Abstract:
An optical lens system comprises, in order from an object side to an image side: the first lens element with negative refractive power having a convex object-side surface and a concave image-side surface; the second lens element with positive refractive power; the third lens element with positive refractive power having the object-side surface and the image-side surface being aspheric; the fourth lens element with negative refractive power having a concave image-side surface and at least one aspheric surface. There are four lens elements with refractive power. Such arrangements can enable a larger field of view, reduce the volume of the system, and further obtain higher resolution for the optical lens system of the present invention.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical lens system, and more particularly to a miniaturized optical lens system used in electronic products. 
     2. Description of the Prior Art 
     In recent years, with the popularity of the portable electronic products with video recording function, the optical lens system has become smaller and smaller, and the electronic imaging sensor of a general digital camera is typically a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor. Due to advances in semiconductor manufacturing, the pixel size of sensor has been reduced continuously, and miniaturized optical lens systems have increasingly higher resolution. Therefore, there&#39;s an increasing demand for an imaging lens system with better image quality. 
     Conventional miniaturized lens systems used in portable electronic products mostly consist of three lens elements, from an object side to an image side: the first lens element with positive refractive power, the second lens element with negative refractive power and the third lens element with positive refractive power. 
     Due to advances in semiconductor manufacturing and the trend of miniaturization of electronic products, the pixel size of electronic imaging sensors gradually becomes smaller and smaller, which makes the system require an optical lens system providing higher image quality. The conventional optical lens system comprising three lens elements cannot satisfy the requirements of higher resolution optical lens systems. 
     Another type of conventional optical system is a four-piece lens assembly for example, in which the first lens element and the second lens element are both glass spherical lens elements and bonded to each other to form a doublet lens element for eliminating chromatic aberration. However, it suffers from the following disadvantages: the degree of freedom available in the optical system is limited since there are too many glass spherical lens elements; and the manufacturing difficulty is increased due to the difficult process of bonding between the glass lens elements. 
     The present invention can effectively mitigate the aforementioned disadvantages. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide an optical lens system comprising four lens element, which is capable of providing a larger field of view and higher resolution while effectively reducing the volume of the optical lens system. 
     An optical lens system in accordance with the present invention comprises, in order from an object side to an image side: the first lens element with negative refractive power having a convex object-side surface and a concave image-side surface; the second lens element with positive refractive power; the third lens element with positive refractive power, the object-side and the image-side surfaces of the third lens element being aspheric; and the fourth lens element with negative refractive power having a concave image-side surface, the object-side and the image-side surfaces of the fourth lens element being aspheric. In the optical lens system, there are four lens elements with refractive power. The distance on an optical axis between the first lens element and the second lens element is T 12 , the focal length of the optical lens system is f, and the center thickness of the first lens element is CT 1 . The optical lens system is further provided with an aperture stop, the distance from the aperture stop to an image plane along the optical axis is SL, the distance from the object-side surface of the first lens element to the image plane along the optical axis is TTL, and they satisfy the relations:
 
0.1 &lt;T 12 /f&lt; 0.3;
 
0.30 &lt;CT 1 /f&lt; 0.75;
 
0.52 &lt;SL/TTL&lt; 0.82.
 
