The 4 x 4" Neutral Density Filter Starter Kit with 93mm Adapter Ring from Hitech includes 0.6 and 0.9 neutral density filters made from high quality optical resin as well as a 4" filter holder and 93mm adapter ring. Neutral density filters create a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than normally required. By slowing your exposure time or increasing your aperture, you are able to control depth of field and convey movement more easily. Neutral density filters do not affect the overall coloration of the image.