Abstract:
A lens unit including a first lens including a first lens section having a first optical axis along which light passes, and a second lens. The second lens includes a second lens section having a second optical axis along which light passes, and a flange provided at the outer circumferential part of the second lens section and having a surface opposed to the first lens, and a tubular section extending from the flange in the direction of the second optical axis and having an inner side face opposed to the second lens section. The first lens is fitted in the tubular section and in contact with the inner side face of the tubular section of the second lens. The tubular section of the second lens has a plurality of protrusions protruding in the direction of the second optical axis and a plurality of valleys provided between the protrusions.

Description:
TECHNICAL FIELD 
     The present invention relates to a camera lens unit including plural lenses and used in a camera device. 
     BACKGROUND ART 
     Small digital camera devices, such as digital cameras and portable telephones with camera have been recently used. According to the decreasing of the sizes and high image quality of the digital camera devices, camera lens units including plural lenses, having short optical axes, and being applicable to high image quality are used in these digital camera devices. 
     A conventional camera lens unit including plural lenses is disclosed in Japanese Patent Laid-Open Publication No. 2004-302225. These lenses face each other. Each of the lenses has a lens section as an optical system and a flange which is provided at an outer circumference of the lens section for positioning and holding the lens. The flange is held with a lens holder. The lenses are positioned with respect to each other while flanges thereof contacting each other. 
     The camera lens unit receives not only light for forming an image on an image sensor but also unnecessary light. The unnecessary light, upon reflecting diffusely in a lens holder, may enter into the image sensor and produce flare on a taken image. In this conventional lens unit, light may reflect diffusely at the flanges contacting each other. In order to prevent the diffuse reflection, a light-shield sheet is provided between the flanges of the lenses. 
     One of the lenses has a cylindrical section extending from the flange thereof along an optical axis, and another of the lenses is engaged with the cylindrical section, so that the center of each of the lenses can be positioned regardless of the lens holder. 
     The conventional lens unit may produce the flare due to the diffuse reflection of the unnecessary light at a surface on which the lenses contact each other. 
     SUMMARY OF INVENTION 
     A camera lens unit includes a first lens including a first lens section having a first optical axis along which light runs, and a second lens. The second lens includes a second lens section having a second optical axis along which the light runs, a flange provided on an outer circumference of the second lens and having a surface facing the first lens, and a cylindrical section having an inner circumference extending from the flange along the second optical axis. The inner circumference of the cylindrical section faces the second lens section. The first lens contacts the inner circumference of the cylindrical section of the second lens and is engaged into the cylindrical section. The cylindrical section of the second lens includes plural protrusions protruding along the second optical axis, such that plural crenels are provided between the protrusions and have heights along the second optical axis lower than the protrusions. 
     The camera lens unit prevents diffuse reflection caused by unnecessary incident light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a camera lens unit in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  is a sectional view of the camera lens unit at line  2 - 2  shown in  FIG. 1 . 
         FIG. 3A  is a perspective view of a light shield of the lens unit in accordance with the embodiment. 
         FIG. 3B  is a perspective view of a second lens of the lens unit in accordance with the embodiment. 
         FIG. 4  is a perspective view of another second lens of the lens unit in accordance with the embodiment. 
     
    
    
     REFERENCE NUMERALS 
     
         
           1  First Lens 
           2 A Second Lens 
           3  First Lens Section 
           4  Flange 
           5  Cylindrical Section 
           6  Second Lens Section 
           7  Flange 
           8  Protrusion 
           14  Light Shield Sheet (Light Shield) 
           15  Light Shield Board 
           16  First Annular Section 
           17  Second Annular Section 
           18  Joint 
           20  Lens Holder 
           21  Hole 
           22  Notch 
           23  Crenel 
           102 A Lens (Second Lens) 
           108  Cylindrical Section 
           208  Protrusion 
       
