JP3927730B2 - Variable magnification optical system with anti-vibration function - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable magnification optical system having an anti-vibration function, and in particular, when the variable magnification optical system vibrates (tilts) by moving a part of the lens group of the variable magnification optical system in a direction perpendicular to the optical axis. Is suitable for video cameras, silver salt photography cameras, electronic still cameras, digital cameras, etc. The present invention relates to a variable magnification optical system having
[0002]
[Prior art]
If an attempt is made to shoot from a moving object such as an ongoing car or aircraft, vibrations are transmitted to the photographic system, causing camera shake and blurring of the captured image.
[0003]
Conventionally, various anti-vibration optical systems have been proposed that have a function of preventing blurring of captured images.
[0004]
For example, in Japanese Patent Application Laid-Open No. 56-21133, a part of 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 a vibration state in the optical device. Stabilize the image. In JP-A-61-223819, in an imaging system in which a variable apex angle prism is arranged closest to the object side, the apex angle of the variable apex angle prism is changed in accordance with the vibration of the imaging system to stabilize the image. ing.
[0005]
In Japanese Patent Application Laid-Open Nos. 1-116619 and 2-124521, vibration of the photographing system is detected using an acceleration sensor or the like, and a part of the lens group of the photographing system is placed on the optical axis according to a signal obtained at this time. A still image is obtained by vibrating in the vertical direction.
[0006]
In Japanese Patent Laid-Open No. 7-128619, the third lens group of the variable power optical system having a four-group structure composed of lens groups having positive, negative, positive and positive refractive powers is composed of two lens groups having positive and negative refractive powers. A positive lens group is vibrated to prevent vibration and obtain a still image.
[0007]
In Japanese Patent Laid-Open No. 7-199124, in the variable magnification optical system having a four-group configuration including positive, negative, positive, and positive refractive power lens groups, the entire third lens group is vibrated to prevent vibration. .
[0008]
On the other hand, in Japanese Patent Application Laid-Open No. 5-60974, in a variable power optical system having a four-group structure composed of positive, negative, positive, and positive refractive power lens groups, the third lens group is a telephoto lens having a positive lens and a meniscus negative lens. It consists of a photo type to shorten the overall lens length.
[0009]
[Problems to be solved by the invention]
In general, a method for obtaining a still image by arranging a vibration-proof optical system in front of a photographing system, vibrating a part of the movable lens group of the vibration-proof optical system to eliminate a blur of a photographed image, There has been a problem that a moving mechanism for moving the movable lens group becomes complicated.
[0010]
In addition, in an optical system that performs vibration isolation using a variable apex angle prism, the amount of decentered chromatic aberration that occurs during image stabilization, particularly on the long focal length side, may increase.
[0011]
On the other hand, in an optical system that performs vibration isolation by decentering some lenses of the photographing system in a direction perpendicular to the optical axis, there is an advantage that no extra optical system is required for image stabilization. However, there is a problem that a space for the lens to be moved is required, and that the amount of decentering aberration generated during vibration isolation increases.
[0012]
In addition, when the entire third lens unit of the variable power optical system having a four-group configuration including four lens units having positive, negative, positive, and positive refractive power is moved in the direction perpendicular to the optical axis, When the three lens units are configured with a telephoto type of a positive lens and a meniscus negative lens in order to shorten the overall length, there has been a problem that image quality deteriorates due to decentration aberrations such as decentration coma and decentered field curvature.
[0013]
Further, in the above conventional example, a zoom ratio of 8 times or more can be applied to a video camera or the like, but it is insufficient in terms of aberration correction for use in an electronic still camera equivalent to 1 million pixels.
[0014]
The present invention corrects image blurring when the zoom optical system vibrates (tilts) by moving a relatively small and lightweight lens group constituting a part of the zoom optical system in a direction perpendicular to the optical axis. In addition, the lens group for correcting the shake is made appropriate, thereby reducing the size of the entire apparatus, simplifying the mechanism, and reducing the load on the driving unit. An object of the present invention is to provide a variable magnification optical system having an image stabilization function that corrects decentration aberrations when the lens is decentered, and in particular, an image stabilization function that can be applied to an electronic still camera having 1 million pixels or more.
