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Alexa blacks looking red

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Roger Zammit
Alexa blacks looking red
on Jun 30, 2013 at 9:26:44 pm

Hi

I recently had a shoot on the Alexa and had several shots with black clothes in them show up as a redish colour. Any idea how i could prevent this?


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David Namir
Re: Alexa blacks looking red
on Jul 1, 2013 at 11:22:49 am

Hi Roger
If you were using ND 1.2 and up that would be the reason. Some blacks will turn to be reddish while others will remain black. This is the way the sensor reacts to infrared with high ND filters. The solution is using IRND filter or adding a T1 filter


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gary adcock
Re: Alexa blacks looking red
on Jul 1, 2013 at 3:01:34 pm

[David Namir] "If you were using ND 1.2 and up that would be the reason. Some blacks will turn to be reddish while others will remain black. This is the way the sensor reacts to infrared with high ND filters. The solution is using IRND filter or adding a T1 filter"

David,

the level of ND does not affect the IR as much as multiple filters does, IRND filters should be used on all newer digital cameras as conventional IR filters were designed for film and not the specific issues of "compounding" where the IR signal coming out of the first filter does not fall in line with the narrower parameters of flim's IR resistance as it passes thru the second filter in order.

Tiffen and to a larger extreme Schneider have worked tirelessly to create new filters designs that have adopted a wider latitude for IR blocking that is required on the more IR sensitive digital sensors than it ever was for film recording.

gary adcock
Studio37

Post and Production Workflow Consultant
Production and Post Stereographer
Chicago, IL


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Roger Zammit
Re: Alexa blacks looking red
on Jul 1, 2013 at 9:19:21 pm

Thanks for your replies, i had a feeling it might be the IRND, and yes we were using multiple high ND's.

What's annoying is that we asked for them but they weren't available i just didn't expect such a drastic colour shift


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