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Lighting for UHP/NSH projector poorman's


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#1 Matthew OSullivan

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Posted 08 October 2008 - 09:39 AM

Hi,

We're experimenting with using an LCD projector for background plates outside windows on sets in a studio. We rear-project a still or video of, say, a street outside a livingroom window, in place of a translight or painted backdrop.

The projectors use high pressure mercury arc lamps, which are very blue and have a temperature of something like 7600-8000. Everything works fine when we light the set with HMI and shoot daylight stock, but obvious problems ensue if we shoot the scene with tungsten film. We make the plates very warm to compensate, so the projections look quite red/golden to the eye, and when we meter them they show as low as 3000K (though with a lot of green), but it seems no matter how much we warm up the images they still look VERY blue on tungsten film.

Filtering the beam with a single or double 85 should fix this, or go a long way towards fixing it, but we can't really afford to lose that much brightness.

Wondering if anyone has any experience with this scenario? Any outside-the-box solutions? I'm thinking of wacky ideas like making the screen yellow and then front projecting instead of rear..

Any thoughts?
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#2 Mark Dunn

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Posted 08 October 2008 - 11:29 AM

David Mullen will be along with a more practical answer, but here comes the physics.
Arc lamps have a discontinuous spectrum with strong output in the green and, as you've found, blue. The eye can compensate but film can't, and filtration doesn't really work. The problem has been solved for HMI lamps but not, as you've found out, for LCD projectors.
Unhelpful, and probably not entirely accurate,but there you are.
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#3 Matthew OSullivan

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Posted 08 October 2008 - 05:15 PM

Thanks Mark. We're going to do some camera tests with various filters soon and I'm still hopeful, but I'm starting to think the only way to pull this off is to light for daylight.
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#4 Ryan Patrick OHara

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Posted 23 September 2009 - 03:09 AM

Thanks Mark. We're going to do some camera tests with various filters soon and I'm still hopeful, but I'm starting to think the only way to pull this off is to light for daylight.


Can I resurface this thread in hopes that the previous poster or another member can discuss this more?

I'm in preproduction for a film where translights are too expensive to have made and the scenery is not generic enough to rent... or at least I haven't found a suitable drop quite yet.

I am curious how shooting with warmed plates and perhaps slight filtration works. If anyone can add to this conversation, I would be terribly grateful.

Thanks in advance!
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Broadcast Solutions Inc

Visual Products

Media Blackout - Custom Cables and AKS

Tai Audio

CineTape

Aerial Filmworks

Abel Cine

CineLab

Metropolis Post

Gamma Ray Digital Inc

Technodolly

rebotnix Technologies

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