[0015]
[Means for Solving the Problems]
The zoom optical system having the image stabilization function according to the first aspect of the present invention includes a first lens unit having a fixed positive refractive power and a negative refraction having a zoom function in the order of zooming and focusing in order from the object side. A variable power optical system including a second lens group having a positive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power that corrects an image plane fluctuating due to zooming and has a focusing function. The third lens group is moved in the direction perpendicular to the optical axis to correct image blurring when the variable magnification optical system vibrates, and the second lens group is arranged in order from the object side to the image plane side. A negative meniscus lens having a concave surface, a negative lens, a positive lens having a convex surface facing the object side, and a negative lens. The third lens group is a positive lens having a convex surface on the object side, Consists of a meniscus negative lens having a concave surface, and a positive lens, and the fourth lens group includes two positive lenses. When the focal length of the second lens group is f2 and the focal length of the negative lens closest to the image plane in the second lens group is f24, 1.4 <| f24 / f2 | < 4.6
It satisfies the following conditional expression.
[0016]
The invention of claim 2 is the invention of claim 1, wherein the focal length of the second lens group is f2, and the focal lengths of the entire system at the wide-angle end and the telephoto end are fw and ft, respectively.
It is characterized by satisfying the following conditions.
[0017]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the focal lengths of the meniscus negative 32nd lens and the entire third lens group of the third lens group are f32 and f3, respectively. 1.1 <| F32 / f3 | <3.5
It satisfies the following conditional expression.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic diagram showing a paraxial refractive power arrangement of numerical embodiments 1 to 5 described later of the present invention, and FIGS. 2, 3, 4, and 5 are sectional views of lenses of the numerical embodiment 1 of the present invention, wide angle It is an aberration diagram at the end, middle, and telephoto end. 6, FIG. 7, FIG. 8, and FIG. 9 are lens cross-sectional views of the second numerical embodiment of the present invention, and aberration diagrams at the wide-angle end, the middle, and the telephoto end. 10, FIG. 11, FIG. 12, and FIG. 13 are lens cross-sectional views of the third numerical embodiment of the present invention, and aberration diagrams at the wide-angle end, the middle, and the telephoto end. 14, FIG. 15, FIG. 16, and FIG. 17 are lens cross-sectional views of the numerical example 4 of the present invention, and aberration diagrams at the wide-angle end, the middle, and the telephoto end. 18, 19, 20, and 21 are lens cross-sectional views of the numerical value example 5 of the present invention, and aberration diagrams at the wide-angle end, in the middle, and at the telephoto end. FIG. 22 is an explanatory diagram of the optical principle of the vibration isolation system according to the present invention.
[0025]
In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, and L3 is a third group having a positive refractive power.
[0026]
In this embodiment, the third group L3 is moved in the direction perpendicular to the optical axis to correct blurring of the captured image when the variable magnification optical system vibrates (tilts).
[0027]
L4 is a fourth group having a positive refractive power. SP is an aperture stop, which is disposed in front of the third lens unit L3. G is a glass block such as a face plate. IP is the image plane. FP is a flare-cut stop, which is disposed on the image plane side of the third group, and cuts off the flare component when the third group performs image stabilization.
[0028]
In this embodiment, when zooming from the wide-angle end to the telephoto end, the second group is moved to the image plane side as indicated by an arrow, and the image plane variation accompanying zooming is corrected by moving the fourth group.
[0029]
In addition, a rear focus type is employed in which focusing is performed by moving the fourth group on the optical axis. The solid curve 4a and the dotted curve 4b of the fourth group shown in the figure show the image plane fluctuations accompanying the zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at close distance, respectively. The movement trajectory for correction is shown. The first group and the third group are fixed during zooming and focusing, but may be moved as necessary.
[0030]
In the present embodiment, the fourth group is moved to correct the image plane variation accompanying zooming, and the fourth group is moved to perform focusing. In particular, as shown by the curves 4a and 4b in the figure, the zoom lens is moved so as to have a convex locus toward the object side upon zooming from the wide-angle end to the telephoto end. As a result, the space between the third group and the fourth group is effectively used, and the overall length of the lens is effectively shortened.
