ND filters are darkened glass that uniformly reduces the amount of light entering the lens, which allows a photographer to lengthen the shutter speed in order to achieve effects that are not reproducible by post-processing alone. The duration of shutter speed prolongation depends on how dark the filter is. Â ND Filters are also helpful when the contrast between the highlights and shadows is too high to get a quality exposure.
ND Filters enable you to capture sharper images and photograph at larger apertures allowing you to control diffraction.  For example, if the subject is a waterfall during the day and the target shutter speed is 2 seconds to smooth out the flowing water, without an ND the aperture will be small ie f/22 and this will cause a reduction in sharpness due to diffraction. With an ND Filter, it will allow you to reduce the aperture ie f/10 to get a sharper image.
Some common examples of using an ND include:
- Smoothing or softening of water
- Emphasizing water flow
- Smoothing or softening of clouds
- Emphasizing movement in an image
- Creating cloud movement
- Removing moving objects
ND8 (3 Stop) to smooth out water flow.
ND1000 (10 Stop) to smooth out clouds and show cloud movement.
