GB2268285A

GB2268285A - Image stabilizing apparatus

Info

Publication number: GB2268285A
Application number: GB9318926A
Authority: GB
Inventors: Koichi Maruyama
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1989-09-06
Filing date: 1993-09-13
Publication date: 1994-01-05
Anticipated expiration: 2010-09-06
Also published as: GB9318926D0; GB2268285B

Abstract

The apparatus comprises an imaging lens system 20 for forming an image of a subject onto an imaging surface 10 and a pair of movable prisms 91, 92 which are pivotable on an axis parallel with the optical axis of the imaging lens system. An angle theta is formed by axes representative of deflecting functions of the pair of prisms, as projected onto a plane vertical to the optical axis of the imaging lens system, with the angle being 45 DEG < theta < 135 DEG in an initial state. A control means 42 changes the direction of the deflecting function in order to correct a displacement of the image on the imaging surface. <IMAGE>

Description

IMAGE STABILIZING APPARATUS This invention relates to an image stabilizing apparatus capable of correcting a displacement of the image in order to prevent image deterioration caused by accidental inclination or so called camera shake when a picture is being taken.

When taking a photograph from a moving car or airplane, a taking image tends to be displaced due to vibration of the moving car or airplane, particularly where the exposure time is long. Thus, a precise image is difficult to take. Also, the same problem tends to occur when a long focus lens is used because it is easily adversely affected by vibration.

An object of the present invention is to provide an image stabilizing apparatus which is capable of correcting an image displacement even when a taking image is inclined in any direction caused by inclination of an imaging optical system.

According to the present invention there is provided an image stabilizing apparatus comprising: an optical system for imaging an image of a subject onto an imaging surface; optical path deflecting means comprising at least one pair of movable prisms which are pivotable on an axis parallel with an optical axis of said optical system; wherein an angle e formed by axes representative of deflecting functions of the or each pair of said prisms, as projected onto a plane vertical to the optical axis of said optical system, being 450 < 8 < 1350 in an initial state; and control means for changing a direction of said deflecting function in order to correct a displacement of the image on said imaging surface.

Preferably, the or each pair of movable prisms is disposed in a generally afocal optical path of said optical system.

Conveniently, the or each pair of movable prisms is disposed at the most extreme subject side of said optical system.

It is preferred that said angle e formed by said axes representative of the deflecting functions is 90" in the initial state.

In one case, said optical path deflecting means comprises a single pair of prisms.

The optical path deflecting means may further comprise a solid prism having a deflecting function for offsetting the deflecting function of said pair of prisms in the initial state.

Conveniently, said movable prisms and said solid prism are generally equal in dispersion.

In another case, said optical path deflecting means comprises two pairs of prisms.

Preferably, the angle e of said each pair of prisms is 90" and a deflecting function of one pair of prisms is offset by a deflecting function of the other pair of prisms in the initial state.

Conveniently, said control means pivots first and second movable prisms of one pair in a reverse direction by a same angle and pivots first and second movable prisms of the other pair in a reverse direction by a same angle.

In a preferred embodiment, each said movable prism is a chromatic abberation correction prism formed of a plurality of prism bodies cemented together.

Examples of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic view showing a first embodiment of an image stabilizing apparatus embodying the present invention; Fig. 2 is a schematic view showing the deflecting function caused by a prism of the image stabilizing apparatus of the first embodiment; Fig. 3 is a sectional view of a lens showing a specific example of a taking lens system which is provided with the image stabilizing apparatus of the first embodiment; Fig. 4 is a schematic view showing a second embodiment of an image stabilizing apparatus embodying the present invention; Fig. 5 is a schematic view showing the deflecting function caused by a prism of an image stabilizing apparatus of the second embodiment;; Fig. 6 is a sectional view of a lens showing a specific example of a taking lens system which is provided with the image stabilizing apparatus of the second embodiment; Fig. 7 is a schematic view showing the deflecting function caused by a prism of a conventional image stabilizing apparatus; and Fig. 8 is a schematic view for defining a deflecting function of the prism.

The term "prism" when used herein includes a single prism and cemented prisms for correcting chromatic aberration.

A known apparatus for correcting image displacement will now be explained. In Japanese Patent Early Laid-Open Publication No. Sho 63-169614, the angle formed by axes representative of the deflecting function of two prisms is 180 in an initial state as shown in Fig. 7. Fig. 7 shows the deflecting function of the prisms projected onto a plane vertical to the optical axis of the optical system. Therefore, the deflecting function necessary to correct the displacement of an image, which is corrected when the two prisms are pivoted by a micro angle, is perpendicular to the axes indicating the initial deflecting function.The term "axes of the deflecting function" refers to a vector OP which, as shown in Fig; 8, is drawn from a point of intersection between an optical axis Ax of the optical system and a plane II vertical to the optical axis Ax with respect to a point of intersection from a ray deflected after being made incident onto the prism after passing the optical axis Ax and the plane H. The plane Il is, in general, an image plane in an imaging optical system.

Fig. 7 shows coordinates explaining the deflecting function of the prisms on the image planes, and the origin 0 is a point of intersection between the optical axis of the lens system and the image plane, The amount of deflecting function of the two prisms is the same.

In the figure, the deflecting function on the image plane for the first prism in the initial state is expressed by vector AO and the deflecting function for the second prism is likewise expressed by vector BO. In the initial state, the two vectors form an angle of 1800 and the two vectors are offset from each other. The image is not displaced.

In the case that the first prism is pivoted clockwise or in the case that the second prism is pivoted counterclockwise, the vectors indicating the deflection function of the respective prisms are expressed by a line of which the starting point is the origin 0 and a terminal point is a point of a circular arc R. In the figure, the respective circular arcs indicate, with angles used as a coordinate for explanation, the vector composed of the deflecting functions of the two prisms. The radius of each reference arc is the same for the vectors AO and BO and the terminal points are points divided by 100 units on the circular arc R.

The reference arc indicated by a plus angle is an aggregation of dots which may be the terminal point of the vector indicating the deflecting function composed when the vector AO is pivoted by that angle. The reference arc expressed by the same minus angle, is an aggregation of dots when may be the terminal point of the vector composed when the vector BO is pivoted by that angle. Therefore, with the angles of pivot for both prisms apparent, the deflecting function can be indicated as the vector drawn from the origin O to the point determined by the pivot angles.

For example, the deflecting function is indicated by vector C when the first prism (vector AO) is pivoted by 30 from the initial state and the second prism (vector BO) is pivoted by -20 .

With'the above mentioned construction, in the case that the direction of the deflecting function in order to cross an image displacement is not coincident with the initial deflecting function AO, BO, the first and second prisms must be pivoted normally and reversely by 90" instantaneously and there arises a problem with the response. Also, a signal for controlling the pivot of the prisms become a complicated function based on the initial positions of the prisms.

A first embodiment of an image stabilizing apparatus embodying the present invention has two movable prisms set such that an angle e formed by an axis respective of the deflecting function of the prism becomes 45" < e < 1350 in its initial state.

With such a construction as mentioned above, as the vector of the image displacement caused by a micro pivot from the initial states of the first and second prisms is not coincident with a straight line, correction can be instantaneously made for displacement of an image in any direction.

Also, in the case that the amount of the deflecting functions of both prisms are the same, the displacement of the image can be corrected only by pivoting by an angle proportional to the displacement component of the image differentially and the control of the pivot of the prisms becomes easy.

Figs. 1 to 3 show the first embodiment of the image stabilizing apparatus. The general construction of this apparatus will be described first with reference to Fig. 1.

The arrangement shown in this embodiment includes an imaging lens system 20 for forming an image on an image receiving surface 10, and an optical path deflecting portion 30.

The optical path deflecting portion 30 includes first and second movable prisms 91 and 92 which are pivotably supported on an optical axis Ax of the imaging lens system 20. These movable prisms are arranged such that an angle e formed by an axis indicating the deflecting function is 45" < e < 1350 in their initial states.

The movable prisms 91 and 92 are provided on their outer peripheries with gears 91a and 92a to mesh with drive gears 80a and 81a which are mounted on an axis of motors 80 and 81 to comprise a pivot mechanisms. With the foregoing construction, the two prisms can be pivoted by the corresponding motors 80 and 81 respectively to deflect the optical path and prevent the displacement of an image which is caused by inclination of the whole arrangement.

Control means for controlling the motors 80 and 81 includes a sensor 41 and a controller 42.

With the above mentioned construction, in the case that the arrangement is inclined, the sensor 41 detects the inclination, and the controller 42 pivots the prisms 91 and 92 through the motors 80 and 81 to correct for the displacement of the image on the image receiving surface 10.

A signal for controlling the pivot of the movable prisms is produced by a calculation utilizing the angular position of the pivot of the prisms.

Next, the displacement of an image caused by pivoting of the two movable prisms will be described with reference to the Fig. 2. Fig. 2 shows an example in which an angle e formed by the deflecting function of the respective prisms is arranged to be e = 900 and the amount of the deflecting function of the two prisms is equal to each other.

The origin 0 of Fig. 2 is a point of intersection between the optical axis of the lens system and the image receiving surface 10, and the vector AO and the vector BO express the initial deflecting functions of the first and second prisms.

A vector CO expresses the composed deflecting function of the two prisms in the initial states.

