Optical imaging system
An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens having negative refractive power, a fifth lens having positive refractive power, a sixth lens having a convex image-side surface, and a seventh lens, disposed sequentially from an object side. The optical imaging system satisfies −5.0<f2/f<−2.0, where f is a focal length of the optical imaging system and f2 is a focal length of the second lens. An F No. of the optical imaging system is less than 1.7.
1. An optical imaging system comprising:
a first lens comprising a convex object-side surface and a concave image-side surface;
a second lens comprising a refractive power;
a third lens comprising positive refractive power and a convex object-side surface;
a fourth lens comprising a refractive power;
a fifth lens comprising a refractive power and a concave object-side surface in a paraxial region;
a sixth lens comprising a refractive power; and
a seventh lens comprising a refractive power,
wherein the first to seventh lenses are sequentially disposed in ascending numerical order from an object side toward an imaging plane,
wherein a radius of curvature of an object-side surface of the seventh lens is greater than a radius of curvature of an image-side surface of the sixth lens, and
wherein −5.0<f2/f<−2.0 and 3.0<|f4/f|, where f is a focal length of the optical imaging system, f2 is a focal length of the second lens, and f4 is a focal length of the fourth lens.
2. The optical imaging system of claim 1 , wherein the second lens has a convex object-side surface.
3. The optical imaging system of claim 1 , wherein the fourth lens has a convex object-side surface.
4. The optical imaging system of claim 1 , wherein the sixth lens has positive refractive power.
5. The optical imaging system of claim 1 , wherein the seventh lens has negative refractive power.
6. An optical imaging system comprising:
a first lens comprising a convex object-side surface;
a second lens comprising a refractive power;
a third lens comprising a refractive power;
a fourth lens comprising a convex object-side surface;
a fifth lens comprising a refractive power;
a sixth lens comprising a refractive power; and
a seventh lens comprising a refractive power,
wherein the first to seventh lenses are sequentially disposed in ascending numerical order from an object side toward an imaging plane,
wherein a radius of curvature of an object-side surface of the fifth lens is greater than a radius of curvature of an object-side surface of the sixth lens, and
wherein −5.0<f2/f<−2.0 and 3.0<|f4/f|, where f is a focal length of the optical imaging system, f2 is a focal length of the second lens, and f4 is a focal length of the fourth lens.
7. The optical imaging system of claim 6 , wherein the second lens has a convex object-side surface.
8. The optical imaging system of claim 6 , wherein the third lens has a convex object-side surface.
9. The optical imaging system of claim 6 , wherein the fourth lens has a concave image-side surface.
10. The optical imaging system of claim 6 , wherein the sixth lens has positive refractive power.
11. The optical imaging system of claim 6 , wherein the seventh lens has negative refractive power.
12. The optical imaging system of claim 6 , wherein the seventh lens has a concave object-side surface.
13. The optical imaging system of claim 6 , wherein
f 5/ f< 1.0,
where f5 is a focal length of the fifth lens.