Abstract:
the An optical imaging lens includes four lens elements positioned in order from the object side to the image side of the optical imaging lens. Through controlling the convex or concave shape of the surfaces of lens elements, the refracting power of lens elements, the thickness of the at least one lens element, one or more air gaps between lens elements along the optical axis, and a half field of view HFOV of the optical imaging lens, an embodiment satisfies the relation: 4.21≦T 3 /(G12×tan(HFOV))≦7.55, for which T 3  is the thickness of the third lens element and G 12  is the air gap between the first lens element and the second lens element. The optical imaging lens provided by embodiments of the present invention has better optical characteristics and a reduced total length in comparison to conventional lenses.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/549,477, filed on Nov. 20, 2014, which is a continuation of U.S. patent application Ser. No. 13/770,838, filed on Feb. 19, 2013, now U.S. Pat. No. 8,929,000, which claims priority to China Patent Application No. 201210252531.0, filed on Jul. 20, 2012, the contents of which are hereby incorporated by reference in their entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a mobile device and an optical imaging lens thereof, and particularly, relates to a mobile device applying an optical imaging lens having four lens elements and an optical imaging lens thereof. 
     BACKGROUND OF THE INVENTION 
     The ever-increasing demand for smaller sized mobile devices, such as cell phones, digital cameras, etc. has correspondingly triggered a growing need for smaller sized photography modules contained therein. Size reductions may be contributed from various aspects of the mobile devices, which includes not only the charge-coupled device (CCD) and the complementary metal-oxide semiconductor (CMOS), but also the optical imaging lens mounted therein. When reducing the size of the optical imaging lens; however, achieving good optical characteristics becomes a challenging problem. 
     U.S. Pat. Nos. 7,715,119, 7,848,032, 8,089,704, 7,920,340, US Patent Publication No. 2011009572, U.S. Pat. Nos. 7,777,972, 7,969,664 and U.S. Pat. No. 7,274,518 all disclosed an optical imaging lens constructed with an optical imaging lens having four lens elements. In the first embodiment of U.S. Pat. No. 7,920,340, the length of the optical imaging lens is over 7 mm, which is not beneficial for the smaller design of mobile devices. 
     How to effectively shorten the length of the optical imaging lens is one of the most important topics in the industry to pursue the trend of smaller and smaller mobile devices. 
     Therefore, there is needed to develop optical imaging lens with a shorter length, while also having good optical characteristics. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a mobile device and an optical imaging lens thereof. With controlling the convex or concave shape of the surfaces of the lens elements, the central thickness along the optical axis, and the air gap, etc., the length of the optical imaging lens is shortened and meanwhile the good optical characteristics, such as high resolution, are sustained. 
     In an exemplary embodiment, an optical imaging lens comprises, in order from an object side to an image side, first, second, third and fourth lens elements, each of the first, second, third, and fourth lens elements having an object-side surface facing toward the object side and an image-side surface facing toward the image side. The first lens element has positive refracting power and the object-side surface thereof is a convex surface. The second lens element has negative refracting power, the object-side surface thereof comprises a concave portion in the vicinity of the optical axis and the image-side surface thereof comprises a concave portion in the vicinity of the optical axis. The third lens element has positive refracting power, the object-side surface thereof is a concave surface and the image-side surface thereof being a convex surface. The object-side surface of the fourth lens element comprises a convex portion in the vicinity of the optical axis, and the image-side surface thereof comprises a concave portion in the vicinity of the optical axis and a convex portion in the vicinity of a periphery of the fourth lens element. Lens as a whole has only the four lens elements with refracting power, wherein a central thickness of the third lens element along the optical axis is T 3 , an air gap between the third lens element and the fourth lens element is G 34 , and a sum of all air gaps from the first lens element to the fourth lens element along the optical axis is G aa , and they satisfy the relations:
 
( T 3/ G   34 )&gt;4; and
 
( G   aa   /T 3)&gt;1.
 
     In another exemplary embodiment, assuming the thickness of the third lens element is not changed, when the air gap G 34  between the third lens element and the fourth lens element along the optical axis is shortened to satisfy the relation of “(T 3 /G 34 )&gt;4”, the length of the optical imaging lens is shortened. In another exemplary embodiment, assuming the sum of all air gaps from the first lens element to the fourth lens element along the optical axis, G aa , is not changed, when the central thickness T 3  of the third lens element along the optical axis is shortened to satisfy the relation of “(G aa /T 3 )&gt; 1 ”, the length of the optical imaging lens is also effectively shortened. 
     In another exemplary embodiment, other related parameters, such as the central thickness of lens element along the optical axis and other ratio of the central thickness of lens element along the optical axis to the sum of all air gaps, focal length, and/or other related parameters could be further controlled. For example, these related parameters could be a central thickness of the second lens element along the optical axis, T 2 , an air gap between the first lens element and the second lens element, G 12 , an effective focal length, EFL, of the optical imaging lens, a back focal length, BFL, of the optical imaging lens, a focal length of the first lens element, f 1 , and a focal length of the third lens element, f 3 , satisfying at least one of the relations:
 
(EFL/ G   12 )&lt;24;
 
( T 3/ G   12 )&lt;5;
 
0.5≦( T 2+ T 3)≦0.83(mm);
 
1.5&lt;[ T 2+ T 3)/ T 3]&lt;2.5;
 
0.07&lt;( G   12   +G   34 )&lt;0.25(mm);
 
2&lt;( f 1+ f 3)&lt;4(mm); and/or
 
(BFL/EFL)≧0.5,
 
wherein, BFL is defined by the distance between the image-side surface of the fourth lens element and an image plane along the optical axis.
 
