Patent Application
20060050412
1. Field of the Invention
The present invention relates to an optical unit capable of changing the focal length, an image taking apparatus having an image taking lens using the optical unit, and an optical finder using the optical unit.
2. Description of the Related Art
As a variable-focus lens capable of changing the focal length, a liquid crystal lens capable of changing the focal length by using the electro-optic effect of a liquid crystal is known. For example, Japanese Patent Laid-Open No. 2002-341311 (patent document 1) discloses a liquid crystal lens having first and second light-transmissive substrates in the form of a flat plate, a third light-transmissive substrate having two concave surfaces and provided between the first and second light-transmissive substrates, and a liquid crystal enclosed in each of a space between the first and third light-transmissive substrates and a space between the second and third light-transmissive substrates. In this liquid crystal lens, the orientation of liquid crystal molecules is changed according to the level of an applied voltage to change the refractive index of the liquid crystal lens. The focal length of the lens is thereby changed.
A fluid lens which can be changed in shape by application of a voltage to change its focal length is also known as a variable-focus lens. For example, a fluid lens in which an immiscible fluid constituted of a non-electroconductive oil and an electroconductive aqueous solution is enclosed in a tube having its inner wall surface covered with a water-repellent coating is proposed in “Philips' Fluid Lenses”, [online], Mar. 3, 2004, Royal Philips Electronics, [found on Mar. 31, 2004], Internet <URL: http://www.dpreview.com/news/0403/04030302philipsfluidle ns.asp> (non-patent document 1). In this fluid lens, when no voltage is applied, the aqueous solution constituting the immiscible fluid is a semispherical mass and the interface of the aqueous solution on the oil is convex. This interface changes between the convex state and a concave state according to the level of the applied voltage. Consequently, the radius of curvature of the lens can be changed and the focal length of the lens is freely variable.
In the technique disclosed in the patent document 1, the focal length of the lens is changed by using the difference Δn (nψ-nζ) between the refractive index (nψ) in the major-axis direction and the refractive index (nζ) in the minor-axis direction of liquid crystal molecules. However, there is a problem that the difference Δn is so small that the refractive index of the lens cannot be freely changed.
In the technique proposed in the non-patent document 1, the focal length of the fluid lens is changed by applying a voltage to the immiscible fluid. When a voltage is applied to the immiscible fluid, a current flows through the electroconductive aqueous solution constituting the immiscible fluid. Therefore, there is a risk of the aqueous solution being decomposed by electrolysis to generate hydrogen and oxygen, and there is a problem that during use over a long time period a gas constituted of generated hydrogen and oxygen is accumulated to form bubbles which scatter light and deteriorate the performance of the lens.
The above-described problems arise generally with plane-parallel plates and the like as well as with lenses.
The present invention has been made in view of the above circumstances and provides an optical unit capable of freely changing the refractive power and operating with a reduced deterioration in performance, an image taking apparatus employing an image taking lens using the optical unit, and an optical finder using the optical unit.
The present invention provides an optical unit including:
In the optical unit of the present invention, a dispersoid which is dispersed in a light-transmissive dispersion medium enclosed in a container, which is light-transmissive, and which has a refractive index different from the refractive index of the dispersion medium, is moved by an electromagnetic force, thereby changing the focal length of the light passage region at least in three steps. There can be obtained a variable-focal-length optical unit whose focal length can be changed at least in three steps according to a refractive index determined by the dispersion medium and the amount of dispersoid moved in the light passage region by the electromagnetic force. The dispersoid dispersed in the dispersion medium is moved by an electric field or a magnetic field generated by the electromagnetic field generator. No current is caused in the dispersion medium. Therefore, the optical element of the present invention is capable of reducing the risk of electrolysis and limiting the deterioration of the lens performance over a long time period in comparison with the technique that is proposed in the nonpatent document 1, and that entails a current flowing through an electroconductive aqueous solution.
Preferably, the electromagnetic field generator in the optical unit of the present invention is an electrode which receives application of a voltage to cause electrophoresis of the dispersoid, and the focal length changing section controls the voltage applied to the electrode.
In the electrophoretic optical unit using this electrophoresis, electrophoresis of the dispersoid is caused by the electric field applied from the electrode, thereby controlling the focal length. The amount of the dispersoid moved by electrophoresis can be freely controlled according to the waveform and the pattern of a voltage applied to the electrode, the placement, shape and structure of the electrode, and other factors. Therefore, the refractive index distribution can be determined with flexibility in comparison with the technique of controlling the refraction of light by using the refractive index of liquid crystal molecules as proposed in the patent document 1.
Preferably, the dispersoid in the electrophoretic optical unit of the present invention is constituted of titanium oxide.
If the dispersoid is constituted of titanium oxide, an optical member having a high refractive index can be realized. Also, titanium oxide is easily available as a material for manufacture of the optical element.
Preferably, the dispersoid in the electrophoretic optical unit of the present invention is constituted of alumina.
If the dispersoid is constituted of alumina, the cost of the dispersoid can be reduced.
Preferably, the dispersion medium in the electrophoretic optical unit of the present invention is an organic dispersion medium.
Preferably, the dispersion medium in the electrophoretic optical unit of the present invention is a hydrocarbon-based organic dispersion medium.
If the dispersion medium is a hydrocarbon-based organic dispersion medium, the electrical stability is further improved in comparison with organic dispersion mediums having functional groups.
Preferably, the inner surface of the electrode in the electrophoretic optical unit of the present invention is coated with an insulating film which is placed adjacent to the dispersion medium.
Agglomeration of the dispersoid on the electrodes can be prevented in this way.
Also, the insulating film in the electrophoretic optical unit of the present invention is preferably a polyimide insulating film.
An Electrode having improved heat resistance and durability can be obtained by using a polyimide insulating film.
