An optical mask can be made by providing a transparent mask substrate; depositing a first layer of opaque material, forming an aperture in the first layer; depositing a second layer of transparent material, depositing a third layer of transparent material; patterning the third layer to produce a disc-shaped region, heating the third layer until the disc-shaped region reflows into a lens-shaped region and cross-links, depositing a fourth layer, patterning the fourth layer to produce a cavity extending to the surface of the lens-shaped region, and dry etching the end of the cavity until the second layer develops a shape corresponding to the lens-shaped region.