fig1 is a cross - sectional diagram showing a structure of a varifocal lens relating to an embodiment of the present invention . this varifocal lens 10 has a first liquid chamber 14 which accommodates a first liquid 12 ( corresponding to a “ first liquid ”) and a second liquid chamber 24 which accommodates a second liquid 22 ( corresponding to a “ second liquid ”). a circular opening 18 is formed in a partition plate 16 which divides ( demarcates ) the first liquid chamber 14 from the second liquid chamber 24 , and a sealed vessel 26 structure is obtained in which the first liquid chamber 14 and the second liquid chamber 24 are mutually connected via the opening 18 . the first liquid 12 which is filled into the first liquid chamber 14 and the second liquid 22 which is filled into the second liquid chamber 24 have respectively different refractive indices , and are mutually immiscible liquids . these two types of liquid ( 12 , 22 ) make contact with each other at the location of the opening 18 in the partition plate 16 , and a two - liquid interface 30 is formed at this opening 18 . this interface 30 forms a refractive surface which refracts light , and serves ( functions ) as a lens . more specifically , an interface 30 between the first liquid 12 and the second liquid 22 is formed at the opening 18 , and a lens section 31 having this interface 30 as a refractive surface is formed . if used as a convex lens , the refractive index of the lower liquid ( the first liquid ) is greater . in fig1 , the first chamber structure 32 which demarcates a bottom face and side faces of the first liquid chamber 14 includes a bottom plate member 33 which seals the bottom face of the first liquid chamber 14 and a side wall member 34 which covers the side faces of the first liquid chamber 14 . similarly , the second chamber structure 42 which demarcates a ceiling face and side faces of the second liquid chamber 24 includes a ceiling plate member 43 which seals the ceiling face of the second liquid chamber 24 and a side wall member 44 which covers the side faces of the second liquid chamber 24 . the bottom plate member 33 and the ceiling plate member 43 are both members which ensure sealing properties for enclosing the liquid , as well as having light transmitting properties that allow light to enter into the lens section 31 and exit to the exterior after having passed through the lens section 31 . the side wall members 34 , 44 may be members having light transmitting properties ( transparent members ) or may be members not having light transmitting properties ( opaque members ). in the case of the present embodiment , the side wall member 34 is made of a transparent glass material which is integrated with the base plate member 33 . furthermore , the side wall member 44 is made of a transparent glass material which is integrated with the ceiling plate member 43 . for example , it is possible to obtain the first chamber structure 32 by forming a recess section ( corresponding to the “ first recess section ”) which forms a space for the first liquid chamber 14 by cutting out ( grinding down ) one surface of a glass substrate . similarly , it is possible to obtain the second chamber structure 42 by forming a recess section ( corresponding to the “ second recess section ”) which forms a space for the second liquid chamber 24 by cutting out ( grinding down ) one surface of a glass substrate . by coupling the first chamber structure 32 and the second chamber structure 42 via the partition plate 16 , a sealed vessel 26 having a first liquid chamber 14 and a second liquid chamber 24 is formed . a piezoelectric actuator 50 having a diaphragm structure is provided as a device for changing the shape of the lens section 31 ( in other words , the shape of the interface 30 ), in a portion of the partition plate 16 which is disposed inside the sealed vessel 26 . this portion of the piezoelectric actuator 50 corresponds to an “ elastic deformation section ”. the piezoelectric actuator 50 has a structure in which a piezoelectric element 53 ( corresponding to a “ drive section ”) is formed on top of a diaphragm 52 . in other words , the piezoelectric actuator 50 has a structure in which a lower electrode 54 , a piezoelectric film 56 and an upper electrode 58 are layered in this order on a diaphragm 52 . the piezoelectric element 53 is formed by a layer structure in which a piezoelectric film 56 is interposed between the lower electrode 54 and the upper electrode 58 . the piezoelectric element 53 can be manufactured by thin film forming technology , such as bonding of bulk ceramic , sputtering , a sol - gel method , or the like . various methods can be used as a method for forming a piezoelectric film on the diaphragm , but sputtering and a sol - gel method are desirable from the viewpoint of being able to form a film at low temperature in order to reduce stress and being able to form a thin film of not less than several μm thickness , which has a high drive torque . in fig1 , in order to simplify the description , the film thickness ratios are depicted differently to the actual ratios , in order to emphasize the visual appearance of each layer . to give one example of the implemented dimensions , the film thickness of the piezoelectric film 56 is 2 to 3 μm , and the film thickness of each electrode ( 54 , 58 ) is 0 . 