Rear Curtain Synch and Off Camera Flash

apersson850 wrote in post #15836858
I explained that in the post above your's. The way they did the whole thing they can't trigger 2nd curtain remotely.

That doesn't explain why it was configured like that, and why the opportunity of radio to revise it with the RT system was passed over when third-party brands can do remote second-curtain sync with no problems.

apersson850 wrote in post #15835296
Whether it's E-TTL or E-TTL II is entirely up to the camera body.

Agreed. Perhaps I should have added the word "compatible" ? i.e. The 550 EX is ETTL compatible and not ETTL-II compatible.

Thanks for the insight into how the protocol works though, Anders. I'm intrigued to know where you found out that info. Is it in the public domain or from workshop manuals perhaps? I'd be very interested in what feedback the camera needs from the flash in order to "think" there is an ETTL compatible flash connected. Perhaps I could then fool the camera into giving me 2nd curtain sync when i wanted it.

Any how, the point (actually 2 points) that I clearly failed to get across were...

1. all EOS bodies are 'capable' of sending a signal to fire just before the second curtain. But Canon in their infinite wisdom have decided that we as photographers don't want that second curtain sync signal UNLESS there is an ETTL or ETTL-II compatible flash mounted to the camera hot shoe, NOT in slave OR master mode.

and

2. I dont want 2nd curtain sync when using the flash in ETTL mode. I want it in manual mode. No preflash, no flash metering, nothing. All I want the camera to do is open the shutter, expose and image, tell me its about to close the shutter and then close it. I can do the rest.

The fact that Canon can't make their ETTL-II protocol work for grouped slave flashes with 2nd curtain sync really doesn't bother me. The fact that I can't have that 2nd curtain sync for off camera flash REALLY DOES bother me. Especially since (with the 550 attached to either camera) I can turn off ETTL on the flash and still get 2nd curtain sync in manual mode. I can then use that flash to trigger my other flashes but oh look! Ive got a big bright light making thing on axis with my lens.... just where i don't want it.

Personally, i tend to only make use of ETTL for flash control when I'm not in full control of the scene. When I am in full control of the scene, I want to also be in full control of the lighting. I don't want some algorithm inside the camera designed by an engineer twelve thousand miles away in Osaka back in 2003 to decide my key, fill and kicker ratios.

Hoppy1 wrote in post #15836882
That doesn't explain why it was configured like that, and why the opportunity of radio to revise it with the RT system was passed over when third-party brands can do remote second-curtain sync with no problems.

But the third party devices supply the remote flash with a hot shoe to connect to, and then forward (some of) the connections in the hot shoe to the flash. Then 2nd curtain is possible.

It would also indeed have been possible for Canon to make it possible with the new radio control in their 600 EX-RT, or by having some sort of recover procedure for the optically controlled slaves, should they lock up in waiting for a trigger flash which turned out never to occur, and thus not being able to properly respond to the next command flash.

alunh wrote in post #15836945
Agreed. Perhaps I should have added the word "compatible" ? i.e. The 550 EX is ETTL compatible and not ETTL-II compatible.

No. The 550 EX is E-TTL, and therefore also E-TTL II compatible, since the difference is within the camera body, not in the flash.

From Canon's more detailed descriptions of how their slave flash system works.

But it already does, when you have the flash on the camera. And if you use Canon's optical slave control system, it's not technically possible, since the slaves will not respond to any 2nd curtain sync.

A slave flash can never sit on the hot shoe. Slave mode will be cancelled automatically. The camera can trigger on 2nd curtain regardless of whether there's a flash or not in the hot shoe, but the slaves can't receive such a signal. Thus you aren't allowed to select it when you have a master flash on the camera. Cameras where 2nd curtain is set through a custom function can fire any flash with 2nd curtain sync.

Fine, that works too, as long as the flash is on the camera.

But it's the same thing. Canon's optical remote control works in the same way regardless of whether you use E-TTL or manual flash settings. Just remove items 1, 2 and 3 in my list above, and you have the control sequence for a manual remote flash setup.

Yes, because then you don't use Canon's master-slave protocol, but use the slaves in normal mode. Having an external trigger firing them like that is no problem.

...but oh look! Ive got a big bright light making thing on axis with my lens.... just where i don't want it.

You can't aim it elsewhere, or just reduce the power to a minimum required to trigger your slave triggers?

Since he's 7500 km away, he's hardly turning your knobs for you.