     When 0.1&lt;T 12 /f&lt;0.3 is satisfied, it will be favorable for correcting the high order aberrations of the system, and the lens system can be more balanced. Also, it will be favorable to reduce the total track length of the optical lens system, so as to maintain the objective of miniaturization of the optical lens system. When T 12 /f satisfies the relation: 0.07&lt;T 12 /f&lt;0.50, the total track length of the optical lens system can be reduced and the image quality can be improved. When 0.30&lt;CT 1 /f&lt;0.75 is satisfied, the thickness of the first lens element is suitable, which reduces manufacturing difficulties while increasing manufacturing yield. When 0.52&lt;SL/TTL&lt;0.82 is satisfied, the wide field of view is emphasized, it will be favorable to correct the distortion and the chromatic aberration of magnification, and the optical system is less sensitive as well. 
     In the present optical lens system, the first lens element with negative refractive power has a convex object-side surface and a concave image-side surface, it will be favorable to enlarge the field of view of the optical lens system. 
     The second lens element with positive refractive power provides partial refractive power of the optical lens system, it will be favorable to reduce the total track length of the optical lens system. 
     The third lens element with positive refractive power can effectively distribute the positive refractive power of the second lens element in such a manner that the sensitivity of the optical lens system will be reduced. In the present optical lens system, if the object-side and the image-side surfaces of the third lens element are convex, it will be favorable to increase the positive refractive power of the third lens element, and the total track length of the optical lens system will become much shorter. 
     The fourth lens element with negative refractive power has a concave image-side surface, so that the principal point of the system will be far away from the image plane, and it will be favorable to reduce the total track length of the optical lens system, so as to maintain the objective of miniaturization of the optical lens system. In addition, the inflection points can be formed on the fourth lens element, which can better correct the incident angle of the off axis light with respect to the sensor and further correct the off-axis aberration of the system. 
     According to one aspect of the present optical lens system, the focal length of the second lens element is f 2 , and the focal length of the third lens element is f 3 . When f 3 /f 2  satisfies the relation: 0.2&lt;f 3 /f 2 &lt;0.7, the third lens element can effectively distribute the refractive power of the optical lens system so as to prevent the refractive power of individual lens elements from becoming too large, and thus reducing the sensitivity of the optical lens system. 
     According to another aspect of the present optical lens system, an air distance exists between the first lens element and the second lens element, the center thickness of the first lens element is CT 1 , and the center thickness of the second lens element is CT 2 . When CT 2 /CT 1  satisfies the relation: 0.2&lt;CT 2 /CT 1 &lt;0.50, the thickness of the first lens element and the second lens element will not be too large or too small, it will be favorable to assemble the lens elements. 
     According to another aspect of the present optical lens system, the focal length of the first lens element is f 1 , and the focal length of the fourth lens element is f 4 . When f 4 /f 1  satisfies the relation: 0.2&lt;f 4 /f 1 &lt;0.6, the refractive power of the first lens element and the fourth lens element are more balanced, it will be favorable for correcting the high order aberrations of the system. In addition, when f 4 /f 1  satisfies the relation: 0.2&lt;f 4 /f 1 &lt;0.45, the high order aberrations of the system will be corrected even better. 
     According to another aspect of the present optical lens system,  FIG. 1C  is an illustrative view showing SAG 32  and Y 32 . The vertical distance from the furthest position of the light passing through the image-side surface of the third lens element to the optical axis is Y 32 , the distance between the position Y 32  from the optical axis on the image-side surface of the third lens element and a vertex on the image-side surface of the third lens element on the optical axis is SAG 32 . When SAG 32 /Y 32  satisfies the relation: 0.4&lt;SAG 32 /Y 32 &lt;0.6, the shape of the third lens element will not be too curvy, it will be favorable to the manufacturing of the lens elements. Also, it will be favorable to reduce the space required to assemble the lens elements of the system, making the optical lens system more compact. 
     According to another aspect of the present optical lens system, the Abbe number of the third lens element is V 3 , and the Abbe number of the fourth lens element is V 4 . When V 3 −V 4  satisfies the relation: 30&lt;V 3 −V 4 &lt;42, it will be favorable to correct the chromatic aberration caused by the optical lens system. 
     According to another aspect of the present optical lens system, the radius of curvature of the object-side surface of the first lens element is R 1 , and the radius of curvature of the image-side surface of the first lens element is R 2 . When R 1 /R 2  satisfies the relation: 2.0&lt;R 1 /R 2 &lt;3.0, it will be favorable to correct the spherical aberration caused by the system. 
     According to another aspect of the present optical lens system, the distance from the object-side surface of the first lens element to the image plane along the optical axis is TTL, wherein an electronic imaging sensor is provided on the image plane and half of a diagonal length of an effective pixel region of the electronic imaging sensor is ImgH. When TTL/ImgH satisfies the relation: TTL/ImgH&lt;3.8, it will be favorable to maintain the objective of miniaturization of the optical lens system, enabling the lens system to be used in the portable electronic products. 
     The present invention will be further explained in details from the following description in connection with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiments in accordance with the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows an optical lens system in accordance with a first embodiment of the present invention; 
         FIG. 1B  shows the aberration curves of the first embodiment of the present invention; 
         FIG. 1C  shows SAG 32  and Y 32  of the first embodiment of the present invention; 
         FIG. 2A  shows an optical lens system in accordance with a second embodiment of the present invention; 
         FIG. 2B  shows the aberration curves of the second embodiment of the present invention; 
         FIG. 3A  shows an optical lens system in accordance with a third embodiment of the present invention; and 
         FIG. 3B  shows the aberration curves of the third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1A , which shows an optical lens system in accordance with the first embodiment of the present invention, and  FIG. 1B  shows the aberration curves of the first embodiment of the present invention. An optical lens system in accordance with the first embodiment of the present invention comprises, in order from an object side to an image side: 
     A plastic first lens element  110  with negative refractive power has a convex object-side surface  111  and a concave image-side surface  112 , and the object-side surface  111  and the image-side surface  112  of the first lens element  110  are aspheric. 
     A plastic second lens element  120  with positive refractive power has a convex object-side surface  121  and a convex image-side surface  122 , and the object-side surface  121  and the image-side surface  122  of the second lens element  120  are aspheric. 
     A plastic third lens element  130  with positive refractive power has a convex object-side surface  131  and a convex image-side surface  132 , and the object-side surface  131  and the image-side surface  132  of the third lens element  130  are aspheric. 
     A plastic fourth lens element  140  with negative refractive power has a convex object-side surface  141  and a concave image-side surface  142 , the object-side surface  141  and the image-side surface  142  of the fourth lens element  140  are aspheric, and inflection points are formed on the object-side surface  141  and the image-side surface  142  of the fourth lens element  140 . 
     An aperture stop  100  is located between the second lens element  120  and the third lens element  130 . 
     An IR cut filter  170  made of glass is located between the image-side surface  142  of the fourth lens element  140  and an image plane  190 , and it has no influence on the focal length of the optical lens system. 
     The equation for the aspheric surface profiles of the first embodiment is expressed as follows: 
     
