JP2003043348A - Optical system with anti-vibration function - Google Patents

Abstract

(57) [Problem] To provide a medium telephoto lens that is compact and has good performance. SOLUTION: In order from an object side, there are a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, and the third lens group is a 3a lens. A third lens group having a positive refractive power and a third lens group. The third lens group includes one positive lens or one positive lens and one negative lens. The group includes one or two positive lenses and one negative lens, and performs focusing by moving the second lens group on the optical axis.
When the 3b lens group is displaced in a direction substantially perpendicular to the optical axis to correct the image blur of the captured image, and when the focal length of the i-th lens group is fi and the focal length of the entire system is f, each conditional expression To be satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system (photographing lens) having an image stabilizing function, and an optical system having a so-called image stabilizing function for correcting image blur of a photographed image due to vibration of the optical system. In particular, the present invention relates to a compact and high-performance inner focus type middle telephoto lens suitable for still cameras such as single-lens reflex cameras and electronic still cameras.

[0002]

2. Description of the Related Art When photographing from a moving object such as a car or a ship in progress, vibration is transmitted to a photographing system and a photographed image is blurred.
Further, in hand-held photography with a lens having a long focal length or a lens having a large FNo, camera shake may cause blur in a captured image. In recent years, silver salt cameras and video cameras that optically or electrically correct these blurs have been put on the market.

As an optical system having a vibration isolation function,
JP-A-50-80417 and JP-B-56-2113
3, JP-A-61-223819, JP-A-8-304698 (Canon / Hayakawa), JP-A-8-201691 (Nikon / Suzuki), and the like.

Japanese Unexamined Patent Publication No. 50-80147 discloses a zoom lens having two afocal variable magnification systems.
When the angular magnification of the first variable power system is M1 and the angular magnification of the second variable power system is M2, the variable power is performed in each variable power system so as to have a relationship of M1 = 1−1 / M2. , The second variable power system is spatially fixed to correct the blurring of the image to stabilize the image.

In Japanese Patent Publication No. 56-21133, some optical members are moved in a direction that cancels the vibrational displacement of an image due to vibration in accordance with an output signal from a detecting means for detecting the vibrational state of an optical device. To stabilize the image.

In Japanese Patent Laid-Open No. 61-223819, in a photographing system in which a refracting variable apex angle prism is arranged closest to the subject, the apex angle of the refracting variable apex prism is changed in response to the vibration of the photographing system. The image is deflected to stabilize the image.

According to Jikaihei 81304698,
Disclosed is a telephoto lens including three lens units having negative and positive refracting powers, in which the third lens unit is divided into negative and positive lens units, and image stabilization is performed by the negative lens unit.

In Japanese Unexamined Patent Publication No. 8-201691, positive,
Disclosed is a telephoto lens which is composed of three lens units having negative and positive refracting powers and whose image stabilization is performed by the negative lens in the third lens unit.

In addition to this, Japanese Patent Publication No. 56-34847,
In Japanese Patent Publication No. 57-7414, an optical member that is spatially fixed against vibration is arranged in a part of the photographing system, and a photographed image is deflected by utilizing the prism action generated by the vibration of the optical member. A still image is obtained on the image plane.

Further, the acceleration sensor is used to detect the vibration of the photographing system, and a part of the lens group of the photographing system is vibrated in the direction orthogonal to the optical axis in accordance with the signal obtained at this time to obtain a still image. There are also ways to get it.

[0011]

Generally, when a part of the lens group of the photographing system is moved for image stabilization, the moving lens group has a small lens weight, a small outer diameter, and a still image is obtained. Therefore, that is, it is required that the moving amount of the moving lens group for image stabilization is small. Further, aberrations, eccentric coma, eccentric astigmatism, eccentric chromatic aberration, eccentric field curvature, eccentric distortion, etc., which occur due to moving the movable lens group substantially perpendicular to the optical axis for image stabilization. Is required to be satisfactorily corrected.

In an optical system having an optical member having a vibration-proof function, in which an optical member that is spatially fixed against vibration is arranged, it is difficult to support the optical member, and a small optical system is realized. Therefore, it was not suitable for the construction of a small and lightweight device. Further, the optical system in which the variable apex angle prism is arranged on the most object side of the photographing system has an advantage that aberrations other than eccentric chromatic aberration hardly occur at the time of displacement correction, but it has a drawback that the driving member becomes large and the prism There is a drawback that it is difficult to simply correct the eccentric chromatic aberration that occurs.

