Allows the use of optical old FD honorably on EOS. WARNING to book those who know how the manual in photo, because you lose autofocus and diaphragm. Set the reflex aperture priority mode, it will adjust the speed. To mount the ring on the lens FD, it must pass its manual aperture ring, and turn the locking ring on the ring open. 1-up ring on the FD, 2 - mount the FD + baque the EOS case, 3 - close the ring of the ring (closed position). We may lose a dive with the lens, but a good FD 28mm f2.8 (45mm equiv 24x36) make good pictures 10x30 no problem. The only downside is that the focusing of EOS has no rangefinder, and to do development with the LCD screen in LiveView after activating the magnifying glass. So overall good solution for reuse an old goal.