Neutral density filter with additional infrared blocking, combining light reduction with accurate color reproduction.
Technical Details
IRND filters consist of multi-layer optical coatings on high-quality Schott glass or Corning substrate. The IR-blocking layer efficiently blocks wavelengths from 680-720nm with over 99% efficiency, while the neutral density coating achieves spectral accuracy of ±2nm across 400-680nm. Standard filter sizes include 4x4", 4x5.65", 6x6", and 138mm round filters. High-end variants like Schneider IRND or ARRI FSNDs achieve T-stop transmission values from T-stop 0.6 to T-stop 2.7 with minimal color deviation below 1% Delta-E.
The multi-layer coating prevents reflections between sensor elements and the filter, which is critical for CMOS sensors with Bayer patterns.
History & Development
IRND filters emerged in 2009 as a response to the increasing IR sensitivity of digital cinema cameras like the RED ONE. Schneider-Kreuznach developed the first commercial IRND filters in 2010, followed by Tiffen and Formatt-Hitech in 2011. ARRI revolutionized the standard in 2014 with FSNDs (Full Spectrum Neutral Density) through improved spectral linearity.
Development accelerated with cameras like the Sony FX9 or Canon C300 Mark III, whose extended IR sensitivity leads to unusable skin tones without IRND filters.
Practical Application in Film
For exterior shots in "Blade Runner 2049" (2017), DoP Roger Deakins used IRND 1.2 filters to achieve the characteristic shallow depth of field at f/1.4. "1917" (2019) employed IRND 0.9 filters for continuous exposure adjustments during Steadicam sequences.
The workflow requires precise exposure metering, as IRND filters can influence in-camera metering by 0.1-0.3 stops. Critical in mixed lighting situations: IRND filters eliminate IR contamination from tungsten light, which causes magenta shifts when unfiltered.
Comparison & Alternatives
Standard ND filters only reduce visible light but allow IR radiation to pass through – problematic for CMOS sensors without integrated IR-blocking filters. Variable ND filters (VND) offer flexibility but produce cross-polarization and are not IR-corrected.
Internal ND filters in modern cameras (Sony FX6: 1/4, 1/16, 1/64) often combine ND and IR-cut functions but limit filter selection. IRND filters remain the standard in high-end productions where external filter control and maximum optical quality are required.