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reflection image when shotting flames

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yaron harel
reflection image when shotting flames
on Mar 3, 2009 at 5:03:05 pm

hi all.
one of our costumer try to shut a frame that the lower half of the frame light with flames and the upper half is dark the flames are feed with diesel fuel and there is diesel fume above the flame.
when they look at the monitors they see an image reflection of the flames on the dark half of the frame and they see it also in the camera PB (they haven't try PB on RED cine or RED alert).
did anyone ever bump in to such phenomenon?
thank, Yaron.



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Uli Plank
Re: reflection image when shotting flames
on Mar 3, 2009 at 6:39:09 pm

Depends on contrast, if it's extreme, you can see inner reflections in some situations – no optical system with more than one layer of glass is totally free of them…

Which lens did they use?

Director of the Institute of Media Research (IMF) at Braunschweig University of Arts


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yaron harel
Re: reflection image when shotting flames
on Mar 4, 2009 at 7:53:36 am

Hi, I'm copying the answer of Keith Walters and it might be the answer.
"Sounds like the old infrared problem.
Invisible infrared light from the flames might be reflecting off the smoke and fumes.
Your eyes don't see it but the camera does.
Are they using NDs?
If so, the problem is that most NDs were only designed to reduce visible light, since until single-chip cameras came along, most cameras did not pick up infrared.
If this is the problem all they can do is either get better filters or a hot mirror, or use the lens iris to reduce the exposure and live with the large depth of field."
Tanks, Yaron.



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Uli Plank
Re: reflection image when shotting flames
on Mar 4, 2009 at 8:32:42 am

That sounds like a valid solution too. We use a hot mirror on anything where you can expect lots of IR.

Uli

Director of the Institute of Media Research (IMF) at Braunschweig University of Arts


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