Rollei Retro Adapter for EL lenses - or lenses with Bay IV to 67mm Filter thread rings
I picked this item up recently in a trade for a new Hy6 Film back. It appears to be a one off custom job, but well made and fully functional. There is no retro or reversing adapter from Rollei that works with the EL lenses that have screw in filter threads instead of bayonet mounts - so if you have those lenses and want a retro adapter - this is for you! But you can also use with with the regular Rollei lenses with one of the bay IV to screw thread filter adapter rings so you could consider this more of a universal retro adapter.
A retro adapter allows the photographer to reverse mount lenses with full electronic function for high magnification macro or close up work. You can read more about retro adapters in the Rollei Closeup guide that I have in my free downloads section: Rollei Close up Guide to Macro Equipment