Neutral Density Filter permits less depth of filed under bright light, since the aperture has to be open. Long time exposures are possible with Neutral Density filters in sunlight. ND filters can be use for color or black and white photography.
ND 0.3/50% Light Loss/2x Filter Factor/ -1 Exposure Correction: A light gray filter with minimum light absorbtion.
ND 0.6/25% Light Loss/4x Filter Factor/ -2 Exposure Correction: : A medium gray filter used for portraits and out-of-focus backgrounds.
ND 0.9/12.5% Light Loss/8x Filter Factor/ -3 Exposure Correction: : A dark gray filter which increases the effect of the medium gray.