Abstract:
There is provided an optical system including: a first lens having negative refractive power and having a meniscus shape of which an object-side surface is convex; a second lens having positive refractive power; a third lens having refractive power; and a fourth lens having positive refractive power and having a meniscus shape of which an object-side surface is convex, wherein the first to fourth lenses are sequentially disposed from an object side, whereby an aberration improvement effect, a wide field of view and a high degree of resolution may be realized.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority and benefit of Korean Patent Application No. 10-2014-0113300 filed on Aug. 28, 2014, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    The present disclosure relates to an optical system. 
         [0003]    Recent mobile communications terminals have commonly been provided with camera modules, allowing users to make video calls, as well as to capture still and moving images. In addition, as the degree of functionality of camera modules included in mobile communications terminals has gradually increased, camera modules for mobile communications terminals have come to be required to have high levels of resolution and high degrees of performance. 
         [0004]    However, since there is a trend for mobile communications terminals to be miniaturized and lightened, there are limitations in implementing camera modules having the high levels of resolution and high degrees of performance. 
         [0005]    In order to solve these problems, recently, lenses included in such camera modules have been formed of plastic, a material lighter than glass, and lens modules have been configured with five or more lenses, in order to achieve high levels of resolution in images captured thereby. 
       SUMMARY 
       [0006]    An aspect of the present disclosure may provide an optical system in which an aberration improvement effect, a high degree of resolution, and a wide field of view are realized. 
         [0007]    According to an aspect of the present disclosure, an optical system may include: a first lens having negative refractive power and having a meniscus shape of which an object-side surface is convex; a second lens having positive refractive power; a third lens having refractive power; and a fourth lens having positive refractive power and having a meniscus shape of which an object-side surface is convex, wherein the first to fourth lenses are sequentially disposed from an object side, whereby an aberration improvement effect, a wide field of view and a high degree of resolution may be realized. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]    The above and other aspects, features and advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a configuration diagram of an optical system according to a first exemplary embodiment of the present disclosure; 
           [0010]      FIG. 2  is graphs having curves representing aberration characteristics of the optical system shown in  FIG. 1 ; 
           [0011]      FIG. 3  is a table illustrating respective characteristics of lenses in the optical system illustrated in  FIG. 1 ; 
           [0012]      FIG. 4  is a table illustrating respective aspherical surface coefficients of lenses in the optical system illustrated in  FIG. 1 ; 
           [0013]      FIG. 5  is a configuration diagram of an optical system according to a second exemplary embodiment of the present disclosure; 
           [0014]      FIG. 6  is graphs having curves representing aberration characteristics of the optical system illustrated in  FIG. 5 ; 
           [0015]      FIG. 7  is a table illustrating respective characteristics of lenses in the optical system illustrated in  FIG. 5 ; 
           [0016]      FIG. 8  is a table illustrating respective aspherical surface coefficients of lenses in the optical system illustrated in  FIG. 5 ; 
           [0017]      FIG. 9  is a configuration diagram of an optical system according to a third exemplary embodiment of the present disclosure; 
           [0018]      FIG. 10  is graphs having curves representing aberration characteristics of the optical system illustrated in  FIG. 9 ; 
           [0019]      FIG. 11  is a table illustrating respective characteristics of lenses in the optical system illustrated in  FIG. 9 ; and 
           [0020]      FIG. 12  is a table illustrating respective aspherical surface coefficients of lenses in the optical system illustrated in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. 
         [0022]    The disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. 
         [0023]    In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements. 
         [0024]    In the following lens configuration diagrams, thicknesses, sizes, and shapes of lenses may be exaggerated for clarity. Particularly, the shapes of spherical surfaces and aspherical surfaces, as illustrated in the lens configuration diagrams, are only illustrated by way of example, but are not limited to those illustrated in the drawings. 
         [0025]    In addition, a first lens refers to a lens that is the closest to an object side, and a fourth lens refers to a lens that is the closest to an imaging surface. 
         [0026]    Further, a first surface of each lens refers to a surface thereof closest to an object (or an object-side surface) and a second surface of each lens refers to a surface thereof closest to an imaging surface (or an image-side surface). Further, all numerical values of radii of curvature, thicknesses, and the like, of lenses are represented by millimeters (mm). 
         [0027]    An optical system according to exemplary embodiments in the present disclosure may include four lenses. 
         [0028]    That is, the optical system may include a first lens, a second lens, a third lens, and a fourth lens. 
         [0029]    However, the optical system is not limited to including only the four lenses, but may further include other components, if necessary. For example, the optical system may include an aperture stop controlling an amount of light. In addition, the optical system may further include an infrared cut-off filter filtering infrared light. Further, the optical system may further include an image sensor converting an image of a subject incident thereon into an electrical signal. Further, the optical system may further include a gap maintaining member adjusting a gap between lenses. 
         [0030]    The first to fourth lenses configuring the optical system according to exemplary embodiments may be formed of plastic. 
         [0031]    In addition, at least one of the first to fourth lenses may have an aspherical surface. Alternatively, each of the first to fourth lenses may have at least one aspherical surface. 
         [0032]    Here, the aspherical surfaces of the first to fourth lenses may be represented by the following Equation 1: 
         [0000]    
       
