Fader ND is a variable neutral density filter that reduces the amount of light entering the lens by multiple stops (from 2 to 8), using a design similar to CPL filters. The Fader ND adjustable filter allows you to vary density from 2 to 8 stops by rotating the filter, as with CPL filters.
To avoid vignetting, the manufacturer uses glass with a front diameter one step larger. For example, an 82 mm filter is a dual filter with an 82 mm rear thread and an 86 mm front thread (a cap for the front thread is included). These adjustable ND filters are ideal for use with lenses up to 200 mm focal length. With lenses above 200 mm, image quality may decrease.