Model building

[Terry Lee]

I would really like to understand the concepts of model building for movies. I have this shot that I want to do where a small building blows up and I thought it would be awesome to do with a model. However, I have no idea how to make the model look as if its the building itself. I've built models from scratch before but never nothing to scale or for the screen. I've searched amazon for books but haven't really found anything that explains in a step by step process. Anyone have any experience?

[Shawn McCalip]

I Don't know of any books that exclusively cover model-building, but you might want to try looking into working with miniatures and practical effects. Have you ever read CineFX magazine? If you can get your hands on some of the older issues from the 80's and 90's, there are all sorts of cool articles about how certain effects and looks were achieved in a whole bunch of films. There is also a large, hardcover book from Industrial Light and Magic that covers all sorts of films that they worked on like Star Wars, E.T., and Jurassic Park. The older editions of that book were released before CG became super prevalent, so most of what you see in there comes from model building.

Try looking at this: Amazon.com: miniatures special effects: Books

[Terry Lee]

I guess model building is a thing of the past now eh? The reason I thought building a model for this paticular scene would be cool was primarily inspired by Star Wars. I can't really think of the name of a movie I saw a replica model house in but I know i've seen it..

Thanks for the reference. That books looks like it would cover what I am confused about. Honestly the only thing I need to know is how to film a model to make it look as if its an actual full scale building.. the model I can take care of.

Thanks for the info :)!

[Ben Syverson]

Three big things you want to pay attention to...

1) Lighting. It's always a dead giveaway when the lighting on a model doesn't match the scene. I'm assuming this building blows up at night... You may need to use physically smaller lights, unless your model is huge. If you light a 12" tall model with an 8" light, it looks like you're using an impossibly large light source. In terms of the scene, there will probably be a couple lights on the exterior of the building, some lights on inside, and the rest of the lighting might come from streetlights. You're probably best off getting a bunch of small, very bright LEDs and wire them up inside and outside the model.

2) Camera height. You'll probably need to cut a hole in the plywood that your model rests on so you can get your camera low enough to look realistic, unless you have a lot of crane shots in the rest of the film. Measure the distance from the nodal point of the lens to the ground plane, and then multiply it by your scale. For example, if you're using 1:12 scale, and the nodal point of the lens is 5 inches from the plywood "ground," it will look like your camera is on a 5 foot tall tripod.

3) Lens aperture. This is crucial. To get the right DOF for a miniature shot, you need to scale the aperture. Start by figuring out what aperture you would have used if the miniature was full scale, then convert it to a linear measurement so you can scale it along with your other measurements.

For example, let's assume you're using a 1:12 scale as above, a 35mm lens, and you would have shot at f/2.8. Apertures don't scale linearly, so divide the focal length by the aperture (that's why it's written f/X). 35mm / 2.8 = 12.5mm. That's the physical size of the lens aperture.

12.5mm has to be scaled the same as every other measurement for the miniature shoot, which is 1:12 scale, so we divide it by 12. 12.5mm / 12 = 1.041666mm

Now, to convert the physical aperture back to an f/number, divide the focal length by it. So 35 / 1.041666 = f/33.6

So ideally you'd want to be at f/32. Some lenses don't close down that much, so you'd have to fudge it to f/22. The tiny aperture means you'll need a lot of light... If you wind up with an aperture that's much too small, like f/64 or f/150, you may want to think about building a larger model. Inappropriately shallow depth of field is another dead giveaway that you're looking at a model.

[Terry Lee]

Wow! I am so greatful that you told me that. Have you worked with models on a film before?

[Ben Syverson]

Not really -- only on my own little projects. But I'm gearing up for a miniature shoot for a music video, so it's all fresh in my mind!

Two things I forgot to mention, which are very important for miniature pyro in particular:

1) You should really have a professional handle the rigging and detonation, because even at a small scale, it's pretty easy to lose a finger or an eye. Beyond that, a pro will know the right mix of materials to use in the explosion. Using different ratios of combustibles, you can get a different look (more or less black smoke, bigger fireball, etc). There's gotta be someone in or around Louisville who would be qualified and would probably get a kick out of doing it!

2) You absolutely need to film miniature pyro in slow-mo. There's a rough formula cinematographers sometimes (?) use for calculating the appropriate FPS for Pyro and Water miniatures:
Pyro FPS = Normal FPS * SquareRoot(Scale)

So if the rest of the film is at 24fps, and your scale is 1:12 (to continue the previous example), then it's:
24 * SquareRoot(12) = 83.138 fps

But honestly, I don't know how much this formula is actually used in Hollywood. If the director wants a bigger-feeling explosion, they may overcrank even more. I'd probably start at 96 fps no matter what the scale -- you can always speed it up, but it's a lot harder to slow it down!

Needless to say, it's worth renting the high-speed camera for one day to get the pyro shot. You probably aren't going to be happy with the results if you just film it at 60p and slow it down. After all the time you spent making the model, you want to make sure you capture the destruction in all its glory!