Thanks for your input Anders

This is a popular way to enable remote second-curtain sync in manual - optical slave picks up second-curtain pulse from on-camera flash (pop-up or separate) and triggers the radio transmitter (RF-602, Sonia slave). This is a rough mock up, originally to enable tail-hypersync firing (off the HSS pulse) and I have a much neater version that works with a 270EX gun - small and neat and also enclosed so there is no flash visible from the 270EX

IMAGE LINK: http://s448.photobucke​t.com …t/media/IMG_487​0.jpg.html

Ok Anders, I see your point regarding ettl-ii being in camera. I just thought that the 550EX was not able to integrate fully with every feature of ETTL-II and thus certain aspects of the protocol were not implemented when using that flash. This probably stems for the fact that in the external flash menu of the 500d, 'ETTL-II' is greyed out when i connect the 550 but not greyed out when i connect a friends 580EXII.

However, you do say "cameras where 2nd curtain is set through a custom function can fire any flash with 2nd curtain sync" to which i have to disagree. The 1DS has this custom function. Yet, my experience is that even when that is set, it will only send the 2nd curtain sync signal to fire when there is a Canon EX flash on top of the camera. If I put a dumb flash or a basic remote trigger on the hotshoe or connect a studio flash via the PC sync socket, the camera only sends the 1st curtain sync fire signal. Even when 2nd curtain is selected in the custom menu...I have tried it.

In the manual, it says "If an EX series speedlite having this capability is set for 2nd-curtain sync, it will override this Custom Function." What the manual fails to point out is that if an EX series speedlite having this capability is set NOT set for 2nd-Curtain sync it will ALSO override this function.

You are right I can aim the flash elsewhere... If I mount one of the 550s on the hotshoe and set it to 2nd curtain, gaffer tape an optical trigger to the end, connect that optical trigger to a hot shoe, mount the ST-E2 to the hotshoe and gaffer that to the side of the flash, I can still control the other 550's as slaves from the ST-E2 master and get 2nd curtain sync. But that is an untidy, unsafe and completely unnecessary bodge-up. I'm also losing one of my flash guns to act as a trigger.

The ST-E2 is capable of just sending a 'fire' command to the slaved flashes. The camera is capable of just sending a 'fire' command just before 2nd curtain. I'm pretty sure if I put the ST-E2 on a Nikon body set to RCS, it would fire the 550s at 2nd curtain, but i haven't tried that yet.

The point that seems to be getting overlooked here is that the ability to send that 'fire' command from a Canon camera has been disabled by Canon. The only time it is allowed to send that 'fire' command on 2nd curtain is when the camera gets confirmation from a Canon flash, mounted to the hotshoe that enough money has been spent. I understand that Canon wants me to buy a Canon flash and I think they are so good that I bought three. The problem is, I cant use them how I want to because Canon don't think that I should.

Canon UK's marketing slogan used to be "If Anyone Can, Canon Can". How ironic!..
Perhaps their new strap line should be "If anyone Can, Canon Can but don't really want to. But luckily, some enterprising third party companies from China will" - not so catchy!

Hoppy1 wrote in post #15837043
Thanks for your input Anders

This is a popular way to enable remote second-curtain sync in manual - optical slave picks up second-curtain pulse from on-camera flash (pop-up or separate) and triggers the radio transmitter (RF-602, Sonia slave). This is a rough mock up, originally to enable tail-hypersync firing (off the HSS pulse) and I have a much neater version that works with a 270EX gun - small and neat and also enclosed so there is no flash visible from the 270EX

IMAGE LINK: http://s448.photobucke​t.com …t/media/IMG_487​0.jpg.html

I didn't see this before sending my last post, but that's kind of what i was getting at Hoppy1. We shouldn't need to do that.

alunh wrote in post #15837504
I didn't see this before sending my last post, but that's kind of what i was getting at Hoppy1. We shouldn't need to do that.

Quite

The Canon system as natively configured looks like a foot-shooting operation for advanced users that want/need certain features, as it forces us to go third-party. But the remote second-curtain thing is so obvious I suspect there must be a reason for it and the best I can can up with is some patent restriction, and I have a hazy memory that Nikon acquired some TTL flash rights from Minolta way back in the day that possibly closed a door for Canon, but that's only a guess.

As I mentioned before though, PW has some good solutions for advanced users with optimised second-curtain sync, optimised high-speed sync, plus both peak-hypersync and tail-hypersync.

alunh wrote in post #15837473
Ok Anders, I see your point regarding ettl-ii being in camera. I just thought that the 550EX was not able to integrate fully with every feature of ETTL-II and thus certain aspects of the protocol were not implemented when using that flash. This probably stems for the fact that in the external flash menu of the 500d, 'ETTL-II' is greyed out when i connect the 550 but not greyed out when i connect a friends 580EXII.

Aha, I see where you got it from. It's greyed out not because the function isn't supported, but because changing the mode from the camera's menu system isn't supported.

I could be wrong about the 2nd curtain and non-Canon flashes. It was so very long ago that I actually tried that, so that I may be confusing it with something else. Today, I hardly ever use anything but Canon's flashes, and hardly ever use any camera body which doesn't do the setup through the menu system, so I'm not up to date there. Sorry if I mislead anyone.