Flash firing when not fully charged…..

treeman · 20 Sep 2016

So I learnt something new today, or at least re-learnt something I’d forgotten, and that is some flash units will still fire even when not fully recycled. The theory being that rather than miss the shot all together, your shot may be just a bit underexposed but still recoverable. Whilst other manufactures choose to not allow the flash to fire at all until its fully recycled and can deliver the correct amount of light.

So I know what works for me, just wondered what others think is the best option, not be able to shoot until its fully recycled and thus deliver the correct output, or be able to shoot anytime even if it doesn’t deliver the correct output?

simonbarker · 21 Sep 2016

I hate equipment that doesn't react when I try to use it, especially heads that don't fire until they've dumped enough energy.

boyfalldown · 21 Sep 2016

I'd rather my kit delivered whats asked of it, rather then some half assed effort

sk66 · 21 Sep 2016

I suppose it depends on what you are shooting and how important the shots are. Chances are a crap exposure is going to be a crap image that winds up in the bin.

HoppyUK · 21 Sep 2016

Neither option is acceptable IMHO. What you really need is a flash that recycles at least as fast as you want to shoot - around 1.0secs works for me, certainly less than 1.5sec.

It's very common for many flash units, of all types, to fire before they're fully charged. Worst of all is a beeper or ready-light that sounds or shows at less than 100% charge, so you then have to estimate 'a bit longer' before shooting. Some manufacturers appear to use the ready-light indicator as the claimed recycle time, too. Flash specs in general are often hit and miss when you actually measure them.

treeman · 22 Sep 2016

I wonder why some makes of light favour one method over the other?

HoppyUK · 22 Sep 2016

treeman said:
I wonder why some makes of light favour one method over the other?

I'm no expert on this, but I have an idea that capacitors, at least some types, can reach a high percentage of charge quite quickly and it's the last bit that takes a disproportionately longer time, ie they might hit 75% charge in half the 100% time. Something like that?

If I had to choose, I guess firing at maybe 90% charge would be better than not firing? It might also depend on the camera with some of the latest sensors responding very well to under-exposure, like a stop or so, with very little penalty if any at lower ISOs. It would also depend on the subject and the importance of shadow detail? And if you're using fill-flash or over-powering the sun, then anything less than 100% charge is going to ruin the flash/ambient balance.

mike weeks · 26 Sep 2016

Exponential charge and discharge of a capacitor circuit is generally quoted as 5CR, C being capacitance and R being resistance

Each CR is a charge of approximately 63% of what is left to charge

1CR 63%
2CR 86%
3CR 95%
4CR 98%
5CR 100%

Discharge is the reverse, i.e. 63% discharges of remaining charge

Mike

HoppyUK · 26 Sep 2016

mike weeks said:
Exponential charge and discharge of a capacitor circuit is generally quoted as 5CR, C being capacitance and R being resistance

Each CR is a charge of approximately 63% of what is left to charge

1CR 63%
2CR 86%
3CR 95%
4CR 98%
5CR 100%

Discharge is the reverse, i.e. 63% discharges of remaining charge

Mike

Erm, what does that actually mean in practise Mike?

I just thought of another thing against flash units firing before they're fully charged. If you have two or more units at different power settings, they're all going to fire at different and disproportional outputs :thumbsdown:

mike weeks · 26 Sep 2016

HoppyUK said:
Erm, what does that actually mean in practise Mike?

I just thought of another thing against flash units firing before they're fully charged. If you have two or more units at different power settings, they're all going to fire at different and disproportional outputs (n)

It means that in practice most lights could be fired at about 60% of charge time and most would not notice, earlier and you will,

The characteristics change with power level, so there is no 1 answer fits all

Mike

treeman · 27 Sep 2016

I'm not sure what the argument is for having to wait until its fully charged to be able to shoot, as I presume speed is not of the essence, so just wait between each shot?

However when you need to shoot quickly, and a little bit of underexposure is easily recoverable these days, why not be able to fire away?

HoppyUK said:
I just thought of another thing against flash units firing before they're fully charged. If you have two or more units at different power settings, they're all going to fire at different and disproportional outputs (n)

Yes, this is the only issue I see with them firing too early, as you say, not so good if the balance in outputs is out of whack.

HoppyUK · 27 Sep 2016

treeman said:
I'm not sure what the argument is for having to wait until its fully charged to be able to shoot, as I presume speed is not of the essence, so just wait between each shot?

However when you need to shoot quickly, and a little bit of underexposure is easily recoverable these days, why not be able to fire away?

Yes, this is the only issue I see with them firing too early, as you say, not so good if the balance in outputs is out of whack.

The situation when I want fast recycle is portraiture. It applies to all sitters, but particularly young children.

Good expressions are often fleeting and can change very quickly. During a session, you can usually see a good expression coming and I coach it along with a steady rate of firing, then when it's there I tend to shoot very fast, like once a second for as long as it lasts, maybe half a dozen shots. In that time, every frame will be different and with luck one will be good. With kids, that might be the only chance you get before it turns to tears.

Shooting in ambient light, I usually have the camera on slow continuous firing mode, like 3fps, and take a couple of shots each time - a kind of double-tap technique! Again, both will be different, even just a fraction of a second apart, and it guards against the odd image being spoiled by blinking. One of the beauties of IGBT controlled flash is at say quarter power you always have two or three accurate exposures instantly available as fast as the camera can fire. That's because the flash doesn't actually have to recharge at all - it has enough power in one full capacitor charge for that, in fact at 1/4 power in theory it should be able to deliver four correctly exposed images in instant succession.

Edit: watch this slo-mo video of people smiling, shot at 1000fps

View: https://vimeo.com/112147240