       
         
           
             
               X 
               ⁡ 
               
                 ( 
                 Y 
                 ) 
               
             
             = 
             
               
                 
                   ( 
                   
                     
                       Y 
                       2 
                     
                     ⁢ 
                     
                       / 
                     
                     ⁢ 
                     R 
                   
                   ) 
                 
                 / 
                 
                   ( 
                   
                     1 
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           
                             
                               ( 
                               
                                 1 
                                 + 
                                 k 
                               
                               ) 
                             
                             * 
                             
                               
                                 ( 
                                 
                                   Y 
                                   ⁢ 
                                   
                                     / 
                                   
                                   ⁢ 
                                   R 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                         ) 
                       
                       
                         1 
                         / 
                         2 
                       
                     
                   
                   ) 
                 
               
               + 
               
                 
                   ∑ 
                   i 
                 
                 ⁢ 
                 
                   
                     ( 
                     Ai 
                     ) 
                   
                   * 
                   
                     ( 
                     
                       Y 
                       i 
                     
                     ) 
                   
                 
               
             
           
         
       
     
     wherein: 
     X: the height of a point on the aspheric lens surface at a distance Y from the optical axis relative to the tangential plane at the aspheric surface vertex; 
     Y: the distance from the point on the curve of the aspheric surface to the optical axis, 
     k: the conic coefficient; 
     Ai: the aspheric surface coefficient of order i. 
     In the first embodiment of the present optical lens system, the focal length of the optical lens system is f, and it satisfies the relation:
 
 f= 3.02.
 
     In the first embodiment of the present optical lens system, the f-number of the optical lens system is Fno, and it satisfies the relation:
 
 Fno= 2.05.
 
     In the first embodiment of the present optical lens system, half of the maximal field of view is HFOV, and it satisfies the relation:
 
 HFOV= 37.4.
 
     In the first embodiment of the present optical lens system, the Abbe number of the third lens element  130  is V 3 , the Abbe number of the fourth lens element  140  is V 4 , and they satisfy the relation:
 
 V 3 −V 4=32.5.
 
     In the first embodiment of the present optical lens system, the distance on the optical axis between the first lens element  110  and the second lens element  120  is T 12 , the focal length of the optical lens system is f, and they satisfy the relation:
 
 T 12 /f= 0.19.
 
     In the first embodiment of the present optical lens system, the center thickness of the first lens element  110  is CT 1 , the focal length of the optical lens system is f, and they satisfy the relation:
 
 CT 1 /f= 0.56.
 
     In the first embodiment of the present optical lens system, the center thickness of the first lens element  110  is CT 1 , the center thickness of the second lens element  120  is CT 2 , and they satisfy the relation:
 
 CT 2 /CT 1=0.29.
 
     In the first embodiment of the present optical lens system, the radius of curvature of the object-side surface  111  of the first lens element  110  is R 1 , the radius of curvature of the image-side surface  112  of the first lens element  110  is R 2 , and they satisfy the relation:
 
 R 1 /R 2=2.55.
 
     In the first embodiment of the present optical lens system, the focal length of the second lens element  120  is f 2 , the focal length of the third lens element  130  is f 3 , and they satisfy the relation:
 
 f 3 /f 2=0.43.
 
     In the first embodiment of the present optical lens system, the focal length of the first lens element  110  is f 1 , the focal length of the fourth lens element  140  is f 4 , and they satisfy the relation:
 
 f 4 /f 1=0.38.
 
     In the first embodiment of the present optical lens system, the vertical distance from the furthest position of the light passing through the image-side surface  132  of the third lens element  130  to the optical axis  150  is Y 32 , the distance between the position Y 32  from the optical axis  150  on the image-side surface  132  of the third lens element  130  and a vertex on the image-side surface  132  of the third lens element  130  on the optical axis  150  is SAG 32 , as shown in  FIG. 1C , and they satisfy the relation:
 
 SAG 32 /Y 32=0.52.
 