     Aforesaid exemplary embodiments are not limited and could be selectively incorporated in other embodiments described herein. 
     In example embodiments, an aperture stop is provided for adjusting the input of light of the system. For example, the aperture stop is preferably provided but not limited to be positioned in front of the first lens element, or positioned between the first lens element and the second lens element. 
     In some exemplary embodiments, more details about the convex or concave surface structure and/or the refracting power could be incorporated for one specific lens element or broadly for plural lens elements to enhance the control for the system performance and/or resolution. For example, for the first lens element, an image-side surface is comprised, but the image-side surface need not be limited to a convex portion in the vicinity of a periphery of the first lens element. 
     In another exemplary embodiment, a mobile device comprises a housing and an optical imaging lens assembly positioned in the housing. The optical imaging lens assembly comprises a lens barrel, any of aforesaid example embodiments of optical imaging lens, a module housing unit, and an image sensor. The lens comprising four lens elements with refracting power as a whole is positioned in the lens barrel, the module housing unit is for positioning the lens barrel, and the image sensor is positioned at the image-side of the optical imaging lens. 
     In some exemplary embodiments, the module housing unit optionally comprises an autofocus module and/or an image sensor base. The autofocus module may comprise a lens seat and a lens backseat, wherein the lens seat is positioned close to the outside of the lens barrel along with an axis; the lens backseat is positioned along the axis and around the outside of the lens seat; and the lens barrel and the optical imaging lens positioned therein are driven by the lens seat for moving along the axis to control the focusing of the optical imaging lens. The image sensor base could be positioned between the lens backseat and the image sensor, and closed to the lens backseat. 
     Through controlling the ratio among at least one central thickness of lens element along the optical axis, an air gap between two lens elements along the optical axis, and a sum of all air gaps between the four lens elements along the optical axis in a predetermined range, and incorporated with the arrangement of the convex or concave shape of the surfaces of the lens element(s) and/or refracting power, the mobile device and the optical imaging lens thereof in exemplary embodiments achieve good optical characters and effectively shorten the length of the optical imaging lens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments will be more readily understood from the following detailed description when read in conjunction with the appended drawings, in which: 
         FIG. 1  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 1 of the invention; 
         FIG. 2  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 1 of the invention; 
         FIG. 3  shows another cross-sectional view of a lens element of the optical imaging lens according to embodiment 1 of the invention; 
         FIG. 4  shows a table of aspherical data of the optical imaging lens according to embodiment 1 of the invention; 
         FIG. 5  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 1 of the invention; 
         FIG. 6  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 2 of the invention; 
         FIG. 7  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 2 of the invention; 
         FIG. 8  shows a table of aspherical data of the optical imaging lens according to embodiment 2 of the invention; 
         FIG. 9  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 2 of the invention; 
         FIG. 10  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 3 of the invention; 
         FIG. 11  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 3 of the invention; 
         FIG. 12  shows a table of aspherical data of the optical imaging lens according to embodiment 3 of the invention; 
         FIG. 13  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 3 of the invention; 
         FIG. 14  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 4 of the invention; 
         FIG. 15  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 4 of the invention; 
         FIG. 16  shows a table of aspherical data of the optical imaging lens according to embodiment 4 of the invention; 
         FIG. 17  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 4 of the invention; 
         FIG. 18  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 5 of the invention; 
         FIG. 19  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 5 of the invention; 
         FIG. 20  shows a table of aspherical data of the optical imaging lens according to embodiment 5 of the invention; 
         FIG. 21  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 5 of the invention; 
         FIG. 22  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 6 of the invention; 
         FIG. 23  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 6 of the invention; 
         FIG. 24  shows a table of aspherical data of the optical imaging lens according to embodiment 6 of the invention; 
         FIG. 25  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 6 of the invention; 
         FIG. 26  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 7 of the invention; 
         FIG. 27  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 7 of the invention; 
         FIG. 28  shows a table of aspherical data of the optical imaging lens according to embodiment 7 of the invention; 
         FIG. 29  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 7 of the invention; 
         FIG. 30  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 8 of the invention; 
         FIG. 31  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 8 of the invention; 
         FIG. 32  shows a table of aspherical data of the optical imaging lens according to embodiment 8 of the invention; 
         FIG. 33  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 8 of the invention; 
         FIG. 34  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 9 of the invention; 
         FIG. 35  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 9 of the invention; 
         FIG. 36  shows a table of aspherical data of the optical imaging lens according to embodiment 9 of the invention; 
         FIG. 37  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 9 of the invention; 
         FIG. 38  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 10 of the invention; 
         FIG. 39  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 10 of the invention; 
         FIG. 40  shows a table of aspherical data of the optical imaging lens according to embodiment 10 of the invention; 
         FIG. 41  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 10 of the invention; 
         FIG. 42  shows a cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to embodiment 11 of the invention; 
         FIG. 43  shows a table of optical data of each lens element of the optical imaging lens according to embodiment 11 of the invention; 
         FIG. 44  shows a table of aspherical data of the optical imaging lens according to embodiment 11 of the invention; 
         FIG. 45  shows charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to embodiment 11 of the invention; 
         FIG. 46  shows a comparison table for the values of T 3 /G 34 , G aa /T 3 , EFL/G 12 , T 3 /G 12 , T 2 +T 3 , (T 2 +T 3 )/T 3 , G 12 +G 34 , f 1 +f 3 , and BFL/EFL of all 11 example embodiments shown in  FIGS. 1 ˜ 45 ; 
         FIG. 47  shows a structure of an example embodiment of a mobile device; and 
         FIG. 48  shows a partially enlarged view of a structure of another example embodiment of a mobile device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features. Persons having ordinary skill in the art will understand other varieties for implementing example embodiments, including those described herein. The drawings are not limited to specific scale and similar reference numbers are used for representing similar elements. As used in the disclosures and the appended claims, the terms “example embodiment,” “exemplary embodiment,” and “present embodiment” do not necessarily refer to a single embodiment, although it may, and various example embodiments may be readily combined and interchanged, without departing from the scope or spirit of the present invention. Furthermore, the terminology as used herein is for the purpose of describing example embodiments only and is not intended to be a limitation of the invention. In this respect, as used herein, the term “in” may include “in” and “on”, and the terms “a”, “an” and “the” may include singular and plural references. Furthermore, as used herein, the term “by” may also mean “from”, depending on the context. Furthermore, as used herein, the term “if” may also mean “when” or “upon”, depending on the context. Furthermore, as used herein, the words “and/or” may refer to and encompass any and all possible combinations of one or more of the associated listed items. 
     Example embodiments of an optical imaging lens may comprise a first lens element, a second lens element, a third lens element, and a fourth lens element. These lens elements may be arranged in an order from an object side to an image side, and example embodiments of the lens as a whole may comprise only the four lens elements with refracting power. In an example embodiment: the first lens element has positive refracting power and the object-side surface thereof is a convex surface; the second lens element has negative refracting power, the object-side surface thereof comprises a concave portion in the vicinity of the optical axis and the image-side surface thereof comprises a concave portion in the vicinity of the optical axis; the third lens element has positive refracting power, the object-side surface thereof is a concave surface and the image-side surface thereof being a convex surface; the object-side surface of the fourth lens element comprises a convex portion in the vicinity of the optical axis, and the image-side surface thereof comprises a concave portion in the vicinity of the optical axis and a convex portion in the vicinity of a periphery of the fourth lens element. The central thickness of the third lens element along the optical axis, T 3 , an air gap between the third lens element and the fourth lens element, G 34 , and the sum of all air gaps between the first lens element to the fourth lens element along the optical axis, G aa , satisfy the relations as followed:
 
( T 3/ G   34 )&gt;4   relation (1); and
 
( G   aa   /T 3)&gt;1   relation (2).
 
     Preferably, the first lens element having positive refracting power have better light converge ability and the third lens element and the fourth lens element could eliminate the astigmatism aberration and distortion aberration to reduce the aberration of the whole system to achieve good optical characters and shortened the length of the optical imaging lens. 
     Reference is now made to relation (1). A person having ordinary skill in the art would readily understand that when the air gap G 34  between the third lens element and the fourth lens element along the optical axis is shortened to satisfy relation (1), assuming the thickness of the third lens element is not changed, the length of the optical imaging lens would be shortened. If relation (1) is not satisfied, i.e. (T 3 /G 34 )&lt;4, the air gap between the third lens element and the fourth lens element may be large that it would cause a long optical imaging lens. Relation (1) may be further restricted by an upper limit, for example but not limited to, 15&gt;(T 3 /G 34 )&gt;4. 
     Reference is now made to relation (2). A person having ordinary skill in the art would readily understand that when the central thickness T 3  of the third lens element along the optical axis is shortened to satisfy relation (2), assuming the sum of all air gaps from the first lens element to the fourth lens element along the optical axis, G aa , is not changed, the length of the optical imaging lens would also be effectively shortened. If relation (2) is not satisfied, i.e. (G aa /T 3 )&lt;1, the thickness of the third lens along the optical axis may be so large that it would cause a long optical imaging lens. Relation (2) may be further restricted by an upper limit, for example but not limited to, 2&gt;(G aa /T 3 )&gt;1. By applying these techniques, the length of the optical imaging lens can be shortened. 
     In some example embodiments, other related parameters, such as the central thickness of lens element along the optical axis, focal length, and/or other related parameters could be further controlled. For example, these related parameters could be a central thickness of the second lens element along the optical axis, T 2 , an air gap between the first lens element and the second lens element, G 12 , an effective focal length, EFL, of the optical imaging lens, a back focal length, BFL, of the optical imaging lens, a focal length of the first lens element, f 1 , and a focal length of the third lens element, f 3 , satisfying at least one of the relations:
 
(EFL/ G   12 )&lt;24   relation (3);
 
( T 3/ G   12 )&lt;5   relation (4);
 
0.5≦( T 2+ T 3)≦0.83(mm)   relation (5);
 
1.5&lt;[( T 2+ T 3)/ T 3]&lt;2.5   relation (6);
 
0.07&lt;( G   12   +G   34 )&lt;0.25(mm)   relation (7);
 
2&lt;( f 1+ f 3)&lt;4(mm)   relation (8); and/or
 
(BFL/EFL)≦0.5   relation (9),
 
wherein, BFL is defined by the distance between the image-side surface of the fourth lens element and an image plane along the optical axis.
 
