Abstract:
To provide a small lens for optical use which enables a lens per se to be coated easily and securely and to be readily positioned in a lens barrel into which it is mounted subsequently. Either a circumferential shape of a flange is formed polygonally on a plane orthogonal to an optical axis or at least two sides of the flange are formed linearly in a length equal to or longer than a diameter of the lens per se.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a small lens for optical use, and more particularly to a small lens for optical use suitable for coating of the lens per se to prevent reflection or some other purpose.  
           [0003]    2. Description of the Related Art  
           [0004]    To form a small lens for optical use according to the prior art, made of plastic for instance as shown in FIG. 1 through FIG. 4, pelletized plastic material  102  is dried by putting it into a drier  101  of an injection molding unit  100 ; the plastic material  102  is melted in a cylinder  103 ; this molten plastic material  102  is injected into a metallic mold  104  using a screw  105 ; the metallic mold  104  is opened after waiting until it cools down; a pair of gates  108  are provided at a tip of each of runners  107  extending in four directions from a spool  106  as shown in FIG. 5, and a molded lens  200  is formed at the tip of each of the gates  108 . In FIG. 5 and FIG. 6, respectively the same reference signs are assigned to what are formed in the positions corresponding to the spool  106 , the runners  107  and the gates  108  of the metallic mold  104 . A front view of one of these molded lenses  200  is shown in FIG. 7. The diameter of this lens  200  is 3 mm. All around the outer circumference of the lens per se  200 A is formed a circular flange  200 B, of which one face is referred to as a bearing surface A 1 ; the other face, as a bearing surface A 2 ; and the side circumference of the circle is denoted by R. When both faces of the lens per se  200 A are to be coated, these bearing surfaces A 1  and A 2  and the side circumference R are supported by coat jigs  110  as illustrated in FIG. 8. In a state in which the lenses  200  are supported by the coat jigs  110 , both optically functional faces of the lenses per se  200 A are coated by vapor deposition. Then, each of these lenses  200  is fitted to a lens mount  300  in the lens barrel by utilizing the bearing surface A 1  and the side circumference R as shown in FIG. 9.  
           [0005]    The coating method and the means for fitting into the lens barrel according to the prior art pose no problem where the thickness and the radial length of the circular flange  200 B are sufficiently great, but a small lens of less than 3 mm, or even 2 mm or less, would pose a problem because the area of its bearing surface A 1  becomes too small. As shown in FIG. 10, if a lens  200  of this size is coated (by vapor deposition) while it is supported by coat jigs  110  having the largest hole (φD) compatible with the optically functional face (φF) of the lens per se  200 A, the coat on the periphery of the optically functional face will become shadowed. Thus, the coat layer on the periphery of the optically functional face will become thinner than the central part or uneven. Moreover, when the lens  200  is set to the coat jigs  110  by an automatic machine, the lens  200  may not fit stably on account of the small area of its bearing surface A 1 , possibly resulting in inclined setting of the lens  200  to the coat jigs  110  and accordingly in faulty coating. Furthermore, when the lens  200  is mounted into the lens barrel after it is coated, the small area of the bearing surface A 1  would make the positioning difficult.  
         SUMMARY OF THE INVENTION  
         [0006]    In view of these problems, the present invention is intended to provide a small lens for optical use which enables the lens per se to be coated easily and securely and to be readily positioned in the lens barrel into which it is mounted subsequently.  
           [0007]    In order to attain the object stated above, in a small lens for optical use having a flange formed around the lens per se according to the present invention, either the circumferential shape of the flange is formed polygonally on a plane orthogonal to the optical axis or at least two sides of the flange are formed linearly in a length equal to or longer than the diameter of the lens per se, and preferably the circumferential shape of the flange should be rectangular.  
