JPH03260615A - Variable power optical system having oscillation preventing function - Google Patents

Abstract

PURPOSE:To correct the blurring of an image with a compact device when a variable power system is oscillated by constituting the 1st lens group with three lenses and rotating the center lens as oscillation preventing lens. CONSTITUTION:The 1st group I of the variable power optical system is constituted of three lenses, i.e. the 1a-th group having negative refractive power, the 1b-th oscillation preventing and rotatable group having positive refractive power focal distance f1b and the 1c-th fixed group. When it is defined that the focal distance of the 1a-th group is f1a and the image formation magnification of the 1b-th group is beta1b, a point 3 on the optical axis separated from the images side only by an approximate distance beta1b.f1a/(1-beta1b) is used as a fulcrum and the 1b-th group is rotated around the supporting point. Consequently, the blurring of an image due to the oscillation of the optical system can be corrected and the oscillation preventing mechanism having simple and compact constitution can be obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a variable magnification optical system having an anti-vibration function, and in particular to a variable magnification optical system that rotates a part of the lens group of the variable magnification optical system about a point on the optical axis as a fulcrum. A photographic camera, a video camera, etc. that stabilizes the photographed image by optically correcting the blurring of the photographed image when the variable magnification optical system vibrates (tilts) and obtains a still image by moving the variable magnification optical system. The present invention relates to a variable magnification optical system having an image stabilization function suitable for

(Prior Art) When attempting to photograph a moving object such as a moving car or aircraft, vibrations are transmitted to the photographing system, causing blur in the photographed image.

2. Description of the Related Art Various anti-vibration optical systems having a function of preventing blur in photographed images have been proposed.

For example, in Japanese Patent Publication No. 56-21133, an optical device is provided with an image by moving some optical members in a direction that offsets the vibrational displacement of the image due to vibration, in response to an output signal from a detection means for detecting a vibration state. We are trying to stabilize the situation.

Japanese Patent Laid-Open No. 61-223819 discloses an imaging system in which a refractive variable apex angle prism is disposed closest to the subject, and an image is captured by changing the apex angle of the refractive variable apex prism in response to vibrations of the imaging system. The image is stabilized by deflecting it.

Special Publication No. 56-34847, Special Publication No. 57-7414
In the above publication, an optical member that is spatially fixed against vibrations is placed in a part of the imaging system, and by utilizing the prism effect produced in response to vibrations of this optical member, the photographed image is deflected and the imaging plane is A still image is obtained above.

In addition, we use an acceleration sensor to detect vibrations in the shooting system.
There is also a method of obtaining a still image by vibrating a lens group in the photographing system in a direction perpendicular to the optical axis in response to the signal obtained at this time.

In addition, in US Pat. No. 2,959,088, an afocal system consisting of two lens groups, a first group and a second group, each having negative and positive refracting powers with the same absolute value of focal length Hf, is placed in front of the photographing system, and We have proposed an anti-vibration optical system using an inertial pendulum method in which the second group is a movable lens group for anti-vibration when the system vibrates, and the lens is supported at its focal point.

(Problems to be Solved by the Invention) In general, an anti-vibration optical system is placed in front of the photographing system, and a part of the movable lens group of the anti-vibration optical system is vibrated to eliminate blur in the photographed image and to produce a still image. If this were to be achieved, the overall size of the device would increase, and the relationship between the amount of correction for blur in the photographed image and the amount of movement of the movable lens group would become complicated, making the mechanism of the entire device complicated.

Especially in a shooting system where focusing is performed with the front lens group closest to the object, if the anti-shake optical system is placed in front of the shooting system, the movement space for the front lens group to focus can be reduced by the anti-shake optical system. Since it has to be installed between the lens and the front lens group, there is a problem in that the anti-vibration optical system becomes even larger.

In addition, since the height from the optical axis through which the off-axis light beam passes through the anti-vibration optical system increases, the amount of eccentric aberration that occurs when the movable lens group for anti-vibration is rotated increases, and the optical The problem is that the performance will drop significantly.

The present invention aims to simplify the relationship between the amount of vibration of the variable magnification optical system and the rotation of the movable lens group for image stabilization, and to decenter the movable lens group in order to reduce the blurring of photographed images that occurs when the variable magnification optical system vibrates. It is an object of the present invention to provide a variable magnification optical system which has a well-corrected image stabilization function, which generates less decentering aberration when the object is rotated, and which reduces the size of the entire device.

