or an easily machined metal then converted into a hard mold component by nickel electroforming replication one specific u201c lens component u201d that can usefully be manufactured by the invention is an array of many small lenses such as spherical or aspheric lenses arranged in a square or hexagonal array or an array of many cylindrical lenses lying parallel to each other on a surface a nickel tool will work well for this purpose and may be made by electroforming from a master of the correct shape formed in any convenient material one example is the ruled patterns of cylindrical lenses depicted in fig3 and 4 of u s pat no 3 848 980 by plummer and incorporated herein in its entirety by reference diffractive structures such as those depicted in u s pat no 5 260 828 by londono et al that may be used for athermalization achromatization or beam splitting can also be usefully manufactured in this way the 39 828 patent is also incorporated herein in its entirety by reference another diffractive structure that can be manufactured in this way might be a diffraction grating or might be a computer generated surface relief transmission hologram formed by use of.