A user on the Arduino forums built this high-speed photo flash trigger –
I used Arduino to build a trigger for my camera’s flash. It turned out to work really well! The write up includes an explanation of how camera triggers work and the benefits of using Arduino. One benefit of using a microcontroller like Arduino is that it’s easy to have multiple sensors and then have intelligent triggering algorithms.
See the code & more info/pics -Triggering a camera’s flash with sound and light
In the Maker store: High-Speed Photography Kit Version 4