           [0008]    Since either the circumferential shape of the flange is formed polygonally on a plane orthogonal to the optical axis or at least two sides of the flange are formed linearly in a length equal to or longer than the diameter of the lens per se according to the invention, when the optically functional faces of the lens are to be coated, coating can be accomplished easily and securely by supporting the long flange in the outward extending part of the lens per se with coat jigs. At the time of mounting the lens into the lens barrel, the lens can be prevented from turning within the lens barrel by utilizing one side of the polygon or the linear sides of the flange. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic diagram of an apparatus for forming a lens by injection molding;  
         [0010]    [0010]FIG. 2 shows a section in a state immediately before plastic material is injected into a metallic mold;  
         [0011]    [0011]FIG. 3 shows a section in a state in which the plastic material has been injected into the metallic mold;  
         [0012]    [0012]FIG. 4 shows a section in a state in which the plastic material has been cooled and solidified and the metallic mold has been opened;  
         [0013]    [0013]FIG. 5 shows a perspective view of a plastic product taken out of the metallic mold;  
         [0014]    [0014]FIG. 6 shows a perspective view of a state in which molded products have been removed from the gates;  
         [0015]    [0015]FIG. 7 shows a front view of a molded lens;  
         [0016]    [0016]FIG. 8 shows a section in a state in which the molded lens is supported by coat jigs;  
         [0017]    [0017]FIG. 9 shows a section in a state in which the lens is mounted in a lens barrel;  
         [0018]    [0018]FIG. 10 is a sectional diagram illustrating an inconvenience suffered in coating a small lens;  
         [0019]    [0019]FIG. 11 shows a plan of a small lens for optical use according to the present invention;  
         [0020]    [0020]FIG. 12 show a section of FIG. 11 along a line X-X;  
         [0021]    [0021]FIG. 13 shows a section of a lens held between the coat jigs;  
         [0022]    [0022]FIG. 14 shows a plan of a lens mounted in a lens barrel;  
         [0023]    [0023]FIG. 15 shows a section of FIG. 14 along a line A-A;  
         [0024]    [0024]FIG. 16 shows a section of FIG. 14 along a line B-B;  
         [0025]    [0025]FIG. 17 shows a horizontal section of the lens barrel before a lens is mounted therein;  
         [0026]    [0026]FIG. 18 shows a plan of a lens representing another mode of implementing the present invention; and  
         [0027]    [0027]FIG. 19 shows a plan of a lens representing still another mode of implementing the present invention in a state in which it is set to coat jigs. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.  
         [0029]    [0029]FIG. 11 shows a plan of a lens  1 , in which a flange  11  is formed around a lens per se  10 , and a circumferential shape of this flange  11  is formed in a square. One side of this square flange  11  constitutes a gate  2 . The size of this small lens  1  for optical use is such that each side of the flange  11  is 1.3 mm. Further, each side of the square formed by this flange  11  is tangent to a circle formed by a round body (convex  4 ) around the lens per se  10 .  
         [0030]    [0030]FIG. 12 show a section of FIG. 11 along a line X-X. Either the top of one optically functional face  10 A and that of the periphery  3  are set to be as high or that of the periphery is set higher, the convex  4  is formed on the periphery of the other optically functional face  10 B, and the top of this convex  4  is formed higher than (or as high as) that of the optically functional face  10 B. The projecting height of this convex  4  from the flange  11  is supposed to be 0.1 mm in this embodiment.  
         [0031]    The small lens  1  for optical use shown in FIG. 11 and FIG. 12 is formed from the plastic material  102  by injection molding using the injection molding unit  100  described above.  
         [0032]    The upper and lower parts of the flange  11  outward in the radial direction from the round body of the aforementioned convex  4  respectively constitute bearing surfaces  11 A and  11 B.  
         [0033]    The small lens  1  for optical use formed by injection molding from the plastic material in this manner undergoes coating of its optically functional faces  10 A and  10 B for the prevention of reflection, for instance. In this coating process, the bearing surfaces  11 A and  11 B of the flange  11  of the lens  1  are held between and supported by a pair of plates  20 A and  20 B of coat jigs  20  (see FIG. 13). At this time, with the bore of the hole in the plate  20 A, one of the paired plates  20 A and  20 B, being represented by D 1  and that of the other plate  20 B by D 2 , the diameter of the optically functional face  10 A by f 1  and that of the optically functional face  10 B by f 2 , there can be allowed a sufficient gap between f 1  and D 1 , and so can be between f 2  and D 2 , with the result that the coat in the peripheries of the optically functional faces are not shadowed when the optically functional faces  10 A and  10 B are coated. Coating of the optically functional faces  10 A and  10 B is usually accomplished by vapor deposition. A plurality of holes to support a plurality of lenses  1  are bored in the pair of plates  20 A and  20 B, and each of the lenses  1  is set into one or another of the holes in the plate  20 B in a state in which the plate  20 A is opened. By closing the plate  20 A, the lens  1  is held between the plates  20 A and  20 B. In this state, the coat jigs  20  are brought into the vapor deposition chamber, wherein vapor deposition material evaporating from the vapor deposition source is deposited on the optically functional faces  10 A and  10 B.  
