Neutral density filters have four main uses:

• They allow for the use of slow shutter speeds, especially with high-speed films, to capture motion in subjects such as waterfalls, clouds, or cars.
• They reduce depth of field, allowing for the use of larger apertures, helping to separate subjects from their background.
• They decrease the effective ISO of high-speed films (above ISO 400) and allow their use in bright outdoor conditions.
• They facilitate film and video cameras (which have fixed shutter speeds) in capturing subjects like snow, sand, or other bright scenes that may cause overexposure.

Neutral density factors:

• 2x = ND.3 (exposure adjustment = 1 stop, reduces ISO 1/2)
• 4x = ND.6 (exposure adjustment = 2 stops, reduces ISO 1/4)
• 8x = ND.9 (exposure adjustment = 3 stops, reduces ISO 1/8)