Neutral density filters are important for filmmakers and photographers because they allow you to precisely control the amount of light passing through the lens for greater creative control over exposure. For filmmakers, this means shutter speeds that match your frame-rate while maintaining the depth-of-field you want. For photographers, it means you can use longer exposures or achieve a shallow depth-of-field in bright sunlight.The downside to most neutral density filters is unpredictable ""color shift"". This shift is caused by low-quality materials, poor manufacturing, and ignoring the infrared band of the light spectrum. This ""High Red"" transmission spike results in unpredictable color shifts that can change drastically as filter density and exposure times increase.