JP3927684B2 - 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. The present invention relates to a variable magnification optical system having an image stabilization function suitable for a photographic camera, a video camera, etc., in which a still image is obtained by optically correcting a blur of the captured image in order to stabilize the captured image. .
[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 having a function of preventing blurring of a photographed image at this time have been proposed.
[0004]
For example, in Japanese Examined Patent Publication No. 56-21133, an image is obtained by moving some optical members in a direction that cancels the vibrational displacement of the image due to the vibration in accordance with an output signal from a detecting means for detecting a vibration state in the optical device. We are trying to stabilize.
[0005]
In JP-A-61-223819, in an imaging system in which a refractive variable apex angle prism is arranged closest to the subject, an image is obtained by changing the apex angle of the refractive variable apex angle prism in response to vibration of the imaging system. The image is stabilized by deflecting.
[0006]
In Japanese Patent Publication No. 56-34847, Japanese Patent Publication No. 57-7414, etc., an optical member spatially fixed with respect to vibration is arranged in a part of the photographing system, and the prism action generated against the vibration of this optical member is arranged. By utilizing this, the captured image is deflected to obtain a still image on the imaging plane.
[0007]
In JP-A-1-116619 and JP-A-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 moved to the optical axis according to a signal obtained at this time. There is also a method of obtaining a still image by vibrating in a direction orthogonal to.
[0008]
Japanese Patent Laid-Open No. 7-128619 discloses a first group having a positive refractive power, a second group having a negative refractive power having a zooming function, and an aperture stop in order from the object side during zooming and focusing. A third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power fourth group having both a correction function for correcting an image plane fluctuating due to zooming and a focusing function. In the double optical system, the third group is composed of two lens groups of a negative refractive power group 31 and a positive refractive power group 32, and the group 32 is moved in a direction perpendicular to the optical axis. Thus, blurring of the photographed image when the variable magnification optical system vibrates is corrected.
[0009]
In Japanese Patent Application Laid-Open No. 7-199124, in a variable power optical system having a four-group configuration including four lens groups having positive, negative, positive and positive refractive powers, the entire third group is vibrated in a direction perpendicular to the optical axis. Anti-vibration is performed.
[0010]
On the other hand, in Japanese Patent Application Laid-Open No. 5-60974, in a variable power optical system having a four-group configuration including four lens groups having positive, negative, positive and positive refractive powers, the third group is a positive lens and a meniscus negative lens. The telephoto type is used to shorten the overall lens length.
[0011]
[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, and increasing the overall size of the apparatus. There is a problem that a moving mechanism for moving the movable lens group becomes complicated.
[0012]
Another problem is that the amount of decentration aberration generated when the movable lens group is vibrated increases and the optical performance is greatly reduced.
[0013]
In an optical system that performs vibration isolation using a variable apex angle prism, there is a problem that the amount of decentered chromatic aberration generated increases during image stabilization, particularly on the long focal length side (telephoto side).
[0014]
On the other hand, in an optical system that performs image stabilization by decentering a part of the lens of the imaging system in the direction perpendicular to the optical axis, there is an advantage that no special optical system is required for image stabilization. There is a problem that a space for the lens to be operated is required, and the amount of decentration aberrations generated during image stabilization increases.
[0015]
In the above-described four-unit variable magnification optical system including the four lens units having the positive, negative, positive, and positive refractive powers, the entire third unit is moved in the direction perpendicular to the optical axis to perform vibration isolation. When the third lens unit is configured with a telephoto type of a positive lens and a meniscus negative lens in order to shorten the total lens length, a large amount of decentration aberration, particularly decentration distortion, is generated. When this is used for moving images such as a video camera, there is a problem that the deformation of the image at the time of image stabilization is conspicuous.
[0016]
The present invention corrects blurring of an image 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. When the lens group is appropriately configured, the occurrence of decentration occurs when the lens group is decentered while reducing the size of the entire apparatus, simplifying the mechanism, and reducing the load on the driving means. An object of the present invention is to provide a variable magnification optical system having an image stabilization function in which the amount is reduced and the decentration aberration is corrected well.
