A mask comprises a mask frame defining an opening; a plurality of support bars installed in the opening of the mask frame; a plurality of movable bars, each of which is installed over a corresponding one of the plurality of support bars and movable relative to the corresponding support bar, wherein the plurality of support bars and the plurality of movable bars are arranged to divide the opening into a plurality of mask holes; and a plurality of actuators installed between the plurality of movable bars and the corresponding support bars and configured to move the movable bars relative to the plurality of support bars.