         [0034]    [0034]FIG. 14 shows a plan of the lens  1  mounted on a lens mount  30  within the lens barrel. A section along a line A-A in this FIG. 14 is as shown in FIG. 15, and represents the position in which the convex  4  of the round body of the lens  1  is mounted. FIG. 16 shows a section of FIG. 14 along a line B-B, wherein rotation regulating convexes  31  are formed integrally with the lens mount  30  and have a function to restrain rotation. The outer circumferential part of the convex  4  formed on the lens  1 , denoted by sign  4 A, enables the lens  1  to be positioned by utilizing this circumference, namely the circular part. A side of the flange  11 , positioned above this convex  4  in the drawing is linear, and the rotation regulating convexes  31  come into contact with this linear part  11 Z to prevent the lens  1  from turning within the lens barrel. Incidentally, at the time of trying to position the lens  1 , the part matching the gate  2  should be brought into a prescribed position.  
         [0035]    [0035]FIG. 17 shows a horizontal section of the lens barrel deprived of the lens  1  in the state of FIG. 16. Between the paired rotation regulating convexes  31 , right and left, there is a hole  32 , and on the circumference of this hole  32  is formed a stepped part  33 , the convex  4  of the lens  1  being mounted on this stepped part  33 .  
         [0036]    To add, although the aforementioned flange  11  is formed in a rectangle, or a square in this particular embodiment, its circumferential shape can as well be formed in a hexagon as shown in FIG. 18, or in a pentagon or a triangle, too. Or, as shown in FIG. 19, the circumferential shape of the flange  11  need not be hexagonal, but forming at least two sides of it straight would also be adequate. The gate  2  can be formed on one of the straight sides. In the injection molding of a plastic lens, with the flow (orientation) of resin taken into consideration, the greater the gate width, the more favorable the optical characteristics of the resultant lens. Therefore it is preferable to provide the gate  2  on one of the straight sides. Furthermore, since this would make the protrusion in the radial direction smaller, there will be no dependence on the shape of the lens barrel, the coat jigs or the like. Moreover, the absence of prominent protrusion makes it possible for the coat jigs to accommodate a correspondingly greater number of lens, and therefore the productivity will also rise. However, where it is imperative to use two linear sides to restrain rotation, the orientation would not pose so much of a problem because the gate  2  can secure a width substantially equal to the lens diameter even if the gate  2  is formed on a curvilinear face. Therefore, if the lens barrel, the coat jigs or the like provide a part into which the protrusion of the gate can escape, the gate  2  can as well be arranged there. Where the circumferential shape of the flange  11  is polygonal, one side of it can be formed into the gate  2 . FIG. 19 shows a plan of a state in which this lens is supported by the coat jigs  20 .  
         [0037]    What constitutes the largest circle on the outside of the lens per se  10  is the convex  4  in this embodiment, and the flange  11  is formed outside this round body. Since extension of equally long parts of the flange  11  from the whole circumference of this round body would be a waste of the material, where the flange  11  is rectangular, it is so configured that its four sides be tangent on the outermost circle (the outer circumference of the convex  4 ) and each corner be supported on one of the coat jigs  20 . Even where each side of the flange  11  is not tangent on the round body, the rectangular flange  11  should be so formed that each of its sides be close to a tangent on the circle.  
         [0038]    Or in the flange  11  in which at least two sides are linear, these two sides should be linear parts to which tangents on the round body are close.  
         [0039]    Although the lens  1  is supposed to be formed by injection molding of plastic material in the above-described embodiment of the present invention, this process can undoubtedly be applied as well to glass lenses formed by pressing molten glass.