Lens unit and image taking apparatus

Mutually non-mixable light-transmitting insulative liquid and conductive liquid having different refractive indices are accommodated in a light-transmitting liquid container forming a lens unit. The lens unit includes a first electrode which is in contact with the conductive liquid, one or more second electrodes which are insulated from the conductive liquid, and a correcting section which controls voltage to be applied between the first electrode and at least one of the second electrodes in accordance with a gravity direction, thereby changing a shape of an interface between the insulative liquid and the conductive liquid to correct distortion of the interface caused by the gravity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens unit through which light passes, and an image taking apparatus which obtains image data by forming an image of a subject.

2. Description of the Related Art

Some of electronic still cameras which form an image of a subject on a solid imaging element such as a charge coupled device (CCD) and which captures image data representing the subject as a signal, and some of film cameras which shoot a subject on a photographic film include zoom function for freely setting shooting angle of view. Such a camera includes a shooting lens whose focal length is varied in accordance with operation of a zoom switch. This shooting lens generally is a compound lens comprising a combination of lens elements, and relative positions of the lens elements are adjusted in accordance with focal length which is set by the zoom switch. Such a camera includes a cam mechanism, the cam mechanism transmits rotation of a motor in accordance with operation of the zoom switch, thereby moving the lens elements forward and backward in an optical axis to adjust the relative positions, and the focal length is changed.

A focus lens for adjusting focus is included in the lens elements. A lens driving mechanism for moving the focus lens is disposed independently from the cam mechanism in some cases.

As an alternative lens of the shooting lens having the driving mechanism, it is recently proposed a liquid lens having variable focal length in which two kinds of mutually non-mixable liquids having different refractive indices are accommodated (see non-patent document “Philips Fluid Lenses”, [online], dated Mar. 3, 2004, by Royal Philips Electronics, [Searched on Mar. 31, 2004], the Internet <URL: http://www.dpreview.com/news/0403/04030302philipsfluidlens.asp> for example).

The two kinds of mutually non-mixable liquids having different refractive indices are accommodated in the liquid lens proposed in the non-patent document. One of the two kinds of liquids is conductive aqueous solution, and the other liquid is insulative oil. The two kinds of liquids are accommodated in a short glass tube liquid container. Both ends of the liquid container are closed with light-transmitting clear endcaps. An inner wall of this tube and an inner wall of one of the endcaps are covered with repellency films. According to the liquid lens having such a structure, the conductive aqueous solution of the two kinds of liquids is repulsed from the inner wall of the tube covered with the repellency film and from the inner wall of the one endcap. Since the conductive aqueous solution stays in a form of a semi-spherical shape in a state in which the conductive aqueous solution is in contact with the other endcap, an interface portion between the conductive aqueous solution and the insulative oil functions as a concave lens. The liquid lens is also provided with two electrodes for applying voltage to the conductive aqueous solution. One of the two electrodes is disposed in contact with the conductive aqueous solution, and the other electrode is disposed behind the repellency film. If voltage is applied to such electrodes, the electrode disposed in contact with the conductive aqueous solution discharges electric charge into the conductive aqueous solution, and the discharged electric charge is accumulated in the interface portion between the conductive aqueous solution and the insulative oil therein. The electric charge accumulated in the interface portion and electric charge collected in the electrode disposed behind the repellency film having opposite pole from that of the former electric charge attract each other due to the Coulomb force, and the electric charge in the conductive aqueous solution is attracted close to the repellency film. As a result, the conductive aqueous solution starts wetting the repellency film which covers the inner wall of the tube, and the interface shapes of the two kinds of liquids are changed. That is, as the voltage is strongly applied to the conductive aqueous solution, the radius of curvature of the interface portion of the conductive aqueous solution between the insulative oil and the conductive aqueous solution which first functioned as the concave lens is changed, and for example, the interface portion becomes completely flattened or the conductive aqueous solution functions as a convex lens, and the focal length is changed.

According to such a liquid lens, since the focal length can be changed without moving the lens, it is possible to realize zoom function and focus function without providing the cam mechanism or the lens driving mechanism. Therefore, the device can be made compact, and the device can be applied to a small device such as a mobile phone.

