The problem I had was manifestated with the close-up portraits:
Since I was using the iTTL system of Nikon, it was required that all three light sources needed to be in the line of sight of the master flash, placed on the camera. The problem was with the rim light source (C). Since it was a strip softbox (30x100 cm) and it was quite deep (30 cm), the flash unit placed at the rear side of the softbox was not always reachable by the master flash. There are several options to solve it (at least that I came with in the first instance):
- Put the omnibouncer on the master unit to create the broader light bundle used for controlling other flashes
- Use a radio frequency wireless trigger
- Don't come so close to the subject (for example by using a lens with a longer focal length)
The first option helped a bit, but didn't solve the problem completely. To be honest, it was required anyway, to control the base light (A) in a reliable way.
The second option is nice, but I don't have a wireless trigger and my budget for photography is for this year really, really up.
Third option is the probably something I'd love to try, if I had a proper lens. I was shooting with the 24-70mm lens. If I had a lens with a longer focal lenght (e.g. 70-200) that would solve my problem. And I think it would also create a lot of new opportunities for the composition of a close up portrait, but alas - something for the future.
There is actually a fourth option, coming from the observation that iTTL is a one-way control system, where the master unit sends the control signals in the form of short light pulses. So the basic light principles, like the reflection of light apply for these signals. The solution was born. I simply put a highly reflective surface ensuring the light from the control unit reaches the remote flash. Something like on the picture below:
Now the best part. The "high reflective surface" was a silver foam that is used to protect the windscreen of a car from freezing. To buy in the Netherlands for 2 or 3 Euro.
The result: 100% efficiency in the controlling of the rim light.