Canon Optical Wireless Systems
As we’ve seen in the previous section there are plenty of different radio communications systems available. Some support just simple manual flash firing while other are able to communicate all the information required for full E-TTL II metering and flash head zoom settings. Most manufacturers have their own proprietary system and some such as Yongnuo having several systems that incompatible.
When it comes to optical wireless communication things are much simpler. There are two main systems: Canon optical wireless compatible with their E-TTL / E-TTL II metering system and Nikons optical wireless system compatible with the Nikon I-TTL metering system. On this website we’ll just be discussing the Canon system.
Canon Optical Wireless (EX)
Before radio wireless communication between speedlites became popular the original method whereby a master speedlite could communicate with a slave speedlite was using a series of very quick light pulses a bit like a strobe light. This method is still included in the many of the more recent speedlites together with radio wireless system. The light pulses work in a similar way to morse code since it’s the spacing of flashes that contains the instructions to the slave unit.
The Canon 580EX II can function as an optical master and can control optical slave speedlites such as other Canon 580EX II or the Canon 430EX II. The Canon 430 EX II can only act as an optical slave and not an optical master.
Canon optical masters:
Canon 580EX II, Canon 580EX, Canon 600EX-RT, Canon 600EX II-RT and the Canon ST-E2 transmitter.
Canon optical slaves:
Canon 580EX II, Canon 580EX, Canon 430EX II, Canon 430EX, Canon 600EX-RT, Canon 600EX II-RT, Canon 430EX III-RT, Canon 470EX-AI.
The Canon ST-E2 is a optical transmitter. Rather than firing pulses of visible light it fires pulses of infra-red light which can’t be seen. The Canon ST-E2 is much smaller and lighter and more convenient to use on your camera compared to a Canon 580EX II speedlite. It also incorporates the infra-red auto-focus assist beam which is useful during low lighting conditions.