Variable focal length lens

Technical Field

0001The present invention relates to a variable focal length lens whose focal length varies by varying a voltage applied thereto, and to a focal length adjusting device and imaging device using the same.

Background Art

0002The miniaturization of imaging devices is progressing. Imaging devices are primarily composed of a lens and an imaging sensor. In order to form an image of a subject on an imaging sensor in an imaging device, the distance between the lens and the imaging sensor may need to be adjusted depending on the distance between the subject and the imaging device. Conventionally in such cases, the distance between the lens and the imaging sensor is adjusted, for example, by moving a lens coupled to a focal length adjusting device using an actuator such as a motor. However, with this configuration, there is a problem in that the configuration of the focal length adjusting device for moving the lens via the motive power of a motor becomes complex and miniaturizing the imaging device becomes difficult.

0003In addition, Unexamined Japanese Patent Application KOKAI Publication <patcit id="pcit0001" dnum="JP2003215429A"><text>2003-215429</text></patcit> discloses a technology wherein the distance between a lens and an imaging sensor is adjusted by moving a lens holder using an actuator composed of an electrostrictive material.

0004This lens driving mechanism results in a construction that is simpler than that of a lens driving mechanism that uses an electromagnetic motor or similar device. However, guides or springs are needed to control the flexing of the electrostrictive material. For this reason, there are many component parts, and construction remains complex.

0005Instead of varying the position of the lens, lenses (lens systems) whose focal lengths can be varied are also being used. These types of lens systems comprise a plurality of single lenses. By mutually varying the positions thereof, the focal length of the lens system is varied. However, the configuration whereby the single lenses are moved in order to vary the focal length is identical to that of the above lens driving devices. Consequently, the configuration of conventional lens systems is complex, and focal length adjustment is difficult. <patcit id="pcit0002" dnum="JP62151824B"><text>JP 62151824</text></patcit> discloses vari-focal lens comprising a high polymer gel material which varies in volume with electric energy, e.g. acryl amide gel is charged in an external shell formed of a transparent high polymer elastic material. Further, electrodes are provided to the periphery of the external shell by vapor-depositing metal. In this constitution, a specific electric field is applied from the electrodes and to expand the internal material, which spreads the external shell to vary the curvature of the lens, so that the focal length varies from f2 to f1. <patcit id="pcit0003" dnum="US4989958A"><text>US 4,989,958 A</text></patcit> discloses a focus adjusting apparatus comprising a focus lens device provided in an optical system. The focus lens device comprises a transparent container of a rectangular prism form, a lens member supported in the container and formed of poly(acrylic amide) gel as a polymer gel substance having electro-reactive deformability, and a pair of transparent electrodes, the container being filled with water-aceton mixture solution. The lens member is formed by two lens materials having different proportions of acrylic acid group. A voltage is applied to the transparent electrodes under control of an automatic focusing circuit to cause electric field in the container, whereby the lens member is deformed in a concentric spherical form to form a lens.

Disclosure of Invention

Problem to be Solved by the Invention

0006It is an object of the invention to provide a variable focal length lens that is of simple construction and is miniaturizable, as well as a focal length adjusting device and an imaging device using the same. In addition, it is a further object of the invention to provide a lens whose curvature is suitably adjustable.

Means for Solving the Problem

0007The above-described object is achieved by a variable focal length lens according to claim 1. When a voltage is applied between the first electrode and the second electrode, the first layer and the second layer respectively deform so as to be drawn toward the first electrode, thereby varying the curvature of the lens.

0008The second layer may also be formed so as to be harder than the first layer.

0009The first layer and the second layer are formed from a polymer to which a plasticizer has been added. The hardness of the first layer and the second layer are mutually different as a result of being mutually different in at least one of the polymer type, the added quantity of plasticizer, or the plasticizer type.

0010The first electrode and the second electrode may also be formed as a ring shape.

0011The first electrode and the second electrode may also be configured from a plurality of electrodes divided symmetrically about the optical axis of the lens as a center.

0012The second layer may also be formed so as to cover the entire light incident surface of the first layer.

0013The variable focal length lens provided by the invention may be used for a focal length adjusting device comprising: a lens, the lens having a first layer formed from a polymer and a second layer formed from a polymer upon at least one light transmission region of the first layer, the second layer determining the curvature of the lens; a lens holder that holds the lens; a first electrode provided in a region contacting the lens in the lens holder; and a second electrode provided in a region contacting the lens in the lens holder. The first electrode and the second electrode contact at least the first layer of the lens. When a voltage is applied between the first electrode and the second electrode, the first layer and the second layer respectively deform so as to be drawn toward the first electrode, thereby varying the curvature of the lens and changing the focal length.

