Imaging lens comprising seven lenses of +−+−−+− or +++−−+− refractive powers
There is provided an imaging lens with excellent optical characteristics which satisfies demand of a wide field of view, a low profile and a low F-number. An imaging lens comprises, in order from an object side to an image side, a first lens with positive refractive power in a paraxial region, a second lens, a third lens having an image-side surface being convex in the paraxial region, a fourth lens, a fifth lens with negative refractive power in the paraxial region, a sixth lens with positive refractive power in the paraxial region, and a seventh lens with negative refractive power having an image-side surface that is concave in the paraxial region and is formed as an aspheric surface having at least one pole point in a position off the optical axis.
1. An imaging lens comprising in order from an object side to an image side,
a first lens with positive refractive power in a paraxial region,
a second lens,
a third lens with positive refractive power, and having both an image-side surface and an object-side surface that are convex in the paraxial region,
a fourth lens with negative refractive power having an image-side surface being convex in the paraxial region,
a fifth lens with negative refractive power in the paraxial region, wherein an object-side surface of the fifth lens is convex in the paraxial region and has at least one pole point in a position off the optical axis,
a sixth lens with positive refractive power in the paraxial region, and
a seventh lens with negative refractive power in the paraxial region having an object-side surface being concave in the paraxial region and an image-side surface that is concave in the paraxial region and is formed as an aspheric surface having at least one pole point in a position off the optical axis,
wherein the first lens to the seventh lens are single lenses, respectively, and an image-side surface of the fifth lens is concave in the paraxial region and is formed as an aspheric surface having at least one pole point in a position off the optical axis, an object-side surface of the sixth lens is convex and is formed as an aspheric surface having at least one pole point in a position off the optical axis, and an image-side surface of the sixth lens is convex in the paraxial region, and the following conditional expressions (1), and (4′) are satisfied:
1.8< vd 3/ vd 4<4.0 (1)
6.0<( D 6/TTL)*100≤9.97 (4′)
where
vd3: an abbe number at d-ray of the third lens,
vd4: an abbe number at d-ray of the fourth lens,
D6: a thickness of the sixth lens along the optical axis, and
TTL: a total track length.
2. The imaging lens according to claim 1 , wherein the first lens is formed in a meniscus shape having an object-side surface being convex in the paraxial region.
3. The imaging lens according to claim 1 , wherein the fourth lens has an object-side surface being concave in the paraxial region.
4. The imaging lens according to claim 1 , wherein the following conditional expression (2) is satisfied:
0.80< T 2/ T 3<15.0 (2)
where
T2: a distance along the optical axis from an image-side surface of the second lens to an object-side surface of the third lens, and
T3: a distance along the optical axis from an image-side surface of the third lens to an object-side surface of the fourth lens.
5. The imaging lens according to claim 1 , wherein the following conditional expression (3) is satisfied:
0.70<Σ d/f< 1.30 (3)
where
Σd: a distance along the optical axis from an object-side surface of the first lens to an image-side surface of the seventh lens, and
f: a focal length of the overall optical system of the imaging lens.