Abstract:
Provided is an imaging lens, the imaging lens including in an orderly way from an object side, a first lens including an incidence surface having a positive (+) refractive power and incident with light, a reflecting surface reflecting the incident light and an exit surface outputting the reflected light; a second lens having a negative (−) refractive power; a third lens having a positive (+) refractive power; a fourth lens having a positive (+) refractive power; a fifth lens having a negative (−) refractive power; a sixth lens having a positive (+) refractive power; and a seventh lens having a positive (+) refractive power, wherein the second lens through the seventh lens are disposed in an orderly way from an exit surface of the first lens.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119 of Korean Application No. 10-2009-0124946, filed on Dec. 15, 2009, which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Invention 
     The present invention relates to an image lens, and in particular, to a wide angle lens widen with a viewing angle. 
     2. Discussion of the Related Art 
     Recently, vigorous research efforts are being made in the field of a mobile phone-purpose camera module, a digital still camera (DSC), a camcorder, and a PC camera (an imaging device attached to a person computer) all connected with an image pick-up system. One of the most important components in order that a camera module related to such an image pickup system obtains an image is an imaging lens producing an image. 
     A camera module generally realizes an image by refracting light using optical material. A wide angle lens favorable when photographing many people in a small space by ampling an imaging angle embodies a wide angle optical system by a negative and positive (−)(+) structure group (retro-focus) formulating several pieces of negative (−) power lenses at the front side to enlarge an imaging angle range. In this case, a cost allocation is much required, and a thickness due to construction of several pieces when compacted cameras should be realized becomes burdensome. 
     BRIEF SUMMARY 
     The present invention provides a wide angle lens devoid of a thickness burden due to a lens constituting in several pieces, especially, it provides a wide angle lens excellent in aberration characteristic. 
     An image lens according to one embodiment of the present invention comprises in an orderly way from an object side, a first lens including an incidence surface having a positive (+) refractive power and incident with light, a reflecting surface reflecting the incident light and an exit surface outputting the reflected light; a second lens having a negative (−) refractive power; a third lens having a positive (+) refractive power; a fourth lens having a positive (+) refractive power; a fifth lens having a negative (−) refractive power; a sixth lens having a positive (+) refractive power; and a seventh lens having a positive (+) refractive power, wherein the second lens through the seventh lens are disposed in an orderly way from an exit surface of the first lens. 
     A wide angle lens module according to the present embodiment provides a wide angle lens without thickness concern in the result of applying a reflecting surface of an aspheric surface to a first lens to enlarge an imaging angle. A wide angle lens superior in optical characteristic may be realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a construction diagram of an imaging lens according to the present embodiment; 
         FIG. 2  is a graph showing Coma aberration according to the present embodiment; and 
         FIG. 3  is a graph showing MTF (modulation transfer function) characteristic according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Since the present invention can be applied with various changes thereto and have several types of embodiments, specific embodiments intend to be exemplified in the drawings and minutely described in the detailed description. However, it does not limit the present invention to a specific example but should be appreciated to include all the changes, equivalents and replacements which fall in the spirit and technical scope of the present invention. 
     Stated that any component is “connected” or “conjunctive” to another component, it will be appreciated to be directly connected or conjunctive to the very another component or otherwise that there exists any component in the midst of them. 
     In the following, the present invention will be described in detail referring to the attached drawings, but without regard to a drawing sign, an identical or corresponding component is assigned the same reference numeral and a redundant description regarding this will be omitted. 
     As a construction diagram of an imaging lens according to the present embodiment,  FIG. 1  is a lateral surface construction diagram exemplifying a layout state of a lens around an optical axis ZO. In the construction of  FIG. 1 , a thickness, size, and shape of a lens are rather overdrawn for description, and a spheric or aspheric shape has been only presented as one embodiment, but obviously not limited to this shape. 
     Referring to  FIG. 1 , an imaging lens of the present invention has a layout construction with a first lens  10 , a second lens  20 , a third lens  30 , a fourth lens  40 , a fifth lens  50 , a sixth lens  60 , a seventh lens  70 , a filter  80 , and a light receiving element  90  in order from an object side. Light corresponding to image information of a subject passes through the first lens  10 , the second lens  20 , the third lens  30 , the fourth lens  40 , the fifth lens  50 , the sixth lens  60 , the seventh lens  70  and the filter  80  to be incident on the light receiving element  90 . 
     Hereinafter, in description of a construction of each lens, “object side surface” means a surface of a lens facing an object side to an optical axis, and “image side surface” means a surface of a lens facing an image surface to an optical axis. 
     A first lens  10  includes an incidence surface S 12 , S 13  having a positive (+) refractive power and on which light is incident, a reflecting surface S 11 , S 17 , S 18  reflecting incident light and an exit surface S 16  where there outputs reflected light, wherein an object side surface is concavely formed. A surrounding part of an object side surface S 10  of a first lens  10  may include an incidence surface S 12 , S 13 , a central part may include a reflecting surface S 11 , and a reflecting surface S 11  is concavely formed. A surrounding part of an imaging side surface S 20  of a first lens  10  may include a reflecting surface S 17 , S 18  and a central part may include an exit surface S 16 . 
     A second lens  20  has negative (−) refractive power, and constructed of a meniscus form in which an object side surface S 30  is convexly formed. 
     A third lens  30  has positive (+) refractive power, and constructed of a meniscus form convexly formed at an object side surface S 50 . A fourth lens  40  has positive (+) refractive power, both surfaces of an object side surface S 70  and S 80  are forms formulated convexly. An object side surface S 80  of a fourth lens  40  may act as an aperture, and in this case, an imaging lens of the present embodiment may not need an additional aperture. Also, an aperture is placed between a fourth lens  40  and a fifth lens  50 . 
     A fifth lens  50  has negative (−) refractive power, and constructed of a form formulated concavely at both an object side surface S 90  and an imaging side surface S 100 . 
     A sixth lens  60  has positive (+) refractive power, and is a meniscus form formulated convexly at an object side surface S 110 . A seventh lens  70  has positive (+) refractive power, and is a meniscus form in which an object side surface S 130  is concavely formed. 
     As shown in the figure, an incidence surface S 12 , S 13  and an reflecting surface S 17 , S 18  of the first lens  10  and an object side surface S 130  and an imaging side surface S 140  of a seventh lens  70  are constructed of an spheric face. The first lens  10  is a lens containing a reflecting surface, the second lens  20  through the sixth lens  60  are formed of glass, and the seventh lens  70  may be formed of a plastic lens. 
     The filter  80  is at least any one of optical filters such as an infrared filter and a cover glass. A filter  40 , in a case an infrared filter is applied, blocks such that radiating heat emitting from external light does not transfer to the light receiving element  90 . Also, an infrared filter penetrates visible light and reflects infrared for outflow to an external part. 
     The light receiving element  90  is an imaging sensor such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor). 
     The first lens  10  uses an aspheric lens like a later-described embodiment, thereby improving resolution of a lens and taking an advantage of superior aberration characteristic. A later-described conditions and embodiment is a preferred embodiment raising an action and effect, and it would be understood by a person in the art that the present invention should be constructed of the following conditions. For example, a lens construction of the invention will have a raised action and effect only by satisfying part of conditions among lower-part described condition equations.
 
