Abstract:
A variable mirror accurately mountable and capable of maintaining constant an optical path, comprising a first substrate having a reflective part reflecting light and a second substrate opposed to the first substrate and having portions for changing at least one of the shape and attitude of the reflective part. The second substrate further comprises a mounting area for a mounted member formed on the side of the second substrate opposed to the first substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a Continuation Application of PCT Application No. PCT/JP2004/007640, filed May 27, 2004, which was published under PCT Article 21(2) in Japanese.  
         [0002]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-163925, filed Jun. 9, 2003, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates to a variable mirror, and in particular, to a variable mirror used to correct for example, image blur in an image capture apparatus (camera shake).  
         [0005]     2. Description of the Related Art  
         [0006]     Jpn. Pat. Appln. KOKAI Publication No. 2002-214662 proposes a variable mirror having a reflection surface the tilt angle of which is varied by an electrostatic force, as means for correcting image blur in an image capture apparatus. Jpn. Pat. Appln. KOKAI Publication No. 11-258678 discloses an image capture apparatus having a bending optical system in a lens barrel module.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     A variable mirror according to a first aspect of the present invention comprises a first substrate having a reflection portion which reflects light and a second substrate located opposite the first substrate and having a part used to vary at least one of a shape and a position of the reflection portion, wherein the second substrate has an attachment area on a surface of the second substrate, which is located opposite the first substrate.  
         [0008]     A variable mirror according to a second aspect of the present invention comprises a first substrate having a reflection portion which reflects light and a second substrate located opposite the first substrate, the variable mirror being configured so that the first substrate and the second substrate interact with each other, wherein the second substrate has a projecting portion on a surface of the second substrate, which is located opposite the first substrate. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0009]      FIG. 1  is a perspective view schematically showing the external configuration of an image capture apparatus in accordance with first and second embodiments of the present invention.  
         [0010]      FIG. 2  is a block diagram showing the configuration of the image capture apparatus in accordance with the first and second embodiments of the present invention.  
         [0011]      FIG. 3  is a diagram illustrating the principle of image blur correction in the image capture apparatus in accordance with the first and second embodiments of the present invention.  
         [0012]      FIG. 4  is a diagram showing an example of the configuration of a variable mirror in accordance with the first embodiment of the present invention.  
         [0013]      FIGS. 5A and 5B  are diagrams showing an example of arrangement of electrodes in the variable mirror in accordance with the first embodiment of the present invention.  
         [0014]      FIG. 6  is a diagram showing how the variable mirror in accordance with the first embodiment of the present invention is attached.  
         [0015]      FIG. 7  is a sectional view showing an example of the configuration of a variable mirror in accordance with the second embodiment of the present invention.  
         [0016]      FIG. 8  is a perspective view showing an example of the configuration of the variable mirror in accordance with the second embodiment of the present invention.  
         [0017]      FIGS. 9A  to  9 E are sectional views showing an example of a method for manufacturing the variable mirror in accordance with the second embodiment of the present invention.  
         [0018]      FIG. 10  is a diagram showing how the variable mirror in accordance with the second embodiment of the present invention is attached.  
         [0019]      FIG. 11  is a perspective view showing another example of the configuration of the variable mirror in accordance with the second embodiment of the present invention.  
         [0020]      FIG. 12  is a perspective view showing an example of the configuration of a lower substrate in the variable mirror in accordance with the first embodiment of the present invention.  
         [0021]      FIG. 13  is a perspective view of a variation of the variable mirror in accordance with the first embodiment of the present invention.  
         [0022]      FIG. 14  is a perspective view of a variation of the variable mirror in accordance with the first embodiment of the present invention.  
         [0023]      FIG. 15  is a perspective view of a variation of the variable mirror in accordance with the first embodiment of the present invention.  
         [0024]      FIGS. 16A and 16B  are diagrams showing positions at which springs are arranged in accordance with the first embodiment of the present invention.  
