One of the things photographers often struggle with is the challenge of creating a reliable off-camera flash setup. Off-camera flash triggering, in particular, can be an area of confusion. In this article, I’m going to briefly discuss some of the methods used to trigger remote/slave flash units.
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, through-the-lens flash metering (TTL) isn’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, Nikon, Sony or flash systems you’re probably familiar with their respective versions of automatic flash exposure control (e.g. E-TTL II, 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. This allows the camera to calculate the flash output necessary for the actual exposure. When the flash is mounted to the camera, the camera sends 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 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 systems 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.
These camera makers have other ways to control remote units using their proprietary flash systems, including dedicated sync cords, special transmitter units and radio transmitter/receiver capabilities of certain flash models, such as the Speedlite 600EX II-RT and the ST-E3-RT unit for Canon. Radio options eliminate the line-of-sight limitations of the standard TTL light pulse communications between master and slave units. You can find both TTL and non-TTL radio triggers from 3rd-party makers as well.
Radio Triggers, Manual Flash
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 TTL II 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.
Watch this video about simple radio trigger use:
While not a wireless solution, (and not E-TTL II/i-TTL compatible), the PC cord is a quick and easy way to sync your camera to a manually set flash unit. 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 the fact that they’re a wired solution, makes them less versatile 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.
Optical slaves are a simple low-budget wireless solution for syncing any number of manually controlled flash units. 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. It does this 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:
- 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.
- Make sure you 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.
Of course, with optical slaves 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. 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 is going to depend on your budget and working style. If you are not comfortable with manual flash and camera settings, you’ll have to use gear compatible with your system’s automatic flash control. However, I encourage you to explore manual off-camera flash solutions, too. These will help you gain more control over your lighting and give you the option of basic triggering should a more sophisticated method fail.
Other videos related to this topic: