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Thread started 16 Oct 2009 (Friday) 12:32
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Canon EOS 7D - Wireless ETTL flash FAQ

 
int2str
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Oct 16, 2009 12:32 |  #1

Below is a collection of frequently asked questions regarding the 7D's new wireless flash control functionality.

I'll try to update this list with any new frequently asked questions down the road to provide a comprehensive resource for the new wireless flash control feature.

Please post any additional questions you may have or revisions to the existing answers.

Last update: 2009/10/16 - V.3 Re-worded to indicate flash always fires.

---------------

1. What is wireless ETTL flash control?

From the 7D camera manual:
"The camera's built-in flash can work as a master unit with Canon Speedlites having wireless slave feature and wirelessly trigger the Speedlite to fire".

In a nutshell, the 7D can control your Canon flashes as well as some Canon compatible 3rd party flashes.

---------------

2. What external flashes can I use?

Currently, the list of confirmed flashes includes:
- Canon 580 EX II
- Canon 580 EX
- Canon 550 EX
- Canon 430 EX II
- Canon 430 EX
- Canon 420 EX
- Sigma EF 500 DG Super
- Sigma EF 530 DG Super

Flash compatibility is also discussed in this thread:
http://photography-on-the.net/forum/showthre​ad.php?t=760227

---------------

3. How does it work?

The built-in flash emits a burst of flashes before the cameras shutter is opened to instruct the remote flashes to fire and to communicate the requested flash ratios and measure flash exposure. When the shutter actually opens, the built-in flash will fire again in one of two modes:

1) If the built-in flash iss enabled for the actual exposure, it will fire at a predetermined output level to contribute to the exposure.

2) If the built-in flash is only used to control the external Speedlites, it will fire at a very low power just to finally trigger the external flashes and not to contribute to the final exposure.

---------------

4. I only want the external flashes to fire, but my built-in flash still fires?

When you set the camera to only control the external Speedlites, the built-in flash will still fire it's pre-flash to communicate with the external Speedlites. After the preflash, the built-in flash will emit a very low power flash when the shutter opens to signal the external flashes to fire. This sync-flash will not contribute to the final exposure (or minimally so).

---------------

5. I thought the flash control uses IR, why do I see the flash?

The built-in flash is not capable of only emitting IR light - unlike Canon's ST-E2 flash controller, which uses IR LED's to communicate with the external flashes. The built-in flash emits the full spectrum of light which includes IR light that is received by the slave flashes. The ST-E2 pulses light in the same manner, you just can't see it.

---------------

6. Do I need line of sight to all my flashes?

Yes, but ...

The IR receiver of the flashes needs to be able to "see" the flash emitted by the 7D. But that does not necessarily mean that the camera needs to be aimed directly at the flash. In an outdoor setting, you have to point the camera directly at the flash. In an indoor studio or smaller room however, the pre-flash may be reflected by the walls and ceilings however and still reach the flash even without direct line of sight.

---------------

7. Can I use "dumb" optical slaves in combination with this wireless ETTL control feature?

No. Most regular optical slaves will trigger already when they see the pre-flash from the camera. Some optical slaves that are designed specifically to work with the Canon system and ignore the pre-flash may exist however and can be used.

---------------

8. Does the 7D support wireless high-speed sync?

No. Unlike the 580 EX II in master mode as well as the ST-E2, the built-in wireless flash control on the 7D cannot enable wireless high-speed sync or 2nd curtain flash.

---------------

9. How many flash groups/ratios does the 7D support?

The built-in wireless flash controls supports three flash groups - A, B and C.




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Raginl3ull
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Oct 16, 2009 12:45 |  #2

Great info! Thank you so much for clearing this up! bw!


| Canon 5D Mark II + BG-E6 | Canon 7D | 24-105mm F4 L IS | 70-200mm F4 L IS| 50mm F1.4 | 28-135mm IS F3.5-56 | 430EX II | 580EX II |
http://www.flickr.com/​photos/dgatan/external link

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Nervous
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Oct 16, 2009 13:00 |  #3

Add the item about not supported HSS by the built-in flash.


7D | 5D classic | EF-S 10-22 | EF 24-105 L IS | EF 70-300 IS USM | EF 85/1.8 | EF 50/1.8 II | Sigma 24-60/2.8 | Tamron 90/2.8 | 580EXII | 2x 420EX | 055XPro + 488RC2

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int2str
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Oct 16, 2009 13:05 |  #4

Thanks Nervous! Added HSS/2nd curtain info.




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Nervous
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Oct 16, 2009 13:07 |  #5

A correction for HSS item: "Unlike 580EXII.... and ST-E2...."


7D | 5D classic | EF-S 10-22 | EF 24-105 L IS | EF 70-300 IS USM | EF 85/1.8 | EF 50/1.8 II | Sigma 24-60/2.8 | Tamron 90/2.8 | 580EXII | 2x 420EX | 055XPro + 488RC2

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int2str
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Oct 16, 2009 13:10 |  #6

Done.




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eelnoraa
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Oct 16, 2009 13:35 as a reply to int2str's post |  #7

wow, I cannot believe Canon left out #8. I thought it will be very easy to include this feature. Well, I guess we cannot have it all.


5Di, 5Diii, 28, 50, 85, 16-35II, 24-105, 70-200F2.8 IS

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Nervous
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Oct 16, 2009 13:40 |  #8

There are two reasons for #8: the item #5 (lack of IR in built-in flash) and the second - limited power of built-in flash to provide reliable HSS.