[0017]
[Means for Solving the Problems]
The variable power optical system having the image stabilization function according to the present invention includes, in order from the object side, a first group of fixed positive refractive powers during zooming and focusing, and a second negative refractive power having a variable power function. group, a third lens unit of positive refractive power, and is composed of four lens groups in the fourth lens unit of positive refractive power having a function of both the compensation function and the focusing function of correcting an image plane which varies with zooming The third group includes a positive thirty-first lens having aspheric surfaces on both lens surfaces, a meniscus negative thirty-second lens having a concave surface facing the image surface side, and a positive thirty-third lens. The lens comprises a lens, and the third group is moved in a direction perpendicular to the optical axis to correct blurring of a captured image when the variable magnification optical system vibrates .
When the focal lengths of the entire system at the 32nd lens, the third group, and the wide-angle end are f32, f3, and fw in this order,
0.8 <| f32 / f3 | <1.7 (1)
3.5 <f3 / fW <5.0 (2)
It is characterized by satisfying the following conditions .
In addition, the variable power optical system having the image stabilization function according to the present invention includes, in order from the object side, a first group of fixed positive refractive powers upon zooming and focusing, and a negative refractive power having a zooming function. And a fourth group of positive refractive power and a fourth group having both a correction function for correcting an image plane fluctuating due to zooming and a focusing function. The third lens unit includes a positive 31st lens having aspheric surfaces on both lens surfaces, a meniscus negative 32nd lens with a concave surface facing the image surface, a positive lens The third lens unit is moved in a direction perpendicular to the optical axis to correct blurring of a captured image when the variable magnification optical system vibrates ,
When the focal lengths of the thirty-second lens, the thirty-third lens, and the third group are f32, f33, and f3 in this order,
0.8 <| f32 / f3 | <1.7 (1)
1.6 <f33 / f3 <2.4 (3)
It is characterized by satisfying the following conditions .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic diagram showing a paraxial refractive power arrangement of numerical embodiments 1 to 3 described later of the present invention, and FIGS. 2 to 4 are sectional views of lenses at the wide angle end of numerical embodiments 1 to 3 of the present invention. 5 to 13 are aberration diagrams of Numerical Examples 1 to 3 of the present invention.
[0019]
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. 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). 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 stop (fixed stop), which cuts off the flare component when the third group performs vibration isolation. In the aberration diagrams, d is the d-line, g is the g-line, ΔM is the meridional image plane, ΔS is the sagittal image plane, and W is the half field angle.
[0020]
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. 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.
[0021]
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.
[0022]
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.
[0023]
The zoom lens according to the present embodiment employs a zoom system in which a virtual image formed by the combined system of the first group and the second group is formed on the photosensitive surface by the third group and the fourth group.
[0024]
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. 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.
[0025]
In Numerical Examples 1 to 3 of the present invention, image blur is corrected when the third lens unit L3 is moved in the direction perpendicular to the optical axis to vibrate the variable magnification optical system. 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.
[0026]
Next, the optical principle of the image stabilization system that corrects the blur of the captured 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.
[0027]
As shown in FIG. 14A, the optical system is composed of three parts, a fixed group Y1, an eccentric group Y2, and a fixed group Y3, and an object point P on the optical axis 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. Assuming that the entire optical system including the imaging surface IP is instantaneously tilted due to camera shake as shown in FIG. 14B, the object point P is also instantaneously moved to the image point p ′, resulting in a blurred image. . 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. 14C, and the amount and direction of movement depend on the power arrangement, and the lens group Expressed as eccentric sensitivity.
[0028]
Therefore, the image point p ′ shifted due to the camera shake in FIG. 14B is returned to the original imaging position p by moving the decentration 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.
[0029]
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
[0030]
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. 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.
[0031]
Therefore, if the accuracy of the mechanism (mechanism) is approximately the same, the remaining correction on the screen becomes relatively large. 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.
[0032]
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.
[0033]
In the present embodiment, in the third lens unit, from the object side, 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 facing the image surface side, and both lens surfaces It is composed of a positive 33rd lens L33 having a convex surface. The 31st lens has both lens surfaces aspherical.
[0034]
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.
[0035]
When such a meniscus negative lens is provided, positive distortion occurs on the lens surface.
