This video is about measuring the lag between when a flash is triggered and when light is emitted from that flash. I show the setup I’m using to measure this and then I measure this flash lag for a Yongnuo YN460, Canon 580EX, and a Canon 580EXII. I found the flash lag to be around 50-60 microseconds which is 1000x faster than your typical shutter lag.
Other related videos:
* Understanding Shutter Lag