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a sectional view of camera lens unit  1001  in accordance with an exemplary embodiment of the present invention.  FIG. 2  is a sectional view of lens unit  1001  at line  2 - 2  shown in  FIG. 1 .  FIGS. 3A and 3B  are perspective views of light shield sheet  14  as a light shield and second lens  2 A of lens unit  1001 . Lens unit  1001  includes first lens  1  and second lens  2 A located in this order from an object along direction D 1 . Lens unit  1001  has optical axis  1001 A extending through these lenses. 
     First lens  1  includes first lens section  3 , flange  4 , and cylindrical section  5 . First lens section  3  is placed at center portion  101  through which optical axis  1001 A extends. Flange  4  is provided at an outer circumference of first lens section  3 . Cylindrical section  5  extends in direction opposite to direction D 1 , i.e., extends from an outer circumference of flange  4  toward an imaging surface  2001 . First lens section  3 , flange  4 , and cylindrical section  5  are unitarily formed together as first lens  1  made of light-transmittable material, such as glass or resin. First lens  3  through which optical axis  1001 A extends has first optical axis  1 E coinciding with optical axis  1001 A, and functions as an optical system for transmitting light from the object to imaging surface  2001 . 
     Second lens  2 A includes second lens section  6  placed at center portion  12 A through which the optical axis extends, flange  7  provided on an outer circumference of second lens section  6 , and cylindrical section  108  extending from the outer circumference in direction D 1 . Second lens  6 , flange  7 , and cylindrical section  108  are unitarily formed together as second lens  2 A made of light-transmittable material, such as glass or resin. Second lens section  6  through which optical axis  1001 A extends has second optical axis  2 E coinciding with optical axis  1001 A and functions as the optical system for transmitting the light from the object to imaging surface  2001 . Cylindrical section  108  is cut out to have a comb-tooth shape having its height in a direction along optical axis  1001 A changing at six positions at constant intervals along the circumference direction of the cylindrical section. Crenels  23  are provided between respective ones of protrusions  8  adjacent to each other. Height H 1  of protrusions  8  in the direction of optical axis  1001 A ( 2 E) is larger than height H 2  of crenels  23  in the direction of optical axis  1001 A ( 2 E). Height H 2  of lens unit  1001  shown in  FIGS. 1 to 3B  is zero. 
     Cylindrical section  108  has inner wall  108 A extending along second optical axis  2 E and facing second lens section  6 . First lens  1  securely contacts inner wall  108 A and engaged into cylindrical section  108 . 
     According to this embodiment, surface  1 C of first lens section  3  is convex toward the object, and surface  1 D is concave from imaging surface  2001 . Surface  2 C of second lens section  6  is convex from the object, and surface  2 D is convex toward imaging surface  2001 . Lens sections  3  and  6  may have any shapes according to their optical design. 
     While second optical axis  2 E of second lens  2 A coincides with first optical axis  1 E of first lens  1 , flange  4  and cylindrical section  5  of first lens  1  is engaged into cylindrical section  108  of second lens  2 A. Flange  7  of second lens  2 A has top surface  7 A facing first lens  1 . Light shield sheet  14 , the light shield, has surface  14 A and surface  14 B opposite to surface  14 A. Light shield sheet  14  is placed on top surface  7 A of flange  7 , so that surface  14 A of sheet  14  contacts top surface  7 A of flange  7 . End surface  5 A of cylindrical section  5  of first lens  1  faces imaging surface  2001  and contacts surface  14 B of light shield sheet  14 . In other words, light shield sheet  14  is placed between end surface  5 A of cylindrical section  5  of first lens  1  and top surface  7 A of flange  7  of second lens  2 A. 
     Light shield sheet  14  is made of resin, such as polyethylene telephthalate (PET), in black color, and has an annular shape. Outer diameter  14 C of sheet  14  is substantially identical to the outer diameter of flange  7  facing the object. Sheet  14  has six notches  22  provided at its outer circumference into which protrusions  8  of second lens  2 A are inserted. Hole  21  provided in the center of sheet  14  has an area such that sheet  14  does not block light path  1001 B through which the light from the object runs through the optical systems (lens sections  3  and  6 ) of lenses  1  and  2 A. Light shield sheet  14  may function as an aperture designed with the optical system. Sheet  14  covers top surface  7 A of flange  7  and crenels  23  provided between protrusions  8  of cylindrical section  108 , thereby blocking the light. 
     Lens unit  1001  includes light shield board  15  placed between lens  1  and lens  2 A. Light shield board  15  has first annular section  16  contacting surface  1 D of first lens  1 , second annular section  17  contacting surface  14 A of light shield sheet  14 , and joint  18  coupling an inner circumference of first annular section  16  to an outer circumference of second annular section  17 . Light shield board  15  blocks unnecessary incident light entering into lens unit  1001  securely, thereby preventing diffuse reflection of the incident light. Lens unit  1001  is held with an inner wall of lens holder  20 . 
