The production capabilities for optical multilayer coatings were improved significantly in the last decade. So called "shift free" coatings have become a standard in the coating production. Direct optical monitoring plays a key role to improve the layer thickness accuracy and takes advantage of error compensation effects. For the production of DWDM filters direct monitoring was introduced in the last decade. Continuous measurement is applied on relatively small substrate areas. (Ø < 200 mm). The paper reports substantial progress which has been achieved for coating systems with large area substrate holders (up to Ø 1050 mm). The stationary light spot of a single wavelength optical monitor is far out of centre of the rotating substrate holder. Intermittent monitoring on a substrate or a witness is applied. This technique enables rapid prototyping with tight specifications and high yields in large area batch coaters. Application results of challenging optical multilayer systems are demonstrating clearly the potential of this powerful monitoring technique. The monitoring capability was investigated for a lot of different layer systems such as dielectric mirrors, anti-reflection coatings, sophisticated edge filters, polarizer coatings, beam splitters and multiple cavity band-pass filters. Strong coincidence of theory with experiment was achieved with PIAD and magnetron sputtering. Reproducibility experiments have clearly shown the benefits of this monitoring technique.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.