According to the liquid lens described in the non-patent document, even if voltage is applied and a target shape of the interface between the liquids can be obtained, since gravity is applied, the interface shape is distorted. As a result, there is a problem that the focus position of the liquid lens is deviated, and image deviation is generated in a shooting image.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances and provides a lens unit and an image taking apparatus in which deterioration of optical characteristics caused by gravity is suppressed.

The present invention provides a lens unit comprising a liquid container in which mutually non-mixable light-transmitting insulative liquid and conductive liquid having different refractive indices are accommodated, and light passing through the liquid container at least in a predetermined optical axis;

a first electrode which comes into contact with the conductive liquid in the liquid container;

one or more second electrodes which are insulated from the conductive liquid in the liquid container; and

a correcting section which controls voltage to be applied between the first electrode and at least one of the second electrodes in accordance with a gravity direction, thereby changing a shape of an interface between the insulative liquid and the conductive liquid to correct distortion of the interface caused by the gravity.

According to the lens unit of the invention, if voltage is applied between the first electrode and the second electrodes, electric charge is discharged in the conductive liquid from the first electrode, electric charge having pole that is opposite from the former electric charge is collected in the second electrodes, the electric charges having opposite poles are attracted each other by Coulomb force, and the shape of the interface between the conductive liquid and the insulative liquid is changed. At that time, although the gravity is applied to the lens unit, since the distortion of the interface between the conductive liquid and the insulative liquid is corrected by the shape change of the interface by the Coulomb force, the optical performance of the lens unit is maintained.

It is preferable that the number of second electrodes is two or more,

the correcting section applies voltages having different magnitude between the first electrode and the second electrodes.

If the voltages having different magnitudes are applied between the first electrode and the second electrodes, the correction precision of the distortion of the interface between the conductive liquid and the insulative liquid by the gravity is enhanced. The voltages are applied between the first electrode and one or more of the second electrodes, the shape of the interface between the conductive liquid and the insulative liquid matches with a shape having desired optical characteristics, voltage is applied to the first electrode and the remaining second electrode, the distortion of the interface by the gravity is corrected, and a lens unit having desired optical characteristics can be realized precisely.

It is preferable that the lens unit further comprises an attitude sensor for detecting attitude of the lens unit,

the correcting section applies voltage corresponding to output of the attitude sensor between the first electrode and the at least one of the second electrodes.

The degree of distortion of the interface between the conductive liquid and the insulative liquid by the gravity and the shape thereof are different depending upon the attitude of the lens unit, but according to the lens unit of a preferred embodiment of the invention, the distortion of the interface is precisely corrected by applying voltage corresponding to the attitude of the lens unit.

The invention provides an image taking apparatus comprising a liquid container in which mutually non-mixable light-transmitting insulative liquid and conductive liquid having different refractive indices are accommodated, and light passing through the liquid container at least in a predetermined optical axis;

a first electrode which comes into contact with the conductive liquid in the liquid container;

one or more second electrodes which are insulated from the conductive liquid in the liquid container;

a correcting section which controls voltage to be applied between the first electrode and at least one of the second electrodes in accordance with a gravity direction, thereby changing a shape of an interface between the insulative liquid and the conductive liquid to correct distortion of the interface caused by the gravity; and

an imaging element in which subject light which passed through the insulative liquid and the conductive liquid is formed on a surface of the imaging element and an image signal representing the subject light is produced.

According to the image taking apparatus of the invention, like the lens unit of the invention, it is possible to suppress the distortion of the interface of liquid by the gravity, and to maintain the optical performance.

Only a basic form of the image taking apparatus of the invention is described here to avoid redundant explanation, but the image taking apparatus of the invention includes not only the basic form, but also various forms corresponding to the various forms of the lens unit.

According to the present invention, it is possible to provide a lens unit and an image taking apparatus in which deterioration of optical performance caused by gravity is suppressed.

DETAILED DESCRIPTION OF THE INVENTION

Prior to explanation of embodiment of the present invention, problems of the liquid lens described in the non-patent document will be explained in detail.

FIGS. 1(A) and 1(B)are schematic diagram showing a structure of a liquid lens of a comparative example. In the following explanation, light passes in the direction of the arrow O from left (inFIG. 1(A)) to right (inFIG. 1(B)).