     Lens holder  20  includes flange  9 . Flange  9  extends from the bottom which directs toward imaging surface  2001  to the inside along the radial direction. Recess  10  is provided in the inner wall near the top end directing toward the object, so that the inner diameter is large at recess  10 . Outer circumference  7 C of flange  7  securely contacts inner wall  20 A of lens holder  20 . Flange  7  of second lens  2 A contacts the top surface of flange  9  of lens holder  20  facing towards the object. This structure allows lens holder  20  to accommodate second lens  2 A while the center axis of lens holder  20  coincides with second optical axis  2 E of second lens  2 A. 
     Aperture  11  including annular section  12  is placed on surface  1 C of first lens  1  facing toward the object. The outer circumference of annular section  12  bent inside toward imaging surface  2001 , and the inner circumference thereof is bent outside toward the object. Aperture  11  is engaged into recess  10  provided near the top end of lens holder  20 , so that annular section  12  securely contacts top surface  4 A of flange  4  of first lens  1 . Energy, such as ultrasonic wave energy, is applied to top end  20 B so that top end  20 B can be softened and squashed, and aperture  11  is fixed to lens holder  20  together with first lens  1  and second lens  2 A. 
     Flange  9  of lens holder  20  has flaring section  13  having an inner wall flaring toward imaging surface  2001 . Flaring section  13  prevents light coming from second lens  2 A from diffusely reflecting on the inner wall of flange  9 . 
     Lens unit  1001  together with lens holder  20  is engaged into a lens-barrel, and are placed on an image sensor, such as a CCD or a CMOS. Light running through lens unit  1001  forms an image on a light receiving section of the image sensor, and the image is then converted into electronic data. 
     Top surface  7 A of flange  7  of second lens  2 A is flush with crenels  23  provided between protrusions  8  of cylindrical section  108 . This structure allows single light shield sheet  14  to block the light between lens  1  and lens  2 A, hence simplifying processes of manufacturing lens unit  1001  and reducing its cost. Top surface  7 A may not be necessarily flush with crenels  23 . 
       FIG. 4  is a perspective view of another second lens  102 A of lens unit  1001 . Lens  102 A includes lens section  106  at the center portion through which optical axis  1001 A runs, flange  107  provided on an outer circumference of lens section  106 , and cylindrical section  118  extending from an outer circumference of flange  107  along direction D 1 . Lens section  106 , flange  107 , and cylindrical section  118  are unitarily formed together as lens  102 A made of light-transmittable material, such as glass or resin. Lens section  106  through which optical axis  1001 A runs has second optical axis  2 E coinciding with optical axis  1001 A, and functions as an optical system transmitting the light from the object to imaging surface  2001 . Cylindrical section  118  has a height changing at six positions apart at constant intervals along the circumferential direction, that is, is cut out to have a comb tooth shape having plural protrusions  208 . Crenels  208  are provided between respective ones of protrusions  208  adjacent to each other. Height H 1  of protrusions  208  along optical axis  1001 A ( 2 E) is larger than height H 2 B of crenels  123  along optical axis  1001 A ( 2 E). 
     Cylindrical section  118  has inner wall  118 A extending from flange  107  facing lens section  106  along second optical axis  2 E. That is, protrusions  208  and crenels  123  have inner walls  208 A and inner walls  123 A facing lens section  106 , respectively. First lens  1  securely contacts another second lens  102 A at inner wall  118 A of cylindrical section  118  of lens  102 A. That is, first lens  1  securely contacts inner wall  208 A of protrusions  208  and inner wall  123 A of crenels  123 , so that lens  1  is engaged into cylindrical section  118 . 
     The lens unit including second lens  102 A instead of second lens  2 A has cylindrical section  118  cut out to have a comb tooth shape along the circumferential direction, thus having protrusions  208 . A small contacting area is provided between the outer circumference of first lens  1  and inner wall  208 A of protrusions  208  of lens  102 A. This structure reduces diffuse reflection caused by unnecessary incident light into the lens unit. As a result, the structure having second lens  102 A reduces diffuse reflection caused by unnecessary incident light into the lens unit, accordingly providing a clear image. 
     Lens unit  1001  in accordance with this embodiment is not limited to that discussed above. Lens unit  1001  is applicable to any application. For instance, in lens unit  1001  in accordance with this embodiment, first optical axis  1 E of first lens  1  coincides with second optical axis  2 E, and coincides with optical axis  1001 A of lens unit  1001 . However, these optical axes may not necessarily coincide with each other. 
     The number of the lenses may be three or more. Cylindrical sections  108  (protrusions  8  and  208 ) are provided at the interface between the lenses, providing the same effects. 
     The size and intervals of protrusions  8  along the circumferential direction may be changed appropriately. 
     INDUSTRIAL APPLICABILITY 
     A camera lens unit according to the present invention reliably prevents diffuse reflection caused by unnecessary incident light, thus being applicable for a camera lens unit including plural lenses.