Abstract:
A diaphragm comprising a single plate, the single plate comprising: a first plate portion having an aperture; and a second plate portion formed at an outer side of the first plate portion, wherein a first thickness of the first plate portion is thinner than a second thickness of the second plate portion.

Description:
[0001]     This application is based on Japanese Patent application JP 2004-257683, filed Sep. 3, 2004, the entire content of which is hereby incorporated by reference. This claim for priority benefit is being filed concurrently with the filing of this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field of the Invention  
         [0003]     The present invention relates to a diaphragm inserted with an optical system, such as an imaging lens into a lens barrel and put to use.  
         [0004]     2. Description of the Related Art  
         [0005]     A diaphragm is incorporated in a lens unit of a camera and the like. A variable diaphragm unit a diameter of an aperture of which can be regulated in accordance with the brightness and the like is often used as a diaphragm incorporated in a lens unit. The lens units incorporated in, for example, a simplified photographic camera like a lens-carrying film unit, and the lens units of a simplified digital camera incorporated in a portable telephone also include a lens unit not mounted with a variable diaphragm. The light unnecessary for a photographing operation enters a lens unit in no small quantities to cause a flare and a ghost to occur, and the nobility of a photographic image to lower in some cases. For this reason, a fixed diaphragm having a constant diameter of a diaphragm aperture, and capable of preventing the incidence of harmful light and setting a F-value of a lens is used for the lens unit for the above-mentioned simplified camera.  
         [0006]     A diaphragm formed by kneading carbon black and the like in a plastic sheet so as to give the light shielding property thereto, and providing the resultant plastic sheet with a diaphragm aperture has heretofore been utilized as such a fixed diaphragm. However, in order to maintain the strength and light shielding property of the plastic sheet, it is necessary that the sheet has a thickness of at least around 0.2 to 0.3 mm. However, a photographic lens used for, for example, a portable telephone has been miniaturized to the extent that a total length of the lens is reduced to around several millimeters. A further reduction of the thickness of the diaphragm as a whole has also been demanded with consideration given to a space in which the diaphragm is to be inserted. In the diaphragm made of one piece of the above-mentioned plastic sheet, the thickness thereof cannot be reduced satisfactorily since the diaphragm has the problems of the strength and light shielding property thereof. Even when a sheet of around 0.2 to 0.3 mm in thickness is used, a ghost/a flare occurring due to the reflected light from the edge portion of the diaphragm necessarily causes the deterioration of the property of the diaphragm.  
         [0007]     The diaphragm known from JP-A-11-212138 (hereafter “JPA &#39;138”) is formed by laminating a thin sheet provided with a diaphragm aperture of a predetermined diameter therein on a thick sheet provided with an aperture of a diameter slightly larger than that of an object aperture. Since the diaphragm aperture is formed in the thin sheet, the unnecessary reflection of the light on an inner circumferential surface of the diaphragm is reduced, and the strength and light shielding property of the diaphragm is maintained owing to the thick sheet.  
         [0008]     However, the diaphragm disclosed in JPA &#39;138 needs to prepare two pieces of sheets formed by the press working respectively, and an operation for pasting the sheets on each other accurately with a bonding agent so that the centers of the diaphragm aperture are aligned with each other becomes necessary, so that the manufacturing cost increases. Since the thin sheet provided with the diaphragm aperture is as thin as 0.04 to 0.09 mm, the surrounding portion of the aperture, which is not laminated on the thick sheet, of the thin sheet has light transmission of around 5%, i.e., the light shielding property was unsatisfactory.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a diaphragm maintaining satisfactory strength and not permeating the light even when the thickness of the diaphragm is reduced, and capable of reducing the occurrence of a flare and a ghost.  
         [0010]     In order to achieve this object, the diaphragm according to an embodiment of the present invention is made of one sheet of thin metal plate, wherein the thickness of the area of the plate in which the diaphragm aperture is formed is smaller than that of the area thereof which surrounds an outer side of the aperture.  
         [0011]     The same diaphragm as is defined above, wherein an inner edge of the aperture-carrying thin plate is preferably chamfered.  