         
           
             
               
                 
                   Z 
                   = 
                   
                     
                       
                         cY 
                         2 
                       
                       
                         1 
                         + 
                         
                           
                             1 
                             - 
                             
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   K 
                                 
                                 ) 
                               
                                
                               
                                 c 
                                 2 
                               
                                
                               
                                 Y 
                                 2 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       AY 
                       4 
                     
                     + 
                     
                       BY 
                       6 
                     
                     + 
                     
                       CY 
                       8 
                     
                     + 
                     
                       DY 
                       10 
                     
                     + 
                     
                       EY 
                       12 
                     
                     + 
                     
                       FY 
                       14 
                     
                     + 
                     … 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
         [0033]    Here, c is curvature (the inverse of a radius of curvature) at an apex of the lens, K is a conic constant, and Y is a distance from a certain point on the aspherical surface of the lens to an optical axis in a direction perpendicular to the optical axis. In addition, constants A to F refer to aspherical surface coefficients. In addition, Z is a distance between the certain point on the aspherical surface at the distance Y and a tangential plane meeting the apex of the aspherical surface of the lens. 
         [0034]    The optical system including the first to fourth lenses may have negative refractive power/positive refractive power/positive or negative refractive power/positive refractive power in respective lenses thereof, sequentially from the object side. 
         [0035]    The optical system configured as described above may have a wide field of view and improve optical performance through aberration improvement. 
         [0036]    The optical system according to exemplary embodiments may satisfy Conditional Expression 1. 
         [0000]      FOV≧80  [Conditional Expression 1]
 
         [0037]    Here, FOV is a field of view of the optical system. 
         [0038]    The optical system according to exemplary embodiments may satisfy Conditional Expression 2. 
         [0000]      FOV/ TTL&gt; 25  [Conditional Expression 2]
 
         [0039]    Here, FOV is the field of view of the optical system, and TTL is a distance from the object-side surface of the first lens to an imaging surface of the image sensor. 
         [0040]    The optical system according to exemplary embodiments may satisfy Conditional Expression 3. 
         [0000]        TTL/F≦ 2.30  [Conditional Expression 3]
 
         [0041]    Here, TTL is the distance from the object-side surface of the first lens to the imaging surface of the image sensor, and F is an overall focal length of the optical system. 
         [0042]    The optical system according to exemplary embodiments may satisfy Conditional Expression 4. 
         [0000]      −2.3&lt; F 1/ F&lt;− 2.0  [Conditional Expression 4]
 
         [0043]    Here, F 1  is a focal length of the first lens, and F is the overall focal length of the optical system. 
         [0044]    The optical system according to exemplary embodiments may satisfy Conditional Expression 5. 
         [0000]        F 2/ F≧ 0.73  [Conditional Expression 5]
 
