Enna Werke in Munich had developed an interchangeagle lens socket for several cameras. You could use the same lens in different sockets on different cameras without losing the auto-stop-down feature. And you needed only one socket per camera to use all their auto-stepdown lenses, changing only the optical part. If you bought an Enna lens for the Alpa with an Alpa adapter, you could use all the other automatic Enna lenses with it.

The black ALPA 6c shown here carries the production number 47580 and was manufactured in 1964