Rear Curtain Synch and Off Camera Flash

thanks guys for the clarifications

Heck, this an old thread, but rather than create a new one on the same subject, I'd like to add another question...

Would it be THAT hard for Canon to implement rear curtain sync from the body, rather than ONLY if you have an ETTL flash physically on the camera?

I have an STE2 and 3 550EXs but can't do off camera flash with rear curtain sync! From what I understand, the reason for this is that the exposure info which is used to control the flash power of remote devices in ETTL mode uses visible light and would therefore be seen in the exposure just prior to the 2nd curtain. But why not allow it for manual mode?

Nikon have done this for years. But I wonder, do any of the newer bodies cater for this? I can't find anything in the write ups.

I suspect that who owns which patents is the cause of this inability.

I use the YN-622C triggers with the 550s in 2nd-curtain sync, in Manual mode. E-TTL doesn't work - the subject is not in place for the camera to take a reading.

They would work with your 500D but not your 1DS.

I don't know for sure why 2nd curtain sync is not an option with the Canon Wireless Flash system, but it's such a specialized option that few people truly have a need for it.

Most people who use 2nd curtain sync would get the same results with 1st curtain.

Agreed to both.

My use was mountain bike night races in forest. 8s to 10s exposure for dim environment and cycle lamp capture, to close flash of rider. 600 competitor passes. No access to gear during racing and flashes some metres away from subject.

My Phottix Odins to 2nd curtain sync with OCF.

CliveyBoy wrote in post #15831950
I suspect that who owns which patents is the cause of this inability.

I use the YN-622C triggers with the 550s in 2nd-curtain sync, in Manual mode. E-TTL doesn't work - the subject is not in place for the camera to take a reading.

They would work with your 500D but not your 1DS.

I wasn't aware of the YN-622c's so thanks for bringing them to my attention CliveBoy... and Manual Mode is how I roll - I think I confused things by my talk of ETTL! I had a read up on the 622's. Indeed, the initial 'review' units shipped without the ability to work with the 1D series, but also read that this facility has been fixed. However, although the Yongnuo manual lists some of the 1D and 1DS bodies as compatible, it doesnt list mine specifically. To confuse matters, the manual describes the different types of Canon cameras as 'type A' and 'type B' but the type of bodies contained in those lists do not correlate with Canon's own naming convention of Type A, Type A-II and Type B. <--(click to see the link) Perhaps this could be verified?

I see from the manual, that the YN-622C can provide 2nd curtain sync from the PC port, Clive. Does this mean that if you already have a set of wireless triggers with a PC port input, you could trigger a transmitter /multi receiver set-up by just adding a single YN622c to the hotshoe? That would be VERY useful!!

For the record, because the 550EX is only ETTL (not ETTLII) when mounted to my 500d, the external flash control menu is greyed out. I can get 2nd curtain sync from the 550EX by selecting 'Manual' on the flash, then pressing +and- together to access the >>> option. BUT, the only way to trigger the remaining flashes off camera in 2nd curtain is to put a hood over the top of the hotshoe'd 550 with a wein pnut inside and link that to a radio trigger which can then fire the other off-camera flash/es ('Strobes') - Which is a pain... and very unwieldy to boot!

To my mind, Canon cameras are capable of sending the 2nd curtain signal since they can do it when you slap one of their ETTLII flashes on top. It just amazes me why they would go out of their way to disable that feature for off camera flash! Furthermore, why would Canon force their customers to buy a third party device in order to be able to use canon equipment in a more creative way? It's Illogical!!

I think if the option were there (as it is in the entire Nikon range) people would embrace it and use it more. Plenty of Pro Nikon users have their cameras set to RCS (rear curtain sync) all the time. Joe McNAlly, David Hobby (A.K.A. Strobist) etc.

When it comes to motion blur, 1st curtain just looks silly - all the motion created by muted ambient light appears ahead of the moving object, thus creating the appearance that the object is moving backwards. With 2nd curtain, the motion blur is captured through the ambient exposure and then the target is frozen by the flash with the motion trailing away as one would expect. Even if there is no ambient but the target is itself lit (such as a passing car driving away from you with tail lights on) you'd have to get the car to drive backwards to get the right effect with 1st curtain.