Preferably, the dispersoid in the electrophoretic optical unit of the present invention is magnetic; the electromagnetic field generator is a magnetic field generator which causes magnetophoresis of the dispersoid; and the focal length changing section controls a magnetic field generated by the magnetic field generator.
In the magnetophoretic optical unit using this magnetophoresis, the focal length is controlled by causing magnetophoresis of the magnetic dispersoid in the dispersion medium instead of causing electrophoresis. Control of an electric field is required for electrophoresis of a dispersoid. However, control of a magnetic field easier than control of an electric field suffices for magnetophoresis of the magnetic dispersoid, thus enabling the focal length to be reliably adjusted.
Preferably, the dispersoid in the magnetophoretic optical unit of the present invention is constituted of titanium-cobalt oxide.
Titanium-cobalt oxide can form magnetic particles having high optical transmissivity and easily producible.
Preferably, the dispersoid in the optical unit of the present invention is nanoparticles.
Electrophoresis of the dispersoid can be effected even in a case where the dispersoid is nanoparticles.
Preferably, the dispersoid in the optical unit of the present invention is nanoparticles having a particle size of 5 to 100 nm.
If the dispersoid is nanoparticles having a particle size of 5 to 100 nm, scattering of light can be avoided and the desired light transmissivity can be maintained. Also, nanoparticles having a particle size in this range can be easily handled.
Preferably, the dispersion medium in the optical unit of the present invention is water.
If the dispersion medium is water, the dispersibility of the dispersoid is high and the cost of the dispersion medium is reduced.
Preferably, the container in the optical unit of the present invention has the shape of a lens.
If the container has the shape of a lens, the optical unit can be used as a focusing lens, a zoom lens or the like.
In the optical unit of the present invention, at least the light passage region of the container may have the shape of a lens with a positive refractive power.
If the container is formed in this manner, the optical unit of the present invention can be used as a convex variable-focus lens.
In the optical unit of the present invention, at least the light passage region of the container may have the shape of a lens with a negative refractive power.
If the container is formed in this manner, the optical unit of the present invention can be used as a concave variable-focus lens.
In the optical unit of the present invention, at least the light passage region of the container may have the shape of an aspheric lens.
If the container is formed in this manner, the optical unit of the present invention can be used as an aspheric variable-focus lens.
In the optical unit of the present invention, the container may have the shape of a flat plate.
If the container has the shape of a flat plate, the optical distance to a subject can be changed.
The present invention also provides a first image taking apparatus including an image taking lens in which the optical unit of the present invention is used as a focusing lens, wherein an image signal is generated by performing an image taking operation including capturing subject light which enters the image taking apparatus through the image taking lens.
The first image taking apparatus of the present invention has an image taking lens in which the optical unit of the present invention is used as a focusing lens, and can therefore be realized as an image taking apparatus simpler in construction, reduced in size and having improved impact resistance in comparison with the conventional image taking apparatus requiring a mechanism for driving a focusing lens.
Preferably, the first image taking apparatus also includes a focus detection section which detects an in-focus position of the image taking lens by changing the focal length by means of the focusing lens and detecting a change in contrast of a subject image.
According to the preferable form of the first image taking apparatus of the present invention, the focal length of the optical unit can be controlled with accuracy over a long time period to take high-quality images.
The present invention also provides a second image taking apparatus including an image taking lens whose focal length is changed by the optical unit of the present invention, wherein an image signal is generated by performing an image taking operation including capturing subject light which enters the image taking apparatus through the image taking lens.
The second image taking apparatus of the present invention has an image taking lens whose focal length is changed by the optical unit of the present invention, and can therefore be realized as an image taking apparatus simpler in construction, reduced in size and having improved impact resistance in comparison with the conventional image taking apparatus requiring a mechanism for changing a focal length.
The present invention also provides a third image taking apparatus including an image taking lens in which the optical unit of the present invention is used as an aberration correction lens, wherein an image signal is generated by performing an image taking operation including capturing subject light which enters the image taking apparatus through the image taking lens.
The third image taking apparatus has an image taking lens in which the optical unit of the present invention is used as an aberration correction lens, and is, therefore, capable of performing aberration correction as desired to suitably correct an aberration peculiar to the image taking lens.
The present invention further provides an optical finder using the optical unit of the present invention as a diopter correction lens.
The optical finder of the present invention uses the optical unit of the present invention as a diopter correction lens and can therefore be realized as an optical finder simplified in construction, reduced in size and having improved impact resistance in comparison with the conventional optical finders requiring a mechanism for driving a portion of the optical system for diopter correction.
The optical unit of the present invention is capable of freely changing the refractive power and limiting the deterioration of the performance. The image taking apparatus having an image taking lens using the optical unit of the present invention as a focusing lens requires no mechanism for driving the focusing lens and can therefore be simplified in construction and reduced in size and have improved impact resistance. The image taking apparatus having an image taking lens whose focal length is changed by using the optical unit of the present invention requires no mechanism for changing the focal length and can therefore be simplified in construction and reduced in size and have improved impact resistance. The image taking apparatus having an image taking lens in which the optical unit of the present invention is used as an aberration correction lens can perform aberration correction as desired to suitably correct an aberration peculiar to the image taking lens. The optical finder of the present invention uses the optical unit of the present invention as a diopter correction lens and can therefore be simplified in construction and reduced in size and have improved impact resistance in comparison with the conventional optical finders requiring a mechanism for driving a portion of the optical system for diopter correction.
The present invention will be described with respect to embodiments thereof.
Optical units in accordance with the present invention are roughly divided into electrophoretic optical units capable of changing the focal length by causing electrophoresis of a dispersoid dispersed in a dispersion medium, and magnetophoretic optical units capable of changing the focal length by causing magnetophoresis of a dispersoid. Description will first be made of an electrophoretic optical unit.
An optical unit of electrophoretic type having a lens shape will be described first.
The variable-focus lens 1 shown in
In the lens body 2, a light-transmissive dispersion medium 12 is provided in a state of being enclosed in the container 11. The dispersion medium 12 is an example of the dispersion medium in accordance with the present invention.
In the lens body 2, a dispersoid 13 is also provided which is dispersed in the dispersion medium 12, which is light-transmissive, and which has a refractive index higher than that of the dispersion medium 12. In general, a dispersion is constituted of a dispersion medium and a dispersoid. The dispersoid is, for example, particles. More specifically, the dispersoid 13 is nanoparticles 13b negatively charged. The dispersoid 13 is an example of the dispersoid in accordance with the present invention.
The lens body 2 is also provided with a first electrode 151 and a second electrode 152 for controlling the refraction of light passing through the light passage region 10a by effecting electrophoresis of the dispersoid 13 dispersed in the dispersion medium 12. The first electrode 151 is placed in such a position as to surround the light passage region 10a in the container 11. The second electrode 152 is placed on a back surface of the container 11 in the light passage region 10a. The second electrode 152 is constituted by a certain number of electrode elements 152a. The first and second electrodes 151 and 152 are an example of the electromagnetic field generator in accordance with the present invention as well as an example of the electrode in accordance with the present invention.
The focal length changing section 3 is a section for changing the focal length of the light passage region 10a at least in three steps by controlling voltages applied to the first and second electrodes 151 and 152. The focal length changing section 3 corresponds to an example of the focal length changing section in accordance with the present invention.
When a negative voltage and a positive voltage are respectively applied to the first and second electrodes 151 and 152 from the focal length changing section 3, the first and second electrodes 151 and 152 function as a cathode and an anode, respectively. When a positive voltage and a negative voltage are respectively applied to the first and second electrodes 151 and 152, the first and second electrodes 151 and 152 function as an anode and a cathode, respectively.
In the variable-focus lens 1, the refraction of light passing through the light passage region 10a is controlled through electrophoresis of the dispersoid 13 which is dispersed in the light-transmissive dispersion medium 12 enclosed in the container 11 of the lens body 2, which is light-transmissive and which has a refractive index higher than that of the dispersion medium 12, by the way that the voltage applied between the first and second electrodes 151 and 152 for electrophoresis being controlled by the focal length changing section 3. The focal length of the light passage region 10a is thereby changed at least in three steps. The variable-focus lens 1 is therefore obtained as a lens whose focal lens is changed at least in three steps according to a refractive index determined by the dispersion medium 12 and the amount of movement of the dispersoid 13 to the light passage region 10a caused by electrophoresis. The principle of the operation of the lens body 2 will be described before description of the operation of the variable-focus lens 1. For ease of description, description will be made with respect to a lens body shown in
The lens body 10 shown in parts (a) and (b) of
In the lens body 10, a light-transmissive dispersion medium 12 is provided in a state of being enclosed in the container 11.
In the lens body 10, a dispersoid 13 is also provided which is dispersed in the dispersion medium 12, which is light-transmissive, and which has a refractive index higher than that of the dispersion medium 12.
The lens body 10 is also provided with a cathode 14 and an anode 15 which are an electrode for controlling the refraction of light passing through the light passage region 10a by effecting electrophoresis of the dispersoid 13 dispersed in the dispersion medium 12. More specifically, the dispersoid 13 is nanoparticles 13a positively charged and nanoparticles 13b negatively charged, the cathode 14 which is a negative electrode for attracting the dispersoid 13 and the anode 15 which is a positive electrode for attracting the dispersoid 13 are placed at such positions on the container 11 as to surround the light passage region 10a.
Any material may be used as the material of the nanoparticles. The nanoparticles are, for example, particles of silica, alumina, zirconia, titanium oxide, tungsten oxide, zinc oxide, tin oxide or barium titanate. Preferably, the nanoparticles are particles of titanium oxide, silica gel (SiO2), alumina or a polymer. The nanoparticles may be prepared by any of a solid phase method, a liquid phase method and a vapor phase method. Preferably, a liquid phase method or a vapor phase method is used. A method suitable for preparation of the nanoparticles is described in detail in a document “Preparation of Nanoparticles and Control of and Evaluation of Dispersion and Agglomeration of Nanoparticles, Technical Information Institute Co., Ltd., 2003”. The particle size is preferably 100 nm or less. If the particle size exceeds 100 nm, scattering of light occurs to impair the transparency (transmissivity).
It is preferable to modify the surface of the nanoparticles for the purpose of improving the stability of dispersion in the dispersion medium 12. Examples of a method of modifying the surface are a method using a titanium coupling agent (such as isopropyl triisostearoyl titanate), a silane coupling agent (such as pentadecafluorodecyl trimethylsilane) or an aluminum coupling agent (such as acetoalkoxyaluminum diisopropylate) and graft polymerization. Polyethylene graft polymerization or polystyrene graft polymerization may be used as graft polymerization on titanium oxide. Graft polymerization using a silanol group may be used as graft polymerization on silica gel.
As the dispersion medium 12 in which the nanoparticles are dispersed, water or a non-aqueous organic dispersion medium may be used. A mixture of water and an organic dispersion medium may also be used. Examples of a non-aqueous organic dispersion medium preferably used as the dispersion medium 12 are hydrocarbons (such as hexane, heptane, pentane, octane and ISOPAR (a product from Exxon Corporation)), hydrocarbon aromatic compounds (such as benzene, toluene, xylene, mesitylene and ethylbenzene), halogen hydrocarbons (such as difluoropropane, dichloroethane, chloroethane and bromoethane), halogen hydrocarbon aromatic compounds (such as chlorobenzene), ether compounds (such as dibutyl ether, anisole and diphenyl ether), alcohol compounds (such as glycerin), compounds having a carbonyl group (such as propylene carbonate), nitro compounds (such as nitromethane), nitrile compounds (such as acetonitrile and benzonitrile).
