In poor light, any kind of event photography will almost certainly demand flash. Action shots nearly always need it, and group or portrait shots with an action element are now part of any successful event specialists' portfolio. But choosing a flash has been slightly complicated by the advent of digital photography, because all the major 35mm-SLR based digital systems - those that started from earlier film based ranges - were forced to redesign their through-the-lens flash exposure control systems to make them work in the absence of a film surface.

Distant connections

Wireless remote flash was first introduced by Minolta in 1992, using a mixture of visible light pulses and an infrared signal to identify off-camera flash units and control exposure. Full infrared control was possible, and a command unit that emitted no visible flash was made for the professional 9xi camera, which had no built-in flash. Other than this model, all later SLRs could control wireless flash using pulses from the built in pop-up flash. But it took 10 years for the mainstream manufacturers to introduce similar wireless systems. Both Canon and Nikon used the switchover to DSLRs, and the need to rework the TTL-OTF exposure systems, as an opportunity to launch similar IR-controlled wireless flash.

Until recently, special controllers were needed to trigger the remotes, and the built-in flash could not do so. But this has now changed, with the EOS 7D, the first model in Canon's range to command wireless flash using its pop-up unit. Nikon added a similar function in the D90. For both systems, controllers can be either a flash unit mounted on the camera, or a much cheaper command module with no flash.

Each system has its own protocol, including channels, groups and power ratio setting for the remote flashguns. It will generally cost about £700-1000 to have a three head system with two high guide number heads (GN48 or greater, ISO100/m) and one lower power (around GN36). For DSLRs without a built-in flash, or earlier models where the pop-up cannot control remotes, one flash unit must be on-camera or a commander is also needed.

The advantage of these systems is that exposure should be perfect. Lighting ratios between the guns can be controlled from the camera position and previewed by making a test shot; factorial exposure adjustment, balancing with ambient light, and exposure bracketing are all possible. These systems also support high-speed synchronisation burst mode flash, which allows wide apertures and fast focal plane shutter speeds. In the past this has been limited to close subjects, but the arrival of high quality ISO settings up to 6400 extends the range.

The disadvantage of the camera makers' systems is that they are based on adapted camera-top speedlights. The 'feet' supplied often have only a plastic 1/4 inch tripod thread to allow mounting on a light stand, when lighting stands use 3/8 inch threads; and there is no modelling light function other than preview burst modes which drain battery power. The battery capacity limits both the number of shots you can take and your speed of working, with several seconds' gap between shots to ensure all heads have recycled.

Further drawbacks include the line-of-sight and good reflective surroundings needed for the IR or visible light-based communication to function. You can't place a flash head behind you, or aiming away from your commander; swivel and bounce heads must be used to ensure the receptor on the flash body is more or less aiming at the photographer.

Unless you pre-arrange with other photographers, there is a significant risk that with popular systems (notably Canon), someone else at a busy event will be using the same channel, and will trigger your flash and vice-versa. It's not as great risk as the bad old days of optical slave triggers, where every remote flash in the room would fire. If there does happen to be an optical slave switched on nearby - such as a mains-powered studio flash in an exhibition hall - the preflash pulses of the wireless system may set this off. It will have no effect on exposure, as the optical slave will have fired before your shutter opens.

For all these reasons, camera makers' wireless flashes aren't that attractive. There are plenty of other options, but if you are on a budget check out the compatible systems from Sigma, Mecablitz and Nissin. You can mix different makes into any one system such as Canon or Nikon, but it's not possible to change the make-protocol of the independent gun. If you buy a wireless Mecablitz for Nikon, you can't buy a module to convert it to Canon. The channel and group options are identical to respective models from the camera makers.

The radio alternative

For large events such as conferences, you may want remote heads positioned in the wings of a stage or overhead for whole room fill-in. The line of sight communication of camera system flash is unreliable once you go beyond 15 metres (and often less).

Wireless triggering was pioneered by PocketWizard, and this remains the most popular brand. The main advantage of a classic PocketWizard system is brand independence - you can mix hot shoe flash, mains powered studio heads and high power battery press guns. As long as the flash has, or can be fitted with, a sync terminal, a PocketWizard receiver can fire it.

This does not rule out automatic exposure. A versatile professional flash such as the Mecablitz 45CT (any model) has an auto exposure sensor in the flash, as an alternative to possible TTL control. It can be set for a manual fractional output, or a lens aperture as metered from the flash position. The camera bracket is equipped with both tripod and lighting stand threads and the wireless receiver can be mounted on it.

The range of wireless triggers using radio frequency is into hundreds of feet, not tens, and line of sight is not needed. Flash heads can be placed behind or above the camera position, round corners or concealed behind furniture.

The first ultra-compact alternative to PocketWizard was Elinchrom's Skyport. Though the range is not as impressive, Skyport is capable of dealing with any normal banqueting room, marquee or exhibition hall. The transmitter and receivers are tiny, using the kind of micro switches found on computer circuit boards to set channels and groups.

