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Radio triggers: An overview

Wireless triggers to fire flashes or the camera's shutter
by Gisle Hannemyr

This article is an introduction for photographers looking for radio triggers for flash and digital cameras. A lot of different triggers exists, and this article tries to gives an overview for the entire field, with links to other articles that discusses specific radio trigger systems.

If you also are interested in optical triggers, please see this article.

While optical triggers may be fine for wireless control of off-camera flash indoors, nothing beats radio for range and reliability outdoors. Also, if you want to have off-camera flash inside cars or behind furniture, radio is your best option.

Radio Frequencies

Several radio bands are made available for more or less unregulated use in different geographical areas this includes the bands used for RKE (Remote Keyless entry, i.e. garage openers) in North America, and the ISM (Industrial/Scientific/Medical) bands.

Equipment designed to operate in these bands is designed to be tolerant for interference by other equipment operating at the same frequency.

The common ISM and RKE bands available for industrial and commercial applications are:

  • 220 MHz (ISM, China).
  • 315-317 Mhz (RKE, North and South America, Japan).
  • 340-354 Mhz (ISM, North and South America).
  • 433-435 Mhz (ISM, Europe, Australia, Africa, China, India and some other countries).
  • 869 MHz (ISM, Europe).
  • 900-930 MHz (ISM, North America, and some other countries).
  • 2.4 GHz (ISM, worldwide).

Note that because of the different frequency allocations, use of the 315-317, 340-354 Mhz and 900-930 MHz devices is illegal in Europe, and the use of the 433-435 Mhz and 869 MHz devices is illegal in the USA.

Types of triggers

To make it simpler to find a particular trigger, we've separated the triggers into five types, as follows:

  1. Basic manual triggers
  2. Grouping triggers
  3. TTL pass-through triggers
  4. Premium manual triggers
  5. Third party dedicated TTL radio triggers
  6. Canon dedicated TTL radio triggers

At the end of each section describing the type, there is a list (with links) to those units that has been evaluated by DPanswers, along with an indication of what price you typically will have to pay for a kit consisting of one transmitter (TX) and one receiver (RX), or a pair of tranceivers. Note that one particular model may be listed more than once, if it has features matching the criteria of more than one type.

We plan to add more as we can find the time for testing. Watch this page for updates.

1. Basic manual triggers

If all you want to do is to trigger a manual flash or a camera's shutter release wirelessly by means of a radio signal, and you do not care about additional features such as grouping or TTL power control, then you're looking for a basic manual radio trigger.

This is the cheapest type of radio trigger available (for even cheaper, take a look at optical triggers.

The basic manual radio triggers are all produced in China and are sometimes referred to as Poverty Wizards or FleaBayTriggers.

2. Grouping triggers

A step up from basic manual triggers, both in price and in functionality, are triggers that let you operate groups or zones of flash units from camera position.

A grouping trigger let you distribute your remote flashes into groups or zones (usually 3 or 4). You can assign each receiver to belong to a specific group, and choose from the transmitter which of combinations of these groups you’d like to trigger. Grouping can save photographers a lot of time in complex lighting setups without having to go back and forth between flash and camera switching units on and off.

3. TTL pass-through triggers

A TTL pass-through trigger does not offer TTL wireless control. But the TX unit has a dedicated hot-shoe on top that pass-through the any TTL communication from the camera to a TTL commander mounted on top of the TX. The pass-through feature let you fire both TTL-controlled flash units (controlled by a commander mounted in the hot-shoe of the TX that is sitting in the camera's hot-shoe) and manual units (triggered by radio and connected to a radio RX) at the same time. However, the TTL computation does not take the light from the manually controlled units into account, so mixing modes like this is only practical when TTL is used for key and the manual units are used to light up the background.

4. Premium manual radio triggers

This segment consists of radio triggers that are built to take a lot of abuse, are very reliable, and packs a lot of power for an extended range. What they do not support is TTL exposure control, since that tend to have a negative impact on both reliability and range.

5. Third party dedicated TTL radio triggers

For some time, third party vendors has provided Canon and Nikon users with dedicated flash control systems that use radio instead of light to signal remote flash units.

While Canon has developed its own TTL radio protocol (described in the next section), no third party vendor supports this (yet). Instead, the third party dedicated TTL radio triggers currently on the market can be divided into into three different types. These are described below.

Systems simulating a wired connection

The most popular approach, used by four different manufacturers (PocketWizard, Phottix, Pixel and YongNuo) is to design radio units that makes the remote flash “believe” it is still connected to the camera. I.e. the remote flash is not set up to use the wireless TTL protocol that is part of any modern flash system these days, but is controlled by a radio relay circuit that relays the control signal from the camera's hot-shoe to the remote unit, just as you would do when using a TTL off-camera shoe cord to get the flash away from the camera.

All the systems in these groups let you use original flash units that support i-TTL (Nikon) or E-TTL II (Canon) as remote units, including units such as Nikon Speedlight SB-400 and Canon Speedlite 270EX that does not support the manufacturer's own wireless protocol. This is because the radio control systems simulate a wired connection, rather than relying on the manufacturer's own wireless protocol.

The most advanced of these radio control units let you operate multiple groups with power ratios, just as the manufacturer's light-based wireless systems do. The simpler units only let you control a single group with TTL exposure control.

Click for more detailed description:

Hybrid system using radio to relay IR

For a long time RadioPopper (established in 2007) was the only manufacturer that makes this type of hybrid system. However in 2012, Aokatec launched a competing product.

Unlike the radio systems that simulates a wired connection, hybrid relay systems uses IR-light to control remote units. However, to get around the range and reliability limitations of light, the system somehow intercepts the signal emitted by the master unit, converts it into radio signals, relay it, and converts it back from radio into light at the receiver end. This reconstructed IR-light signal is then fed to the remote flash's IR-port using fibre optics.

Because the system only relays the manufacturer's own light-based wireless protocol, it is compatible with it. This means that the photographer can freely mix remote units controlled directly by light, and by light relayed by radio.

Click for more detailed description:

Proprietary systems

The third and last type of system is prorietary. Unlike the two other type of dedicated TTL radio triggers, this type of system does not let you use the camera manufacturer's own flash units as remotes. Instead, you must use proprietary flash units with integrated radio receivers that is part of the radio control system.

Two manufacturers, Quantum and YongNuo offer this type of dedicated TTL flash control system.

Click for more detailed description:

5. Canon dedicated TTL radio triggers

In addition to its light-based flash control system, Canon also offer a full-featured radio based system for controlling remote flashes. The system operates in the 2.4 GHz band, and offers full E-TTL II support, better integreation, more features, and more groups than any of the third party radio control systems.

The main component of this system is the Speedlite 600EX-RT flash, which can be used both as a master on top of the camera, and as a remote (slave) Speedlite. There is also the Speedlite Transmitter ST-E3-RT. This can only be used as master on top of the camera. No Canon DSLR have (yet) a built-in radio master unit.

Both the 600EX-RT and the ST-E3-RT can be used to control up to 15 compatible Speedlites in up to five groups by radio.

For more information about Canon's flash system, see our introduction to the Canon flash system.

7. Final remarks

If you know about other radio triggers that deserves mentioning on this page, please use the comment field below to add your experiences.

Radio trigger suppliers:
Alien Bees
Bowens Pulsar
Elinchrom EL-Skyport
Gadget Infinity
Hensel Studiotechnik
MicroSync
Pixel Enterprise Ltd.
PocketWizard
RadioPopper
Quantum
Secu-Line
YongNuo
Zap-Shot
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