As shown inFIGS. 1(A) and 1(B), a liquid lens1has a glass container11comprising a tube11a. Both ends of the tube11aare closed with caps11band11c. Clear water21to which support electrolyte is added, and clear oil22which is insulative liquid are accommodated in the container11such that the water21and the oil22are not mixed with each other. Since oil22has higher refractive index of light than that of the water21, the oil22functions as a lens which refracts light in the liquid lens1.

An inner surface of the tube11aand an inner surface of the cap11bwhich closes the left end of the tube11aof the container11are covered with repellency films15having repellency. An inner surface of the cap11cwhich covers the right end of the tube11ais covered with a hydrophilic film16which has an affinity for water.

An insulative film14is provided between the tube11aand the repellency film15. The liquid lens1is also provided with a first electrode12which is in contact with water21, and a second electrode13which is insulative from water21by means of the insulative film14.

When voltage is not applied between the first electrode12and the second electrode13, as shown inFIG. 1(A), the water21repulses from the repellency film15and comes into contact with the hydrophilic film16. Thus, a contact portion P1between the water21and the repellency film15becomes small. Therefore, water21is accumulated in a form of a semi-spherical shape, and oil22pushed by the water21is accumulated in a form obtained by subtracting the semi-spherical shape from a cylindrical shape. Since the shape of the interface between the water21and the oil22as viewed from the oil22is recessed shape, the liquid lens1functions as a concave lens inFIG. 1(A).

For example, if positive voltage is applied to the first electrode12and negative voltage is applied to the second electrode13, positive electric charge31ais discharged from the first electrode12to the water21, and negative electric charge31bis accumulated in the second electrode13. At that time, the positive electric charge31adischarged to the water21is attracted by the negative electric charge31bof the second electrode13by the Coulomb force, and a contact portion P2between the water21and the repellency film15becomes great in accordance with the applied voltage. InFIG. 1(B), the shape of the interface between the water21and the oil22is a projecting shape when viewed from the oil22, and the liquid lens1functions as a convex lens. It is possible to change the shape of the interface between the water21and the oil22little by little by adjusting the voltage applied to the first electrode12and the second electrode13.

In this manner, even if a mechanism for moving the lens is not provided, it is possible to realize the zoom function and the focus function by changing the shape of the interface between the water21and the oil22.

Here, it is ideal that the shape of the interface between the water21and the oil22matches with the shape shown with solid lines inFIGS. 1(A) and 1(B)by applying voltage to the first electrode12and the second electrode13. However, since the gravity is applied to the liquid lens1, the interface shape is distorted as shown with the chain line inFIGS. 1(A) and 1(B)in the actual case. As a result, the optical axis of the liquid lens1is deviated, and there is a problem that the optical performance of the liquid lens1is deteriorated.

The present invention is made based on the detailed analysis as described above.

An embodiment of the present invention will be explained with reference to the drawings.

FIG. 2is an outward perspective view of a digital camera as viewed from front and diagonally upper direction, to which an embodiment of the present invention is applied.

As shown inFIG. 2, this digital camera100is provided at its central portion of its front surface with a shooting lens101. The digital camera100is provided at its upper portion of its front surface with an optical finder object window102and an auxiliary light emitting portion103. The digital camera100is provided at its upper surface with a slide type power switch104and a release switch150.

FIG. 3is a schematic block diagram of the digital camera100shown inFIG. 2.

As shown inFIG. 3, the digital camera100is roughly divided into a shooting optical system110and a signal processor120. In addition, the digital camera100is also provided with an image display130for displaying a shot image, an external recording medium140for recording a signal of the shot image, a zoom switch170, a shooting mode switch160and a release switch150for allowing the digital camera100to carry out various processing for shooting, and an attitude sensor180for detecting the attitude of the digital camera100. The attitude sensor180corresponds to one example of an attitude sensor of the present invention.

The structure of the shooting optical system110will first be explained with reference toFIG. 3.

