Flash duration

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Calzor Suzay

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I started a new thread after reading bit of this one.

Basically there's talk of flash heads having a duration of 1/2000th + etc but how does this work with the sync speed of the camera? I know and use flash guns quite often but obviously when you go above the sync speed you have to use high speed sync to get the flash to pulse to get around the shutter slit, how does this work with studio lights? :bonk:
 
With flash heads you arent syncing your shutter speed to 1/2000th, like high speed sync, your max shutter speed must remain as specified in the manual, usually either 1/160, 1/200 or 1/250 for dslrs.

The flash duration is the duration in which the flash tube is illuminated and contributing to your exposure, measured at varying points though, hence the "t" figures quoted.
 
With flash, the position as far as x-sync is concerned is basically the same, whther it's studio flash or hot-shoe guns. Basically the flash duration is very brief, anything from around 1/1000sec to 1/30,000sec depending.

But it makes no odds in terms of shutter speed. Either way the flash has got to fire in the brief 'window' period when the focal plane shutter is fully open. That's at your max x-sync speed (1/250sec on a 7D) or anything longer.

Two things to note. If you use radio triggers, most of them introduce a small delay while they process the signals, which means they miss the window and you don't get the full frame area exposed at the normal max x-sync speed. Just knock it back a notch or two. 1/200sec should be fine on a 7D, 1/160sec to be cetain - it doesn't matter unless there is ambient light involved, which there shouldn't be with studio work.

Then there's high speed sync, which you know about, that enables suitably enabled hot-shoe guns to work around the shutter problems when shooting in bright light - fill-in flash for example. Doesn't apply to studio heads.
 
Two further questions then... :)

What's the idea and I guess selling point of a flash with a shorter illuminated duration?
Is it for a crisper image i.e. when your exposure is pure flash

If you was outside, ambient light is f/2.8 want shallow dof), ISO 100, 1/500th. You want to underexpose the background by 2 stops so go to 1/2000th. I guess none of that is shootable with studio lights as you'll hit the sync speed of the shutter?

Hoppy's message just popped up as I replied which kind of confirms my outside theory, I'll stick with hot-shoe flashguns for now although I do have a Studio lighting trainging day coming up.
 
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Calzor Suzay said:
Two further questions then... :)

What's the idea and I guess selling point of a flash with a shorter illuminated duration?
Is it for a crisper image i.e. when your exposure is pure flash

If you was outside, ambient light is f/2.8 want shallow dof), ISO 100, 1/500th. You want to underexpose the background by 2 stops so go to 1/2000th. I guess none of that is shootable with studio lights as you'll hit the sync speed of the shutter?

Hoppy's message just popped up as I replied which kind of confirms my outside theory, I'll stick with hot-shoe flashguns for now although I do have a Studio lighting trainging day coming up.
Click to expand...
Yes, the selling point is the (increased) ability to freeze movement.
As other people have said, when using studio lights in a studio environment you mustn't exceed the stated synch speed for your camera, and if you're using a radio trigger then the delay introduced by it will often stop you from using the stated max anyway - but there is limited point in using the max speed anyway because, in most studio lighting situations, the level of ambient light is too low to affect the exposure if, say, you use 1/125th instead of 1.250th. However, with all studio flash heads (some more than others) there is a curve as the flash tails off, and the tail is a much warmer colour (and increasingly so) towards the end of the tail. Because of that there can be a point in using the fastest shutter speed that works, because a faster speed can/will clip off the end of the tail and maintain a more neutral colour temperature.

BTW, using a flashgun outside, mixed with daylight, you might want to try using a fast shutter speed (say 1/1000th) to reduce the effect of the ambient light. By no means all of the image will benefit from the flash because the shutter will only be partly open, but if you hold the camera at whatever angle is needed to put the flash where you want it, or if you zoom out to cover more of the principal subject with the flash (losing image quality in the process of course) then it can work - worth trying anyway.
 
Calzor Suzay said:
Two further questions then... :)

What's the idea and I guess selling point of a flash with a shorter illuminated duration?
Is it for a crisper image i.e. when your exposure is pure flash

If you was outside, ambient light is f/2.8 want shallow dof), ISO 100, 1/500th. You want to underexpose the background by 2 stops so go to 1/2000th. I guess none of that is shootable with studio lights as you'll hit the sync speed of the shutter?

Hoppy's message just popped up as I replied which kind of confirms my outside theory, I'll stick with hot-shoe flashguns for now although I do have a Studio lighting trainging day coming up.
Click to expand...

Using flash with high shutter speeds and low f/numbers is difficult, ie fill-in flash.

You can do it using high speed sync, but is very inefficient and wastes a lot of power, hence you're stuck with close range only and have no chance of over powering the sun.

If you want to do that, standard method is to use a big flash (ie portable studio head) then fit an ND filter to bring the overall exposure down under the x-sync ceiling.

If you must have both high shutter speeds and lots of flash power, then you just have to chuck money at it. Like this guy, with eight Nikon SB900 guns :eek: http://www.youtube.com/watch?v=xNDAINwhTWU
 
I've seen the four square vid before, might of been linked off Syl Arena's web site.

Thanks all I have better idea now :)
 
Not sure if this helps much but with regard to flash duration and shutter speed, if your shutter is set to say 1/250 and no ambient light is being picked up and your flash duration is 1/1000 then during that 1/250 of a second there will be a fast flash of light (at 1/1000 of a second) which is what captures the exposure.

The diagram kind of shows this lol

Flash%20Duration.gif
 
I guess the point of shorter duration is to better freeze the motion. If you do still portrait or some photos of jumping subject, this might be not an issue since most of strobes in the current market have short enough duration (say 1/900s), but if you shoot faster moving subject such as racing car, you can hardly get a clean sharp image.
 
How they shot bullets in motion, only using the speed of the flash, because the speed of the camere is limited to 16000/1, or actually to 8000/1, but flashes doing 30000/1 its easy, all the light are turn off and you can do the shots with long exposures like 1 second exposure.
 
gongua said:
How they shot bullets in motion, only using the speed of the flash, because the speed of the camere is limited to 16000/1, or actually to 8000/1, but flashes doing 30000/1 its easy, all the light are turn off and you can do the shots with long exposures like 1 second exposure.
Click to expand...
Sorry, but you're way out there. Airgun pellets can move pretty slowly but I've got a rifle that has a muzzle velocity of around 4000 fps, and another with a mv of 2550 fps - and a bullet travelling across the frame at anywhere near that speed travels a very long way in 1/30000th of a second.

That's why specialised equipment is used, not ordinary hotshoe flashguns.
 
Ok, normally ordynary hotshoe flash guns are slower, but pretty fast for the majority off thing, you can use an simple flash head, and it will be faster. The main problem is faster the flash less the power of him..
 
At least with hotshoe flashes, there is a significant trade off between power and flash duration. At full power, a hotshoe flash usually is not any better than a much more powerful cheap studio flash. However, when you dial your hotshoe flash down, the flash duration will be much shorter, enabling you to freeze motion.

Example:
SB600 at full power


SB600 at 1/4power
 
How do we know that you didn't pull the plug out of the wall in the second one? ;)
 
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