I dunno how to explain this professionally coz am merely new to this technique. My husband could explain it better but he's not here right now.
So, we had this session few weeks ago for a book cover project that I was working on. They wanted a rain droplets but I was running out of time. And to look information for the next rain fall is not what I wanted to do. So my husband offered to help me capture homemade rain droplets. So he construct a homemade strobe. We used the flash light as external lighting and set our kitchen to pitch dark. We set the camera to a bulb mode for super-long exposures: the shutter remains open for as long as the shutter release is pressed; in our case we use remote control. We set the ISO to 200. My husband's main task was to hold a bag of water on one hand and to handle the flash light on the other. My task was to press the remote control soon as he presses the flash light and continue doing so until his hands are all cramped. Before we began capturing, we focused on an object in the middle of the tray so that we get a focused image of droplets later. We used 55mm lens.
This is our kitchen :PAt first we used, blue tray but the images were not good; here's a sample:

We need something without color, so we switched to white tray (luckily I have two trays at home; yup they're IKEAs). But my husband was not satisfied with the outcome:

Then he had this idea of putting black cloth beneath the tray. It was better!

Got even better over times and cramped hands.