an apparatus for depositing thin films on a plurality of substrates has a vacuum chamber , a source of the material or materials to be deposited as the thin film , a source of energy for causing the material to be vaporized , and mechanical apparatus for imparting super - planetary and planetary motion to each substrate while the substrate is exposed to the vapors of the material . when a predetermined thickness of the film on any given substrate is reached the super - planetary motion is halted and only planetary motion and spinning are continued for the given substrate . during this process the thickness of the film being deposited is monitored accurately by an optical instrument having a linear axis of measurement which coincides with the center of the orbiting planetary motion of the substrate and is on the substrate itself .