Tiffen 72mm Variable ND Filter
The Tiffen Variable ND filter is a unique and flexible tool, affording you the convenience of using several Neutral Density filters in one.  Primarily used for controlling depth of field and exposure, the Variable ND is being sought in the video market as well because it is fast, easy to use, small, lightweight, and does not require additional accessories.  Neutral density filters reduce the amount of light going through the lens into your camera. By reducing the light you are able to use of slow shutter speeds, with high speed films or digital cameras, to record movement/image blur in subjects such as waterfalls or any fast moving subject.  It also gives you full control over your depth of field and enables cine and video cameras (which have fixed shutter speeds) to film subjects such as snow, sand or other bright scenes which could cause overexposure.  The Tiffen Variable ND filter operates on the same principle as a Circular Polarizer – rotate until you reach your desired effect and shoot. It allows you to have continuous control over the amount of light coming through your lens in an approximate range of 2 (ND 0.6) to 8 (ND 2.4) stops – while maintaining the integrity of your image.