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How to Expose for Explosions


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#1 Peter Ellner

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Posted 05 July 2011 - 09:04 PM

In many Hollywood feature films, there are explosions, and they look great. But I'm curious as to how shots with explosions are exposed so that the explosions don't completely blow out and yet the surrounding areas are not underexposed.

Do they expose for the explosions, or do they expose for the background/environment? And how do they end up getting both the explosions and the environment/background properly exposed in the final product, as it seems that properly exposing for one would incorrectly expose the other.

Thanks for the enlightenment!
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#2 Chris Keth

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Posted 05 July 2011 - 09:23 PM

It's just a matter of lighting the set to a level that is closer to the level of exposure you need for the explosion. In daylight scenes, this isn't really a problem. You have the biggest lamp any of us have available. Night scenes and interiors become more difficult. In those cases, it's often "light to the highest level you can."
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#3 David Mullen ASC

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Posted 05 July 2011 - 11:45 PM

In many Hollywood feature films, there are explosions, and they look great. But I'm curious as to how shots with explosions are exposed so that the explosions don't completely blow out and yet the surrounding areas are not underexposed.

Do they expose for the explosions, or do they expose for the background/environment? And how do they end up getting both the explosions and the environment/background properly exposed in the final product, as it seems that properly exposing for one would incorrectly expose the other.

Thanks for the enlightenment!


Just depends - you almost can't underexpose an explosion but on the other hand, a viewer accepts a brighter or darker explosion, whatever you give them. So the general rule is that you light your exterior night scene to as high a level as you can get away with. For example, "Terminator 2" lit the exterior of the exploding building to T/5.6, which was more or less as much as they could. After that, you hope the film negative holds detail in the brightest parts. Now if there are multiple cameras running and some are zoomed into the fire and won't be used in the cut until after the explosion, they may be stopped down more to hold detail in the flames and let the foreground movement go more silhouette, as long as it is not a dramatic exposure difference from the wider angle. As the fire dies down, the cameras may have to open up the irises on the lenses to compensate.
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#4 John Sprung

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Posted 06 July 2011 - 01:03 AM

... a viewer accepts a brighter or darker explosion, whatever you give them....


That's the crux of the matter, it really isn't all that critical. Shoot some bracketing tests of an ordinary camp fire, a fireplace, or whatever.... Explosions are the same sort of thing, only they happen fast. Tests are the best thing for confidence and comfort level.




-- J.S.
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