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I have read that cinema cameras such as the ARRI monochromatic series have no IR filter, allowing them to "capture the non-visible infrared light that renders white foliage, milky skin, black eye pupils, and moody skies".

I consider myself adequately informed on how IR "contamination" can lead to false color images and hence it made me wonder how the ability of the camera to see IR would affect the tonalities of the monochromatic image.

I am aware that there is no more color discrimination, but wouldn't things react differently and appear different as each object has its own SPD (spectral power distribution), reacting differently to different wavelengths in the IR band? I mean I suppose they do hence why the quote that I referenced, but how do they ensure that these deviancies from our eyes vision don't affect the image too much to still appear realistic?

I hope the question makes sense and thank you for taking your time read it.

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    \$\begingroup\$ Your premise for the question, 'don't affect the image too much to still appear realistic', is wrong. One of the main purposes for using IR sensitive cameras for artistic purposes (or film for that sake, IR sensitive B&W film has been around for about a century), is to create surrealistic images where the tonality of certain objects deviate from our real life perception. \$\endgroup\$
    – jarnbjo
    Commented Mar 1 at 15:25
  • \$\begingroup\$ I understand what you mean but to me knowledge the monochromatic cameras that I am referring to for cinema are not supposed to provide any noticeable deviation / added surrealistic touch. Their main purpose it to provide a monochromatic image, yet there must be some inherit benefit of using infrared and Im asking how they implement it without as you mention making the image appear surrealistic. \$\endgroup\$
    – vannira
    Commented Mar 1 at 15:28
  • \$\begingroup\$ I don't know if this makes sense but I am referring to "standard" black and white photography, not infrared photography that is monochromatic. I hope that makes sense, apologies for any confusion. \$\endgroup\$
    – vannira
    Commented Mar 1 at 15:30
  • \$\begingroup\$ I do suppose that the answer to my question is that they most likely just very carefully limit the amount of infrared or region of infrared or the like, to produce an image that deviates slightly from "standard" visible spectrum black and white to maintain a realistic look, whilst implementing some artistic flair to improve the image slightly. But perhaps someone has a better or more precise answer, which is why I asked the question \$\endgroup\$
    – vannira
    Commented Mar 1 at 15:32
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    \$\begingroup\$ "Standard" (panchromatic) black and white film is not significantly sensitive to IR. Before panchromatic film was invented, the standard was orthochromatic film, which is not even sensitive to red light. \$\endgroup\$ Commented Mar 1 at 21:28

3 Answers 3

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Digital monochrome camera is somewhat of a specialized tool and removing IR filter from the sensor simply expands it's usages:

  1. sensing IR shifts tonal balance between different materials and light sources. Some objects emit near IR, some don't, some reflect, some don't.
  2. sensing IR significantly increases sensitivity of the sensor, it can then be used in very dark scenes.
  3. there is no reason why you can't put the filter back behind (some feature rear filter holders) or in front of lens.
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The benefit is that you can shoot IR footage with an IR pass filter for effect. And if the IR sensitivity becomes a problem for normal black and white shooting, you can always use an external IR cut filter, as Euri Pinhollow points out in their answer.

Although, in my experience of shooting with a mirrorless camera that has had its IR cut filter removed, you are unlikely to need an IR cut filter in most cases. While the IR light will ruin any colour photograph, it tends to be overpowered by the visible light in monochrome. To get white foliage, moody skies, et cetera, you are going to need to shoot with an IR pass filter and increase the exposure time a little (or open up the aperture or turn up the ISO instead).

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Humans (in general) do not see in monochrome, so anything in monochrome doesn't appear realistic.

renders white foliage, milky skin, black eye pupils, and moody skies

Which part of that sounds realistic? If it was realistic/normal; it wouldn't be noteworthy...

I suppose they do hence why the quote that I referenced, but how do they ensure that these deviances from our eyes vision don't affect the image too much to still appear realistic?

If you watch some clips taken with those cameras you will see that even the same type of object reacts/records differently at different times and from different angles; e.g. foliage doesn't consistently record as white.

IDT they are ensuring anything; objects reflect IR much as they reflect visible light, and it's close/consistent enough that it doesn't look confusingly odd in monochrome... which already looks "wrong" anyway.

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