Imaging lens
There is provided a compact imaging lens configured to properly correct aberrations. The imaging lens includes, in order from an object side to an image side, a first lens L 1 with positive refractive power, a second lens L 2 with negative refractive power, a third lens L 3 with positive refractive power, a fourth lens L 4 with positive refractive power, a fifth lens L 5 , a sixth lens L 6 , a seventh lens L 7 with positive refractive power, and an eighth lens L 8 with negative refractive power. The eighth lens L 8 is formed in a shape of a meniscus lens in a paraxial region, and has an aspheric image-side surface having at least one inflection point. In addition, the following conditional expressions are satisfied: −5.00< f 2/ f <−2.00 10.00< f 4/ f <25.00 where f: a focal length of the overall optical system of the imaging lens, f2: a focal length of the second lens, and f4: a focal length of the fourth lens.
1. An imaging lens forming an image of an object on an image sensor and comprising, in order from an object side to an image side,
a first lens with positive refractive power,
a second lens with negative refractive power,
a third lens with positive refractive power,
a fourth lens with positive refractive power,
a fifth lens,
a sixth lens,
a seventh lens with positive refractive power, and
an eighth lens with negative refractive power,
wherein said eighth lens has an aspheric image-side surface having at least one inflection point, and is in a form of a meniscus lens with the image-side surface being concave in the paraxial region, and the following conditional expressions are satisfied:
−5.00< f 2 /f<− 2.00
10.00< f 4 /f< 25.00
where
f: a focal length of the overall optical system of the imaging lens,
f2: a focal length of the second lens, and
f4: a focal length of the fourth lens.
2. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
1.20< f 3 /f 1<5.50
where
f1: a focal length of the first lens, and
f3: a focal length of the third lens.
3. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
1.50< f 34 /f< 3.50
where
f34: a composite focal length of the third lens and the fourth lens, and
f: a focal length of the overall optical system of the imaging lens.
4. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
0.030< D 34 /f< 0.100
where
D34: a distance along the optical axis between the third lens and the fourth lens, and
f: a focal length of the overall optical system of the imaging lens.
5. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
1.40< f 7 /f< 4.50
where
f: a focal length of the overall optical system of the imaging lens, and
f7: a focal length of the seventh lens.
6. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
35 <vd 7
35< vd 8
where
vd7: an abbe number at d-ray of the seventh lens, and
vd8: an abbe number at d-ray of the eighth lens.