$400 OBO. This mount adapter lets you mount an older Arri Standard mount or Arri Bayonet mount lens on a PL mount camera. This is the much more complex type with two spring-loaded push buttons for release, and is compatible with lenses like old Cooke Speed Panchros in Arri Standard mount. Those lenses need the holding tab that this adapter has to let you focus. Very easy to pop lenses in and out by just pressing two the side buttons. Les Bosher was known for making these, although I'