         [0025]      FIGS. 17A and 17B  are diagrams showing a variation of the variable mirror in accordance with the first embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     Embodiments of the present invention will be described below with reference to the drawings.  
       First Embodiment  
       [0027]      FIG. 1  is a perspective view schematically showing the external configuration of a digital camera (image capture apparatus) in accordance with a first embodiment of the present invention.  FIG. 2  is a block diagram showing the configuration of the digital camera in accordance with the first embodiment.  
         [0028]     A shutter button  102  is provided at the top of a main body  101  of a digital camera  100 . A three-axis acceleration sensor  103  and an angular velocity sensor  104  (including sensors  104   a  and  104   b ) are provided inside the main body  101 ; the three-axis acceleration sensor  103  detects a translation component of motion and the angular velocity sensor  104  detects a rotation component of motion.  
         [0029]     A lens barrel module  105  is provided with a first group lens  106 , a second group lens  107 , a third group lens  108 , a fourth group lens  109 , a diaphragm  110 , and a variable mirror  111 . Light for a subject image passes through the first group lens  106  and second group lens  107  and is then reflected by the variable mirror  111 . The light further passes through the third group lens  108  and fourth group lens  109  and is then formed into the subject image on a CCD (imaging device)  112 . CCD  112  photoelectrically converts the resulting subject image into an electric signal. An optical axis traveling from the first group lens  106  to the variable mirror  111  corresponds to a Y axis shown in  FIG. 1 . An optical axis traveling from the variable mirror  111  to CCD  112  corresponds to a Z axis.  
         [0030]     A controller  113  controls the whole digital camera. A control program is pre-stored in ROM in a memory  114 . The memory  114  also includes RAM used as a working storage area when the control program is executed.  
         [0031]     A zoom control section  115  controls the second group lens  107  on the basis of instructions from the controller  113 . A zoom control section  116  controls the third group lens  108  and the fourth group lens  109  on the basis of instructions from the controller  113 . These control operations adjust the angle of view. A focus control section  117  drives the fourth group lens  109  on the basis of instructions from the controller  113  for focusing. A diaphragm control section  118  controls the diaphragm  110  on the basis of instructions from the controller  113 .  
         [0032]     A mirror control section  119  varies the tilt angle of a reflection surface of the mirror  111  on the basis of instructions from the controller  113 . The tilt angle is controlled on the basis of output signals from the three-axis acceleration sensor  103  and the angular velocity sensor  104 . The present digital camera  100  also comprises a distance detecting section  120  that detects the distance to the subject. Distance information form a distance detecting section  120  is also used to control the tilt angle. Image blur during image capturing is corrected by thus controlling the tilt angle of the mirror  111 . This will be described below in detail.  
         [0033]     A control circuit  121  controls CCD  112  and an image capture processing section  122  on the basis of instructions from the controller  113 . The image capture processing section  122  includes a CDS (Correlated Double Sampling) circuit, an AGC (Automatic Gain Control) circuit, and ADC (Analog to Digital Converter). The image capture processing section  122  executes a predetermined process on an analog signal output by CCD  112  and converts the processed analog signal into a digital signal.  
         [0034]     The signal processing section  123  executes a process such as white balancing or γ correction on image data output by the image capture processing section  122  or a compression/decompression processing section  124 . The signal processing circuit  123  also includes an AE (Automatic Exposure) detection circuit or an AF (Automatic Focus) detection circuit.  
         [0035]     The compression/decompression processing section  124  executes a compressing process and a decompressing process on image data. The compression/decompression processing section  124  executes a compressing process on image data output by the signal processing section  123  and a decompressing process on image data output by a card interface (I/F)  125 . The compressing process and the decompressing process are executed on image data using for example, a JPEG (Joint Photographic Experts Group) system. The card I/F  125  enables transmissions between the present digital camera  100  and a memory card  126 . The card I/F  125  writes and reads image data. The memory card  126  is semiconductor recording media for data recording. The memory card  126  can be installed in and removed from the present digital camera  100 .  
