An improved optical system having diffractive optic elements is provided for scanning a beam. This optical system includes a laser source for emitting a laser beam along a first path. A deflector, such as a rotating polygonal mirror, intersects the first path and translates the beam into a scanning beam which moves along a second path in a scan plane. A lens system (F-.theta. lens) in the second path has first and second elements for focusing the scanning beam onto an image plane transverse to the scan plane. The first and second elements each have a cylindrical, non-toric lens. One or both of the first and second elements also provide a diffractive element, which provides not only astigmatic correction, but may further provide chromatic aberration correction of the scanning beam. This astigmatic correction is achieved without the presence of any lens having a toroidal (toric) surface. The system may further have a third element in the first path of the beam prior to the deflector. This third element provides a lens having another diffractive element. This diffractive element can correct chromatic and spherical aberration of the scanning beam in the cross-scan plane, a plane perpendicular to the scan plane.