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I understand that with remote triggers like PocketWizard we can set them to work on different channels and zones, but those things aside, from the view of just firing multiple flashes, should I just put my remote flashes on "Slave" mode? Or should I buy one "PocketWizard" for each flash to fire them? What is the difference?

  • Which PocketWizard (TTL or manual), flash, and "slave" mode are we talking about, here? Because, depending on the answers, the differences can vary widely. – inkista Jun 5 '15 at 2:03
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The goal of all of them is to fire a flash that's not on the camera.

Let's take a look at what all this means

  • radio trigger (e.g. PocketWizard) They talk to each other via radio, which means there's no flash firing just for communication purposes.

    • You will definitely need a sender unit on the camera, because no camera (as of yet) has built in sender. This is because the triggers are third party solutions. Not even Canon, who have speedlights with built in radio receiver have a sender in any camera model.

    • In general, you also need a receiver on each flash unit. Some higher end studio strobes come with built in PocketWizard receivers or radio receivers of their own system (you usually also get a sender for the camera)

    This has the advantage of working in situations where line of sight is not possible. The communication works better around corners and in general over bigger distances.

    • You can have "dumb" communication that basically tells the slave units to fire.

    • Or you can have full TTL via radio.

    Different systems provide different feature sets.

  • "slave mode" This term is a bit confusing in this context. The radio trigger communication also requires a master to trigger several slave units. What you are referring to is the communication built into the flash unit itself. Most flashes can be set to be slave.

    • The flash unit has a little light sensor to detect if another flash fires. This is a "dumb" slave mode, which fires as soon as it sees the other flash. A dumb slave will work across systems (fire FUQ690 flash with Buzz Lightyear camera ;) ) There are "smarter" slaves that will wait a certain amount of flashes, before firing. This allows them to be used in conjunction with TTL flashes. The TTL flashes will fire a bunch of times to get their communication done. The "smart" slave know how many flashes the communication takes an fires after that, in sync with the other flashes. Both smart and dumb slaves are just firing the flash, there are no groups or metering, whatsoever. You pretty much replace pushing the fire/test button on the unit or closing the middle pin on its socket.

    • If you pair a flash unit and camera of one manufacturer, chances are the camera can act as a master for the remote slave units either via its pop-up flash or another flash unit on-camera. This allows you to do TTL: The slaves and the master talk to each other and figure out the best flash output power. But there's more. At the end of the whole TTL dialog, each flash will fire with a certain power setting. If you take away the communication, that means this also allows you to remotely dial in a manual value for each unit. And there usually is exactly such an option: set the power output level of each flash unit. This is very useful, because you do not have to go to each slave unit to change its setting. Or maybe you have a unit on a stand up high above. If you take it down to change the power, chances are you will not be able to set it up in the same hight and orientation. You'd have to fiddle around a bit to get it right again, which can be undesirable. This option usually means groups for flashes, TTL as mentioned, ratios of groups, etc.

  • cable We live in a wireless world. That's why we curse when the wifi is slow because a dozen people share it with us. Or we cannot make a phone call because the building blocks the signal. Cables do not have this problem. A cable is the most reliable, most cheap way to trigger a remote flash. There are cables to make "dumb" slaves but also advanced cables that allow TTL.


Confused? Yeah, it's a bit of a mess. Here's a conclusion:

What do the flashes use to communicate? radio, infrared line of sight or cable

What are they communicating? dumb signal "fire now", TTL, remote manual control and/or advanced stuff like rear curtain sync or readiness of the slave to fire

What is compatible with what? dumb remotes work with pretty much everything across different brands, anything more advanced will usually only work with one brand or if third party manufacturers reverse engineer the system to be compatible to that brand specific system

  • 1
    Also worth adding a mention that the possible sync speeds vary with methods... – junkyardsparkle Jun 5 '15 at 19:38
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If you're talking about optical slave mode, where slave flashes detect the flash from the master flash, then two primary reasons are that optical slave is much less effective/reliable in daylight, and also requires line of site, whereas radio triggers/radio slaves don't, and can typically work over a higher distance. For reliability, I would definitely use radio slaves (I use cheaper non-TTL radio slaves from Yongnuo, they're reliable enough) on each camera. One of my flashes has radio built in, so it obviously doesn't need a separate slave trigger, and if I'm just taking one flash with me, I choose this one as it is a bit less to carry around with me.