Hope this helps!!

[Jim Andrada]

Something else to be aware of - scaling time! If part of the model falls down in the scene, you have to slow its motion down. The time it takes a model building 3 feet tall to fall is a fraction of what it would take the real thing to fall. Even if it explodes or falls apart, there is a big difference in the acceleration of the model versus the real thing, although it may not be as obvious to a casual viewer as an object falling under the influence of gravity.

Whoops - Ben posted his comment while I was typing mine!

I remember when they used to use large models of warships in a huge swimming pool for naval battles and the trick was to get the apparent speed of falling masts etc looking "right"

There was a good article in American Cinematographer about it but I think it was in 1960 or 1970 or thereabouts! I think their battleship models were like 30 or 40 feet long and they had people inside driving them around the pool. Fascinating. Getting wave motion to look right was also a challenge due to the scale.

Now it's all done with computer simulations. Which wouldn't be such a bad way to get a model building to blow up, come to think of it. Using a real model has the problem that you may not (probably won't) get it right the first few times and the model will have to be reassembled correctly each time, and parts can get damaged in the process. And no danger of setting fire to yourself or your house with the pyrotechnics when its all virtual.

Another thought is to make the building blow apart by blasting some compressed air up from below. This would minimize the danger of burning the model (or yourself) in the process. Adding a fireball in post is fairly easy - you can generate them easily in most decent 3D animation packages, or there are places that sell clips of explosions - can't remembr exactly where at the moment, though.

[Terry Lee]

Hmm.. Well the problem is I have no clue where to get a high speed camera that can crank up to 96fps.. I don't think anyone around here has one and chances are they are pretty expensive per day.

Are you saying that a highspeed camera would be necessary for a slow motion shot of the explosion or regular speed as well? For this paticular shot i'd like it to look as if it remains at 24fps.

Thank you so much for explaining this stuff. This really helps me be able to make this happen.

[Ben Syverson]

Yeah... the smaller the explosion, the faster you have to shoot. If you shoot a miniature exploding at 24fps, it will look ridiculously fast. To get the look of filming a full-scale explosion at 24fps, you have to overcrank to about the range suggested by that formula. It's because a miniature might explode in 1/4 second or less. You want to stretch out that 1/4 second to at least a couple seconds of screen time.

This place supposedly has highspeed film cameras, but their website is down:
Inde-Post
711 Fox Creek Lane, Suite 100
Cincinnati OH 45245
Phone: (513) 947-1689
Fax: (413) 643-5361

Honestly, you might want to post a message to the CML describing your situation. Odds are, there's someone closer to you that has a camera that would work. A lot of camera owner-operators don't necessarily have big web presences, so they can be tough to google.

Of course, worst case scenario, you can just rent something from Chicago, which is probably the closest production hub with real rental houses. But that's an annoying drive to have to make just for the camera.

Good luck, and keep us posted!

[Ben Syverson]

Just one more thought... If you do post to CML, be sure to explain your situation/budget. I would offer the camera operator at least some money for their time and the use of their gear (just ask them what they think would be fair, and then negotiate from there, but expect to give them at least $100-200), give them credit on the film, and allow them to use the shot for their reel or even for stock video sales. Hopefully someone will see it as a fun project and decide to spend their Sunday with you blowing stuff up. :)

The end result will be a MUCH better shot than you could have gotten on your own.

The ultimate last resort is filming your model and then digitally compositing explosion footage on top. They do this a lot for TV, but it always looks terrible to me.

[Jim Andrada]

Well, within limits you can slow things down in your NLE

Maybe some combination of overcranking to the limits of your camera and then slowing it down in post would give the effect you're looking for.

I think the key to the whole thing is "the effect you're looking for"

Physical versimilitude it one thing, but real explosions are usually nowhere near as interesting looking as you want in a film. 50 years ago more or less I worked in a government lab where among other things we did explosives research. I was a computer jockey - (yes we had computers) - so didn't get my hands dirty so to speak, but I saw a lot of explosions and the real thing was over a lot faster than what it looks like in a Hollywood film. We test fired large guns (think battleship-size) right outside my building and while dramatic, it all happened fast. By the way, even at that time we could film at an effective rate of several million fps to study how individual powder grains burned as a function of their shape and size.

Another issue you're going to have with a model is getting it to look real even before you blow it up. ie texturing etc is non trivial. You might want to make it blow up at night because it will make it easier to get away with a less convincingly textured model, and the explosion will be more dramatic at night.

But I seriously doubt if miniature pyrotechnics will produce the effect you really want - think about how exciting a firecracket looks when it explodes - poof, a flash of light, a sharp noise, a whisp of smoke, and it's over. Almost instantly.

And you will almost cetainly have to do this over and over and over again, so the model will have to be "re-usable" after each shot.

