Beginner question: Why does the standard camera flash *flash* when using the off-camera flash (wireless)?

Question

So I'm just now beginning to do off-camera flash on a light stand with an umbrella-diffuser.

The thing is, the standard built-in flash for some reason has to flash along with the off-camera flash on the light stand. Won't that disrupt the light? Or is it not effecting it? I want the off-camera diffused flash, not the flash from the camera. Is there a way to turn it off? Or is it no big deal?

I'm using a Canon 7D with a 580 EX that I'm borrowing from someone..

Sorry for the beginner question but I just don't understand why simply the off-camera flash can't be the only thing flashing. Why would I need the built-in flash? Or will the built-in flash have no effect as it would be drowned out by the off-camera flash?

Answer 1

Both are correct. The 7D was the 1st Canon body to have the flash controller built in, finally!



The Canon E-TTL system, like the Nikon iTTL system, is optically controlled from the camera body. In your 7D manual, it tells you how to set this up so that the pop-up flash does, or does not, contribute to the exposure. If you are very close to the subject, like within 2 feet, the pop-up will add to the exposure no matter what.



To fire your flash off camera, without the popup flash controlling it but still using E-TTL exposure control, you would have to use off camera shoe cords, or very expensive Pocket Wizard radio controllers that send E-TTL info. Before the 7D, you had to add at least a $250 flash controller to do what you are doing now!

Answer 2

I don't know how Canon's wireless flash system works, but Nikon has a similar thing. The built in flash acts as a commander to the wireless flashes. It basically flashes BEFORE the shot is taken to instruct the wireless flashes what to do - these have sensors built in which detect that flash and read information from it.



If you don't have your built in flash set to be active as well, then it shouldn't really affect the image. If you take a shot of your mirror image, then you likely still see some afterglow in the popup flash, but that one won't be strong enough to have a big impact on the illumination of the scene itself. So...don't worry about it.



Personally i even find it welcome and leave the popup flash active on a very low power setting to get a nice highlight in the eyes, yet without having much other influence on the illumination of the subject.

Answer 3

It is because your on camera flash is triggering the off camera flash. Either the 580 is in an optical slave mode and the on camera is acting purely as a flash of light to trigger it, OR (more likely) the 7D is wirelessy triggering the flash in TTL mode (I'm not a Canon user, but I believe the 7D has wireless flash capability, like Nikon's CLS system).



With branded wireless flash systems (like Nikon's CLS, and you 7D), the off camera flash can be controlled wirelessly by the on camera flash. With Nikon, even when this flash is set to '--' (ie off) it still fires as it has to, to trigger the off camera flash. It's meant to not contribute to the image in '--' mode, but it can be seen as a small speck of light if you are close to the subject or at a wide open aperture.



Some people have used IR filters (Nikon do one called SG3) over the flash, which allows the IR triggering signal through, but stops visible light (a piece of exposed & developed 35mm film will do the same).



I used to use the Nikon CLS system but have now switched to radio triggers - A set of RF602 triggers costs £25. You'll .lost TTL functionality, which means you'd need to set the flash output on the 580 manually, but the advantages are greater range, and no 'flash' on camera.

Answer 4

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