         [0012]     The same diaphragm as is defined above, wherein an inner circumferential surface of the aperture-carrying thin plate is preferably subjected to a light reflection suppressing surface treatment.  
         [0013]     The diaphragm according to an embodiment of the present invention is made of one sheet of thin metal plate, and the thickness of the area thereof in which the diaphragm aperture is formed is smaller than that of the area which surrounds an outer side of the aperture-carrying area. Since the diaphragm is made of one sheet of thin metal plate, the transmission of the light therethrough can be prevented. Moreover, since the thickness of the area of the diaphragm in which the aperture is formed is smaller than that of the area thereof which surrounds the outer side of the aperture-carrying area, the reflection of the light on the inner circumferential surface of the aperture can be further held down as the strength of the diaphragm is maintained. This enables a diaphragm maintaining a satisfactory strength thereof, not permeating the light therethrough, and reducing the occurrence of a flare and a ghost therein to be provided.  
         [0014]     Since the edge of the diaphragm aperture of the aperture-carrying thin plate is chamfered, the diaphragm aperture is diverged toward the edge on the incidental side thereof and toward the outgoing side thereof. Therefore, even when the diaphragm aperture is narrowed with the miniaturization of the diaphragm based on the miniaturization of the optical system, the occurrence of an eclipse and the like can be held down.  
         [0015]     Since the inner circumferential surface of the thin plate in which the aperture is formed is subjected to a surface treatment for suppressing the light reflection thereon, the reflection of the light on the inner circumferential surface of aperture can be held down. This makes it possible to provide a diaphragm in which the occurrence of a ghost and a flare are further reduced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIGS. 1A  to  1 B are perspective views of a camera-carrying portable telephone in which the diaphragm according to one embodiment of the present invention is incorporated.  
         [0017]      FIG. 2  is a cross-sectional view taken longitudinally along the optical axes of the photographing lens, diaphragm, CCD image sensor and the like.  
         [0018]      FIG. 3  is a perspective view of the diaphragm having a circular diaphragm aperture and observed from the diagonally front side thereof.  
         [0019]      FIG. 4  is a cross-sectional view of the surroundings of the diaphragm aperture taken longitudinally in the direction of the thickness thereof.  
         [0020]      FIG. 5  is a flow chart roughly describing the method of manufacturing the diaphragm.  
         [0021]      FIG. 6A  is a cross-sectional view of a metal plate obtained by the press working,  FIG. 6B  is a cross-sectional view of the metal plate on which the first and second resist layers are formed, and  FIG. 6C  is a cross-sectional view of the metal plate in which an etching solution is made to flow to form a diaphragm aperture.  
         [0022]      FIG. 7  is an explanatory drawing describing the operation of the diaphragm conceptually by utilizing a cross-sectional drawing of the diaphragm cut in the direction of the thickness thereof.  
         [0023]      FIG. 8  is a perspective view showing a diaphragm in which a square diaphragm aperture is formed.  
         [0024]      FIG. 9  is a cross-sectional view taken longitudinally in the direction of the thickness of a diaphragm in which the inner circumferential surface of the diaphragm aperture is made of first, second and third inclined portions. 
     
    
       [0025]     Reference numerals are used to identify various elements in the drawings including the following: 
     2  Camera-carrying portable telephone      24  First lens      25  Second lens      26  Third lens      28  Diaphragm      28   a  First plate type portion      28   b  Second plate type portion      28   c  Front surface      28   d  Rear surface      35  Diaphragm aperture      35   a  Inlet      35   b  Outlet      35   c  Inner circumferential surface      35   d  Inlet peripheral portion      35   e  Outlet peripheral portion    
 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0041]      FIG. 1  shows a camera-carrying portable telephone containing the diaphragm according to one embodiment of the present invention therein. As shown in  FIG. 1A , the camera-carrying portable telephone  2  is provided at an upper portion thereof with a communication antenna  4 , and at an upper portion of a front surface thereof with a receiving speaker  5  for outputting the voice of the opposite speaking party, an image displaying liquid crystal frame  7 , an operating buttons  9  for carrying out various operations including the inputting of a telephone number and the like, a transmission microphone  11  for transmitting the voice of a user to the opposite speaking party, and the like.  FIG. 1B  is a perspective view showing a rear surface of the camera-carrying portable telephone. A first lens  24  provided in a lens unit, which will be described later, is exposed to the outside of the rear surface of the camera-carrying portable telephone  2 . The camera-carrying portable telephone  2  can switch to each other a speaking mode for making a telephone call to someone and a photographing mode in which the photographing of an object can be done. When the camera-carrying portable telephone  2  is set to a photographing mode with a predetermined photographing operation carried out by a user, picture plane data on an object are formed by a first lens  13  and the like.  
