Miniature Explosion in front of Greenscreen

[Sodac]

Hi Guys, I#m planning to do some Miniature Test explosions of Model airships in front of a greenscreen. Has anyone here some experiences with stuff like that? I'll post the results and any troubles there where during shooting/post.

But for example the time issue. Normaly they shoot explosions, especially small ones with highspeed cameras. But for the first few tests i don't want to rent one. Does onyone know good plugins for after effects or combustion that can interpolate frames without looking jerky?

Greetings Markus

[opus13]

i have had some 'OK' results with twixtor and AE; but if i was trying to replicate high speed footage it sure wouldnt be my first choice... but then again i was using it on a DV shot (which i really couldnt expect much from in the first place). your mileage may vary.

a week ago i had the chance to play with Kronos from The Foundry on shake. that was surprisingly nice. i dont know if there is an AE or c* version available.

unfortunately i dont have any realviz experience.

[stevenbray1]

The honest answer is "No." I DON'T know of any plugins that will produce a decent result for explosions. And yes I have tried retiming such footage.

What scale are you working at? And what explosives are you using? I remember the story that when 'Star Wars' was gearing up the FX crew didn't know what explosives to use? They tried primacord and even at extreme frame-rates, the model dissapeared in a single frame!

You'll need the largest model you can build, then the "softest", slowest explosive you can buy.

By the way, didn't airships, like the Hindenburg, burn rather than explode?

Good luck and don't lose any fingers!

[Sodac]

Hi, thanks for your replys

I'm Pyrotechnician (so i hope i won't burn my fingers and I'm goin to use Benzoyl Peroxid, for the reasons you just said. It explodes very easily but slow, and also very important, it produces thick black smoke and a small fireball that doesn't shoot up in the air but stays relatively low.

For the test we use models of aprox. 50 cm lenght. I know that this is too small to get good results, but it would be too expensive to use bigger models for the tests.

Markus

[Sodac]

PS: and primacord is a very strong and quick exploding explosive. You can bring down a tree with it.

Actually i have to say i'm not really sure about the exploding/burning thing. But i'm gonna ask a friend of mine whos airplane engineer, i hope he knows this. But personally i think they have these big kerosene tanks in the wings, so just theoretically they could explode.

[stevenbray1]

http://www.cinefex.com/index/48-02.html

'The Rocketeer'! You should be able to find the back issue at a movie shop. And the DVD;

http://www.play.com/play247.asp?sear...er&page=search

Not the greatest movie ever made but it has a dynamic Zeppelin destruction scene!

Zeppelins were full of hydrogen, which is very flammable but you need the right fuel/air mix to get an explosion. The newsreel footage and photos of the Hindenberg show it burning.

http://www.arts.rpi.edu/~ruiz/Lesson...hindenburg.jpg

If you want quick way to get your shot try this, bottom of the page;

http://www.ccs.neu.edu/home/katz/balloons/products.html

[BlackKnight]

Just a quick note, the reason why the Hindenburg burned so much was because of the coating applied to the skin, it was seriously flammible.

[stevenbray1]

http://www.apple.com/trailers/paramo...rldoftomorrow/

Includes some burning/exploding Zeppelin action!

The skin of the Hindenburg burned so well because it contained aluminium, which is one the ingredients of flash powder!

[Pogel]

Well if the ships are in the air, I'd probably shot them bluescreen, because sky s blue.
If you work really hard in Twixtor or Retimer with thousands of masks and manual rotoing, painting, copy past stuff, you could probably retime it. But otherwise I strongly doubt that this would be efficient. Especially with all the small debry and uncontrolable fire.
I can always recomment stock explosion. Maybe you can comp in CG paarticle work and stock footage, to make the result more seemless.

[ShadowMaker SdR]

The thing is with these kinds of explosives. If there's nothing there to retime than you won't be able to slow it down. No matter how good the software is. If there's an airship in the first frame and no airship in the second frame, there is nothing to slow down. So I think it might be especially important for the tests to rent a highspeed camera, since then you can determine if you would really need it for the real stuff.

Does that make any sense?

Sander de Regt

ShadowMaker SdR
Culemborg
The Netherlands

[BNelso]

i would shoot it in front of a black screen, not green. then retime the footage. then composite.

[stevenbray1]

That's what I was trying to say with reference to explosive speeds. Thanks for being a LOT clearer than I was.

One possible solution is the create your own mock airship shape, in black, as BIG as you can, burn that, then comp it over your detailed model, at whatever scale it is.

As long as the shape is the same and any camera movement is scaled correctly, it will look like your model is burning.

It all depends on how big a space you have to work in?

[Hugh]

BNelso: Explosions on their own are great in front of a black background, but if he's shooting the airship at the same time, then he may have problems with doing a lumakey with the black...

[fin]

I was actually about to say the same thing about a dark background. I worked on set for second unit model shots. They basically destroyed a bunch of models on film. I was just there for 3D integration. I took lighting reference and measurements. Anyway when the explosions were shot they would either shoot it outside at night or with a black background, and there would be no lights involved in order to capture the true sparks and flame. It's much better to capture the natural light of the explosion. Otherwise it could look really flashed and over exposed, and you could lose some information. Plus there is nothing worse than trying to extract the smoke from a green screen. Especially if it picks up light from the explosion.

-Fin

[Pogel]

But the problem with black background is a) you can't see (the very violent looking) black smoke and b) if you have bright daylight shots, you basically can forget about comping it in without a tremendous efford. (in my experience at least and from what I've seen even in pro-productions)

And I think with tools like ultimatte it's not so difficult to extract greenscreen smoke.
I'm of course no pro, but not everything has to be "natural" in frame. In my eyes, it's totally OK to fade color out till the smoke is grey and then after comping it coloring it again. Maybe you do loose that "infomation", but hey VFX is tricking the eye, and at the end of the day you "color-correct" half of the information out of the shot anyway, so I don't see no harm in that.