0014The lens holder may also be provided with a planar portion having an aperture, the lens being held in the planar portion.

0015The first electrode may be formed as a ring shape upon the planar portion, with the second electrode being formed on the inner peripheral surface of the aperture of the planar portion.

0016The first electrode may also be formed upon one face of the planar portion, with the second electrode being formed on the opposite face of the planar portion so as to cover the aperture of the planar portion, the second electrode furthermore being formed from a material provided with light transmitting properties.

0017The first electrode and the second electrode may also be configured from a plurality of electrodes divided symmetrically about the optical axis of the lens as a center.

0018The variable focal length lens of the present may be used in an imaging device, which may comprise: the focal length adjusting device ; a printed circuit board provided with the focal length adjusting device thereupon; and an imaging sensor disposed upon the printed circuit board.

Effects of the Invention

0019In the present invention, by using a variable focal length lens that deforms and whose curvature varies according to the voltage applied thereto, it becomes possible to provide a focal length adjusting device that is of simple construction and is miniaturizable, as well as an imaging device using the same. Brief Description of Drawings

0020<figref idref="f0001">Fig. 1</figref> is a cross-sectional view (taken along the dashed line A - A in <figref idref="f0002">Fig. 2</figref>) of an imaging device. <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0002">Fig. 2</figref> is a plan view of an imaging device of <figref idref="f0001">Fig. 1</figref>.</li><li><figref idref="f0003">Fig. 3</figref> is a cross-sectional view schematically showing the state wherein a voltage has been applied to a variable focal length lens provided in a focal length adjusting device that constitutes an imaging device of <figref idref="f0001">Fig. 1</figref>.</li><li><figref idref="f0004">Fig. 4(a)</figref> schematically shows the operation of a variable length focal lens of the invention.</li><li><figref idref="f0004">Fig. 4(b)</figref> schematically shows the operation of a variable length focal lens of the invention.</li><li><figref idref="f0005">Fig. 5</figref> is a cross-sectional view (taken along the dashed line B to B in <figref idref="f0006">Fig. 6</figref>) of an imaging device.</li><li><figref idref="f0006">Fig. 6</figref> is a plan view of an imaging device.</li><li><figref idref="f0007">Fig. 7</figref> is a cross-sectional view (taken along the dashed line C to C in <figref idref="f0008">Fig. 8</figref>) of an imaging device.</li><li><figref idref="f0008">Fig. 8</figref> is a plan view of an imaging device.</li><li><figref idref="f0009">Fig. 9</figref> is a cross-sectional view showing a modified configuration of an imaging device.</li><li><figref idref="f0010">Fig. 10</figref> is a cross-sectional view showing a modified configuration of an embodiment of the invention, wherein the lens comprises three layers.</li></ul>

Reference Numbers

002110: Variable focal length lens <ul id="ul0002" list-style="none" compact="compact"><li>11: Lens</li><li>11a: First layer</li><li>11b: Second layer</li><li>11c: Third layer</li><li>13: Positive electrode</li><li>14: Negative electrode</li><li>20: Focal length adjusting device</li><li>21: Lens holder</li><li>22: Lens</li><li>30: Imaging device</li><li>31: Imaging sensor</li><li>32: Printed Circuit Board</li><li>52: Imaging device</li><li>53: Imaging device</li><li>62: Focal length adjusting device</li><li>63: Focal length adjusting device</li><li>80: Variable focal length lens</li><li>90: Variable focal length lens</li><li>93: Positive electrode</li><li>94: Negative electrode</li><li>100: Focal length adjusting device</li><li>101: Variable focal length lens</li><li>111: Controller</li><li>112: Controller</li></ul>

Best Mode for Carrying Out the Invention

0022Hereinafter, a variable focal length lens in accordance with the present invention, as well as a focal length adjusting device and an imaging device using the same, will be described with reference to the accompanying drawings.

First Embodiment

0023An imaging device 30 comprising a variable focal length lens 10 in accordance with the first embodiment of the present invention will now be described with reference to <figref idref="f0001 f0002 f0003 f0004">Figs. 1 to 4</figref>.

0024The imaging device 30 is provided with a focal length adjusting device 20, an imaging sensor 31, and a printed circuit board 32, as shown in cross section in <figref idref="f0001">Fig. 1</figref>.

