Patent Publication Number: US-2015077861-A1

Title: Five-piece wide-angle lens module

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an optical system, and more particularly to a five-piece wide-angle lens module. 
     2. Description of the Related Art 
     When a driver backs a car, he or she usually relies on the rear-view mirror and the side-view mirrors to see the road behind the car. However, the driver is still unable to see somewhere behind the car, which is called the “blind zone”. Therefore, rear-view video cameras are installed on vehicles to assist the driver to have better rear visibility and the wider field of view. 
     In some areas having obvious season changes, the temperature can go down to −20° C. or lower in winter and up to 60° C. or higher in summer. Therefore, the rear-view video cameras must have excellent and consistent imaging quality in high/low temperature environment, otherwise the rear-view video cameras can be unsatisfying. 
     SUMMARY OF THE INVENTION 
     It is a main objective of the present invention to provide an optical system which can provide excellent imaging quality in both high and low temperature environments. 
     It is another main objective of the present invention to provide a wide-angle optical system. 
     To achieve the above and other objectives of the present invention, a five-piece wide-angle lens is provided, in which the lens includes in a sequence from an object side to an image side of a first lens, a second lens, a third lens, a stop, a fourth lens, and a fifth lens. The first lens has a negative refractive power, a convex surface on the object side, and a concave surface on the image side. The second lens has a negative refractive power and two concave surfaces on both the object side and the image side respectively. The third lens has a positive refractive power. The fourth lens has a positive refractive power and two convex surfaces on both the object side and the image side respectively. The fifth lens has a negative refractive power. Each of the second lens, the third lens, the fourth lens and the fifth lens has at least one aspheric surface. The five-piece wide-angle lens module satisfies the following relationships: −0.6&lt;f 2 /f 3 &lt;−0.3, and −0.25&lt;f 4 /f 5 &lt;−0.15, in which f 2  is a focal length of the second lens, f 3  is a focal length of the third lens, f 4  is a focal length of the fourth lens, and f 5  is a focal length of the fifth lens. 
     When the five-piece wide-angle lens satisfies the above-mentioned relationships, they can have a good refractive configuration. Thus the optical aberration of the wide-angle system can be modified, and the five-piece wide-angle lens module can still have excellent image quality in the severe environment (e.g. temperature ranging from −50° C. to 100° C.). 
     The following detailed description will further explain the full scope of applications for the present invention. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those with the proper technical knowledge from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be understood more fully by referring to the detailed description below, as well as the accompanying drawings. However, it must be understood that both the descriptions and drawings are given by way of illustration only, and thus do not limit the present invention. 
         FIG. 1  is a schematic view of a lens module in accordance with the first embodiment of the present invention; 
         FIG. 2  is a diagram showing the optical aberration of the lens module in accordance with the first embodiment of the present invention at 25° C.; 
         FIG. 3  is a diagram showing the optical aberration of the lens module in accordance with the first embodiment of the present invention at −50° C.; 
         FIG. 4  is a diagram showing the optical aberration of the lens module in accordance with the first embodiment of the present invention at 100° C.; 
         FIG. 5  is a diagram showing the field curvature and the distortion of the lens module in accordance with the first embodiment of the present invention; 
         FIG. 6  is a diagram showing the lateral color aberration of a lens module in accordance with the first embodiment of the present invention; 
         FIG. 7  is a schematic view of a lens module in accordance with the second embodiment of the present invention; 
         FIG. 8  is a diagram showing the optical aberration of the lens module in accordance with the second embodiment of the present invention at 25° C.; 
         FIG. 9  is a diagram showing the optical aberration of the lens module in accordance with the second embodiment of the present invention at −50° C.; 
         FIG. 10  is a diagram showing the optical aberration of the lens module in accordance with the second embodiment of the present invention at 100° C.; 
         FIG. 11  is a diagram showing the field curvature and the distortion of the lens module in accordance with the second embodiment of the present invention; 
         FIG. 12  is a diagram showing the lateral color aberration of a lens module in accordance with the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIG. 1  for a five-piece wide-angle lens module in accordance with the first embodiment of the present invention. The lens module  100  includes in a sequence from an object side A to an image side B of: a first lens  110 , a second lens  120 , a third lens  130 , a stop  140 , a fourth lens  150 , and a fifth lens  160 . CCD, CMOS or other image sensor can be disposed at the image side B. One or more plate glasses  170  such as an optical filter and/or a protection glass can be additionally disposed between the image sensor and the fifth lens  160 , in which the amount of the plate glass  170  can be adjusted subject to the requirements. 
     The first lens  110  is a meniscus lens with a negative power and has a convex surface on the object side and a concave surface on the image side so as to provide the wide angle characteristic. 
     The second lens  120  also has a negative refractive power and shares the refractive power loading with the first lens  110 , such that the system aberration can be controlled. Both the object side and the image side of the second lens  120  are concave surfaces, which can lead to modification of aberration caused by marginal rays. 
     The third lens  130  has a positive refractive power to balance out the negative refractive power of the first and second lenses  110  and  120  in order to further modify the aberration. The object side of the third lens  130  is a convex surface, and the image side thereof is a concave surface. 
     The stop  140  is designed to locate between the third lens  130  and the fourth lens  150 . Such arrangement is helpful to balance out the system refractive power and efficiently reduce the system sensitivity. 
     The fourth lens  150  has a positive refractive power and two convex surfaces on both the object side and the image side. 
     The fifth lens  160  has a negative refractive power, a concave surface on the object side and a convex surface on the image side. 
     The optical feature data of the five-piece wide-angle lens module  100  in accordance with the first embodiment are listed in Table 1: 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Lens 
                 Surface 
                 Radius 
                 Thickness 
                 Nd 
                 Vd 
                 Conic 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Object 
                   
                 ∞ 
                 ∞ 
                   
                   
                 0 
               
               
                 First  
                 Object surface 1 
                 25 
                 1 
                  1.834 
                 42.7 
                 0 
               
               
                 lens 
                 Image surface 2 
                 5.5 
                 4.225 
                   
                   
                 0 
               
               
                 Second  
                 Object surface 3 
                 −4.4 
                 3.1 
                 1.53 
                 56.1 
                 −6.67 
               
               
                 lens 
                 Image surface 4 
                 4.92 
                 0.39 
                   
                   
                 0.97 
               
               
                 Third  
                 Object surface 5 
                 4.55 
                 8 
                 1.64 
                 23.5 
                 −0.87 
               
               
                 lens 
                 Image surface 6 
                 4.15 
                 0.3 
                   
                   
                 −38.17 
               
               
                 Stop 
                   
                 ∞ 
                 −0.168 
                   
                   
                 0 
               
               
                 Fourth  
                 Object surface 8 
                 2.6 
                 2.8 
                 1.53 
                 56.1 
                 −11.16 
               
               
                 lens 
                 Image surface 9 
                 −1.47 
                 0.1 
                   
                   
                 −0.57 
               
               
                 Fifth  
                 Object surface 10 
                 −1.65 
                 0.8 
                 1.64 
                 23.5 
                 −0.55 
               
               
                 lens 
                 Image surface 11 
                 −2.4 
                 0.05 
                   
                   
                 −8.69 
               
               
                 Plate  
                 Object surface 12 
                 ∞ 
                 0.9 
                 1.52 
                 64.1 
                 0 
               
               
                 glass 
                 Image surface 13 
                 ∞ 
                 3.27 
                   
                   
                 0 
               
               
                 Image 
                   
                 ∞ 
                   
                   
                   
                 0 
               
               
                   
               
            
           
         
       
     
     All the object sides and the image sides of the second lens  120 , the third lens  130 , the fourth lens  150  and the fifth lens  160  are aspheric surfaces, whose shapes satisfy the following formula: 
     
       
         
           
             z 
             = 
             
               
                 
                   ch 
                   2 
                 
                 
                   1 
                   + 
                   
                     
                       [ 
                       
                         1 
                         - 
                         
                           
                             ( 
                             
                               k 
                               + 
                               1 
                             
                             ) 
                           
                            
                           
                             c 
                             2 
                           
                            
                           
                             h 
                             2 
                           
                         
                       
                       ] 
                     
                     
                       1 
                       2 
                     
                   
                 
               
               + 
               
                 Ah 
                 4 
               
               + 
               
                 Bh 
                 6 
               
               + 
               
                 Ch 
                 8 
               
               + 
               
                 Dh 
                 10 
               
               + 
               
                 Eh 
                 12 
               
               + 
               
                 Fh 
                 14 
               
               + 
               
                 Gh 
                 16 
               
             
           
         
       
     
     wherein z is a value of a reference position with respect to a vertex of the surface along an optical axis of the lens module at a position with a height h, c is a reciprocal of a radius of curvature of the surface, k is a conic constant, A is a coefficient of fourth level aspheric surface, B is a coefficient of sixth level aspheric surface, C is a coefficient of eighth level aspheric surface, D is a coefficient of tenth level aspheric surface, E is a coefficient of twelfth level aspheric surface, F is a coefficient of fourteenth level aspheric surface, and G is a coefficient of sixteenth level aspheric surface. 
     The coefficients of the aspheric surface of the second lens  120  to the fifth lens  160  in the present embodiment are listed in Table 2: 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                   
                 Object surface 3 
                 Image surface 4 
                 Object surface 5 
                 Image surface 6 
               
