Patent Publication Number: US-9854140-B2

Title: Imaging lens, and electronic apparatus including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Chinese Application No. 201410159396.4, filed on Apr. 18, 2014. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an imaging lens and an electronic apparatus including the same. 
     2. Description of the Related Art 
     In recent years, as use of portable electronic devices (e.g., mobile phones and digital cameras) becomes ubiquitous, much effort has been put into reducing dimensions of portable electronic devices. 
     Moreover, as dimensions of charged coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) based optical sensors are reduced, dimensions of imaging lenses for use with the optical sensors must be correspondingly reduced without significantly compromising optical performance. 
     However, it is difficult to reduce the system length of the imaging lens while maintaining satisfactory optical performance. Many factors may affect yield rate of the imaging lens, for example, the material for making the imaging lens, the assembling process, etc. 
     Therefore, it is required to develop a miniaturized optical imaging lens having a reduced dimension and good imaging quality that may satisfy requirements of consumer electronic products. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide an imaging lens having a shorter overall length while maintaining good optical performance. 
     According to one aspect of the present invention, an imaging lens comprises an aperture stop, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element and a sixth lens element arranged in order from an object side to an image side along an optical axis of the imaging lens. Each of the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element and the sixth lens element has a refractive power, an object-side surface facing toward the object side and an image-side surface facing toward the image side. 
     The image-side surface of the first lens element has a convex portion in a vicinity of a periphery of the first lens element. The second lens element is made of a plastic material. The image-side surface of the third lens element has a concave portion in a vicinity of a periphery of the third lens element. The image-side surface of the fourth lens element has a convex portion in a vicinity of the optical axis. The image-side surface of the fifth lens element has a concave portion in a vicinity of the optical axis and a convex portion in a vicinity of a periphery of the fifth lens element. The image-side surface of the sixth lens element has a concave portion in a vicinity of the optical axis. 
     The imaging lens satisfies ALT/G34≦9.00, where ALT represents a sum of thicknesses of the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element and the sixth lens element at the optical axis, and G34 represents an air gap length between the third lens element and the fourth lens element at the optical axis. 
     Another object of the present invention is to provide an electronic apparatus having an imaging lens with six lens elements. 
     According to another aspect of the present invention, an electronic apparatus includes a housing and an imaging module. The imaging module is disposed in the housing, and includes the imaging lens of the present invention, a barrel on which the imaging lens is disposed, a holder unit on which the barrel is disposed, and an image sensor disposed at the image side of the imaging lens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic diagram to illustrate the structure of a lens element; 
         FIG. 2  is a schematic diagram that illustrates the first preferred embodiment of an imaging lens according to the present invention; 
         FIG. 3  shows values of some optical parameters corresponding to the imaging lens of the first preferred embodiment; 
         FIG. 4  shows values of some parameters of an optical relationship corresponding to the imaging lens of the first preferred embodiment; 
         FIGS. 5( a ) to 5( d )  show different optical characteristics of the imaging lens of the first preferred embodiment; 
         FIG. 6  is a schematic diagram that illustrates the second preferred embodiment of an imaging lens according to the present invention; 
         FIG. 7  shows values of some optical parameters corresponding to the imaging lens of the second preferred embodiment; 
         FIG. 8  shows values of some parameters of an optical relationship corresponding to the imaging lens of the second preferred embodiment; 
         FIGS. 9( a ) to 9( d )  show different optical characteristics of the imaging lens of the second preferred embodiment; 
         FIG. 10  is a schematic diagram that illustrates the third preferred embodiment of an imaging lens according to the present invention; 
         FIG. 11  shows values of some optical parameters corresponding to the imaging lens of the third preferred embodiment; 
         FIG. 12  shows values of some parameters of an optical relationship corresponding to the imaging lens of the third preferred embodiment; 
         FIGS. 13( a ) to 13( d )  show different optical characteristics of the imaging lens of the third preferred embodiment; 
         FIG. 14  is a schematic diagram that illustrates the fourth preferred embodiment of an imaging lens according to the present invention; 
