The Science of Smoke

Smoke, haze, atmos, whatever you want to call it, anyone who knows me knows that I’m a big fan. But how does it work and what is the purpose of smoking up a set?

 

Aerial perspective

At the most basic level, smoke simulates a natural phenomenon called aerial perspective. If you look at – for example – a range of mountains receding into the distance, the further mountains will appear bluer, lighter, less contrasty and less colour-saturated than the nearer mountains.

An example of aerial perspective

This effect is due to light being scattered by particles naturally suspended in the air, and by molecules of the air itself. It is described by the scary-looking Rayleigh Equation:

We don’t need to get into what all the variables stand for, but there are a few things worth noting:

  • The symbol on the far right represents the angle between the incident light and the scattered light. In practice this means that the more you shoot into the sun – the more the air you’re photographing is backlit – the more scattering there will be. Place the sun behind your camera and scattering will be minimal.
  • is the distance from the particle that’s doing the scattering, so you can see that scattering increases with distance as per the Inverse Square Law.
  • Lamda (the sort of upside-down y next to the x) is the wavelength of the light, so the shorter the wavelength, the more scattering. This is why things look bluer with distance: blue light has a shorter wavelength and so is scattered more. It’s also why shooting through an ultraviolet filter reduces the appearance of aerial perspective/atmospheric haze.

 

How smoke works

An Artem smoke gun

Foggers, hazers and smoke machines simulate aerial perspective by adding suspended particles to the air. These particles start off as smoke fluid (a.k.a. “fog juice”) which is made of mineral oil, or of a combination of water and glycol/glycerin.

In a smoke machine or gas-powered smoke gun (like the Artem), smoke fluid is pushed into a heat exchanger which vaporises it. When the vapour makes contact with the colder air, it condenses to form fog.

A hazer uses compression rather than heat to vaporise the fluid, meaning you don’t have to wait for the machine to heat up. The particles are smaller, making for a more subtle and longer-lasting effect.

As a general rule, you should use only hazers for interior cinematography, unless there is a story reason for smoke to be present in the scene. Outdoors, however, hazers are ineffective. An Artem or two will work well for smaller exterior scenes; for larger ones, a Tube of Death is the best solution. This is a long, plastic inflatable tube with regularly-spaced holes, with a fan and a smoke machine (usually electric) at the end. It ensures that smoke is distributed fairly evenly over a large area.

A Tube of Death in action on the set of “The Little Mermaid”

 

The effects of smoke

Just like aerial perspective, smoke/haze separates the background from the foreground, as the background has more smoke between it and the camera. The background becomes brighter, less contrasty, less saturated and (depending on the type of smoke) bluer, making the foreground stand out against it.

Since smoke also obeys the Rayleigh Equation, it shows up best when it’s backlit, a bit when it’s side-lit and barely at all when front-lit.

Here are some of the other things that smoke achieves:

  • It diffuses the image, particularly things further away from camera.
  • It lowers contrast.
  • It brightens the image.
  • It lifts the shadows by scattering light into them.
  • If it’s sufficiently thick, and particularly if it’s smoke rather than haze, it adds movement and texture to the image, which helps to make sets look less fake.
  • It volumises the light, showing up clear shafts of hard light and diffuse pools of soft light. (For more on this, read 5 Tips for Perfect Shafts of Light.)
  • Backlit smoke in front of a person or an object will obscure them, concealing identity.
Heavy smoke (from an Artem) pops Lyanna (Dita Tantang) out of the background in “Ren: The Girl with the Mark” (dir. Kate Madison).
Backlit smoke through a roof of branches creates magical shafts of light in “Ren: The Girl with the Mark”.
The final day/sunset look. From each side an orange-gelled and a pink-gelled par can light the backdrop. A 2K tungsten fresnel provides backlight, while a 650W fresnel with a cucoloris provides dappled light on the tree and tarsier. An LED panel off right supplies fill, and a second panel is inside the cave with a turquoise gel.
The colour-washed infinity cove in the background of this music promo for Lewis Watson’s “Droplets” (dir. Tom Walsh) is softened and disguised by smoke.
Haze gives the LED panels their glowing appearance in this video for “X, Y & Z Rays” (dir. Tom Walsh) by Revenge of Calculon.
This torch beam in “Above the Clouds” (dir. Leon Chambers) shows up so well because the set is heavily fogged.
Smoke backlit by an HMI creates the blue background glow against which the heroes of “The First Musketeer” (dir. Harriet Sams) stand out.
Haze creates the shafts of light from HMIs outside the windows, and adds to the gothic feel of “Heretiks” (dir. Paul Hyett).
The Science of Smoke

