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Arri Alexa IR Pollution - Tiffen T1 Filter and Green Hue Shift


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#1 Andrew Waruszewski

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Posted 18 March 2011 - 10:04 PM

I am shooting a new documentary on the Arri Alexa, and recently discovered some IR pollution when using ND filters heavier than .9 I have been experimenting with the Tiffen T1 filters to correct it (both the combo IRNDs and the straight T1 with the standard NDs), and have seen some major color shift with each filter. The IRND9 is green, the IRND12 is much greener, and the IRND15 leans more towards a brownish tone.

Has anyone else had this issue, and what have you done to solve it? I know that I can shift green/magenta in the Alexa menu, but I am not sure that that is a route that I'd like to go. Any information would be great!!!

Thanks in advance.

Andrew
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#2 Davon Slininger

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Posted 07 September 2011 - 03:35 PM

We have straight Schneider ND's on the show I'm on now. Apparently Schneider has the least color abberration when shooting HD, or so we heard from comrades in the industry that had done may tests. We noticed that ND15 and higher had a much more dramatic color shift that any ND below that. If we used an IR (T1 specifically) with anything less than an ND15 it would be much too green as well.

We've compromised and have been using the IR only on ND15 and higher. It is quite a noticeable difference from 12 to 15 but the grading in post has been much more manageable sticking to this routine now.

I feel like you just get what you get with HD these days and even if you are using the same camera it still needs some fine tuning and a bit of testing until you figure out a solution appropriate for your shoot.

Hope that helps! Have a great shoot!
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#3 Andrew Rawson

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Posted 07 September 2011 - 06:18 PM

Yeah the Schneider ND's are the best especially the new Platinum series which are hard to get your hands on. We have been doing several things , the first is after throwing the ND in white balancing to an 18% grey, this often times gets rid of the majority of the problem, from there our DIT talks the camera assistants in by tweaking kelvin, green and magenta to match both cameras. It's not an exact science but it's working for us.
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