Z pro 153 gray neutral density nd 4x resin filter neutral density filters have several uses and offer the possibility to achieve otherwise unachievable results nd filters appear gray and reduce the amount of light reaching the film they have no effect on color balance the z pro series is recommended for focal lengths of 20mm onwards in the 35mm format this filter is made of cr39 resin which is a reputable lightweight and unbreakable optical material also used for ophthalmic glasses ne