When to shoot the real thing

A surprising amount of the fire, smoke and rain in finished films was never simulated. It was shot for real, on its own, and composited in later. That footage is called a practical element.

An element is real footage of a real thing: flame, smoke, dust, rain, a splash, drifting embers. It's shot separately, usually against black or a dark set, so it can be layered into another shot down the track. Not shot in the scene. Shot for the scene. Compositors keep whole libraries of them.

What the camera gets for free

Point a camera at real fire and you get three things no simulation gets for free.

The first is chaos. Real flame misbehaves in ways no artist would invent. It licks sideways for no reason, spits an ember, collapses and recovers. Audiences have watched real fires all their lives, and they clock fake movement fast, even when they can't say why.

The second is light behaviour. Flame is a light source photographed through a real lens. The flicker, the bloom, the way the highlights roll off: it all arrives in the footage, already correct.

The third is grain. An element is photography, so it carries the same texture as the rest of your film. Sensor noise, lens softness, motion blur. It belongs in the frame before a compositor touches it.

A good simulation chases all of this, and a good artist gets close. It takes weeks. The camera does it in a take.

When simulation wins

So why simulate anything? Because there are jobs real fire can't do.

• Direction. When flame has to hit a beat, grow on a line, or curl a particular way, a sim takes notes. Real fire doesn't.
• Scale. A burning city block or a wall of water can't be shot, and shouldn't be attempted.
• Interaction. When smoke has to wrap around a CG object, the sim knows the geometry. An element doesn't.
• Safety. Anything that puts real flame near cast, sets or locations is a simulation conversation, not a shoot.

On most strong shots the honest answer is both. A common build puts real flame in the foreground, where the audience is looking hardest, with simulated smoke and heat behind it, filling space at a scale you could never shoot. The real layer sells the sim. The sim carries the scale the real layer can't. Done well, you can't tell where one stops.

The element shoot, and the maths

An element shoot is one of the least glamorous days in visual effects. A dark stage. A locked-off camera. A fire officer standing by, and a small crew working through a written list: low flames, tall flames, a gust, embers, smoke wisps, each at a couple of framings and speeds. Elements are usually shot at high frame rates so they can be retimed later. Slowed down, a small flame reads as a much bigger one. The whole session fits in an afternoon.

We did exactly this on Testament. For the Pentecost sequence we shot real flame elements on a stage against dark brick, then retimed them and composited them around the cast. The fire in those finished frames actually burned. The steps are laid out in the Pentecost fire breakdown.

Now the maths. An afternoon of elements can replace weeks of simulation work, because the sim artist's hardest job, the chaos, is the thing a camera captures without being asked. But the saving only exists if the element shoot is planned before the main shoot. Planned early, it can share a stage day and crew the production is already paying for, and the element list gets written from the shot list, so you capture what the shots actually need. Decided after the edit, it becomes its own hire: a stage, a camera package, safety, another day. By then the schedule usually pushes you back into the sim anyway.

What to take away:

• Real elements carry what a simulation chases: chaos, light behaviour, grain. If it can burn safely on a stage, shoot it.
• Simulation wins on direction, scale, interaction with CG, and safety. Most strong shots use both.
• The saving is only real if the elements are planned before the main shoot. After the edit, they're a new line item.

If the script has fire, smoke, rain or dust in it, that's a conversation for the planning session, before anyone builds a rig or opens a sim package.