Use 1/2 sections of plastic straws to make a honeycomb for your scope. Glue the pieces together wall to wall. Draw the diameter you need on a piece of paper. Lay the straw honeycomb on the outline and trim to fit with a razor blade or Xacto knife. Paint to suit, and install. Works great, and is super cheap to make. 3 or 4 straws is all it took for my 50mm.