2 μm . therefore , the surface undulation caused by the layered structure in which a piezoelectric element 53 is formed on top of the diaphragm 52 is extremely small . the first liquid chamber 14 side of the diaphragm 52 contacts with the first liquid 12 . on the other hand , the side of the diaphragm 52 on which the piezoelectric element 53 is formed ( the upper surface side in fig1 ) contacts the second liquid 22 in the second liquid chamber 24 . the first liquid 12 and the second liquid 22 are sealed completely inside the lens ( inside the sealed vessel 26 ), and therefore it is possible to prevent evaporation of the liquid due to contact with the air , without the liquid leaking to the exterior . moreover , according to the structure of the present embodiment , looking in particular at the portion of the diaphragm 52 , the volume of the first liquid chamber 14 is decreased in accordance with the removed volume produced by the bending and deformation of the diaphragm 52 in the downward direction in fig1 , and the volume of the second liquid chamber 24 is increased on the upper side of the diaphragm 52 in accordance with the decrease in volume of the first liquid chamber 14 . in other words , if the amount of volume change of the first liquid chamber 14 due to displacement of the diaphragm 52 is δv1 , and the amount of volume change of the second liquid chamber 24 is δv2 , a volume increase being indicated by a “+” symbol and a volume decrease being indicated by a “−” symbol , then the relationship therebetween is δv1 =− δv2 . in this case , in the lens section 31 , the first liquid 12 presses the interface 30 upward in accordance with the decrease in the volume of the first liquid chamber 14 and the second liquid 22 is retracted accordingly . in this way , it is possible to change the shape ( curvature ) of the interface 30 by changing the diaphragm 52 in such a manner that the focal length of the lens section 31 can be changed . furthermore , as described above , if the focal length is changed , then the interface 30 of the lens section 31 can be driven in a resistance - free state , and therefore residual vibration of the lens section 31 can be suppressed . by this means , it becomes possible to achieve high - speed response in the lens . furthermore , the interface 30 is close to an ideal spherical surface shape due to surface tension , and hence a lens having high resolving power is obtained . fig2 shows an example of the composition of a piezoelectric actuator 50 . for the device which causes the diaphragm 52 to deform elastically , an actuator employing a piezoelectric element such as that shown in fig2 is used . as shown in fig2 , this piezoelectric actuator 50 is an actuator having a diaphragm structure constituted by layering a lower electrode 54 , a piezoelectric film 56 and an upper electrode 58 on top of a diaphragm 52 . this actuator is a so - called unimorph type actuator in which the periphery of a movable portion of the diaphragm 52 is supported ( fixed ) by a supporting body 60 , and the diaphragm 52 bends due to displacement of the piezoelectric film 56 in the d31 direction . the supporting body 60 can be realized by a thick portion of the partition plate 16 which is described in relation to fig1 . furthermore , in fig2 , the portion of the piezoelectric film where a voltage is not applied ( in other words , the portion where the upper electrode 58 does not exist ) is removed by etching , thus making it possible to drive the diaphragm 52 efficiently . in the present embodiment , the shape of the diaphragm 52 which forms a movable part capable of performing elastic deformation is a square shape in plan view , and the width of the opening of the supporting body 60 is expressed as d in fig2 ( the length of one edge of the square diaphragm ). next , one example of a method of manufacturing a varifocal lens 10 relating to the present embodiment will be described . a varifocal lens according to one example of the present embodiment of the present invention was manufactured by the following steps . firstly , an soi ( silicon on insulator ) substrate having a 10 μm - thick active layer , a 1 μm - thick oxide film and a 500 μm - thick supporting body layer was prepared , and by etching the supporting body layer , a diaphragm ( reference numeral 52 in fig1 ) constituted by the active layer and the oxide film was fabricated . moreover , by then etching the whole of the supporting body layer , the oxide layer and the active layer to form a through hole , an opening ( reference numeral 18 in fig1 ) corresponding to the lens section ( reference numeral 31 in fig1 ) was manufactured . the size ( in plan view ) of the diaphragm manufactured in this step was a 1 mm square shape ( a square shape having edges of length d = 1 mm ), and the opening of the lens section was a circular shape having a diameter of 3 mm . next , a piezoelectric element was formed by depositing a lower electrode , a piezoelectric film and an upper electrode by sputtering , on top of the diaphragm , and the center of the 1 mm - square diaphragm was patterned to produce an 800 μm - square shape . fig3 shows a partial enlarged diagram of a piezoelectric actuator . in fig3 , elements which are the same as or similar to fig2 are labeled with the same reference numerals and further explanation thereof is omitted here . in fig3 , reference numeral 61 represents a supporting body layer and reference numeral 51 represents an oxide film ( sio 2 film ), and reference numeral 62 represents an active layer ( si layer ). in this step , a “ diaphragm ” was formed by the layered body of the oxide film 51 and the active layer 62 corresponding to the region where the supporting body layer 61 had been removed by etching ( the region which was capable of elastic deformation ). the member corresponding to the partition plate 16 illustrated in fig1 was obtained by means of steps 1 and 2 described above . it is also possible to further remove the oxide film 51 so as to form a diaphragm by means of the active layer 62 only , and it is also possible to adopt a mode which uses a silicon substrate instead of an soi substrate . next , glass substrates in each of which a groove ( recess section ) had been excavated ( the first chamber structure 32 and the second chamber structure 42 shown in fig1 ) were prepared as vessels for accommodating the first liquid 12 and the second liquid 22 . two through holes were formed in the glass vessel which accommodates the second liquid 22 ( the second chamber structure 42 ), as an inlet port and an outlet port for filling liquid ( see fig4 a , where reference numeral 72 denotes an inlet port and reference numeral 74 denotes an outlet port ). the partition plate 16 ( soi substrate ) obtained in step 2 and the glass vessels ( first chamber structure 32 and second chamber structure 42 ) prepared in step 3 were bonded together by epoxy adhesive . more specifically , an adhesive was applied to a thickness of about 2 μm on the bonding surfaces of the soi substrate and the glass vessels , and the soi substrate and the glass vessels were bonded together . in this step , wires for the lower electrode 54 and the upper electrode 58 were laid so as to extend to the exterior of the sealed vessel 26 which is enclosed in glass ( see fig4 a to 4d ). next , valves 82 and 84 connected to tubes 76 and 78 along which liquid can flow were fixed by epoxy adhesive bonding , to the portions of the second chamber structure 42 corresponding to the inlet port 72 and the outlet port 74 ( see fig4 a to 4d ). in this way , a vessel structure such as that shown in fig4 a was obtained . the valve 82 provided with the inlet port 72 corresponds to a “ first valve ”, and the valve 84 provided with the outlet port 74 corresponds to a “ second valve ”. fig5 shows a plan view perspective diagram for reference purposes . in fig5 , reference numeral 55 denotes a wiring electrode which is connected to the lower electrode 54 , and reference numeral 59 denotes a wiring electrode which is connected to the upper electrode 58 . the inlet port 72 and the outlet port 74 are desirably formed in corners of a diagonal of the substantially rectangular - shaped second liquid chamber 24 when observed in plan view , as shown in fig5 . by adopting an arrangement of this kind , the air inside the vessel is expelled readily to the exterior when liquid is introduced . firstly , pure water ( specific gravity 1 , refractive index 1 . 33 ) ( which corresponds to a “ first liquid ”) was introduced from the inlet port 72 via a tube 76 in a state where both valves 82 and 84 were open , and the pure water was filled into the first liquid chamber 14 and the second liquid chamber 24 ( see fig4 b ). in this step , the pure water was filled into the vessel after being sufficiently deaerated . next , a mixed solution ( specific gravity 1 , refractive index 1 . 