RED RENTAL reccomends TRUE ND as the preferable ND filter for digital cameras due to the excellent optical quality, IR cut and absolutely no color shift
TRUE ND is a clear glass coated with metallic alloy film on both sides.
Manufactured under strict quality control, TRUE ND will offer you accurate transmittance and true neutrality. Troublesome infrared will also be filtered out by its flat spectral curve up to 750nm. TRUE ND is simply how ND filters are supposed to be.
The ND 2.1 filter reduces the amount of light going through the lens by 7 stops.