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Depends on system and vintage. Canon's newish 600RT has built-in radio. Not sure if/when Nikon switched built-in slaves to radio.

But for the older (not saying ancient, just not-last-year) built-in infrared remote systems there are definite issues. They're line-of-sight and they're very short range in daylight.

OTOH the infrared systems support TTL, the older/cheaper radio systems are simple triggers dependent on manual power settings on the flash.

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On your other question, you mention SB910s and CLS (Creative Light System), so I'm going to assume you mean using CLS's slave mode, vs. manual PocketWizard radio triggers (like the PlusX units); and not "dumb"/SU-4 mode, or the flex/mini TTL-capable PocketWizard triggers.

The main advantages are range, reliability, and no line-of-sight requirements when used outdoors in bright light.

Optical slaving requires that the optical sensor on the flash can "see" the master signal from the camera. That means you can't put the flash behind anything that will physically block the light from reaching the sensor. And in brighter light conditions (sunlight outside), the master signal is relatively weaker to the ambient light. And without bounce surfaces around, the line-of-sight requirements become more stringent. Radio doesn't have any direction requirements and can be used over much longer distances, and (obviously) isn't affected by ambient light conditions.

The main disadvantages with manual radio triggers, are a lack of remote setting controls and features like TTL (through-the-lens flash metering--an automated way to set the flash's power) and HSS/FP (high-speed sync/focal plane flash--being able to use shutter speeds higher than the camera body's maximum sync speed).

If you're using manual radio triggers, however, while you gain on reliability and range, you can lose a lot of features that CLS offers you--TTL, HSS/FP, remote power control, etc. etc. These are all features that CLS supports that a manual radio trigger can't. TTL radio triggers (like the PocketWizard Flex/Mini units) can. So the differences become smaller if those are the units you're talking about. Manual units, like the PlusX can mostly only relay the "fire" signal.

Also understand that the SU-4 slave mode is manual-only and optical, so with it you don't have any of the fancy features and all the vulnerabilities of an optical system--but it's more universally compatible and could be used with, say, a Canon setup.

And some flashes, like the Canon 600EX-RT, have radio slave capability built-in that does pretty much most of what CLS can do, but over radio. So your question can be answered in a variety of ways. :)

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Some have already answered this, but I'd like to add a bit and summarize.

1) With optical you first need to actually fire a flash. Sometimes you can fire the built-in flash. But you will contaminate the scene with that first flash. You do not want that when you really want a mood.

Radio trigger = Problem solved.

2) Optical slaves do not fire in some bright situations, not only in daylight, but also indoors where some spotlight is over one of your slaves.

Radio trigger = Problem solved.

3) Optical. You need a line of sight. This limits you on the setup.

Radio trigger = Problem solved.

4) Distances. With optical, the slave won't detect at some range. Let's say 5 m.

Radio trigger = Problem solved. Some triggers work with ranges at least 10 times larger.

You can have a flash on the other side of a room and trigger it.

5) Flash firing contamination. You are at a wedding with your optical flashes...and everyone is firing their own flashes... you are in a trouble.

Radio trigger = Problem solved.

6) In some models you can remotely adjust the intensity of the flash from the trigger itself.

You can set up 3 groups for example, and change group A to 1/2 power, group B to 1/4, and group C to 1/8 or whatever combination you want. No need to run to your flashes.

7) And in some models you also have TTL. TTL on an offshoe flash!

Flexibility That is the difference.


Nowadays there are some cheap but sturdy radio triggers and receivers, and some flashes with radio receivers built in. Price is not a real issue anymore.

  • I edited that smart phone part. The flash contamination is an issue. And I separated the flexibility point as a final one. – Rafael Oct 13 '15 at 11:15

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