Photo Studio Flash Slaves and Trigger Systems
Flash-activated slaves are the oldest type of wireless flash used in photographic studios, but their use can be problematic if they're not used in a studio or controlled environment. Should other flashes be used at the same time as you remote flash is triggered, they could set off your flash units at the wrong time.
Flash triggers relay signals from a digital SLR camera to the flash unit, triggering it to fire. However, there are some limitations such as some flash units are connected to the camera. Wireless triggers are more reliable and do not require cables, but they are more expensive to buy than standard wired versions.
Alternatives to a flash trigger
Digitally encoded triggering systems for flash use digitally encoded pulses of visible light or infrared to ensure that the slaved flash units are not accidentally triggered by other flash units. The system using the encoded infrared has triggering units that don't emit a visible light, or the flash unit can be sent to send out an infrared triggering beam. Greater flexibility is gained when lighting setups are arranged, avoiding direct flash from a camera position.
However, all infrared-activated or light-activated wireless systems must have an unobstructed path between the triggering beam and the receiving flash. Some systems have a test button on the master flash to check that the slaved unit will fire.
There are a wide range of radio-controlled triggering systems capable of firing a flash up to 1,600 feet away, around corners, in a different room or in a non-reflective environment where no bounced or infrared light can reach a light-activated sensor. With up to 32 channels, photographers can avoid having their flashes triggered inadvertently.
It is worth bearing in mind that these systems are usually larger than other types of flash slave units, so they may not be as easy to transport. They also need battery power and may not have through the lens operation or flash ratio settings.
Nikon has a creative lighting system that includes two sophisticated wireless close-up units. The Nikon R1 Wireless Close-Up Speedlight and the Nikon R1C1 offer ratio-control and i-TTL Balanced Fill Flash. The Nikon SU-800 Wireless Speedlight Commander uses a pulsed infrared system to control older Nikon flash units.
The Quantum wireless QTTL system links Quantum Qflash 5d-series strobes wireless using adapters with a FreeXWire Transmitter to send radio commands to one more remote receivers that are connected to Qflashes.