         [0045]    Here, F 2  is a focal length of the second lens, and F is the overall focal length of the optical system. 
         [0046]    The optical system according to exemplary embodiments may satisfy Conditional Expression 6. 
         [0000]      −5.0&lt; F 3/ F&lt; 20.0  [Conditional Expression 6]
 
         [0047]    Here, F 3  is a focal length of the third lens, and F is the overall focal length of the optical system. 
         [0048]    The optical system according to exemplary embodiments may satisfy Conditional Expression 7. 
         [0000]      4.0&lt; F 4/ F&lt; 8.0  [Conditional Expression 7]
 
         [0049]    Here, F 4  is a focal length of the fourth lens, and F is the overall focal length of the optical system. 
         [0050]    The optical system according to exemplary embodiments may satisfy Conditional Expression 8. 
         [0000]      2.1&lt; TTL /Img H&lt; 2.7  [Conditional Expression 8]
 
         [0051]    Here, TTL is the distance from the object-side surface of the first lens to the imaging surface of the image sensor, and ImgH is a diagonal length of the imaging surface of the image sensor. 
         [0052]    Next, the first to fourth lenses configuring the optical system according to exemplary embodiments will be described. 
         [0053]    The first lens may have negative refractive power. In addition, the first lens may have a meniscus shape of which an object-side surface is convex. In detail, first and second surfaces of the first lens may be convex toward the object. 
         [0054]    At least one of the first and second surfaces of the first lens may be aspherical. 
         [0055]    The second lens may have positive refractive power. In addition, both surfaces of the second lens may be convex. 
         [0056]    At least one of first and second surfaces of the second lens may be aspherical. For example, both surfaces of the second lens may be aspherical. 
         [0057]    The third lens may have positive or negative refractive power. In addition, the third lens may have a meniscus shape of which an image-side surface is convex. In detail, first and second surfaces of the third lens may be convex toward the imaging surface. 
         [0058]    At least one of the first and second surfaces of the third lens may be aspherical. For example, both surfaces of the third lens may be aspherical. 
         [0059]    The fourth lens may have positive refractive power. In addition, the fourth lens may have a meniscus shape of which an object-side surface is convex. In detail, first and second surfaces of the fourth lens may be convex toward the object. 
         [0060]    At least one of the first and second surfaces of the fourth lens may be aspherical. For example, both surfaces of the fourth lens may be aspherical. 
         [0061]    In addition, the fourth lens may have at least one inflection point formed on the first surface thereof, and also have at least one inflection point formed on the second surface thereof. For example, the second surface of the fourth lens may be concave in the paraxial region and become convex at an edge thereof. 
         [0062]    In the optical system configured as described above, a plurality of lenses perform an aberration correction function, whereby aberration performance may be improved. 
         [0063]    In addition, the optical system may have a wide field of view (FOV). 
         [0064]    In addition, in the optical system, all of the lenses are formed of plastic, whereby costs associated with lens module manufacturing may be decreased and efficiency in the lens module manufacturing may be increased. 
         [0065]    An optical system according to a first exemplary embodiment of the present disclosure will be described with reference to  FIGS. 1 through 4 . 
         [0066]    The optical system according to the first exemplary embodiment may include a first lens  110 , a second lens  120 , a third lens  130 , and a fourth lens  140 , and may further include an infrared cut-off filter  150  and an image sensor  160 . 
         [0067]    Here, as shown in Table 1, a field of view (FOV) of the optical system may be 90 degrees, a distance (TTL) from an object-side surface of the first lens  110  to a first surface (imaging surface) of the image sensor  160  may be 3.04 mm, and a diagonal length (ImgH) of the first surface (imaging surface) of the image sensor  160  may be 1.39 mm. 
         [0068]    In addition, a focal length (F 1 ) of the first lens  110  may be −2.83 mm, a focal length (F 2 ) of the second lens  120  may be 1.02 mm, a focal length (F 3 ) of the third lens  130  may be 20.10 mm, a focal length (F 4 ) of the fourth lens  140  may be 10.04 mm, and an overall focal length (F) of the optical system may be 1.36 mm. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 FOV 
                 90 
               