Preferably, the refractive index, specific gravity, viscosity, resistivity and dielectric constant of the dispersion medium 12 are adjusted in relation to use of the lens body 10. This adjustment may be performed by mixing a certain number of dispersion mediums.
Additives including stabilizing agents for stabilization under an acid, an alkali and a salt, a stabilizing agent for stabilization of dispersion, stabilizing agents for antioxidation and ultrasonic absorption, an antibacterial agent and a preservative agent may be added to the dispersion medium 12.
As a member forming the container 11, a glass base plate, a film or a base plate of a high polymer such as polyester, polyimide, polymethyl methacrylate, polystyrene, polypropylene, polyethylene, polyamide, nylon, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyether sulfone, a silicone resin, a polyacetal resin, a fluororesin, a cellulose derivative or polyolefin, or an inorganic base plate such as a metallic base plate or a ceramic base plate is preferably used. The container 11 has a transmissivity of preferably 50% or higher, more preferably 80% or higher.
As the cathode 14 and the anode 15, an electrode member on which a layer of gold, silver, copper, aluminum, magnesium, nickel, platinum, carbon, an electroconductive high polymer or a metal oxide typified by tin oxide-indium oxide (ITO), tin oxide or zinc oxide is formed is preferably used. For use on a portion through which light is to be transmitted, transparent electrodes are preferably used. A metal oxide typified by tin oxide-indium oxide (ITO), tin oxide or zinc oxide is preferred.
In the lens body 10 shown in
When no voltage is applied between the cathode 14 and the anode 15, the dispersoid 13 is uniformly dispersed in the dispersion medium 12, as shown in part (a) of
When a predetermined voltage is applied between the cathode 14 and the anode 15, the positively charged nanoparticles 13a in the dispersoid 13 uniformly dispersed in the dispersion medium 12 are attracted to the cathode 14 and the negatively charged nanoparticles 13b are attracted to the anode 15, as shown in part (b) of
The amount of the dispersoid 13 moved from the state of being positioned in the light passage region 10a with electrophoresis can be freely controlled according to the waveform and the pattern of the voltage applied between the cathode 14 and the anode 15, the placement, shape and structure of the cathode 14 and the anode 15, and other factors. Therefore, the distribution rate can be determined with flexibility in comparison with the technique of controlling the refraction of light by using the refractive index of liquid crystal molecules as disclosed in the patent document 1. Also, the dispersoid 13 dispersed in the dispersion medium 12 is moved by an electric field produced by applying a voltage between the cathode 14 and the anode 15 and no current is caused therebetween. Therefore, the risk of electrolysis is reduced in comparison with the technique using a current flowing through an electroconductive aqueous solution as proposed in the non-patent document 1. Consequently, the deterioration of the performance of the lens can be limited over a long time period.
A method of changing the refractive index stepwise by electrophoresis will be described. When the nanoparticles positively charged and negatively charged (hereinafter referred to as charged particles) are moved by electrophoresis, the amount of the moved charged particles can be changed according to the waveform and the pattern of the applied voltage. An optical element capable of changing the refractive index stepwise can be obtained as a result of use of the method of changing the amount of the charged particles positioned in the light passage region 10a in the lens body 10. A method of applying a rectangular wave is preferably used to change the amount of charged particles. In a document “IDWO3 Proceedings (Proceedings of the 10th International Display Workshops), p 239, 2003”, an example of 4-step-gradation display by electrophoresis is reported. An example of 8-step-gradation display is also reported in “IDWO3 Proceedings, p 243, 2003”. It is possible to change the amount of charged particles stepwise by using one of the application methods for the display described in this document.
An embodiment of the lens body will be described.
Nanoparticles of titanium oxide were used as dispersoid 13 in the embodiment of the lens body 10. The titanium oxide nanoparticles were prepared by a method described below. Hydrous titanium oxide was made formless by an alkali, thereafter aged in hydrochloric acid, and formed into particles having a particle size of 10 nm by a heat treatment. The surfaces of the particles were processed by using a titanium coupling agent (isopropyl triisostearoyl titanate) solution. An optical element was made as the lens body 10 by dispersing the thus-obtained titanium oxide nanoparticles in ISOPAR (a product from Exxon Corporation).
When about 20% by volume of the titanium oxide nanoparticles (having a refractive index of 2.30) were mixed in ISOPAR (having a refractive index of 1.48), the refractive index changed from 1.48 to 1.644. In the case of mixing of about 30% by volume, the refractive index changed from 1.48 to 1.726. By using these mixtures, lenses (mediums containing nanoparticles) having the following shape as shown in
(1—1) In the case where only ISOPAR (refractive index: 1.48) was contained,
(1—2) In the case where 20% of titanium oxide nanoparticles were mixed (refractive index: 1.644)
(1—3) In the case where 30% of titanium oxide nanoparticles were mixed (refractive index: 1.726)
Thus, the lens was capable of changing the focal length from 10.42 to 7.76 or to 6.89.
When the refractive index was selectively set to 1.48, 1.644 and 1.726, the focal length of the lens body was 10.42, 7.76 and 6.89, as described above. Back focus values corresponding to these focal length values are as shown in
A lens (a medium containing nanoparticles) using a combination of an ordinary glass (BK7; refractive index 1.51633) and the above-described lens body was made, as described below.
(2—1) In the case where only ISOPAR (refractive index: 1.48) was contained,
(2—2) In the case where 20% of titanium oxide nanoparticles were mixed (refractive index: 1.644)
(2—3) In the case where 30% of titanium oxide nanoparticles were mixed (refractive index: 1.726)
Thus, the variable-focus lens was capable of changing the focal length from −137.6 to 39.2 or to 23.8.
Further, a lens having nanoparticles enclosed in an ordinary glass (BK7; refractive index 1.51633) was made, as described below.
(3—1) In the case where only ISOPAR (refractive index: 1.48) was contained,
(3—2) In the case where 20% of titanium oxide nanoparticles were mixed (refractive index: 1.644)
(3—3) In the case where 30% of titanium oxide nanoparticles were mixed (refractive index: 1.726)
Thus, the variable-focus lens was capable of changing the focal length from −223.7 to 64.1 or to 39.1.
The operation of the variable-focus lens 1 shown in
The illustration of the focal length changing section 3 is omitted to simplify the figure.
If a negative voltage and a positive voltage are respectively applied from the focal length changing section 3 to the first and second electrodes 151 and 152 provided on the lens body 2 shown in part (a) of
If a positive voltage of a highest level is applied to the electrode elements 152a at the opposite ends in the electrode elements constituting the second electrode 152; a positive voltage of a lowest level is applied to the central electrode 152a; and a positive voltage of a medium level is applied to the electrode elements 152a positioned between the electrode elements 152a at the opposite ends and the central electrode element 152a, then the largest amount of nanoparticles 13b, the smallest amount of nanoparticles 13b and a medium amount of nanoparticles 13b are respectively attracted to the electrode elements 152a at the opposite ends, the central electrode element 152a and the electrode elements 152a positioned between the electrode elements 152a at the opposite ends and the central electrode element 152a, as shown in part (b) of
Further, if a positive voltage and a negative voltage are respectively applied to the first and second electrodes 151 and 152, then the first and second electrodes 151 and 152 function as an anode and a cathode, respectively, and nanoparticles 13b are attracted to the first electrode 151, as shown in part (c) of
The lens body 4 shown in
The lens body 5 shown in
Electrodes 1_141 and 1_151 shown in
Referring to
Referring to
If a positive voltage of a highest level is applied to the electrode elements 152a at the opposite ends in the electrode elements constituting the second electrode 152; a positive voltage of a lowest level is applied to the central electrode 152a; and a positive voltage of a medium level is applied to the electrode elements 152a positioned between the electrode elements 152a at the opposite ends and the central electrode element 152a, then the largest amount of nanoparticles 13b, the small amount of nanoparticles 13b and a medium amount of nanoparticles 13b are respectively attracted to the electrode elements 152a at the opposite ends, the central electrode element 152a and the electrode elements 152a positioned between the electrode elements 152a at the opposite ends and the central electrode element 152a, as shown in part (b) of
Further, if a positive voltage and a negative voltage are respectively applied to the first and second electrodes 151 and 152, then the first and second electrodes 151 and 152 function as an anode and a cathode, respectively, and nanoparticles 13b are attracted to the first electrode 151, as shown in part (c) of
In the lens body 180 shown in
The lens body 190 shown in
The lens body 200 shown in
An electrode 210 shown in
The electrophoretic optical unit having the shape of a lens has been described. Description will now be made of an electrophoretic optical unit having a flat shape. The same components of the optical unit described below as those of the optical unit having the shape of a lens are indicated by the same reference characters, and description will be made only of points of difference.
The lens body 310 shown in part (a) and part (b) of
When no voltage is applied between the cathode 14 and the anode 15, the dispersoid 13 is uniformly dispersed in the dispersion medium 12, as shown in part (a) of
When a predetermined voltage is applied between the cathode 14 and the anode 15, the positively charged nanoparticles 13a in the dispersoid 13 uniformly dispersed in the dispersion medium 12 are attracted to the cathode 14 and the negatively charged nanoparticles 13b are attracted to the anode 15, as shown in part (b) of
An imaging point at which an image is formed by subject light from a convex lens is imaged is shown in part (A) of
In a case where two lens bodies having the same thickness d and having different refractive indices (n1 and n2) are provided and selectively inserted in the image space, the difference Δd between the imaging points determined by the lens bodies is d (1/n1−1/n2), as shown in part (C) of
The operation of a variable-refractive-index plate will be described with reference to
If a negative voltage and a positive voltage are respectively applied from the focal length changing section 3 shown in
If a positive voltage of a highest level is applied to the electrode elements 152a at the opposite ends in the electrode elements constituting the second electrode 152; a positive voltage of a lowest level is applied to the central electrode 152a; and a positive voltage of a medium level is applied to the electrode elements 152a positioned between the electrode elements 152a at the opposite ends and the central electrode element 152a, then the largest amount of nanoparticles 13b, the small amount of nanoparticles 13b and a medium amount of nanoparticles 13b are respectively attracted to the electrode elements 152a at the opposite ends, the central electrode element 152a and the electrode elements 152a positioned between the electrode elements 152a at the opposite ends and the central electrode element 152a, as shown in part (b) of
Further, if a positive voltage and a negative voltage are respectively applied to the first and second electrodes 151 and 152, then the first and second electrodes 151 and 152 function as an anode and a cathode, respectively, and nanoparticles 13b are attracted to the first electrode 151, as shown in part (c) of
The lens body 330 shown in
The lens body 340 shown in
In the lens body 410 shown in
The lens body 420 shown in
The lens body 430 shown in
The anode 432 shown in
Referring to
Referring to
Referring to
The electrophoretic optical units in which the refraction of light is controlled through electrophoresis of a dispersoid dispersed in a dispersion medium have been described. Magnetophoretic optical units in which refraction of light is controlled by effecting magnetophoresis of a magnetic dispersoid dispersed in a dispersion medium will now be described.
