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Light is strange stuff. Paradoxically, light is invisible unless it hits something. While we are primarily concerned with what happens at the end of our light beams, there are occasions when we're at least as interested in seeing the beam itself.

To make a light beam visible requires something in the atmosphere that will scatter some light without compromising the beam's characteristics, or blocking it entirely. In the natural world, that something may be dust, smog, mist, smoke, drizzle or fog. When the extent of the scattering needs to be of controlled intensity or duration, then it's up to us.

During the 2000 Summer Olympic Games, I was on the roof of the tallest building in Sydney, Australia, trying with limited success to get some usable images of the beams from some 40 W YAG lasers. These powerful devices were part of the laser and searchlight show that ran several times each night during the Olympic Games. The lighting designer was fervently hoping that as the night got cooler, there would be enough condensation in the spring air to help reveal the beams.

Unfortunately, the Pacific Ocean breeze had all but blown away the light smog over downtown Sydney. There are no such problems with the "Symphony of Light," a laser and searchlight show that runs every night in Hong Kong. The smog from the nearby industrial cities of southern China provides ample light scattering.

Although widely employed in drama and music production, the complexity of using atmospheric effects in television is not something to be sneezed (or coughed) at. It's vital to consult with the facility air handling and fire alarm specialists when planning to use atmospheric effects. Many types of smoke detectors are triggered by theatrical smokes, hazes and even the so-called water-based (actually glycol-based) fogs that are the mainstay of modern atmospherics. Knowing which detectors need to be isolated to avoid false alarms while still maintaining maximum fire safety can save a lot of confusion and angst.


Having knowledge and control of the air-exchange system can also make it easier to prevent your carefully constructed atmospheric effect from inadvertently being vented into the open air or distributed throughout the studio complex.

It is very easy to underestimate the density of effect required to produce a particular look on-screen. Camera tests are vital for assessing the type and number of effects machines required, not just to create the desired pictures, but also to maintain them for the duration of the scene. I once sat in a control room watching my monitors and asking the effects operator for more and more fog, while trying to get just the right look. On commenting about how slowly things were going on the studio floor, I was encouraged to look down through the window. Despite looking like a light haze on camera, the entire set had been swallowed into the mists like Brigadoon.

Needless to say, your vision controllers also need a thorough briefing on the look that you're aiming to achieve. The ability to override the camera's automatic exposure and levels programs is absolutely critical to any attempt to use atmospheric effects. Even a minor adjustment to camera black levels can produce quite drastic changes in the appearance of atmospherics.

Continuity is a significant consideration when using atmospheric effects. Getting the right density is important, but keeping that density and distribution from shot to shot and from scene to scene, can be a major source of delays and distress.

Most effects machines have an output controller that theoretically ought to allow the effect to be replenished at precisely the rate that it's dissipating.

In practice, the effect tends to be constantly changing in distribution, requiring assistance from fans and crew members waving sheets of cardboard or lightweight reflectors to cajole it into place.

Camera, scenic and talent movements can disturb both the density and distribution of the effect. Where possible, during shooting, the set should be locked down; doors kept closed, crew movement kept to a minimum and air-exchange systems either wound back or shut off. Hours of painstaking work can be ruined by something as innocent as a production assistant delivering a revised schedule to the set. It is also worth considering shooting atmospheric effects scenes in script sequence. Then, variations in the effect tend to be clustered together in editing, rather than becoming more obvious problem cuts jumping from a few gentle wisps to a full-density London fog.

Although it's difficult to get enough atmospheric effect onto the set in the first instance, getting rid of it again can also present difficulties. If you're going live or working under a tight shooting schedule, clearing the effects from the air may require some planning and coordination with your air-handling adviser.

Unassisted, your air-exchange system may take hours to eliminate all visible traces of the effect, particularly if it was smoke or haze. As the camera is generally quite insensitive to such effects, these will disappear from pictures long before the air is actually clear. One technique for quickly clearing the air is to open the dock doors and vent the studio to the outside world, providing of course, that you're not passing the effect on to an unsuspecting neighboring studio. News presenters have a hard enough job to do without having their studio filled with fog, although it might improve that closing wide shot.

Unlike their predecessors, contemporary atmospheric effects are achievable, affordable and generally quite safe. Substantial research into nontoxic, low-irritation effects generators has taken us to the point where there are workable recommended exposures for most effects. (A future column will look at how these generators work.) Even opera singers, a group notoriously finicky about their lungs, voices and working conditions, are willing to perform in the current generation of fog effects. If only they were easier to use.