     In the first embodiment of the present optical lens system, the distance from the aperture stop  100  to the image plane  190  along the optical axis  150  is SL, the distance from the object-side surface  111  of the first lens element  110  to the image plane  190  along the optical axis  150  is TTL, and they satisfy the relation:
 
 SL/TTL= 0.64.
 
     In the first embodiment of the present optical lens system, the distance from the object-side surface  111  of the first lens element  110  to the image plane  190  along the optical axis  150  is TTL, an electronic imaging sensor (not shown) is provided on the image plane  190 , half of a diagonal length of an effective pixel region of the electronic imaging sensor is ImgH, and they satisfy the relation:
 
 TTL/ImgH= 3.21.
 
     The detailed optical data of the first embodiment is shown in table 1, and the aspheric surface data is shown in table 2, wherein the units of the radius of curvature, the thickness and the focal length are expressed in mm. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 (Embodiment 1) 
               
               
                 f(focal length) = 3.02 mm, Fno = 2.05, HFOV (half of field of view) = 37.4 deg. 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                   
                 Focal 
               
               
                 Surface # 
                   
                 Curvature Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
             
          
           
               
                 0 
                 Object 
                 Plano 
                 Infinity 
                   
                   
                   
                   
               
               
                 1 
                 Lens 1 
                 4.61300(ASP) 
                 1.681 
                 Plastic 
                 1.633 
                 23.4 
                 −6.13 
               
               
                 2 
                   
                 1.80897(ASP) 
                 0.565 
               
               
                 3 
                 Lens 2 
                 5.25030(ASP) 
                 0.481 
                 Plastic 
                 1.544 
                 55.9 
                 4.42 
               
               
                 4 
                   
                 −4.30090(ASP)  
                 −0.080  
               
               
                 5 
                 Aperture 
                 Plano 
                 1.016 
               
               
                   
                 Stop 
               
               
                 6 
                 Lens 3 
                 5.97140(ASP) 
                 1.442 
                 Plastic 
                 1.544 
                 55.9 
                 1.90 
               
               
                 7 
                   
                 −1.14510(ASP)  
                 0.070 
               
               
                 8 
                 Lens 4 
                 6.26370(ASP) 
                 0.789 
                 Plastic 
                 1.633 
                 23.4 
                 −2.33 
               
               
                 9 
                   
                 1.13536(ASP) 
                 0.700 
               
               
                 10 
                 IR-filter 
                 Plano 
                 0.300 
                 Glass 
                 1.517 
                 64.2 
               
               
                 11 
                   
                 Plano 
                 0.489 
               
               
                 12 
                 Image 
                 Plano 
               
               
                   
               
               
                 Note: 
               
               
                 reference wavelength is: d-line 587.6 nm. 
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Aspheric Coefficients 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Surface # 
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
               
               
                   
               
               
                 k = 
                 −3.76838E+00 
                 2.08872E−01 
                 −6.90403E+00 
                 −5.76824E+00 
               
               
                 A4 = 
                 1.51898E−02 
                 7.93221E−02 
                 −1.75207E−02 
                 −8.01426E−02 
               
               
                 A6 = 
                 5.53584E−04 
                 5.97215E−02 
                 −7.80536E−02 
                 −8.95492E−03 
               
               
                 A8 = 
                 −1.12401E−04 
                 −5.46253E−02 
                 1.13287E−01 
                 −5.72068E−02 
               
               
                 A10 = 
                 3.67082E−05 
                 9.56046E−02 
                 −1.52277E−01 
                 −3.49583E−03 
               
               
                 A12 = 
                 6.97925E−07 
                 −2.95433E−03 
               
               
                   
               
             
          
           
               
                   
                 Surface # 
               
             
          
           
               
                   
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 k = 
                 −1.00000E+00 
                 −1.23459E+00 
                 0.00000E+00 
                 −5.27192E+00 
               
               
                 A4 = 
                 8.50819E−03 
                 9.38324E−02 
                 −1.28980E−01 
                 −7.34751E−02 
               
               
                 A6 = 
                 −2.03305E−02 
                 −7.26449E−02 
                 4.00835E−02 
                 2.53783E−02 
               
               
                 A8 = 
                 7.17970E−03 
                 3.58678E−02 
                 −1.71595E−02 
                 −7.76618E−03 
               
               
                 A10 = 
                 −1.23253E−03 
                 −1.08802E−02 
                 5.65423E−03 
                 1.46486E−03 
               
               
                 A12 = 
                 −1.60548E−04 
                 1.50030E−03 
                 −7.01499E−04 
                 −1.30260E−04 
               
               
                 A14 = 
                 3.72855E−05 
                   
                   
                 2.89973E−06 
               
               
                   
               
             
          
         
       
     
