Imaging lens comprising seven lenses of −+−−++−, −+−+++−, ++−−++−, ++−−+−− OR ++−−++− refractive powers
There is provided an imaging lens with excellent optical characteristics which satisfies demand of wide field of view, low profile and low F-number. An imaging lens comprises, in order from an object side to an image side, a first lens, an aperture stop, a second lens with positive refractive power in a paraxial region, a third lens with negative refractive power in the paraxial region, a fourth lens, a fifth lens with the positive refractive power in the paraxial region, a sixth lens being a double-sided aspheric lens, and a seventh lens with negative refractive power having an image-side surface being concave in the paraxial region and 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,
an aperture stop,
a second lens with positive refractive power in a paraxial region,
a third lens with negative refractive power in the paraxial region,
a fourth lens,
a fifth lens with the positive refractive power in the paraxial region,
a sixth lens being a double-sided aspheric lens, and
a seventh lens with negative refractive power having an image-side surface being concave in the paraxial region and an aspheric surface having at least one pole point in a position off the optical axis,
wherein the first lens has the positive refractive power,
the second lens is formed in a biconvex shape having convex object-side and image-side surfaces in the paraxial region,
the fifth lens has a concave object-side surface in the paraxial region,
the sixth lens has a convex object-side surface in the paraxial region,
the seventh lens has a convex object-side surface, and
the following conditional expressions (1) and (7) are satisfied:
40< vd 7<70 (1)
0.50<( T 1/TTL)×100<1.20 (7)
where
vd7: an abbe number at d-ray of the seventh lens,
T1: a distance along the optical axis from an image-side surface of the first lens to an object-side surface of the second lens, 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 a convex object-side surface in the paraxial region.
3. The imaging lens according to claim 1 , wherein the third lens has a convex object-side surface in the paraxial region.
4. The imaging lens according to claim 1 , wherein the object-side surface of the sixth lens has at least one pole point in a position off the optical axis.
5. The imaging lens according to claim 1 , wherein the object-side surface of the seventh lens is formed as an aspheric surface having at least one pole point in a position off the optical axis.
6. The imaging lens according to claim 1 , wherein the following conditional expression (2) is satisfied:
TTL/ ih< 2.0 (2)
where
TTL: a total track length, and
Ih: a maximum image height.