5 ) of toluene and chlorobenzene which were oil - based liquids , was introduced slowly so as not to disturb the liquid inside the vessel ( fig4 c ). the liquid ( corresponding to the “ second liquid ”) of mixed toluene and chlorobenzene which had 44 . 4 wt % ( weight percent ) content of toluene in order to achieve a specific gravity of 1 was immiscible with pure water , and therefore , when this liquid ( hereinafter , called “ oil - based liquid ”) was introduced into the second liquid chamber 24 , the pure water that had been filled into the second liquid chamber 24 was replaced by this oil - based liquid . more specifically , the pure water which had been filled into the second liquid chamber 24 exited to the exterior from the outlet port 74 as the oil - based liquid was introduced , and was thereby replaced by the oil - based liquid . in this step , a two - liquid interface 30 was formed in the upper portion of the opening 18 ( through hole ). as shown in fig4 d , when the pure water in the second liquid chamber 24 was replaced completely with oil - based liquid , the vessel was sealed by closing the valves 82 , 84 , in the sequence of inlet port 72 followed by outlet port 74 . the operation of the varifocal lens manufactured by the procedure described above was confirmed in the following manner . a drive circuit was connected to the wiring electrodes ( see reference numerals 55 and 59 in fig5 ) extracted to the exterior of the vessel , and a 50v dc voltage was applied to the piezoelectric actuator , causing the diaphragm to deform convexly downwards in fig4 d and causing the interface 30 of the lens section 31 to deform convexly upwards . the volume change amount ( removed volume ) of the diaphragm was measured by a laser doppler vibrometer , and a change of approximately 2 pl ( picoliter ) was recorded , and hence it could be confirmed that a sufficient amount of displacement was obtained for the lens section 31 having a diameter of 3 mm . moreover , when the displacement of the diaphragm upon application of a 50 v , 1 ms pulse wave was measured with a laser doppler vibrometer , a similar amount of displacement to that achieved upon application of the dc voltage described above was obtained , and there was no residual vibration . from this , it can be seen that the diaphragm deforms within 1 ms , and therefore it could be confirmed that high - speed response is possible . in the varifocal lens manufactured by means of the procedure described above , the piezoelectric element 53 contacts the oil - based liquid , and therefore the durability of the piezoelectric element is improved . if the piezoelectric body contains lead ( pb ), then the lead dissolves into the water , thus causing deterioration of the element . according to the present embodiment , it is possible to prevent dissolution of lead into the water by causing the piezoelectric element 53 to make contact with the oil - based liquid , and therefore the lifespan of the piezoelectric element 53 can be increased . in the present embodiment , the whole of the bottom plate member 33 and the ceiling plate member 43 is made from light - transmitting members , but it is also possible to form light - transmitting window sections in portions of the bottom plate member 33 and the ceiling plate member 43 . for example , it is possible to form through holes in a portion of the bottom plate member 33 and in a portion of the ceiling plate member 43 , and to fill a transparent glass or a transparent resin into the portion of these through holes . in the embodiment described above , only one piezoelectric actuator 50 is provided inside the sealed vessel 26 , but it is also possible to adopt a mode in which a plurality of piezoelectric actuators are provided . for example , by providing a plurality of diaphragm - type piezoelectric actuators in a portion of the partition plate and driving these actuators simultaneously , it is possible to obtain a larger volume change and hence to increase the range of variation of the focal length . a varifocal lens according to embodiments of the present invention is capable of high - speed response and has high spatial resolving power , and therefore is suitable for high - speed three - dimensional scanners and omnifocal microscope systems , and the like , and is capable of high - speed tracking of moving objects . furthermore , by miniaturization , the lens can also be mounted in an electrical device , such as a portable telephone . it should be understood that there is no intention to limit the invention to the specific forms disclosed , but on the contrary , the invention is to cover all modifications , alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims .