ND FILTERS CHART
ND4 - 0.6 OD/2-stop light reduction stops
Sunrise, Sunset, low light
ND8 - 0.9 optical density/3-stop light reduction stops
Cloudy day, softbox
ND16 - 1.2 OD/4-stop light reduction stops
Daytime, few/no clouds, bright light
ND32/64- 1.5/1.8 OD/5/6-light reduction stops...