A linear aperture deposition apparatus and process are provided for coating substrates with sublimed or evaporated coating materials. The apparatus and process are particularly suited for producing flexible films having an optical interference coating with a very high surface thickness uniformity and which is substantially free of defects from particulate ejection of a source material. The apparatus includes a source box containing a source material, a heating element to sublime or evaporate the source material, and a chimney to direct the source material vapor from the source box to a substrate. A flow restricting baffle having a plurality of holes is positioned between the source material and the substrate to confine and direct the vapor flow, and an optional floating baffle is positioned on the surface of the source material to further restrict the vapor flow, thereby substantially eliminating source material spatter.