by combining an angular velocity sensor for detecting the vibration of the lens system and a driving member for eccentrically driving the whole or a part of the lens group in accordance with the vibration of the lens system, the vibration of the lens system can be improved. It is clear that the image stabilizing effect of correcting the fluctuation of the image position caused by the above can be obtained.

[0036]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a refractive power distribution of a variable power optical system according to each embodiment of the present invention and a state of movement of each lens group during zooming from a wide-angle end state (W) to a telephoto end state (T). It is. As shown in FIG. 1, a variable power optical system according to each embodiment of the present invention includes a positive lens group G1 having a positive refractive power and a negative refractive power arranged on the image side of the positive lens group G1. And a negative lens group G2. Then, at the time of zooming from the wide-angle end state to the telephoto end state, each lens group moves toward the object side so that the air gap between the positive lens group G1 and the negative lens group G2 decreases.

In each embodiment, the aspherical surface has a height y in a direction perpendicular to the optical axis, a displacement (sag amount) in the optical axis direction at the height y of S (y), and a reference paraxial radius of curvature. Is R, the conic coefficient is κ, and the nth order aspherical coefficient is Cn, and is represented by the following equation (a).

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

[First Embodiment] FIG. 2 is a diagram showing a lens configuration of a variable power optical system according to a first embodiment of the present invention. The variable magnification optical system in FIG. 2 includes, in order from the object side, a negative meniscus lens L1 having a concave surface facing the object side, a negative meniscus lens L2 having a convex surface facing the object side, and a positive lens group G1 including a biconvex lens L3; The negative lens group G2 includes a positive meniscus lens L4 having a concave surface facing the object side and a negative meniscus lens L5 having a concave surface facing the object side.

The aperture stop S is disposed between the positive lens group G1 and the negative lens group G2, and moves together with the positive lens group G1 when changing magnification from the wide-angle end state to the telephoto end state. FIG. 2 shows the positional relationship between the lens groups in the wide-angle end state, and moves on the optical axis along a zoom trajectory indicated by an arrow in FIG. 1 during zooming to the telephoto end state.

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, and Bf represents the back focus. Furthermore, the surface number indicates the order of the lens surface from the object side along the direction in which the light rays travel,
The refractive index and Abbe number are each d-line (λ = 587.6).
nm). In the lens specifications of Table (1), a surface having a radius of curvature of ∞ (infinity) represents a plane. The radius of curvature of the surface representing the aperture stop S is ∞
However, there is no lens surface on the surface representing the aperture stop S.

[0041]

[Table 1] f = 39.0-63.1-104.1 FNO = 3.8-6.2-10.3 2ω = 55.9-37.3-23.4 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 -68.6158 1.262 1.75520 27.5 2 -272.9574 1.010 3 * 31.7481 1.893 1.58518 30.2 (Polycarbonate) 4 25.2870 3.534 5 74.9079 6.311 1.48749 70.5 6 -12.3908 1.262 7 ∞ (d7 = Variable) (Aperture stop S) 8 * -56.7963 3.786 1.58518 30.2 (Polycarbonate) 9 -29.1266 4.670 10 -10.9563 1.262 1.71700 48.0 11- 56.7140 (Bf) (Aspherical surface data) R κ C ₄ 3 faces 31.7481 1.0000 -1.10903 × 10 ^-4 C ₆ C ₈ C ₁₀ -9.88867 × 10 ^-7 + 9.79079 × 10 ^-10 -1.08850 × 10 ^-10 R κ C ₄ 8 planes -56.7963 1.0000 + 4.60428 × 10 ^-5 C ₆ C ₈ C ₁₀ + 5.53412 × 10 ^-7 -5.77 346 × 10 ^-9 + 5.34985 × 10 ^-11 (variable interval in variable magnification) f 39.0003 63.1078 104.1294 d7 13.6976 7.0901 2.8791 Bf 9.8468 31.3329 67.8939 (Conditional value) f1a = −78.660 f2 = −24.520 f1 = + 27.512 TLt = 95.763 (1) r22 / D = 2.277 (2) D23 / | f1a | = 0.045 (3) D45 / | f2 | = 0.190 (4) f2 / f1a = 0.312 ( 5) (f1 + | f2 |) / (fw · ft) ^1/2 = 0.817 (6) (Bfw / TLt) · (ft / fw) = 0.275 (7) | f1a | / (fw · ft) ) ^1/2 = 1.234

