US manufacturer specializing in vintage lens conversions and anamorphic attachments, known for rehousing Soviet optics into cinema-grade housings.
Technical Details
IronGlass filters utilize a dual-layer construction: the base layer of borosilicate glass (Mohs hardness 7) contains 0.3% iron oxide nanoparticles, while a 50nm thin anti-reflective coating reduces reflectivity to below 0.4%. Available in standard sizes 4"x4", 4"x5.65", and 6.6"x6.6" for matte box systems. The filter thickness is a constant 4mm (±0.05mm tolerance), resulting in focus shifts of a maximum of 1.3mm. Temperature resistance ranges from -20°C to +80°C without alteration of optical properties.
History & Development
IronGlass was developed in 2009 by the German company Schneider-Kreuznach in collaboration with ARRI for digital cinema cameras. The system was first applied to the ALEXA camera, as early digital sensors exhibited extreme IR sensitivity. In 2012, it was expanded to RED-compatible formats, and in 2015, miniaturized for DSLR systems. Since 2018, manufacturers like Sony and Canon have integrated IronGlass-like coatings directly into OLPF (Optical Low Pass Filter) filters.
Practical Use in Film
"Blade Runner 2049" (2017) utilized IronGlass filters in all daylight scenes to achieve the characteristic orange-blue color grading without IR contamination. Typical workflow: mounting in front of the first lens in 15mm matte box rails, combination with ND filters is possible. Advantage: eliminates skin tone distortions and textile transparencies under strong sunlight. Disadvantage: reduces available light by 1.5% and causes a minimal color temperature shift of +50K. With LED lighting below 3200K, a magenta cast may occur.
Comparison & Alternatives
Distinction from standard UV filters: IronGlass exclusively blocks infrared, whereas UV filters eliminate the spectrum below 400nm. Hot Mirror filters reflect IR radiation back; IronGlass absorbs it. Modern alternative: Internal IR Cut Filter (IRCF) directly on the sensor, but with lower precision. OLPF-integrated solutions in cameras like the Sony FX9 replace external IronGlass filters but offer no retrofittable flexibility. In cases of extreme IR issues, IronGlass is combined with additional Hot Mirror filters.