This is the final part of a three-part series on Canon Speedlite flashes, written for the Canon Digital Learning Center by Gordon Lewis:

1. Choosing the Right Flash (click to read)
2. Beyond the Instruction Manual (click to read)
3. Multiple Flash and Lighting Ratios: A Wireless Primer

New on the CDLC: For a detailed, step-by-step exploration of the External Flash Functions and Wireless Flash Settings menus on compatible EOS cameras, watch these educational videos by Explorer of Light Bruce Dorn, Part I: External Speedlite Controls, and Part II: External Speedlite Ratio Controls

Let’s start with why you might need more than one Speedlite. The primary reason is that there’s a limit to what you can do with one flash unit mounted to your camera. Multiple units give you many more options for light placement. For example, if you’re doing portraiture you can use one Speedlite on a light stand as your main light and a second on your camera for shadow fill. Add a third Speedlite on a light stand and you can use it for backlight or to light a background.

Architectural and real estate photographers use multiple flash units to light multiple areas of a room, separately and independently. Want to a photograph a large painting? For the most even lighting you’ll need at least two Speedlite on light stands (one on each side of the artwork). As long as you aren’t trying to light anything huge or far away, the possibilities are limited only by your imagination and bank account.

Until the advent of the Canon Wireless Speedlite System, using multiple flash units required you either to:

1. Connect them to the camera with flash sync cords,


2. Synchronize them with wireless infrared triggers, or


3. Synchronize them with wireless radio triggers.

The good thing about flash cords is that they are relatively inexpensive. Unfortunately, they can also be delicate: You never can tell when some sort of internal damage will render them useless. Another major problem is that they’re dangerous: If someone trips over a cord, that person and anything the cord is connected to could go crashing to the ground. Trust me, it’s not a pretty sight.

Wireless infrared devices trigger remote flash units in sync with the flash from a master flash unit. Infrared triggers have the advantage of being wireless, but depending on what type you use, they can either be too sensitive (i.e., triggered by a flickering florescent light) or not sensitive enough. Also, because they react to any flash pulse, they can be triggered by any other photographer’s flash unit, not just your own.

The advantage of wireless radio triggers is that they can be set to a channel different from that of other photographers. Another advantage is that their effective range is measured in yards rather than feet. The drawback is that the better units can cost as much as the flash unit they are connected to, and they have their own learning curve to use effectively.

The one major drawback that all three approaches have in common is this: They are mostly incompatible with Canon’s dedicated T-TTL/E-TTL II flash system (except for some versions of wireless radio triggers such as PocketWizards^® or RadioPoppers^®). You therefore have to set each unit’s output manually, one-by-one, until you get the exposure balance you want. The more flash units you use, the more inconvenient and time-consuming this can be.

Canon’s Wireless Speedlite System requires one “master” unit mounted to the camera. The master unit emits a series of flash signals before the actual exposure to communicate with and control the so-called “slave” (off-camera remote) units. It controls which Speedlites flash and how much light they emit. It also synchronizes their output with each other and with the camera’s shutter. Because it uses flash signals it requires that the master and slaves be within each other’s line of sight.

With the Wireless E-TTL flash system, perhaps the most important thing to remember is that it’s all automatic flash exposure control. Nearly anything you can do with a single flash on-camera in terms of flash exposure control is also possible with multiple flashes off-camera with Canon’s wireless system. The sole thing you cannot do in wireless that you can with a single flash on-camera is 2nd curtain flash sync.

Another huge benefit of using the Canon Wireless Speedlite system is that it allows you to maintain full communication and automation between multiple flash units and your camera. This means you can control your remote Speedlites, individually or all at once, all from your camera position. In fact, Canon’s most recent DSLRs, such as the EOS 40D, 50D, 5D Mark II and 1D/Ds Mark III series, allow you to control your Speedlites with a menu built into the camera. If your camera doesn’t have this feature, you can use the control menu on your Speedlite (some basic set-up instructions are explained in this tip such as assigning groups, channels, and master/slave status -- for all other set-up instructions please refer to your flash manual).

