A method for printing a periodic pattern having a first symmetry and a first period into a photosensitive layer that includes providing a mask bearing a pattern of at least two overlapping sub-patterns which have a second symmetry and a second period, the features of each sub-pattern being formed in a transmissive material, providing a substrate bearing the layer, arranging the mask with a separation from the substrate, providing light having a central wavelength for illuminating the mask to generate a light-field in which light of the central wavelength forms a range of intensity distributions between Talbot planes, illuminating said mask pattern with said light whilst maintaining the separation or changing it by a distance whereby the photosensitive layer is exposed to an average of the range of intensity distributions, wherein the light transmitted by each sub-pattern is shifted in phase relative to that transmitted by another sub-pattern.