An optical system may include: in order from an object side, a first lens having positive refractive power and an object-side surface convex in the object side direction; a second lens having negative refractive power; a third lens having negative refractive power; a fourth lens having positive refractive power and an image-side surface convex in an image side direction; a fifth lens having negative refractive power and an image-side surface convex in the image side direction; and a sixth lens having negative refractive power and an image-side surface concave in the image side direction, such that bright, high resolution images may be implemented.