FIGS. 3 to 5 show the d-line (λ = 587.6n).
FIG. 7 is a diagram illustrating various aberrations of the first example with respect to m). FIG. 3 is a diagram of various aberrations in the wide-angle end state (the shortest focal length state).
FIG. 4 is a diagram of various aberrations in the intermediate focal length state, and FIG.
FIG. 8 is a diagram of various aberrations in the telephoto end state (the longest focal length state). In each aberration diagram, FNO represents the F number, Y represents the image height, and A represents the angle of view for each image height.
In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane.
Further, in the aberration diagram showing the spherical aberration, a broken line indicates a sine condition (sine condition). As is clear from the aberration diagrams, in this embodiment, various aberrations are satisfactorily corrected in each focal length state, and excellent image forming performance is obtained.

[Second Embodiment] FIG. 6 is a diagram showing a lens configuration of a variable power optical system according to a second embodiment of the present invention. The variable power optical system of FIG. 6 includes, in order from the object side, a negative meniscus lens L1 having a concave surface facing the object side, a negative meniscus lens L2 having a convex surface facing the object side, and a positive lens group G1 including a biconvex lens L3; The negative lens group G2 includes a positive meniscus lens L4 having a concave surface facing the object side and a negative meniscus lens L5 having a concave surface facing the object side.

The aperture stop S is disposed between the positive lens group G1 and the negative lens group G2, and moves together with the positive lens group G1 when changing magnification from the wide-angle end state to the telephoto end state. FIG. 6 shows the positional relationship between the lens groups in the wide-angle end state, and moves on the optical axis along a zoom trajectory indicated by an arrow in FIG. 1 during zooming to the telephoto end state.

Table 2 below summarizes the 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, and Bf represents the back focus. Furthermore, the surface number indicates the order of the lens surface from the object side along the direction in which the light rays travel,
The refractive index and Abbe number are each d-line (λ = 587.6).
nm). In the lens specifications of Table (2), a surface having a radius of curvature of ∞ (infinity) represents a plane. The radius of curvature of the surface representing the aperture stop S is ∞
However, there is no lens surface on the surface representing the aperture stop S.

[0046]

[Table 2] f = 38.6 to 62.5 to 103.1 FNO = 4.0 to 6.5 to 10.7 2ω = 56.3 to 37.6 to 23.6 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 -67.9559 1.250 1.75520 27.5 2 -305.1296 1.000 3 * 30.0902 1.875 1.58518 30.2 (Polycarbonate) 4 25.0438 3.500 5 74.1874 6.250 1.48749 70.5 6 -12.3343 1.250 7 ∞ (d7 = Variable) (Aperture stop S) 8 * -58.0641 3.750 1.58518 30.2 (Polycarbonate) 9 -23.9338 3.875 10 -11.0381 1.250 1.78590 43.9 11- 59.9494 (Bf) (Aspherical surface data) R κ C ₄ 3 planes 30.0902 1.0000 -1.11473 × 10 ^-4 C ₆ C ₈ C ₁₀ -9.71609 × 10 ^-7 -5.61576 × 10 ^-9 + 1.14622 × 10 ^-11 R κ C ₄ 8 planes -58.0641 1.0000 + 4.41581 × 10 ^-5 C ₆ C ₈ C ₁₀ + 7.65030 × 10 ^-7 -9.89839 × 10 ^-9 + 8.21306 × 10 ^-11 (variable interval in zooming) f 38.6250 62.5000 103.1251 d7 13.5999 6.9969 2.7887 Bf 10.3124 31.9432 68.7497 (Conditional value) f1a = −81.342 f2 = −24.595 f1 = + 27.146 TLt = 95.538 (1) r22 / D = 2.277 (2) D23 / | f1a | = 0.043 (3) D45 / | f2 | = 0.158 (4) f2 / f1a = 0.302 ( 5) (f1 + | f2 |) / (fw · ft) ^1/2 = 0.820 (6) (Bfw / TLt) · (ft / fw) = 0.288 (7) | f1a | / (fw · ft) ) ^1/2 = 1.289