         FIG. 15  shows values of some optical parameters corresponding to the imaging lens of the fourth preferred embodiment; 
         FIG. 16  shows values of some parameters of an optical relationship corresponding to the imaging lens of the fourth preferred embodiment; 
         FIGS. 17( a ) to 17( d )  show different optical characteristics of the imaging lens of the fourth preferred embodiment; 
         FIG. 18  is a schematic diagram that illustrates the fifth preferred embodiment of an imaging lens according to the present invention; 
         FIG. 19  shows values of some optical parameters corresponding to the imaging lens of the fifth preferred embodiment; 
         FIG. 20  shows values of some parameters of an optical relationship corresponding to the imaging lens of the fifth preferred embodiment; 
         FIGS. 21( a ) to 21( d )  show different optical characteristics of the imaging lens of the fifth preferred embodiment; 
         FIG. 22  is a schematic diagram that illustrates the sixth preferred embodiment of an imaging lens according to the present invention; 
         FIG. 23  shows values of some optical parameters corresponding to the imaging lens of the sixth preferred embodiment; 
         FIG. 24  shows values of some parameters of an optical relationship corresponding to the imaging lens of the sixth preferred embodiment; 
         FIGS. 25( a ) to 25( d )  show different optical characteristics of the imaging lens of the sixth preferred embodiment; 
         FIG. 26  is a schematic diagram that illustrates the seventh preferred embodiment of an imaging lens according to the present invention; 
         FIG. 27  shows values of some optical parameters corresponding to the imaging lens of the seventh preferred embodiment; 
         FIG. 28  shows values of some parameters of an optical relationship corresponding to the imaging lens of the seventh preferred embodiment; 
         FIGS. 29( a ) to 29( d )  show different optical characteristics of the imaging lens of the seventh preferred embodiment; 
         FIG. 30  is a schematic diagram that illustrates the eighth preferred embodiment of an imaging lens according to the present invention; 
         FIG. 31  shows values of some optical parameters corresponding to the imaging lens of the eighth preferred embodiment; 
         FIG. 32  shows values of some parameters of an optical relationship corresponding to the imaging lens of the eighth preferred embodiment; 
         FIGS. 33( a ) to 33( d )  show different optical characteristics of the imaging lens of the eighth preferred embodiment; 
         FIGS. 34 and 35  are tables each listing values of parameters of other optical relationships corresponding to the imaging lenses of the first to eighth preferred embodiments; 
         FIG. 36  is a schematic partly sectional view to illustrate a first exemplary application of the imaging lens of the present invention; and 
         FIG. 37  is a schematic partly sectional view to illustrate a second exemplary application of the imaging lens of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
     In the following description, “a lens element has a positive (or negative) refractive power” means the lens element has a positive (or negative) refractive power in a vicinity of an optical axis thereof. “An object-side surface (or image-side surface) has a convex (or concave) portion at a certain area” means that, compared to a radially exterior area adjacent to said certain area, said certain area is more convex (or concave) in a direction parallel to the optical axis. Referring to  FIG. 1  as an example, the lens element is radially symmetrical with respect to an optical axis (I) thereof. The object-side surface of the lens element has a convex portion at an area A, a concave portion at an area B, and a convex portion at an area C. This is because the area A is more convex in a direction parallel to the optical axis (I) in comparison with a radially exterior area thereof (i.e., area B), the area B is more concave in comparison with the area C, and the area C is more convex in comparison with an area E. “In a vicinity of a periphery” refers to an area around a periphery of a curved surface of the lens element for passage of imaging light only, which is the area C in  FIG. 1 . The imaging light includes a chief ray Lc and a marginal ray Lm. “In a vicinity of the optical axis” refers to an area around the optical axis of the curved surface for passage of the imaging light only, which is the area A in  FIG. 1 . In addition, the lens element further includes an extending portion E for installation into an optical imaging lens device. Ideally, the imaging light does not pass through the extending portion E. The structure and shape of the extending portion E are not limited herein. In the following embodiments, the extending portion E is not depicted in the drawings for the sake of clarity. 
     Referring to  FIG. 2 , the first preferred embodiment of an imaging lens  10  according to the present invention includes an aperture stop  2 , a first lens element  3 , a second lens element  4 , a third lens element  5 , a fourth lens element  6 , a fifth lens elements  7 , a sixth lens element  8  and an optical filter  9  arranged in the given order along an optical axis (I) from an object side to an image side. The optical filter  9  is an infrared cut filter for selectively absorbing infrared light to thereby reduce imperfection of images formed at an image plane  100 . 
