Rollei Bay III Rolleinar .75 Mystery Lens

This is a mysterious lens with very little online documentation. It may or may not be for macro. My guess is that it is not for normal Rolleinar use as it appears to be late productions and does not fit the styling or naming of other Rolleinars (and is a single).

One source said that it was for turning your Rollei into a projector (they thought of everything in the old days).

If you know the use please enlighten us.

Whatever it is, it is in great condition with clean scratch-free glass and comes in the beautiful box.

SKU: 250210-17