Optical imaging system
An optical imaging system includes lenses sequentially disposed from an object side toward an imaging plane. A third lens, a fourth lens, and a fifth lens of the lenses each have a negative refractive power. An F number of the optical imaging system is 1.7 or less.
1. An optical imaging system comprising:
a first lens comprising positive refractive power;
a second lens comprising positive refractive power and a convex object-side surface;
a third lens comprising a concave image-side surface;
a fourth lens comprising a refractive power;
a fifth lens comprising negative refractive power; and
a sixth lens comprising a convex object-side surface in a paraxial region,
wherein the first to sixth lenses are sequentially disposed from an object side of the optical imaging system,
wherein the optical imaging system has a total number of six lenses with refractive power,
wherein the optical imaging system satisfies TTL/f12<1.90, where TTL is a distance from an object-side surface of the first lens to an imaging plane and f12 is a composite focal length of the first lens and the second lens, and
wherein a distance from the image-side surface of the third lens to an object-side surface of the fourth lens is greater than a distance from an image-side surface of the fourth lens to an object-side surface of the fifth lens.
2. The optical imaging system of claim 1 , wherein the first lens has a convex object-side surface.
3. The optical imaging system of claim 1 , wherein the first lens has a concave image-side surface.
4. The optical imaging system of claim 1 , wherein the third lens has a convex object-side surface.
5. The optical imaging system of claim 1 , wherein the fourth lens has a concave object-side surface.
6. The optical imaging system of claim 1 , wherein the sixth lens has a concave image-side surface in a paraxial region.
7. The optical imaging system of claim 1 , wherein a radius of curvature of an image-side surface of the first lens is greater than a radius of curvature of an object-side surface of the second lens.
8. The optical imaging system of claim 1 , wherein a radius of curvature of the image-side surface of the fourth lens is greater than a radius of curvature of the object-side surface of the fifth lens.
9. The optical imaging system of claim 1 , wherein the optical imaging system satisfies 1.0<f1/f<2.0, where f is a focal length of the optical imaging system and f 1 is a focal length of the first lens.