7 minute read
Replay: A glimpse at the pre-digital vfx practical tools and the techniques that have been used over the decades to make an audience's collective jaw hit the floor
Contrary to popular opinion it's not all smoke and mirrors. Mirrors have been used since time immemorial to create VFX shots, stretching back to the days when Pepper's Ghost baffled and amazed packed audiences in eighteenth century music halls. But, while careful lighting and attention to the different scales involved can allow them to combine both miniature and full size sets for an in-camera shot in a technique that has survived all the way through to the modern day, really practical VFX is all about making your models look good.
Giving Models Depth
In the same way that the human eye can quickly detect unrealistic character movement in animation, so an audience can very quickly rumble an unsuccessful model shot. Build quality is, of course, vital, but the real key is in proper photography of a scene and that starts with depth of field.
The depth of field of a model shoot ideally should replicate that of a full-sized one, ie typically relatively deep. To reproduce that the camera needs to get very close to the model in question, in a roughly analogous ratio to the model size. Use a 1:25 scale model and your lens will need to be 25x closer to it than for a full-sized shoot, which, of course, leads to problems then emerging with a shallow depth of field. Work arounds include using wide angle lenses or a small aperture, the latter having to be bolstered with extremely bright lighting or using faster film stocks.
Then there's the problem of depth perception too, which tends to mean that models have to be shot in correspondingly thicker atmospheres, often provided by a fine smoke.
But as well as a model shoot having to carefully balance film speed, focal length, aperture and depth perception, camera speed also has to be considered too as models tend to look oddly lightweight when filmed at a conventional framerate. Happily there is a formula that gives a rough guideline for this which reveals that our 1:25 model would have to be filmed at a framerate of 150fps (a 1:10 model would have to be filmed at 76fps) though it is only a guideline and there are a host of other variables that tend to make the calculations fuzzy.
And over the years many different types of model have been used.
Hanging miniatures
These foreground miniatures, usually some form of set extensions, are hung in the top of the frame, and were especially popular for hiding studio paraphernalia (lights, booms etc) in the studio-bound era of the 30s and 40s. Still in use up to digital era, though care needed to be taken with camera movement, use of atmospherics etc.
Landscapes
Cities are difficult, the natural world is worse. The watchword is care and attention, both to weathering effects and the actual geography of places the audience might know. Buildings to be destroyed need some interior components, while filming natural environments out in the open air in proper sunlight is considered to be a great advantage, as is using natural materials, pebbles for boulders etc.
Water has been a problem for VFX since the early days, but seascapes have always been in demand. Any aerial view of the UK's Pinewood Studios, for example, is dominated by its huge 806,000 gallon exterior tank with infinite horizon, which is dominated in turn by Europe's largest green screen behind it (the studio also has an underwater filming stage with nigh on perfect filtration for shooting astonishingly clear underwater and space scenes).
The big challenge is making water scale down, or at least appear to scale down. Waves are produced by fans, with detergent sometimes added to produce foamy crests, though these only last for a short while before unrealistic ripples caused by reflections from the sides of the tank are introduced (baffling is never perfect). Storms and tsunami are produced using flood tanks which can dump gallons of the stuff into tank in very short order.
Higher framerates help mitigate many of the watery problems, with anything between 75-125fps giving quite good scaled water, while ships tend to be built as large as practical to further minimise the dreaded 'small water' effect. This means they zip around the tanks at a fair old rate, typically towed by underwater cables, though wee pumps also tend to be added to the models and used to help strengthen the effect of the bow slicing through the water and the wake spreading out behind.
Lastly, many tanks have a sinking hole in the middle, as scuttling some of the behemoths that sail round them can prove difficult otherwise. Pinewood's standard 1m depth surrounds an 'inner tank' that is double that, for instance.
And while we're talking about tanks, they were also for a long time the most effective way of creating clouds. First off, you take a large tank and carefully - and this is a very delicate process - add a layer of fresh water on top of salt water. Inject various different types of dye into the tank and it sinks until it hits the saline layer where it then spreads out and creates the illusion of bruised and battered storm clouds roiling towards the lens.
Up, Up & Away
Spaceships and aeroplanes: you build them, then you have to fly them, and the traditional way is via wires.
As you might expect, this is less than easy. Tension has to be kept in the wires to prevent the model wandering about in the sky, meaning effectively that it has to be constantly accelerating or decelerating. And then you have the job of hiding the wires. Pre-digital that was done in a variety of ways: smearing vaseline over part of the lens, smoke, a glass matte, or even using small motors to vibrate the wires at a high frequency (though this of course required a model heavy enough not to be affected).