FIGS. 7 to 9 show the d-line (λ = 587.6n).
FIG. 10 is a diagram illustrating various aberrations of the second example with respect to m). FIG. 7 is a diagram illustrating various aberrations in the wide-angle end state, FIG. 8 is a diagram illustrating various aberrations in the intermediate focal length state, and FIG. 9 is a diagram illustrating various aberrations in the telephoto end state. In each aberration diagram, FNO represents the F number, Y represents the image height, and A represents the angle of view for each image height. In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. Further, in the aberration diagram showing the spherical aberration, a broken line indicates a sine condition (sine condition).
As is clear from the aberration diagrams, in this embodiment, various aberrations are satisfactorily corrected in each focal length state, and excellent image forming performance is obtained.

[Third Embodiment] FIG. 10 is a diagram showing a lens configuration of a variable power optical system according to a third embodiment of the present invention.
The variable power optical system shown in FIG.
1. A positive meniscus lens L1 including a negative meniscus lens L2 having a convex surface facing the object side and a biconvex lens L3, a positive meniscus lens L4 having a concave surface facing the object side, and a negative meniscus lens L5 having a concave surface facing the object side And a negative lens group G2.

The aperture stop S is arranged between the positive lens group G1 and the negative lens group G2, and moves together with the positive lens group G1 when changing the magnification from the wide-angle end state to the telephoto end state. FIG. 10 shows the positional relationship between the lens groups in the wide-angle end state, and moves on the optical axis along a zoom trajectory indicated by an arrow in FIG. 1 during zooming to the telephoto end state.

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, and Bf represents the back focus. Furthermore, the surface number indicates the order of the lens surface from the object side along the direction in which the light rays travel,
The refractive index and Abbe number are each d-line (λ = 587.6).
nm). In the lens specifications of Table (3), a surface having a radius of curvature of ∞ (infinity) represents a plane. The radius of curvature of the surface representing the aperture stop S is ∞
However, there is no lens surface on the surface representing the aperture stop S.

[0051]

[Table 3] f = 39.1 to 63.3 to 104.4 FNO = 3.8 to 6.2 to 10.2 2ω = 55.8 to 37.3 to 23.4 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 -106.8616 1.265 1.74000 28.2 2 1013.0365 0.380 3 * 31.2778 1.898 1.58518 30.2 (Polycarbonate) 4 25.3443 4.175 5 72.8197 6.325 1.48749 70.5 6 -13.2490 1.265 7 ∞ (d7 = Variable) (Aperture stop S) 8 * -50.1759 3.795 1.58518 30.2 (Polycarbonate) 9 -23.8931 4.428 10 -12.1268 1.265 1.78590 43.9 11 -59.2933 (Bf) (Aspherical surface data) R κ C ₄ 3 surface 31.2778 1.0000 -9.53770 × 10 ^-5 C ₆ C ₈ C ₁₀ -6.06670 × 10 ^-7 -2.52850 × 10 ^-9 -4.91140 × 10 ^-11 R κ C ₄ 8 sides -50.1759 1.0000 + 3.69420 × 10 ^-5 C ₆ C ₈ C ₁₀ + 1.59790 × 10 ^-7 -3.85190 × 10 ^-10 + 1.13840 × 10 ^-11 (variable interval in zooming) f 39.0885 63.2500 104.3625 d7 15.1503 7.2372 2.1940 Bf 9.4766 32.5876 71.9126 (Conditional value) f1a = −85.003 f2 = −27.830 f1 = + 29.09 (1) r22 / D = 2.154 (2) D23 / | f1a | = 0.049 (3) D45 / | f2 | = 0.159 (4) f2 / f1a = 0.327 (5) (f1 + | f2 |) / (fw · ft) ^1/2 = 0.891 (6) (Bfw / TLt) · (ft / fw) = 0.256 (7) | f1a | / (fw · ft) ^1/2 = 1.331

