JPH10246855A - Variable power optical system with vibration-proof function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently compensate the image blur of a photographing image when a variable power optical system is inclined due to vibration, etc., while suppressing the generated amount of eccentric aberration by giving an aspherical surface to a variable power vertical prism at the time of compensating the image blur of photographing image caused by the inclination of the variable power optical system. SOLUTION: This system is provided with a first group L1 of a positive refractive power, a second group L2 of a negative refractive power and a third group L3, a fourth group L4 of positive refractive powers and an aperture diaphragm SP is arranged in front of the third group L3. This is provided with a glass block G such as a low pass filter, a variable power vertical angle prism KP. By imparting an aspherical surface to one surface composing the variable power vertical angle prism, the generation of eccentric aberration at the time of compensating an image blur is reduced by changing the vertical angle of the prism. Namely, at the time of compensating the image blur of photographic image due to the tilt of the variable power optical system by changing the vertical angle of the variable power vertical angle prism KP, the variable power vertical angle prism has at least one aspherical surface.

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 a function of correcting image blur (image blur) of a photographed image due to vibration, that is, a so-called anti-shake function, and more particularly, to using a variable apex prism for anti-shake. A high zoom ratio of about 15 which is suitable for a photographic camera or a video camera, etc., in which the image blur is corrected by changing the prism apex angle of the variable apex angle prism according to the vibration of the zoom optical system. The present invention relates to a variable power optical system having a magnification-stabilizing function.

[0002]

2. Description of the Related Art Conventionally, various types of video cameras and cine cameras equipped with an image stabilizing function for optically or electronically correcting an image blur generated when a photographing system vibrates have been proposed. I have.

As a method for optically correcting image blur, a variable apex angle prism is provided in a lens system, and the variable apex angle prism is driven eccentrically so that the prism apex angle changes with vibration. There is a method of correcting blur.

The applicant of the present invention has disclosed, for example, Japanese Patent Application Laid-Open No.
In the publication No. 7, in order from the object side, the first positive refractive power
Group, second group of negative refractive power, aperture, third group of positive refractive power,
A fourth lens group having a positive refractive power and a variable apex angle prism on the object side or the image plane side of the diaphragm; and moving the second group to the image plane side to move the second group from the wide-angle end. A variable power optical system that performs zooming to a telephoto end, corrects an image plane variation caused by zooming by moving the fourth unit, and focuses by moving the fourth unit. By changing the prism apex angle of the angular prism, a variable power optical system having an image stabilizing function that corrects image blurring of a captured image caused when the variable power optical system is tilted by vibration is proposed. I have.

[0005]

Generally, a variable apex angle prism is provided in a part of a photographing system, and when the photographing system vibrates, the prism apex angle of the variable apex angle prism is changed in accordance with the vibration to reduce image blur of a photographed image. The correction method has a feature that a still image can be obtained relatively easily.

However, when the apex angle of the variable apex angle prism is changed, there is a problem that many eccentric aberrations such as eccentric coma and eccentric astigmatism are generated.

Particularly, in the variable power optical system, there is a problem that eccentric magnification chromatic aberration due to the prism action is often generated on the long focal length side (telephoto side).

The present invention provides a variable power optical system by appropriately configuring the position and shape of a variable apex angle prism in a lens system in a variable power optical system having an image stabilizing function previously proposed by the present applicant. Even when the zoom ratio of the system is increased, image blurring of the captured image that occurs when the zooming optical system is tilted due to vibration or the like is corrected satisfactorily while keeping the amount of eccentric aberration small, and high image quality It is an object of the present invention to provide a variable power optical system having an image stabilizing function capable of easily obtaining a still image of the above type and greatly reducing manufacturing costs.

[0009]

According to the present invention, a variable power optical system having a vibration-proof function according to the present invention is a (1-1) variable power optical system having a lens group for zooming on the object side of the stop. A variable apex angle prism is provided in the vicinity of the stop, and by changing the prism apex angle of the variable apex angle prism, when correcting image blurring of a captured image caused when the variable power optical system is tilted, The variable apex angle prism has at least one aspheric surface.

