Master/slave speedlite triggering - When does it NOT work?

I usually use studio strobes, but I have 580EX and 580EX II speedlites and only recently started playing around with them as master and slave (with ETTL). I put the 580EX off camera in a beauty dish. The 580EX II is on camera. I set the A:B ratio to 1:3 so my off-camera flash in the beauty dish is my main light and the on-camera flash is my fill. I tried this first with my on-camera flash "bare" and aimed straight at the subject. This worked exactly as expected. I then repeated this experiment with the Lastolite Softbox III on my on-camera flash to soften the fill light. Since I don't believe the preflash works with this small softbox on the flash, I wasn't all that surprised to see that my off-camera flash was not triggered, and all the light came from my on-camera flash. I then removed the softbox III and tried a few other things, only changing the on-camera flash and leaving everything else constant. I tried pointing the flash up at the ceiling (bare). It didn't trigger the off-camera flash. I tried aiming the flash forward again with the diffuser screen pulled down, and it didn't trigger the off-camera flash. In each case, I then would try aiming it forward (bare) and making sure it would still trigger the off-camera flash, and it would. Apparently, there are configurations where it simply won't trigger the slave, and I couldn't find this in the documentation, unless my 580EX II is defective. I want to find a solution where I can use the 580EX II as fill but a softer fill than the bare bulb, preferably using modifiers I already have, but I haven't found a solution yet. I'm just thinking it would be handy for location work when I don't want to drag around the studio strobes.

Are you making sure to point the optical sensor (aka wireless sensor) of the slave toward the master?

When I mount the Lastolite Softbox on the flash head, I think it blocks the wireless sensor and is probably the reason it didn't trigger it in that case. However, it surprised me when I positioned the flash head to bounce off the ceiling (bare - so wireless sensor not blocked), and it didn't trigger the slave. I reposition the flash head to point straight ahead, and it triggers the slave. The wireless sensor is in the same position in both cases. I guess it could be pilot error, but I was being pretty careful. I'll give it another try. I wanted it to work with the flash head positioned this way so I could try the Lumiquest Promax System on the flash head, leaving the wireless sensor unobstructed.

This is something I might use under special conditions but not all the time. Just looking for something very portable and quick and easy to set up for when I need that.

I havent worked with the Lastolite softbox, but I believe its setup ends up with a hotshoe at the back of the softbox correct? If so, you should be able to mount the flash so the wireless sensor faces your master, then rotate the head so that it faces into the softbox.

I did some quick Google searching and found this example (it is utilizing the PW Flex trigger, but the flash mounting orientation is the same idea): http://www.bz1-img.com …/19531963_14187​9_full.jpg

Edit - ... and another: http://jefflynchdev.fi​les.wordpress.com …w_close_up_blog​.jpg?w=640

Sdipirro,
Yes, the problem is that the Softbox III is blocking the signal from the master and preventing it from reaching the slave. If you have the master on camera with the Softbox III on it, you will have to rotate the flash body in the beauty dish toward the camera to be able to control it as a slave. I use two 430EXs wirelessly off camera all the time with softboxes, including the Softbox III. Both are controlled by the pop-up on my 60D, and both always fire within the range specified by Canon. This works even with a mini-softbox on my pop-up. However, the sensors on the wireless flashes have to be pointed toward the camera.

That appears to be all it was. When I turned the sensor of the off-camera flash with the beauty dish to face the camera, it all worked, with and without the softbox on the flash on camera. Thanks, guys. Appreciate the help.

Glad you were able to get it working! It seems that a lot of people have the same problem...

I've had multiple Canon Speedlites for at least 6 months now... I really want to take them outside one afternoon sometime between 2-4pm when the sun [here in Florida it has to be brighter than anywhere else right?!?! ] is really bright and fairly directional to see what kind of results I am truly able to get. It seems to me that if you understand the system and take both the system and the sunlight into consideration it shouldn't be much of an issue. I just haven't had a need to actually do it, and I've been too lazy to go set it up just to try it...