There are 3 kinds of off camera flash systems, that is, three different methods of how to trigger flashes that are not attached to your camera. This is not a discussion about brands, though I’ll give you my recommendation of a brand/product for each category, but it is more about the technology behind how lights communicate with one another when they are not directly attached to a hotshoe. The term for these units that trigger external flashes is slaves. If you are looking for recommendations on flash units and modifiers, I’ve got an article all about that, too! If not, read on.
The three systems, optical slaves, infrared slaves, and radio slaves, all offer different advantages and disadvantages depending on what the environment is that you need to light in.
The first and most basic system is optical slave system. They are far and away the cheapest system and they work very simply. The optical slave has a light sensor on it, and when it “sees” a flash, it triggers the flash that it is connected to, too. This works because the speed and duration of the flash occurs well within the timeframe that the shutter is open. Even the best rated ones on amazon have mixed reviews, but I don’t think it’s because they are particularly bad, it’s just that they have the shortcomings that every optical slave unit has. They’ll certainly get the job done under the right conditions, but there is a reason they are the cheapest of the 3 options.
If you are working in an enclosed studio environment, these little cheapies may be plenty good for your needs. As previously stated, they work in an open game of “monkey see monkey do.” They trigger a flash when they see a flash. The units linked above support hotshoe connectivity as well as the PC cord connection, as many others do.
The down-sides to this style of flash unit are that if you were planning to shoot on location, you might run into two different kinds of problems. One problem arises if you are outdoors. These slaves work in line-of-sight, so if something is blocking your flash unit, or even if your flash isn’t bright enough to compete with the surrounding ambient light, there’s a high chance that your optical slave on the other end will never get the message it needs to get to be able to perform its duties. A different issue arises indoors if you are not the sole photographer. Imagine yourself at a wedding and planning to use an optical flash system in a reception area for the bride and groom’s first dance. Do you think maybe you won’t be the only person taking a picture in the space? Won’t Aunt Dottie want her own picture in the here-and-now because she wants to share an image on her Facebook profile? Count on it. So if you show up with your optical slaves and set up the right just light, if Aunt Dottie’s flash goes off before yours, they are popping your flashes for her picture and not yours. Factor in the time it takes for flashes to recharge after they’ve popped, and you might have your flashes hijacked for most of the night. This situation will simply not do when there are other people with cameras around, professional or not. Another downside is that there is no quality of communication between only units, they speak in only 1s and 0s, only “flash” and “not flash” are what they say to one another.
For these reasons, many people gravitate away from optical slave systems, though if your needs are simple and closed, they might be right for you. Infrared (IR) systems eliminate some of these problems by using bursts of infrared light instead of visible light between units. This way, Aunt Dottie can’t get all up in your business, because Aunt Dottie isn’t outputting any IR light, so your slaves pay no attention to her or anyone else using regular on-camera/popup flash. The IR slave system is also a step above optical slave systems because it doesn’t only trigger the light, it can communicate with other flashes and tell them how much light to put out when they do pop. As a result, IR slave systems can create complex and creative lighting ratios if the user knows how to instruct them to do so. This makes them outstanding for studio lighting.
IR systems solve some of the most serious concerns that plague optical slaves, but IR slaves aren’t without their disadvantages, either. First of all, IR systems aren’t simple, inexpensive units you can just plug your existing flashes into and start shooting like optical systems are. Most, if not all, IR systems are built into branded flash units. That means you can’t cross platforms; you’re more or less committed to the brand of your camera body, which isn’t the worst thing if you like your brand, but it almost certainly means you’re not getting the cheapest option available. Another downside it shares with the optical system is that we are still operating with light, meaning you still have the challenges of line of sight and if it’s too bright outside.
The third style, Radio slaves, are the chief of all triggers in my mind. There were brands that dominated the space in a third party fashion for a long time. PocketWizard was one of them that still exists and makes great, high quality, trusted-by-professionals products. But brands started paying attention to where they were losing parts of the market, and got wise. Today, brands like Canon and Nikon are working them into their units as they come out of the box, a really great idea. I highly encourage you to go that route. Radio triggers share all of the benefits and solve all of the problems the others have: they are not able to be hijacked by common folk at your event, they are not line-of-sight dependent, which means you can shoot with them through walls or at GREAT distances (hundreds of yards), they can be told to shoot with auto modes or power can be changed at a distance, and they are, these days, relatively inexpensive if you have to go with a third party brand if you already own flashes that aren’t radio enabled. Brands like Yongnuo are also taking shots at big names like PocketWizard by offering similarly functional units at half the price, a real game changer from when I was jumping into the radio-trigger world.
So do I know what radio trigger system is right for you? Maybe not, but I feel like if I said “Radio is right for you,” the number of people who would come back to me and tell me I was wrong would be in the ballpark of zero. They are increasingly less expensive, and for all the other reasons I mentioned, I would be very confident in going that route if I were venturing into off-camera flash for the first time. There just isn’t a scenario where they disappoint.
