Optical system

1. An optical system, comprising:

a first lens comprising a positive refractive power and a convex object-side surface;

a second lens comprising a negative refractive power and a convex object-side surface;

a third lens comprising a positive refractive power and a convex image-side surface;

a fourth lens comprising a negative refractive power, wherein the fourth lens comprises a concave object-side surface and a convex image-side surface;

a fifth lens comprising a concave object-side surface and a concave image-side surface; and

a sixth lens comprising a convex object-side surface, a concave image-side surface, and an inflection point formed on an image-side surface thereof,

wherein the optical system comprises only a total of six lenses, and

wherein (r7−r8)/(r7+r8)<0 is satisfied, where r7 is a radius of curvature of an object-side surface of the fourth lens, and r8 is a radius of curvature of an image-side surface of the fourth lens.

2. The optical system of claim 1 , wherein SD/f<0.6 is satisfied, where SD is a diameter of a stop, and f is an overall focal length of the optical system.

3. The optical system of claim 1 , wherein 10<|V1−V4| is satisfied, where V1 is an Abbe number of the first lens, and V4 is an Abbe number of the fourth lens.

4. The optical system of claim 1 , wherein TTL/f<1.3 is satisfied, where TTL is a distance from an object-side surface of the first lens to an imaging plane, and f is an overall focal length of the optical system.

5. The optical system of claim 1 , wherein 10<V1−V5 is satisfied, wherein V1 is an Abbe number of the first lens, and V5 is an Abbe number of the fifth lens.

6. The optical system of claim 1 , wherein 0.5≤SD/f is satisfied, where SD is a diameter of a stop, and f is an overall focal length of the optical system.

7. The optical system of claim 1 , wherein |V4−V5|<10 is satisfied, where V4 is an Abbe number of the fourth lens, and V5 is an Abbe number of the fifth lens.