         [0042]      FIG. 2  shows a lens unit shown in section by cutting a lens unit, which is made of a lens barrel and the like holding the first lens therein, longitudinally along the optical axis. A lens unit  20  includes a lens barrel  22 , first, second and third lenses  24 ,  25 ,  26 , a diaphragm  28 , a CCD image sensor  30 , etc. The first to third lenses  24  to  26  and diaphragm  28  are held in the lens barrel  22 , and the outer diameter of the first, second and lenses  24 ,  25 ,  26  are around 7 to 8 mm, the first to third lenses  24  to  26  being arranged so that the optical axes thereof are aligned with one another. The diaphragm  28  is provided as an aperture diaphragm between the first lens  24  and second lens  25 , and a bundle of rays inputted from the first lens  24  into the second lens  25  is restricted by this diaphragm  28 . The diaphragm  28  is provided with a diaphragm aperture  35  for passing the light therethrough, and the diaphragm aperture  35  is provided in the interior of the lens barrel  22  so that the optical axes of the first to third lenses  24  to  26  pass a predetermined position in the diaphragm aperture  35 . The CCD image sensor  30  is provided on the side of an image surface of the third lens  26 , and fixed on a circuit substrate of the same.  
         [0043]      FIG. 3  shows the diaphragm  28  in perspective. The diaphragm  28  is formed in the shape of a disc, and includes a first plate portion  28   a  provided with a diaphragm aperture  35 , and a second plate portion  28   b  formed so as to be continued to a circumference of the first plate portion  28   a . The diaphragm aperture  35  is formed so as to extend from a front surface  28   c  (refer to  FIG. 4 ) of the first plate portion  28   a  to a rear surface  28   d  (refer to  FIG. 4 ), and a diameter of the diaphragm aperture  35  is set so as to gradually increase toward an inlet and an outlet of the diaphragm aperture  35 . The first plate portion  28  is provided at the side of a front surface  28   c  thereof with an inlet  35   a  of the diaphragm aperture  35 , and at the side of a rear surface  28   d  thereof with an outlet  35   b  of the diaphragm aperture  35 .  
         [0044]      FIG. 4  is a sectional view showing the surroundings of the diaphragm aperture  35 , in which the surroundings of the aperture are cut longitudinally in the direction of the thickness thereof. The thickness of the first plate portion  28   a  is set smaller than that of the second plate portion  28   b . The thickness of the first plate portion  28   a  is preferably 0.01 to 0.02 mm, and the thickness of the second plate portion  28   b  preferably to 0.05 to 0.10 mm. The distance between a boundary portion between the second plate portion  28   b  and first plate portion  28  and the diaphragm aperture  35  is preferably 0.2 to 0.5 mm. When the thickness of the second plate portion  28   b  is thus set larger than that of the first plate portion  28   a  in which the aperture  35  is formed, the strength of the diaphragm  28  is maintained satisfactorily.  
