Method and apparatus for coating a thin film upon substrate means in a pressure vessel using the plasma vapor deposition technique known as sputtering. The substrate means are arranged on the exterior of a cylindrical drum for rotation and have the convex surface thereof exposed to the plasma vapor during rotation. An assembly of a plurality of circumferentially spaced arcuate target segments forming generally a cylinder is arranged coaxially and telescopically with respect to the drum whereby to form an annular belt of plasma vapor cloud segments occupying the gap exterior of the drum between the target means and the drum. The target means comprise the cathode of the high voltage electrical circuit and the drum comprises the anode.The projecting unit target area is larger than the unit exposed substrate area enabling radially converging plasma vapor and hence high rates of uniform coating.The drum may rotate the substrate means in the belt repeatedly or serve as transport means to bring the substrate means through the belt on one pass. The cylindrical belt is not closed but has a discontinuance which is somewhat greater than the distance between target segments. The substrate means are led onto the drum from the exterior of the assembly of target segments and likewise led off the drum and conveyed to the exterior of the assembly of target segments by way of such discontinuance.