When the first and second prisms are pivoted, the vectors indicating the deflecting functions of the respective prisms are pivoted on the origin 0 and terminal points of the vectors are points on a circular arc R. Tn the drawing, the respective circular arcs drawn by thin lines in the drawing are coordinates for explaining the vectors composing the deflecting function caused by the two prisms, the radius is the same as the vectors AO and BO, and the centre is a spot divided by 10" units on the circular arc R.

In the figure, the respective circular arcs indicated with angles are used as coordinates for explaining the vector composed of the deflecting functions of the two prisms. The radius of each reference arc is the same as the vectors AO and BO, and the terminal points are points divided by 10 units on the circular arc R.

The reference arcs indicated by angles are aggregations of dots which may be the terminal point of a vector indicating the deflecting function composed. The reference arcs of which centres are located on the left hand side in the coordinate are the aggregation of dots which can serve as a terminal point indicating the deflecting function at the time the vector AO has been pivoted by that angle. Likewise, the references arcs of which centres are located on the right hand sides are the aggregation of dots which can serve as a terminal point of the composed vector at the time the vector BO has pivoted by that angle. Therefore, if the angles of pivot for both prisms are apparent, the deflecting function can be indicated as the vector drawn from the origin 0 to the point determined by the pivot angles.

As described above, since the direction of the deflecting function of the two prisms are perpendicular to each other, the directions for correcting the image by means of a micro pivot of the respective prisms become components generally perpendicular to each other. The correcting of the image displacement is expressed as the vector of which the starting point is on the terminal point of the vector CO. Accordingly, by resolving the vector of the displacement of the image into two perpendicular components corresponding to the deflecting function of the respective prisms iri their initial states and by pivoting the respective prisms independently based on these components, displacement of the image can be corrected.

However, since the moving directions of the image are not linear components perpendicular to each other but components along the circular arc, an error occurs. However, tis error can be reduced within 4% in a region surrounded by arcs indicating angles of pivot + 5 of both prisms.

In the case that the optical path deflecting portion is formed only of two movable prisms, the image is already shifted in its initial state as indicated by the vector CO.

However, in the case that the shift of the image does not become a problem, say as when using a short focal length lens, there can be obtained a favourable performance if the generation of chromatic aberration is reduced. In that case, by using a material of a high Abbe number (low dispersion) or by employing a cemented prism for the movable prisms, chromatic aberration can be corrected.

On the contrary, in the case when shift of an image and chromatic aberration of magnification becomes significant, say as when using a telephoto lens, it may be designed such that a stationary prism having such a deflecting function as shown by the vector D is added to the above mentioned construction.

In this construction, the image shift in its initial state by the movable prism can be cancelled.

Fig. 3 shows a specific example of a taking lens provided with an optical path deflecting portion 30 formed of two movable prisms 91 and 92 and a single stationary prism 93 and disposed on a subject side of the imaging lens system 20.

In the case that the Abbe numbers of the movable prisms 91 and 92 and of the stationary prism 93 are the same, the chromatic aberration of magnification can also be corrected by cancelling the shift of the image position.

Also, by arranging the stationary prism 93 at the most extreme subject side of the lens, it can be prevented that the movable prisms 91 and 92 are touched during operation thereof.

Furthermore, in the case that the chromatic aberration of a prism greatly affects the image efficiency as when used in a telephoto lens, it is preferable that chromatic aberration is corrected for all prisms.

Figs. 4 to 6 show a second embodiment of an image stabilizing apparatus embodying the present invention.

The arrangement in this embodiment includes, as shown in Fig. 4, an imaging lens 20, an image receiving surface 10 and an optical path deflecting portion 30.

The optical path deflecting portion 30 includes first, second, third and fourth movable prisms, 94, 95, 96 and 97 pivotably supported on an optical axis Ax of the imaging lens system 20. These movable prisms, as shown in Fig. 5 are arranged such that the angles formed by an axis representative of the deflecting functions are 0 , 1800, 90" and 270" in their initial states.

The first and second movable prisms 94 and 95 are provided on opposite surfaces thereof with ring-shaped inner gears 94a and 95a, with which a drive gear 80a mounted on a rotational shaft of a motor 80 is meshed. The motor 80 acts as a first drive mechanism for pivoting the first and second movable prisms 94 and 95 by the same angle in the opposite directions.

Likewise, the third and fourth movable prisms 96 and 97 are provided on opposite surfaces thereof with ring shaped inner gears 96a and 97a, with which a drive gear 81a mounted on a rotational shaft of a motor 81 is meshed. The motor 81 acts as a second drive mechanism for pivoting the third and fourth movable prisms 96 and 97 by the same angle in opposite directions.