     Each of the first, second, third, fourth, fifth and sixth lens elements  3 - 8  and the optical filter  9  has an object-side surface  31 ,  41 ,  51 ,  61 ,  71 ,  81 ,  91  facing toward the object side, and an image-side surface  32 ,  42 ,  52 ,  62 ,  72 ,  82 ,  92  facing toward the image side. Light entering the imaging lens  10  travels through the aperture stop  2 , the object-side and image-side surfaces  31 ,  32  of the first lens element  3 , the object-side and image-side surfaces  41 ,  42  of the second lens element  4 , the object-side and image-side surfaces  51 ,  52  of the third lens element  5 , the object-side and image-side surfaces  61 ,  62  of the fourth lens element  6 , the object-side and image-side surfaces  71 ,  72  of the fifth lens element  7 , the object-side and image-side surfaces  81 ,  82  of the sixth lens element  8 , and the object-side and image-side surfaces  91 ,  92  of the optical filter  9 , in the given order, to form an image on the image plane  100 . Each of the object-side surfaces  31 ,  41 ,  51 ,  61 ,  71 ,  82  and the image-side surfaces  32 ,  42 ,  52 ,  62 ,  72 ,  82  is aspherical and has a center point coinciding with the optical axis (I). 
     The lens elements  3 - 8  are made of a plastic material in this embodiment, and at least one of the lens elements  3 - 8  may be made of other materials in other embodiments. For example, the first, third, fourth, fifth and sixth lens elements  3 ,  5 ,  6 ,  7 ,  8  except for the second lens element  4  may be made of other materials. 
     In the first preferred embodiment, which is depicted in  FIG. 2 , the first lens element  3  has a positive refractive power. The object-side surface  31  of the first lens element  3  is a convex surface that has a convex portion  311  in a vicinity of the optical axis and a convex portion  312  in a vicinity of a periphery of the first lens element  3 . The image-side surface  32  of the first lens element  3  is a convex surface that has a convex portion  321  in a vicinity of the optical axis (I), and a convex portion  322  in a vicinity of the periphery of the first lens element  3 . 
     The second lens element  4  has a positive refractive power. The object-side surface  41  of the second lens element  4  has a concave portion  411  in a vicinity of the optical axis (I), and a convex portion  412  in a vicinity of a periphery of the second lens element  4 . The image-side surface  42  of the second lens element  4  has a convex portion  421  in a vicinity of the optical axis (I), and a concave portion  422  in a vicinity of the periphery of the second lens element  4 . 
     The third lens element  5  has a negative refractive power. The object-side surface  51  of the third lens element  5  is a convex surface that has a convex portion  511  in a vicinity of the optical axis (I), and a convex portion  512  in a vicinity of a periphery of the third lens element  5 . The image-side surface  52  of the third lens element  5  is a concave surface that has a concave portion  521  in a vicinity of the optical axis (I), and a concave portion  522  in a vicinity of the periphery of the third lens element  5 . 
     The fourth lens element  6  has a positive refractive power. The object-side surface  61  of the fourth lens element  6  is a concave surface that has a concave portion  611  in a vicinity of the optical axis (I), and a concave portion  612  in a vicinity of a periphery of the fourth lens element  6 . The image-side surface  62  of the fourth lens element  6  has a convex portion  621  in a vicinity of the optical axis (I), and a concave portion  622  in a vicinity of the periphery of the fourth lens element  6 . 
     The fifth lens element  7  has a negative refractive power. The object-side surface  71  of the fifth lens element  7  has a convex portion  711  in a vicinity of the optical axis (I), and a concave portion  712  in a vicinity of a periphery of the fifth lens element  7 . The image-side surface  72  of the fifth lens element  7  has a concave portion  721  in a vicinity of the optical axis (I), and a convex portion  722  in a vicinity of the periphery of the fifth lens element  7 . 