The lens body 510 shown in
In the lens body 510, coils 540 for generating magnetic fields for causing magnetophoresis of magnetic nanoparticles 530 are provided in place of the electrodes (cathode 14 and anode 15) of the lens body 10 shown in
Part (a) of
Three wound coils 540 are placed side by side on upper and lower surfaces of the container 511. A magnetic field control section 550 for controlling magnetic fields generated from the coils 540 by causing currents to flow through the coils 540 are connected to the coils 540.
Part (b) of
For example, the magnetic field control section 550 shown in part (a) of
A further description will be made by referring again to
When no magnetic fields are generated by the coils 540, the magnetic nanoparticles 530 are uniformly dispersed in the dispersion medium 520, as shown in part (a) of
When currents are supplied to the coils 540 by the magnetic field control section 550 shown in part (a) of
Thus, the refraction of light passing through the lens body 510 can be controlled by effecting magnetophoresis of the dispersoid dispersed in the dispersion medium instead of electrophoresis.
The lens body 550 shown in
Coils 540 for generating magnetic fields for magnetophoresis of nanoparticles 530 are placed in such a position on the container 551 as to surround a light passage region 550a, as are those in the lens body 510 shown in
When no magnetic fields are generated by the coils 540, the nanoparticles 530 are uniformly dispersed in the dispersion medium 520, as shown in part (a) of
When currents are supplied to the coils 540, magnetic fields are generated by the coils 540. The magnetic nanoparticles 530 are attracted by the magnetic fields generated by the coils 540, as shown in part (b) of
Thus, a variable-refractive-index plate capable of changing the focal length can also be formed in a magnetophoretic optical element.
If plural small coils are placed in a stripe pattern, a magnetic field pattern similar to the electric field pattern in the case of use of the anode 181 shown in
While the coils capable of generating magnetic fields by being supplied with currents have been described as an example of the magnetic field generator in accordance with the present invention, the magnetic field generator in accordance with the present invention may be a permanent magnet which generates a magnetic field by itself. In such a case, magnetophoresis of the dispersoid is realized by moving the permanent magnet.
Basic embodiments for implementation of the concept of the present invention have been described. For practical use of an optical element provided as the lens body used in the present invention, however, it is preferable to use a device for preventing foreign materials or water droplets from being attached to a portion on the optical path to cause a deterioration of the lens performance.
For example, it is preferable to apply a water-repellent film on an external surface intersecting the optical path of the container containing a fluid (which surface hereinafter referred to as “light-transmissive surface”). If the light-transmissive surface is given water repellency, attachment of foreign materials and water droplets or the like is prevented and high transmissivity of the optical element can be maintained. As a material constituting this water-repellent coating, a silicone resin, a block copolymer of organopolysiloxane, a fluorine-based polymer, polytetrafluoroethane and the like are preferred.
It is also preferable to apply a hydrophilic film on the light-transmissive surface of the container constituting the lens body. Attachment of foreign materials to the light-transmissive surface can also be prevented by giving a hydrophilicity and oil repellency to the light-transmissive surface. As the hydrophilic film, a film formed of an acrylate polymer, a film coated with a surfactant such as a nonionic organosilicone-based surfactant and the like are preferred. As a method of making the hydrophilic film, plasma polymerization of a silane monomer, ion beam processing or the like may be used.
It is also preferable to apply a photocatalyst such as titanium oxide on the light-transmissive surface of the container constituting the lens body. The photocatalyst reacting with light decomposes a contamination or the like to keep the light-transmissive surface clean.
Further, it is preferable to apply an antistatic film on the light-transmissive surface of the container constituting the lens body. If static electricity is accumulated on the light-transmissive surface of the container, or if the light-transmissive surface is charged through the electrodes, there is a possibility of foreign materials and dust sticking to the light-transmissive surface. Attachment of such unnecessary materials can be prevented by applying an antistatic film on the light-transmissive surface. The transmissivity of the lens body is thereby maintained. Preferably, the antistatic film is formed of a polymer alloy-based material. Particularly preferably, the polymer alloy-based material is a polyether-based material, polyether ester amide-based material, a material having a cationic group, or Reolex (commercial name, DAI-ICHI KOGYO SEIYAKU CO., LTD.). Preferably, the antistatic film is made by a mist method.
An antifouling material may be used for the container constituting the lens body. A fluororesin is preferred as the antifouling material. More specifically, a fluorine-containing alkyl alkoxysilane compound, a fluoroalkyl group-containing polymer or oligomer and the like are preferred. One having a functional group crosslinkable to the above-mentioned curable resin is particularly preferred. Preferably, the amount of addition of the antifouling material is set to the minimum necessary amount for the desired antifouling effect.
A digital camera incorporating one of the various optical units will be described.
Part (a) of
The lens barrel 610 of the digital camera 600 shown in
This digital camera 600 is realized as a thin camera in which the rear group lens is withdrawn from the image taking optical axis when the image taking lens is collapsed, as described below.
An auxiliary light emitting section 612 and a finder objective window 613a are provided in upper front portions of the digital camera 600 shown in
A power switch 615, a finder ocular window 613b, an image monitor 620, a setting display button 616, a recording command button 617, an image display on/off button 620a, a cross key 619 and a zoom operation change button 618 are provided in the rear surface of the digital camera 600. A zoom operation mode is set by maintaining the zoom operation change button 618 in a depressed state for a predetermined time period. In the zoom operation mode, the lens barrel 610 is moved toward a telephoto position by depressing a portion of the cross key 619 with an “Up” mark. This movement is continued while this depressed state is being maintained. The lens barrel 610 is moved toward a wide-angle position by depressing a portion of the cross key 619 with a “Down” mark. This movement is continued while this depressed state is being maintained. The zoom operation mode is cancelled by again depressing the zoom operation change button 618 and maintaining the depressed state for a predetermined time period.
The image display on/off button 620a is a button for direction as to whether or not image display on the image monitor 620 is performed. In the digital camera 600, an image obtained by image taking is displayed on the image monitor 620 even when the image display on/off button 620a is off. Image taking of a subject in the state where the image monitor 620 is off is performed while the subject is being checked through the finder ocular window 613b.
The setting display button 616 is operated when the values of a shutter speed, sensitivity, etc., presently set are displayed. The recording command button 617 is operated when a taken image is recorded in a memory.
The finder ocular window 613b and the finder objective window 613a in the front surface side constitute an optical finder.
The power switch 615 is a switch operated to activate the digital camera 600. In the digital camera 600, a “REPRODUCTION” position for designating a reproduction mode which is a mode for displaying on the image monitor 620 an image recorded in a memory or the like, a “COLLAPSE” position for designating collapsed-position image taking and a “NORMAL” position for designating ordinary picture taking including a movie mode are provided. The power switch 615 is slidable between these positions and an “OFF” position for power-off. Part (c) of
The digital camera 600 shown in
In the digital camera 600, when “NORMAL” is selected by the power switch 615, the lens barrel 610 is extended until the field angle becomes equal to a predetermined wide angle. When “COLLAPSE” is selected by the power switch 615 to select collapsed-position image taking, the lens barrel 610 is not extended. In this case, image taking using a fixed focus determined by the front group lens and the focusing lens can be performed.
An image of a subject formed on the image pickup device 622 through the image taking lens 601 and the shutter unit 621 is converted into an analog image signal by the image pickup device 622. The shutter unit 621 limits the occurrence of smear caused by light when the analog signal is read out from the image pickup device 622.
The digital camera 600 has the auxiliary light emitting section 612 which emits auxiliary light as required. The finder having the finder objective window 613a and the finder ocular window 613b provided in the digital camera 600 is an optical finder, as mentioned above, and control linked to focal length adjustment and focusing is performed by the drive circuit 625 when “NORMAL” is selected by the power switch 615. When “COLLAPSE” is selected by the power switch 615 to select collapsed-position image taking, fixed-focus image taking is performed as described above and the finder is controlled according to focusing such that the focal point is set at a distance of 1 to 2 m from the camera.
The digital camera 600 also has an analog signal processing section 623, an A/D section 626, a digital signal processing section 627, a temporary memory 628, a compression/expansion section 629, an internal memory (or a memory card) 630, the image monitor 620 (see
The digital camera 600 further has a CPU 624 which performs overall control of the digital camera 600, a group of operating switches 631 including a zoom operation switch, the shutter button 614 and the like. Desired image taking conditions including a desired field angle setting are set by operating the group of operating switches 631 and the shutter button 614 is operated to perform picture taking.
In an internal space 610a of the lens barrel 610 shown in
An opening 602 through which the image taking lens 601 faces outward is formed at the front end of the internal space 610a of the lens barrel 610, while a wall member 603 fixed on the camera body or forming a portion of the camera body is placed at the rear end. The shape of the internal space 610a is defined by the wall member 603 and a certain number of cylindrical members (not shown).
The front group lens 601a is held inside a front group frame 680 smallest in outside diameter in the cylindrical members and placed at the foremost position on the optical axis when the lens barrel 610 is extended. The outside diameter of the front group lens 601a is smaller than the inside diameter of the front group frame 680. Therefore, a space is formed beside the front group lens 601a between the front group lens 601a and the front group frame 680. In the following description, the space between the front group lens 601a and the front group frame 680 is referred to as “front group lens side space 606”.
In the wall member 603, the image pickup device (CCD) 622 is mounted in a state of projecting in the internal space 610a. Since the image pickup device (CCD) 622 is mounted in such a position as to project in the internal space 610a, a recessed portion 604 defied by the image pickup device 622 and the wall member 603 is formed beside the image pickup device 622.
A fixed cylinder 640 is fixed on the wall member 603. A rotatable cylinder 650 is provided inside the fixed cylinder 640. The rotatable cylinder 650 is driven and rotated by a barrel drive motor through a column gear (not shown). A cam groove 641 is formed in the inner wall surface of the fixed cylinder 640. A cam pin 652 fixed on the rotatable cylinder 650 is fitted in the cam groove 641. Therefore, when the rotatable cylinder 650 receives the rotating drive force through the column gear, it moves frontward or rearward along the optical axis while being rotated.
A rotatable-cylinder-side rectilinear motion key ring 654 inside of the rotatable cylinder 650 is provided so as to be rotatable relative to the rotatable cylinder 650 but unable to move along the optical axis relative to the rotatable cylinder 650. A key plate 655 is fixed on the rotatable-cylinder-side rectilinear motion key ring 654. The key plate 655 is fitted in a key groove 642 formed in the inner wall surface of the fixed cylinder 640 so as to extend along the optical axis. The rotatable-cylinder-side rectilinear motion key ring 654 is thereby stopped from rotating relative to the fixed cylinder 640 stops while being allowed to move along the optical axis. Therefore, when the rotatable cylinder 650 rotates and moves along the optical axis, the rotatable-cylinder-side rectilinear motion key ring 654, stopped by the fixed cylinder 640 from rotating, does not rotate but moves along the optical axis together with the rotatable cylinder 650.
A rotatable intermediate cylinder 660 is provided inside the rotatable cylinder 650. A cam groove 656 shown in a bottom portion of
An intermediate-cylinder-side rectilinear motion key ring 664 is provided inside the intermediate cylinder 660. A rectilinear motion key groove 658 is formed in the fixed-cylinder-side rectilinear motion key ring 654 described above. The intermediate-cylinder-side rectilinear motion key ring 664 is fitted in the rectilinear motion key groove 658 of the fixed-cylinder-side rectilinear motion key ring 654. The intermediate-cylinder-side rectilinear motion key ring 664 is rotatable relative to the intermediate cylinder 660 but it is stopped from moving along the optical axis relative to the intermediate cylinder 660. Therefore, when the intermediate cylinder 660 rotates and moves along the optical axis relative to the rotatable cylinder 650, the intermediate-cylinder-side rectilinear motion key ring 664 moves rectilinearly along the optical axis by following the movement of the intermediate cylinder 660 without rotating.
A cam groove 665 for guiding a rear group guide frame 670 is formed in the inner wall surface of the intermediate cylinder 660. A cam pin 671 fixed on the rear group guide frame 670 is fitted in the cam groove 665 in a state of being stopped from rotating relative to the intermediate-cylinder-side rectilinear motion key ring 664. Therefore, when the intermediate cylinder 660 rotates, the rear group lens guide frame 670 moves rectilinearly along the optical axis according to the shape of the cam groove 665 in the inner wall surface of the intermediate cylinder 660.
A rear group lens holding frame 672 on which the shutter unit 621 is provided and which holds the rear group lens 601b is supported on the rear group lens guide frame 670 by a rotary shaft 673 so as to rotate relative to the rear group lens guide frame 670. When “OFF” is selected by the power switch 615, the rear group lens holding frame 672 retreats into the recessed portion 604 by the side of the image pickup device 622 together with the rear group lens 601b and the shutter unit 621, as shown in
In the intermediate cylinder 660, another cam groove 666 for guiding the front group frame 680 in which the front group lens 601a is held is formed. A cam pin 681 provided on the front group frame 680 is entered in the cam groove 666. The front group frame 680 is stopped from rotating relative to the intermediate-cylinder-side rectilinear motion key ring 664 while being allowed to move along the optical axis. Therefore, when the intermediate cylinder 660 rotates, the front group frame 680 moves rectilinearly along the optical axis relative to the intermediate cylinder 660 according to the shape of the cam groove 666.
When “OFF” is selected by the power switch 615 in the extended state shown in
When “NORMAL” is selected by the power switch 615 and when image taking is performed, the group of zoom operating switches are operated and the rear group lens 601b is moved along the optical axis to adjust the focal length between the telephoto end and the wide-angle end. The image taking field angle is thereby set as desired. The focusing lens 601c is not moved in the optical axis direction but focusing is performed by controlling the refraction in the focusing lens functioning as a variable-focus lens so that the contrast according to the result of detection of the contrast based on the image signal obtained by the image pickup device 622 is maximized. Thereafter, when the shutter button 614 is depressed, the image signal representing the subject is generated by the image pickup device (CCD) 622, undergoes suitable image processing and is thereafter recorded.
The digital camera which is an embodiment of the second image taking apparatus of the present invention is identical in external appearance to the digital camera 600. Therefore, the illustration of the digital camera described below is omitted.
As the rear group lens constituting the image taking lens provided in the digital camera which is an embodiment of the second image taking apparatus of the present invention, a variable-focus lens having a lens body 700 (e.g., the lens body 8 shown in
The optical finder 800 shown in
If the operator is nearsighted, control with the correction plate 804 is performed so as to set a predetermined increased emergence angle α1, as shown in part (a) of
The digital camera which is an embodiment of the third image taking apparatus of the present invention is identical in external appearance to the digital camera 600. Therefore, the illustration of the digital camera described below is omitted.
The zoom lens 900 shown in
The arrangement may be such that a lens body 901 is disposed in place of the lens 922 constituting the second lens group 920; an aberration correction table formed of data for correcting an aberration of the lenses in the first, second and third lens groups 910, 920, and 930 is prepared; and the aberration of the lenses is corrected through control of the distribution of nanoparticles performed by applying voltages to the electrodes of the variable-focus lens according to the data in the aberration correction table. In this embodiment, an image taking lens using a variable-focus lens using such a lens body 901 is provided and, therefore, aberration correction can be performed as desired to suitably correct an aberration peculiar to the image taking lens.
For example a variable-focus lens capable of changing the focal length in eight steps may be provided in a digital camera to suitably perform automatic focusing.
Automatic focusing based on a “mountain-climbing method” can be performed by using as a focusing lens a focal-length-variable lens having a lens body whose focal length is changed in eight steps according to a positive refractive index determined by a dispersion medium and the amount of movement of nanoparticles in a light passage region caused by electrophoresis, as described below.
The abscissa of
A maximum-contrast point is obtained by changing the refractive index of the lens body and checking the direction of change in contrast, and an in-focus point is obtained by assuming that a subject to be focused at the maximum point exists. Thus, focusing is performed by obtaining an in-focus point by performing an automatic focusing search using a variable-focus lens whose focal length is changed in eight steps. In this case, there is no need for a drive mechanism such as a motor in contrast with the conventional technique of performing focusing by moving the focusing lens in the optical axis direction. Consequently, an image taking lens having a simplified construction, a reduced size and improved impact resistance can be implemented.
While applications of the embodiments of the image taking apparatus in accordance with the present invention to digital cameras have been described by way of example, the image taking apparatus of the present invention may also be applied to a silver-salt camera, a portable telephone, and other devices.
Also, examples of optical units using an optical element having the shape of a lens and an optical element having the shape of a flat plate have been described. The optical element in accordance with the present invention, however, may have, for example, the shape of a prism.
Also, applications of electrophoretic optical units having the shape of a lens in the image taking apparatus and the optical finder in accordance with the present invention to the image taking apparatus and the optical finder in accordance with the present invention have been described by way of example. However, an electrophoretic type of optical finder having the shape of a flat plate, a magnetophoretic type of optical finder or the like may be applied thereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-259153 | Sep 2004 | JP | national |
| 2004-259926 | Sep 2004 | JP | national |
| 2005-67009 | Mar 2005 | JP | national |
| 2005-238433 | Aug 2005 | JP | national |
