Wetenschap - 21 april 2011

Time travel by camera

High-speed filming is a form of time travel: you find yourself in a timespan in which seconds last for ever and flight suddenly seems like an art form. The participants in the Wageningen project 'Flight artists' will have a chance to experience this in the course of the coming months. And Resource gets to look over their shoulders.

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Foto: .

'You are all experienced with film or photography. Well, forget what you know about it. High-speed film is something else entirely. Remember the technique but forget everything else.' It is nine o'clock in the morning. In a small room at Zodiac there are nine course participants. The happy few. These nine are among a select group that is to be allowed to spend a couple of days in the field with the Phantom, an extremely pricy high-speed camera belonging to the department of David Lentink and his Flight Artists (see text box: The Art of Flight). Outside the sun is shining, but the course is scheduled to go on until nine o'clock this evening. But it will be worth it, says Lentink encouragingly. 'You are going to see things nobody else has ever seen.'
For example: Lentink shows a film of a fruit fly that is just about to fly away. Look carefully, he warns. The tiny fly sticks one of its wings straight up in the air, waits a second and then flies off. 'Never seen by anyone before', says Lentink with a triumphant glance around the room. 'Every time, first one wing and then the other. You see things you have never seen before. And that is the kick you get out of high-speed filming.' The reason is that what we see comes about through the vast number of frames per second with which the image is created. In this example there were 5,000 frames per second. Playing the film at the normal tempo of 30 frames per second then gives a tremendous degree of slow motion. One second is spread over nearly three minutes: an eternity. Or, in Lentink's words: 'You zoom in on a tiny moment in time and enlarge it hugely.'

Nocturnal filming
Jeroen Voogd from Ede sees quite a few things no one else sees, actually. He studies nocturnal life and can be found, once a week on average, in the pitch dark at Planken Wambuis on the edge of the Veluwe moorlands. There he spreads out a sheet of two by two metres and shines three 250 Watt lamps on it. Then he sits and waits. Sometimes he lures the moths by smearing syrup on the surrounding trees. That brings them in. Voogd is crazy about moths and their caterpillars. Always has been. 'I think it is the metamorphosis that used to fascinate me. That a caterpillar turns into a moth just like that.'
Voogd collects the females in order to breed caterpillars at home. He sees a great deal of flapping and flight in the course of his nocturnal adventures, and that is what he wants to film. He pays special attention to the take-off procedure. What you might call the warm-up. Voogd: 'Moths can only fly if their muscles are warm enough: about 30 to 25 degrees. Butterflies use the sun for this. But moths do it by vibrating their muscles.'
All the course participants have their own story, and their own reasons for wanting to make use of the Phantom. A birdwatcher wants to see how hoverflies keep still in the air. A teacher at the film academy wants to film the way mosquitoes escape from being swatted with a newspaper. An artist is looking for 'what you don't see'. She honestly admits that she doesn't know anything about nature. There are in fact four artistic types in this group of nine, and just one scientist. That is no coincidence, explains Lentink. 'I consciously avoided scientists. What I am interested in is precisely how other sorts of people think and look. That is the idea behind the Annual Academic Prize: involving a broader public in science.'
A full 800 people responded to the call made by Flight Artists for people interested in filming flight behaviour. Ninety of them were selected to do this with the Phantom and the rest will be setting off with Phantom's little brother, the Casio. Which also makes films at 600 frames per second, slowing down reality by twenty times.


Extremely high-speed images
But some training is required: there is quite an art to high-speed filming. Forget about composition, for example, says Lentink. 'You just don't have time for that. If you spend time on the composition, you will miss everything. You have to be ready before you start.' That is a direct consequence of the large number of frames taken per second. For the highest quality (HD) this means up to 7,500, and for lesser quality as much as 22,000 per second. And the camera's memory can 'only' store 10,000 frames (16 gigabytes). So it is a question of 'cut and paste, otherwise your filming day is over in no time', says Lentink. And you have to keep on saving your material onto the hard disc of 126 gigabytes.
But you do not need such extreme high speeds for recording the majority of flight movements, reckons Lentink. 'To get a fluent image of the wing beat of a bird you need forty frames a second. That means that per shoot you can film 250 wing beats before the memory is full.' For insects there are other rules. It becomes clear that when you film at high-speed, you have to weight things up and make choices. That seems complicated but with a couple of rules of thumb, anyone can make a go of it.
The first Phantom filmmakers are setting off at the end of this month. Lentink does not really mind what they come back with. As long as it flies. 'High-speed films are almost always interesting', in his experience. Mating hoverflies, seeds being carried by the wind, fighting flies, hunting raptors. 'Very little is known about even the wing beat frequency of most birds. And with so many people making films there is a big chance that one of them strikes lucky and films something really special.'
The Art of Flight
Flight Artists is a project with which David Lentink and his team won the Academic Prize last year. Lentink wants to give people a new perspective on flight in the natural world by letting them film it with high-speed cameras. Eight hundred naturelovers will be setting off over the coming months, with a high-speed camera (the Casio) or a super-high-speed camera (the Phantom). The collections of videos that this will generate will be put on Youtube. The best films will be shown on TV on VARA's 'Early Birds' programme and will be on display in the science museums Nemo and Naturalis. And a high-speed film festival is planned for next year in Wageningen. All the participants follow a course before they are let loose with the expensive equipment (the Phantom costs 140,000 euros).

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