     Reference is now made to relation (3). A person having ordinary skill in the art would readily understand that when relation (3) is satisfied, assuming the air gap G 12  between the first lens element and the second lens element along the optical axis is not shortened, the effective focal length of the optical imaging lens would be shorter to effectively shorten the length of the optical imaging lens. If relation (3) is not satisfied, i.e. (EFL/G 12 )&gt;24, the effective focal length of the optical imaging lens is so long that a long optical imaging lens is caused. Relation (3) may be further restricted by a lower limit. For example, a lower limit may be, but is not limited to, 17&lt;(EFL/G 12 )&lt;24. 
     Reference is now made to relation (4). A person having ordinary skill in the art would readily understand that if relation (4) is not satisfied, i.e. (T 3 /G 12 )&gt;5, the central thickness of the third lens element along the optical axis is so thick that a long optical imaging lens is caused. Relation (4) may be further restricted by a lower limit. For example, a lower limit may be, but is not limited to, 2&lt;(T 3 /G 12 )&lt;5. 
     Reference is now made to relation (5). A person having ordinary skill in the art would readily understand the results if relation (5) is not satisfied. If the lower limit is exceeded, i.e. (T 2 +T 3 )≦0.5 (mm), the central thickness of the second lens element or third lens element along the optical axis would be so thin that making the optical imaging lens would be difficult. If the upper limit is exceeded, i.e. 0.83≦(T 2 +T 3 ) (mm), the central thickness of the second lens element or the third lens element along the optical axis would be so thick as to cause a long optical imaging lens. 
     Reference is now made to relation (6). A person having ordinary skill in the art would readily understand the results if relation (6) is not satisfied. If the lower limit is exceeded, i.e. [(T 2 +T 3 )/T 3 ]&lt;1.5, the central thickness of the third lens element along the optical axis would be so thick as to cause a long optical imaging lens. If the upper limit is exceeded, i.e. [(T 2 +T 3 )/T 3 ]&gt;2.5, assuming the thickness of the third lens element is not changed, the central thickness of the second lens element along the optical axis would beso thick as to cause a long optical imaging lens. 
     Reference is now made to relation (7). A person having ordinary skill in the art would readily understand the results if relation (7) is not satisfied. If the lower limit is exceeded, i.e. (G 12 +G 34 )≦0.07 (mm), the air gap between the first lens element and the second lens element or the air gap between the third lens element and the fourth lens element along the optical axis would be so narrow that manufacturing the optical imaging lens would be difficult. If the upper limit is exceeded, i.e. (G 12 +G 34 )&gt;0.25 (mm), the sum of the air gap between the first lens element and the second lens element and the air gap between the third lens element and the fourth lens element along the optical axis is so large that a long optical imaging lens is caused. 
     Reference is now made to relation (8). A person having ordinary skill in the art would readily understand the results if relation (8) is not satisfied. If the lower limit is exceeded, i.e. (f 1 +f 3 )&lt;2 (mm), the focal length of the first lens element or the third lens element would be short and the refracting power of the first lens element or the third lens element would be large. Arrangement of the refracting power for such a system is difficult. If the upper limit is exceeded, i.e. (f 1 +f 3 )&gt;4 (mm), the focal length of the first lens element or third lens element would be so long as to cause a long optical imaging lens. 
     Reference is now made to relation (9). A person of ordinary skill in the art would readily understand that when relation (9) is satisfied, the effective focal length of the optical imaging lens would be shorter. If relation (9) is not satisfied, i.e. (BFL/EFL)&lt;0.5, the effective focal length of the optical imaging lens would be so long as to cause a long optical imaging lens. 
     When implementing example embodiments, more details about the convex or concave surface structure and/or the refracting power may be incorporated for one specific lens element or broadly for plural lens elements to enhance the control for the system performance and/or resolution, as illustrated in the following embodiments. It is noted that the details listed here could be incorporated in example embodiments if no inconsistency occurs. 
     Several exemplary embodiments and associated optical data will now be provided for illustrating example embodiments of optical imaging lens with good optical characters and a shortened length. Reference is now made to  FIGS. 1-5 .  FIG. 1  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a first example embodiment.  FIG. 2  illustrates an example table of optical data of each lens element of the optical imaging lens according to an example embodiment.  FIG. 3  depicts another example cross-sectional view of a lens element of the optical imaging lens according to an example embodiment.  FIG. 4  depicts an example table of aspherical data of the optical imaging lens according to an example embodiment.  FIG. 5  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to an example embodiment. 
     As shown in  FIG. 1 , the optical imaging lens  1  of the present embodiment comprises, in order from an object side A 1  to an image side A 2 , an aperture stop  100 , a first lens element  110 , a second lens element  120 , a third lens element  130  and a fourth lens element  140 . Both of a filtering unit  150  and an image plane  160  of an image sensor are positioned at the image side A 2  of the optical imaging lens  1 . Each of the first, second, third, fourth lens elements  110 ,  120 ,  130 ,  140  and the filtering unit  150  has an object-side surface  111 / 121 / 131 / 141 / 151  facing toward the object side A 1  and an image-side surface  112 / 122 / 132 / 142 / 152  facing toward the image side A 2 . The aperture stop  100 , positioned in front of the first lens element  110 , and together with the first lens element  110  having positive refracting power could effectively shorten the length of the optical imaging lens  1 . The example embodiment of the filtering unit  150  illustrated is an IR cut filter (infrared cut filter) positioned between the fourth lens element  140  and an image plane  160 . The filtering unit  150  filters light with specific wavelength from the light passing optical imaging lens. For example, IR light is filtered, and this will prohibit the IR light which is not visible by human eyes from producing an image on the image plane  160 . 
     Exemplary embodiments of each lens elements of the optical imaging lens  1  will now be described with reference to the drawings. 
     The first lens element  110  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  111  and the image-side surface  112  are convex surfaces. The convex surface  111  and convex surface  112  may both be aspherical surfaces. 
     The second lens element  120  may have negative refracting power, which may be constructed by plastic material. Both the object-side surface  121  and the image-side surface  122  are concave surfaces. The concave surface  121  and concave surface  122  may both be aspherical surfaces. 
     The third lens element  130  may have positive refracting power, which may be constructed by plastic material. The object-side surface  131  is a concave surface and the image-side surface  132  is a convex surface. The concave surface  131  and the convex surface  132  may both be aspherical surfaces. 
     The fourth lens element  140  may have negative refracting power, which may be constructed by plastic material. The object-side surface  141  comprises a convex portion  1411  in the vicinity of the optical axis and a concave portion  1412  in the vicinity of the periphery of the fourth lens element  140 . The image-side surface  142  has a concave portion  1421  in the vicinity of the optical axis and a convex portion  1422  in the vicinity of a periphery of the fourth lens element  140 . The object-side surface  141  and the image-side surface  142  may both be aspherical surfaces. 
     In example embodiments, air gaps exist between the four lens elements  110 ,  120 ,  130 ,  140 , the filtering unit  150  and the image plane  160  of the image sensor. For example,  FIG. 1  illustrates the air gap d 1  existing between the first lens element  110  and the second lens element  120 , the air gap d 2  existing between the second lens element  120  and the third lens element  130 , the air gaps d existing between the third lens element  130  and the fourth lens element  140 , the air gap d 4  existing between the fourth lens element  140  and the filtering unit  150  and the air gap d 5  existing between the filtering unit  150  and the image plane  160  of the image sensor. However, in other embodiments, any of the aforesaid air gaps may or may not exist. For example, the profiles of opposite surfaces of any two adjacent lens elements may correspond to each other, and in such situation, the air gaps may not exist. The air gap d 1  is denoted by G 12 , the air gap d 3  is denoted by G 34 , and the sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
       FIG. 2  depicts the optical characters of each lens elements in the optical imaging lens  1  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=11.45;
 
( G   aa   /T 3)=1.21;
 
(EFL/ G   12 )=23.87;
 
( T 3/ G   12 )=4.06;
 
( T 2+ T 3)=0.69(mm);
 
[( T 2+ T 3)/ T 3]=1.73;
 
( G   12   +G   34 )=0.13(mm);
 
( f 1+ f 3)=3.21(mm);
 
(BFL/EFL)=0.5;
 
wherein the distance from the object-side surface  111  of the first lens element  110  to the image plane  160  is 3.063 (mm), and the length of the optical imaging lens is shortened.
 
     Please note that, in example embodiments, to clearly illustrate the structure of each lens element, only the part where light passes, is shown. For example, taking the first lens element  110  as an example,  FIG. 1  illustrates the object-side surface  111  and the image-side surface  112 . However, when implementing each lens element  110 ,  120 ,  130 ,  140  of the present embodiment, a fixing part for positioning the lens elements inside the optical imaging lens may be formed selectively. Based on the first lens element  110 , please refer to  FIG. 3 , which illustrates the first lens element  110  further comprising a fixing part. Here the fixing part is not limited to a protruding part  113  for mounting the first lens element  110  in the optical imaging lens, and ideally, light will not pass through the protruding part  113 . 
     The aspherical surfaces, including the convex surface  111  and the convex surface  112  of the first lens element  110 , the concave surfaces  121 ,  122  of the second lens element  120 , the concave surface  131  and the convex surface  132  of the third lens element  130 , and the object-side surface  141  and the image-side surface  142  of the fourth lens element  140  are all defined by the following aspherical formula: 
               Z   ⁡     (   Y   )       =           Y   2     R     /     (     1   +       1   -       (     1   +   K     )     ⁢       Y   2       R   2               )       +       ∑     i   =   1     n     ⁢           ⁢       a     2   ⁢   i       ×     Y     2   ⁢   i                   
wherein:
         R represents the radius of the surface of the lens element;   Z represents the depth of the aspherical surface (the perpendicular distance between the point of the aspherical surface at a distance Y from the optical axis and the tangent plane of the vertex on the optical axis of the aspherical surface);   Y represents the perpendicular distance between the point of the aspherical surface and the optical axis;   K represents a conic constant;   a 2i , represents a aspherical coefficient of 2i th  level;   and the values of each aspherical parameter are represented in  FIG. 4 .       

