New edge-blackening techniques for refractive optical elements

There is a trend in the optical industry to automate the edge-blackening of optical components. The goal of edge-blackening is to coat the areas outside the functional region of optical components, namely the peripheral areas including the surface edge or "diaphragm" and apertures, with light absorbing, index-matched material to minimise scattering light. The common method today is the manual application with brush or ink-writer of quick-drying liquid pigmented synthetic resin. The lenses are fitted at a rotary table with a vacuum-pump or with plug-in socket. The increasing diversity of components and the decreasing quantity of batch size are a considerable disadvantage inhibiting the automation. Another problem is the use of a high number of lacquers with different or partly unknown properties, due to varying chemical bases. There were developed some automatic techniques to black the optical components: airbrush, microdispensation, application by a canula. The optical and mechanical p roperties of the lacquer were investigated.