−2 &lt;k 1&lt;−1.0  [Condition 1]
 
−1 &lt;k 2&lt;0  [Condition 2]
 
3 &lt;d 1 /d 2&lt;5  [Condition 3]
 
where, k1 is an aspheric constant of the surface S 12 , S 13  of a first lens  10 , k2 is an aspheric constant of the surface S 17 , S 18  of a first lens  10 , d1 is a diameter of the surface S 12 , S 13  of a first lens  10 , and d2 is a diameter of the surface S 17 , S 18  of the first lens  10 .
 
     Hereinafter, an action and effect of the present invention will be presented with reference to a specific embodiment. An aspheric shape mentioned in the following embodiment is obtained from a known Equation 1, and Conic constant and ‘E and its continuing number’ used in aspheric coefficient A, B, C, D, E, F indicate power of 10. For example, E+01 indicates 10 1 , and E-02 indicates 10 −2 . 
                   z   =         cY   2       1   +       1   -       (     1   +   K     )     ⁢     c   2     ⁢     Y   2               +     AY   4     +     BY   4     +     CY   4     +     DY   4     +     EY   4     +     FY   4     +   …             Equation   ⁢           ⁢   1               
where, z: distance in optical axis direction from top point of lens
 
     c: basic curvature of lens 
     Y: distance in perpendicular direction to optical axis 
     K: Conic constant 
     A, B, C, D, E, F: aspheric coefficient 
     Embodiment 
     The following Table 1 shows an embodiment complying with the above-described Condition. 
     