[0036]
Now, suppose that the entire third lens group has positive distortion. If it demonstrates using FIG. 3 as an example, suppose that the 3rd whole group decentered upwards, as shown to FIG. 3 (A), for vibration isolation. At this time, the height at which the off-axis ray coming to the point S1 passes through the third group is reduced, and the positive distortion is reduced. On the contrary, the positive distortion increases in the light ray coming to the point S2. Therefore, the quadrangular object is deformed on the image plane as shown by the solid line in FIG.
[0037]
On the contrary, when the third group moves downward, it deforms into the shape shown by the dotted line in FIG. 3B. Therefore, when vibration is applied, the image is deformed accordingly, especially in the case of moving images. Gives a sense of incongruity. In order to reduce this decrease, it is only necessary to reduce the distortion occurring in the entire third group.
[0038]
In this embodiment, by disposing the positive 33rd lens L33 on the image plane side of the meniscus negative 32nd lens L32, the distortion is corrected in the 3rd group while maintaining the telephoto configuration, and the 3rd group. The occurrence of eccentric distortion that occurs when the image is shifted to reduce vibration is reduced.
[0039]
In this embodiment, by providing aspherical surfaces on both lens surfaces of the 31st lens L31, spherical aberration is suppressed in the third group, and decentration coma that occurs during image stabilization is reduced.
[0040]
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.
[0041]
(A-1) When the focal lengths of the thirty-second lens and the third group are f32 and f3, respectively.
0.8 <| f32 / f3 | <1.7 (1)
To satisfy the following conditions.
[0042]
Exceeding the lower limit of conditional expression (1) and increasing the refractive power of the negative 32nd 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. It is not good because it is difficult to correct the curvature. If exceeds the upper limit value length reductions becomes insufficient reversed.
[0043]
(A-2) When the focal length of the third lens unit is f3 and the focal length of the wide-angle end of the entire system is fW,
3.5 <f3 / fW <5.0 (2)
To satisfy the following conditions.
[0044]
Conditional expression (2) is for appropriately setting the sensitivity of the shift lens group for anti-vibration and maintaining good anti-vibration performance while shortening the total lens length. If the refractive power of the third lens unit is increased beyond the lower limit of conditional expression (2), the sensitivity of the shift lens unit will become too high, and if the mechanical accuracy is not tightened, the remaining correction during vibration isolation will increase. Not good. Conversely, if the upper limit is exceeded and the refractive power of the third group is weakened, the shift amount of the third group necessary for image stabilization becomes large and the total lens length becomes large, which is not good.
[0045]
(A-3) When the focal lengths of the 33rd lens and the third group are f33 and f3, respectively.
1.6 <f33 / f3 <2.4 (3)
To satisfy the following conditions.
[0046]
Conditional expression (3) is for maintaining the optical performance at the time of image stabilization by correcting the distortion and astigmatism in the third group while maintaining the telephoto type of the third group. If the lower limit of conditional expression (3) is exceeded and the refracting power of the 33rd lens becomes too strong, the telephoto type of the third lens group will not be maintained, and the effect of shortening the overall lens 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 at the time of image stabilization will deteriorate.
[0047]
(B-4) When the focal length of the second group is f2, and the focal lengths of the wide-angle end and the telephoto end of the entire system are fW and fT, respectively.
[0048]
[Expression 2]
To satisfy the following conditions.
[0049]
If the refractive power of the second lens unit becomes too strong beyond the lower limit of conditional expression (4), it is advantageous for shortening the total lens length, but it is difficult to correct variations over the entire range of field curvature and distortion. It ’s not good. If the refractive power of the second group becomes too weak beyond the upper limit of conditional expression (4), the amount of movement of the second group necessary for zooming becomes too large, which is not good.
[0050]
(B-5) The second group is a meniscus negative 21st lens with a strong concave surface facing the image side in order from the object side, a negative 22nd lens with both lens surfaces concave, and a positive 23rd lens. Although it is preferable to configure the zoom lens, a four-lens configuration in which a negative lens is further added on the image plane side may be used to further increase the zoom ratio.
[0051]
(A-6) In order to correct astigmatism and distortion fluctuation at the time of zooming, it is preferable to introduce an aspherical surface to the second group.
