Elementary analysis shows that maximizing the aerial-image contrast in printing dense lines and spaces leads to a monotonically increasing relationship between (1−n) and κ, where n and κ are real and imaginary parts of the refractive index of the absorber material of the photomask, respectively, and this relationship is affected by the space-to-pitch ratio in the mask absorber. For the tantalum boron nitride mask absorber presently in use, improvement in image contrast can be made by displacing the illuminating dipoles away from their nominal positions in conjunction with a focus offset.