Joan, my guess is it is a helicoid adapter that let's you do close up with rangefinder lenses. That is what I use on my NEX 7 with my Leica Ms and Zeiss ZMs. Here is one example with the Summilux 50, probably at 1/3 of the "regular" MFD. I did crop some, as well, but still, the bug gives you an indication of the magnification.