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 negative 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 fourth lens is formed in a shape of a meniscus lens having an object-side surface being concave in a paraxial region. The eighth lens L 8 has an aspheric image-side surface having at least one inflection point. Furthermore, the following conditional expression is satisfied: 0.04< D 34/ f <0.15 where f: a focal length of the overall optical system of the imaging lens, and D34: a distance along the optical axis between the third lens and 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 negative 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 fourth lens is formed in a shape that curvature radii of an object-side surface and an image-side surface are both negative,
said eighth lens has an aspheric image-side surface having at least one inflection point, and
the following conditional expressions are satisfied:
0.04< D 34/ f< 0.15,
(9′) 1.00 <R 7 r/R 7 f<= 2.08 (9′)
where
f: a focal length of the overall optical system of the imaging lens,
D34: a distance along the optical axis between the third lens and the fourth lens,
R7f: a curvature radius of an object-side surface of the seventh lens, and
R7r: a curvature radius of an image-side surface of the seventh 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:
−5.50< f 4/ f 3<−0.80
where
f3: a focal length of the third lens, and
f4: a focal length of the fourth lens.
4. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
0.02< D 45/ D 34<1.00
where
D34: a distance along the optical axis between the third lens and the fourth lens, and
D45: a distance along the optical axis between the fourth lens and the fifth lens.
5. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
0.80< f 67/ f< 3.50
where
f: a focal length of the overall optical system of the imaging lens, and
f67: a composite focal length of the sixth lens and the seventh lens.
6. The imaging lens according to claim 1 , wherein the following conditional expression is satisfied:
−1.20< f 8/ f 7<−0.35
where
f7: a focal length of the seventh lens, and
f8: a focal length of the eighth lens.