Standard, Master and Slave Flash Modes
A speedlite can have 3 operating modes:
(i) Standard (on-camera with wireless turned off)
(ii) Master (wireless) – can control other speedlites
(iii) Slave (wireless) – can be controlled by a master speedlite
Not all speedlites include all three modes. Very basic speedlites may only be able to be used in the standard on-camera mode. Some can only be used as slave units and other more advanced models can be used in all 3 modes: on-camera, as a master and as a slave unit. I’ll explain what the three operating modes are below.
Standard Operating Mode / Wireless Off
When placing a speedlite into the hotshoe on top of your camera it will automatically default to standard mode. The camera assumes the speedlite is working on it’s own and not in conjunction with any other speedlites. It will stay in this mode until you tell it otherwise. When the speedlite and camera are compatible (e.g. Canon speedlite used on a Canon EOS camera) the camera can pass information about lens type, focal length, sensor size and exposure readings to the speedlite which will help in achieving a correct exposure. The camera can also pass on information about the distance to the subject, and in low light conditions the speedlite can fire a pattern of infra-red light at the subject to help with focusing. Many of the speedlite settings and functions can be controlled from the camera’s menu.
The standard operating mode works great when you are using just one speedlite. However when you introduce a second speedlite the speedlite mounted on your camera can be switched to master mode (if it has this function) which will then allow it to control the settings of the second speedlite without you physically having to go over to the second speedlite and make changes to the settings. The second speedlite has to be set to slave mode so it knows to look out for instruction being sent from the master. A master speedlite can control many slave speedlites at the same time. This is done dividing the slaves into groups. The Canon 600EX ii-RT has the ability to control up to 5 groups with a maximum of 15 speedlites in each group !
Communication between the master speedlite (on the camera) and the slave speedlite is by wireless communication. The wireless signal can either be by using radio waves (which are more efficient and can travel up to 100m) or by using an older optical system of short bursts of flash (strobe). The optical wireless master speedlite literally send out short pulses of light strobes in a similar way to morse-code that is then understood by the slave unit. Canon first introduced their optical wireless EX system on the Canon 550EX back in 1998. This very same EX system is still incorporated on their most recent speedlites although their much newer RT 2.4GHz radio communication is more reliable and able to travel further distances.
When setting the master speedlite to master mode you also have to select the form of wireless communication that is going to be used. i.e. select either radio master or optical master. Older speedlites such as the Canon 580EX II or the Canon 430EX II only have optical wireless, whereas the newer speedlites such as the Canon 600EX II-RT can act as either radio master or optical master. The Canon 430EX III-RT can only act as a radio master.
Before a speedlite can be used as a slave unit it has to be set to slave mode. It’s also important to set it to the same method of radio communication. If using a radio master then the speedlite needs to be set as a radio slave. If using an optical master then the speedlite needs to be set an optical slave. Once this has been set and the master and slave can communicate together you can forget about the slave speedlite apart from positioning it. All slave settings can now be controlled on the master speedlite.
A full featured speedlite such as the Canon 600EX II-RT can have 3 operating modes which are: On-camera wireless off, wireless master and wireless slave. Wireless communication can be either optical pulse wireless (EX) or radio wireless (RT).
Therefore if you press the wireless button on the control panel of the 600EX II-RT you will be given the following options which, hopefully, will now make complete sense to you.
- Wireless off – (standard on-camera mode)
- Radio master
- Radio slave
- Optical master
- Optical slave