         [0036]     DAC (Digital to Analog Converter)  127  converts a digital signal (image data) output by the signal processing section  123 , into an analog signal. A liquid crystal display monitor  128  displays an image on the basis of the analog signal output by DAC  127 . The liquid crystal display monitor  128  is provided on a rear surface of the camera main body  101 . A user can capture an image while viewing the liquid crystal display monitor  128 .  
         [0037]     An interface section (I/F section)  129  enables transmissions between the controller  113  and a personal computer (PC)  130 . The interface section  129  is for example, an interface circuit for USB (Universal Serial Bus). When the present digital camera is manufactured, the personal computer  130  is used to write data required to correct the focus sensitivity of CCD  112 , to the memory  114  and to pre-provide the mirror control section  119  with various data. Accordingly, the personal computer  130  does not constitute the present digital camera  100 .  
         [0038]     Now, with reference to  FIG. 3 , description will be given of the principle of image blur correction in the present digital camera.  
         [0039]     In  FIG. 3 , it is assumed that the digital camera is swung from a camera position A to a camera position B around a reference point S (for example, the position of the user&#39;s shoulder) within a predetermined time of exposure. In this case, a swing angle θ is determined by integrating output signals from the angular velocity sensor  104 . However, since the swing center (reference point S) is located away from the camera, the angle θ is smaller than that to be actually corrected. It is thus necessary to add the angle θ to an angle φ to determine an angle (θ+φ).  
         [0040]     The angle φ can be determined as described below. If θ is sufficiently small, it is possible to determine a movement b′ approximate to the movement b, in the X axis direction, of the central position of the camera by twice integrating output signals for the X axis direction (see  FIG. 1 ) of the three-axis acceleration sensor  103 . The distance detecting section  120  can determine the distance a from the camera to the subject. Once the movement b′ and the distance a are found, the angle φ can be determined from arctan(b′/a). By thus finding the actually required corrected angle (θ+φ), it is possible to determine the corrected tilt angle for the mirror  111 . The image blur can thus be corrected appropriately.  
         [0041]     The distance a to the subject can be determined by an auto focus operation performed before the start of image capturing. Further, if detection is carried out at a sampling rate of for example, 2 kHz, sampling interval is 0.5 milliseconds. The rotation amount  0  during 0.5 milliseconds is sufficiently small. This enables the above correction process to be achieved sufficiently precisely.  
         [0042]      FIG. 4  is a diagram showing an example of the configuration of the variable mirror  111  in accordance with the present embodiment.  FIGS. 5A and 5B  are diagrams showing an example of an electrode arrangement in the variable mirror  111 . The variable mirror  111  shown in  FIGS. 4, 5A , and  5 B is produced using what is called a MEMS (Micro Electro-Mechanical System) technique to which a semiconductor manufacturing technique is applied.  
         [0043]     As shown in  FIG. 4 , the variable mirror  111  comprises an upper substrate  201 , a lower substrate  221  placed opposite the upper substrate  201 , and springs (elastic members)  251  to  254  each having opposite ends connected to the upper substrate  201  and lower substrate  221 . The lower substrate  221  has a pivot (projecting portion)  261  that abuts against the substantial center of gravity of the upper substrate  201  to support the upper substrate  201 . In the present example, the center of gravity of the upper substrate  201  almost corresponds to a central position of the upper substrate  201 .  
         [0044]     As shown in  FIG. 12 , in the present example, the pivot  261  is manufactured separately from the main body of the lower substrate  221 . The pivot  261  is then bonded to the main body of the lower substrate  221 . A tip portion of the pivot  261  is formed like a substantial sphere. Further, a concave portion  250  is formed in the substantial center of gravity (central position) of the upper substrate. That is, the concave portion  250  is formed at a position against which the tip of the pivot  261  abuts. A bottom portion of the concave portion  250  has a slightly larger curvature than the tip portion of the pivot  261 .  
