We all know that the Olympus wireless flash system is great: it can be finely adjusted, can command several flash units, etc. You name it: it's there, on par with other manufacturers' systems. Still, there is room for improvement. Fortunately, we do not have to wait for Olympus in these cases. We have already written about how the ehm, simple FL-BKM03 double flash bracket can be substituted using two gorilla pods and some DIY. If you want to use a TTL cable, Canon comes to the help to replace the reportedly not wo well build FL-CB05 cable with the aptly named and sturdy OC-E3.
With the new features of the off-camera TTL system, we have new problems to solve along with the new features. Because using the small on-camera flash as a commander unit is simple, while implementing and certifying a radio-based system is expensive and difficult, Olympus opted for the "light" solution to remote control the off-camera TTL flashes. To see what problems might arise, we have to think about how TTL works in case of an on and off-camera setup.
Even if not using remote control, digital TTL flash uses one or more brief flash pulses before emitting the main flash light to calculate the required light for the desired exposure. Using the flash unit mounted on the camera and aimed directly at them (which you should not do anyways, but that's another story), people often blink after these initial pulses, no matter how weak they are. Because the main flash pulse comes right after those used for metering, you often end up capturing a person with closed eyes. Fortunately there is no such problem with off-camera flash in general: the flash does fire at least twice, but as the flash unit is not staring into eyes, it causes no problem.
But, as there is always a but, the flash-based commander system introduces additional flash pulses before the one used to measure exposure. Although we do not know how it goes exactly, it must not be very different from this: 1) the commander sends a flash pulse to trigger the remote flash(es) to initiate the flash for measuring exposure. 2) the remote flash(es) fire the pulse used to measure exposure. 3) after the camera has calculated the required amount of light, it sends flash pulses carrying the lighting information that the remote flashes. 4) the remote flashes interpret the command and fire accordingly. As you see, there are probably two additional flash pulses compared to wired TTL flash operation, coming right from the camera. Shooting a portrait for example, your subject will see brief, but kind of blinding lights which can make her go hmmmmm. Even if not, you will have to retouch the image to get rid of the commander lights (if the shutter is open long enough to include that) and have a good chance to have to repeat the photo itself.
Olympus, to my knowledge, does not offer a solution to this problem. Fortunately Nikon has a similar system and does offer a solution, with its SG-3IR unit. The small blocking unit pops right into the hot shoe of the camera and once you open up its built-in flash, it provides a (tiltable) blocking plate to go in front of it. Note that the current unit, the SG-3IR has a black-looking plate (the old one was plastic, mimicing frosted-glass). This is not actually pitch-black, but is made of IR-transmitting plastic. Although the light emitted by the flash is not very rich in infra-red light, it is more than enough in itself to command the remote flashes. But how does it help an Olympus user? Well, in case of the E-3 at least, you can confortably, if not perfectly fit it into the hot-shoe and use as desired. Once you mount it, your subject will not be blinded. You not only spare photoshopping out the light-circly of the flash, but will also be able to capture her eyes as well:
Note the minuscule red light on the blocking plate. Now that is what is commanding the remote flash - behind my back!