There is a lot of confusion around IRND filters for Cinematography. IRND filters are neutral density filters that have an infrared light suppression to create true black colors in modern digital camera sensors.
There are four kinds of IRND. Hot mirror, dye based, carbon coated, and bonded carbon coated.
Hot Mirror IRND
The Hot Mirror were a quick response by both Schneider and Tiffen in 2006/2007 to IR pollution on the Panavision Gensis and Red One cameras. The issue with Hot Mirror is the angle of incidence relative to the optical axis must be about 40 degrees or less diagonal field of view to avoid imaging the diffraction of light through the coating layers on the filter. This means you can only use about a 32mm or longer focal length when using a HM or HM IRND filter in most lighting conditions.
Further HM filters are highly reflective and can reflect into the talent’s eyes or create a nice little red/orange/green spotlight on reflective surfaces in the scene.
Dye Based IRND
Dye based are the older IRND technology that started in 2008 with the Tiffen IRND and the Schneider Platinum IRND. The hot mirror style were merely a mirror applied to a standard bonded ND.Dye based IRND filters hit the scene first by Tiffen in 2008/2009 and then by Schneider in 2009/2010. These filters were rife with color shift issues due to the rare earth elements being activated in the dye with UV light causing yellow color shift. I recall Tiffen issued a warning that their original IRND formulation filters had to be stored in a foil bag supplied with the filter when not in use to avoid color shift. Schneider had the same problem but were able to fix it without the need for a storage bag.
The original dye based IRND were bonded sandwich substrate type and had a spectral cut off that was designed specifically for the Alexa classic. Schneider Rhodium filters are a similar bonded dye based but are full spectrum cutting IR wave lengths well out to 1200nm where older dye based IRND cut at 680nm-710nm and then let IR light pass again around 850-900nm.
Ultimately Schneider won the Academy Technical Achievement Award for the Platinum IRND but this filter was tuned for Alexa classic camera and since their Rhodium and the carbon coated (bonded or not) filters such as Firecrest, PRO IRND, True-ND, and Arri FSND have all eclipsed those with superior technology.
Carbon Coated Full Spectrum IRND
Carbon coated IRND suppress IR wave lengths well out into 1200nm+ however they have the advantages of a single piece of coated glass. They are fragile as mentioned before.
Bonded carbon coated IRND have the advantages of the standard coated IRND but they are significantly more durable as the coating is inside the filter. Of course you lose some performance on a technical micro level compared to a single piece of glass but it isn’t enough to make an appreciable difference in performance.
Mitomo True ND is a surface coated full spectrum ND. This type of IRND is the best from a pure technical standpoint. It is a single piece of glass that can be polished more precisely than two pieces of bonded glass in a traditional ND that requires a substrate to be sandwiched between. Also the carbon coating is deposited with an electrolytic process that is very accurate in thickness of the coating. The downside is that it is nearly impossible to practically manufacture a surface coating that is durable in this case. It can be done but the cost would be astronomical because so few cinema filters are manufactured.
Kenko Tokina is expert in coating technology and does OEM coating for many filter brands. Kenko Tokina originally manufactured the True ND until Mitomo changed vendors when Kenko Tokina took the same coating and bonded it internally in their PRO IRND filter.
The Schneider Rhodium are a substrate bonded IRND that has similar IR suppression performance. The optical quality is sufficient for cinema use however not on a purely technical level as good as the carbon electrolytic coated IRNDs. Many shows and Features that have used the Rhodiums with success.
The Alpha IDX filters are a similar bonded electrolytic carbon IRND so they are equivalent to the Tokina PRO IRND and Firecrest IRND filters.
IRND Filter List (2019)
Hot Mirror IRND
Tiffen Hot Mirror ND
Schneider Hot Mirror IRND
Panchro HM ND
Rosco Hot Mirror ND
Dye Based Bonded IRND
Schneider Platinum IRND
Schneider Rhodium FSND
Carbon Surface Coated IRND
Mitomo True ND
Lee ProGlass Cine IRND
Bonded Carbon Coated IRND
Tokina PRO IRND
Formatt Firecrest IRND
Tiffen NATural IRND
What is different among the various brands today is quality of manufacturing as it relates to quality control and color shift from one copy to another. We have found the True ND, Arri FSND, IDX Alpha, and Tokina PRO IRND to be the absolute best in terms of color matching from one copy to another from different manufacturing batches.
As always, test for yourself and consider the fact that modern digital sensors are all tuned differently so your IRND selection may change as the sensors evlolve.