The principle is simple, when the optical slave sees another flash fire, it fires too. Kinda like yawning. Once one of goes, it is catchy.
Of course optical slaves have their limitations, one of which is that they are too dump to understand the difference between a flash and a pre-flash. There are a few more limitations to optical dumb slaves, but this post is about overcoming the pre-flash issue with a cool gizmo called Arduino. [Read more...]