I recently purchased a Series VI Stopper No. 1. It is a polished steel disk with a very small aperture that fits into a standard Series VI adapter. The backside is painted flat black. I have not had any success finding information on the use of this its use on the net, and I was hoping the folks here might help me out. I can figure out the equivalent f-stop but I was wondering how well the aperture would work in front of a lens. Thanks for your help.

Sounds like a form of pinhole, which is interchangable. Why don't you just try it and report your findings?