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Rear-projection questions


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#1 Matthew OSullivan

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Posted 03 September 2009 - 01:01 AM

Hi, I've been working with rear-projected plates from an LCD projector with pretty good success for a couple of years, but recently we've run into some problems. We're shooting film, and the projections are from a Christie LX1500 LCD (15000 lumens) fed by a laptop. Up until a few weeks ago it was working well... always a battle to light it right, but the filmed results were pretty good. But, suddenly, we've got flicker on the film (not visible to the eye or through the finder, only on the printed film). As far as we can tell, NOTHING has changed in our setup (but obviously something has)

It's really baffling, and we've swapped out the projector and the laptop for identical units, but no luck. The flicker shows up with still image plates as well as motion at any frame rate, so it's not a frame rate issue.

Camera shutter is at 180, and we're rolling at 24.

The flicker is very consistent, and not overly pronounced. It's a faint, fast flicker.

Laptop is feeding projector at 60hz.

I'm wondering if anyone has run into a situation like this, or had any issues with flicker from LCD projectors in general?

And while I'm at it ... has anyone got any tips for how to balance the projector for tungsten film? The UHP bulbs it uses run very high, like around 6500-7500, and it's a battle to get rid of that blue. We do our best to correct the plates, and then play around with orange and magenta gels over the beam, but it's always a bit of a crapshoot (though not too bad).

I'll seriously send a bottle of the finest whiskey on the planet to anyone who has any clue why this flicker problem would have suddenly appeared out of nowhere. If I had any hair left I'd be pulling it out.

matt
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#2 Robert Houllahan

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Posted 03 September 2009 - 02:35 PM

I would look at the power situation, has there been any construction nearby? What factors might cause this a bad transformer or another problem at the power delivery system?

Then try another camera?

-Rob-
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#3 Daniel Madsen

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Posted 03 September 2009 - 02:43 PM

I would shoot at 144 degree shutter to make the exposure time (1/60 sec) the same as the refresh rate on your projector.
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#4 Matthew OSullivan

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Posted 03 September 2009 - 10:36 PM

Thanks guys... power and shutter are my best guesses too, but if it's a shutter I'm confused why we've never had the problem before, and also in theory an LCD projector should have enough decay that refresh rate is a non-issue. But trying a 144 degrees is definitely a good idea.

Robert...power... do you have any experience with a "ghost in the machine" causing flicker? Our gaffer has run a line test on the power sources (220 for the projector and 120 for the laptop) and the power is good and steady... do you think there could be another problem in the line, like some kind of EMF or other anomalie? We're literally right next door to the main power station for the whole area so I've often wondered if that's causing some sort of weirdness... though if anything the proximity should be good not bad.

Thanks again

matt
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Glidecam

Media Blackout - Custom Cables and AKS

rebotnix Technologies

Wooden Camera

FJS International, LLC

Metropolis Post

Willys Widgets

Gamma Ray Digital Inc

Paralinx LLC