an improvement in a contact printer which comprises means for supporting a film and an original in superposed relationship on a vacuum table , means for providing a source of light for exposing the film through the original , and means for moving the light over the surface of the superposed film and original . a substantially impervious , flexible and transparent cover sheet carried by the light moving means is arranged to cover the superposed film and original as the exposing light is scanned across the film and original whereby the vacuum is applied to the film and the original to remove air from therebetween as the film is exposed by the light through the cover sheet and the original . the improvement comprises means for contacting the surface of the cover sheet during use and removing dust and dirt thereon to assure that the optical path for the exposing light remains clear and unobstructed .