JPH11295594A - Variable power optical system provided with vibration proof function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress and eccentricity generation amount to be small and to excellently correct an eccentric aberration while miniaturizing the entire device, simplifying a mechanism and reducing the load of a driving means by appropriately constituting the lens constitution of a lens group at the time of moving the small-sized and light- weight lens group in a direction perpendicular to an optical axis and correcting the blur of images when a variable power optical system is vibrated. SOLUTION: This variable power optical system is provided with the four lens groups L1-L4. A third group L3 is composed of a positive 31st lens for which both lens surfaces are made aspherical, a meniscus negative 32nd lens whose concave surface is turned to an image surface side IP and a positive 33rd lens, the third group L3 is moved in the direction perpendicular to the optical axis and the blur of photographing images when the variable power optical system is vibrated is corrected. At the time of defining the focus distances of the 32nd lens and the third group L3 respectively as f32 and f3, 0.8<|f32/f31|<1.7 is satisfied. At the time of defining the focus distance of the wide angle end of the entire system as fw, 3.5<f3/fw<5.0 is satisfied. At the time of defining the focus distance of the 33rd lens as f33, 1.6<f33/f3<2.4 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable power optical system having an image stabilizing function, and more particularly to a variable power optical system by moving a part of a lens group of the variable power optical system in a direction perpendicular to an optical axis. A camera having a vibration reduction function suitable for a photographic camera, a video camera, or the like that stabilizes the captured image by optically correcting a blur of the captured image when the camera vibrates (tilts) to obtain a still image. It relates to a magnification optical system.

[0002]

2. Description of the Related Art When an image is taken from a moving object such as a car or an aircraft in progress, vibration is transmitted to an image taking system, resulting in camera shake and blurring of the taken image.

Conventionally, various anti-vibration optical systems having a function of preventing blurring of a photographed image at this time have been proposed.

For example, in Japanese Patent Publication No. 56-21133, some optical members are moved in a direction to cancel the vibrational displacement of an image due to vibration in response to an output signal from a detecting means for detecting a vibration state in an optical device. This stabilizes the image.

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

Japanese Patent Publication No. 56-34847, Japanese Patent Publication No. 5
In JP-A-7-7414, an optical member spatially fixed to vibration is arranged in a part of a photographing system, and a photographed image is deflected by utilizing a prism effect generated by vibration of the optical member. A still image is obtained on the image plane.

[0007] Japanese Patent Application Laid-Open Nos.
In Japanese Patent Application Laid-Open No. -125211, vibration of a photographing system is detected using an acceleration sensor or the like, and according to a signal obtained at this time,
There is also a method of obtaining a still image by vibrating a part of a lens group of a photographing system in a direction orthogonal to an optical axis.

[0008] In Japanese Patent Application Laid-Open No. Hei 7-128619,
A first group of positive refractive power fixed at the time of zooming and focusing in order from the object side, a second group of negative refractive power having a zooming function, an aperture stop, a third group of positive refractive power, and A variable power optical system having four lens units of a fourth group having a positive refractive power and having both a correction function of correcting an image plane that varies due to zooming and a focusing function, wherein the third group is Is composed of two lens units, a 31st lens unit having a negative refractive power and a 32nd lens unit having a positive refractive power. When the 32nd lens unit is moved in a direction perpendicular to the optical axis and the zoom optical system vibrates, The camera shake is corrected.

In Japanese Patent Application Laid-Open No. 7-199124,
In a variable power optical system having a four-unit configuration including four lens units having negative, positive, and positive refractive power, the entire third unit is vibrated in a direction perpendicular to the optical axis to perform image stabilization.

On the other hand, JP-A-5-60974 discloses that
In a four-unit variable magnification optical system including four lens units having positive, negative, positive, and positive refractive powers, a third unit includes a telephoto type of a positive lens and a meniscus-shaped negative lens, and the entire length of the lens is reduced. We are trying to shorten it.

[0011]

In general, an anti-vibration optical system is disposed in front of a photographing system, and a part of the movable lens group of the anti-vibration optical system is vibrated to eliminate a blur of a photographed image and obtain a still image. The method has a problem that the whole apparatus becomes large and a moving mechanism for moving the movable lens group becomes complicated.