In an optical system in which a part of the lens groups of the photographing system is decentered, the device can be downsized by appropriately selecting and arranging the lens groups to be decentered, but various aberrations caused by decentering, that is, However, there is a problem in that it is difficult to realize a sufficiently large displacement correction with a sufficiently small driving amount while satisfactorily correcting the eccentric coma aberration, the eccentric astigmatism aberration, the eccentric field curvature, and the like.

According to the present invention, when a part of the lens group of the photographing system is moved in a direction substantially perpendicular to the optical axis to perform image stabilization, the focal length of each lens group and the lens configuration are appropriately set to prevent image stabilization. The aberration at the time is corrected well, and the inner focus system is adopted to enable quick focusing, especially in an autofocus camera.
We covered the mid-telephoto castle from about mm to 150 mm,
It is daily to provide a compact telephoto lens with good performance.

[0015]

The present invention has, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, The third lens group includes a 3a lens group and a 3b lens group having a positive refractive power, and the 3a lens group includes one positive lens or one positive lens and one negative lens. The third b lens group is composed of one or two positive lenses and one negative lens, and the second lens group is moved on the optical axis for focusing to perform the third b lens. The image blur of the photographed image is corrected by displacing the group in a direction substantially perpendicular to the optical axis, and the focal length of the i-th lens group is fi and the focal length of the entire system is f.
Then, 0.5 <f1 / f <1.1 (1) 0.5 <f2 / f <0.8 (2) 0.6 <f3 / f <1.5. .. (3) The conditional expression is satisfied.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on Examples.

1 to 4 are lens cross-sectional views of Numerical Embodiments 1 to 4 of the present invention, in which I to III are positive, negative, and
The first to third groups of positive refracting power are IIIa and IIIb, 3a group and 3b group, and S is an aperture stop. When focusing from infinity to a close range, the second lens group is indicated by an arrow. The third lens group b is moved in the direction perpendicular to the optical axis for vibration isolation.

5 to 8 are longitudinal aberration diagrams of Numerical Examples 1 to 4 of the present invention. In spherical aberration, the solid line is the d line, the two-dot silver line is the g line, and the dotted line is the sine condition. In the astigmatism, the solid line is sagittal and the dotted line is meridional.

9 to 12 are numerical examples 1 to 4 of the present invention.
6A and 6B are lateral aberration diagrams at image heights of 0 mm and ± 15 mm, in which (a) is an aberration diagram of an object at infinity, and (a ′) is an object image relationship when the imaging system is tilted by 0.3 °. FIG. 9 is a lateral aberration diagram when the 3b-th group is moved in the direction perpendicular to the optical axis so as to be in the same state as when the imaging system is not tilted, the solid line represents a sagittal ray, and the dotted line represents a meridional ray.

In this embodiment, by satisfying the conditional expressions (1) to (3) based on such a constitution, the inner focus is compact and has good optical performance, and in particular, the aberration-corrected inner focus is excellent. Achieved the anti-vibration optical system.

Next, the meaning of the conditional expression will be described.

Conditional expression (1) defines the range of the focal length of the first lens group with respect to the focal length of the entire system. When the lower limit is exceeded and the positive refractive power of the first lens group becomes strong, the lens system becomes Although the overall telephoto tendency becomes stronger and the total lens length becomes shorter, various aberrations generated in the lens group increase and the optical performance deteriorates. When the upper limit is exceeded and the positive refractive power of the first lens unit becomes weak, it is preferable for aberration correction, but the total lens length becomes long, which is not preferable.

Conditional expression (2) defines the range of the focal length of the second lens group with respect to the focal length of the entire system, and when the negative refracting power of the second lens group becomes strong beyond the lower limit, focusing of the second lens group becomes strong. However, if the negative refracting power of the second lens group becomes weaker than the upper limit value, the movement of the lens group for focusing becomes difficult. This is not preferable because the amount increases and the total lens length increases.

Conditional expression (3) defines the range of the focal length of the third lens group with respect to the focal length of the entire system. When the lower limit is exceeded and the positive refractive power of the third lens group becomes strong, the total lens length is increased. When the positive refractive power of the third lens group becomes weaker than the upper limit value, the total lens length tends to be shortened, but the asymmetry of the refractive power arrangement of the entire lens system is remarkably destroyed, and various aberrations worsen. come.

Next, the image stabilization will be described. In the present invention, so-called shift image stabilization is used to correct image blur by moving a part of lens groups of the photographing system in a direction perpendicular to the optical axis.

More specifically, when vibration due to camera shake occurs during photographing, vibration of the photographing system is detected by vibration detecting means such as a vibration gyro / acceleration sensor.
By driving the anti-vibration lens group in the direction perpendicular to the optical axis by the anti-vibration lens group driving means, the position of the image on the film surface is displaced in the vertical direction to cancel the image blur caused by the vibration. Since the vibration detecting means and the anti-vibration lens group driving means consume electric power, in order to reduce battery consumption,
An anti-vibration optical system that consumes as little power as possible is required, and it is also necessary to reduce the weight and size of the anti-vibration lens group in order to improve the followability of the anti-vibration lens group to the vibration of the photographing system.

