This is partly due to the residual secondary image being reflected onto the back surface of the beamsplitter and down into camera etc forming veiling glare. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding widespread application in fibre optic telecommunications. In its. Plate beamsplitters are made using a coated substrate, and thus exhibit beam offset and ghost reflections from the second surface. When using a plate beamsplitter for visual optics the. A beamsplitter plays a crucial role in optical systems that use coaxial illumination.