In particular, (1-1-1) the variable apex angle prism has one of an incident surface and an outgoing surface fixed, and the other surface is rotated to change the prism apex angle, The aspherical surface is provided on the fixed surface.

[0011]

FIG. 1, FIG. 3, FIG. 5, and FIG. 7 are lens cross-sectional views of a variable power optical system according to numerical examples 1, 2, 3, and 4 of the present invention, respectively. 2, 4, 6, and 8 are aberration diagrams of Numerical Examples 1, 2, 3, and 4. In the aberration diagrams, (A) shows the wide-angle end, and (B) shows the telephoto end.

In the drawing, L1 is a first lens unit having a positive refractive power, L2 is a second lens unit having a negative refractive power, L3 is a third lens unit having a positive refractive power, and L4 is a positive lens.
Denotes a fourth group having a positive refractive power. SP is an aperture stop,
It is arranged in front of the third group 3. IP is an image plane. G
Is a glass block such as a low-pass filter or an infrared cut filter. KP is a variable angle prism.

11 and 12 are transparent glass plates (transparent substrates)
Reference numeral 13 denotes a bellows portion made of a material such as polyethylene. A transparent liquid 14 of, for example, silicon oil or the like is sealed in the interior surrounded by the glass plate and the bellows.

At least one surface of the transparent glass plate 11 or 12 has an aspheric surface. The surface on which the aspherical surface is provided is provided on the surface of the fixed glass plate that does not rotate when the prism apex angle is changed (in this embodiment, the entrance surface of the glass plate 11).

The variable apex angle prism 1 thus configured
By applying an aspherical surface to one of the surfaces, the occurrence of eccentric aberration when performing image blur correction by changing the prism apex angle is reduced to maintain good image quality.

In this embodiment, each of these elements 1
1, 12, 13, and 14 constitute a part of the variable apex angle prism KP. In the figure, the two glass plates 11 and 12 are in a parallel state, and in this case, the variable apex angle prism KP
The incident angle and the outgoing angle of the light beam to the light are equal.

At least one of the transparent members 11 and 12 (the transparent member 12 in this embodiment) can be independently rotated by an external biasing force. For example, transparent member 1
Numeral 2 is rotatable about the point 12a or the point 12b as a rotation axis. Thereby, a variable prism having an arbitrary prism apex angle is formed by the two transparent members 11 and 12.

In the present embodiment, the variable apex angle prism KP having such a configuration is arranged on the image surface side of the third lens unit L3. Then, when the variable magnification optical system vibrates and an image blur occurs in the photographed image, the blur is detected by a known blur detecting means, and the prism apex angle of the variable apex prism KP is determined by a known driving means according to the amount of blur at that time. Is changed to deflect the passing light beam by a predetermined amount, thereby correcting image blurring.

In the variable power optical system according to the present embodiment, the second lens unit L2 is moved to the image plane side as indicated by an arrow at the time of zooming from the wide-angle end to the telephoto end, and the image plane fluctuation accompanying zooming is changed to the fourth lens unit. L4
Is moved for correction.

Also, a rear focus system is employed in which the fourth unit L4 is moved on the optical axis to perform focusing. 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.

At the telephoto end, focusing from an object at infinity to an object at close distance is performed by moving the fourth lens unit L4 toward the object side as indicated by an arrow 4c. All the lenses that constitute each lens group are composed of spherical lenses to simplify the lens system. The first lens unit L1, the third lens unit L3, and the variable vertex prism KP are fixed during zooming and focusing.

Incidentally, in this embodiment, the correction of the image plane fluctuation accompanying the magnification change may be performed by moving the image sensor provided on the image plane IP.

The variable power optical system having an anti-vibration function, which is the object of the present invention, is achieved by satisfying the above conditions, but further achieves a high variable power of about 15 in the variable power ratio. In order to obtain an image with good image quality over the entire zoom range, it is preferable to satisfy at least one of the following conditions.

(A1) The first group includes a negative meniscus lens having a convex surface facing the object side, a positive lens having both lens surfaces convex, and a positive meniscus lens having a convex surface facing the object side.
The second group includes three lenses: a meniscus negative lens having a convex surface facing the object side, a negative lens having both lens surfaces concave, and a meniscus positive lens having a convex surface facing the object side. The third unit includes a positive lens having both convex lens surfaces, and the fourth unit includes a negative meniscus lens having a convex surface facing the object side and a positive lens having both convex lens surfaces. That is.

