An optical system includes: a first lens having refractive power and comprising an object-side surface which is convex in a paraxial region; a second lens having refractive power and comprising an object-side surface which is convex in the paraxial region; a third lens having refractive power; a fourth lens having refractive power; and a fifth lens having refractive power. The first to fifth lenses are sequentially disposed from an object side. An Abbe number of the first lens is between 30 and 50. Deteriorations in resolution at high temperatures and/or low temperatures may be decreased, MTF performance may be maintained even during temperature changes, and changes in focusing positions may be decreased. In addition, an aberration improvement effect, a wide field of view and a high degree of resolution may be implemented.