In the digital camera100, subject light enters from left side inFIG. 3, the subject light passes through a zoom lens115and a focus lens114and passes through an iris113which adjusts light quantity of the subject light. Then, when a shutter112is opened, an image is formed on a solid imaging element111. A CCD or CMOS sensor is used as the solid imaging element111. The solid imaging element111corresponds to one example of an imaging element of the present invention. Usually, lenses are disposed in a shooting optical system. At least one of the lenses is largely involved in adjustment of focus, and relative positions of the lenses are involved in the focal length. InFIG. 3, the zoom lens115is schematically illustrated as a lens which is involved in changing the focal length, and the focus lens114is schematically illustrated as a lens which is involved in adjustment of the focus.

The zoom lens115, the iris113and the shutter112are driven and moved by a zoom motor115a, an iris motor113aand a shutter motor112a, respectively. The focus lens114is provided with a focus controller114ainstead of a motor for changing a lens shape of the focus lens114. Instructions for operating the zoom motor115a, the iris motor113aand the shutter motor112aare transmitted through a motor driver120cfrom a digital signal processor120bin the signal processor120, and instructions for operating the focus controller114ais transmitted directly from the digital signal processor120b. A detection result (attitude of the digital camera100) detected by the attitude sensor180is transmitted to the focus controller114a. The focus controller114ais operated in accordance with the instructions transmitted from the digital signal processor120band the detection result transmitted from the attitude sensor180.

The zoom lens115is moved by the zoom motor115ain a direction along the optical axis. If the zoom lens115is moved to a position corresponding to a signal from the signal processor120, the focal length is changed, and shooting magnitude is determined.

The focus lens114realizes TTLAF (Through The Lens Auto Focus) function. Generally, this TTLAF function carries out such an action that a focus lens is moved in a direction along the optical axis and in this state, contrast of an image signal obtained by the solid imaging element111is detected by an AF/AE calculator126of the signal processor120, and the focus lens114is adjusted to the focus position using a lens position where a peak of the contrast is obtained as the focus position. With this TTLAF function, it is possible to shoot an image while automatically bringing a subject (closest subject) where the contrast becomes peak into focus. In this embodiment, the closest subject is brought into focus by changing the lens shape of the focus lens114by means of the focus controller114ainstead of moving the focus lens114. The structure of the focus lens114and a method for changing the lens shape will be explained in detail later.

The iris113is driven based on the instructions given from the AF/AE calculator126of the digital signal processor120b, thereby adjusting the light quantity of the subject light.

The structure of the shooting optical system110is as described above.

Next, a structure of the signal processor120will be explained. A subject image formed on the solid imaging element111by the shooting optical system is read out into an analog processor (A/D)120aas an image signal, an analog signal is converted into a digital signal by the analog processor (A/D)120a, and the digital signal is supplied to the digital signal processor120b. The system controller121is disposed in the digital signal processor120b, and the signal in the digital signal processor120bis processed in accordance with a program describing procedure of action in the system controller121. Data is sent and received between the system controller121, an image signal processor122, an image display controller123, an image compressing section124, a media controller125, an AF/AE calculator126, a key controller127, a buffer memory128and an internal memory129through a bus1200. When data is sent and received therebetween through the bus1200, the internal memory129is used as a buffer. Data that represents a variable is written in the internal memory129whenever necessary in accordance with the progress of the processing process of each section. In the system controller121, the image signal processor122, the image display controller123, the image compressing section124, the media controller125, the AF/AE calculator126and the key controller127, appropriate processing is carried out by referring to the data. That is, instructions from the system controller121are transmitted to the above elements through the bus1200, and processing process of the elements rises. The data in the internal memory129is rewritten in accordance with the progress of the process, the data is referred to by the system controller121, and actions of these elements are managed. In other words, the power is turned ON, and processes of the elements rise in accordance with procedure of the program in the system controller121. For example, if the release switch150, the zoom switch or the shooting mode switch is operated, information representing the fact that the switch was operated is transmitted to the system controller121through the key controller127, and processing corresponding to this operation is carried out in accordance with the procedure of the program in the system controller121.

