The invention relates to apparatus and a method for depositing material onto substrates, particularly optical substrates, to form a coating thereon. The apparatus and method incorporates the use of a series of magnetrons provided to be controlled to sputter deposit material provided in targets mounted therein, on to the substrates. There is provided a voltage to the magnetrons to operate the same and the level of voltage which is required to form required coating or coating layer characteristics is determined by using monitoring apparatus, at least when forming the coating or coating layer for the first time. The appropriate voltage level data for operation of the magnetrons can be held in a database and subsequently used to control the voltage level when forming an identified coating or layers of coatings.