               
                   
                 TTL 
                 3.04 
               
               
                   
                 ImgH 
                 1.39 
               
               
                   
                 F  
                 1.36 
               
               
                   
                 F1 
                 −2.83 
               
               
                   
                 F2 
                 1.02 
               
               
                   
                 F3 
                 20.1 
               
               
                   
                 F4 
                 10.04 
               
               
                   
                   
               
             
          
         
       
     
         [0069]    In addition, respective characteristics (radii of curvature, thicknesses of lenses or distances between the lenses, refractive indices, and Abbe numbers) of lenses are shown in  FIG. 3 . 
         [0070]    In the first exemplary embodiment, the first lens  110  may have negative refractive power, and have a meniscus shape of which an object-side surface is convex. The second lens  120  may have positive refractive power and both surfaces thereof may be convex. The third lens  130  may have positive refractive power and have a meniscus shape of which an image-side surface is convex. The fourth lens  140  may have positive refractive power and have a meniscus shape of which an object-side surface is convex. In addition, the fourth lens  140  may have at least one inflection point formed on each of first and second surfaces thereof. 
         [0071]    Meanwhile, the respective surfaces of the first to fourth lenses  110  to  140  may have aspherical surface coefficients as shown in  FIG. 4 . That is, the first to fourth lenses  110  to  140  may have aspherical surfaces, respectively. 
         [0072]    In addition, the optical system configured as described above may have aberration characteristics shown in  FIG. 2 . 
         [0073]    An optical system according to a second exemplary embodiment of the present disclosure will be described with reference to  FIGS. 5 through 8 . 
         [0074]    The optical system according to the second exemplary embodiment of the present disclosure may include a first lens  210 , a second lens  220 , a third lens  230 , and a fourth lens  240 , and may further include an infrared cut-off filter  250  and an image sensor  260 . 
         [0075]    Here, as shown in Table 2, a field of view (FOV) of the optical system may be 100 degrees, a distance (TTL) from an object-side surface of the first lens  210  to a first surface (imaging surface) of the image sensor  260  may be 3.13 mm, and a diagonal length (ImgH) of the first surface (imaging surface) of the image sensor  260  may be 1.39 mm. 
         [0076]    In addition, a focal length (F 1 ) of the first lens  210  may be −2.96 mm, a focal length (F 2 ) of the second lens  220  may be 1.01 mm, a focal length (F 3 ) of the third lens  230  may be −22.74 mm, a focal length (F 4 ) of the fourth lens  240  may be 6.46 mm, and an overall focal length (F) of the optical system may be 1.36 mm. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
             
               
                   
                 FOV 
                 100 
               
               
                   
                 TTL  
                 3.13 
               
               
                   
                 ImgH 
                 1.39 
               
               
                   
                 F  
                 1.36 
               
               
                   
                 F1 
                 −2.96 
               
               
                   
                 F2 
                 1.01 
               
               
                   
                 F3 
                 −22.74 
               
               
                   
                 F4 
                 6.46 
               
               
                   
                   
               
             
          
         
       