(A2) When the focal length of the i-th lens unit is Fi and the focal lengths of the entire system at the wide-angle end and the telephoto end are FW and FT, respectively:

[0026]

(Equation 2) Satisfying the following conditions.

Conditional expression (1) relates to the ratio of the focal length of the third lens unit to the focal length of the fourth lens unit, and is mainly for achieving compactness after the stop SP and maintaining good optical performance. . If the focal length of the third lens unit becomes short beyond the lower limit value of the conditional expression (1), the aberration at the time of image stabilization becomes worse. There are also problems such as difficulty in securing a sufficient back focus, shortening of the exit pupil at the intermediate zoom position, and an increase in the amount of movement of the fourth lens unit, resulting in large fluctuations in aberrations during zooming and focusing. Come up.

Conversely, if the focal length of the third lens unit is increased beyond the upper limit, the divergence of the light beam emitted from the third lens unit increases, the effective diameter of the fourth lens unit increases, and the lens becomes heavier, so that focusing can be performed smoothly. Problems such as disappearance occur.

Conditional expression (2) relates to the focal length of the second lens unit. If the focal length of the second lens unit becomes shorter than the lower limit of conditional expression (2), the Petzval sum increases in the under direction, and it becomes difficult to correct aberrations such as image plane tilt. Conversely, if the focal length of the second lens unit becomes longer than the upper limit value, the amount of movement of the second lens unit due to zooming increases, and the diameter of the front lens increases.

In the present invention, more preferably, the numerical range of conditional expressions (1) and (2) is

[0031]

(Equation 3) It is good to set as follows.

(A3) The distance between the third and fourth units when focusing on an object at infinity with the fourth unit at the telephoto end is D34.
T, when the height from the optical axis of 70% of the effective diameter of the aspheric surface applied to the variable apex angle prism is ΔH, and the amount of aspheric surface in the optical axis direction with respect to the paraxial R at the height ΔH is ΔX.

[0033]

(Equation 4) Satisfying the following conditions.

Conditional expression (3) relates to the distance between the third lens unit and the fourth lens unit when focusing on an object at infinity at the telephoto end in the fourth lens unit. If the distance between the third lens unit and the fourth lens unit is widened beyond the upper limit value of the conditional expression (3), the incident height of the off-axis light beam incident on the fourth lens unit becomes high, so that it becomes difficult to correct aberrations and the fourth lens unit. The problem that the effective diameter becomes large arises.
Conversely, if the interval becomes narrower than the lower limit, a problem arises in that it becomes difficult to secure the extension amount by focusing on the closest object of the fourth group.

Conditional expression (4) relates to the amount of displacement of the aspherical surface. If the amount of displacement of the aspherical surface exceeds the upper limit value or the lower limit value of the conditional expression (4), spherical aberration cannot be sufficiently corrected, causing a problem that flare occurs.

In the present invention, it is more preferable that the numerical range of conditional expressions (3) and (4) be

[0037]

(Equation 5) Satisfying the following conditions.

(A4) The aspherical surface applied to the variable apex angle prism is set so as to have a low-pass filter function. This is to achieve a compact and inexpensive zoom lens, specifically, a quartz lens placed in front of the CCD by providing a curved surface having the function of a low-pass filter on a variable apex prism. The low-pass filter can be eliminated, and the difference in optical path length by the thickness of the crystal can be reduced. Also, quartz is very expensive compared to glass, so eliminating it can significantly reduce costs.

(A5) To make the variable apex angle prism unit have an infrared cut effect. Specifically, an infrared cut coat is provided on the entrance surface or the exit surface of the variable apex angle prism, or a material that absorbs infrared light is mixed with the enclosed liquid to thereby arrange the infrared light disposed immediately before the CCD. The cut filter can be abolished, the difference in the optical path length corresponding to the thickness of the infrared cut filter can be shortened, and the cost can be reduced by the abolition.

