The Invisibleman vs The Fly! Yes This was a real movie!

  Yes way back in the 50's there was a japanese Invisibleman flick and it did quite well so a follow-up was made. In it a man aquires the ability to shrink himself to the size of a housefly and uses this ability to commit murder of beautiful ladies. The police dub him The Fly.  A physicist developes a machine to make objects invisible and he and his colleagues decid to use it on the physicist to make him invisible so he can stop the murderous Fly. This reminds me of an unmade Toho follow-up to the Human Vapor where he was to battle a human torch type of person.