     Referring to  FIG. 2A , which shows an optical lens system in accordance with the second embodiment of the present invention, and  FIG. 2B  shows the aberration curves of the second embodiment of the present invention. The second embodiment of the present invention comprises, in order from an object side to an image side: 
     A plastic first lens element  210  with negative refractive power has a convex object-side surface  211  and a concave image-side surface  212 , and the object-side surface  211  and the image-side surface  212  of the first lens element  210  are aspheric. 
     A plastic second lens element  220  with positive refractive power has a concave object-side surface  221  and a convex image-side surface  222 , and the object-side surface  221  and the image-side surface  222  of the second lens element  220  are aspheric. 
     A plastic third lens element  230  with positive refractive power has a convex object-side surface  231  and a convex image-side surface  232 , and the object-side surface  231  and the image-side surface  232  of the third lens element  230  are aspheric. 
     A plastic fourth lens element  240  with negative refractive power has a concave object-side surface  241  and a concave image-side surface  242 , the object-side surface  241  and the image-side surface  242  of the fourth lens element  240  are aspheric, and inflection points are formed on the object-side surface  241  and the image-side surface  242  of the fourth lens element  240 . 
     An aperture stop  200  is located between the first lens element  210  and the second lens element  220 . 
     An IR cut filter  270  made of glass is located between the image-side surface  242  of the fourth lens element  240  and an image plane  290 , and it has no influence on the focal length of the optical lens system. 
     The equation for the aspheric surface profiles of the second embodiment has the same form as that of the first embodiment. 
     In the second embodiment of the present optical lens system, the focal length of the optical lens system is f, and it satisfies the relation:
 
 f= 3.11.
 
     In the second embodiment of the present optical lens system, the f-number of the optical lens system is Fno, and it satisfies the relation:
 
 Fno= 2.40.
 
     In the second embodiment of the present optical lens system, half of the maximal field of view is HFOV, and it satisfies the relation:
 
 HFOV= 36.5.
 
     In the second embodiment of the present optical lens system, the Abbe number of the third lens element  230  is V 3 , the Abbe number of the fourth lens element  240  is V 4 , and they satisfy the relation:
 
 V 3 −V 4=32.5.
 
     In the second embodiment of the present optical lens system, the distance on an optical axis between the first lens element  210  and the second lens element  220  is T 12 , the focal length of the optical lens system is f, and they satisfy the relation:
 
 T 12 /f= 0.15.
 
     In the second embodiment of the present optical lens system, the center thickness of the first lens element  210  is CT 1 , the focal length of the optical lens system is f, and they satisfy the relation:
 
 CT 1 /f= 0.58.
 
     In the second embodiment of the present optical lens system, the center thickness of the first lens element  210  is CT 1 , the center thickness of the second lens element  220  is CT 2 , and they satisfy the relation:
 
 CT 2 /CT 1=0.34.
 
     In the second embodiment of the present optical lens system, the radius of curvature of the object-side surface  211  of the first lens element  210  is R 1 , the radius of curvature of the image-side surface  212  of the first lens element  210  is R 2 , and they satisfy the relation:
 
 R 1 /R 2=2.69.
 
     In the second embodiment of the present optical lens system, the focal length of the second lens element  220  is f 2 , the focal length of the third lens element  230  is f 3 , and they satisfy the relation:
 
 f 3 /f 2=0.57.
 
     In the second embodiment of the present optical lens system, the focal length of the first lens element  210  is f 1 , the focal length of the fourth lens element  240  is f 4 , and they satisfy the relation:
 
 f 4 /f 1=0.33.
 
     In the second embodiment of the present optical lens system, the vertical distance from the furthest position of the light passing through the image-side surface  232  of the third lens element  230  to the optical axis  250  is Y 32 , the distance between the position Y 32  from the optical axis on the image-side surface  232  of the third lens element  230  and a vertex on the image-side surface  232  of the third lens element  230  on the optical axis  250  is SAG 32 , and they satisfy the relation:
 
 SAG 32 /Y 32=0.49.
 
     In the second embodiment of the present optical lens system, the distance from the aperture stop  200  to the image plane  290  along the optical axis  250  is SL, the distance from the object-side surface  211  of the first lens element  210  to the image plane  290  along the optical axis  250  is TTL, and they satisfy the relation:
 
 SL/TTL= 0.71.
 
     In the second embodiment of the present optical lens system, the distance from the object-side surface  211  of the first lens element  210  to the image plane  290  along the optical axis  250  is TTL, an electronic imaging sensor (not shown) is provided on the image plane  290 , half of a diagonal length of an effective pixel region of the electronic imaging sensor is ImgH, and they satisfy the relation:
 
 TTL/ImgH= 3.29.
 
     The detailed optical data of the second embodiment is shown in table 3, and the aspheric surface data is shown in table 4, wherein the units of the radius of curvature, the thickness and the focal length are expressed in mm. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 (Embodiment 2) 
               
               
                 f(focal length) = 3.11 mm, Fno = 2.40, HFOV (half of field of view) = 36.5 deg. 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                   
                 Focal 
               
               
                 Surface # 
                   
                 Curvature Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
             
          
           
               
                 0 
                 Object 
                 Plano 
                 Infinity 
                   
                   
                   
                   
               
               
                 1 
                 Lens 1 
                 5.01110(ASP) 
                 1.800 
                 Plastic 
                 1.634 
                 23.8 
                 −6.03 
               
               
                 2 
                   
                 1.86572(ASP) 
                 0.416 
               
               
                 3 
                 Aperture 
                 Plano 
                 0.040 
               
               
                   
                 Stop 
               
               
                 4 
                 Lens 2 
                 −12.70120(ASP) 
                 0.620 
                 Plastic 
                 1.544 
                 55.9 
                 3.65 
               
               
                 5 
                   
                 −1.74519(ASP) 
                 0.735 
               
               
                 6 
                 Lens 3 
                 6.09200(ASP) 
                 1.784 
                 Plastic 
                 1.544 
                 55.9 
                 2.07 
               
               
                 7 
                   
                 −1.24014(ASP) 
                 0.140 
               
               
                 8 
                 Lens 4 
                 −3694.17090(ASP) 
                 0.880 
                 Plastic 
                 1.633 
                 23.4 
                 −2.00 
               
               
                 9 
                   
                 1.26839(ASP) 
                 0.700 
               
               
                 10 
                 IR-filter 
                 Plano 
                 0.300 
                 Glass 
                 1.517 
                 64.2 
               
               
                 11 
                   
                 Plano 
                 0.237 
               
               
                 12 
                 Image 
                 Plano 
               
               
                   
               
               
                 Note: 
               
               
                 reference wavelength is: d-line 587.6 nm. 
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Aspheric Coefficients 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Surface # 
               
             
          
           
               
                   
                 1 
                 2 
                 4 
                 5 
               
               
                   
               
               
                 k = 
                 −2.01897E−01 
                 4.61276E+00 
                 −2.00000E+02 
                 −1.59670E+00 
               
               
                 A4 = 
                 1.67912E−02 
                 9.01319E−02 
                 −1.68088E−02 
                 −9.99461E−02 
               
               
                 A6 = 
                 1.97553E−04 
                 1.57734E−02 
                 −6.46144E−02 
                 −8.88059E−02 
               
               
                 A8 = 
                 −2.06226E−05 
                 −1.96185E−02 
                 1.81826E−01 
                 5.78090E−02 
               
               
                 A10 = 
                 7.01962E−05 
                 1.98965E−01 
                 −2.92921E−01 
                 −1.04741E−01 
               
               
                 A12 = 
                 −4.15320E−06 
                 −2.95459E−03 
               
               
                   
               
             
          
           
               
                   
                 Surface # 
               
             
          
           
               
                   
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 k = 
                 −1.00000E+00 
                 −1.30617E+00 
                 0.00000E+00 
                 −5.88550E+00 
               
               
                 A4 = 
                 1.44048E−02 
                 1.00462E−01 
                 −1.06455E−01 
                 −6.77336E−02 
               
               
                 A6 = 
                 −1.53558E−02 
                 −7.28408E−02 
                 2.98416E−02 
                 2.40053E−02 
               
               
                 A8 = 
                 4.82026E−03 
                 3.53262E−02 
                 −1.75754E−02 
                 −7.77911E−03 
               
               
                 A10 = 
                 −1.88557E−03 
                 −1.01433E−02 
                 5.70567E−03 
                 1.47844E−03 
               
               
                 A12 = 
                 2.35414E−04 
                 1.14122E−03 
                 −5.59810E−04 
                 −1.31093E−04 
               
               
                 A14 = 
                 −1.41928E−04 
                   
                   
                 3.58137E−06 
               
               
                   
               
             
          
         
       
     
     Referring to  FIG. 3A , which shows an optical lens system in accordance with the third embodiment of the present invention, and  FIG. 3B  shows the aberration curves of the third embodiment of the present invention. The third embodiment of the present invention comprises, in order from an object side to an image side: 
     A plastic first lens element  310  with negative refractive power has a convex object-side surface  311  and a concave image-side surface  312 , and the object-side surface  311  and the image-side surface  312  of the first lens element  310  are aspheric. 
     A plastic second lens element  320  with positive refractive power has a concave object-side surface  321  and a convex image-side surface  322 , and the object-side surface  321  and the image-side surface  322  of the second lens element  320  are aspheric. 
     A plastic third lens element  330  with positive refractive power has a convex object-side surface  331  and a convex image-side surface  332 , and the object-side surface  331  and the image-side surface  332  of the third lens element  330  are aspheric. 
     A plastic fourth lens element  340  with negative refractive power has a convex object-side surface  341  and a concave image-side surface  342 , the object-side surface  341  and the image-side surface  342  of the fourth lens element  340  are aspheric, and inflection points are formed on the object-side surface  341  and the image-side surface  342  of the fourth lens element  340 . 
     An aperture stop  300  is located between the second lens element  320  and the third lens element  330 . 
     An IR cut filter  370  made of glass is located between the image-side surface  342  of the fourth lens element  340  and an image plane  390 , and it has no influence on the focal length of the optical lens system. 
     The equation for the aspheric surface profiles of the third embodiment has the same form as that of the first embodiment. 
     In the third embodiment of the present optical lens system, the focal length of the optical lens system is f, and it satisfies the relation:
 
 f= 3.09.
 
     In the third embodiment of the present optical lens system, the f-number of the optical lens system is Fno, and it satisfies the relation:
 
 Fno= 2.10.
 
     In the third embodiment of the present optical lens system, half of the maximal field of view is HFOV, and it satisfies the relation:
 
 HFOV= 36.5.
 
     In the third embodiment of the present optical lens system, the Abbe number of the third lens element  330  is V 3 , the Abbe number of the fourth lens element  340  is V 4 , and they satisfy the relation:
 
 V 3 −V 4=32.5.
 
     In the third embodiment of the present optical lens system, the distance on an optical axis between the first lens element  310  and the second lens element  320  is T 12 , the focal length of the optical lens system is f, and they satisfy the relation:
 
 T 12 /f= 0.16.
 
     In the third embodiment of the present optical lens system, the center thickness of the first lens element  310  is CT 1 , the focal length of the optical lens system is f, and they satisfy the relation:
 
 CT 1 /f= 0.65.
 
     In the third embodiment of the present optical lens system, the center thickness of the first lens element  310  is CT 1 , the center thickness of the second lens element  320  is CT 2 , and they satisfy the relation:
 
 CT 2 /CT 1=0.24.
 
     In the third embodiment of the present optical lens system, the radius of curvature of the object-side surface  311  of the first lens element  310  is R 1 , the radius of curvature of the image-side surface  312  of the first lens element  310  is R 2 , and they satisfy the relation:
 
 R 1 /R 2=2.63.
 
     In the third embodiment of the present optical lens system, the focal length of the second lens element  320  is f 2 , the focal length of the third lens element  330  is f 3 , and they satisfy the relation:
 
 f 3 /f 2=0.36.
 
     In the third embodiment of the present optical lens system, the focal length of the first lens element  310  is f 1 , the focal length of the fourth lens element  340  is f 4 , and they satisfy the relation:
 
 f 4 /f 1=0.30.
 
     In the third embodiment of the present optical lens system, the vertical distance from the furthest position of the light passing through the image-side surface  332  of the third lens element  330  to the optical axis  350  is Y 32 , the distance between the position Y 32  from the optical axis  350  on the image-side surface  332  of the third lens element  330  and a vertex on the image-side surface  332  of the third lens element  330  on the optical axis  350  is SAG 32 , and they satisfy the relation:
 
 SAG 32 /Y 32=0.48.
 
     In the third embodiment of the present optical lens system, the distance from the aperture stop  300  to the image plane  390  along the optical axis  350  is SL, the distance from the object-side surface  311  of the first lens element  310  to the image plane  390  along the optical axis  350  is TTL, and they satisfy the relation:
 
 SL/TTL= 0.63.
 
     In the third embodiment of the present optical lens system, the distance from the object-side surface of the first lens element to the image plane  390  along the optical axis  350  is TTL, an electronic imaging sensor (not shown) is provided on the image plane  390 , half of a diagonal length of an effective pixel region of the electronic imaging sensor is ImgH, and they satisfy the relation:
 
 TTL/ImgH= 3.39.
 
     The detailed optical data of the third embodiment is shown in table 5, and the aspheric surface data is shown in table 6, wherein the units of the radius of curvature, the thickness and the focal length are expressed in mm. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 (Embodiment 3) 
               
               
                 f(focal length) = 3.09 mm, Fno = 2.10, HFOV (half of field of view) = 36.5 deg. 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                   
                 Focal 
               
               
                 Surface # 
                   
                 Curvature Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
             
          
           
               
                 0 
                 Object 
                 Plano 
                 Infinity 
                   
                   
                   
                   
               
               
                 1 
                 Lens 1 
                 6.50060(ASP) 
                 2.000 
                 Plastic 
                 1.634 
                 23.8 
                 −7.81 
               