The variable apex angle prism according to the present invention is not limited to a variable power optical system, but can be similarly applied to an optical system such as a telephoto lens having a single focal length. In this case, the variable apex angle prism may be arranged at an arbitrary position in the optical system.

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. In the aspherical shape, the radius of curvature at the center of the lens surface is R, the optical axis direction (the traveling direction of light) is the X axis, and the direction perpendicular to the optical axis is the H axis.
When B, C, D, E, and F are aspheric coefficients, respectively,

[0042]

(Equation 6) It is assumed that

Note that the notation “ ^ex ” represents “× 10 ^−x ”. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. In Numerical Examples 1, 2, 3
Reference numerals 15 to R18 and R14 to R17 in Numerical Example 4 indicate variable apex angle prisms.

[0044]

[Outside 1]

[0045]

[Outside 2]

[0046]

[Outside 3]

[0047]

[Outside 4]

[0048]

[Table 1]

[0049]

According to the present invention, as described above, the position and the shape of the variable apex angle prism in the variable power optical system having the image stabilizing function are appropriately configured so as to provide the variable power optical system. Even when the zoom ratio of the system is increased, image blurring of the captured image that occurs when the zooming optical system is tilted due to vibration or the like is corrected satisfactorily while keeping the amount of eccentric aberration small, and high image quality A variable power optical system having a vibration reduction function that can easily obtain the still image of the present invention can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Embodiment 1 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 4 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Example 2 of the present invention.

FIG. 5 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 6 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Embodiment 3 of the present invention.

FIG. 7 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 8 is an aberration diagram at a wide angle end and a telephoto end according to Numerical Embodiment 4 of the present invention.

[Explanation of symbols]

 L1 First group L2 Second group L3 Third group L4 Fourth group KP Variable vertex angle prism 11, 12 Transparent substrate 14 Transparent liquid 13 Bellows part SP stop IP Image plane d d-line g g-line ΔM Meridional image plane ΔS sagittal image Surface G Glass plate

Claims (6)

[Claims] A variable power optical system having a variable power lens group on the object side of the stop, wherein a variable apex angle prism is provided near the stop, and a prism apex angle of the variable apex angle prism is set. A variable vertex angle prism having at least one aspherical surface when correcting the image blurring of a photographed image caused when the variable power optical system is tilted by changing the angle. Variable power optical system having 2. The variable apex angle prism has one of an incident surface and an exit surface fixed, and the other surface is rotated to change the prism apex angle, and the aspheric surface is fixed. 2. The variable power optical system according to claim 1, wherein the variable power optical system is provided on a surface. 3. A first group of positive refractive power, a second group of negative refractive power, a stop, a third group of positive refractive power, and a fourth group of positive refractive power in order from the object side. A lens unit and a variable apex angle prism in the vicinity of the stop; moving the second unit to the image plane side to perform zooming from the wide-angle end to the telephoto end; The fourth group is moved and corrected, and the fourth group is corrected.
A variable power optical system that performs focusing by moving a group,
By changing the prism apex angle of the variable apex angle prism, the variable apex angle prism has at least 1
A variable power optical system having an anti-vibration function characterized by having two aspheric surfaces. 4. The variable power optical system according to claim 3, wherein the variable apex angle prism is provided on the image plane side of the third lens unit. 5. The first group includes three lenses: a negative meniscus lens having a convex surface facing the object side, a positive lens having both lens surfaces convex, and a positive meniscus lens having a convex surface facing the object side. The second group includes a meniscus negative lens having a convex surface facing the object side, a negative lens having both lens surfaces concave, and a meniscus positive lens having a convex surface facing the object side.
The third group is composed of a positive lens having both lens surfaces convex, and the fourth group is composed of a meniscus negative lens having a convex surface facing the object side and a positive lens having both lens surfaces convex. 5. The variable power optical system according to claim 3, wherein the variable power optical system comprises a lens. 6. When the focal length of the i-th lens unit is Fi, and the focal lengths at the wide-angle end and the telephoto end of the entire system are FW and FT, respectively. 6. A variable power optical system having an anti-vibration function according to claim 3, wherein the following condition is satisfied.