From the Manufacturer:
Kenko’s uniquely designed variable neutral density filter provides the equivalent brightness range of ND 2.5 to ND 1,000 (practical use being up to ND450).
Polarizing Effect Cancellation
The Variable NDX filter changes the brightness of light using a polarized filter. This new filter uses a “polarizing effect cancellation” where a polarized filter is used, but purely for controlling the amount of light with no effect on color balance, glare or reflections.
Easy to Operate / Easy Framing / Easy Focus
With a tripod mounted camera, use the brightest setting for framing and focus and then increase the density to your desired level by simply turning the outer filter ring.
The singular versatility of the Variable NDX filter not only replaces a whole set of stacking neutral density filters it also removes vignetting which may be caused by using multiple filters.
DMC - Digital Multi-Coated
Digital multi-coated filters greatly reduce the appearance of lens flare and ghosting caused by reflections.
Prevents Overexposure / Highlight Clipping
Even with a shutter speed of 1/8000 seconds, a large aperture of F1.4 or F1.2 can cause overexposure / highlight clipping. With the Variable NDX filter, this overexposure is eliminated.
For HDSLR Movie
For HD video-enabled cameras, use the Variable NDX filter to easily adjust light control and shutter speed. The Variable NDX filter makes it simple to produce blurred background effects, simulate a night scene or create manual fade in / fade out effects. It is also perfect for use in bright locations such as beach or snow scenes and city scapes.