Why does a non-firing Speedlite master still flash?

The master flash still flashes even when set not to…

When using the pop-up flash or another Speedlite flash as a master to control slave flashes off-camera it is necessary for the master to send control signals as pulses of light. The pulses come from the master flash’s main flash tube.

Could someone please explain how to turn off internal flash and use just slave flash on the 650d using the 430ex. I know the flash should be up but how do you stop it firing or can it be done?

Thank’s in advance.

- Josephine

The quote above was left in the comments on my popular Better Looking Pictures with Easy Wireless flash article, so here’s the answer.

If you have an EOS 600D, EOS 650D, EOS 60D or EOS 7D then that is the camera’s pop-up or built-in flash that emits the pulses. If you are using a Speedlite 90EX, 550EX, 580Ex, 580EX II, Speedlite 600EX, MR-14EX or MT-24EX as the master then it will also illuminate it’s flash tube to send the control signals to the slaves.

Non-firing master confusion

For the cameras with built-in Speedlite transmitters, and for each of the Speedlite master flashes, the master can be configured as a non-firing master. This would make you think that it won’t fire at all. However the master flash still needs to send the pulses of light to the slaves instructing them what to do. There are several kinds of commands that a master flash can send to make E-TTL II work. In simplistic terms the messages sent as coded pulses are something like these listed below.

  • Slave please fire a pre-flash
  • Slave please go to manual mode or E-TTL mode
  • Slave please set a specific power level (E-TTL II calculated or manual power level)
  • Slave please fire now

These message have to happen in order for the slave flashes to work, so the master will still have to fire to send the messages, but if you set it as a non-firing master, it will not add additional light from itself to the exposure.

The way E-TTL II works, the camera sends the commands to the flashes after the photographer has pressed the shutter to take a picture. These commands happen in rapid sequence.

EOS 600D & EOS 650D Easy Wireless

If you set the EOS 600D or EOS 650D to the Easy Wireless mode then it sets the camera as a non-firing master, but obviously the built-in flash will still appear to fire.

Make sure to read these other articles to find out more about Easy Wireless flash…