FIGS. 11 to 13 show the d-line (λ = 587.
FIG. 9 is a diagram illustrating various aberrations of the third example with respect to (6 nm). FIG.
12 is a diagram illustrating various aberrations at the wide-angle end state, FIG. 12 is a diagram illustrating various aberrations at the intermediate focal length state, and FIG. 13 is a diagram illustrating various aberrations at the telephoto end state. In each aberration diagram, FNO represents the F number, Y represents the image height, and A represents the angle of view for each image height. In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. Further, in the aberration diagram showing the spherical aberration, a broken line indicates a sine condition (sine condition). As is clear from each aberration diagram, in the present embodiment, various aberrations are favorably corrected in each focal length state,
It turns out that it has excellent imaging performance.

[Fourth Embodiment] FIG. 14 is a diagram showing a lens configuration of a variable power optical system according to a fourth embodiment of the present invention.
The variable magnification optical system in FIG. 14 includes, in order from the object side, a negative meniscus lens L1 having a concave surface facing the object side, a negative meniscus lens L2 having a convex surface facing the object side, and a positive lens group G1 including a biconvex lens L3; The negative lens group G2 includes a positive meniscus lens L4 having a concave surface facing the object side and a negative meniscus lens L5 having a concave surface facing the object side.

The aperture stop S is arranged between the positive lens group G1 and the negative lens group G2, and moves together with the positive lens group G1 when changing magnification from the wide-angle end state to the telephoto end state. FIG. 14 shows the positional relationship between the lens groups in the wide-angle end state, and moves on the optical axis along a zoom trajectory indicated by an arrow in FIG. 1 during zooming to the telephoto end state.

Table 4 below summarizes the data values of the fourth embodiment of the present invention. In Table (4), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, and Bf represents the back focus. Furthermore, the surface number indicates the order of the lens surface from the object side along the direction in which the light rays travel,
The refractive index and Abbe number are each d-line (λ = 587.6).
nm). In the lens specifications of Table (4), a surface having a radius of curvature of ∞ (infinity) represents a plane. The radius of curvature of the surface representing the aperture stop S is ∞
However, there is no lens surface on the surface representing the aperture stop S.

[0056]

[Table 4] f = 39.1 to 63.3 to 104.4 FNO = 3.9 to 6.3 to 10.3 2ω = 55.3 to 37.1 to 23.3 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 -35.2008 1.265 1.86074 23.0 2 -51.5066 0.380 3 * 28.8300 1.898 1.58518 30.2 (Polycarbonate) 4 24.7508 3.795 5 64.6983 4.934 1.48749 70.5 6 -11.8803 1.265 7 ∞ (d7 = Variable) (Aperture stop S) 8 * -60.0708 3.795 1.58518 30.2 (Polycarbonate) 9 -29.1522 4.048 10 -9.5882 1.265 1.77250 49.6 11- 41.0970 (Bf) (Aspherical surface data) R κ C ₄ 3 planes 28.8300 1.0000 -1.23738 × 10 ^-4 C ₆ C ₈ C ₁₀ -1.30031 × 10 ^-6 -2.36070 × 10 ^-10 -1.41375 × 10 ^-10 R κ C ₄ 8 planes -60.0708 1.0000 + 6.73719 × 10 ^-5 C ₆ C ₈ C ₁₀ + 1.18785 × 10 ^-6 -1.73419 × 10 ^-8 + 2.03159 × 10 ^-10 (variable interval in zooming) f 39.0885 63.2500 104.3625 d7 10.6062 5.6660 2.5175 Bf 11.4022 31.4748 65.6298 (Conditional value) f1a = -95.246 f2 = -20.493 f1 = + 24.668 TLt = 90.791 (1) r22 / D = 2.477 (2) D23 / | f1a | = 0.040 (3) D45 / | f2 | = 0.198 (4) f2 / f1a = 0.215 ( 5) (f1 + | f2 |) / (fw · ft) ^1/2 = 0.707 (6) (Bfw / TLt) · (ft / fw) = 0.335 (7) | f1a | / (fw · ft) ) ^1/2 = 1.491

