Piece of cardboard from a recent tent purchase (not a light tent, the camping kind) with a round hole cut in and a toilet paper roll cardboard tube stuck in the hole tightly. All taped on with some masking tape. Worked. No more to say.
And here is the result, well two of them really, one with a white background and one with a black background:
And the compulsory "set up" shot just to give you an idea of what was going down: