technical question regarding flash synch

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hi





I have a technical question regarding the shutter/ flash synch timing



I have a Canon EOS-1D-C and am attempting to use the flash synch output on the hot-shoe mount to trigger a timing pulse to some external equipment which will record GPS data.



My question is: is there any time latency between the moment the picture is taken and the moment the flash synch is triggered?



The concern is that even a tiny difference in timing between the image capture and flash trigger might upset the GPS.



Best regards
 
The flash pulse clearly occurs during the time that the shutter is open otherwise the light from the flash wouldn't be captured....or am I misunderstanding your question.

Bob
 
Few cameras have a synch speed higher than 1/250th of a second which is a period of time, even if relatively tiny. As Bob's said, the flash fires while the shutter's open so for most purposes you should be OK. FWIW, there's usually a slight delay between the button being pressed and the exposure actually being started and there may also be a pre-flash to help determine the flash power.
 
First curtain opens, flash fires, second curtain starts moving to close. If you're using speeds higher than the sync speed you'd need some fairly complex timing gear to see when the flash fire command actually occurs, but it's still during the exposure, so the answer is as simple or complicated as you want to make the question.

Even at 1/8000 sec the flash fire command is during the exposure, but if you need to know when during:confused:
 
Phil V said:
Even at 1/8000 sec the flash fire command is during the exposure, but if you need to know when during
Click to expand...

It's most likely still the point at which the first curtain is fully open. Which at 1/8000 will also be the point at which the second curtain is almost closed!

I think the fancy pants camera/flash combinations which can do high speed flash sync probably use a hotshoe connection other than the PC sync as a trigger.


Steve.
 
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rb67 uses pc sync and goes to 500th?
there was a video on adarama tv on youtube about syncing pics to a external gps watch, could be worth looking at.
your more likely to get positional errors from gps side than flash sync I would of thought
 
Steve Smith said:
It's most likely still the point at which the first curtain is fully open. Which at 1/800 will also be the point at which the second curtain is almost closed!

I think the fancy pants camera/flash combinations which can do high speed flash sync probably use a hotshoe connection other than the PC sync as a trigger.

Steve.
Click to expand...
You're probably right re the flash timing.

The canon HSS pulses from the first curtain opening all the way through the exposure, I think the Nikon one does similar.

But I don't know how tail hyper sync does it as that's just the back end of the flash pulse dying through the shutter curtain movement, presumably the peak of the flash happens just before the shutter opens, but how this timing works makes my little brain hurt whenever I think about it.

Cue Richard to come along and tell me it's really simple.
 
pingu666 said:
rb67 uses pc sync and goes to 500th?
there was a video on adarama tv on youtube about syncing pics to a external gps watch, could be worth looking at.
your more likely to get positional errors from gps side than flash sync I would of thought
Click to expand...
But that's a leaf shutter, they're much better at the 'fully open' trick, ie. the shutter blades clear the aperture much more efficiently than shutter curtains clear.

It's why wedding photographers loved MF, it often offered as much as 3 stops faster shutter speeds for fill flash over older shutter curtain designs.
 
Phil V said:
The canon HSS pulses from the first curtain opening all the way through the exposure, I think the Nikon one does similar.
Click to expand...
I think it's more logical that the pulses start when the second curtain starts moving Phil...ie, the gap between the curtains is constant.

Bob
 
Phil V said:
<snip>

Cue Richard to come along and tell me it's really simple.
Click to expand...

It's really simple :D Tail Hypersync uses the HSS timing moment that happens fractionally before the first curtain begins to travel, so the flash is fully lit up when it opens. PW and some others can apply an adjustable delay to that, to optimise the exposure either for brightness or evenness.

I'm not sure exactly what the OP wants to know, but here's a super slo-mo of a Canon 5D shutter in action, with timings. There are quite a lot of these on YouTube etc.

 
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FWIW, ISTR that the D70 can synch at 1/500th. IIRC it uses some sort of hybrid shutter - the metal blind and an electronic one. Not being a huge user of flash, I've never really played with that feature!
 
Nod said:
FWIW, ISTR that the D70 can synch at 1/500th. IIRC it uses some sort of hybrid shutter - the metal blind and an electronic one. Not being a huge user of flash, I've never really played with that feature!
Click to expand...
At the time everyone believed that the future of DSLRs was shutterless. There is no reason that a capture can't be made off the sensor without the need for a shutter to sync, but even the D70 only half used the technology. Why stop at 1/500 max? I'm sure the technology is available to give us a flash sync of 1/8000 and I'm certain it'll be available before I retire.
 
Phil V said:
At the time everyone believed that the future of DSLRs was shutterless. There is no reason that a capture can't be made off the sensor without the need for a shutter to sync, but even the D70 only half used the technology. Why stop at 1/500 max? I'm sure the technology is available to give us a flash sync of 1/8000 and I'm certain it'll be available before I retire.
Click to expand...

Nikon capped it officially at 1/500sec, but I know that feature was/is used at much higher speeds. It was a characteristic of CCD sensors that made it possible, but they're all CMOS now.

A fully electronic sensor-switching global (no scanning down) shutter is the Holy Grail. It would revolutionise flash photography. Some cameras already have fully electronic shutters, Nikon-1 series for example, but it still scans.
 
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