Further, as the decentering sensitivity of the image stabilizing lens group, that is, the amount of displacement of the image plane relative to the driving amount of the image stabilizing lens group, the smaller the driving amount of the image stabilizing lens group, the smaller the amount of drive of the image stabilizing lens group. There is a demand for an optical system with a high degree of heart sensitivity.
In this embodiment, the third group having a relatively small lens outer diameter is divided into a plurality of lens groups, a 3a group and a 3b group, and the 3b group is moved in the direction perpendicular to the optical axis to perform image stabilization. . In the present embodiment, the third group b has a simple structure with only one negative lens and one positive lens, and achieves both optical performance during vibration reduction and weight reduction.

In Examples 1 and 2, when the third lens group is divided into a negative refractive power group 3a and a positive refractive power group 3b, and the focal lengths are f3a and f3b, respectively: The conditional expression 3 <| 3a | / f3b <1.5 (4) is satisfied. By setting the ratio of the focal lengths of the 3a-th group and the 3b-th group so as to satisfy the conditional expression (4), excellent aberration correction can be performed while ensuring the vibration-proof sensitivity.

In Embodiments 3 and 4, when the third lens group is divided into a positive refractive power group 3a and a positive refractive power group 3b, and the focal lengths are f3a and f3b, respectively: The conditional expression 3 <f3a / f3b <2.1 (5) is satisfied. By making the third lens group have a positive refractive power, the third lens group has a positive refractive power, which is shared by the third lens group and the third lens group.
Compared with the case where the lens unit has a negative refractive power, the vibration reduction sensitivity of the 3b-th lens unit is small, but the lens system can have a simple structure. By setting the ratio of the focal lengths of the 3a-th group and the 3b-th group so as to satisfy the conditional expression (5), good aberration correction is possible while ensuring the vibration-proof sensitivity.

In the present embodiment, the first lens group is composed of three positive lenses and one negative lens from the object side, and the second lens group which moves during focusing is composed of a positive lens and a negative lens. By making up the cemented lens of
It realizes a medium telephoto lens with good performance.

Further, the magnification of the 3b-th lens group is β3b.
Then, the conditional expression 0.004 <(1-β3b) / f <0.009 (6) is satisfied. This is an expression expressing the image stabilization sensitivity, and if the lower limit value is exceeded, the image stabilization sensitivity will decrease, and the amount of movement of the 3b group in order to obtain the desired image stabilization angle will increase. If it exceeds, it becomes difficult to correct aberration.

When the length from the most object side surface to the most image side surface of the 3b-th lens group is D3b, then 0.04 <D3b / f <0.15 (7) The conditional expression is satisfied. Beyond the lower limit, 3b
The reduction of the lens thickness of the group means that the weight of the lens of the 3b group becomes lighter, and the load of the image stabilizing drive system tends to decrease, but there is a problem such as securing the edge thickness in lens processing.
An increase in the lens thickness of the 3b-th group beyond the upper limit means that the lens weight of the 3b-th group becomes heavy, which is not preferable because the load of the image stabilization drive system increases.

When the distance at the object infinity from the lens surface of the second lens group closest to the image side to the lens surface of the third lens group closest to the object is L2, 0.09 <L2 / The conditional expression f <2 (8) is satisfied. This is to secure a moving space of the second lens group for performing focusing in the second lens group, and when the lower limit value is exceeded, the moving space of the second lens group becomes small, and the shortest distance. Becomes longer, and if the upper limit is exceeded, the total lens length becomes longer, which is not preferable.

In the numerical example, ri is i-th from the object side.
The radius of curvature of the th lens surface, di is the i-th lens thickness or air gap from the object side, and ni and νi are the refractive index and Abbe number of the i-th lens.

[0035]

[Outer 1]

[0036]

[Outside 2]

[0037]

[Outside 3]

[0038]

[Outside 4]

[0039]

As described above, according to the present invention,
It is composed of a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power from the object side,
By providing an appropriate refracting power arrangement and lens configuration, dividing the third group into a plurality of lens groups, and moving the third group b substantially perpendicularly to the optical axis direction for vibration isolation, it is compact and particularly vibration-proof. At times, we were able to achieve a medium telephoto lens with good optical performance.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 5 is a longitudinal aberration diagram of Numerical Example 1 of the present invention.

FIG. 6 is a longitudinal aberration diagram of Numerical Example 2 of the present invention.

