referring to fig1 a , which shows a six - piece optical lens system in accordance with a first embodiment of the present invention , and fig1 b shows the longitudinal spherical aberration curves , the astigmatic field curves , and the distortion curve of the first embodiment of the present invention . a six - piece optical lens system in accordance with the first embodiment of the present invention comprises , in order from the object side a to the image side b : a first lens element 110 with a positive refractive power made of plastic has a convex object - side surface 111 and a convex image - side surface 112 , and the object - side surface 111 and the image - side surface 112 of the first lens element 110 are aspheric . a second lens element 120 with a negative refractive power made of plastic has a convex object - side surface 121 and a concave image - side surface 122 , and the object - side surface 121 and the image - side surface 122 of the second lens element 120 are aspheric . a third lens element 130 with a positive refractive power made of plastic has a concave object - side surface 131 and a convex image - side surface 132 , and the object - side surface 131 and the image - side surface 132 of the third lens element 130 are aspheric . a fourth lens element 140 with a positive refractive power made of plastic has a concave object - side surface 141 and a convex image - side surface 142 , and the object - side surface 141 and the image - side surface 142 of the fourth lens element 140 are aspheric . a fifth lens element 150 with a negative refractive power made of plastic has a concave object - side surface 151 and a convex image - side surface 152 , and the object - side surface 151 and the image - side surface 152 of the fifth lens element 150 are aspheric . a sixth lens element 160 with a negative refractive power made of plastic has a convex object - side surface 161 and a concave image - side surface 162 , and the object - side surface 161 and the image - side surface 162 of the sixth lens element 160 are aspheric . an ir cut filter 170 made of glass is located between the image - side surface 162 of the sixth lens element 160 and an image plane 180 and has no influence on the focal length of the six - piece optical lens system . the equation for the aspheric surface profiles of the first embodiment is expressed as follows : z represents the value of a reference position with respect to a vertex of the surface of a lens and a position with a height h along the optical axis 190 ; a , b , c , d , e , g , . . . : represent the high - order aspheric coefficients . in the first embodiment of the present six - piece optical lens system , the focal length of the six - piece optical lens system is f , and it satisfies the relation : in the first embodiment of the present six - piece optical lens system , the f - number of the six - piece optical lens system is fno , and it satisfies the relation : in the first embodiment of the present six - piece optical lens system , the field of view of the six - piece optical lens system is 2ω , and it satisfies the relation : in the first embodiment of the present six - piece optical lens system , the focal length of the first lens element 110 is f1 , the focal length of the second lens element 120 is f2 , and they satisfy the relation : in the first embodiment of the present six - piece optical lens system , the focal length of the second lens element 120 is f2 , the focal length of the third lens element 130 is f3 , and they satisfy the relation : in the first embodiment of the present six - piece optical lens system , the focal length of the fifth lens element 150 is f5 , the focal length of the sixth lens element 160 is f6 , and they satisfy the relation : in the first embodiment of the present six - piece optical lens system , the focal length of the first lens element 110 , the second lens element 120 and the third lens element 130 combined is f123 , the focal length of the six - piece optical lens system is f , and they satisfy the relation : in the first embodiment of the present six - piece optical lens system , the focal length of the fourth lens element 140 , the fifth lens element 150 and the sixth lens element 160 combined is f456 , the focal length of the six - piece optical lens system is f , and they satisfy the relation : in the first embodiment of the present six - piece optical lens system , the focal length of the first lens element 110 is f1 , the focal length of the second lens element 120 and the third lens element 130 combined is f23 , and they satisfy the relation : in the first embodiment of the present six - piece optical lens system , the focal length of the third lens element 130 and the fourth lens element 140 combined is f34 , the focal length of the fifth lens element 150 and the sixth lens element 160 combined is f56 , and they satisfy the relation : in the first embodiment of the present six - piece optical lens system , the focal length of the six - piece optical lens system is f , the distance between the object - side surface 111 of the first lens element 110 and the image plane 180 is tl , and they satisfy the relation : the detailed optical data of the first embodiment is shown in table 1 , and the aspheric surface data is shown in table 2 , wherein the units of the radius of curvature , the thickness and the focal length are expressed in mm . in the tables 1 and 2 , the surfaces 2 and 3 represent the object - side surface 111 and the image - side surface 112 of the first lens element 110 , respectively , the surfaces 4 and 5 represent the object - side surface 121 and the image - side surface 122 of the second lens element 120 , respectively , the surfaces 6 and 7 represent the object - side surface 131 and the image - side surface 132 of the third lens element 130 , respectively , the surfaces 8 and 9 represent the object - side surface 141 and the image - side surface 142 of the fourth lens element 140 , respectively , the surfaces 10 and 11 represent the object - side surface 151 and the image - side surface 152 of the fifth lens element 150 , respectively , and the surfaces 12 and 13 represent the object - side surface 161 and the image - side surface 162 of the sixth lens element 160 , respectively . referring to fig2 a , which shows a six - piece optical lens system in accordance with a second embodiment of the present invention , and fig2 b shows the longitudinal spherical aberration curves , the astigmatic field curves , and the distortion curve of the second embodiment of the present invention . a six - piece optical lens system in accordance with the second embodiment of the present invention comprises , in order from the object side a to the image side b : a first lens element 210 with a positive refractive power made of plastic has a convex object - side surface 211 and a convex image - side surface 212 , and the object - side surface 211 and the