With the foregoing construction,the movable prisms 94, 95, 96 and 97 , when pivoted by the motors 80 and 81, deflect the optical path to correct for the displacement of the image caused by inclination of the arrangement. At that time, the direction for correcting the image displacement by means of a micro pivot of the first and second movable prisms 94 and 95 becomes 90" and 270 directions, and the direction for correcting the image displacement by means of a micro pivot of the third and fourth movable prisms 96 and 97, becomes 0 and 1800 directions, as shown by a thick line in Fig. 5.The deflecting function of the set of the first and second movable prisms and that of tie third and fourth movable prisms are perpendicular to each other.

As these movable prisms do not adversely affect the image efficiency in their initial states, it is preferable that at least the prisms within a set have the same chromatic aberration and the same deflecting function.

Control mean for controlling the motors 80 and 81 include a sensor 41 and a controller 42 similar to those of the above mentioned embodiment.

With this construction, when the arrangement is inclined, the sensor 41 detects the inclination, and the controller 42 resolves such a detected inclination into two perpendicular components in a plane perpendicular to the optical axis. The controller 42 calculates the pivoting amount of the first and second movable prims 94 and 95 required for correcting the moving components in the 90" and 270 directions and actuates the motor 80, and also calculates the pivoting amount of the third and fourth movable prisms 96 and 97 required for correcting the moving components in the 0" and 1800 directions and actuates the motor 81. In this way, by pivoting four prisms, displacement of an image on the image receiving surface 10 can be corrected.

Fig. 6 shows a specific example of a taking lens provided with an optical path deflecting portion 30 formed of four movable prisms and disposed on the subject side of the image lens 20.

In order to reduce the generation of ghost, the respective movable prisms are arranged such that each surface of the prism is not vertical to the optical axis.

Also, in the case that the chromatic aberration of the prisms greatly affects the image efficiency, say as when used in a telephoto lens, it is preferable that chromatic aberration is corrected for the respective prisms.

In the above mentioned embodiment, the prisms of each set are driven by a single motor and gear so that the prisms are driven by the same amount through a simple driving mechanism.

However, it may be designed such that separate driving means are provided for each prism and the driving means are controlled by software in order to drive the prisms of each set by the same amount.

With the second embodiment, by resolving the inclination of the arrangement into two perpendicular components in a plane perpendicular to the optical axis and by correcting the respective components using two prisms, the displacement of an image caused by inclination can be corrected rapidly and easily. Also, if it is constructed such that the prisms of each set are driven by the same driving mechanism, the driving mechanism does not become complicated.

Claims

1. An image stabilizing apparatus comprising: an optical system for imaging an image of a subject onto an imaging surface; optical path deflecting means comprising at least one pair of movable prisms which are pivotable on an axis parallel with an optical axis of said optical system; wherein an angle e formed by axes representative of deflecting functions of the or each pair of said prisms, as projected onto a plane vertical to the optical axis of said optical system, being 45" < e < 135 in an initial state; and control means for changing a direction of said deflecting function in order to correct a displacement of the image on said imaging surface.

2. An image stabilizing apparatus according to claim 1 wherein the or each pair of movable prisms is disposed in a generally afocal optical path of said optical system.

3. An image stabilizing apparatus according to claim 1 or 2 wherein the or each pair of movable prisms is disposed at the most extreme subject side of said optical system.

4. An image stabilizing apparatus according to any preceding claim wherein said angle e formed by said axes representative of the deflecting functions is 90" in the initial state.

5. An image stabilizing apparatus according to any preceding claim wherein said optical path deflecting means comprises a single pair of prisms.

6. An image stabilizing apparatus according to claim 5 wherein said optical path deflecting means further comprises a solid prism having a deflecting function for offsetting the deflecting function of said pair of prisms in the initial state.

7. An image stabilizing apparatus according to claim 6 wherein said movable prisms and said solid prism are generally equal in dispersion.

8. An image stabilising apparatus according to any one of claims 1 to 4 wherein said optical path deflecting means comprises two pairs of prisms.

9. An image stabilizing apparatus according to claim 8 wherein the angle e of said each pair of prisms is 90" and a deflecting function of one pair of prisms is offset by a deflecting function of the other pair of prisms in the initial state.

10. An image stabilizing apparatus according to claim 8 or 9herein said control means pivots first and second movable prisms of one pair in a reverse direction by a same angle and pivots first and second movable prisms of the other pair in a reverse direction by a same angle.

11. An image stabilizing apparatus according te any preceding claim where each movable prism is a chromatic abberation correction prism formed of a plurality of prism bodies cemented together.

12. An image stabilizing apparatus substantially as herein described with reference to Figures 1 to 6.