Kodak Neutral Density Gels are available in small increments and have many uses. They offer the possibility to achieve otherwise unachievable results. ND filters appear grey and reduce the amount of light reaching the film.
Most Kodak gelatin filters are available in 3 x 3" (75 x 75mm), 4 x 4" (100 x 100mm), 6 x 6" (150 x 150mm), and 14 x 18" (350 x 450mm).
These filters are available in increments from 1/3 stop to 13.33 stops exposure reduction.
Wratten 2 Improvements
Easier to handle
Color consistent today, and 6 months from now as well
Wratten 2 Optical Filters are less sensitive to humidity, less prone to static cling
Fingerprint removal is also easier
Neutral Density filters have four main uses
To enable slow shutter speeds to be used, especially with high speed films, to record movement in subjects such as waterfalls, clouds, or cars
To decrease depth of field by allowing wider apertures to be used, which helps separate subjects from their background
To decrease the effective ISO of high speed film (above ISO 400) and allow it to be used outdoors in bright situations
To allow cine and video cameras (which have fixed shutter speeds) to film subjects such as snow, sand or other bright scenes which could cause overexposure