[0031]
In the present embodiment, for example, when focusing from an infinitely distant object to a close object at the telephoto end, the fourth group is moved forward as indicated by a straight line 4c in FIG.
[0032]
In the present embodiment, the rear focus method as described above is used in the so-called four-group zoom lens in the conventional so-called four-group zoom lens, and the first group is used for focusing. This effectively prevents an increase in effective lens diameter of one group.
[0033]
By arranging the aperture stop in front of the third lens group, aberration fluctuation due to the movable lens group is reduced, and by shortening the distance between the lens groups in front of the aperture stop, the front lens diameter can be easily reduced. is doing.
[0034]
In Numerical Examples 1 to 5 of the present invention, the third lens unit L3 is moved in the direction perpendicular to the optical axis to correct image blur when the variable magnification optical system vibrates. As a result, as compared with the conventional image stabilization optical system, image stabilization is performed without newly adding an optical member such as a lens group or a variable apex angle prism for image stabilization.
[0035]
Next, the optical principle of the image stabilization system for correcting the blur of the photographed image by moving the lens group in the direction perpendicular to the optical axis in the variable magnification optical system according to the present invention will be described with reference to FIG.
[0036]
As shown in FIG. 22A, the optical system is composed of three parts, that is, a fixed group Y1, an eccentric group Y2, and a fixed group Y3. An object point P on the optical axis that is sufficiently away from the lens is on the imaging surface IP. Assume that an image is formed at the center as an image point p.
[0037]
If the entire optical system including the imaging surface IP is instantaneously tilted due to camera shake as shown in FIG. 22B, the object point P is also instantaneously moved to the image point p ′, resulting in a blurred image. .
[0038]
On the other hand, when the eccentric group Y2 is moved in the direction perpendicular to the optical axis, the image point p moves to p ″ as shown in FIG. 22C, and the amount and direction of movement depend on the power arrangement, and the lens group Expressed as eccentric sensitivity.
[0039]
Therefore, the image point p ′ shifted due to the camera shake in FIG. 22B is returned to the original imaging position p by moving the eccentric group Y2 by an appropriate amount in the direction perpendicular to the optical axis. As shown in FIG. 4, camera shake correction, that is, image stabilization is performed.
[0040]
Now, the movement amount (shift amount) of the shift lens group (eccentric group) necessary for correcting the optical axis by θ ° is Δ, the focal length of the entire optical system is f, and the eccentric sensitivity of the shift lens group Y2 is TS. Then, the movement amount Δ is
Δ = f · tan (θ) / TS
Is given by
[0041]
Now, if the decentering sensitivity TS of the shift lens group is too large, the movement amount Δ becomes a small value, and the shift lens group movement amount necessary for image stabilization can be reduced, but it is difficult to control for proper image stabilization. As a result, the correction remains.
[0042]
Particularly in video cameras and digital still cameras, the image size of an image sensor such as a CCD is smaller than that of a silver halide film, and the focal length for the same angle of view is short, so the shift amount Δ of the shift lens group for correcting the same angle is Get smaller.
[0043]
Therefore, if the accuracy of the mechanism (mechanism) is approximately the same, the remaining correction on the screen becomes relatively large.
[0044]
On the other hand, if the eccentricity sensitivity TS is too small, the amount of movement of the shift lens group necessary for control increases, and the driving means such as an actuator for driving the shift lens group also increases.
[0045]
In the present invention, the decentration sensitivity TS of the third group is set to an appropriate value by setting the refractive power arrangement of each lens group to an appropriate value, and there is little residual vibration correction due to a mechanical control error. An optical system with a small load on the driving means is achieved.
[0046]
In the present embodiment, the third lens unit in the order from the object side is a positive 31st lens L31 having a convex lens surface on the object side, a meniscus negative 32nd lens L32 having a strong concave surface on the image surface side compared to the object side, It is composed of a positive thirty-third lens L33 with the convex surface facing the image side surface. The image surface side lens surface of the positive thirty-first lens L31 has an aspherical shape.
