The authors describe an improved production route for silicon nanofocusing lenses for hard x rays using e-beam lithography and deep reactive ion etching. As compared to previous prototypes, these optics have a significantly improved from fidelity, reducing spherical aberrations. Close to an ideal performance for the focusing of hard x rays is achieved with these optics, reaching a lateral beam size of about 50 nm. The lens profile is checked by scanning electron microscopy. (C) 2007 American Vacuum Society.