I was going to post this at some point but a couple of people have asked how I got those shots so here goes.
The basic theory:
The theory behind this sort of photo is to take a picture of something happening that only last’s for about, perhaps, 1/10,000th of a second or less. Of course shutter speeds don’t generally go to this speed, but flashes do. If you have a pitch black room and open the shutter on the camera, obviously the image will be black, at any shutter speed. If you fire a flash during that shutter speed, the image captured on the sensor will be only what happens during the duration of the flash, at any shutter speed.
So the theory is: use any shutter speed, a darkened room, and a flash to capture the moment of a splash. If you have a light(ish) room, a quicker shutter speed will eliminate as much stray light from possible from being captured on the sensor and adding unwanted motion blur to the image.
Exif and Flash Control:
The quicker the flash, the less motion blur there is, of course. External flash will generally have a “Manual” mode, and by using this you can alter the brightness of the flash. As you decrease the brightness of the flash, what is achieved is making the flash quicker, which is desirable. Many flashes will go down to 1/8th or 1/16th power, and this should certainly be enough. Some go further down to 1/128 or so, which is even better. I shot at 1/64 which is as far as my 430EX will go.
If you don’t have an external flash, the onboard flash can be used as well. Go into “Flash Exposure Compensation” (FEC) or similar in the menu, and lower the flash down to as low as you can while still achieving bright enough results. -1 to -1 2/3 should do. If you're using water, however, lighting from behind with an external flash works much better.
Use the flash “test” button to trigger the flash, without it being attached to the camera. For this no other wires/triggers are needed. Set the shutter speed to something with which you can press the shutter, then move your hand to the flash and press the button to fire the flash. Perhaps 2-3 seconds. Again ensure that without the flash the image captured is nothing but pure blackness.
For both, I would use about F/16 aperture – this gives you good depth of field and stops the edges of collisions being out of focus. ISO 100 – use the lowest value possible to give you the best quality results when cropping down.
So, I set up the camera with my 70-300mm Sigma lens set at 300mm focused on a pyrex dish filled with water that had been coloured using food colouring. Behind this I placed a white reflector and bounced the flash off that to light the water from behind. On some of the shots I put a coloured gel on the flash. (I used a dedicated photography reflector but anything white will work - indeed any patterned reflector might give an interesting effect)
My lovely assistant was positioned above the dish with a kitchen syringe filled with water of another colour and when I opened the shutter she let the water drip into the dish. As soon as I heard the drops hit the surface I fired the flash.
A couple of shots of the set up:
The chopping board was to stop white light escaping onto the side of the shot when shooting through the gel.
My final entry was shot using yellow water, dropped into blue (which gradually turned green of course) and no gel on the flash.
It can be quite tricky to get the timing right but if I'd had a delivery system that didn't mean the Mrs had to hold a syringe directly above a 2cm square we'd have got a lot more right. I would have used my reflector arm to hold the syringe in place but I only have one and it was holding the reflector.