DIFFSYS is a Windows® program for the generation of optical surfaces on precision CNC machines, particularily diamond-turning machines. It was primarily developed for aspheres, diffractives, fresnels and hybrids, and has now expanded in various directions, to include 3D surfaces (non-circularily symmetric), special tool configurations, and also measurement corrections. DIFFSYS outputs jobfiles in several ASCII formats, compatible with most commercial machines. The strengths of DIFFSYS lie in its: Ease of use & clear graphics, Ability to accept design data in many different formats, Comprehensive tool corrections, to ensure accurate machining, Excellent technical support. DIFFSYS was first released in 2000, and has become a market leader, with sales worldwide. It is recognised and recommended by the leading manufacturers of ultra-precision machines. The red region is a 3D off-axis asphere. The purple region is a transitional blend from the central 3D surface, to the outer ‘2D’ edge segments. Slow tool servos: Some surfaces can become very steep or mathematically ‘illegal’. You now specify a ‘cutoff’, at which point DIFFSYS adds a curved corner and a flat at the edge. Micro-lens arrays: aspheric, any diameter, spacing, and grid size.