[0047]
By providing a meniscus negative 32nd lens having a concave surface facing the image surface side in the third group, the entire third group is made into a telephoto configuration, and the principal point interval between the second group and the third group is shortened. The overall length has been shortened.
[0048]
When such a meniscus negative lens is provided, positive distortion occurs on the lens surface. This positive distortion causes a large eccentric distortion during vibration isolation.
[0049]
In order to reduce this distortion, the distortion generated in the entire third lens group may be reduced.
[0050]
In this embodiment, the positive 33rd lens 33 is arranged on the image plane side of the meniscus negative 32nd lens 32 to correct a distortion occurring in the third lens group while maintaining a certain telephoto configuration. In addition, the occurrence of decentration distortion that occurs when the third lens unit is shifted to perform image stabilization is reduced.
[0051]
In this embodiment, by providing an aspherical surface on the 31st lens, spherical aberration generated in the third lens group is suppressed, and decentration coma aberration generated at the time of image stabilization is reduced.
[0052]
Further, in the present invention, the fourth lens group is composed of two positive lenses and one negative lens, so that the spherical aberration and the curvature of field caused by the movement of the fourth lens group during zooming or focusing are reduced. Reduced.
[0053]
The variable magnification optical system having the image stabilization function of the present invention is realized by satisfying the above-mentioned conditions, but in order to achieve good optical performance while further shortening the total lens length, It is desirable to satisfy at least one of the following conditions.
[0054]
(A-1) The second lens group has at least three negative lenses and one positive lens.
[0055]
In an optical system that requires high resolving power, such as a photographic lens for a digital still camera, it is necessary to correct lateral chromatic aberration associated with zooming compared to a photographic lens for a normal video camera.
[0056]
For this purpose, it is desirable that the second lens group has at least three negative lenses and one positive lens. If only two negative lenses are used, if the refractive power of the second lens unit is increased to reduce the movement amount in order to shorten the overall length, it becomes difficult to correct lateral chromatic aberration.
[0057]
(A-2) The second lens group includes a meniscus negative lens having a concave surface facing the image surface side in order from the object side, a negative lens, a positive lens having a convex surface facing the object side, and a negative lens. .
[0058]
Accordingly, the present invention improves the achromatic effect of the principal point by reducing the front-rear symmetry of the second lens group, and effectively corrects the lateral chromatic aberration.
[0059]
(A-3) When the focal length of the second lens group is f2, and the focal length of the negative 24th lens closest to the image plane in the second lens group is f24, 1.4 <| f24 / f2 | < 4.6 (1)
The following conditional expression is satisfied.
[0060]
Conditional expression (1) is mainly for effectively correcting the lateral chromatic aberration. When the upper limit of conditional expression (1) is exceeded and the focal length of the negative 24th lens 24 becomes too small, the effect of correcting chromatic aberration becomes insufficient. Conversely, when the lower limit is exceeded, it becomes difficult to correct distortion at the wide-angle end.
[0061]
(A-4) When the focal lengths of the entire system at the wide-angle end and the telephoto end are fw and ft, respectively.
[Equation 3]
[0063]
To satisfy the following conditions.
[0064]
Conditional expression (2) is for shortening the total lens length while maintaining high optical performance. When the refractive power of the second lens unit is increased beyond the lower limit of conditional expression (2), the amount of movement of the second lens unit during zooming decreases, but the Petzval sum increases in the negative direction as a whole, and the image It is not good because it is difficult to correct the surface curvature. Conversely, if the upper limit of conditional expression (2) is exceeded, the amount of movement of the second lens unit during zooming will increase, and the entire lens system will not be miniaturized, and it will be disadvantageous in terms of changes in the amount of peripheral light during image stabilization. Absent.
[0065]
(A-5) The maximum aperture diameter of the aperture stop is variable according to the focal length at the time of zooming.
[0066]
In order to achieve a reduction in the change in the amount of light during image stabilization, it is preferable to relatively increase the amount of peripheral light by reducing the aperture diameter on the telephoto side during zooming to limit the central beam.
