An optical system includes a first lens having refractive power; a second lens having refractive power, both surfaces thereof being convex in a paraxial region; a third lens having refractive power and having an object-side surface that is convex in the paraxial region; a fourth lens having refractive power; a fifth lens having refractive power and having an image-side surface that is concave in the paraxial region; and a sixth lens having refractive power, wherein the first to sixth lenses are sequentially disposed from an object side, and when an Abbe number of the first lens is v1 and an Abbe number of the second lens is v2, |v1−v2|