ebay trigger problem...

[HoppyUK]

This might help and explain why it works with Canon and Ettl.

Ettl works by doing a micro-flash immediately before the main flash and calculating the main flash required from the micro flash. For this to work the shutter must be open at the micro flash stage. This pre-flash time could be added to the main flash maximum sync speed to give a faster sync speed if you could 'trap' the pre-flash trigger. I suspect this is what PW are doing.

What this means is that the shutter is actually fully open for longer than the stated maximum sync time (it has to be for the pre-flash to work) and that by using this pre-flash time as well as the maximum actual sync time you could get a faster apparent sync speed. This would be Canon Ettl specific and would use one (or a combination) of the other pins to sense the micro flash trigger signal.

Only a theory on my part but I cannot see any other way that would work and is Canon Ettl specific.

John

John, nice try but that isn't how the pre-flash works at all. The pre-flash happens before the mirror rises let alone the shutter opening.

 

[Steve Smith]

Let's just say they have found a clever way of making it work!

If they wanted to, they could make a wired version of it but I doubt that there would be much call for it.


Steve.

 

[david1701]

what if the camera does say 'firing first curtain now' milliseconds earlier than it fires the curtain would give enough wiggle room to up a conservative rated sync speed to 1/500

 

[Steve Smith]

what if the camera does say 'firing first curtain now' milliseconds earlier than it fires the curtain would give enough wiggle room to up a conservative rated sync speed to 1/500

That's exactly what I think is happening but it obvioulsly can't use the standard sync. signal for this so it must use another signal on another pin.


Steve.

 

[Flash Harry]

They should sync up to 1/200th - mine drove me crazy - wouldn't fire when they should have, and did fire when I didn't want them to - had to get rid of them after only a couple of weeks and replace them with Skyports...

Mine dove me around the twist. They just do their own thing and make you look a right numpty...Skyports are the way forward.

 

[Angus1]

I'm happy with my ebay triggers, work fine up to 1/160 when i get a black bar at the top (firing late) with my a200 and 24 year old Minolta 2800af

 

[david1701]

That's exactly what I think is happening but it obvioulsly can't use the standard sync. signal for this so it must use another signal on another pin.


Steve.

dammit why did I go for the lazy way that meant I didn't need to decode the pins

 

[jpwone]

Hi Hoppy

that is what happens after a very long day

I realised a few hours after I had posted that I had probably got that one wrong and that the shutter did not need to be open at all for the pre-flash as the exposure is obviously measured (as you quite rightly say) with the mirror down. My reasoning was that the pre-flash and the main flash are so close to each other that the shutter must already be moving or you would have a noticeable lag between pre and main flash. However, I was completely forgetting that you can use FEL (as the pre-flash) and that definitely does not move the mirror or open the shutter.

So, I stand rightly corrected and would also like to know how the apparent faster sync speed is being achieved.

John

 

[HoppyUK]

Hi Hoppy

that is what happens after a very long day

I realised a few hours after I had posted that I had probably got that one wrong and that the shutter did not need to be open at all for the pre-flash as the exposure is obviously measured (as you quite rightly say) with the mirror down. My reasoning was that the pre-flash and the main flash are so close to each other that the shutter must already be moving or you would have a noticeable lag between pre and main flash. However, I was completely forgetting that you can use FEL (as the pre-flash) and that definitely does not move the mirror or open the shutter.

So, I stand rightly corrected and would also like to know how the apparent faster sync speed is being achieved.

John

Morning John. Yes, with the pre-flash not only is the shutter closed and the mirror down, it has to be that way for the metering sensors in the pentaprism to see it.

The higher sync speed is not apparent, it's actual. Because of the way the triggering works, flash with the E-TTL Pocket Wizards can be fired at any time within the 'window' of tolerance. Basically there is a brief delay while the shutter remains fully open at normal max x-sync speed and by fine tuning the timing there is scope to tighten things up a bit and get a higher sync speed.

 

[Splog]

Interesting thread Anyway thought I'd post this, which was in answer to a question about ETTL and multiple flashes: This was provided by Zack at Pocket Wizard
Don't know if it clarifies anything.....

Here's a brief overview of how ETTL flash works:

1. The camera/PocketWizard tells the Speedlite to fire a brief preflash.

2. The light from the preflash bounces off the camera's reflex mirror and is metered in the prism.

3. The camera does some calculations to determine the proper exposure based on the light from the preflash as well as ambient.

4. The camera/PocketWizard sends that exposure information to the Speedlite.

5. The Speedlite fires with the appropriate power level (in sync with the camera's shutter) as instructed by the camera's calculations.

Bam. You have a properly exposed image.


This same process applies regardless of how many flashes you're using or their distance from the subject. The camera will measure the total light from all the preflashes and send flash power information to each Speedlite based on that. Since the camera is seeing more light because you've got more preflashes going off, it'll send a reduced power level to each Speedlite compared to using just one flash.

To clarify further:

We actually *do* fiddle with the ETTL process. At least in the sense that we read information from the camera, process it, modify it if we want, and then get it to the Speedlites.

All the standard flash metering and power level decisions are still up to the camera of course, so that can still be a limiting factor. Using bounce flash or a light modifier can sometimes mean that not enough of the preflash light will reach the camera's sensor.

We can even change the decisions the camera makes about exposure calculations. Preflash boost in the beta firmware is a good example. The PocketWizards instruct the Speedlites to fire their preflash at two stops brighter than the camera would normally expect. We actually have to modify the power level that the camera sends the Speedlite after it reads that extra bright preflash. It's neat stuff.

-Zack at PocketWizard