Canon DSLRs can trigger Canon Speedlites using the pop-up flash. If you try triggering those same Speedlites with a different camera’s flash, it doesn’t work, which means that there’s actual light-based communication going on between the DSLR and Speedlite.
In this 9-minute video, Roger Nieh of Science’n’me explores the technology behind this communication. “Have you […]. petapixel.com