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#1 Simon Gamache

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Posted 16 June 2009 - 01:29 PM

I need your expert advice on a project of mine.

I'm directing a movie in which there is the suggestion of explosion (of a nuclear nature) outside the room into which the story is set. For this purpose I have covered the window with a fairly thin drape that let light passes throught without the camera being able to actually see through the fabric.

We'll shoot during the day and the window is facing north-east (past 10AM the sun doesn't hit it directly).

Now, I talked with my DOP about it and at first suggested a HMI fresnel 2.5k to be placed at about 1.5 meter from the window. He then suggested what he called a "chime", which he described as some sort of big search light supposed to simulate the light of the sun.

First: I have no idea what he's talking about. I'm new to all this stuff and need some education. What's a "chime" (he had to spell it out for me)? Would certain type produce more light than a HMI 2.5K and fit into a 40 amp circuit?

Second: Out of those two option (provided you know what he was refering to), which one would be the better? Keep in mind that have to be able to modulate the intensity of the light during the shooting.

Third: Any other suggestions? I essentially need the maximum light output possible that can fit into a 40 amp circuit. As said above, modulating the intensity of the light is also important.

The whole project is dependent on the quality of the lighting. Advice would be greatly appreciated.
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#2 Adrian Sierkowski

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Posted 16 June 2009 - 01:40 PM

well that's what it looks like.
Where it me, I'd maybe look into getting some go the lightning strike units used to simulate well, lightning, they're bright and powerful, for that initial flash, and then gang that with some kind of other unit for the "afterglow"
I'd warm up the lightning strikes a lot with a bit of a reddish/brownish/orange color, and then the "afterglow" light I'd go with something rather warm as well. Maybe something like a 9-light or the like.
You'd need a way to set off both of these lights @ once, so that as soon as the initial flash from the lightning strike ends, the afterglow begins, also i'd back 'em far away to it looks more like a "distant" explosion casting very hard long shadows.
my 2 cents.
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#3 David Mullen ASC

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Posted 16 June 2009 - 01:57 PM

I'd be tempted to just light the interior to a high stop and then crank open the iris for the nuclear "flash" (maybe simultaneously dimming the interior lighting to compensate so that the windows are mainly what are blowing out.) Because I'm not sure any HMI light is really going to give you a nuclear explosion effect in a real daytime interior. I'd almost go with a row of mirror boards simultaneously cued to reflect the sun into the room, though that would require a sunny day and enough people on the mirrors. But I think the iris pull would be more realistic.

Don't know what a "chime" is, lighting-wise.
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#4 Chris Keth

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Posted 16 June 2009 - 02:29 PM

I'd be tempted to just light the interior to a high stop and then crank open the iris for the nuclear "flash" (maybe simultaneously dimming the interior lighting to compensate so that the windows are mainly what are blowing out.) Because I'm not sure any HMI light is really going to give you a nuclear explosion effect in a real daytime interior. I'd almost go with a row of mirror boards simultaneously cued to reflect the sun into the room, though that would require a sunny day and enough people on the mirrors. But I think the iris pull would be more realistic.

Don't know what a "chime" is, lighting-wise.


This would be super cool. Though I've never experienced one (thank God), I think of a nuclear explosion as so hot it's just white, not really warm colored.
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#5 K Borowski

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Posted 16 June 2009 - 05:56 PM

No, I think they are actually redish-colored.
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#6 Adrian Sierkowski

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Posted 16 June 2009 - 05:58 PM

From what I've seen the flash is whitish, but the afterglow is reddish because it's, well a mushroom cloud of burning things.....
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#7 David Mullen ASC

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Posted 16 June 2009 - 06:02 PM

I think the brightness basically overrides issues like color temperature, but in theory, the color would be based on whatever was being consumed by the explosion. At first, I guess it would be hydrogen fuel in a fusion bomb, then whatever else was burned. What color is burning hydrogen? Judging from this:
http://en.wikipedia....spectral_series
The H-alpha Balmer line is in the red range for hydrogen.
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#8 Justin Hayward

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Posted 16 June 2009 - 06:16 PM

This would be super cool. Though I've never experienced one (thank God), I think of a nuclear explosion as so hot it's just white, not really warm colored.


Well, what we've seen from footage shot during one, the iris pull that David said would certainly match it the closest.
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#9 K Borowski

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Posted 16 June 2009 - 06:31 PM

Or, hell, if you send the North Koreans a 35mm camera, or even 16 and film, and let them use the footage for propaganda purpsoes, they might let you film a real one underground.

Then you just need to matte out the cave and add in a city :blink:
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#10 Michael Collier

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Posted 16 June 2009 - 06:34 PM

I don't know that hydrogen would impart its color onto the explosion for very long. Only very little is used in a fusion bomb, and a disproportionate amount of fire is created. What I have always thought was true was the heat from the explosion causes the atmosphere itself to catch fire, so the color would be a mix of oxygen and nitrogen burning, whatever color that would impart. I have always assumed orange/red, because when stopped down enough in those test explosions, thats the color they read on film. But the initial flash is too bright, like david says, for it to even matter. Perhaps you have the room to be impressionistic with the color of light....how many of your audience have actually really seen a nuclear explosion?

The most effective nuclear hits I have seen on screen is always a brilliant white light that comes on quickly, then slowly fades as the color shifts more red, and then the light travels up (usually causing the window light to move down) as the mushroom cloud moves up.

I would think you can get this with something like a 100k flagged off, then at the point of impact, drop the flag, slowly dim down the light, and start a chaser sequence on gelled par cans. Seems like the initial hit would be hard, and then as the mushroom cloud starts to raise and grow, it could get softer, perhaps by adding more par cans per row on the chasers. if not chasers are out, then you can consider something like a crankovator (though that might raise to slow) or put your light on some kind of counter weighted rope system.

But in addition to that you have unlimited options for what the lights in the building do. They could just flicker. They could go out all together to be replaced with a 'no light' look, the emergency lights could come on in brilliant colors. You have a lot of options, and a lot of ways to have some fun there.
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#11 Joe Giambrone

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Posted 22 June 2009 - 09:47 PM

The initial flash takes milliseconds and blinds anyone looking in that direction. It's many times brighter than the sun and would be the only thing people see or could discern. Many would be instantly blinded, permanently.
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#12 Robert Houllahan

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Posted 22 June 2009 - 10:59 PM

The initial flash takes milliseconds and blinds anyone looking in that direction. It's many times brighter than the sun and would be the only thing people see or could discern. Many would be instantly blinded, permanently.



In the excellent documentary "The day after Trinity" a witness to the first atomic detonation describes how her daughter saw the flash which was exceptional because her daughter was blind.

-Rob-
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#13 Frank Barrera

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Posted 22 June 2009 - 11:22 PM

David, how many stops would you want to be able to over expose it? At what stop would be the pre explosion exposure? keeping in mind that he only has 40 amps to work with it doesnt seem possible to use too many footcandles.

perhaps he could use the 2.5 to simulate some type of after glow as has been discussed and then the explosion would just have to be some type of post effect.
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#14 David Auner aac

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Posted 23 June 2009 - 02:24 AM

David, how many stops would you want to be able to over expose it? At what stop would be the pre explosion exposure? keeping in mind that he only has 40 amps to work with it doesnt seem possible to use too many footcandles.


I guess that's where the sun comes in handy. But if you were shooting with a fast lens, say opening up to a T1.3 40 amps should be enough. At least, in 230V country it would be.

Cheers, Dave
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#15 Karel Bata

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Posted 23 June 2009 - 05:08 AM

My 2p:

Mount your HMI on a DIY jib (you're on a budget right?). There's several ways you can do this. One I've used to get a shot in the middle of nowhere was using a borrowed steel ladder, the type with hollow rungs. If you lay it flat on it's side and poke a strong metal rod through a rung you create a see-saw (do you Americans know what a see-saw is? :D ) Put the light on one end and a counterweight and a grip on the other. Clearly you need a strong ladder! And make sure it's earthed. You'll also need someone to adjust the angle of the light so you can tilt it down as you raise it. This is where those scaff clamps you've been hanging on to for years come in handy.

Light the room conventionally without the HMI. For the flash turn all your lighting off, run the HMI with it pointed horizontally through the window, open the camera lens and run it at the slowest speed it will go (you don't say what you're using). If on video turn the gain right up. Blow it right out. If you're unsure shoot several takes at different stops. You'll need a few seconds of this. For the mushroom's light, turn your room lighting on and run the camera as normal, pause for two seconds then slowly raise the HMI. While doing so tilt it down and slip an orange filter over the HMI's lens. That way it goes up and changes color. You could rig a gel on a stand so the light moves into it as it raises. Have it very close to the lamp. Cutting an irregular edge will minimise the risk of what you're doing being too obvious.

In post you go from normal lighting, cut to your flash shot, then mix to moving mushroom shot to get the final effect. You'll have to mark very carefully where the talent are!


Wish I was doing this. :D

Edited by Karel Bata, 23 June 2009 - 05:12 AM.

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#16 Patrick Kaplin

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Posted 23 June 2009 - 06:45 AM

David, how many stops would you want to be able to over expose it? At what stop would be the pre explosion exposure? keeping in mind that he only has 40 amps to work with it doesnt seem possible to use too many footcandles.

perhaps he could use the 2.5 to simulate some type of after glow as has been discussed and then the explosion would just have to be some type of post effect.


For the film Sunshine, Alwin Kuchler overexposed 500t 5218 stock by about 9-10 stops for certain scenes involving the sun.

"When we wanted the image to really burn out, I had to overexpose by 8, 9, even 10 stops to really burn the information away to the point where we couldn’t get it back. We wanted to physically attack the stock with light to get the right effect. When Searle [played by Cliff Curtis] is exposed to the sun, that’s 10 stops overexposed, and what you see is literally the only information left on the negative — there’s nothing else there.”


Might want to look at that film as a reference.

http://www.theasc.co...shine/page2.php
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#17 Simon Gamache

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Posted 29 June 2009 - 11:52 AM

Thank you all for your replies.

I went for a HMI fresnel 4k and tried to get the best effect with that.

It worked in some instances, not in others.

You're one of the most useful group of people I've encountered.
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#18 John Sprung

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Posted 29 June 2009 - 01:14 PM

I don't know that hydrogen would impart its color onto the explosion for very long. Only very little is used in a fusion bomb, and a disproportionate amount of fire is created. What I have always thought was true was the heat from the explosion causes the atmosphere itself to catch fire, so the color would be a mix of oxygen and nitrogen burning, whatever color that would impart.


Correct that the spectral signature of hydrogen wouldn't be of any importance here. What you see is plain old Planckian incandescence, the light just comes from the heat. You wouldn't get the oxygen or nitrogen spectra either, any more than an ordinary light bulb gives you the spectral signature of tungsten. It's all just plain old Planck.... Start with a massively overexposed white flash, then fade down through orange and red over several seconds.

There isn't a significant "burning" of oxygen and nitrogen, they pretty much just heat up to incandescence and cool down. Fire only happens where there's fuel, such as wooden buildings. The desert tests merely burned what little vegetation there was out there.



-- J.S.
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