         [0045]     As shown in  FIG. 5A , the upper substrate  201  comprises an upper electrode  202  and an external lead electrode  203 . The upper electrode  202  is separated and electrically insulated from the concave portion  250 . A reflection portion  204  is provided on a surface of the upper substrate  201  which is located opposite the surface on which the upper electrode  202  is formed. The reflection portion  202  reflects and guides light from the subject to CCD. The upper electrode  202  is provided parallel to a reflection surface of the reflection portion  204  so as to be sandwiched between thin films  205 . As shown in  FIG. 5A , the upper electrode  202  is formed almost like a rectangle. The external lead electrode  203  is used to electrically connect the upper electrode  202  to an external component. A surface of the external lead electrode  203  is exposed.  
         [0046]     In the lower substrate  221 , the semiconductor substrate  230  is provided with four lower electrodes  222  to  225  and four external lead electrodes  226  to  229 . The lower electrodes  222  to  225  are provided opposite the upper electrode  202  so that the lower electrodes  222  to  225  are substantially symmetric with respect to the pivot  261 . The lower electrodes  222  to  225  are sandwiched between thin films  231  and separated and electrically insulated from the pivot  261 . The external lead electrodes  226  to  229  are used to electrically connect the lower electrodes  222  to  225  to external components. Surfaces of the external lead electrodes  226  to  229  are exposed.  
         [0047]     The four springs  251  to  254  are arranged between the upper substrate  201  and the lower substrate  221 . The upper substrate  201  and the lower substrate  221  are connected together via the springs  251  to  254 . The four springs  251  to  254  are arranged on substantially the same circumference at substantially equal intervals (periods of 90°). The pivot  261  is placed at a position corresponding to the center of the four springs  251  to  254 , that is, the center of the four lower electrodes  222  to  225  (the intersecting point between an X axis and an Y axis in  FIG. 5B ).  FIG. 16A  is a diagram showing positions P 1  to P 4  at which the springs are arranged, with respect to the upper substrate  201 .  FIG. 16B  is a diagram showing the positions P 1  to P 4  at which the springs are arranged, with respect to the lower substrate  221 . The upper substrate  201  and the lower substrate  221  are pulled toward each other by the springs  251  to  254 . The tensile force of the springs causes the pivot  261  to press the center of gravity of the upper electrode  201 .  
         [0048]     In the variable mirror  111  configured as described above, the tilt of the upper substrate  201  relative to the lower substrate  221  can be electrostatically varied by using the difference between a potential applied to the upper electrode  202  and a potential applied to each of the lower electrodes  222  to  225 . This varies the tilt angle (reflection angle) of the reflection portion  204  (that is, varies the position (posture) of the reflection portion  204 ). Image blur can thus corrected by controlling the tilt angle.  
         [0049]     In the example shown in  FIGS. 4, 5A , and  5 B, the upper electrode is composed of a single electrode, whereas the lower electrode is divided into a plurality of pieces. In contrast, the lower electrode may be composed of a single electrode, whereas the upper electrode may be divided into a plurality of pieces.  
         [0050]     It is also possible to use a variation such as the one shown in  FIGS. 13 and 14 . In the present variation, as shown in  FIG. 13 , the upper electrode  202  is in electric communication with the concave portion  250 . Further, as shown in  FIG. 14 , a lead electrode  234  is connected to the conductive pivot  261 . This configuration enables the lead electrode  234  to supply a voltage to the upper electrode  202  via the pivot  261  and concave portion  250 . That is, the potential of the upper electrode  202  becomes equal to that of the pivot  261 . It is thus possible to omit a feeding line to the upper electrode  202 . This makes it possible to prevent the degradation of controllability resulting from the spring property of the feeding line and to reduce costs.  
