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Rear Projection on a window


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#1 Matthew Skala

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Posted 22 May 2007 - 06:49 PM

Hello All,

I am shooting a short film and there is a scene in a bedroom where we need to have imagery showing on a window. Its not supposed to look like there is anything going on outside the window. It needs to be a surreal effect similar to stuff in Natural Born Killers, If I am remembering that movie correctly. We will be shooting the short on HD with my HVX200 package.

I have some ideas myself but would love to get some of yours. Such as what kind of Projector I could use. What kind of material should I use on the window that would look natural. Should I shoot the scene at night or day, or at night for day. At this point we are flexible as to what time of day in the story the scene takes place. If we shot it during the day I would have to tent the window, at night we may have to flag off some street lights, etc. Just let me know what you guys think.

Thanks!

Matt
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#2 Nick Mulder

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Posted 22 May 2007 - 07:18 PM

Sounds like you have a few of the more important aspects in your headspace already (like masking off stray light) ...

Have you thought about how you are going to create a rear projection screen on the window ? I'd use some sort of tracing paper / diff gel set up ... For something more transparent you might have to spray on some sort of matte surface spray, this way you could get gradients of where the projection is strongest - Anything that disperses the light randomly on the glass plane instead of letting it pass through as a direct ray

Do you expect to see out of the window at the beforehand/after or at the same time as the projection ?

Are there any issues with rigging the projector outside ? what sort of throw lens do you need on it ? etc...
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#3 Michael Nash

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Posted 22 May 2007 - 07:18 PM

You can get an LCD projector and a rear-projection screen from an A/V rental house. Shoot at night and put the screen right up against the window.

I gaffed a music video with the HVX and LCD rear projection "walls" you can see here. It actually wasn't that hard to get the rear projection bright enough, but balancing the color was a little tougher. The projectors are 5600K or higher, and it takes time to tweak it toward a tungsten balance. Make sure you flag as much ambient light off the screen as possible, to ensure deep blacks in the projected image.
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#4 Matthew Skala

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Posted 22 May 2007 - 08:46 PM

Sounds like you have a few of the more important aspects in your headspace already (like masking off stray light) ...

Have you thought about how you are going to create a rear projection screen on the window ? I'd use some sort of tracing paper / diff gel set up ... For something more transparent you might have to spray on some sort of matte surface spray, this way you could get gradients of where the projection is strongest - Anything that disperses the light randomly on the glass plane instead of letting it pass through as a direct ray

Do you expect to see out of the window at the beforehand/after or at the same time as the projection ?

Are there any issues with rigging the projector outside ? what sort of throw lens do you need on it ? etc...


I like the matte surface spray idea, definitly worth experimenting with! I wonder if we could use steam, that would be pretty hot!

Seeing outside the window is not important and we can put the projector right outside the window with plenty of room to move it back and forth.to be out of shot it will probably have to be about 10 to 15 feet away from the window.
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#5 Nick Mulder

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Posted 22 May 2007 - 09:19 PM

proper rear-pro screens are a lot darker and translucent than steam or spray on clear/translucent gunk will be - steam even less so ... so you'll have a large proportion of the light still entering the room

Can only suggest experimenting as you say ...

keep us updated ;)
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#6 Matthew Skala

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Posted 23 May 2007 - 02:00 AM

Thank you nick, I will keep you updated.
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#7 Hal Smith

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Posted 23 May 2007 - 09:48 AM

The easiest way to color correct any projector is with CTB/CTO gel. For instance, I color correct my 3200K 35mm Simplex movie projector to balance modern release prints with a full CTB. Those prints are balanced for Xenon projectors and a CTB very nicely balances the Simplex's tungsten source to 5000K. If you own, or have access to, a color meter like a Minolta II/III the process is very simple, measure the projector's CT and use whatever the meter says you need.
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#8 Matthew Skala

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Posted 23 May 2007 - 12:19 PM

Hey Hal,

That sounds pretty logical to me. I hope it doesn't take away too much brightness. I can start with a full CTO. It doesn't have to be perfect for it is a surreal effect.

Thanks
Matt
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#9 Joseph Nesbitt

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Posted 23 May 2007 - 09:20 PM

hey you are right that Stone used projection in Natural Born Killers, but in the commentary he said it was an incredible hasstle. Plus what's your budget? Projectors can be expensive, yeah you can rent one but if you need to get one for a few days that's another hole in your pocket, with that money, make yourself a blue or green screen, I did and it's helped alot. Projection can look better than blue or green screen, but if you do go all out, get creative, there's this great shot in natural Born killers when Mallory is Driving down the street on her own and she drives by this guy on the street mugging another guy, the guy eventually shots the victem but in the back is this huge projection on the wall behind him of like a wolf or soething, that's when Stone brought the hassle situation up but unless you plan to do something like that I reccomend the blue or green screen
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#10 Matthew Skala

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Posted 23 May 2007 - 09:45 PM

Hello Joseph,

You bring up a good point using green/blue screen, It would be a lot simpler and cheaper especially if there isn't any action in front of it, which I am not sure if there is at this point. Thanks for the input!

M
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Wooden Camera

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