     The sixth lens element  8  has a positive refractive power. The object-side surface  81  of the sixth lens element  8  has a convex portion  811  in a vicinity of the optical axis (I) and a concave portion  812  in a vicinity of a periphery of the sixth lens element  8 . The image-side surface  82  of the sixth lens element  8  has a concave portion  821  in a vicinity of the optical axis (I) and a convex portion  822  in a vicinity of a periphery of the sixth lens element  8 . 
     In the first preferred embodiment, the imaging lens  10  does not include any lens element with refractive power other than the aforesaid lens elements  3 - 8 . 
     Shown in  FIG. 3  is a table that lists values of some optical parameters corresponding to the surfaces  31 - 91 ,  32 - 92  of the first preferred embodiment. The imaging lens  10  has an overall system effective focal length (EFL) of 3.917 mm, a half field-of-view (HFOV) of 36.037, an F-number of 2.195, and a system length of 5.01 mm. The system length refers to a distance between the object-side surface  31  of the first lens element  3  and the image plane  100  at the optical axis (I). 
     In this embodiment, each of the object-side surfaces  31 - 81  and the image-side surfaces  32 - 82  is aspherical, and satisfies the optical relationship of 
     
       
         
           
             
               
                 
                   
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     where: 
     Y represents a perpendicular distance between an arbitrary point on an aspherical surface and the optical axis (I); 
     Z represents a depth of the aspherical surface, which is defined as a perpendicular distance between the arbitrary point on the aspherical surface that is spaced apart from the optical axis (I) by a distance Y, and a tangent plane at a vertex of the aspherical surface at the optical axis (I); 
     R represents a radius of curvature of the aspherical surface; 
     K represents a conic constant; and 
     a 2i  represents a 2i th  aspherical coefficient. 
     Shown in  FIG. 4  is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the first preferred embodiment. 
     Relationships among some of the aforementioned optical parameters corresponding to the first preferred embodiment are shown in  FIG. 34 , where: 
     T1 represents a thickness of the first lens element  3  at the optical axis (I); 
     T2 represents a thickness of the second lens element  4  at the optical axis (I); 
     T3 represents a thickness of the third lens element  5  at the optical axis (I); 
     T4 represents a thickness of the fourth lens element  6  at the optical axis (I); 
     T5 represents a thickness of the fifth lens element  7  at the optical axis (I); 
     T6 represents a thickness of the sixth lens element  8  at the optical axis (I); 
     G12 represents an air gap length between the first lens element  3  and the second lens element  4  at the optical axis (I); 
     G23 represents an air gap length between the second lens element  4  and the third lens element  5  at the optical axis (I); 
     G34 represents an air gap length between the third lens element  5  and the fourth lens element  6  at the optical axis (I); 
     G45 represents an air gap length between the fourth lens element  6  and the fifth lens element  7  at the optical axis (I); 
     G56 represents an air gap length between the fifth lens element  7  and the sixth lens element  8  at the optical axis (I); 
     Gaa represents a sum of air gap lengths among the first lens element  3 , the second lens element  4 , the third lens element  5 , the fourth lens element  6 , the fifth lens element  7 , and the sixth lens element  8  at the optical axis (I), i.e., a sum of G12, G23, G34, G45 and G56; 
     ALT represents a sum of the thicknesses of the first lens element  3 , the second lens element  4 , the third lens element  5 , the fourth lens element  6 , the fifth lens element  7  and the sixth lens element  8  at the optical axis (I), i.e., a sum of T1, T2, T3, T4, T5 and T6; 
     TTL represents a distance at the optical axis (I) between the object-side surface  31  of the first lens element  3  and the image plane  100  at the image side; 
     BFL represents a distance at the optical axis (I) between the image-side surface  82  of the sixth lens element  8  and the image plane  100 ; and 
     EFL represents a system length of the imaging lens  10 . 
       FIGS. 5( a ) to 5( d )  respectively show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the first preferred embodiment. In each of the simulation results, curves corresponding respectively to wavelengths of 470 nm, 555 nm, and 650 nm are shown. 
     It can be understood from  FIG. 5( a )  that, since each of the curves corresponding to longitudinal spherical aberration has a focal length at each field of view (indicated by the vertical axis) that falls within the range of ±0.03 mm, the first preferred embodiment is able to achieve a relatively low spherical aberration at each of the wavelengths. Furthermore, since the curves at each field of view are close to each other, the first preferred embodiment has a relatively low chromatic aberration. 
     It can be understood from  FIGS. 5( b ) and 5( c )  that, since each of the curves falls within the range of ±0.2 mm of focal length, the first preferred embodiment has a relatively low optical aberration. 
     Moreover, as shown in  FIG. 5( d ) , since each of the curves corresponding to distortion aberration falls within the range of ±10%, the first preferred embodiment is able to meet requirements in imaging quality of most optical systems. 
     In view of the above, even with the system length reduced down to 5.01 mm, the imaging lens  10  of the first preferred embodiment is still able to achieve a relatively good optical performance. 
     Referring to  FIG. 6 , the differences between the first and second preferred embodiments of the imaging lens  10  of this invention reside in modifications of some optical data, aspherical coefficients and the lens parameters of the lens elements  3 - 8 . It should be noted that the reference numerals of the concave portions and the convex portions in the second embodiment that are the same as those recited in the first embodiment are omitted in the drawings herein for the sake of brevity. 
     Shown in  FIG. 7  is a table that lists values of some optical parameters corresponding to the surfaces  31 - 91 ,  32 - 92  of the second preferred embodiment. The imaging lens  10  has an overall system focal length of 3.880 mm, an HFOV of 35.727°, an F-number of 2.193, and a system length of 4.95 mm. 
     Shown in  FIG. 8  is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the second preferred embodiment. 
     Relationships among some of the aforementioned optical parameters corresponding to the second preferred embodiment are shown in  FIG. 34 . 
       FIGS. 9( a ) to 9( d )  respectively show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the second preferred embodiment. It can be understood from  FIGS. 9( a ) to 9( d )  that the second preferred embodiment is able to achieve a relatively good optical performance. Moreover, it can be appreciated that the system length of the second preferred embodiment is shorter than that of the first preferred embodiment and the F-number of the second preferred embodiment is smaller than that of the first preferred embodiment. Additionally, manufacture of the second embodiment is relatively easier as compared to the first embodiment, such that yield rate of the second preferred embodiment may be greater than that of the first preferred embodiment. 
     Referring to  FIG. 10 , the differences between the first and third preferred embodiments of the imaging lens  10  of this invention reside in the following. The image-side surface  42  of the second lens element  4  has a convex portion  423  in a vicinity of the periphery of the second lens element  4  and a concave portion  424  disposed between the convex portions  421 ,  423 . The object-side surface of the third lens element  5  has a concave portion  513  in a vicinity of the periphery of the third lens element  5 . The image-side surface  62  of the fourth lens element  6  is a convex surface that has a convex portion  623  in a vicinity of the periphery of the fourth lens element  6 . 
     Shown in  FIG. 11  is a table that lists values of some optical parameters corresponding to the surfaces  31 - 91 ,  32 - 92  of the third preferred embodiment. The imaging lens  10  has an overall system focal length of 4.288 mm, an HFOV of 35.736, an F-number of 2.193, and a system length of 5.40 mm. 
     Shown in  FIG. 12  is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the third preferred embodiment. 
     Relationships among some of the aforementioned optical parameters corresponding to the third preferred embodiment are shown in  FIG. 34 . 
       FIGS. 13( a ) to 13( d )  respectively show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the third preferred embodiment. It can be understood from  FIGS. 13( a ) to 13( d )  that the third preferred embodiment is able to achieve a relatively good optical performance. 
     It is noted that the F-number of the third preferred embodiment is smaller than that of the first preferred embodiment. Additionally, manufacture of the third embodiment is relatively easier as compared to the first embodiment, such that yield rate of the third preferred embodiment may be greater than that of the first preferred embodiment. 
     Referring to  FIG. 14 , the differences between the first and fourth preferred embodiments of the imaging lens  10  of this invention reside in that: the object-side surface  511  of the third lens element  51  has a concave portion  513  in a vicinity of the periphery of the third lens element  51  and the object-side surface  61  of the fourth lens element  6  has a convex portion  613  disposed between the concave portions  611 ,  612 . 
     Shown in  FIG. 15  is a table that lists values of some optical parameters corresponding to the surfaces  31 - 91 ,  32 - 92  of the fourth preferred embodiment. The imaging lens  10  has an overall system focal length of 4.050 mm, an HFOV of 38.088, an F-number of 2.193, and a system length of 5.38 mm. 