               
                   
               
               
                 A 
                 0.0010963265 
                 0.022099817 
                 0.012841651 
                 0.040596125 
               
               
                 B 
                 −3.0299061e−005 
                 −0.0022800517 
                 −0.0014392631 
                 0.017826591 
               
               
                 C 
                 −4.4873152e−006 
                 −3.4888069e−005 
                 5.944269e−005 
                 −0.0091502209 
               
               
                 D 
                   2.5440967e−007 
                   1.8727775e−005 
                  5.22602e−006 
                 0.00071855887 
               
               
                 E 
                 −3.5544596e−009 
                 −1.1285088e−006 
                 −5.1219614e−007    
                 0.002294535 
               
               
                 F 
                 0 
                 0 
                 0 
                 0 
               
               
                 G 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
               
                   
                 Object surface 8 
                 Image surface 9 
                 Object surface 10 
                 Image surface 11 
               
               
                   
               
               
                 A 
                 0.041539684 
                 0.0015924177 
                 −0.019767887 
                 −0.0692465 
               
               
                 B 
                 0.014245223 
                 0.032582198 
                 0.035192349 
                 0.026160088 
               
               
                 C 
                 −0.019099719 
                 −0.0087874901 
                 −0.0031484984 
                 −0.0042433034 
               
               
                 D 
                 0.0076090621 
                 0.00048587656 
                 −0.0019634767 
                 7.2802262e−006 
               
               
                 E 
                 −0.0001419018 
                 −8.2859808e−006 
                 −4.076445e−005 
                 3.6374827e−005 
               
               
                 F 
                 0 
                 0 
                 0 
                 0 
               
               
                 G 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
            
           
         
       
     
     Based on the afore-mentioned design, the total focal length f of the present embodiment is 1.22 mm, the total length thereof is 24.8 mm, the angle of view is 166 degrees, the focal length of the first lens  110  is −8.6 mm, the focal length of the second lens  120  is −3.9 mm, the focal length of the third lens  130  is 10.67 mm, the focal length of the fourth lens  150  is 2.3 mm, and the focal length of the fifth lens  160  is −14.06 mm. 
     The ratio of the focal length of the second lens  120  to that of the third lens  130  (f 2 /f 3 ) is −0.37, and the ratio of the focal length of the fourth lens  150  to that of the fifth lens  160  (f 4 /f 5 ) is −0.16. These ratios satisfy the relationships of −0.6&lt;f 2 /f 3 &lt;−0.3 and −0.25&lt;f 4 /f 5 &lt;−0.15. Therefore, the system has a good refractive power arrangement and can effectively modify the aberration of the wide-angle system. Such arrangement also enables the lens module  100  to have excellent and consistent image quality in the environment having severe temperature changes. Test results of which are shown in  FIGS. 2-5 . 
     In addition, the focal lengths of the first lens  110  and the second lens  120  also need to coordinate with each other. The ratio of the focal length thereof preferably satisfies the following relationship: 1.6&lt;f 1 /f 2 &lt;2.9, in which f 1  is the focal length of the first lens  110 . In the present embodiment, f 1 /f 2  is 2.2 and satisfies the above-mentioned relationship. Therefore, the second lens  120  shares the negative refractive power of the first lens  110  in order to reduce the system aberration. 
     Since the image surface of the first lens  110  is a concave surface, and the object surface of the second lens  120  is also a concave surface, the radii of curvature thereof need to coordinate with each other, preferably satisfying the following relationship: 8&lt;(r 2 −r 3 )/(r 2 +r 3 )&lt;22, in which r 2  is the radius of curvature of the image surface of the first lens  110 , and r 3  is the radius of curvature of the object surface of the second lens  120 . In the present embodiment, (r 2 −r 3 )/(r 2 +r 3 ) is 9, which satisfies the above-mentioned relationship, and therefore the system aberration can be modified. 
     Moreover, since the object-sided surface and the image-sided surface of the fourth lens  150  are both convex, the radii of curvature thereof also need to coordinate with each other, preferably satisfying the following relationship: 2&lt;(r 8 −r 9 )/(r 8 +r 9 )&lt;4.2, in which r 8  is the radius of curvature of the object surface of the fourth lens  150 , and r 9  is the radius of curvature of the image surface of the fourth lens  150 . In the present embodiment, (r 8 −r 9 )/(r 8 +r 9 ) is 3.6, which satisfies the above-mentioned relationship, and therefore an incident angle of a ray incident from the stop  140  to the fourth lens  150  is smaller, which is helpful to reduce the system sensitivity. 
     To mitigate the problem that a wide-angle system tends to have lateral color aberration, the Abbe numbers of the fourth lens  150  and the fifth lens  160  need to coordinate with each other, preferably satisfying the following relationship: Vd 4 −Vd 5 &gt;25, in which Vd 4  is the Abbe number of the fourth lens  150 , and Vd 5  is the Abbe number of the fifth lens  160 . In the present embodiment, Vd 4 −Vd 5  is 32.6, which satisfies the above-mentioned relationship, and therefore the lateral color aberration can be modified. A test result of which is shown in  FIG. 6 . 
     Please refer to  FIG. 7  for a five-piece wide-angle lens module  200  in accordance with the second embodiment of the present invention. The structural arrangement of the second embodiment is similar to that of the first embodiment, and the optical feature data thereof are listed in Table 3: 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Lens 
                 Surface 
                 Radius 
                 Thickness 
                 Nd 
                 Vd 
                 Conic 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Object 
                   