[0067]
(A-6) When the focal lengths of the meniscus negative 32nd lens and the entire third lens group of the third lens group are f32 and f3, respectively, 1.1 <| f32 / f3 | <3.5. (3)
The following conditional expression is satisfied.
[0068]
Conditional expression (3) is for achieving downsizing of the entire optical system by using the third lens group as a telephoto type. Exceeding the lower limit of conditional expression (3) and increasing the refractive power of the negative lens in the third lens group is advantageous for shortening the overall length of the lens, but the Petzval sum increases in the negative direction, causing curvature of field. It is not good because it becomes difficult to correct. On the contrary, if the lower limit is exceeded, the total length is not shortened sufficiently, and the chromatic aberration in the third lens group is not sufficiently corrected, and the eccentric chromatic aberration becomes large.
[0069]
(A-7) Properly setting the sensitivity of the shift group for anti-vibration greatly affects the anti-vibration performance.
[0070]
In the present invention, when the focal length of the third lens unit is f3 and the focal length of the entire system at the wide angle end is fw, 3.3 <f3 / fw <4.8 (4)
To satisfy the following conditions.
[0071]
Thereby, the sensitivity of the shift lens group is set to an appropriate value while shortening the total lens length. If the lower limit of conditional expression (4) is exceeded and the refractive power of the third lens unit is increased, the sensitivity of the shift lens unit will become too high, and the remaining correction will be increased when the mechanical accuracy is not tightened. So not good. On the contrary, if the refractive power of the third lens unit is weakened beyond the upper limit value, the shift amount of the third lens unit necessary for image stabilization becomes large or the total length of the lens becomes large.
[0072]
(A-8) In order to correct the distortion and astigmatism in the third lens group while maintaining the telephoto configuration of the third lens group, to maintain the optical performance at the time of image stabilization well, the 33 lens When the focal length is f33, 1.2 <f33 / f3 <2.0 (6)
To satisfy the following conditions.
[0073]
If the lower limit of conditional expression (5) is exceeded and the refracting power of the 33rd lens becomes too strong, the telephoto property of the third lens group will not be maintained and the effect of shortening the total length will be lost. On the other hand, if the upper limit is exceeded, correction of distortion and astigmatism in the third lens group will be insufficient, and optical performance during image stabilization will deteriorate.
[0074]
(A-9) An aspherical surface may be introduced into the fourth lens group in order to correct astigmatism and distortion fluctuation during zooming.
[0075]
(A-10) In the present invention, it is necessary to increase the lens diameter by an amount corresponding to the movement of the third lens group for image stabilization.
[0076]
Therefore, in order to prevent an excessive on-axis light beam from entering excessively, a fixed stop (flare stop) is disposed on the object side or the image plane side of the third lens group. In this embodiment, a fixed stop is disposed between the third lens group and the fourth lens group to effectively use the space and prevent unnecessary light flux from entering.
[0077]
(A-11) To achieve good optical performance while shortening the overall lens length, the fourth lens unit is configured with a positive lens, a negative lens, and a positive lens in order from the object side, or a positive lens, a positive lens, It is good to have a lens and negative lens configuration.
[0078]
Next, numerical examples of the present invention will be shown. In numerical examples, Ri is the radius of curvature of the i-th surface in order from the object side, Di is the thickness or air spacing of the i-th member in order from the object side, and Ni and νi are i-th in order from the object side. The refractive index and Abbe number of the member. Table 1 shows the relationship between the above-described conditional expressions and numerical examples.
[0079]
The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, and A, B, C, D, and E are the aspheric coefficients. When [0080]
[Expression 4]
[0081]
It is expressed by the following formula. f is a focal length, Fno is an F number, and ω is a half angle of view. “E-0X” means 10 ^−X .