     Shown in  FIG. 16  is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the fourth preferred embodiment. 
     Relationships among some of the aforementioned optical parameters corresponding to the fourth preferred embodiment are shown in  FIG. 34 . 
       FIGS. 17( a ) to 17( d )  respectively show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the fourth preferred embodiment. It can be understood from  FIG. 17( a ) to 17( d )  that the fourth preferred embodiment is able to achieve a relatively good optical performance. 
     It is noted that the F-number of the fourth preferred embodiment is smaller than that of the first preferred embodiment. Additionally, manufacture of the fourth embodiment is relatively easier as compared to the first embodiment, such that yield rate of the fourth preferred embodiment may greater than that of the first preferred embodiment. 
     Referring to  FIG. 18 , the differences between the first and fifth preferred embodiments of the imaging lens  10  of this invention reside in that: the image-side surface  42  of the second lens element  4  has a convex portion  423  in a vicinity of the periphery of the second lens element  4  and a concave portion  424  disposed between the convex portions  421 ,  423 . The object-side surface  51  of the third lens element  5  has a concave portion  513  in a vicinity of the periphery of the third lens element  5 . 
     Shown in  FIG. 19  is a table that lists values of some optical parameters corresponding to the surfaces  31 - 91 ,  32 - 92  of the fifth preferred embodiment. The imaging lens  10  has an overall system focal length of 4.227 mm, an HFOV of 36,503, an F-number of 2.193, and a system length of 5.44 mm. 
     Shown in  FIG. 20  is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the fifth preferred embodiment. 
     Relationships among some of the aforementioned optical parameters corresponding to the fifth preferred embodiment are shown in  FIG. 35 . 
       FIGS. 21( a ) to 21( d )  respectively show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the fifth preferred embodiment. It can be understood from  FIGS. 21( a ) to 21( d )  that the fifth preferred embodiment is able to achieve a relatively good optical performance. 
     It is noted that the F-number of the fifth preferred embodiment is smaller than that of the first preferred embodiment and the HFOV of the fifth preferred embodiment is larger than that of the first preferred embodiment to thereby achieve better optical performance as compared to the first preferred embodiment. Additionally, manufacture of the fifth embodiment is relatively easier as compared to the first embodiment, such that yield rate of the fifth preferred embodiment may greater than that of the first preferred embodiment. 
       FIG. 22  illustrates the sixth preferred embodiment of an imaging lens  10  according to the present invention, which has a configuration similar to that of the first preferred embodiment. The differences between the first and sixth preferred embodiments reside in that the object-side surface  51  of the third lens element  5  has a concave portion  513  in a vicinity of the periphery of the third lens element  5 . The image-side surface  62  of the fourth lens element  6  is a convex surface that has a convex portion  623  in a vicinity of the periphery of the fourth lens element  6 . 
     Shown in  FIG. 23  is a table that lists values of some optical parameters corresponding to the surfaces  31 - 91 ,  32 - 92  of the sixth preferred embodiment. The imaging lens  10  has an overall system focal length of 4.200 mm, an HFOV of 37.344°, an F-number of 2.193, and a system length of 5.35 mm. 
     Shown in  FIG. 24  is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the sixth preferred embodiment. 
     Relationships among some of the aforementioned optical parameters corresponding to the sixth preferred embodiment are shown in  FIG. 35 . 
       FIGS. 25( a ) to 25( d )  respectively show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the sixth preferred embodiment. It can be understood from  FIGS. 25( a ) to 25( d )  that the sixth preferred embodiment is able to achieve a relatively good optical performance. 
     It is noted that the F-number of the sixth preferred embodiment is smaller than that of the first preferred embodiment and the HFOV of the sixth preferred embodiment is larger than that of the first preferred embodiment to thereby achieve better optical performance as compared to the first preferred embodiment. Additionally, manufacture of the sixth embodiment is relatively easier as compared to the first embodiment, such that yield rate of the fifth preferred embodiment may be greater than that of the first preferred embodiment. 