Anyhow, if it were me, I'd add the pyrotechnics in post either by buying a clip from one of the outfits that sells explosion clips, or doing one in a 3D package that has a decent particle generator. Safer, more predictable, more "tunable" to get the effect you want. If you know anyone who does animation using Lightwave or Maya or Cinema 4D etc I'm sure they could generate a nice explosion for you. Come to think of it, there are probably ways to add explosions in After Effects (I'm not much of an After Effects jockey)

I found the following though

How to create an outward explosion in After Effects | Wonder How To

[Ben Syverson]

Originally Posted by Jim Andrada

Well, within limits you can slow things down in your NLE

It's one thing to slow footage down, but you can't take four frames and turn them into 60.

Like you say, miniature explosions are over almost instantaneously. You really do need a highspeed camera.

It's true that compositing pre-shot explosions would be easier, but getting it to look halfway decent will be even harder than filming it.

[Jim Andrada]

I guess one question that we haven't asked yet that might have a bearing on all this is the anticipated scale of the models - are we talking about a tabletop model of the Empire State Building, or a dollhouse sized model of a Bungalow, or a storage shed sized model of a vacation cabin.

Makes quite a difference.

I guess I'm not sure how easy it would be to make a really small explosion perform like what you see in the movies now, with billowing smoke and raging flames tossing automobiles through the air. I think youll definitely need someone who knows how to make explosions to order. Plus the high speed camera.

I'm not an After Effects maven, but I know that you can make some really quite nice explosions in today's 3D packages and with enough control of the particle emitters underlying them you can get a lot of control over propagation speed, smokiness, etc.

Doing it in miniature I think it will be really hard (unless you're a real pyrotechnics guy/gal) to get the roiling and dense smoke cloud/ fireball effects.

If you can get the effect you want, the next issue would be the frame rate you needed as Ben said

I remember some of those old articles from the pre CG days and it always seemed like they had 40 or 50 people running around. Which is why CG is so much cheaper and faster

[Terry Lee]

Alright well maybe if I outline some of the parameters I am working within we can better figure this situation out. By the way I greatly appreciate it..

This film is primarily a learning tool for myself and others who are interested in making a movie. We all sort of pitched in things we'd like to do and are working on fitting those things into a solid script. Since this has no preperation for distribution and will more than likely not be submitted to a film festival, the budget will be as low as we can get it, however not limited by money. Therefore if money is required to do what we want then money will be spent although we would like to keep the expenses down. A tune familiar to any film maker... Since everyone involved has the title of producer, pulling a good amount of this film's money into one shot will more than likely be voted out. But thats the way I would like it. I want to see everyone's ideas come to life.


The model I am wanting to build is of an already existing building which I can get the measurments of. Since I have never done this for the screen, any scale you guys suggest would be fine with me. I just want to have a reason to build a model :) As suggested by Jim, designing the pyrotechnics and the model so that the model is re-usable or even building several model sounds most like the most practicle approach.

I think what I will have to do is take several shots of various explosions to simulate how this shot will look using what Ben has pointed out about lighting, apeture, camera height etc. However 60p might be all we can get unless I can find someone close. I have talked to the place in Ohio before and their prices are quite high and I'd have to drive an hour and a half to retrieve the camera.

You guys have told me so much great information that I feel bad not being able to utilize everything. Hopefully I can make something happen that looks decent.

Thanks alot.
Terry.

[Jim Andrada]

Well, the less the size difference between the real thing and the model, the less you'll have to speed up the camera

Aside from that I think it's just a matter of just how much space you have to work in. And a few practical things like not kaking it so small that it's unduly fragile, nor so big that you'd get hurt by flying pieces.

I think also you'll have to plan where the model is supposed to fly apart or what pieces are supposed to fly off or fall off and make sure there is a separate piece of the model for any piece that is supposed to part company with the rest of it.

If there are doors that should blow off, you have to think whether you want them to just blow outward, or whether you want them to swing outward on their hinges a bit before tearing off.

In other words, you need to choreograph the destruction and then engineer the model so it separates as desired.

You also need to figure out how you will make it come apart. Just depending on the force of the explosion won't work because explosions are notoriously hard to control at the level of precision you want.

I think if I were doing it, I'd limit the debris to a few fairly well defined panels like a front door, a window, maybe one side of the building falling out, maybe the roof jumping up a bit. I think you could rig springs inside the panels and trip them in sequence by pulling strings - maybe a few mouse traps or rat traps would do the trick

I haven't been to Universal Studios in ages, but they used to have things like the dock from Jaws that would fall down on schedule and then re-assemble itself, or a full size subway car (maybe from the original Pelham 123 in '74???) that would ride up onto a platform and sort of disintegrate, then reassemble itself - I think they did it all with programmed hydraulics.

If you have a good reference library near you I'd go over and see if they have old copies of things like American Cinematographer from the 70's or so either original or microfilm, and then I'd just rummage through whatever you find looking for this kind of stuff.