This is a special 100mm System adaptor ring for the Nikon PC NIKKOR 19mm f/4E ED Tilt-Shift lens.
This new ring has been specifically designed to fit this popular lens. This allows the use of the full range of LEE 100mm Filters despite the bulbous front element of this lens. The Adaptor consists of a front ring, a compressor ring and a locking ring that form a collar which remains on the lens at all times. (An adaptor is also available for the SW150 System).
This adaptor ring does not allow full lens movement without vignetting. However, the SW150 adaptor does allow full movement.