FIGS. 15 to 17 show the d-line (λ = 587.
FIG. 10 is a diagram illustrating various aberrations of the fourth example with respect to (6 nm). FIG.
FIG. 16 is a diagram illustrating various aberrations at the wide-angle end state, FIG. 16 is a diagram illustrating various aberrations at the intermediate focal length state, and FIG. 17 is a diagram illustrating various aberrations at the telephoto end state. In each aberration diagram, FNO represents the F number, Y represents the image height, and A represents the angle of view for each image height. In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. Further, in the aberration diagram showing the spherical aberration, a broken line indicates a sine condition (sine condition). As is clear from each aberration diagram, in the present embodiment, various aberrations are favorably corrected in each focal length state,
It turns out that it has excellent imaging performance.

[Fifth Embodiment] FIG. 18 is a diagram showing a lens configuration of a variable power optical system according to a fifth embodiment of the present invention.
The variable power optical system of FIG. 18 includes, in order from the object side, a negative meniscus lens L1 having a concave surface facing the object side, a negative meniscus lens L2 having a convex surface facing the object side, and a positive lens group G1 including a biconvex lens L3; The negative lens group G2 includes a positive meniscus lens L4 having a concave surface facing the object side and a negative meniscus lens L5 having a concave surface facing the object side.

The aperture stop S is arranged between the positive lens group G1 and the negative lens group G2, and moves together with the positive lens group G1 when changing magnification from the wide-angle end state to the telephoto end state. FIG. 18 shows the positional relationship between the lens groups in the wide-angle end state, and moves on the optical axis along a zoom trajectory indicated by an arrow in FIG. 1 during zooming to the telephoto end state.

Table 5 below summarizes the data values of the fifth embodiment of the present invention. In Table (5), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, and Bf represents the back focus. Furthermore, the surface number indicates the order of the lens surface from the object side along the direction in which the light rays travel,
The refractive index and Abbe number are each d-line (λ = 587.6).
nm). In the lens specifications of Table (5), a surface having a radius of curvature of ∞ (infinity) represents a plane. The radius of curvature of the surface representing the aperture stop S is ∞
However, there is no lens surface on the surface representing the aperture stop S.

[0061]

[Table 5] f = 30.9 to 50.0 to 72.5 FNO = 4.1 to 6.7 to 9.7 2ω = 67.2 to 46.0 to 33.0 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 -22.8115 1.250 1.80518 25.4 2 -35.8489 0.375 3 * 28.6144 1.875 1.58518 30.2 (Polycarbonate) 4 24.1589 3.250 5 49.3944 3.000 1.48749 70.5 6 -10.1096 1.250 7 ∞ (d7 = Variable) (Aperture stop S) 8 * -38.4669 3.000 1.58518 30.2 (Polycarbonate) 9 -21.5864 4.125 10 -8.9318 1.250 1.78800 47.5 11- 39.5226 (Bf) (Aspherical surface data) R κ C ₄ 3 planes 28.6144 1.0000 -2.12818 × 10 ^-4 C ₆ C ₈ C ₁₀ -2.51648 × 10 ^-6 -1.29851 × 10 ^-8 -6.08610 × 10 ^-10 R κ C ₄ 8 planes -38.4669 1.0000 + 7.59706 × 10 ^-5 C ₆ C ₈ C ₁₀ + 1.63450 × 10 ^-6 -2.17223 × 10 ^-8 +2.80 180 × 10 ^-10 (variable interval in zooming) f 30.8750 50.0000 72.4999 d7 9.9 230 4.9247 2.4206 Bf 7.8629 24.7511 44.6195 (Conditional value) f1a = −62.822 f2 = −18.375 f1 = + 21.375 T t = 66.415 (1) r22 / D = 3.221 (2) D23 / | f1a | = 0.052 (3) D45 / | f2 | = 0.224 (4) f2 / f1a = 0.292 ( 5) (f1 + | f2 |) / (fw · ft) ^1/2 = 0.840 (6) (Bfw / TLt) · (ft / fw) = 0.278 (7) | f1a | / (fw · ft) ) ^1/2 = 1.328

FIGS. 19 to 21 show the d-line (λ = 587.
FIG. 10 is a diagram illustrating various aberrations of the fifth example with respect to 6 nm). FIG.
FIG. 20 is a diagram illustrating various aberrations in the wide-angle end state, FIG. 20 is a diagram illustrating various aberrations in the intermediate focal length state, and FIG. 21 is a diagram illustrating various aberrations in the telephoto end state. In each aberration diagram, FNO represents the F number, Y represents the image height, and A represents the angle of view for each image height. In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. Further, in the aberration diagram showing the spherical aberration, a broken line indicates a sine condition (sine condition). As is clear from each aberration diagram, in the present embodiment, various aberrations are favorably corrected in each focal length state,
It turns out that it has excellent imaging performance.

In each of the embodiments described above, examples are shown in which polycarbonate is used as the plastic material. However, it is also possible to use a plastic material such as polyethylene or acrylic, and it is naturally possible to use a glass material instead of the plastic material.

[0064]

As described above, according to the present invention, it is possible to realize a compact, high-performance, compact variable-power optical system having a variable power ratio (zoom ratio) exceeding 2 times and having a simple configuration. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a refractive power distribution of a variable power optical system according to each embodiment of the present invention and a state of movement of each lens group during zooming from a wide-angle end state (W) to a telephoto end state (T). It is.

FIG. 2 is a diagram showing a lens configuration of a variable power optical system according to a first example of the present invention.

FIG. 3 is a diagram illustrating various aberrations of the first example in a wide-angle end state.

FIG. 4 is a diagram illustrating various aberrations of the first example in an intermediate focal length state.

FIG. 5 is a diagram illustrating various aberrations of the first example in a telephoto end state.

FIG. 6 is a diagram showing a lens configuration of a variable power optical system according to Example 2 of the present invention.

FIG. 7 is a diagram illustrating various aberrations of the second example in a wide-angle end state.

FIG. 8 is a diagram illustrating various aberrations of the second example in an intermediate focal length state.

FIG. 9 is a diagram illustrating various aberrations of the second example in a telephoto end state.

FIG. 10 is a diagram showing a lens configuration of a zoom optical system according to Example 3 of the present invention.

FIG. 11 is a diagram illustrating various aberrations of the third example in a wide-angle end state.

FIG. 12 is a diagram illustrating various aberrations of the third example in an intermediate focal length state.

FIG. 13 is a diagram illustrating various aberrations of the third example in a telephoto end state.

FIG. 14 is a diagram showing a lens configuration of a variable power optical system according to Example 4 of the present invention.

FIG. 15 is a diagram illustrating various aberrations of the fourth example in a wide-angle end state.

FIG. 16 is a diagram illustrating various aberrations of the fourth example in an intermediate focal length state.

FIG. 17 is a diagram illustrating various aberrations of the fourth example in a telephoto end state.

FIG. 18 is a diagram illustrating a lens configuration of a zoom optical system according to Example 5 of the present invention.

FIG. 19 is a diagram illustrating various aberrations of the fifth example in a wide-angle end state.

