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.


4 Answers 4


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?

  • \$\begingroup\$ Ooh. I hadn't considered the problems in sunlight. Have you tried it at all in sunlight? Aside from indoor work, I was also hoping to try outdoor portraiture with the "overpowering the sun" technique. Do you know if the wireless trigger will be completely ineffective in broad daylight? \$\endgroup\$ Nov 22, 2011 at 3:29
  • \$\begingroup\$ I have only tried it under sunlight few times, as I said, most of the time I use it indoor. I have a 580EXII and when I use the wireless function in sunlight, I do turn the flash head so the sensor (red plastic part) is always directly facing the popup flash. I hold it at arm's length and I had it fires most of the time. However I rarely use that function outdoor so you need to test it yourself. Like I said, you must buy a flash no matter what, so just buy it and go try it out :) \$\endgroup\$
    – Gapton
    Nov 22, 2011 at 3:39

I can't answer precisely for Canon, but I use Pentax's similar wireless P-TTL all the time. Since the basics are the same, I think it should be helpful.

If you are in a relatively small space, and light from the control flash is able to bounce to the sensor, it works just fine. Even if the line of sight isn't direct, there's usually some surface that will reflect the pulse of light that is the control signal. That means that most home situations are no problem, but large rooms and dark walls or ceilings can be problematic. In a studio setup, you may have similar problems, as you may have dark surfaces designed intentionally to not reflect stray light.

My understanding is that the wireless sensor on your 580 EX II is relatively open to light from all sorts of angles. The Metz flash I use has the light sensor placed on the side rather than the front, which works just fine except when I forget and turn the flash the wrong direction and leave the sensor shaded by fabric or something. This is a reason it's convenient to have a swivel flash even when you're mounting the flash off-camera — the sensor is on the base of the flash, so you can point that in a more convenient direction while still aiming the reflector (flash head) in the direction you want it.

Even with the less-forgiving Metz sensor and without giving much consideration to flash placement, I find the optical system works in all sorts of amazing situations, including firing from the next room.

One way to make the system more reliable is to use a more powerful controller — like another flash mounted on the hotshoe. That lets you A) have a much more powerful control flash since the unit is simply much stronger than the built-in flash and B) you can aim that flash so it's pointing more conveniently to trigger the remote unit or units. I find this arrangement annoyingly unwieldy and contrary to the reason I want to use wireless triggers in the first place, but some people swear that this is really the only way to go.


Line of sight doesn't mean directly facing you, that would be fairly useless for optical slaving! In traditional portrait setups, where fill and key lights would be to the side and angled, any of the optical slave systems I'm aware of would function just fine and, to be honest, Canon has one of the better ones. So, from that perspective, you have nothing to be worried about.

Now, having said that, the space you're in matters. Go outdoors, or into cavernous studios, and the optical options start to suffer, if not fail entirely. At that point, radio triggers are the way to go if you want freedom to move. I don't think you're at that stage yet, but when you do, you can spend very little or you can spend a lot. For amateur work, to be honest, I would spend little. I went with the Cactus v4 set and they've been great. I have them hooked up to Alien Bees studio strobes and they've yet to fail to fire and the price is really, really, hard to beat.


I have a T3i, which has the same wireless trigger mechanism used by the 7D. It's not strictly line-of-sight... but more "within flash range." The wireless trigger works by emitting a flash from the on-camera flash an instant before shutter release, which the remote flash detects. So long as the on-camera flash is detectible by the remote flash, you're good.

Of course line-of-sight is the best way to ensure this, but you can acheive the same thing by bouncing the on-camera flash to the remote flash. Especially indoors, this can work well.

If you have the off-camera flash behind you, then you just need some way to bounce the on-camera flash back to the off-camera flash. If you're shooting indoors, the walls/ceiling may be sufficient for this.


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