Canon’s Speedlite 600EX-RT and ST-E3-RT make a fantastic combination for effortless off-camera flash with more control than has ever been available from a Canon Speedlite system before. Combine this with simplicity, radio that just works seamlessly and only one set of batteries to worry about there is much to like about Canon Speedlite flash, ok price maybe not so nice. To use all the features though you need to be using a 2012 model camera, so that’s the EOS-1D X, EOS 5D Mark III or EOS 650D, what if you have an older camera like the EOS 7D, EOS 5D Mark II or EOS-1D Mark IV?

Radio controlled off-camera flash

So taking a trusty EOS 7D with firmware 1.2.5 as a test camera I set about working out what actually works and what is not working, along the process I found a mid-ground of things that work but aren’t officially supposed to. I’m really hoping that some of the mid-ground things are moved to the “it works” category when the new firmware v2 comes in August.

EOS 7D fitted with Speedlite 600EX-RT as a master

From the camera Flash control menu select External flash func setting  you will be able to set the flash mode to E-TTL II, Manual or MULTI flash (stroboscopic). You can select 1st curtain or Hi-speed shutter sync (HSS), Flash exposure bracketing, flash exposure compensation, evaluative or average metering, the zoom setting for the flash on the camera, and the wireless functions. If you already set up the radio then the Wireless func. will show disable, setting enable will switch the master from radio flash to regular pulsed light type operation, and the only way to go back to radio is using the buttons and menu on the flash.

Sync speed reduced or is it?

EOS 7D with ST-E3-RT showing sync speed warning !Tv

When you use radio controlled mode, the manual says that the effective camera sync speed is 1-stop less than normal, so 1/250s becomes 1/125s sync speed. Choose a shutter speed on the camera faster than 1/125s and you get a !Tv warning on the display of the master flash, but you can set faster shutter speeds right up to the cameras 1/250s. In my tests using 1/160s, 1/200s and 1/250s I couldn’t see the edge of the shutter in pictures.

High Speed Sync (HSS)

Again the manual says HSS is not supported over radio with pre-2012 cameras. Oddly I can set the feature either on the flash or from the camera menu, and all the way up to 1/8000s it works for me. While using HSS you also get the !Tv warning on the master flash display.

Beeping flash

One of  the things I like about the radio flash is the confirmation you get that the slaves are re-charged. It still works on the EOS 7D too. Normally I turn off my cameras beeps, but for flash it’s really helpful to know if the slaves are charged especially if you can’t see them or they are far away.

Ratio control

Speedlite 600EX-RT on EOS 7D set for E-TTL II ratio control A:B

With the older cameras you have the same choices for ratio and groups as you did with pulsed light control, so all flashes can fire at the same power with automatic exposure, you can ratio A:B or A:B C. Even in manual you can set the power of individual groups directly from the master.

Custom functions (C.Fn)

From the cameras menu it is only possible to set C.Fn 01 thru to C.Fn 13. The flash also has C.Fn 20, 21, 22 and 23 plus Personal Functions (P.Fn) which can only be set on the flash itself.

No group mode

A great new feature Canon added to the radio flash system is Group mode, kind of like ratios but on steroids. A maximum of five groups is available, and each group can be in E-TTL II, manual, switched off or even External Auto Metered mode. I’m finding that I am using group mode a lot with the EOS 5D Mark III. On the EOS 7D you can select it on the flash, but as soon as you take a picture the master flash will switch back to regular E-TTL II with all groups firing at the same power. There’s also no way to trigger a slave flash in Group D or Group E from a pre-2012 camera.

Linked shot needs a cable

It’s possible to set the radio system so a remote flash can be a radio controlled remote shutter release, Linked shot mode. On 2012 cameras this works and the flash or ST-E3-RT will inform the camera to take the picture via the hotshoe connection. Older cameras require a cable from a small connector on the flash/transmitter to the remote release port of the camera. The cable is the Release cable SR-N3 and at around £50 in the UK I don’t think too many will be sold…

EOS 7D fitted with Speedlite Transmitter ST-E3-RT

EOS 7D with Speedlite Transmitter ST-E3-RT set for high speed sync

I really think the ST-E3-RT is a great bit of kit, it does all that the 600EX-RT can do as a master flash except flash or send AF illumination signals. I’ve gone for an ST-E3-RT and use the 600EX-RTs as slaves it works out cheaper than using another 600EX-RT as the master. The ST-E3-RT is much more feature packed than the old ST-E2.

With the ST-E3-RT on the EOS 7D hotshoe then the flash menu on the camera allows the selection of E-TTL II, manual or Multi flash modes. High Speed sync or 1st curtain sync can be selected. I had really hoped that Canon would add 2nd curtain sync over radio to the system at least for the latest cameras. Flash exposure compensation, flash exposure bracketing (FEB) and evaluative or average metering patterns can be chosen. No possibility to change or influence the radio settings from the camera. Custom Functions C.Fn 1, 2, 3, 4, 7 and 13 can be set. C.Fn 20 and 22 and the personal functions can only be set on the ST-E3-RT directly.

My view on the flash system disparities

I’ve given some thought to the reasons for the disparity between what I have seen in practice and the statements in the instruction books.

I think that when in radio mode the communication overhead is greater than in pulsed light mode due to the need for the master device to receive confirmations from the slaves. More slaves and the overhead becomes greater. To cope with this I suspect that the new 2012 cameras work differently with the radio mode of the flash to allow for the extended communication time.

However if the flash is used with older cameras that don’t know about the modern radio language then the 600EX or ST-E3 will use a compatibility mode that accepts older pulsed light mode language, but knows that sometimes – maybe with large numbers of slaves or large distances between slave and masters (i’m not sure) – the radio system cannot work fast enough.

Canon says the features don’t work to be clear that it’s not expected to work, even if it does in some/many cases. I don’t think it’s ideal since unfortunately it’s a grey area, however I am happy to see that they didn’t directly disable the features. How bad could it be if no HSS was possible with radio on older cameras, or every older camera was limited to 1-stop slower sync speed? A lot of people with an EOS 5D Mark II would be looking at 1/100s as their sync speed!

- Brian Worley / p4pictures.com

Apart from the direct testing with my kit, the quote above is my “best guess” about this. I’d love to hear if anyone has encountered problems with the older cameras and the new radio flashes.