     Referring to  FIG. 26 , the differences between the first and seventh preferred embodiments of the imaging lens  10  of this invention reside in that: the image-side surface  42  of the second lens element  4  is a convex surface that has a convex portion  423  in a vicinity of the periphery of the second lens element  42 . The object-side surface  51  of the third lens element  5  has a concave portion  514  disposed between the convex portions  511 ,  512 . 
     Shown in  FIG. 27  is a table that lists values of some optical parameters corresponding to the surfaces  31 - 91 ,  32 - 92  of the seventh preferred embodiment. The imaging lens  10  has an overall system focal length of 3.935 mm, an HFOV of 38.148°, an F-number of 2.205, and a system length of 5.09 mm. 
     Shown in  FIG. 28  is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the seventh preferred embodiment. 
     Relationships among some of the aforementioned optical parameters corresponding to the seventh preferred embodiment are shown in  FIG. 35 . 
       FIGS. 29( a ) to 29( d )  respectively show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the seventh preferred embodiment. It can be understood from  FIGS. 29( a ) to 29( d )  that the seventh preferred embodiment is able to achieve a relatively good optical performance. 
     It is noted that the HFOV of the seventh preferred embodiment is larger than that of the first preferred embodiment to thereby achieve better optical performance as compared to the first preferred embodiment. Additionally, manufacture of the seventh embodiment is relatively easier as compared to the first embodiment, such that yield rate of the seventh preferred embodiment may be greater than that of the first preferred embodiment. 
     Referring to  FIG. 30 , the differences between the first and eighth preferred embodiments of the imaging lens  10  of this invention reside in that: the image-side surface  42  of the second lens element  4  is a convex surface that has a convex portion  423  in a vicinity of the periphery of the second lens element  4 . The object-side surface  51  of the third lens element  5  has a concave portion  514  disposed between the convex portions  511 ,  512 . 
     Shown in  FIG. 31  is a table that lists values of some optical parameters corresponding to the surfaces  31 - 91 ,  32 - 92  of the eighth preferred embodiment. The imaging lens  10  has an overall system focal length of 3.991 mm, an HFOV of 37.101°, an F-number of 2.209, and a system length of 5.10 mm. 
     Shown in  FIG. 32  is a table that lists values of some optical parameters of the aforementioned optical relationship (1) corresponding to the eighth preferred embodiment. 
     Relationships among some of the aforementioned optical parameters corresponding to the eighth preferred embodiment are shown in  FIG. 35 . 
       FIGS. 33( a ) to 33( d )  respectively show simulation results corresponding to longitudinal spherical aberration, sagittal astigmatism aberration, tangential astigmatism aberration, and distortion aberration of the eighth preferred embodiment. It can be understood from  FIG. 33( a ) to 33( d )  that the eighth preferred embodiment is able to achieve a relatively good optical performance. 
     It is noted that the HFOV of the eighth preferred embodiment is larger than that of the first preferred embodiment to thereby achieve better optical performance as compared to the first preferred embodiment. Additionally, manufacture of the eighth embodiment is relatively easier as compared to the first embodiment, such that yield rate of the eighth preferred embodiment may be greater than that of the first preferred embodiment. 
     Shown in  FIGS. 34 and 35  are tables that list relationships among some of the aforementioned optical parameters corresponding to the eighth preferred embodiments for comparison. When each of the optical parameters of the imaging lens  10  according to this invention satisfies the following optical relationships, the system length may be reduced while maintaining good optical performance: 
     ALT/G34≦9.00; ALT/G45≦40.0; ALT/T6≦7.90; BFL/G34≦5.20; BFL/G45≦17.00; BFL/T6≦3.50; G34/T1≦2.00; Gaa/G34≦4.00; Gaa/G45≦15.00; Gaa/T2≦4.50; Gaa/T4≦2.00; T2/G45≦4.00; T4/G45≦9.00; TTL/G34≦20.00; TTL/G45≦69.00; TTL/T2≦19.00; and TTL/T4≦9.0. 