     As illustrated in  FIG. 5 , the optical imaging lens of present example embodiments show great optical characteristics in the longitudinal spherical aberration (a), astigmatism aberration in the sagittal direction (b), astigmatism aberration in the tangential direction (c) and distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of example embodiments indeed achieve great optical performance and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 6-9 .  FIG. 6  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a second example embodiment.  FIG. 7  shows an example table of optical data of each lens element of the optical imaging lens according to the second example embodiment.  FIG. 8  shows an example table of aspherical data of the optical imaging lens according to the second example embodiment.  FIG. 9  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to an example embodiment. 
     As shown in  FIG. 6 , the optical imaging lens  2  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  200 , a first lens element  210 , a second lens element  220 , a third lens element  230  and a fourth lens element  240 . The aperture stop  200 , positioned in front of the first lens element  210 , and together with the first lens element  210  having positive refracting power could effectively shorten the length of the optical imaging lens  2 . Both of a filtering unit  250  and an image plane  260  of an image sensor are positioned at the image side A 2  of the optical imaging lens  2 . Each of the first, second, third, fourth lens elements  210 ,  220 ,  230 ,  240  and the filtering unit  250  has an object-side surface  211 / 221 / 231 / 241 / 251  facing toward the object side A 1  and an image-side surface  212 / 222 / 232 / 242 / 252  facing toward the image side A 2 . In an example embodiment, the filtering unit  250  is an IR cut filter positioned between the fourth lens element  240  and the image plane  260 . The filtering unit  250  filters light with specific wavelength from the light passing optical imaging lens  2 . For example, IR light is filtered, and this will prohibit the IR light which is not visible by human eyes from producing an image on image plane  260 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  210 ,  220 ,  230 ,  240 , the filtering unit  250  and the image plane  260  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the second embodiments and the first embodiments is that the central thickness of lens T 3  of the third lens element  230 , the air gap G 34  between the third lens element  230  and the fourth lens element  240  and the sum of all air gaps G aa  from the first lens element  210  to the fourth lens element  240  are different. Please refer to  FIG. 7  for the optical characteristics of each lens elements in the optical imaging lens  2  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=7.01;
 
( G   aa   /T 3)=1.26;
 
(EFL/ G   12 )=23.80;
 
( T 3/ G   12 )=3.84;
 
( T 2+ T 3)=0.73(mm);
 
[( T 2+ T 3)/ T 3]=1.77;
 
( G   12   +G   34 )=0.17(mm);
 
( f 1+ f 3)=3.23(mm);
 
(BFL/EFL)=0.51;
 
wherein the distance from the object-side surface  211  of the first lens element  210  to the image side of the image plane  260  is 3.266 (mm) and the length of the optical imaging lens  2  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  2  may comprise the following example embodiments: 
     The first lens element  210  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  211  and the image-side surface  212  are convex surfaces. The convex surface  211  and convex surface  212  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 8  for values of the aspherical parameters. 
     The second lens element  220  may have negative refracting power, which may be constructed by plastic material. Both the object-side surface  221  and the image-side surface  222  are concave surfaces. The concave surfaces  221 ,  222  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 8  for values of the aspherical parameters. 
     The third lens element  230  may have positive refracting power, which may be constructed by plastic material. The object-side surface  231  is a concave surface and the image-side surface  232  is a convex surface. The concave surface  231  and the convex surface  232  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 8  for values of the aspherical parameters. 
     The fourth lens element  240  may have negative refracting power, which may be constructed by plastic material. The object-side surface  241  is a convex surface. The image-side surface  242  has a concave portion  2421  in the vicinity of the optical axis and a convex portion  2422  in the vicinity of a periphery of the fourth lens element  240 . The convex surface  241  and the image-side surface  242  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 8  for values of the aspherical parameters. 
     As shown in  FIG. 9 , the optical imaging lens  2  of the present embodiment shows great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) and distortion aberration (d). Therefore, according to the above illustration, the optical imaging lens of the present embodiment indeed shows great optical performance and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 10-13 . FIG. 10  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a third example embodiment.  FIG. 11  depicts an example table of optical data of each lens element of the optical imaging lens according to the third example embodiment.  FIG. 12  depicts an example table of aspherical data of the optical imaging lens according to the third example embodiment.  FIG. 13  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the third example embodiment. 
     As shown in  FIG. 10 , the optical imaging lens  3  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  300 , a first lens element  310 , a second lens element  320 , a third lens element  330  and a fourth lens element  340 . Both of a filtering unit  350  and an image plane  360  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  3 . Each of the first, second, third, fourth lens elements  310 ,  320 ,  330 ,  340  and the filtering unit  350  has an object-side surface  311 / 321 / 331 / 341 / 351  facing toward the object side A 1  and an image-side surface  312 / 322 / 332 / 342 / 352  facing toward the image side A 2 . The aperture stop  300 , positioned in front of the first lens element  310 , and together with the first lens element  310  having positive refracting power could effectively shorten the length of the optical imaging lens  3 . Here an example embodiment of the filtering unit  350  is an IR cut filter positioned between the fourth lens element  340  and the image plane  360 . The filtering unit  350  filters light with specific wavelength from the light passing optical imaging lens. For example, the IR light is filtered, and this will prohibit the IR light which is not visible by human eyes from producing an image on image plane  360 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  310 ,  320 ,  330 ,  340 , the filtering unit  350  and the image plane  360  of the image sensor. Please refer to 
       FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the third embodiment and the first embodiment is that the central thickness of lens T 3  of the third lens element  330 , the air gap G 34  between the third lens element  330  and the fourth lens element  340  and the sum of all air gaps G aa  from the first lens element  310  to the fourth lens element  340  are different. Please refer to  FIG. 11  for the optical characteristics of each lens elements in the optical imaging lens  3  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=4.90;
 
( G   aa   /T 3)=1.46;
 
(EFL/ G   12 )=18.69;
 
( T 3/ G   12 )=2.88;
 
( T 2+ T 3)=0.73(mm);
 
[( T 2+ T 3)/ T 3]=1.91;
 
( G   12   +G   34 )=0.21(mm);
 
( f 1+ f 3)=3.21(mm);
 
(BFL/EFL)=0.48;
 
wherein the distance from the object-side surface  311  of the first lens element  310  to the image side of the image plane  360  is 3.158 (mm), and the length of the optical imaging lens  3  is shortened.
 
     Example embodiments of the lens elements  3  of the optical imaging lens may comprise the following example embodiments: 
     The first lens element  310  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  311  and the image-side surface  312  are convex surfaces. The convex surfaces  311 ,  312  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 12  for values of the aspherical parameters. 
     The second lens element  320  may have negative refracting power, which may be constructed by plastic material. Both the object-side surface  321  and the image-side surface  322  are concave surfaces. The concave surfaces  321 ,  322  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 12  for values of the aspherical parameters. 
     The third lens element  330  may have positive refracting power, which may be constructed by plastic material. The object-side surface  331  is a concave surface and the image-side surface  332  is a convex surface. The concave surface  331  and convex surface  332  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 12  for values of the aspherical parameters. 
     The fourth lens element  340  may have negative refracting power, which may be constructed by plastic material. The object-side surface  341  comprises a convex portion  3411  in the vicinity of the optical axis and a concave portion  3412  in the vicinity of the periphery of the fourth lens element  340 . The image-side surface  342  has a concave portion  3421  in the vicinity of the optical axis and a convex portion  3422  in the vicinity of a periphery of the fourth lens element  340 . The object-side surface  341  and the image-side surface  342  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 12  for values of the aspherical parameters. 
     As illustrated in  FIG. 13 , it is clear that the optical imaging lens of the present embodiment may achieve great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) and distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 14-17 .  FIG. 14  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a fourth example embodiment.  FIG. 15  shows an example table of optical data of each lens element of the optical imaging lens according to the fourth example embodiment.  FIG. 16  shows an example table of aspherical data of the optical imaging lens according to the fourth example embodiment.  FIG. 17  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the fourth example embodiment. 
     As shown in  FIG. 14 , the optical imaging lens of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  400 , a first lens element  410 , a second lens element  420 , a third lens element  430  and a fourth lens element  440 . Both of a filtering unit  450  and an image plane  460  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  4 . Each of the first, second, third, fourth lens elements  410 ,  420 ,  430 ,  440  and the filtering unit  450  has an object-side surface  411 / 421 / 431 / 441 / 451  facing toward the object side A 1  and an image-side surface  412 / 422 / 432 / 442 / 452  facing toward the image side A 2 . The aperture stop  400 , positioned in front of the first lens element  410 , and together with the first lens element  410  having positive refracting power could effectively shorten the length of the optical imaging lens  4 . Here an example embodiment of filtering unit  450  is an IR cut filter, which may be positioned between the fourth lens element  440  and the image plane  460 . The filtering unit  450  filters light with specific wavelength from the light passing optical imaging lens  4 . For example, IR light may be filtered, and this will prohibit the IR light which is not visible by human eyes from producing an image on image plane  460 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  410 ,  420 ,  430 ,  440 , the filtering unit  450  and the image plane  460  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the fourth embodiment and the first embodiment is that the central thickness of lens T 3  of the third lens element  430 , the air gap G 34  between the third lens element  430  and the fourth lens element  440  and the sum of all air gaps G aa  from the first lens element  410  to the fourth lens element  440  are different. Please refer to  FIG. 15  for the optical characteristics of each lens elements in the optical imaging lens  4  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=14.23;
 
