Promaster 49mm Variable ND Filter:
Promaster Neutral Density Filters have various applications and offer the ability to achieve otherwise unattainable results. ND filters appear gray and reduce the amount of light that reaches the film, they have no effect on the color balance.
The main uses of a promaster ND filter are:
To decrease the depth of field, allowing wider apertures to be used, which helps separate subjects from their backgrounds.
To enable slow shutter speeds to be used, especially with fast movies, to record movement in subjects such as waterfalls, clouds, cars, seas, etc.
To lower the effective ISO of high speed film (ie: above ISO400) and allow it to be used outdoors in bright light situations.
To allow camcorders (that have fixed shutter speeds) to film subjects such as snow, sand, or other bright scenes that would normally cause over-exposure.