                 ∞ 
                 ∞ 
                   
                   
                 0 
               
               
                 First lens 
                 Object surface 1 
                 18 
                 1 
                 1.834 
                 42.7 
                 0 
               
               
                   
                 Image surface 2 
                 5.75 
                 4.29 
                   
                   
                 0 
               
               
                 Second lens 
                 Object surface 3 
                 −5.22 
                 3.08 
                 1.53 
                 56.1 
                 −6.245 
               
               
                   
                 Image surface 4 
                 4.08 
                 0.33 
                   
                   
                 0.125 
               
               
                 Third lens 
                 Object surface 5 
                 4 
                 8.27 
                 1.64 
                 23.5 
                 −1.041 
               
               
                   
                 Image surface 6 
                 5.7 
                 0.235 
                   
                   
                 −23.52 
               
               
                 Stop 
                   
                 ∞ 
                 −0.147 
                   
                   
                 0 
               
               
                 Fourth lens 
                 Object surface 8 
                 3.52 
                 3.37 
                 1.53 
                 56.1 
                 6.284 
               
               
                   
                 Image surface 9 
                 −1.42 
                 0.07 
                   
                   
                 −1.478 
               
               
                 Fifth lens 
                 Object surface 10 
                 −1.58 
                 0.63 
                 1.64 
                 23.5 
                 −1.07 
               
               
                   
                 Image surface 11 
                 −2.3 
                 0.05 
                   
                   
                 −2.774 
               
               
                 Plate glass 
                 Object surface 12 
                 ∞ 
                 0.9 
                 1.52 
                 64.1 
                 0 
               
               
                   
                 Image surface 13 
                 ∞ 
                 3.42 
                   
                   
                 0 
               
               
                 Image 
                   
                 ∞ 
                   
                   
                   
                 0 
               
               
                   
               
            
           
         
       
     
     Likewise, all the object sides and the image sides of the second lens  220 , the third lens  230 , the fourth lens  250  and the fifth lens  260  are aspheric surfaces and satisfy the above-mentioned shape formula, the coefficients of the aspheric surface thereof are listed in Table 4: 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                   
                 Object surface 3 
                 Image surface 4 
                 Object surface 5 
                 Image surface 6 
               
               
                   
               
               
                 A 
                 0.00094198026 
                 0.014897377 
                 0.0087719657 
                 0.054573334 
               
               
                 B 
                 −5.1966273e−005 
                 −0.0013911648 
                 −0.00042873058 
                 0.0077799809 
               
               
                 C 
                   6.6589612e−007 
                   9.8304251e−006 
                 −2.4132455e−006 
                 −0.003256489 
               
               
                 D 
                   9.1307441e−009 
                 −2.3053745e−007 
                 −6.9203833e−008 
                 −0.00060016498 
               
               
                 E  
                 −2.2637996e−010 
                 −3.8091874e−008 
                 −5.7609957e−008 
                 −0.0012027896 
               
               
                 F 
                 0 
                 0 
                 0 
                 0 
               
               
                 G 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
               
                   
                 Object surface 8 
                 Image surface 9 
                 Object surface 10 
                 Image surface 11 
               
               
                   
               
               