If the releasing operation is carried out, the image data read out from the solid imaging element is converted from an analog signal to a digital signal by the analog processor (A/D)120a, and this digitalized image data is once stored in the buffer memory128in the digital signal processor120b. An RGB signal of this digitalized image data is converted into a YC signal by the image signal processor122, the YC signal is compressed in JPEG compression manner by the image compressing section124, and this image signal is stored in the external recording medium140through the media controller125as an image file. The image data stored as the image file is reproduced in the image display130through the image display controller123. At the time of this processing, the AF/AE calculator126carries out the calculation of the focus adjustment and of the exposure. The AF/AE calculator126detects contrast for each subject distance from the RGB signal to adjust the focus. The focus is adjusted by the focus lens114based on this detection result. A bright signal is extracted from the RGB signal by the AF/AE calculator, and field brightness is detected therefrom. Based on this result, the exposure is adjusted by the iris113such that the light quantity of the subject light given to the solid imaging element becomes appropriate value.

The basic structure of the digital camera100is as described above.

The digital camera100of this invention is characterized in the focus lens114whose shape is adjusted in accordance with the detection result of the attitude sensor180.

The attitude sensor180will be explained first.

FIG. 4schematically shows a structure of the attitude sensor180.

The attitude sensor180includes a cylindrical hermetic container181, and electrodes182inserted into the hermetic container181radially. Conductive liquid183(mercury in this embodiment) is charged into the hermetic container181. The attitude sensor180is disposed in the digital camera100such that the axis of the cylindrical hermetic container181extends along the optical axis of the digital camera100.

Different numbers corresponding to the positions of the electrodes182are respectively allocated to the electrodes182.

If the digital camera100is moved, liquid183in the hermetic container181flows in the vertical direction by the gravity, and the liquid183comes into contact with one or some of the electrodes182which are located vertically lower side in the attitude of the digital camera100at that time. The electrode182being in contact with the liquid183is energized, and the attitude of the digital camera100is judged based on the number allocated to the energized electrode182. The judgment result is transmitted to the focus controller114ashown inFIG. 3.

Next, the focus lens114will be explained.

FIG. 5schematically shows a structure of the focus lens. Subject light enters from left side inFIG. 5in the direction of the arrow O. In the following explanation, the entering side of the light (left side inFIG. 5) is defined as front, and the going side of the light (right side inFIG. 5) is defined as rear.

The focus lens114includes a liquid container201comprising a tube201a. Both ends of the tube201aare closed with caps201band201c. Conductive liquid301and insulative liquid302which can not be mixed with the conductive liquid301are accommodated in the liquid container201. The liquid container201is made of clear glass, and the liquid container201corresponds to one example of the liquid container of this invention.

A surface (inner surface) of the cap201cwhich covers the rear end of the tube201athat comes into contact with liquid is covered with a hydrophilic film206. A portion of an inner surface of the liquid container201other than that covered with the hydrophilic film206is covered with a hydrophobic film205.

The liquid container201is also provided with a first electrode202which is disposed such as to sandwich the hydrophilic film206and which comes into contact with liquid, an insulative film204sandwiched between the tube201aand the hydrophobic film205, and second electrodes203insulated from liquid by the insulative film204.

As shown inFIG. 6, the second electrodes203(203a,203b,203c,203d,203e,203f,203g,203h) are provided such as to surround the tube201a.

The first electrode202and the second electrodes203are connected to the focus controller114ashown inFIG. 3. Voltage is applied between the first electrode202and the second electrodes203by the focus controller114a. The first electrode202corresponds to one example of the first electrode of the present invention, and the second electrode corresponds to the second electrode of the invention. The focus controller114acorresponds to one example of a correcting section of the invention.

The conductive liquid301and the insulative liquid302having different refractive index of light are accommodated in the liquid container201. In this embodiment, water to which support electrolyte (tetrabutyl ammonium perchlorate 0.1 mol/L) is added is used as the conductive liquid, and organic solvent (Isopar: produced by Exxon Corp.) is used as the insulative liquid302. The conductive liquid301corresponds to one example of the conductive liquid of the present invention, and the insulative liquid302corresponds to one example of the insulative liquid of the invention.

When voltage is not applied between the first electrode202and the second electrodes203, the conductive liquid301repulses from the repellency film205, and the interface between the conductive liquid301and the insulative liquid302takes a shape shown with the solid lines shown inFIG. 5. At that time, the first electrode202and the conductive liquid301come into contact with each other.

