One of the things photographers often struggle with is the challenge of creating a reliable off-camera flash setup.  If you’re reading this, you’re probably already aware of the benefits of off-camera flash photography versus using only a flash that is mounted to the hotshoe of your camera.  In this article, I’m going to briefly discuss some of the methods used to trigger remote/slave flash units.  If you’d like to read more about setting up your flash units on light stands, using light modifiers, and proper positioning for portraiture, please grab a copy of my free eBook, Mini-Guide to Off-Camera Flash (also available when signing up for my free newsletter).

There are several ways to trigger one or more remotely positioned flash units. However there are big differences between each method with regard to effectiveness and functionality.  For example, one thing that often comes as a surprise to photographers who are new to off-camera flash is the fact that through-the-lens metering (TTL) and automatic flash output control aren’t available in every scenario; some of these solutions require you to use manual camera and flash settings.

Here’s a breakdown of the major off-camera flash syncing methods:

E-TTL II and i-TTL
If you use either the Canon or Nikon flash system you’re probably familiar with their respective versions of automatic flash exposure control (E-TTL II and i-TTL/CLS).  Essentially, these systems allow the camera and flash to work together to maintain proper flash output.  Each time the shutter release button is depressed, and just before the shutter is released, an almost imperceptible preflash is fired allowing the camera to calculate the flash output necessary for the actual exposure.  When the flash is mounted to the camera, the camera sends communication signals to the flash via electronic contacts located on the camera’s hot shoe and on the foot of the flash.

What’s great about these systems is that some of the flash units can, aside from their ability to fire a preflash, also send E-TTL II or i-TTL control signals to remote flash units via flash pulses.  This means that higher-end flash units and some built-in flash units can serve as “master” flash controllers to remote “slave” flash units.  These systems can work great in normal shooting situations, especially indoors, but can suffer from spotty signal reception where there are line-of-sight obstructions or very bright daylight conditions to compete with the signals.  What’s also interesting to note, is that even though these system were designed to make automatic flash output control possible with remote units, they can be used to trigger flash units set to manual mode giving the photographer more precise, direct control over flash output.

Canon and Nikon have other ways to control remote units using their proprietary flash systems, including dedicated sync cords, special transmitter units and Canon’s new radio transmitter/receiver capabilities of the Speedlite 600EX-RT and the ST-E3-RT unit.  Radio options eliminate the line-of-sight limitations of the standard E-TTL II and i-TTL light pulse communications between master and slave units.  Although Nikon does not currently have an integrated radio solution, as you’ll see later, other companies have provided work-arounds for native optical transmission.

Canon’s ST-E2 is only one way optical wireless transmission can be achieved for E-TTL II communication between camera and remote flash units.  Built-in flash (integrated Speedlite transmitter), and the 580EX, 580EX II, and 600EX-RT can all control remote units.  Similar solutions are available with Nikon.

Radio Triggers
Although Canon has a new radio transmission solution to the line-of-sight problem associated with the optical wireless transmission of E-TTL II signals, third-party radio solutions have been available for quite some time.  RadioPopper, PocketWizard and others have come up with ways to capture and relay the proprietary signals from Canon and Nikon cameras to their Speedlite/Speedlight units.

But if you’re less interested in automatic flash output and exposure control, and would like to focus more more on manual flash shooting, there are plenty of good solutions out there to make off-camera flash really work for you. These solutions won’t allow you to use E-TTL II or i-TTL to manage your flash, but they will allow you to trigger flash units from the camera position. Of course, you’ll have to manage flash output via the flash units themselves (this is possible with flash units that allow you to adjust and set their output levels).  Things like lighting ratios and other elements of flash exposure will have to be managed by you, but it will allow you full control over your lighting, which can ultimately produce amazingly consistent results.

There are many basic radio triggering solutions available for non-TTL applications, including the PockeWizard Plus II, and other PocketWizard models, and many low-cost triggers from other manufacturers.  One note of caution:  before investing in a set of radio triggers, make sure you do your research and look for models with good reviews.  A lower-priced set of radio triggers might sound like a bargain until you’re having to deal with frustratingly unreliable flash syncing.

PocketWizard Plus II attached to a hot shoe adapter.  The flash unit will mount to the hot shoe adapter and will be triggered when this PocketWizard receives the “flash” signal from the matching PocketWizard mounted to the camera.  The umbrella bracket shown is what I typically use to mount my flash to a light stand.

PC Cords
While not a wireless solution, and certainly not E-TTL II/i-TTL compatible, the PC cord (having nothing to do with “personal computers”) is a quick and easy way to sync your camera to a manually set flash unit located somewhere away from the shooting position.  If your camera has a PC connector terminal or a hot shoe adapter that provides this type of connection, you can plug a PC cord into it, and plug the other end to a flash with a similar connector or adapter.  PC cords with the screw lock feature are less prone to accidentally detaching from their terminals than their more basic counterparts, but they still have a reputation for unreliability.  This, and fact that they’re a wired solution, makes them less flexible and more prone to accidents and failure. Also, it’s not always possible to reliably hook up more than one flash unit at a time using PC cords.  The one advantage a PC cord (or any simple cord connector) has over optical wireless transmission is that there is no line-of-sight signal problem to contend with.

Canon Speedlite 580EX II with PC cord (locking screw type) connected.  If your flash does not have a built-in PC terminal, you’ll need a PC cord adapter that mounts to the foot of the flash.

Optical Slaves
If you’re looking for a very simple low-budget wireless solution for syncing any number of manually controlled flash units, optical slaves might be a good option.  These are typically small units that connect to your flash, either directly or via a hot shoe adapter.  An optical slave flash trigger is  essentially an “electronic eye” that responds to the flash burst from a “master” flash by sending an electric signal to the flash it’s connected to, causing that flash to also fire.  So, when you take a picture and the flash connected to your camera fires, each remotely positioned flash, equipped with an optical slave, will also fire.  This happens instantaneously so all flash units contribute to the exposure.  There are a couple of important things to be aware of when using optical slaves:

1. Do not use E-TTL II/i-TTL or any automatic feature that creates a preflash or otherwise uses a connected flash for anything but the actual exposure.  Since any flash-type pulse of light will trigger a standard optical slave, the remote flash will likely fire during the first pulse it sees. In the case of preflash, the optical slave will react to the preflash, causing the remote flash to fire and end milliseconds before the shutter opens. Of course, this means the remote flash won’t fire during, or contribute to, the actual exposure.  Some optical slaves are designed to take preflash into account, ignoring a first pulse, and triggering on the second pulse (presumably the flash of the actual exposure). These however, have received mixed reviews from users.  It’s just best to set the camera for manual flash when using optical slave triggers.
2. Make sure your use an optical slave that is compatible with your specific type and/or brand of flash unit.  When using Canon Speedlites, for example, it’s recommended that you attach optical slaves that are explicitly compatible with the EX series of flashes.

Canon Speedlite 430EX II mounted to a PC connection adapter with Sonia brand optical slave attached.  This optical slave is compatible with EX series flash units.

Of course, there will still be a line-of-sight limitation, as with any optical wireless transmission/reception solution, but, again, you won’t have a problem with most close-quarters indoor shooting because even if your optical slaves aren’t directly in-line with your master flash, they’ll likely pick up the light pulse as it bounces off other surfaces (i.e. walls).  Outdoors during bright daylight, might be more of a challenge.

The method you decide to use for triggering off-camera flash units for your work is going to depend on your budget and working style.  Naturally, if you are not comfortable or willing to work with manual flash and camera settings, you’ll have to use a method and gear compatible with your system’s automatic flash control.  However, I encourage you to explore manual off-camera flash solutions, too.  These will not only help you gain more control over your lighting, but also give you the option to use basic triggering should a more sophisticated method fail.

You can read more about these technologies and their applications in the new book I co-authored with David Busch, David Busch’s Guide to Canon Flash Photography.