         [0051]     Such a variation as shown in  FIG. 15  can also be used. In the above example, the pivot  261  is manufactured separately from the main body of the lower substrate  221  and bonded to the substrate. However, in the present variation, a semiconductor manufacturing process or the like is used to form the pivot  261  integrally with the main body of the lower substrate  221 . In this case, the curvature of the tip portion of the pivot  261  can be set at about several tens of nanometers by applying a process equivalent to that for a cantilever used in AFM (Atomic Force Microscope).  
         [0052]     Furthermore, in the above example, the tilt of the upper electrode  201  relative to the lower substrate  221  is varied using the electrostatic force (attractive force) acting between the upper electrode  202  and the lower electrodes  222  to  225 . However, the tilt may be varied using an electromagnetic force.  FIGS. 17A and 17B  are diagrams showing examples of the configurations of the upper substrate  201  and lower substrate  221 , respectively, when electromagnetic force is used.  
         [0053]     As shown in  FIG. 17A , magnets  271  to  274  are provided on the upper substrate  201 . As shown in  FIG. 17B , coils  281  to  284  are provided on the lower substrate  221  at positions corresponding to the magnets  271  to  274 . External lead electrodes  285   a  and  285   b  are connected to the opposite ends of the coil  281 . External lead electrodes  286   a  and  286   b  are connected to the opposite ends of the coil  282 . External lead electrodes  287   a  and  287   b  are connected to the opposite ends of the coil  283 . External lead electrodes  288   a  and  288   b  are connected to the opposite ends of the coil  284 . By controlling a current flowing through each coil, it is possible to vary the electromagnetic force (attractive force and repulsive force) exerted between the upper substrate  201  and the lower substrate  221 . This enables the variation of the tilt of the upper substrate  201  relative to the lower substrate  221 .  
         [0054]     If the above variable mirror  111  is attached to a lens barrel (attached member) in an image capture apparatus, an attachment area  240  is provided on a surface of the lower substrate  221  which lies opposite the upper substrate  201 , that is, the top surface of the lower substrate  221 . The attachment area  240  is then tightly contacted with the lens barrel. As shown in  FIGS. 4, 5A , and  5 B, the lower substrate  221  has a larger area than the upper substrate  201 . The lower substrate  221  thus has an area that does not overlap the upper electrode  201 . Thus, the non-overlapping area can be partly used as the attachment area.  
         [0055]      FIG. 6  is a diagram schematically showing how the above variable mirror  111  is attached to a lens barrel in an image capture apparatus. As shown in  FIG. 6 , the variable mirror  111  is fixed to a lens barrel  150  so that the top surface of the lower substrate  221  abuts against an outer surface of the lens barrel  150 .  
         [0056]     If the variable mirror  111  is attached to the lens barrel  150 , what is important is the precision of position of the reflection portion (reflection surface)  204  of the variable mirror  111  with respect to the lens barrel  150 . The upper substrate  201  of the variable mirror  111  is movable. Accordingly, if the upper substrate  201  is attached to the lens barrel  150 , the variable mirror  111  cannot be appropriately controlled. Further, if the bottom surface of the lower substrate  221  is used for attachment, it is difficult to improve the precision of position of the reflection portion  204  of the variable mirror  111  owing to a variation (tolerance) in the thickness of the semiconductor substrate used for the lower substrate  221 .  
         [0057]     The present embodiment uses the top surface of the lower substrate  221  for attachment. This makes it possible to avoid the above problems and improve the positional precision of the reflection portion  204 . Further, the attachment is carried out using the area of the lower substrate  221  which does not overlap the upper substrate  201 . The variable mirror  111  can be is workably easily attached to the lens barrel  150 .  
         [0058]     The present embodiment provides the pivot  261 , which abuts against the position of center of gravity of the upper substrate  201 . Consequently, even with a variation in the tilt angle of reflection portion  204  of the variable mirror  111 , a fixed distance is maintained between the lower substrate  221  and the center of gravity of the upper substrate  201 . This enables a fixed optical path length to be maintained in a central portion. Therefore, the control of the focus or the like can be simplified without the need for considerations for a variation in optical path length.  
       Second Embodiment  
       [0059]     Now, description will be given of a second embodiment of the present invention. The basic configuration of the image capture apparatus shown in FIGS.  1  to  3 , the principle of image blur correction, and the like are similar to those in the first embodiment. Accordingly, their description is omitted.  
         [0060]      FIG. 7  is a sectional view showing an example of the configuration of the variable mirror  111  in accordance with the present embodiment.  FIG. 8  is a perspective view showing an example of the configuration of the variable mirror  111  in accordance with the present embodiment. The variable mirror  111 , shown in  FIG. 7  and  8 , is produced using the MEMS technique to which the semiconductor manufacturing technique is applied.  
         [0061]     As shown in  FIGS. 7 and 8 , the variable mirror  111  comprises an upper substrate  301 , a lower substrate  321  placed opposite the upper substrate  301 , and a spacer member  341  placed between the upper substrate  301  and the lower substrate  321  to define a spacing (distance) between the upper substrate  301  and the lower substrate  321 .  
         [0062]     The upper substrate  301  has a silicon dioxide thin film (insulating thin film)  303  and a reflection film electrode  304  stacked on one principal surface of a silicon substrate (semiconductor substrate)  302  and a silicon dioxide thin film  305  formed on the other principal surface of the silicon substrate (semiconductor substrate)  302 . A void  306  is formed in a central portion of the silicon substrate  302 . Parts of the silicon dioxide thin film  303  and reflection film electrode  304  which correspond to the void  306  function as an effective reflection portion  307 .  
         [0063]     The lower substrate  321  has an opposite electrode  323  formed on an insulating substrate  322  such as glass and formed of a conductive thin film.  
         [0064]     In the variable mirror  111  configured as described above, the reflection portion  307  is electrostatically deformed into a concave dented toward the opposite electrode  323  when there is a potential difference between the reflection film electrode  304  and the opposite electrode  323 . Then, the displacement of the reflection portion  307  varies (that is, the shape of the reflection portion  307  varies) depending on the potential difference between the reflection film electrode  304  and the opposite electrode  323 . This in turn varies the reflection angle of the reflection portion  307 . Therefore, image blur can be corrected by controlling the displacement of the reflection portion  307 .  
         [0065]     If the above variable mirror  111  is attached to the lens barrel in the image capture apparatus, an attachment area  330  is provided on a surface of the lower substrate  321  which lies opposite the upper substrate  301 , that is, the top surface of the lower substrate  321 . The attachment area  330  is then tightly contacted with the lens barrel. As shown in  FIGS. 7 and 8 , the lower substrate  321  has a larger area than the upper substrate  301 . The lower substrate  321  thus has an area that does not overlap the upper electrode  301 . Thus, the non-overlapping area can be partly used as the attachment area.  
         [0066]     Now, with reference to  FIGS. 9A  to  9 E, description will be given of a method for manufacturing the above variable mirror  111 .  
         [0067]     First, as shown in  FIG. 9A , a silicon substrate (silicon wafer)  302  is provided which has mirror-polished opposite surfaces and a plane direction &lt;100&gt;. Silicon dioxide thin films  303  and  305  of thickness about 400 to 500 nm are formed on the respective surfaces of the silicon substrate  302 . Subsequently, a gold thin film  304  of thickness about  100  nm is formed on the silicon dioxide thin film  303 .  
         [0068]     Then, as shown in  FIG. 9B , a photo resist pattern  311  having a circular opening is formed on the silicon dioxide thin film  305 . Subsequently, with the bottom surface of the substrate protected, the silicon dioxide thin film  305  is etched using the photo resist pattern  311  as a mask. A window corresponding to the opening in the photo resist pattern  311  is formed in the silicon dioxide thin film  305 . For example, a fluoro acid-based etchant can be used for etching.  