0025The imaging sensor 31 converts an optical image of a subject into an electrical signal. The imaging sensor 31 is constructed from a CCD (charge-coupled device) or CMOS (complementary metal oxide semiconductor) or other image sensor. The imaging sensor 31 is provided upon the printed circuit board 32.

0026The focal length adjusting device 20 is provided with a variable focal length lens 10, a lens holder 21, and a lens 22.

0027As shown in <figref idref="f0001">Figs. 1</figref>, <figref idref="f0004">4(a), and 4(b)</figref>, the variable focal length lens 10 is provided with a lens 11, a positive electrode 13 and a negative electrode 14. The lens 11 is provided upon the surface of a planar portion 21c of the lens holder 21 that faces a planar portion 21a. The lens 11 comprises a first layer 11a, and a second layer 11b provided upon the first layer 11a.

0028Both the first layer 11a and the second layer 11b are formed from a polymer that deforms in response to the application of voltage. In the present embodiment, these layers are formed from polyvinyl chloride to which a plasticizer has been added. As described below, the polyvinyl chloride and the plasticizer are determined from the desired amount of displacement, strength, etc., for the respective layers. For example, the polyvinyl chloride and the plasticizer may be mixed in a ratio of 1:9 (polyvinyl chloride: plasticizer).

0029The first layer 11a is provided contacting the positive electrode 13 and the negative electrode 14 formed on the planar portion 21c of the lens holder 21. The second layer 11b is formed adhering to the first layer 11a, so as to cover at least a light transmission region on one face (the face facing the side of the lens 22, i.e., the light incident face) of the first layer 11a. The second layer 11b determines the curvature of the lens 11. In addition, the second layer 11b is formed such that variation in the lens curvature is less than that of the case wherein the entire lens is composed of the first layer 11a. The second layer 11b is also formed having hardness to the degree that a protective membrane for the variable focal length lens 10 is unnecessary.

0030The lens 11 is formed such that its shape when the voltage applied to the positive electrode 13 and the negative electrode 14 is zero, i.e., its shape in the initial state, is that of a ring shape, as shown in <figref idref="f0002">Fig. 2</figref>. When the voltage applied to the positive electrode 13 and the negative electrode 14 is raised from zero, the first layer 11a constituting the lens 11 deforms along the positive electrode 13, as shown in <figref idref="f0003">Fig. 3</figref>. In addition, the second layer 11b also deforms so as to be drawn toward the positive electrode 13. In so doing, the curvature of the lens 11 changes, and thus the focal length changes.

0031The hardness of the first layer 11a and the second layer 11b constituting the lens 11 is determined according to the polymerization of the polyvinyl chloride used, the mixing quantity of plasticizer, and the properties of the plasticizer used. For this reason, the hardness of the first layer 11a and the second layer 11b is determined by appropriately adjusting these parameters according to the desired properties of the first layer 11a and the second layer 11b.

0032More specifically, consider for example the degree of polymerization of polyvinyl chloride. Upon comparing polyvinyl chloride samples with polymerization degrees of n=1100 and n=3700, the polyvinyl chloride with n=3700 is, for example, stronger and more plasticizer can be added thereto. However, this polyvinyl chloride has a transparency that is low compared to the polyvinyl chloride with n=1100. Consequently, in this case, the polyvinyl chloride with n=1100 is more preferable for use as the variable focal length lens 10. Next, the plasticizer is preferably an phthalic acid ester. More particularly, dibutyl phthalate (DBF), di-2-ethylhexyl phthalate (DEHP(DOP)), di-n-octyl phthalate (DnOP), di-isononyl phthalate (DINP), di-isodecyl phthalate (DIDP), and di-undecyl phthalate (DUP) are preferable. Typically, as the quantity of these plasticizers added to polyvinyl chloride is increased, the polyvinyl chloride gel becomes more flexible, and exhibits a tendency of increased amount of displacement when a voltage is applied. In addition, as the linear chains of the ester groups become longer for each of these plasticizers, the polyvinyl chloride exhibits a tendency of decreased amount of displacement when a voltage is applied. Moreover, in the case where the ester groups are branching, the polyvinyl chloride exhibits a tendency of little amount of displacement when a voltage is applied.

0033Consequently, by utilizing these properties, the properties and mixing quantity of plasticizer are appropriately adjusted according to the desired amount of displacement, strength, etc., by the variable focal length lens. For example, if a particularly large amount of displacement is sought for the variable focal length lens 10, it is necessary for a flexible gel to be produced. In order to do so, the mixing quantity of plasticizer can be increased, a plasticizer having short linear chains of ester groups may be used, a plasticizer with a low degree of branching of ester groups may be used, etc. By using one or a combination of the above, the hardness of the gel is adjusted.

