Neutral density filters have four main uses:

• They allow for the use of slow shutter speeds, especially with high-speed film, to capture motion in subjects such as waterfalls, clouds, or cars.
• They reduce depth of field, allowing for the use of wider apertures, which helps in blurring subjects from their background.
• They reduce the effective ISO of high-speed film (above ISO 400) and allow its use in bright outdoor conditions.
• They enable film cameras and camcorders (which have fixed shutter speeds) to shoot subjects like snow, sand, or other bright scenes that could cause overexposure.

Neutral density factors:

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