IMAGING LENS

1 . An imaging lens for forming an image of an object on an image sensor comprising:

in order from an object side to an image side,

a first lens having positive refractive power;

a second lens having negative refractive power;

a third lens having positive refractive power;

a fourth lens having negative refractive power;

a fifth lens;

a sixth lens;

a seventh lens; and

an eighth lens having negative refractive power,

wherein the eighth lens has an aspheric image-side surface having at least one inflection point, and a conditional expression below is satisfied:

−12.0 <f 4 /f< −3.0

where

f: a focal length of entire optical system of the imaging lens, and

f4: a focal length of the fourth lens.

2 . The imaging lens according to claim 1 , wherein a conditional expression below is satisfied:

1.0< R 6 f/R 6 r< 30.0

where

R6f: a curvature radius of an object-side surface of the sixth lens, and

R6r: a curvature radius of an image-side surface of the sixth lens.

3 . The imaging lens according to claim 1 or 2 , wherein a conditional expression below is satisfied:

−2.50 <f 2 /f 6<−0.30

where

f2: a focal length of the second lens, and

f6: a focal length of the sixth lens.

4 . The imaging lens according to any one of claims 1 to 3 , wherein a conditional expression below is satisfied:

−15.00 <f 7 /f< −3.50

where

f: a focal length of entire optical system of the imaging lens, and

f7: a focal length of the seventh lens.

5 . The imaging lens according to any one of claims 1 to 4 , wherein a conditional expression below is satisfied:

1.0 <R 8 f/R 8 r< 100 . 0

where

R8f: a curvature radius of an object-side surface of the eighth lens, and

R8r: a curvature radius of an image-side surface of the eighth lens.