I wanted to make my lighting a bit fancier, so I bought a second Speedlite (580EX II) and a Lastolite EzyBox Hotshoe (//www.lastolite.com/ezybox-hotshoe.php, thanks for the recommendation, jwillerton).
My idea was to place the second Speedlite with the softbox at an angle and use the first on-camera, either just to trigger the first or as additional fill light.
Now, when I set the on-camera flash to "off" (in master mode), sometimes it fires, but the second (in slave mode) doesn't. Or they fire both. Does anyone know why this happens? Does the first fire if it cannot communicate with the second? And how do they communicate? Is it infrared, do they need to see each other? Or does one react to the firing of the other?
The master sends a series of high-speed light impulses to communicate with the slave, and vice versa. You could compare it to morse code to get the idea. If you set the options so that the master does not flash during the exposure, it will still emit visible light before the actual exposure for the communication. If your slave doesn't always fire, it may not be able to see the light from the master properly.
What Gloda said.. I was initially under the misconception that wireless was something akin to RC and it sent out the data require in a kind of `wifi` method, but as Gloda says, the exposure info is encoded in a very high speed burst of (pre)flashes that the slave can translate. As such, you must have the front of the slave flash pointed towards the master flash so that it can `see` the initial burst.
Ok, so if I turn the on-camera flash off in master mode, I should point it toward the slave to make sure it gets the message, right? If there is no direct line of sight between slave and master (and you are outdoors where light is not bounced off walls) this kind of communication won't work. Are there any real radio methods that you would recommend?
Strobist.com goes into all manner of techniques for using hot-shoe flash for nearly every conceivable lighting arrangement. They make suggestions as to RF controllers as well. Pocket Wizards are great, but spendy. I've used the import controllers recommended by Strobist with ok luck.
