This came in a box of miscelaneous stuff I got in a trade. My best
guess is that it fits around a Bronica lens and provides a "handle" to
assist in quick focusing. If you shoot kids, or fashion models or
other fast-moving subjects, this would be a handy item to have.

The opening is 84mm or about 3.3 inches in diameter. The ring is
split to fit onto a lens. It's in very good condition.

http://cgi.ebay.com/ws/eBayISAPI.dll...m=330015748629