Also, make sure your devices are on the same Channel.
Anytime you use wireless (whether optical or radio) methods to trigger off-camera flash, there's a possibility that this could be used at events where other photographers are doing the same thing. You wouldn't want some other photographer's transmitter triggering your flashes (and they probably don't want that happening either).
Canon lets you assign a "channel" number. You pick one and make sure everything you own (assuming you want them to work together) is on that same channel.
The radio triggering system also has an "ID" value (4 digit number) that it adds in to the mix ... but it's the same idea.
There is also a concept called "groups" but you should be able to tell the transmitter to use group "all". But it is possible to assign a flash to a group (a, b, c, etc.) and then have the transmitter fire only flashes in certain groups. e.g. transmitter is ordering "group a" flashes to fire, but the remote flash was assigned to "group b". But if you only have one off-camera flash, then you can tell the transmitter to use group "all" (which means all flashes on your channel regardless of group assignment).
A great book on the Canon Speedlite system is "Speedliter's Handbook" by Syl Arena. But the prices for a "printed" copy are insane. Checking Amazon, they claim "new" books start at $999.99 (no kidding) but you can save a bundle by purchasing a "used" copy for the bargain price of merely $480.00. (ummm... no thanks).
The only place I know where you can get it at a reasonable price is via the Apple "Books" store (if you have an iPad, iPhone, or Mac). I only know this because a burst pipe damaged most of my printed books and when I decided to rebuy the books I wanted, I converted to digital. At the time, few Kindle books were in color and any books on Photography looked horrible on Kindle, so I sort of standardized on the Apple Books platform. Apple "Books" store still has the book ($43.99). I cannot find it on the Kindle store. All other websites (when I do a Google search) simply say "no longer in print")
Anyway, if you happen to own any Apple products, it's the cheapest way I've found to get the book and the book is easily the best book I've found on the Canon Speedlite system.
Tim Campbell
5D III, 5D IV, 60Da
