The adapter ring is crucial to the LEE Filters system. It screws onto the camera’s lens and the Lee Filter holder is then secured to the adapter ring with the locking dial. It sits in front of the lens’s front thread.
The wide angle adapter ring is suitable for use with wide angle lenses. It differs from the standard adapter ring by sitting closer to the front element of the camera’s lens, as the threads are recessed into the adapter ring so that the adapter ring slightly overlaps the lens. As a result, the likelihood of vignetting is dramatically reduced.
The wide angle adapter ring could really be considered a universal adapter ring as it can be used on any lens, even if it is not a wide angle lens.