( G   aa   /T 3)=1.02;
 
(EFL/ G   12 )=20.87;
 
( T 3/ G   12 )=3.58;
 
( T 2+ T 3)=0.83(mm);
 
[( T 2+ T 3)/ T 3]=1.87;
 
( G   12   +G   34 )=0.15(mm);
 
( f 1+ f 3)=3.15(mm);
 
(BFL/EFL)=0.5;
 
wherein the distance from the object-side surface  411  of the first lens element  410  to the image plane  460  is 3.258 (mm), and the length of the optical imaging lens  4  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  4  may comprise the following example embodiments: 
     The first lens element  410  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  411  and the image-side surface  412  are convex surfaces. The convex surfaces  411 ,  412  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 16  for values of the aspherical parameters. 
     The second lens element  420  may have negative refracting power, which may be constructed by plastic material. Both the object-side surface  421  and the image-side surface  422  are concave surfaces. The concave surfaces  421 ,  422  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 16  for values of the aspherical parameters. 
     The third lens element  430  may have positive refracting power, which may be constructed by plastic material. The object-side surface  431  is a concave surface and the image-side surface  432  is a convex surface. The concave surface  431  and the convex surface  432  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 16  for values of the aspherical parameters. 
     The fourth lens element  440  may have negative refracting power, which may be constructed by plastic material. The object-side surface  441  comprises a convex portion  4411  in the vicinity of the optical axis and a concave portion  4412  in the vicinity of the periphery of the fourth lens element  440 . The image-side surface  442  has a concave portion  4421  in the vicinity of the optical axis and a convex portion  4422  in the vicinity of a periphery of the fourth lens element  440 . The object-side surface  441  and the image-side surface  442  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 16  for values of the aspherical parameters. 
     As illustrated in  FIG. 17 , it is clear that the optical imaging lens of the present embodiment may achieve great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) and distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 18-21 .  FIG. 18  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a fifth embodiment.  FIG. 19  shows an example table of optical data of each lens element of the optical imaging lens according to the fifth example embodiment.  FIG. 20  shows an example table of aspherical data of the optical imaging lens according to the fifth example embodiment.  FIG. 21  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the fifth example embodiment. 
     As shown in  FIG. 18 , the optical imaging lens  5  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  500 , a first lens element  510 , a second lens element  520 , a third lens element  530  and a fourth lens element  540 . Both of a filtering unit  550  and an image plane  560  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  5 . Each of the first, second, third, fourth lens elements  510 ,  520 ,  530 ,  540  and the filtering unit  550  has an object-side surface  511 / 521 / 531 / 541 / 551  facing toward the object side A 1  and an image-side surface  512 / 522 / 532 / 542 / 552  facing toward the image side A 2 . The aperture stop  500 , positioned in front of the first lens element  510 , and together with the first lens element  510  having positive refracting power could effectively shorten the length of the optical imaging lens  5 . Here an example embodiment of filtering unit  550  is an IR cut filter, which may be positioned between the fourth lens element  540  and the image plane  560 . The filtering unit  550  filters light with specific wavelength from the light passing optical imaging lens. For example, IR light may be filtered, and this will prohibit the IR light which is not visible by human eyes from producing an image on image plane  560 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  510 ,  520 ,  530 ,  540 , the filtering unit  550  and the image plane  560  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the fifth embodiments and the first embodiments is that the central thickness of lens T 3  of the third lens element  530 , the air gap G 34  between the third lens element  530  and the fourth lens element  540  and the sum of all air gaps G aa  from the first lens element  510  to the fourth lens element  540  are different. Please refer to  FIG. 19  for the optical characteristics of each lens elements in the optical imaging lens  5  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=4.86;
 
( G   aa   /T 3)=1.03;
 
(EFL/ G   12 )=24.00;
 
( T 3/ G   12 )=4.73;
 
( T 2+ T 3)=0.76(mm);
 
[( T 2+ T 3)/ T 3]=1.66;
 
( G   12   +G   34 )=0.19(mm);
 
( f 1+ f 3)=3.12(mm);
 
(BFL/EFL)=0.51;
 
wherein the distance from the object-side surface  511  of the first lens element  510  to the image plane  560  is 3.081 (mm), and the length of the optical imaging lens  5  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  5  may comprise the following example embodiments: 
     The first lens element  510  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  511  and the image-side surface  512  are convex surfaces. The convex surfaces  511 ,  512  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 20  for values of the aspherical parameters. 
     The second lens element  520  may have negative refracting power, which may be constructed by plastic material. Both the object-side surface  521  and an image-side surface  522  are concave surfaces. The concave surfaces  521 ,  522  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 20  for values of the aspherical parameters. 
     The third lens element  530  may have positive refracting power, which may be constructed by plastic material. The object-side surface  531  is a concave surface and the image-side surface  532  is a convex surface. The concave surface  531  and convex surface  532  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 20  for values of the aspherical parameters. 
     The fourth lens element  540  may have negative refracting power, which may be constructed by plastic material. The object-side surface  541  comprises a convex portion  5411  in the vicinity of the optical axis and a concave portion  5412  in the vicinity of the periphery of the fourth lens element  540 . The image-side surface  542  has a concave portion  5421  in the vicinity of the optical axis and a convex portion  5422  in the vicinity of a periphery of the fourth lens element  540 . The object-side surface  541  and surface  542  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 20  for values of the aspherical parameters. 
     As illustrated in  FIG. 21 , it is clear that the optical imaging lens of the present embodiment may show great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) or distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 22-25 .  FIG. 22  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a sixth example embodiment.  FIG. 23  shows an example table of optical data of each lens element of the optical imaging lens according to the sixth example embodiment.  FIG. 24  shows an example table of aspherical data of the optical imaging lens according to the sixth example embodiment.  FIG. 25  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the sixth example embodiment. 
     As shown in  FIG. 22 , the optical imaging lens  6  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  600 , a first lens element  610 , a second lens element  620 , a third lens element  630  and a fourth lens element  640 . Both of a filtering unit  650  and an image plane  660  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  6 . Each of the first, second, third, fourth lens elements  610 ,  620 ,  630 ,  640  and the filtering unit  650  has an object-side surface  611 / 621 / 631 / 641 / 651  facing toward the object side A 1  and an image-side surface  612 / 622 / 632 / 642 / 652  facing toward the image side A 2 . The aperture stop  600 , positioned in front of the first lens element  610 , and together with the first lens element  610  having positive refracting power could effectively shorten the length of the optical imaging lens  6 . Here an example embodiment of filtering unit  650  may be an IR cut filter, which may be positioned between the fourth lens element  640  and the image plane  660 . The filtering unit  650  filters light with specific wavelength from the light passing optical imaging lens  6 . For example, IR light may be filtered, and this may prohibit the IR light which is not visible by human eyes from producing an image on image plane  660 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  610 ,  620 ,  630 ,  640 , the filtering unit  650  and the image plane  660  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the sixth embodiments and the first embodiments is that the central thickness of lens T 3  of the third lens element  630 , the air gap G 34  between the third lens element  630  and the fourth lens element  640  and the sum of all air gaps G aa  from the first lens element  610  to the fourth lens element  640  are different. Please refer to  FIG. 23  for the optical characteristics of each lens elements in the optical imaging lens  6  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=4.07;
 
( G   aa   /T 3)=1.39;
 
(EFL/ G   12 )=23.91;
 
( T 3/ G   12 )=3.59;
 
( T 2+ T 3)=0.81(mm);
 
[( T 2+ T 3)/ T 3]=1.91;
 
( G   12   +G   34 )=0.22(mm);
 
( f 1+ f 3)=3.97(mm);
 
