How limiting are the line-of-sight requirements of Canon's optical wireless flash system?

Question

I have a Canon 7D and 580EX II Speedlite, and am trying to make the jump into flash photography, particularly portrait work. I understand that the 7D's wireless trigger works by line-of-sight. Will this prohibit me from triggering flashes that are off center? For example, an umbrella to the side (either directly to the side or front-and-to-the-side) of the subject pointing toward the subject. I'd assume that the back of the flash wouldn't be facing directly at my camera.

I haven't bought the gear yet, but I was hoping the trigger on my camera would be good enough to forego the need to purchase any additional triggers.

Answer

The flash is triggered by the popup-flash of the 7D.

The signal is transmitted by light, it is just way too fast for the naked eye to see. The popup flash would strobes rapidly, like sending out morse-codes, and the external flash would pick it up and fires in sync. The whole thing is super fast, like in 1/500 of a second.

Understanding that, you now know that the limitation of such approach is that when the light is too weak, it will not reach the flash, and the external flash will not fire.

Another situation is that, when the surrounding it very bright (under direct sunlight for example), the popup flash is relatively weak, and the "morse-code" signals cannot be properly detected by the external flash.

Reducing the distance between the popup flash and external flash should solve this.

I use the 60D, and it has the same system too. I do not do a lot of outdoor daytime shot, I usually have a cable with me should I need off-center external flash. However I use the wireless flash system indoor very often. It is sufficiently reliable when you are in an indoor settings. Provided that you have some walls to bounce some of the light around, it really isn't a must that the flash must be at line of sight.

Ultimately, in an indoor settings, in a small room, I can place the external flash anywhere I want, and it fires no problem. If your portrait work focus on indoor shooting, its absolutely fine.

Finally, you already have the 7D, you do not seem to have the flash unit yet. You must buy a flash regardless which wireless option you choose, right? So why don't you buy a good flash unit, try out the wireless function on the 7D, then decide if you really need other wireless solution?

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