Are IR ND's necessary for 16 and 35mm film?

[Gerrit Fahr]

Are IR ND filters necessary when shooting on film, or does a regular ND filter work just fine? My understanding is that film is less sensitive to Infrared light than most digital cameras, but I want to avoid any strange color shift.  

[Tyler Purcell]

Its not like digital, the IR doesn't effect the film as much. 

[David Mullen ASC]

“Invictus” supposedly had IR issues with 500T Kodak film in sunlight with heavy ND filters causing the colors of the rugby team jerseys to shift. But that’s the only time I’ve heard of a problem. I usually shoot 250 ASA or slower stocks in sunlight so an ND.9 is the heaviest I need to go, so I haven’t seen any IR issues.

[Ludwig Hagelstein]

On 6/7/2022 at 9:11 PM, David Mullen ASC said:

“Invictus” supposedly had IR issues with 500T Kodak film in sunlight with heavy ND filters causing the colors of the rugby team jerseys to shift. But that’s the only time I’ve heard of a problem. I usually shoot 250 ASA or slower stocks in sunlight so an ND.9 is the heaviest I need to go, so I haven’t seen any IR issues.

But that's a case of color conversion filter + ND, so more than one variable that might mess up a specific color. Then, if the HD-LD spread isn't optimal during processing, things might even get trickier, if its a very very specific color, as these jerseys can be. In my opinion, there's no real reason to shoot 5219 in daylight if you don't need the speed for some reason. I know, preference is powerful, but 5207 has the exact same sensitometric behaviour as 5219, just sensitised for daylight. The toe of the curve is almost congruent to the 5219 toe. But that's just my two cents, curious to hear other opinions. 

[David Mullen ASC]

I don't think there is much color reproduction difference between tungsten and daylight Vision3 stocks, they use the same color filters, the only difference is that the daylight stock has a slower-speed blue record (i.e. the monochrome silver grains are smaller, the filter is the same) to compensate for increased level of blue wavelengths in daylight. Color shifting tends to be more due to the use of heavy NDs rather than the 85B correction, which can sometimes be less than neutral plus some allow IR pollution. Since the arrival of digital cameras, manufacturers have been making ND filters that also cut IR, but in the days of film, that wasn't much of a consideration.

All the 85B filter is doing is cutting some of the blue wavelengths so that record is not overexposed compared to the others when shooting in daylight on tungsten film.

Stocks can also have crosstalk issues that cause certain colors that fall between the primaries to shift one direction or the other.