Flash trigger

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Glossary Terms

Flash trigger refers to a method of remotely achieving flash sync without the need for a wired connection between the camera and the flash units illuminating the scene. Flash triggers are useful in any situation where a light source must be located at some distance from the camera; or when multiple flashes are to be synched simultaneously.

Optical slaves

An optical slave is essentially a fast-acting, light-operated switch. It includes a photocell with a wide acceptance angle; and circuitry able to detect the rapidly-rising light intensity of any other flash being fired nearby. This closes its own sync contact, and triggers any flash attached to it. This approach requires at least one "master" flash to be triggered by a wired connection to the camera. It is also unsuitable e.g. at public events, where flashes from other photographers would cause spurious triggering.

Slave flash triggers arose as standalone accessories by the 1960s, or as all-in-one multipurpose flashes including both an electronic flash and an optical slave circuit in a single case.

Infrared triggers

In this system, the camera (or a dedicated flash) sends out an invisible infrared signal which is recognized by compatible brands of flashes and also triggers them. Typically these are used in systems proprietary to one camera manufacturer. Full flash automation may be possible, however obstructions in the line of sight between the controller and the remote units may prevent the system from working.

Radio triggers

A wireless remote trigger, radio trigger, or radio slave represents a more advanced solution to the problem of remote flash triggering. A single transmitter unit (typically equipped with a foot that fits a camera hot shoe) may trigger any number of receiving stations—none of which need a wired connection to the camera. Furthermore, the transmitter/receiver pairs may offer a selection of radio channels, allowing several photographers to work nearby without mutual interference.

Typically a basic remote trigger only sends a signal for the flash to fire, and does not communicate other control signals between the camera and the flash unit. However more sophisticated triggers are able to pass through the camera's TTL exposure measurements, providing full flash-exposure automation wirelessly. Another function of more advanced models is allowing remote flashes to be assigned to different groups, permitting the photographer select different lighting options without leaving the camera position.

At one time radio device technology was expensive enough that only working professionals were likely to own radio triggers. However in the 2000s, photographer communities online (largely inspired by the Strobist blog) had sharing techniques for off-camera flash. And just in time for this, a flood of inexpensive Chinese-built radio triggers (some of questionable reliability) appeared on the market. Thus radio triggers are currently becoming a more mainstream accessory for enthusiast amateurs to own.


Brands which at some time have offered remote flash triggers include:

  • Bowens
  • Cactus
  • Calumet
  • Elinchrom
  • FreeWave
  • Interfit
  • Nisha
  • Norman
  • Photoflex
  • PocketWizard
  • Quantum
  • RadioPopper
  • RPS Lighting
  • MicroSync
  • Morris
  • Yongnuo