7D | 5D classic | EF-S 10-22 | EF 24-105 L IS | EF 70-300 IS USM | EF 85/1.8 | EF 50/1.8 II | Sigma 24-60/2.8 | Tamron 90/2.8 | 580EXII | 2x 420EX | 055XPro + 488RC2

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mrkgoo
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Oct 16, 2009 14:31 |  #9

Sorry, I don't know anything about flashes, let along wireless ones, but does this tech allow you to have an externally flash that you can hold away (on its own with its own powersupply) and trigger it simply by taking the shot from the 7D? That just sounds like a timing control - what was preventing previous (or lower end) models from incorporating this? Or is there some other form of wireless communication?

Sorry for the noob question.




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int2str
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Oct 16, 2009 14:45 |  #10

mrkgoo wrote in post #8835506external link
Sorry, I don't know anything about flashes, let along wireless ones, but does this tech allow you to have an externally flash that you can hold away (on its own with its own powersupply) and trigger it simply by taking the shot from the 7D?

Yes. You can take a Canon flash (or compatible; see above) and have it "off camera" on a light-stand or similar. The you can fire it remotely using the 7D's internal built-in flash and even control power output from your camera.

That just sounds like a timing control - what was preventing previous (or lower end) models from incorporating this? Or is there some other form of wireless communication?

Some lower end flashes (Nikon esp.) have optical slaves built in. Those only fire the flash though when any other bright flash is detected. They don't adjust the power output. You have to do that manual.

On the 7D now (like Nikon's CLS system for a while already) can control compatible flashes in a smart fashion, not just "SHOOT!" :)




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mrkgoo
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Oct 16, 2009 15:52 |  #11

int2str wrote in post #8835588external link
Yes. You can take a Canon flash (or compatible; see above) and have it "off camera" on a light-stand or similar. The you can fire it remotely using the 7D's internal built-in flash and even control power output from your camera.

Some lower end flashes (Nikon esp.) have optical slaves built in. Those only fire the flash though when any other bright flash is detected. They don't adjust the power output. You have to do that manual.

On the 7D now (like Nikon's CLS system for a while already) can control compatible flashes in a smart fashion, not just "SHOOT!" :)

Thanks. So I can buy an external flash and just hold it in my hand? It triggers using an IR sensor that 'just' detects bright lights? What is preventing other photographer's flashes from triggering it?

How do you control power output of the external flash from the camera? Does it adjust its own flash to 'signal' the slave? Or is it by some other communication method?




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int2str
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Oct 16, 2009 15:58 |  #12

mrkgoo wrote in post #8835945external link
Thanks. So I can buy an external flash and just hold it in my hand? It triggers using an IR sensor that 'just' detects bright lights? What is preventing other photographer's flashes from triggering it?

Let's not mix concepts here. Canons wireless flash control that's built into the 7D can trigger compatible Speedlites in a "smart" way. You can hold them in your hands as long as it's somewhat line of sight to the flash on camera since the built-in flash "tells" the remote flash what to do and when to do it.

I mentioned "dumb" optical slaves only in response to your question, they have nothing to do with this FAQ. Those optical slaves trigger from any one bright flash. Nothing prevents those from going off when any other photographers flash goes off.

Canon's wireless flash control lets you select channels. So if multiple photographers use this system, you can switch to a different channel and only trigger your own flashes.

How do you control power output of the external flash from the camera? Does it adjust its own flash to 'signal' the slave? Or is it by some other communication method?

On the camera there is a "Flash control" menu that allows you to select ratios between flash groups and flash exposure compensation to brighten the external flashes or to lessen their output. That information is communicated to the external flashes using the built-in flash during a sequence of brief "pre-flashes".




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mrkgoo
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Oct 16, 2009 15:59 |  #13

int2str wrote in post #8835971external link
Let's not mix concepts here. Canons wireless flash control that's built into the 7D can trigger compatible Speedlites in a "smart" way. You can hold them in your hands as long as it's somewhat line of sight to the flash on camera since the built-in flash "tells" the remote flash what to do and when to do it.

I mentioned "dumb" optical slaves only in response to your question, they have nothing to do with this FAQ. Those optical slaves trigger from any one bright flash. Nothing prevents those from going off when any other photographers flash goes off.

Canon's wireless flash control lets you select channels. So if multiple photographers use this system, you can switch to a different channel and only trigger your own flashes.

On the camera there is a "Flash control" menu that allows you to select ratios between flash groups and flash exposure compensation to brighten the external flashes or to lessen their output. That information is communicated to the external flashes using the built-in flash during a sequence of brief "pre-flashes".


Ah, gotcha, thanks again.

What's the communication protocol? It's not just the pre-flashes, right? I assume something like infrared?




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int2str
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Oct 16, 2009 16:15 |  #14

Again, mixing concepts ;)

Yes, the receiver on the Canon flashes are infrared. But the 7D just uses regular flashes. The visible white flashes contain a full spectrum of visible and non-visible light, including IR. So it is IR, but it's part of the normal flash that you see, not a normal infrared LED. There is no other emitter on the 7D, just the flash bulb.

The communication protocol is a form of high-speed morse code essentially. Except it's so fast that to the human eye it looks like one or maybe two short flashes. But on the 7D you can hear the pre-flash pulsing because it buzzes like a bee for a short bit.




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mrkgoo
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Oct 16, 2009 16:24 |  #15

int2str wrote in post #8836077external link
Again, mixing concepts ;)

Yes, the receiver on the Canon flashes are infrared. But the 7D just uses regular flashes. The visible white flashes contain a full spectrum of visible and non-visible light, including IR. So it is IR, but it's part of the normal flash that you see, not a normal infrared LED. There is no other emitter on the 7D, just the flash bulb.

The communication protocol is a form of high-speed morse code essentially. Except it's so fast that to the human eye it looks like one or maybe two short flashes. But on the 7D you can hear the pre-flash pulsing because it buzzes like a bee for a short bit.

Thanks for clearing that up.




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Canon EOS 7D - Wireless ETTL flash FAQ
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