Here’s the set-up for the Water Drop Collision shots.
There are two Yungnuo flashes (YN460 & YN465) – one triggered by the Arduino unit on the left when it detects the laser beam being cut. The YN465 & the Arduino are connected via a PC Sync cable. The second flash on the right is in ‘optical slave’ mode.
The shot is taken in a dark room, with the camera on bulb mode and manually pre-focussed.
The laser is held on with a piece of tape, and pointed at the light detector. The dropper is lined up so the first drop will break the beam. The arduino trigger was set to ~140-160ms delay from detecting the laser beam break to firing the flash.