               
                 2 
                   
                 2.47425(ASP) 
                 0.489 
               
               
                 3 
                 Lens 2 
                 −33.67000(ASP)  
                 0.482 
                 Plastic 
                 1.544 
                 55.9 
                 5.43 
               
               
                 4 
                   
                 −2.73214(ASP)  
                 −0.070  
               
               
                 5 
                 Aperture 
                 Plano 
                 1.115 
               
               
                   
                 Stop 
               
               
                 6 
                 Lens 3 
                 5.50040(ASP) 
                 1.469 
                 Plastic 
                 1.544 
                 55.9 
                 1.97 
               
               
                 7 
                   
                 −1.20316(ASP)  
                 0.140 
               
               
                 8 
                 Lens 4 
                 6.31300(ASP) 
                 0.756 
                 Plastic 
                 1.633 
                 23.4 
                 −2.33 
               
               
                 9 
                   
                 1.14079(ASP) 
                 0.700 
               
               
                 10 
                 IR-filter 
                 Plano 
                 0.300 
                 Glass 
                 1.517 
                 64.2 
               
               
                 11 
                   
                 Plano 
                 0.500 
               
               
                 12 
                 Image 
                 Plano 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                 Aspheric Coefficients 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Surface # 
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
               
               
                   
               
               
                 k = 
                 −5.53939E+00 
                 1.47656E+00 
                 −1.29641E+02 
                 −2.98316E+00 
               
               
                 A4 = 
                 1.37327E−02 
                 9.14610E−02 
                 −1.63317E−02 
                 −8.39426E−02 
               
               
                 A6 = 
                 4.71795E−05 
                 5.02224E−02 
                 −7.43426E−02 
                 −3.01665E−03 
               
               
                 A8 = 
                 −7.91231E−05 
                 −4.80674E−02 
                 1.25266E−01 
                 −9.54436E−02 
               
               
                 A10 = 
                 3.68356E−05 
                 1.14708E−01 
                 −1.84266E−01 
                 3.99353E−02 
               
               
                 A12 = 
                 −2.26837E−06 
                 −2.95469E−03 
               
               
                   
               
             
          
           
               
                   
                 Surface # 
               
             
          
           
               
                   
                 6 
                 7 
                 8 
                 9 
               
               
                   
               
               
                 k = 
                 −1.00000E+00 
                 −1.30628E+00 
                 0.00000E+00 
                 −4.74023E+00 
               
               
                 A4 = 
                 1.29292E−02 
                 9.78797E−02 
                 −1.10014E−01 
                 −6.78327E−02 
               
               
                 A6 = 
                 −1.18506E−02 
                 −7.41212E−02 
                 3.19850E−02 
                 2.32048E−02 
               
               
                 A8 = 
                 5.23052E−03 
                 3.56386E−02 
                 −1.72820E−02 
                 −7.56544E−03 
               
               
                 A10 = 
                 −1.55440E−03 
                 −9.87958E−03 
                 5.65889E−03 
                 1.48004E−03 
               
               
                 A12 = 
                 2.95220E−04 
                 1.25012E−03 
                 −6.11120E−04 
                 −1.35790E−04 
               
               
                 A14 = 
                 −9.65038E−06 
                   
                   
                 3.94060E−06 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Embodiment 1 
                 Embodiment 2 
                 Embodiment 3 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 f 
                 3.02 
                 3.11 
                 3.09 
               
               
                 Fno 
                 2.05 
                 2.40 
                 2.10 
               
               
                 HFOV 
                 37.4 
                 36.5 
                 36.5 
               
               
                 V3 − V4 
                 32.5 
                 32.5 
                 32.5 
               
               
                 T12/f 
                 0.19 
                 0.15 
                 0.16 
               
               
                 CT1/f 
                 0.56 
                 0.58 
                 0.65 
               
               
                 CT2/CT1 
                 0.29 
                 0.34 
                 0.24 
               
               
                 R1/R2 
                 2.55 
                 2.69 
                 2.63 
               
               
                 f3/f2 
                 0.43 
                 0.57 
                 0.36 
               
               
                 f4/f1 
                 0.38 
                 0.33 
                 0.30 
               
               
                 SAG32/Y32 
                 0.52 
                 0.49 
                 0.48 
               
               
                 SL/TTL 
                 0.64 
                 0.71 
                 0.63 
               
               
                 TTL/ImgH 
                 3.21 
                 3.29 
                 3.39 
               
               
                   
               
             
          
         
       
     
     It is to be noted that the tables 1-6 show different data from the different embodiments, however, the data of the different embodiments is obtained from experiments. Therefore, any product of the same structure is deemed to be within the scope of the present invention even if it uses different data. Table 7 lists the relevant data for the various embodiments of the present invention 
     While we have shown and described various embodiments in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.