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