     
         [0077]    In addition, respective characteristics (radii of curvature, thicknesses of lenses or distances between the lenses, refractive indices, and Abbe numbers) of lenses are shown in  FIG. 7 . 
         [0078]    In the second exemplary embodiment, the first lens  210  may have negative refractive power, and have a meniscus shape of which an object-side surface is convex. The second lens  220  may have positive refractive power and both surfaces thereof may be convex. The third lens  230  may have negative refractive power and have a meniscus shape of which an image-side surface is convex. The fourth lens  240  may have positive refractive power and have a meniscus shape of which an object-side surface is convex. In addition, the fourth lens  240  may have at least one inflection point formed on each of first and second surfaces thereof. 
         [0079]    Meanwhile, the respective surfaces of the first to fourth lenses  210  to  240  may have aspherical surface coefficients as shown in  FIG. 8 . That is, the first to fourth lenses  210  to  240  may have aspherical surfaces, respectively. 
         [0080]    In addition, the optical system configured as described above may have aberration characteristics shown in  FIG. 6 . 
         [0081]    An optical system according to a third exemplary embodiment in the present disclosure will be described with reference to  FIGS. 9 through 12 . 
         [0082]    The optical system according to the third exemplary embodiment may include a first lens  310 , a second lens  320 , a third lens  330 , and a fourth lens  340 , and may further include an infrared cut-off filter  350  and an image sensor  360 . 
         [0083]    Here, as shown in Table 3, a field of view (FOV) of the optical system may be 80 degrees, a distance (TTL) from an object-side surface of the first lens  310  to a first surface (imaging surface) of the image sensor  360  may be 3.11 mm, and a diagonal length (ImgH) of the first surface (imaging surface) of the image sensor  360  may be 1.17 mm. 
         [0084]    In addition, a focal length (F 1 ) of the first lens  310  may be −2.88 mm, a focal length (F 2 ) of the second lens  320  may be 0.99 mm, a focal length (F 3 ) of the third lens  330  may be −6.07 mm, a focal length (F 4 ) of the fourth lens  340  may be 5.63 mm, and an overall focal length (F) of the optical system may be 1.36 mm. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
             
               
                   
                 FOV 
                 80 
               
               
                   
                 TTL 
                 3.11 
               
               
                   
                 ImgH 
                 1.17 
               
               
                   
                 F  
                 1.36 
               
               
                   
                 F1 
                 −2.88 
               
               
                   
                 F2 
                 0.99 
               
               
                   
                 F3 
                 −6.07 
               
               
                   
                 F4 
                 5.63 
               
               
                   
                   
               
             
          
         
       
     
         [0085]    In addition, respective characteristics (radii of curvature, thicknesses of lenses or distances between the lenses, refractive indices, and Abbe numbers) of lenses are shown in  FIG. 11 . 
         [0086]    In the third exemplary embodiment, the first lens  310  may have negative refractive power, and have a meniscus shape of which an object-side surface is convex. The second lens  320  may have positive refractive power and both surfaces thereof may be convex. The third lens  330  may have negative refractive power and have a meniscus shape of which an image-side surface is convex. The fourth lens  340  may have positive refractive power and have a meniscus shape of which an object-side surface is convex. In addition, the fourth lens  340  may have at least one inflection point formed on each of first and second surfaces thereof. 
         [0087]    Meanwhile, the respective surfaces of the first to fourth lenses  310  to  340  may have aspherical surface coefficients as shown in  FIG. 12 . That is, the first to fourth lenses  310  to  340  may have aspherical surfaces, respectively. 
         [0088]    In addition, the optical system configured as described above may have aberration characteristics shown in  FIG. 10 . 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                 First Exemplary  
                 Second Exemplary  
                 Third Exemplary  
               
               
                   
                 Embodiment 
                 Embodiment 
                 Embodiment 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 FOV/TTL 
                 29.61 
                 31.95 
                 25.72 
               
               
                 TTL/F 
                 2.24 
                 2.30 
                 2.29 
               
               
                 F1/F 
                 −2.08 
                 −2.18 
                 −2.12 
               
               
                 F2/F 
                 0.75 
                 0.74 
                 0.73 
               
               
                 F3/F 
                 14.78 
                 −16.72 
                 −4.46 
               
               
                 F4/F 
                 7.38 
                 4.75 
                 4.14 
               
               
                 FOV 
                 90 
                 100 
                 80 
               
               
                 TTL/ImgH 
                 2.18705036 
                 2.25179856 
                 2.6581197 
               
               
                   
               
             
          
         
       
     
         [0089]    Meanwhile, it may be appreciated from Table 4 that the optical systems according to the first to third exemplary embodiments satisfy Conditional Expressions 1 to 8 described above. Therefore, a wide field of view may be obtained, and optical performance may be improved. 
         [0090]    As set forth above, with the optical systems according to exemplary embodiments of the present disclosure, the wide field of view may be broadened, and the aberration improvement effect may be increased to improve optical performance. 
         [0091]    While exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention as defined by the appended claims.