The 138mm Variable ND filter allows continuous control over the amount of light coming through the lens. This is approximately, 2 (ND 0.6) to 8 (ND 2.4) stops and is focal length dependent.
By rotating the 138mm ring between the index points, the light transmission is changed. The filter’s ability to reduce light is focal length dependent. We advise to check each lens for the maximum point at which either, edge vignetting or a visible “cross” occurs in the picture area.
A basic observation is that a wide-angle lens will see this effect sooner than standard and longer focal length.
The unit is supplied with a 114mm light prevention ring. It is threaded to accept a wide variety of step down light prevention rings for use with multiple lenses.