I've been having trouble getting repeatable results....I can get a nice collision image perhaps one or two times in ten attempts, but I'm not sure why I can't get the same style of collision with every image taken.
You could try splitting the camera shutter and flash firing. Operate the camera shutter immediately and the flash after the delay.
Another alternate is to separate the timing. Drips can be fired as per your code, but time the firing of the flash from when the first drop breaks a light beam. You could use a photo-interrupter (they do ones with a wide gap) or use a separate IR LED and transistor.
Have fun & don't mix up 5V, 3.3V and 12V )