image - side surface 212 of the first lens element 210 are aspheric . a second lens element 220 with a negative refractive power made of plastic has a convex object - side surface 221 and a concave image - side surface 222 , and the object - side surface 221 and the image - side surface 222 of the second lens element 220 are aspheric . a third lens element 230 with a positive refractive power made of plastic has a convex object - side surface 231 and a convex image - side surface 232 , and the object - side surface 231 and the image - side surface 232 of the third lens element 230 are aspheric . a fourth lens element 240 with a positive refractive power made of plastic has a concave object - side surface 241 and a convex image - side surface 242 , and the object - side surface 241 and the image - side surface 242 of the fourth lens element 240 are aspheric . a fifth lens element 250 with a positive refractive power made of plastic has a concave object - side surface 251 and a convex image - side surface 252 , and the object - side surface 251 and the image - side surface 252 of the fifth lens element 250 are aspheric . a sixth lens element 260 with a negative refractive power made of plastic has a concave object - side surface 261 and a concave image - side surface 262 , and the object - side surface 261 and the image - side surface 262 of the sixth lens element 260 are aspheric . an ir cut filter 270 made of glass is located between the image - side surface 262 of the sixth lens element 260 and an image plane 280 and has no influence on the focal length of the six - piece optical lens system . the equation for the aspheric surface profiles of the second embodiment is expressed as follows : z represents the value of a reference position with respect to a vertex of the surface of a lens and a position with a height h along the optical axis 290 ; a , b , c , d , e , g , . . . : represent the high - order aspheric coefficients . in the second embodiment of the present six - piece optical lens system , the focal length of the six - piece optical lens system is f , and it satisfies the relation : in the second embodiment of the present six - piece optical lens system , the f - number of the six - piece optical lens system is fno , and it satisfies the relation : in the second embodiment of the present six - piece optical lens system , the field of view of the six - piece optical lens system is 2ω , and it satisfies the relation : in the second embodiment of the present six - piece optical lens system , the focal length of the first lens element 210 is f1 , the focal length of the second lens element 220 is f2 , and they satisfy the relation : in the second embodiment of the present six - piece optical lens system , the focal length of the second lens element 220 is f2 , the focal length of the third lens element 230 is f3 , and they satisfy the relation : in the second embodiment of the present six - piece optical lens system , the focal length of the fifth lens element 250 is f5 , the focal length of the sixth lens element 260 is f6 , and they satisfy the relation : in the second embodiment of the present six - piece optical lens system , the focal length of the first lens element 210 , the second lens element 220 and the third lens element 230 combined is f123 , the focal length of the six - piece optical lens system is f , and they satisfy the relation : in the second embodiment of the present six - piece optical lens system , the focal length of the fourth lens element 240 , the fifth lens element 250 and the sixth lens element 260 combined is f456 , the focal length of the six - piece optical lens system is f , and they satisfy the relation : in the second embodiment of the present six - piece optical lens system , the focal length of the first lens element 210 is f1 , the focal length of the second lens element 220 and the third lens element 230 combined is f23 , and they satisfy the relation : in the second embodiment of the present six - piece optical lens system , the focal length of the third lens element 230 and the fourth lens element 240 combined is f34 , the focal length of the fifth lens element 250 and the sixth lens element 260 combined is f56 , and they satisfy the relation : in the second embodiment of the present six - piece optical lens system , the focal length of the six - piece optical lens system is f , the distance between the object - side surface 211 of the first lens element 210 and the image plane 280 is tl , and they satisfy the relation : the detailed optical data of the second embodiment is shown in table 3 , and the aspheric surface data is shown in table 4 , wherein the units of the radius of curvature , the thickness and the focal length are expressed in mm . in the tables 3 and 4 , the surfaces 2 and 3 represent the object - side surface 211 and the image - side surface 212 of the first lens element 210 , respectively , the surfaces 4 and 5 represent the object - side surface 221 and the image - side surface 222 of the second lens element 220 , respectively , the surfaces 6 and 7 represent the object - side surface 231 and the image - side surface 232 of the third lens element 230 , respectively , the surfaces 8 and 9 represent the object - side surface 241 and the image - side surface 242 of the fourth lens element 240 , respectively , the surfaces 10 and 11 represent the object - side surface 251 and the image - side surface 252 of the fifth lens element 250 , respectively , and the surfaces 12 and 13 represent the object - side surface 261 and the image - side surface 262 of the sixth lens element 260 , respectively . it is to be noted that the tables 1 - 4 show different data from the different embodiments , however , the data of the different embodiments is obtained from experiments . therefore , any product of the same structure is deemed to be within the scope of the present invention even if it uses different data . table 5 lists the relevant data for the various embodiments of the present invention . in the present six - piece optical lens system , the lens elements can be made of glass or plastic . if the lens elements are made of glass , there is more freedom in distributing the refractive power of the six - piece optical lens system . if the lens elements are made of plastic , the cost will be effectively reduced . in the present six - piece optical lens system , if the object - side or the image - side surface of the lens elements is convex , the object - side or the image - side surface of the lens elements in proximity of the optical axis is convex . if the object - side or the image - side surface of the lens elements is concave , the object - side or the image - side surface of the lens elements in proximity of the optical axis is concave . while we have shown and described various embodiments in accordance with the present invention , it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention .