Shutter speed with wireless flash...

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JaackBrown

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When I have the built in flash on, the fastest shutter speed is 250, if I had a wireless flash, could I have the highest shutter speed which is 4000?
 
The limitation of flash and fast shutter speed is that the shutter moves so fast that it does not expose the whole sensor. As the first curtain is opening the second is closing behind it. This would leave you with a strip of light across the middle of the exposure.

Having a wireless flash will not help that, why do you want to use flash with faster shots?
 
If anything, it will introduce a bit of a delay requiring a slightly slower speed.


Steve.
 
chris-red said:
The limitation of flash and fast shutter speed is that the shutter moves so fast that it does not expose the whole sensor. As the first curtain is opening the second is closing behind it. This would leave you with a strip of light across the middle of the exposure.

Having a wireless flash will not help that, why do you want to use flash with faster shots?
Click to expand...

I never even thought about that haha, stupid me... I was just testing shots with water, but I needed more light...
 
Really depends on what gear you have.

Without that information it's impossible to say.

My gear will sync at any speed up to 1/8000 sec.
 
Cameras and flashes with high speed sync.

There are wireless triggers which support hss too.
 
Do you realise that where the flash is the primary light source it'll freeze movement very well. Forget the shutter speed, the flash 'exposure' is possibly faster than your fastest shutter speed (depending on flash model and power setting).
Your built in flash probably fires quicker than 1/4000 but I can't find figures on line.
 
chris-red said:
The limitation of flash and fast shutter speed is that the shutter moves so fast that it does not expose the whole sensor. As the first curtain is opening the second is closing behind it. This would leave you with a strip of light across the middle of the exposure.

Having a wireless flash will not help that, why do you want to use flash with faster shots?
Click to expand...

I'm going to pick up on this.

The problem is not the shutter speed being so fast, it is in actual fact the flash duration being so short.

The duration of an external flashgun can be as low as 1/10000th of a second. That is incredibly short... The reason for having a lower sync speed is to ensure that the shutter is open long enough to catch that quick burst of flash.
 
The reason for having a low sync speed is to ensure that the whole of the film or sensor is uncovered when the flash fires. At faster speeds, the second curtain starts to close before the first curtain has fully opened.


Steve.
 
RichardtheSane said:
I'm going to pick up on this.

The problem is not the shutter speed being so fast, it is in actual fact the flash duration being so short.

The duration of an external flashgun can be as low as 1/10000th of a second. That is incredibly short... The reason for having a lower sync speed is to ensure that the shutter is open long enough to catch that quick burst of flash.
Click to expand...

As others have said, this is not right.

The duration of the flash is irrelevant for normal sync, and it's not the speed that the shutter curtains move as such.

On a focal plane shutter (ie all DSLRs) the shutter curtains always move at a fixed speed down the frame, one after the other, and the exposure time is the difference between the first curtain moving and the second curtain.

That's straightfoward enough, but it means that at faster speeds the second curtain has to start before the first curtain has reached the bottom of the frame and the curtains form a strip as they travel down in parallel together (that strip is less than 1mm wide at highest speeds). Therefore, the whole of the sensor area is never uncovered at any single moment and if the flash was fired then, all you'd get would be a thin strip across the image.

The x-sync speed (which is 1/200sec on a Canon 600D, not 1/250sec) is the fastest speed when the whole of the sensor is uncovered. Go any higher, and a dark band will appear at the bottom of the picture, and it gets deeper the faster you go.

From this, it is also evident that shutter speed (exposure) and shutter cycle time are not the same thing. In round figures, even at 1/8000sec effective expose, the shutter takes 1/100-1/200sec for both curtains to travel from top to bottom. They work like a scanning shutter, like mobile phones, so if you get something moving very fast like propeller blades or similar, they will appear slighty curved.

It also explains why high speed sync works the way it does. Instead of one big bright pulse of light, HSS divides it up into hundreds of much smaller pulses that effectively become continuous light for the duration of the shutter cycle time. It works very well too, but because the outpot of the gun is spread over a much longer time, there is a substantial loss of brightness. Maximum range is reduced and recycle times get longer.
 
Thanks Richard for that detailed explanation. Very useful as always :thumbs:

Makes perfect sense when I think about it now.
 
You're welcome Richard :)

I should have mentioned with HSS that the higher the shutter speed, the more effective brightness is lost - because it is behaving like normal ambient light, rather than flash, in exposure terms.

And the reason they're called shutter curtains is because the first focal plane shutters were made of rubberised cloth and ran horizontally - basically like curtains :D

This is a very good high-speed slo-mo vid of a Nikon D3s shutter in action, with timings http://www.youtube.com/watch?v=0dVmGVa3Rbw Also a great comparison with Canon 5D2 at the end showing how much faster a top end pro camera's shutter functions.

While I'm at it, also found these clips of an old cloth focal plane shutter trundling along. Cloth shutter at 1/125sec http://www.youtube.com/watch?v=PQfrEmkfNcw and at 1/500sec
http://www.youtube.com/watch?v=s7fOxvo-yK4 X-sync on those older shutters was usually only 1/60sec.
 
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