There is also a problem that the amount of eccentric aberration generated when the movable lens group is vibrated increases, and the optical performance is greatly reduced.

An optical system that performs image stabilization using a variable apex angle prism has a problem that the amount of chromatic aberration of eccentric magnification increases during image stabilization, especially on the long focal length side (telephoto side).

On the other hand, an optical system that performs image stabilization by decentering some lenses of the photographing system in a direction perpendicular to the optical axis has the advantage that no special optical system is required for image stabilization. However, there is a problem that a space for the lens to be moved is required, and the amount of eccentric aberration generated during image stabilization increases.

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 a direction perpendicular to the optical axis to reduce vibration. If this is done, when the third lens unit is made up of a telephoto type of a positive lens and a meniscus negative lens for shortening the overall length of the lens, a large amount of eccentric aberration, especially eccentric distortion, is generated. If you use this for video shooting such as a video camera,
There has been a problem that the image deformation during image stabilization is noticeable.

According to the present invention, a relatively small and light lens group constituting a part of a variable power optical system is moved in a direction perpendicular to the optical axis, and an image obtained when the variable power optical system vibrates (tilts) is obtained. When correcting blur, when the lens group is decentered while appropriately reducing the load on the driving unit by reducing the load on the drive unit by reducing the size of the entire apparatus, simplifying the mechanism, and appropriately configuring the lens configuration of the lens group. It is an object of the present invention to provide a variable power optical system having an image stabilizing function in which the amount of occurrence of eccentricity is suppressed to a small value and eccentric aberration is corrected well.

[0017]

According to the present invention, there is provided a variable power optical system having an anti-vibration function comprising: (1-1) a first positive refractive power which is fixed during zooming and focusing in order from the object side; Group, a second group of negative refractive power having a zooming function,
A zoom lens having four lens groups, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power having both a correction function and a focusing function for correcting an image plane which fluctuates due to zooming. An optical system, wherein the third unit includes a positive 31st lens having aspheric surfaces on both lens surfaces, a negative 32nd meniscus lens having a concave surface facing the image surface side, and a 33rd positive lens. The third lens unit is moved in a direction perpendicular to the optical axis to correct a blur of a captured image when the variable power optical system vibrates.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view showing a paraxial refractive power arrangement of Numerical Embodiments 1 to 3 of the present invention to be described later, and FIGS. It is a lens sectional view of. 5 to 13 are aberration diagrams of Numerical Examples 1 to 3 of the present invention.

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 the present embodiment, the third group L3 is moved in the direction perpendicular to the optical axis to correct the blur of the captured image when the variable magnification optical system vibrates (tilts). L4 is a fourth unit having a positive refractive power. SP denotes an aperture stop, which is arranged in front of the third lens unit L3. G is a glass block such as a face plate. IP is an image plane. FP is a flare stop (fixed stop), which cuts off a flare component when performing vibration isolation in the third group.

In this embodiment, when zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by an arrow, and the image plane fluctuation due to zooming is corrected by moving the fourth lens unit. ing. In addition, a rear focus type in which the fourth unit is moved on the optical axis to perform focusing is adopted. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. The first and third units are fixed during zooming and focusing, but may be moved as needed.

In the present embodiment, the fourth unit is moved to correct the image plane fluctuation accompanying zooming, and the fourth unit is moved to perform focusing. In particular, as shown by curves 4a and 4b in the same figure, the zoom lens is moved so as to have a convex locus toward the object side when zooming from the wide-angle end to the telephoto end. Thereby, the space between the third and fourth units is effectively used, and the overall length of the lens is effectively reduced.

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end, the fourth unit is moved forward as indicated by a straight line 4c in FIG.

The zoom lens of the present embodiment employs a zoom system in which a virtual image formed by a combined system of the first and second units is formed on the photosensitive surface by the third and fourth units.

