This is a special LEE100 System adaptor ring for Nikon PC NIKKOR 19mm f/4E ED Tilt-Shift lens.
This ring has been specifically designed to fit this popular 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.
Please note: this adaptor ring does not allow full lens movement without vignetting.