[0052]
(B-7) The third lens unit has a larger lens diameter as it moves to prevent vibration. Therefore, in order to prevent an excessive on-axis light beam from entering excessively, it is preferable to dispose a fixed stop (flare stop) FP on the object side or the image plane side of the third group. In the present embodiment, the fixed stop FP is disposed between the third group and the fourth group to effectively use the space and prevent unnecessary light flux from entering the photosensitive surface.
[0053]
Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are respectively the i-th lens in order from the object side. Refractive index and Abbe number of glass. f is a focal length, Fno is an F number, and ω is a half angle of view.
[0054]
Table 1 shows the relationship between the above-described conditional expressions and numerical values in the numerical examples.
[0055]
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
[0056]
[Equation 3]
It is expressed by the following formula. “E-0X” means 10 ^−X .
[0057]
[Table 1]
[0058]
[Table 2]
[0059]
[Table 3]
[0060]
[Table 1]
[0061]
【The invention's effect】
According to the present invention, a relatively small and light lens group constituting a part of a zoom optical system is moved in a direction perpendicular to the optical axis, and image blurring occurs when the zoom optical system vibrates (tilts). When the lens group is decentered while properly reducing the overall size of the apparatus, simplifying the mechanism, and reducing the load on the driving means. It is possible to achieve a variable magnification optical system having an anti-vibration function in which the amount of decentration is reduced and the decentration aberrations are corrected well.
[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. 4 is a lens cross-sectional view at the wide-angle end of Numerical Example 3 of the present invention. FIG. 5 is a diagram of various aberrations at the wide-angle end of Numerical Example 1 of the present invention. FIG. 7 is a diagram of various aberrations at the telephoto end of Numerical Example 1 according to the present invention. FIG. 8 is a diagram of various aberrations at the wide-angle end according to Numerical Example 2 of the present invention. FIG. 10 is a diagram of various aberrations at the telephoto end of Numerical Example 2 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. FIG. 12 is a diagram of various aberrations at the telephoto end of Numerical Example 3 of the present invention. FIG. 13 is a diagram of various aberrations at the telephoto end of Numerical Example 3 of the present invention. Illustration of a biological principle DESCRIPTION OF SYMBOLS
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 (5)

In order from the object side upon zooming and focusing, the first group of fixed positive refractive power, the second group of negative refractive power having a zooming function, the third group of positive refractive power, and the zooming A variable power optical system composed of four lens units of a fourth lens unit having a positive refractive power having both a correction function for correcting a fluctuating image plane and a focusing function. It consists of a positive 31st lens with an aspherical lens surface, a meniscus negative 32nd lens with a concave surface facing the image surface, and a positive 33rd lens. The third group is perpendicular to the optical axis. The blurring of the captured image when the variable magnification optical system is vibrated and moved is corrected ,
When the focal lengths of the entire system at the 32nd lens, the third group, and the wide-angle end are f32, f3, and fw in this order,
0.8 <| f32 / f3 | <1.7
3.5 <f3 / fW <5.0
A variable magnification optical system having an anti-vibration function characterized by satisfying the following conditions: In order from the object side, when zooming and focusing, the first group of fixed positive refractive power, the second group of negative refractive power having a zooming function, the third group of positive refractive power, and the zooming A variable power optical system composed of four lens units of a fourth lens unit having a positive refractive power having both a correction function for correcting a fluctuating image plane and a focusing function. It consists of a positive 31st lens with an aspherical lens surface, a meniscus negative 32nd lens with a concave surface facing the image surface, and a positive 33rd lens. The third group is perpendicular to the optical axis. The blur of the captured image when the variable magnification optical system is vibrated and moved is corrected ,
When the focal lengths of the thirty-second lens, the thirty-third lens, and the third group are f32, f33, and f3 in this order,
0.8 <| f32 / f3 | <1.7
1.6 <f33 / f3 <2.4
A variable magnification optical system having an anti-vibration function characterized by satisfying the following conditions: When the focal length of the entire system at the wide angle end is fW,
3.5 <f3 / fW <5.0
The variable power optical system having a vibration isolating function according to claim 2 , wherein the following condition is satisfied. When the focal length of the second group is f2, and the focal lengths of the wide-angle end and the telephoto end of the entire system are fW and fT, respectively.
The zooming optical system having a vibration isolating function according to claim 1, 2 or 3, wherein: 5. A camera comprising a variable magnification optical system having the image stabilization function according to claim 1.