Abstract: There is disclosed herein an aspheric grating which is operable to image local or distant point sources sharply in a designated wavelength, i.e. produce a perfectly stigmatic image in the given wavelength at grazing angles of incidence. The grating surface comprises a surface of revolution defined by a curve which does not have a constant radius of curvature but is defined by a non-linear differential equation specified in terms of the diffraction condition expressed as (m.lambda./.sigma.).sup.2 =A>O where m is the diffraction order, .lambda. is the wavelength and .sigma. is the grating surface ruling interval.