Water Splash Photography

Two drops of water colliding, frozen in time using the power of high speed flash photography produce an infinite variety of shapes. While this can be done with a pipette, a camera, a single flash gun, practice and good hand/eye co-ordination. I have an Arduino Uno and I am going to use it. IMG_8887What is happening in this picture? Two carefully timed water droplets have been released from above and are plummeting towards a bowl of water. The first drop has hit the water and is rebounding, just as the up-spout reaches its zenith, the second drop collides with the top resulting in a mushroom shaped splat, with the event captured in the camera with a frame of 1/10,000th of a second. In this post I’ll be sharing my experiences in creating these water drop images, I’ll be looking at the photography equipment, electronics, and technique.
up meets down

Photography Equipment

Camera: This can be any DSLR or advanced compact, it must have Bulb mode, and be triggerable by an electronic wired connection, some have an IR remote but I found this to be difficult to setup. Set the ISO to be around 200.

Lens: I use a 100mm Macro, with focus set to manual and image stabilisation off. The aperture is set high, at least f22 to give a suitable depth of field and improve image sharpness.

Tripod: A good solid one with easy to adjust ball head.

Flash: I use up to five flash guns for my photos, two for back light, one to give an under-light through the glass bowl, another for front light and finally one handheld. Rechargeable batteries for the flashes are recommended, I use 2400mAh NiMh Duracells.

The flash guns need to be in manual mode at their lowest power setting, this is to give the shortest duration of flash for the sharpest results. As you increase the flashes power the duration of the light emitted gets longer, causing burred images. On my Canon flash I set it to 1/128 second and on the Nissin Di622 set the EV to -1.5.

6N2A5694  6N2A5698

For connecting the Arduino to the flashes I use a 2.4GHz wireless remote trigger, with four receivers and a modified hotshoe mount attached to the transmitter Look for the Yongnuo RF-602 Remote Flash trigger on ebay, (not to be confused with the remote shutter release).  Most modern TTL flash guns appear to be missing the wired remote trigger connection that you can just plug into.

The flashes also have a built in slave trigger, where it sees that one flash has gone off so it set itself off too. On the Canon flashes this appears to only work in ETTL mode and can’t be used for this, but the Nissins work well.

Hardware

The frame is bits of wood held together with glue and stands about 75cm high this is to allow the water to accelerate and produce decent sized splashes. At the base is an extra large seed tray, the type without holes, to contain any spillages. This normally has a glass bowl full of water acting as the drip splash event zone. Halfway up the fame is mounted the laser and detector and at the top a reservoir of water and solenoid valve.

The reservoir is a one litre plastic storage tub from Poundland with a hole drilled in the base and a short length of 8mm PVC tubing hot glued into place. The tubing can be difficult to glue as its rather flexible, pushing down a short section of solid tube made from the outer of a disposable biro fixes that. This pipe is connected to the solenoid, observing the correct direction of flow marked on the valve.

The reservoir has a Mariotte Syphon fitted to the lid, this is to provide a constant and stable water pressure to the valve, the pipe from the lid ends about 2cm short of the reservoir base.
resevoir

Electronics

The Arduino and control electronics are all set to produce this photo taking sequence:Trigger Prototype

  1. press ‘play’ button on remote control
  2. lights out – dark room
  3. open shutter on camera
  4. solenoid releases two drops of water
  5. drips pass through laser detector – timer started
  6. drops arrive and do their thing
  7. flash guns triggered by timer – picture taken
  8. shutter closed on camera
  9. lights on

The electronic circuit can be broken down into these five blocks; lights, laser, IR receiver, solenoid control, flash control, camera control, each diagram shows the label name for the pin used rather than a pin number. The diagrams can be enlarged by clicking on them.

IR Receiver: The IR receiver allows use of an old TV remote control. My original design was to have a rotary dial and a small OLED display, but this simplified everything considerably. If you don’t have a spare remote one can be gotten from Poundland. I have the Arduino send any text output to a laptop on the USB port.

ir_rx

Laser: Warning: keep away from eyes, permanent damage can occur with exposure to any laser. The laser is used with a photo-transistor to detect drips of water as they plummet to their splash event. I used a small 3 Volt 5mW red laser with a built-in lens, I have added a resistor and diode in series to prevent over voltage as they’re a bit delicate. Although a modified laser pointer will do just as well. The TEPT4400 phototransistor is a type rated for visible light and has higher sensitivity to change than a photoresistor.

laser control
Laser Control

Lights: Warning: Mains Electricity Can Kill, this is to be avoided. If you are uncertain about this part then don’t do it. I rapidly found that working in darkness between shots just made life difficult, and finding the light switch became a hassle. To fix that I got a pre-made 5v Relay circuit and wired this up to a table lamp to provide some illumination. Using a standard wall socket and backbox connect live through the normally open side of the relay, and the neutral and earth to the socket.

 6N2A5700 6N2A5705

Remember to keep the electricity away from fingers (and any other body parts) and water.

Solenoid Control: I use a 12v solenoid, (search for “12v solenoid valve water arduino” on ebay, a couple of sellers have suitable models with connectors included). I use a mosfet transistor to switch the power, this has been detailed in one of my previous blog postings.

solenoid_control
Solenoid Control

Flash and Camera Control: The electronics for the camera and flash are closely related. Both use the ILD74 optocoupler to electrically isolate the camera and flash equipment from the Arduino. Although the camera focus connection is not used here I have included it as it may be useful later on.

camera control
camera and flash

The Canon camera has two different types of wired connection on the shutter release depending on the model of camera, a standard three pin 2.5mm jack or a N-3 connector (search for “canon N3 connecting cable” on ebay). A list of connectors for other makes of cameras can be found here.

canon remote
Remote shutter connections for Canon

Sound: Although not used here, this setup works well with a piezo microphone for use with popping water balloons and the like, use a buzzer that is enclosed in a plastic housing with a hole on top and buzzes when DC power is applied. Connect the output to an analogue pin on the Arduino, your software can use a very similar method to that for the laser.

sound
Sound Detect
water balloon pop
Balloon pop with sound detector

Setup and Use

Have plenty of dish cloths or towels to hand, this can get a bit moist. Keep an eye on your camera equipment making sure it doesn’t get wet.

For setting up a shot I use a steel ruler with a magnet stuck to it I set the water dripping to make sure it lands where I want on the magnet, the camera is then focused on the magnet, take away the ruler and you have your properly focused splash event.

IMG_8502
Splash Hat on Magnet

Add colour with food dies, adding these to the reservoir seems to work best and keeping the water in the splashdown area clean. Guar Gum thickens the water and makes larger drops and bigger splashes, you only need to add a small amount, about a teaspoon per litre and you’ll need to sieve out any lumps before use. Fluorescein is quite entertaining when used with a UV lamp, adding a green glow to your splashes. Adding diluted water based paints to the reservoir can add a lot of colour, but has a tendency to block the solenoid.

Sparkly backdrops can be gotten from the craft section in stationers. An A4 sized (21cm x 30cm) sheet is normally enough. Try bouncing the flash off the backdrop.

It is all about experimentation, expect to take lots of photos, many of which will be poor. Make notes of timings when you get good results, when you get a good shot, very small changes in timings can produce fairly dramatic effects.

Software

Here is an Arduino sketch, press Play on the remote to start a two drip sequence. adjust the amount of time in milliseconds between the laser detect and flash – flashWait with Volume +/-: +10,-10, Channel +/-: +5,-5, Fast Fwd/Rev: +2,-2, and the time betweenDrips with 4 (+1) and 7 (-1).

Links and Sources

My water drop photos on flickr:

Two Drops of Water

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