In this embodiment, the rear focus method is used to prevent the performance deterioration due to the eccentric error of the first group, as compared with the conventional so-called four-group zoom lens in which the first group is extended and focused. First while doing
This effectively prevents the effective lens diameter of the group from increasing. By arranging the aperture stop immediately before the third lens unit, aberration variation due to the movable lens unit is reduced, and the distance between the lens units in front of the aperture stop is shortened, so that the diameter of the front lens can be easily reduced. doing.

In the first to third numerical embodiments of the present invention, the third
The group L3 is moved in the direction perpendicular to the optical axis to correct image blurring when the variable magnification optical system vibrates. As a result, compared to the conventional anti-vibration optical system, anti-vibration is performed without newly adding an optical member such as a lens group or a variable apex prism for anti-vibration.

Next, referring to FIG. 14, the optical principle of an image stabilizing system for correcting blurring of a photographed image by moving a lens group in a direction perpendicular to the optical axis in a variable power optical system according to the present invention will be described.

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 far from the lens.
Is formed as an image point p at the center of the imaging plane IP. Now, the entire optical system including the imaging plane IP is shown in FIG.
As shown in (B), if the camera is tilted momentarily due to camera shake,
The object point P also instantaneously moves 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 the movement depends on the power arrangement. Expressed as eccentric sensitivity.

In FIG. 14B, the image point p 'shifted by the camera shake is returned to the original image forming position p by moving the eccentric group Y2 by an appropriate amount in the direction perpendicular to the optical axis. As shown in (D), camera shake correction, that is, image stabilization is performed.

Now, the shift amount (shift amount) of the shift lens group (eccentric group) required to correct 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 Is the TS, the movement amount Δ is given by the following equation: Δ = f · tan (θ) / TS.

If the sensitivity TS of the eccentricity of the shift lens group is too large, the amount of movement Δ becomes small, and the amount of movement of the shift lens group necessary for image stabilization can be reduced. Becomes difficult, and the correction remains.
Especially in a video camera or a digital still camera, the image size of an image pickup device 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. Therefore, the shift amount Δ of the shift lens group for correcting the same angle is small. Become smaller.

Therefore, if the accuracy of the mechanism (mechanism) is almost the same, the uncorrected portion on the screen will be relatively large. On the other hand, if the eccentric sensitivity TS is too small, the amount of movement of the shift lens group necessary for control becomes large, and driving means such as an actuator for driving the shift lens group also becomes large.

In the present invention, by setting the refractive power arrangement of each lens group to an appropriate value, the eccentricity sensitivity TS of the third group is set to an appropriate value, and there is little residual vibration compensation due to mechanical control errors. An optical system in which the load of driving means such as an actuator is small is achieved.

In this embodiment, the third lens unit includes, in order from the object side, a positive 31st lens L31 having a convex lens surface on the object side, a negative 32nd meniscus lens L32 having a strong concave surface facing the image surface side, The lens surface is constituted by a positive 33rd lens L33 having a convex surface. Also, the thirty-first lens has both aspheric surfaces.

By providing a meniscus negative second lens having a concave surface facing the image surface side in the third lens unit, the entire third lens unit has a telephoto configuration, and the distance between the principal points of the second lens unit and the third lens unit is reduced. In addition, the overall length of the lens has been reduced.

When such a meniscus negative lens is provided, positive distortion occurs on the lens surface.

It is now assumed that the entire third lens unit has a positive distortion. To explain with reference to FIG. 3 as an example, it is assumed that the entire third group is eccentric upward as shown in FIG. At this time, the height at which the off-axis ray coming to the point S1 passes through the third lens unit decreases, and the positive distortion decreases. Conversely, a light beam coming to the side of the point S2 increases the positive distortion. Accordingly, the quadrilateral object is deformed on the image plane into a shape as shown by the solid line in FIG.

Conversely, when the third unit moves downward, FIG.
Since the image is deformed into a shape as indicated by the dotted line in (B), when vibration is applied, the image is deformed in accordance with the vibration, and the viewer is particularly uncomfortable with a moving image. To reduce this decrease a third
What is necessary is just to reduce the distortion generated in the entire group.