       
         
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Embodiment 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 k1 
                 −1.2 
               
               
                   
                 k2 
                 −0.17 
               
               
                   
                 d1 
                 16.57 
               
               
                   
                 d2 
                 4.8 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 1, k1 is −1.2, so that it can be known to match with Condition 1, k2 is −0.17, and thus matching to Condition 2 can be known. Also, since d1/d2 is 3.45, and it can be appreciated matching with Condition 3. 
     An embodiment of Table 2 shows a more specific embodiment over an embodiment of Table 1. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Surface 
                 Curvature 
                 Thickness or 
                 Refractive 
               
               
                   
                 number 
                 Radius (R) 
                 Distance (d) 
                 index (N) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1* 
                 12.0 
                 20 
                 1.52 
               
               
                   
                  2* 
                 −13.0 
                 −18.0 
                 1.52 
               
               
                   
                  3 
                 −21.77 
                 17.45 
                 1.52 
               
               
                   
                  4 
                   
                 0.5 
               
               
                   
                  5 
                 11.70 
                 2.5 
                 1.67 
               
               
                   
                  6 
                 3.97 
                 0.54 
               
               
                   
                  7 
                 3.69 
                 2.38 
                 1.75 
               
               
                   
                  8 
                 2.8 
                 1.36 
               
               
                   
                  9 
                 5.71 
                 2.5 
                 1.62 
               
               
                   
                 10*stop 
                 −5.71 
                 1.60 
               
               
                   
                 11 
                 −36.08 
                 1.0 
                 1.76 
               
               
                   
                 12 
                 36.08 
                 1.34 
               
               
                   
                 13 
                 6.50 
                 2.5 
                 1.61 
               
               
                   
                 14 
                 24.83 
                 2.61 
               
               
                   
                 15* 
                 −1.32 
                 2.45 
                 1.53 
               
               
                   
                 16 
                 −1.41 
                 5.06 
               
               
                   
                 image 
                   
                 0 
               
               
                   
                   
               
             
          
         
       
     
     In the above Table 2 and the following Table 3, notation * stated next to surface numbers indicates an aspheric surface, and continuingly, surface number  1  indicates surfaces S 12 , S 13  of a first lens  10 , surface number  2  indicates surfaces S 17 , S 18  of a first lens  10 , surface number  3  indicates surface S 11  of a first lens  10 , and surface number  4  indicates surface S 16  of the first lens  10 . Commencing from surface number  5  to surface number  16  denote an object side surface and an imaging surface of a second lens  20  through a seventh lens  70  in regular sequence. 
     The following Table 3 indicates a value of an aspheric coefficient of each lens in an embodiment of the Table 2. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Surface 
                   
                   
                   
                   
                   
               
               
                 Number 
                 K 
                 A 
                 B 
                 C 
                 D 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  1* 
                 −1.2 
                   
                   
                   
                   
               
               
                  2* 
                 −0.17 
               
               
                 15* 
                 −164335.02 
                 −0.3065E−02 
                 0.30597E−05 
                 0.17963E−04 
                 −0.46813E−0 
               
               
                 16* 
                 −0.7098E15 
                 −0.2009983 
                 0.8336E−04 
                 −0.6496E−06 
                 −0.8921E−06 
               
               
                   
               
             
          
         
       
     
     As a graph measuring coma aberration,  FIG. 2  is a graph measuring tangential aberration and sagittal aberration of each wavelength based on a field height. In  FIG. 2 , as a graph showing a test result approaches to an X axis at a positive axis and a negative axis, respectively, it is explained that a coma aberration correction function is good. In measurement examples of  FIG. 2 , a value of images in nearly all fields appear proximate to an X axis, it is explained that all of them show a superior commatic aberration correction function. 
       FIG. 3  is a graph showing MTF (modulation transfer function) characteristic according to one embodiment of the invention.  FIG. 3  has measured an MTF characteristic depending on a variation of spatial frequencies at cycle per millimeter (cycle/mm). Here, an MTP characteristic refers to a rate obtained by calculating a difference between light starting from an original subject surface and a formed image that passes through a lens, wherein a case of MTF figure ‘1’ is the most idealistic, and as MTF values decrease, resolution falls down. 
     Referring to  FIG. 3 , since  FIG. 3  indicating that an MTF value is high, it can be known that a wide angle lens module according to an embodiment is superior in optical performance. 
     While the present invention has been described with reference to embodiments in the above part, it would be understood by those skilled in the art that various changes and modifications can be made without departing from the spirit or scope of the present invention. Therefore, not confined to the above-described embodiment, the invention would be asserted to include all embodiments within the scope of the accompanying claims.