Motion blur with flash, why?

Hi,

I've been using my flashes for a while, but today was the first time I shot something moving fast (a girl dancing). Some of the pictures seem soft because of motion blur, in particular the hands that move fast, although I always thought that the flashes were fast enough to prevent this!

Basic setup was rather simple, two Elinchrom D-Lite 4 it with umbrellas, the 5D2 in full manual with 1/100 exposure time which guarantees to not miss the flash but is fast enough to give me a black picture from only the not very bright overhead lighting.

Are the flashes not as fast as I expected, or is it that the two of them don't fire exactly at the same time (triggered wirelessly with an Elinchrom SkyPort Eco trigger), or is there anything else I might be doing wrong?

Thanks, Colin

Take a look at this:

http://forums.dpreview.com/forums/th...-post-40326681

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Originally Posted by Sean Setters

Take a look at this:

http://forums.dpreview.com/forums/th...-post-40326681

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Thanks, that clears it up a bit, and shows that I really had a blind spot regarding the whole timing thing!

So there is a catch with the cheap ones, and I need to look for something better for moving subjects.

There are two ways for a flash to output less than full power. Generally speaking, monolights achieve lower output by reducing voltage to reduce the light intensity, meaning no change in duration. Speedlites achieve lower power by reducing the flash duration. That means a Speedlite at lower power is great for stopping action (and why hummingbird shooters use a group of several Speedlites at low power to get enough light with that short duration). A monolight is generally not a good choice for stopping action. There is an affordable exception - the PCB Einstein 640 has an 'action mode' that allows reduced duration. See this:

http://www.robgalbraith.com/bins/mul...=7-10053-10715

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Originally Posted by neuroanatomist

There are two ways for a flash to output less than full power. (...)

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Thanks, lot's of interesting technical details there. Since sport photography is, by far, not my main field, I won't throw my equipment out of the window. And the next time I need to stop "a bit" of action with what I have I'll try them at full power to not make things worse than necessary.

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Originally Posted by Colin500

...the next time I need to stop "a bit" of action with what I have I'll try them at full power to not make things worse than necessary.

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Actually, what he was saying is that you get a shorter flash duration as the power goes down on a flash. So full power would be worse to stop the action. In other words, the lower the power the better... as far as stopping fast action goes.

Exactly. It's just that with most monolights, reducing the power doesn't reduce the flash duration all that much...

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Originally Posted by conropl

Actually, what he was saying is that you get a shorter flash duration as the power goes down on a flash. So full power would be worse to stop the action. In other words, the lower the power the better... as far as stopping fast action goes.

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As far as I understood for speedlights the duration goes down with the power, but not for monolights like I am using, which might even be fastest at full power...?

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Originally Posted by Colin500

As far as I understood for speedlights the duration goes down with the power, but not for monolights like I am using, which might even be fastest at full power...?

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For many monolights, that's true - the lower voltage actually spreads out the peak, meaning a longer duration (slightly) at lower power.

Quote:

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Originally Posted by Colin500

As far as I understood for speedlights the duration goes down with the power, but not for monolights like I am using, which might even be fastest at full power...?

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Sorry... that is my blind spot. When I see flash, I think of on camera flashes, or speedlite like devises off camera. My bad.:o