         [0069]     Then, as shown in  FIG. 9C , the substrate is immersed into a water solution of ethylene diamine picatechol to etch the silicon substrate  302 . The etching of the silicon substrate  302  starts from the window formed in the silicon dioxide thin film  305  and ends when the silicon dioxide thin film  303  is exposed. Thus, a void  306  is formed in the central portion of the silicon substrate  302 . A reflection portion  307  is formed in the area corresponding to the void  306 ; the reflection portion  307  includes the silicon dioxide thin film  303  and the reflection film electrode  304 . In this manner, the upper substrate  301  is obtained.  
         [0070]     On the other hand, as shown in  FIG. 9D , a glass substrate  322  of thickness about 300 μm is provided. An opposite electrode  323  is formed on the glass substrate  322 ; the opposite electrode  323  being formed of a metal film of thickness about 100 nm. In this manner, the lower substrate  321  is obtained.  
         [0071]     After the upper substrate  301  and the lower substrate  321  are thus formed, the spacer member  341  is interposed between the upper substrate  301  and the lower substrate  321  as shown in  FIG. 9E ; the spacer member  341  is made of polyethylene and has a thickness of about 100 nm. The upper substrate  301  and the lower substrate  321  are then bonded together by the spacer member  341 .  
         [0072]     As described above, such a variable mirror  111  as shown in  FIGS. 7 and 8  is produced.  
         [0073]      FIG. 10  is a diagram-schematically showing how the above variable mirror  111  is attached to the lens barrel in the image capture apparatus. As shown in  FIG. 10 , the variable mirror  111  is fixed to the lens barrel  150  so that the top surface of the lower substrate  321  abuts against the outer surface of the lens barrel  150 .  
         [0074]     As already described, if the variable mirror  111  is attached to the lens barrel  150 , what is important is the precision of position of the reflection portion (reflection surface)  307  of the variable mirror  111  with respect to the lens barrel  150 . If the upper substrate  301  is used for attachment, it is difficult to increase the positional precision of reflection portion  307  of the variable mirror  111  because of for example, a variation (tolerance) in the thickness of the semiconductor substrate used as the upper substrate  301  or warpage that may occur during a manufacturing process. On the other hand, if the bottom surface of the lower substrate  321  is used for attachment, it is also difficult to increase the positional precision of reflection portion  307  of the variable mirror  111  because of for example, a variation in the thickness of the lower substrate  321 .  
         [0075]     In contrast, if the top surface of the lower substrate  321  is used for attachment, it is possible to very precisely manage the spacing between the top surface of the lower substrate  321  and the bottom surface of the upper substrate  301  by using a member with a high dimensional precision (for example, precisely formed glass beads) as the spacer member  341 . Further, the glass substrate used as the lower substrate  321  generally has a high flatness. The positional precision of the reflection portion  307  can thus be increased by using the top surface of the lower substrate  321  for attachment as in the present embodiment. According to the present embodiment, as in the case of the first embodiment, the attachment is carried out using the area of the lower substrate  321  which does not overlap the upper electrode  301 . Therefore, the variable mirror  111  can be workably easily attached to the lens barrel  150 .  
         [0076]      FIG. 11  is a perspective view showing another example of configuration of the variable mirror  111  in accordance with the present embodiment. In the example shown in  FIGS. 7 and 8 , the attachment area  330  is provided at the opposite ends of the lower substrate  321 . However, in the present example, the attachment area  330  is provided in the four corners of the lower substrate  321 . That is, notch portions  315  are formed in the four corners of the upper substrate  301 , and the attachment areas  330  are provided in association with the notch portions  315 . The notch portions  315  can be formed by etching away the four corners of the upper substrate  301  before or after the upper substrate  301  is laminated to the lower substrate  321 .  
         [0077]     The use of such a configuration as shown in  FIG. 11  also makes it possible to exert effects similar to those of the example shown in  FIGS. 7 and 8 . The size of the lower substrate  321  can be reduced by forming notch portions  315  and providing the attachment areas  330  in association with the notch portions  315 .