B+W Neutral Density Filter 102 reduces the light by two f-stops (log density 0.6), and it is the most popular ND filter in photographic work. It offers many benefits, for instance f/4 instead of f/8 for selective sharpness instead of a great depth of field, or 1/15 s. instead of 1/60 s. for a flowing instead of a "frozen" waterfall. It has excellent color neutrality, costs less than the denser filters, and is recommended as part of a basic outfit. The filter factor is 4x.