I am out on the road, I wonder what I have with me that I could also make one..well I am going to drill out a hole with the smallest bit i can find, then place a foil patch on the back of the lens cap and secure with black tape. Then will gently puncture the foil with the tip of a pin to make the smallest hole i can with the cleanest edges. Not sure how small that will be. I did read somewhere online that something on these lines would be the equivalent of f/200 or thereabouts!
You must be reading my mind!!! I was thinking the same thing.I wonder if you could do star trails with a pinhole camera ?