Jones-ASC (all spherical camera) This is another medial design but is a photographic system. It has a flat field better suited for modern sensors. It is related to the Houghton and Busack but has better performance than either. At f/3 a 12.5 inch design is diffraction limited over a 1.8 inch field from 0.4 microns to 0.9 microns. It can be useful down to F/2 and unlike the Schmidt has a flat field with a large BFL supported by the second lens.