5 Principles of Cinematography We Can Learn from Turner

Yesterday I took a trip to The Tate Britain to see what I could learn about light and composition from the world of traditional art. My background is more technical than fine art, so this world is quite new to me. Within quarter of an hour of arriving, I had fallen in love with the work of JMW Turner. The way this man captured the natural moods of light and weather is breathtaking.

Here are five of Turner’s techniques for creating beautiful images which we can apply to cinematography.

 

1. Negative space

One of the most powerful things you can do with an area of the frame is to let it go black. A great example is Bill Pope’s work on The Matrix. But 200 years before that, Turner was embracing the darkness, emphasising those areas in the light, and allowing the viewer’s imagination to fill in the gaps.

“Jason” (1802) – That dragon is lurking in the shadows like a dodgy monster costume in a B-movie.
“Sketch of a Bank, with Gipsies” (1809) – The titular gypsies are barely visible in the black shadows, betrayed only by the smoke from their fire.

 

2. Layering

Any artist creating a 2D image strives to give the impression of depth and dimensionality. There are a number of techniques that can be used to achieve this, but one which Turner uses repeatedly is layering. See how the paintings below delineate foreground (light), midground (dark) and background (light again). The midgrounds sink into shadow, becoming negative space, reinforcing the link and relationship between the foregrounds and backgrounds. At the same time, the foreground figures stand out clearly and eye-catchingly against the shade behind them.

“The Tenth Plague of Egypt” (1802)
“The Goddess of Discord Choosing the Apple of Contention in the Garden of the Hesperides” (1806) – This painting contains five layers: light-dark-light-dark-light, highlighting the two groups of people and the monster in the distance.

 

3. Framing

Although most images we see are framed, be it by a gilt picture frame or by the black edges of a phone screen, there is something aesthetically pleasing about adding a second frame within the image itself. An extreme example would be shooting through a window, framing the image on all four sides, but more commonly we frame two or three sides of the image. Turner frequently does this using trees, buildings and shadowy ground.

“The Decline of the Carthaginian Empire” (1817) – A backwards-‘J’-shaped frame is created by the dark foreground: the wall on the left, the shadowed floor across the bottom, and the dark space in the lower right. To balance the shorter part of the ‘J’ on the righthand side, the sun and its reflection (the focal point of the image) are placed left of centre.
“England: Richmond Hill, on the Prince Regent’s Birthday” (1819) – The dark ground and dark tree to the right create a backwards-L-shaped frame which appears to cradle the rest of the image like a waiter cradling plates in the crook of his elbow.

 

4. Dynamic Composition

The composition of the two paintings below fascinates me. Both seem to be two images in one: a deep view of a settlement on the left, and a tapering tunnel perspective on the right. As I studied them, I found my eyes “panning” from one side to the other. As cinematographers, we can use actual camera movement to create a dynamic shot, but we should not forget Turner’s lesson here, that there can also be dynamism in static frames.

“Rome, from the Vatican. Raffaelle, Accompanied by La Fornarina, Preparing his Pictures for the Decoration of the Loggia” (1820)
“Palestrina – Composition” (1828)

 

5. Colour Contrast

Apart from stunningly demonstrating Turner’s power to create mood and atmosphere (a core skill for any DP), the two paintings below are great examples of warm/cool colour contrast. The yellows, oranges and reds of fire and sunset are juxtaposed with the blues of the sky. The result is pictures that really “pop”, arresting the viewer’s attention. A modern cinematographer can readily achieve a similar effect by playing natural daylight, and daylight sources like HMIs and Kinos, against practicals and other tungsten sources.

“Peace – Burial at Sea” (1842) – Contrast in both hue and luminance make this a powerfully evocative painting.
“War. The Exile and the Rock Limpet” (1842) – Note how Napoleon’s blue uniform causes him to stand out against the oranges of the sky, whilst the unimportant, red-garbed soldier behind him is allowed to blend into the background.

 
See also: my trip to the National Portrait Gallery.

5 Principles of Cinematography We Can Learn from Turner