If the focus controller114aapplies voltage between the first electrode202and the second electrodes203, electric charge is discharged from the first electrode202to the conductive liquid301, and electric charge having pole opposite from the electric charge discharged to the conductive liquid301is collected in the second electrodes203. The electric charge discharged to the conductive liquid301and the electric charge of the second electrodes203are attracted to each other by the Coulomb force, and the electric charge in the conductive liquid301is attracted close to the repellency film205. As a result, the shape of the interface between the conductive liquid301and the insulative liquid302is changed to a shape shown with dotted line inFIG. 5.

Using this focus lens114, the TTLAF function is realized in the following procedure.

First, the solid imaging element111shown inFIG. 3obtains an image signal while changing the shape of the interface between the conductive liquid301and the insulative liquid302by changing the voltage applied between the first electrode202and the second electrodes203little by little. Then, the AF/AE calculator126detects contrast of the image signal, and voltage when peak of the contrast is obtained is applied between the first electrode202and the second electrodes203. By shooting in a state in which the lens shape is thus determined, it is possible to bring a closest subject into focus.

Here, if the focus controller114aapplies the same voltages between the first electrode202and the second electrodes203in accordance with the operation instructions transmitted from the AF/AE calculator126, the interface between the conductive liquid301and the insulative liquid302is distorted by the gravity applied to the focus lens114. To correct this distortion, the focus controller114aapplies different voltages between the first electrode202and the second electrodes203corresponding to the detection result of the attitude sensor180in addition to the voltages corresponding to the operation instructions transmitted from the AF/AE calculator126.

In the internal memory129shown inFIG. 3, there is previously stored a corresponding relation between an attitude of the digital camera100and a correction voltage value which is necessary to correct the distortion caused by gravity of the interface between the conductive liquid301and the insulative liquid302in that attitude. For example, when the digital camera100is in such an attitude that the second electrode203ecomes up as shown inFIG. 6, the second electrodes203are in association with such correction voltages that voltage applied between the first electrode202and the second electrodes203a(voltage applied to the first electrode202and the second electrodes203xis called voltage203x, hereinafter)>(voltage203band voltage203h)>(voltage203cand voltage203g)>(voltage203dand voltage203f)>voltage203e. By applying such correction voltages, a preferable shape of the interface between the conductive liquid301and the insulative liquid302is maintained.

If voltage for realizing the TTLAF function is instructed from the AF/AE calculator126, the focus controller114aobtains a detection result of the attitude of the digital camera100from the attitude sensor180. Then, the focus controller114aobtains a correction voltage value corresponding to the attitude of the digital camera100transmitted from the attitude sensor180in the corresponding relation stored in the internal memory129shown inFIG. 3. If the correction voltage value corresponding to the attitude of the digital camera100is obtained, voltage to which voltage for realizing the TTLAF function and the correction voltage are added is applied between the first electrode202and the second electrodes203.

If voltage is applied between the first electrode202and the second electrodes203, the shape of the interface between the conductive liquid301and the insulative liquid302is changed in accordance with the instructions from the AF/AE calculator126by the Coulomb force caused by the voltage for realizing the TTLAF function, and the distortion of the interface is corrected by the correction voltage. Deterioration of the optical characteristics of the focus lens114caused by the gravity is suppressed, and the TTLAF function can be precisely realized by the digital camera100.

Although the two kinds of liquids, i.e., the conductive liquid and insulative liquid are accommodated in the liquid container of this embodiment, three or more kinds of liquids may be accommodated in the liquid container of the invention.

Although two or more second electrodes are provided in the embodiment, only one second electrode may be provided when the lens unit of the invention is applied to a camera which carries out vertical TTLAF function. In this case, in addition to voltage for TTLAF function which vertically deforms the interface of the liquid, if the correction voltage for changing the interface of the liquid is applied to direction opposite from the gravity direction (vertical direction), the distortion of the interface of the liquid caused by the gravity can be corrected.