(BFL/EFL)=0.36;
 
wherein the distance from the object-side surface  611  of the first lens element  610  to the image plane  660  is 3.24 (mm), and the length of the optical imaging lens  6  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  6  may comprise the following example embodiments: 
     The first lens element  610  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  611  and the image-side surface  612  are convex surfaces. The convex surfaces  611  and  612  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 24  for values of the aspherical parameters. 
     The second lens element  620  may have negative refracting power, which may be constructed by plastic material. Both the object-side surface  621  and the image-side surface  622  are concave surfaces. The concave surfaces  621 ,  622  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 24  for values of the aspherical parameters. 
     The third lens element  630  may have positive refracting power, which may be constructed by plastic material. The object-side surface  631  is a concave surface and the image-side surface  632  is a convex surface. The concave surface  631  and convex surface  632  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 24  for values of the aspherical parameters. 
     The fourth lens element  640  may have negative refracting power, which may be constructed by plastic material. The object-side surface  641  comprises a convex portion  6411  in the vicinity of the optical axis and a concave portion  6412  in the vicinity of the periphery of the fourth lens element  640 . The image-side surface  642  has a concave portion  6421  in the vicinity of the optical axis and a convex portion  6422  in the vicinity of a periphery of the fourth lens element  640 . The object-side surface  641  and the image-side surface  642  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 24  for values of the aspherical parameters. 
     As illustrated in  FIG. 25 , it is clear that the optical imaging lens of the present embodiment may show great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) or distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 26-29 .  FIG. 26  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a seventh example embodiment.  FIG. 27  shows an example table of optical data of each lens element of the optical imaging lens according to the seventh example embodiment.  FIG. 28  shows an example table of aspherical data of the optical imaging lens according to the seventh example embodiment.  FIG. 29  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the seventh example embodiment. 
     As shown in  FIG. 26 , the optical imaging lens  7  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  700 , a first lens element  710 , a second lens element  720 , a third lens element  730  and a fourth lens element  740 . 
     Both of a filtering unit  750  and an image plane  760  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  7 . Each of the first, second, third, fourth lens elements  710 ,  720 ,  730 ,  740  and the filtering unit  750  has an object-side surface  711 / 721 / 731 / 741 / 751  facing toward the object side A 1  and an image-side surface  712 / 722 / 732 / 742 / 752  facing toward the image side A 2 . The aperture stop  700 , positioned in front of the first lens element  710 , and together with the first lens element  710  having positive refracting power could effectively shorten the length of the optical imaging lens  7 . Here an example embodiment of filtering unit  750  may comprise an IR cut filter, which is positioned between the fourth lens element  740  and the image plane  760 . The filtering unit  750  filters light with specific wavelength from the light passing optical imaging lens  7 . For example, IR light is filtered, and this may prohibit the IR light which is not seen by human eyes from producing an image on image plane  760 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  710 ,  720 ,  730 ,  740 , the filtering unit  750  and the image plane  760  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the seventh embodiments and the first embodiments is that the central thickness of lens T 3  of the third lens element  730 , the air gap G 34  between the third lens element  730  and the fourth lens element  740  and the sum of all air gaps G aa  from the first lens element  710  to the fourth lens element  740  are different. Please refer to  FIG. 27  for the optical characteristics of each lens elements in the optical imaging lens  7  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=4.15;
 
( G   aa   /T 3)=2.07;
 
(EFL/ G   12 )=23.90;
 
( T 3/ G   12 )=2.72;
 
( T 2+ T 3)=0.54(mm);
 
[( T 2+ T 3)/ T 3]=1.93;
 
( G   12   +G   34 )=0.17(mm);
 
( f 1+ f 3)=3.34(mm);
 
(BFL/EFL)=0.51;
 
wherein the distance from the object-side surface  711  of the first lens element  710  to the image plane  760  is 3.064 (mm), and the length of the optical imaging lens  7  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  7  may comprise the following example embodiments: 
     The first lens element  710  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  711  and the image-side surface  712  are convex surfaces. The convex surfaces  711  and  712  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 28  for values of the aspherical parameters. 
     The second lens element  720  may have negative refracting power, which may be constructed by plastic material. The object-side surface  721  is a convex surface. The image-side surface  722  has a concave portion  7221  in the vicinity of the optical axis and a convex portion  7222  in the vicinity of a periphery of the second lens element  720 . The convex surface  721  and the image-side surface  722  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 28  for values of the aspherical parameters. 
     The third lens element  730  may have positive refracting power, which may be constructed by plastic material. The object-side surface  731  is a concave surface and the image-side surface  732  is a convex surface. The concave surface  731  and convex surface  732  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 28  for values of the aspherical parameters. 
     The fourth lens element  740  may have negative refracting power, which may be constructed by plastic material. The object-side surface  741  is a convex surface. The image-side surface  742  has a concave portion  7421  in the vicinity of the optical axis and a convex portion  7422  in the vicinity of a periphery of the fourth lens element  740 . The convex surface  741  and the image-side surface  742  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 28  for values of the aspherical parameters. 
     As illustrated in  FIG. 29 , it is clear that the optical imaging lens of the present embodiment may show great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) or distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 30-33 .  FIG. 30  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to an eighth example embodiment.  FIG. 31  shows an example table of optical data of each lens element of the optical imaging lens according to the eighth example embodiment.  FIG. 32  shows an example table of aspherical data of the optical imaging lens according to the eighth example embodiment.  FIG. 33  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the eighth example embodiment. 
     As shown in  FIG. 30 , the optical imaging lens  8  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  800 , a first lens element  810 , a second lens element  820 , a third lens element  830  and a fourth lens element  840 . Both of a filtering unit  850  and an image plane  860  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  8 . Each of the first, second, third, fourth lens elements  810 ,  820 ,  830 ,  840  and the filtering unit  850  has an object-side surface  811 / 821 / 831 / 841 / 851  facing toward the object side A 1  and an image-side surface  812 / 822 / 832 / 842 / 852  facing toward the image side A 2 . The aperture stop  800 , positioned in front of the first lens element  810 , and together with the first lens element  810  having positive refracting power could effectively shorten the length of the optical imaging lens  8 . Here an example embodiment of filtering unit  850  may comprise an IR cut filter, which is positioned between the fourth lens element  840  and the image plane  860 . The filtering unit  850  filters light with specific wavelength from the light passing optical imaging lens  8 . For example, IR light is filtered, and this may prohibit the IR light which is not seen by human eyes from producing an image on image plane  860 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  810 ,  820 ,  830 ,  840 , the filtering unit  850  and the image plane  860  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the eighth embodiments and the first embodiments is that the central thickness of lens T 3  of the third lens element  830 , the air gap G 34  between the third lens element  830  and the fourth lens element  840  and the sum of all air gaps G aa  from the first lens element  810  to the fourth lens element  840  are different. The object-side surface  841  of the fourth lens element  840  facing toward the object side A 1  further comprises a convex portion  8412  in the vicinity of a periphery of the fourth lens element  840 . Please refer to  FIG. 31  for the optical characteristics of each lens elements in the optical imaging lens  8  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=11.72;
 
( G   aa   /T 3)=1.01;
 
(EFL/ G   12 )=20.38;
 
( T 3/ G   12 )=4.11;
 
( T 2+ T 3)=0.81(mm);
 
[( T 2+ T 3)/ T 3]=1.51;
 
( G   12   +G   34 )=0.18(mm);
 
( f 1+ f 3)=2.50(mm);
 
(BFL/EFL)=0.51;
 
wherein the distance from the object-side surface  811  of the first lens element  810  to the image plane  860  is 3.408 (mm), and the length of the optical imaging lens  8  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  8  may comprise the following example embodiments: 
     The first lens element  810  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  811  and the image-side surface  812  are convex surfaces. The convex surfaces  811  and  812  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 32  for values of the aspherical parameters. 
     The second lens element  820  may have negative refracting power, which may be constructed by plastic material. Both the object-side surface  821  and the image-side surface  822  are concave surfaces. The concave surfaces  821  and  822  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 32  for values of the aspherical parameters. 
     The third lens element  830  may have positive refracting power, which may be constructed by plastic material. The object-side surface  831  is a concave surface and the image-side surface  832  is a convex surface. The concave surface  831  and convex surface  832  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 32  for values of the aspherical parameters. 
     The fourth lens element  840  may have negative refracting power, which may be constructed by plastic material. The object-side surface  841  has a convex portion  8411  in the vicinity of the optical axis and a convex portion  8412  in the vicinity of a periphery of the fourth lens element  840  and the image-side surface  842  has a concave portion  8421  in the vicinity of the optical axis and a convex portion  8422  in the vicinity of a periphery of the fourth lens element  840 . The object-side surface  841  and the image-side surface  842  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 32  for values of the aspherical parameters. 
     As illustrated in  FIG. 33 , it is clear that the optical imaging lens of the present embodiment may show great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) or distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 34-37 .  FIG. 34  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a ninth example embodiment.  FIG. 35  shows an example table of optical data of each lens element of the optical imaging lens according to the ninth example embodiment.  FIG. 36  shows an example table of aspherical data of the optical imaging lens according to the ninth example embodiment.  FIG. 37  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the ninth example embodiment. 
     As shown in  FIG. 34 , the optical imaging lens  9  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  900 , a first lens element  910 , a second lens element  920 , a third lens element  930  and a fourth lens element  940 . Both of a filtering unit  950  and an image plane  960  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  9 . Each of the first, second, third, fourth lens elements  910 ,  920 ,  930 ,  940  and the filtering unit  950  has an object-side surface  911 / 921 / 931 / 941 / 951  facing toward the object side A 1  and an image-side surface  912 / 922 / 932 / 942 / 952  facing toward the image side A 2 . The aperture stop  900 , positioned in front of the first lens element  910 , and together with the first lens element  910  having positive refracting power could effectively shorten the length of the optical imaging lens  9 . Here an example embodiment of filtering unit  950  may comprise an IR cut filter, which is positioned between the fourth lens element  940  and the image plane  960 . The filtering unit  950  filters light with specific wavelength from the light passing optical imaging lens  9 . For example, IR light is filtered, and this may prohibit the IR light which is not seen by human eyes from producing an image on image plane  960 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  910 ,  920 ,  930 ,  940 , the filtering unit  950  and the image plane  960  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the ninth embodiment and the first embodiment is that the central thickness of lens T 3  of the third lens element  930 , the air gap G 34  between the third lens element  930  and the fourth lens element  940  and the sum of all air gaps G aa  from the first lens element  910  to the fourth lens element  940  are different. The object-side surface  921  of the second lens element  920  further comprises a convex portion  9212  in the vicinity of a periphery of the second lens element  920 . Please refer to  FIG. 35  for the optical characteristics of each lens elements in the optical imaging lens  9  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=9.09;
 
( G   aa   /T 3)=1.02;
 
(EFL/ G   12 )=23.90;
 
( T 3/ G   12 )=4.98;
 
( T 2+ T 3)=0.59(mm);
 
[( T 2+ T 3)/ T 3]=1.79;
 
( G   12   +G   34 )=0.10(mm);
 
( f 1+ f 3)=2.98(mm);
 
(BFL/EFL)=0.51;
 
wherein the distance from the object-side surface  911  of the first lens element  910  to the image plane  960  is 2.415 (mm), and the length of the optical imaging lens  9  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  9  may comprise the following example embodiments: 
     The first lens element  910  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  911  and the image-side surface  912  are convex surfaces. The convex surfaces  911  and  912  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 36  for values of the aspherical parameters. 
     The second lens element  920  may have negative refracting power, which may be constructed by plastic material. The image-side surface  922  is a concave surface. The object-side surface  921  has a concave portion  9211  in the vicinity of the optical axis and a convex portion  9212  in the vicinity of a periphery of the second lens element  920 . The object-side surface  921  and image-side surface  922  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 36  for values of the aspherical parameters. 
     The third lens element  930  may have positive refracting power, which may be constructed by plastic material. The object-side surface  931  is a concave surface and the image-side surface  932  is a convex surface. The concave surface  931  and convex surface  932  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 36  for values of the aspherical parameters. 
     The fourth lens element  940  may have negative refracting power, which may be constructed by plastic material. The object-side surface  941  is a convex surface. The image-side surface  942  has a concave portion  9421  in the vicinity of the optical axis and a convex portion  9422  in the vicinity of a periphery of the fourth lens element  940 . The convex surface  941  and image-side surface  942  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 36  for values of the aspherical parameters. 
     As illustrated in  FIG. 37 , it is clear that the optical imaging lens of the present embodiment may show great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) or distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 38-41 .  FIG. 38  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a tenth example embodiment.  FIG. 39  shows an example table of optical data of each lens element of the optical imaging lens according to the tenth example embodiment.  FIG. 40  shows an example table of aspherical data of the optical imaging lens according to the tenth example embodiment.  FIG. 41  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the tenth example embodiment. 
     As shown in  FIG. 38 , the optical imaging lens  10  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises an aperture stop  1000 , a first lens element  1010 , a second lens element  1020 , a third lens element  1030  and a fourth lens element  1040 . Both of a filtering unit  1050  and an image plane  1060  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  10 . Each of the first, second, third, fourth lens elements  1010 ,  1020 ,  1030 ,  1040  and the filtering unit  1050  has an object-side surface  1011 / 1021 / 1031 / 1041 / 1051  facing toward the object side A 1  and an image-side surface  1012 / 1022 / 1032 / 1042 / 1052  facing toward the image side A 2 . The aperture stop  1000 , positioned in front of the first lens element  1010 , and together with the first lens element  1010  having positive refracting power could effectively shorten the length of the optical imaging lens  10 . Here an example embodiment of filtering unit  1050  may comprise an IR cut filter, which is positioned between the fourth lens element  1040  and the image plane  1060 . The filtering unit  1050  filters light with specific wavelength from the light passing optical imaging lens  10 . For example, IR light is filtered, and this may prohibit the IR light which is not visible by human eyes from producing an image on image plane  1060 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  1010 ,  1020 ,  1030 ,  1040 , the filtering unit  1050  and the image plane  1060  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the tenth embodiments and the first embodiments is that the central thickness of lens T 3  of the third lens element  1030 , the air gap G 34  between the third lens element  1030  and the fourth lens element  1040  and the sum of all air gaps G aa  from the first lens element  1010  to the fourth lens element  1040  are different. Please refer to  FIG. 39  for the optical characteristics of each lens elements in the optical imaging lens  10  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=4.62;
 
( G   aa   /T 3)=1.36;
 
(EFL/ G   12 )=23.48;
 
( T 3/ G   12 )=3.42;
 
( T 2+ T 3)=0.93(mm);
 
[( T 2+ T 3)/ T 3]=2.31;
 
( G   12   +G   34 )=0.21(mm);
 
( f 1+ f 3)=3.06(mm);
 
(BFL/EFL)=0.31;
 
wherein the distance from the object-side surface  1011  of the first lens element  1010  to the image plane  1060  is 3.16 (mm), and the length of the optical imaging lens  10  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  10  may comprise the following example embodiments: 
     The first lens element  1010  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  1011  and the image-side surface  1012  are convex surfaces. The convex surfaces  1011  and  1012  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 40  for values of the aspherical parameters. 
     The second lens element  1020  may have negative refracting power, which may be constructed by plastic material. Both the object-side surface  1021  and the image-side surface  1022  are concave surfaces. The concave surfaces  1021 ,  1022  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 40  for values of the aspherical parameters. 
     The third lens element  1030  may have positive refracting power, which may be constructed by plastic material. The object-side surface  1031  is a concave surface and the image-side surface  1032  is a convex surface. The concave surface  1031  and convex surface  1032  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 40  for values of the aspherical parameters. 
     The fourth lens element  1040  may have negative refracting power, which may be constructed by plastic material. The object-side surface  1041  comprises a concave portion  10411  in the vicinity of the optical axis and a concave portion  10412  in the vicinity of the periphery of the fourth lens element  1040 . The image-side surface  1042  has a concave portion  10421  in the vicinity of the optical axis and a convex portion  10422  in the vicinity of a periphery of the fourth lens element  1040 . The object-side surface  1041  and the image-side surface  1042  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 40  for values of the aspherical parameters. 
     As illustrated in  FIG. 41 , it is clear that the optical imaging lens of the present embodiment may show great characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) or distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Reference is now made to  FIGS. 42-45 .  FIG. 42  illustrates an example cross-sectional view of an optical imaging lens having four lens elements of the optical imaging lens according to a eleventh example embodiment.  FIG. 43  shows an example table of optical data of each lens element of the optical imaging lens according to the eleventh example embodiment.  FIG. 44  shows an example table of aspherical data of the optical imaging lens according to the eleventh example embodiment.  FIG. 45  shows example charts of longitudinal spherical aberration and other kinds of optical aberrations of the optical imaging lens according to the eleventh example embodiment. 
     As shown in  FIG. 42 , the optical imaging lens  11  of the present embodiment, in an order from an object side A 1  to an image side A 2 , comprises a first lens element  1110 , an aperture stop  1100 , a second lens element  1120 , a third lens element  1130  and a fourth lens element  1140 . Both of a filtering unit  1150  and an image plane  1160  of an image sensor may be positioned at the image side A 2  of the optical imaging lens  11 . Each of the first, second, third, fourth lens elements  1110 ,  1120 ,  1130 ,  1140  and the filtering unit  1150  has an object-side surface  1111 / 1121 / 1131 / 1141 / 1151  facing toward the object side A 1  and an image-side surface  1112 / 1122 / 1132 / 1142 / 1152  facing toward the image side A 2 . Here an example embodiment of filtering unit  1150  may comprise an IR cut filter, which is positioned between the fourth lens element  1140  and the image plane  1160 . The filtering unit  1150  filters light with specific wavelength from the light passing optical imaging lens  11 . For example, IR light is filtered, and this may prohibit the IR light which is not visible by human eyes from producing an image on image plane  1160 . 
     Similarly, in the present embodiment, air gaps exist between the lens elements  1110 ,  1120 ,  1130 ,  1140 , the filtering unit  1150  and the image plane  1160  of the image sensor. Please refer to  FIG. 1  for the positions of the air gaps. The sum of all air gaps d 1 , d 2 , d 3  between the first and fourth lens elements is denoted by G aa . 
     One difference between the eleventh embodiments and the first embodiments is that the central thickness of lens T 3  of the third lens element  1130 , the air gap G 34  between the third lens element  1130  and the fourth lens element  1140  and the sum of all air gaps G aa  from the first lens element  1110  to the fourth lens element  1140  are different. The apersure stop is positioned between the first lens element  1110  and the second lens element  1120 . Please refer to  FIG. 43  for the optical characteristics of each lens elements in the optical imaging lens  11  of the present embodiment, wherein the values of the relations (1)˜(9) are:
 
