The 4.5" Round Solid Neutral Density 2.1 Filter from Tiffen has several uses and offers the possibility to achieve otherwise unachievable results. It enables the shooter to adjust exposure without affecting color balance. An ND filter appears gray and reduces the amount of light reaching either the sensor of a digital camera or the film plane of a traditional film camera.
A Neutral Density filters is used to create some unusual special effects such as capturing the "blur" of the rippling water of a waterfall or the swirling effect of city traffic. Since it allows the use of slower shutter speeds in bright light, it becomes possible to create these special effects that would normally not be possible to capture without the filter. And, since it can also help to control your depth of field, it permits you to shoot at wider apertures. Ultimately, its value is in helping to prevent bright, overly washed out images shot in bright light.
A 2.1 (7 stop) Neutral Density filter causes such a distinction between fore/background that your subject will become completely isolated from the rest of the image. Water will appear to be flowing at a rapid rate even though in reality, it was just a trickle. Using this filter on a very bright beach with a high ISO will prevent the shot from being completely washed out and overexposed.
Water White glass is characterized by a high transmission quality. Typically, it will transmit 98-99% of the light. It also features an anti-glare and anti-reflective quality that makes it useful in a wide range of uses including the movie theater industry, store and art displays. The glass is virtually defect-free and is becoming more and more prevalent in digital equipment.