And yet another advantage is that you can assign all of your remote flash units to one of four “channels.” As long as no other Canon EOS photographer is shooting with Wireless E-TTL flash and using the same channel, your Speedlites can be triggered only by your master unit and no one else’s. Ordinary flash illumination from other people’s cameras at an event will never set off Canon wireless flashes.

You will need at least one master unit and one slave unit. The master flash can be either a Speedlite 580EX II (or equivalent, such as a 580EX or even the older 550EX) or an ST-E2 Speedlite Transmitter. The Speedlite 430EX or EX II (and older models) can only operate as an off-camera slave unit -- not a master unit. An important point is that you can effectively have an unlimited number of off-camera slave units, as long as they’re positioned within range of the triggering device that’s on the camera. Furthermore, you can easily mix and match off-camera slave units, using any combination of 580EX II, 430EX II, or previous compatible models with slave unit functionality.

The ST-E2 transmitter provides most of the flash control functions mentioned above, but provides no visible light of its own. Instead, it uses near-infrared pre-flashes to control the slaves. This can be an advantage when you’re working with skittish subjects. Another benefit is that the ST-E2 is much smaller and lighter than a flash unit. That makes a big difference when you’re shooting handheld for long periods. On the other hand, its lower output reduces the maximum indoor operating range to approximately 30 feet. If you’re shooting with ratio control (more on that in a moment), with the Speedlite Transmitter ST-E2, you’re limited to only two groups of Speedlites, not three.

Although the Speedlite 580EX II is the larger, heavier, more expensive option, it also the most versatile. The 580EX II has the benefits of contributing light of its own as needed, and expanding your maximum indoor operating range to about 49 feet. Used as a “master” unit, the 580EX II can control multiple slave units to fire evenly (at same power level), or you can assign flash ratios, where one or more flashes fire at greater power than another group of slave units. You also have the option of setting it to control any slaves units without the on-camera master unit firing during the actual exposure.

PLEASE NOTE: Even if the master unit's flash firing is 'disabled', the flash will still appear to go off. However, it will NOT in any way affect the image exposure, because the flash you see is simply a pulse light signal that the master flash emits to transmit settings/shooting data to any slave flashes. This pulse light flashes a fraction of a second BEFORE the photo is taken.

Off-camera slave units can be grouped together so that you can control multiple flashes as one group. A “group” can consist of only one flash unit, or accommodate as many as you need.

The Wireless Speedlite system allows for up to three groups: A, B and C. The master flash unit is always in Group A. Slave units can be assigned to Group A, B, or C via the control menu on the slave unit’s LCD panel (see above animated image of the rear flash LCD -- basically, use the flash's 'Zoom/z' button to activate the wireless menu, and use the Sel/Set button/wheel to navigate and select various options). Once you’ve set each slave unit to be in a particular group, you don’t have to touch the slave units again, except to actually position them to light your subject. Each group can then be controlled remotely, from the camera position, using either the controls on the master Speedlite, the ST-E2 transmitter, or your camera’s Flash Control Menu.

Finally, Canon’s Wireless Speedlite System allows you to use ratios to control the relative output between one flash group and another. (Remember, a group can consist of only one flash, or as many flashes as you need). For example, if you wanted Group B to output twice as much light as Group A for one stop more exposure, you simply set an A:B ratio of 1:2 and the EOS flash system automatically takes care of the rest.

If you prefer, you can control each group’s output manually so that it emits a fixed amount of light, regardless of subject distance or reflectivity. This is best done with a handheld flash meter and is beyond the scope of this article, however suffice it to say that if you’re advanced enough to want this feature, the Speedlite system can accommodate you.

The only real limitation you need to keep in mind is that because the Wireless Speedlite System relies on flash pulses for control and communication, each slave unit you use has to be able to “see” the pulses from the master flash unit (this is why the master flash appears to go off, whether or not you have 'enabled' it). When you’re outdoors this means that all of your Speedlites should be within direct line of sight of each other. This is less essential indoors, when you can rely on reflections from nearby walls. Wherever you are, you have to avoid using light modifiers, such as light boxes, that block the flash sensor on the front of the Speedlite. The following diagram illustrates the basic indoor and outdoor ranges (within an 80-degree angle from the master unit; anything more than that and the flashes may not 'see' each other):

Here are a few simple examples of how theory works in practice. Let’s start with the most basic set-up: a portrait using two Speedlites, with one unit mounted on your camera and the other mounted to a light stand. The unit mounted on the light stand functions as the main light source—the one that provides the dominant highlight and shadows. The unit mounted on your camera functions as the fill light—the one that fills (lightens) the shadow cast by the main light.

The simplest way to control this set-up would be to assign both Speedlites to Group A. Since they are in the same group they would output the same amount of light relative to each other. Your camera’s flash exposure system would automatically adjust their combined output to match whatever aperture and ISO you set on your camera. (As I mentioned in Part 2, the shutter speed affects the ambient light exposure, not the flash exposure.)

Now let’s say you wanted the shadow side of your subject to be darker relative to the highlight side. The way to do this would be to reduce the output of the fill light relative to the main light. This takes just three simple steps:

1. Set the fill light (the master flash unit) to Group A.


2. Set the main light (the off-camera slave unit) to Group B.


3. Set the desired A:B output ratio.

Splitting the Speedlites into separate groups allows you to control the output of one group independently of the other. Your camera’s flash exposure system will automatically produce the ratio you set. You can set any ratio you like within a range of 8:1 to 1:8, in 1/2-stop increments. In the example above, a good starting point would be an A:B ratio of 1:2 or 1:4 — meaning the B group fires with more intensity than the A group. The accompanying illustration shows how you would set a 1:4 ratio on a camera that has the Flash Control Menu feature.

The following table explains how output ratios correspond to differences in f-stops. Advanced photographers reading this should note that for the purposes of our portrait lighting example above, where the 'A' flash is enabled to fire from the camera's hot shoe, any ratio where A is greater than B (2:1, 4:1, etc.) would look pretty much the same in a photograph. That’s because when the frontal “fill” light (A) is more powerful than the “main” light (B) there are no longer any shadows to fill.

If any of this seems complicated, don’t worry. In practice all you have to do set the exposure you want to use on your camera, check to make sure the shutter speed is at or below the correct sync speed, and shoot. If the shadows are too light, increase the output ratio so that A outputs less light than B. If they are too dark, decrease the ratio. The interactive illustration below shows the visual effects of various ratios and mimics what you would see on the rear LCD of your camera.

Let’s say you were using the lighting set-up above and you were happy with the results but you wanted to lighten the background. Adding a third Speedlite to light the background would accomplish that task nicely. Since you’ve already got the ratio you want for your subject in the foreground there’s no need to change the A:B ratio. You simply set the third Speedlite to Group C and change the overall ratio setting on your camera or master flash unit to A:B C. The Speedlite flash system then allows you to control the output of C independently of the ratio for A and B so you can change the brightness of the background without affecting your foreground ratio. In fact, the C group is intended for lighting backgrounds or other accent-type lighting; you don’t want any C-flashes to be directly lighting the main subject. Once you’ve set A:B C as a ratio, you adjust the C group using a +/- control relative to the total output of the A:B lighting on your main subject.

Once again, the benefit of using a digital SLR is that what you’re never shooting blind. What you see is what you get—and what you see when you expand your Speedlite system can often exceed your expectations.

Using multiple Canon Speedlites gives you a degree of control and a range of creative lighting possibilities you simply can’t get with a single flash unit—yet you don’t have to sacrifice the ease of use that has made Canon DSLRs so popular. You can start out with two Speedlites, set them up in different configurations and experiment with different ratios to see what happens. As you gain familiarity with the various configurations and controls you’ll gain confidence in your lighting skills and valuable insights into what works best for you. You’ll also understand why, for thousands of photographers who need a compact, portable, wireless lighting solution, Canon Speedlites are the one accessory they won’t leave home without.

Take a look at the images below -- all of these were created with the use of off-camera, multi-point lighting. Whether you want a bright high-key effect, or a moody low-key feel, or even the subtle fill-flash used in environmental portraiture to compliment the existing sunlight while making your subject 'pop' -- the possibilities are endless!