0034In addition, the first layer 11a and the second layer 11b constituting the lens 11 are formed in the following way. First, a plasticizer such as di butyl phthalate is added to polyvinyl chloride. This mixture is then dissolved in tetrahydrofuran (THF). Subsequently, this solution is poured into a mold that has been formed in advance in the shape of the variable focal length lens 10, and left for several days. Left in the mold, the tetrahydrofuran evaporates; hence a gel lens is formed.

0035As shown in <figref idref="f0001">Fig. 1</figref>, the positive electrode 13 is formed upon the face of the planar portion 21c of the lens holder 21 that faces the planar portion 21a. As shown in <figref idref="f0002">Fig. 2</figref>, the positive electrode 13 is formed in a ring shape. The positive electrode 13 may be formed, for example, from inorganic conducting materials such as carbon black, gold, silver, aluminum, and phosphor bronze, or from organic conducting materials such as organic conducting polymers.

0036The negative electrode 14 is formed in a ring shape so as to cover the inner peripheral surface of the aperture 21d formed on the planar portion 21c of the lens holder 21. The negative electrode 14 is also be formed, for example, from inorganic conducting materials such as carbon black, gold, silver, aluminum, and phosphor bronze, or from organic conducting materials such as organic conducting polymers.

0037In addition, the positive electrode 13 and the negative electrode 14 are connected to a controller 111. The controller 111 controls a voltage V applied between the positive electrode 13 and the negative electrode 14 in accordance with an exteriorly provided control signal.

0038By applying a voltage V between the positive electrode 13 and the negative electrode 14, the lens 11 is drawn toward the positive electrode 13 and deforms along the positive electrode 13. The drawing strength (degree of deformation) roughly increases as the applied voltage increases. In the first embodiment, the positions of the positive electrode 13, the negative electrode 14, and the edge of the lens 11 exist in the positional relationship shown in <figref idref="f0001">Figs. 1</figref> and <figref idref="f0002">2</figref>. For this reason, when the voltages V+ and V- are respectively applied to the positive electrode 13 and the negative electrode 14, the lens 11 deforms radially outward (elongation).

0039Next, the operation by which the variable focal length lens 10 varies its focal length will be described using <figref idref="f0004">Fig. 4</figref>. In the initial state wherein the voltage V applied between the positive electrode 13 and the negative electrode 14 is zero, the first layer 11a of the lens 11 contacts the negative electrode 14, and the peripheral edge thereof contacts the positive electrode 13, as shown in <figref idref="f0004">Fig. 4(a)</figref>.

0040When the voltage applied to the positive electrode 13 and the negative electrode 14 is raise from zero, the polyvinyl chloride constituting the first layer 11a and the second layer 11b of the lens 11 is drawn toward the positive electrode 13. In so doing, the first layer 11a and the second layer 11b are deformed radially outward (elongation) so as to cover the positive electrode 13, as shown in <figref idref="f0004">Fig. 4(b)</figref>. As the radius of the lens 11 increases, the thickness of the lens 11 decreases from Ta to Tb (thinning). Due to the voltage applied between the positive electrode 13 and the negative electrode 14, the second layer 11b is also deformed radially outward (elongation), and the thickness of the second layer 11b becomes thinner. For this reason, the radius of curvature of the second layer 11b becomes larger. In other words, the curvature of the lens 11 becomes smaller, and thus the focal length of the lens 11 becomes more distant.

0041In the second layer 11b, a mixing quantity of plasticizer that is small in advance, and/or a plasticizer with a small amount of displacement is used. For this reason, when a voltage is applied between the positive electrodes 13 and 14, the degree to which the second layer 11b is drawn toward the positive electrode 13 is small compared to that of the first layer 11a. On the other hand, the first layer 11a is strongly drawn and greatly deformed. However, since the first layer 11a and the second layer 11b are formed from nearly identical materials and only differ in the mixing quantity, type, etc., of plasticizer, both layers have excellent adhesion. Consequently, even when there is a difference between the first layer 11a and the second layer 11b with regard to the degree of deformation as described above, detachment of the interface of the layers, introduction of air, etc., do not occur, and the layers provide excellent light transmission properties.

0042In addition, when the voltage applied to the positive electrode 13 and the negative electrode 14 is returned to zero, the polyvinyl chloride constituting the first layer 11a and the second layer 11b cease being drawn toward the positive electrode 13, and thus the lens 11 returns to the initial state shown in <figref idref="f0004">Fig. 4(a)</figref> .

0043The lens holder 21 is cylindrically shaped, as shown in <figref idref="f0001">Figs. 1</figref> and <figref idref="f0002">2</figref>, and holds the variable focal length lens 10 as well as the lens 22 on the inner side thereof. In addition, the lens holder 21 is provided with a planar portion 21a and a planar portion 21c. The planar portion 21a has an aperture 21b corresponding to the diameter of the lens 22. The planar portion 21c is provided with an aperture 21d corresponding to the variable focal length lens 10. In addition, the positive electrode 13 is formed upon the surface of the planar portion 21c that faces the planar portion 21a, and the negative electrode 14 is formed spanning the entire inner peripheral surface of the aperture 21d of the planar portion 21c. In this way, the positive electrode 13 and the negative electrode 14 are formed on the planar portion 21c of the lens holder 21. Consequently, it is preferable that at least the planar portion 21c of the lens holder 21 be formed from an insulating material, specifically being formed from PET (polyethylene terephthalate).

0044The lens 22 is configured of a plastic lens, glass lens, or other lens, and in conjunction with the variable focal length lens 10, focuses the light of an optical image of a subject.

0045The variable focal length lens 10 varies in curvature according to the voltage applied between the positive electrode 13 and the negative electrode 14, as described above. On the other hand, the curvature of the lens 22 is fixed.

0046The variable focal length lens 10 of the first embodiment is provided with a lens 11 comprising a second layer 11b and a first layer 11a. In addition, a controller 111 controls a voltage V applied between electrodes 13 and 14. The curvature of the lens 11 is easily controlled by the application of voltage of controller 111. The curvature of the lens 11 is determined by the lens surface. For this reason, it is necessary that the deformation of the surface of the lens 11 is controlled, in order to obtain a set degree of variation in the curvature of the lens 11. However, if the entirety of the lens 11 is formed with the same hardness, the degree of deformation changes greatly due to voltage applied between the electrodes 13 and 14, as a result of minute differences in shape, etc., of the lens 11. For this reason, it is difficult to control the shape of the surface of the lens 11, i.e., the curvature of the lens 11.

0047However, since a second layer 11b is provided on a surface region determining the curvature of the lens 11, it is possible to control only the shape of the second layer 11b. In so doing, it is possible to control the curvature of the lens 11. Consequently, other regions, i.e., the amount of displacement of the first layer 11a, etc., do not significantly affect the curvature of the lens 11. For this reason, the curvature of the lens 11 is easily controlled.

0048In addition, in the case where the lens constituting the variable focal length lens is formed of a single layer, it is necessary to cover the lens surface with a thin film having flexibility, such as polyurethane, poly-paraxylene resin (parylene), etc., in order to protect the surface of the lens from the exterior environment. However, since the protective film and the lens are of different materials, adhesion is poor. For this reason, when the lens deforms, there is the problem in that gaps developing between the protective film and the lens. Consequently, when curvature is controlled by deforming the lens, there has been the problem of the difficulty of accurately controlling curvature without developing gaps, etc. However, as a result of the second layer 11b being formed as in the first embodiment, the lens surface is resistant from being affected by the exterior environment. For this reason, the protective film that was necessary in the case wherein the lens is formed of a single layer can be omitted.

0049As described above, by applying a voltage to the variable focal length lens 10 of the first embodiment, the lens 11 itself deforms, and as a result, the curvature thereof changes, and thus the focal length changes. Consequently, unlike the conventionally used configuration wherein focal length is adjusted by an actuator, etc. moving a lens holder holding a lens along the optical axis, the actuator, the power transmission means, guides, etc., can be omitted. As a result, the focal length adjusting device 20 can be miniaturized, and furthermore the imaging device 30 can be easily adapted for miniaturization.

Second Embodiment

0050An imaging device 52 comprising a variable focal length lens 80 of the second embodiment of the present invention will now be described with reference to <figref idref="f0005">Figs. 5</figref> and <figref idref="f0006">6</figref>. A variable focal length lens 80 in accordance with the second embodiment differs from the variable focal length lens 10 of the first embodiment in that the number and shape of the positive electrode and negative electrode are different from that of the positive electrode and negative electrode of the first embodiment. The portions in the second embodiment that are common to first embodiment are referred to using identical reference numbers.