FIG. 20 is a diagram illustrating various aberrations of the fifth embodiment in an intermediate focal length state.

FIG. 21 is a diagram illustrating various aberrations of the fifth example in a telephoto end state.

[Explanation of symbols]

 G1 Positive lens group G2 Negative lens group Li Each lens S Aperture stop

Claims (8)

[Claims] 1. A positive lens group G1 having a positive refractive power;
A negative lens group G2 having a negative refractive power disposed on the image side of the positive lens group G1. An aperture stop S is provided in an optical path between the positive lens group G1 and the negative lens group G2. The positive lens group G1 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, and a third lens L3 having a positive refractive power. By changing the air gap between the lens group G1 and the negative lens group G2, the focal length of the entire optical system is changed, and the radius of curvature of the image-side surface of the second lens L2 is r22,
When the distance along the optical axis between the image-side surface of the second lens L2 and the aperture stop S is D, the following condition is satisfied: 1.5 <r22 / D <4 (1) Features a small variable power optical system. 2. The second lens L2 and the third lens L
0.03 <D23 / | f1a | <0.08 (2) where D23 is the on-axis air distance from the lens 3 and f1a is the combined focal length of the first lens L1 and the second lens L2. 2. The compact variable power optical system according to claim 1, wherein the condition is satisfied. 3. The negative lens group G2 includes, in order from the object side, a fourth lens L4 having a positive refractive power and a fifth lens L5 having a negative refractive power. The fourth lens L4 and the fifth lens The on-axis air distance from L5 is D45, and the focal length of the negative lens group G2 is f2.
3. The compact variable power optical system according to claim 1, wherein the following condition is satisfied: 0.08 <D45 / | f2 | <0.40 (3) 4. The first lens L1 and the second lens L
2. The condition of 0.1 <f2 / f1a <0.5 (4) is satisfied, where f1a is the composite focal length of the negative lens group G2 and f2 is the focal length of the negative lens group G2. 4. The compact variable power optical system according to any one of 1 to 3. 5. A lens system comprising: a positive lens group G1 having a positive refractive power and a negative lens group G2 having a negative refractive power, in order from the object side, wherein the positive lens group G1 and the negative lens group G2 The focal length of the entire optical system is changed by changing the air gap, the focal length of the positive lens group G1 is f1, the focal length of the negative lens group G2 is f2, and the focal length of the entire optical system in the wide-angle end state. When the distance is fw and the focal length of the entire optical system in the telephoto end state is ft, the following condition is satisfied: 0.5 <(f1 + | f2 |) / (fw · ft) ^1/2 <1.2 (5) A compact variable power optical system characterized by satisfying. 6. A positive lens group G1 having a positive refractive power and a negative lens group G2 having a negative refractive power are arranged in this order from the object side. The focal length of the entire optical system is changed by changing the air interval, the back focus in the wide-angle end state is Bfw, the total length of the lens in the telephoto end state is TLt, and the focal length of the entire optical system in the wide-angle end state is fw. , When the focal length of the entire optical system in the telephoto end state is ft, the following condition is satisfied: (Bfw / TLt) · (ft / fw) <0.4 (6) system. 7. The positive lens group G1 includes a negative subgroup G1a having a negative refractive power, and a positive subgroup G1b having a positive refractive power disposed on the image side of the negative subgroup G1a. When the focal length of the negative subgroup G1a is f1a, the focal length of the entire optical system in the wide-angle end state is fw, and the focal length of the entire optical system in the telephoto end state is ft, 1 <| f1a | / (fw · The compact variable power optical system according to claim 5, wherein a condition of ft) ^1/2 <4 (7) is satisfied. 8. The positive lens group G1 includes at least one plastic lens PL1, the negative lens group G2 includes at least one plastic lens PL2, and the refractive power of the plastic lens PL1 and the plastic lens. The compact variable power optical system according to any one of claims 1 to 7, wherein a sign of the refractive power of the PL2 is different from that of the PL2.