In the present embodiment, the negative 32nd meniscus
By disposing a positive 33rd lens L33 on the image plane side of the lens L32, distortion is corrected in the third group while maintaining the telephoto configuration, and the third group is shifted to perform image stabilization. Eccentric distortion is reduced.

In this embodiment, the spherical aberration is suppressed by the third lens unit and the eccentric coma generated during image stabilization is reduced by providing aspherical surfaces on both lens surfaces of the 31st lens L31.

The variable power optical system having the image stabilizing function of the present invention can be realized by satisfying the above conditions. However, in order to achieve a good optical performance while further shortening the overall length of the lens. Preferably satisfies at least one of the following conditions.

(A-1) Assuming that the focal lengths of the 32nd lens and the third unit are f32 and f3, respectively, 0.8 <| f32 / f3 | <1.7 (1) Is to satisfy.

If the refractive power of the negative 32nd lens in the third lens unit is increased beyond the lower limit of conditional expression (1), it is advantageous for shortening the total length of the lens, but the Petzval sum increases in the negative direction. As a result, it becomes difficult to correct the curvature of field, which is not good. Conversely, if the value exceeds the lower limit, the overall length will be insufficiently reduced.

(A-2) When the focal length of the third lens unit is f3 and the focal length at the wide-angle end of the entire system is fW, 3.5 <f3 / fW <5.0 (2) Satisfy the conditions.

Conditional expression (2) is intended to appropriately set the sensitivity of the shift lens group for image stabilization and to maintain good image stabilization performance while shortening the overall length of the lens. If the refractive power of the third lens unit is increased beyond the lower limit value of the conditional expression (2), the sensitivity of the shift lens unit becomes too large, and if the mechanical accuracy is not strict, the remaining correction during image stabilization becomes large. Not good. Conversely, if the refractive power of the third lens unit is weakened beyond the upper limit, the amount of shift of the third lens unit required for image stabilization is increased, and the overall length of the lens is undesirably increased.

(A-3) When the focal lengths of the 33rd lens and the third group are f33 and f3, respectively, the following condition is satisfied: 1.6 <f33 / f3 <2.4 (3) It is to be.

Conditional expression (3) is for correcting distortion and astigmatism in the third lens group while maintaining the telephoto type of the third lens group, and maintaining good optical performance during image stabilization. is there. If the refractive power of the 33rd lens is too strong beyond the lower limit of conditional expression (3), the telephoto type of the third lens unit will not be maintained, and the effect of shortening the entire length of the lens will be lost. Conversely, if the upper limit is exceeded, the correction of distortion and astigmatism in the third lens unit becomes insufficient, and the optical performance during image stabilization deteriorates.

(A-4) When the focal length of the second lens unit is f2, and the focal lengths of the entire system at the wide-angle end and the telephoto end are fW and fT, respectively:

[0048]

(Equation 2) Satisfying the following conditions.

If the refractive power of the second lens unit becomes too strong beyond the lower limit value of the conditional expression (4), it is advantageous for shortening the overall length of the lens. However, it is necessary to correct the variation of the field curvature and distortion over the entire zoom range. Is not good because it becomes difficult. If the refractive power of the second lens unit becomes too weak beyond the upper limit value of the conditional expression (4), the amount of movement of the second lens unit required for zooming becomes too large.

(A-5) The second lens unit includes, in order from the object side, a negative twenty-first meniscus lens having a strong concave surface facing the image surface side, a negative twenty-second lens having both lens surfaces concave, and a positive second lens. It is preferable to use 23 lenses, but if it is desired to further increase the zoom ratio, a four-lens structure in which a negative lens is further added to the image plane side may be used.

(A-6) In order to correct fluctuations in astigmatism and distortion during zooming, it is preferable to introduce an aspheric surface into the second lens unit.

(A-7) The third group moves for vibration isolation.
The lens diameter is increased accordingly. Therefore, in order to prevent excessive on-axis light flux from entering, the third group on the object side,
Alternatively, a fixed stop (flare stop) FP is preferably arranged on the image plane side. In the present embodiment, by disposing a fixed stop FP between the third and fourth units, the space is effectively used and unnecessary light flux is prevented from entering the photosensitive surface.