0051The imaging device 52 is provided with a focal length adjusting device 62, an imaging sensor 31, and a printed circuit board 32. The focal length adjusting device 62 is provided with a variable focal length lens 80, a lens holder 21, and a lens 22.

0052Similarly to the first embodiment, the variable focal length lens 80 comprises a lens 11, a positive electrode 83, and a negative electrode 84.

0053Similarly to the first embodiment, the first layer 11a and the second layer 11b constituting the lens 11 are formed from polyvinyl chloride to which a plasticizer has been added. The second layer 11b is formed harder than the first layer 11a by a set degree, and additionally is formed so as to cover at least a light transmission region upon the first layer 11a. Thus, the second layer 11b determines the curvature of the lens 11.

0054The positive electrode 83 comprises four electrodes 83a to 83d, disposed symmetrically about a point on the central axis (optical axis), as shown in <figref idref="f0006">Fig. 6</figref>. In other words, the electrodes 83a to 83d have a shape formed by dividing the positive electrode 13 in <figref idref="f0001">Fig. 1</figref> into four equal portions. These electrodes 83a to 83d are referred to collectively as the positive electrode 83. In addition, the positive electrode 83 is provided upon the planar portion 21c of the lens holder 21 to form a ring shape in the entirety thereof, as shown in <figref idref="f0005">Fig. 5</figref>. The positive electrode 83 comprises, for example, inorganic conducting materials such as carbon black, gold, silver, aluminum, and phosphor bronze, or organic conducting materials such as organic conducting polymers.

0055Corresponding to the electrodes 83a to 83d constituting the positive electrode 83, the negative electrode 84 comprises four electrodes 84a to 84d, disposed symmetrically about a point on the optical axis, as shown in <figref idref="f0006">Fig. 6</figref>. In other words, the electrodes 84a to 84d have a shape formed by dividing the negative electrode 14 in <figref idref="f0001">Fig. 1</figref> into four equal portions. These electrodes 84a to 84d are referred to collectively as the negative electrode 84. The electrodes 84a to 84d are formed on the inner surface of the aperture 21d formed on the planar portion 21c of the lens holder 21, corresponding to the disposed positions of the electrodes 83a to 83d. The negative electrode 84 comprises, for example, inorganic conducting materials such as carbon black, gold, silver, aluminum, and phosphor bronze, or organic conducting materials such as organic conducting polymers.

0056The four electrodes 83a to 83d constituting the positive electrode 83 and the four electrodes 84a to 84d constituting the negative electrode 84 are respectively connected to a controller 112. The controller 112 applies a voltage Va+ to the electrode 83a, a voltage Va- to the electrode 84a, and similarly applies the voltages Vb+, Vc+, and Vd+ to the electrodes 83b to 83d, as well as the voltages Vb-, Vc-, and Vd- to the electrodes 84b to 84d. Each voltage is independently controllable. In other words, the controller 112 independently controls the voltages applied between the electrodes 83a and 84a, between the electrodes 83b and 84b, between the electrodes 83c and 84c, and between the electrodes 83d and 84d.

0057In the variable focal length lens 80 having the above configuration, an identical first voltage is mutually applied to the electrodes 83a to 83d, and an identical second voltage is mutually applied to the electrodes 84a to 84d. In so doing, the lens 11 can be radially stretched in a nearly uniform manner over the entire circumference thereof. In so doing, the curvature of the lens 11 changes, and thus the focal length changes.

0058Furthermore, in the variable focal length lens 80 of the second embodiment, the controller 112 may set voltage values such that the voltage Va applied between the electrode 83a and the electrode 84a, the voltage Vb applied between the electrode 83b and the electrode 84b, the voltage Vc applied between the electrode 83c and the electrode 84c, and the voltage Vd applied between the electrode 83d and the electrode 84d may be mutually different voltages.

0059Consequently, for example in the case where the lens 11 includes errors (lens distortions) with respect to the optical axis, it is possible to adjust the deformation of the first layer 11a and the second layer 11b by setting, for example, a value for the voltage Va applied between the electrode 83a and the electrode 84a that is different from the other voltages Vb to Vd, thereby it is also possible to correct (compensate for) these errors.

0060In addition, since errors by applied voltages may be corrected with dividing each of the electrodes symmetrically about the central axis, the work to secure lens while aligning it with the optical axis when installing the lens that was necessary in the case where the positive electrode is formed in a ring shape, such as the first embodiment may be omitted.

