The Science Behind How Pop-Up Flashes Can Optically Trigger Off-Camera Flashes

Your camera may have the option to trigger off-camera flashes using the built-in pop-up flash. It’s a system that works wirelessly, but not by radio signals. Find out how the camera’s optical trigger is able to communicate to external flashes in this self-proclaimed super-duper nerdy video.

In this video by Roger Nieh for Science’n’me, he examines what really happens when you trigger the pop-up flash while the camera is in wireless flash shooting mode. Using a oscilloscope, Nieh is able to analyze and decode the pre-flash signal pattern that is rapidly emitted when the shutter button is pressed. Using this information of Canon’s communications protocol, he takes it a step further and also emulates the trigger by using a microcontroller that he has programmed. In the end he is able to trigger a flash without the camera’s pop-up flash, and just through using an infrared LED on his microcontroller chip.

The video is an interesting deep dive on how simple yet impressive the wireless optical flash system works. Were you surprised that it could be hacked by anyone and rebuilt? I thought for sure there was more to it. Leave your comments below.

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kevin hoehne's picture

My head hurts after watching that video.

Jon Kellett's picture

Cool vid, though I wonder how many it would appeal to.

Looking at his assembly code reminds me of why I love and loathe assembly in equal measure.

John Dawson's picture

Very cool!