[0082]
[Outside 1]
[0083]
[Outside 2]
[0084]
[Outside 3]
[0085]
[Outside 4]
[0086]
[Outside 5]
[0087]
[Table 1]
[0088]
【The invention's effect】
According to the present invention, as described above, when the relatively small and light lens group constituting a part of the variable magnification optical system is moved in the direction perpendicular to the optical axis, the variable magnification optical system vibrates (tilts). The amount of decentration aberration when the lens group is decentered can be reduced while reducing the overall size of the apparatus, simplifying the mechanism, and reducing the load on the driving means. Therefore, it is possible to achieve a variable magnification optical system having an image stabilization function that suppresses and corrects decentration aberrations favorably.
[0089]
In particular, in the present invention, while having a large zoom ratio of about 8 zoom ratios, it has higher optical performance than conventional video camera lenses, and can be applied to an electronic still camera having 1 million pixels or more. Anti-vibration optical system can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a paraxial refractive power arrangement of a variable magnification optical system according to the present invention. FIG. 2 is a lens cross-sectional view at the wide-angle end of Numerical Example 1 of the present invention. FIG. 4 is a diagram showing aberrations in the middle of Numerical Example 1 of the present invention. FIG. 5 is a diagram showing various aberrations at the telephoto end of Numerical Example 1 in the present invention. Cross-sectional view of the lens at the wide-angle end of Example 2 [FIG. 7] Various aberration diagrams at the wide-angle end of Numerical Example 2 of the present invention [FIG. 8] Various aberration diagrams at the middle of Numerical Example 2 of the present invention [FIG. FIG. 10 is a lens cross-sectional view at the wide-angle end of Numerical Example 3 according to the present invention. FIG. 11 is a diagram of various aberrations at the wide-angle end according to Numerical Example 3 of the present invention. 12 is a diagram showing various aberrations in the middle of Numerical Example 3 of the present invention. FIG. 13 is a diagram showing various aberrations at the telephoto end of Numerical Example 3 of the present invention. FIG. 14 is a wide angle of Numerical Example 4 of the present invention. FIG. 15 is a diagram showing various aberrations at the wide-angle end of Numerical Example 4 of the present invention. FIG. 16 is a diagram showing various aberrations in the middle of Numerical Example 4 of the present invention. FIG. 18 is a lens cross-sectional view at the wide-angle end of Numerical Example 5 of the present invention. FIG. 19 is a diagram of various aberrations at the wide-angle end of Numerical Example 5 of the present invention. FIG. 21 is a diagram showing various aberrations at the telephoto end of Numerical Example 5 according to the present invention. FIG. 22 is a diagram illustrating the optical principle of the image stabilization system according to the present invention. ]
L1 First group L2 Second group L3 Third group L4 Fourth group SP Aperture IP Image plane FP Flare aperture (fixed aperture)
d d line g g line ΔM meridional image plane ΔS sagittal image plane

Claims (3)

A first lens unit having a fixed positive refractive power, a second lens unit having a negative refractive power having a variable power function, a third lens group having a positive refractive power, A variable power optical system that is composed of a fourth lens unit having a positive refractive power that corrects an image plane fluctuating due to magnification and has a focusing function, and moves the entire third lens unit in a direction perpendicular to the optical axis. The second lens group is a meniscus negative lens having a concave surface facing the image surface in order from the object side, a negative lens, and a convex surface on the object side. The third lens group is composed of a positive lens having a convex surface on the object side, a meniscus negative lens having a concave surface on the image side, and a positive lens. fourth lens group is composed of two positive lenses and a negative lens, focus of the second lens group Distance f2, the focal length of the negative lens on the most image side of the second lens group and f24
1.4 <| f24 / f2 | <4.6
A variable magnification optical system having an anti-vibration function characterized by satisfying the following conditional expression: When the focal length of the second lens group is f2, and the focal lengths of the entire system at the wide-angle end and the telephoto end are fw and ft, respectively.
The zooming optical system having a vibration isolating function according to claim 1 , wherein the following condition is satisfied. 1.1 <| f32 / f3 | <3.5 when the focal lengths of the meniscus negative 32nd lens and the entire third lens group of the third lens group are f32 and f3, respectively.
The variable magnification optical system having a vibration isolating function according to claim 1 or 2 , wherein the following conditional expression is satisfied.