( T 3/ G   34 )=4.29;
 
( G   aa   /T 3)=2.33;
 
(EFL/ G   12 )=23.85;
 
( T 3/ G   12 )=3.62;
 
( T 2+ T 3)=0.75(mm);
 
[( T 2+ T 3)/ T 3]=1.55;
 
( G   12   +G   34 )=0.25(mm);
 
( f 1+ f 3)=3.76(mm);
 
(BFL/EFL)=0.33;
 
wherein the distance from the object-side surface  1111  of the first lens element  1110  to the image plane  1160  is 3.818 (mm), and the length of the optical imaging lens  11  is shortened.
 
     Example embodiments of the lens elements of the optical imaging lens  11  may comprise the following example embodiments: 
     The first lens element  1110  may have positive refracting power, which may be constructed by plastic material. Both the object-side surface  1111  and the image-side surface  1112  are convex surfaces. The convex surfaces  1111  and  1112  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 44  for values of the aspherical parameters. 
     The second lens element  1120  may have negative refracting power, which may be constructed by plastic material. The object-side surface  1121  comprises a concave portion  11211  in the vicinity of the optical axis and a convex portion  11212  in the vicinity of the periphery of the second lens element  1120 . The image-side surface  1122  is a concave surface. The object-side surface  1121  and the image-side surface  1122  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 44  for values of the aspherical parameters. 
     The third lens element  1130  may have positive refracting power, which may be constructed by plastic material. The object-side surface  1131  is a concave surface and the image-side surface  1132  is a convex surface. The concave surface  1131  and convex surface  1132  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 44  for values of the aspherical parameters. 
     The fourth lens element  1140  may have negative refracting power, which may be constructed by plastic material. The object-side surface  1141  comprises a convex portion  11411  in the vicinity of the optical axis and a concave portion  11412  in the vicinity of the periphery of the fourth lens element  1140 . The image-side surface  1142  has a concave portion  11421  in the vicinity of the optical axis and a convex portion  11422  in the vicinity of a periphery of the fourth lens element  1140 . The object-side surface  1141  and the image-side surface  1142  may both be aspherical surfaces defined by the aspherical formula. Please refer to  FIG. 44  for values of the aspherical parameters. 
     As illustrated in  FIG. 45 , it is clear that the optical imaging lens of the present embodiment may show great optical characteristics in longitudinal spherical aberration (a), astigmatism in the sagittal direction (b), astigmatism in the tangential direction (c) or distortion aberration (d). Therefore, according to above illustration, the optical imaging lens of the present embodiment indeed achieves great optical performance, and the length of the optical imaging lens is effectively shortened. 
     Please refer to  FIG. 46 , which shows the values of (T 3 /G 34 ), (G aa /T 3 ), (EFL/G 12 , (T 3 /G 12 ), (T 2 +T 3 ), [(T 2 +T 3 )/T 3 ], (G 12 +G 34 ), (f 1 +f 3 ), (BFL/EFL) and fno of all eleven embodiments. 
     Reference is now made to  FIG. 47 , which illustrates an example structural view of an example embodiment of mobile device  20  applying an aforesaid optical imaging lens. The mobile device  20  comprises a housing  210  and an optical imaging lens assembly  220  positioned in the housing  210 . An example of the mobile device  20  may be, but is not limited to, a mobile phone. 
     As shown in  FIG. 47 , the optical imaging lens assembly  220  may comprise an aforesaid optical imaging lens, for example the optical imaging lens  1  of the first embodiment, a lens barrel  230  for positioning the optical imaging lens  1 , a module housing unit  240  for positioning the lens barrel  230  and an image sensor  161  which is positioned at an image side of the optical imaging lens  1 . The image plane  160  is formed on the image sensor  161 . 
     In some other example embodiments, the structure of the filtering unit  150  may be omitted. In some example embodiments, the housing  210 , the lens barrel  230 , and/or the module housing unit  240  may be integrated into a single component or assembled by multiple components. In some example embodiments, the image sensor  161  used in the present embodiment is directly attached to the substrate  162  in the form of a chip on board (COB) package, and such package is different from traditional chip scale packages (CSP) since COB package does not require a cover glass before the image sensor  161  in the optical imaging lens  1 . 
     Aforesaid exemplary embodiments are not limited to this package type and could be selectively incorporated in other described embodiments. 
     The module housing unit  240  comprises a lens backseat  2401  and an image sensor base  2402  positioned between the lens backseat  2401  and the image sensor  161 . The lens barrel  230  and the lens backseat  2401  are positioned along a same axis, and the lens barrel  230  is positioned inside the lens backseat  2401 . 
     Because the length of the optical imaging lens  1  is merely 3.063 (mm), the size of the mobile device  20  may be quite small. Therefore, the embodiments described herein meet the market demand for smaller sized product designs. 
     Reference is now made to  FIG. 48 , which shows another structural view of an example embodiment of mobile device  22  applying the aforesaid optical imaging lens  1 . One difference between the mobile device  22  and the mobile device  20  may be the module housing unit  240  further comprising an autofocus module  2403 . The autofocus module  2403  may comprise a lens seat  2404 , a lens backseat  2401 , a coil  2405  and a magnetic unit  2406 . The lens seat  2404 , which is close to the outside of the lens barrel  230 , and the lens barrel  230  are positioned along an axis II′, and the lens backseat  2401  is positioned along with the axis II′ and around the outside of the the lens seat  2404 . The coil  2405  is positioned between the lens seat  2404  and the inside of the lens backseat  2401 . The magnetic unit  2406  is positioned between the outside of the coil  2405  and the inside of the lens backseat  2401 . 
     The lens barrel  230  and the optical imaging lens  1  positioned therein are driven by the lens seat  2404  for moving along the axis II′. The sensor backseat  2402  is close to the lens backseat  2401 . The filtering unit  150 , for example IR cut, is positioned on the sensor backseat  2402 . The rest structure of the mobile device  22  is similar to the mobile device  1 . 
     Similarly, because the length of the optical imaging lens  1 , 3.063 (mm), is shortened, the mobile device  22  may be designed with a smaller size and meanwhile good optical performance is still provided. Therefore, the present embodiment meets the demand of small sized product design and the request of the market. 
     According to above illustration, it is clear that the mobile device and the optical imaging lens thereof in example embodiments, through controlling ratio of at least one central thickness of lens element to an air gap along the optical axis between two lens elements and the ratio of a sum of all air gaps along the optical axis between four lens elements to a central thickness of lens in a predetermined range, and incorporated with detail structure and/or refection power of the lens elements, the length of the optical imaging lens is effectively shortened and meanwhile good optical characters are still provided. 
     While various embodiments in accordance with the disclosed principles have been described above, it should be understood that they have been presented by way of example only, and are not limiting. Thus, the breadth and scope of exemplary embodiment(s) should not be limited by any of the above-described embodiments, but should be defined only in accordance with the claims and their equivalents issuing from this disclosure. Furthermore, the above advantages and features are provided in described embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages. 
     Additionally, the section headings herein are provided for consistency with the suggestions under 37 C.F.R. 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings herein.