flash (exposure) time

Anyone know if there is a difference between makes and nominal power, when it comes to the duration of the actual flash exposure?
I am finding my Metz is not stopping moving objects even on very low power.
Are powerful flashes slower even when set to low power?
Is the Metz a 'slow' flash?
is the Canon Speedlight so called because of the duration of the flash, or the cycle times?

Surely it's more to do with shutter speed than flash? They are all much faster than the camera (hundreths of thousandths of a second).

Huh?

If the flash is the primary source of light then the flash will always be faster than the shutter!!! A typical flash is something like 1/10000s. And yes, the lower the power the faster the flash.

(Shutter speed will have nothing to do with an image that is lit primarily and mainly by flash.)

If the ambient light is within 1 or 2 stops then the flash will have a limited "freezing" ability - which is why you have the "Trailing Curtain Sync" option

Best way to tell: set camera to "M"; set up the aperture and shutter speed for your flash; if the metering bar isn't all the way to the left then the ambient lighting will have an effect.

Does that make sense?
(And have you got my e-book on flash??)

Matt

Thanks for the response guys.
Matt, yes the ambient was essentially dark, everything manual.

My question tho is more about whether some flashes are slower than others for a given output.
My mains flashes seem to be very slow, although it's possible some ambient crept in on those tho I guess (I'll test that again sometime).

BTW, what's the real world difference between trailing curtain and slow shutter? Apart from the direction of the blur?

What on earth are you trying to freeze??

There will be some minor variation in flash duration, but I can't imagine we're talking about anything significant in anything I can think of! With a scene that has dark ambient conditions, the flash duration should be in the realm of 1/1000 to 1/20000s (mainly depending on power output).

The main question is how much light do you get for a given brief flash. More expensive gear can deliver larger amounts of light in a shorter time - but even the slooooowest flash is going to be shorter than 1/1000s.


It'd be helpful to see an example of what you're trying to achieve


Normal curtain: Shutter opens; Flash fires; shutter stays open for the selected duration; shutter closes.

Trailing curtain: Shutter opens; shutter stays open for the selected duration; flash fires; shutter closes.

So - no difference except for when the flash fires.

Matt

Flash duration varies enormously, my lightwieght studio flashes are very slow indeed, I'll try to find the manual later, but I'm never trying to stop action with them and since they are more powerful than any of my on camera 'guns then I think they just put out less light for longer.

Ken

Thanks Ken that's interesting. Makes sense.

I'd rather not upload an example, but I'll do some more tests and make sure no stray light is finding it's way into the water droplets (oops! what a giveaway...)

I'll post some results if I get some time.

Cheers

Just remember that the way the flash gets lower power is by "cutting off" the light output earlier.

So it may be a balancing act of lower ambient light + lower flashgun power + higher ISO + aperture control.

You need to balance all four (essentially ignore shutter speed) to find the "sweet spot" that will give you low flash duration with enough light and sufficient sensitivity to get the image you want.

Matt

Matt, I'm talking about fully manual flashes so there is no cutting off power involved; you are quite correct about balancing light sources and I'm wondering just when Pentax will introduce 35mm and 55mm DA LS lenses - fat chance I think!

Ken

Sorry, but there is
Even a fully manual flash will charge the capacitor fully. When you set 1/4 power the flash will achieve that by letting power into the xenon tube for a shorter period of time.

Think of it like a bath full of water (the capacitor), and the plug hole (the flash tube). If you open the plug hole for a long time then the whole bath will empty. Open the plug for a shorter time and less power is discharged.


Matt

I know this

I just use them on full power and move them to change the output - too many years spent using tungsten lamps!

LOL! Then they'll be pretty slow at full power

Just had a look at my Metz 48 manual and the longest flash output is 1/125th up to a 1/25000th.

I don't normally use studio lights, but I've recently had some training on the new Elinchrom BXRI's and Bowens 500R's. I accept that I may have been slightly confused, but essentially the trainers led me to believe that with these lights the shortest flash duration is at full power, which seems to be the opposite to how it is with speedlights...

Does this make sense to anyone?

Jonathan

No

AFAIK, studio lights use essentially the same technology - big capacitor, electronic control & xenon flash tube. It still takes a finite time to dump all the energy into the flash tube, and the less energy you slurp from the cap, the shorter the time - otherwise how would they control the amount of light?

Matt