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Flashmotion – Or: How to Speed up Your Camera

Logo http://tutorial.fsp-fel.de/flashmotion
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High-speed cameras record some thousand frames per second. The more frames per second they shoot the more details are visible when the movie is played at normal speed. The results are impressive slow motion recordings. The downside is that professional high-speed cameras can cost as much as a full-fledged family car.
The good news: You don't have to spend that much money to produce a slow motion movie. All you need is your standard digital camera, your mobile phone, a simple DIY flash unit and a little time. With this more affordable equipment you will be able to produce slow motion movies with 1000 frames per seconds. In addition the images will all be in color and in full HD quality at the very least. 
It’s simple. Just follow our Flashmotion tutorial! 

Before you start, please read our Disclaimer / Haftungshinweis.

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Flashmotion is a do-it-yourself version of a technique which was the key for Ahmed Zewail to win the Nobel Prize in Chemistry in 1999. The technique he used, also known as the pump-probe technique, enables scientists to make super slow motion movies of chemical reactions, exploding nanoparticles or plasma phenomena.
It is also an essential technology in our  research with free-electron lasers.With their ultrashort x-ray flashes we resolve smallest time steps that fit into a second about as often as a bee's wing swing in human life time. Thus movies at 10 trillion frames per second are possible!

Want more background on the pump-probe technique? See how scientists recently observed magnetic memory,spin waves,exploding nanoparticlesand got a record entry at Guinness.

Learn to use the Nobel Prize technique at home ...

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First: Instead of shooting in a permanently illuminated room we shoot in the dark and light each frame with a short flash. That’s why we call it Flashmotion. Second:  We don’t shoot all the frames in one go, like a movie camera does. Instead we repeat the motion over and over again. In each cycle we capture a different moment. If we do this skillfully we can record the same individual frames that a high-speed camera would deliver. At the end we align all the frames using movie editing software: The result is a movie!
We always trigger the camera a short period after the motion has started. This short period – the »delay« – is the key: We increase the delay in precise small steps for each new cycle. Thereby we can capture (almost) any moment of the motion. Controlling the delay means zooming in on time.

Enough theory. Let's get started with Flashmotion. On the next page you will find an illustration of the ideas behind pump-probe and Flashmotion.

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Before/after view

It’s not Rocket Science

Don't worry, even if you’ve never soldered before, you can do this.
Start out with your electronics components as shown on the left and assemble them as shown on the right. The pulse amplifier is shown above, the flash below. Move the arrow to see how to arrange the pieces.

See where things go

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Do you need more background information? The following FAQs will give you some useful facts in addition to our »Behind the Scenes« video. Alternatively move on to the flow diagram beneath or browse through the résumé on the next page.

Workflow cycle edit
When you hit the play button two beats begin a journey from the smartphone (a), each through a different stereo channel. When they reach the pulse amplifier (b) they are steered towards the magnet and the flash respectively. As soon as the pulses reach their destinations the magnet (c) drops the astronaut and almost instantly the flash (d) illuminates a particular moment of the falling motion. This moment is captured by the camera (e). The timing of the moment is determined by the delay between the two beats in the song file. The next sound file (f) in the playlist will also have two beats, but with a slightly longer delay.
Fullscreen

How do I do Flashmotion in practice?

Short answer
Trial and error! In addition to »learning by doing« you can have a look at our TIPS & TRICKS document.

Long answer
Follow these steps

> get your equipment ready,
> switch off the lights,
> open the camera shutter,
> play the song,
> wait for the astronaut to land, and
> switch the lights back on.

Congratulation on your first snapshot!

> move to the next song in the playlist,
> attach the astronaut back to the magnet,
> get your equipment ready… and so on.


How does the camera record an image?


Short answer
Dark – Bright – Dark! While the camera shutter is kept open.

Long answer
In Flashmotion the camera shutter is hacked by using a self-made flash. This allows the electronics to do the timing. Keep the camera shutter open for about a second, so that it can record the moment, that certain moment, when the flash occurs. Small downside: You need to shoot in complete darkness.


How do I time the flash relative to the drop?

Short answer
Loud – Quiet – Loud! The timing is stored in a number of two-beat audio filesthat you play in sequence using your smartphone. In each file the first beat triggers a magnet which drops the astronaut, the second beat triggers the flash which lights up the scene. Select a song = select a moment.

Long answer
The songs in our playlistare probably the most minimalistic tracks ever composed, but they are also very effective: By choosing a song you determine the exact moment that your camera will capture.
Each song (wav-format) is nothing more than a moment of silence between two short beats which are used to initiate the fall and the flash. The crucial part of the song is the duration of the silence between the two beats: the delay. The number in the filename indicates the duration of the delay in milliseconds. For example: Using file delay050.wav means the flash trigger beat will arrive fifty milliseconds after the magnet trigger beat. The delay increases throughout the playlist in steps of milliseconds and determines which instant of motion you record. Hence you can capture almost any moment by going through the playlist and repeating the recording steps. It takes persistence to record enough frames but the reward is a real slow motion movie.
Note: You can use any .wav playing device with a headphone output. If it doesn’t work with your phone, try a tablet or a laptop instead.



How do the home-made electronic devices work?


Short answer
The home-made pulse amplifier boosts the power of the trigger beats in order to operate the magnet and the flash.

Long answer
When you play the audio files your phone sends out two sequential electric pulses – these are the trigger beats. They propagate through the audio cable in opposing stereo channels. At the pulse amplifier (one of your home-made Flashmotion devices) this signal is split: The first beat travels to the magnet, the second to the flash (the other home-made Flashmotion device). Furthermore, the pulse amplifier adjusts the signal amplitudes in order to make magnet and flash react. As you’ve already guessed, these components respond with magnet release and light flash respectively.


Browse the résumé on the next page.



Workflow cycle edit
When you hit the play button two beats begin a journey from the smartphone (a), each through a different stereo channel. When they reach the pulse amplifier (b) they are steered towards the magnet and the flash respectively. As soon as the pulses reach their destinations the magnet (c) drops the astronaut and almost instantly the flash (d) illuminates a particular moment of the falling motion. This moment is captured by the camera (e). The timing of the moment is determined by the delay between the two beats in the song file. The next sound file (f) in the playlist will also have two beats, but with a slightly longer delay.
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