     Additionally, when each of the optical parameters of the imaging lens  10  further satisfies the following optical relationships, the optical performance is still relatively good even with the reduced system length: 
     3.00≦ALT/G34≦9.00; 8.00≦ALT/G45≦40.0; 4.00≦ALT/T6≦7.90; 1.20≦BFL/G34≦5.20; 4.00≦BFL/G45≦17.00; 1.40≦BFL/T6≦3.50; 0.45≦G34/T1≦2.00; 1.70≦Gaa/G34≦4.00; 3.00≦Gaa/G45≦15.00; 2.00≦Gaa/T2≦4.50; 0.50≦Gaa/T4≦2.00; 0.50≦T2/G45≦4.00; T4/G45≦9.00; 5.00≦TTL/G34≦20.00; 15.00≦TTL/G45≦69.00; 14.00≦TTL/T2≦19.00; and 5.00≦TTL/T4≦9.0. 
     Better arrangement may be achieved when the following relationship is satisfied: 2.00≦BFL/T5. Additionally, when 2.00≦BFL/T5≦4.00 is satisfied, reduced of the system length may be ensured. 
     Although the design of an optical system is generally associated with unpredictability, satisfaction of the aforementioned relationships may enable the imaging lens  10  to have reductions in the system length and the F-number, to have increase in field of view, to have enhancement of image quality, or to have a relatively higher yield rate of assembly, thereby alleviating at least one drawback of the prior art. 
     To sum up, effects and advantages of the imaging lens  10  according to the present invention are described hereinafter. 
     1. By virtue of the convex portion  322 , the concave portion  522 , the convex portion  621 , the convex portion  722 , and the concave portion  821 , optical aberration may be corrected, thereby ensuring imaging quality of the imaging lens  10 . Additionally, the aperture stop  2  disposed in front of the first lens element  3  facilitates reduction of the system length. Furthermore, since the second lens element  4  is made of a plastic material, weight and cost of the imaging lens  10  may be reduced. 
     2. Through design of the relevant optical parameters, optical aberrations, such as spherical aberration, may be reduced or even eliminated. Further, through surface design and arrangement of the lens elements  3 - 8 , even with reduced system length, optical aberrations may still be reduced or even eliminated, resulting in relatively good optical performance. 
     3. Through the aforesaid eight preferred embodiments, it is known that the system length of this invention may be reduced down to below 5.50 mm, so as to facilitate developing thinner relevant products with economic benefits. 
     Shown in  FIG. 36  is a first exemplary application of the imaging lens  10  of this invention, in which the imaging lens  10  is disposed in a housing  11  of an electronic apparatus  1  (such as a mobile phone, but not limited thereto), and forms a part of an imaging module  12  of the electronic apparatus  1 . The imaging module  12  includes a barrel  21  on which the imaging lens  10  is disposed, a holder unit  120  on which the barrel  21  is disposed, and an image sensor  130  disposed at the image plane  100  (see  FIG. 2 ). 
     The holder unit  120  includes a first holder portion  121  in which the barrel  21  is disposed, and a second holder portion  122  having a portion interposed between the first holder portion  121  and the image sensor  130 . The barrel  21  and the first holder portion  121  of the holder unit  120  extend along an axis (II), which coincides with the optical axis (I) of the imaging lens  10 . 
     Shown in  FIG. 37  is a second exemplary application of the imaging lens  10  of this invention. The differences between the first and second exemplary applications reside in that, in the second exemplary application, the holder unit  120  is configured as a voice-coil motor (VCM), and the first holder portion  121  includes an inner section  123  in which the barrel  21  is disposed, an outer section  124  that surrounds the inner section  123 , a coil  125  that is interposed between the inner and outer sections  123 ,  124 , and a magnetic component  126  that is disposed between an outer side of the coil  125  and an inner side of the outer section  124 . 
     The inner section  123  and the barrel  21 , together with the imaging lens  10  therein, are movable with respect to the image sensor  130  along an axis (III), which coincides with the optical axis (I) of the imaging lens  10 . The optical filter  9  of the imaging lens  10  is disposed at the second holder portion  122 , which is disposed to abut against the outer section  124 . Configuration and arrangement of other components of the electronic apparatus  1  in the second exemplary application are identical to those in the first exemplary application, and hence will not be described hereinafter for the sake of brevity. 
     By virtue of the imaging lens  10  of the present invention, the electronic apparatus  1  in each of the exemplary applications may be configured to have a relatively reduced overall thickness with good optical and imaging performance, so as to reduce cost of materials, and satisfy requirements of product miniaturization. 
     While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.