Lay down a piece of poster board on a flat surface.
Place the lens you wish to cover face down on the poster board.
Trace around the lens using a marker.
Cut out the lens shape from the poster board.
Lay the cut-out on top of a sheet of red cellophane.
Cut out the lens shape from the red cellophane leaving approximately 1/4-inch of excess all the way around.
Lay the red plastic shape on top of the lens cover.
Secure the red plastic by pushing it down inside the recessed lens cover. If not recessed, secure with a rubber band using the excess red plastic.