Traditional 3D layer-by-layer printing cannot make optically transparent objects. However, some very clever thinking has made it possible to 3D print lenses, from mm down to μm and perhaps even nm sized ones. For mm size lens, Luxexcel a Dutch company leads the way with their UV curable acrylic technology. The process uses acrylic droplets that fuses and forms a solid optically clear object when UV cured. No post-processing such as grinding and polishing needed. For μm lenses, a technology borrowed from ultra high resolution imaging 2-photon microscopes was needed. German company, Nanoscribe has developed a 2-photon near-infrared laser polymerization process which is capable of achieving feature size down to 150 nm. That process has enabled microfabricated lenses for a variety of applications such as placing a micro compound lens on an image sensor chip.