TTL radio trigger guide
This article discusses TTL radio triggers for flash and digital cameras. To be more precise, it is a survey of radio triggers that can be used to wirelessly control several groups of remote flashes while retaining TTL control over exposure.
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.
Most such wireless triggers just trigger the flash or camera by means of a radio signal. But, now there also exist several different wireless radio triggers that offer full TTL with the great Canon and Nikon wireless flash systems. For some time, two systems known as RadioPopper PX and PocketWizard ControlTL has dominated the marked. But three additonal third party systems: Phottix Odin, Pixel King and Quantum FreeXWire also exist. In 2012, Canon introduced its own dedicated radio-based flash control system..
Aokatec AK-TTL (2.4 GHz)
Pending a DPanswers in-depth review of this unit. please see our blog entry discussing the specifications.
Phottix Odin (2.4 GHz)
Phottix produces a dedicated wireless trigger named Phottix Odin. It exists in two different versions, compatible with the dedicated TTL flash systems of Canon and Nikon.
Pending a DPanswers in-depth review of this unit. please see our blog entry discussing the specifications.
Pixel King (2.4 GHz)
Pixel Enterprise Ltd. produces a dedicated wireless trigger named Pixel King. It exists in three different versions, compatible with the dedicated TTL flash systems of Canon, Nikon and Sony.
The King is a second generation system, with the TTL-control based upon the Knight first released in 2009. Like the Pixel Knight, it does not support the TTL wireless protocol, but works by making the remote flash “think” it is in the camera's hot-shoe.
The body is similar to the Pixel Bishop. It uses the 2.4 GHz frequency (unregulated worldwide), and Pixel indicates that has a reach of around 100 meters.
The King provides 7 channels and 3 different groups (7 combinations). For power, both the TX and RX use two AA-sized batteries. Both the TX and RX have an USB-socket to allow firmware updates. Both the TX and RX have a hot-shoe. The RX hot-shoe is for mounting remote Speedlites. However, the TX hot-shoe is not a TTL pass-through shoe, and can not be used to mount an additional Speedlite. Instead Pixel has hinted that they may later introduce a separate control unit (dubbed “N-ETTL”) that can be mounted in the TX hot-shoe and used like the PocketWizard AC3 Zone Controller.
Here is a rundown of its main features:
- Frequency: 2,4 GHz.
- May trigger both dedicated flash units and generic studio strobes.
- Compatible with Canon's E-TTL II, Nikon's i-TTL or Sony's P-TTL for automatic power control.
- May control up to 3 different groups (7 combinations).
- May be set to one of 7 different channels.
- Wireless TTL control from camera position of flash units with a compatible DSLR.
- Maximum sync. speed is 1/250 second unless using high-speed sync. mode.
- High-speed sync./FP-sync, up to 1/8000 second, for dedicatedflash units connected through the RX hot-shoe.
- Hypersync, up to 1/8000 second, for studio strobes connected through the RX pc-socket.
- USB interface for firmware updates. Can also be used for 5 volts DC power supply.
- Maximun trigger voltage: 36 volt.
It does not support the stroboscopic mode. For wireless TTL, the flash in the RX hot-shoe must be E-TTL II (Canon), i-TTL (Nikon) or P-TTL (Sony) compatible. Compatible Canon Speedlites are: 580EX II, 430EX II, 320EX, 270EX II. Compatible Nikon Speedlights are: SB-910, SB-900, SB-800, SB-700, SB-600, SB-400. The manual also says that compatible units from third party manufacturers Metz, Sigma, Sunpak and Nissin (no specific models listed) may work.
The TX has very sparse controls, and to make full use of the unit, you need to be able to control flash settings from the camera's external flash menu. At the time of writing, only newer Canon DSLRs let you do this.
To set it up on Canon, you use the camera's external flash func. setting-menu. The following Canon EOS bodies are listed as compatible: 450D, 500D, 550D, 600D, 40D, 50D, 60D, 7D, 5D II, 1D III, 1D IV, 1Ds III. Older Canon DSLRs does not let you control the flash from the camera menu. On these bodies it will “dumb down” and operate like a wireless grouping TTL trigger where individual groups can be toggled on or off, but not set up with power ratios.
Nikon and Sony cameras gives you little control over the flash from the camera menu. The Nikon and Sony versions of the Pixel King will operate like a wireless grouping TTL trigger where individual groups can be toggled on or off, but not set up with power ratios.
The Pixel King is reported to behave erratic (typically not exposing correctly) if you slide it into the hot-shoe when the camera is powered up, or you connect a flash to it when the device is powered up. It is recommend to power down all devices (flash, camera and TX/RX) before setting up, and to power them up in the following sequence: flash, Pixel King TX/RX and finally the camera.
- Downloads available on the Pixel website:
- Instruction manuals.
- User reports about various radio triggers:
- PocketWizard MiniTT1, FlexTT5 for Nikon, by Rob Galbraith
PocketWizard ControlTL (US: 344 Mhz, EU: 433 MHz)
Recently PocketWizard started to sell the PocketWizard ControlTL compatible with dedicated Canon and Nikon DSLRs and flash units.
Unlike the Aokatec AK-TTL and RadioPopper PX systems, this is a pure radio system where you place a radio transmitter in the camera's hot-shoe, and then use a radio receiver with a dedicated hot-shoe to trigger the remote flash through its dedicated hot-shoe.
The ControlTL uses a transceiver called FlexTT5 that can be used both as a transmitter and receiver, or a cheaper transmitter called MiniTT1. Two FlexTT5 units cost about USD 410, while the cost of a MiniTT1 and a FlexTT5 is USD 390. (Check prices for the FlexTT5 at: Adorama, Amazon USA, Amazon UK, B&H, eBay.)
The PocketWizard system require you to have remote flash units mounted in the hot-shoe of FlexTT5 transceivers to be set to normal mode, not remote mode. This is because they are controlled by electric signals through the hot-shoe, not by light (as they are in Canon's and Nikon's wireless systems). I.e.: PocketWizard has engineered the system so that the remotes “think” they are in the camera's hot-shoe.
On its own, a MiniTT1 transmitter or the FlexTT5 transceiver in the camera's hot-shoe can only control a single remote group. This default group is unrelated to the remote groups of Canon's or Nikon's wireless system. This mode is called basic wireless TTL by PocketWizard. In this mode, the system behaves just as as one or more wireless off-camera shoe cords (similar to the less expensive Pixel Knight radio triggering system).
The AC3 let you extend this single group to three zones (A, B and C). Each zone can be set to Auto (A, i.e. TTL), Manual (M) , or Off (Ø). There can be as many flash units as you want in each zone, but each must be attached to a separate FlexTT5 tranceiver.
For each zone, in TTL mode you can set FEC/FOLC within a range of +/- 3 stops in steps of 1/3rd stops.
In Manual mode, you use the same control wheels to set manual levels for each zone. In this mode +3 means 1/1 (full power), +2 means 1/2 (half power), +1 means 1/4, 0 means 1/8, -1 means 1/16, -2 means 1/32 and -3 means 1/64 power.
You piggyback the AC3 ZoneController in the hot-shoe of the MiniTT1 transmitter or the FlexTT5 transceiver that is mounted on the camera's hot-shoe. With this gadget, you can dial up and down the power of each of the three zones in both TTL-mode and manual mode. To place a remote unit in a specific zone, you just set the zone selector on each remote FlexTT5 tranceiver to the zone you want it to be in. The flash unit mounted in the remote FlexTT5 tranceiver's hot-shoe must remain set to normal mode.
Zones are not groups, but you can use the zones to control the power ratios of remote flash units from your camera's position, just as you would use the groups of Canon's and Nikon's original wireless systems. But if you are not happy with the zones, but want to control groups and ratios exactly as Canon's and Nikon's original wireless systems let you, you can do that as well.
To do so, you use the mode called advanced wireless TTL. To use this mode you must piggyback a dedicated TTL commander (e.g. Canon 580EX2/ST-E2 or Nikon SB-910/SB-900/SU-800) on the MiniTT1 transmitter or the FlexTT5 transceiver that is mounted on the camera's hot-shoe. This let program your groups, power and ratios, etc. on the manufacturer's dedicated commander unit. In advanced mode the zone selector on the FlexTT5 tranceiver turns into a group selector. As with zones the flash unit mounted in the remote FlexTT5 tranceiver's hot-shoe must be set to normal mode.
Both units features a dedicated hot-shoe on the top. When you use the unit as a transmitter on the camera, this hot-shoe is used by a commander unit mounted in its hot-shoe to communicate zone or group identifiers and power ratios to the transmitter.
The Canon version of the ControlTL system let you place an optical commander (i.e. a 580EX2 or an ST-E2) in the shoe of a MiniTT1 or FlexTT5 for optically controlling remote group A (groups B and C can only be controlled by radio).
In the Nikon version, this is not an option. The Nikon versions of the MiniTT1 and FlexTT5 always squelches the pre-flash sequences that constitutes Nikon's optical protocol, so nothing can be controlled optically. The benefit is a faster and more responsive system. In manual mode, there is no pre-flash. In TTL mode, the only pre-flash is a single blink to determine TTL flash exsposure.
The PocketWizard ControlTL system supports HSS/FP mode and is capable of syncing flash with the camera's shutter speed up to 1/8000th second.
When you put something in the hot-shoe of the FlexTT5 tranceiver, it automatically detects whether it is a dedicated or a generic unit. It dumbs down and becomes a plain slave trigger if it detects a generic flash.