Blowing Things Up - the Model Version
The movies being what they are, once you have lovingly built all this detailed, miniature stuff, it's usually time to blow it up in a variety of interesting ways.
Again film speed is a major consideration, with the rough rule of thumb that the smaller the scale of the model, the faster it will be filmed. Most also tend to be pre-exploded, in other words the models are pre-weakened along certain stress lines so that it blows up in exactly the way the director wants.
Petrol is one of the main ways of blowing things up, with various chemicals added to the mix to produce different coloured explosions along the way, alongside various bits and pieces of the model leftover from the build to simulate debris. All this is usually stuffed in a tube called a mortar to shape the explosion. Detonator cord can also be used, which is wonderfully stable and safe until it's hit with a solid object and, due to its remarkable explosive speed (7000 metres per second), is often used for the more destructive form of explosion...
Blowing Things Up - Full Scale
All of which brings us to the world of the full scale practical effect and the serious art of movie pyrotechnics. Most of this is based around the admirably descriptively named 'black powder', essentially a mix of charcoal and potassium nitrate to which are added the same sort of chemicals as above to produce different coloured effects. In the main it produces a powerful blast with a bright flash and plenty of smoke, with petrol often added to create the de rigeur fireball. Other petroleum derivatives such as isopropanol can also be used sometimes, which bring the added benefit of burning up extremely quickly and not raining down on scenery, performers, surrounding countryside, wildlife etc.
Black powder is usually used to crash cars as well, an explosive charge firing a wooden pole out of the bottom of the car and flipping it over at exactly the right point. In fact, it's used for most things until you get to water-based explosions, at which point genuine high explosives are used tethered very firmly to the sea or river bed.
Adding Atmosphere & Weather
As anyone who has watched anything to do with vampires on TV knows, to get atmospheric effects such as fog and so on right digitally takes money that a lot of TV productions don't have. Which is why dry ice is still used quite extensively: dropping it in warm water will create dense clouds that dissolve quickly, cooler water gives you less fog that hangs around longer.
Rain is created just as you would expect, via hoses, sprinklers, bars and the like ('rain machine' is a bit of a falsely grandiose term most of the time, though spinners exist that can give a nice 360 degree deluge on command) with the artificial stuff tending to have slightly larger droplet size so that it looks good on film. Downpours are usually confined close to the lens, with only enough used beyond the resultant rain curtain to look realistic.
Wind machines are, as you would expect, giant fans essentially, though some of the converted aircraft engines used for the larger productions take this to a fairly ludicrous degree.
Snow remains a big challenge, though the fake stuff is still infinitely easier to film in than the real thing. Ground snow can be made from several different substances, including paper, which is a bit of leap upwards from the powdered asbestos that was popular in Hollywood for several decades before anyone realised how lethal it was. Falling snow tends to be used less often, though companies such as SNOWboy have made it a successful niche market with their primarily water-based Snowfluid. You can rent various machines to disperse it around from them, everything from a £75/day unit suitable for a small set (or indeed a children's party) up to their Brobdingnagian Snowtruck which costs £800/day and will cover a 40m radius with the white stuff.
Making it Up
Lastly, the role of make-up should never be undersold in cinema, especially given how it is involved in absolutely every single scene you will ever see. For VFX in particular, special effects make-up hasn't looked back since the invention of foam latex in the 1930s.
In many cases it's an area where digital has had less of an impact than you might expect too. For all its pioneering work in the virtual world, for example, the dwarf make-up for Peter Jackson's Hobbit trilogy produced by Weta's in-house wizards required over four tons of silicone in making the casts of the faces. As the normal head: body ratio for a dwarf is 5:1 as opposed to a baseline 8:1, Thorin's band were expanded sideways, with big ears and large wigs used as a 'cheat' to make the heads seem bigger, while the actors also wore prosthetic hands.
A differing level of prosthetic enhancement and beard pattern was deployed across the thirteen in a bid to make sure that they could be easily told apart by the audience, while the team also had to pioneer a new technique to blend the prosthetics and human skin at the sub-micron level to ensure audiences wouldn't notice the transition between the two at 48fps.
In other words, no matter how far we've come digitally, there will still be gruesome tales of actors getting up in the middle of the night to spend hours in a make-up chair having various latex and silicone components glued to them before they can start shooting.
Some things never change, computers or no computers.
Tags: Post & VFX
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