Ahh, OK. The StopShot is an intervalometer ("fully programmable 3 channel" controller) that can be purchased from Cognisys here: [link]
. The water droplet kit can be seen here: [link]
. Basically, you pass the droplet(s) through a sensor that triggers the first of StopShot's timers. You set that timer for the amount of time it takes for the droplet to travel from the sensor to the water, and when that time is reached (which you can program to the millisecond) you have StopShot fire the camera and/or flash(es).
You then of course run into things I'd never even considered before, such as the variable time it takes for my camera's shutter to fire, depending on what other functions I've got enabled, and whether it's the first shot in a series (which for some reason always seems to take longer by about 15 milliseconds). But hey, that's all part of the fun