FIG. 7 is a longitudinal aberration diagram of Numerical Example 3 of the present invention.

FIG. 8 is a longitudinal aberration diagram of Numerical Example 4 of the present invention.

FIG. 9 is an image height of 0 mm and ± 1 according to Numerical Example 1 of the present invention.
Transverse aberration diagram at 5mm

FIG. 10 is an image height 0 mm and ± of Numerical Example 2 of the present invention.
Transverse aberration diagram at 15mm

FIG. 11 is an image height 0 mm and ± of Numerical Example 3 of the present invention.
Transverse aberration diagram at 15mm

FIG. 12 is an image height 0 mm and ± of Numerical Example 4 of the present invention.
Transverse aberration diagram at 15mm

[Explanation of symbols]

Group I II Second group III Group 3 IIIa Group 3a IIIb Group 3b S aperture

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA02 KA03 LA01 LA02 MA07                       NA07 PA06 PA07 PA08 PA16                       PA19 PB09 PB10 QA02 QA06                       QA07 QA12 QA14 QA21 QA25                       QA32 QA34 QA37 QA41 QA42                       QA45 QA46 RA32

Claims (8)

[Claims] 1. A first lens unit having a positive refracting power, a second lens unit having a negative refracting power, and a third lens unit having a positive refracting power are arranged in this order from the object side, and the third lens unit is a third lens unit. And a third lens group 3b having a positive refractive power, wherein the third lens group 3a comprises one positive lens or one positive lens and one negative lens. The lens group is composed of one or two positive lenses and one negative lens, and the second lens group is moved on the optical axis for focusing.
When the image blur of the captured image is corrected by displacing the 3b-th lens group in a direction substantially perpendicular to the optical axis, and the focal length of the i-th lens group is fi and the focal length of the entire system is f, the following conditions are satisfied. An optical system having an anti-vibration function, which satisfies the formula. 0.5 <f1 / f <1.1 0.5 <f2 / f <0.8 0.6 <f3 / f <1.5 2. A first lens group having a positive refracting power, a second lens group having a negative refracting power, and a third lens group having a positive refracting power are arranged in this order from the object side, and the third lens group is a negative lens group. It has a 3a lens group having a refractive power and a 3b lens group having a positive refractive power, and the 3a lens group is composed of one positive lens and one negative lens. The group is composed of one positive lens and one negative lens. The second lens group is moved on the optical axis for focusing, and the third lens group is displaced in a direction substantially perpendicular to the optical axis. An optical system having a vibration-proof function characterized by satisfying the following conditional expression when the image blur of a photographed image is corrected and the focal length of the i-th lens group is fi and the focal length of the entire system is f. system. 0.5 <f1 / f <1.1 0.5 <f2 / f <0.8 0.6 <f3 / f <1.5 1.3 <| f3a | / f3b <1.5 3. A first lens group having a positive refracting power, a second lens group having a negative refracting power, and a third lens group having a positive refracting power are arranged in this order from the object side, and the third lens group is a positive lens group. It has a 3a lens group having a refractive power and a 3b lens group having a positive refractive power, the 3a lens group is composed of one positive lens, and the 3b lens group is one, or It is composed of two positive lenses and one negative lens. The second lens group is moved on the optical axis for focusing, and the 3b lens group is displaced in a direction substantially perpendicular to the optical axis. The optical system having a vibration-proof function, wherein the following conditional expression is satisfied, where f is the focal length of the i-th lens group and f is the focal length of the entire system. 0.5 <f1 / f <1.1 0.5 <f2 / f <0.8 0.6 <f3 / f <1.5 1.3 <f3a / f3b <2.1 4. The image stabilizing function according to claim 1, 2 or 3, wherein the first lens group is composed of three positive lenses and one negative lens from the object side. Optical system. 5. The optical system having a vibration-proof function according to claim 1, 2 or 3, wherein the second lens group is composed of a cemented lens composed of a positive lens and a negative lens. 6. An optical system having an image stabilizing function according to claim 1, 2 or 3, wherein the following conditional expression is satisfied, where β3b is the magnification of the 3b-th lens group. 0.004 <(1-β3b) / f <0.009 7. The following conditional expression is satisfied, where D3b is the length from the most object-side surface to the most image-side surface of the 3b-th lens group. Or 3
An optical system having the described anti-vibration function. 0.04 <D3b / f <0.15 8. The following conditional expression is satisfied, where L2 is the distance from the most image-side lens surface of the second lens group to the most object-side lens surface of the third lens group at object infinity. The optical system having a vibration isolation function according to claim 1, 2, or 3. 0.09 <L2 / f <2