These filters come in various degrees of strength, referring to how dark is the gray section of the filter, and how much light is blocked. This measurement is called stops, i.e. two stops or three stops, with three stops being darker or holding back more light than a two stop filter. Neutral Density filters also have another measurement term referring to how gradual the gray area of the filter fades to clear. For hard stop filter, the area of demarcation is sharp with little or no faded area. Soft stop filters have a much greater area of fade from gray to clear; a much greater transition area for a softer blending effect.