Neutral density filter ND X 4:- Shutter speed increase or aperture: by 2 stops- Apparent sensitivity change: quartering e.g. from ISO 800/30° to ISO 200/24°- HMC (Hoya Multi Coated): Multi-coated filters are known to have extremely weak reflections from their glass surfaces, further suppressing flare and ghosting.- Filter Diameter: 52mm Neutral Density filters are not even noted by many photographers, but can be very useful in some cases, providing results that would not be possible at all otherwise. ND (Neutral Density) filters appear gray and reduce the amount of light reaching the film without affecting color balance. There are four main uses for them: 1. they allow slow shutter speeds even with higher sensitivity film to show motion, such as waterfalls and streams, fountains, clouds, or moving cars. 2. they allow larger apertures for shallower depth of field, which helps to make a subject, such as a portrait, stand out clearly from its background. 3. they act as if the film speed has been lowered accordingly, so that even high-sensitivity film (i.e., above ISO 400/27°) can be used in bright daylight. 4. they allow film and video cameras with non-adjustable shutter speeds to shoot correctly even in bright environments such as snow and sandy beaches, or in extremely bright lighting, while otherwise overexposure occurs.