0061In addition, even in the hypothetical case where the lens is secured by alignment with the optical axis in the rest state, there has been the possibility of the problem of large individual image quality differences when the variable focal length lens is operated, as a result of imperfections in the shape of the formed lens or minute differences with the electrode boundary. However, as a result of forming each electrode divided as in the second embodiment, the voltage applied between each of the electrodes can be adjusted to compensate for deviation from the optical axis, even for cases wherein the lens is not strictly aligned with the optical axis during lens installation. Consequently, by utilizing the variable focal length lens 80 of the second embodiment adjusting functions adapted for individual lenses are provided, the allowable value for individual differences (shapes, etc.) during fabrication of variable focal length lenses is increased, and fabrication costs can be lowered.

0062Typical variable focal length lenses have focal adjusting functions along the optical axis (z axis) only, but the variable focal length lens 80 of the second embodiment is able to finely adjust the focus with respect to the plane perpendicular to the optical axis (i.e., the xy axes). Consequently, even for the case of, for example, a security camera or similar camera that is stationary, a desired image of a subject can be captured by adjusting the lens.

Third Embodiment

0063An imaging device 53 comprising a variable focal length lens 90 of the third embodiment of the present invention is shown in <figref idref="f0007">Figs. 7</figref> and <figref idref="f0008">8</figref>. The variable focal length lens 90 of the third embodiment differs from the variable focal length lenses 10 and 80 described above in the region where the negative electrode is formed. Portions common to the above-described embodiments will be referred to using identical reference numbers.

0064As shown in <figref idref="f0007">Figs. 7</figref> and <figref idref="f0008">8</figref>, the imaging device 53 is provided with a focal length adjusting device 63, an imaging sensor 31, and a printed circuit board 32. The focal length adjusting device 63 is provided with a variable focal length lens 90, a lens holder 21, and a lens 22.

0065The variable focal length lens 90 comprises a lens 11, a positive electrode 93, and a negative electrode 94. The variable focal length lens 90 is provided on the planar portion 21c of the lens holder 21, as shown in <figref idref="f0007">Fig. 7</figref>.

0066Similarly to the first embodiment, the second layer 11b and the first layer 11a constituting the lens 11 are formed from polyvinyl chloride to which has been added a plasticizer. The second layer 11b is formed harder than the first layer 11a to a set degree, and additionally is formed so as to cover at least a light transmission region upon the first layer 11a. Thus, the second layer 11b determines the curvature of the lens 11. Moreover, in the third embodiment, the first layer 11a is formed packed into the aperture 21d of the planar portion 21c of the lens holder 21 so as to contact the negative electrode 94, the negative electrode 94 being formed on the surface that faces the printed circuit board 32 (the bottom surface) of the planar portion 21c.

0067The positive electrode 93 may be formed, from inorganic conducting materials such as carbon black, gold, silver, aluminum, and phosphor bronze, or from organic conducting materials such as organic conducting polymers, etc. , for example phosphor bronze plate. The positive electrode 93 is formed so as to cover the top surface of the planar portion 21c of the lens holder 21.

0068The negative electrode 94 is formed from a conducting material having light transmission properties, such as ITO (indium tin oxide), for example. As shown in <figref idref="f0007">Fig. 7</figref>, the negative electrode 94 is provided upon the bottom surface of the planar portion 21c so as to seal the aperture 21d.

0069Since the variable focal length lens 90 of the third embodiment is provided with a lens 11 comprising a first layer 11a and a second layer 11b in the same manner as the first embodiment, the curvature thereof can be easily controlled. Furthermore, in the third embodiment, since the negative electrode 94 is formed below the first layer 11a constituting the variable focal length lens 90, the bottom surface of the variable focal length lens 90 is made uniform, and the occurrence of optical image distortion is decreased. In addition, the negative electrode 94 is configured to be formed on the inner peripheral surface of the aperture 21d of the planar portion 21c by forming the negative electrode 94 on the bottom surface of the planar portion 21c, and for this reason, the negative electrode 94 is easily formed.

0070The present invention is not limited to the foregoing embodiments, and may be subjected to various alterations or modifications thereof. For example, in each of the embodiments described above, a case was described by way of example wherein the second layer 11b of the lens 11 is formed so as to cover at least a light transmission region of the first layer 11a. However, the present invention is not limited to the above, and a second layer 101b may be formed so as to cover the entirety of a first layer 101a, as shown in a variable focal length lens 100 in <figref idref="f0009">Fig. 9</figref>.