(Means for Solving the Problems) The variable magnification optical system having an image stabilization function of the present invention has a fixed first lens group, a variable magnification lens group, and a focusing lens group in order from the object side when changing magnification and focusing. A variable magnification optical system having a variable power optical system, wherein the first group includes at least two lens groups, a 1a group having a negative refractive power and a 1b group having a positive refractive power, and a focal point of the 1a group. Distance f 1
a, when the imaging magnification of the 1b group is β1b, approximately a distance β1b·f1a from the image plane side principal point of the 1b group to the image plane side
/(1-β1b) By making the 1b group rotatable about a point on the optical axis that is far apart, the blurring of the photographed image when the variable magnification optical system is tilted is corrected. It is a feature.

In addition, in the present invention, the holding member that holds the 1b group is provided with a counterweight that balances the weight of the 1b group with respect to the fulcrum, and the focusing lens group is Its feature is that it consists of a lens group that is a magnification group.

(Example) FIG. 1 is a schematic diagram of an optical system of a first practical example of the present invention.

In the figure, the lens has a first lens group that is fixed during zooming and focusing, and a rotatable anti-vibration lens group Ib, which will be described later. ■ is the second group for zooming, ■ is the third group for correcting the image plane that changes with zooming, and from the second group ■ and the third group m is the zooming group P.
For example, by moving the lens as shown by the arrow, the magnification is changed from the wide-angle end to the telephoto end. (2) is the fourth group, and the light beam emitted from the third group is made almost afocal. (2) is a fifth group for image formation that is fixed during zooming, and has a fixed lens group Va and a lens group Vb for focusing. SP is a fixed aperture.

The first group consists of three groups: the 1a group with negative refractive power and a focal length of f 1 a, the 1b group with a rotatable positive refractive power and focal length fib for image stabilization, and the fixed 1c group. It consists of a group of lenses. As mentioned above, when the imaging magnification of the 1b group is β1b, the fulcrum is point 3 which is approximately β1b·ffa/(1-βib) away from the image plane side principal point of the 1b group on the image plane side. It is configured to be rotatable.

In addition, in FIG. 1, 4 is a counterweight, which is provided at the other end of the holding member 5 that holds the 1b group.
The weight of the 1b group is balanced when the 1b group is rotated about the fulcrum 3 in accordance with the tilt of the variable magnification optical system.

In this way, in this example, the first group is composed of three lens groups, and by rotating the third group 1b for vibration isolation, the need for special tilt detection means such as an angular velocity sensor is eliminated. It becomes possible to perform vibration isolation without

Further, in this embodiment, focusing is made possible by moving part of the lens group vb in the fifth group as shown by the arrow on the optical axis. In other words, when focusing on an object at infinity, the lens group v
b is fixed as shown by a straight line 51 when changing magnification from the wide-angle end to the telephoto end, and when focusing on a close object, lens group vb moves as shown by a curve 52 when changing magnification from the wide-angle end to the telephoto end. are doing.

In this embodiment, the 1b lens group in the 1st lens group is provided with an image stabilization function, and the lens group vb in the 5th lens group behind the variable power group is provided with a focusing function. This achieves a variable magnification optical system that effectively corrects image blur caused by vibrations, etc., while avoiding complication in the structure of the lens barrel.

In particular, in this embodiment, by configuring the anti-vibration lens group Ib and the focusing lens group vb as described above, the optical system created when focusing is performed with the lens group before the variable magnification section. In addition to preventing the lens from becoming too large, focusing can be performed using a lightweight lens group, which reduces the burden on motors and other equipment used to drive the focusing lens.

As described above, in this embodiment, when the variable magnification optical system (camera body) is tilted by an angle θ, the 1a group and the 1c group are tilted by the same angle θ together with the variable magnification optical system. On the other hand, the 1bth group is spatially fixed by the counterweight 4. In other words, the initial posture is maintained. At this time, the first group is configured as described above, and the 1b group is made to produce the same angle of ray deflection as the tilt angle of the variable magnification optical system, simplifying the rotational relationship, and the 1b group The fulcrum 3 on which the camera rotates is located as close to the object as possible, thereby reducing the size of the entire device and correcting blur in the photographed image to obtain a still image.