In the above embodiment, voltage for realizing the TTLAF function, and voltage for correcting the distortion of the interface of the liquid caused by the gravity are applied between the first electrode and all of the second electrodes. Alternatively, in the lens unit of the present invention, the second electrodes may be divided into electrodes for realizing the TTLAF function and electrodes for correcting the distortion, voltage for realizing the TTLAF function may be applied between the first electrode and the TTLAF second electrodes, and voltage for correcting the distortion of the interface of the liquid caused by the gravity may be applied between the first electrode and the distortion correcting second electrodes.

Although the lens unit of the present invention is applied to the focus lens in the embodiment, the lens unit may be applied to a zoom lens.

Although correction in the rotation direction around the optical axis of the digital camera is explained, it is also possible to correct in an elevation angle direction in addition to the rotation direction around the optical axis by providing electrodes in the spherical hermetic container as the attitude sensor.

Various embodiments capable of being employed for the various elements which constitute the present invention will be described next.

The conductive liquid and the insulative liquid of the present invention may be two or more kinds of liquids having different refractive indices and which are not mixed with each other. It is preferable that a difference of specific gravity of these liquids is 0.1 or less.

The combination of these liquids is not limited, but a combination of water and organic solvent is preferable. Preferable organic solvents are hydrocarbon (hexane, heptane, pentane, octane, Isopar (produced by Exxon Corp.)), hydrocarbon-based aromatic compound (benzene, toluene, xylene, mesitylene and the like), halogen-based hydrocarbon (difluoro propane, dichloroethane, chloroethane, bromoethane and the like), halogen-based or hydrocarbon-based aromatic compound (chloro benzene and the like), ether-based compound (diphenyl ether, anisole, diphenyl ether and the like).

It is preferable that support electrolyte is added to water to enhance the electric conductivity. As the support electrolyte, TMAP: Tetramethylammonium perchlorate or TBAF: Tetrabutylammonium hexafluorophosphate is used.

The basic embodiment for realizing the conception of the present invention has been explained. To bring the lens unit employed for the invention into practical use, it is preferable to take a measure for preventing inconvenience that dust or water attaches to the optical path and the lens performance is deteriorated.

It is preferable that a repellency film is provided on an outer surface (light-transmitting surface, hereinafter) which intersects with the optical path of the container in which the liquids are accommodated. If the light-transmitting surface is provided with repellency, dust or water drop is prevented from attaching, and high light-transmission of the lens unit can be maintained. Preferable materials of the repellency film are silicon resin, block copolymer of organo polysiloxane, fluorine polymer, and polytetrafluoroethane.

It is also preferable to provide the light-transmitting surface of the container constituting the lens unit with a hydrophilic film. By providing the light-transmitting surface with hydrophilic characteristics also, dust can be prevented from attaching. Preferable materials of the hydrophilic film are surface-active agent such as acrylic polymer, non-ion organo silicon surface-active agent. To produce the hydrophilic film, silane-based monomer plasma polymerization, or ion beam processing may be used.

It is also preferable that the light-transmitting surface of the container constituting the lens unit is provided with light catalyst such as titanium oxide. Contamination is dissolved by light catalyst which reacted with light, and the light-transmitting surface can be kept clean.

It is preferable that the light-transmitting surface of the container constituting the lens unit is provided with an antistatic film. If static is accumulated in the light-transmitting surface of the container or the electrode bears electrical charges, dust may be adversely attached. If the light-transmitting surface is provided with the antistatic film, it is possible to prevent such unnecessary material from attaching, and the light-transmission of the lens unit can be maintained. It is preferable that the antistatic film is made of polymer alloy material. It is especially preferable that the polymer alloy material is polyether-based material, polyether ester amid-based material, material having cationic group, and Reolex (tradename: Dai-Ichi Kogyo Seyaku Co., LTD.). It is preferable that the antistatic film is produced by mist method.

A soil-resistant material may be used for the container constituting the lens unit. Preferable soil-resistant material is fluorine resin. Concretely, preferable materials are fluorine alkyl alkoxy silane compound, polymer including fluorine alkyl group and oligomer, and functional group which can be cross-linked with hardening resin is especially preferable. It is preferable that the amount of soil-resistant material to be added is minimum amount which is necessary to exhibit the soil-resistant performance.