Next, numerical examples of the present invention will be described. 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 the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R is a paraxial radius of curvature,
When A, B, C, D, and E are aspheric coefficients, respectively,

[0056]

(Equation 3) This is represented by "E-0X" means 10- ^X .

[0057]

[Outside 1]

[0058]

[Outside 2]

[0059]

[Outside 3]

[0060]

[Table 1]

[0061]

According to the present invention, a relatively small and light lens group constituting a part of the variable power optical system is moved in the direction perpendicular to the optical axis, and the variable power optical system vibrates (tilts). When correcting blurring of the image at the time, by appropriately configuring the lens group of the lens group, it is possible to reduce the load on the drive unit while reducing the size of the entire apparatus, simplifying the mechanism, and reducing the load on the driving unit. It is possible to achieve a variable power optical system having an image stabilizing function in which the amount of eccentricity generated when eccentricity is reduced is reduced and the eccentric aberration is favorably corrected.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a paraxial refractive power arrangement of a variable power optical system according to the present invention.

FIG. 2 is a sectional view of a lens at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 3 is a sectional view of a lens at a wide-angle end according to a second numerical embodiment of the present invention;

FIG. 4 is a sectional view of a lens at a wide-angle end according to a third numerical embodiment of the present invention.

FIG. 5 is a diagram illustrating various aberrations at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 6 is a diagram illustrating various aberrations at the telephoto end according to Numerical Embodiment 1 of the present invention.

FIG. 7 is a diagram showing various aberrations at the telephoto end according to Numerical Embodiment 1 of the present invention.

FIG. 8 is a diagram illustrating various aberrations at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 9 is a diagram showing various aberrations at the telephoto end according to Numerical Example 2 of the present invention.

FIG. 10 is a diagram showing various aberrations at the telephoto end according to Numerical Example 2 of the present invention;

FIG. 11 is a diagram illustrating various aberrations at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 12 is a diagram illustrating various aberrations at the telephoto end according to Numerical Example 3 of the present invention.

FIG. 13 is a diagram illustrating various aberrations at the telephoto end according to Numerical Example 3 of the present invention.

FIG. 14 is an explanatory diagram of the optical principle of the vibration isolation system according to the present invention.

[Explanation of symbols]

 L1 First group L2 Second group L3 Third group L4 Fourth group SP stop IP image plane FP flare stop (fixed stop) d d-line g g-line ΔM meridional image plane ΔS sagittal image plane

Claims (5)

[Claims] 1. A first lens unit having a fixed positive refractive power, a second lens unit having a negative refractive power having a zooming function, and a third lens unit having a positive refractive power during zooming and focusing in order from the object side. A variable power optical system having four lens units of a fourth lens unit having a positive refractive power and having both a correction function and a focusing function of correcting an image plane that fluctuates due to zooming; The third unit includes a positive 31st lens having an aspheric surface on both lens surfaces, a negative 32nd meniscus lens having a concave surface facing the image surface side, and a 33rd positive lens. A variable-power optical system having an image stabilizing function, wherein the variable-power optical system is moved in a vertical direction to correct blurring of a photographed image when the variable-power optical system vibrates. 2. The condition that 0.8 <| f32 / f3 | <1.7 is satisfied, where f32 and f3 are the focal lengths of the 32nd lens and the third group, respectively. Item 6. A variable power optical system having the image stabilizing function according to item 1. 3. The condition that 3.5 <f3 / fW <5.0 is satisfied, where f3 is the focal length of the third lens unit and fW is the focal length at the wide-angle end of the entire system. 3. A variable power optical system having the image stabilizing function according to claim 1. 4. The lens system according to claim 1, wherein, when the focal lengths of said 33rd lens and said third group are f33 and f3, respectively, a condition of 1.6 <f33 / f3 <2.4 is satisfied. Or a variable power optical system having an anti-vibration function. 5. When the focal length of the second lens unit is f2, and the focal lengths at the wide-angle end and the telephoto end of the entire system are fW and fT, respectively. 3. The variable power optical system according to claim 1, wherein the variable power optical system satisfies the following conditions.