I have a large sheet of matboard that's white on one side and black on the other. I have a couple of different pieces from it with a hole in each, usually sorta closer to one end and side since I rarely need to burn a spot right in the middle. I have other pieces I can adjust the hole size with as well. The pieces that got cut out got taped to coat hangar remains for dodging. The larger pieces are also what I use when making test strips to cover what isn't getting exposed.