Figure 2 shows the 1a group and 1b group as the anti-vibration optical system at this time.
This is a schematic diagram for explaining the anti-vibration effect by taking a group as an example, and in the figure, the anti-vibration optical system is shown as a thin lens.

Group 1a and optical axis 11 when the variable power optical system is not tilted
Let A be the intersection point with a, and B be the intersection point between the 1b group and the optical axis 11a.

When the variable magnification optical system is tilted upward by a small angle θ1 due to vibration or the like, the 1a group similarly tilts by an angle θ1, or the 1b group maintains its initial attitude.

In Figure 2, for simplicity, the imaging system is relatively fixed, and the subject moves downward at an angle of -01 degrees, and point B also moves to point B1, which is tilted downward at 101 degrees around fulcrum 3. Indicates the condition.

(However, B, B1 = β1b - f1a - θ1/(1β1b)
It is. ) Now, consider the imaging state of point C at the center of the screen. The object in the first non-vibrating state is located at a point on the optical axis 11a. When tracing the ray in the opposite direction from point C, the ray connecting point C and point B1 is not subject to refraction, so it travels straight and moves downward from the rear focal position of group 1a, that is, from the object point position of group 1b. The image is formed on point D1. Here BC= (1-fib) ・
fib.

It becomes C1.

Considering the state of image formation by the 1a group of images at this time, the 1st
Imaging light at a point D1 on the image-side focal plane of the a group, which is separated from the optical axis 11a by a distance f1a·θ, is emitted from the 1a group in parallel, and if the inclination is ZD-A·Dl-θ, the imaging relationship is formula, D
Since -D1=f1a·θ, θ=−01.

That is, the light is emitted parallel to the same direction as the object in the initial state. Conversely, this means that the subject does not move from point C at the center of the screen even if the variable magnification optical system is tilted.

Next, consider the imaging state at points other than the center of the screen.

FIG. 3 is a schematic diagram for explaining the image stabilizing effect of the image stabilizing optical system when the variable magnification optical system is tilted at an angle C1, similar to FIG. 2. In this figure, the same symbols as in FIG. 2 have the same meanings.

Point C2 indicates a point around the screen. Let D2 be an arbitrary point on the image-side focal plane of the 1a group. If ZDl·A·D2−ω, then Dl·D2=f 1 a·ω. Point D2. Bl
Letting C2 be the intersection of the extension of and the focal plane of the entire system, C-C2=D1-D2-β2-f1a·ω·fib from the magnification relationship.

The focal length fT of the entire anti-vibration optical system is fTf1a・β1b
Therefore, the light beam having the optical axis 11a and the inclination ω in the initial state forms an image at a position at a distance f1a, fib, ω from the optical axis on the focal plane. This is the same as C-C2 described above.

By the way, 4D-A-D1=-01, and the object at the center of the screen is imaged at a constant point C regardless of the tilt of the variable magnification optical system (camera body).

As a result, an arbitrary point C2 around the image 1ff1 is imaged at a constant point regardless of the tilt of the camera body, and an image stabilization effect can be obtained.

In this embodiment, the fulcrum position for rotating the 1b group is strictly fib·f1a/(1-
fib) Even if the distance is not too far, as long as an acceptable still image can be obtained due to vibration, for example, ±10
It is sufficient to set it within the permissible range of %.

Further, in this embodiment, an auxiliary mechanism for holding the ib group at the fulcrum or a damping mechanism may be provided to prevent adverse effects caused by contact of the end points.

4th. FIG. 5 is a schematic diagram of an optical system according to a third embodiment of the present invention. In the figure, the same elements as those shown in FIG. 1 are given the same reference numerals.

In the second embodiment shown in FIG. 4, the third lens group m constituting the variable magnification unit P is provided with a focusing function for correcting the image plane that changes due to variable magnification. In the figure, when the object is at infinity, the third lens group m is moved from the wide-angle end to the telephoto end as shown by curve 41, and when the object is close, the magnification is changed from the wide-angle end to the telephoto end as shown by curve 42. It's being moved.

In this way, by providing the third group with both the function of correcting image plane fluctuations associated with zooming and the focusing function, the number of movable lens groups is reduced and the lens barrel structure is simplified. .