0071In addition, in the second embodiment described above, a case was described by way of example wherein the positive electrode 83 and negative electrode 84 are respectively divided into four portions symmetrically about the central axis. However, the number of divided portions is not limited to four, and may be an arbitrary integer equal to or greater than two. In addition, the configuration in the second embodiment wherein the electrodes are formed divided may also be applied to the third embodiment.

0072In addition, the voltage applied to the variable focal length lens 10 is not limited to one step. The applied voltage may be varied continuously (in an analog manner) , or may be varied in multiple steps (in a stepped manner). If such a voltage application method is adopted, the curvature of the variable focal length lens 10 can be varied in multiple steps or in a step-less, continuous manner.

0073In addition, in the first embodiment, a configuration was described by way of example wherein the positive electrode 13 is formed upon the planar portion 21c of the lens holder 21, the negative electrode 14 is formed upon the inner peripheral surface of the aperture 21d of the planar portion 21c, and wherein the first layer 11a and the second layer 11b deform radially outward. However, in an embodiment which is not part of the present invention, the region where the positive electrode 13 and the negative electrode14 or the direction in which the first layer 11a and the second layer 11b are formed may be arbitrarily modified. For example, a configuration may be selected wherein the negative electrode 14 is formed upon the planar portion 21c, the positive electrode 13 is formed farther radially inward than the negative electrode 14, and wherein the first layer 11a and the second layer 11b deform radially inward. In addition, a configuration may be selected wherein the positive electrode 13 and the negative electrode 14 are formed upon the same surface of the planar portion 21c.

0074In each of the foregoing embodiments, a case was described by way of example wherein the second layer 11b is formed only on the light incident side (the side facing the lens 22). However, the invention is not limited to the above, and a configuration may be selected wherein a layer, similar to the second layer 11b, that is harder than the first layer 11a is formed on the surface that faces the imaging sensor 31, and wherein the curvature on both sides of the variable focal length lens 10 is changed.

0075In each of the foregoing embodiments, a case was described by way of example wherein polyvinyl chloride is used. However, materials other than polyvinyl chloride may also be used if such materials have the property of deforming according to a voltage applied between a positive electrode and a negative electrode.

0076In addition, in each of the foregoing embodiments, a configuration was described by way of example wherein an optical image of a subject is formed using two lenses. However, the invention is not limited to the above, and for example a configuration using three lenses may also be selected. In addition, the position of the variable focal length lens may be arbitrarily selected, and a configuration wherein a lens is provided between the variable focal length lens and the imaging sensor may also be selected.

0077The number of layers constituting the lens was described to be two, but three or more layers may also be configured.

0078In addition, an example was given wherein the curvature of only one side is varied, but both sides may also be varied. In this case, the configuration for controlling the curvature of one side of the lens shown in <figref idref="f0001 f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009">Figs. 1 to 9</figref> may, for example, be provided for the bottom side thereof, as shown in <figref idref="f0010">Fig. 10</figref>. For example, a second positive electrode having a similar configuration to the positive electrode 13 (83) shown in <figref idref="f0001">Fig. 1</figref> or <figref idref="f0005">5</figref> may be provided on the bottom side of the planar portion 21c, and a portion of the first layer 11a may be made to contact this positive electrode 13 (83). In addition, on the bottom side of the first layer 11a, a third layer 11c may be provided that is harder than the first layer 11a for determining the curvature of the bottom side of the lens.

0079In addition, in the first through the third embodiments, a case was described wherein the lens shape is that of a convex lens, but the lens shape may also be that of a concave lens. In this case, the components determining the curvature of the lens of the embodiment of the invention are, from among the layers 11a, 11b, and 11c formed from a polymer, the second layer 11b and the third layer 11c, which are provided on the outer surface of and formed harder than the first layer 11a.

0080This application is based on Japanese Patent Application No. <patcit id="pcit0004" dnum="JP2005241863A"><text>2005-241863</text></patcit>, filed in the Japan Patent Office on August 23, 2005.

0081In addition, this application includes portions common to the technology disclosed in Japanese Patent Application No. <patcit id="pcit0005" dnum="JP2005104630A"><text>2005-104630</text></patcit>, filed in the Japan Patent Office on March 31, 2005, and published as <patcit id="pcit0006" dnum="JP2006309112A"><text>JP 2006-309112</text></patcit>. However, this application does not disclose the construction of a lens from a plurality of layers.

Industrial Applicability

0082A variable focal length lens is provided that varies curvature by deforming according to an applied voltage. In addition, with the use of the variable focal length lens, a focal length adjusting device that is of simple construction and miniaturizable may be formed, as well as an imaging device using the same.