Thread: Controlling IR Pollution

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  1. #1 Controlling IR Pollution 
    Senior Member Ben Roper's Avatar
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    Hello all,

    I'm looking for some advice on Infrared control. When using a lot of ND i've noticed quite a bit of IR flare and even IR-typical milky skin tones and black eyes.

    How do you deal with this? Circular filters on lenses? Square hot mirror in the mattebox? IR NDs?

    I'd love to hear about your various approaches!

    Thanks!

    Ps. Is UV pollution a thing?
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  2. #2  
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    You can get IR-CUT ND filters in both screw-on and Matte-box versions.

    And yes, UV-pollution is a thing though not usually as common as IR-pollution. If you are shooting in an environment where UV light affects your image, your Eyes and skin are going to damaged as well.
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  3. #3  
    Senior Member Nick Morrison's Avatar
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    What camera are you using? Dragon has very little IR pollution, if any.

    Nevertheless, the best solution seems to be FIRECREST ND's, they are perfectly color matched up and down the set.
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  4. #4  
    Senior Member Dr. Sassi's Avatar
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    UV Pollution, some thoughts.

    I tried to investigate for UV photography. I got no facts from RED based on my question, what UV filtration is included.

    https://en.wikipedia.org/wiki/Ultraviolet_photography

    Perhaps you can reverse "engineer" the data ;o) from the wiki.

    What I collected from various resources was, that to make UV photography, one needs special lenses, as "normal" glass filters UV, more or less. UV by itself from the sun has several qualities. UV starts where Micro-Waves ends. It is classified in different qualities, based on the "nm", and it can be dangerous, like sitting too long close to an HMI spot, for example.

    Similar to IR but (in opposite strength), UV is refracted differently than average visible light, and leaves (to my knowledge) some charges on the sensor, which might change your image. All of that has many variables, and my little post here certainly can scratch only the surface.

    https://en.wikipedia.org/wiki/Infrared

    "Sunlight, at an effective temperature of 5,780 kelvins, is composed of nearly thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlightprovides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts isultraviolet radiation.[10]…"

    Perhaps that brings the amount in perspective. But as others wrote above, it depends where your UV light comes from. It is not without danger.

    ====

    I remember that Phil Holland wrote a while ago about UV cut filters, to limit CA, perhaps he can elaborate on that a little bit more.

    http://www.reduser.net/forum/showthr...=1#post1352694
    Last edited by Dr. Sassi; 07-05-2015 at 10:09 PM. Reason: add link UV cut PH
    Dr. Sassi V. Sassmannshausen PhD
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  5. #5  
    Senior Member Ben Roper's Avatar
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    We're shooting Epic-X.

    I've found there to be very little IR cut on the sensor. Can anyone recommend a screw on circular hot mirror that doesn't cause a colour cast?

    I also wonder if there is any UV cut on the stock sensor?
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  6. #6  
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    You don't say what size filters your lenses take, but Tiffen makes a set of IR-Cut ND filters.
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  7. #7  
    Senior Member Nick Morrison's Avatar
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    MX doesn't protect for IR anywhere near as well as Dragon, so you're wise to be more cautious. Firecrest NDs are well matched and come in 77mm screw in sizes.
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  8. #8  
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    On MX, darker than ND0.9 you'll definitely need an IR-Cut filters. The state of the art Formatt Firecrest filters are the only fully neutral NDs out there. All the others have at least a little colour tint.

    Having said that the Formatt IRNDs and Formatt Prostops were very good solutions for MX, as well as the Tiffen IRNDs.

    Or you could just get one Formatt Hot Mirror to go in front of standard ND filters - but obviously it takes up a filter slot.

    MX sensors (as all silicon based sensors) are not very sensitive to UV light, and don't need UV filtering unless there is such intense UV radiation it would be a hazard to the cameraperson operating!
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  9. #9  
    Senior Member Ben Roper's Avatar
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    Thanks for the thoughts all.

    Does anyone know of an affordable screw-in hot mirror ONLY that doesn't cause a colour shift? (i.e. not an IRND or ND in any way?)
    Epic-X #7473
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