In this embodiment, the fifth group (3) for image formation, which is fixed during zooming, consists of one lens group. The lens configuration of the first lens group (2) and the configuration for rotating the vibration-proofing lens group 1b around the fulcrum 3 to correct image blur caused by vibration are the same as those in the first embodiment shown in FIG.

In the third embodiment shown in FIG. 5, the variable magnification optical system is composed of four lens groups as a whole. ■ is the first group that is fixed when changing magnification and focusing, TI is the second group that is used for changing magnification, ■ is the third group that is fixed,
(2) has both a correction function for correcting the image plane that changes as the magnification changes, and a focusing function. In the figure, when the fourth group (2) is an object at an infinite distance, the magnification is changed from the wide-angle end to the telephoto end by moving it as shown by a curve 51, and when the object is at a close distance, the magnification is changed from the wide-angle end to the telephoto end as shown by a curve 52. I'm moving it around like this.

In this embodiment, the number of movable lens groups is reduced as in the second embodiment shown in FIG. 4, the lens barrel structure is simplified, and the variable magnification optical system is made up of four lens groups, thereby reducing the number of lenses. However, the lens configuration can be simplified. Furthermore, the overall length of the lens is shortened by making effective use of the air gap between the third and fourth groups.

The lens configuration of the first lens group (2) and the configuration for rotating the vibration-proofing lens group 1b around the fulcrum 3 to correct image blur caused by vibration are the same as those in the first embodiment shown in FIG.

Next, numerical examples of concrete paraxial refractive power arrangements of the first to third embodiments of the variable magnification optical system according to the present invention will be shown. In the numerical examples, the focal length and principal point interval of each lens group, and the distance ML of the fulcrum 3 from the image plane side principal point of the 1b group are shown.

Numerical Example 1 L = 80.3 Numerical Example 2 Numerical Example 3 L = 74.4 (Effects of the Invention) According to the present invention, as described above, the variable magnification optical system is fixed during variable magnification and focusing. The first group is made up of at least two lens groups, a fixed 18n lens group and a rotatable 1b group, and the 1b group is rotatable. By configuring the variable magnification optical system to correct image blurring when the variable magnification optical system vibrates, it is possible to achieve a variable magnification optical system having an anti-vibration function that simplifies and downsizes the entire device. I can do it.

In addition, by providing a counterweight to the 1b group, it is possible to correct the blurring of the photographed image without using a vibration detection means such as an acceleration sensor, and it has an anti-shake function that has features such as being able to easily obtain a still image. It is possible to achieve a variable magnification optical system.

[Brief explanation of drawings]

1, 4, and 5 are the first and second sections of the present invention. A schematic diagram of the main parts of the third embodiment, 2nd. FIG. 3 is a schematic diagram for explaining the anti-vibration effect of the anti-vibration optical system of the present invention. In the figure, ■ is the first group, ■ is the second group, ■ is the third group, and ■ is the fourth group.
group, ■ is the fifth group, P is the variable power unit, 3 is the fulcrum, 4 is the counterweight, and 5 is the holding member.

Claims (4)

[Claims] (1) A variable magnification optical system having, in order from the object side, a first lens group that is fixed during magnification changing and focusing, a variable magnification lens group, and a focusing lens group, the first group having at least a negative refractive power. It has two lens groups, a 1a group with a positive refractive power and a 1b group with positive refractive power, and when the focal length of the 1a group is f1a and the imaging magnification of the 1b group is β1b, the 1b group The 1b group can be rotated about a point on the optical axis that is approximately a distance β1b·f1a/(1−β1b) away from the image side principal point of the image plane side toward the image plane side,
A variable magnification optical system having an anti-shake function, characterized in that blurring of a photographed image when the variable magnification optical system is tilted is corrected. (2) The anti-vibration function according to claim 1, characterized in that the holding member that holds the 1b group is provided with a counterweight that balances the weight of the 1b group with respect to the fulcrum. variable magnification optical system. (3) A 1c group having a fixed positive refractive power during zooming and focusing is arranged on the image plane side of the 1b group of the first group. A variable magnification optical system with the image stabilization function described. (4) A variable magnification optical system having an image stabilizing function according to claim 1, wherein the focusing lens group is constituted by a part of the lens group of the variable magnification group.