When used with Elinchrom RX, BXri, Ranger Quadra and other compatible kit the Skyport enables remote adjustment of multiple flash heads from the camera. The latest heads have the receiver built-in. There is no local display for monitoring output, it's on a suck-it-and-see basis or a matter of remembering the maximum and minimum power of a head, and stepping up or down.

Challenged by both the IR wireless systems and dedicated RF wireless like Skyport, PocketWizard introduced Mini TT1 and Flex TT5 in 2009, a pair of modules little larger than Skyport which effectively convert Canon or Nikon wireless flash to RF control. Fitting to the camera and the flash (or between flash and camera when on-camera flash is also needed), the components of the ControlTL system also add new functions. Channels and synchronisation timings are adjusted using a program on a laptop, and USB connection to the module. PocketWizard has managed to set up commands that allow sync up to 1/500th with some DSLRs in regular TTL (not high speed burst) mode.

At present, the PocketWizard ControlTL system is limited to Canon and Nikon. To fill a gap at the lower end, many low-cost Chinese radio flash sync devices have appeared in the last year. No doubt these will one day be developed to control flash as well as trigger it, but right now choices are limited.

Integrated systems

At the top end of the market for location off-camera flash there have always been higher power offerings approaching studio flash versatility. In the 1970s I used a Braun Hobby with a lead-acid battery pack accepting two heads; later on, a Mecablitz 502 with a Mecatwin second head. These were robust shoulder-slung battery supplies with high power hammerhead flashguns.

The Norman and Lumedyne systems from the USA offered a wider choice of battery capacities, and heads with interchangeable reflectors or bare bulb facility. Though these systems eventually developed exposure control, even today they remain best when used with manually set output as a replacement for mains flash.

The TTL-age successor to these respected systems is Quantum. Starting more or less as a hybrid between the simplicity of Norman and the familiar shape of a camera-top flash, the Q-Flash provides the bare bulb, accessory reflectors and lightshapers of classic location flash plus auto exposure and TTL control.

Like the SCA system used by Braun, Cullmann, Metz and others, which uses interchangeable modules to adapt a common flash unit to different camera makes, Quantum's QFlash 5-Dr offers modules for Nikon, Canon, Olympus, Hasselblad, Contax and Mamiya. But it also offers RF wireless remote operation up to 500 feet range - an option similar to using PocketWizard ControlTL, but with four times the power output of any camera-system flash unit. Quantum QFlash is expensive, but a single solution for a studio using (for example) both Hasselblad and Nikon.

Reverting to purely manual control, the power can go even higher using Elinchrom's Ranger Quadra system. With plans in hand to add a backpack or body strap to hold the rather large power pack which also contains the flash generator circuits, the Quadra heads are very small and light and well suited to use on camera brackets as well as remote stands. No auto exposure is possible, let alone TTL - this is purely manual. Each pack has a built-in Skyport receiver and the basic kit with one or two heads (wired to the pack, of course) comes with a transmitter-controller you use on camera.

Ranger Quadra is best used for very ambitious event coverage such as arena sports, fashion catwalk or theatre shoots, where two or more two-head rigs with a power pack each may be expected to provide many hundreds of exposures. It's possible to get durations as short as 1/6000s and recycling times to keep up with five frames a second motordrive for short bursts. There is a useful modelling lamp function, using LED illumination, that is either missing or very limited in other battery-powered options.

The overall cost of a two-head basic Quadra system is a little above that for two of the highest power camera speedlights with a controller. The cost of a two-head Quantum system is considerably more.

Mixing systems

While Quantum's TTL protocol cannot be mixed with the camera makers' own flash units, by switching to manual power with no preflash bursts and using optical or infrared slaves it's possible to link systems. A wireless transmitter on the camera can fire one or more remote flashes set to a manual power. Any other similarly set flash, of a different make, with a regular slave cell will fire if within range.

This means you can cover the difficult bit - camera to subject distance - using RF triggering but locate extra flash heads which don't have a wireless function close to the subject, using the slave cell. Sigma's EF 530 Super DG is a dedicated digital TTL flash, limited to the camera make you buy it for. But it's also got an old style slave cell setting allowing it to fire with manually set variable power output as an extra head in any manual set up.

Some new studio flash systems, such an Elinchrom's BXri heads, can be programmed to ignore the wireless protocol or TTL pre-flash sequences of camera system flashguns and only fire when the final 'actual exposure' burst arrives. Mecablitz is introducing this technology too, and the Chinese independents are busy devising slave cells with programmable firing. All these advances make it easier to add an accent light by repurposing a gun or head that normally lives in your studio or in the camera bag, rather than in your location lighting kit.

The great thing about digital shooting is that you can now test all the possible combinations and see straight away if anything is failing to fire, mistimed, or at the wrong power. The one thing I have not even mentioned is a flash meter - because so many photographers, even at fast moving events or covering weddings, no longer use one. A little experience plus a test shot or two on the LCD screen has replaced all that measuring and hoping.