         [0045]     The edge of the aperture on the incidental side of the first plate portion  28   a  in which the diaphragm aperture  35  is formed, and the edge of the aperture on the outgoing side are chamfered respectively. An inner circumferential surface  35   c  is formed so as to extend from an inlet  35   a  of the diaphragm aperture  35  to an outlet  35   b  thereof. Out of the inner circumferential surface  35   c  of the diaphragm aperture, an inlet peripheral portion  35   d  and an outlet peripheral portion  35   e  are made round. The inlet peripheral portion  35   d  and outlet peripheral portion  35   e  are made of curved surfaces, which are formed with a point P, which is positioned in the interior of the first plate portion  28   a , as a center of curvature. This structure causes a cross section S (refer to  FIG. 7 ) of the diaphragm aperture  35  substantially parallel to the surface  28   c  of the first plate portion  28   a  to increase gradually toward the inlet  35   a  and outlet  35   b . The inner circumferential surface  35   c  of the diaphragm  35  is coated with a light absorbing coating material, by which the reflection of light on the inner circumferential surface  35   c  is held down. In this embodiment, the center of curvature of the curved surfaces constituting the inlet peripheral portion  35   d  and outlet peripheral portion  35   e  is positioned in the interior of the first plate portion  28   a  but a curved surface the center of curvature of which is positioned in the interior of the second plate portion may constitute the inlet peripheral portion and outlet peripheral portion.  
         [0046]     A method of manufacturing the diaphragm will be described by using  FIG. 5  and  FIGS. 6A  to  6 C. As shown in  FIG. 6A , a metal plate  39  of which the diaphragm  28  is made is prepared in advance. This metal plate  39  is subjected to a preliminary treatment, such as the removal of fine recesses and projections existing in and on the surface thereof and the washing of the metal plate. For example, phosphor bronze and stainless steel are used as a raw material for the metal plate.  
         [0047]     After the metal plate is preliminarily processed, a first resist layer  42  is laminated on a surface  39   c  of the metal plate  39 , and a second resist layer  43  on a rear surface  39   d  of the metal plate  39 . Ultraviolet rays are applied to the first and second resist layers  42 ,  43 . After the ultraviolet rays are applied to the metal plate, the portions of the metal plate to which the ultraviolet rays are not applied are removed therefrom by a liquid developer. As a result, a first aperture  45  and a second aperture  46  are formed in the first and second resist layers  42 ,  43  as shown in  FIG. 6B . The second aperture  46  is made small as compared with the first aperture  45 . In this embodiment, the first aperture  45  and second aperture  46  are formed by utilizing a positive method permitting the portions of the first and second resist layers  42 ,  43  which are not irradiated with the ultraviolet rays to be left on the metal plate. The first aperture  45  and second aperture  46  may also be formed in the first and second resist layers  42 ,  43  by utilizing a negative method which permits the portions irradiated with ultraviolet rays to be left on the metal plate  39 .  
         [0048]     After the first aperture  45  and second aperture  46  are formed, the metal plate  39  is immersed in an etching liquid for a predetermined period of time, and the etching liquid corrodes the metal plate  39  from the first aperture  35  and second aperture  46 . As shown in  FIG. 6C , the shapes of the inner circumferential surfaces of the diaphragm apertures are completed. After the shapes of the inner circumferential surfaces of the diaphragm apertures are formed, the first and second resist layers  42 ,  43  are removed, and the outer shape of the diaphragm  28  is completed.  
         [0049]     After the first and second resist layers  42 ,  43  are removed from the metal plate  39  in which the diaphragm aperture is formed, the surface of the metal plate  39  including the inner circumferential surface and the like of the diaphragm aperture is subjected to a light absorption surface treatment to complete the diaphragm  28 . The surface treatment methods include, for example, a method of applying light absorbing coating material to the surface of the metal plate, and a method of subjecting the surface of the metal plate to a delustering treatment, by which the reflection of the light can be held down. When the diaphragm  28  is thus manufactured by using an etching process, the provision of a highly accurate diaphragm member can be expected. The phosphor bronze and stainless steel are preferably used as raw materials for the metal plate. The raw metal materials are not limited to these, and, when there is other suitable material, it may be used suitably.  
         [0050]     The operation of the present invention will now be described.  FIG. 7  is an explanatory drawing describing the operation of the diaphragm  28  conceptually by using a sectional view of the diaphragm  28  cut in the direction of the thickness thereof. The diaphragm  28  is provided between the first lens  24  and second lens  25 , and a periphery of the diaphragm  28  is held in the lens barrel. The axes of the first to third lenses  24  to  26  pass through a predetermined position in the diaphragm aperture  35  formed in the diaphragm  28 . Since the second plate portion  28   b  of the diaphragm  28  is formed thicker than the first plate portion  28   a , the strength of the diaphragm  28  is maintained so that the diaphragm  28  is not easily deformed. Since the diaphragm aperture  35  is formed in the first thin plate type portion  28   a , the reflection of light on the inner circumferential surface  35   c  of the diaphragm  35  can be held down, so that the quality of an image is improved.  