Wedding 'togs often shoot in low ambient light conditions with an assistant on 'off camera duties'. e.g. happy couple /first dance /low ambient lit dance floor... you get the idea. You can use an ETTL (TRIP HAZARD!) lead... but there's usually alcohol at weddings.

I have heard of the Odin (thanks sempaidavid for confirming) supporting the same but they seem like overkill (money wise) just to get a 2nd sync in manual mode.

I bet that every Canon Body since the first EOS digital could be made to trigger the shoe at 2nd curtain sync with a quick firmware update. That way, the ST-E2 could fire multiple 'EXs without all the faff! Please, if anyone from Canon reads this do us AND YOURSELVES a favour!

...I'm ranting now, aren't I!
:o

alunh wrote in post #15833241
When it comes to motion blur, 1st curtain just looks silly - all the motion created by muted ambient light appears ahead of the moving object, thus creating the appearance that the object is moving backwards. With 2nd curtain, the motion blur is captured through the ambient exposure and then the target is frozen by the flash with the motion trailing away as one would expect. Even if there is no ambient but the target is itself lit (such as a passing car driving away from you with tail lights on) you'd have to get the car to drive backwards to get the right effect with 1st curtain.

2nd curtain solves that problem only if you have a stationary camera and a subject moving in a predictable direction.

For any other situation, 2nd curtain makes it difficult to capture the moment because you have to wait, while looking through a dark viewfinder, for the flash to fire.

As for using 2nd curtain all the time - It's an option that kicks in only when the shutter speed is slower than 1/120 or 1/60 (depending on the camera body). So it makes no difference at all unless you're deliberately using a slow shutter speed.

Curtis N wrote in post #15833272
2nd curtain solves that problem only if you have a stationary camera and a subject moving in a predictable direction.

For any other situation, 2nd curtain makes it difficult to capture the moment because you have to wait, while looking through a dark viewfinder, for the flash to fire.

As for using 2nd curtain all the time - It's an option that kicks in only when the shutter speed is slower than 1/120 or 1/60 (depending on the camera body). So it makes no difference at all unless you're deliberately using a slow shutter speed.

I totally agree Curtis and what you said before is correct - most people wouldn't notice.

But what you have just described is a method I'd 'like' to be able to use but can't because Canon won't let me. At least not without buying some more third party kit for (what I consider to be) no logical reason!

I'd like to create a series of night shots with a car rolling up towards and stopping in front of the camera (on tripod) at a fixed point. The ambient street lighting and headlights will provide the motion streak. The long duration shutter will be opened once the car is a known distance from it's final resting place and the final 'Pop' (as the car comes to a halt) provided by two 550s fired into a large panel diffuser to light the outside of the car and a third 550 in the car to light the driver. Not easy with 1st Curtain. Not possible with a single on camera flash.

I will probably drop some money on the YN622Cs since they appear to be what I need to get the job done. Also, having tried (and failed) using the ST-E2 outdoors too many times, I knew I would need to go radio at some point. I've thought about trying to hack an ETTL cord and some Cactus V5s but thankfully haven't wasted any money on that yet.

I wonder, has anyone else has achieved a working solution in a different way?...

Easiest (and works with studio strobes as well): have the car drive backwards.
Another option: http://ocfgear.com …ttl/ettl-cord-extra-long/

There are optical slaves designed to work with EX flash units, for not a lot of money. You'll need one dedicated flash unit on the hotshoe (or connected via long TTL cord as Rene suggests), Manual mode, 2nd curtain. Use an optical slave for anything else.

alunh wrote in post #15833241
I had a read up on the 622's. Indeed, the initial 'review' units shipped without the ability to work with the 1D series, but also read that this facility has been fixed. However, although the Yongnuo manual lists some of the 1D and 1DS bodies as compatible, it doesnt list mine specifically. To confuse matters, the manual describes the different types of Canon cameras as 'type A' and 'type B' but the type of bodies contained in those lists do not correlate with Canon's own naming convention of Type A, Type A-II and Type B. <--(click to see the link) Perhaps this could be verified?

IDs users have confirmed that it does not play nicely with the 622s. Look at page 4 of TOYUG, where it is specificly excluded from the YN Type B group, and is therefore in YN Type C.

Note that I have been specific - TOYUG describes the categories as "YN-622C 'Type C' Camera". To differentiate the Canon and YN nomenclatures. They describe different capability sets.

alunh wrote in post #15833241
I see from the manual, that the YN-622C can provide 2nd curtain sync from the PC port, Clive. Does this mean that if you already have a set of wireless triggers with a PC port input, you could trigger a transmitter /multi receiver set-up by just adding a single YN622c to the hotshoe? That would be VERY useful!!

Yes, using a pc-sync cable. Mounting another trigger on a 622 hot-shoe prevents it from working above x-sync, and provides only 1st curtain sync.

alunh wrote in post #15833241
For the record, because the 550EX is only ETTL (not ETTLII) when mounted to my 500d, the external flash control menu is greyed out.

The 550EX does not determine the E-TTL flavour - the camera does, and I thought that the 500D is programmed for E-TTL II. The menu is greyed out because the 550EX cannot be controlled by camera menus - see Flash Compatibility on P.4 of TOYUG.

However, the YN-622C is seen as a fully-capable Master Flash, like the 580EXII. But because it handles its own comms, it can permit things that Canon doesn't.

TOYUG - see my signature.

Again, Curtis has it right in post# 38

alunh wrote in post #15833241
For the record, because the 550EX is only ETTL (not ETTLII) when mounted to my 500d, the external flash control menu is greyed out.

That has nothing to do with E-TTL vs. E-TTL II. Whether it's E-TTL or E-TTL II is entirely up to the camera body. The oldest flash supporting E-TTL at all also supports E-TTL II on a camera that's new enough (made in 2003 or later, I think it is).

They don't "go out of their way" to do this. It has to do with how the master/slave signalling protocol is designed. When using slave flashes in E-TTL mode, the process is like this:

1. Send two byte command flash from master to slaves to tell group A to fire the pre-flash.
   
2. Group A slaves fire the pre-flash, which is measured and remembered by the camera.
   
3. Repeat for groups B and C, if used.
   
4. Send five byte command code from master to slaves, telling all groups which power level to use and to get ready to fire when they see the sync flash. Note that at this moment, the slaves enter "dumb slave mode", i.e. they fire at first light pulse seen.
   
5. Shutter opens in camera.
   
6. Sync flash is fired from master, and the slaves react and fire their flashes, according to the commanded strenght, immediately.
   
7. Slave flashes terminate "dumb slave mode" and goes back to "clever slave mode", looking for multi-byte command flashes again.

Curtis N wrote in post #15833272
2nd curtain solves that problem only if you have a stationary camera and a subject moving in a predictable direction.

For any other situation, 2nd curtain makes it difficult to capture the moment because you have to wait, while looking through a dark viewfinder, for the flash to fire.

As for using 2nd curtain all the time - It's an option that kicks in only when the shutter speed is slower than 1/120 or 1/60 (depending on the camera body). So it makes no difference at all unless you're deliberately using a slow shutter speed.

It's worse than that. Both Canon and Nikon don't switch to second-curtain sync until the shutter speed drops below 1/30sec, even when it's enabled, and even then it's more like 'middle-curtain' if you take my meaning. It needs longer speeds than that before the timing gets relatively closer to the second curtain closing. AFAIK only Pocket Wizard's Mini/Flex system can improve on this.

I agree that second-curtain is no magic bullet and the upsides/downsides are commonly misunderstood, but it does have advantages over first-curtain in quite a lot of situations where the ghosting is overlaid on the trailing edge rather than the leading edge of a moving subject - illustrated here http://neilvn.com …ync-vs-rear-curtain-sync/ Good for portraits and other more common subjects than the car headlights example usually given.

I have no idea why Canon's native sytem doesn't allow remote second-curtain sync - maybe a patent thing. I think every third-party radio TTL trigger offers it, but it's not even available with the new Canon RT radio units.

Hoppy1 wrote in post #15836070
I have no idea why Canon's native sytem doesn't allow remote second-curtain sync...

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