Canon 580EX compatible with xxxEX II flashes?

Question

I've got a Canon 580EX (original, not the II) flash, and now I'm interested in adding a slave flash. I stopped by a camera store this evening to look at the 430EX II, but the salesman advised me that:

• an important difference between the xxxEX and xxxEX II flashes is that the latter uses a new communication protocol

• due to the previous point, the 580EX won't reliably trigger a xxxEX II slave; it'll probably work some of the time, but it won't be dependable

• ETTL only works with multiple 600EX RT units; lesser units don't communicate about exposure

• most photographers use Pocket Wizards specifically because they preserve ETTL

All this came as quite a shock as I've always understood that a big advantage of Canon's system is that the body and Speedlite work together, etc. It seems unlikely that Canon would update their line in a way that's not backward compatible. So I went home and reviewed the manuals for the various units. It's pretty clear that the guy simply doesn't know what he's talking about on the third and fourth points; all the Speedlites seem to support wireless ETTL-II. But what about the first two points -- can I expect my 580EX to work well as a master with a 430EX II slave?

Answer 1

The 580EX should work just fine as a master unit to the 430EXII. Let's go through the bunk the salesman told you:

...an important difference between the xxxEX and xxxEX II flashes is that the latter uses a new communication protocol

This is a difference, but not one that breaks compatibility with the Canon optical wireless signalling protocol on older units. The communication protocol here is the one between the flash and the camera that allows a camera menu to be used to change settings on the flash. This also, btw, only works if the camera body is Digic 4 or later.

due to the previous point, the 580EX won't reliably trigger a xxxEX II slave; it'll probably work some of the time, but it won't be dependable

This is an outright lie. From the Canon Europe website (bold mine):

There are several Canon flashguns – plus one Speedlite Transmitter and an Integrated Speedlite Transmitter – that can be used as master units in the Canon optical wireless flash system. These are the Speedlites 550EX, 580EX, 580EX II and 600EX, Macro Ring Lite MR-14EX, Macro Twin Lite MT-24EX and Speedlite Transmitter ST-E2. An Integrated Speedlite Transmitter is found on the EOS 7D, EOS 60D, EOS 600D and EOS 650D DSLR cameras.

The ST-E2 and 550EX have less function than the later masters (only A:B groups and ratios; no C group or manual power ratio control); but they remain compatible.

ETTL only works with multiple 600EX RT units; lesser units don't communicate about exposure

Another lie. The eTTL-II protocol remains unchanged for the 600EX-RTs. What was added was an entirely new radio protocol with additional capabilities. The only features the older units cannot access are the ones that were added with the -RT and 2012+ camera bodies: groups D & E, ID codes, using the flash as a shutter release, Groups mode, and the RT radio communication protocol itself.

most photographers use Pocket Wizards specifically because they preserve ETTL

Again a lie, if he didn't specify which specific Pocket Wizard models he was talking about. The Plus, Plus II, Plus III, Plus X, and MultiMax units are all Pocket Wizard manual triggers, and professional photographers use them for their reliability and range, not eTTL. And, in fact, to judge by POTN board postings, most Canon hobbyist shooters who want eTTL radio triggering are either going to the 600EX-RT/ST-E3-RT gear, or the el cheapo Yongnuo YN-622C triggers to accomplish this, given the interference issues that the TTL PocketWizard units have with the 580EXII.

Answer 2

Were you at BestBuy by any chance? It sounds like the guy wanted to sell 600EX-RTs. As far as I know, the optical sync system has never changed, at least in a compatibility breaking way. The new RT system supports some features that the optical system didn't support, but it only works between RT units which are currently only the 600EX-RT.

I don't have an older unit to test with, but I would expect that at worst, some control features that the newer flash supports might not be available, but I believe the basic firing protocol has been the same since the start of the system.