                 A 
                 0.010475574 
                 0.028244503 
                 0.015520676 
                 −0.031109108 
               
               
                 B 
                 0.010495202 
                 −0.00083714195 
                 0.012002875 
                 0.0099240437 
               
               
                 C 
                 −0.020090321 
                 −0.00271942 
                 −0.0032935255 
                 −0.00091942668 
               
               
                 D 
                 −0.0015571378 
                 0.00017213507 
                 −0.00033941001 
                 −6.4505856e−005 
               
               
                 E  
                 0.0075440299 
                 −0.0016519109 
                 −0.002205681 
                 −0.00016946594 
               
               
                 F 
                 −0.0045331302 
                 0.00053027025 
                 0.00069011378 
                   4.1576431e−005 
               
               
                 G 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
            
           
         
       
     
     Based on the above-mentioned design, the total focal length f of the present embodiment is 1.39 mm, the total length thereof is 25.5 mm, the angle of view thereof is 166 degrees, the focal length of the first lens  210  is −10.45 mm, the focal length of the second lens  220  is −3.82 mm, the focal length of the third lens  230  is 7.20 mm, the focal length of the fourth lens  250  is 2.47 mm, and the focal length of the fifth lens  260  is −11.95 mm. 
     The ratio of the focal length of the second lens  220  to that of the third lens  230  (f 2 /f 3 ) is −0.53, and the ratio of the focal length of the fourth lens  250  to that of the fifth lens  260  (f 4 /f 5 ) is −0.21. These ratios satisfy the relationships of −0.6&lt;f 2 /f 3 &lt;−0.3 and −0.25&lt;f 4 /f 5 &lt;−0.15. Therefore, the system has a good refractive power arrangement and can effectively modify the aberration of the wide-angle system. Such arrangement also enables the lens module  200  to have excellent and consistent image quality in the environment having severe temperature changes. Test results of which are shown in  FIGS. 8-11 . 
     Furthermore, the ratio of the focal length f 1  of the first lens  210  to the focal length f 2  of the second lens  220  is 2.74, which satisfies the relationship of 1.6&lt;f 1 /f 2 &lt;2.9. Therefore, the second lens  220  shares the negative refractive power of the first lens  210  in order to reduce the system aberration. 
     In the present embodiment, the radius of curvature r 2  of the image surface of the first lens  210  also coordinates with the radius of curvature r 3  of the object surface of the second lens  220 , in which (r 2 −r 3 )/(r 2 +r 3 ) is 20.7, which satisfies the relationship of 8&lt;(r 2 −r 3 )/(r 2 +r 3 )&lt;22. Therefore, the system aberration can be modified. 
     In the present embodiment, the radius of curvature r 8  of the objet surface of the fourth lens  250  also coordinates with the radius of curvature r 9  of the image surface of the fourth lens  250 , in which (r 8 −r 9 )/(r 8 +r 9 ) is 2.35, which satisfies the relationship of 2&lt;(r 8 −r 9 )/(r 8 +r 9 )&lt;4.2. Therefore, an incident angle of a ray incident from the stop  240  to the fourth lens  250  is smaller, which is helpful to reduce the system sensitivity. 
     In addition, the difference between the Abbe numbers of the fourth lens  250  and the fifth lens  260 , i.e. Vd 4 −Vd 5 , is 32.6, which satisfies the relationship of Vd 4 −Vd 5 &gt;25. Therefore, the lateral color aberration can be modified. A test result of which is shown in  FIG. 12 . 
     In light of foregoing, the view of angle of the present invention can reach up to 166 degrees. Meanwhile, the image quality thereof is also significantly elevated and consistent in the environments of high temperature (100° C.) and low temperature (−50° C.). Therefore, the present invention meets the practical needs. 
     It is noticed that although both the object surface and the image surface of each of the second lens to the fifth lens in accordance with the above-mentioned embodiments are aspheric surfaces, each of the second lens to the fifth lens is only required to have at least one aspheric surface. And because of the aspheric surfaces, the second lens to the fifth lens are preferably made of plastic to reduce manufacturing cost and increase yield rate. The first lens is preferably made of glass that has better wear resistance and scrape resistance. However, the material of the lenses is not limited to the above-mentioned material. Furthermore, the five-piece wide-angle lens module of the present invention can not only be utilized in vehicle-use cameras but also in surveillance cameras and other purposes. 
     The invention described above is capable of many modifications, and may vary. Any such variations are not to be regarded as departures from the spirit of the scope of the invention, and all modifications which would be obvious to someone with the technical knowledge are intended to be included within the scope of the following claims.