Cinematography Mailing List - CML

Earth Explosion - fps

We'd like to shoot a very large earth explosion as a miniature.

Not sure which scale / fps ratio would work best.

Any pointers would be welcome...


Jim Radford
VFX, MPC, London

At least 6th scale if not quarter scale and at least 96 fps, 120 fps might even be better.

Tony Magaletta
1st Assistant Cameraman,
Local 600, Non Rostered
Los Angeles CA.
New Orleans LA.

It depends a lot on what "very large" means.

Things to think about :

If you mean "very large" like a buried atomic bomb explosion as seen from far enough away that you do not see the sizes of the clumps of dirt flying by, then you can mess around with various scales and various mixtures of fullers earth and talc and sand and whatever – you are probably looking at very high frame rates with that sort of thing.

Can't make a useful recommendation without more discussion of scale.

Obviously, the smaller the scale, the higher the frame rate to get the physics to look right...but we are so used to seeing explosions over cranked in full scale that you might want to speed up even more than the usual "rules of thumb" regarding frame rates for scaled events.

You also get very different physics from different ways of creating the explosion - det cord (aka prima cord ) is VERY fast and would require higher frame rates than a similar-sizes event done with buried air mortars. I think powder would be somewhere in between. One issue is the smoke that may accompany some sorts of explosives - might be just want you want - or might mean you have to cut away from the shot sooner than you were planning.

I would recommend that you try a couple of things and either film or shoot with a high capture-rate video system so you can narrow down your choices before you spend all that money to properly light and set up your hero shot.

The money you spend on the test will save you time and money on the real shoot - unless you just need elements, in which case you should set up an assortment "on the day"

As you know, if you are not going for an in-camera shot, it is a lot easier to add motion blur than to try and "crisp up" and extend a short shot.

Mark H. Weingartner
LA based but Pinewood/Shepperton savvy

Thanks for the replies so far.

The type of explosion we'd be trying to reproduce would be this :

There's a image halfway down the page, of a mine being detonated.

We'd be looking to get a few like this - a few mines, but mainly shells. They all fall in churned-up mud.

Jim Radford
VFX, MPC, London

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