The MiniTT1 uses a disposable CR2450 3 volt lithium button battery, while the FlexTT5 use two AA-size 1.5 volt batteries. The AC3 uses no battery, but is powered by the unit it is attached to.
Both the MiniTT1 and the FlexTT5 have a USB-port and the firmware can be upgraded by the user with a software program called PocketWizard Utility.
Some newer Canon Speedlites, in particular 430EX, 580EX and 580EX II, are reported to have significantly reduced range with the ControlTL units. This is because these models emits strong RF noise across a broad spectrum of frequencies that interferes with the radio triggers. To resolve this, you can fit an external barrier that shields the RF noise, or modify the circuits inside the flash to filter the noise. See this note for details. Some Speedlites, for example the 550EX, 430EX II, 420EX, and 270EX do not have this problem.
The versions for different geographical regions use different radio frequencies, and are not compatible with each other. Make sure you get the version that uses a frequency that is legal in the region you are going to use the unit.
Quantum FreeXWire (EU: 433 MHz)
Quantum Instruments is a company whose main product is a very flexible, powerful, and expensive modular flash system that include flash units, interchangeable reflectors, external power packs, wireless controls and more. Part of the Quantum system is a proprietary radio-based TTL system called FreeXWire.
Commanded by a Quantum Trio or Quantum Pilot in the camera hotshoe, this system is capable of wirelessly firing and controlling the company's own Qflash flashes, as well dedicated remote flash units from Canon and Nikon that are connected to FreeXWire 8R receivers via a Qlink hot-shoe adapter. Three independent groups are controllable with using the Quantum Pilot as commander, or two groups with the Quantum Trio.
I've never used Quantum FreeXWire. I've only included it in this survey for completeness.
RadioPopper PX (US: 916 Mhz, EU: 433 MHz)
RadioPopper PX was the first system available to offer the combination of TTL power control and radio, and it still the most popular system available today. It is available for both Nikon i-TTL and Canon E-TTL II. (Check prices at: eBay.)
Unlike the dedicated triggers offered by Phottix, Pixel and PocketWizard, the RadioPopper PX is a hybrid system that takes the light signal that the manufacturer uses for flash wireless control and converts it into radio signals. This radio signal is then converted back into light at the receiver end. The hybrid approach means that the in-camera commander unit signals by means of light, and the remote flash receives a light signal. The PX is just a relay, using radio to greatly extend the distance this signal is able to travel.
Both the transmitter and the receiver use two AAA-size batteries. Both disposable alkaline and rechargeable NiMH will work.
Because the PX is a hybrid system, you actually need to have a dedicated flash that can provide the master flash signal. The hybrid system makes use short fibre-optic cables to convert the signal from light to radio and back again. To make it work, most users put a dedicated master flash (such as the Canon 580EX2 or Nikon SB-910) in the camera's hot-shoe, attach a RadioPopper PX transmitter to this with Velcro, and use a short fibre-optic cable to make sure the light from the flash reaches a sensor on the PX transmitter. DSLRs with a pop-up flash and a built-in commander mode (such as Canon EOS 7D and Nikon D7000) can use the pop-up flash as master. At the remote end, a RadioPopper PX receiver is attached to the remote flash with Velcro, and a bendable fibre optic cable goes from the the PX receiver and into the remote flash's optical sensor. It sounds like a bit of a kludge, but users report that it works very reliable.
This is different from the other systems described on this page, where the transmitter goes in the hot-shoe to pick up electrical signals from the body. The RadioPopper PX system is the only radio system that pick up light signals from the master flash, and control the remotes by means of light.
The PX-system supports Canon's HSS and Nikon's FP modes and is capable of syncing flash with the camera's shutter speed up to 1/8000th second.
RadioPopper do not say what range to expect, but users report that they work reliable up to at least 180 meters if there are no obstacles blocking the signal between the transmitter and receiver.
3. E-TTL metering
Canons flash metering system likes to take distance information (relayed from from the lens) into account when computing flash power in E-TTL II mode. Since the radio based flash control systems from Pixel, Phottix and PocketWizard work by making the remote flash “think” it is in the camera's hot-shoe, this distance data may be wrong. In that case, E-TTL II exposure control may become erratic if the flashes are closer to the subject than the camera. If you experience this, reliabilty may improve if you switch metering mode from evaluative to centre-weighted average.
Nikons flash control system lets the flash control whether distance information from the lens is taken into account, and does not seem to produce the same type of problems with i-TTL exposure control.
The RadioPopper system works different and should not be affected by this.
4. Final remarks
If you know about other TTL radio triggers that belong in this guide, please use the comment field below to add your experiences.
Also, if you are using the Quantum FreeXWire system and is willing to contribute a review, please send me a note.