Be my (radio-controlled) slave

A very effective way to control off-camera flash

Here’s why pros prefer radio slaves, and how you can choose between the top two systems on the market.

A definition first: A slave, in photographic jargon, is a piece of hardware that is either built into or plugs into a flash unit and fires that flash when the slave is actuated, either by a short, intense pulse of light (a light-actuated slave), an infrared beam (an infrared slave), or a radio signal (a radio slave).

While slaves can be separate pieces of hardware, many flash units available today have built-in slaves. Often, they are the light-actuated type, but there are also some flash units that offer radio slave receivers built into them. To make things even more convenient there’s also one brand of light meter available with a built-in radio slave transmitter that can fire flash units equipped with compatible radio slave receivers, so you can easily take readings of their output.

Of the three types of slaves, this column deals with one: the radio slave. A radio slave is both more expensive and complex than a light-actuated slave but, very importantly and unlike light actuated slaves, it allows your flash/slave combination to discriminate, so only you can fire it, instead of the masses of flashes on point-and-shoot cameras getting the benefit of your lighting setup.

What's wrong with infrared slaves?

The third category of slave, those actuated by an infrared beam, also discriminate between you and the army of point-and-shoot-camera flashes at a typical wedding, but are more limited in range, and offer fewer distinct channels than radio slaves. That can be a problem when multiple professional photographers are working near each other. Lastly, the performance of infrared-actuated slaves is affected by some of the fabrics and materials found in typical wedding hall venues. Velvet draperies and the sound-absorbing foam sprayed on ceilings are also very good at absorbing infrared beams, thus limiting the range of infrared-actuated slaves.

Radio-Actuated Slaves

Originally, radio slaves were nothing more than glorified remote-controlled garage door openers, and were once limited to a handful of brands, including Quantum, Dynalite, Venca, and Hawk. All have disappeared. However, all of these early crystal-based radio slaves had limitations imposed upon them by the radio technology of that time, which included short range, 12-inch (or longer) antennas, high battery-power consumption, and erratic performance.

Although digital radio slaves offer superior performance to analog radio slaves, analog units are often good buys because used radio slave systems go on the market when a photographer updates to a digital radio slave system.

The Quantum Radio Slave 4i is a digital system that uses two different-sized boxes for the transmitter and receiver modules. The transmitter is powered by a 9-volt battery and the receiver uses 4 AA cells, but since the transmitter is only powered up when you fire it, its 9-volt battery seems to last forever. The transmitter (which always must be on the alert to accept a signal) runs for about 400 hours off its set of AA cells. The range for the 4i is 200 feet with the receiver antenna down and 350 feet with it extended.

Today’s Digital Radio-Actuated Slaves

As I write this (in late 2004), there are two brands of digital radio slaves that vie to be included in the professional photographer’s equipment arsenal. Alphabetically, they are the PocketWizard (distributed by Mamiya America Corp) and the FreeXwire made by Quantum. In all honesty, I feel that the FreeXwire is superior in design when compared to the PocketWizard, but I also must admit that I personally use and prefer the PocketWizard brand of radio slaves.

The FreeXwire is the newer addition to this field, and after examining both brands, some may conclude it’s the better choice. The FreeXwire consists of a transceiver module and any module can be used as either a transmitter or receiver by choosing which way to throw a switch. It features simple operation and the ability to turn on or off 4 different lights by throwing switches on the unit’s face. It also provides an antenna that folds out of the way, and an optional hot shoe attachment if you’re using it on a camera so equipped.

Not surprisingly, it works seamlessly with the Quantum Q-Flash or, through the use of an appropriate cable, can also fire a remote camera. As either a flash slave or a remote camera control the FreeXwire’s range is approximately 500 feet and a set of two AAA batteries will power it for about 120 hours. Interestingly, because of the transceiver design, when a module is attached to a flash far from the triggering module, the receiving module rebroadcasts its signal that can energize a second module mounted on a flash unit located up to another 500 feet away from the transmitter.

Unlimited range

This creates a daisy-chain effect that results in a virtually unlimited range…providing you have enough FreeXwire modules. In the act of rebroadcasting the signal, the transmitter is also notified that the signal has reached the receiving module. It’s a design that is elegant in its simplicity and it’s loaded with features…. almost too many to mention here. For more info on the FreeXwire, go to:

This multiple exposure photo, right, of a FreeXwire shows how the antenna pivots from extended position to a position safely tucked in against the module’s side. Acting as either a receiver or transmitter, it measures approximately 3-1/3x2-1/4x3/4 inches, or about the same size as the 4i’s transmitter. Its swiveling antenna adds about another 2 inches in length.

Pocket Wizard

The other key player in the radio slave game is the well-established PocketWizard. While PocketWizard units can do just about everything that a FreeXwire does, their real claim to fame is in brilliant marketing.

Wisely, PocketWizard made deals for the inclusion of their receivers in flash units made by Profoto, Norman, and Dynalite. PocketWizard transmitters can be retrofitted into Nikon D, D1, and D1x cameras, the Kodak DC14n, and (you heard it here first!) they are in negotiations with Canon to do the same thing!

For their final and greatest coup, they added a transmitter module that plugs into two different Sekonic light meters. The inclusion of the transmitter module in the Sekonic meters was the biggest selling point for me! Until this brilliant move, every pro photographer I knew had a radio slave transmitter taped or velcroed (used as a verb referring to the act of attaching two things together using Velcro™) to his flash meter.

Like the other contender’s units, they can also fire a remote camera, but because of their inclusion in so many other photographic lighting and metering products, they have become the de facto standard for many professionals.

Two systems compared

Unlike the FreeXwire, the PocketWizard is available in two different models. Also unlike the FreeXwire, the PocketWizard Plus has two distinct modules; a transmitter and a receiver, and is limited to four user-selectable channels.

The PocketWizard MultiMax is like the FreeXwire in that there is one transceiver module that can play the role of either transmitter or receiver, and it offers many more features than the Plus model. Although I have and use both of the PocketWizard models, I have found that for wedding work the simpler Plus model is more than adequate.

Both the MultiMax and the less expensive Plus models have a range of about 1600 feet and either a receiver, transmitter, or transceiver can run them for about 150 hours on two AA batteries. However, the 150 hours is a conservative figure and can be increased approximately fourfold (to 600 hours) by using two lithium AAs instead of alkaline batteries. I make note of this because there are as yet no lithium AAA cells available to do the same for the FreeXwire. For more info on the PocketWizard line, check out the following website:

Both PocketWizard models fit in the same sized case (4x2.1x1.4 inches, not counting the 2.4-inch flexible antenna) but the MultiMax has an LCD display to help you keep track of all its functions and available channels. While the Plus model has just 4 channels, selected by sliding a switch, the MultiMax has 32 channels that are set by the toggle buttons, and they are shown on the display.

Buying advice

Only you can make a choice between the two brands of radio slaves I have mentioned here--after all it’s your money and only you know the other equipment that the radio slave must work with. But if I were using Quantum’s Q-Flash, I would look long and hard at the FreeXwire but, for me, the combination of the PocketWizard in the hot shoe on my camera, a Sekonic meter with the PocketWizard transmitter module in it, and a Dynalite pack with a built in PocketWizard receiver is one sweet deal.