         [0051]     The inlet peripheral portion  35   d  and outlet peripheral portion  35   e  of the inner circumferential surface  35   c  of the diaphragm aperture  35  are formed round. Therefore, the size of the cross section S of the diaphragm aperture  35  parallel to the surface  28   c  of the first plate portion  28   a  increases toward the inlet  35   a  and outlet  35   b . Therefore, even in a portable telephone in which the dimensions of a lens unit are small, the occurrence of eclipse can be held down. The inner portion of the diaphragm aperture  35  is subjected to a coating treatment using light absorbing coating material or a treatment using a black delustering material. This enables the reflection of the light, which enters the first lens  24 , on the inner circumferential surface  35   c  of the diaphragm aperture  28   a  to be held down, and the occurrence of a ghost and a flare to be further reduced.  
         [0052]     In the above-described embodiment, an example in which a lens barrel  22  with a diaphragm  28  incorporated therein is provided in a camera-carrying portable telephone  2  is shown but an apparatus provided with a lens barrel in which a diaphragm is incorporated is not limited to this. For example, the diaphragm may be incorporated in a lens barrel provided in a photographing apparatus, such as a digital camera for forming image data on the basis of an image signal from an imaging element. When a lens barrel in which the diaphragm according to the present invention is incorporated is provided in a photographing apparatus, the provision of a photographing apparatus of a more compact structure and capable of obtaining an image of a higher quality can be expected.  
         [0053]     In the above-described embodiment, the shape of the diaphragm aperture was circular shape but the shape of the diaphragm aperture is not limited to this. The shape may be elliptic shape and rectangular shape.  FIG. 8  shows the diaphragm  50  in perspective having a diaphragm aperture  52  formed squarely. The second plate portion  50   b  is formed so as to enclose therewith the circumference of the first plate portion  50   a  in which the diaphragm aperture  52  is formed. Since the thickness of the first plate portion  50   a  is set smaller than that of the second plate portion  50   b , the occurrence of a flare and a ghost can be held down in accordance with the shape of the square CCD image sensor positioned on the side of an image of the photographing lens. Since the shape of the, diaphragm aperture is thus made square, the suppression of the occurrence of a flare and a ghost in accordance with the image obtained can be expected, and the obtainment of an image of a higher quality becomes possible.  
         [0054]     In the above-described mode of embodiment, the inlet peripheral portion  35   d  and outlet peripheral portion  36   e  out of the inner circumferential surface  35   c  of the diaphragm aperture  35  are formed round but the shape of the inner circumferential surface of the diaphragm aperture is not limited to this. For example, as shown in  FIG. 9 , the inner circumferential surface  58   c  of the diaphragm  55  may be made of a first inclined portion  58   d , a second inclined portion  58   f  and a third inclined portion  58   e . The first inclined portion  58   d  and third inclined portion  58   e  extend diagonally so that the diameter of the aperture increases toward the inlet  58   a  and outlet  58   b . This enables an eclipse, which occurs when the diaphragm aperture is made small, to be prevented. The inner circumferential surface made of the first to third inclined portions may be formed in this manner.  
         [0055]     In the above-described embodiment, the diaphragm  28  was utilized as an aperture-carrying diaphragm for the purpose of restricting the quantity of light entering the CCD image sensor  30 . According to the present invention, the purpose of using the diaphragm is not limited to such but the diaphragm may be utilized as a light shielding diaphragm for the purpose of only eliminating harmful light which causes a flare and a ghost to occur. Since the harmful light out of the light inputted from the photographing lens into the CCD image sensor  30  is cut off by the light shielding diaphragm, the entry of the harmful light into the CCD image sensor  30  can be prevented, and the obtainment of a high-quality image becomes possible.